Effect of shot peening and ultrasonic shot peening duration on surface integrity and electrochemical behavior of AZ31 magnesium alloy

Abstract

This study examines the impact of conventional shot peening (SP) duration (20, 40, and 80 minutes) on the surface properties and electrochemical behavior of AZ31 magnesium alloy in 3.5 % NaCl. SP with 2 mm steel balls generated nanocrystalline surface layers, with thickness increasing from 50 µm (20 min) to 200 µm (80 min). Microhardness improved by 216 % after 80 minutes, while surface roughness rose from 8.2 µm to 12.4 µm with prolonged peening. Electrochemical tests revealed optimal behavior resistance at 20 minutes, attributed to grain refinement. Extended peening (80 min) degraded electrochemical performance due to increased surface roughness and energy. For comparison, ultrasonic shot peening (USP) was also applied, showing superior grain refinement (>250 µm layers, ∼12 nm crystallites) and lower roughness. The results highlight the critical role of SP duration in balancing mechanical enhancement and corrosion resistance for AZ31 alloy applications.