Age hardening and thermal stability of Al–Cu alloy processed by high-pressure torsion

An age-hardenable Al–4 wt% Cu alloy is severely deformed using high-pressure torsion (HPT) to refine the microstructure to an average gain size of ~210 nm. High saturation hardness of 205 Hv and high tensile strength of 820 MPa are achieved after the HPT processing. It is shown that the strength of the HPT-processed alloy is further improved by natural aging at room temperature or by artificial aging at 353 K. A peak hardness followed by softening appears within a few days after natural aging and within a few minutes after aging at 353 K, suggesting the low thermal stability of the alloy. Quantitative evaluation of different strengthening mechanisms shows that the grain boundary hardening through the Hall–Petch relationship and the precipitation hardening through the Orowan relationship are dominant strengthening mechanisms.