Microstructure and Mechanical Behavior of a New α+β-Type Mg-9Li-3Al-2.5Sr Alloy

The as-cast Mg-9Li-3Al-2.5Sr (LAJ932) alloy ingots with diameters of 10 mm and 90 mm were prepared. The extrusion of Φ90 mm as-cast LAJ932 alloy ingot was carried out at 533 K with an extrusion ratio of 28. The microstructure and the mechanical properties of the as-cast and extruded LAJ932 alloys were discussed. The microstructure evolution during extrusion was analyzed. The results show that both the as-cast and the extruded LAJ932 alloys contain hcp α-Mg, bcc β-Li and Al4Sr phase. The grain size of as-cast Φ10 mm specimen is smaller than that of Φ90 mm specimen. The microstructure evolution during extrusion is governed by continuous dynamic recrystallization (CDRX) in α-Mg phase whereas discontinuous dynamic recrystallization (DDRX) occurs in β-Li phase. {100}<100> texture is formed in the hcp α-Mg phase whereas {110}<101> texture is formed in the bcc β-Li phase during the extrusion process. Both the strength and the ductility of the LAJ932 alloy is improved by extrusion. The extruded LAJ932 alloy shows a favorable combination of the strength and the ductility with the tensile strength of 235 MPa, yield strength of 221 MPa and the elongation of 19.4%.