Zinc and zinc alloy body products shall be passivated

In recent years, ceramic chemicals have been widely used in various fields of life, such as automobiles, building materials, home appliances, etc., but some zinc coatings are prone to corrosion in hot and humid environments. In order to further improve the corrosion resistance of the coating, ceramic chemicals manufacturers need to carry out passivation treatment. The traditional passivation treatment is chromate passivation treatment, which has the advantages of simple process, good film adhesion, beautiful appearance, high corrosion resistance and self-repairing function. However, it contains hexavalent chromium, a carcinogen, which has serious harm to people and the environment. Therefore, in recent years, countries around the world have been committed to the study of chromium-free passivation process for zinc coating, mainly including inorganic passivation and organic passivation.

Inorganic passivation processes mainly include molybdate passivation, tungstate passivation, silicate passivation, rare earth metal salt passivation, etc. Organic passivation processes mainly include phytic acid passivation, tannic acid passivation, diaminotriazoline and derivative passivation, acrylic resin passivation, etc.

Aluminum alloy passivation mainly refers to the surface passivation of products such as electro-galvanized coating, hot-dip galvanized coating and zinc alloy castings. Due to the active chemical properties of zinc, it is easy to be corroded in various environmental media and form white rust. Its structure causes surface corrosion damage, and also damages the decorative performance of the surface. Therefore, zinc and zinc alloy body products should be passivated.

Aluminum alloy passivation process flow

Aluminum alloy → stainless steel shot blasting and deoxidization → degreasing → two water washes → two water washes → passivation (soaking for 4-6 minutes) → two water washes → drying (hot air blowing and drying, temperature: 60-65 ℃) → packaging and delivery.

1. Cylinder opening method: add 4 parts of pure water, add 1 part of passivation solution, and then measure the PH value after mixing evenly (generally, it is not necessary to adjust the PH value after new cylinder opening, and add passivation agent or dilute sulfuric acid or 2% sodium hydroxide after using for a period of time), and then heat it to the operating temperature before putting into production.

2. PH value control: With the increase of production times, the PH value of the passivation tank solution will rise continuously. At this time, dilute sulfuric acid or concentrated passivation solution can be used to adjust the PH value. If too much sulfuric acid is inadvertently used during the commissioning process, which will cause the PH value to be too low, 2% sodium hydroxide solution can be used to increase the PH value to the normal range.

3. Concentration control: add according to the consumption of concentration titration analysis (1-3L concentrated solution/100 ㎡ surface area). When a large area of yellow spots or white spots appear on the processed workpiece, it is invalid after adjustment, and it is recommended to reconfigure the groove.

The above is the zinc alloy passivation process analyzed by the ceramic agent manufacturer for you. I hope it can help you!