Excimer Laser Processing of Al Containing Mg Alloys for Improved Corrosion Resistance

The implementation of Mg-based alloy components in Cl- containing environments is limited by the poor intrinsic corrosion resistance of the wrought alloys. Galvanic coupling of cathode secondary phase particles to the anodic Mg matrix combined with a low electrochemical potential result in an accelerated H-2 evolution reaction, the controlling reaction of Mg corrosion. This behavior is closely followed by anodically induced cathodic behavior. To mitigate the accelerated corrosion rates, localized dissolution of secondary phases was performed by laser processing on three Al containing Mg alloys: AZ31B-H24, AM60B, and AZ91D. Mixed dissolution of the secondary phases was observed by electron and chemical microscopy. An order of magnitude increase in the electrochemical impedance estimated corrosion resistance was observed for the laser processed specimens immersed in a 0.6 M NaCl solution (18-60 h). The substantial increase in corrosion resistance stems from the reduced density of electrochemically noble secondary phase particles and localized enrichment of Al.