CHARACTERIZATION OF INTERMEDIATE LAYERS IN HOT-DIP ZINC COATED STEELS

The intention of this work is the full characterisation of morphology, composition and structure of so-called intermediate layers in continu ously galvanised steel sheets, These layers grow as a reaction product of the sheet with the liquid zinc which contains a few tenth % of mas s fraction aluminium. Conventional methods of surface analysis combine d with ion sputtering fail to resolve the layers because of extreme su rface roughness of the zinc coating induced by the sputter process. Be tter access to the intermediate zones can be attained after carefully removing the zinc coating by etching or chemical polishing without att acking the layers. The uncovered layers can be analysed by EPMA, AES-l ine scanning and SEM. Especially an EPMA-thin film analysis technique turns out to be most suitable to analyse quantitatively the compositio n and stoichiometry of phases in the layer(s). Also layer thicknesses can be determined in terms of mass coverage. The results of these anal yses are in good agreement with literature data from metallurgical and constitutional investigations, The applied techniques can be recommen ded for quality assurance and failure analysis in industrial productio n of continuously hot-dip zinc coated steel sheets.