Optimization of tribocorrosion performance, wear resistance, surface integrity and residual stress of AZ31 magnesium alloy via ultrasonic shot peening

Abstract

Ultrasonic shot peening (USP) was applied to improve the surface characteristics, wear resistance, and corrosion behavior of AZ31 magnesium alloy. The effects of peening duration on surface roughness, microhardness, residual stress, wear performance, and corrosion resistance were systematically investigated. USP produced a modified surface layer and transformed the residual stress state from 43 MPa tensile stress in the untreated alloy to 130 MPa compressive stress after 80 min of treatment. The surface hardness increased significantly from approximately 65 HV in the untreated specimen to 230 HV in the USP80 specimen, corresponding to an enhancement of about 254%. Tribological evaluation revealed a substantial improvement in wear resistance, with mass loss decreasing from 0.30 mg in the untreated specimen to 0.085 mg in the USP80 specimen, representing a reduction of nearly 72%. Electrochemical polarization measurements in 3.5 wt.% NaCl solution demonstrated enhanced corrosion resistance, as the corrosion current density decreased from 57.035 to 8.22 μA cm−2, corresponding to an 85.6% reduction. Although surface roughness increased with peening duration, the beneficial effects of surface refinement, hardening, and compressive residual stresses outweighed its adverse influence. Among all conditions, the USP80 specimen exhibited the best overall performance, demonstrating the effectiveness of USP as a promising surface engineering technique for AZ31 magnesium alloy.