Dissimilar friction stir welding of 2219-T8 and 2195-T8 aluminum alloys for fuel tanks: part II—effect of multi-pass repair welding

During the fabrication of fuel tanks by adopting friction stir welding (FSW), welding defects were almost unavoidable. The multi-pass repair FSW is the preferred repair welding technique for fuel tanks. However, the effect of muti-pass repair FSW on the microstructure and mechanical properties of dissimilar FSW 2219Al/2195Al joints lacks of investigation. In the present study, 2219Al-T8/2195Al-T8 plates were subjected to 1 3 passes repair FSW under 600 rpm–200 mm min−1 based on the initial joint 800 rpm–200 mm min−1 with placing 2219Al-T8 plates on the advancing side (AS). The results showed that, sound 1–3 passes repair FSW joints were obtained. The low hardness zone (LHZ) on the 2219Al-T8 side, characterized by the dissolution/coarsening of θ′ (Al2Cu) precipitates, showed the minimum hardness in the initial joint. Compared to the initial joint, the 1–3 passes repair FSW resulted in the moving of the location of LHZs far away from the weld center and coarser θ precipitates with higher density, and the hardness of the LHZ therefore decreased on the 2219Al-T8 side. The joint strength at − 196 °C was much higher than that at room temperature for both the initial and repair FSW joints. The 1 pass repair FSW weakened the joint strength at both the room temperature and − 196 °C. When increasing the repair pass from 1 to 2 and 3, the joint strength further decreased at room temperature but was unchanged at − 196 °C. The enlarged hardness gap between the nugget zone (NZ) and LHZ caused the narrowing of the necking zone at the LHZ on the 2219Al-T8 side for the multi-pass repair FSW joints. The material flow uniformity at the top of the NZ was improved by the 1 3 passes repair FSW, making the up bending failure location changing from the “S” line for the initial joint to the HAZ on the 2195Al-T8 side for the repair FSW joints.