| With increasingly serious environmental pollution, automotive lightweight has become an indispensable problem to be solved, and using welding structure of dissimilar metal for steel/aluminum is an effective means to solve the problem of lightweight.However, due to the difference of physical and chemical properties between steel and aluminum and brittle intermetallic compounds formed in the welding process, the mechanical properties of the joint decrease as a result. Due to rapid speed, high energy density and small deformation, laser welding is regarded as one of prospective methods to join steel to aluminum successfully.In this paper, the influence of the form of lap joint and laser power on the appearance of weld was studied concerning dissimilar metal for steel/aluminum by using the thickness of 1.00 mm 05 Cu PCr Ni weathering steel and the thickness of 1.4 mm 6082 aluminum alloy. In addition, the effect of interlayer(Fe-B-Si 〠Cu 〠Al-Cu-RE) on microstructure, hardness distribution and fracture morphology of the joints were also discussed.The experimental results show that when welding speed and laser power were20mm/s and 0.82 k W~0.83 k W, the formation quality of the lap joint between steel and aluminum joint without interlayer was well. The Fe-Al intermetallic compounds formed at the interface of the welded joint were Fe3 Al, Fe Al, Fe Al2, Fe2Al5, Fe Al3, and some of Fe Al3 showed needle-like morphology. At the same time, the solute zone and the island region were also formed by agitation of the molten pool. The hardness of the weld center was higher than that of the base metal, and the hardness at the interface of the welded joint where Fe-Al intermetallic compound form reached 300~380HV. The welded joint easily fractured in intermetallic compounds. The fracture surface of the aluminum alloy side presented ice-sugar morphology, which belonged to the intergranular fracture.The experiment was carried out with Fe-B-Si, Cu and Al-Cu-RE as interlayer, and the three kinds of interlayers could inhibit the formation of Fe-Al intermetallic compounds in different degree. All the fracture surfaces of the welded joint were smooth,belonging to brittle fracture. When Fe-B-Si was used as interlayer, the interface was more flat,and the number of island zone and needle-like Fe Al3 decreased. The hardness of the weld center is reduced by 30~50HV. The welded joint fractured in intermetallic compounds, and when fusion zone of aluminum alloy existing the crack, fracture may occur in the crack. When Cu was used as interlayer, the grain size of needle-like Fe Al3 became fine and the quantity was less. The hardness of the weld center was reduced by30~50HV. The welded joint fractured in Fe Al2, Fe Al3 and the junction of spherical Fe Al and Fe3 Al. When Al-Cu-RE was used as interlayer, the number of needle-like Fe Al3 is greatly decreased, and only the bottom of the weld pool existed needle-like Fe Al3 with a smaller grain size. The welded joint fractured in the spherical Fe-Al intermetallic compound, Fe Al3 and Fe Al3+Al eutectic. |
