Strain rate dependence of compressive behavior in an Al-Zn-Mg alloy processed by ECAP

Experiments were conducted to study the compressive mechanical properties of an Al-Zn-Mg alloy after solid solution treatment and equal-channel angular pressing (SS-ECAP) using strain rates ranging from 1.0 × 10⁻³ to 3.0 × 10³ s⁻¹. The results show that SS-ECAP processing enhances the compressive strength due to the high dislocation density, large numbers of fine precipitates and grain refinement. The alloy in both the peak-aged (as-received) and the SS-ECAP states shows a strain rate strengthening effect such that the strain rate sensitivity increases with increasing strain rate. The high volume fraction of fine precipitates in the SS-ECAP alloy decreases the strain rate sensitivity. The coarse precipitates in the peak-aged alloy are fragmented while their sizes increase in the SS-ECAP alloy due to dynamic precipitation assisted by the high density of dislocations during compressive testing. With increasing strain rate, the size of the precipitates further increases for the SS-ECAP alloy and this is influenced by accelerated dislocation motion. During compression, the T (Al₂₀Cu₂Mn₃) and E (Al₁₈Mg₃Cr₂) phases evolve into a new tetragonal phase containing Mg, Mn, Cr and Zn with Al.