How Can Aluminum Materials Improve The Corrosion Resistance Of Building Structures?

1, The natural corrosion-resistant barrier of aluminum: the "armor effect" of alumina film
The corrosion resistance of aluminum comes from the naturally formed aluminum oxide (Al ₂ O ∝) protective film on its surface. When aluminum is exposed to air, it undergoes a chemical reaction with oxygen, forming a dense oxide film on the surface with a thickness of only 3-5 microns. This film has three core characteristics:
Chemical stability: Aluminum oxide film can maintain stability in conventional, industrial, and oceanic atmospheres, and can block the permeation of oxygen, moisture, and most acidic gases. For example, in coastal buildings, aluminum veneer curtain walls can still maintain a smooth surface after 10 years of sea wind erosion, while traditional carbon steel materials have suffered severe corrosion.
Self repair ability: If the oxide film is locally damaged due to mechanical damage or chemical corrosion, the aluminum substrate will quickly react with oxygen to regenerate the oxide film at the damaged area, achieving dynamic protection.
Insulation: The resistivity of aluminum oxide film is as high as 10 ¹⁴Ω· cm, which can effectively block the electronic conduction path of electrochemical corrosion and prevent galvanic corrosion when aluminum comes into contact with other metals.
However, natural oxide films will fail in strong acid, strong alkali, and halide ion environments. For example, in acidic environments with pH<4 or solutions with Cl ⁻ concentration exceeding 0.1mol/L, the oxide film will dissolve, resulting in exposure of the aluminum substrate. Therefore, it is necessary to further enhance its corrosion resistance through alloying and surface treatment techniques.
2, Alloying Strengthening: Evolution from Pure Aluminum to High Performance Aluminum Alloys
The strength of pure aluminum is relatively low (tensile strength of about 40-50 MPa), making it difficult to meet the load-bearing requirements of building structures. By adding alloying elements such as magnesium, zinc, copper, and manganese, the mechanical properties and corrosion resistance of aluminum can be significantly improved
Rust resistant aluminum alloys (such as 5052, 5083): Adding 4% -5% magnesium element to form Mg ₂ Al Ⅲ phase, while maintaining good corrosion resistance, the tensile strength is increased to 240-310MPa, widely used in coastal building curtain wall keels.
Forged aluminum alloys (such as 6061, 6063): 0.15% -0.4% magnesium and 0.4% -0.8% silicon are added, and T6 heat treatment (solution treatment+artificial aging) is used to achieve a tensile strength of over 340MPa and excellent intergranular corrosion resistance. They are commonly used in high-rise building door and window frames.
Aluminum magnesium manganese alloy (such as 3003): Adding 1.0% -1.5% manganese element can improve the uniform corrosion resistance by refining the grain size. The corrosion rate in a 3% NaCl+1% H ₂ O ₂ solution is reduced by 60% compared to pure aluminum, making it suitable for industrial plant roofs.
Alloying not only enhances strength, but also reduces the penetration path of corrosive media by optimizing the microstructure. For example, after T6 treatment, a uniformly distributed Mg ₂ Si precipitate phase is formed at the grain boundaries of 6061 aluminum alloy, which can block the propagation of corrosion cracks and significantly improve the stress corrosion cracking resistance.
3, Surface treatment technology: building a multi-layer protective system
To cope with extreme corrosive environments, aluminum materials need to construct a composite protective layer of "physical isolation+chemical passivation" through surface treatment technology. The mainstream technologies include:
Anodizing treatment: Using aluminum as the anode, applying electricity in sulfuric acid or chromic acid electrolyte to generate an oxide film of 10-30 microns on the surface. The membrane has low porosity and high hardness (HV500-600), and can be further reduced in porosity through sealing treatment. For example, aluminum profiles treated with sulfuric acid anodizing can withstand 1000 hours of corrosion free testing in salt spray, which is 5 times longer than untreated materials.
Fluorocarbon Spray Coating (PVDF): Using trifluorochloroethylene vinyl ether copolymer (FEVE) or polyvinylidene fluoride (PVDF) resin, a coating of 0.08-0.12mm is formed on the surface of aluminum by electrostatic spraying. This coating contains over 70% fluorocarbon resin and has super weather resistance (no fading for 20 years), chemical corrosion resistance (resistant to 5% hydrochloric acid and 10% sodium hydroxide), and self-cleaning properties (contact angle>90 °). It is widely used in curtain walls of super high-rise buildings.
Powder coating: Using epoxy resin and polyester resin as base materials, a 0.06-0.1mm coating is formed on the surface of aluminum through electrostatic adsorption. This technology is solvent-free, environmentally friendly, and has a uniform coating thickness. It can withstand salt spray testing for more than 1000 hours and is suitable for indoor decorative aluminum materials.
Electrophoretic coating: The anodized aluminum material is immersed in an electrophoretic paint bath, and charged resin particles are deposited on the surface by direct current to form a uniform coating of 0.02-0.04mm. This technology can fill the micropores of the anode oxide film, improving the salt spray resistance to over 2000 hours, and is commonly used in high-end building doors and windows.
4, Engineering Application Practice: Performance Verification of Aluminum Materials in Typical Corrosive Environments
Coastal architecture: In a coastal resort hotel project in Hainan, 6063-T5 aluminum alloy curtain wall keel+fluorocarbon spraying technology is used. After 5 years of actual testing, there are no corrosion spots on the surface of the aluminum material, while the adjacent carbon steel keel has shown extensive corrosion, verifying the durability of the aluminum material in high salt spray environments.
Industrial building: The factory building in a chemical industrial park in Shanghai adopts a 3003 aluminum alloy roof. After 10 years of operation, the corrosion rate of aluminum in an industrial atmosphere containing SO ₂ and Cl ⁻ is only 0.002mm/year, far lower than the 0.1mm/year of carbon steel, significantly reducing maintenance costs.
Cross sea Bridge: The main project of the Hong Kong Zhuhai Macao Bridge adopts 6061-T6 aluminum alloy guardrails. After 3 years of testing in the South China Sea, the corrosion rate in the splash zone (Cl ⁻ concentration>3mol/L) is only 0.001mm/year, meeting the requirement of a design life of 120 years.