A Study on the Effect of Mechanical Surface Preparation on Zinc Phosphating of Plain Carbon Steel

The effect of mechanical surface preparation such as grinding of surface by 180 grade emery papers, sand blasting and shot blasting on the quality of zinc phosphate coating was discussed inthis paper. The morphology of formed layer was investigated by Scanning Electron Microscopy(SEM) technique. These observations showed that a uniform and fine-grained coating with anaverage crystallite size of 57.65 μm in length was formed on the sand blasted surface comparedwith the coating formed on the grinded surface with average crystallite size of 118.14 μm in length. Also, preparation of surface by shot blasting led to the formation of the non-uniform phosphate layer with average crystallite size of 169.72 μm in length. Furthermore, the corrosionresistance of samples were described and compared through the neutral salt spray (NSS) test and the electrochemical measuring techniques such as polarization and Electrochemical Impedance Spectroscopy (EIS). The results showed that preparation operation of surface by sand blasting has evident influence on improving protection properties of formed phosphate layer. As well,preparation of surface by sandblasting, improved the paint adhesion.

Keywords:

plain carbon steel , mechanical surface preparation , phosphating , morphology of coating , protection properties , paint adhesion