| Si C particles reinforced aluminum-silicon matrix composites have many excellent properties, such as high specific strength and specific stiffness, low density, low thermal expansion, good wear resistance, and so on. Compared with SiC particles reinforced aluminum matrix composites, it has better dimension stability. SiCp/Al-Si composite has attracted much attention in the field of aerospace and electronic packaging, which has a broad application space and has became a hot spot of current research materials. SiCp/Al-Si composite prepared by powder metallurgy has thermal or stress field coupling action, and has the interfacial reaction and the second phase precipitation phenomenon on the microstructure which makes its physical and mechanical properties of hard to control, comprehensive performance low, and limited its application in aviation and space fields.Al-19Si-1.5Cu-0.6Mg alloy power was chosen prepared by atomization as matrix, SiC particles chosen as reinforcing phase in the aluminum matrix composites. Composite powders were mixed through the high-energy ball milling and the process parameters were: the ratio of steel balls and materials 2:1, the speed of ball-milling machine 250 r/min, the time of ball milling 2 h, adding 1% sodium stearate as dispersant. Cold-pressing billets of SiCp/Al-Si composite material were prepared by using one-way mould pressing method. The green compacts were sintered in nitrogen atmosphere, the sintering process is: the heating rate at 2 for /min slow step heating and sintering temperature for 560 ℃, insulation for 4 h, cooling in the furnace. The sintered composite compacts were pressed by thermal extrusion of XT-500 type heat.The sintered composite billets were extruded at high temperature and the effects on hot extrusion bars squeezed under different extrusion process parameters were discussed. The extruded composite samples were heated for 480 ℃, 490 ℃, 500 ℃, 510 ℃, preserving heating for 4 h and aging treatment of 190 for 6 h.℃The density and mechanical properties of the materials were measured before and after extrusion, the microstructure of materials were characterized by scanning electron microscope taped JSM-5610 LV and transmission electron microscope taped JEM-2100. The composites were analyzed by D-8X ray diffraction. The effects of the cold pressing process on composite cold pressure forming, and the defects in the process of the preparation was analyzed on the extrusion process of composite extrusion forming of the bar.The law of solid solution element in the preparation process, and the influence on the microstructure and properties of composite materials was studied by preparation process variables. The results show that : the prepared composite has smooth surface and complete shape by the process of the cold pressure of 500 MPa, pressure holding time for 30 min, holding time for 30 min.A optimal hot extrusion process was got: extrusion temperature of 480 ℃, extrusion ratio of 15:1, extrusion speed of 1 mm/s. The surface appearances of extrusion bars prepared by this technology were well. After hot extrusion, the density of the composite material has been greatly improved, reached 98%; the separated out second phase can effectively hinder the movement of dislocations, forming the dislocation structure in great quantities which makes the microstructure and mechanical properties of composites increase significantly. After solid solution at 500 ℃ for 4 h, aging at 190 ℃ for 6 h, SiCp/Al-Si composites had the highest tensile strength, reached about 290 MPa. |
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