Translated Abstract
The running speed of rapid train is high, the transportation of it is strong. The characteristics of Aluminum alloy is that its weight is light, the strength and corrosion resistance of stainless steel are very well. The sandwich board structure is made of the two materials, with that, the high strength and the light quality can be aquired. But, there are large differences between the two metals, such as melting point, expansion coefficient, thermal conductivity, heat capacity , and Al-Fe intermetallic produced in welding process, this difficulties can affect the connection of the two metals. Laser welding has the characteristics which is heat input is concentration, especially suitable for welding plate, with it, the welding deformation can be decreased. So, in the research process, laser welding is choosed as the connections method for aluminum alloy and stainless steel, and the Ni layer is joined between the two metal to reduce Al-Fe intermetallic compound formation in the welding process.The proper welding parameters were optimized from studing the laser welding process,and the organization of morphology, material composition, element distribution, microhardness and shear strength of welding joints were analyzed.The study shows that,when the laser power is between 1.5 kW and 1.9 kW, welding speed is between 1000 mm/min and 1500 mm/min, and the line energy in 85 J/mm is more appropriate, the good quality of the welding joints can be get. The microstructure of joint is made up of the columnar crystal and the equiaxial crystal, with the increasing of the heat input, the size of the crystal grain increases gradually, and the columnar crystal change into the equiaxial crystal.The downward diffusion of the Fe elements and the upward diffusion of the Al elements were hindered when the weld joints was joined with a layer of Ni, so the Al-Fe intermetallic formation of the welding point is hindered. The shape of the microhardness curve of the welding joint is "saddle", the maximum of the microhardness is near the fusion line, the influence of the organization form and the crystal grain size is bigger. When the welding joint is in part of the fusion, the shear strength of the welding joints is the biggest of all, the fracture mode is ductile fracture. When the welding joint is all of the fusion, the shear strength of the welding joints is pooer, the fracture mode is brittle fracture.
Translated Keyword
[Aluminum alloy Stainless steels Laser welding Ni coating Al-Fe intermetallic compound]
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