Effects of abnormal grain growth at longitudinal weld on the aging behavior and mechanical properties of 2196 Al Cu Li alloy profile

Abnormal grain growth (AGG) at longitudinal weld of 2196 AlCuLi profile was observed during solution treatment, and the effects of AGG on the aging behavior and mechanical properties of the profile were investigated. The results show that the AGG area almost contained no low angle grain boundaries (LAGBs) while the fine extrusion fibers in the matrix area contained numerous LAGBs. The AGG structure at weld seam leads to precipitated phases coarsening, PFZ widening and a sharp decrease of elongation in profiles. During aging process, the AGG area precipitated more coarse S′/S and T2 phases and exhibited a faster age hardening rate than the matrix area, while the numerous LAGBs in the matrix area promoted the precipitation of strengthening phases (T1, δ′/β′) and suppressed the formation of coarse phases. The phases formed along the grain boundaries are mainly coarse quasi-crystal T2 phases while abundant fine T1 phases formed along the LAGBs of the matrix area, and the PFZ of AGG area is far wider than that in matrix area. During the pre-stretching process, the fine grains and LAGBs of the matrix area conduced to form and store more dislocations, which provided more nucleation sites for T1 phases.