Researches On Microstructure And Mechanical Properties Of Mg-6Al-2Ca-xNd Alloys

The rare earth element Nd was added into Mg-6Al-2Ca in this paper, andexperimental alloys were prepared by vacuum induction furnace under an Aratmosphere. The chemical composition was tested by X ray fluorescence spectrometer;microstructures of alloys were observed by Axiovert40MAT optical metallographicmicroscope and TESCAN VEGAⅡ scanning electron microscope equipped with anINCA Energy350energy dispersive X-ray spectrometer （EDS）, Phase structures werecharacterized by a Rigaku D/max2500PC X-ray diffractometer using Cu Kα radiation,mechanical properties were performed using SANSI computer-controlled electronicuniversal tester and Webster microhardness tester, and analysis the effect of Nd onmicrostructures and properties of alloys.The results show that as-cast Mg-6Al-2Ca alloy is dendritic morphology, itconsists of eutectic phase Mg₁₇Al₁₂,Mg2Ca and Al4Ca, Nd was added into alloys, theirmicrostructures change from dendritic to equiaxed grains, and the grains become small.Mg₁₇Al12phase decreases while the high melt-point phase Al-Nd appears. Al-Nd phasechanges into bar and block-like with Nd addition increased. Microstructures of alloysare refined by extruded and there are some dynamic recrystallization areas in extrudedalloys, the precipitations are zonal distribution along extrusion direction and someblock-like phases are broken into small particles.Mechanical properties of as-cast alloys first increase and then decrease withaddition of Nd increases and the ultimate strength, yield strength and coefficient ofelongation get their maximum value when Nd is3%. Extrusion could enhance the alloysmechanical performances and the RT ultimate strength （UTS） and yield strength （YS）increase with Nd added, when Nd addition is4%, maximum values of UTS and YS are319MPa and210MPa respectively, elongation is first decreases and increases. Whentemperature gets150℃and200℃, theUTS and YS of alloys are increasing and thendecrease, and the addition of Nd is2%,the UTS are265MPa and223MPa respectively,YS are₁₇9MPa and₁₇2MPa.Mechanical performances of Mg-6Al-2Ca-xNd alloys are enhanced by heattreatment. After T6, UTS and YS at room temperature are347MPa and288MParespectively; while temperature gets150℃and200℃, UTS are275MPa and234MParespectively, YS are187MPa and₁₇9MPa. The properties of alloys are performed at room temperature and higher test temperatures, while elongation has barely changed.The rupture way of experimental alloys is ductile.When Nd added into experimental alloys, refinement strengthen and solutionstrengthen are mainly schedule of reinforcement at room temperature, whiletemperature enhances, the schedule of reinforcement is precipitation strengthen.