Study On The Surface Color Development Mechanism And Quantitative Characterization Method Of Metal Galvanized Layer

Electroplating zinc passivation process is one of the most widely used metal anti-corrosion methods.In order to improve the corrosion resistance and decorative appearance of galvanized layer,passivation is a good choice.However,in order to meet the requirements of environmental protection,the traditional chromate passivation system has been basically replaced.At present,there is a trend towards the research of chromium-free passivation system,and it has gradually matured.With the increasing demand for decorative performance,the research and application of chromium-free blue-white passivation and color passivation systems have been further improved.This article mainly studies the blue and white passivation,but people mainly focus on the process research of the chromium-free blue and white passivation system,but lack of exploration of the appearance color of the film,and the study of the characterization methods of the film color is even less.Nowadays,the traditional visual method can no longer meet the needs.We need to establish a unified,scientific and accurate digital characterization system to promote the research and development of chromium-free passivation to reach a standardized level.In this paper,silicate blue and white passivation system is selected.Based on the mature passivation process in the laboratory,the components of the silicate passivation solution and the passivation process conditions are further optimized.Through single-factor experiments to study the composition,content and passivation process conditions of the passivation solution,the influence on the color characteristics of the film appearance was determined.Finally,orthogonal experiments were designed,and the optimal formula and process conditions were optimized:Na₂Si O₃10g/L,Na NO₃10g/L,KF 2g/L,Ti Cl₃2ml/L,H₂O₂5ml/L,and the p H of the passivation solution was adjusted with sulfuric acid 1.8-2.0,passivation time 60s,drying method is hot air drying or 40℃～60℃incubator.The surface morphology,element distribution and valence analysis of the passivation film under the best process were analyzed.The results show that:the appearance color quality is further improved;according to the SEM surface morphology analysis,it can be obtained that the surface of the optimized passivation film layer is uniform and dense,and has a good covering effect on the surface of the zinc layer;through EDS and XPS analysis of the passivation film It can be obtained that the passivation film is mainly composed of Si,Ti,O,Zn,C and other elements,so as to study and verify the film formation and color development mechanism of the passivation film.The method of characterizing the appearance color of the passivation film is studied,the difference of the passivation film color is analyzed,and the CIE-RGB system,CIE-XYZ system and CIE Lab uniform color space are used to characterize the color properties of the passivation film layer.Including measuring the R,G,B and X,Y,Z standard chromaticity tristimulus values,comparing and verifying the measurement results,and calculating the chromaticity coordinates x and y according to the chromaticity formula,introducing the CIE Yxy chromaticity Map,and then visually calibrate the overall trend and change of the color of the passivation film.Test the brightness value L and chromaticity values a and b of the film layer to characterize the color difference,analyze the chromaticity difference curve chart,and summarize the rules.A quantitative characterization method for the appearance color of blue-and-white passivation films was established.Finally,through the quantitative characterization of the color passivation film and the application of its color properties,the research results show that the surface color properties of the passivation film can scientifically judge the surface color quality of the passivation film,the scientificity and standardity of color judgment,and provide a color basis for the further development and application of the chromium-free blue and white passivation system,and serve as a reference method for other color systems,And then promote the development of the electroplating industry.