Influence of pre-torsion and low-temperature aging on ZK60 magnesium alloy

Abstract

Magnesium alloys are widely used in aerospace and automotive industries due to their lightweight. However, their poor fatigue performance limits the broader application, especially in dynamic stress environments. This study explores novel coupled pretreatments of free-end large-angle pre-torsion and low-temperature aging to improve the fatigue resistance of rolled ZK60 magnesium alloy. STA (pre-torsion followed by low-temperature aging) and SAT (low-temperature aging followed by pre-torsion) samples were prepared to investigate the influences of pretreatment coupling sequences. The results of microstructure characterization reveal that pre-torsion significantly enhances the formation of tensile twins and introduces a gradient microstructure with increased dislocation density from the center to the edges. STA process resulted in the highest twinning area fraction of 35.2 % and a kernel average misorientation of 0.94 at the edge. Mechanical testing demonstrated that the coupled pre-treatment obtained a better combination of strength and plasticity, significantly improved the yield strength in the compression stage, and increased the tensile-compressive yield ratio to >0.9. In the low-cycle fatigue test, the STA samples exhibited lower cyclic mean stress, a smaller cyclic hardening trend, and better hysteretic symmetry, leading to an improvement in fatigue life of up to 256 %. The findings suggest that the combined pre-torsion and low-temperature aging treatments offer a promising approach to enhance the mechanical properties and fatigue resistance of ZK60 magnesium alloy, making it suitable for structural applications in demanding environments.