Abstract: Laser butt welding is held on 08Al steel to 5083 aluminum alloy with Cu foil interlayer. Laser spot is shifted to the side of steel during the test. Optimal process parameters are determined by analysis and contrast of the welding formation. The influence of Cu elements on interface fusion, elements distribution and microstructure of weld zone are analysised by using optical microscope and scanning electron microscope. The results show that welding quality is best while the beam offset distance is 0.4 mm, defocusing amount is 0 mm, laser power is 2 kW, welding speed is 10 mm/s, flow of He gas is 15 L/min. The copper foil interlayer forms a bridge between aluminum and steel, which makes the transition of the physical properties of aluminum/steel more smooth and effectively reduced the temperature gradient and heat transfer rate at the interface of the liquid metal, while the residence time of high temperature of the molten pool is extended, so that the lower metal obtains more effective heat and the melting increased significantly. The section shape of weld changes from “T” to approximate “X”. The interface fusion line is irregularly curved, aluminum and steel meshed and connect closely. The cu foil inhibits the diffusion of al to the side of steel, and the second phase particles within ferrite grains significantly reduced. Aluminum/copper/steel joint combines cleavage fracture and quasi cleavage fracture. The brittle phrase of (Fe, Cu)4Al13、(Fe, Cu)2Al5 and CuAl2 are formed at the interface which is the main reason for the low improvement of joint strength.

Key words: laser welding;aluminum/steel;copper foil;brittle phase, Equivalent conicity, Tread design, Vehicle stability, Wheel-rail contact relationship