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Study on Vacuum Brazing Technology of Silver-Cu-Based Solder
Vacuum brazing technology is one of the important processes in engine production. It is mainly used for the processing of stator rings, cold air passages of air-cooled blades, fuel main pipes and conduits, and metal honeycomb sealing structures. The welding of fuel pipes, oil inlet pipes, and ventilation pipes in the pipeline system often uses high-frequency vacuum brazing technology. The catheter high-frequency induction vacuum brazing process is divided into two categories: one is fixed vacuum brazing, and the other is installation vacuum brazing. The volume of the engine is large, the installation space of the pipe to be welded is small, and the structure is complicated. Vacuum brazing is often used for on-site welding of the engine. Installation Vacuum brazing refers to vacuum brazing for a certain part of large parts on the assembly site. Its power supply and sensors can be easily moved, and vacuum brazing equipment is mostly portable. After the test run, the engine needs to be disassembled and reassembled several times according to the requirements, so the pipeline needs to be desoldered and vacuum brazed repeatedly.
Vacuum brazing is carried out on the inner duct of the engine, and the brazing material is a copper-based brazing material. Due to the high melting temperature of the brazing filler metal (800~11200 C), and the conduit material is 1Cr8NiT and GH4033 heated by vacuum brazing with drill-based brazing filler metal, and repeated heating for many times, it has a great influence on the base metal; in addition, the brazing filler metal The material and the base metal form a firm bond, resulting in depressions and bulges on the surface of the catheter after desoldering. Reuse will easily lead to unqualified vacuum brazing, and the replacement of the catheter needs to disassemble more parts, so the brazing material is no longer suitable. For desoldering and repeated vacuum brazing. In order to meet the re-use requirements of the original conduit, it is necessary to select a solder that not only meets the requirements of the engine, but also facilitates the desoldering of the conduit.
1.Introduction of solder
Silver-copper-based solder is based on AgCu solder by adding a variety of other alloying elements, such as NiMn, to improve its strength and heat resistance.
2.Pipe specifications include: straight pipe, bent pipe and other shapes. Vacuum brazing materials include: copper-based solder, silver-copper-based solder, brazing flux, argon and other auxiliary materials. The thickness of the solder is 0.9mm and the width is 2.5mm to make a solder ring of corresponding diameter.
3.Vacuum brazing test process
The outer diameters of the tubes selected for the test were: 165, 85, 125, and 22 mm, and the vacuum brazing tests of straight tubes and curved tubes were carried out respectively.
3.1 Vacuum brazing parameter test
The vacuum brazing parameters are gradually explored on the basis of the vacuum brazing parameters of the original solder copper-based solder. Carry out vacuum brazing according to the original catheter vacuum brazing steps. When vacuum brazing, visually observe the color of the 5-7mm section of the exposed catheter is deep bright red, which is the time for the brazing filler metal to reach the temperature. In the field test, through visual inspection of the color, it is judged that the temperature of the vacuum brazing temperature is above 800~900°C, but not above 1000°C. At the same time, in the test, a thermocouple is placed in the conduit, and it should be in contact with the inner wall of the conduit as much as possible. However, due to the short time of high-frequency vacuum brazing and the thermocouple cannot be placed on the solder, the measured data is a reference value, and the actual temperature should be greater than The test temperature value. In the test, the temperature displayed by the galvanic couple is 790°C, so the actual vacuum brazing temperature of the solder is greater than 790°C.
Through visual X-ray detection, the vacuum brazing parameters are preliminarily determined, including: the amount of solder, current, heating time, etc. Understand the weldability of this brazing filler metal by preliminary test, test shows: this brazing filler metal fluidity is better.
3.2 Appearance and X-ray inspection
The welding seam is inspected according to the quality standard of vacuum brazing of the catheter.
Visual inspection: After vacuum brazing, the weld between the bushing and the conduit should be a concave crescent-shaped smooth connection, and the appearance of the weld is 100% continuous, except for some of the conduits that have weld bumps, and the appearance quality meets the requirements.
X-ray detection: The detection index meets the requirements of the original technical standard for vacuum brazing quality, and the conclusion is qualified.
3.3 Metallographic examination
Dissect along the axial direction of the welded conduit, and carry out metallographic inspection: the total length of vacuum brazing of each conduit should not be less than 3mm. 0.02mm maximum 02mm, evenly formed brazing joints, indicating that the fluidity of the brazing material and the effect of filling the gap are better.
3.4 Desoldering and repeated vacuum brazing tests
On the basis of the vacuum brazing test and the qualified inspection, the catheter desoldering and repeated vacuum brazing tests were carried out. The desoldering heating parameters refer to the vacuum brazing parameters. When the vacuum brazing temperature is reached, the induction device is separated from the catheter. In the test: the catheter does not melt when desoldering, and the surface quality of the catheter is better after desoldering. That is, the desoldering effect is better. After desoldering, the tubes were polished and cleaned and then vacuum brazed again, and the quality of vacuum brazing was better. The test shows that the use of silver-copper-based solder successfully achieves the effect of detachment between the conduits.
In order to determine the influence of the silver-copper-based solder on the matrix, and to investigate the growth of the matrix material grains of the catheter under repeated heating, the grain size detection was carried out. The sample was heated 5 times and 9 times respectively, and the grain size of the sample was checked after dissection. The test showed that repeated heating 9 times with silver-copper-based solder in vacuum brazing had no effect on the matrix.
3.5 Tensile comparison test
In order to further verify the performance of the brazing filler metal, we carried out tensile tests on the tubes after vacuum brazing with copper-based brazing filler metal and silver-copper-based brazing filler metal. It shows that when the quality of vacuum brazing is qualified, the strength of vacuum brazing of the two solders is much greater than that of the parts.
The above tests and related tests show that the vacuum brazing performance of silver-copper-based solder is better, the quality of vacuum brazing for conduit installation meets the requirements, and the desoldering effect is better. It can be used for repeated vacuum brazing to achieve the purpose of the test.
According to the process and parameters obtained from the test, the vacuum brazeability of the solder was reviewed, and various follow-up vacuum brazing tests for conduits were completed, and the parameters were finally confirmed. The process and parameters obtained through the test have been successfully applied to Vacuum brazing of a certain type of engine duct and other parts.
5.1 A certain silver-copper-based solder has better vacuum brazing performance, and its desoldering performance is better than that of the original high-temperature copper-based solder, which meets the needs of vacuum brazing and desoldering for engine conduit installation.
5.2 The process and parameters determined by the vacuum brazing and desoldering process tests for the brazing filler metal conduit can be applied to engine development and repair.
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