The Effect Of Rare Elements On The Strcuture Evolutions And Properties Of Mgmagnesiu Alloys

The microstructure evolutions and properties of the rare earth magnesium alloys were investigated by a simple,efficient and reliable way,like metal mold casting,extrusion deformation,near-rapid solidification,heat treatment and so on.The results indicated that the structures were refined by adding Y and Ho into magnesium alloys cast in metal mold.Adding multiply rare earth elements was better than adding single one rare earth element in term of refining structure and improving properties.The structures were greatly refined by adding Zr and Mn.The refining effect of adding Zr was the best.However,adding both Zr and Mn achieved higher tensile strength and elongation.Dynamic recrystallization took place in Mg-4%Y alloy during extrusion,Compared to metal mold casting,extrusion processing improved evidently the mechanical properties of the Mg-4%Y alloy.Two typical structure appeared in the near-rapid solidified sample: the first structure was in the form of dendrite which was like the shape of flower or pine needle;another structure was in the form of columnar grains.It was assumed that near-rapid cooling give rise to rapid movement of the interface of liquid/solid.The element added was covered by the interface of liquid/solid which limited the diffusing and inoculation.Therefore dendrite structure formed.In the other hand,when the melt with very high temperature was chilled from one side by mold,high temperature gradient formed and resulted in columnar structure.Comparing to metal mold casting,The near-rapid solidification did not remarkably improve the tensile strength,however,increased the elongation significantly due to the dendrites structure produced by the near-rapid cooling.Rare earth magnesium alloy produced by metal mold casting was annealed at 450? for10 h,and rare earth magnesium alloy produced by near-rapid solidification was annealed at350? for 2h.It was found that the dendrites transformed into equiaxed grains totally.The equiaxed grains don't grow up because grains boundaries moving was blocked by second phase particles and single phase particles,Moreover,the hardness did not change basically during annealing due to aging hardening.