Research On Adding Si At Low Temperature And Modification Of Al-Si Alloy

Resource and energy source are attended in 21 century.Aluminum is rich in the earth's crust,has good strength and can be recycled,so people give many attentions to aluminum.Aluminum has been used in many areas of the national economy,for example:daily necessities,architectures,cars, aircraft,rockets and so on.Aluminum consumption has became the second metal compared to iron.Al-Si alloy is an important branch of aluminum. Al-Si alloy is widely used in many areas.Good preparation is useful to produce good Al-Si alloy and save energy sources.The methods of Electric Reduction Act,Electrolysis and Melting are used to produce Al-Si alloy.This paper compared with several schemes of melting Al-Si alloy.Al-13Si eutectic and Al-20Si hypereutectic alloys are melt with the method of adding Si blocks at low temperature.Practice has proved that the method can keep good quality,economize energy sources and protect environment.The relationship between the melting temperature and the microstructure are analyzed.The melting point of Si is 1414℃,but Si can be dissolved in liquid aluminum at low temperature.The paper contrasts microstructures in melting processes using the method that crucibles are cooled in the atmosphere and detects the proliferation laws of Si.The thermodynamic analysis proves that the melting heat which Si is dissolved in liquid aluminum is about 608J/g.The value is only one third of the data(1808.69J/g)which Si melts.The experiment proves that Si melting is different from Si melting in liquid aluminum.With cluster theory we lodge that the mode of Si melting in liquid aluminum complies with the model of "Si cluster on Si block→Al-Si cluster→Si-Si cluster".The model describes the mechanism of Si melting in liquid aluminum and analyses the reason of liquid Al-Si alloy structural changes.There are many long and massive silicon phases which adversely affect the mechanical properties when Al-Si alloy contains more than 6%Si,so it is necessary to modify silicon phases.This paper modifies Al-20Si hypereutectic alloy with phosphorous salt and rare earth alloy.The primary silicon particles are modified from 140μm to 15μm and the eutectic silicon particles are modified from 100μm to 10μm.Mechanisms of the modifier are analyzed with cluster theory and lattice similarity theory.