Vaporizing foil actuator welding
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Introduction Solid-state welding (SSW) is an important alternative to traditional, fusion-based welding, and can be useful for joining materials that have disparate melting points or contain brittle intermetallic compounds.1,2 Impact welding is one class of SSW technique that has been practiced as explosive welding3 and magnetic pulse welding4 for several decades. In impact welding, as the name suggests, two or more pieces of metal are impacted with each other at a high speed, typically above 300 m/s, and at an oblique angle, typically 10° to 30°. The speed of impact causes jetting of the surface layers, which allows intimate contact of the nascent metallic surfaces; the high-pressure contact largely removes voids and results in a metallurgical bond between the materials. In addition to the ability to weld dissimilar materials, impact welding does not produce a heat-affected zone, a typically negative feature induced in traditional welding that changes the local temper condition of the material, often resulting in a softer region around the joint. When joints are created by impact the base-metal properties are retained in the joint. The interface that is formed can be, but is not necessarily always, as strong as the base metals. Explosive welding cannot be practiced in traditional industrial settings due to handling, storage, and noise constraints. Magnetic pulse welding, an alternative to explosive welding,
is a technique employing electromagnetic coils driven with large transient current pulses (more than 50,000 amps) to provide driving pressure to a metal sheet, in which an opposite current is induced due to the changing magnetic flux of the coil. In this process, an impact weld is created when a sheet of metal is repelled from the coil at a high speed, and then collides with a stationary target sheet at an appropriate impact angle. Magnetic pulse welding has limitations in terms of which materials and thicknesses can be used for welding sheet metals. Magnetic pulse welding is suitable for high conductivity materials, and the currents required to accelerate metals greater than 2 mm of thickness can damage the solenoid actuator coil itself through high magnetically induced pressures within the coil as well as through heating.5 The vaporizing foil actuator welding (VFAW) technique shows promise as a small-scale, low-energy impact welding technology for joining both similar and dissimilar metals. In this article, we discuss the various aspects of the VFAW method, which has been used for welding a wide variety of material combinations including aluminum-steel, aluminummagnesium, aluminum-titanium, aluminum-copper, titaniumsteel, copper-titanium, and copper-bulk metallic glass.6,7 The aluminum-steel pairing, given its relevance to the vehicle weight reduction effort, has especially been a major focus of development for VFAW. The results of welding the 5000
Brian P. Thurston, Department of Materials Science, The Ohio State University, USA; [email protected] Anupam Vivek, Department of Materials Science and Enginee
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