Interface Mass Transfer Behavior And Crystal Growth Control Of Hypereutectic Al-Si Alloy During Electromagnetic Separation Process

At present,chemical method is the main method for the preparation of solar grade Si,but the cost and energy consumption are high,so it is difficult to meet the healthy and rapid development of photovoltaic industry.The development of low cost and low energy consumption solar grade Si is the only way for the sustainable development of photovoltaic industry.The purification of solar grade Si by Al-Si alloy refining has many advantages,such as low cost,low energy consumption and environmental friendliness,and has become a research hotspot in the field of Si purification.However,the traditional solidification technology is difficult to effectively separate the primary Si in the alloy,which leads to the unsatisfactory recovery and utilization of flux metal Al.In addition,the distribution characteristics and segregation behavior of metal impurities in the solidification process of Al-Si alloys are still not systematically studied,and further exploration is urgently needed.In view of the existing problems in the purification of Si in Al-Si alloy,this paper systematically studies the growth behavior,separation mechanism and removal of metal impurities by means of experimental research and theoretical analysis.The main conclusions are as follows:(1)The migration velocity of solid-liquid interface was obtained by high temperature interface real-time detection technology,and the relationship between the height of solid-liquid interface and the drop distance of Al-Si alloy was established.The results show that with the increase of Si content or dropdown rate,the enrichment zone of primary Si increases and the average growth rate of primary Si increases.(2)The morphology analysis of the primary Si in Al-Si alloy shows that when the Al-45 wt% Si,Al-55 wt% Si and Al-65 wt% Si alloy solidify under the condition of 5 ?m/s,the Si crystals in the primary Si enrichment region are bulk,cellular and cellular dendrites.With the increase of the enrichment zone height,the morphologies of primary Si are: bulk to cellular to cellular dendrites.When the drop rate of Al-45 wt% Si alloy increases from 5 ?m/s to 10 ?m/s,15 ?m/s,20 ?m/s,the morphology of Si crystals in the primary Si enrichment zone is cellular and cellular dendrites,and with the increase of enrichment zone height,the morphology changes from cellular to cellular dendrites.The enrichment ratio of primary Si in Al-Si alloy shows that the enrichment rate of primary Si decreases with the increase of the concentration of Si in the Al-Si alloy.In addition,the average enrichment rate of primary Si increases with the increase of Si content or the decrease of dropdown rate.(3)Al-65 wt% Si alloy was used for electromagnetic directional solidification.The removal rates of typical metallic impurities Al,Ca,Ti and Fe in primary Si were 58.62 wt%,61.77 wt%,88.69 wt% and 96.26 wt% respectively.By analyzing the distribution and content of impurity Al,Ca,Ti and Fe,it is found that with the continuous growth of the primary Si,the impurity elements are repelled to the interface between the primary Si enriched zone and the Al-Si melt,and thus the primary Si is purified.The apparent segregation coefficient is used to study the segregation behavior of impurities during solidification.It is found that the apparent segregation coefficient is much larger than the equilibrium segregation coefficient.