7075 Aluminum alloy welded by laser-TIG hybrid with homogeneous filler wire: Microstructure evaluation and molten pool behavior

Abstract

7075 aluminum alloy has poor weldability and low joint quality, which seriously restricts its development. In this work, laser-TIG (tungsten inert gas) hybrid with homogeneous filler wire was adopted to weld 7075 aluminum alloy, and the microstructure evolution and molten pool behavior of the welded joint were mainly studied. The microstructure of the weld zone showed twin dendrites with main axis grew along the 〈110〉 direction and the symmetrical plane was {111}. When laser-arc hybrid was applied, the decrease of G × R (from 359.54 K/s to 16.15 K/s), increase of G/R (from 0.14 × 108 (K·s)·m−2 to 4.86 × 108 (K·s)·m−2). The strong convection (0.41 m/s) inside the molten pool jointly promoted the formation of twin dendrites. Furthermore, the ultimate tensile strength (475 ± 11.1 MPa) reached 80 % of the base material. By filling the homogeneous wire, it was possible to homogenize the welded joint, alleviate the loss of Zn, reinforce the precipitation of η′, and enhance the mechanical properties.