Mechanical properties and microstructures of laser coaxially assisted friction stir welded 2219-T6 aluminum alloy

Laser coaxially assisted friction stir welding process of 2219-T6 aluminum alloy was investigated, concentrating on weld appearance, mechanical properties and microstructure characteristics of the joints. The results show that assisted laser heat can effectively prevent tunnel defect, thus improving joint performance. However, high laser power increases softening of the welded zone and decreases joint performance. Assisted laser heat enlarges the nugget zone (NZ) and increases the size of θ phase (Al₂Cu), but has no obvious effect on microstructures of thermo-mechanically affected zone(TMAZ). T6 heat treatment of the welded joints can obviously increase the joint strength (from 76% of base metal to 100%). The grain sizes in NZ and TMAZ of joints with assisted laser heat are smaller than those without assisted laser after heat treatment.