Research On Preparation Of Semi-solid AZ91D Alloy Slurry By Rotary Pouring Method

Semi-solid metal processing technology is regarded as one of the near-net shape forming technologies with wide application in the 21st century, and the preparation of semi-solid slurry is the key technique. Research on semi-solid magnesium alloys is seldom to date. In this paper,the semi-solid magnesium alloy slurry was prepared by rotary pouring method. A series of experiments on magnesium alloy were carried out to investigate the effects of processing parameters (pouring temperatures,rotating speeds and inclinations of the barrel) on the semi-solid microstructure. The primary phase evolution behavior and formation mechanisn of non-dendritic structures were investigated.The experiment results show that pouring temperatures,rotating speeds and inclinations of the barrel affect the grain structure and dimension evidently. Proper low pouring temperature can fabricate near-roud grains.However,high pouring temperature make the coarse dendrite grains because many nuclei remelt and cannot survive at the outlet of barrel. Rotating speeds and inclinations of the barrel also have important effects on the semi-solid microstructure of magnesium alloy.The distributing of melt temperature in the rotating barrel is influenced by the interaction of pouring temperature, rotating speeds and inclinations of the barrel,then the effective nucleation rate changes consequently,and the structure and dimension of primary particles change finally. Matched pouring temperature, rotating speeds and inclinations of the barrel can increase effective nucleation rate and obtain high quality semi-solid slurry.In addition,the researches show that the morphology of primary phase is determined by both the number of free crystals in semi-solid slurry and the cooling intensity of semi-solid slurry. Increasing the number of free crystals and decreasing the cooling intensity of semi-solid slurry can enhance the formation of spherical primary phase. Under rotary pouring process,low superheat pouring combined with localized rapid cooling and vigorous mixing during the initial stage of solidification can enhance wall nucleation,crystal separation and crystal survival. This is the key to obtain high quality semi-solid microstructure.