Influence of Surface Roughness of Cold-rolled Steel Sheet on Quality of Phosphate Coating

The influence of surface roughness of cold-rolled steel sheet on the quality of phosphate coating was studied by SEM, roughness meter and M398 electrochemical measure system. The results showed that the roughness strongly affected the quality of phosphate layer. The activity of the cold-rolling steel sheet was lowered when the roughness increased, and thus the quality of phosphate layer was improved. When Ra was between 0.75~0.95 μm, RPc was between 60~80 PC/cm, the grain size was small, the phosphate layer was uniform, the coating weight was improved from 1.59 g/m2 to 2.24 g/m2. The anti-corrosion ability was improved, the corrosion width of the rip of painted steel sheet with phosphate layer was decreased from 6mm to 2.5 mm.