Study On Separation Of Silica Phase By Electromagnetic Directionally Solidification Process Of Hypereutectic Al - Si Alloy Melt

Solar grade silicon (SOG-Si) and hypereutectic Al-Si alloys with low silicon (silicon composition below 25%) can be successfully obtained by separating of hypereutectic Al-Si alloy with high silicon (silicon composition above 30%) in the electromagnetic directional solidification process.Separation mechanism, separation efficiency, and the optimization of separation method in the electromagnetic directional solidification process is proposed in this paper. To explore the separation mechanism in detail, experiments were conducted in this study using a high-frequency induction furnace with different pulling conditions of the crucible which is loaded with Al-45 wt.% Si melt. Results demonstrate that the separation of hypereutectic Al-Si alloy is feasible through either a pull-up or drop-down process, and the separation effect of the drop-down sample is preferably. The height of each separation interface between the compact and sparse parts of the primary silicon decrease as the pull-up distance rose. When the pulling rate is very low, resultant morphologies of compact primary silicon are rounded and polygonal, allowing for more effective separation of the primary silicon. A novel physical model is presented here based on the experimental results and simulation (for the temperature field and flow field). The model can be used to effectively describe the separation mechanism of primary silicon from hypereutectic Al-Si melts in the electromagnetic directional solidification process. To explore the separation effect, a quantitative evaluating method for separation efficiency of silicon phase from the hypereutectic Al-Si melt has been established. And some experiments have been conducted under different pulling conditions: pulling distance, pulling rate, current in the induction coils and cooling-water tube at the cold end. Experimental results show that the maximum silicon mass fraction in the dense area of primary silicon is 75.96%, and the quantitative calculation results show that the maximum separation efficiency of sample can reach 57.02% at present. By the quantitative evaluating method, the influence rule of the experimental conditions on the separation efficiency is also acquired in the electromagnetic directional solidification process. Base on the discussion, an experimental optimization strategy is put forward to improve separation efficiency of sample...