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.