Usually, the surface treatment of metal alloys will choose electroplating or anodic oxidation. What is the difference between these two processes.
As product designers, they should understand the limitations of different processes, so the important points are mentioned above:
- The surface treatment of aluminum alloy is usually anodic oxidation, which is not suitable for electroplating.
- The common surface treatment of zinc alloy die casting is electroplating, which is not suitable for anodic oxidation.
- Aluminum alloy die castings are not suitable for anodizing, and those with high appearance requirements should be used with caution.
Different Treatment Methods
Electroplating uses the material to be plated as the cathode, the same metal material as the coating metal as the anode (insoluble anode is also used), and the electrolyte is a solution containing the coating metal ions; A certain current is input between anode and cathode. The coating material and the material to be plated are two different materials, such as beryllium copper nickel plating, beryllium copper as the substrate and nickel as the coating.
Anodic oxidation uses chemical or electrochemical treatment to form a coating layer containing the metal component on the metal surface. It is a kind of material protection that the material to be treated acts as an anode and forms a film on its surface through an applied current in a specific electrolyte. For example, aluminum alloy is oxidized. A layer of aluminum oxide film is formed on the surface of aluminum alloy. Aluminum oxide is chemically stable, will not be oxidized again, will not be corroded by acid, and can be dyed into various colors.
Different Processing Objects
The objects to be treated by electroplating method are mainly metal, and can also be non-metal. The most commonly used plating metals are nickel, chromium, tin, copper, silver and gold. That is to say, nickel plating, chromium plating, gold plating, etc.
Anodic oxidation is the method of metal surface treatment. Most metal materials (such as stainless steel, zinc alloy, aluminum alloy, magnesium alloy, copper alloy, titanium alloy) can be anodized in a suitable electrolyte.
Different Treatment Principles
Electroplating uses electroplating materials as cathode and anodic oxidation zone treatment materials as anode
Electroplating is due to the charge effect, the metal anode ions move to the cathode, and get electrons at the cathode and deposit on the material to be plated. At the same time, the metal dissolution of the anode continuously replenishes the metal ions in the electrolyte.
Firstly, the electroplating solution has six elements: main salt, additional salt, complexing agent, buffer, anode activator and additive.
Electroplating principle includes four aspects: electroplating solution, electroplating reaction, electrode and reaction principle, and metal electrodeposition process.
Anodic oxidation is to control the formation of oxide layer by electrochemical method to prevent further oxidation of aluminum and increase the mechanical properties of the surface.
Generally speaking, aluminum or aluminum alloy is used as anode for anode, and lead plate is selected as cathode. Aluminum and lead plate are put together in aqueous solution, including sulfuric acid, oxalic acid, chromic acid, etc. for electrolysis, so that an oxide film is formed on the surface of aluminum and lead plate. Among these acids, the most extensive is the anodic oxidation with sulfuric acid.
Aluminum alloy anodizing technology is the most widely used and successful at present. Aluminum alloy anodizing can greatly improve the surface hardness, wear resistance and other indicators.
There are a large number of micropores in the thin layer of oxide film, which can absorb various lubricants, and is suitable for manufacturing engine cylinders or other wear-resistant parts. The membrane has strong adsorption capacity and can be colored into various beautiful colors. Non ferrous metals or their alloys (such as aluminum, magnesium and their alloys) can be anodized. This method is widely used in mechanical parts, aircraft and automobile parts, precision instruments and radio equipment, daily necessities and architectural decoration.
Why Is Aluminum Alloy Not Suitable For Electroplating?
The chemical property of aluminum is relatively active. If electroplating, aluminum ions on the cathode will generate aluminum salt and hydrogen while obtaining electronic reduction in acid electrolyte. If it is an alkaline electrolyte, aluminum hydroxide and hydrogen will be generated. Therefore, aluminum cannot be plated by electroplating. This is the same reason that sodium hydroxide is obtained instead of metallic sodium by electrolysis of salt water.