Effect of aging treatment on evolution of S′ phase in rapid cold punched Al−Cu−Mg alloy

Abstract High-resolution transmission electron microscopy (TEM), X-ray diffractometer (XRD), and hardness test were used to study the evolution of long plate-shaped S′ phase in the spray-formed fine-grained Al−Cu−Mg alloy during aging after rapid cold punching deformation. Results show that the long plate-shaped S′ phase in the extruded Al−Cu−Mg alloy undergoes evident distortion, brittle failure, separation and redissolution, during rapid cold punching deformation, leading to the transformation of long plate-shaped S′ phase into short rod or even redissolution and disappearance, causing the matrix to become a supersaturated solid solution. After the aging treatment, the reprecipitation of the phases occurs, and these aging phases are mainly long plate-shaped and granular. The incompletely dissolved S′ phase acts as nucleation core, promoting uphill diffusion of the surrounding solute atoms. The S′ phase gradually grows with increasing the aging time. The completely dissolved S′ phase forms the incoherent equilibrium phase with the matrix to reduce its free energy. After rapid cold punching, the aging response of the deformed Al−Cu−Mg alloy is accelerated, and the hardness of the alloy is substantially increased.