Influence of the thermal treatment on the microstructure and hardness evolution of 7075 aluminium layers in a hot-rolled multilayer laminate composite

The microstructure and mechanical properties of the Al 7075 alloy present in a hot roll-bonded laminate consisting of Al 7075/Al 2024 layers have been characterized by high resolution electron backscattering diffraction (EBSD) analysis and Vickers microhardness, respectively. The as-rolled deformation structure consisted in lamellar bands aligned parallel to the rolling direction. It was found that a post-rolling tempering at 175 deg. C/6 h, prior to the T6 treatment has a profound effect on the microstructure and the mechanical properties of the Al 7075 alloy. This tempering reduces the driving force for recrystallization during the usual solution treatment of 30 min that is part of the T6 treatment. The performed procedures favour a more homogeneous precipitation during the following age hardening step and the achievement of a noticeable increase in Vickers microhardness.