Microstructure and mechanical properties of extruded Mg-9Li-3Al-xSr alloys
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Abstract:
The microstructure and mechanical properties of extruded Mg-9Li-3Al-xSr (LA93-xSr, x=0, 1.5, 2.5, 3.5 wt%) alloys are investigated by SEM, EDS, XRD, TEM and mechanical property test. The influence of Sr content on microstructure and mechanical properties the extruded alloys is discussed. The results show that LA93-xSr alloys contain both α-Mg (hcp) and β-Li (bcc) matrix phases. The effect of Sr on the grain size of the extruded alloys is not significant. The addition of Sr leads to the formation of intermetallic compound (Al4Sr), which is mainly distributed along the α/β interface and appears fibrous structure along the extrusion direction. The mechanical properties of alloys initially enhance and then decrease while the elongation declines with the increase of Sr content. When Sr addition is 2.5wt%, the extruded Mg-9Li-3Al-2.5Sr (LAJ932) alloy exhibits a favorable combination of strength and ductility with an ultimate tensile strength of 235.2 MPa, yield strength of 220.6 MPa and an elongation of 19.4%. Microstructure evolution during extrusion is governed by deformation induced grain refinement in the α-Mg phase whereas dynamic recrystallization occurs in the β-Li phase.
