Development Status and Future Prospects of Space Aluminum Alloy Welding Wire
1. Aluminum alloys have the characteristics of high specific strength, good manufacturing processability, and low cost, and are the preferred structural materials for aerospace products. Carrier rocket tanks, satellite tanks, and tactical missile shells are made of aluminum alloys. Aluminum alloy welding wire is a filler material necessary for aluminum alloy welding, and it is one of the factors that determine the quality of the weld. It plays an important role in aerospace aluminum alloy welding production.
Different aluminum alloys need different welding wires. The corresponding relations between aluminum alloys used in China's space industry and welding wires are shown in Table 1. The main aerospace aluminum alloy wire is BJ-380 series and 5B06 wire, which is used for the welding production of rocket tanks, satellite tanks and tactical missile shells.
BJ-380 series welding wire consists of BJ-380, BJ-380A and BJ-380B. BJ-380 welding wire was developed by Institute of Aerospace Materials and Technology and Beijing Nonferrous Metals Co., Ltd. for 2A14 aluminum alloy in the 1960s. The welded joint has good room temperature and low temperature performance, and basically solved the welding problem of 2A14 alloy. However, the welding seam of BJ-380 welding wire has a problem of “storage crackingâ€. In the 1980s, the BJ-380A welding wire with better crack resistance and “storage crack†was developed by the Institute of Aerospace Materials and Technology and Beijing Nonferrous Metals Co., Ltd. However, the low temperature performance of BJ-380A welding wire is poor, and it can not be used for low temperature tank welding production. For this reason, BJ-380 welding wire welding low temperature tank is still used, and BJ-380A welding wire is used to weld the room temperature tank. In the ground equipment thick plate 2A14 alloy MIG welding production, BJ-380, BJ-380A welding wire were found welding cracks, Aerospace Materials and Technology Research Institute and Beijing Nonferrous Metals Co., Ltd. again developed a suitable BJ- suitable for heavy plate 2A14 alloy MIG welding. 380B welding wire.
This article summarizes the current status of BJ-380 series and 5B06 welding wire, and forecasts the development direction of space aluminum alloy welding wire.
2 status
1) Production status
The production process of aluminum alloy welding wire is: casting - suede - extrusion - drawing (multiple) - annealing (multiple) - oil seal (or surface brightening) - packaging. Welding wire is available in two ways: (1) in a semi-rigid state, with surface oil seals, and must be pickled before welding; (2) in a semi-rigid state, with a bright surface, without pickling before welding.
The oil seal must be pickled before welding to remove surface oil and oxide film. Generally suitable for manual welding, used for automatic welding when welding quality is not easy to guarantee, prone to weld porosity, welding inclusion defects. There are many pits on the surface of pickled wire from the microscopic view, with corrosion products, and it is easy to absorb moisture. Figure 1 is a photograph of the acid pickling surface and bright surface of the wire, which clearly shows the bad condition of the pickling surface, while the bright surface is It has obvious advantages. Pickling welding wire can be used to remove surface pit deposits by using scraping method to ensure weld quality. Because the welding wire must be mounted on the wire feeder of the welding machine in automatic welding, the surface scraping after pickling is very difficult, and the pickling welding wire is not recommended for automatic welding. The use of bright welding wire for manual welding eliminates pre-weld pickling and scraping, which is more convenient.
The shelf life of oil seal wire is long-term, and the shelf life of bright wire is generally 1 year. Expired bright wire can be used as pickling before welding.
BJ-380 welding wire because Ti, Zr content exceeds the theoretical solid solubility in aluminum, easy to produce Ti, Zr segregation, welding wire production yield is very low. The composition of BJ-380A, BJ-380B and 5B06 welding wire is reasonable, and the production rate of welding wire is normal. All wire specifications are supplied in the form of discs. The bright wire φ1.2, φ1.6, φ2.4 is supplied in disc form, and φ3.0, φ4.0, φ5.0 are supplied in straight wire.
2) Application
2A14 alloy is currently the main structural material of China's carrier rocket tanks, with a total of three kinds of welding wire, 5A06 alloy used for part of the tank main structural materials, with welding wire 5B06, application conditions are shown in Table 3.
BJ-380 welding wire production to solve the welding problem of 2A14 aluminum alloy, is China's previous generation of space aluminum alloy welding wire, to ensure the aerospace aluminum alloy welding production, but it also has some problems, mainly as follows: (1) welding wire Ti, Zr The components are easy to segregate, and the qualification rate of the welding wire is low, and the welding defects may be caused at the segregation sites of Ti and Zr. (2) Inclusions are likely to be present in the welding wire, causing blackening of the weld surface and dirt; (3) The hydrogen content of the welding wire is high. Prone to weld porosity. In order to improve the BJ-380 welding wire, BJ-380A and BJ-380B welding wire have been developed. The current production and application are relatively stable. When the BJ-380A welding wire is used to weld the 2A14 alloy, welding cracks sometimes occur at the welding site. This crack is a liquefaction crack and must be welded. Exclude, otherwise it will reduce the reliability of the tank. Since the low temperature performance of the BJ-380 welding head is better than that of the BJ-380A welding wire, the BJ-380 welding wire is still used in the carrier rocket cryogenic tank. 5B06 welding wire application is relatively stable and mature. The problems in production are mostly pores and inclusions.
3 Outlook
In order to improve the quality of welding, for current mature welding wire, such as 5B06, BJ-380A and BJ-380B welding wire, the focus should be on solving the problem of hydrogen content and inclusions, and developing low-hydrogen and high-purity welding wire.
The common welding defect in aerospace aluminum alloy welding is the porosity of the weld seam. According to data, the porosity of the weld seam accounts for more than 70% of all defects. The over-standard porosity repair welding will bring many new defects, such as the use of BJ-380A welding wire. Repair welding 2A14 alloy often appears liquefied cracks, showing the importance of controlling weld porosity. There are many factors affecting the porosity of the weld. Except for the process factors and the factors of the parent metal, the hydrogen content of the welding wire is an important factor. The hydrogen in the welding wire will directly enter the weld pool to form the weld porosity. For this reason, it is very important to manufacture low-hydrogen welding wire. Generally, the hydrogen content should be controlled below 0.2ml/100g metal.
Inclusions in the wire will cause inclusions in the weld or dirt on the surface of the weld, which will seriously affect the quality of the weld. Although there are requirements for control of inclusions at low magnifications in welding wire production standards, it is difficult to detect inclusions through low-power tissue inspection in actual work. Controlling the inclusion of aluminum alloy wire should control the two steps of casting and wire drawing. The quality of the ingot determines the wire quality. Bad wire drawing technology can also cause foreign matter to become entangled in the wire to form inclusions.
Although the existing aluminum alloy welding wire has many problems, it basically guarantees the existing model welding production needs. In order to solve the problems existing in production and meet the needs of future model welding production, space aluminum alloy welding wire will be developed in the following aspects.
1) Development brought about by production problems
The problems existing in BJ-380 welding wire are seriously plagued with model production. In order to solve this problem, the Aerospace Materials and Technology Research Institute has newly developed a welding wire suitable for cryogenic tank welding, the brand name is BJ-380C, to replace BJ- 380 welding wire. Table 4 shows the performance of the welded joints of BJ-380C and BJ-380 welding wires. BJ-380C welding wire has good smeltability, wiremaking processability, welding processability, crack resistance, medium compatibility, joint mechanical properties and BJ-380 welding wire is quite equivalent, can completely replace BJ-380 welding wire, need to do further work for the assessment of large test pieces.
2) Development of automatic welding
The degree of welding automation is getting higher and higher in the welding of aerospace aluminum alloy products, and the requirements for welding wire are also correspondingly improved. It is not only required that the stiffness (hardness) of the welding wire be suitable for the wire feeding requirements, but also that the surface quality of the wire must be high, it cannot be a pickling surface, and it should be a bright surface, because the pickling surface will not only cause inclusions and pores due to corrosion products and moisture, In addition, the wire feeding mechanism partially scrapes the welding wire to form a scraping powder, blocking the normal feeding of the wire, and interrupting the welding process. Therefore, bright welding wire will be an important direction for the development of aerospace aluminum alloy welding wire. The Institute of Aerospace Materials and Technology has done more work on the study of wire brightening and has been able to produce BJ-380A, BJ-380B, 5B06 bright welding wire, which can meet the needs of aerospace welding production.
3) Development brought by new materials
With the development of aerospace new models, new aluminum alloy materials will play a major role. If a new generation of launch vehicles is to be made of 2219 aluminum alloy, the world's transportation system will use a more advanced lithium-lithium alloy 2195 or 1460, and the satellite tank will use aluminum-antimony alloy to achieve the lightweight of the spacecraft. Bring new welding wire to the world.
2219 aluminum alloy with welding wire has been developed by the Institute of Aerospace Materials and Technology, and the performance compared with foreign welding wire is shown in Table 5. The newly developed wire has good smelting properties, easy wire making, good crack resistance, and good welding processability. The joint performance meets the design requirements and can be completely used for the welding production of a new generation of rocket tanks.
For the 2195 aluminum-lithium alloy domestic multiple units are engaged in the development of welding wire, have not made breakthroughs in progress, the focus is on crack resistance.
Aluminium-antimony alloys are expected to replace 5A06 alloys for satellite tanks due to their excellent yield strength. Due to the good weldability of aluminum-antimony alloys, it is not difficult to develop welding wires.
4) Development brought by new technologies
The grain size of the domestic welding wire is generally 2-3 grades, and the grain size of the foreign welding wire is 10 grades. The finer the crystal grain of the welding wire, the better the performance of the welding wire and the better the flexibility, the easier the wire feeding, and the brighter the surface is. It is easy to obtain good results. For this reason, the development of fine-grained welding wire using new technologies is the development direction of aluminum alloy welding wire.
The development of nanotechnology will drive the advancement of welding wire manufacturing technology. Nanotechnology can not only obtain fine-grained welding wire, but also can obtain fine-grained welds. From the 2219 aluminum alloy exploration test results, the grain size of the nanowire can reach 10 or more, the grain size of the welded weld is much thinner than the conventional welding wire, and the yield strength of the weld can be significantly improved.
4 Conclusion
Aerospace aluminum alloy wire occupies a special position in the production of aerospace aluminum alloy welding structures. It should recognize the importance of aerospace aluminum alloy welding wire in localization. The civil industry can use it in large quantities or even rely on imported aluminum alloy welding wire. Aerospace aluminum alloy welding wire cannot, easily Being stuck abroad has affected the development of China's aerospace industry. The quality standards for aerospace aluminum alloy welding wire should be perfected as soon as possible, and the wire production process control should be strengthened, such as reducing the hydrogen content in the wire to control the weld porosity, and fully adopting the light wire to meet the requirements of automatic welding, so that the quality of aerospace aluminum alloy welding structure can be guaranteed. The development of aerospace aluminum alloy welding wire should be emphasized, not only that new materials can be equipped with welding wire in a timely manner, but also that the existing welding wire should be improved and the welding quality should be continuously improved.
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