Effects of Heat Treatment on Microstructure and Mechanical Properties of an ECAPed Al-Zn-Mg-Cu Alloy

Equal-channel angular pressing (ECAP) has a considerable advantage in the preparation of bulk fine-grained alloys. To investigate the effect of solid solution treatment (SST) on the microstructure and mechanic properties of an Al-Zn-Mg-Cu alloy after ECAP, a comparative study is conducted using experimental techniques. It is shown that ECAP processing introduces a strong grain refinement, while the SST induces precipitation of skeleton-like second phases distributed discontinuously at the grain boundary and needle-like second phases in the grain. In addition, SST can also improve significantly the fractions of both high angle grain boundaries and recrystallization. The {110}<001 > texture is introduced and the polar density is reduced during SST. Microstructural evolution involves three typical characteristics, namely, shear bands, substructure, and precipitates. The corresponding mechanism of microstructure evolution is proposed, considering the effect of dislocations, precipitates, and grain boundaries. After SST, the improvement of strength and hardness is not obvious, but significant in plasticity by 33.3%. Different strengthening mechanisms are also examined during ECAP and subsequent SST.