Aluminum alloys and industrial aluminum materials usually require surface treatment to meet different needs. Common aluminum alloy surface treatments include electroplating, spraying, wire drawing, anode, sandblasting, passivation, polishing, oxide film treatment, etc.
1. Sandblasting, the main function is surface cleaning. Sandblasting before spraying (spraying or spraying) can increase the surface roughness and help improve adhesion, but the contribution is limited, not as good as before the chemical coating.
2. Coloring: There are two main processes for aluminum coloring: one is aluminum oxidation coloring process, and the other is aluminum electrophoretic coloring process. Various colors are formed on the oxide film to meet certain application requirements, such as black for optical instrument parts and gold for medals.
3. Conductive oxidation (chromate conversion film)-used for protection and conductive occasions.
4. Chemical oxidation: The oxide film is relatively thin, with a thickness of about 0.5-4 microns, and is porous, soft, and has good adsorption properties. It can be used as the bottom layer of organic coatings, but its wear resistance and corrosion resistance are not the same As an anodic oxide film;
The chemical oxidation process of aluminum and its alloys can be divided into alkaline oxidation and acid oxidation according to the nature of the solution.
According to the nature of the film, it can be divided into: oxide film, phosphate film, chromate film, chromic acid-phosphate film.
5. Electrochemical oxidation, aluminum and aluminum alloy chemical oxidation treatment equipment is simple, easy to operate, high production efficiency, no energy consumption, wide application range, and is not limited by the size and shape of parts. The thickness of the oxide film is about 5-20 microns (the thickness of the hard anodized film can reach 60-200 microns), high hardness, good heat resistance and insulation, corrosion resistance higher than chemical oxide film, and porous. Good adsorption capacity.
6. Spraying: used for external protection and decoration of equipment, usually based on oxidation. Aluminum parts should be pretreated before painting, so that the coating and the workpiece are firmly combined. There are generally three methods: 1. Phosphating (phosphate method) 2. Chromizing (chromium-free) 3. Chemical oxidation.
7. Anodizing: The process of plating a thin layer of other metals or alloys on the surface of some metals by using the principle of electrolysis. Brush plating is used for partial plating or repair. Roll plating is used for small parts such as fasteners, washers, pins, etc. Through electroplating, decorative protection and functional surface layers can be obtained on mechanical products. It can also repair worn and mishandled workpieces. The bath has a mixture of acidic, alkaline and neutral chromium. Regardless of the coating method used, the plating tank and suspension in contact with the electroplating product and the electroplating solution should have a certain universality.
8. Chemical polishing is a chemical treatment method that uses aluminum and aluminum alloys to selectively self-dissolve in acid or alkaline electrolyte solutions to smooth the surface of the polished surface to reduce its surface roughness and pH. The polishing method has simple equipment, no power supply, no limitation of workpiece size, fast throwing speed, and low processing cost. The purity of aluminum and aluminum alloys has a great influence on the quality of chemical polishing. The higher the purity, the better the polishing quality, and vice versa.
9. Passivation is a method to transform the surface of industrial aluminum materials into a state that is not easy to oxidize and slow down the corrosion rate of metals.
An active metal or alloy whose chemical activity is greatly reduced and becomes a precious metal state, which is called passivation.
If the metal corrosion product due to the action of the medium has a dense structure, a thin film (usually invisible) is formed, which closely covers the metal surface, which changes the surface state of the metal, thereby greatly increasing the electrode potential of the metal. The positive direction changes and becomes a passive state of corrosion resistance. For example, when Fe→Fe++, the standard potential is -0.44V, after passivation, it jumps to +0.5~1V, showing corrosion-resistant precious metal performance. This film is called a passivation film.