Effect of recrystallization annealing, solid solution and pre-aging intermediate treatment on microstructure and mechanical properties of Al-Mg-Si rolled sheet

Abstract

The intermediate heat treatment plays an important role in the severe deformation processing of aluminum alloys. In this study, the effects of recrystallization annealing, solid solution and pre-aging intermediate treatments on the microstructure and mechanical properties of Al-Mg-Si sheet were analyzed, and the strengthening ability of grain boundary, residual dislocation and precipitation was explored. The tensile results show that the pre-aging treatment can significantly improve the mechanical properties, increasing the yield strength, ultimate tensile strength and elongation by 22.9 %, 19.9 % and 10.9 %, respectively, compared with the alloy without intermediate treatment. Further studies present that the recrystallization annealed alloys are mainly composed of elongated recrystallized tissue and isometric crystals, and the strength enhancement is mainly attributed to precipitation strengthening. Solid solution treated alloys are composed entirely of fine equiaxed crystals with a higher density of residual dislocations, showing significant grain boundary strengthening and improving the plasticity. Pre-aging treatment obtains the benefits of solid solution treatment, while also forming a large number of GP zones and quasi-β'' phases, which impede the dislocation movement during cold rolling and then increase the effective nucleation sites of precipitation during T6 treatment. This promotes the generation of the strengthening β'' phase, and enhances the precipitation strengthening effect of the alloy from 165.7 MPa in solid solution treatment to 195.6 MPa in pre-aging treatment.