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Silver based brazing materials mainly form different series of brazing materials by adding some other alloy elements on the basis of silver copper and other alloys. Alloy elements affect silver based brazing alloys in different ways.
01
Element: Zn
The addition of Zn in the Ag-Cu-Zn ternary system forms a system with good plasticity and strength α One (Cu Zn) and α-- (Ag Zn) phase, high strength, medium plasticity β Phase, Others β、γ、η、ε Equibrittle phase. It can reduce the melting point, improve the wettability of Cu, Al, Fe, Ni, and enhance the alloy's resistance to sulfide corrosion. Excessive content can lead to an increase in brittle phases, making it difficult to process, and the Zn content generally does not exceed 40wt%.
02
Element: Mn
Improve the plasticity and high-temperature strength of silver based brazing materials, reduce melting point, improve wetting performance, do not affect the plasticity of the brazing materials, have secondary deoxidation effect, improve the wettability of the brazing alloy to stainless steel and titanium alloy, and increase the strength of the brazing joint.
03
Element: Ni
Improve the wettability of silver based brazing materials on stainless steel and hard alloys, improve the plasticity of brazing joints, and increase the connection strength of brazing joints by increasing the spreading area. It can improve the uniformity of the brazing material and the corrosion resistance and thermal strength of the brazing joint, but it can also increase the liquidus temperature of the brazing material.
04
Element: Sn
Significantly reduce the solid-liquid phase temperature of AgCuZn ternary alloy, narrow the temperature range, improve the flowability of solder, improve wetting performance, and joint strength. Add 2-5wt.% The microstructure of tin alloy is mainly composed of Cu rich phase, CuZn compound phase, Cu5.6Sn compound phase, Cu40.5Sn11 compound phase, and Ag precipitated phase. After adding excessive Sn element, coarse dendrites are formed, which increases the brittleness of the solder.
05
Element: In Ga
Significantly reduce the melting temperature of Ag Cu Zn system, improve wettability, mechanical properties of brazing seam, and microstructure of brazing material. Ga can form solid solutions with Ag, Cu, and Zn, while Cu Ga forms a peritectic binary state diagram. Ga can dissolve 17.5wt% in Cu, forming a single-phase solid solution with good plasticity and processability. But excessive Ga makes the Ag-Ga alloy brittle, making it difficult to add T. The research results of Nanjing University of Aeronautics and Astronautics show that adding 3wt.% Ga can reduce the solidus and liquidus of Ag Cu Zn solder by 52 ℃ and 68 ℃ respectively; Adding 2.0wt.% In to a Ga content of 3.0wt.% can reduce the solidus of Ag-Cu-Zn solder by 81 ℃ and the liquidus by 140 ℃. As the content of Ga and In increases, the overall wettability of the solder shows an upward trend, and the trend of the solder spreading on red copper and brass is consistent. The spreading area of silver based brazing materials containing Ga and In on red copper and brass increased by about 60% compared to silver based brazing materials without Ga and In, and the spreading area of brazing materials with the same content on brass was greater than that on red copper. The best spreading effect is achieved when it contains 3.0wt.% Ga and 1.5-2.0wt.% steel.
06
Element: Pd
Increase the melting temperature and reduce the diffusion of brazing alloy to the substrate.
07
Element: P
It can greatly reduce the melting temperature, reduce the surface tension between the liquid solder and the specimen, and improve the wettability and flowability of the solder. At the same time, the overflow, filling performance, and mechanical properties of brazing all decrease. Microstructure analysis shows that the microstructure of AgCuZnSn alloy is mainly composed of CuZn compound phase, Cu5.6Sn compound phase, and Ag precipitation phase. AgCuZnSn brazing alloy is added with Р Afterwards, a black gray Cu3P compound is generated.
08
Element: Zr
Capable of pinning grain boundaries and subgrain boundaries, refining grains, suppressing the effect of Ag precipitation during heat treatment, enhancing matrix strength, without significantly reducing conductivity and thermal conductivity。
09
Element: Al
Reduce the melting point, increase the high-temperature oxidation resistance and salt spray corrosion resistance of the brazing alloy.
10
Element: Si
Significantly reduce the melting temperature of Ag Cu Pd.
11
Element: Li
Improve fluidity and wettability.
12
Element: Cd
It can significantly reduce the melting point of the alloy, narrow the melting temperature range, and improve the brazing process performance.
13
Element: Re
Improve the wetting performance of the solder and refine the grain size, prevent silver based solder oxidation during the brazing process, and purify the grain boundaries of the fiber joints, thereby improving the fatigue strength of the fiber joints. Adding trace amounts of rare earth can refine the microstructure of the solder, inhibit the growth of intermetallic compounds, make the distribution of intermetallic compounds more uniform, and improve the wettability of the solder. However, as the rare earth content increases, the wettability of the solder decreases. There is no significant effect on the melting temperature of Ag Cu Ti solder, but it can significantly improve the wettability and microhardness of the solder.
