Combining resistance spot welding and friction element welding for dissimilar joining of aluminum to high strength steels

摘要

A multi-process joining technique that combined resistance spot welding and friction element welding was used to produce a three-sheet multi-stack of advanced high strength steel and precipitation hardened aluminum. Each weld process was tested independently and as a combination to better understand how multi-step welding affects joint performance. Weld interfaces and surrounding heat affected zones were investigated using microstructural and mechanical techniques, including scanning electron microscopy and nanoindentation. All tests indicated that excellent strength was maintained above the maximum breaking force threshold regardless of offset distance between the friction element weld and the center of the resistance spot weld nugget. A change in fracture mode was observed with interfacial fracture occurring at offset distances below 7 mm and nugget pull out or partial thickness failure occurred at offset distances above 7 mm. The present study indicates that hybrid joining techniques have minimal effect on both the mechanical and microstructural weld properties and allow for new dissimilar metal weld designs to be implemented in the automotive industry.