Influence of extrusion temperature on microstructure and mechanical behavior of duplex Mg-Li-Al-Sr alloy

In this study, as-cast alloy Mg-9Li-3Al-2.5Sr (LAJ932) ingots were extruded at different temperatures using an extrusion ratio of 28, and the underlying microstructural evolution and mechanical behavior were investigated. The results show that grains in the extruded LAJ932 alloy are much finer than those in the as-cast one, which indicates that the microstructural evolution during extrusion is governed by dynamic recrystallization. With increasing extrusion temperature, the grain size of the extruded alloy increases, and the strength decreases whereas the elongation increases. The alloy extruded at 250 °C possesses the highest strength of 238 MPa with an elongation of 18.1%, whereas1 the alloy extruded at 350 °C has the largest elongation of 21.6% with a strength of 208 MPa. The differences in microstructure characteristics between the α-Mg phase and β-Li phase in the alloy extruded at 250 °C suggest that continuous dynamic recrystallization (CDRX) occurs in the α-Mg phase during extrusion whereas the microstructure evolution in β-Li phase is governed by discontinuous dynamic recrystallization (DDRX). DDRX occurs in α-Mg phase to some extent and the fraction of DDRX grains in the alloys increases with increasing extrusion temperature.