Thermo-mechanical response, anisotropy, and texture evolution of two overaged Al 7056 alloy plates in T761 and T721 tempers: Experiments and Modeling

Abstract

The purpose of this research is to investigate the thermo-mechanical response, anisotropy, and texture evolution of two overaged AA7056 plates, in T761 and T721 tempers, over a wide range of strain rates (10-4 � 3 x 103 s-1) and temperatures (22 � 300?C) under uniaxial compression and tension loading along the rolling, 45? to rolling, transverse, and normal directions. First, a detailed study of the initial microstructure reveals an increase in precipitate size and decrease in density of precipitates, as the alloy is aged from the T761 to T721 temper; which in turn affects the flow stress and strain hardening behavior. Second, the thermo-mechanical behavior and texture evolution of the two tempers are measured over a strain rate range of 10-4 s-1 to 3 x 103 s-1 and temperature range of 22?C to 300?C under uniaxial tension and compression loading along different loading directions. Experimental results show that the anisotropic response, as well as the differences in flow strength, strain hardening rate, and tension-compression asymmetry in the two tempers, are apparent at the lower temperatures (22?C & 100?C) and decrease significantly at the higher temperatures (200?C & 300?C). The initial texture measurements show a strong texture gradient along the normal direction of the plate. This texture gradient does not affect the ultimate stress. However, it does have a considerable effect on the failure strains of specimens taken from different locations through the thickness. It is also evident that the initial texture does not affect the yield stress; however, it does have a strong impact on the strain hardening behavior and plastic strain ratio. Third, the Khan-Liang-Liu model is modified to correlate with the measured thermo-mechanical responses of the two tempers over the studied, wide range of strain rates and temperatures. The Khan-Liang-Liu model is verified using strain rate jump and non-proportional loading experiments in compression and free-end torsion experiments. In addition, the modified Khan-Liang-Liu model is used along with the Khan-Yu yield criterion to correlate the yield loci of the AA7056-T761 and AA7056-T721 plates at different plastic strains and deformation temperatures.