Microstructure Evolution and Strength Enhancement of Extruded 6061-T6 Aluminum Alloy Metal Inert Gas Welded Joints by Localized Deformation and Stable Annealing

Abstract The joint strength of extruded 6xxx series aluminum alloys deteriorates after MIG welding. A process combining localized deformation with stable annealing has been specifically designed to enhance the strength of 6061-T6 MIG-welded joints. The weld zone (WZ) undergoes varying degrees of localized deformation using a mechanical press at room temperature, followed by distinct stable annealing treatments. Posttreatment analyses reveal microstructural evolution and changes in mechanical properties. Results indicate that localized deformation in the WZ induces the formation of high-density dislocations within a microstructure exhibiting ⟨111⟩Al//WD (welding direction) orientation, leading to the disappearance of the original as-welded microstructure. Subsequent stable annealing develops a {111}⟨110⟩Al plate texture in the WZ, characterized by {111}Al//WD and ⟨110⟩Al//PD (pressing direction). Localized deformation levels between 48% and 58% in the WZ combined with annealing at 220–250 °C yield the best overall mechanical performance, enhancing tensile strength by 29.1% and restoring joint efficiency to 80%. This deformation shifts the joint's weakest point from the WZ to the heat-affected zone (HAZ). Stable annealing promotes static recovery through dislocation annihilation and rearrangement rather than recrystallization. Although strengthening particles precipitate during stable annealing, the primary strengthening mechanism in this process is attributed to strain hardening.