Characterisation of the deposition and protection performance of Zr conversion coatings on steel and zinc substrates using the response surface methodology
Ana Kraš, Davorin Kramar, Ingrid Milošev
Abstract
The response surface methodology (RSM) was used to explore the experimental space, characterise the influence of deposition and drying conditions on corrosion resistance, and evaluate the interactions between these factors for zirconium conversion coatings on cold-rolled steel and zinc. A combination of non-electrochemical drop tests and electrochemical methods were utilised to evaluate corrosion resistance in a dilute Harrison's solution. The surface analysis confirmed the electrochemical results obtained under the conditions chosen by RSM. The uniform corrosion of both substrates guides the subsequent conversion process, while the best coating performance results from the interaction of pH, conversion time and bath concentration. • The best ZrCC conditions and evaluation technique feasibility assessed by RSM • Drop test post-conversion (CRS) and 24-hr air-drying (Zn) suitable for screening • High-frequency EIS loop confirms satisfactory ZrCC formation on CRS • Zn EIS at pH ≥ 4.0 influenced by ZrCC thickness; at pH < 4.0, by porous ZnO nature