Effect Of Melt Treatment On Solidification Characteristics Of356Alloy

356aluminum alloy is widely used in aerospace and civil industry domain because of its highwear resistance, heat resistance, corrosion resistance and good casting properties. In recent years,modification, heat treatment and the theory of solidification of aluminum alloy were studied byscholars, but do not form a complete research system. The effect of melt temperature andsolidification conditions on356aluminum alloys modificated by rare earth has been reported rarely.So the effect of rare earth Y on the structure and performances of356aluminum alloys were studied,and the influences of melt temperature and cooling rate on the deterioration of the alloys wereresearched for further study in this paper.The primary α-Al grains were refined and the secondary dendrite arm was reduced as a result ofthe addition of rare earth Y. Part of Y atoms were adsorbed on the growth steps of Si, hindering thegrowth of Si into a long sheet, and the others were used to strengthen the alloys in the form of Al3Y.The morphology of eutectic silicon got from striation texture to fibrous and granular so that theisolation of matrix was weakened. When the content of Y was0.2%, the mechanical properties of thealloys performs best, and the hardness, tensile strength and elongation were raised to75HV,183MPaand4.1%from56HV,154MPa and1.9%with no addition of Y.With the increasement of overheating temperature, primary crystal α-Al grain changed fromsmall to big, and then small, meanwhile, its distribution become regular. But melt temperaturetreatment on α-Al dendrites thinning effect is not significant. With the increasement of overheatingtemperature, the modification effect of rare earth Y decreased first and then increased. When theoverheating temperature reached900℃, the primary crystal α-Al dendrites become well developedand complete but the morphology of eutectic Si changed from granular and fibrous to small pieceswith the increase in holding time.As the cooling rate decreased, primary crystal α-Al grains become coarse and messy, secondarydendrite arm spacing increases and the eutectic silicon changed from fibrous and granular to sheet andneedles. When the cooling rate was122.7K/s, microhardness, tensile strength and elongation are75HV,183MPa and4.1%. When the cooling rate lowered down to26.8K/s, microhardness, tensilestrength and elongation are52.1HV,142MPa and1.6%and the fracture occurred by ductile fracture tobrittle fracture. Eutectic Si grows by the modification shape only when the modification of rare earthY keeping a certain cooling rate. The modification effect of rare earth Y is very sensitive to cooling rate.