Effects Of Electromagnetic Levitation Melting On The Microstructure And Properties Of The Cast Al-Si Alloy

Electromagnetic levitation melting is a new high-efficiency technology of levitating,simultaneously heating and melting materials and stirring the melt by electromagnetic force and electromagnetic induction.Because the alloy melt dose not contact with the crucible,the contamination and heterogeneous nucleation from the wall of crucible are avoided.Thus,the technology has been widely applied to melting and forming of reactive metals,materials with high melting points and other special-purpose materials.In this paper,AlSi20,ZL102 and ZL101A,these three Al-Si alloys were melted at three different temperatures adjusted through changing supplied power by electromagnetic levitation method,the microstructures of the samples were observed and the tensile property tests,density and hardness tests were performed.Compared the experimental results with that of the alloy melted by traditional methods,the effects of the electromagnetic levitation melting on the microstructure and mechanical properties were studied.The results show that the microstructure of the Al-Si alloys melted by the electromagnetic levitation method is notably refined and the cast defects such as pinhole,shrinkage and impurities are reduced.Under the conditions of electromagnetically levitating and stirring,the morphology of the needle-shaped eutectic Si crystals is modified into short bars with blunted tips,and well-distributed inαphase matrix.In ZL101A and ZL102 alloys,theα-Al dendrites are refined to ellipsoid and spheroid particles,and the proportion of equal-axial crystals is increased.In AlSi20 alloy,the large plate-shaped primary Si are transformed into small pieces, but the segregation layer of primary Si appears on the surface and some small particles of primaryα-phase in non-equilibrium solidification occur in the centre part of the alloy.By electromagnetic levitation melting,the density,hardness and fracture resistance of the alloys are greatly improved.The ability of plastic deformation of AlSi20 and ZL101A alloys is enhanced.Compared with the sample made by traditional melting methods,the tensile strength is increased more than 50%and the elongation is 2～3 times higher than that of the traditional samples.But too much Si in the Al-Si alloy will have negative influences on their plasticity and toughness.The results also show that the microstructure in the top part of the samples is finer than that in the bottom part and lateral part.With the output electric current increasing,the crystals are refined at first,but then they are thickened instead.When the output electric current is 70A,the improving effects of the microstructure and mechanical properties are the best at three different melting temperatures.