Blowhole Generation Phenomenon and Quality Improvement in GMAW of Galvanized Steel Sheet

In the automotive industry, galvanized steel sheets have been applied for quality improvement. However, it has a problem of the weldability debasement by porosity defect (blowhole, pit) and spatter increase. In this study, the blowhole generating behavior which was not clarified until now has been observed by the high-intensity X-ray imaging apparatus. And the method to make reduce both of the porosity defects and the spatter has been examined. In the result, the measure was effective that the porosity defect is released as zinc vapor from just under the arc to outside of the molten pool. Based on this knowledge, a solution to problem was accomplished by optimizing (a) composition and size of welding wire, (b) shielding gas composition and (c) current pulse wave pattern.