Study on interfacial structure and mechanical properties of high frequency induction brazed joint of aluminum alloys to pre-coated stainless steel

The high frequency induction brazing of LF12 aluminum alloy to 0Cr18Ni9 stainless steel was successfully performed with a layer of hot-dip pure aluminum on the surface of stainless steel. The results showed that the thickness of clad layer increased from 7 μm to 20 μm, and FeAl₃ turned to Fe₂Al₅ when the time of hot-dipping increased from 10 s to 50 s. The coated layer formed well when the time is 10 s and the temperature is 750℃ during the hot-dipping process. The optimum welding current is 270 A and the holding time is 30 s. Under the optimum welding conditions, the maximum tensile strength of brazing joint is 167.12 MPa which is about 63.8% higher than the joint without hot-dip pretreatment. In the brazing process, Fe₂Al₅ turns to Fe(Al,Si)₂, instead of the formation of τ-Al₈Fe₂Si because the coating layer limits the inter-diffusion of Fe atoms in steel and Al, Si atom in aluminum alloy. The increase of the tensile strength of the joint is due to the decrease of brittle compounds like τ-Al₈Fe₂Si.