Microstructural Evolution and Mechanical Properties in Superlight Mg-Li Alloy Processed by High-Pressure Torsion

Qian Su; Jie Xu; Yuqiao Li; Jae Ik Yoon; Debin Shan; Bin Guo; Hyoung Seop Kim

doi:10.3390/ma11040598

Microstructural Evolution and Mechanical Properties in Superlight Mg-Li Alloy Processed by High-Pressure Torsion

Materials (Basel). 2018 Apr 13;11(4):598. doi: 10.3390/ma11040598.

Authors

Qian Su^{1

2}, Jie Xu^{3

4}, Yuqiao Li^{5

6}, Jae Ik Yoon⁷, Debin Shan^{8

9}, Bin Guo^{10

11}, Hyoung Seop Kim¹²

Affiliations

¹ Key Laboratory of Micro-Systems and Micro-Structures Manufacturing of Ministry of Education, Harbin Institute of Technology, Harbin 150080, China. 14B909052@hit.edu.cn.
² School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China. 14B909052@hit.edu.cn.
³ Key Laboratory of Micro-Systems and Micro-Structures Manufacturing of Ministry of Education, Harbin Institute of Technology, Harbin 150080, China. xjhit@hit.edu.cn.
⁴ School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China. xjhit@hit.edu.cn.
⁵ Key Laboratory of Micro-Systems and Micro-Structures Manufacturing of Ministry of Education, Harbin Institute of Technology, Harbin 150080, China. liyuqiaohit@126.com.
⁶ School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China. liyuqiaohit@126.com.
⁷ Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 37673, South Korea. suq33023@gmail.com.
⁸ Key Laboratory of Micro-Systems and Micro-Structures Manufacturing of Ministry of Education, Harbin Institute of Technology, Harbin 150080, China. shandebin@hit.edu.cn.
⁹ School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China. shandebin@hit.edu.cn.
¹⁰ Key Laboratory of Micro-Systems and Micro-Structures Manufacturing of Ministry of Education, Harbin Institute of Technology, Harbin 150080, China. guobin@hit.edu.cn.
¹¹ School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China. guobin@hit.edu.cn.
¹² Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 37673, South Korea. hskim@postech.ac.kr.

Abstract

Microstructural evolution and mechanical properties of LZ91 Mg-Li alloy processed by high-pressure torsion (HPT) at an ambient temperature were researched in this paper. The microstructure analysis demonstrated that significant grain refinement was achieved after HPT processing with an average grain size reducing from 30 μm (the as-received condition) to approximately 230 nm through 10 turns. X-ray diffraction analysis revealed LZ91 alloy was consisted of α phase (hexagonal close-packed structure, hcp) and β phase (body-centered cubic structure, bcc) before and after HPT processing. The mean value of microhardness increased with the increasing number of HPT turns. This significantly increased hardness of specimens can be explained by Hall-Petch strengthening. Simultaneously, the distribution of microhardness along the specimens was different from other materials after HPT processing due to the different mechanical properties of two different phases. The mechanical properties of LZ91 alloy processed by HPT were assessed by the micro-tensile testing at 298, 373, 423, and 473 K. The results demonstrate that the ultra-fine grain LZ91 Mg-Li alloy exhibits excellent mechanical properties: tensile elongation is approximately 400% at 473 K with an initial strain rate of 1 × 10^−2 s^−1.

Keywords: Mg-Li alloys; high-pressure torsion; mechanical property; microstructure; ultrafine-grains.