The twin mechanism of Portevin Le Chatelier in Mg–5Li–3Al–1.5Zn–2RE alloy

The small serrated flow, severe Portevin Le Chatelier (PLC) phenomenon and abnormal strain rate sensitivity (SRS) were observed from the tensile curves of extruded Mg–5Li–3Al–1.5Zn–2RE alloy. The serrated curves were investigated by optical microscopy, step-tensile test and transmission electron microscopy. The small serrated flow is due to the traditional dynamic strain ageing. The positive SRS is caused by dynamic strain ageing. The severe Portevin Le Chatelier phenomenon and the negative SRS are attributed to a larger number of twins. Transmission electron microscope diffraction pattern reveals the {101¯2} twin and {101¯1} twins.

► Serrated flow phenomenon and abnormal strain rate sensitivity exist in the tensile curves.
► The negative strain rate sensitivity is attributed to the twin shear transformation.
► The new twin mechanism of Portevin-Le Chatelier was observed in Mg-5Li-3Al-1.5Zn-2RE alloy.