| In the modern automobile industry, automotive lightweighting has become the effectivemeasure of energy saving and emission reduction, as well as better fuel economy. Using thewelding structure of dissimilar metal for steel/aluminum is one of the essential ways ofautomotive lightweighting. The welding of dissimilar metal for steel/aluminum has alwaysbeen a difficult problem, and the main reason is that the big difference of physical andchemical properties between steel and aluminum. In addition, as the solid solubility of ironin aluminum is low, it’s easy to form iron aluminum brittle intermetallic compounds duringwelding, which decreases the mechanical properties of the joint.Aiming at the present situation of more and more applications of welding structure ofdissimilar metal for steel/aluminum in the automotive industry, laser welding of SUS301Lstainless steel on the6082aluminum alloy is proposed. In this paper, the effects of the laserpower on surface forming and combinative condition of welded joints have been investigatedwithout interlayer and with Ni foil, Cu foil, Al-Si alloy as interlayer respectively. Besides,microstructure and component distribution and mechanical properties have been alsoinvestigated. The study of this paper can provide theoretical basis and technical support forwelding dissimilar metal for stainless steel/aluminum alloy. Besides, the experimental resultshave broad prospect of application.The experimental results show that when the laser power is at the range of2750W to2900W, the forming quality of laser welded stainless steel/aluminum alloy joint withoutinterlayer is well. With the increase of laser power, the spatter and collapse laser weldedstainless steel/aluminum alloy in the joint increase, and cracks and holes appear on theinterface reaction zone of stainless steel/aluminum alloy. The welded joint cross section islike nail, and the distribution of microstructure and component in the interface reaction zoneis not homogeneous. The composition of Fe and Al in the interface reaction zone changescontinuously and a certain amount of Al exists near the side of stainless steel weld bead.Besides, the weld bead near the side of aluminum alloy contains FeAl, Fe3Al, FeAl2, Fe2Al5brittle intermetallic compounds. When Ni foil, Cu foil and Al-Si alloy are used as interlayerrespectively, welding can be realized with the laser power from2750W to2900W. With theincrease of laser power, the surface forming quality of welded joint gets worse. What is more,the surface forming quality of welded joint with Ni interlayer is a little better than thatwithout interlayer. The surface forming quality of welded joint with Cu interlayer is equal ofthat without interlayer. The surface forming quality of welded joint with Al-Si interlayer is alittle worse than that without interlayer. Interface of stainless steel/aluminum alloy hasdiscontinuity in the space. Microstructure and component distribution in the interface reaction zone is not homogeneous. The interface reaction zone mainly contains FeAl, Fe3Al,FeAl3, Fe2Al5, Fe3(Ni,Al)2intermetallic compounds with Ni interlayer. The interfacereaction zone mainly contains FeAl, FeAl2, Fe2Al5intermetallic compounds with Cuinterlayer. The interface reaction zone mainly contains FeAl, Fe3Al intermetallic compoundswith Al-Si interlayer. In the condition of this experiment, there is no obvious influence onproperties of laser welded stainless steel/aluminum alloy lap joint by using interlayer. Theresults of microhardness test show that microhardness of stainless steel/aluminum alloyinterface reaction zone is low, as well as base metal and nearby the fusion line. In addition,the microhardness in the weld center is high. When the laser power is2800W, the maximumtensile shear load of welded joint without interlayer is4073N. When the laser power is2900W, the maximum tensile shear load of welded joint with Ni interlayer is3505N. Whenthe laser power is2800W, the maximum tensile shear load of welded joint with Cu interlayeris3321N. When the laser power is2900W, the maximum tensile shear load of welded jointwith Al-Si interlayer is2727N. Fracture surface of laser welded stainless steel/aluminumalloy lap joint has characteristic of brittle fracture. Fracture initiates stainless steel/aluminumalloy interface reaction zone, and crack extends through the brittle intermetallic compoundlayer, until the joint fractures. |
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