Interfacial structure and bond strength of ultrasonic brazed Al–304 stainless steel dissimilar joints

Abstract

A filler alloy (Zn–14 at.-%Al) was used to join aluminium to 304 type stainless steel by ultrasonic brazing at 673 K for different ultrasound application times. Different reaction layers could be observed at the interface, containing Fe–Al, Fe–Zn, and Al–Zn solid solutions. As the amount of these solid solutions increased at the interface, there was a gradual improvement in the joint bond strength. The maximum bond strength of 146 MPa was obtained for the Al–304 joint brazed at 673 K for 3 s ultrasound application time. A critical remaining thickness of the filler alloy after ultrasonic application improves the interfacial joining. Extending the ultrasound application time beyond 3 s causes a bulk escape of the brazing alloy from the interface and leads to a direct interaction between aluminium and 304, which increases the possibility of forming intermetallics, and consequently decreases the joint bond strength.