Application examples of anodic oxide films on aluminum and aluminum alloys
Aluminum and aluminum alloy anodized films, due to their excellent corrosion resistance and hardness, are widely used in key components in the aerospace industry. For example, on aircraft aluminum alloy skins and wing leading edges, sulfuric acid anodizing creates an oxide film with a thickness of 15-25μm. This dense oxide film effectively resists high-altitude ultraviolet rays, ozone, and water vapor, protecting the aluminum alloy substrate from corrosion. Service data from an airline shows that anodized aluminum alloy skins can achieve a service life of over 8,000 flight hours, while untreated skins will show visible corrosion pitting after around 3,000 flight hours. Hard anodized films (30-50μm thick, ≥300HV hardness) applied to aluminum alloy structural components of spacecraft can withstand aerodynamic wear and tear during high-speed flight. Their wear resistance is 2-3 times that of conventional anodized films, ensuring the stability of structural components in extreme environments.
In the construction industry, anodized aluminum and aluminum alloys, due to their excellent weather resistance and decorative properties, have become the preferred surface treatment for aluminum doors, windows, curtain walls, ceilings, and other decorative materials. For example, the aluminum curtain walls of a super-high-rise building were treated with oxalic acid anodizing, resulting in an oxide film with a thickness of 10-15μm. After accelerated aging (equivalent to 15 years of outdoor exposure), the film showed no signs of powdering or flaking, and its gloss retention exceeded 90%. Anodized films can also be electrolytically colored to achieve a variety of colors, such as silver, bronze, and black, to meet the needs of diverse architectural styles. In coastal areas, aluminum doors and windows treated with chromic acid anodizing exhibit excellent salt spray resistance. After 5000 hours of neutral salt spray testing, the surface showed only slight discoloration and no corrosion, far superior to conventional anodized doors and windows, which exhibit significant corrosion after 2000 hours.
In the automotive industry, anodized coatings on aluminum and aluminum alloys are primarily used on demanding components such as aluminum alloy wheels, decorative strips, and engine cooling fins to enhance their corrosion and wear resistance. After hard anodizing, the film on aluminum alloy wheels reaches a thickness of 20-30μm and a hardness exceeding 350HV. This effectively resists the impact and abrasion of road debris and offers excellent salt spray resistance, ensuring the wheels are rust-resistant in rainy and snowy conditions. Test data from one automaker showed that anodized aluminum alloy wheels maintained a smooth surface with no visible scratches or corrosion after 100,000 kilometers, while untreated wheels showed severe oxidation and scratching after just 50,000 kilometers. On engine cooling fins, the porous structure of the anodized film helps improve heat dissipation efficiency while protecting the fins from corrosion from engine coolant, extending their service life.
In the electronic device sector, the insulating, wear-resistant, and decorative properties of anodized films on aluminum and aluminum alloys have led to widespread application. For example, the aluminum alloy casings of smartphones and tablets, after anodizing, form an oxide film with a thickness of 5-10μm. This film not only offers a pleasant feel and wear resistance, but also effectively prevents fingerprints, enhancing the product’s appearance. Tests by a mobile phone manufacturer showed that anodized aluminum alloy casings showed no noticeable surface wear after 1,000 friction cycles (with a load of 500g), while untreated casings showed visible scratches after only 200 cycles. In electronic devices, such as aluminum alloy heat sinks, the insulating properties of anodized films prevent short circuits, while their porous structure enhances heat dissipation, increasing heat dissipation efficiency by 15%-20%. Furthermore, anodized films can be dyed and sealed to achieve personalized decorative effects on electronic device casings, meeting the diverse needs of consumers.
In the medical device sector, the biocompatibility and corrosion resistance of anodized aluminum and aluminum alloys make them an ideal surface treatment option, widely used in aluminum alloy surgical instruments and medical device housings. For example, after anodizing, the oxide film formed on aluminum alloy surgical forceps exhibits excellent corrosion resistance and can withstand repeated high-temperature and high-pressure sterilization (121°C, 0.1 MPa, 30 minutes). After 500 sterilization cycles, the film shows no peeling and the metal substrate remains corrosion-free, ensuring the safety and reliability of surgical instruments. On the aluminum alloy housings of medical devices, anodized films resist the erosion of disinfectant solutions, maintaining a clean and aesthetically pleasing surface. Their insulating properties also prevent electrical leakage, ensuring the safety of medical personnel. Practical data from a medical device company shows that anodized aluminum alloy device housings show no noticeable corrosion or discoloration after three years of use, while untreated housings exhibit severe oxidative corrosion after just one year, compromising the device’s performance. Furthermore, the surface roughness of anodized films can be adjusted through process control, making them suitable as carriers for biomaterials. They also show promising application prospects in the surface treatment of orthopedic implants.
