مواد نوین (Oct 2023)
Comparison of properties of zinc, zinc/nickel, zinc/nickel/manganese phosphate coatings on 41Cr4 steel substrate
Abstract
Abstract Introduction: In this research, the properties of zinc phosphate (single cation), zinc/nickel (double cation) and zinc/nickel/manganese (three cation) coatings were investigated. Methods: The basic phosphating solution was prepared based on previous experiences including phosphoric acid, nitric acid, accelerators and modifiers to create an optimal coating structure. The concentration of compounds and operational parameters of temperature, time and solution pH were fixed during the process. The amount of zinc-nickel-manganese cations by zinc oxide is 1.5; Nickel nitrate 4 and manganese carbonate 3.8 (g/liter) were added to the bath. In the zinc phosphate coating solution (monocation), manganese nitrate and nickel nitrate were removed from the solution in Table 1. Zinc/nickel phosphating solution (bi-cationic) was also obtained by removing manganese carbonate from the solution. Measuring the thickness and weight of the surface unit, determining the amount of total and free acid, studying the morphology and microstructure of the coating; Corrosion resistance tests including resistance to alkali solubility, salt spray test were performed. Also, after painting the phosphated samples, paint layer thickness test, scratch and bending test, impact test and paint layer hardness were performed. Finding: The comparison of phosphating baths showed that the weight of the coating decreased with the introduction of nickel and manganese ions. The low zinc phosphate coating has a cluster structure, while the zinc-nickel phosphate coating crystals are clustered and sheet-like, and the tri-cationic phosphate coating has a mixture of cubic and sheet-shaped structures. The difference in height and height in zinc-nickel-manganese phosphate coating; It has the lowest Ra and Rz values compared to single-cationic and double-cationic phosphate coatings. Also, the optimal three-cation coating has the highest corrosion resistance, which is due to greater uniformity, less porosity, fine crystal structure, and a high percentage of corrosion-resistant phases in the coating composition. The coating color studies indicate that the best adhesion of the paint layer is related to the tri-cationic coating. According to the researches, the zinc-nickel-manganese three-cation coating provided better results than the zinc-nickel and zinc-nickel two-cation coatings.
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