The hottest welding wonder in aviation manufacturi

2022-08-22
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Welding wizards in aviation manufacturing

in the aviation field, the connection of new materials and the manufacture of fine structures have promoted the rapid development of brazing technology, and its application in aviation manufacturing is more and more extensive

the development of new materials and technologies has provided a large development space for aviation technology, and new materials and technologies have also been widely used in aviation manufacturing industry. Brazing technology can well complete the connection of some new materials and the manufacture of fine structures. All kinds of new brazing materials and the corresponding brazing technology have been deeply studied. Therefore, brazing technology is more and more used in aviation manufacturing industry, and can be applied to the connection of important components

brazing technology of new aviation materials

1 Brazing technology of titanium alloy

Figure 1. The U.S. F-22 stealth fighter

titanium alloy is a key technology in the aviation field. The U.S. F-22 stealth fighter uses up to 45% titanium metal. Figure 1 shows the U.S. F-22 stealth fighter. In the aviation manufacturing industry, such as aircraft components and aircraft engines, there are many titanium alloy components that need brazing. In the early aviation industry, the brazing of silver based solder and aluminum based solder was mostly used. Titanium has been paid attention to because of its strength, mild and corrosion resistance. Since the 1970s, titanium alloy brazing technology has been greatly developed and began to be used in the aviation industry. Figures 2 and 3 show the military engine cover made of titanium alloy and the joints of aircraft titanium alloy that usually have high requirements on the tensile properties of materials, such as heat shrinkable film and tensile film

Figure 2 cover of ultra-high strength titanium alloy military engine

Figure 3 aircraft titanium alloy joint

research and test of Ti3Al Based titanium alloy brazing show that the tensile strength of Ti Cu Ni brazing joint at room temperature is close to that of the base metal, but it is only 70% - 80% of the base metal at 649 ℃ and 760 ℃. In recent years, the brazing process of Ti3Al Based titanium alloy has been deeply studied at home and abroad, and the strength of the brazed joint is close to that of the base metal. Good test results have been obtained by brazing TiAl based alloy with ti-15cu-15ni brazing filler metal. For example, the shear strength of the obtained samples can reach 319 ~ 322mpa by using the process of 1100 ~ 1200 ℃/30 ~ 60s infrared induction heating

2. Brazing technology of composites

(1) brazing of particle reinforced aluminum matrix composites

adding graphite, SiC and Al2O3 particles to aluminum matrix alloys can effectively improve the elastic modulus, high and low temperature strength, fatigue performance and wear resistance of the matrix. Therefore, brazing of this kind of composite materials has broad application prospects in aerospace manufacturing and other fields

brazing process is simple and feasible, which is the most suitable welding method for Al based alloy. Soft soldering usually uses CD Ag or Zn Al solder to braze b/al in the environment below 450 ℃. The joint shear strength of the Ovi satellite launcher with brazed b/al tubes made in the United States can reach 80MPa

it is worth noting that the temperature of the welding process has a certain impact on the interface strength of the joint, and will reduce the performance of the composite itself. Therefore, the goal of vacuum brazing of metal matrix composites is to find brazing filler metals with low brazing temperature. The commonly used vacuum brazing filler metals abroad are cu-50ni and Ti Zr Cu Ni, and the welding methods are laminate or amorphous foil. The tensile strength of the brazed joint with Ti Zr Cu Ni amorphous foil can be equivalent to that of the substrate

(2) brazing of composite solder for electronic packaging

generally, composite solder for electronic packaging design will not affect the wettability and other process performance parameters of the alloy system in the province, so the cycle from test to application is short, and it will become simple, convenient and practical to apply them directly to production. Electronic packaging, microelectromechanical systems, automotive, aerospace, national defense and other fields will become the primary benefit areas of this technology

in the aerospace and national defense fields, because these service environments often contain heat fluctuations, brazed joints have excellent thermal fatigue performance, which is very important for the application of brazed joints. In order to simulate the demand of brazed joints in aerospace and national defense fields. 2. Different industries for experimental machines: service environment, the temperature limit of thermal fatigue test will be determined as -40 ~ 125 ℃. Figure 4 shows the curve of simulated thermal fatigue test and the structure of brazed joint

Figure 4 simulated thermal fatigue test temperature curve

(3) brazing of ceramics and ceramic matrix composites

ceramics and ceramic matrix composites are excellent structural materials in the high temperature zone of high-performance turbine engines, which can be used in flame stabilizers and turbine blades, and are important materials for future advanced aero engines

brazing can effectively complete the connection between ceramics and metals. However, the strength and heat-resistant temperature of ceramic joint are still far from the requirements of practical application. Therefore, the development of high temperature solder has always been a research hotspot

foreign research institutions try to use new high-temperature solders containing precious metals or based on precious metals Au, PD, Pt or Ag PD to complete the connection between Si3N4 ceramics and metals, but its heat-resistant temperature is generally not more than 700 ℃. In addition, using ni-50ti brazing filler metal to complete the brazing of SiC ceramics and metals, the shear strength of the joint can reach 260mpa at 700 ℃, but its heat-resistant temperature is still not high enough, and the corresponding brazing temperature is as high as 1550 ℃, which is obviously not suitable for the connection between ceramics and ordinary superalloys

at present, Beijing Institute of aeronautical materials has designed Co Ni Fe Cr Ti superalloy brazing filler metal for SiC Ceramic brazing. Using quenched amorphous filler metal thin strip, the three-point bending strength of sic/sic brazed joint can be stabilized between 160 and 184mpa in the temperature range of room temperature to 800 ℃. However, the mechanical properties of the brazed joint with this filler metal still need to be further improved

brazing technology of new aviation structures

1 Brazing of composite laminate air-cooled structure

porous composite laminate air-cooled structure is an advanced cooling structure used in high thrust weight ratio high-performance engines, which is mostly used in combustion chambers and turbine blades. Usually, the porous laminate with complex cooling circuit is compounded into pore structure by brazing technology, and the integrated cooling mode of impact cooling, internal forced cooling and film cooling is adopted to achieve the best cooling effect

2. Vacuum brazing of complex and fine aluminum alloy structural parts

structural parts in modern aviation manufacturing industry are becoming more and more complex and fine. For example, the array unit and mounting base of aluminum alloy brazing structure are often used in the new generation phased array antenna. When the flat slot array antenna is manufactured abroad, the antenna elements are machined by precision numerical control or EDM, and then welded into one by salt bath brazing or vacuum brazing. However, salt bath brazing has the disadvantages of polluting the environment, difficult to clean the residual dissolved salt and unsuitable for closed structures, so it is gradually replaced by vacuum brazing

in recent years, Beijing Institute of aeronautical materials has cooperated with relevant units to study the vacuum brazing of relevant antennas. The vacuum brazing has been used to complete the brazing of multi-layer flat panel slot array antennas. The brazing rate of the brazed antenna is basically 100%, the overall flatness is less than 0.1mm, and the brazing joint is beautiful

the problems to be further studied in the vacuum brazing process of aluminum alloy are the need to develop brazing filler metals with low melting point and study the low temperature vacuum brazing technology suitable for heat-treatment strengthening aluminum alloy. The Al Si Cu Ni re solder developed by Beijing Institute of aeronautical materials has a melting temperature range of 508 ~ 524 ℃. It has good wettability for a variety of aluminum alloys and can be processed into amorphous foil

3. Induction brazing of aviation ducts

induction brazing is widely used in the welding of hydraulic and pneumatic ducts on aircraft. Induction brazing of conduit is divided into fixed brazing and installation brazing. The design principle of the induction brazing device is that it is light in weight and convenient for brazing operation. The shape of the induction ring should make the heating temperature of the workpiece uniform, and at the same time, it can position the conduit

application of brazing technology in the repair of aero-engine components

in the production of aero-engine high-pressure turbine blades and hot end components, because these components have complex structures and are mostly precision castings, "Wang Wanjie said, the qualification rate is often very low, and the components are often scrapped because of small defects such as sand holes, pores, cracks and slag inclusions; After working for a period of time, a certain number of qualified parts will always fail due to defects (such as cracks, wear, ablation, etc.). If the defects generated in the production and use process can be repaired so that the parts can be put into use again, the benefits will be very considerable

brazing and some new repair technologies based on brazing are important parts of aero-engine component repair technology

the performance grades of aeroengine bolts repaired by Canadian liburdi company using powder brazing technology are divided into more than 10 grades of blades, such as 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, so as to achieve the same service life as the new blades, and can be used on the active engine. Beijing Institute of Aeronautical Materials successfully repaired the casting crack of the secondary guide vane of a high pressure turbine of an engine by using the large gap brazing technology. The repaired vane has passed the ground test and air flight test, and the effect is good. K417 alloy joint brazed by vacuum arc brazing process in Beijing Institute of Aeronautical Manufacturing Engineering has excellent mechanical properties at 900 ~ 950 ℃ and can also be used to repair turbine blades

nondestructive testing technology of brazed joints

as new brazed structures will be widely used in aircraft and engines in the future, the nondestructive testing technology for detecting the quality of brazed joints of such structures also needs further research. For the structure where one side of the weld is plane or approximately plane, ultrasonic C-scan can be used to detect defects such as non welding and pores in the weld. Eddy current testing technology has been used to detect the distribution of solder in brazed honeycomb, while penetration testing technology has been used to detect the welding of the outer edge of the weld. In recent years, China has also carried out research on the nondestructive testing of brazed joints, such as using ultrasonic C-scan to detect the brazed honeycomb sealing ring, brazed radar slot array antenna, surface welds of porous laminates, etc., which has achieved good testing results, but no suitable testing method has been found for the internal welds of multilayer structures

the development of new materials and the design requirements of new high-performance aerospace structures provide a broad application space for brazing technology, and at the same time, it puts forward great challenges. In fact, the connection of many new materials, such as high-temperature structural materials and aviation composite solder, is basically still blank, and many technical problems need to be further studied and solved. (end)

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