An investigation of microstructural stability in an Al-Mg alloy with submicrometer grain size

The microstructural stability of an Al-3%Mg solid solution alloy with a submicrometer-grained (SMG) structure (∼0.2 μm) was evaluated using both static annealing and transmission electron microscopy over a range of temperatures from 443 to 803 K and differential scanning calorimetry (DSC) up to 773 K. The results show that the SMG structure contains many non-equilibrium grain boundaries but recrystallization occurs at the higher temperatures giving large grains with boundaries having high-angle equilibrium configurations. There are significant differences between the DSC curves of the SMG alloy and a standard cold-rolled Al-3%Mg alloy, due primarily to the advent of significant heat release at low temperatures in the SMG alloy because of recovery at the non-equilibrium grain boundaries. A temperature of ∼500 K, close to half the absolute melting temperature, represents an effective upper limit for utilization of the SMG structure in this material.