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Study of Making Casting Grade Al-Si Alloys with Coarse Al-Si Alloy Produced by Electrothemal Reduction of Aluminous Ore

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Tutor: FengNaiXiang
School: Northeastern University
Course: Non-ferrous metallurgy
Keywords: electrothermal reduction,coarse Al-Si alloy,iron removal,steady electromagnetic
Type: PhD thesis
Year:  2008
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Al-Si alloy has the most species and extensive use in aluminum alloy. At present, most Al-Si alloys are produced by melting pure aluminum and silicon. The energy consumption of the technics is high, the line of production is long and it need high grade ore. It recognized at the present in the world wide that Electrothermal reduction is superior to the method of melting pure Al and Si. The electrothermal reduction has short line of production and can use low grade bauxite and other resource. However, this method also suffers its defect that there are so many impurities in coarse Al-Si alloy. The main impurities are metal and non-metal slag. In order to gain casting Al-Si alloy conforming to industrial standard, refined and removed iron should be done first. This article studies the process of the coarse Al-Si alloy which is gotten by the kaolin with electrothermal reduction to produce the casting grade Al-Si alloy after diluting by Al, refining by flux and iron removal by manganese.The coarse Al-Si alloy produced by submerged arc furnace has the main slag are Al2O3 and SiO2 and the slag is mainly in the Al2O3¡€SiO2 compound oxidate form. The metal impurities are Ca, Fe and Ti. The impurity Fe is mainly in the FeAl3 and Al4FeSi2 form. The impurity Ca is mainly in the CaAl2Si2 form. And the impurity Ti is mainly in the form of TiSi2.The test use the Al as the dilution agent for the the coarse Al-Si alloy first. And then adopts a refining method by flux to remove slag, and treating the alloy with a molten mixture of sodiume chloride, potassium chloride and cryolite at 960¡æ. It can be concluded after the experiment that the net quantity of slag increases and the contents of Al and Si decline linearly with increasing of the purificant addition initially, but the change becomes unobvious after the purificant addition exceeded a specific value. The optimal addition of purificant is about 3.5% of the mass of aluminum-silicon alloy.Iron is the major impurity in aluminum-silicon alloy after the refining and slag removal, and the content of iron is one of the crucial scales for grading Al-Si alloy quality. After refining the iron in the alloy is 5 phase. Adding manganese into the molten alloy at 960¡æ and then filtering after cooling, the content of Si and Fe decrease with the increasing of manganese until the contents reached a particular value. The content of Si and Fe also increase with the increasing of filtration temperature and decrease with the decreasing of aggregate size. Manganese¡¯s optimal addition is which make the mol ratio of Mn and Fe valuing 1.2:1, the filtration temperature is 580¡æ,and the filtration aggregate size is 3-5mm and the thickness is 4cm.The iron removal is mainly in three ways. A small amount of iron is fusing into the slag in the form of Fe2O3 and FeMnO3 (the slag contains first slag and second slag). Some of iron settling in the bottom of melting pot becomes semisolid multivariant intermetallic compound. And some of iron is in the filtration slag. The iron settles in the bottom of alloy and generates the new alloy when the sum content of Mn and Fe in the iron-rich phase(quaternary intermetallic compound) is more. But when the sum content of Mn and Fe in the ron-rich phase is little, the bigger iron phase is removed not by the way of the free settling but the filtration. The remainder of Fe phase is in the casting grade Al-Si Alloys.It can have the same iron removal result when the manganese chloride is used as deferrization agent. But the loss of Al is too high, the agent is not appropriate.The free settling speed of Cr is too high and cannot generate the intermetallic compound that containing more Cr with iron-rich phase. So the method of iron removal by Mn and Cr is not suitable.In the direct current electromagnetic field, the Fe phase volume in the Al-Si alloy is growing. The iron-rich phase is mainly in the forms of long flakes and small flakes but still has the acicular phase of the iron-rich phase when the electromagnetic current is small. But when the electric current achieves 950A, rich-iron phase in the alloy already completely turned into spherical phase. The contents in the rich-iron phase of the Al-Si alloy had changed in the adding of steady magnetic field, the content of manganese had increased. The manganese in iron-rich phase of the alloy is getting higher as approaching the alloy¡¯s bottom. The effect of iron removal is fairly good when the manganese and the electromagnetic field are both used. Under same filtration condition, the iron content of the alloy is lower than using the manganese.The chemical compositions of ZL101 and ZL102 produced by the coarse Al-Si alloy can meet the national standard. And after modification by strontium the mechanical property of the ZL101 and the ZL102 can meet the commercial production request. During the process of producing the casting grade Al-Si alloy with the coarse Al-Si alloy, the casting grade Al-Si alloy which the iron content is under0.7% is gotten by choosing the suitable conditions including the filtration temperature, the aggregate size, the aggregate thickness, and iron removal method.
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