Al-25Si and Properties of organizational control

Title: Al-25Si and Properties of organizational control
　　Author: Zhao Junfeng
　　Degree awarded: Shenyang University of Technology
　　Keywords: semi-solid forming;; hypereutectic Al-Si alloy;; primary silicon;; secondary heating;; deterioration
　　Summary:
　　Hypereutectic Al-Si alloys have low expansion, high wear resistance, the smaller the proportion and good thermal conductivity, but the hypereutectic Al-Si alloy in the prevalence of coarse primary silicon phase, which seriously split the matrix, Magnetic lifter deterioration of the mechanical properties of the alloy, limiting its wide application in industry. Effective way to solve such problems is to refine the primary silicon phase. At present, the refinement of primary silicon phase method more, for example: the primary silicon phase modification, extrusion, using rapid solidification technology. In addition to effects of rapid solidification technology, however, the ideal, other methods to improve the alloy properties is still no clear break, and rapid solidification process, there are high costs and complicated issues. In this paper carried out to improve the hypereutectic Al-Si alloy microstructure, thereby enhancing the mechanical properties of alloy research. For Al-25Si alloy, through modification, the electromagnetic casting, and semi-solid forming a combination of preparation techniques, and thus the hypereutectic Al-Si alloys with size of primary silicon refinement or control, to achieve the purpose of improving the mechanical properties of alloys.
　　Studies have shown that: Al-25Si by RE metamorphism, the morphology of primary silicon thick irregular shape by the deterioration of the former rules into small spherical; primary silicon size of about 300μm from the bad before the left and right down to 35μm; also found that the rare earth play metamorphism when the right time with a range, 30min ~ 40min can take advantage of rare earth oxides on hypereutectic Al-Si alloy modification effect of primary silicon. Semi-solid forming, the alloy has undergone significant changes, elongated eutectic silicon phase into small granules, large primary silicon phase has also undergone a significant round crushing http://www.999magnet.com/products/131-magnetic-lifter refine and shape of the distribution is more uniform . Semi-solid forming process used in the higher extrusion ratio, the more obvious refinement alloy.
　　The rare earth deterioration, the cast hypereutectic Al-25% Si alloy by the deterioration of the Brinell hardness of 91.3 to 99.8 before; tensile strength of the deterioration before 134.4MPa to 178.4 MPa, increased by 32.7%; by half After the solid forming, Al -25% Si alloy tensile strength by 78.9% to 240.5MPa, elongation rate from 0.2% to 4.3%, Brinell hardness of 120; with the extrusion ratio increases, the mechanical properties also increases.
　　Degree Year: 2010