Investigation on the Stress Relaxation Property of 2A97 Al-Li Alloy Assisted by Electric Pulse

The influence of the strain on the formability of 2A97-T3 Al-Li alloy during electric pulse-assisted forming was investigated in the research. Electrically assisted stress relaxation tests were conducted, and a corresponding stress relaxation model was developed and validated. The mechanism of the pulsed current influences stress relaxation in the alloy was revealed based on the analysis of stress relaxation curves and microstructure. Optimal processing performance for the 2A97-T3 Al-Li alloy was obtained at 450 A, 12 ms pulse width, 60% duty cycle, and 50 Hz frequency. A yield strength of 89 MPa and an elongation of 13.2% were obtained under the conditions. Furthermore, a residual stress of only 0.142 MPa was recorded after relaxation at ε = 0.0667. Under combined the strain and the Joule heating, the grains were refined by dynamic recovery and recrystallization. Grains first coarsened and then they were elongated, while the proportion of low-angle grain boundaries increased concurrently. Concurrently, the <101> texture strength increased markedly. Its maximum intensity rose from 2.225 to 4.755, which was attributed to the mechanism of continuous dynamic recrystallization. It was demonstrated that the stress was effectively reduced and the formability of the alloy was significantly improved by means of electric pulse-assisted forming.