Microstructure evolution and corrosion behavior of Ti-6Al-4V alloy induced by laser shock peening without coating

Abstract

Ti-6Al-4V alloy has been widely used in various engineering fields due to its excellent mechanical properties. However, when applied in marine environments, its surface is susceptible to electrochemical corrosion caused by chloride ion erosion, which significantly restricts the long-term service performance and reliability of the alloy under harsh marine conditions. Therefore, it is imperative to enhance its corrosion resistance through surface modification techniques. To address this issue, the laser shock peening without coating (LSPwC) technique was applied to enhance the alloy surface properties. A hydrophobic structure and an oxide layer were fabricated on the Ti-6Al-4V surface through controlled gradient laser energy and multiple impact passes. The corrosion resistance mechanism induced by LSPwC was systematically investigated. Results indicated that LSPwC treatment increased the alloy's surface roughness while generating a dense oxide layer. The microhardness of the treated alloy increased by 30 %, and the residual compressive stress increased from −120 MPa in the base state to −615 MPa. Through contact angle testing, it was found that the contact angle of the alloy surface after LSPwC treatment increased to over 100°. After LSPwC treatment, the average grain size of the alloy decreased from 1.38 μm to 1.10 μm, while the average KAM value increased from 0.63° to 0.72°. Simultaneously, the alloy subjected to LSPwC generated a significant number of dislocation structures. Electrochemical analyses further demonstrated that the treated alloy exhibited a larger impedance arc radius, elevated charge transfer resistance, a positive shift in corrosion potential, and a substantial reduction in corrosion current density. These findings provide critical theoretical support for applying LSPwC-treated Ti-6Al-4V alloys in marine corrosion-resistant applications.