The strain-rate dependence of flow stress and work-hardening rate in threeAl-Mg alloys

Uniaxial compression tests have been carried out on Al-0.5% Mg, Al-1.0% Mg and Al-3.0% Mg alloys at 265 degrees C and at constant true strain-rates in the range 10(-3) to 10 s(-1). Uniaxial compression tests with true strain- rate sudden change from 1 to 10 s(-1), which are applied at true strains of 0.1, 0.3 and 0.5, have been performed at 160, 365 and 520 degrees C. The w ork-hardening rate, theta = partial derivative sigma/partial derivative eps ilon, has been evaluated at 265 degrees C and found to exponentially decrea se with increasing strain. The total strain-rate exponent, m(t), at 265 deg rees C and the instantaneous strain-rate exponent, mi, at 160, 365 and 520 degrees C are determined. It is found that mi is strain independent irrespe ctive of temperature, while m(t) is less sensitive to strain when strain-ra tes are high (10(-1) to 10 s(-1)); however, it increases with strain when s train-rates become low (10(-3) to 10(-1) s(-1)). The difference between m(i ) and m(t) could be attributed to the strain-rate dependence of the work-ha rdening rate. The possible correlation between the strain-rate exponents of flow stress (m(i) and m(t)) and the strain-rate exponent of work-hardening rate (m(h)) could be outlined as m(t) = alpha m(i) + m(h), where alpha is a correlation coefficient.