A Study On Phosphating And The Process Of Electrogalvanized Sheet

It extends service life of the steels with sacrificial corrosion of zinc. Because of the improvement of the anticorrosion demand of the automobile it cause the car body steel to use electrogalvanized sheet in a large amount during the past 20 years. Because electrogalvanized sheet have poor painting performance, it is important measure for a good painting pretreatment to improve the ability of bearing surface corrosion of electrogalvanized sheet car body.The performance of NaNO3, NaF, Mn2+, Ni2+, Fe2+are studied by SEM> XREK electropotential-time change^ film heaviness-time change.The study on the phosphating of electrogalvanized sheet indicates that NaNO3 is a kind of accelerator which has good accelerating performance, producing phosphate film with good protecting performance. NaF can promote forming of phosphate film, increase film weight and make the film more uniform.Mn2+, Ni2+, Fe2+ are fine modifying agent of electrogalvanized sheet phosphating .The ions can make crystallization thinning obviously, which make phosphate film more uniform and compact.Research and solve the technological difficulty of electrogalvanized sheet in forming 'P' ratio and find that Fe2+ have unique effect of forming 'P' ratio like the steel phosphating, a amount of Fe2+ make electrogalvanizied sheet form phosphate film with 'P' ratio. The study on 'P' ratio indicate, the ability of corrosion-resisting of phosphate film-paint film double-layer and the corrosion expansion-resisting with high 'P' ratio is better than the double-layer with low 'P' ratio and the adhersion of phosphate film-paint film double-layer with high 'P' ratio is better than the double-layer with low 'P' ratio in the process of salt spraying experiment.LP phosphating composition, the process and the parameters are studied by orthogonal experiment LP performance test indicate LP has light phosphatefilm, compact, fine and smooth crystallization and high 'P' ratio, the adhersion of LP with electropainting is very good, salt spraying performance is better than the advanced domestic phosphating and foreign phosphating.Through research on thermodynamics of electrogalvanized sheet , calculating out phosphating reaction H >0, namely the phosphating reaction is endothermic under the 25C, it is just beneficial for phosphating reaction to elevate the temperature; By adding NaNO3 oxidize accerlator, calculating out H < 0, phosphating reaction is the exothermic reaction, does not need the heating outside,can take place under low temperature .Discussion on chemical balance in phosphating indicate PO4, FT (pH) and Zn2+are factors influencing phosphating.When PO4 is certain,it require pH to be getting higher relatively in value if Zn2+ concentration is lower namely free acidity should be keeped lower.Author: Hailin Tan (Material science)Directed by: prof, zhaoji Pan, profxinli Li...