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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, when it comes to the total number of metal-based space structures, traditional steel structures still dominate the market, with aluminum alloy structures making up only a small portion. One of the main reasons for this is the higher cost associated with aluminum alloy materials compared to steel. In some countries, the price of aluminum alloy profiles with identical specifications can be as high as 7 to 10 times that of steel. When considering the material cost per unit strength, aluminum alloys can be 3 to 4 times more expensive than steel. Another reason is that the number of aluminum alloy space structures built so far is significantly smaller than that of steel structures, leading many architects and structural engineers to rely on conventional steel solutions due to limited familiarity with aluminum's properties.
Wrought aluminum alloys are divided into two main categories: wrought and cast. Wrought aluminum is produced through hot working or cold forming of aluminum billets, while cast aluminum is made by pouring molten aluminum into molds. The nomenclature system for these alloys was first introduced by the Aluminum Association in 1954 and is now widely accepted globally, including in China. Different grades of forged aluminum alloys exhibit varying levels of strength, ductility, and corrosion resistance based on their chemical composition. For example, the 4xxx series is primarily used for welding and is not typically included in comparative analyses. Additionally, the treatment process after casting—such as heat treatment (T) or cold working (H)—can significantly affect mechanical properties. Among these, the 2xxx, 6xxx, and 7xxx series are heat-treatable, whereas others are strengthened through cold working. The 6xxx series, which contains magnesium and silicon, offers good corrosion resistance and strength comparable to Q235 steel, making it ideal for extrusion and commonly used in building structures like 6061-T6.
Compared to steel, aluminum alloys have a lower density, approximately 2.7 × 10³ kg/m³, which is about one-third that of structural steel (7.85 × 10³ kg/m³). Their elastic modulus ranges between 69.6 to 75.2 × 10³ MPa, roughly three times less than that of steel (205 × 10³ MPa). The modulus decreases with temperature, dropping to 67 × 10³ MPa at 100°C and 59 × 10³ MPa at 200°C. The thermal expansion coefficient of aluminum is around 23 × 10â»â¶/°C, nearly double that of steel (12 × 10â»â¶/°C), meaning aluminum structures are more sensitive to temperature changes. However, when restrained, the deformation caused by thermal expansion in aluminum is only about two-thirds that of steel under similar conditions.
At lower temperatures, the tensile strength and elongation of aluminum increase, making it perform well in cold environments. The Poisson’s ratio of aluminum is about 1/3, slightly decreasing with temperature, but this change is negligible in most structural designs. Aluminum’s unique extrusion process allows for the production of complex cross-sections, making it ideal for prefabrication and assembly. This makes it highly suitable for large-scale projects with repetitive elements. Its excellent formability also supports intricate architectural designs.
Moreover, aluminum has a high reflectivity for light, contributing to its aesthetic appeal. Its reflective surface helps regulate indoor temperatures, keeping spaces cooler in summer and warmer in winter. This makes it popular in greenhouses, exhibition halls, and sports facilities. Due to its natural oxide layer, aluminum is inherently corrosion-resistant, eliminating the need for additional anti-corrosion treatments. It is especially beneficial in humid or chemically aggressive environments such as swimming pools, ice rinks, and petrochemical plants. Overall, aluminum alloys offer advantages in weight, durability, and adaptability, making them an ideal choice for large-span spatial structures and buildings exposed to harsh conditions.