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Aluminum alloy material characteristics for space grid structure
Aluminum alloys have increasingly been used in the design and construction of large-span space structures both domestically and internationally in recent years. However, despite their growing application, steel structures still dominate the market in terms of total volume. Aluminum alloys account for only a small portion of all metal space structures, primarily due to two main factors. First, the cost of aluminum alloy materials is significantly higher than that of steel. In certain countries, the price of aluminum alloy profiles with identical section specifications can be as high as 7 to 10 times that of steel. When considering material cost per unit strength, aluminum alloys can be 3 to 4 times more expensive than steel. Second, the number of aluminum alloy space structures built so far is much smaller compared to steel structures. As a result, architects and structural engineers often rely on traditional steel structures when designing, lacking sufficient understanding of the unique properties of aluminum alloys.
Wrought aluminum alloys are categorized into different series based on their composition and processing methods. These alloys are produced through hot working or cold forming, while cast aluminum is made by pouring molten aluminum into molds. The American Aluminum Association (AA) introduced a standardized naming system in 1954, which is now widely adopted globally, including in China. Different grades of forged aluminum alloys exhibit varying levels of strength, ductility, and corrosion resistance depending on their chemical composition. For instance, the 4xxx series is mainly used for welding and is not included in comparative analysis. Additionally, heat treatment processes—such as T-temper for 2xxx, 6xxx, and 7xxx series—significantly influence mechanical properties, while non-heat-treated alloys are typically strengthened through cold working (H-temper). Among these, the 6xxx series, containing magnesium and silicon, offers good corrosion resistance and strength comparable to Q235 steel, making it ideal for architectural applications like 6061-T6, commonly used in space structures.
In structural engineering, aluminum alloys share similarities with steel but also have distinct differences. Their density is approximately 2.7 × 10³ kg/m³, about one-third that of steel (7.85 × 10³ kg/m³). The elastic modulus of aluminum alloys ranges from 69.6 to 75.2 × 10³ MPa, roughly one-third of steel’s 205 × 10³ MPa. At elevated temperatures, the modulus decreases: to 67 × 10³ MPa at 100°C and 59 × 10³ MPa at 200°C. The thermal expansion coefficient of aluminum (23 × 10â»â¶/°C) is nearly double that of steel (12 × 10â»â¶/°C), meaning aluminum structures are more sensitive to temperature changes. This requires careful consideration during design and construction to manage deformation caused by thermal expansion.
At lower temperatures, the tensile strength and elongation of aluminum increase, improving its mechanical performance. The Poisson’s ratio of aluminum is around 1/3 and remains relatively stable, making it negligible in most structural calculations. One of the key advantages of aluminum is its excellent formability, allowing for complex cross-sections through extrusion. This makes it suitable for mass production of repetitive components, which is ideal for large-scale aluminum space structures. Its good surface reflectivity also enhances energy efficiency, especially in buildings like greenhouses and exhibition halls, where it helps regulate indoor temperatures. Moreover, aluminum naturally forms a protective oxide layer, offering strong corrosion resistance without the need for additional treatments. This makes it particularly valuable in environments such as swimming pools, stadiums, and industrial facilities where moisture and corrosive conditions are common. Overall, aluminum alloys offer a lightweight, durable, and aesthetically pleasing alternative to steel, especially in large-span spatial structures and high-corrosion environments.