Effect of Mechanical Activating of Plain Carbon Steel Surface on the Morphology of Applied Zinc Phosphate Coating

Low temperature phosphating is a very slow process and needs to be accelerated by some means. Acceleration of the phosphating process could be achieved by chemical، mechanical and electrochemical methods. In this paper، the effect of mechanical surface preparation such as surface grinding by 180 grade emery paper، sand blasting and shot blasting on the quality of zinc phosphate coating was investigated. Scanning Electron Microscopy (SEM) investigations showed that the very rough shot blasted surface is not suitable for getting a compact and fine-grained coating. In contrast، surface preparation by sand blasting produces a great number of active sites on the substrate which resulted in a higher rate nucleation، and thus reduction of final sizes of phosphate crystallites in comparison with what obtained by grinding operation. Also، measuring thickness، weight and density of applied Phosphate coatings، revealed that the surface activation by sand blasting، leads to formation of dense and light weight coatings at shorter time of phosphating