What is corrosion?
Corrosion is an electrochemical change process. There are a small number of electric ions on the surface of untreated metal. These electric ions will move from a high potential area (cathode) to a low potential area (anode), thus generating an electric current. Under the action of this current, the destructive attack on the metal will be accelerated and corrosion will occur in the weak parts of the metal potential, which is the so-called rust.
 
Passivation of Aluminum Alloys
Aluminum alloys are widely used in various industries due to their excellent properties, such as high strength-to-weight ratio and corrosion resistance. However, these alloys are still susceptible to corrosion under certain conditions. To enhance their corrosion resistance, passivation techniques are employed. Passivation is a process that forms a protective oxide layer on the surface of aluminum alloys. This oxide layer acts as a barrier against corrosive agents, preventing further oxidation and degradation of the material. The passivation process involves immersing the alloy in an acidic solution or applying an electric current to promote the formation of a stable oxide layer. One commonly used method for passivating aluminum alloys is chromate conversion coating. This technique involves treating the alloy with a solution containing hexavalent chromium compounds, which react with the surface to form a thin chromate film. This film provides excellent protection against corrosion and also improves adhesion for subsequent coatings or paints. Another approach is anodizing, which involves creating an artificial oxide layer on the surface of aluminum alloys through electrolysis. Anodized coatings can be dyed or sealed to enhance their appearance and durability. Passivation techniques not only improve corrosion resistance but also provide additional benefits such as increased hardness and wear resistance. However, it is important to note that some passivation methods involve toxic substances like hexavalent chromium, which poses environmental concerns and health risks.
 
Passivation is a process in which metal is oxidized by strong oxidants or electrochemical methods to turn the surface into an inactive state, that is, passivation. It is a method to transform the metal surface into a state that is not easily oxidized and slows down the corrosion rate of the metal.
 
Pure aluminum has undergone natural oxidation, forming a thin surface layer of aluminum oxide when it comes into contact with oxygen. This transformation creates a protective barrier that helps prevent further corrosion. Unfortunately, not every aluminum alloy forms this oxide layer well, which means additional protection may be needed. If you don't want to plate or coat aluminum, you have two main options for creating a passivating layer. The first is called chromate conversion coating. This coating can vary in thickness from 0.00001 to 0.00004 inches, which is amorphous in structure, and has a gel-like composition when hydrated with water. If you deal with other metals such as zinc, cadmium, copper, silver, magnesium, or tin alloys, you may already be familiar with chromate conversion. The second option is called anodizing. This is when the aluminum goes through an electrolysis process to thicken the oxide layer. The anodic coating will form a layer of hydrated aluminum oxide that is more resistant to corrosion than the natural passivation layer. The process will enhance the appearance of the metal, making it shine. Technically, the passivation process is a form of corrosion because the metal reacts with the environment to form a hard, relatively inert surface. As it happens, the formation of this surface layer will help reduce any further corrosion. This is in contrast to rust, whereas rust progresses, the metal surface degrades, actually accelerating further corrosion rather than stopping it. Therefore, passivation adds added value to aluminum products while making operation easier.
 
Advantages of passivation of aluminum alloys
Passivation of aluminum alloys has several advantages that make it an essential step in the manufacturing and maintenance of aluminum alloys, which are as follows:
 
(1) Making the metal economical: the passivation process is carried out in a non-reactive state. Also, the continuous addition of passivating agents in the process makes the metal more economical.
 
(2) Self-healing of scratches: Through passivation, the oxygen molecular structure on the surface of aluminum alloy die castings is improved. This makes the film layer dense and provides a self-healing effect. This means that aluminum alloys themselves are gaining popularity.
 
(3)Stability: Compared with traditional anti-corrosion methods, passivation is a more stable and corrosion-resistant method of protecting aluminum products.
 
(4) Improving corrosion resistance: By forming a thin oxide layer on the surface, it acts as a barrier against environmental factors such as moisture, chemicals, and pollutants that can cause oxidation. This protective layer prevents the formation of rust or other forms of corrosion, thereby extending the lifespan of aluminum alloys.
 
(5) Enhancing the aesthetic appeal: The oxide layer created during this process can be further treated with various techniques like anodizing or coloring to achieve desired finishes. This makes passivated aluminum alloys suitable for applications where appearance plays a crucial role, such as architectural structures or consumer products.
 
(6) Improving the biocompatibility and safety aspects when used in medical devices or implants: The oxide layer reduces any potential reactivity between the alloy and body tissues or fluids, minimizing adverse reactions or complications.
 
In conclusion, passivation offers numerous advantages for aluminum alloys. It provides enhanced corrosion resistance, improves aesthetics versatility through various finishing techniques, and ensures compatibility with biological systems when used in medical applications. Therefore, incorporating passivation into manufacturing processes is crucial for maximizing both performance and longevity in various industries where aluminum alloys are utilized.
 
By the way, the price of passivation is not cheap, it is expected to be 0.1 to 0.5 RMB/square decimeter. Therefore, if passivation is required, the cost of an electronic control housing is expected to increase by about 10 to 50RMB. The general process flow of passivation is as follows: Degreasing, Cleaning, Alkali washing, Pickling, Phosphating, Cleaning and Drying.