High-Temperature Stability of Mg–1Al–12Y Alloy Containing LPSO Phase and Mechanism of Its Portevin–Le Chatelier (PLC) Effect

In this study, the high-temperature stability and the generation mechanism of the Portevin–Le Chatelier (PLC) effect in solid-solution Mg–1Al–12Y alloy with different heat treatment processes were investigated by adjusting the content of long-period stacking ordered (LPSO) phases. It was found that the content of LPSO phases in the alloys differed the most after heat treatment at 530 °C for 16 h and 24 h, with values of 13.56% and 3.93% respectively. Subsequently, high-temperature tensile experiments were conducted on these two alloys at temperatures of 150 °C, 200 °C, 250 °C, and 300 °C. The results showed that both alloys exhibited the PLC effect at temperatures ranging from 150 to 250 °C. However, at a temperature 300 °C, only the alloy with a greater concentration of LPSO phases exhibited the PLC effect, whereas the alloy with a lower proportion of LPSO phases did not exhibit this phenomenon. Additionally, both alloys exhibited remarkable high-temperature stability, with the alloy containing a greater percentage of LPSO phases also demonstrating superior strength. The underlying mechanism for this phenomenon lies in the exceptional high-temperature stability exhibited by the second phase within the alloy. Furthermore, the LPSO phase effectively obstructs the movement of dislocations, and it also undergoing kinking to facilitate plastic deformation of the alloy. The results indicate that the PLC effect can be suppressed by reducing dislocation pile-up at grain boundaries, which leads to a decrease in alloy plasticity but an increase in strength. The presence of the PLC effect in the WA121 alloy is attributed to the abundant dispersed second phase within the alloy, which initially hinders the movement of dislocations, leading to an increase in stress, and subsequently releases the dislocations, allowing them to continue their movement and thereby reducing in stress.