Enhancement of Mechanical Properties of Rolled AZ31 Alloy by Utilizing Ultrasonic Nano-crystalline Surface Modification (UNSM) Treatment and Heat Treatment

Mg alloysMagnesium alloys (Mg alloys) have great potential as lightweight structural materials due to their low density, but their application is limited due to lower mechanical propertiesMechanical Properties compared to other lightweight alloys. The Ultrasonic Nano-crystalline Surface ModificationUltrasonic Nano-Crystalline Surface Modification (UNSM) (UNSM) technique, which induces severe plastic deformationPlastic deformation on the material surface using ultrasonic impacts, can result in a gradient microstructureGradient microstructure with a refined surface consisting of nano-sized grains, and an intermediate microstructure with residual strain, ultimately enhancing mechanical properties. While the nano-crystalline surface contributes to improved strength and ductility, the residual strain in the intermediate microstructureMicrostructure brings about a significant reduction in ductility. However, the residual strain can be beneficial for both strength and ductility through recovery and recrystallizationRecrystallization, achieved through an appropriate annealing treatment. In this study, we applied the UNSMUltrasonic Nano-Crystalline Surface Modification (UNSM)-treatment, followed by subsequent annealing at 200 °C, to a homogenized rolled AZ31 alloyAZ31 alloy to simultaneously improve strength and ductility by generating a gradient microstructureGradient microstructure.