High Value Application Of Iron-rich Phases Separation In Course Al-Si Alloy

As a common casting alloy,Al-Si alloy is widely used for its advantages of good fluidity,high thermal conductivity and good mechanical properties.The electrothermal method is a promising technique for the production of Al-Si alloys,which not only has low energy consumption,but also can use low-grade bauxite and non-bauxite resources as raw materials.A large amount of high-alumina coal gangue with alumina content up to 50% is produced in Zhungeer coalfield,Inner Mongolia,which is a typical highalumina coal series solid waste resource and can replace bauxite as raw material for producing course Al-Si alloy by electrothermal method.However,due to the high content of iron in course Al-Si alloy produced from high alumina coal series solid waste,it cannot be directly used as casting alloy,but can only be used as a cheap deoxidizer for steelmaking.Therefore,this paper proposes to use the high gravity separation technology to separate the iron phase in the course Al-Si alloy,which can not only effectively reduce the iron content in the alloy,produce the high-value cast AlSi alloy that meets the industrial requirements,but also produce the industrial silicon at low cost,thus realizing the high-value application of the course Al-Si alloy.Al-42.5 wt.% Si-2.5 wt.%Fe alloy was prepared based on the composition characteristics of course Al-Si alloy produced by high alumina coal measure solid waste,and its crystallization law was studied.The results show that the particle size of primary silicon decreases with decreasing temperature,but the number of particles increases.The primary silicon particles grow larger with the increase of crystallization time until they grow to a certain extent and stop.The particle size of iron phase will increase with the decrease of temperature and will be more evenly dispersed in aluminum matrix with the increase of crystallization time.The study on the crystallization law of course Al-Si alloy lays a theoretical foundation for the subsequent experiments of iron phase separation.On the basis of the understanding of the crystallization law of the alloy,the supergravity step centrifugal separation of course Al-Si alloy was studied.The course Al-Si alloy melt was centrifuged by high gravity,and the primary silicon in the alloy remained in the centrifugal upper alloy after precipitation,and the remaining melt entered the lower layer to achieve the preliminary separation of primary silicon.The separation effect of various factors on primary silicon was studied by the yield and element content of superalloy centrifuged.The optimal process conditions were determined as follows: crystallization temperature 800 ?,crystallization time 2 h,high gravity coefficient G=403,centrifugal time 7 min.Under these conditions,the aluminum iron content in the superalloy decreases and the silicon content increases from 42.5 % to 86.67 %.The next step is to further centrifuge the alloy melt in the lower layer,so that the dense iron phase in the alloy is enriched in the bottom of the alloy,so as to achieve the purpose of iron removal.The effect of centrifugation on melt separation was studied by the microstructure morphology and iron content of each part of the alloy after centrifugation.The optimum process conditions were determined as follows: crystallization temperature 750 ?,crystallization time 30 min,high gravity coefficient G=70.Under these conditions,the content of iron in the upper part of the alloy after centrifugation is less than 0.7 %,which meets the casting Al-Si alloy standard.In order to further improve the utilization value of centrifugal superalloy,the superalloy was purified by acid solution method.The results show that the acid dissolution time and solid-liquid ratio have great influence on the aluminum and iron dissolution rate,while the concentration of hydrochloric acid and acid dissolution time have little influence.When the concentration of hydrochloric acid is 10%,the ratio of solid to liquid is 1 : 5,the solution time is 3 h,and the solution temperature is 60 ?,the dissolution rate of aluminum iron impurity in the superalloy can reach above 94 %,and the industrial silicon meeting the national standard is obtained.On the basis of the above study on separation of test gold,the separation and purification of course Al-Si alloy produced from high-alumina coal gangue was applied in practice.Using high-alumina coal gangue from Zhungeer coal field in Inner Mongolia as raw material,the course Al-Si alloy was produced on a large scale by electrothermal method,and the iron phase separation process of the course Al-Si alloy was carried out by using the optimal process route obtained from the foregoing research.The results show that the process can successfully separate the iron phase in course Al-Si alloy,and obtain industrial silicon and cast Al-Si alloy products that meet the requirements of national standard.Thus,the high value application of course Al-Si alloy is realized and has high practical application value.