Effect Of Y On Microstructure And Performance Of Mg-14Li-1Al Alloy

The application of Mg-Li alloys in the aircraft, electronics and communication industries has been expanding at a high rate due to their low density, high strength-to-weigh and rigidity-to-weigh ratio, good damping capacity and good electromagnetic shielding properties. Research works of this thesis aim at the super light magnesium lithium alloy- Mg-14Li-lAl(LA141) and mainly focuses on the effects of the homogenizing treatment, the addition of rare earth Y, the extrusion and rolling on microstructure and mechanical properties of alloys. And the effects of Y addition on the microstructure and mechanical properties were studied.The typical test alloys of Mg-14Li-lAl-xY were prepared in vacuum inductance furnace. The influence of Y on the as-cast microstructure of a Mg-14Li-lAl alloy was investigated by optical microscope(OM),scanning electron microscope(SEM),and X-ray diffraction(XRD), et al. The mechanical properties and microstructure of Mg-14Li-lAl alloy with Y addition processed by rolling and extrusion were investigated as well. The mechanism of grain refine of minor rare earth in Mg-14Li-1Al-xY system alloy after rolling and extrusion were investigated.The results showed that the high quality Mg-14Li-1Al-xY magnesium alloys can be prepared in vacuum inductance. Mechanical properties of the Mg-14Li-lAl alloys were improved by the addition of Y. Rare earth changed the morphology ofβphase grain and the new phase Al₂Y was found. In addition, the as-cast alloy with 0.5wt% Y shows the best mechanical properties with the highest strength and a relative good elongation. The proof strength of extrusion is 77 MPa and the elongation is 11%. The proof strength of rolling after extrusion increased greatly and reached 142MPa and its elongation is 19% The mechanism of grain refine of minor rare earth in Mg-14Li-lAl system alloy after rolling and extrusion are investigated. The mechanism of grain refinement of rare earth on Mg-14Li-lAl alloy after extrusion and rolling is the dynamic recrystallization effect which makes the tensile strength of Mg-14Li-lAl alloy increase greatly. This could be attributed to grain refinement and the homogeneous distribution of Al₂Y phase. The amount and distribution of the Al₂Y phase has great effect on mechanical properties. The addition of Y could decrease the amount of the Al element inβphase and might cause the agglomeration of Al₂Y, which reduce the mechanical properties of Mg-14Li-1Al. On the contrary, minor content of Y can both improve mechanical properties at room and high temperature.