Developing of thin chromium-free multifunctional treatments on hot dip galvanized steel: strategy, implementation and experience

Since the use of hexavalent chromium in automotive and electronic equipment is largely prohibited, many different hexavalent chromium free conversion layers have been developed. In this work, different Cr-free phosphate and polycarboxylate based conversion coatings were characterized (with electron microscopy and other surface analytical methods) for the usage of a multifunctional property layer for hot dip galvanised steel strips. The different corrosion resistance of such conversion coatings on ZM[1] (ZnAlMg) and Z(Zn) will be another topic of this paper [2]. The corrosion protection properties of these phosphate based conversion coatings on Z and ZM were characterized in a standardized salt spray test. Finally the conversion layers and the barrier protection effect on Cr-free treated zinc and zinc magnesium was investigated by cyclovoltammetry.