In the aerospace manufacturing industry, the application of new materials is increasing, and it also promotes the development of corresponding new welding methods. Laser hybrid welding of aluminum-lithium alloys is one of them.

The development trend of modern aircraft structural materials is: vigorously develop high-strength, high-specific modulus, corrosion-resistant, high-tolerance, low-temperature multi-functional structural materials to achieve structural weight reduction; improve materials and structural preparation techniques, reduce manufacturing costs and maintenance costs . Modern body materials are still dominated by aluminum alloys, the amount of steel tends to decrease, and the amount of titanium alloys increases significantly. Aeroengine main materials are aluminum alloys, titanium alloys, high temperature alloys and various types of high temperature composite materials. Aluminum-lithium alloys are the most rapidly developing field in aviation metal materials in the past decade.

Aluminum lithium alloy profile

Industrial production of aluminum-lithium alloys refers to aluminum alloys containing 1% to 3% of Li with Li as the main strengthening element. The purpose of adding Li to the alloy is to increase the elastic modulus of the alloy and decrease the density of the alloy (density is 5% to 12% lower than that of the general aluminum alloy, and the elastic modulus is 5% to 8% higher). Al-Li alloy has low density, high specific strength, high specific stiffness, excellent low temperature performance, good corrosion resistance and excellent superplastic forming properties; its strength, fracture toughness, yield strength, fatigue properties are all with temperature. Reduced and increased; it has good superplasticity, can be made into complex shapes, difficult to form parts, reduce labor intensity and reduce the weight of the structure. Using it to replace the conventional aluminum alloy can reduce the mass of the components by 15% and increase the stiffness by 15% to 20%. It is considered as an ideal structural material in the aerospace industry. In this field, aluminum-lithium alloys have replaced conventional high-strength aluminum alloys on many components.

According to the distribution of the Airbus A380 (Figure 1), aluminum alloys account for the largest proportion and reach 61% of the weight of the machine body. Therefore, in order to achieve performance improvement, it is necessary to develop innovative aluminum alloy materials and process technologies, specifically to increase the strength. And damage tolerance, enhance stability and improve corrosion resistance. The Airbus A380 uses aluminum lithium alloys such as 2099, 2199, and 2196. Floor beams used in the A380, such as beams, seat rails, cockpits, and emergency cabin floor structures, electronic equipment mounting brackets and angles, can be reduced by several hundred kilograms. Russia's next-generation narrow-body passenger aircraft, the MS-21, will use composite wings and fins, while the fuselage will be made of advanced alloys such as aluminum-lithium alloys.

Laser hybrid welding technology

With the mature application of laser welding technology in the industry, the shortcomings of laser welding technology are also gradually exposed. First of all, laser welding equipment investment is large, the electrical efficiency is low (usually less than 10%, the current laser fiber laser power efficiency has only increased to about 30%); followed by high requirements on the workpiece welding assembly accuracy, such as docking clearance, The amount of misalignment is less than 0.1mm or 10% of the plate thickness, which not only requires special fixtures and processing, but also brings great difficulties for practical applications; in addition, the absorption and reflection of laser light by the plasma of the high-power laser welding process. Role, to reduce welding stability and utilization of laser energy, and high welding speed leads to rapid solidification of welded joints, can easily lead to pores, undercut defects, weld structure brittleness, and even weld cracks; In addition to high reflectivity materials (aluminum alloys , copper alloy) is difficult to achieve laser welding. To solve these problems, domestic and foreign scholars have been working to improve the adaptability of laser welding. The most important method at present is to use laser-arc hybrid welding.