Evaluation of tensile creep behavior of spray formed and extruded 7075 aluminum alloy by equivalent stress

Abstract

This work attempted to investigate the creep behavior of a 7075 aluminum alloy in spray formed and extruded (SFEed) and peak aged (PAed) states by equivalent stress. Arrhenius model and Mukherjee-Bird-Dorn (MBD) model were used to calculate creep parameters. The effects of applied stress or equivalent stress on the creep deformation of SFEed and PAed alloys were discussed and compared. The results showed that the equivalent stress could reasonably evaluate the creep resistance of 7075 Al alloys from the aspects of the steady-state creep rate, creep mechanism and dominate deformation texture, except creep rupture life. Under close equivalent stress, the PAed alloys exhibited superior steady-state creep rates and inferior creep rupture life to the SFEed alloys. The Arrhenius model and MBD model had appropriate ranges of temperature and applied stress to estimate and predict steady-state creep rates, and the accuracy of the MBD model was significantly superior. The stress exponents are computed as 7.03–7.24 for SFEed alloy and 8.11–8.62 for PAed alloy, and the tensile creep mechanism of SFEed and PAed alloys was both dislocation creep. The creep plastic deformation at 0.45–0.65Tm is processed along Cu texture orientation by dislocation climbing rather than S texture. The higher temperature and equivalent stress promote the Cu texture intensity. The applied stress or equivalent stress initiates the slipping and climbing of dislocations, and facilitates the transformation of dominant deformation texture. The main factor that affects grain boundary migration on creep deformation is grain boundary energy rather than stress or equivalent stress.

Keywords

• 7075 Al alloy
• Tensile creep
• Creep resistance
• Equivalent stress
• Applied stress