1.Why are galvanized coils (electroplated zinc) unsuitable?
Insufficient Corrosion Resistance
Thin Zinc Coating: Air freight containers travel globally, encountering harsh environments-from wet harbors to de-icing airport runways in winter. The zinc coating of ordinary electroplated galvanized coils (typically 10-30µm) quickly deteriorates under these conditions due to scratches and corrosion, leading to rust on the substrate.
Limited Sacrificial Protection: Once the zinc coating is scratched or worn away, its "sacrificial anode" protection ceases, and rust spreads rapidly across the steel substrate.
Surface Finish Issues
Poor Coating Adhesion: Air freight containers typically require high-quality, abrasion-resistant, and weather-resistant colored coatings for brand recognition and further protection. An overly smooth electroplated surface hinders paint adhesion, easily causing paint peeling.
Compatibility with Topcoat: The zinc coating can chemically react with some paints, affecting paint curing and causing defects.
2.What are the advantages and disadvantages of aluminum alloys used in air cargo containers?
Advantages:
Lightweight and high strength: Its biggest advantage is its significantly lighter weight compared to steel.
Excellent corrosion resistance: Aluminum naturally forms a dense oxide film on its surface, providing strong corrosion resistance and preventing red rust.
Easy maintenance: Mature surface treatment technology.
Disadvantages: Higher cost and lower strength compared to steel of the same volume.
3.What are the advantages and disadvantages of composite materials (such as glass fiber and carbon fiber reinforced plastics)?
Advantages:
Extremely lightweight: Lighter than aluminum alloys.
Excellent corrosion resistance: Completely resistant to moisture, salt spray, and chemicals.
Highly designable: Can be molded in one piece, reducing seams and resulting in a more complete structure.
Easy maintenance.
Disadvantages: Highest initial manufacturing cost; impact resistance and repair methods differ from metals.
4.Is it possible to use "steel"?
Weathering steel: A protective rust layer forms on the surface through alloy composition (such as Cu, P, Cr, Ni), preventing corrosion from penetrating deeper. However, a specialized coating system is required.
Pre-treated high-strength steel sheets: Such as those treated with phosphate or using the Dacromet process. These treatments provide superior corrosion resistance and coating adhesion compared to ordinary electro-galvanizing.
Hot-dip galvanized steel sheets: While better than electro-galvanizing, their surface quality and weight issues make them uncommon in the aerospace industry.
5.What are the conclusions and recommendations?
Technically speaking: its corrosion resistance, surface treatment compatibility, and durability cannot meet the extreme requirements of air freight.
Economically speaking: its short service life and high maintenance costs lead to increased total life cycle costs.
From an industry practice perspective: it does not meet mainstream material selection standards and cannot pass stringent industry certifications.