Modelling of strain hardening and its relation to the onset of Portevin-Le Chatelier effect in Al-Mg alloys

Deformation behaviour of two pure aluminium-magnesium polycrystalline alloys with actual concentrations of 2.57% Mg and 4.8% Mg, respectively, was investigated at room temperature. Tensile tests with constant cross-head speed were performed for the initial strain rates from the interval 6.8 × 10−7 s−1 ≤ ge0 ≤ 4.3 × 10−2 s−1. The critical strains for the onset of the Portevin-Le Châtelier (PLC) effect at low strain rates were measured as a function of strain rate. Experimental data are fitted according to the model proposed by Kubin and Estrin. In addition to this, the work hardening behaviour of both alloys is analyzed with respect to the model equations proposed by Malygin and by Balík and Lukáč. On this basis a modification of the evolution equations of the mobile and immobile dislocation densities, which are used in the model of Kubin and Estrin, is suggested.