High temperature tensile properties, fracture behaviors and nanoscale precipitate variation of an Al–Zn–Mg–Cu alloy

In order to assess Al–Zn–Mg–Cu alloys as potential high temperature structural materials, the hardness, tensile properties and fracture behaviors of 7085 Al alloy were investigated at various temperatures from room temperature to 175 °C. High-resolution transmission electron microscopy was used to investigate the evolutions of precipitates at different temperatures, particularly on the relationship between microstructural evolution and tensile strength. The results reveal that both the microstructure and mechanical properties of the alloy are quite sensitive to the environmental temperature. As the temperature increases, the hardness and strength decrease while the elongation and reduction of area increase. As tensile testing temperature rises, the strain hardening exponent (n) decreases due to the thermal softening effect. The fracture mode of the alloy transforms from mixture of intergranular and transgranular fracture to completely transgranular dimples when tensile testing temperature reaches 150 °C. The precipitate sequence during high temperature tests is coincident with that of aging. With the increase of tensile testing temperature, the mean precipitate radius grows larger, and the distribution of grain boundary precipitates transforms from continuous to discontinuous.