Joining Aluminum to Steel with Transition Material

1006 steel clad aluminum has been used as a transition material to directly spot weld steel to aluminum. Advantages of the clad metal transition include the ability to spot weld with existing equipment and reduction of dissimilar metal crevice corrosion at the steel-aluminum interface. Sheet steel between 0.8mm and 2.0mm has been spot welded to aluminum between 0.8mm and 3.0mm in a variety of combinations with the transition material.

This paper contains specific spot welding parameters for a variety of joints containing steel and aluminum at thicknesses normally encountered in body applications. The mechanism of weld nugget formation for aluminum-transition-steel joints is evaluated. Weld lobes established according to SAE and Aluminum Association guidelines are presented. The effect of electrode design on joint strength and heat balance are discussed.

A portion of the paper deals with the use of transition material clips for reducing galvanic corrosion when joining aluminum sheet to steel. Results of accelerated laboratory, marine atmospheric exposure and field test plate studies are reviewed. Quantitative data on crevice corrosion rates for various joints are included.