Effect of Cerium Nitrate on Zinc Phosphating of Aluminum Alloys at Ambient Temperature

【ALUMINIUM NETWORK】ALUMINUM ALLOY IS A MORE ACTIVATED METAL MATERIALS. In order to improve and enhance its surface properties in the coating process, it is often necessary to carry out surface conversion treatment in order to increase the binding force between aluminum alloy and organic coating. Corrosion resistance of organic coatings. In the surface treatment of aluminum alloys, the traditional anodizing and chromate treatment technologies are already mature, but the cost of anodizing is high, and chromate technology is strictly limited due to the use of hexavalent chromium. Aluminum phosphating is a An alternative method sought.
Aluminum alloy phosphating is essentially an electrochemical process. Alloying elements added to improve the mechanical properties of aluminum alloys (eg, copper, iron, silicon, magnesium, manganese, etc.) often form intermetallic compounds in the aluminum alloy matrix. These intermetallic compounds become either micro-cathodes or micro-anodes in the phosphating process of aluminum alloys. From electrochemical theory, the formation of a phosphating film depends on the dissolution of the aluminum alloy at the anode and the deposition of the metal phosphate on the cathode.
Zinc phosphate is widely used in the coating process of iron and steel materials. There are relatively few reports on the zinc phosphating of aluminum alloys. 6061 aluminum alloy is an aluminum alloy material used in the coating industry.
By adding a small amount of yttrium nitrate to the phosphating solution, the zinc alloy phosphating at room temperature will have some positive effects, including:
1. The addition of lanthanum nitrate will affect the chemical composition of the phosphating film. Within a certain range, the proportion of Zn2Fe(PO4)2·4H2O in the phosphating film can be increased, so that the corrosion resistance of the phosphating film can be improved.
2. Niobium nitrate has the function of activating the surface of the aluminum alloy substrate, and is easily adsorbed on the surface of the substrate to form an activation point, which plays a nucleation accelerating effect, so that the phosphating crystal grains are refined, and the resulting phosphate film is more dense.
3. Lanthanum nitrate has good oxygen-carrying and depolarization effects, and it plays a role in accelerating cathodic reactions in the phosphating process of aluminum alloys. It accelerates the phosphating film formation rate, and thus shortens the phosphating time.
4. The phosphating film formed is mainly composed of Zn3Fe(PO4)2·4H2O and Zn2Fe(PO4)2·4H2O crystals, and the yttrium nitrate does not constitute the constituent of the phosphating film.