The mechanical properties of LA40 magnesium alloy were investigated under compression at room temperature. In the applied strain rate range from 1.33×10-4s-1 to 6.66×10-4s-1,this alloy shows positive strain rate sensitivity (SRS). Most importantly, the Portevin-Le Chatelier(PLC) effect which is an interesting and dominant feature in tensile tests disappears under compressive conditions. Only one twinning system is activated under tensile deformation, while at least two twinning modes are operative during compression. Additionally, the effect of dynamic strain aging (DSA), and the main mechanism for the onset of PLC phenomenon during tension, will be weakened because the strengthened obstructing influence of twins on solute atoms and the disappearance of PLC is inevitable.
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