Effect of dynamic plastic deformation on the microstructure and mechanical properties of an Al–Zn–Mg alloy

A supersaturated Al–Zn–Mg alloy was processed by dynamic plastic deformation (DPD) using a Split-Hopkinson pressure bar (SHPB) facility with strain range from 0.5 to 1.5 and then subjected to compressive testing at strain rates of 1 × 10⁻³–4 × 10³ s⁻¹. The results show that there is concurrent occurrence of grain refinement, increase in dislocation density and precipitation of fine precipitates in different morphologies during DPD at strain over 1. This enhances the yield strength of the Al alloy after DPD over the as-received material in peak-aging state (T6). Grains are refined through the formation of low angle grain boundaries (LAGBs) by rearrangement of dislocations which leads to the subdivision of original grains. Heterogeneous coarse precipitates mainly of T (Al₂₀Cu₂Mn₃) and E (Al₁₈Mg₃Cr₂) phases distribute along dislocations and grain boundaries after DPD. Dynamic precipitation of very fine η′ and η during DPD occurs where the volume fraction of precipitates increases with increasing the number of presses. The influence of precipitates on the strain rate sensitivity is also discussed.