Effect of friction stir repair welding on microstructure and corrosion properties of 2219-T8 Al alloy joints

The single-pass friction stir welding (FSW) of 2219-T8 aluminum alloy (AA2219-T8) with cavity defects were repaired utilizing the FSW repair technique. Combined with the results of thermal cycling, differential scanning calorimetry, transmission electron microscopy, and electrochemical characteristics, the precipitate evolution and its effect on the mechanical and corrosive properties of the FSW repaired joint were studied. The results show that the repair welding eliminated the void defects which formed in the first welding, and obtained a sound weld. Compared with the original joint, owing to the re-thermal action on the heat-affected zone of the repaired joint, the size of the theta' phases thicken but the amount decreased; a larger precipitate-free zone was formed along the grain boundaries, which triggered more severe intergranular corrosion. The theta phase particles in the weld nugget zone (WNZ) of the repaired joint were re-dissolved and re-broken resulting in the size and amount becoming smaller; the grains in the WNZ became refined, and the corrosion resistance was improved.