Degradation mechanism of electrode tip during alternate resistance spot welding of zinc-coated galvannealed and uncoated steel sheets

This study investigated the electrode life and the electrode degradation mechanism during alternate resistance spot welding of galvannealed steel sheets and bare steel sheets. As a result, it was found that the electrode life in this type of welding was extremely short in comparison to welding of only galvannealed steel sheets. The reason for this short life is explained by the sticking of the alloy layers formed on the electrode top to the bare steel sheet surface, so that the narrower and sharper shape the original electrode top is the better to prolong the life. Although the ring-shaped nuggets were not formed during alternate resistance DC welding, the electrode degradation mechanism is similar to that during the resistance DC welding of only galvannealed steel sheets.