From aluminum intensive processing

(2) 2XXX aluminum alloy

2XXX series high strength aluminum alloy, based on its strength, toughness and fatigue resistance characteristics, on the one hand, it is necessary to constantly reveal the law and mechanism of the effect of alloy composition and precipitated phase types on strength and toughness. As shown in Figure 4, when Cu/Mg ratio reaches 4.9, S phase and ω phase can be precipitated simultaneously, which is conducive to improving toughness. On the other hand, the strength, toughness and damage resistance of the alloy can be improved by reducing and optimizing the impurity content, controlling the plastic deformation and recrystallization, and developing a new thermo-mechanical treatment technology.

Precipitated phases S and ω in Al-3.48Cu-0.71Mg alloy: (a) HRTEM image (B=[100]);(b) FFT obtained from area A ( Phase S); (c) FFT obtained from area B (Phase ω)

With high strength, Gao Ren, corrosion resistant, weldable high comprehensive performance properties of 2519 alloy composition of 2519 a alloy after optimization design, by using thermal mechanical treatment, intermittent secondary aging technology, such as refinement of the second phase, improve the aging distribution density of precipitated phase, greatly improved the mechanical properties of alloy and the elastic energy. As shown in FIG. 5, 2519A alloy can obtain finer and dispersed precipitated phase than T87 state by adopting appropriate discontinuous secondary aging system, thus improving mechanical properties. 2519A alloy has been officially listed as domestic aluminum alloy brand 2A19.

Precipitation phase distributions in 2519A aluminum alloy after different heat treatments: (a) T87; (b) T8I6; (c) T9I6

On the basis of improving the damage resistance of 2524 alloy material, aiming at its weakness of low strength, through the optimization design of Cu and Mg principal components and reducing the impurity content of Fe, Si and Ti, Alcoa and Faal have developed 2026 and 2027 alloys with high strength and high damage tolerance. Compared with 2024 alloy, the properties of extruded parts (12~82 mm thick) and plates (12~55 mm thick) are 20%~25% and 10% higher, respectively.

In the mid-1990s, the prototype alloys C415 and C417 were successfully developed due to the discovery of atomic clusters formed by Ag microalloying in 2XXX series aluminum alloy or the mechanism and effect of new phase interaction. The Ag-containing alloy has good plasticity, toughness and heat resistance, and can be used for a long time at 200 ℃. The high damage tolerance 2139-T8× plate containing 0.15%~0.6%(mass fraction) Ag with thickness up to 152 mm has better performance than 2×24-T3×, which has been applied in supersonic aircraft.

(3) Aluminum lithium alloy

Aluminum alloy containing lithium is generally referred to as aluminum lithium alloy, high-performance aluminum lithium alloy in addition to high specific strength and high specific modulus of common, for service requirements, both damage resistance, weldability, corrosion resistance, high/low temperature stability, has broad application prospects in aerospace and other high-end equipment.

At present, in the AA brand system, engineering al-li alloy respectively belong to two digital series (2xxx, 8xxx), such as 2020, 2090, 2097, 2060,2065, 2076,8090, 8091. It belongs to 2XXX al-Li alloy, in which the largest content of alloying element is Cu, and belongs to 8xxx al-Li alloy, in which the largest content of alloying element is Li, generally Li content is more than 2%. In China’s aluminum alloy brand system, engineering al-li alloy also belongs to two digital series (5XXX, 2XXX), such as 5A90, 2A97. After 2010, aluminum lithium alloy 2A66, 2A68 and so on were reported.

The development of al-Li alloy, based on the advantages of specific modulus and specific strength of this kind of alloy, further optimize the Li content, and pay attention to the role of microcombination, develop new al-Li alloy with high comprehensive performance. At the same time, it is necessary to pay attention to the research and development of special technology such as high cleanliness and large size ingot, protective atmosphere plastic deformation, heat treatment, etc., to improve the toughness, corrosion resistance, damage resistance and formability of the aluminum alloy, as well as the uniformity of microstructure and performance of large size material.

In the new round of aluminum and lithium alloy research carried out internationally, Russia mainly developed 1460 alloy, the United States mainly developed Weldlite series alloy and 2097, 2197 and 2195 aluminum and lithium alloy. 2097-T861 alloy has been used in the rear fuselage frame and middle fuselage girder of F-16 aircraft. At the beginning of this century, the research and development of 2098/2198, 2099/2199 and other new generation of aluminum lithium alloy. 2198-T8× alloy has high strength, high damage tolerance, high thermal stability and good forming and welding properties.

The recently developed al-Cu-Li alloys 2050 and 2060 with low Li content reflect the development trend of a new generation of aluminum alloys with high strength and comprehensive properties to reduce density. The performance of 2050-T851 thick plate is not only better than 7050-T7451 alloy, but also lower density, strength, toughness, fatigue crack propagation resistance and heat resistance. The weight of 2050-T851 alloy can be reduced by 5% instead of 7050 alloy. Of course, the heterogeneity of microstructure and performance in the direction of plate thickness is still a technical problem to be solved in the future.

The research of al-li alloy in China started later than the developed countries of aluminum processing industry abroad. In the early 1960s, northeast light alloy processing factory developed the first aluminum lithium alloy plate named S141 in China, referring to Alcoa’s 2020 aluminum lithium alloy. However, due to poor plasticity and other reasons, the alloy has not been mass-produced and put into use. Subsequently, the research progress of al-Li alloy in China is slow and rarely reported. Until the seventh five-year Plan period, in view of the urgent demand of al-li alloy materials in the aerospace and defense industry, the research and development of al-Li alloy attracted attention again with the support of the national project. After more than 30 years of follow-up research and imitation, China has accumulated a lot of achievements and experience in the alloying principle, composition design, strength and toughness, fatigue resistance, corrosion resistance and welding of al-li alloys. C919 is designed and used the third generation of al-li alloy plates and profiles produced by Faal and Alcoa, which has accumulated successful experience in the application of al-li alloy in large-scale equipment in China. At the same time, it also puts forward the urgent task of localization of high-performance al-li alloy materials.

At present, the production of aluminum and lithium alloy ingot in China mainly depends on the 6 T grade aluminum and lithium alloy casting equipment introduced from Russia by Southwest Aluminum, which has been able to produce 1420, 2195, 2A97, 2099/2199 and other small specification materials. It is urgent to build a complete production line of large specification aluminum and lithium alloy materials.