What is Microarc Oxidation

Microarc oxidation (Microarc oxidation, MAO), also known as microplasma oxidation (Microplasma oxidation, MPO), is through the electrolyte and the corresponding combination of electrical parameters, in aluminum, magnesium, titanium and its alloy surface rely on the arc discharge generated by transient high temperature high voltage, the growth of a ceramic film layer based on the base metal oxide. The surface of aluminum, magnesium, titanium and their alloys grows a ceramic film layer based on the base metal oxide by the action of transient high temperature and high pressure generated by arc discharge. In the micro-arc oxidation process, chemical oxidation, electrochemical oxidation, plasma oxidation exists at the same time, so the formation of ceramic layer is very complex, so far there is no reasonable model can fully describe the formation of ceramic layer. The micro-arc oxidation process introduces the working area from the Faraday region of common anodic oxidation to the high-voltage discharge region, which overcomes the defects of hard anodic oxidation and greatly improves the comprehensive performance of the film layer. The micro-arc oxidized film layer combines firmly with the substrate, has a dense structure and high toughness, and has good wear resistance, corrosion resistance, high temperature impact resistance and electrical insulation properties. The technology has the characteristics of simple operation and easy to realize the function adjustment of the film layer, and the process is not complex, does not cause environmental pollution, is a new green environmentally friendly material surface treatment technology, in the aerospace, machinery, electronics, decorative and other fields has a broad application prospects. Principle and characteristics of micro-arc oxidation technology: micro-arc oxidation or micro-plasma surface ceramization technology, refers to the ordinary anodic oxidation on the basis of the use of arc discharge to enhance and activate the reaction that occurs on the anode, so as to form a high-quality strengthened ceramic film on the surface of the workpiece aluminum, titanium, magnesium metal and its alloys as the material of the method, is through the use of special micro-arc oxidation power supply voltage applied on the workpiece, so that the workpiece surface metal and electrolyte solution. By applying voltage to the workpiece with a special micro-arc oxidation power supply, the metal on the surface of the workpiece interacts with the electrolyte solution to form a micro-arc discharge on the surface of the workpiece, and under the action of high temperature, electric field and other factors, a ceramic film is formed on the surface of the metal to achieve the purpose of strengthening the surface of the workpiece. The outstanding features of the micro-arc oxidation technology are: (1) significantly improve the surface hardness of the material, micro-hardness of 1000 to 2000 HV, up to 3000 HV, comparable to cemented carbide, greatly exceeding the hardness of heat-treated high-carbon steel, high-alloy steel and high-speed tool steel; (2) good wear resistance; (3) good heat resistance and corrosion resistance. This fundamentally overcomes the shortcomings of aluminum, magnesium, titanium alloy materials in the application, so the technology has a broad application prospects; (4) good insulation properties, insulation resistance of up to 100MΩ. (5) The solution is environmentally friendly, in line with the requirements of environmental protection emissions. (6) The process is stable and reliable, and the equipment is simple. (7) The reaction is carried out at room temperature, convenient operation, easy to master. (8) The substrate in situ growth of ceramic film, the combination of solid, dense and uniform ceramic film. Micro-arc oxidation equipment required: 1, the input power supply: micro-arc oxidation power supply

Three 380V voltage. 2, micro-arc oxidation power supply because of the higher voltage requirements (generally between 510-700V), need to be specially customized. Usually equipped with silicon transformer. Power supply output voltage: 0-750V adjustable Power supply output maximum current: 5A, 10A, 30A, 50A, 100A and so on optional. 3、Micro-arc oxidation tank and ancillary facilities Slot body can choose PP, PVC and other materials, stainless steel jacket reinforcement. It can be equipped with cooling facilities or cooling liner. 4, hangers and cathode materials hangers can choose aluminum or aluminum alloy material, cathode material selection of insoluble metal materials, recommended stainless steel. Micro-arc oxidation tank liquid: Micro-arc oxidation is mainly for aluminum, magnesium, titanium and other materials. Aluminum and titanium can choose the same liquid. 1. Oxidizing liquid density: different liquids have different specific gravity, the general specific gravity of 1.0-1.1 varies. 2. Oxidizing liquid working voltage: 400V-750V. 3. Current density: different liquids, different workpiece current density. Roughly about: 0.01-0.1 amps per square decimeter. But there are also large currents, and more than 8 amps per square decimeter. 4. Micro-arc oxidation time: 10-60 minutes, the longer the time, the denser the film layer, but the roughness also increases. 5. Liquid pH: alkaline, PH is usually 8-13 6. Micro-arc oxidation process: degreasing ---- washing ---- micro-arc oxidation ---- pure water washing ---- closed Micro-arc oxidation factors affecting the work 1. workpiece material and surface condition (1) micro-arc oxidation of aluminum material is not demanding, regardless of whether it is difficult to anodize aluminum alloys containing copper or silicon can be For micro-arc oxidation, and can get the ideal film layer. (2) The surface state generally does not need to be polished, for the rough surface, after micro-arc oxidation, can be repaired flat and smooth; for the low roughness (i.e., smooth) surface, it will increase the roughness. 2. Liquid composition on the oxidation of the impact caused by the electrolyte composition is the key factor in obtaining a qualified film layer. Micro-arc oxidizing solution is generally selected to contain certain metal or non-metallic oxides alkaline salt solution, such as silicates, phosphates, borates, etc.. In the same micro-arc electrolysis voltage, the greater the electrolyte concentration, the faster the film rate, the slower the solution temperature rise, and vice versa, the film rate is slower, the solution temperature rises faster. 4. The effect of temperature on the micro-arc oxidation micro-arc oxidation is different from anodic oxidation, the required temperature range is wider. Generally 10-90 degrees. The higher the temperature, the faster the film, but the roughness also increases. And the high temperature will form water vapor. The general recommendation is 20-60 degrees. Due to the micro-arc oxidation in the form of heat release, so the liquid temperature rises faster, the micro-arc oxidation process must be equipped with a larger capacity heat exchange refrigeration system to control the tank temperature. 5. the impact of time on the micro-arc oxidation micro-arc oxidation time is generally controlled in 10 ~ 60 min. the longer the oxidation time, the better the densification of the film, but its roughness increases. 6. cathode material cathode material can be selected stainless steel, carbon steel, nickel, etc., the above materials can be suspended or made into a cathode tank body. 7. The influence of post-processing on the micro-arc oxidation After the micro-arc oxidation, the workpiece can not be used directly after the task treatment, can also be closed, electrophoresis, polishing and other subsequent processing. Advantages, disadvantages and scope of use The use of micro-arc oxidation technology for aluminum and its alloy materials for surface strengthening treatment, with a simple process, covers an area of small, strong processing capacity, high production efficiency, suitable for large-scale industrial production and other advantages. Micro-arc oxidation electrolyte does not contain toxic substances and heavy metal elements, electrolyte anti-pollution ability and regeneration reuse rate is high, so the environmental pollution is small, to meet the needs of high-quality clean production, but also in line with the needs of China's sustainable development strategy. Micro-arc oxidation treatment of aluminum-based surface ceramic film layer has a high hardness (HV>1200), corrosion resistance (CASS salt spray test>480h), good insulation (film resistance>100MΩ), the film and the substrate metal bonding force is strong, and has a very good wear resistance and thermal shock resistance and other properties. Micro-arc oxidation technology process processing capacity, can change the process parameters to obtain different characteristics of the oxide film layer to meet the needs of different purposes; can also be changed or adjusted by the composition of the electrolyte so that the film layer has a certain characteristic or present different colors; can also use different electrolytes on the same workpiece for multiple micro-arc oxidation treatment to obtain a multilayer ceramic oxidation film layer with different properties. As the micro-arc oxidation technology has the above advantages and features, so in the mechanical, automotive, defense, electronics, aerospace and civil construction and other industrial fields have a very wide range of prospects for application. Mainly can be used for wear-resistant, corrosion-resistant, heat shock-resistant, high insulation and other properties have special requirements of aluminum-based parts of the surface strengthening treatment; also can be used for construction and civil industry on the decorative and wear-resistant and corrosion-resistant high requirements of the aluminum substrate surface treatment; also can be used for conventional anodic oxidation can not be dealt with by the surface strengthening of special aluminum-based alloy materials. For example, automobile and other vehicles of aluminum-based piston, piston seat, cylinder and other aluminum-based parts; machinery, chemical industry in a variety of aluminum-based molds, a variety of aluminum cans of the inner wall, aircraft manufacturing in a variety of aluminum-based parts such as the cargo floor, roller bar, guide rail, etc.; as well as civil industry, a variety of aluminum-based hardware products, fitness equipment and so on. Micro-arc oxidation technology currently still has some shortcomings, such as process parameters and supporting equipment research needs to be further improved; oxidation voltage is much higher than the conventional aluminum anodic oxidation voltage, the operation should be good safety measures; and electrolyte temperature rises faster, need to be equipped with a larger capacity of refrigeration and heat exchange equipment.