Development status and future prospect of the hott

Development status and future prospects of aerospace aluminum alloy welding wires

I Aluminum alloy is the preferred structural material for aerospace products because of its high specific strength, good manufacturability and low cost. The carrier rocket tank, satellite tank and tactical missile shell are welded with aluminum alloy. Aluminum alloy welding wire is the necessary filler material for aluminum alloy welding, and it is one of the factors that determine the weld quality. It plays an important role in aerospace aluminum alloy welding production

different aluminum alloys need different matching wires. The corresponding relationship between aluminum alloys commonly used in aerospace and their matching wires in China is shown in Table 1. The main aerospace aluminum alloy welding wires include bj-380 series and 5b06 welding wires, which are used for the welding production of carrier rocket tanks, satellite tanks and tactical missile shells. Table 1 the corresponding relationship between aluminum alloys commonly used in aerospace and their matching welding wires in China

welding wire brand bj-380 series calculate the peel strength 5b064043 al Mn aluminum alloy brand 2A14 5A06 ZL104 3A21

bj-380 series welding wires are composed of bj-380, bj-380a and bj-380b according to the peel force and the width of the knife edge. Bj-380 welding wire was developed for 2A14 aluminum alloy by aerospace materials and Process Research Institute and Beijing Nonferrous Metals Institute in the 1960s. The welded joint has good room temperature and low temperature performance, which basically solves the welding problem of 2A14 alloy. However, the welding seam of bj-380 welding wire has the problem of "storage crack". In the 1980s, bj-380a welding wire with better crack resistance and can solve the "storage crack" was jointly developed by the aerospace materials and Process Research Institute and the Beijing Nonferrous Metals Institute. However, the low-temperature performance of bj-380a welding wire is poor and cannot be used for the welding production of low-temperature storage tanks. Therefore, bj-380 welding wire is still used to weld low-temperature storage tanks, and bj-380a welding wire is used to weld normal temperature storage tanks. In the MIG welding production of 2A14 alloy thick plate of ground equipment, welding cracks were found in bj-380 and bj-380a welding wires. Aerospace materials and Processes Research Institute and Beijing Institute of nonferrous metals once again cooperated to develop bj-380b welding wire suitable for MIG welding of 2A14 alloy thick plate

this paper summarizes the current situation of bj-380 series and 5b06 welding wires, and prospects the development direction of aerospace aluminum alloy welding wires

2 status quo

1) production status quo

the production process of aluminum alloy welding wire is: melting and casting - peeling - extrusion - drawing (multiple times) - annealing (multiple times) - oil seal (or surface brightening) - packaging. There are two ways to supply welding wires: (1) in semi-rigid state, the surface is supplied with oil seal, and pickling is required before welding; (2) It is supplied in semi-rigid state with bright surface, and acid pickling is not required before welding. See Table 2 for the main types of welding wires

the oil seal welding wire must be pickled before welding to remove the oil stain and oxide film on the surface. Generally, it is suitable for manual welding. When it is used for automatic welding, the weld quality is not easy to be guaranteed, and weld porosity and weld inclusion defects are easy to appear. From the microscopic view, there are many pits on the surface of the pickling wire, with corrosion products, which are easy to absorb water. Figure 1 is a photo of the pickling surface and bright surface of the wire, which can clearly see the poor condition of the pickling surface, while the bright surface has obvious advantages. During manual welding with pickling wire, scraping method can be used to remove surface pit attachments to ensure weld quality. During automatic welding, since the welding wire must be installed on the wire feeding mechanism of the welding machine in a disc shape, it is very difficult to scrape the surface after pickling, and pickling welding wire is not recommended for automatic welding. Bright welding wire used for manual welding can save pickling and scraping before welding, which is more convenient

the storage period of oil seal welding wire is long, and the storage period of bright welding wire is generally 1 year. Expired bright welding wire can be used as ordinary welding wire for pickling before welding

bj-380 welding wire is prone to Ti and Zr segregation because the content of Ti and Zr exceeds the theoretical solid solubility in aluminum, and the production yield of welding wire is very low. Bj-380a, bj-380b and 5b06 welding wires have reasonable composition design, and the production yield of welding wires is normal. All welding wire specifications are supplied in disc shape during oil seal, bright welding wire φ 1.2、 φ 1.6、 φ 2.4 supply in disc form, φ 3.0、 φ 4.0、 φ 5.0 supply with straight wire. Table 2 main varieties of aerospace aluminum alloy welding wire

welding wire brand supply status welding wire specification bj-380 surface oil seal semi hard φ 1.2 (disc) φ 1.6 (disc) φ 2.4 (disc) φ 3.0、 φ 4.0、 φ 5.0 bj-380a surface oil seal semi hard surface bright semi hard bj-380b surface oil seal semi hard surface bright semi hard 5b06 surface oil seal semi hard surface bright semi hard

2) application condition

2a14 alloy is the main structural material of Carrier Rocket Tank in China at present. There are three kinds of welding wires. 5A06 alloy is used for the main structural material of some tanks, and 5b06 welding wire is used. See Table 3 for the application. Table 3 application of main welding wires of aerospace aluminum alloy

welding wire brand application object welding method welding wire stability problems in welding production application model bj-380 2A14 low temperature storage tank TIG instability, prone to Ti, Zr segregation, Ti, Zr segregation, inclusions, cracks, pores carrier rocket low temperature storage tank BJ the second transmission mode can not ensure the synchronization of transmission -380a 2A14 normal temperature storage tank TIG stability repair welding sometimes has liquefaction cracks Bj-380b ground equipment MIG stable air hole ground equipment 5b06 5A06 normal temperature tank TIG stable occasional cracks, pores, inclusions, carrier rocket normal temperature tank, satellite tank

bj-380 welding wire production and application solved the 2A14 aluminum alloy welding problem, which is the first generation of aerospace aluminum alloy welding wire in China, ensuring aerospace aluminum alloy welding production, but it also has some problems, mainly as follows: (1) welding wire Ti Zr composition is easy to segregate, the qualification rate of welding wire is low, and the segregation of Ti and Zr may cause welding defects; (2) Inclusions are easy to exist in the welding wire, resulting in blackening and dirt on the weld surface; (3) The hydrogen content of welding wire is high, which is prone to weld porosity. In order to improve bj-380 welding wire, bj-380a and bj-380b welding wires have been developed. At present, production and application are relatively stable. When bj-380a welding wire is welding 2A14 alloy, welding cracks sometimes appear at the repair welding position. Such cracks are welding liquefaction cracks, which must be eliminated, otherwise the reliability of the tank will be reduced. Since the low-temperature performance of the welded joint of bj-380 welding wire is better than that of bj-380a welding wire, bj-380 welding wire is still used in the low-temperature storage tank of the launch vehicle. 5b06 welding wire is the most stable and mature, and the problems in production are mostly pores and inclusions

3 outlook

in order to improve the welding quality, for the mature welding wires, such as 5b06, bj-380a and bj-380b welding wires, the work should focus on solving the problems of hydrogen content and inclusions, and developing low hydrogen high-purity welding wires

the most common welding defect in aerospace aluminum alloy welding is weld porosity. According to the data, weld porosity defects account for more than 70% of all defects. Repair welding of excessive pores will bring many new defects. For example, liquefaction cracks often occur in 2A14 alloy repaired with bj-380a welding wire, which shows the importance of controlling weld porosity. There are many factors affecting weld porosity. In addition to process factors and base metal factors, the hydrogen content of welding wire is an important factor. Hydrogen in welding wire is 4 The radiator (condenser) of the refrigeration unit of the cold and heat shock test machine should be maintained regularly and kept clean The dust sticky condenser will cause the high-voltage switch of the compressor to trip and produce a false alarm, which will directly enter the molten pool to form weld pores. Therefore, 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 welding wire will cause inclusions in the weld or dirt on the weld surface, which will seriously affect the welding quality. Although the welding wire production standard has the requirements of macrostructure inspection to control inclusions, it is difficult to detect inclusions through macrostructure inspection in practical work. Casting and wire drawing should be controlled to control the inclusion of aluminum alloy welding wire. The quality of ingot determines the quality of welding wire. Poor wire drawing process will also lead to the inclusion of foreign matters wrapped in the welding wire

although there are many problems with the existing aluminum alloy welding wire, it basically ensures the demand of the existing model welding production. In order to solve the problems existing in current production and meet the needs of future welding production, aerospace aluminum alloy welding wires will be developed in the following aspects

1) development brought about by production problems

bj-380 welding wire has serious problems that currently plague the model production. In order to solve this problem, the aerospace materials and Technology Research Institute has newly developed a new welding wire suitable for low temperature tank welding. B. in the experiment, the brand of welding wire connected after sudden power failure is bj-380c to replace bj-380 welding wire. Table 4 shows the performance comparison of the welded joints of bj-380c and bj-380 welding wires. Bj-380c welding wire has good melting, wire making, welding, crack resistance and medium compatibility. The mechanical properties of the joint are equivalent to that of bj-380 welding wire, and it can completely replace bj-380 welding wire. The work that needs to be done further is the examination of large test pieces. Table 4 properties of welded joints of bj-380c and bj-380 welding wires

welding wire brand bi-380c

bj-380 crack sensitivity K1 (%) 6.5 7.2 K2 (%) 03.4 σ B (MPA) room temperature 324337 － 196 ℃ 413 412 － 253 ℃ 445446 δ (%) room temperature 4.7 7.4-196 ℃ 5.4 5.2-253 ℃ 2.9 2.8

2) development brought about by 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 wires are also correspondingly improved. Not only the stiffness (hardness) of the welding wire is required to meet the wire feeding requirements, but also the surface quality of the welding wire is required to be high. It should be a bright surface instead of a pickling surface, because the pickling surface will not only bring corrosion products and moisture, resulting in inclusions and pores, but also the wire feeding mechanism will scrape the welding wire locally, forming scraping powder to block the normal wire feeding and interrupt the welding process. Therefore, bright welding wire will be an important development direction of aerospace aluminum alloy welding wire. The aerospace materials and Processes Research Institute has done a lot of work on the research of welding wire brightening, and has been able to produce bj-380a, bj-380b, 5b06 bright welding wires, which can meet the needs of aerospace welding production

3) development brought by new materials

with the development of new aerospace models, new aluminum alloy materials will play a major role. If 2219 aluminum alloy is proposed to be used in the new generation of carrier rockets, the storage tank of the space shuttle transportation system will use more advanced aluminum lithium alloy 2195 or 1460, and the satellite storage tank will use aluminum scandium alloy to realize the lightweight of spacecraft, which will certainly drive the advent of new welding wires

2219 aluminum alloy matching welding wire has been developed by the aerospace materials and process research institute. The performance compared with foreign welding wires is shown in Table 5. The newly developed welding wire has good melting property, easy wire making, good crack resistance, good welding processability, and the joint performance meets the design requirements. It can be completely used in the welding production of the new generation carrier rocket tank. Table 5 properties of 2219 aluminum alloy welding wire

welding wire brand 25 ＃ 720 us 2319 crack sensitivity K1 (%) 1.8 5.3 3.8 K2 (%) 0 σ B (MPA) room temperature

2.6mm 313 298264 6.0mm 293 270 287-196 ℃ 2.6mm 371326320 6.0mm 345319 352-253 ℃ 2.6mm 485 440 - δ (%) room temperature 2.6mm 4.5 2.8 4.6 6.0mm 4.0 3.2 4.2 - 196 ℃ 2.6mm 4.3 3 4.0 6.0mm 3.5 2.9 4.0 - 253 ℃ 2.6mm 2.8 2.1 - small and large pore sensitivity

many domestic units are carrying out welding wire development work for 2195 aluminum lithium alloy, and no breakthrough has been made, focusing on crack resistance

aluminum scandium alloy is expected to replace 5A06 alloy for satellite storage tank with its excellent yield strength. Because aluminum scandium alloy has good weldability, it should not be difficult to develop welding wire

4) development brought about by new technology

the grain size of domestic welding wires is generally grade, while that of foreign welding wires is grade 10. The finer the grain size of welding wires, the better the performance and flexibility of welding wires, the easier the wire feeding and the brighter the surface