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In the modern mechanical processing industry, surface treatment technology is a crucial aspect that determines the performance and lifespan of parts. Among them, oxidation treatment is a common and highly efficient method for modifying the surface of metals. It is widely used in aerospace, automotive manufacturing, electronic equipment, mold manufacturing, and medical devices due to its enhanced corrosion resistance, improved aesthetics, and optimized friction performance.
This article will systematically review the process principle, classification methods, application advantages in mechanical processing, industry comparisons, and development trends of oxidation treatment, helping enterprises and engineers gain a deeper understanding of the significant value of this process.
The parts produced through mechanical processing (such as turning, milling, drilling, and grinding) merely possess the required geometric shapes and dimensional accuracy. However, their surface conditions are often directly exposed to complex and variable working environments, facing multiple challenges:
Corrosion threat: Moisture in the air, oxygen, and acidic or alkaline media in industrial environments can rapidly cause rusting of metals such as steel, oxidation of aluminum, affecting appearance and further damaging functionality.
Wear and tear: When components are in relative motion, they will generate friction, resulting in dimensional changes, loss of accuracy, and even failure.
Appearance requirements: Many products, such as automotive parts, tools, and consumer electronics, not only demand excellent performance but also have extremely high requirements for surface aesthetics.
Special functional requirements: Such as reducing the friction coefficient, increasing the surface hardness, enhancing the bonding force with the coating, etc.
Oxidation treatment is precisely the key technology designed to address these challenges. It artificially creates a stable and dense oxide layer on the surface of the metal substrate. Without altering the internal structure and core performance of the part, it endows its surface with completely new characteristics. Although this layer is thin, it plays a crucial role of “lifting a thousand pounds with just two ounces”.
The essence of oxidation treatment is a controllable corrosion process. Through chemical or electrochemical methods, the metal surface reacts with the medium to form aprotective layer mainly composed of the metal’s oxide.
In the field of mechanical processing, the two main types of oxidation treatments are:
Chemical oxidation of steel (treatment for darkening or bluing)
Anodic oxidation of aluminum and aluminum alloys
Oxidation treatment involves forming an oxide layer on the surface of a metal through chemical or electrochemical reactions, thereby enhancing the performance of the metal material.
The core principle is:
Under certain temperature or electric field conditions, metals react with oxygen, air or oxidative ions in the electrolyte.
Form a dense and stable oxide film.
This coating layer can significantly enhance the corrosion resistance, wear resistance and insulation property of the metal.
Applicable materials: mainly aluminum and aluminum alloys.
Process principle: The workpiece is used as the anode and placed in the electrolyte solution. Under the action of an external current, an oxide film is formed on the surface.
Advantages: Dense film layer, high hardness, adjustable color.
Application: Widely used in aviation components, automotive parts, building profiles and consumer electronic enclosures.
Features: The oxide film thickness is large (generally 25 to 150 μm), with excellent wear resistance, insulation properties and corrosion resistance.
Typical applications: Pistons, hydraulic components, molds, and mechanical parts for motion machinery.
Applicable materials: aluminium, magnesium, titanium, stainless steel.
Process principle: No current is required. A film is formed by the reaction between the oxidant in the solution and the metal.
Advantages: Low cost, simple process.
Disadvantages: The film layer is relatively thin and has poor wear resistance.
Applicable materials: carbon steel, alloy steel, stainless steel.
Process principle: In a high-temperature alkaline solution, the metal reacts with the oxidant to form a black tricobalt oxide film.
Advantages: Attractive appearance, enhanced rust resistance.
Application: Tools, fasteners, gun parts.
Process method: Heat the metal workpiece to a certain temperature, and naturally form an oxide film in the presence of oxygen.
Application: Commonly found in titanium alloys, heat-resistant steels, etc.
Defatting: Similar to the darkening process, it must be done thoroughly.
Alkali etching: Apply a mild solution of sodium hydroxide to the surface for corrosion, removing the natural oxide layer and surface impurities, resulting in a uniform matte surface.
Neutralization (Polishing): Using nitric acid or sulfuric acid solutions to remove the dust adhering to the surface after alkali corrosion, thereby making the surface shiny.
Place the part as the anode into the holder and immerse it in the electrolytic cell (such as a 20% sulfuric acid solution).
Control the voltage, current density, temperature and time. For example, the conditions for sulfuric acid anodic oxidation are typically: 12-20V, 1-1.5 A/dm², 15-22°C, and the duration is 20-60 minutes.
The thickness of the film layer is directly proportional to the oxidation time, and it is usually controlled within the range of 5 to 25 micrometers.
Dyeing: By taking advantage of the porous nature of the oxide film, the parts are immersed in an organic or inorganic dye solution. The pores absorb the dyes and the parts acquire various vivid colors (such as gold, red, blue, etc.).
Sealing: Regardless of whether staining or not, sealing treatment must be carried out after the process to seal the porous structure, stabilize the color, and significantly enhance corrosion resistance and wear resistance. Common methods include:
Hot water sealing: This process is carried out in deionized water that is close to boiling point. The hydrated volume of alumina expands, thereby sealing the pores.
Medium-temperature sealing of holes: Utilizing solutions containing nickel and cobalt salts, this method is environmentally friendly and highly effective.
Cold sealing hole: A solution based on nickel fluoride is used, which has low energy consumption.
The oxide film can effectively prevent corrosive media such as oxygen, water and salt fog from penetrating, thereby extending the service life of the parts.
The hard anodic oxide film can significantly increase the hardness and wear resistance of the part’s surface.
The surface of the oxide film can be treated with dyeing, allowing for multiple color options, meeting the aesthetic requirements of consumer electronics and high-end products.
The oxide film has excellent insulation properties and is widely used in electrical components and electronic devices.
The oxide film can precisely control its thickness by adjusting the process conditions, meeting the requirements of high-precision mechanical processing parts.
In the manufacturing of mechanical parts, oxidation treatment is the core means to enhance the performance of the parts. For example, wear-resistant parts such as engine cylinder liners and piston pins, after oxidation treatment, the surface hardness increases, enabling them to withstand long-term high-speed friction and reducing wear; hydraulic parts such as hydraulic valves and pump bodies, the compactness of the oxide film can prevent the corrosion of hydraulic oil, ensuring no leakage in the hydraulic system and prolonging the operating life of the equipment. According to statistics, the average failure interval time of mechanical parts treated with oxidation treatment can be extended by more than 60%.
The aerospace field has strict requirements for part performance, and oxidation treatment plays a key role. The aluminum alloy skins of aircraft fuselages, after chromic acid oxidation treatment, are resistant to high-altitude ultraviolet rays and humidity changes corrosion, ensuring the safety of the fuselage structure; the titanium alloy components of rocket engines, through oxidation treatment, form a high-temperature resistant oxide film, capable of withstanding temperatures above 1000°C, avoiding the corrosion of the components by high-temperature gas, and ensuring the safety of rocket launch.
Electronic and electrical products have high requirements for insulation and stability, and oxidation treatment is widely applied. For example, the aluminum alloy shells of mobile phones and computers, after oxidation treatment, have both insulation and wear resistance, preventing leakage during use or surface scratches; the conductive terminals in precision instruments, the oxide film can avoid the contact failure caused by metal oxidation, improving the measurement accuracy of the instrument; the antenna components of wireless electrical appliances, oxidation treatment can reduce the interference of environmental factors on signal transmission, ensuring stable communication.
In the fields of daily necessities and architectural decoration, oxidation treatment combines practicality and aesthetics. In the kitchenware sector, aluminum alloy frying pans and saucepans, after oxidation treatment, form an odorless and wear-resistant oxide film, preventing the release of metal ions during cooking, and being easy to clean; in architectural decoration, aluminum alloy doors, windows, and curtain wall profiles, after oxidation coloring, can present various colors, resistant to wind and rain corrosion, and not fading easily over a long period of use, with low maintenance costs; in addition, daily necessities such as bicycle frames and luggage handles, oxidation treatment can also enhance their wear resistance and aesthetic appeal, prolonging their service life.
Green and environmentally friendly: Gradually phase out oxidizing solutions containing harmful substances such as chromates.
Functionalized development: Moving towards high-performance membrane layers such as conductive oxides and nano-oxide films.
Automation and Intelligence: The oxidation production line is trending towards automated control to ensure consistency.
Cross-domain application: Continuously expanding in the fields of new energy, 5G communication equipment, and medical implants.
Oxidation treatment, whether it is the blackening or bluing of steel, or the anodizing of aluminum materials, is an indispensable part of the mechanical processing industry chain. Through relatively low-cost processes of “meticulous carving” on the surface of parts, it achieves a significant leap in performance and value. Understanding its principles, mastering its techniques, and strictly controlling its quality are the necessary paths for every manufacturing professional to enhance product competitiveness and move towards high-end manufacturing.
Choosing and implementing the appropriate oxidation treatment process for your mechanical parts is like giving them a tailor-made “immortal armor”. This armor not only resists the erosion of time and the challenges of the environment, but also endows them with a charming appearance and outstanding performance, ultimately enabling them to stand invincible in the fierce market competition.
Start your project today. Get free DFM from professional engineer at ProtoTi.
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