Fundamental understanding of the corrosion performance of laser-melted metallic alloys

It is generally accepted that laser surface melting (LSM) can be used for improving the corrosion resistance of metallic alloys as a result of homogenization/refinement of microstructure, dissolution/redistribution of precipitates or inclusions and phase transformation. However, some studies have shown that laser-treated surfaces do not always exhibit enhanced corrosion performance. To date, no satisfactory explanation has been given for the findings, in particular concerning the relationship between microstructure and electrochemical responses. This paper summarises the results of the investigations into the corrosion performance of various laser-melted metallic alloys, including AA 2014-T6 and AA 2024-T351 aluminium alloys, AISI 304L austenitic stainless steel and 3CR12 dual-phase steel, to enhance the knowledge of important, but poorly understood relationships between corrosion and microstructural characteristics of surfaces following laser treatment. It has been found that apart from the refinement/homogenization of microstructure, other factors, such as the electrochemical nature of various intermetallics with respect to the solid solution matrix and heat-affected zones produced by overlapping, and phase transformation determined by cooling rate, play key roles in corrosion behaviour after the laser treatment.