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I.

INTRODUCTION

MAGNESIUM (Mg) and its alloys, due to their lightweight, high specific strength, high specific stiffness, and good processability, are considered as a new type of lightweight material with great application value and research prospect, which are widely used in structural components of aerospace, high-speed trains, automobile and other fields.[1] The deformation mechanism and cracking behavior of Mg alloys under quasi-static

Y.C. DENG, Z.J. HUANG, and D.D. YIN are with the Key Laboratory of Advanced Technologies of Materials, Ministry of Education, School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, 610031, Sichuan P.R. China. Contact e-mail: [email protected] T.J. LI and J. ZHENG are with the International Joint Laboratory for Light Alloys (Ministry of Education), College of Materials Science and Engineering, Chongqing University, Chongqing, 400044, P.R. China. Contact email: [email protected] Y.C. Deng and Z.J. Huang have contributed equally to this work. Manuscript submitted August 22, 2020; accepted October 23, 2020.

METALLURGICAL AND MATERIALS TRANSACTIONS A

loading have been extensively investigated.[2–5] During actual service, structural components are often subjected to alternate loading (fatigue), and it is well known that materials show significantly different deformation mechanism and cracking behavior during fatigue compared to quasi-static uniaxial loading.[6,7] Therefore, research on the deformation mechanism and cracking behavior of Mg alloys during fatigue is essential. It has been shown that the data obtained from strain-controlled fatigue experiments under fully constrained loading conditions are closer to the actual service conditions.[8] Thus, understanding the deformation mechanism and cracking behavior of Mg alloys during strain-controlled fatigue is critical for regulating the service performance of structural components under alternate loading and accelerate the application of Mg alloys. Due to the hexagonal close-packed (HCP) crystal structure, Mg alloys have limited deformation modes at [9,10] Usually, basal hai slip and room  temperature.

   1012 1011 tension twinning are the two dominated deformation modes.[11,12] The limited deformation modes together with strong texture formed in thermomechanical processing caused strong anisotropy and low ductility of traditional Mg alloys at room

temperature,[13–15] which hinders their wide application. It has been demonstrated that addition of rare-earth (RE) element yttrium (Y) can greatly influence the deformation mechanism and resultantly alter the deformation behavior and improve the mechanical property of Mg. Lu et al.[16] reported more than 30 pct tensile elongation of the extruded Mg-Y sheets at room temperature. Zhang et al.[17] observed tension-compression yield symmetry in Mg-7.4Y (wt pct) alloy at room temperature. Long et al.[18] investigated the deformation mechanisms of extruded Mg-Y sheets with various Y contents during room temperature compression. They found that Y can remarkably