Influence of surface condition on laser brazing of aluminum to steel

Abstract

Traditional fusion joining of aluminum to steel is often complex due to high heat input process which promotes the excessive formation of thick intermetallics at the interface of the joint which leads to low strength and premature failure. Brazing would be a probable solution which utilizes a filler material which eliminates melting of the base metal and can potentially avoid intermetallics formation but requires careful selection of the filler metal. Laser brazing would be a potent tool for joining of aluminum to galvanized steel. In this work, laser weld-brazing was carried out using Al-Si eutectic filler wire for joining of AA 6082 T6 with galvanized steel and AA 6082 T6 with galvannealed steel in lap configuration. The microstructural characteristics of the laser brazed joints were studied under SEM, and it revealed cast structure in the brazed zone and intermetallics formation at the steel interface under both surface conditions. Interface layer was indexed as binary Al-Fe Intermetallics, and its thickness varied along the interface. The average shear strength of AA6082 T6 with galvannealed steel joint was only 210 N/mm with typical interfacial failure due to mechanical osculation, while that of AA6082 with galvanized steel increased the joint strength to 290 N/mm and it failed at the HAZ of AA6082.