Application of Laser Technology in Repairing Aircraft Structure Damage

Since the invention of the first laser in the 1960s, laser has been widely used in many fields due to its high directivity, high brightness, high monochromaticity and high coherence, and has become an ideal processing heat source. After the laser is focused, the power density on the spot can reach 104~1015W/cm2, and the metal material will instantly heat up, melt or even vaporize instantly under the irradiation of high power density light. Therefore, the application of different power density and heating time, the laser can achieve different processing purposes such as surface heat treatment, surface remelting, alloying, cladding, welding, cutting, drilling, surface impact strengthening, etc. It is a very ideal heating source. The surface modification technology of laser processing has been applied in the fields of aircraft structure and aero engine manufacturing. my country has used laser cladding technology to melt and cast the crown of aero-engine turbine blades and turbine guides, and successfully restored the shape, size and performance of the damaged parts.

　　 In recent years, with the rapid equipping of new aircraft, titanium alloys and composite materials have become the main structural materials of our military’s active aircraft. The laser is widely used in various fields because of its excellent qualities such as high directivity, high brightness, and high coherence. It will also play an important role in the field of aircraft structure repair.

Application of 　　laser processing technology

　　1, laser heat treatment technology

When a laser beam moving at a certain speed irradiates the metal surface, the surface metal quickly heats up after absorbing energy. When the light spot moves, the base material absorbs the heat of the surface layer to make the temperature of the surface layer metal drop rapidly at an extremely high speed, forming a self-quenching that is different from conventional quenching. Due to the extremely high cooling rate of self-quenching, a special surface modification layer with microstructure can be obtained, which has a good effect on improving the hardness, wear resistance, corrosion resistance and fatigue resistance of metals. Laser heat treatment is the earliest laser processing technology developed, and now it has formed a relatively complete theory and engineering application technology. For carbon steels and alloy structural steels that can be strengthened by phase transformation, laser surface quenching can produce higher hardness than traditional quenching, and even for some low-carbon steel materials that do not have hardenability.

2. Laser surface remelting technology

　　 Applying a higher laser power density than laser surface quenching to irradiate the metal surface will melt the surface metal. After the spot moves, the base metal absorbs heat and makes The metal liquid in the molten pool rapidly solidifies to form a strongly chilled microstructure with extremely fine grains and supersaturated solid solution. Due to the effect of fine grain strengthening and solid solution strengthening, the hardness and wear resistance of the material surface can be significantly improved. Studies have shown that through remelting, the hardness of aluminum alloys can be increased by 30% to 100%. This is the simplest laser processing technology, but the range of strengthening is limited. For aircraft structural aluminum alloy profiles and plates that bear alternating loads, the fatigue quality of the superheated layer that must exist after laser remelting is the key to determining the service life of the structure. Therefore, it is necessary to test and verify the effect of laser remelting on the material before entering the engineering application. The effect of fatigue performance. For structural steel materials, the remelting hardening effect is significant.

3. Laser surface alloying technology

　　 When the surface metal is melted by laser, the designed alloy elements are added to the molten pool, which can be obtained on the surface without changing the composition of the base alloy. Performance alloyed layer. This technology is very beneficial to the manufacture of parts that require special performance, and can produce metal or composite parts with non-uniform materials and non-uniform properties that cannot be achieved by traditional manufacturing technology. Due to the extremely high cooling rate of the molten pool during the laser surface alloying process, alloys and structures that are difficult to achieve under traditional metallurgical process conditions can be formed. Therefore, an alloyed layer with high hardness, wear resistance, good corrosion resistance and heat resistance can be formed as required. For aluminum alloys, laser surface alloying processes of various alloy systems have been tested, such as Cu, Fe, Si, Ni, Cr, WC, SiC and so on. Among them, the nickel-based alloyed layer is dispersed with intermetallic compounds AlNi and Ni3Al, which has high hardness and wear resistance, but the alloyed layer is brittle and cracks. The bonding interface of laser cladding must have an alloying metallurgical process between the matrix and the cladding material.