Numerical Simulation On Semi-solid Magnesium Alloy Rheocasting-rolling Based On Porous Medium

Magnesium alloy semi-solid rheocasting-rolling integrate pulping, roll castingand forming, in the same time of shortening the processing process to reduce theproduction cost, greatly expanded the scope of the magnesium alloy sheet processingand improve the quality. due to the unique nature of semi-solid rheocasting-rolling,the heat transfer process has a very complicated phenomenon, and with its hugetesting quantity. Therefore, establisheing a reasonable physical model for heat flowfield numerical simulation analysis has the very vital significance of studying therheological roll casting magnesium alloy.By conventional fluid model as reference, this paper creatively use the porousmedia model to describe the physical form of semi-solid magnesium alloysolid-liquid coexistence. Using the basic theorem of heat transfer and porous mediaseepage, and numerical simulation software FLUENT, to simulate the condition ofsemisolid magnesium alloy rheorolling-casting about this two models. In this paper,the main work and achievements are as follows:1) Use volume average theory and the Darcy’s law to descript percolation. Underthe assumption that porous medium in the process of phase change heat and masstransfer of each particle in local thermodynamic equilibrium, establish the threeconservation equation of porous media. Use the enthalpy method to deal with latentheat of solidification, and use the carreau model dealing with the apparent viscosity ofalloy. Combine the Mathematical model and several calculation model in FLUENT todo simulation. These calculation model conclude the corresponding solidificationmodel, porous media model and a custom function.2)The simulation and test exports that the best casting temperature is840Kunder the condition of10r/min rolling speed, casting entry fixed temperature, freeboundary and10000w/(m2. K) convective heat transfer coefficient, which is in orderto ensure the AZ91D magnesium alloy sheet be frozen just at the exit and not cause ofroll forming (export alloy is still liquid) or interruption of roll casting (solidificationin full before finishing). 3)Under the same conditions of semi-solid magnesium alloy rheocasting-rolling,the simulation results of porous media model and fluid model are different. With theincrease of pouring temperature, the difference of simulation results between porousmedium model and the conventional fluid become smaller and smaller. When pouringtemperature is low (alloy solid rate greater than0.6), the difference between the twomodels is large.To the contrary, two models differ slightly when the pouringtemperature is high(alloy solid rate less than0.4).4)Under the porous medium model, the melt and the roll contact area has theobvious temperature drop, range of temperature of the export area is less than thesame of conventional fluid model. In conclusion, the porous medium model ofsemi-solid magnesium alloy rheocasting-rolling is real and accurate, and moreaccordant to the actual situation about high solid rate(f>0.4) with worse fluxility.