Research On Corrosion Resistance Of Copper-based And Copper-tungsten-based Phosphate Coatings On Steel

Iron and steel is the most important structural materials in China’sindustrial and agricultural production which is widely used. Corrosionprotection against steel surface is of great strategic significance for China’seconomic development. Phosphate coatings provide very good protection forsteel and are widely used in machine manufacturing and weaponry industry.Meanwhile, the accelerator in the phosphating solution can shorten thephosphating time, speed up the phosphate forming speed and reduce thephosphating temperature. The heavy metal salts of copper are very goodaccelerators. This paper studied the anti-corrosion of copper and coppertungsten phosphating through film Phosphate treatment of iron substrate.The copper phosphate film experiments used iron as the substrate andchanged the concentration of Cu²⁺in the phosphating solution to study thephosphate coatings formed in various concentrations solution about their surfacemorphology, film composition, the growth mechanism and corrosion resistanceand then compare them to that of the phosphate coating without copper. Theexperiments showed that the addition of copper ions can increase the thicknessof the phosphate film, change the phosphate film growth mechanism andimprove the corrosion resistance of phosphate film. But there is a criticalconcentration of copper irons.The critical concentration range was from6g/LCuSO45H₂O to8g/L, exceeded which with the concentration of Cu²⁺increasingthe film thickness and corrosion resistance reduced.Copper-tungsten phosphating film experiments used iron as substrate andchanged the phosphating reaction temperature to compare the phosphate coatingformed in the various temperatures about their surface morphology, the filmcomposition, the growth mechanism and corrosion resistance and comparedthem to the copper phosphate coating without tungsten. Experimental resultsshowed that copper-tungsten phosphating film thickness and the corrosionresistance enhanced with increasing temperature. But there is a criticaltemperature. The critical temperature range was from70℃to90℃, above which with the temperature increasing the corrosion resistance was reducedwhile the film thickness was steel increased.Contrast copper phosphate film to copper-tungsten phosphate coating, theaddition of tungstate can significantly improve the grain size of ZPO and copperoxide of the phosphate films. But they are similar in the growth process, theaddition of tungsten on the phosphate film has little effect on the growth processwhile tungstate can improve the corrosion resistance of phosphate coatings.