Fundamental study of an arc welding procedure for hot-dip zinc-coated steel sheet

Summary

Arc welding of hot-dip zinc-coated steel sheet faces a number of problems, such as the generation of spatter, blowholes, and pitting, through the zinc being vaporised during the welding process. To solve these problems, this paper examines the method of zinc vaporisation being positively promoted both in front of the weldpool and in the joint gap. This exploits the property of easy zinc vaporisation in an ordinary single electrode process which is extensively applicable in practice. The results suggest that, to reduce spattering, it is effective to perform high-speed welding at a relatively high current as well as to avoid short-circuiting through the droplets from the wire being refined using a pulse current waveform with a high peak current and short peak time. Both the welding current and welding speed have little effect on the number of blowholes generated. To reduce blowholes, the general rule is that the application of pulsed MAG welding with a high arc time ratio is more advantageous than short-circuiting prone CO₂ welding. It is also appropriate to avoid welding positions in which the molten metal is apt to cover zinc layers by arranging for it to be drawn back. Even under conditions where numerous blowholes are generated, pitting is only slightly generated in either the flat or horizontal welding position but heavily generated in the vertical down welding position. To reduce pitting in the vertical down welding position, it is advantageous to decrease the welding speed, to add oxygen to the shielding gas, and to tilt the welding torch at a push angle.