Effect of TiC/TiC–TiB2 on microstructure and mechanical properties of spray formed 7055 aluminum alloy TIG welded joints

Owing to the notorious hot-crack susceptibility and severe softening fusion-weld joints of Al–Zn–Mg–Cu alloys, they are generally considered unweldable. In this study, TiC/7xxx (TC) and TiC–TiB2/7xxx (BC) aluminum matrix composites, fabricated by in-situ mixed-salt reaction, were used as filler rods of spray formed 7055 alloys to modify the microstructure and mechanical properties of TIG weld joints. Compared with 7055-weld metal (WM), the grain sizes of TC-WM and BC-WM were refined from 100 μm to 24 μm and 26 μm, respectively. The precipitation of eutectic phases in WM was reduced by ceramic particles, which decreased the hot-crack susceptibility of joints. In the as-welded state, the ultimate tensile strength of TC and BC joints increased from 240 ± 5 MPa to 274 ± 5 MPa and 300 ± 5 MPa, respectively. The addition of ceramic particles also improved the impact toughness and hardness of weld joints. Grain refinement, load-bearing strengthening, coefficients of thermal expansion mismatch strengthening, and Zener pinning strengthening are the dominant strengthening mechanisms of weld joints with ceramic particles.