Effects of temperature and welding heat input on abnormal grain growth in friction-stir welds of 2219 aluminum alloy

Abnormal grain growth occurring during post-weld heat treatment deteriorates the mechanical properties of friction stir-welded joints. This study investigates abnormal grain growth behavior at different temperatures in 2219 aluminum alloy welds produced under various welding parameters. The underlying mechanisms were analyzed using quasi-in-situ EBSD, a modified Humphreys’ model, and cellular automata simulations. Results indicate that the mean size of the largest abnormal grains in the stir zone peaks at a critical temperature, which increases from 733 K to 783 K as the rotational speed rises from 800 rpm to 1600 rpm. At 808 K, abnormal grains exhibit lower mean dislocation density and Zener pinning than normal grains, with these differences amplified by lower temperatures or higher welding heat inputs. Projecting the modified Humphreys’ criterion into a 3D parameter space reveals that elevated temperatures increase the proportion of abnormal grains by reducing Zener pinning. Conversely, a higher welding heat input decreases abnormal grain number by increasing the initial grain size. The cellular automata model successfully captures the competitive growth dynamics among abnormal grains, providing mechanistic verification of the experimental observations and enabling analysis of key factors governing abnormal grain growth evolution under varying thermal conditions.