Low energy impact welding of aluminum and steel

A. Vivek
Ohio State University,
United States

Keywords: welding, lightweighting, aluminum, steel

Summary:

High specific strength materials such as 6000 and 7000 grade aluminum alloys and dual phase and boron steels are experiencing increasing use in a vehicle structure. They offer vehicle lightweighting potential while maintaining high crash resistance and handling performance. This is one of the strategies of the automotive industry to meet its fuel economy and greenhouse gas emission targets. Currently, there are two primary methods of assembling such multimaterial structures: fasteners and adhesives, both of which pose further manufacturing challenges. While fasteners are expensive and add further weight to the structure, adhesives increase process time due to the requisite cure cycle. Vaporizing foil actuator welding (VFAW) is a solid state welding technique, which enables joining of dissimilar materials without a third body. It utilizes a large pulsed current to turn a thin conductor into a highly kinetic gas, which launches one sheet of metal into another and creates an impact weld. While impact welding has been performed with explosives in the past, VFAW enables doing the same at much smaller scale and in a traditional industrial environment. As compared to resistance spot welding, which is the current state of the art welding technology in automotive industry, VFAW uses 10% of the energy and retains full strength of the parent materials. The technology is currently available in the form of a semi-automated pedestal welding machine and, through current project, is on track to transform into a fully automated robotic welding machine. In this work, aluminum alloys type 5052 and 6111-T4 were welded to DP 980 and Usibor 1500 steels with VFAW. Optical and electron microscopy of the welded interface showed a wavy morphology and near absence of brittle intermetallic compounds. Mechanical testing resulted in fracture in parent materials rather than in the weld, which is the desired failure mode. Some welded samples were electro-coated and subjected to 30 days of intermittent salt spray testing. Those samples also failed through the base material during mechanical testing, thereby showing that the galvanic corrosion was mitigated.