How To Prevent Oxidation And Corrosion Of Aluminum Processing Materials For Curtain Walls?

一, Material selection: Control corrosion risk from the source
1. Optimization of alloy composition
The corrosion resistance of aluminum alloy is closely related to its composition. 6063-T5 and 6061-T6 are mainstream alloys in the curtain wall field, with better corrosion resistance than 2xxx and 7xxx alloys. Research has shown that the silicon (Si) content in 6063 alloy needs to be strictly controlled within the range of 0.2% -0.6%. Excessive silicon will form free Si phase and β phase (Al9Fe3Si2), which accelerate the anodic dissolution of the aluminum matrix and lead to spot corrosion. For example, a certain aluminum plate profile in Chengdu experienced severe corrosion after two years of use in coastal environments due to excessive silicon content, resulting in the formation of white flocculent Al (OH) 3 deposits on the surface.
2. Impurity element control
Zinc (Zn) and iron (Fe) are typical impurity elements in aluminum alloys. Zinc will dissolve in the form of Zn (OH) 4 Ω⁻ during alkaline washing and deposit in corrosion pits, forming galvanic corrosion micro cells. Industry standards require that the zinc content in aluminum alloys used for curtain walls should be ≤ 0.1% and the iron content should be ≤ 0.35%. In addition, chloride ions (Cl ⁻) are strong catalysts for aluminum alloy corrosion, and their content needs to be reduced by controlling the purity of raw materials (such as using pure aluminum ingots with a purity of 99.7% or higher) and optimizing production processes (such as avoiding the use of chlorine containing degreasing agents).
二, Surface treatment: Building multiple protective barriers
1. Anodizing technology
Anodizing is the most fundamental protective process for aluminum alloys, forming a 10-30 μ m oxide film on the surface through electrolytic action. The membrane layer has a porous structure and requires further sealing treatment (such as hot water sealing or nickel salt sealing) to enhance corrosion resistance. For example, the aluminum profile of curtain wall of Shanghai center Building adopts sulfuric acid anodizing+nickel salt sealing process. After 2000 hours of salt spray test, the film has no corrosion points and meets the requirements of AAMA 2605 standard.
2. Fluorocarbon spraying technology
Fluorocarbon coatings (PVDF) have become the preferred choice for high-end curtain walls due to their excellent weather resistance and chemical resistance. Its core component, polyvinylidene fluoride resin (KANAR500), has a fluorine content of up to 70% and can resist UV, acid rain, and salt spray erosion. Engineering practice has shown that curtain wall aluminum panels coated with three layers of fluorocarbon spray (primer+topcoat+varnish) maintain uniform color and no powdering after 15 years of use in coastal areas of Hainan. Attention should be paid to thoroughly removing oil stains and oxide films on the surface of the aluminum material before spraying, otherwise it will affect the adhesion of the coating.
3. Powder spraying technology
Powder spraying evenly applies epoxy resin or polyester resin powder onto the surface of aluminum through electrostatic adsorption, and forms a coating of 0.06-0.12mm after curing at a high temperature of 200 ℃. This process is more environmentally friendly than fluorocarbon spraying, but has slightly weaker weather resistance. Suitable for curtain wall projects in dry inland areas, such as a commercial complex in Xi'an that uses polyester powder sprayed aluminum panels. After 5 years of testing, the coating gloss retention rate still reaches over 90%.
三, Structural design: Avoid corrosion sensitive scenarios
1. Optimization of drainage system
The joint of the curtain wall is a high-risk area for corrosion, and a reasonable drainage path needs to be designed. For example, the curtain wall of Shenzhen Ping An Financial Center adopts a "constant pressure chamber+drainage hole" structure, which prevents rainwater from flowing back through air pressure balance. At the same time, 5mm diameter drainage holes are set up to ensure timely drainage of moisture at the joints. Tests have shown that this design keeps the humidity inside the curtain wall below 60% for a long time, effectively suppressing electrochemical corrosion.
2. Prevention and control of galvanic corrosion
Contact between different metals can cause galvanic corrosion, and the principle of "same material first" should be followed. When it is necessary to connect dissimilar metals, isolation measures must be taken:
Aluminum and steel connection: Use 3mm thick nylon gaskets for isolation, or use stainless steel bolts and galvanized steel connectors (galvanized layer thickness ≥ 8 μ m).
Aluminum and copper connection: must be isolated by non-metallic gaskets (such as PTFE) to avoid direct contact.
3. Thermal expansion compensation
The coefficient of linear expansion of aluminum alloy is twice that of steel, and expansion space needs to be reserved in the fixing method. For example, the aluminum keel of the curtain wall of the Buddha Peak Palace in Niushou Mountain, Nanjing adopts a "sliding support+elastic gasket" design, which allows the aluminum material to freely expand and contract when the temperature changes, avoiding coating cracking caused by stress concentration.
四, Construction process: Ensure the integrity of the protective layer
1. Finished product protection
Scratches and bumps during the construction process can damage the protective layer, and a full process protection system needs to be established:
Transportation stage: Aluminum plates need to be elevated with wooden blocks to avoid direct contact with hard objects; The glass panel needs to be placed upright, with a grass mat at the bottom.
Installation stage: Welding operations require the use of a fire socket to prevent sparks from splashing and damaging the surface of the aluminum material; The installed curtain wall needs to be covered with protective film until completion and acceptance.
2. Sealing treatment
Joint sealing is a crucial step in preventing corrosion. Silicone weather resistant sealant that meets the GB/T 14683 standard should be selected, with a displacement capacity of ≥ 25% to adapt to the micro deformation of the curtain wall. For example, a super high-rise project in Guangzhou uses neutral silicone sealant for sealing, and after 5 years of testing, there is no cracking or water leakage at the joints.
五, Maintenance management: Extend the service life of materials
1. Regular cleaning
Conduct a comprehensive cleaning of the curtain wall every six months to remove surface pollutants such as dust and bird droppings. Neutral detergent and soft bristled brush should be used for cleaning, and steel wire balls or strong acid and alkali solutions should be avoided. For example, a landmark building in Shanghai uses high-pressure water guns and neutral cleaning agents for cleaning, which can reduce coating loss rate by 30% annually.
2. Coating repair
When there is local damage to the coating, it needs to be repaired in a timely manner. The repair process includes:
Mechanical polishing: Remove the damaged area and the coating within a 10cm radius around it, exposing the metal substrate.
Primer coating: Spray epoxy zinc rich primer with a thickness of ≥ 40 μ m.
Topcoat repair: Use fluorocarbon coating of the same color as the original coating, spray in two coats, with a total thickness of ≥ 60 μ m.
3. Environmental monitoring
In coastal or industrial polluted areas, it is necessary to regularly check the chloride ion content and pH value on the surface of the curtain wall. When the chloride ion concentration exceeds 0.06% or the pH value is less than 4, additional protective measures should be taken (such as applying anti-corrosion coatings or increasing cleaning frequency).