Studies on zinc-nickel alloy coatings have found that alloys containing 10% and 216% nickel (optimal value of 13%) have excellent corrosion resistance, and the salt resistance at the same thickness is 5 to 6 times that of the galvanized layer. The acidity of the alloy layer and its hardness are significantly improved. And less than 15% of the alloy can also be passivated. Obviously, to meet the same life, the thickness of the zinc-nickel alloy coating can be reduced by 5 to 6 times. In theory, it is more suitable for the protection of fasteners.
Zinc-nickel alloy cyanide-free alkaline plating process alloy plating formation in a plating solution composed of a zinc salt, a nickel salt, a conductive salt and an additive, a metal having a large potential difference between zinc and nickel at the same polarization potential The deposition forms a single γ phase structure, and after passivation treatment, a highly corrosion resistant alloy plating layer is obtained. Process degreasing - running water cleaning - no light corrosion - running water cleaning - electroplating zinc-nickel alloy - running water cleaning - passivation treatment - air retention - flow water dip 2 times - heating aging - inspection.
Study on the properties of zinc-nickel alloy coatings: Structure of zinc-nickel alloy: In zinc-nickel alloys containing 8% to 15% of Ni, zinc and nickel are present as a mixture of two metal compounds, NiZn and Ni2Zn2l. In addition to the zinc 2 zinc bond between the molecules, the nickel 2 zinc bond is also added, so the bonding strength is enhanced, and the hardness and wear resistance are improved.
In the pure zinc coating, the zinc atom is large in volume and is a large skeleton, so the grain boundary gap is large. The volume of nickel atoms is smaller than that of zinc atoms. In the zinc-nickel alloy structure, the nickel atoms in the nickel-zinc bond are located in the center of the zinc grid, that is, in the gap of the zinc skeleton, and naturally fill the gap of the zinc grid, so that the corrosive medium is not easily infiltrated. In addition, for the corrosive medium of nature, nickel itself has stronger corrosion resistance than zinc, so nickel does not destroy corrosion resistance.
Passivation film structure: After the passivation treatment, the contact surface of the plating layer and the passivation film forms a nickel-rich layer (metal zinc is selectively eluted), that is, a nickel-rich separator with strong corrosion resistance is formed. The passivation film is formed by using nickel metal and a trivalent chromium compound as a skeleton and hexavalent chromium as a filler, and the content of hexavalent chromium is high, so the passivation film has two advantages and is more difficult to be destroyed. Has a stronger self-healing ability. Coating appearance: The coating is bright silver white, which is passivated to form a rainbow-colored passivation film.
The relationship between nickel content and passivation in zinc-nickel: alloys with a mass fraction of 15% or less can be passivated. Matchability with paints: Zinc-nickel alloys have a standard potential of -0.8V, which is essentially equal to zinc and similar in polarity, and is suitable for pairing with zinc. Corrosion resistance of zinc-nickel alloy: The standard potential of zinc-nickel alloy is lower than that of steel, which provides cathodic protection for steel fasteners.
Conclusion Electroplated zinc-nickel alloy coating is a long-term protection method that is easy to operate, low cost and cost-effective. In addition to being suitable for industrial atmospheric environment, it is more suitable for the protection of harsh marine atmosphere; in addition to the protection of steel fasteners, it is also suitable for the protection of steel structural parts and copper and copper alloys. It can be used in combination with zinc. In protection.
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