Research on new brazing process of dissimilar metals in 6063 aluminum alloy/red copper joint
Abstract: A new brazing process with dissimilar metal for 6063 aluminum alloy/red copper joint was developed. This method uses zinc-aluminum flux cored wire as welding material, combines the characteristics of TIG welding and brazing,and has the advantages of conven- ient operation and high efficiency. The wettability, shear strength and microstructure of the joint were analyzed by comparing with traditional brazing in furnace. The results show that the new brazing process can effectively realize the welding of 6063 aluminum alloy/red cop- per joint,and obtain higher joint shear strength , up to 70.2 N/mm2.
Key words: aluminum copper joint; brazing; flux cored brazing wire; zine aluminum fill- er metal.
Aluminum and copper are widely used in fields such as electricity transmission, heat exchange and daily necessities due to their good electrical and thermal conductivity. Compared with the two, aluminum's electrical and thermal conductivity are not as good as copper.
The market price of aluminum is 1/3 of copper, and the density of aluminum is only 1/3 of copper.
Without considering mechanical properties and electrothermal properties, the cost of aluminum materials for the same components is 1/9 of copper materials. Therefore, people use the technology of "substituting aluminum for copper" in many industries to reduce production costs, such as the preparation of microelectronic devices, energy equipment, hybrid vehicle batteries and energy batteries." There are many ways to connect aluminum to copper, ranging from process and Starting from different aspects such as materials, fusion welding and brazing can be used. Among them, fusion welding of aluminum/copper joints has high production efficiency and beautiful shape, but the joints are brittle, low in strength and prone to cracks; the brazing method is strictly controlled. Under the premise of improving the solder composition and brazing process, copper/aluminum joints with excellent performance can be obtained. Therefore, brazing is a promising copper-aluminum connection technology. However, the low production efficiency of traditional brazing methods is an obstacle to its promotion. Big problem.
This experiment adopts a new brazing process, which uses flux-cored brazing wire as the welding material, flame as the heat source, and tungsten argon arc welding operation method, in order to achieve efficient connection of the 6063 aluminum alloy/red copper joint.
Test materials and methods:
The test plate materials used in this test are 6063 aluminum alloy and red copper. The solder materials are Zn75Al25 and Zn92AI8, two zinc-aluminum flux-cored brazing wires, and zinc-aluminum solid core solder with corresponding components. The fluxes are all CsF-AlF, which is a medium-temperature non-corrosive flux.
From the analysis of the test results, the wettability of the flux cored brazing wire solder on 6063 aluminum alloy and copper is not much different from that of the solder covering the flux. This is due to the lower melting point of the zinc-aluminum alloy. After melting quickly at high temperature, the flux liquefies in time and effectively removes the surface oxides of the base metal, ensuring the wetting ability of the solder to the base metal. Compared with Zn92Al8, Zn75Al25 has better wettability whether on 6063 aluminum alloy plate or copper plate. Both can spread well on 6063 aluminum alloy. However, the wettability on red copper is average. The spreading area of Zn75Al25 is about 50mm, which is acceptable, while that of Zn92Al8 is only about 30mm, which can easily cause defects during brazing. It can be seen that as the zinc content increases, the wettability of the solder on copper becomes worse. This is because in addition to surface tension, the factors that affect the wettability between the liquid solder and the base metal are more importantly the relationship between the solder and the base metal. The aluminum and zinc elements in the solder will interact with each other. The copper base metal reacts to form intermetallic compounds. The spreadability of zinc-aluminum solder on copper is related to the form and amount of intermetallic compounds produced. When the aluminum content is low, copper-zinc intermetallic compounds will be generated, which have a high melting point. When they are generated, they will grow in dendrites and shoots, which will hinder the spread of liquid solder.
It can be seen from the test results that when brazing 6063 aluminum alloy/red copper joints with different solders, the shear strength of the joints obtained by the new brazing process is greater than that obtained by the traditional flame brazing method. The shear strength of the joint obtained by using flux-cored brazing wire Zn75Al25 is the highest, which is 70.20 N/mm2.
From a process analysis, when the traditional brazing process is used for furnace brazing, the brazing filler metal and flux are laid on the test plate in advance. After the brazing filler metal is melted at high temperature, it relies on its wettability to the base metal to spontaneously Flow into the brazing seam to complete the brazing connection. During this process, factors such as the surface quality of the base metal, the placement level of the test plate, and the brazing seam gap will all affect the welding quality. Due to the poor wettability of Zn92Al8 on copper, the shear strength of the joint is only 26.96 N/mm, and defects such as partial lack of fusion of the joint are prone to occur. The new brazing process uses manual wire filling, which is easy to operate and is similar to the operation of argon arc welding in the fusion welding method. Therefore, it can effectively avoid the effects of brazing seam gaps and other effects, and form a plump and beautiful weld. Since filling wire and adding flux are performed simultaneously, the ratio of solder and flux is scientifically fixed, which also reduces welding defects caused by improper operation. Therefore, in terms of process methods, the new brazing process has better flexibility, stability and reliability than traditional furnace brazing.
From the analysis of brazing materials, the shear strength of joints using Zn75Al25 solder is higher than that of Zn92Al8 solder. On the one hand, this is because the wetting performance of Zn75A125 on 6063 aluminum alloy and copper is better than that of Zn92Al8. During welding, the solder It is easier to flow and wet in the brazing seam; on the other hand, the shear strength of the joint is the macroscopic manifestation of the microstructure of the brazing seam, and further observation and analysis of the microstructure of the joint is required.
Conclusion:
For solder materials of the same composition, the 6063 aluminum alloy/copper joint obtained by the new brazing process has a finer and denser structure and higher shear strength than the joint brazed in a traditional furnace; Zn78A122 solder material on copper and aluminum The wettability and shear strength of the joint are higher than those of Zn92AI8 solder joint.
The structure of the 6063 aluminum alloy/copper joint using the new Zn75Al25 brazing process on the aluminum side of the brazing seam is a white network distribution of precipitated α wrapped with black (ax+βzm) eutectic; the structure on the copper side is copper-zinc Aluminum solid solution interface compound, white massive βz structure and dendritic structure, and the rest are a large number of black (ax1+βzm) eutectic.
The new brazing process can effectively realize the welding of 6063 aluminum alloy/red copper joints, with easy operation, high welding efficiency, and high joint shear strength, up to 70.2 N/mm2.
