The Portevin–Le Chatelier effect in β-phase Mg–14.3Li–0.8Zn alloy

Abstract

The effects of strain rate, ε̇, and temperature, T, on the occurrence of the Portevin–Le Chatelier (PLC) effect in tensile hot-rolled (HR) and solid-solution treated (SS) β-phase LZ141 magnesium alloy were studied. The HR alloy has an intrinsically higher dislocation density and fewer solute atoms than the SS alloy. This characteristic, in terms of the dynamic strain aging (DSA) mechanism, explains why the PLC effect does not occur in HR alloy for ε̇ ranging from 3.33×10−4s−1 to 6.67×10−2s−1 but does occur in SS alloy, in which Type B and Type C serrations appear at ε̇=(3.33–6.67)×10−3s−1 and at ε̇=(3.33–6.67)×10−4s−1, respectively. The SS alloy exhibits a negative strain rate sensitivity (SRS) at room temperature. The negative SRS also supports the proposition that the DSA mechanism causes the PLC effect. In the study of the effect of T on the occurrence of the serrated flow, for HR alloy at T≤0°C, Type A serrations were observed. In contrast, in the SS alloy, Type C serrations occurred in the curves at 25°C and 0°C, and Type B serrations occurred at −25°C and −50°C. These results can also be explained by the DSA mechanism. Large serrated stress variations were found in the tensile curves of SS alloy at −25°C and −50°C, but no twinning was found near the fractured surface.