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 mm to 24 mm and 26 mm, 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. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).