The Evolution of Abnormal Grains during the Heating Stage of a Post-Weld Solution Treatment in a Friction-Stir-Welded 2519 Aluminium Alloy

This work presents an in-depth investigation of the early stages of abnormal grain growth (AGG) in a friction-stir-welded (FSWed) 2519-T820 aluminium alloy. Microstructural evolutions, which occurred during the heating stage of a solution heat treatment (SHT), were studied. It was found that the welded materials underwent a complex sequence of precipitation phenomena, which eventually led to AGG. The evolution of precipitates was found to be heavily dependent on the FSW temperature condition. In a weld produced with a low-heat input, a significant portion of the precipitates were retained in the stir zone after FSW and then underwent coarsening and a subsequent dissolution during the annealing that followed. This led to a reduction in precipitation-pinning forces and thus promoted rapid grain coarsening. In a weld produced with a high-heat input, the initial precipitates were completely dissolved during the FSW, owing to the higher temperature, and then partially re-precipitated during the heating stage of the post-weld heat treatment. Due to the fine-grain structure of the stir zone, re-precipitation typically occurred at grain boundaries, thus promoting significant thermal stability. However, at temperatures approaching the SHT temperature, the new precipitates coarsened and then dissolved, resulting in AGG.

Automated summary

This study investigates the early stages of abnormal grain growth (AGG) in a friction-stir-welded 2519-T820 aluminium alloy. Microstructural evolutions during the heating stage of a solution heat treatment (SHT) were studied. The study found that the welded materials underwent a complex sequence of precipitation phenomena, which eventually led to AGG. The evolution of precipitates was heavily dependent on the FSW temperature condition.