After zinc electroplating, the surface of plating layer may be adhered with alkaline solution, metal oxides or organic pollutants, the light out process dissolves the residues through nitric acid solution (commonly used concentration of more than 30 ml/L), eliminating the whitish, grayish or mottled phenomenon on the surface of the layer.
Author: Anna
I. Enhance the surface finish of plating layer
Remove the residual impurities on the surface
After zinc electroplating, the surface of plating layer may be adhered with alkaline solution, metal oxides or organic pollutants, the light out process dissolves the residues through nitric acid solution (commonly used concentration of more than 30 ml/L), eliminating the whitish, grayish or mottled phenomenon on the surface of the layer.
For zincate galvanizing process, polishing can remove the accumulation of zinc ions in the plating solution or impurities (such as iron, lead), to avoid the passivation of the fish scale or flake-like color difference.
Chemical polishing role
Nitric acid and other reagents micro-etching of zinc plating layer, dissolve the surface microscopic bumps, so that the plating layer shows a uniform bright effect (Ra value reduced by about 30-50%).
After the light out treatment, the surface reflectivity of the galvanized layer is improved, and the mirror effect can be achieved to meet the decorative requirements.
II. Optimize passivate film quality
Passivate stability guarantee
The residual lye in the unglazed plated layer will change the passivate pH (e.g. low chrome passivate with strict pH requirements), resulting in a grayed passivate film or reduced bonding; glazing reduces the frequency of passivate adjustments and maintains the pH in the ideal range of 2.0-3.0.
Enhance passivation film densification
After surface impurities are removed, the passivation solution can uniformly form a film, so that the thickness of the passivation layer is controlled at 0.2-0.5μm, and the coverage of hexavalent chromium conversion film is increased by more than 20%.
The salt spray resistance of passivation film is significantly improved, and the salt spray test time of blue-white zinc passivation film can be extended from 48 hours to more than 96 hours.
III. Plating quality inspection function
Quick judgment of impurity content
If the plating layer is yellow in the high current area after the light comes out, it indicates that the plating solution is contaminated with organic matter; if the plating layer is gray-black, it suggests that the iron impurity exceeds the standard (need to prioritize the treatment of plating solution instead of passivation).
By observing the change of brightness after polishing (e.g. brightness decreases in case of lead impurities), the passivation effect can be predicted, avoiding the flow of defective products into the subsequent processes.
Zinc electroplating polishing process creates an ideal substrate for passivation through chemical polishing and impurity removal, which is the core link to ensure the beauty, corrosion resistance and process stability of the plated layer.