Chemical pretreatment of metal surfaces prior to coating application

An efficient pretreatment is absolutely necessary to achieve the required coating properties such as adhesion, corrosion protection, resistance to diverse mechanical and chemical, as well as environmental influences and stresses and, last but not least, a defect-free surface finish. In general, all material surfaces are in a non-adhesive surface condition after manufacturing, joining and mechanical treatments. Therefore, the metal surfaces to be coated must be cleaned and pretreated appropriately according to the requirements of the metallic material and the required coating properties. In the industrial sector, pretreatment is usually carried out in a multi-stage process, starting with cleaning and degreasing, followed by pickling and conversion treatments.

The presentation will provide insights into the nature of metal surfaces and the important prerequisites for coating wetting process to achieve good adhesion of the coating. The individual process steps are outlined with their chemistry and resulting changes in micromorphology, especially the conversion layers produced. The special requirements of multi-metal pretreatment and solutions will be described. In addition, replacement technologies for the high standards of zinc phosphating and chromating pretreatments which have been used for decades and new thin film pretreatments are special focuses of the presentation.