Study on the mechanism of grain size and residual stress coupling distribution on the intergranular corrosion susceptibility of AZ31B magnesium alloy

Abstract

In this paper, homogenization heat treatment and laser shock peening (LSP) processes were successfully carried out regulate the microstructure (grain size, residual stress, and element distribution, etc.) of the AZ31B magnesium alloy substrate surface. Based on the regulated AZ31B magnesium alloy substrate surface, it further explored and analyzed the mechanism and influence pattern of the coupling distribution of grain size and residual stress on the intergranular corrosion susceptibility of the substrate surface. Scanning electron microscopy (SEM) was used to observe the surface morphology, scanning Kelvin probe force microscopy (SKPFM) to observe the surface potential, zero resistance ammeter (ZRA) and scanning vibrating electrode technique (SVET) to measure the galvanic current on the surface, and electrochemical tests were conducted to evaluate its surface corrosion behavior. The experimental results showed that in the residual tensile stress region (large grain region), tensile stress expanded the cracks on both sides of the grain boundaries, allowing corrosive media to penetrate deeper into the material. Under tensile stress, corrosion cavities expanded along grain boundaries and potentially connected to other areas via intragranular microcracks, highlighting the pronounced initiation of corrosion cavities. In areas with residual compressive stress (fine grain regions), the corrosion reaction rate at the grain boundaries decreased, and the initiation of corrosion cavities was delayed or slowed down, resulting in a more uniform corrosion surface. The coupling effect of grain size and residual stress exhibited an inhibitory effect on the initiation of corrosion cavities and corrosion susceptibility at the grain boundaries. Overall, this paper provides an important reference for further understanding and controlling the corrosion resistance of AZ31B magnesium alloy.