Research Of The Partial Remelting Microstructural Evolution Of Mg-xCu Magnesium Alloys

Magnesium alloys, as the lightest structural metallic materials, have large applicationpotential. Semisolid forming has been consinder as the most promising forming technologyfor magnesium alloys. Thixoforming, one of semisolid processing methods, is the mainmethod of semisolid forming because it is more convenient for billet heating, andtransportation and easier for the realization of automatic control. Therefor, it is profitable todevelop the semi-solid magnesium alloys.This article will study the amount of Cu alloy affect on microstructure and properties andsemi-solid non-dendritic organization. The microstructure evolution in the isothermal heattreatment process is analyzed，and its mechanism is discussed.According to binary phasediagram of Mg-Cu，formulate the Cu of the investigated alloy as0.5%、1%、3%、5%、7%、9%and11%.Test shows that with the increase of Cu, the microstructure of the alloy change fromdendrite to rose-shaped equiaxed grains and the grain size of the alloy decreases；The tensilestrength and the hardness increase as the Cu content increases. When the content of Cu is11%,the tensile strength gets the maximum value of166MPa and the hardness reaches themaximum value56.9HV. With the increase of Cu, the tensile strength decreases at first, thenincreases. When the content of Cu is11%, the tensile strength reaches the maximum value6.62%. The fracture morphology of the alloy change from little torn edges to more torn edgesand lieele dimple as the Cu content increases.In the process of Mg-x Cu magnesium alloy prepared for non-dendritic slurry byisothermal heat treatment, the minimum temperature of preparing semi-solid、equivalentdiameter and shape factor slurry reduced with the Cu content increased and the regularity withthe heating temperature and time turned better. During partial melting, the microstructureevolution of the refined magnesium alloys could be divided into four steps, the initialcoarsening due to the dissolution of interdendritic eutectic, structure separation resulted fromthe melting of residual eutectic, spheroidization due to partial melting of primary particles andfinal coarsening attributed to mergence and Ostwald ripening. Analy the average equivalentdiameter of globular patical, the shape factor and the fraction of solid phase of semi-solidnon-dendritic organization can get the result as follows. When the content of Cu is7%、9%and11%，equivalent diameter of semi-solid non-dendritic organization become smaller and itseasy to reach better semi-solid non-dendritic organization. Mg-7%Cu alloy treated at620℃for45min，the average equivalent diameter of globular patical was68μm，and the shape factor was1.58，the fraction of solid phase was34.1%；Mg-9%Cu alloy treated at610℃for45min，the average equivalent diameter of globular patical was53μm，and the shape factorwas1.55，the fraction of solid phase was40.03%；Mg-11%Cu alloy treated at600℃for30min，the average equivalent diameter of globular patical was58μm，and the shape factor was2.07，the fraction of solid phase was49.62%.