Gas pocket generation in MAG welding of galvanized steel sheet

摘要

The effects of welding parameters, wire compositions and others on the gas pocket (pit, blowhole) generation have been studied regarding MAG welding of galvanized steel sheets, and the mechanism of the gas pocket generation also has been investigated. As to the welding joint type and position, lap joint and vertical-down position make the number of generations large in comparison with others. The increase in welding current and speed or Ar content of shielding gas also furthers the gas pocket generation. In contrast, the application of metal-cored wire in CO_2 welding or pulsed current welding machine in MAG welding with Ar-CO_2 mixture gas reduces the generation. The increase in C, Ti and P content of the metal-cored wire is effective for the reduction of gas pocket generation. Through these investigations, special metal-cored wire for CO_2 welding of galvanized steel sheets has been developed, and the wire is currently used in car manufacturing, house construction and other fields. Based on the above phenomena, zinc vapor seems to be the main cause of gas pocket generation. These phenomena can be mainly explained by the penetration depth which corresponds to the amount of zinc vapor, and by the stability of short-circuiting arc which influences the coming up and release of zinc vapor through the molten pool.