The Effect of Repeating the Phosphating Operation on Structure and Characteristics of Created Layer on Plain Carbon Steel

Dissolution of base metal as a one of the early stage during initial phosphating, could with changing the surface texture of base metal, affect the morphology of applied coating. In order to study this hypothesis, the microstructure of carbon steel after removing the initial phosphate layer by grinding and elemental distribution on this surface was studied by SEM (Cam Scan MV2300) equipped with the energy-dispersive X-ray (EDX) facility. The results shown that the small particles of the initial phosphate coating containing Zn and P, entrapped in the dissolved regions and notches of grinded surface. These elements could be considered as nuclei for crystal formation in during final phosphating. Beside, with increasing the repeating number of phoaphating, surface roughness increased that could be useful in rising surface activity and nucleation of phosphate crystallites. Thereby, with increasing the repeating number of phoaphating, fine-grained and denser coatings, without of any change in the composition of coating solution, were formed. Also, measuring the optimal-time coverage,thickness, weight and density of the coating showed that, with increasing the repeating number of phoaphating, denser coatings in the shorter time of operating were formed.