| In the near equilibrium solidification condition,the dendrite structure of the cast magnesium alloy is coarse,and there is a continuous brittle eutectic phase at the grain boundary,which makes the strength and creep resistance of the alloy be not ideal.Grain refinement can effectively improve the comprehensive mechanical properties of alloys,and the preparation of fine grained magnesium alloys has become an important research direction of high performance magnesium alloys.SiC is a high melting compound,which has similar crystal structure with Mg and promotes nucleation and crystallization of melt during solidification.The imbalance effect can lead to a variety of atomic diffusion migration and transport phenomena during solidification was inhibited by the increase of cooling rate,the grain could not fully grown solidification had ended,so the nucleation and the non-equilibrium solidification can be effective combination of maximum fine grain structure.However,under non equilibrium conditions for low dimensional fine grained magnesium alloy material prepared by sintering in order to meet the need,the sintering process of metastable phase transformation and grain growth phenomenon will worsen the performance of the alloy,so it is important to research the different heat treatment temperature under rapid cooling of magnesium alloy organization evolution behavior.This paper adopts copper mold casting and single roller strip technology,carry out the non-equilibrium solidification experiment of wide range of cooling rate of nano SiC in AZ91 D alloy under the system of heterogeneous size are the influence of fast cooling grain refinement of magnesium alloy.Then,the isothermal heat treatment experiments of fast cooling samples at different temperatures(200,260,320,370,400)were carried out,and the effect of holding time on precipitate precipitation and grain growth behavior in metastable fine crystalline structure was studied.The experimental results show that the grain refinement,8mm copper mold casting can refine AZ91 alloy,the average grain size decreased from cast 400 ?m to50 ?m;when adding content of 2wt% nano SiC,the average grain size of 15 ?m,fine equiaxed grains into granular crystal;2wt% nano Si C in next,using the single roller rapid solidification of AZ91 alloy with preparation technology,can significantly refine grain,the average grain size of 3 ?m,no eutectic ?-Mg17Al12 beta phase formation,direct solidification of single phase solid solution.The mold spray casting AZ91+2wt% nano SiC alloy was 200? after annealing,the saturated Al atom generated lamellar precipitates on the grain boundary?-Mg17Al12 beta phase,with the prolongation of holding time,the beta precipitated phase increased to 260? alloy.After annealing,the grain boundary and the matrix are lamellar and stripes the shape of the beta precipitation,with the prolongation of holding time in the matrix,precipitation increased significantly,and the split of matrix,the hardness of the alloy decreases.The copper mold cast AZ91+2wt% SiC alloy nano 200? after annealing,crystal Precipitation of granular beta ?-Mg17Al12 precipitates at the boundary.The mold spray casting AZ91+2wt% nano SiC alloy was 320?,370?,400?indicates that the related research of isothermal treatment,with the increase of isothermal time,the average grain size of 15 to 19 ?m range.320? proved that the effect of addition of nano SiC isothermal treatment to inhibit grain growth is good.Is not a complete solid solution alloy,grain boundary disappear;370? after annealing,beta ?-Mg17Al12 phase disappeared,the residual phase in dispersive distribution;400? after annealing beta ?-Mg17Al12 phase disappeared completely with isothermal temperature.The average size of the grain was changed from 5 ?m to 6 ?m.With the increase of isothermal time when the single roll rejection AZ91+2wt% nano SiC alloy was treated at 400 degrees of temperature... |
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