Investigation of the Cathodic Electrodeposition Effect on the Phosphate Layer, on Steel, Galvanized Steel and Electrogalvanised Steel Substrates

Phosphate layer which is used for corrosion resistance improvement in automotive industry, is affected by protective layers applied after that. To make better knowledge of this changing, the effect of voltage and processing time of CED on the phosphate layer was investigated with three types of substrates; i.e. steel, galvanized steel and electrogalvanised steel. The substrates were initially phosphated and then electrodeposited under different voltages and time. The electrodeposited layer was then removed from the substrates by solvent and changes of the phosphate layer was studied. The phosphate layer was characterized by determination of phosphate layer coating weight and SEM technique. Atomic absorption spectroscopy was used to investigate the influence of electrodeposition process on degree of dissolution of different crystals in processing bath. Also the salt spray test was carried out to study the corrosion resistance of electrodeposited film upon changes of the phosphate layer.The results showed that the highest extent of phosphate layer dissolution in CED process respectively obtained on the steel, galvanized steel and electrogalvanised steel substrates. In contrast, the salt spray test showed that the galvanized steel results in highest corrosion resistance, followed by electrogalvanized and carbon steel.

Keywords:

Cathodic electrodeposition , Corrosion , Phosphate layer , Dissolution , Substrate