Study of temperature and material flow during friction spot welding of 7B04-T74 aluminum alloy

Abstract

Temperature and material flow behavior during friction spot welding of Alclad 7B04-T74 aluminum alloy were studied by both numerical simulation and welding experiment. The Alclad 7B04-T74 aluminum alloy sequentially experienced solid solution treatment at 465 °C, low temperature artificial aging at 120 °C, and high temperature artificial aging at 180 °C. During welding, the material which flowed into the sleeve cavity suffered from higher temperature, and the peak temperature in the stir zone was higher than the incipient melting temperature of the base material. Accordingly, the eutectic films along the grain boundaries can be observed in the stir zone after welding. The peak temperatures in the thermo-mechanically affected zone and the heat affected zone were lower than the solution temperature and higher than the artificial aging temperature of the base material. In the sleeve retreating stage of the welding process, the material in the sleeve cavity flowed downward out of the sleeve cavity, and then it flowed laterally and upward to fill the gap left by the retreating sleeve. Such a material flow path resulted in the “U-shaped” morphology of the bonding ligament, the upward curving of the hook, and the upward distortion of the grains in the thermo-mechanically affected zone.