Suppression of softening in TIG welded Al–Cu–Mg alloy

Softening of the weld zone (WZ) in fusion-welded 2024-T4 high-strength aluminum alloys has been a long-term issue, which significantly reduces mechanical properties of the joints. In this study, a post-weld heat treatment process (PWHT) was proposed and optimized to increase the tensile strength and elongation simultaneously. Experimental results demonstrated that the solution treatment has an important effect on eutectic phases and T-Al₂₀Cu₂Mn₃ phases. In particular, compared with the single-stage solution treatment, a two-stage solution treatment led to a 11.59% increase in tensile elongation, which is attributed to a comprehensive modification of the T phase, including a ∼6.0% reduction in size, a 16.0% increase in number density, and an improved uniformity in size distribution. By employing artificial or natural aging after solution processes (S-AA or S-NA), the eutectic phases in the matrix dissolve extensively, resulting in the formation of substantial S–Al₂CuMg/θ′-Al₂Cu precipitates or GP/GPB zones, respectively. The hardness of the WZ approaches that of the base material, and strain localization phenomena are significantly reduced. Quantitatively, the tensile strength and elongation reach 1.03 and 0.65 (S-AA), or 1.01 and 0.74 (S-NA), those of the base material, respectively. This study shows that the PWHT, with flexible processing technologies, is an effective approach to suppress the softening of weld Al alloys, which could be applied in other weld Al alloys.