The Influence Of Cooling Rate On The Alloy Microstructure And Mechanical Properties Of Mg-cu-(y)

Mg-Cu-(Y)alloys were fabricated by casting and melt-revolution. The microstructure and properties of Mg-Cu-(Y)alloys were investigated by XRD,OM,SEM and the tension test.The effect of solidifying rate on the construction and properties of Mg-Cu-(Y)alloys were investigated. The effect of Y content on the construction was studied.The rule and capability of formation amorphous were discussed.The results showed:The solidifying rates were computed by secondary dendritic separation and thin strip process.The solidifying rate of casting on iron was 1～10k/s.The solidifying rate of casting on copper was 100～200k/s. The solidifying rate of hydrocooling on copper was 500～600k/s and the solidifying rate of melt-revolution was 10⁵k/s.Under lower cooling speed,the matrix of Mg-10.2%Cu-15.9%Y alloy and Mg-26.6%Cu-12.6%Y alloy were a(Mg)and then the alloy separated out a(Mg)+ CuMg₂.Y element was dispersed on the grain boundary.The phases of Mg-43.0%Cu-11.9%Y alloy was CuMg₂+α(Mg) +Cu_sY.The element of Y had the effect of refining grains.The Y element can produced thin melt crystal particle effect.By adding Y,the intensity was improved and the plasticity was reduced together in the magnesium alloy.When the content of Y were lower than 15%,the grain were almost refined;When Y content was 15.9%,the grain were refined obviously.When the cooling speed was 10⁵k/s,the grain of Mg-Cu alloy by melt-revolution was very small.By increasing the contents of Cu in the Mg-Cu-Y alloy,the Gibbs liberty of liquid had cut down and the ability of forming amorphous were strengthened when the Mole fraction of Cu were lower than 50%.The microstructure distributed homogeneously. By adding Y element,the viscosity of Mg-Cu alloy were strong. The amorphous of Mg-26.6%Cu-12.6%Y and Mg-50.3%Cu-9.5%Y were obtained.