The English abbreviation of micro-arc oxidation is MAO, and its other name is micro-plasma oxidation, and the English abbreviation is MPO. Through the combination of the electrolyte and the corresponding electrical parameters, the ceramic film layer mainly based on the matrix metal oxide is grown on the surface of aluminum, magnesium, titanium, and its alloys by relying on the instantaneous high temperature and high pressure generated by arc discharge.
Taking the microarc plasma oxidation of aluminum and its alloys as an example, aluminum and its alloys are placed in an electrolyte solution, and spark discharge spots are generated in the micropores of the material through high-voltage discharge. Under the combined action of the α-Al203-based and r-Al203-containing hard ceramic layer, a hard ceramic layer is formed on its surface. The basic principle of microarc oxidation technology is similar to that of anodic oxidation technology, the difference is that the chemical reaction on the anode is enhanced by plasma discharge.
Microarc oxidation is in the spark discharge area, and the voltage is relatively high. When the anodic oxidation voltage exceeds a certain value, the oxide film with a certain degree of insulation initially formed on the surface is broken down, generating micro-arc discharge, and forming an instantaneous ultra-high temperature area ( In this area, the oxide or base metal is melted or even gasified. In the contact reaction with the electrolyte, the molten material is chilled to form a non-metallic ceramic layer; the film layer is uniform and dense, and the pores are relatively large. The area is small, and the comprehensive performance of the film layer is greatly improved. Due to the enhanced ability of the film layer to be broken down under the action of the high-voltage electric field, the diffusion ability of positive and negative ions in the film layer is enhanced, and microarc oxidation can obtain a thicker film than anodic oxidation. layer; and on the surface of some aluminum alloys containing Cu, Si, and other elements that are not easy to form a film in anodic oxidation, a thick film with good performance can also be obtained. Since the micro-arc oxidation ceramic is a dense ceramic layer grown directly on the metal surface in situ, it can improve the corrosion resistance, wear resistance, electrical insulation, and high-temperature impact resistance of the material itself.
Its basic process is:
Degreasing—water washing—micro-arc oxidation—pure water washing—sealing—drying
Bath / Equipment
The composition of the micro-arc oxidation solution is relatively simple. At present, most baths are mainly weakly alkaline aqueous solutions. Sodium silicate, sodium aluminate, or sodium phosphate is often added to the actual bath solution. In order to obtain micro-arc oxidation films of various colors, different metal salts can also be added, and different metal ions can be deposited and doped in the micro-arc oxidation film to obtain corresponding colors, such as Na2WO4, NH4VO3, etc.
Process example:
Electrolyte composition: K2SiO3 5～10g/L, Na2O2 4～6g/L, NaF 0.5～1g/L, CH3COONa 2～3g/L, Na3VO4 1～3g/L; solution pH is 11～13; temperature is 20～ 50°C; the cathode material is stainless steel plate; the electrolysis method is to rapidly increase the voltage to 300V and keep it for 5-10s, then increase the anodic oxidation voltage to 450V and perform electrolysis for 5-10 minutes.
Schematic diagram of microarc oxidation equipment:
Process application
The microarc oxidation film layer has wear resistance, corrosion resistance, high hardness, low wear, and heat resistance. It is generally used in automobiles, aerospace, ships, weapons, and other industries, such as automobile motors, pistons, bearings, and other aluminum alloys. Surface treatment is to use the high hardness and low wear characteristics of the micro-arc oxidation film layer. There are also ship impellers, connectors, pipe fittings, etc. that use their corrosion resistance characteristics.
Process characteristics
- The surface hardness of the material has been greatly improved. The microhardness ranges from 1000 to 2000HV, up to 3000HV, which is comparable to that of cemented carbide, and greatly exceeds that of high-carbon steel, high-alloy steel and high-speed tool steel after heat treatment. hardness;
- Good wear resistance;
- Good heat resistance and corrosion resistance. This fundamentally overcomes the shortcomings of aluminum, magnesium, and titanium alloy materials in the application, so this technology has broad application prospects;
- It has good insulation performance, and the insulation resistance can reach 100MΩ.
- The solution is environmentally friendly and meets environmental protection emission requirements.
- The process is stable and reliable, and the equipment is simple.
- The reaction is carried out at a normal temperature, and the operation is convenient and easy to master.
- The ceramic film is grown in situ on the substrate, the combination is firm, and the ceramic film is dense and uniform.