Anticorrosive performance of new thin layer pretreatments with standard and new materials in automotive coatings

摘要

In a research project the mutual influences on corrosion protection of new thin layer pretreatments on various automotive substrate materials in combination with electro dipping coatings (EC) are investigated. The results are compared to zinc phosphate as state-of-the-art pretreatment. Most investigated systems show good performance in cyclic corrosion test according VDA 233-102 respectively VDEh SEP 1850 which is in good accordance to electro-chemical tests. The high electrochemical homogeneity from SKP results in high barrier properties of the systems. After loading with thermo cyclic stress, most of the systems keep their high barrier function even near the glass transition temperature of the EC-system. Surface and interfacial studies with scanning electron microscopy (SEM), focused ion beam (FIB) and energy dispersive X-ray analysis (EDX) are applied to understand changes after different loadings related to corrosion behaviour. These studies will offer insights into the performance of these systems and will help to identify strengths and weaknesses of specific combinations of the new pretreatment technologies with (new) substrate materials. For some systems exposure to continuous condensation climate results in a weakening of adhesion, but the weakened systems still show good barrier properties and good water uptake reversibility. Further studies and interpretation of the results will provide a deeper insight to the performance characteristics of the material combinations and may help to identify the factors which mainly influence the corrosion protection performance of the investigated systems.