Characterisation of intermediate layers in hot-dip zinc coated steels
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The intention of this work is the full characterisation of morphology, composition and structure of so-called intermediate layers in continuously galvanised steel sheets. These layers grow as a reaction product of the sheet with the liquid zinc which contains a few tenth % of mass fraction aluminium. Conventional methods of surface analysis combined with ion sputtering fail to resolve the layers because of extreme surface roughness of the zinc coating induced by the sputter process. Better access to the intermediate zones can be attained after carefully removing the zinc coating by etching or chemical polishing without attacking the layers. The uncovered layers can be analysed by EPMA, AES-line scanning and SEM. Especially an EPMA-thin film analysis technique turns out to be most suitable to analyse quantitatively the composition and stoichiometry of phases in the layer(s). Also layer thicknesses can be determined in terms of mass coverage. The results of these analyses are in good agreement with literature data from metallurgical and constitutional investigations. The applied techniques can be recommended for quality assurance and failure analysis in industrial production of continuously hot-dip zinc coated steel sheets.
KeywordsZinc Surface Roughness Steel Sheet Intermediate Layer Failure Analysis
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