Fabrication of high-strength Mg-Y-Sm-Zn-Zr alloy by conventional hot extrusion and aging

Significance 

The use of magnesium alloys in various applications have immensely increased over the last few years due to their excellent properties. This has attracted the significant interest of researchers who have been looking for alternative ways of enhancing the properties and efficiency of magnesium alloys. Unfortunately, they have limited mechanical properties. However, precipitate strengthening of magnesium-rare earth alloys can be achieved at both room and elevated temperature. To improve on the mechanical properties, several methods have been used. For instance, methods like hot extrusion, aging and hot rolling have been employed.

Generally, high-strength magnesium-rare earth alloys undergo high precipitation hardening effect due to the expensive rare earth metals even though their ductility properties is still wanting. Therefore, researchers have been looking for alternative ways of improving the mechanical properties of magnesium alloys and have identified the addition of Sm as a promising solution. Consequently, it has the capability of reducing the general cost as well. However, medium solubility of Sm in magnesium results in alloys with limited strength. This effect can be minimized by the combination of Y and Gd in magnesium alloy. Furthermore, the addition of zinc in Mg-Y and Mg-Gd alloys results in significantly improved strength due to increased precipitation as well as long period stacking ordered structure phase.

Recently, Beihang University researchers: Shaoyuan Lyu, Dr. Wenlong Xiao, Dr. Ruixiao Zheng, Fang Wang, Tong Hu and Professor Chaoli Ma investigated the strength and ductility properties of Mg-7Y-5Sm-0.5Zn-0.3Zr. They analyzed the material microstructure based on hot extrusion and aging treatments. Their main focus was to improve the aforementioned properties. The research work is currently published in the research journal, Materials Science and Engineering A.

The authors observed that the alloy solution generally contained alpha magnesium matrix while the 14H long period stacking ordered structure phase were distributed at the grain boundaries. This was attributed to the dissolution of the eutectic compounds and the growth of the grain boundaries towards the matrix interior. Consequently, lamellar long period stacking ordered structure phase with 14H structures precipitated significantly during the hot extrusion process. However, they were retained through aging treatment at a temperature of approximately 2000C. Furthermore, they observed the extruded alloy exhibiting a very good aging hardening response and significant improvement in the mechanical properties of the formed alloys and particularly after peak-aged treatment. For instance, at room temperature, ultimate tensile strength, 0.2% proof strength and elongation were recorded as 465MPa, 413MPa and 6.5% respectively.

Indeed Beihang University scientists successfully investigated the mechanical properties of the of Mg-7Y-5Sm-0.5Zn-0.3Zr alloy. The high strength obtained for the alloys was attributed to the prismatic precipitate as well as the combined action of 14H long period stacking ordered structure phase and the dense distribution of the precipitate. Therefore, the research team are optimistic that the study will advance the improvement of not only the properties of magnesium alloys but also other material alloys. With the desired properties and relatively low cost, the potential applications of high strength magnesium alloys will be effectively realized. Also, the study lays the foundation for future research work on efficient methods for fabrication of high performing Mg-Y-Sm-Zn-Zr alloys.

Fabrication of high-strength Mg-Y-Sm-Zn-Zr alloy by conventional hot extrusion and aging - Advances in Engineering
Figure 1 (a) Mg-Y-Sm-Zn-Zr alloy ingot. (b) Microstructures of as-cast and extrusion of this alloy. (c) Age hardening response, tensile properties, types of precipitates in peak-aged alloy.

About the author

Shaoyuan Lyu is a PhD candidate at Beihang University, School of Materials Science and Engineering.

He is involved in the studies on the microstructure, mechanical properties and strengthening mechanism of the Mg-Y-Sm-Zn-Zr alloys.

About the author

Wenlong Xiao is Associate Professor at the School of Materials Science and Engineering at Beihang University in Beijing city. He got his PhD from Jilin University in 2010. When pursued his PhD degree, he was once a visiting scholar at Monash University for 20 months and worked with Prof. Jianfeng Nie and Prof. Mark Easton. After PhD graduation, he made post-doctoral studies at the University of Queensland in Australia and National Institute for Materials Science in Japan. He then joined Beihang University in Nov. 2013.

His research interest includes development of advanced magnesium alloys (high strength, high ductility, and creep resistance), phase transformation and mechanical behavior of titanium alloys, high performance Al-Si alloys. He has published more than 70 publications in peer-reviewed scientific journals.

Reference

Lyu, S., Xiao, W., Zheng, R., Wang, F., Hu, T., & Ma, C. (2018). Fabrication of high-strength Mg-Y-Sm-Zn-Zr alloy by conventional hot extrusion and aging. Materials Science and Engineering : A, 732, 178-185.

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