Ultrasonic Spot Welding of 301 Stainless Steel to Aluminum 6061-T6

This paper deals with ultrasonic welding of 0.040" (1mm) thick 301 Stainless to 0.063" (1.6mm) thick aluminum 6061-T6. Dissimilar welding of aluminum to stainless steels offer unique advantage in aerospace and automotive industries for improving fuel efficiency.  However, it is a great challenge to join these materials because of the large difference in their melting points and also because of the formation of brittle Al-Fe intermetallic compounds. Ultrasonic welding involves the use of low amplitude high frequency (20 kHz) sound energy to soften the components at the joint interface. Parts to be joined are held together under pressure and are then subjected to ultrasonic vibrations. Disruption of oxide and surface layer takes place with the help of high frequency vibrations thus assisting in the bonding of the two faying surfaces. Successful weld joints were produced without significant melting of the materials.  The spot welds were tested for lap shear strengths and the strengths were correlated with the weld processing parameters (power, normal force and weld time). Results suggest that higher welding power and normal force are required for producing higher strength joints. In this study, dissimilar aluminum alloy to stainless steel spot welds were successfully produced with ultrasonic welding and the effect of weld parameters on the microstructure and strengths were analyzed and discussed.