Effect of thermal exposure on the strength and stress relaxation response of AA-7075-T6 material

Abstract

Commercial AA-7075-T6 material was subjected to thermal exposure for 60 min in the temperature range 100–300 °C with an interval of 20 °C. There was no noticeable effect of exposure temperature on the yield stress, ultimate tensile stress, and fracture stress in the temperature range 100–200 °C. However, each strength parameter decreased rapidly with the increase in exposure temperature from 200 to 300 °C. This behavior was accounted for in terms of dislocation glide by Orowan mechanism in an atmosphere of semi-coherent ή precipitates (MgZn 2 ) in the main matrix. Stress relaxation at a fixed strain for 1000 s was recorded at various stress levels over the entire stress – strain curve of a given AA-7075-T6 specimen. The stress relaxation rate s increased linearly with the strain ε o at which initial stress σ o was allowed to relax in the specimen. The stress relaxation parameter (d s /d ε o ) varied with exposure temperature in a manner similar to that of the strength parameters. The rate process of stress relaxation in the low-strain region was precipitate – dislocation interaction whereas that in the high-strain region was recovery by cross-slip mechanism. • AA-7075-T6 was thermally exposed for 60 min at 100–300 °C. • Strength parameters remained nearly invariant in the range 100–200 °C. • Strength parameters decreased rapidly with temperature rise from 200 to 300 °C. • Stress relaxation is controlled by precipitate-dislocation interaction at low-strains. • Stress relaxation is controlled by recovery due to cross-slip at high-strains.