Experiments were conducted to examine the influence of equal-channel angular pressing (ECAP) and post-ECAP annealing on the microstructures of an Al-Zn-Mg alloy. The results show that precipitates, mainly of the η', η (MgZn 2), T (Al 20 Cu 2 Mn 3) and E (Al 18 Mg 3 Cr 2) phases, are fragmented to fine spherical precipitates during ECAP processing for 4 and 8 passes. After post-ECAP annealing at 393 and 473 K for 20 h, precipitates with larger sizes lie primarily along the grain boundaries and finer particles are evenly distributed within the grains. Increasing the numbers of ECAP passes from 4 to 8 leads to an increase in the volume fraction of the finer precipitates in the ECAP-processed and annealed alloy. After 4 passes and heat treatment at 473 K, the precipitates are slightly larger compared with the alloy processed under identical conditions and annealed at 393 K. Nevertheless, significant coarsening is evident after processing for 8 passes and increasing the annealing temperature from 393 to 473 K. Different types of precipitates are effective in impeding grain growth during the post-ECAP annealing even at 473 K for 20 h. In addition, η precipitates form within the T and E phases after both ECAP and post-ECAP annealing.

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An artificially aged Al-Zn-Mg alloy with a grain size of ~ 1.3 m was processed by equalchannel 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.

An investigation was conducted to study the influence of equal-channel angular pressing (ECAP) and post-ECAP aging at 393 K for 20 h on the microstructures and tensile properties of a supersaturated Al-Zn-Mg alloy together with the effect of pre-ECAP heat treatments on the mechanical properties of the alloy after ECAP and after post-ECAP heat treatments. The results show that during ECAP processing for up to 4 passes for the supersaturated Al alloy there is a simultaneous occurrence of grain refinement, increases in the dislocation density and dynamic aging precipitation forming large numbers of fine spherical well-distributed precipitates which enhance the yield strength but decrease the ductility. During post-ECAP aging, there is a limited dislocation recovery with slight grain growth and the precipitate sizes increase together with the formation of a few larger platelet precipitates and the transformation of G.P. zones to η' and η' to η leading to a strength reduction after 4 passes of ECAP. The precipitates in the ECAP-processed alloy with pre-ECAP in the supersaturated state formed through dynamic aging precipitation are higher in their volume fraction, smaller in their size and more homogeneously distributed in the Al matrix than those in the alloy with pre-ECAP in the peak aging state which mainly come from the fragmented η' existing in the matrix before ECAP. The strengths of the alloy both after ECAP processing and after post-ECAP heat treatments with pre-ECAP in the supersaturation state are higher than with pre-ECAP in the peak aging state.

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