New Technology For Semi-solid Metal Slurry Preparation And Globalization Mechanism

Semi-solid metal process (SSM) is a new near net shape technology. Its drip molding is compaction, high mechanical property; little machining, long mould life and can make complex configuration, environment protection, energy conservation, high efficiency. So, it is taken into more and more account in all over the world. It is considered as one of the most potential metal forming technologies in the 21st century.In this paper, semi-solid AlSi9Cu2 alloy melt was prepared by cooling slope, which used in rheo-die casting. Pouring temperature, slope angle and slope length are studied. Find how they affect the microstructure on AlSi9Cu2 semi-solid alloy. Microstructure evolution of the primary solid phase is analyzed along alloy melt filling process.The experiments show that:pouring temperature has great influence on the microstructure of semi-solid AlSi9Cu2 alloy melt. In this experiment, suitable pouring temperature is 670℃. When pouring temperature is high, the a-Al grains are columnar dendritic or rosette-like. Meanwhile, if the pouring temperature is low, solidification shell can formed on the slope surface easily. The length and angle of the cooling slope govern the flow rate and contact time between the alloy melt and the cooling slope. In this experiment, when the slope angle and slope length is 45°nd 500mm respectively, the average diameter of primary solid phase is 62μm, shape factor is 1.55. For the solidification shell formed on the slope surface, a zebra form coating is put forward. It can solve the problem that solidification shell and microstructure of melt can't be unified. When the melt is poured on the surface of the slope, it goes through two steps. The former step is called cooling stage, and the latter one is called nucleation and globalization stage. The grain shape factor and the size of a-Al are mainly determined by the second stage.Compared to the EMS method, a novel combined method was proposed in this work for the production of semisolid slurry of aluminum alloy. Non-uniform solidification structure, which commonly exists along the radial direction of the ingots with EMS, was prevented by the present route. The solidified shell, usually formed on the surface of the cooling slope, was reduced to some extent simultaneously. The EM voltage has a great impact on the morphology of a-Al grains. The higher of EM voltage imposed, the finer of grains in the final product can be obtained. The average size and shape factor of a-Al grains was reduced to 72μm and 1.3 respectively by applying an a.c. voltage of 300 V.