Preparation And Mechanical Properties On Mg-11Li-3Al-xCe Alloys

The application for 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, rigidity-to-weigh ratio, good damping capacity and good electromagnetic shielding properties. However their commercial application has been limited because of low strength and poor corrosion resistance. In this thesis, Adding Ce to a Mg-Li-Al magnesium alloy which is the most widely used in industry of the Mg-Li-Al magnesium, the effects of Ce addition on the microstructure and mechanical properties was studied.The influence of Ce on the as-cast microstructure of a Mg-11Li-3Al alloy was investigated by optical microscope(OM),scanning electron microscope(SEM),and X-ray diffraction(XRD), et al. The mechanical properties and microstructure of a Mg-11Li-3Al alloy with Ce addition processed by rolling and extrusion are investigated as well. The results show that rare earth changed the morphology ofβphase grain and the new phase Al₂Ce was found. In addition, the as-cast alloy with 1wt% Ce shows the best mechanical properties with the highest strength and a relative good elongation. The mechanism and technique of grain refine of minor rare earth in Mg-11Li-3Al system alloy after rolling and extrusion are investigated. The mechanism of grain refinement of rare earth on Mg Al alloy after extrusion is the dynamic recrystallization effect which makes the tensile strength of Mg-11Li-3Al alloy increase greatly.The relationship between microstructure, the content of Ce and the mechanical performance was discussed. The results showed that mechanical properties of the Mg-11Li-3Al alloys had been improved by the addition of Ce. This could be attributed to grain refinement and the homogeneous distribution of Al₂Ce phase. The amount and distribution of the Al₂Ce phase has great effect on mechanical properties, adding too much Ce could decrease the amount of the Al element inβphase and caused the agglomeration of Al₂Ce, which reduce the mechanical properties of Mg-11Li-3Al. On the contrary, minor content of Ce can both improve mechanical properties at room and high temperature.