| Hybrid structure of aluminum alloy and stainless steel combines the advantages of aluminum and steel, such as light weight, high strength, good thermal and electrical conductivity and corrosion resistance. Its application in the fields of automotive manufacture, shipbuilding and aerospace shows good economic benefits and is paid more and more attention. Nevertheless, joining of aluminum to steel confronts great challenge due to the large difference of thermal-physical properties between aluminum and iron, as well as the formation of brittle Fe-Al intermetallic compounds in the interfacial layer. Direct arc joining of aluminum to bare steel is especially acute and has been few reported.In this paper, TIG fusion-brazing of aluminum alloy to stainless steel was conducted by ZnA115 and AlSi12 flux-cored filler metal. Effects of welding parameters (welding current, travel speed, wire feeding speed and etc.) and parameters of post-weld heat treatment (annealing temperature and duration time) on the microstructure and properties of the joints was investigated.Dissimilar metal joint between aluminum alloy and stainless steel with tensile strength of 121MPa was achieved by ZnA115 filler metal, while higher strength joint about 162MPa was obtained with AlSil2 filler metal. Post-weld heat treatment (PWHT) can obviously enhance the properties of the joints. For 2mm-aluminum alloy/1.5mm-stainless steel joints made with ZnA115 filler metal, PWHT can increase the tensile strength of the joints from 89MPa to 180MPa. Furthermore, for lmm thick aluminum base material sheets, tensile strength of the aluminum/steel joints in PWHT state can reach 203MPa, nearly tripled that in as-welded state (73MPa). Mechanical properties of the joints could be deteriorated by higher annealed temperature and longer duration time.Phases in the weld of joints with ZnA115 filler metal was mainly aluminum-rich solid solution (Al), zinc-rich solid solution (Zn) and zinc oxide, consequently combinations of metal matrix and ceramic phase of zinc oxide promoted the formation of the cermet structure in the weld. The ceramic phase in the weld could enhance the hardness and strength of the joints, and properties of the joints was closely related to the zinc oxide. The thickness of the interfacial layer between the weld and stainless steel was no more than 3μm for joints with ZnAl 15 filler metal both in as-welded and annealed state. Fe-Al intermetallic compound, such as FeAl3 and Fe2Al5, as well as Zn solid solution was both found in the layer. While Al-Fe-Si ternary intermetallic compound ofτs-Al7.4Fe2Si was detected in the interfacial layer of joints made with AlSi12 filler metal, and the thickness of the interfacial layer was not inconsonant due to the jagged growth of the ternary phase.
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