| Aluminum alloy is a premium choice for making shells of electronic products, as it has light density, high specific strength, and excellent corrosion resistance, and it can conduct heat much faster than plastics. Currently, laptops and LCDs with aluminum shells has been released in the domestic markets. In foreign countries aluminum has been applied in manufacturing shells of mobile phones, however the price of aluminum shell is not cheap because of the complicated manufacturing process. Lacking an efficient and reliable method of joining aluminum shells and inner stainless steel components is one of many technical bottlenecks. As one of the most precise and efficient joining method, laser welding has been widely used in industries, especially when a pulse laser is used to weld tiny components in electronic products, it can precisely control the heat input and restrict the deformation to an ideal degree.In this paper, a Nd:YAG pulse laser was used to produce weld spots to make lap joints between SUS301 stainless steel and 6063 aluminum. Effects of current, pulse duration, defocusing distance and other process parameters on the weld size and weld quality were investigated, and it was concluded that cross section of the weld is like a bowl and the shape on the surface approximates to a circle; Both diameter of the weld surface and weld penetration increase with the current and pulse duration: the current has more significant effect on the surface diameter than the pulse duration does, and it can be drawn that weld penetration has a positive correlation with product of the current and the pulse duration; Quality of the weld surface depends on two important factors, one is related to the flowing speed of protecting gases and the distance between the spray head and the specimen, and the other one relates to the laser power density which is decided by the spot size and the current.Two main process parameters including current and pulse duration were optimized in order to obtain the best resistance to tensile-shear test. It was concluded that when the current is 95 A and the pulse duration is 10 ms, weld spot with no macro crack and with reasonable penetration was obtained, and the tensile-shear test showed 25.3N every single weld spot. Based on the optimized parameters, investigation on arrangement of the welds revealed that: when number of weld spots in single row is over 4, performance of the joint cannot improve significantly with the increasing weld spots number, while the performance can increase a lot when the weld spots are arranged into two rows; When weld spots are arranged into several rows, rows aligned with the next would be better than rows unaligned; Distance between every two weld spots has effect on performance of the joint, a larger distance would result in a more even stress distribution, thus showing a better tensile-shear test result.Effects of current and pulse duration on the weld microstructure and the crack tendency were also investigated. The paper analyzed the different characteristics and formation mechanisms of two kinds of cracks, and put forward effective ways to avoid or reduce the weld crack. Also, formation mechanism of pores in weld spots and corresponding ways to avoid were given in the paper.At last, test results of the weld spot performance were carefully analyzed, and fracture modes were classified into two types, both of which correspond to a certain failure mechanism of the welds. Based on the conclusions, relation between the fracture mode and weld spot performance was drawn out, which provides basic data and experience for the joining of tiny aluminum components to steel components. |
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