Influence of Surface Mechanical Attrition Treatment Parameters on Microstructure and Residual Stress of Mg5Zn0.2Ca Alloy

Abstract

Mg5Zn0.2Ca is a promising alloy for medical tools owing to its excellent biocompatibility and biodegradability. This study presents the impact of surface mechanical attrition treatment (SMAT) parameters, explicitly colliding balls velocity (1, 5, and 10 m/s), and surface coverages (500, 1000, and 2000%), on the microstructure, hardness, and residual stress. SMAT forms a layer with a gradient in hardness, crystallite size, and twins. The surface hardness, which ranges between 68 and 118 HV0.05, increases with increased ball velocity and surface coverage. High ball velocity (10 m/s) and surface coverage (2000%) induce high compressive residual stress of about −175.5 MPa at ~600 µm depth. The specimens SMATed with a ball velocity of 5 m/s exhibit the higher surface compressive residual stress for all surface coverages. The maximum compressive residual stress of about −153.5 MPa is observed at the surface for the specimens SMATed at 5 m/s ball velocity and 500% coverage. The overall analysis reveals that the specimen treated at 10 m/s ball velocity and 2000% surface coverage exhibits the most refined grain structure, finely and densely distributed twins, maximum SMAT-induced thickness (~3000 µm), highest surface hardness (~2.1 times the non-SMATed specimen’s hardness), and maximum compressive residual stress. © 2023, ASM International.