Effect of Insert Material on Microstructure and Strength of Aluminum Alloy to Zinc-Coated Steel Dissimilar Metal Weld

Abstract Ultrasonic interlayered resistance spot welding (Ulti-RSW) is a recently developed method for dissimilar metal joining of aluminum alloy to advanced high strength steel. It makes use of a thin insert (or interlayer) which is first ultrasonic spot welded to one of the two sheets. The second sheet is then resistance spot welded to the insert side of the first sheet. In the present study, two inserts were tested, 0.3-mm-thick AA3003-H14 and 0.25-mm-thick stainless steel 316, for joining 0.8-mm-thick Zn-coated (galvannealed) dual phase steel 590 to 1.2-mm-thinck aluminum AA6022-T4. The joint with the aluminum insert achieved a peak tensile-shear strength of 4.1kN and a fracture energy of 1.7J, while the joint with the stainless steel insert achieved a peak strength of 4.5kN and a fracture energy of 2.6J. Both welds were much stronger than a direct resistance spot weld between the two sheets which had a strength of 3.3kN and an inferior fracture energy of 0.87J. The increase in strength and fracture energy achieved using stainless steel insert over aluminum insert was discussed based on the nugget diameter and the interface microstructure.