Change in characteristics of superplastic deformation of the aluminum–lithium alloy under the effect of ultrasonic vibrations

Abstract

The tension of samples of aluminum–lithium alloy 1420 in the superplasticity temperature region T = 320–395°C and the influence of ultrasonic vibrations on deformation characteristics have been investigated. It has been shown that the effect of ultrasound manifests itself in a decrease in resistance to deformation and an increase in total strain. The tension curves plotted in the coordinates true stresses–true strains, in contrast to the standard stress–strain curves, have an extended hardening region, the magnitude of which is larger for the samples deformed with the ultrasound. The stress-rate sensitivity coefficients m have been determined from stress jumps with variations in the tension rate. It has been shown that the quantity m can be assumed to be constant over the entire superplasticity temperature region for different strains with ultrasound and without it, m = 0.46 ± 0.04, and, correspondingly, the stress exponent in the formula for the strain rate is = 2.21 ± 0.23. The activation energies of the deformation process have been evaluated, and it has been concluded that the dislocation motion during the intragrain deformation that is characteristic of the hardening stage is facilitated under the effect of ultrasound.