Study On Meniscus Interface And Casting Technique Of Vertical Twin-roll Continuous Casting For Magnesium Alloy Strips

Magnesium alloy strips with near net shape can be prepared by twin-roll casting, which can shorten the process and reduce the cost. But, in the existing technology of the vertical twin-roll continuous casting, the liquid level of molten pool is directly contacted with the surface of the roller, the stability of meniscus will be destroyed by the level fluctuation of molten pool. So, the initial solidification point of the strip is unstable, the micro-crack is formed easily in the strips surface and the internal quality is wicked. By introducing a high dam to the molten pool system of vertical twin-roll continuous casting, the liquid level of molten pool and the roller surface are separated, the harmful effect of the liquid level fluctuation of molten pool on the meniscus is weakened, and it is advantage to the stability of initial solidification point.In the paper, dynamic interface model of meniscus of vertical twin-roll continuous casting for magnesium alloy strips is proposed. The meniscus profile curves of different casting conditions are calculated. The influence of processing parameters to the interface is analyzed. And the analysis result is tested by the casting experiment. The results show that the model can be used to analyze the molten pool meniscus of vertical twin-roll continuous casting for magnesium alloy strips.The meniscus dynamic interface shapes of vertical twin-roll continuous casting for magnesium alloy strips with and without a high dam are analyzed, and the difference of meniscus shapes under different casting conditions, the method to make the meniscus shape stable is proposed and the shape of high dam is improved. As a result, curvature radius of the meniscus curves of vertical twin-roll continuous casting for magnesium alloy strips with the high dam are reduced, the heights of the interface are increased, and the additional pressure of the meniscuses is increased, so the effect of the pressure on the nucleus which is formed at initial solidification point is enhanced. The meniscus interface tends to be more stable.AZ31 magnesium alloy strips with and without high dam is cast, the surface quality is compared, as well as the microstructure of the cast strips. As a result, with the introduction of high dam, the surface crack and the bulging is reduced obviously. The space between dendrites is smaller, and the grains are finer and more uniform obviously.On the basic of the investigation for magnesium alloy AZ31 strips, the test for AZ61 and AZ91 magnesium alloy strips are developed. The influence of the different casting speeds to the process and the change rule of microstructure are discussed. With the increase of casting speed, the proportion and the size of dendrite reduce.