Study On The Modification And Properties Of Al-Si Alloys With High Silicon Levels

Hypereutectic aluminum-silicon alloy which have high wear resistance, low thermal expansion and good conductivity is a perfect piston alloy. However, the number of coarse and irregular lumps primary and needle-like eutectic silicon is added with the increase of silicon content, which seriously decreases the comprehensive properties of the alloy and limit the further application. In order to expand the application range of hypereutectic Al-Si alloy, the fundamental research on Al-28%Si alloy was studied in this article.The effect of P, RE, Sr single modification and mutual complex modification on the Al-28%Si alloy is investigated. The microstructure of primary silicon and eutectic silicon and the modification mechanism of Al-28% Si alloy under the variety detection methods are discussed. Microstructure, dimension and distribution of primary silicon and eutectic silicon were summarized under the different modification when it is compared with the microstructure of primary silicon and eutectic silicon of unmodified Al-28%Si alloy.The Al-28%Si alloy was modified by the P+RE+Sr triplex modifier using orthogonal test, and the effect of the different addition of compound modification on the microstructure of primary silicon, high temperature tensile properties and thermal expansion are studied in the paper through range analysis. The results reveal the better modification parameter is: 0.3%P, 1.0%RE, 0.06%Sr, the verification tests indicate that the P+RE+Sr triplex modifier can refine primary silicon and eutectic silicon well.The Al-28%Si alloy is alloyed treatment under the optimized complex modification. The article researches the effect of the addition of Cu, Mg and Mn on high temperature tensile properties, wear resistance and thermal expansion. The result reveal that the reasonable composition range of Al-28%Si alloy is: 0.84%².5%Cu, 0.58%¹.2%Mg, 0.27%⁰.31%Mn, and the properties targets of the Al-28%Si alloy is established:σb, 300℃≥123.4MPa,α≤18.3971×10-6/℃, u≤1.1836×10^-14m3·N^-1·m^-1The optimized Al-28%Si alloy must be verified by the test. The morphology of high-temperature tensile fracture and worn surface is studied, and the tensile fracture mechanism and worn mechanism are also analyzed; it is compare the properties of verified alloy with piston alloy AlSi25CuMgNi of Alcan Company, the result shows that the Al-28%Si alloy which is prepared in this test meets the requirement of piston alloy.