Effect of ECAP processing on microstructure evolution and dynamic compressive behavior at different temperatures in an Al-Zn-Mg alloy

An artificially aged Al-Zn-Mg alloy with a grain size of ~1.3 µm was processed by equal-channel angular pressing (ECAP) and then subjected to dynamic compression at a strain rate of 4000 s⁻¹ in the range from room temperature to 673 K. The results show the η′ phase is refined and a η phase is formed during the first pass of ECAP and after further processing 8 passes the GP zones are removed. An ultrafine-grained (UFG) structure with an average grain size of ~200 nm was obtained after 4 passes. It is shown that dynamic compressive deformation assists the precipitation process through precipitate coalescence and by changing the precipitate orientations. The dynamic compressive yield strengths and flow stresses decrease gradually to different degrees with increasing temperature except after ECAP processing for 4 passes where there is thermal stability up to 473 K. The ECAP processing significantly improves the strength of the alloy at elevated temperatures by comparison with the as-received material.