What Are The Common Processing Techniques For Aluminum Alloys in Aerospace?

1, Material preparation: dual control of purity and microstructure
The manufacturing of aerospace aluminum alloys began with the ultimate pursuit of material purity. Taking high-strength aluminum alloys such as 7075 and 2024 as examples, their melting process requires the use of electron beam melting+vacuum degassing technology to control the hydrogen content below 0.1mL/100g, and strictly limit the iron and silicon impurity content to ≤ 0.12%, far below the 0.3% standard of ordinary aluminum alloys. This technological breakthrough significantly reduces the porosity and inclusion content inside the material, increasing fatigue life by more than three times.
In the casting process, the application of electromagnetic stirring technology reduces the grain size from 200 μ m in ordinary casting to below 50 μ m. For example, the aluminum alloy castings of SpaceX rocket fuel tanks have achieved grain refinement and microstructure uniformity through this technology, and have successfully passed the 3000MPa water pressure test. In addition, the two-stage homogenization treatment process (465 ℃/10 ℃/h) can eliminate the low melting point eutectic structure, control the size of β 'phase precipitation within 10-50nm, form a dense precipitation strengthening network, and further improve the fracture toughness of the material.
2, Forming process: a leap from traditional forging to additive manufacturing
1. Forging and Extrusion: Precision Upgrade of Traditional Processes
In the manufacturing of large structural components, multi-directional forging technology has become mainstream. Taking a certain wing beam as an example, a 30000 ton hydraulic press is used to form it at a low speed of 5-10mm/s at 380-420 ℃, so that the angle between the streamline direction and the principal stress axis is ≤ 15 °, which is much better than the 45 ° deviation of ordinary forgings. This technological breakthrough has increased the fatigue life of components by over 50%.
The extrusion molding process achieves pre stress orientation through continuous pultrusion technology, significantly improving the mechanical properties of the profile. For example, 44% of the weight of the Airbus A380 fuselage is composed of aluminum alloy extruded profiles. During the extrusion process, a multi cycle continuous extrusion method is used to optimize the bonding strength between adjacent billet interfaces, avoiding the influence of transverse welds on fatigue life.
2. Additive Manufacturing: A Revolutionary Breakthrough in Complex Structures
Additive manufacturing technology provides a new path for lightweight design of aluminum alloy components. Among them, laser selective melting (SLM) technology can manufacture complex components with few internal defects and excellent mechanical properties through the powder bed powder process. However, due to the uncertainty of powder gaps and laser reflectivity issues, it is currently mainly used in casting aluminum alloys or alloy systems with good weldability.
Arc Additive Manufacturing (WAAM) uses synchronous fuses to accumulate layer by layer, making it suitable for the manufacturing of ultra large and complex parts. For example, a certain satellite bracket has achieved integrated molding through WAAM technology, with a material utilization rate of up to 95%, but residual stress caused by heat input needs to be eliminated through subsequent heat treatment.
Electron beam fuse additive manufacturing (EBFF) uses electron beams as a heat source in a vacuum environment, which has the advantages of fast forming speed and high energy conversion rate. This technology has been successfully applied in the manufacturing of thermal control components for spacecraft, with a formed part density of up to 99.9% and no need for protective gas.
Ultrasonic additive manufacturing (UAM) achieves solid-state forming through high-power ultrasonic energy, with low temperature and low residual stress, making it particularly suitable for connecting dissimilar materials such as carbon fiber and aluminum alloy. However, due to the limitation of ultrasonic power, rapid prototyping can only be performed on aluminum foil with a thickness of ≤ 2mm. In the future, it is necessary to break through the bottleneck of transducer output power.
Friction Stir Welding Additive Manufacturing (FSAM) is based on the principle of friction stir welding, which uses a high-speed rotating stirring head to achieve the filling and stacking of plasticized metals. The microstructure of the heat affected zone produced by this technology has minimal changes and low residual stress, and has been successfully applied in the manufacturing of aircraft wing skins.
3, Heat treatment: precise control of temperature and time
Heat treatment is a key step in optimizing the performance of aluminum alloys. Taking 7050 alloy as an example, its heat treatment process requires controlling the temperature fluctuation of the solid solution window (470-490 ℃) within ± 1.5 ℃ through a laser temperature measurement system under nitrogen protection. During the processing of a certain engine blade, if the temperature deviation exceeds 5 ℃, an over burning defect will occur.
In terms of aging treatment, bipolar aging (200 ℃/2h → 240 ℃/10min → 160 ℃/24h) can improve stress corrosion resistance by 200%, but the energy consumption is three times that of ordinary T6 treatment. In addition, deformation heat treatment can significantly improve the distribution of transition precipitates by combining thermoplastic deformation with heat treatment. For example, the 7050 alloy is embedded with pre deformation technology during the hot rolling stage, which increases fracture toughness by 40% and reduces anisotropy by 50%.
4, Surface treatment: dual enhancement of protection and functionality
The surface treatment of aerospace aluminum alloys needs to balance corrosion resistance and functionality. Taking anodizing as an example, its film thickness needs to reach 50-100 μ m (ordinary parts only 10-20 μ m), microhardness ≥ 400HV, and the chloride ion content in the treatment tank liquid needs to be monitored in real-time ≤ 50ppm. The NiCrAlY coating deposited on the surface of engine blades can increase high-temperature oxidation resistance by 8 times, but the cost can reach up to 3000 yuan/square meter.
In addition, laser cladding technology uses high-energy laser beams to fuse ceramic particles or metal powders onto the surface of the substrate, forming gradient functional materials. For example, the outer shell of a spacecraft was laser coated with TiC ceramic particles, which increased its wear resistance by three times while maintaining the lightweight advantage of aluminum alloy.