Impact Welding of Aluminum to Copper and Stainless Steel by Vaporizing Foil Actuator: Effect of Heat Treatment Cycles on
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TRANSMISSION of a high current pulse through a thin conductor causes rapid vaporization of the solid to occur. This high-rate transformation results in the generation of high-pressure expanding gases and emission of light and sound. A capacitor bank is typically used as the charging source, and the conductor is in the form of a thin wire or foil. This phenomenon, which is commonly referred to as an ‘‘explosion’’ of the conductor, has been studied for over 50 years,[1] but the emphasis has predominantly been on understanding the phenomenon itself or its application in shock physics and explosive detonation. Several studies were performed that utilized rapid vaporization of metal foils to achieve high velocities in flyer plates. Keller and Penning[2] achieved 4 to 5 km/s velocities in thin dielectric flyers that were impacted with target plates. The impacts at pressures of 1 to 10 GPa revealed shock properties of the dielectric and target plates. Stroud[3] ANUPAM VIVEK, Post Doctoral Researcher, STEVEN HANSEN, Graduate Research Associate, JAKE BENZING and MEI HE, Senior Undergraduate Students, and GLENN DAEHN, Professor, are with the Department of Materials Science and Engineering, The Ohio State University, 2041, College Road, Columbus, OH 43210. Contact e-mails: [email protected]; [email protected] Manuscript submitted March 30, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
later produced 100 GPa pressures with an improved method and used the resulting shock pressure as a detonation source for explosives. Even greater pressures, near 500 GPa, were then generated by Chau et al.[4] through the use of a thin metal layer attached to the dielectric plate. This method was used to characterize shock detonation of explosive materials at much higher magnitudes than before. Other applications, such as quick action fuses, discharge pulse sharpening, and nanopowder production have also been explored in the past, but large-scale application of rapid metal vaporization as an industrial metalworking process has been limited to electrohydraulic forming. The vaporizing foil actuator (VFA) process is a recently developed method that uses the pressure created from a rapid metal vaporization event for a variety of metalworking purposes, including impact welding.[5] Impact or collision welding has traditionally been performed using explosively driven impulses[6] or less commonly by the electromagnetic launch of flyers.[7] Application of explosive welding (EXW) has historically been limited by its inability to be applied to processes on a small scale, such as when thin sheets or small weld zones are desired for use. This is mainly because consistent detonation of explosives can only be predicted if a quantity greater than a minimum critical amount is used, as discussed by Cooper.[8] Furthermore, increasingly stringent safety regulations on explosive
materials inhibit their widespread use. The most significant drawback of magnetic pulse welding (MPW) is that actuators often mechanically fail under high magnetic pressure conditions. Th
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