Enhanced strength and ductility of friction stir processed Cu–Al alloys with abundant twin boundaries

Ultrafine-grained Cu–Al alloys were prepared via friction stir processing (FSP) with additional rapid cooling. These FSP Cu–Al alloys exhibited equiaxed recrystallized grains with relatively low dislocation density and a high fraction (96%) of high-angle grain boundaries. Abundant annealing twin boundaries were successfully introduced into the ultrafine grains in FSP Cu–15Al (at.%) alloy, resulting in superior strength–ductility synergy with a yield strength of ∼700 MPa and a uniform elongation of ∼13%.