Characteristics and uses of aluminum-lithium alloy

by:Zeyi     2021-12-24
Among aluminum alloys, lithium and beryllium are the most effective alloying elements to reduce their density. The maximum solubility of lithium in aluminum is 4.2%. Adding 1% Li to aluminum can reduce its density by about 3%, while its positive elastic modulus increases by about 5%. Aluminum alloys containing a small amount of lithium will precipitate a uniform coherent compound δ'during the aging process.   In 1990, the 2094 and 2095 alloys developed by Reynolds Metals and Martin Marritt were registered in the Aluminum Association of America. Their high strength can exceed 700N/mm2 and rank among the strongest aluminum alloys. In 1992, Reynolds Metals also developed 2195 and 2196 alloys, which have low density and high specific strength and toughness. While developing the high-strength Al-Li alloy Weldalite, the company also cooperated with General Dynamics (GD Co.) to successfully develop a thick plate, low-density, high-toughness Al-Li alloy 2197, and was registered with the Aluminum Association of America in 1993. This is an alloy that is not of the Wedalite type. Its strength and stiffness are higher than those of 2124 alloy, while its density is much lower. The 2197 alloy was industrialized in 1996 for the manufacture of F-16 fighters.   Like other heat treatment strengthenable wrought aluminum alloys, the strength of Al-Li alloy is also obtained through solution heat treatment and subsequent artificial aging. The structure of the precipitated phase depends on a series of process parameters, mainly quenching speed, cold working rate before artificial aging, aging temperature and time.  The main deficiencies of Al-Li alloys are insufficient plasticity and fracture toughness. For this reason, the following measures can be taken:    1. Prevent local preferential deformation. Refine the precipitate particles that are not easily cut by dislocations and distribute them evenly; or pre-deform before aging to refine and evenly distribute the θ'and S'phases; or make Al3Zr and other compounds form fine and uniformly distributed precipitates Things.   2. Prevent the concentration of grain boundary stress. Underage, reduce the width of the no-precipitation zone; or pre-deform before aging to reduce the width of the no-precipitation zone and inhibit grain boundary precipitation; or apply thermomechanical treatment; or add elements such as zirconium to refine the grains.  3. Prevent grain boundary embrittlement. Strengthen the refining and purification process, strictly limit the sodium content and reduce the hydrogen content. When the sodium content is high, a small amount of bismuth can be added to neutralize its harmful effects.  4. Reduce the stress concentration source in the crystal grain. Reduce the content of non-metallic inclusions; reduce the insoluble crystals and make them finer to improve the purity of the alloy; dissolve the soluble crystalline phase (primary crystal) in the solid solution. More than 90% of Al-Li alloys are used in the manufacture of aerospace vehicles. This is the current situation in all countries in the world. China’s “Tiangong-1” was launched on September 29, 2011, and it was China’s first low-orbit, long-life large manned person. The spacecraft has a design life of 2 years. The entire aircraft has a mass of 8.6t and is divided into front and rear cabins. The front cabin is a fully sealed environmental test cabin. After the docking is completed, the astronauts enter the cabin for work, training, and some necessary life activities and sleep. The rear cabin is a resource cabin with built-in power system, propulsion system and energy. Its main task is to provide energy guarantee for the flight of Tiangong-1 and control the flight attitude. The resource tank weighs about 1.4t after being filled with fuel. 'Tiangong-1' has been in orbit for two years, and fuel must be refilled. It has always been 'inseparable' from the resource tank in the sky, and weight reduction is imperative. Therefore, the structure of the resource tank uses Al-Li alloy instead of the traditional Aluminum alloy material has successfully reduced the weight of the cabin by more than 10%. The various mechanical properties of the Al-Li alloy materials used are not only equivalent to or higher than those of traditional high-strength aluminum alloys (2024 type) and super-strength duralumin 7xxx alloys, and its density is 8.5 lower than that of traditional aluminum alloys. %~9.5%, so it has a great weight reduction effect and meets the structural design requirements of 'Tiangong No. 1'. The straight section of the front cabin of China's C919 large aircraft is made of Al-Li alloy, but the materials used are imported from the United States. In the future, the amount of domestic materials will be gradually increased. In 2018, domestic aluminum will account for aluminum. More than 40% of the total material consumption. ————The article comes from the Internet. If there is any infringement, please contact to delete it.
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