Abstract
Laser lap welding of zinc coated steel using copper is found to be a promising alternative to resistance spot welding. Copper, which acts as an alloying element for zinc, is sandwiched between the lapped sheets in powder form. Such introduction of copper not only ensures a zero gap, but also assists in reducing violent vaporisation of zinc, the main cause of porosity and spattering during laser welding of zinc coated steel. Emission spectroscopy data recorded during the welding experiments validate the effect of copper on zinc vaporisation. Mechanical tests show acceptable results for laser welds made with copper. Moreover, minimal residual copper in the weld zone, and its extended solid solubility in iron due to non-equilibrium processing rules out the possibility of hot cracking. Concerns regarding electrochemical corrosion due to addition of copper in the weld are addressed and the results are found to be favourable. It is further shown that the fatigue life of a laser weld is ∼25% higher than a standardised spot weld for the same strain energy release rate. Finally, an equivalent laser weld specification is given for the zinc coated steel used in this study.
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