Numerical Simulation And Experimental Study On Twin-roll Casting Magnesium Alloy Strip Process

Due to their excellent properties such as lightness, antiknock, high damping, high heat conduction, electromagnetic interference resistance, and proneness to recovery utilization and so on, magnesium alloy has been deemed as one of the most potential structural materials in 21 century. They are rapidly applied to national defense, aero plane,3C products and automobile industry. Many countries have considered the study and development of new materials and new process of magnesium alloys as an important strategy.Magnesium alloy strips are widely applied to vehicles and 3C product's cover. However, Magnesium alloy strips are hardly formed in room temperature because of Mg's close-packed hexagonal structure. Conventional preparation of magnesium alloy strips mainly by means of hot rolling method, the preparation process is complicated and the yield is low, which will badly limit the wide application of magnesium alloy thin strips. Twin roll casting method is a promising route to directly produce magnesium alloy strip, it possesses the advantages such as short procedure, low energy consumption, less investment. But there are many factors that can affect the stability of the process, it is very difficult to find the optimal operating parameters only by experiment. Using numerical simulation can obtain some useful result in short time and less cost in order to instruct the experiment effectively.In this paper, the casting process of AZ31 magnesium alloy strip has been numerical simulated by finite element method ANSYS. According to the result of numerical simulation, experimental study on the twin roll casting AZ31 magnesium alloy was carried out using laboratory twin-roll caster, the conclusions were obtained as followed:1) With the increment of pouring temperature, the flow tendency in the molten pool was hardly changed, the kissing point moved to exit, and the strip surface and center temperature of exit increased.2) With the increment of casting speed, the kissing point moved to exit, the thickness of strip became thinner, and the strip surface and center temperature of exit increased. The least temperature difference in strip surface and center of exit along width direction was obtained when the casting speed was set at 18-20m/min, the pouring temperature at 923K(650℃)and the angle of water gap at 85°3) Experimental study on the twin roll casting AZ31 magnesium alloy was carried out using laboratory twin-roll caster and the AZ31 magnesium alloy strip which was 250mm in width,1.3-2.0mm in thickness was successfully produced and the optimal operating parameters were obtained, the pouring temperature is 650～655℃, the casting speed is 18-20m/min,and the roller gap is1.0-1.5mm.The values of operating parameters (such as pouring temperature and casting speed) were measured during the experiment and compared with the values of numerical simulation. The result validates the veracity of mathematical modeling and the values of numerical simulation.4) Under optimal operating process, the microstructure of AZ31 magnesium alloy by twin roll casting was fine equiaxed grain, the mean grain size were 20～30μm, some were 10μm. The microstructure was a-Mg solid solution, there was no Mg17Al12 phase at grain boundary. It proves that rapid solidification process can refine the grain size well and reduce the segregation infinitely.