| Silicon particles reinforced aluminum matrix composites has been receiving much attention as a new type of electronic packaging materials due to it’s excellent properties, such as low density, high specific strength, high specific stiffness, high thermal conduction and low coefficient of thermal expansion. Laser welding have been increasingly wide range of applications in aerospace fields, electronic packaging and auto industry because of high precision, high energy density, high automation, small heat affected zone.In this paper, the welding characteristics of(60vol%)Si_p/6063 Al aluminum matrix composites were investigated using the single laser welding and the laser welding with powder. It was found that single laser welding was difficult to obtain good weld surface appearance, weld undercut, cracks at surface, serious porosity, shrinkage defects inside weld. Joint tensile strength was low with each parameter, maximum of them was 34.4MPa only 65.3% of the base material. The thermal conductivity was 110W/(m?K) at room temperature. Laser welding with powder can effectively improve the quality of the weld surface forming with no defects such as undercut, cracks. Shrinkage defect has been effectively controlled at the same time. But, there are still serious porosity defects near the fusion zone. There are rarely primary Si particles and show an uneven distribution inside weld. The width of heat affected zone increased significantly. Tensile strength is only 28.9MPa, however, the thermal conductivity increased significantly than the result of single laser welding, it’s 124.2W/(m?K) about 85.5% of the base material under the same conditions.Achieved quality connection of Si_p/6063 Al composites by the new method that based on the theory of material increase manufacturing processes. Resulting in good weld seam performance with no defects, almost no weld porosity, only small amount of shrinkage in the heat affected zone. And the primary Si phase uniformly distributed over the entire range of the weld. The results show that the silicon exists mainly in two forms, namely, primary silicon and eutectic silicon, in the welds. The primary silicon has varied shapes, such as small massive, granular, polygonal lumps and petals. The eutectic silicon exits with the shape of needle between the particles of primary Si phase.Physical properties such as thermal conductivity and thermal expansion coefficient are closely related to the microstructure of weld. In the paper, powder ratio and heat treatment was investigated to regulate the microstructure of weld. The results showed that with the increase of Si powder in the filling powder, the number of primary Si particles gradually increased inside weld. The shape of primary Si particles by a small massive, granular gradually transformed into polygonal blocks and petals, the average diameter of particles is also gradually increased. With the 30wt%Si filling powder, The thermal conductivity of joint was 127W/(m?K) at room temperature and the average coefficient of thermal expansion lower than 12×10-6/℃ in the temperature 20~100℃.The shape of both primary Si and eutectic Si particles changed significantly after heat treatment, the needle and short rod eutectic silicon have broken and assembled into short strip or spherical, and the sharp-cornered primary silicon has also been passivated, making the structure of the weld uniform. This phenomenon is observed in this study that the primary Si particles connected to each other under the conditions of high temperature or long holding time. |
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