Tension–compression asymmetry in an extruded Mg alloy AM30: Temperature and strain rate effects

The effect of strain rate, ε ̇ , and temperature, T, on the tension–compression asymmetry (TCA) in a dilute and wrought Mg alloy, AM30, over a temperature range that covers both twin accommodated deformation (below 250 °C in compression) as well as dislocation-mediated plasticity (above 250 °C) has been investigated. For this purpose, uniaxial tension and compression tests were conducted at T ranging from 25 to 400 °C with ε ̇ varying between 10−2 and 10 s−1. In most of the cases, the stress–strain responses in tension and compression are distinctly different; with compression responses ‘concaving upward,’ due to {101̄2} tensile twinning at lower plastic strains followed by slip and strain hardening at higher levels of deformation, for T below 250 °C. This results in significant levels of TCA at T<250 °C, reducing substantially at high temperatures. At T=150 and 250 °C, high ε ̇ leads to high TCA, in particular at T=250 °C and ε ̇ =10 s−1, suggesting that twin-mediated plastic deformation takes precedence at high rates of loading even at sufficiently high T. TCA becomes negligible at T=350 °C; however at T=400 °C, as ε ̇ increases TCA gets higher. Microscopy of the deformed samples, carried out by using electron back-scattered diffraction (EBSD), suggests that at T>250 °C dynamic recrystallization begins between accompanied by reduction in the twinned fraction that contributes to the decrease of the TCA.