Effect of cold rolling on microstructural stability and abnormal grain growth in friction stir welded 7075 aluminum alloy

7075 aluminum alloy is extensively employed in aerospace, automotive, and marine sectors due to its superior strength-to-weight ratio. Nevertheless, friction stir welded joints often suffer from abnormal grain growth (AGG) during T6 heat treatment. This study investigates the mechanism behind AGG in FSW joints and explores cold rolling as a mitigation strategy. Welding was carried out on 6.3-mm thick 7075-T651 aluminum alloy plates, using optimized parameters followed by cold rolling with 10–30% thickness reduction before undergoing T6 treatment. Optical macroscopy and electron backscatter diffraction (EBSD) showed severe AGG in joints without rolling, whereas cold-rolled samples exhibited finer grains and strong resistance to AGG. The improvement is attributed to increased dislocation density, texture randomization, and enhanced recrystallization potential induced by cold rolling. Vickers microhardness results showed improved hardness and its uniformity across the weld, with the highest value of 197 HV obtained at 30% reduction. Overall, cold rolling, particularly at 30% reduction, effectively stabilizes the microstructure of FSW 7075 aluminum alloy and improves its reliability in heat-treated conditions.