Microstructure and mechanical properties of aluminum alloy/steel tungsten inert gas fusion-brazed joints

AA5052 aluminum alloy and 304 stainless steel with the thickness of 3 mm are welded with ZnAl22 flux-cored wire by tungsten inert gas （TIG） fusion-brazed welding. The effect of different welding currents and wire feeding speeds on the macro morphology of butt joints，microstructure of weld seam/steel interface，tensile properties and fracture behavior of the joints is studied. The results show that when the welding current is 110 A and the wire feeding speed is 24 mm/s，the maximum average tensile strength of the butt joints reaches 166 MPa. Fracture primarily occurs at the weld seam/steel interface， exhibiting typical brittle fracture characteristics. The weld seam/steel interface is composed of η-Fe2Al5Zn0.4，η-Zn（Al） and α-Al. With the increase of the welding current，the tensile strength of the joint first increases and then decreases. The white granular δ-FeZn10 appears in the η-Fe2Al5Zn0.4 interfacial layer，and Zn elements are segregated at the η-Fe2Al5Zn0.4/steel interface. The Zn-rich phases at the η-Fe2Al5Zn0.4/steel interface are determined to be Γ-Fe3Zn10 by transmission electron microscopy. It is found that excessively high welding current leads to cracking at the η-Fe2Al5Zn0.4/steel interface. With the increase of wire feeding speeds，the thickness of η-Fe2Al5Zn0.4 decreases gradually，and the phase composition at the weld seam/steel interface remains unchanged. Based on thermodynamic analysis，it is concluded that the formation sequence of intermetallic compounds （IMCs） at the weld seam/steel interface is η-Fe2Al5Zn0.4，δ-FeZn10，Γ-Fe3Zn10.