Numerical Simulation Of Direct Chill Casting Of Superlight Magnesium Slab And Optimization Of The Casting Parameters

At the present time,with energy crisis and attention of environment protection, light-weight and recyclable materials are eagerly to be demanded.As the lightest alloys among the metal structural materials,Mg-Li alloys will be more and more widely used in many fields besides of aerospace,aircraft structures,automobile and electric industry.DC casting of nonferrous metals characterized by high productivity and high quality had been widely used in aluminum alloys production,but there were few articles on DC casting of Mg-Li alloys.In this paper,the early studies of the DC casting process of Mg-Li alloys had been done, and the temperature field of this process had been calculated.A 3-D mathematical model of the direct chill(DC) casting process for superlight Mg-Li alloy(LA141) slab has been developed using the finite differential method(FDM).The variations of heat transfer coefficient between slab and dummy block interface resulting from the deformation of the slab have been considered.The primary and secondary cooling heat-transfer coefficients boundary conditions were chosen as a function of the temperatures on slab side surface.The model had been validated by comparing the calculated temperature profiles with the measured temperature profiles.By calculating the temperature distribution,solid-liquid interface shape and position,the influence of casting parameters on DC casting process,such as the pour temperature,cooling water flow rate,casting speed have been analyzed.Calculated results indicated:The impact of increasing the pour temperature in the primary zone is greater than in the secondary zone.Moreover,increasing the pour temperature makes the sump depth deeper.The impact of increasing the cooling water flow rate on solid-liquid interface shape and position is limited,but the temperature distribution on the cross section of the slab tends to becomes inhomogeneous by increasing the cooling water flow rate.The impact of the casting speed on solid-liquid interface shape and position is the largest one in the three casting parameters.Increasing the casting speed,the sump depth becomes deeper,and the shell thickness at the exit of mold obviously becomes thinner.Moreover,the temperature distribution and solid-liquid interface shape and position of LA141 alloy slab and that of AZ31 alloy slab had been compared in the same casting parameters.The results indicated that in the same casting parameters the sump depth of AZ31 alloy slab is deeper than that of LA141 alloy slab.According to results of simulation,during the actual DC casting process of LA141 slab,the proposed casting parameters are shown as follows:the pour temperature is 670～700℃,the casting speed is 1.0～1.25mm/s and the cooling water flow rate is 0.8～1.0m~3/h.