The hump bead is a typical weld defect observed in high-speed welding. Its occurrence limits the improvement of welding productivity. Visualization of hump formation during high-speed gas metal arc welding (GMAW) is helpful in the better understanding of the humping phenomena so that effective measures can be taken to suppress or decrease the tendency of hump formation and achieve higher productivity welding. In this study, an experimental system was developed to implement vision-based observation of the weld pool behavior during high-speed GMAW. Considering the weld pool characteristics in high-speed welding, a narrow band-pass and neutral density filter was equipped for the CCD camera, the suitable exposure time was selected and side view orientation of the CCD camera was employed. The events that took place at the rear portion of the weld pools were imaged during the welding processes with and without hump bead formation, respectively. It was found that the variation of the weld pool surface height and the solid–liquid interface at the pool trailing with time shows some useful information to judge whether the humping phenomenon occurs or not.
The resistance spot welding with intermediate frequency and direct current (RSWIFDC) was conducted to solve the weldability of the Al alloy TL091, The high-quality joint bearing dynamic load is realized for the first time by using the technique with the power of 2 kHz and the double-transformer based on the rapid response speed and stable welding current. By optimizing the welding process parameters, the strength, hardness distribution, microstructures and fracture morphologies of the joints were analyzed in details. The experimental results showed that the joints welded by the technique had better comprehensive mechanical properties, higher tensile strength and plasticity than that of the joints obtained by other spot welding. Shear fracture of the joints was seen at the nugget instead of the HAZ, thus indicating that the strength at the HAZ is higher than that at the nugget. The plastic ring of the joint was narrower as we desired. It was concluded that, by developing this advanced welding method and optimized welding parameters, high-quality joints were acquired to meet with higher design requirements of body-in-white of Al alloy under dynamic load. This is of great significance to the wide application of Al alloy body.
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