The effect of solutionizing heat treatment on ductility loss and damage evolution in AA7075 aluminum sheet deformed at 450°C

Abstract

The high-temperature deformation behavior of AA7075 sheet was investigated using hot tensile testing. The specimens were solutionized at 475 °C for 15 min prior to cooling to a deformation temperature between 300 and 450 °C. AA7075 exhibited a progressive rise in ductility with increasing deformation temperature until a sudden drop in ductility was observed at 450 °C. The loss of ductility is attributed to localized melting at the grain boundaries during the solutionizing step. Increasing the holding time at 450 °C prior to the onset of deformation resulted in the gradual restoration of the ductility of the material as a result of isothermal solidification. Samples which are directly heated to 450 °C, without solutionizing at 475 °C, did not experience any loss of ductility. The elongation of non-solutionized sample was always greater than that of the solutionized one when deformation is carried out at 450 °C. This is attributed to the different distribution of particles on the grain-boundaries within the two materials. Trace analysis revealed that intergranular crack propagation proceeds preferentially on higher-indexed random grain boundary planes such as (533), (420), and (531).