The Ratio Related to: Phosphate Corrosion Resistance

SummaryThe role of the hopeite and phosphophyllite phosphate coating ratios in determining the corrosion resistance of mild steel when coated with cathodic electroprimer and paint are reviewed and discussed. Attention is drawn to the problems associated with adequately defining the ratio, its calculation and broader relevance. Other factors contributing to corrosion resistance are highlighted in terms of method of phosphate application, bath working temperature and chemistry, chromium after rinsing and workpiece vibration, etc. Arguments are forwarded to support the contention that the P/P + H ratio is not sufficient in itself to enable accurate prediction of corrosion performance in all circumstances.