Crack initiation and propagation mechanisms of an extruded dual-phase Magnesium-Lithium alloy in very high cycle fatigue regime
Xiangyu WANG a, Chao HE* a, b, Xue Li a, Yongjie LIUa, b, Qingyuan WANG* a, c, Lang LI a,b, Hong ZHANGa, b, Chong WANG a, b
a Key Laboratory of Deep Earth Science and Engineering, Ministry of Education, College of Architecture and Environment, Sichuan University, Chengdu 610065, China
b Failure Mechanics & Engineering Disaster Prevention and Mitigation, Key Laboratory of Sichuan Province, Sichuan University, Chengdu 610065, China
c School of Architecture and Civil Engineering, Chengdu University, Chengdu 610106, China
Corresponding authors:
Dr. Chao HE
Sichuan University
Email: hechao@scu.edu.cn
Prof. Qingyuan WANG
Sichuan University
Email: wangqy@scu.edu.cn
Abstract: Ultra-light Mg-Li alloy is a promising alloy in aerospace since it is known to the lightest structural alloy at present, but its fatigue behaviors remain to be explored. This work focuses on very-high cycle fatigue (VHCF) strength and small crack initiation behaviors of an extruded dual-phase Mg-Li alloy (LZ91). The fatigue strength of the LZ91 alloy at 109 cycles is about 78 MPa, and the fatigue ratio is approximately 0.46. Microstructure characterization demonstrates that fatigue crack tends to initiate from the β-Li phase-enriched region. The α-Mg phase, presenting <10−10 >  fiber texture with the basal plane, deforms hardly along the extrusion direction and acts as an enhanced phase compared with the β-Li phase. The deformation discrepancy localizes cyclic plasticity at the Li phase and finally leads to the fatigue crack initiation.
Keywords:Magnesium-lithium alloy; very-high cycle fatigue; crack initiation and propagation; microstructural sensitivity.