Severe plastic deformation-induced dissolution of θ" particles in Al–Cu binary alloy and subsequent nature aging behavior

The microstructure and Vickers hardness behavior of Al-4 wt.% Cu alloy bearing θ" precipitates processed by multi-axial compression (MAC) and subsequent nature aging treatment has been studied. θ" precipitates are almost completely dissolved after four passes (ε=1.6) of MAC at room temperature, and a non-equilibrium supersaturated solid solution with a fine grain size of approximately 250 nm is obtained. A slight increase of the hardness occurs during the subsequent nature aging due to the formation of G.P. zones. This is attributed to a large number of vacancies formed during MA compressing, which is sufficient for substantial mass transfer of Cu atom and act as nucleation sites of G.P. zones. Meanwhile, vacancy flux and pipe diffusion of dislocation could greatly enhance the diffusivity and cause a much faster precipitation kinetics compared with the undeformed sample.