The origins of room temperature hardening of Al–Cu–Mg alloys

The most commonly cited mechanisms for the rapid age hardening of Al–Cu–Mg alloys at about 100–200 °C are hardening by Guinier–Preston B zone formation, formation of Cu–Mg co-clusters and a dislocation–solute interaction mechanism. New experiments on ageing–deformation–ageing cycles at room temperature indicate that no substantial additional age hardening occurs with the addition of deformation to the cycle, and hence, a dislocation–solute interaction mechanism appears unlikely. Instead, strengthening due to modulus hardening generated by the difference in shear modulus of Cu–Mg co-clusters and matrix is proposed as the main strengthening mechanism for room temperature hardening.