Microstructure And Properties Of Al - 20Si Alloy Prepared By Spray Deposition Continuous Extrusion

Hypereutectic Al-Si alloy has many advantages, such as low density, good thermal stability and excellent wear resistance,which can be used as an ideal material for the automotive industry and electronic packaging industry, and with the increase of silicon content, wear resistance and physical properties of hypereutectic Al-Si alloy are more obvious. But at the same time,high content of Si would prominently decrease its mechanical properties and processing properties, which greatly limits the popularization and application of hypereutectic aluminum silicon alloys. Spray deposition and continuous extrusion forming (hereinafter referr to spray Conform) is a new metal forming technology, which has a huge advantage in reducing segregation, grain refinement and solve the problems of the hard-alloy forming. In this paper, the spray Conform experiments of Al-20Si alloy were accomplished by self-made equipment.(1) Using as cast Al-20Si aloy as experimental materials, Al-20Si alloy were softening of heated to 450 ℃ and 650 ℃ for the continuous extrusion processing, the results show that:because of the large deformation resistance made by the primary crystal silicon in as cast Al-20Si alloy matrix, fractures were happenedand in the extrusion groove and the cavity couldn’t be filling enough in the extrusion process, which proved that without primary silicon refinement pretreatment conditions, it is difficult for the as cast Al-20Si alloy to achieve continuous extrusion directly.(2) The spray deposition and Conform experiments of Al-20Si alloy in different overheating treatment were accomplished by self-made equipment. Ultimately, the alloy rods with diameter of 8 mm were obtained. The microstructure, density, mechanical properties and wear properties were studied. The results show that:spray deposition and Conform method can effectively inhibit the nucleation and growth of primary silicon. With the increase of overheat temperature, relative density of Al-20Si alloy increased, the primary silicon size decreased and the distribution becomes more homogeneous, the size of primary silicon is about 3-8μm,the mechanical properties of the alloy improved at the same time, the tensile strength is up to 204MPa, the elongation rate is up to 7.2%.Compared with the as cast alloy, the wear resistance of Al-20Si prepared by spray Confrom improved about 2 times.(3) The spray deposition and Conform experiments of Al-20Si alloy in different extrusion ratio were accomplished by self-made equipment. The microstructure, density, mechanical properties of products were studied. The results showed that:the increase of the extrusion ratio can effectively improve relative density of Al-20Si alloy, and reduce the grain size of primary crystal silicon, and with the increase of the extrusion ratio, the ultimate tensile strength of the aluminum silicon alloy increases gradually, when the extrusion ratio is 20, the ultimate tensile strength is up to 213.7MPa. The maximum elongation value appeared with the extrusion ratio of 10 (15.8%).(4) Analyzed and summarized the common failure mode in process of spray Conform, including extrusion force in short supply, deformation and fracture of the plug, the negative effect of the compaction wheel, die cavity overflow etc.. At the same time, Summarized the common defects of spray Conform, including pits, scratches, peeling and crack, and provided the effective solutions to improve the experiment.