With the increasing application of non-ferrous metals, its connection technology has attracted more and more attention. Industrial pure nickel has excellent corrosion resistance. In industrial production, pure nickel is mainly used to make stainless steel and other corrosion-resistant alloys, and can also be used as a catalyst for hydrogenation reaction, as well as the manufacture of ceramic products, electronic circuits, green glass and Ni compounds. Aluminum has low density, good ductility, excellent corrosion resistance, thermal conductivity and electrical conductivity, and can still get satisfactory mechanical properties at very low temperatures. It has been widely used in chemical industry, machinery, transportation, construction, aerospace and daily production and life. Traditional welding methods (such as MIG, TIG, etc.) weld such metals, but the joint strength is insufficient, and the weld is easy to produce gas, slag inclusion, cracks and other defects, and the surface state of the welded metal has a great impact on the welding quality. The weld is prone to welding deformation and porosity, the residual stress is large, and it is sensitive to stress corrosion, which can not give full play to the properties of materials. Therefore, it is very necessary and urgent to explore the application of new welding methods in nickel and aluminum component materials.
1. Influence of welding parameters on surface forming of welded joints
In the aluminum - nickel laser welding test, the welding parameters involved mainly include laser frequency, laser power and welding speed. Because of their different effects on the joint, the degree of influence on the joint performance is also different. According to the literature review and part of the experimental research, when the laser frequency is 200Hz, the welding effect is the best, and the small heat input can be guaranteed.
1.1 Influence of laser power on surface forming of welded joint
When the laser power is small, the overall deformation of the welded specimen is small, there is no obvious porosity and cracks on the weld surface, there is no obvious splashing and biting phenomenon, and there is a ripple texture. In the case of constant welding speed, the welding width of the front will increase with the increase of laser power. When the laser power is less than 1.8kW, the weld center position has obvious depression, and the oxidation phenomenon is not obvious. When the laser power is 2.0kW, the weld is well formed and the oxidation phenomenon is not obvious. When the laser power is 2.2kW, the weld is well formed, the surface is smooth and beautiful, and the texture is clear. When the laser power is 2.4kW, the weld is better formed, the surface oxidation is more serious, and the back is just welded through. When the laser power is 2.6kW, the weld is completely welded through, the molten pool metal rolls up, showing black, and the oxidation is very serious.
1.2 Influence of welding speed on surface forming of welded joint
In the case of constant laser power, with the slowing down of the welding speed, the width of the weld shows an increasing trend. When the welding speed is 50mm/s, the joint melting width is small and there is a linear depression in the center of the weld. When the welding speed is 40mm/s, the weld is well melted and formed, the surface is smooth and beautiful, and the texture is clear. When the welding speed is 30mm/s, the weld width is larger and the surface oxidation is serious. When the welding speed is 20mm/s, the weld oxidation is very serious, the weld begins to produce obvious deformation, the weld is distorted, and the back has been welded through.
2. Influence of laser welding parameters on penetration depth and width
The welding quality of the aluminum-nickel lap welded structure depends not only on the mechanical properties of the joint, but also on the weld forming and oxidation discoloration. The depth and width of weld are important factors to measure the surface forming, the degree of oxidation and discoloration of the back surface and the mechanical properties of the joint. The weld depth mainly affects the quality of the weld back, while the weld width mainly affects the mechanical properties of the joint. Laser welding parameters (laser power, welding speed) are important factors that affect welding quality. In this experiment, the influence of laser power and welding speed on weld depth, weld width, microstructure and tensile properties of stainless steel butt joint was studied, which provided the necessary theoretical basis for the optimization of laser welding parameters of aluminum-nickel lap joint in actual production.
2.1 Influence of laser power on penetration depth and width
The weld depth and width are greatly affected by the laser power, while the residual height of the weld shows no regularity, which may be caused by the direction of the protective gas under some parameters. When the laser power is small (1.8kW), the stainless steel sheet has only a small amount of melting, and the weld penetration is small and the melting width is narrow. With the increase of laser power, the penetration depth and width are significantly increased, when the laser power reaches 2.4kW, the weld is just penetrated, and with the laser power increasing again, the penetration width continues to increase, and the back weld is also widened.
2.2 Influence of welding speed on penetration depth and width
With the reduction of welding speed, the penetration depth and width increase significantly, when the welding speed is only 30mm/s, the weld is about to be completely penetrated, and with the laser power increasing again, the penetration width continues to increase, and the back weld is also penetrated and widened.
3. Conclusion
3.1 When the power increases, the laser heat input increases, the melting amount of the welded metal material will increase, and the size of the weld pool will increase accordingly, thus increasing the weld width. The faster the welding speed, the faster the laser beam moves on the surface of the specimen, the energy input in the weld per unit time and unit length is reduced, the laser welding heat input is reduced, and the melting amount of the welded gold material is reduced, so that the weld width becomes smaller.
3.2 In the aluminium-nickel laser welded joint, when the laser power is low or the welding speed is high, the base metal melting amount of the aluminium-nickel joint interface is less, and the melting width and deformation of the aluminium-nickel joint are smaller. When the laser power increases or the welding speed decreases, the melting amount of the base metal increases and the melting width of the weld increases.
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