2010•Science and Technology of Welding & JoiningRequires access
Degradation mechanism of electrode tip during alternate resistance spot welding of zinc coated and uncoated steel sheets
Motohiro Kondo, Tokujiro Konishi, Koji Nomura, Hiroyuki Kokawa
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Abstract
The operation life and degradation mechanism of electrode during resistance spot alternating current welding of zinc coated galvannealed steel sheets were investigated. The electrode life in alternate resistance spot welding of zinc coated and uncoated steel sheets was extremely short in comparison with welding only on zinc coated steel sheets. During alternate resistance spot welding, the ring shaped nuggets were formed easily. This is attributable to the sticking of the alloy layers formed on the electrode top during the previous welding of zinc coated steel, to the uncoated steel surface at the following welding, so that notable wear took place, and the surface profile of electrode tip became flat. Additionally, an accumulation of highly resistant carbonaceous substance layer at the centre of electrode top caused an annular flow of welding current to hinder the nugget formation.