Microstructure of the post-ECAP aging processed 6061 Al alloys

Microstructural evolution in the post-ECAP aging processed 6061 alloys where remarkable strengthening had been achieved only after a single pressing was investigated. It could be concluded based on the TEM observations that the WQ-ECAPed alloy where ECAP had been applied to the 6061 Al in supersaturated solid-solution state exhibited significantly higher strength than the FC-ECAPed alloy where ECAP had been applied to the 6061 Al in equilibrium state because dislocations were more highly accumulated in the solid solutionized matrix. The further strengthening after the post-ECAP aging in the WQ-ECAPed alloy could be attributed to precipitation of very fine particles with little decrease of dislocation density in matrix. The DSC curves of the unECAPed and ECAPed alloys were analyzed. As the amount of energy released by recrystallization of the severely deformed microstructure was notably smaller than that by precipitation, the DSC results could not provide evidence that the WQ-ECAPed and post-ECAPed alloys possessed higher dislocation densities than the FC-ECAPed alloy. They, however, showed the possibilities that extensive dynamic aging took place during the ECAP process and the matrix retained a high degree of solute-supersaturation even after the post-ECAP aging.