Portevin-Le Chatelier effect of LA41 magnesium alloys

Abstract

Uni-axial tensile deformation of LA41 magnesium alloy has been carried out and the Portevin-Le Chatelier (PLC) effect, also known as serrated flow or plastic instability, is observed. This kind of alloy exhibits negative strain rate sensitivity (SRS) at room temperature, that is, SRS is negative at the strain rate range from 3.33?10^-4 to 6.66?10^-3 s^-1 at ambient temperature. Both ultimate stress (?_b) and 0.2% proof stress (?_0.2) decrease when strain rate (ε°) increases, whilst critical strain (ε_c) of serrated flow is found to rise with enhancing ε°. A new explanation for this unusual phenomenon is presented. The model of dynamic strain aging (DSA) is established through diffusion of solute atoms to mobile dislocations, which are temporarily arrested at obstacles. Such interaction renders the movement of mobile dislocations more difficult so as to necessitate the required force to overcome the obstacles.