Study On The Transmission Characteristics Of Electromagnetic Separation Process Of High Silicon Aluminum Alloy

The electrothermal reduction method is the most promising technique for the industrial production of Al-Si alloy due to its low energy cost and wide raw material source. However, the coarse Al-Si alloy produced by this method contains too many Si, and thus cannot be used in the cast of standard Al-Si alloy before diluted with pure Al.Molten high-silicon aluminum alloy (with Si mass content above 25%) can be separated into concentrated primary silicon and low-silicon hypereutectic Al-Si alloy (with Si mass content below 25%) via the electromagnetic directional solidification process. The separated primary silicon contains few impurities and can be used in the preparation of solar-grade silicon, while the low-silicon hypereutectic Al-Si alloy is grain refined and property modified, which makes the electromagnetic separation method the most promising alternative technique route for the treatment of coarse Al-Si alloy produced by the electrothermal reduction method,In this thesis, Al-45 wt.%Si, as a typical of the composition of the coarse Al-Si alloy, is studied by the electromagnetic directional solidification (EMDS) process as well as the conventional vacuum directional solidification (VDS) process. A continuous bulk growth model of primary silicon from high-silicon aluminum melts is proposed and verified. The essential condition for continuous bulk growth of silicon during a directional solidification process is that V%, the growth rate of silicon crystal, must be larger than Vp, the pulling-down rate of the crucible. The critical growth rate of silicon from Al-Si melts is about 1μm/s in VDS process and 400 μm/s in EMDS process, respectively. The mechanism of the electromagnetic separation of high-silicon aluminum alloy is described as the diffusive mass transfer of Si in Al-Si melts enhanced by the forced convection caused by the electromagnetic stirring accelerates the growth rate of silicon crystal, and therefore the primary silicon can grow into continuous bulk crystal and separate from the low-silicon aluminum alloy. The heat and mass transfer properties in the electromagnetic separation process are studied to find out the effect of the cooling condition, the melt flow pattern, the solidification rate, and the crucible material, respectively, on the concentration and separation of primary silicon from high- silicon aluminum melts. The studies have shown that:(1) better cooling conditions of crucible bottom benefit the separation of primary silicon with fixed solidification rates; (2) slower solidification rates benefit the separation of primary silicon with certain cooling conditions; (3) non-conductive crucible is better than conductive crucible for the concentration of primary silicon in the electromagnetic separation process.