Critical conditions for Portevin Le Chatelier instabilities in Al-4.8%Mg and Al-2.57%Mg alloys

Critical strains for the onset of the Portevin-Le Chatelier effect in two pure aluminium-magnesium alloys with actual concentrations of 4.8 wt.% Mg and 2.57 wt.% Mg, respectively, were measured at various temperatures and initial strain rates from the interval 6.5 . 10(-7)s(-1) less than or equal to epsilon(0) less than or equal to 5.9 . 10(-2)s(-1). Experimental data are compared to the the analytical model developed by Kubin and Estrin using an adoption of the model proposed by Balik and Lukac. It is shown that the strain rate and temperature dependence of the critical strains for the onset of jerky flow is in a good qualitative agreement with the model predictions.