Improving the corrosion resistance of friction stir welding joint of 7050 Al alloy via optimizing the process route

The macro-galvanic effect in friction stir welding (FSW) joints is contributive for accelerating the localized corrosion of 7xxx aluminum alloy weldment. A process route, solid solution treating→FSW→T76 ageing (SSW-T76), was developed to weak the macro-galvanic effect. The microstructure and corrosion of joints prepared from SSW-T76 route and the conventional route (T76→FSW, T76W) were comparatively investigated. It was found that both precipitate coarsening and solute segregation were effectively suppressed when the route was changed from T76W to SSW-T76. The discrepancy in microstructure, micochemistry and corrosion potential between the base material (BM), the heat-affected zone (HAZ) and the nugget zone (NZ) was narrowed, leading to suppressed macro-galvanic effect and thereafter to decreased pitting and IGC.