Grain boundary anodic phases affecting environmental damage

Abstract

Abstract Stress corrosion characterization is analyzed in two alloys, 5083 and binary AL-3Li, both having anodic grain boundary precipitates. The 5083 commercial alloy forms AL3Mg2 (β phase), whereas the AL-3Li alloys have ALLi (δ phase). These are intermetallic phases that form on the grain boundaries and grow in size and area fraction with heat treatment time. When exposed to the NaCl solution, they anodically dissolve and form grain boundary cracks under an applied stress. A brief electrochemical description of these phases reacting with NaCl solution is described. The crack initiation occurs when the appropriate local environmental conditions at the crack tip and stress state is established. Overall, crack initiation mechanism seems to be a combination of mostly anodic dissolution coupled with hydrogen-assisted cracking.