Aluminum is the most abundant metal element on the earth, accounting for 7.5 percent of the earth's crust. However, due to the difficulty of smelting aluminum, it was once extremely rare and worth more than gold. More than a hundred years ago, the Royal Society produced an aluminum cup that was more valuable than gold, and presented it to the Russian chemist Mendeleev (made the first periodic table of elements) in recognition of his expertise in the field of chemistry. Outstanding contribution.
It was not until 1886 that Charles Martin Hall of the United States and L. T. Heroult of France independently invented the smelting technology of electrolytic aluminum. After this method was put into production, the output of metal aluminum increased rapidly, and the price fell sharply. In the daily life of the people.
The application of aluminum in the construction industry has a history of more than 100 years. It was first used as a building decoration material, such as door and window frames, glass curtain wall frames, building outsourcing aluminum panels, and building vertical seaming roofs. In the 1930s, aluminum alloy was used in the load-bearing and maintenance structure of buildings; nowadays, aluminum alloy has become the largest construction metal material except steel, and about 27% of the world's aluminum output is used in construction; There are more and more applications as load-bearing structural materials, such as bridges, warehouses, and space structures.
In 1951, Britain built the world's first aluminum alloy dome "Dome of Discovery", with a mesh shell diameter of 111m and a height of 27m, which was the largest dome in the world at that time.
Pure aluminum has good ductility but low strength, and is generally only used for low-stress structures at room temperature. In order to improve the performance of pure aluminum, people make all kinds of aluminum alloys by adding various metal elements to pure aluminum. The structural aluminum alloys are usually alloys of aluminum, magnesium, and silicon.
Aluminum alloys can be divided into two types: forged aluminum and cast aluminum. The former is to hot or cold work the unmelted aluminum billet, and the latter is to pour molten aluminum into a mold and then cast it into a mold. The commonly used aluminum alloy for the structure is forged aluminum. Forged aluminum alloy grades are usually represented by four digits, and the naming rules were proposed by the American Aluminum Association (AA) in 1954. The strength, ductility, and corrosion resistance of different grades of forged aluminum alloys vary due to their chemical composition (aluminum element and other small amounts of added elements) content.
Among them, the 6xxx series contains magnesium and silicon elements. This series of aluminum alloys has good corrosion resistance and strength similar to Q235 steel, and is easy to be extruded. Most of the aluminum alloy profiles used in building structures belong to this series, such as 6061-T6 aluminum alloy is widely used in aluminum alloy building structures.
Low density
The density of aluminum is about one-third of that of steel. This is undoubtedly a relatively large advantage in the design of building structures where its own weight accounts for a relatively large amount. Therefore, aluminum alloy structures usually give people a light-looking appearance.
Low modulus of elasticity
The modulus of elasticity of aluminum alloy is only one-third of that of steel, so aluminum alloy is easier to buckle than steel structure, and the stability coefficient in the specification is much lower than that of steel structure (Lenovo our common can). Therefore, deformation and stability are more common problems in aluminum alloys, and the advantages of light materials are also offset by large deformations.
Poor solderability
In the design of steel structure welding, the weld can be as strong as the member, while aluminum alloy welding will greatly reduce the strength and ductility of the material. Therefore, mechanical connection is often used in the connection of aluminum alloy. In the actual design, the inability to weld will make it difficult for engineers who are accustomed to steel structure design to adapt. For example, if you want to connect a connecting plate to a component, you need to add bolt holes, and the bolt holes will weaken the strength of the component. It was broken.
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Extrusion
Aluminum alloys are very soft, so unlike traditional steel structures that are usually rolled and welded, aluminum alloys are usually formed by extrusion. God closes a door and always opens a window. The unique extrusion process can produce various components with complex cross-sections, and all the connectors we need can be integrated with the main structure through extrusion. At the same time, aluminum alloy components and nodes can be prefabricated in batches and then assembled. This production mode is very suitable for the factory assembly structure that we now advocate. For large aluminum alloy space structures with a large number of repeated feature members and nodes, it has Good applicability.
preservative
Aluminum alloy also has a big advantage, aluminum alloy itself can form a dense oxide film in the air, so aluminum alloy generally does not require special anticorrosion treatment. Compared with the steel structure, it saves the cost of painting and also reduces the maintenance cost in the later stage. Therefore, aluminum alloy is often used in buildings with high corrosive requirements such as swimming pools and petrochemical industries.
Large linear expansion coefficient
The coefficient of linear expansion of aluminum alloy is about twice that of steel structure. The temperature effect will be more prominent in the design than steel structure by superimposing the characteristics of low elastic modulus and low strength of aluminum alloy. For ultra-long aluminum alloy structure, the temperature effect is very likely. Become the master load condition.
High recovery rate
At the same time, the aluminum alloy material is easy to recycle, has low reprocessing cost, high recycle rate, and high recycling value. It is an energy-saving and environmentally friendly green material. The leftover materials in the actual production can be recycled at a relatively high price, which reduces the loss cost of the aluminum alloy structure.
