Repairing the 7075 Al alloy plate by additive friction stir deposition with different feedstock rods

Structural repair of high-strength 7075 Al alloys is vital in aerospace and defense field. Nevertheless, conventional melting-based welding methods pose challenges in achieving this due to the generation of solidification defects. In this work, 7075 Al alloy plates were successfully repaired by an emerging solid-state additive manufacturing technology, additive friction stir deposition (AFSD). The effect of different heat treatment states of feedstock rod (T6-treated and solution-treated) on the microstructure and mechanical properties of the repaired zone were systematically investigated. The results show that the repaired zone of the T-repair specimen is partly filled with material flowing from the sidewall of the hole and partly with deposited fine equiaxed grains, showing no distinct interface. In contrast, the repaired zone of the S-repair specimen is completely filled with deposited equiaxed grains. The T-repair showed higher mechanical properties of 312.6 MPa and 9.7%, respectively, compared to 252.1 MPa and 7.9% for the S-repair. To further improve the mechanical properties of T-repair, post-repair heat treatment (PRHT) was performed. After PRHT, the tensile strength of T-H-repair increased to 491 MPa, but elongation decreased significantly. The decreased elongation after PRHT can be ascribed to the aggregation of precipitated phases at the repair interface.