- Sep 12, 2018 -
The nickel content in the zinc-nickel alloy coating generally does not exceed 15%, and the corrosion resistance of the coating increases with the increase of the nickel content. When the nickel content reaches 13% to 15%, the corrosion resistance reaches the highest value. Further increasing the nickel content in the plating layer does not contribute to the improvement of corrosion resistance, but also causes an increase in the brittleness of the plating layer and difficulty in forming a color passivation film on the surface of the plating layer.
The electrode potential of the coating teaches that the electrode potential of the steel is negative. Therefore, this alloy plating layer is the same as the zinc plating layer and is an anodic protective plating layer. The advantage of this type of coating is that in the case of mechanical damage to the coating, the coating around the damage is still effective in protecting the steel substrate from corrosion.
The coating has excellent resistance to atmospheric corrosion and seawater corrosion, and its corrosion resistance teaches a metal zinc layer of the same thickness at least 3-4 times higher. The neutral salt spray test showed that the non-chromate passivated zinc-nickel alloy coating with a thickness of 5-8μm showed red rust for about 500h, and the chromate passivated zinc-nickel alloy coating appeared red. The rust time can reach 2000h or more. In addition, after the appearance of red rust in the zinc-nickel alloy coating, the rate of red rust expansion is much slower to teach metal zinc.
The chromate passivation of the zinc coating at 100-150 ° C, the passivation film decomposes black, its corrosion resistance drops sharply, and the chromate passivated zinc-nickel alloy layer can withstand 200-250 ° C high temperature . Neutral salt spray test showed that after the color passivation treatment of zinc-nickel alloy coating was baked at 200 °C for 2 h, the red rust appeared for more than 1000 h.
The coating (including the plated state and the chromate passivation treatment) maintains high corrosion resistance after various mechanical molding such as extrusion and bending.