Improving electrochemical corrosion properties of AZ31 magnesium alloy via phosphate conversion with laser shock peening pretreatment

Abstract

Magnesium alloys are commonly applied in the engineering fields, on account of their superior specific stiffness and specific strength. However, poor corrosion resistance restricts their potential applications. In this study, a new surface treatment method for enhancing corrosion resistance by preparing phosphate conversion coating (PCC) with laser shock peening (LSP) pretreatment is proposed. The effect of PCC with and without LSP pretreatment on electrochemical corrosion behaviors of AZ31 Mg alloy is investigated. The phase, microstructure, and PCC morphologies are characterized. Results indicate that the PCC with LSP pretreatment (LSP-PCC) sample, with lower corrosion current density and higher impedance, exhibits an outstanding corrosion resistance, which is superior to that of the PCC sample. Refined grains and crystal defects induced by LSP are beneficial for increasing the thickness and density of PCC. The improvement in the anticorrosive performance of the LSP-PCC sample is ascribed to the compound effect of the strain strengthened layer and PCC. The strengthening mechanism of the PCC with LSP pretreatment on electrochemical corrosion behavior is revealed.