Laser-arc Hybrid Welding Of Dissimilar6061Aluminum Alloy To304Stainless Steel

Because of small inter-solubility, large differences in thermo-physical properties andeasy formation of brittle intermetallic compounds (IMCs) between Al alloy and stainlesssteel, their dissimilar joining is challenging. Laser-cold metal transfer (CMT) hybridwelding has more precise energy output, faster welding speed to decrease heat input incomparison of conventional laser-arc hybrid welding. It is thus more effective to controlthe growth of IMCs layer, as well as to improve weld quality. In this study, a fiber laserand a CMT welder were integrated to butt join6061aluminum alloy and304stainlesssteel with same thickness of2mm. The morphologies, microstructure and mechanicalproperties of welded joints were studied and the growth mechanism of IMCs layer wasdiscussed in detail. The following were the main results obtained.Optimal ranges of welding parameters were obtained, which were laser power1.5~2.1kW, wire feed speed corresponding to arc current4.8~5.4m/min, laser offset0.4~0.8mm and welding speed2~3m/min. Under these optimum ranges, sound dissimilarjoints were obtained, otherwise, some metallurgical defects such as holes, porosities, lackof fusion or excessive penetration appeared in the joint.By the examinations of SEM, EDS and XRD, a IMCs layer was found at the interfacebetween fusion zone and stainless steel. From top to bottom, the thickness of IMCs layerincreased gradually and the shape changed from jagged to plate. The IMCs layer wasusually composed of two layers, the θ-Fe4(Al,Si)13layer near to stainless steel and theτ5-Al8(Fe,Cr)2Si layer near to fusion zone. As the offset was0.4mm, the optimal range ofheat input was identified as80~110J/mm by experimental results. Within this range, thethickness of IMCs layer was3~6.5μm and the tensile strengths of the joints were greaterthan130MPa, more than80%of aluminum base material.Through thermodynamic calculation, it was found that the growth free energy of possible IMCs in the interface decreased with aluminum content. The kinetic analysisshowed that the growth of IMCs layer depended on the solution rate of Fe atom inaluminum pool due to the fast solidification rate of hybrid welding. To avoid the IMCslayer too thick, the interface temperature must be lower than1100°C by adjusting heatinput. Finally, the formation mechanism of IMCs layer during hybrid welding wassummarized by thermodynamic and kinetic analysis.