| Hybrid structures of aluminum alloy and steel have the comprehensive benefits, such as light weight, high strength and corrosion resistance, etc. Their application has a high technical and economical potential in aerospace vehicle, automobile and shipbuilding. However, joining of aluminum alloy and stainless steel has great difficulty because brittle and hard intermetallic compounds (IMCs) are formed in the joint. Nowadays, brazing-fusion welding with the characteristics of convenient operation and high efficiency offers a great potential for joining of aluminum alloy and steel. The key issues to obtain high-quality brazed-fusion welded joints are to promote the molten filler metal wetting and spreading on steel surface and to control the brittle IMC layer growth in the Al/steel interface.Al alloy plates was lap jointed to galvanized steel sheets by laser+MIG arc hybrid brazing-fusion welding with AlSi5, AlSi12, AlMg5filler wires. The increase of Si element in the fusion weld can make the grain refined, and more Al-Si eutectics were formed in grain boundary, which play a certain improvement on the microhardness of the fusion weld. Si additions in the filler wires effectively control the growth of the Al-Fe IMCs layer by replacing Al-Fe binary phases with Al-Fe-Si ternary phases. The increase of Si content in filler wire can increase microhardness in the fusion weld. The increase of Si content in filler wire can reduce the tensile strength of the brazed-fusion welded joint.By using MIG arc brazing-fusion welding of Al alloy to steel with AlSi5filler wire. The effect of galvanized layer was analyzed. The results show that the filler metal will be promoted to spread on the steel surface after the vapounization of Zinc-coating in the welding process, the vapounization of Zinc-coating has some certain influences on the performance of the welded joint. As a result, it is necessary to develop a suitable flux for aluminum/steel brazing-fusion welding. So the flux for aluminum/steel was developed by quadrature test, the flux composition range:CaF210～20wt%, NaF30wt%, K2SiF62～ 5wt%, K3AIF645～58wt%. The flux has good adhesion and coating, the most important it is high stability during the welding process, which can effectively promote the filler metal in the coating wetting spreading on the surface of the steel.Al alloy was jointed to steel that is coated with alloy elements and flux by MIG arc with AlSi5filler wire. It is studied that the effect of Cu, Zn, Sn element on the surface of weld forming and the tensile strength. The content of each component applicable adding alloying elements in aluminum/steel brazing-fusion welding:Zn20wt%, Sn30wt%, Cu5wt%, flux45wt%.The brazing-fusion welding joint that made by Al alloy joining to steel coated with alloy elements and flux (Zn20wt%, Sn30wt%, Cu5wt%, flux45wt%) by MIG arc with AlSi5filler wire was analyzed, the micro structures in the fusion weld was consisted of a-Al solid solution equiaxed grains and short rod-like Al-Si eutectics at grain boundary. The average thickness of IMCs layer is0.94μm that is less than10μm. The IMCs layer were identified as FeAl2, Fe4A13, Al2CU and Al0.5Fe3Si0.5, the tensile strength of the brazed-fusion joint can reach192.74MPa, it is a typical ductile fracture. The microhardness of near steel side is135.5HV0.01, but it can reach170HV0.01in the brazed interface, which is much higher than78.7HV0.01in the weld. The influence of Cu, Zn and Sn element on the micro structure of the interface layer were analyzed. It is revealed growth mechanism of Cu, Zn, Sn elements controlling interface compounds. |
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