A cadmium-free low-silver solder

Abstract

The application discloses a kind of cadmium-free low silver brazing filler metal.The brazing filler metal is made of 6.0-8.0% Ag, 39.0-43.0% Zn, 13.0-14.5% Sn, 0.05-0.1% In, 0.05-0.1% Ga, 2.5-3.5% Ni, 0.005-0.01% Be, 0.0001-0.0005% nanometer cadmium telluride and the balance of Cu by mass percentage ratio.The solidus temperature of the brazing filler metal is less than or equal to 680 DEG C, and the liquidus temperature is less than or equal to 745 DEG C.When brazing red copper-Q235 steel, red copper-brass, brass-stainless steel with commercially available FB102 flux, the shear strength of the brazed joint is better than that of the existing BAg12CuZn(Si) brazing filler metal and BAg5CuZn(Si) brazing filler metal.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of brazing materials of metal materials, and particularly relates to a cadmium-free low-silver brazing filler metal. BACKGROUND

[0002] The BAg20CuZn(Si) brazing filler metal recommended in the existing document GB / T 10046-2018 "Silver Brazing Filler Metal" has a melting temperature range of a solidus of 690 DEG C and a liquidus of 810 DEG C, and is one of the silver brazing fillers that are most welcomed by brazing filler users and have the highest cost performance in the market. However, the 20%+ / -1% Ag content of the brazing filler metal, in the case that the price of the precious metal silver is rising, silver brazing filler users are facing fierce competition, and the requirement for the material cost is continuously reduced to improve the product competitiveness, the research and development of cadmium-free low-silver silver brazing filler metal with lower silver content and better brazing filler metal performance has been a hot topic for the technical personnel in the related manufacturing industry.

[0003] It is found that the BAg5CuZn(Si) brazing filler metal with lower silver content in GB / T 10046-2018 "Silver Brazing Filler Metal" has a melting temperature range of a solidus of 820 DEG C and a liquidus of 870 DEG C, and the BAg12CuZn(Si) brazing filler metal has a melting temperature range of a solidus of 800 DEG C and a liquidus of 830 DEG C. The above two low-silver brazing fillers provide a cost reduction option for users, but the solidus and liquidus temperatures of the brazing filler metal are higher than 800 DEG C, which is easy to cause "overburning" and "softening" of copper and copper alloy, and thus is not conducive to the brazing of copper and copper alloy structures.

[0004] The inventors found through literature retrieval that there are only a few examples of technical information about new low-silver brazing filler metals in published Chinese patent documents. For example, document CN 115533365A reports a cadmium-free low-silver brazing filler metal with a mass percentage composition of 8.0-10.0% Ag, 38.0-42.0% Zn, 6.0-10.0% Sn, 1.5-2.5% In, 1.5-2.5% Ga, 1.5-2.5% Ni, 0.0001-0.0005% nano-HfC, 0.0001-0.0005% nano-ZrC, and the balance Cu. The solidus temperature of the brazing filler metal is ≤700°C, and the liquidus temperature is ≤750°C. Document CN 116871736A reports a cadmium-free low-silver brazing filler metal and a method for preparing the same. The cadmium-free low-silver brazing filler metal is composed of 4.0-5.0% Ag, 40.0-45.0% Zn, 11.0-13.0% Sn, 0.5-1.5% In, 0.5-1.5% Ga, 0.5-1.5% Ni, 0.01-0.05% nano-CeO2, 0.01-0.05% nano-Y2O3, and the balance Cu. The solidus temperature of the brazing filler metal is ≤735°C, and the liquidus temperature is ≤780°C. The Ag content of the above two low-silver brazing filler metals is less than or equal to 10%, but both contain a high content of In and Ga elements, and the cost is still relatively high.

[0005] A large number of studies have shown that the common feature of reducing the melting temperature (such as the solidus temperature and the liquidus temperature) of cadmium-free silver brazing filler metals is to add at least one or more low-melting-point elements such as Sn (melting point 231.9°C), In (melting point 156.6°C), Ga (melting point 29.76°C), Li (melting point 180.5°C), and alloy elements such as Ni that can reduce the melting point of the brazing filler metal. Since In, Ga, and Li are “rare elements”, the annual production worldwide is also very limited, and the price of In and Ga is comparable to or higher than that of silver; due to the rapid development of new energy vehicles, the price of Li has also skyrocketed to 3 million yuan / ton (30,000 yuan / kg) in recent years, which is much higher than that of Cu (about 80 yuan / kg), so when the In and Ga content is higher than 1.5 wt.%, the value of batch production and application will be greatly reduced; the price of Sn element is not high relative to Ag and the reserves are relatively abundant, but a large amount of Sn addition can form hard and brittle intermetallic compounds Cu6Sn5, causing “processing difficulties” of silver brazing filler metals. According to literature reports, the known high-tin brazing filler metals have a Sn addition amount of 9.5-10.5% in BAg60CuSn brazing filler metal and generally 1.5-2.5% in Ag-Cu-Zn-Sn series brazing filler metals, and only a few types such as BAg56CuZnSn have a Sn addition amount of 4.5-5.5% (see GB / T 10046-2018 “Silver Brazing Filler Metal”, page 4, Table 1 (continued)).

[0006] Although the literature CN 115533365A reports that the addition amount of Sn can be as high as 10.0%, the solid phase line temperature of the obtained cadmium-free low-silver solder is ≤700℃, and the liquid phase line temperature is ≤750℃; the literature CN 116871736A reports that the addition amount of Sn can be as high as 11.0%~13.0%, the solid phase line temperature thereof is ≤735℃, and the liquid phase line temperature is ≤780℃, which is close to or even better than the melting temperature of BAg20CuZn(Si) solder, and basically meets the brazing requirements of copper and copper alloy structures.

[0007] However, since the above-mentioned cadmium-free low-silver solder adds a high content of In and Ga elements, in addition to the high cost factor, In and Ga belong to "rare metals", and both the earth's reserves and the world's annual output are very small, which is not suitable for large-scale use. Therefore, how to use the abundant Sn element to replace In and Ga, and add In and Ga elements as "trace elements" to achieve the purpose of reducing the melting temperature of the new solder and improving the strength of the solder joint still needs a lot of exploration and research. SUMMARY

[0008] The purpose of the present application is to provide a cadmium-free low-silver solder, the Ag content of which is in the range of 6.0%~8.0%, and the liquid phase line temperature is ≤750℃, which is suitable for brazing materials such as red copper-brass, red copper-stainless steel, brass-stainless steel, etc., thereby meeting the needs of solder users to reduce costs, improve product quality, and enhance the market competitiveness of products.

[0009] The technical solution to achieve the purpose of the present application is as follows:

[0010] A cadmium-free low-silver solder, the proportion of which is as follows: 6.0%~8.0% of Ag, 39.0%~43.0% of Zn, 13.0%~14.5% of Sn, 0.05%~0.1% of In, 0.05%~0.1% of Ga, 2.5%~3.5% of Ni, 0.005%~0.01% of Be, 0.0001%~0.0005% of nano cadmium telluride (CdTe), and the balance of Cu.

[0011] Further, the particle size of the nano cadmium telluride is 100nm~150nm.

[0012] The cadmium-free low-silver solder described in the present application uses silver plate, cathode copper, zinc ingot, tin ingot, metal indium, metal gallium, and metal nickel according to the component proportion, and is smelted by using a medium frequency smelting process. Before casting, the trace nano CdTe and Be-Cu powder are wrapped with red copper foil, placed in a graphite "bell jar", and quickly inserted into the molten solder liquid, stirred uniformly, and then cast into an ingot. Then, through extrusion and drawing, the required solder wire material is obtained.

[0013] The brazing filler metal of the present application has a solidus temperature of ≤680℃ and a liquidus temperature of ≤745℃. When used in combination with commercially available FB102 flux, the brazed joint has a shear strength superior to that of the existing BAg12CuZn(Si) and BAg5CuZn(Si) brazing filler metals when brazing red copper-Q235 steel, red copper-brass, and brass-stainless steel.

[0014] Comparative analysis and comparison of the current effective version of the EU RoHS 2.0 directive and the current effective version of GB / T 10046-2018 Silver Brazing Filler Metal standard found that the silver brazing filler metal requires that the cadmium element content is not greater than 0.010% (i.e. Cd ≤ 0.010%), and the brazing filler metal of the present application only adds 0.0001% to 0.0005% nanometer cadmium telluride (CdTe), which is equivalent to a maximum amount of Cd element of only 0.000234%, fully meeting the requirements of the RoHS 2.0 directive and the GB / T 10046-2018 standard. DETAILED DESCRIPTION

[0015] Compared with previous studies, the technical solution of the present application creatively solves the following key technical problems:

[0016] (1) It is found that in a cadmium-free low-silver brazing filler metal with a silver content of 6.0% to 8.0%, the addition of a small amount of nanometer cadmium telluride (particle size of 100nm to 150nm) can significantly refine the Cu6Sn5 grains and significantly inhibit the formation of Cu6Sn5, and at the same time, appropriately increasing the Ni content to 2.5% to 3.5% can significantly convert the brittle and hard Cu6Sn5 into a (Cu, Ni)6Sn5 intermetallic compound with better plasticity, so that the brazing filler metal of the present application can be successfully processed into a wire even when the Sn content is as high as 13.0% to 14.5%.

[0017] Although the document CN 115533366A reports that in high-tin copper-phosphorus brazing filler metal, adding trace rare earth metal Sm, metal Yb element and trace nano Sm2O3, nano Yb2O3 oxide can significantly refine the grain of copper-phosphorus brazing filler metal, especially the grain of intermetallic compound Cu6Sn5 and (Cu, Ni)6Sn5, but the maximum particle size of the intermetallic compound (i.e. (Cu, Ni)6Sn5) can only reach ≤5 μm, and the addition amount of Sn in the brazing filler metal can only reach 8.0%-11.0%. However, by using the technical scheme of adding CdTe, the maximum particle size of Cu6Sn5 and (Cu, Ni)6Sn5 can be refined to ≤3 μm, so that the brazing filler metal of the present application can be successfully processed into a wire even if the Sn content is as high as 13.0%-14.5%, which is not achieved by the prior art and has not been reported. In addition, the addition of 13.0%-14.5% Sn content also significantly reduces the melting temperature range of the cadmium-free low-silver brazing filler metal of the present application, from the solidus 820 ℃ and the liquidus 870 ℃ of BAg5CuZn(Si) brazing filler metal to the solidus ≤680 ℃ and the liquidus ≤745 ℃, fully meeting the brazing requirements of copper-containing and copper alloy structures.

[0018] (2) It is found that on the basis of adding trace 0.0001%-0.0005% nano cadmium telluride (CdTe), adding trace Be can utilize the "synergistic effect" of Te and Be elements to make the cadmium-free low-silver brazing filler metal of the present application have excellent plasticity, so the brazing filler metal of the present application is easy to process and does not need to adjust the original equipment and process during extrusion and drawing.

[0019] By optimizing the addition amounts of main component elements, trace alloying elements, nano CdTe and Be elements, it is determined that the addition amounts of In and Ga elements are 0.05%-0.1% and the addition amount of Be element is controlled in the range of 0.005%-0.01%, which are the best.

[0020] It is found that compared with BAg12CuZn(Si) and BAg5CuZn(Si) brazing filler metals, the brazing filler metal has a significant increase in spread area on red copper, H58 brass, Q235 steel and 304 stainless steel, with an increase of more than 10%; the tensile strength (σ b ) and shear strength (τ) are all increased by more than 20%-30%, reaching and exceeding the level of BAg12CuZn(Si) and BAg5CuZn(Si) brazing filler metals, as shown in Table 1.

[0021] The nano cadmium telluride described in the present application can use commercially available products or self-synthesize nano powder by chemical reduction method. The technical scheme of the present application is further described in detail below in combination with specific examples.

[0022] Example 1

[0023] A cadmium-free low-silver soldering material, with a mass percentage ratio of 6.0% of Ag, 43.0% of Zn, 13.0% of Sn, 0.1% of In, 0.05% of Ga, 3.5% of Ni, 0.005% of Be, 0.0001% of nano CdTe, and the balance of Cu.

[0024] The cadmium-free low-silver soldering material obtained by using the above component ratio has a solidus temperature of ≤680℃ and a liquidus temperature of ≤745℃ (both considering measurement errors). The wetting and spreading performance on red copper, H58 brass, Q235 steel and 304 stainless steel is excellent. When flame soldering is used in combination with FB102 flux, the solder joint strength of the following combinations of base materials is as shown in the brackets: red copper-H58 brass (σ b =260±10MPa, τ=255±10MPa), red copper-Q235 steel (σ b =350±10MPa, τ=350±10MPa), H58 brass-304 stainless steel (σ b =360±10MPa, τ=355±10MPa). The solder joint strength of the new soldering material is significantly higher than that of BAg12CuZn(Si) soldering material and BAg5CuZn(Si) soldering material under the same conditions.

[0025] Example 2

[0026] A cadmium-free low-silver soldering material, with a mass percentage ratio of 8.0% of Ag, 39.0% of Zn, 14.5% of Sn, 0.05% of In, 0.1% of Ga, 2.5% of Ni, 0.01% of Be, 0.0005% of nano CdTe, and the balance of Cu.

[0027] The cadmium-free low-silver soldering material obtained by using the above component ratio has a solidus temperature of ≤680℃ and a liquidus temperature of ≤745℃ (both considering measurement errors). The wetting and spreading performance on red copper, H58 brass, Q235 steel and 304 stainless steel is excellent. When flame soldering is used in combination with FB102 flux, the solder joint strength of the following combinations of base materials is as shown in the brackets: red copper-H58 brass (σ b =260±10MPa, τ=255±10MPa), red copper-Q235 steel (σ b =350±10MPa, τ=350±10MPa), H58 brass-304 stainless steel (σ b =360±10MPa, τ=355±10MPa). The solder joint strength of the new soldering material is significantly higher than that of BAg12CuZn(Si) soldering material and BAg5CuZn(Si) soldering material under the same conditions.

[0028] Example 3

[0029] A cadmium-free low-silver solder with a mass percentage ratio of 7.0% Ag, 41.0% Zn, 14.0% Sn, 0.08% In, 0.07% Ga, 3.0% Ni, 0.008% Be, 0.0003% nanometer CdTe, and the balance Cu.

[0030] The cadmium-free low-silver solder obtained by using the above component ratio has a solidus temperature ≤680℃ and a liquidus temperature ≤745℃ (both considering measurement errors). The wetting and spreading performance on red copper, H58 brass, Q235 steel, and 304 stainless steel is excellent. When using a flame soldering method and cooperating with FB102 flux, the solder joint strength of the following combinations of base materials is as follows (the data in the brackets are the solder joint strength): red copper-H58 brass (σ b = 260±10 MPa, τ = 255±10 MPa), red copper-Q235 steel (σ b = 350±10 MPa, τ = 350±10 MPa), H58 brass-304 stainless steel (σ b = 360±10 MPa, τ = 355±10 MPa). The solder joint strength of the new solder is significantly higher than that of BAg12CuZn(Si) solder and BAg5CuZn(Si) solder under the same conditions.

[0031] Comparative Example 1

[0032] A cadmium-free low-silver solder with a mass percentage ratio of 7.0% Ag, 41.0% Zn, 14.0% Sn, 0.08% In, 0.07% Ga, 3.0% Ni, 0.008% Be, and the balance Cu.

[0033] The cadmium-free low-silver solder obtained by using the above component ratio has no change in the solidus temperature and the liquidus temperature of the solder (for example, the solidus temperature ≤680℃ and the liquidus temperature ≤745℃ (both considering measurement errors)), but the processability is significantly decreased. The wetting and spreading performance on red copper, H58 brass, Q235 steel, and 304 stainless steel is also significantly worse than that of the embodiment. When using a flame soldering method and cooperating with FB102 flux, the solder joint strength of the following combinations of base materials is decreased as follows (the data in the brackets are the solder joint strength): red copper-H58 brass (σ b = 250±10 MPa, τ = 245±10 MPa), red copper-Q235 steel (σ b = 340±10 MPa, τ = 335±10 MPa), H58 brass-304 stainless steel (σ b = 345±10 MPa, τ = 335±10 MPa).

[0034] The brazing seam strength of the brazing filler metal of Comparative Example 1 is higher than that of BAg12CuZn(Si) brazing filler metal and BAg5CuZn(Si) brazing filler metal under the same conditions, but is obviously lower than that of Example 1, Example 2 and Example 3.

[0035] Comparative Example 2

[0036] A cadmium-free low-silver brazing filler metal has the following component proportions by mass percentage: 7.0% of Ag, 41.0% of Zn, 14.0% of Sn, 0.08% of In, 0.07% of Ga, 3.0% of Ni, 0.0003% of nano-CdTe, and the balance of Cu.

[0037] The cadmium-free low-silver brazing filler metal obtained by using the above component proportions has a solidus temperature ≤680°C and a liquidus temperature ≤745°C (both considering measurement errors), but the processing performance is significantly decreased. The wetting and spreading performance on red copper, H58 brass, Q235 steel and 304 stainless steel is also significantly worse than that of the examples. When the brazing filler metal is used in a flame brazing manner, the brazing seam strength is decreased (the data in parentheses) when the brazing filler metal is used in combination with FB102 flux and the base materials are the following combinations: red copper-H58 brass (σ b = 250±10 MPa, τ = 245±10 MPa), red copper-Q235 steel (σ b = 340±10 MPa, τ = 335±10 MPa), H58 brass-304 stainless steel (σ b = 345±10 MPa, τ = 335±10 MPa).

[0038] The brazing seam strength of the brazing filler metal of Comparative Example 2 is higher than that of BAg12CuZn(Si) brazing filler metal and BAg5CuZn(Si) brazing filler metal under the same conditions, but is obviously lower than that of Example 1, Example 2 and Example 3.

[0039] Table 1 is comparative data of the spreading performance (spreading area, mm 2 ) and brazing seam strength of Example 1-Example 3, commercially available BAg5CuZn(Si) brazing filler metal and commercially available BAg12CuZn(Si) brazing filler metal. From the data of Comparative Example 1 and Comparative Example 2, it can be seen that the wetting and spreading performance of the brazing filler metal is deteriorated and the mechanical properties of the brazing seam are also significantly decreased when metal Be or nano-CdTe is added alone, which fully shows the significant influence of the “synergistic effect” of metal Be and nano-CdTe on the wetting and spreading performance of the brazing filler metal and the brazing seam strength.

[0040] Table 1

[0041]

Claims

1. A cadmium-free low-silver solder, characterized by comprising, in mass %, The mass percentage ratio is: 6.0%-8.0% of Ag, 39.0%-43.0% of Zn, 13.0%-14.5% of Sn, 0.05%-0.1% of In, 0.05%-0.1% of Ga, 2.5%-3.5% of Ni, 0.005%-0.01% of Be, 0.0001%-0.0005% of nano cadmium telluride, and the balance of Cu.

2. The cadmium-free low silver solder according to claim 1, characterized in that, The particle size of the nano cadmium telluride is 100-150 nm.

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