Effect of ultrasonic surface rolling process on mechanical properties and corrosion resistance of AZ31B Mg alloy

Abstract

Ultrasonic surface rolling process (USRP) is a novel surface nanocrystallization technique based on high frequency impact of tool head. It can generate severe plastic deformation on the surface layer of the material, and greatly enhance the mechanical properties and corrosion resistance of the material. AZ31B Mg alloy was treated by using HK30C ultrasonic surface rolling process (USRP) machine. The effects of different parameters of USRP on surface roughness, microstructure, mechanical properties and corrosion resistance were investigated. The results of the test indicate that the surface roughness is decreased by 91.8% compared with the untreated specimen. Severe plastic deformation in the surface layer of AZ31B Mg alloy is formed by USRP, and the grains in the surfaces layer are remarkably refined. The obvious grain refinement layer is found in surface region of USRPed specimens whose average grain size is 50 times lower than that of the interior grains. The depth of grain refinement layer reaches about 572.71 ± 13.62 μm after USRP. Meanwhile, the surface microhardness is increased by 83.81% compared with inner part. The residual compressive stress, tensile properties, wear resistance and corrosion resistance increase to different degrees after USRP. As the amount of rolling increases, the depth of grain refining layer increases, and the mechanical properties of samples are better. When the amount of rolling is 0.06 mm, compared with the untreated and other treated specimens, it can obtain minimum surface roughness, superior mechanical properties and corrosion resistance, respectively. The surface roughness reduction, surface grain refinement and severe plastic deformation caused by USRP are the main reasons for improving the mechanical properties and corrosion resistance of AZ31B Mg alloy.