Reprecipitation behavior in Al–Cu binary alloy after severe plastic deformation-induced dissolution of θ′ particles

The microstructure and Vickers hardness behavior of Al–4 wt.% Cu alloy bearing θ′ precipitates, subjected to different pass of multi-axial compression (MAC) and re-aging treatments, has been studied. θ′ precipitates are almost completely dissolved after 12 passes (ɛ = 4.8) of MAC, and a non-equilibrium supersaturated solid solution is obtained. When this solid solution is re-aged at 100 °C, a slight increase of the hardness occurs due to the formation of GP zones. Precipitation of equilibrium θ phase is observed along the grain boundaries during re-aging. That is completely different from that of the coarse grained materials. The discrepancy for this unique re-aging behavior is attributed to extremely increasing of nucleation sites for θ phase at non-equilibrium grain boundaries (GB), as well as a large number of dislocations and vacancies acting as diffusion channel for Cu atoms.