Effect of Aging Treatment on Corrosion Resistance of Al-Li Alloy Joint Welded by Electron Beam Welding

Abstract

The post-weld heat treatment (PWHT) was carried out to Al-Li alloy joints welded by electron beam welding (EBW), and the behaviour of intergranular corrosion (IGC), exfoliation corrosion (EXCO) and electrochemical corrosion of different zones of welded joint before and after PWHT were investigated. Results show that the quantity of phase T1 (Al2CuLi) in grain boundary of weldment increases after solution and aging treatment, and the obvious precipitate free zone (PFZ) forms in grain boundary. The IGC does not occur in the joint in as-welded (AW) condition, while the pitting corrosion occurs in both heat-affected zone (HAZ) and base metal of welded joint. The susceptibility to IGC of joint increases after aging treatment, both the pitting corrosion and IGC occurred in HAZ, and the severe IGC appears in base metal. It has excellent EXCO resistance for both weld metal and HAZ in AW condition, while the susceptibility to EXCO is higher for base metal. The EXCO resistance can be improved in base metal after aging treatment; however the susceptibility to EXCO will increase in HAZ. Results of electrochemical corrosion measurement show that compared to the weldment after aging treatment, the self-corrosion potential of weldment is a little higher in AW condition, and its density of self-corrosion current is lower; consequently, it has the relatively better corrosion resistance.