Thermal stability of the ultrafine grained EN AW 6082 aluminium alloy

Abstract

The initially annealed EN AW 6082 aluminium alloy was processed by ECAP-technique (equal-channel angular pressing) at room temperature following route BC up to 6 passes. Equiaxed ultrafine subgrains (main subgrain size of 370 nm) with a high dislocation density were formed by the severe plastic deformation of the fine grained initially annealed alloy state (main grain size of 6.7 µm). The result of the observed refinement and strain hardening of the solid solution was an increase in tensile strength and, on the other hand, a decrease in tensile ductility of the analysed alloy. The formed ultrafine grained microstructure and mechanical properties of ECAPed alloy state was relatively stable up to post-ECAP annealing temperature of 200◦C. The continuous recrystallization of the solid solution and its uniform grain growth was a result of the post-ECAP annealing at temperatures up to 275◦C. Even though the strength of the severely deformed alloy was considerably reduced by this annealing treatment, its yield strength (Rp0.2) was almost twice that of the fully recrystallized initially annealed alloy state. Annealing at the highest temperature of 350◦C initiated a non-uniform solid solution grain growth and a formation of the bimodal grain size distribution. This discontinuously recrystallized alloy state exhibited the typical strain hardening behaviour with large tensile elongation as the initially annealed one.