| As an important cast alloy, hypereutectic Al-Si alloy has low expansion coefficient and density, good cast performance and wear resistance. With the increase of silicon content, the alloy has a further decrease of linear expansion coefficient but further increase of wear resistance and heat resistance. However, the increased silicon content alloy has a large number of coarse and irregular lumps primary silicon and needle-like eutectic silicon, which seriously decrease the comprehensive performance of the alloy. So,refining its microstructure is a necessary way of improving comprehensive performance of the alloy.On the basis of the single modification of P,RE,Sr elements to the alloys, investigated the effect of modification on the structure and morphology of primary and eutectic silicon and discussed its modification mechanism;Used the orthogonal test to carry through the P-RE-Sr triplex modification of the alloys and gained an efficient P-RE-Sr triplex modifier.Then made use of triplex modifier to modifiy the hypereutectic Al-28wt.%Si alloy ,its average size of the primary silicon was only about 25μm. and made the primary silicon obtuse and nodular.gained the fine size,short bacilliform or vermiform eutectic silicon at the same time.Through normal experiment measure,maximal dispersion and curvilinear regression analysis investigated the effect of the various addition of P, RE on the room temperature tensile strength after heat treatment,high temperature tensile strength at 300℃and the hardness of the hypereutectic piston Al-28wt.%Si alloy,confirmed the best composition extent for the modification.And elicited the following conclusion:under the defined composition of alloy ,and with the adiition of P, RE, Sr elements were changed in the defined extent.the value of the room temperature tensile strength after heat treatment is from 217.034 to 234.173MPa, high temperature tensile strength at 300℃is from 122.839 to 129.045MPa, and the hardness is from 155.52 to 161.83. totally fufilled the capability requrement of piston alloy.the research results may offer a new and helpful approach to improve piston alloys'comprehensive performance at all times and extend its application extent ,so the results have considerable academic and practical significance. |
