Application of the hottest laser processing techno

2022-07-31
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Application of laser processing technology in aviation industry

surface repair of aluminum alloy

a layer of strong and tough oxide film naturally forms on the surface of aluminum and its alloy, which makes it difficult to prevent the oxidation behavior in the exposed area during the actual welding process. Resistance spot welding of aluminum alloy is also very difficult. Although this technology can realize the welding of aluminum alloy, the surface resistance changes due to the existence of surface oxide film [12]. Unlike iron, aluminum has only one allotrope, so that no phase transformation occurs during cooling, resulting in changes in microstructure. The strengthening methods of aluminum alloy mainly include deformation strengthening, solution strengthening and precipitation strengthening. Conventional welding methods usually deteriorate the deformation strengthened or precipitation strengthened aluminum alloy due to the heat input during welding

arc welding and spot welding are commonly used in aluminum alloy welding. Recently, due to the rapid development of laser technology, laser welding technology has been developed rapidly and is more and more widely used in the welding of aluminum alloys. Then, there are different problems due to different types of aluminum alloys. For example, studies have shown that defects such as cracks are easy to form when welding aa6xxx series aluminum alloys due to large solidification temperature range, and loose defects are easy to form when welding AA5083 due to Mg content between 3~6%. Because of the above shortcomings, the laser welding of aluminum alloy is much more complicated than that of steel

Figure 1 porosity defects on the surface of cast Al alloy on Aeroengine

in addition, the high activity between oxygen and aluminum will lead to porosity and porosity in aluminum alloy products during casting. 2.5 defects such as shrinkage holes formed on the surface of cast parts of a certain model of engine and porosity defects formed in ZL104 aluminum alloy are shown in Figure 1. The existence of porosity and porosity will seriously reduce the service performance of the parts, and even cause accidents. However, since most of these aluminum alloy parts are thin-walled parts and generally have been processed into finished products, it is difficult to avoid thermal damage to the substrate by conventional welding repair methods. But metal doctor technology can solve this problem well

Figure 2 how to operate the electro-hydraulic servo universal testing machine on ZL104 alloy

now we have used metal doctor technology to repair the defects such as porosity, porosity and surface cracks of various aluminum alloy components used in aerospace, automobile, motor, etc. After installation and use, the effect is very good. Figure 3 is a cross-sectional view of an aero-engine component repaired by metal doctor technology

Fig. 3 hemaa coating on the surface of Al Si alloy

surface carburization, oxygenation strengthening and repair of titanium alloy

titanium and its alloys are widely used in the fields of aerospace, chemistry, automobile manufacturing and nuclear industry due to their outstanding comprehensive properties. However, titanium alloy is not wear-resistant, so surface carburization is needed to improve its surface wear resistance

conventional carburizing methods include electroplating, carburizing furnace carburizing, EDM, PVD, CVD and other methods, but these methods do not have the advantages of easy processing, low processing temperature, high speed and large area processing. The carburized layer is formed by electric spark carburizing, and the carburized layer is about 5 μ m. It was confirmed by electron probe microanalysis and X-ray analysis that the tic layer was formed by the gradient infiltration of carbon into titanium matrix. This method is a kind of diffusion treatment. The hardened layer obtained is different from the hard layer obtained by coating treatment. It has the same good compactness as the general gradient film. The hardness is hv2200  and the substrate is about hv200. It is found by friction experiment that EDM can reduce the friction coefficient of titanium and improve the wear resistance. In addition, the corrosion resistance of the treated surface to brine and sulfuric acid is also better than that of pure titanium

in addition, we have also conducted electric spark strengthening treatment on the titanium alloy anti ice shell, iron-based superalloy and magnesium alloy parts of the aircraft

surface carburization

titanium alloy is very attractive to be applied after being made into rotating parts, such as automobile valves, chemical pump valves and aircraft parts. However, the wear resistance of titanium alloy is very poor, because it is prone to adhesive wear during movement

carburization of titanium and titanium alloys can be achieved in a non oxidizing atmosphere. According to the ti-c phase diagram, it can be found that the ti-c phase diagram is different from the Ti-O phase diagram and the Ti-N phase diagram, and the solid solubility of C in Ti is very small. The thickness of TiC compound is generally 1 ~ 10 μ m。 However, once tic is formed, it is not easy to form a deeper carburized layer. The carburizing temperature is generally 1050 ℃, and the carburizing process can be completed only when there is carburizing medium

Figure 4 shows the ti-c phase diagram. among γ The phase is tic1-x, where x changes within a certain range

Figure 4 ti-c phase diagram

the traditional carburizing treatment process cannot complete the carburization of the specified area. The metal doctor can carburize the designated area at room temperature

Fig. 5 microhardness of carburized layer on the surface of TC4 titanium alloy. Figure 5 shows the hardness distribution curve obtained after carburizing. The microhardness of the surface layer can reach hv1500, and gradually decreases to the position of the substrate from the surface to the inside. The following chemical reactions will occur during alloying:

c+ α― Ti→ α Ti (c) (1)

c+ti → TiC (2)

now this process has been successfully applied to the carburization of valve surface in chemical plant and the surface strengthening treatment of titanium alloy parts for a certain type of aircraft. Figure 6 shows the actual picture of carburizing treatment on the valve surface of a chemical plant. The black area in Figure 7 is the area where the supply of carburized lithium battery exceeds the demand

surface oxygen infiltration strengthening of titanium alloy wear-resistant parts

the surface carburization and nitriding of titanium alloy cause great damage to titanium alloy wear-resistant parts due to long treatment time and high temperature, which limits the application of this process. However, the surface oxygenation treatment time of titanium alloy gold is not only short, but also the treatment temperature is lower than the carburizing and nitriding temperature. After treatment, the hardness can reach HV (equivalent to HRC). It has a broad application prospect and has been applied in the localization of imported aircraft parts

Figure 6 repair of titanium alloy for valves with alloying and carburizing treatment by metal doctors

(the black area is the treatment part)

titanium alloy used on aerospace components is basically made of high-strength titanium alloy strengthened by heat treatment. These parts are worn and damaged due to operation, corrosion, friction and other working conditions. However, every year, a large number of expensive torpedoes, cartridges and scratched titanium alloy parts need to be repaired due to friction. At the same time, some titanium alloys have casting defects that need to be repaired. Some titanium alloy parts can be repaired by traditional welding technology. Because the traditional welding method will produce a lot of thermal damage to the substrate, and this kind of thermal damage is often harmful, which will lead to the deformation of components, the enhancement of corrosion sensitivity, the decrease of the strength of the heat affected zone, the absorption of hydrogen/nitrogen/oxygen and other consequences. Moreover, some high-strength titanium alloys, such as ti-6a-2sn-4zr-6mo alloy used in weapons or aircraft engines, are considered as non weldable alloys. For the above reasons, the repair of these components generally does not consider the use of conventional welding technology. Figure 7 shows defects due to wear and cracking. Figure 8 is the metallographic photograph of the metal doctor on Ti6Al4V substrate

Figure 7 Ti6Al4V turbine pin shaft after wear and scale reduction

figure 8 metal doctor coating prepared on Ti6Al4V surface

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