Effect Evaluation And Mechanism Analysis Of Modification On A356 Alloy By SB And Y

This paper gives analysis to the influences of Sb,Y and Sb-Y composite modification on the morphology of silicon phase, mechanical property, conductivity, thermodynamic parameters and the friction and wear properties of A356 alloy by test means of DSC, SEM, XRD and discusses their modification mechanism.The experiment shows that:Adding Sb to A356 alloy can turn silicon into needle-like particles which is much smaller than the silicon without modification treatment, the photograph of electrolytic corrosion shows that the distribution of silicon is close-spaced lamellar shape in aluminium substrate; Adding Y to A356 alloy can turn silicon into fibrous which is much smaller than the silicon of Sb modified A356 alloy, the photograph of electrolytic corrosion shows that silicon looks like the cross-linked coral reefs and the ends of silicon becomes smooth and evasive without edges; After Sb-Y composite modification, the silicon almost change to very tiny particle form, the photograph of electrolytic corrosion shows that silicon looks like the watery weeds which is swinging with wind, and not only the ends but also every angles of silicon is rounded.After T6 heat treatment, the silicon of modified A356 alloy turns into a number of separate short-stick, spherical and elliptical shape. They distributes in grain boundaries of primary crystal aluminum and turns more disperse than cast condition. The average size of silicon becomes smaller in proper order according to Sb modified, Y modified and Sb-Y composite modified A356 alloy.The hardness, tensile strength and elongation of non-modified A356 alloy is 36.3 HBS, 143.3MPa and 2.5% respectively. The hardness, tensile strength and elongation of Sb modified, Y modified and Sb-Y composite modified A356 alloy is 50.5 HBS, 222.9MPa, 10.3%;76.3HBS,238.1MPa,5.5%;82.3HBS,263MPa,8.8% respectively.The biggest increase of hardness, tensile strength and elongation reaches 126.7%, 83.5% and 312%.The conductivity of non-modified A356 alloy is 16.37MS/m.The conductivity of Sb modified,Y modified and Sb-Y composite modified A356 alloy is 17.60MS/m, 17.85 MS/m and 18.50MS/m, respectively improved 7.5%, 9.0% and 13.0% than non-modified A356 alloy.The DSC analysis found that in the order of adding Sb modifier, Y modifier and Sb-Y composite modifier to A356 alloy, eutectic supercooling degree of A356 alloy is 2.9℃, 4.9℃and 7℃respectively and eutectic latent heat increases. The increase of eutectic supercooling degree and eutectic latent heat holds up the growth of silicon, so the modification effects get better in order.The friction and wear experiment shows that in the order of Sb modified, Y modified and Sb-Y composite modified A356 alloy, both friction factor and abrasion loss get lower and the spalling of wear surface gets less serious,which reflect modification effects get better.