%0 journal article %@ 0921-5093 %A Shi, H., Yang, L., Huang, Y., Zhou, S., Wang, K., Liu, C., Gavras, S., Xiao, L., Willumeit-Römer, R., Dieringa, H., Hort, N. %D 2024 %J Materials Science and Engineering: A %P 146065 %R doi:10.1016/j.msea.2023.146065 %T Insights into creep behavior of Mg–14Gd–1Zn–0.4Zr (wt.%) alloy containing β- and γ-type precipitates %U https://doi.org/10.1016/j.msea.2023.146065 %X Compressive creep tests were performed on sand-cast and peak-aged Mg–14Gd–1Zn–0.4Zr (wt.%) alloys at 250 °C in this study. The microstructures before creep and at the secondary creep stage were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that plenty of fine precipitates, especially β′-series precipitates or a combination of β-type and γ′ precipitates, could effectively enhance the creep resistance of Mg alloys. Large amounts of β'+β′F precipitate chains in the regions near grain boundaries of the sand-cast alloy blocked the motion of -type dislocations, while the interaction of basal and prismatic dislocations could be inhibited by synergy of γ′ and β-type precipitates. In contrast, transformation of β′-series precipitates to β1 or β precipitates in the peak-aged alloy reduced their capacity to impede the dislocation movement, seemingly presenting worse microstructures for creep resistance. However, the peak-aged alloy exhibited a uniform distribution of numerous semi-coherent β1 precipitates and dense rectangular networks composed of γ′ and β-type precipitates within the whole grain, which was superior to the uneven distribution of β-type and γ′ precipitates as well as a lack of ample precipitates at the center of grain in the sand-cast alloy. Thus, the peak-aged Mg–14Gd–1Zn–0.4Zr alloy obtained better creep resistance than the sand-cast alloy to some extent. %0 journal article %@ 1996-1944 %A Dieringa, H., Nienaber, M., Giannopoulou, D., Isakovic, J., Bohlen, J., Kujur, M.S., Ben Khalifa, N., Klein, T., Gneiger, S. %D 2024 %J Materials %N 2 %P 500 %R doi:10.3390/ma17020500 %T Novel Magnesium Nanocomposite for Wire-Arc Directed Energy Deposition %U https://doi.org/10.3390/ma17020500 2 %X Magnesium alloys play an essential role in metallic lightweight construction for modern mobility applications due to their low density, excellent specific strength, and very good castability. For some years now, degradable implants have also been made from magnesium alloys, which, thanks to this special functionality, save patients a second surgery for explantation. New additive manufacturing processes, which are divided into powder-based and wire-based processes depending on the feedstock used, can be utilized for these applications. Therefore, magnesium alloys should also be used here, but this is hardly ever implemented, and few literature reports exist on this subject. This is attributable to the high affinity of magnesium to oxygen, which makes the use of powders difficult. Therefore, magnesium wires are likely to be used. In this paper, a magnesium-based nanocomposite wire is made from an AM60 (Mg-6Al-0.4Mn) (reinforced with 1 wt% AlN nanoparticles and containing calcium to reduce flammability), using a high-shear process and then extruded into wires. These wires are then used as feedstock to build up samples by wire-arc directed energy deposition, and their mechanical properties and microstructure are examined. Our results show that although the ductility is reduced by adding calcium and nanoparticles, the yield strength in the welding direction and perpendicular to it is increased to 131 MPa. %0 journal article %@ 0921-5093 %A Li, J., Jin, L., Yi, S., Zhang, X., Dong, J., Luo, M. %D 2024 %J Materials Science and Engineering: A %P 145856 %R doi:10.1016/j.msea.2023.145856 %T Deformation mechanisms of β-Li in Mg-Li dual-phase alloy and effects of surface oxide layer %U https://doi.org/10.1016/j.msea.2023.145856 %X This study investigates the deformation mechanisms of β-Li micropillar prepared from a Mg–7Li dual-phase alloy with or without surface oxide layer. The β-Li micropillar with three cross-sectional sizes, 2.5 × 2.5 μm2, 4.0 × 4.0 μm2 and 5.5 × 5.5 μm2, are studied. The results show that the oxide layer improves the strength of micropillar due to the dislocation trapping effect. When increasing the micropillar size, the oxide layer having nanoporous structure becomes relatively thinner, and the strengthening effect resulting from the oxide layer decreases. Regardless of the existence of the surface oxide layer, all β-Li micropillars show continuous deformation characteristics. This is ascribed to the interactions between pre-existing dislocations and non-planar dislocations activated during compression, which induces low-angle grain boundary and effectively traps the dislocations at the central area. %0 journal article %@ 1005-0302 %A Li, J., Jin, L., Yi, S., Zhang, X., Dong, J., Luo, M. %D 2024 %J Journal of Materials Science & Technology %P 114-124 %R doi:10.1016/j.jmst.2023.09.018 %T In-situ study of damage mechanisms in Mg-6Li dual-phase alloy %U https://doi.org/10.1016/j.jmst.2023.09.018 %X Interfaces play a crucial role in influencing the mechanical properties of Mg alloys. For Mg–Li dual-phase alloy, the type of interfaces is complex, which includes both grain boundary and phase boundary, and the influence of such interfaces on the damage nucleation is yet to be explored. In this paper, in-situ scanning electron microscopy (SEM) based measurements were carried out to investigate the meso‑scale damage nucleation mechanisms of the Mg–6Li dual-phase alloy. Results show that 94.8% of cracks are nucleated at the α-Mg grain boundary in the post-uniform elongation stage, while 5.2% are at phase boundary and almost no crack at the β-Li grain boundary. The initiation of α-Mg grain boundary cracks is attributed to strain incompatibility, which induces micro-strain localization, and then causes grain boundary sliding (GBS) and crack nucleation. Deformation compatibility analysis reveals that the geometric compatibility factor (Mk) can be used to predict the nucleation of α-Mg grain boundary crack. When Mk is lower than 0.075, α-Mg grain boundary cracks tend to form. Few cracks are generated at the phase boundary is due to the mild strain partitioning between α-Mg phase and β-Li phase and may also be partly attributed to multiple slip systems in body-centered cubic (BCC)-structured β-Li phase, which can accommodate well with the deformation of adjacent α-Mg phase. %0 journal article %@ 2213-9567 %A Pacheco, M., Aroso, I.M., Silva, J. M., Lamaka, S.V., Bohlen, J., Nienaber, M., Letzig, D., Lima, E., Barros, A.A., Reis, R.L. %D 2023 %J Journal of Magnesium and Alloys %N 11 %P 4301-4324 %R doi:10.1016/j.jma.2023.10.002 %T Understanding the corrosion of Mg alloys in in vitro urinary tract conditions: a step forward towards a biodegradable metallic ureteral stent %U https://doi.org/10.1016/j.jma.2023.10.002 11 %X Ureteral stents play a fundamental role in modern time urology. However, following the deployment, stent-related symptoms are frequent and affect patient health and quality of life. Using biodegradable metals as ureteral stent materials have emerged as a promising strategy, mainly due to the improved radial force and slower degradation rate expected. Therefore, this study aimed to characterize different biodegradable metals in urinary tract environment to understand their propensity for future utilization as base materials for ureteral stents. The corrosion of 5 Mg alloys – AZ31, Mg-1Zn, Mg-1Y, pure Mg, and Mg-4Ag – under simulated urinary tract conditions was accessed. The corrosion layer of the different alloys presented common elements, such as Mg(OH)2, MgO, and phosphate-containing products, but slight variations in their chemical compositions were detected. The corrosion rate of the different metals varied, which was expected given the differences in the corrosion layers. On top of this, the findings of this study highlighted the significant differences in the samples' corrosion and corrosion layers when in stagnant and flowing conditions. With the results of this study, we concluded that Mg-1Zn and Mg-4Ag presented a higher propensity for localized corrosion, probably due to a less protective corrosion layer; Mg-4Ag corroded faster than all the other four alloys, and Mg-1Y stood out due to its distinct corrosion pattern, that showed to be more homogeneous than all the other four samples, making this one more attractive for the future studies on biodegradable metals. %0 journal article %@ 1600-5775 %A Ha, C., Kim, Y.M., Woo, S.W., Maawad, E., Letzig, D., Yi, S. %D 2023 %J Journal of Synchrotron Radiation %R doi:doi.org/10.1107/S1600577523003491 %T Analysis of dislocation activity of Mg-Zn-Y alloy by using synchrotron radiation under tensile loading %U https://doi.org/doi.org/10.1107/S1600577523003491 %X An understanding of deformation behavior and texture development is crucial for the formability improvement of Mg alloys. X-ray line profile analysis using the convolutional multiple whole profile (CMWP) fitting method allows the experimental determination of dislocation densities separately for different Burgers vectors up to a high deformation degree. A wider use of this technique still requires exploration and testing of various materials. In this regard, the reliability of the CMWP fitting method for Mg–Zn–Y alloys, in terms of the dislocation activity during tensile deformation, was verified in the present study by the combined analysis of electron backscatter diffraction (EBSD) investigation and visco-plastic self-consistent (VPSC) simulation. The predominant activity of non-basal ⟨a⟩ dislocation slip was revealed by CMWP analysis, and Schmid factor analysis from the EBSD results supported the higher potential of non-basal dislocation slip in comparison with basal ⟨a⟩ dislocation slip. Moreover, the relative slip activities obtained by the VPSC simulation also show a similar trend to those obtained from the CMWP evaluation. %0 journal article %@ 1359-6454 %A Ovri, H., Markmann, J., Barthel, J., Kruth, M., Dieringa, H., Lilleodden, E. %D 2023 %J Acta Materialia %P 118550 %R doi:10.1016/j.actamat.2022.118550 %T Mechanistic origin of the enhanced strength and ductility in Mg-rare earth alloys %U https://doi.org/10.1016/j.actamat.2022.118550 %X Magnesium (Mg) alloys with low concentrations of rare earth additions are known to exhibit strengths and ductility that are significantly higher than those obtained in traditional Mg alloys. However, the mechanisms that underlie these improvements are still open to debate. We assessed these mechanism(s) by carrying out in-depth analysis of the deformation behavior in single crystals of pure Mg and a homogenized Mg-0.75 at.% Gd alloy oriented for twinning, pyramidal- and basal-slip. We observed a fivefold increase in basal CRSS, an eightfold increase in twinning CRSS and a fourfold decrease of the pyramidal/basal CRSS (P/B) ratio due to Gd addition. We also observed that while twinning and pyramidal slip activities were similar in the two material systems, basal slip was radically different. Specifically, basal slip was planar in the alloy but wavy in pure Mg. Our work reveals that these observations are a consequence of Gd-rich short-range ordered (SRO) clusters in the alloy. We show that interactions between dislocations and the SRO clusters would lead to significant increases in strength and slip activity, and consequently, ductility improvements in homogenized polycrystalline Mg-Gd alloys. %0 journal article %@ 0944-6524 %A Kruse, M., Werner, H.O., Chen, H., Mennecart, T., Liebig, W.V., Weidenmann, K.A., Ben Khalifa, N. %D 2023 %J Production Engineering %P 37-46 %R doi:10.1007/s11740-022-01141-y %T Investigation of the friction behavior between dry/infiltrated glass fiber fabric and metal sheet during deep drawing of fiber metal laminates %U https://doi.org/10.1007/s11740-022-01141-y %X During deep drawing processes of fiber metal laminates, such as the newly developed in-situ hybridization process, fibers and metal sheets come into contact while the dry fabric is infiltrated by a reactive matrix system. The viscosity of the matrix increases as polymerization starts during deep-drawing. In the in-situ hybridization process, a dry fiber metal laminate is deep drawn while a thermoplastic matrix system is injected into the glass fiber fabric layer in a resin transfer molding process. During forming of the fiber metal laminate, friction occurs in tangential direction to the metal sheet. The friction plays the main role in preventing the elongation of the sheets in the deep drawing process. Therefore, the measurement of friction coefficients between fibers and metal sheets is essential. In this paper, the friction between sheet metal and dry or infiltrated glass fiber fabric under high contact pressures of 1.67 MPa, as occurring in deep drawing processes, is characterized. A modified strip drawing test setup is used to analyze the coefficient of friction under a constant high contact pressure. Compression tests were performed to show that Coulomb friction can be assumed. Different types of glass fiber fabrics and liquids with defined viscosities are used. It was found that fluids with higher viscosity decrease the friction coefficients in the interface, which is physically explained. For the in-situ hybridization process, it is deduced that with low viscosities, a better infiltration is achieved, while higher viscosities reduce the friction coefficient for better formability. %0 journal article %@ %A Fan, L., Zhou, M., Zhang, Y., Dieringa, H., Qian, X., Zeng, Y., Lu, X., Huang, Y., Quan, G. %D 2023 %J Materials Science and Engineering: A %P 144344 %R doi:10.1016/j.msea.2022.144344 %T Achieving high strength and ductility in a heterogeneous bimodal grain structured TiC/AZ61 magnesium nanocomposites via powder metallurgy %U https://doi.org/10.1016/j.msea.2022.144344 %X Heterogeneous TiC/AZ61 nanocomposites, consisting of TiC-rare coarse grain (CG) bands and TiC-rich fine grain (FG) zones, were fabricated to simultaneously improve the strength and ductility of nanoparticles reinforced Mg matrix composites. The fraction of CG bands could be optimized by adjusting the mechanical ball milling time to change the proportion of powders with different morphologies. It was found that composites began to form a heterogeneous bimodal grain (HBG) structure after 12 h ball milling. With further increasing the ball milling time from 12 h to 30 h, the proportion of spherical powder decreased, the volume fraction of CG bands decreased from 48.4% to 11.7%. Excellent comprehensive mechanical properties (ultimate tensile strength: 417 MPa, yield strength: 323 MPa, and elongation: 10.2%) were achieved for the composite with ∼25 vol% CG bands after 20 h of ball milling. Moreover, the HBG-20 h composite had significant additional strengthening at ultimate tensile strength owing to the existence of geometrically necessary dislocations (GNDs) inside the coarse grain bands, which were introduced by mechanical incompatibility between the CG band and FG zone. Such dislocations provided optimum back-stress work hardening at the HBG-20 h composite due to its suitable CG band fraction (∼ 25 vol%), contributing to the high strain-hardening. %0 journal article %@ 2213-9567 %A Yang, L., Huang, Y., Hou. Z., Xiao, L., Xu, Y., Dong, X., Li, F., Kurz, G., Sun, B., Li, Z., Hort, N. %D 2023 %J Journal of Magnesium and Alloys %N 8 %P 2763-2775 %R doi:10.1016/j.jma.2021.08.010 %T Microstructure, mechanical properties and fracture behaviors of large-scale sand-cast Mg-3Y-2Gd-1Nd-0.4Zr alloy %U https://doi.org/10.1016/j.jma.2021.08.010 8 %X In order to improve the ductility of commercial WE43 alloy and reduce its cost, a Mg-3Y-2Gd-1Nd-0.4Zr alloy with a low amount of rare earths was developed and prepared by sand casting with a differential pressure casting system. Its microstructure, mechanical properties and fracture behaviors in the as-cast, solution-treated and as-aged states were evaluated. It is found that the aged alloy exhibited excellent comprehensive mechanical properties owing to the fine dense plate-shaped β' precipitates formed on prismatic habits during aging at 200 °C for 192 hrs after solution-treated at 500 °C for 24 hrs. Its ultimate tensile strength, yield strength, and elongation at ambient temperature reach to 319 ± 10 MPa, 202 ± 2 MPa and 8.7 ± 0.3% as well as 230 ± 4 MPa, 155 ± 1 MPa and 16.0 ± 0.5% at 250 °C. The fracture mode of as-aged alloy was transferred from cleavage at room temperature to quasi-cleavage and ductile fracture at the test temperature 300 °C. The properties of large-scale components fabricated using the developed Mg-3Y-2Gd-1Nd-0.4Zr alloy are better than those of commercial WE43 alloy, suggesting that the new developed alloy is a good candidate to fabricate the large complex thin-walled components. %0 journal article %@ 2213-9567 %A Deng, M., Wang, L., Snihirova, D., Bohlen, J., Kurz, G., Lamaka, S.V., Höche, D., Zheludkevich, M.L. %D 2023 %J Journal of Magnesium and Alloys %N 4 %P 1193-1205 %R doi:10.1016/j.jma.2022.12.014 %T Micro-alloyed Mg-Ca: Corrosion susceptibility to heating history and a plain problem-solving approach %U https://doi.org/10.1016/j.jma.2022.12.014 4 %X The exceptionally low corrosion rate (∼0.1 mm y–1 in concentrated NaCl solution for 7 days) enables lean Mg-Ca alloys great potential for diverse applications, particularly if relevant properties (e.g. mechanical strength, electrochemical performance, etc.) can be enhanced by thermomechanical processing. However, herein it is demonstrated that the corrosion performance of lean Mg-Ca is susceptible to the heating process. The corrosion rate of Mg-0.15 wt% Ca alloy is remarkably accelerated after annealing even for a short time (4 h at 400 °C) because Fe precipitation readily takes place. Fortunately, it is found that micro-alloying with dedicated additional elements is able to solve this problem. Nevertheless, the problem-solving capability is dependent on the element category, particularly the ability of the alloying element to constrain the Fe precipitation. Among the three studied elements (i.e. Sn, Ge and In), only In shows good competence of restricting the formation of Fe-containing precipitates, thereby contributing to retention of the superior corrosion resistance after annealing even at a rigorous condition (24 h at 450 °C). The finding creates good foundation for follow-up work of developing lean Mg-Ca-based alloys combining high corrosion resistance, superior electrochemical performance with excellent mechanical properties for applications as biodegradable implants and anode materials for aqueous batteries. %0 journal article %@ 1359-6462 %A Pei, R., Xie, Z., Yi, S., Korte-Kerzel, S., Guénolé, J., Al-Samman, T. %D 2023 %J Scripta Materialia %P 115432 %R doi:10.1016/j.scriptamat.2023.115432 %T Atomistic insights into the inhomogeneous nature of solute segregation to grain boundaries in magnesium %U https://doi.org/10.1016/j.scriptamat.2023.115432 %X In magnesium alloys with multiple substitutional elements, solute segregation at grain boundaries (GBs) has a strong impact on many important material characteristics, such as GB energy and mobility, and therefore, texture. Although it is well established that GB segregation is inhomogeneous, the variation of GB solute composition for random boundaries is still not understood. In the current study, atomic-scale experimental and simulation techniques were used to investigate the compositional inhomogeneity of six different GBs. Three-dimensional atom probe tomography results revealed that GB solute concentration of Nd in Mg varies between 2 and 5 at.%. This variation was not only seen for different GB orientations but also within the GB plane. Correlated atomistic simulations suggest that the inhomogeneous segregation behavior observed experimentally stems from local atomic rearrangements within the GBs and introduce the notion of potential excess free volume in the context of improving the prediction of per-site segregation energies. %0 journal article %@ 2213-9567 %A Fan, L., Zhou, M., Lao, W., Zhang, Y., Dieringa, H., Zeng, Y., Huang, Y., Quan, G. %D 2023 %J Journal of Magnesium and Alloys %R doi:10.1016/j.jma.2023.02.011 %T Improving the ductility and toughness of nano-TiC/AZ61 composite by optimizing bimodal grain microstructure via extrusion speed %U https://doi.org/10.1016/j.jma.2023.02.011 %X In this study, the nano-TiC/AZ61 composites with different heterogeneous bimodal grain (HBG) structures and uniform structure are obtained by regulating the extrusion speed. The effect of HBG structure on the mechanical properties of the composites is investigated. The increasing ductility and toughening mechanism of HBG magnesium matrix composites are carefully discussed. When the extrusion speed increases from 0.75 mm/s to 2.5 mm/s or 3.5 mm/s, the microstructure transforms from uniform to HBG structure. Compared with Uniform-0.75 mm/s composite, Heterogeneous-3.5 mm/s composite achieves a 116.7% increase in ductility in the plastic deformation stage and almost no reduction in ultimate tensile strength. This is mainly because the lower plastic deformation inhomogeneity and higher strain hardening due to hetero-deformation induced (HDI) hardening. Moreover, Heterogeneous-3.5 mm/s composite achieves a 108.3% increase in toughness compared with the Uniform-0.75 mm/s composite. It is mainly because coarse grain (CG) bands can capture and blunt cracks, thereby increasing the energy dissipation for crack propagation and improving toughness. In addition, the CG band of the Heterogeneous-3.5 mm/s composite with larger grain size and lower dislocation density is more conducive to obtaining higher strain hardening and superior blunting crack capability. Thus, the increased ductility and toughness of the Heterogeneous-3.5 mm/s composite is more significant than that Heterogeneous-2.5 mm/s composite. %0 journal article %@ 1996-1944 %A Kurz, G., Ganne, K., Nienaber, M., Bohlen, J. %D 2023 %J Materials %N 12 %P 4227 %R doi:10.3390/ma16124227 %T Microstructure and texture evolution of the magnesium alloy ZMX210 during rolling and annealing %U https://doi.org/10.3390/ma16124227 12 %X The processability during massive deformation of magnesium-wrought products is hampered by the low formability of magnesium alloys. The research results of recent years demonstrate that rare earth elements as alloying elements improve the properties of magnesium sheets, such as formability, strength and corrosion resistance. The substitution of rare earth elements by Ca in Mg-Zn-based alloys results in a similar texture evolution and mechanical behaviour as RE-containing alloys. This work is an approach to understanding the influence of Mn as an alloying element to increase the strength of a Mg-Zn-Ca alloy. For this aim, a Mg-Zn-Mn-Ca alloy is used to investigate how Mn affects the process parameters during rolling and the subsequent heat treatment. The microstructure, texture and mechanical properties of rolled sheets and heat treatment at different temperatures are compared. The outcome of casting and the thermo-mechanical treatment are used to discuss how to adapt the mechanical properties of magnesium alloy ZMX210. The alloy ZMX210 behaves very similarly to the ternary Mg-Zn-Ca alloys. The influence of the process parameter rolling temperature on the properties of the ZMX210 sheets was investigated. The rolling experiments show that the ZMX210 alloy has a relatively narrow process window. %0 journal article %@ 2213-9567 %A Shi, H., Huang, Y., Yang, L., Liu, C., Dieringa, H., Lu, C., Xiao, L., Willumeit-Römer, R., Hort, N. %D 2023 %J Journal of Magnesium and Alloys %P 3161-3173 %R doi:10.1016/j.jma.2023.09.005 %T Microstructural evolution of Mg–14Gd–0.4Zr alloy during compressive creep %U https://doi.org/10.1016/j.jma.2023.09.005 %X The present work reports the creep behavior and microstructural evolution of the sand-cast Mg–14Gd–0.4Zr alloy (wt.%) prepared by the differential pressure casting machine. Their compressive creep tests at 250 °C were performed under various applied stresses (i.e., 60, 80 and 100 MPa). Among them, the sand-cast Mg–14Gd–0.4Zr samples examined under 250 °C/80 MPa for 39 and 95 h, respectively, were chosen to systemically analyze their creep mechanisms using high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). The obtained results showed that the enhancement of creep resistance can be mainly attributed to the coherent β' and β'F phases with an alternate distribution, effectively impeding the basal dislocations movement. However, with the creep time increasing, the fine β'+β'F precipitate chains coarsened and transformed to semi-coherent β1 phase and even to large incoherent β phase (surrounded by precipitate-free areas) in grain interiors. The precipitate-free zones (PFZs) at grain boundaries (GBs) were formed, and they could expand during creep deformation. Apart from the main cross-slip of basal and prismatic dislocations, type dislocations were activated and tended to distribute near the GBs. The aforementioned phenomena induced the stress concentrations, consequently leading to the increment of the creep strain. %0 journal article %@ 2213-9567 %A Pei, R., Zhao, Y., Zubair, M., Yi, S., Al-Samman, T. %D 2023 %J Journal of Magnesium and Alloys %N 7 %P 2312-2325 %R doi:10.1016/j.jma.2023.06.008 %T Solute drag-controlled grain growth in magnesium investigated by quasi in-situ orientation mapping and level-set simulations %U https://doi.org/10.1016/j.jma.2023.06.008 7 %X Critical properties of metallic materials, such as the yield stress, corrosion resistance and ductility depend on the microstructure and its grain size and size distribution. Solute atoms that favorably segregate to grain boundaries produce a pinning atmosphere that exerts a drag pressure on the boundary motion, which strongly affects the grain growth behavior during annealing. In the current work, the characteristics of grain growth in an annealed Mg-1 wt.%Mn-1 wt.%Nd magnesium alloy were investigated by advanced experimental and modeling techniques. Systematic quasi in-situ orientation mappings with a scanning electron microscope were performed to track the evolution of local and global microstructural characteristics as a function of annealing time. Solute segregation at targeted grain boundaries was measured using three-dimensional atom probe tomography. Level-set computer simulations were carried with different setups of driving forces to explore their contribution to the microstructure development with and without solute drag. The results showed that the favorable growth advantage for some grains leading to a transient stage of abnormal grain growth is controlled by several drivers with varying importance at different stages of annealing. For longer annealing times, residual dislocation density gradients between large and smaller grains are no longer important, which leads to microstructure stability due to predominant solute drag. Local fluctuations in residual dislocation energy and solute concentration near grain boundaries cause different boundary segments to migrate at different rates, which affects the average growth rate of large grains and their evolved shape. %0 journal article %@ 2213-9567 %A Woo, S.K., Pei, R., Al-Samman, T., Letzig, D., Yi, S. %D 2023 %J Journal of Magnesium and Alloys %N 2 %P 543-552 %R doi:10.1016/j.jma.2022.12.004 %T Effects of Ca and Nd addition on plastic instability in extruded Mg-Mn alloy deformed under various conditions %U https://doi.org/10.1016/j.jma.2022.12.004 2 %X Plastic instability, called Portevin-Le-Chatelier (PLC) effect, manifests itself as an unstable plastic flow during tensile tests of structural materials. This phenomenon has a strong influence on diverse properties, leading to unexpected vulnerabilities in the service environment. Among various magnesium-based alloys, PLC phenomenon is most prominently observed in the Mg-Mn-Nd alloy under elevated temperature and low strain rate conditions. An important aim of the study is to clarify and compare the significance of the RE and Ca addition, which are known to cause a formation of a largely weakened non-basal type texture, in the occurrence of plastic instability. Due to the PLC phenomenon, there is a risk of weakening texture and formability improvement by the addition of RE and Ca elements in Mg alloys. Based on the understanding of the role of Nd to the PLC phenomenon in Mg-Mn alloy identified in previous studies, the PLC characteristics according to alloying elements and deformation conditions were compared and analyzed. To identify the micromechanical mechanisms of the PLC phenomenon, varies in the microstructure and mechanical properties during deformation of Mg-Mn binary and Ca or Nd-containing Mg-Mn-based ternary alloys in various conditions were systemically analyzed. The addition of Ca did not show a marked PLC effect due to the formation of low number density Mn-Ca and Ca-Ca solute clusters and an unbalanced Mn:Ca ratio. In contrast, the addition of Nd leads to the formation of a higher number density of Nd-Nd and Mn-Nd solute clusters than that of Ca-Ca and Mn-Ca solute clusters of the Mg-Mn-Ca alloy, resulting in a stable solute-dislocation interaction atmosphere under specific ranges of deformation temperature and strain rate. The deformation in the regime of PLC phenomenon, results in a decrease in ductility and an increase in strength, despite deformation at elevated temperatures with maintaining the weakened texture. %0 journal article %@ 1598-9623 %A Lee, H.J., Yi, S., Letzig, D., Park, N. %D 2023 %J Metals and Materials International %P 2955-2964 %R doi:10.1007/s12540-023-01430-w %T Microstructure and Texture Evolution During the Heat Treatment of 0.6Zn–0.6Ca–Mg Alloy Sheet Manufactured via Twin Roll Casting %U https://doi.org/10.1007/s12540-023-01430-w %X This study examined the microstructure evolution during the thermomechanical treatments of the twin roll cast strip of magnesium alloy. Magnesium alloy composed of 0.6 wt% Zn and 0.6 wt% Ca was manufactured by TRC and subsequently rolled at 370 °C, and the rolled sheets were heat treated at 400 °C for various periods of time. In the as-TRC plate, the dendritic cast structure inclined in the rolling direction was observed with the centerline segregation. The as-rolled sheet shows a mixture of fine recrystallized grains and the remaining cast structure. The annealing at 400 °C brings about the recrystallization and a gradual grain coarsening for 16 h. After the 16 h heat treatment, secondary recrystallization accompanying the abnormal grain growth was observed, which is attributed to the easier grain boundary motion resulting from the dissolution of Mg2Ca and Ca2Mg5Zn5 precipitates. The as-TRC plate shows a basal-type texture with a slight basal pole spread in the transverse direction, whereas the basal poles tilted by approximately 10° in the rolling direction are formed in the rolled sheet. During the 2 h heat treatment, the texture significantly weakens accompanying the formation of the basal poles inclined by approximately 30° in the transverse direction. These results suggest that a homogeneous microstructure with a weak texture can be obtained by the hot-rolling and heat treatments of the TRC plate, which is advantageous for an improved sheet formability, whereas the heat treatment longer than 16 h causes abnormal grain growth. %0 journal article %@ 2213-9567 %A Nienaber, M., Bohlen, J., Yi, S., Kainer, K.U., Letzig, D. %D 2023 %J Journal of Magnesium and Alloys %R doi:10.1016/j.jma.2023.09.017 %T Influence of Ca addition on the dynamic and static recrystallization behavior of direct extruded flat profiles of Mg-Y-Zn alloy %U https://doi.org/10.1016/j.jma.2023.09.017 %X This paper investigates the influence of addition of Ca in a Y-Zn-containing magnesium alloy on the dynamic and static recrystallization behaviors and reveals the formation mechanism of the quadrupole texture during thermomechanical processing. Direct extrusion of flat bands has been conducted at various process conditions to study the difference between the two alloys WZ10 and WZX100 in terms of microstructure and texture development. It can be shown that, Ca addition promotes the DRX of WZ10 alloy. During additional heat treatment, the absence of Y segregation at the grain boundaries and the associated lack of solute drag to the boundary mobility leads to a pronounced grain growth during SRX in WZX100 alloy. Furthermore, it is shown that the addition of Ca to Y-Zn is not beneficial in terms of formability. It is demonstrated that alloying elements can have different effects depending on the recrystallization mechanisms. Partially recrystallized microstructure is a prerequisite at the as-extruded status to form the quadrupole texture and during subsequent annealing, which stands for high formability. %0 journal article %@ 2213-9567 %A Kandemir, S., Bohlen, J., Dieringa, H. %D 2023 %J Journal of Magnesium and Alloys %N 7 %P 2518-2529 %R doi:https://doi.org/10.1016/j.jma.2023.06.004 %T Influence of recycled carbon fiber addition on the microstructure and creep response of extruded AZ91 magnesium alloy %U https://doi.org/https://doi.org/10.1016/j.jma.2023.06.004 7 %X In this study, the recycled short carbon fiber (CF)-reinforced magnesium matrix composites were fabricated using a combination of stir casting and hot extrusion. The objective was to investigate the impact of CF content (2.5 and 5.0 wt.%) and fiber length (100 and 500 µm) on the microstructure, mechanical properties, and creep behavior of AZ91 alloy matrix. The microstructural analysis revealed that the CFs aligned in the extrusion direction resulted in grain and intermetallic refinement within the alloy. In comparison to the unreinforced AZ91 alloy, the composites with 2.5 wt.% CF exhibited an increase in hardness by 16–20% and yield strength by 5–15%, depending on the fiber length, while experiencing a reduction in ductility. When the reinforcement content was increased from 2.5 to 5.0 wt.%, strength values exhibited fluctuations and decline, accompanied by decreased ductility. These divergent outcomes were discussed in relation to fiber length, clustering tendency due to higher reinforcement content, and the presence of interfacial products with micro-cracks at the CF-matrix interface. Tensile creep tests indicated that CFs did not enhance the creep resistance of extruded AZ91 alloy, suggesting that grain boundary sliding is likely the dominant deformation mechanism during creep. %0 journal article %@ 1960-6206 %A Azpiazu, L.E., Egea, A., Letzig, D., Ha, C. %D 2023 %J International Journal of Material Forming %P 39 %R doi:10.1007/s12289-023-01758-z %T Advanced direct extrusion process with real-time controllable extrusion parameters for microstructure optimization of magnesium alloys %U https://doi.org/10.1007/s12289-023-01758-z %X The extrusion speed and deformation temperature are important factors affecting the microstructure development during the deformation. Microstructure development plays a crucial role in the performance of the mechanical properties of materials. In direct extrusion, the homogeneous evolution of the microstructure in the length of the extruded bar could be affected due to its non-isothermal exit temperature evolution. Thus, a new set-up is suggested with real-time controllable speed and temperature to characterize the influence of temperature on the microstructure and obtain its homogeneous development for the magnesium alloy. During the extrusion, the temperature of the extruded bar is evaluated by using the infra-red camera, and the extrusion speed is simultaneously controlled in real-time depending on the temperature difference between a set temperature reference and the one obtained from the infra-red camera. This suggested set-up of extrusion is evaluated in terms of the microstructure and temperature evolution of the extruded bar. %0 journal article %@ 0921-5093 %A Shi, H., Huang, Y., Yang, L., Liu, C., Dieringa, H., Lu, C., Xiao, L., Willumeit-Römer, R., Hort, N. %D 2023 %J Materials Science and Engineering: A %P 145422 %R doi:10.1016/j.msea.2023.145422 %T Compressive creep behavior and microstructural evolution of sand-cast and peak-aged Mg–12Gd–0.4Zr alloy at 250 °C %U https://doi.org/10.1016/j.msea.2023.145422 %X Magnesium (Mg) alloys with high concentrations of Gd additions are known to exhibit high strength and good creep resistance at elevated temperatures. However, the main mechanisms including microstructural evolution and dislocation configurations for clarifying the low creep rates of Mg–Gd–Zr alloys are still controversial. The present work investigates the compressive creep behavior of both the sand-cast and peak-aged Mg–12Gd–0.4Zr (wt.%) alloys at a fixed temperature of 250 °C under the applied stress range of 60–100 and 80–120 MPa, respectively. It is revealed that β' and β'F precipitates distribute alternately forming precipitate chains in Mg–Gd–Zr alloys. Furthermore, β'+β'F precipitate chains led to the honeycomb-like structure in the sand-cast alloy during the creep process, improving its creep resistance to some extent. Nevertheless, weakly strengthening β1 precipitates occurred and detrimental β phases coarsened, which weakened the creep performance of the sand-cast alloy. However, the slight improvement of creep resistance in the peak-aged Mg–12Gd–0.4Zr alloy can be mainly attributed to the formation of precipitate-free zones (PFZs) and also the premature coarsening of β'+β'F precipitate chains. During creep, the cross slip of basal and prismatic dislocations become the dominant creep mechanism for the sand-cast alloys. By contrast, the cross-slip of basal dislocations and pyramidal dislocations is the dominant creep mechanism for the peak-aged alloys, which was arrested by precipitates then strengthening the creep resistance of peak-aged alloys. %0 journal article %@ 2213-9567 %A Woo, S., Pei, R., Al-Samman, T., Letzig, D., Yi, S. %D 2022 %J Journal of Magnesium and Alloys %N 1 %P 146-159 %R doi:10.1016/j.jma.2021.07.003 %T Plastic instability and texture modification in extruded Mg-Mn-Nd alloy %U https://doi.org/10.1016/j.jma.2021.07.003 1 %X Even though Mg alloys containing Mn and rare earth elements lead to higher ductility and lower yield asymmetry due to the weak texture after extrusion, plastic instability, commonly known as the Portevin–Le Chatelier (PLC) effect, causes unexpected fragility in the service environment. In the present study, the PLC phenomenon and texture development during the deformation of Mg-Mn and Mg-Mn-Nd extruded alloys were investigated under various temperatures and strain rates. The addition of Nd causes not only texture weakening but also severe PLC phenomenon. The PLC phenomenon was significantly affected by the temperatures and the strain rates, which causes a difference in mechanical properties and development of texture. In the conditions of high temperature and low strain rate, the strength increased while the elongation decreased significantly, and obvious PLC phenomenon with severe serration and negative strain rate sensitivity. The initial texture was maintained even after deformation only under severe PLC conditions, and this is due to the restriction of basal slip and suppression of lattice rotation in PLC conditions. The series of results indicate that the PLC phenomenon causes a reduction of formability even at high temperature. %0 journal article %@ 1438-1656 %A You, S., Huang, Y., Dieringa, H., Maawad, E., Gan, W., Zhang, Y., Kainer, K., Willumeit-Römer, R., Hort, N. %D 2022 %J Advanced Engineering Materials %N 4 %P 2101033 %R doi:10.1002/adem.202101033 %T Effects of Y Additions on the Microstructures and Mechanical Behaviours of as Cast Mg–xY–0.5Zr Alloys %U https://doi.org/10.1002/adem.202101033 4 %X Previous investigations demonstrated that rare-earth elements (REs) could improve their creep properties effectively. Herein, the influence of Y content on the creep properties of magnesium is investigated systematically with different amount of Y additions. The mechanisms responsible for creep deformation are clarified by the analysis of stress exponent and microstructural characterizations. It is found that the addition of Y in Mg can improve both the ambient strength and high temperature strength owing to its effective solid solution strengthening. At room temperature, the yield strength of Mg–Y alloys has a linear relation with the content of Y. When tested at high temperatures, the yield strength reduces. Compared with pure magnesium, Mg–Y alloys exhibit a high thermal stability even above 200 °C. Small amount of Y addition can improve the creep resistance of Mg largely. With further increasing its content, its contribution to the improvement of creep resistance is weakened for Mg. Under the applied stresses 60–100 MPa and at temperatures of 200–250 °C, the responsible creep mechanism is dislocation controlled. During creep deformation, the Y segregation regions play an important role in hindering the movement of dislocations. %0 journal article %@ 1359-6462 %A Victoria-Hernandez, J., Yi, S., Letzig, D. %D 2022 %J Scripta Materialia %P 114322 %R doi:10.1016/j.scriptamat.2021.114322 %T Role of non-basal slip systems on the microstructure and texture development of ZXK-Mg alloy deformed in Plane Strain Compression at elevated temperature %U https://doi.org/10.1016/j.scriptamat.2021.114322 %X This work investigates the deformation mechanisms active during high temperature plane strain compression and their impact on the microstructural and texture evolution of an Mg-Zn-Ca-Zr (ZXK) alloy. The microstructures of samples deformed at different strains and different loading directions were examined using electron backscatter diffraction measurements. Likely activated slip systems in grains and twins were determined by in-grain misorientation axis (IGMA), and their activity was compared to the simulation results using the Viscoplastic Self-Consistent (VPSC) model. The importance of the active deformation modes on texture development, specifically the formation of particular texture components, has been linked with a profuse activity of non-basal dislocations and the preferential activation of pyramidal I slip over pyramidal II slip. Along with prismatic slip, the activation of {} twins and pyramidal slip seems to be pivotal for the stabilization of the so-called TD-texture component in a specific loading configuration. %0 journal article %@ 0921-5093 %A Yang, H., Jiang, B., Huang, G., Huang, Y., Jin, Y., Gavras, S., Dieringa, H. %D 2022 %J Materials Science and Engineering: A %P 142358 %R doi:10.1016/j.msea.2021.142358 %T Revealing the role of Al in the microstructural evolution and creep properties of Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn alloy %U https://doi.org/10.1016/j.msea.2021.142358 %X The influence of Al (0.5 wt%, 1 wt%, 2 wt%) on the microstructural evolution and creep resistance of Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn (El21) alloy was systematically investigated. The creep results revealed that the additions of 0.5 wt% and 1 wt% Al significantly decreased the creep rate of El21 by more than an order of magnitude, whereas 2 wt% Al in El21 led to the reduction of creep properties. Microstructural analyses indicated that the additions of 0.5 wt% and 1 wt% Al led to significant grain coarsening due to the consumption of Zr via the formation of Al2Zr3 and Al2Zr phases. In contrast, the addition of 2 wt% Al caused distinct grain refinement, resulting from the additional formation of lumpy Al2RE in the centre of α-Mg grains. Additionally, the increase of Al content in the El21 gradually led to the disappearance of the Mg3RE phase and left Al2RE as the only dominant phase. The main Al–Zr phase was also changed from Al2Zr3+Al2Zr to Al2Zr phase. Creep data analysis showed that the dominant creep mechanism was dislocation creep for all alloys, which was in agreement with the EBSD and TEM characterizations. The enhanced creep resistance via the addition of 0.5 wt% and 1 wt% Al was ascribed to the high area fraction of intermetallic phases and the additional formation of the thermally stable Al2RE phase. El21 + 0.5Al has better creep resistance than El21+1Al, which was attributed to its stronger dynamic precipitation strengthening from γ precipitates. The deteriorated creep properties caused by adding 2 wt% Al in El21 alloy arose from the bimodal inhomogeneous distribution of grains and the laminar Al2RE phase. Such microstructure might cause significant stress concentrations and could not effectively impede dislocation motion or reinforce the grain/dendritic boundaries during creep, thus deteriorating the creep properties of El21+2Al. %0 journal article %@ 0921-5093 %A Pei, R., Woo, S., Yi, S., Al-Samman, T. %D 2022 %J Materials Science and Engineering: A %P 142685 %R doi:10.1016/j.msea.2022.142685 %T Effect of solute clusters on plastic instability in magnesium alloys %U https://doi.org/10.1016/j.msea.2022.142685 %X The interaction between solute atoms and matrix dislocations during plastic deformation of materials strongly influences the flow behavior and can lead to plastic instability at the macroscopic scale. In this study, Lüders band formation and dynamic strain aging phenomena were investigated in a Mg–1%Mn-1%Nd (wt.%) alloy, deformed in uniaxial tension at ambient temperature and 150 °C. The investigated alloy was studied in the initial as-extruded state and after a subsequent heat treatment at 275 °C for 120 min, which allowed for a variation of solute concentration in the microstructure, and thus for a different type/level of solute – dislocation interaction. Microstructure investigations at near-atomic resolution using three dimensional atom probe tomography were carried out in order to visualize the spatial distribution of alloying elements and reveal potential solute clustering trends in connection with the occurrence of plastic instability. Identified nanoscale solute clusters were analyzed on the basis of their size distribution, chemical composition, and statistical significance. Results demonstrate that the number, as well as the types of solute clusters, play an essential role in triggering plastic instability by interacting with deformation carriers at the atomic scale. %0 journal article %@ 0267-0836 %A Majhi, J., Mondal, A., Basu, A., Dieringa, H., Kumar, S. %D 2022 %J Materials Science and Technology %N 6 %P 377-389 %R doi:10.1080/02670836.2022.2045546 %T Influence of Ca+Bi on tensile and strain hardening behaviour of AZ91 alloy %U https://doi.org/10.1080/02670836.2022.2045546 6 %X The influence of Ca + Bi on the tensile and strain hardening behaviour of the AZ91 alloy at ambient and elevated temperatures have been examined. The values of YS are higher, and ductility is lower of all the modified alloys. The UTS of the modified AZ91 alloys is lower except at 473 K. The UTS values decrease with an increase in test temperature for all the alloys. The improved YS of the modified alloys is owing to reduced grain size. The brittle Mg3Bi2, Al2Ca and Bi3Ca5 phases in the modified alloys reduce their UTS and ductility. The transgranular cleavage fracture at 298 K changes to quasi-cleavage fracture at 473 K. Several dislocations piled up around the β-Mg17Al12 and Al2Ca phases are seen. %0 journal article %@ 0300-9440 %A Korrapati, V., Scharnagl, N., Letzig, D., Zheludkevich, M. %D 2022 %J Progress in Organic Coatings %P 106608 %R doi:10.1016/j.porgcoat.2021.106608 %T Bilayer coatings for temporary and long–term corrosion protection of magnesium–AZ31 alloy %U https://doi.org/10.1016/j.porgcoat.2021.106608 %X Phosphate and silane containing organic self–assembled (SA) layers serve as pre–treatments on magnesium alloy sheet materials. A reliable protection was achieved in this work via application of alkyd–based coatings on the pretreated surface. The idea of adopting SA pre–treatments as functional layers at metal–polymer interface is to influence the adhesive properties between solid metal substrate and alkyd–based coating. Hexadecyltrimethoxysilane (HDTMS) deposited metal surfaces exhibit stronger adhesive strength, while a near homogeneous distribution of the octadecylphosphonic acid (ODPA) and perfluorodecylphosphonic acid (PFDPA) exhibit low adhesive phenomenon, when placed as pre–layers in bilayer coatings. Electrochemical impedance results after 168 h of immersion reveal that the organophosphate and organosilane deposited bilayer films demonstrate protective properties with almost no interface defects. Moreover, organophosphate treated bilayer coatings enhance easy peeling of alkyd coat after protecting the surface from corrosive electrolytes. Bilayer coatings developed on AZ31 sheets can confer temporary or long–term corrosion protection depending on further processing strategy and offer efficient alloy protection for both purposes. %0 journal article %@ 1996-1944 %A Millán-Ramos, B., Morquecho-Marín, D., Silva-Bermudez, P., Ramírez-Ortega, D., Depablos-Rivera, O., García-López, J., Fernández-Lizárraga, M., Almaguer-Flores, A., Victoria-Hernández, J., Letzig, D., Rodil, S. %D 2022 %J Materials %N 9 %P 3142 %R doi:10.3390/ma15093142 %T Degradation Behavior and Mechanical Integrity of a Mg-0.7Zn-0.6Ca (wt.%) Alloy: Effect of Grain Sizes and Crystallographic Texture %U https://doi.org/10.3390/ma15093142 9 %X The microstructural characteristics of biodegradable Mg alloys determine their performance and appropriateness for orthopedic fixation applications. In this work, the effect of the annealing treatment of a Mg-0.7Zn-0.6Ca (ZX11) alloy on the mechanical integrity, corrosive behavior, and biocompatibility-osteoinduction was studied considering two annealing temperatures, 350 and 450 °C. The microstructure showed a recrystallized structure, with a lower number of precipitates, grain size, and stronger basal texture for the ZX11-350 condition than the ZX11-450. The characteristics mentioned above induce a higher long-term degradation rate for the ZX11-450 than the ZX11-350 on days 7th and 15th of immersion. In consequence, the mechanical integrity changes within this period. The increased degradation rate of the ZX11-450 condition reduces 40% the elongation at failure, in contrast with the 16% reduction for the ZX11-350 condition. After that period, the mechanical integrity remained unchanged. No cytotoxic effects were observed for both treatments and significant differentiation of mesenchymal stem cells into the osteoblast phenotype was observed. %0 journal article %@ 1996-1944 %A Jo, S., Bohlen, J., Kurz, G. %D 2022 %J Materials %N 15 %P 5239 %R doi:10.3390/ma15155239 %T Individual Contribution of Zn and Ca on Age-Hardenability and Formability of Zn-Based Magnesium Alloy Sheet %U https://doi.org/10.3390/ma15155239 15 %X This paper reports on the dilemma of the strength and forming behavior of magnesium alloy sheets due to hot rolling and precipitation aging as an obstacle for property adjustment. The effect of the Zn content on the age-hardenability and formability of Mg-Zn-Al-Ca-Mn sheets was investigated. Sheets of two alloys with 2 or 4 wt.% Zn, respectively, were produced by casting and subsequent hot rolling and their microstructure development, precipitation behavior and formability were examined. With higher Zn content the age-hardenability was increased, but at the same time the formability of the sheet decreased, concurrent to the basal-type texture development during rolling. On the other hand, the sheet containing a lower amount of Zn exhibited a weak rolling texture and rather high formability but low age-hardenability. The addition of a larger amount of Zn improved the age-hardenability through the formation of β′1 and β′2 phases. The basal texture was exhibited due to the consumption of solute Ca due to the formation of the Ca2Mg6Zn3 phase. This study suggests that this contradictory exhibition of the age-hardenability and formability of Ca-containing and Zn-based alloy sheets requires a strategical approach in alloy and process design, which allows tailoring the alloying elements and processing for the respective purpose. %0 journal article %@ 1359-6462 %A Jo, S., Kim, Y., Letzig, D., Yi, S. %D 2022 %J Scripta Materialia %P 114880 %R doi:10.1016/j.scriptamat.2022.114880 %T Non-flammable magnesium sheet alloys with an excellent age-hardenability %U https://doi.org/10.1016/j.scriptamat.2022.114880 %X Microstructure, crystallographic texture and age hardenability of the non-flammable Mg-Al-Zn-Ca-Y alloy sheets were investigated as a systematic compositional change. By reducing the Al content to 1 wt.%, fine and homogeneous microstructure was preserved even after the solution-treatment at 500°C, while a weaken texture was obtained. The high Zn/Y ratio and high Ca solute amount in the matrix complementarily instigate the texture weakening with the basal poles tilted away from the sheet normal direction. Age hardenability was significantly improved by decreasing the Al content to 0.6 wt.% and the corresponding increase in the dissolved Ca solute. The increase in the solute elements concomitant with the reduced Al content leads to the retarded recrystallization and enhanced age hardenability. A balanced alloying of Al, Ca and Y enables the Mg sheets with improved mechanical properties as a result of texture and microstructure controls. %0 journal article %@ 2073-4352 %A Mance, S., Dieringa, H., Bohlen, J., Gavras, S., Stark, A., Schell, N., Pereira da Silva, J., Tolnai, D. %D 2022 %J Crystals %N 11 %P 1502 %R doi:10.3390/cryst12111502 %T In Situ Synchrotron Radiation Diffraction Study of Compression of AZ91 Composites Reinforced with Recycled Carbon Fibres %U https://doi.org/10.3390/cryst12111502 11 %X Lightweight structural materials are increasingly sought after in the automotive and aerospace industries for their potential to improve fuel efficiency. Magnesium-based metal-matrix composites are potential candidates for these kinds of applications. The use of recycled carbon fibres offers further energy and cost savings. The recycled carbon fibre composites were manufactured by stir casting with high-dispersion shearing, then were extruded and subsequently heat treated. The compressive deformation mechanisms of the composites compared to AZ91 were investigated using in situ synchrotron radiation diffraction. An increase in ultimate compressive strength was achieved in the composites compared to AZ91. The deformation mechanisms active in the composites were similar to those in AZ91. Magnesium alloys in compression typically show extensive twinning; this was observed in AZ91 and the AZ91 composites. The stress required for twinning onset was increased in the composites, and the twin volume fraction at failure was decreased compared to AZ91. %0 journal article %@ 2079-4991 %A Giannopoulou, D., Bohlen, J., Ben Khalifa, N., Dieringa, H. %D 2022 %J Nanomaterials %N 15 %P 2682 %R doi:10.3390/nano12152682 %T Influence of Extrusion Rate on Microstructure and Mechanical Properties of Magnesium Alloy AM60 and an AM60-Based Metal Matrix Nanocomposite %U https://doi.org/10.3390/nano12152682 15 %X Metal matrix nanocomposites are attracting attention because of their great potential for improved mechanical properties and possible functionalization. These hybrid materials are often produced by casting processes, but they can also develop their property profile after hot working, e.g., by forging or extrusion. In this study, a commercial cast magnesium alloy AM60 was enriched with 1 wt.% AlN nanoparticles and extruded into round bars with varied extrusion rates. The same process was carried out with unreinforced AM60 in order to determine the influences of the AlN nanoparticles in direct comparison. The influence of extrusion speed on the recrystallization behavior as well the effect of nanoparticles on the microstructure evolution and the particle-related strengthening are discussed and assessed with respect to the resulting mechanical performance. %0 journal article %@ 0921-5093 %A Knapek, M., Minárik, P., Greš, A., Zemková, M., Lukáč, F., Bohlen, J., Chmelík, F., Král, R. %D 2022 %J Materials Science and Engineering: A %P 143481 %R doi:10.1016/j.msea.2022.143481 %T Spark plasma sintered Mg-4Y-3Nd with exceptional tensile performance %U https://doi.org/10.1016/j.msea.2022.143481 %X This work utilizes the spark plasma sintering (SPS) technique and exploits the physical mechanisms leading to the preparation of a fully compacted Mg-4wt.%Y-3wt.%Nd (WN43) material to exhibit superb mechanical properties, including outstanding plastic elongation in tension of more than 10 % among the SPS-ed Mg-based materials. To this end, the detrimental effect of oxide shells present on the Mg-Y-Nd powder particles is purposefully suppressed. The essential principle underlying the strong interconnection of the former powder particles is based on the combination of sufficiently high pressure and temperature approaching the eutectic points of Mg-Y/Nd systems. Thus-prepared WN43 material also retains the initial fine powder microstructure and its microstructural features are translated into good ductility and strength of the final product comparable with the conventionally-prepared (e.g. wrought) Mg-RE alloys. At the same time, the advantages of SPS – the production of a relatively large volume of near net-shape material with weak crystallographic texture – are retained. The deformation mechanisms are investigated by means of complementary in-situ techniques (acoustic emission, digital image correlations) and semi in-situ electron backscatter diffraction. A relatively low tension–compression asymmetry is revealed owing to the weak texture and the activity of deformation mechanisms (dislocation slip and twinning) follows the conventions of bulk Mg. In support of potential practical applications of the material, no significant cracking of the residual oxide phases is observed although they seem to play some role in the initiation of critical crack leading to the fracture. The SPS technique offers undemanding fine-tuning of processing parameters leading, in turn, to expeditious modification of material properties and, given the understanding of microstructure evolution unveiled in this work, it can be effectively utilized for the preparation of different Mg-based (or other) materials. %0 journal article %@ 2073-4352 %A Nienaber, M., Kurz, G., Letzig, D., Kainer, K., Bohlen, J. %D 2022 %J Crystals %N 9 %P 1307 %R doi:10.3390/cryst12091307 %T Effect of Process Temperature on the Texture Evolution and Mechanical Properties of Rolled and Extruded AZ31 Flat Products %U https://doi.org/10.3390/cryst12091307 9 %X The application of magnesium flat products is affected by the limited formability at room temperature and the anisotropy of the mechanical properties. The main reason for this is the underlying hexagonal crystal structure of magnesium and the development of strong crystallographic textures during massive forming processes with distinct alignment of basal planes. For an improvement in the properties of semi-finished products, the detailed knowledge of the influence of the manufacturing process on the microstructure and texture evolution of the flat products as a result of dynamic and static recrystallization is required. In this work, flat products made of conventional magnesium alloy AZ31 were manufactured by the rolling process as well as by direct extrusion, with variation in the process temperature. This allowed the development of a distinct variation in microstructures and textures of the flat products. The effects on mechanical properties and formability are highlighted and discussed in relation to the microstructure and texture. It is shown that both the process and the temperature have a major influence on texture and consequently on the material properties. %0 journal article %@ 2075-4701 %A Chavez, L., Veleva, L., Sanchez, G., Dieringa, H. %D 2022 %J Metals %N 12 %P 1997 %R doi:10.3390/met12121997 %T AM60-AlN Nanocomposite and AM60 Alloy Corrosion Activity in Simulated Marine-Coastal Ambience %U https://doi.org/10.3390/met12121997 12 %X The initial stages of AM60-AlN nanocomposite and AM60 corrosion behaviors were compared over 30 days of exposure to solution (NaCl, Na2SO4 and NaHCO3), simulating the marine-coastal environment (SME). The incorporation of AlN nanoparticles (1.0 wt.%) in the AM60 alloy matrix favored the lower roughness of the AM60-AlN, associated with the grain refinement in the matrix. During the immersion of the alloys, pH of the SME solution shifted to alkaline values >9, and therefore, the solubility of AlN aluminum hydroxide phases were raised, followed by a slightly higher release of Mg-ions and corrosion rate increase. The chloride ions attributed to the unstability of the Al-Mn phase and Al(OH)3 corrosion product was formed in a low content. The composite AM60-AlN presented lower value of the electrochemical noise resistance (Rn), suggesting that the corrosion process occurs with less difficulty. The localized corrosion near the Al-Mn cathodes seems to be stronger on the composite surface, in area and depth of penetration. The corrosion current fluctuations suggested that the corrosion is a weakly persistent process, dominated by the fractional Gaussian noise (fGn). %0 journal article %@ 0264-1275 %A Nienaber, M., Braatz, M., Ben Khalifa, N., Bohlen, J. %D 2022 %J Materials & Design %P 111355 %R doi:10.1016/j.matdes.2022.111355 %T Property profile development during wire extrusion and wire drawing of magnesium alloys AZ31 and ZX10 %U https://doi.org/10.1016/j.matdes.2022.111355 %X This paper deals with the impact of the wire manufacturing process on the mechanical property development of two magnesium alloys, AZ31 and ZX10. For this study, wires were produced with different diameters of up to 0.2 mm via direct one-step extrusion as a hot forming route and were directly compared to conventional cold drawing manufacturing routes with diameters up to 0.3 mm and associated heat-treatment. The alloy dependent microstructure development is resolved with respect to the underlying recrystallization mechanisms, which determines the texture development and concurrently the strength and ductility properties of the wires. The experimental results clearly show that the manufacturing process, the degree of deformation (wire diameter) as well as the alloy itself have a major impact on the texture development and mechanical properties of the wires. While AZ31, does not enable a strong impact on the microstructure development, ductility in ZX10 is enhanced with a concurrent weak texture development due to adjusted dynamic recrystallization during hot forming. In contrast, such microstructures cannot be adjusted in the cold forming routes due to static recrystallization. However, it is possible to improve of the properties significantly by drawing, which is limited by the first two drawing passes. %0 journal article %@ 1996-1944 %A Zemková, M., Minárik, P., Jablonská, E., Veselý, J., Bohlen, J., Kubásek, J., Lipov, J., Ruml, T., Havlas, V., Král, R. %D 2022 %J Materials %N 21 %P 7571 %R doi:10.3390/ma15217571 %T Concurrence of High Corrosion Resistance and Strength with Excellent Ductility in Ultrafine-Grained Mg-3Y Alloy %U https://doi.org/10.3390/ma15217571 21 %X In the field of magnesium-based degradable implantable devices, the Mg-Y-RE-Zr alloying system (WE-type) has gained popularity due to its satisfying degradation rate together with mechanical strength. However, utilization of RE and Zr in the WE-type alloys was originally driven to improve Mg-based alloys for high-temperature applications in the industry, while for medical purposes, there is a question of whether the amount of alloying elements may be further optimized. For this reason, our paper presents the Mg-3Y (W3) magnesium alloy as an alternative to the WE43 alloy. This study shows that the omission of RE and Zr elements did not compromise the corrosion resistance and the degradation rate of the W3 alloy when compared with the WE43 alloy; appropriate biocompatibility was preserved as well. It was shown that the decrease in the mechanical strength caused by the omission of RE and Zr from the WE43 alloy could be compensated for by severe plastic deformation, as achieved in this study, by equal channel angular pressing. Ultrafine-grained W3 alloy exhibited compression yield strength of 362 ± 6 MPa and plastic deformation at maximum stress of 18 ± 1%. Overall, the early results of this study put forward the motion of avoiding RE elements and Zr in magnesium alloy as a suitable material for biodegradable applications and showed that solo alloying of yttrium is sufficient for maintaining desirable properties of the material at once. %0 journal article %@ 2073-4352 %A Wiese, B., Harmuth, J., Willumeit-Römer, R., Bohlen, J. %D 2022 %J Crystals %N 8 %P 1036 %R doi:10.3390/cryst12081036 %T Property Variation of Extruded Mg-Gd Alloys by Mn Addition and Processing %U https://doi.org/10.3390/cryst12081036 8 %X This paper presents how the mechanical properties, the microstructure and the degradation rate of extruded Mn-containing Mg-Gd alloys can be modified during extrusion. Gd as a rare earth element is particularly interesting due to the influence on the texture development in Mg, and is therefore studied as a base alloy system. The contents of Gd were investigated between 2 to 9 wt.%, with Mn additions of 0.5 and 1.0 wt.%. The grain sizes and the corresponding textures were modified by varying the extrusion parameters and the alloy content. It was shown that modification with Mn can lead to further grain refinement, an increase in the degree of recrystallization, as well as a decrease in the degradation rate in the biological medium compared with the binary Mg-Gd system from previous studies. The results suggest that the resulting properties are more robust compared with the binary alloy. %0 journal article %@ 2079-4991 %A Şevik, H., Özarslan, S., Dieringa, H. %D 2022 %J Nanomaterials %N 24 %P 4399 %R doi:10.3390/nano12244399 %T Assessment of the Mechanical and Corrosion Properties of Mg-1Zn-0.6Ca/Diamond Nanocomposites for Biomedical Applications %U https://doi.org/10.3390/nano12244399 24 %X In this work, the microstructure, mechanical properties, and corrosion behavior of the Mg-1Zn-0.6Ca matrix alloy (ZX10), reinforced by adding various amounts of nanodiamond particles (0.5, 1, and 2 wt.%), prepared by the ultrasound-assisted stir-casting method, were investigated as they are deemed as potential implant materials in biomedical applications. Microstructure, nanoindentation, mechanical tensile, immersion, and potentiodynamic polarization tests were performed for evaluating the influence of the addition of nanodiamond particles on the alloy’s mechanical and biocorrosion properties. The results revealed that the addition of nanodiamond particles causes a reduction in the alloy’s grain size. The alloy’s nanohardness and elastic modulus values increased when the amount of added nanodiamond particles were increased. The nanocomposite with an addition of 0.5% ND showed the best composition with regard to an acceptable corrosion rate as the corrosion rates are too high with higher additions of 1 or 2% NDs. At the same time, the yield strength, tensile strength, and elongation improved slightly compared to the matrix alloy. %0 journal article %@ 2296-8016 %A Höche, D., Weber, W., Gazenbiller, E., Gavras, S., Hort, N., Dieringa, H. %D 2021 %J Frontiers in Materials %P 575530 %R doi:10.3389/fmats.2021.575530 %T Novel Magnesium Based Materials: Are They Reliable Drone Construction Materials? A Mini Review %U https://doi.org/10.3389/fmats.2021.575530 %X Novel magnesium-based materials are ideal candidates for use in future aviation vehicles because they are extremely light and can therefore significantly increase the range of these vehicles. They show very good castability, are easy to machine and can be shaped into profiles or forgings to be used as components for next generation aerial vehicle construction. In the case of a large number of identical components, high-pressure die casting of magnesium alloys is clearly superior to high-pressure die casting of aluminum alloys. This is due to the lower solubility of iron in magnesium and thus tool/casting life is significantly longer. In addition, the die filling times for magnesium high-pressure die casting are approximately 30% shorter. This is due to the lower density: aluminum alloys are approximately 50% heavier than magnesium alloys, which is a significant disadvantage for aluminum alloys especially in the aerospace industry. There are cost-effective novel die casting alloys, besides AZ91 or AM50/60 such as DieMag633 or MRI230D, which show very good specific strength at room and elevated temperatures. In the case of magnesium-based wrought alloys, the choice is smaller, a typical representative of these materials is AZ31, but some new alloys based on Mg-Zn-Ca are currently being developed which show improved formability. However, magnesium alloys are susceptible to environmental influences, which can be eliminated by suitable coatings. Novel corrosion protection concepts for classical aerial vehicles currently under development might suitable but may need adaption to the construction constraints or to vehicle dependent exposure scenarios. Within this mini-review a paradigm change due to utilization of new magnesium materials as drone construction material is briefly introduced and future fields of applications within next-generation aerial vehicles, manned or unmanned, are discussed. Possible research topics will be addressed. %0 journal article %@ 1044-5803 %A Ha, C., Bohlen, J., Zhou, X., Brokmeier, H., Kainer, K., Schell, N., Letzig, D., Yi, S. %D 2021 %J Materials Characterization %P 111044 %R doi:10.1016/j.matchar.2021.111044 %T Texture development and dislocation activities in Mg-Nd and Mg-Ca alloy sheets %U https://doi.org/10.1016/j.matchar.2021.111044 %X Texture modification during sheet rolling appears differently in binary Mg-RE (rare-earth) or Mgsingle bondCa alloy, compared to their ternary counterparts containing Zn. The differences in texture development and the active deformation mechanisms under tensile loading were investigated in the binary alloys. These analyses are based on in-situ synchrotron experiments and electron backscatter diffraction measurements to reveal direct experimental evidence of the texture development and the active deformation mechanisms. Higher activations of nonbasal  and pyramidal  dislocations were found in the Nd or Ca containing Mg alloys, compared to the Mgsingle bondZn alloy. The texture development shows an obvious feature, which is a broadening of the basal pole intensity distribution perpendicular to the loading direction and a strengthening of the pole at the loading direction in all examined sheets. This texture development relates to the higher activation of prismatic  slip. The addition of Zn in the Mg-RE or Mgsingle bondCa alloys further promotes the activation of nonbasal  and pyramidal  dislocations. This enhanced prismatic  slip in the Zn containing ternary alloys is confirmed by EBSD misorientation analysis. %0 journal article %@ 2213-9567 %A Dobron, P., Drozdenko, D., Fekete, K., Knapek, M., Bohlen, J., Chmelik, F. %D 2021 %J Journal of Magnesium and Alloys %N 3 %P 1057-1067 %R doi:10.1016/j.jma.2020.12.010 %T The slip activity during the transition from elastic to plastic tensile deformation of the Mg-Al-Mn sheet %U https://doi.org/10.1016/j.jma.2020.12.010 3 %X The deformation behavior of the Mg-Al-Mn sheet was investigated during tensile loading along the rolling (RD) and transversal direction (TD) with special attention to the early stage of deformation. The activity of dislocation slip systems during the transition from elastic to plastic deformation was revealed by the acoustic emission (AE) technique. The parametrization and statistical AE analysis using the adaptive sequential k-mean (ASK) clustering provided necessary information about the individual deformation mechanisms and their evolution. The AE findings were supported by microstructural analyses, including in-situ secondary electron (SE) imaging and Schmid factor estimation for the activity of particular dislocation slip systems with respect to the loading direction. It was found that basal slip is the dominating mechanism up to the stress of ∼ 80 MPa in both loading directions with an absolute dominance during the RD-loading, while during the TD-loading, the contribution of prismatic slip to the deformation at stresses above 50 MPa was determined. Below the yielding in both loading directions, the predominance of prismatic over pyramidal slip was found at the stress in the range of 80–110 MPa and the opposite tendency occurred at stresses between 110 and 140 MPa. %0 journal article %@ 1047-4838 %A Victoria-Hernandez, J., Kurz, G., Bohlen, J., Yi, S., Letzig, D. %D 2021 %J JOM: The Journal of the Minerals, Metals and Materials Society %N 5 %P 1460-1470 %R doi:10.1007/s11837-021-04611-3 %T Influence of Twin-Roll Casting Speed on Microstructural Homogeneity, Centerline Segregation, and Surface Quality of Three Different Mg Alloys %U https://doi.org/10.1007/s11837-021-04611-3 5 %X In this work, the influence of twin-roll casting (TRC) speed on the microstructure of the through-thickness uniformity, centerline segregation, and surface quality of three wrought Mg alloys was investigated. The microstructural features of the AZ31, ZX11, and ZWK200 alloys produced at TRC speeds ranging from 1.8 m/min to 2.2 m/min (for the AZ31 and ZWK200), and 1.5–2.5 m/min (for the ZX11 alloy) were analyzed. There were clear differences in the microstructure uniformity depending on the alloy composition. Columnar grains coexisting with globular grains were found in the AZ31 and ZX11 alloys, whereas the ZWK200 alloy showed a homogeneous fine-grained microstructure characterized by a weaker texture even at the highest TRC speed used. While there is a tendency to reduce the centerline segregation as the TRC speed is decreased during casting of the AZ31 alloy, the formation of this defect cannot be prevented in the ZX11 and ZWK200 alloys by only varying the TRC speed. %0 journal article %@ 2213-9567 %A Knapek, M., Zemkova, M., Gres, A., Jablonska, E., Lukac, F., Kral, R., Bohlen, J., Minarik, P. %D 2021 %J Journal of Magnesium and Alloys %N 3 %P 853-865 %R doi:10.1016/j.jma.2020.12.017 %T Corrosion and mechanical properties of a novel biomedical WN43 magnesium alloy prepared by spark plasma sintering %U https://doi.org/10.1016/j.jma.2020.12.017 3 %X Alloying of Mg with rare-earth (RE) elements proved to be beneficial for their in-vitro and in-vivo performance. In this work, a novel WN43 (Mg-4 wt%Y-3 wt%Nd) alloy with a well-defined composition was prepared, where, unlike in the commercial WE43 alloy, the possibly harmful RE mischmetal was substituted by less toxic Nd. A modern spark plasma sintering (SPS) technique was used to effectively produce WN43 samples from atomized powders. Sintering temperatures of 400 °C – 550 °C and holding times of 3 or 10 min were used and well-compacted final materials were successfully prepared. It was shown that a superior combination of corrosion and mechanical properties was attained in the samples sintered at 500 °C and 550 °C, while the effect of sintering time was rather negligible. The performance of this material was exceptional within the group of Mg alloys prepared by powder metallurgy and comparable with conventionally prepared alloys. Moreover, it was shown that a great variety of mechanical and corrosion characteristics can be obtained by altering the SPS parameters so as to fulfill case-specific requirements typical of biomedical materials. Consequently, the novel WN43 alloy prepared by SPS seems to be a particularly suitable material for biomedical use. %0 journal article %@ 1960-6206 %A Chen, H., Giannopoulou, D., Greß, T., Isakovic, J., Mittler, T., Volk, W., Ben Khalifa, N. %D 2021 %J International Journal of Material Forming %N 5 %P 1109-1119 %R doi:10.1007/s12289-021-01626-8 %T Homogenization of the interfacial bonding of compound-cast AA7075/6060 bilayer billets by co-extrusion %U https://doi.org/10.1007/s12289-021-01626-8 5 %X A process chain of compound casting and co-extrusion of AA7075/6060 bilayer billets is introduced to manufacture hybrid components with strength in the core and good corrosion-resistance in the shell. Using optimized compound casting parameter, metallurgical bonding between the shell AA6060 and the core AA7075 can be achieved through remelting and recrystallization of the substrate AA7075. The locally unequal thermal conditions at the interface induces partially weak bonding. The bonding strength in greater distance from the casting gate is generally lower. Hot extrusion is applied to improve the interfacial bonding. Comparisons of the microstructure and the shear strength between as-cast billet and extrudate present the homogenization of the interfacial bonding through the process chain. %0 journal article %@ 2075-4701 %A Palacios Trujillo, C., Victoria-Hernandez, J., Hernandez-Silva, D., Letzig, D., Garcia-Bernal, M. %D 2021 %J Metals %N 4 %P 606 %R doi:10.3390/met11040606 %T Superplasticity at Intermediate Temperatures of ZK60 Magnesium Alloy Processed by Indirect Extrusion %U https://doi.org/10.3390/met11040606 4 %X Magnesium alloys usually exhibit excellent superplasticity at high temperature. However, many Mg alloys have poor formation ability near room temperature. Therefore, preparation of Mg alloys with suitable microstructures to show low or intermediate temperature superplasticity is an important goal. In this work, the superplastic behavior at intermediate temperatures of a commercial ZK60 magnesium alloy processed by indirect extrusion was investigated. After extrusion, the alloy showed a refined and homogeneous microstructure with an average grain size of 4 ± 2 μm. Overall texture measurement indicated that the alloy showed a strong prismatic texture with the highest intensity oriented to pole ⟨101¯0⟩. A texture component ⟨1¯21¯1⟩ parallel to the extrusion direction was found; this type of texture is commonly observed in Mg alloys with rare earth additions. Tensile tests were performed at temperatures of 150, 200, and 250 °C at three strain rates of 10−2, 10−3, and 10−4 s−1. A very high ductility was found at 250 °C and 10−4 s−1, resulting in an elongation to failure of 464%. Based on calculations of the activation energy and on interpretation of the deformation mechanism map for magnesium alloys, it was concluded that grain boundary sliding (GBS) is the dominant deformation mechanism. %0 journal article %@ 0010-938X %A Mei, D., Wang, C., Nienaber, M., Pacheco, M., Barros, A., Neves, S., Reis, R., Zhu, S., Bohlen, J., Letzig, D., Guan, S., Zheludkevich, M., Lamaka, S. %D 2021 %J Corrosion Science %P 109567 %R doi:10.1016/j.corsci.2021.109567 %T Corrosion behavior of Mg wires for ureteral stent in artificial urine solution %U https://doi.org/10.1016/j.corsci.2021.109567 %X Ureteral stents are a relatively new potential application for biodegradable Mg alloys. In this study, the corrosion behavior of Mg-1Zn wires and pure Mg wires in artificial urine solution (AUS) is investigated. It is found that AUS possesses a strong pH buffer effect. Hydrogen evolution measurement cannot be used for Mg corrosion test in this AUS due to the oxygen scavenging effect of sulfite, which is a component of AUS. The corrosion products consist of two layers, MgNH4PO4·6H2O and Mg(OH)2. The partially protective MgNH4PO4·6H2O slows down the Mg corrosion, but it indicates the encrustation risk on bare Mg-based ureteral stents. %0 journal article %@ 1005-0302 %A Jin, Y., Blawert, C., Hang, H., Wiese, B., Bohlen, J., Mei, D., Deng, M., Feyerabend, F., Willumeit, R. %D 2021 %J Journal of Materials Science & Technology %P 214-224 %R doi:10.1016/j.jmst.2021.04.005 %T Deteriorated corrosion performance of micro-alloyed Mg-Zn alloy after heat treatment and mechanical processing %U https://doi.org/10.1016/j.jmst.2021.04.005 %X The corrosion performances of the as-cast and solution-treated Mg-0.5Zn samples were investigated in 0.9% NaCl solution and compared. From the electrochemical measurement results and corrosion morphology observations, it is found that the corrosion resistance of Mg-0.5Zn deteriorated with the extension of solution treatment duration. The main reason was the formation of Fe-Si precipitates with higher Fe concentrations during heat treatment. The Fe-Si precipitates, especially the ones with high Fe contents influenced the corrosion initiation and propagation significantly. In regard of corrosion performance, the solution-treated and then extruded sample was also performing not as good as the cast and then directly extruded sample. %0 journal article %@ 2075-4701 %A Chavez, L., Veleva, L., Feliu, S., Giannopoulou, D., Dieringa, H. %D 2021 %J Metals %N 6 %P 990 %R doi:10.3390/met11060990 %T Corrosion Behavior of Extruded AM60-AlN Metal Matrix Nanocomposite and AM60 Alloy Exposed to Simulated Acid Rain Environment %U https://doi.org/10.3390/met11060990 6 %X The present work compared the initial stages of corrosion process development on the AM60-AlN metal matrix nanocomposite surface and on AM60, during their exposure for 30 days to simulated acid rain solution (SAR). The AlN nanoparticles were observed as “attached” to those of Mn-rich AlMn intermetallic particles, forming clusters. The introduction of 1.0 wt.% AlN (≈ 80 nm) in the AM60 alloy carried a slight grain refinement and favored the formation of a denser and more protective corrosion layer, suggested by the electrochemical impedance spectroscopy (EIS) values of higher charge transfer resistance (R2) and capacitance, characteristic of the double layer in the presence of corrosion products, and also suggested by Rn (EN) values, compared to those of the AM60 alloy. Thus, the concentration of the released Mg-ions from the composite surface was lower. Due to the increase in time of the SAR solution pH, Al de-alloying may occur, as well as Al(OH)3 formation, as confirmed by XPS analysis. Due to the presence of Cl-ions in SAR solution, localized corrosion was observed, suggested as fractional Gaussian noise of a stationary and persistent process in time, according to the PSD of the corrosion current fluctuations (EN). %0 journal article %@ 2405-4615 %A Yang, H., Patel, J., Yang, X., Gavras, S., Dieringa, H. %D 2021 %J Current Nanomaterials %N 2 %P 106-118 %R doi:10.2174/2405461506666210420133620 %T Properties of Mg-based Metal Matrix Nanocomposites Processed by High Shear Dispersion Technique (HSDT) - A Review %U https://doi.org/10.2174/2405461506666210420133620 2 %X Metal Matrix Nanocomposites (MMNCs) often show excellent properties as compared to their non-reinforced alloys due to either the achieved grain refinement or Orowan strengthening. Especially in light metals such as aluminium and magnesium as the matrix has the potential to be significantly improved in relation to mechanical properties. Functionalisation can also be achieved in some cases. However, the challenge lies in the homogeneous distribution of the ceramic nanoparticles in the melt if MMNCs have been processed via melt metallurgical processes. The large surface area of the nanoparticles generates large van der Waals forces, which need to be overcome. Furthermore, the wettability of the particles with molten metal is difficult. Additional forces can be applied by ultrasound, electromagnetic stirring, or even high-shearing. In this paper, properties of MMNCs with a light metal matrix, which have been produced with the High-Shearing Dispersion Technique are discussed. First, the process with its different characteristics and the underlying theory is presented, and then property improvements are discussed by comparing MMNCs to their matrix materials. %0 journal article %@ 0007-8506 %A Ben Khalifa, N., Isakovic, J., Bohlen, J. %D 2021 %J CIRP Annals %N 1 %P 231-234 %R doi:10.1016/j.cirp.2021.04.006 %T New concepts of extrusion dies to reduce the anisotropy of extruded profiles by means of additive manufacturing %U https://doi.org/10.1016/j.cirp.2021.04.006 1 %X The directionality of material flow in established forming processes often leads to a material-specific development of anisotropic mechanical properties. The significance is determined by the process related state variables. A new approach to control the state variables and to reduce the mechanical anisotropy is based on an extrusion die design concept where material flow components perpendicular to the extrusion direction (ED) are adjusted. Specially shaped internal free-form surfaces require additive manufacturing for the establishment of the dies. A concept for a flat band profile is elaborated and the impact on exemplary lightweight alloys, aluminum alloy AA6060 and magnesium alloy AZ31 is discussed. %0 journal article %@ 2213-9567 %A Kandemir, S., Gavras, S., Dieringa, H. %D 2021 %J Journal of Magnesium and Alloys %N 5 %P 1753-1767 %R doi:10.1016/j.jma.2021.03.029 %T High temperature tensile, compression and creep behavior of recycled short carbon fibre reinforced AZ91 magnesium alloy fabricated by a high shearing dispersion technique %U https://doi.org/10.1016/j.jma.2021.03.029 5 %X The present study seeks the feasibility of using short carbon fibres recycled from polymer matrix composites as alternative to virgin carbon fibres in the reinforcement of magnesium alloys. The microstructures, high temperature mechanical and creep properties of AZ91 alloy and its composites with various recycled carbon fibre contents (2.5 and 5 wt.%) and lengths (100 and 500 μm) were investigated in the temperature range of 25–200 °C. The microstructural characterization showed that the high shear dispersion technique provided the cast composites with finer grains and relatively homogenous distribution of fibres. The materials tested displayed different behaviour depending on the type of loading. In general, while enhancements in the mechanical properties of composites is attributed to the load bearing and grain refinement effects of fibres, the fluctuations in the properties were discussed on the basis of porosity formation, relatively high reinforcement content leading to fibre clustering and interlayer found between the matrix and reinforcement compared to those of AZ91 alloy. The compressive creep tests revealed similar or higher minimum creep rates in the recycled carbon fibre reinforced AZ91 in comparison to the unreinforced AZ91. %0 journal article %@ 2213-9567 %A Millán-Ramos, B., Morquecho-Marín, D., Silva-Bermudez, P., Ramírez-Ortega, D., Depablos-Rivera, O., García-López, J., Fernández-Lizárraga, M., Victoria-Hernández, J., Letzig, D., Almaguer-Flores, A., Rodil, S.E. %D 2021 %J Journal of Magnesium and Alloys %N 6 %P 2019-2038 %R doi:10.1016/j.jma.2021.07.010 %T Biocompatibility and electrochemical evaluation of ZrO2 thin films deposited by reactive magnetron sputtering on MgZnCa alloy %U https://doi.org/10.1016/j.jma.2021.07.010 6 %X Biodegradable magnesium alloys are promising candidates for temporary fracture fixation devices in orthopedics; nevertheless, its fast degradation rate at the initial stage after implantation remains as one of the main challenges to be resolved. ZrO2-based coatings to reduce the degradation rate of the Mg-implants are an attractive solution since they show high biocompatibility and stability. In this work, the degradation, cytotoxicity, and antibacterial performance of ZrO2 thin films deposited by magnetron sputtering on a Mg-Zn-Ca alloy was evaluated. Short-term degradation of ZrO2-coated and uncoated samples was assessed considering electrochemical techniques and H2 evolution (gas chromatography). Additionally, long term degradation was assessed by mass-loss measurements. The results showed that a 380 nm ZrO2 coating reduces the degradation rate and H2 evolution of the alloy during the initial 3 days after immersion but allows the degradation of the bare alloy for the long-term. The ZrO2 coating does not compromise the biocompatibility of the alloy and permits better cell adhesion and proliferation of mesenchymal stem cells directly on its surface, in comparison to the bare alloy. Finally, the ZrO2 coating prevents the adhesion and biofilm formation of S. aureus. %0 journal article %@ 2213-9567 %A Krüger, D., Zeller-Plumhoff, B., Wiese, B., Yi, S., Zuber, M., Wieland, F., Moosmann, J., Willumeit-Römer, R. %D 2021 %J Journal of Magnesium and Alloys %N 6 %P 2207-2222 %R doi:10.1016/j.jma.2021.07.029 %T Assessing the microstructure and in vitro degradation behavior of Mg-xGd screw implants using µCT %U https://doi.org/10.1016/j.jma.2021.07.029 6 %X Although differences were observed in the degree of screw's near surface microstructure being influenced from machining, the degradation rates of both materials appeared to be suitable for application in orthopedic implants. From the degradation homogeneity point of view no obvious contrast was detected between both alloys. However, the higher degradation depth ratios between the crests and roots of Mg-5Gd ratios may indicated a less homogeneous degradation of the screws of these alloys on contract to the ones made of Mg-10Gd alloys. Due to its lower degradation rates, its more homogeneous microstructure, its weaker texture and better degradation performance extruded Mg-10Gd emerged more suitable as implant material than Mg-5Gd. %0 journal article %@ 2075-4701 %A Jo, S., Letzig, D., Yi, S. %D 2021 %J Metals %N 4 %P 468 %R doi:10.3390/met11030468 %T Effect of Al Content on Texture Evolution and Recrystallization Behavior of Non-Flammable Magnesium Sheet Alloys %U https://doi.org/10.3390/met11030468 4 %X The effect of Al content on the texture evolution and recrystallization behavior of the non-flammable Mg sheet alloys containing Ca and Y was investigated in this study. With a decrease in the Al content from 3 wt.% to 1 wt.%, the amounts of the other alloying elements dissolved in the matrix, especially Ca, are increased. The increase of the alloying elements in a solid solution brought out the retarded recrystallization and weakened texture with the basal poles tilted toward the sheet transverse direction. Extension twinning activity increased when Al content with decreasing, resulting in the texture broadening towards the sheet transverse direction in the as-rolled sheets. The textures of the AZXW1000 and AZXW2000 sheets weaken uniformly in all sample directions during annealing, while the AZXW3000 sheet shows less weakening of the rolling direction split component. The texture weakening of the alloys with lower Al contents is attributed to the retarded recrystallization caused by the larger amount of the dissolved Ca solutes. Based on the non-basal texture and relatively stable grain structure, the Mg alloy sheet containing a relatively small amount of Al is advantageous to improve the formabili