Aluminum is a widely distributed element, and its content in the earth's crust is second only to oxygen and silicon, and it is the highest among metals. Pure aluminum has a low density of 2.7 g/cm3, good thermal and electrical conductivity (second only to Au, Ag and Cu), good ductility and high plasticity, and can be used in various mechanical processing. Aluminum has active chemical properties, and rapidly oxidizes in air to form a dense and firm oxide film, so it has good corrosion resistance. However, the strength of pure aluminum is low, and only by alloying can it be used as a structural material for users.
According to the composition and production process characteristics of aluminum alloys, they are usually divided into two categories: wrought aluminum alloys and cast aluminum alloys. The main industrial applications are Al-Mn, Al-Mg, Al-Mg-Cu, Al-Mg-Si-Cu, Al-Zn-Mg-Cu and other alloys. Deformed aluminum alloy, also known as wrought aluminum alloy, can be divided into rust-proof aluminum, hard aluminum, superhard aluminum and forged aluminum according to its composition and performance characteristics.
The outstanding characteristics of aluminum alloy are low density and high strength. Aluminum-manganese and aluminum-magnesium alloys formed by adding manganese and magnesium to aluminum have good corrosion resistance, good plasticity and high strength. They are called rust-proof aluminum alloys and are used to manufacture oil tanks, containers, pipes and rivets. The strength of hard aluminum alloy is higher than that of rust-proof aluminum alloy, but its corrosion resistance decreases. These alloys include aluminum-copper-magnesium system and aluminum-copper-magnesium-zinc system. The strength of the newly developed high-strength hard aluminum is further improved, but the density is lower than that of ordinary hard aluminum 15%, which can be extruded and can be used as motorcycle frames and rims. Al-Li alloy can be used to manufacture aircraft parts and high-grade sports equipment that bear heavy loads.
All kinds of aircraft use aluminum alloy as the main structural material. Aircraft skins, beams, ribs, stringers, frames and landing gears can all be made of aluminum alloy. The amount of aluminum varies according to the purpose of the aircraft. Economic-oriented civil aircraft are widely used because of the low price of aluminum alloy. For example, the aluminum alloy used in Boeing 767 aircraft accounts for about 865,438+0% of the structural weight of the aircraft. Because military aircraft require good performance, the amount of aluminum is relatively reduced. For example, the F- 15 high-performance fighter with a maximum flight speed of Mach 2.5 uses only 35.5% aluminum alloy. Some aluminum alloys have good low temperature performance, and are neither cold nor brittle at-183 ~-253 [2OC]. They can work in the environment of liquid hydrogen and liquid oxygen, but they are not compatible with concentrated nitric acid and unsymmetrical dimethylhydrazine. The fuel tank, oxidizer tank, inter-tank section, inter-stage section, tail section and instrument cabin of Apollo spacecraft launched by Saturn V carrier rocket are all made of aluminum alloy.
The crew cabin, front fuselage, middle fuselage, rear fuselage, vertical tail, flap, lifting aileron and horizontal tail of the space shuttle are all made of aluminum alloy. The main structural material of various artificial earth satellites and space probes is also aluminum.