Study Of Semi-solid Slurry Preparation Of High-silicon Aluminum Alloy Prepaired By Powder Spraying Method And Its Pressure Molding

Because of good heat resistance,wear resistance,corrosion resistance and low coefficient of thermal expansion of High-silicon aluminum alloy,it is an ideal material for manufacturing heat-resistant and wear-resistant parts such as pistons,cylinder liners of automobile engines and brake discs.In traditional manufacturing processes,metamorphic agents were usually used to refine or modify the primary Si of high-silicon aluminum alloys,in which not only fails to achieve the desired refining effect,but also causes low refining efficiency,pollution of melt,and so on.That was always a constraint in application of high silicon aluminum alloy.In this paper,Al-20%Si alloy was prepared by the semisolid technology of the powder spraying with inert gas method and molded under pressure machine.OM,SEM,EDS,friction and wear tests,etc.was used to study the influence of process parameters of powder spray method on the microstructure and properties of high-silicon aluminum alloy.and at the meantime it also was investigated the microstructure and properties of the semi-solid slurry of Al-20%Si alloy molded by pressure.Which hope to provide a theoretical and experimental basis for the industrial application of high silicon aluminum alloy such as pistons and brake disc.The results showed that the morphology of Al-20%Si particles obtained by atomization of the self-made granulator was mainly spherical;the smaller the diameter of the particles,the smaller the primary Si and eutectic silicon in the microstructure.From 3mm to 0.075mm of Al-20%Si particles,the average size of primary silicon grains decreased from 25.68?m to 2.38?m.Compared with the internal cooling method and the gas stirring method,the powder spray method could obtain a much finer and highly rounded semi-solid slurry structure of high-silicon aluminum alloy.The experimental results showed that the optimum process parameters for the preparation of semi-solid Al-20%Si alloy slurry by powder spray method were as follows:the slurry-making temperature of the alloy was700?,the mass ratio of the powder/melt was 9%.,and the powder particle composition was Al-20%Si,the particle diameter was0.075mm,stirring speed of rod was 900rpm,which achieved the good microstructure and property such as the average grain size of primary Si was 18.12?m,the shape factor was 0.82,the hardness of the alloy was123.4 HB,and the tensile strength was150.9MPa respectively.The pressure forming results of the semi-solid slurry of Al-20%Si alloy showed that the metamorphic effect on the eutectic Si microstructure was very obvious,not for the refining effect of primary Si on the Al-20%Si alloy under pressure,in which the eutectic Si of the Al-20%Si was transformed from a long needle shape into a point shape and a short rod shape uniformly distributed in the matrix.And meanwhile it appeared the hypoeutectic characteristics of the a-Al under pressure test.The property of Al-20%Si semi-solid slurry formed by pressure,comparing with ordinary liquid pressure molding,increased greatly,that the hardness of the alloy was increased from120.5HB to 134.8HB,improving 10.6%,and the tensile strength was increased from 100.3MPa to 167.4MPa improving67%respectively.The high-silicon aluminum alloy of Al-20%Si prepared by powder spray semisolid method significantly well refined the microstructure of the alloy.The addition of powders of the powder spray semisolid method to the alloy melt was a key factor in grain modification of the Si phase.The stirring effect of the powder spray sticks had also synergistically refining effect on the microstructure of the Al-20%Si.The molding pressure increased the eutectic temperature of the alloy,thus increased the supercooling rate and the cooling rate of the Al-20%Si.And make it have a significant refinement effect on the Si phase of Al-20%Si.