Low-melting-point aluminum-based brazing filler metal with low Cu content and preparation method and application of low-melting-point aluminum-based brazing filler metal

Abstract

The invention relates to the technical field of aluminum-based brazing filler metal for new energy automobiles, and provides low-Cu-content low-melting-point aluminum-based brazing filler metal and a preparation method and application thereof.The low-Cu-content low-melting-point aluminum-based brazing filler metal is prepared from, by weight, 7.5%-11% of silicon, 5.0%-10.0% of copper, 2.0% of nickel, 0%-2.0% of magnesium, 0%-4.0% of tin, 0%-6.0% of zinc and the balance aluminum. Wherein the weight percentage of at least one of magnesium, tin and zinc is larger than 0%. The prepared brazing filler metal is good in spreadability and wettability, and the average spreading area of the brazing filler metal per unit mass is larger than 7.5 cm < 2 > / g. According to the brazing filler metal, the requirement for the low melting point is met, meanwhile, a vacuum environment is not needed during brazing of the brazing filler metal, smelting equipment and brazing equipment are simple in structure, convenient to operate, low in manufacturing cost and capable of being produced on a large scale, and the content of Cu is reduced by adding Zn, Mg, Sn and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum-based solders for new energy vehicles, and in particular relates to a low-Cu content, low-melting-point aluminum-based solder, a preparation method, and applications thereof. Background Art

[0002] Since the beginning of the 21st century, with the development of a low-carbon economy, there has been a clear trend toward lightweighting everyday transportation, with aluminum replacing steel. Aluminum alloys, with their light weight, high strength, corrosion resistance, excellent thermal and electrical conductivity, good processability, and recyclability, have become ideal materials for applications in aviation, automotive, electronics, and other fields. The growing demand for lightweighting in the automotive, aerospace, and refrigeration industries has led to a surge in aluminum alloy usage. For example, aluminum alloys account for over 70% of all-aluminum vehicles, and approximately 15% to 20% of these aluminum alloy structures require brazing. The use of low-melting-point brazing filler metals enables reliable welding of thin-walled structures, precision piping (such as air conditioning condensers), and dissimilar materials (such as aluminum-titanium), driving the development of high-end manufacturing for applications such as heat pumps for new energy vehicles and aircraft engine components.

[0003] Traditional aluminum alloy brazing filler metals (such as Al-Si eutectic filler metals) generally have melting points above 577°C, requiring brazing temperatures of around 600°C, close to the solidus temperature of the aluminum alloy parent metal (for example, the solidus temperature of 6061 aluminum alloy is 582°C). This can easily lead to problems such as overburning, grain coarsening, and dissolution of the parent metal. Therefore, the melting point of the designed brazing filler metal must be below 550°C. Furthermore, traditional brazing filler metals rely on precious metals (such as Ag), rare elements (such as Ge), or copper, resulting in high costs. This is because copper is a relatively expensive element, and excessive addition directly increases raw material costs. Furthermore, excessive copper forms more Al2Cu and Q-Al5Cu2Mg8Si6 phases, increasing melt viscosity, affecting fluidity, and leading to casting defects such as shrinkage cavities and segregation. Heat treatment (such as solution treatment followed by aging) is required to improve performance, but this increases subsequent processing costs. In summary, research on low-melting-point aluminum alloy brazing filler metals is of great significance and has significant potential for development. Therefore, it is urgent to design a low melting point aluminum-based brazing filler metal with low Cu content to solve the above-mentioned problems. Summary of the Invention

[0004] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a low-Cu content, low-melting-point aluminum-based solder, a preparation method and an application thereof. The low-Cu content, low-melting-point aluminum-based solder has low cost, high strength, high toughness, good spreadability and low melting point, and can prevent overburning and corrosion of the base material.

[0005] In order to solve the above technical problems, the present invention provides a low melting point aluminum-based brazing filler metal with low Cu content, which is made of the following raw materials in the following weight percentages: Silicon 7.5%-11%, copper 5.0%-10.0%, nickel 2.0%, magnesium 0%-2.0%, tin 0%-4.0%, zinc 0%-6.0%, and the balance is aluminum, wherein the weight percentage of at least one of magnesium, tin and zinc is greater than 0%.

[0006] Preferably, the silicon comprises 7.5%, copper 6.0%, nickel 2.0%, magnesium 2.0%, tin 4.0%, zinc 6.0%, and the balance is aluminum.

[0007] Preferably, the weight percentage value of the low melting point aluminum-based solder with low Cu content is preferably calculated as follows: Considering the influence of Ni and Mg contents on the strength and melting point of aluminum-based solder, the Mg content was controlled to be 2wt%, the Ni content was 2wt%, and the Cu content was 5wt%. The effect of Si content on the solid-liquid phase temperature was calculated using the Solidification software of JMatPro, and Al-xSi-5Cu-2Mg-2Ni was obtained, where x was 7.5%~11%. Si was fixed within the range of x from 7.5% to 11%, and the effect of Cu content on the solid-liquid temperature of the solder was calculated, resulting in Al-7.5Si-18Cu-2Mg-2Ni; Based on Al-7.5Si-18Cu-2Mg-2Ni, with Si and Cu contents fixed, the effect of Mg content on the solid-liquid temperature of the solder was calculated, and Al-7.5Si-18Cu-2Mg-2Ni was obtained; Based on Al-7.5Si-18Cu-2Mg-2Ni, the Si and Mg contents were controlled, and the effect of Cu content on the solid-liquid temperature of the solder was calculated to obtain Al-7.5Si-14Cu-2Mg-2Ni; Based on Al-7.5Si-14Cu-2Mg-2Ni, with Si, Cu and Mg contents fixed, the effect of Zn content on the solid-liquid temperature of the solder was calculated, and Al-7.5Si-14Cu-2Mg-2Ni-6Zn was obtained; Based on Al-7.5Si-14Cu-2Mg-2Ni-6Zn, the Si, Mg and Zn contents were controlled, and the effect of Cu content on the solid-liquid temperature of the solder was calculated to obtain Al-7.5Si-12Cu-2Mg-2Ni-6Zn; Based on Al-7.5Si-12Cu-2Mg-2Ni-6Zn, Si, Cu, Mg and Zn were fixed, and the effect of Sn content on the solid-liquid temperature of the solder was studied, and Al-7.5Si-12Cu-2Mg-6Zn-4Sn-2Ni was obtained; Based on Al-7.5Si-12Cu-2Mg-6Zn-4Sn-2Ni and combined with the liquidus temperature below 550℃, Al-7.5Si-6Cu-2Mg-4Sn-6Zn-2Ni was calculated.

[0008] Preferably, the raw material of the low-melting-point aluminum-based solder is pure aluminum, pure magnesium, pure tin, pure zinc, aluminum-silicon master alloy, aluminum-copper master alloy, or aluminum-nickel master alloy; The aluminum-silicon master alloy is Al-20Si, the aluminum-copper master alloy is Al-50Cu, and the aluminum-nickel master alloy is Al-10Ni. Using Al-20Si, Al-50Cu, and Al-10Ni as alloy raw materials instead of pure silicon, copper, and nickel effectively reduces burnout of alloying elements, facilitates accurate control of the alloy content of the brazing filler metal, and improves compositional uniformity.

[0009] The present invention also provides a method for preparing a low melting point aluminum-based solder with a low Cu content, comprising the following steps: Cleaning pure aluminum, pure magnesium, pure tin, pure zinc, Al-20Si, Al-50Cu and Al-10Ni; The cleaned pure aluminum, Al-20Si, Al-50Cu, and Al-10Ni are charged into a furnace and covered with a covering agent for heating and smelting. Under the protection of the covering agent, the Al-20Si, Al-50Cu, and Al-10Ni are melted, stirred, descummed, and allowed to stand. The temperature is then lowered, and the cleaned pure tin, pure magnesium, and pure zinc are charged into a furnace for heating and smelting. The mixture is stirred, descummed, and allowed to stand. A refining agent is added for refining, and the scum is removed after standing. A refiner is added for melting, stirred, and descummed to obtain a molten solution. The molten solution is cooled to obtain a casting, and the casting is cut to obtain a low melting point aluminum-based brazing filler metal with low Cu content.

[0010] Preferably, the covering agent is a binary molten salt formed by mixing sodium chloride and potassium chloride in a mass ratio of 1: (1.3-1.5), and the mass of the covering agent is 3wt.%-5wt.% of the mass of the pure aluminum, Al-20Si, Al-50Cu and Al-10Ni smelting solution.

[0011] Preferably, the temperature of the pure aluminum, Al-20Si, Al-50Cu, and Al-10Ni after being charged into the furnace and heated and smelted is 750° C. to 850° C.

[0012] Preferably, the melting temperature after cooling is 700°C to 750°C.

[0013] Preferably, the refining agent is hexachloroethane, and the mass of the refining agent is 0.2wt.%~0.5wt.% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10Ni, pure tin, pure magnesium and pure zinc smelting solution.

[0014] Preferably, the refining agent is aluminum titanium boron, the mass fraction of titanium in the aluminum titanium boron is 4.5wt.%~5wt.%, the mass fraction of boron is 1wt.%~1.2wt.%, and the mass of the aluminum titanium boron is 3wt.%~5wt.% of the mass of pure aluminum, Al-20Si, Al-50Cu, Al-10Ni, pure tin, pure magnesium and pure zinc smelting solution.

[0015] The invention also provides the application of low melting point aluminum-based solder with low Cu content in welding 3003 aluminum alloy and 6061 aluminum alloy.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The component formula of the low-Cu content, low-melting-point aluminum-based solder provided by the present invention is 7.5%-11% silicon, 5.0%-10.0% copper, 2.0% nickel, 0%-2.0% magnesium, 0%-4.0% tin, 0%-6.0% zinc, and the balance being aluminum. The addition of low-melting-point magnesium, zinc, and tin can inhibit the formation of Al2Cu phase and Q-Al5Cu2Mg8Si6 in the aluminum-based solder, thereby reducing the cost. The addition of low-melting-point magnesium, zinc, and tin can form a local low-melting-point liquid phase (such as eutectic or enriched area such as Al-Mg, Al-Zn, Mg-Zn, Al-Sn, Mg-Sn, etc.) at the initial stage of solder melting. Since these formed low-melting-point liquid phases have excellent diffusion and capillary flow effects, they can reduce the melt viscosity, improve the fluidity of the Cu element, and increase the spreadability and wettability of the aluminum-based solder, so that the average spread area of ​​the solder per unit mass is greater than 7.5 cm 2 / g, promoting the metallurgical bonding of Cu with the parent material Al. Furthermore, the addition of magnesium, zinc, and tin can form lower-melting-point multi-element eutectic reaction products with elements such as aluminum and copper, further lowering the melting point of the overall alloy. This also allows Cu to dissolve earlier and more fully, participating in the formation of low-melting-point multi-element eutectic phases such as Al-Cu-Si, Al-Cu-Mg-Si, Al-Cu-Zn, and Al-Cu-Sn. This significantly lowers the melting point of aluminum-based brazing filler metals, keeping their liquidus below 560°C. This allows them to be used for brazing aluminum alloys with solidus temperatures above 580°C, avoiding overburning and corrosion of the parent material. The addition of nickel strengthens the matrix through solid solution, improves the corrosion resistance of the joint (especially inhibiting galvanic corrosion), and refines the grain size.

[0017] The aluminum-based brazing alloy of the present invention does not require a vacuum environment during brazing. The melting and brazing equipment are simple in structure, easy to operate, and low in manufacturing cost, making it suitable for large-scale production. When brazing 3003 aluminum alloy and 6061 aluminum alloy, the aluminum-based brazing alloy of the present invention achieves a maximum shear strength of 120.6 MPa when brazing 3003 aluminum alloy and 6061 aluminum alloy at a temperature of 570°C to 580°C, a holding time of 10 to 20 minutes, furnace cooling to 400°C, and air cooling to room temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 are the effects of Si and Cu on the solid-liquid phase temperature of Al-based solder, where a is the effect of Cu fixed at 5wt%, Mg fixed at 2wt%, Ni fixed at 2wt%, and Si on the solid-liquid phase temperature of Al-based solder, b is the effect of Si fixed at 7.5wt%Cu on the solid-liquid phase temperature of Al-based solder, c is the effect of Si fixed at 8wt%Cu on the solid-liquid phase temperature of Al-based solder, d is the effect of Si fixed at 9wt%Cu on the solid-liquid phase temperature of Al-based solder, e is the effect of Si fixed at 10wt%Cu on the solid-liquid phase temperature of Al-based solder and f is the effect of Si fixed at 11wt%Cu on the solid-liquid phase temperature of Al-based solder.

[0019] Figure 2 Figure 2 shows the effect of Mg on the solidus-liquidus temperature of Al-based solder. Figure 2a shows the effect of Mg on the solidus-liquidus temperature of Al-based solder when Si is fixed at 7.5wt%, Cu is fixed at 18wt%, and Ni is fixed at 2wt%. Figure 2b shows the effect of Cu on the solidus-liquidus temperature of Al-based solder when Si is fixed at 7.5wt%, Mg is fixed at 2wt%, and Cu is fixed at 2wt%. Figure 2c shows the effect of Cu on the solidus-liquidus temperature of Al-based solder when Si is fixed at 7.5wt%, Mg is fixed at 4wt%, and Cu is fixed at 4wt%.

[0020] Figure 3 Figure 3 is the effect of Zn on the solid-liquid phase temperature of Al-based solder, where a is the effect of Zn on the solid-liquid phase temperature of Al-based solder when Si is fixed at 7.5wt%, Cu is fixed at 18wt%, Mg is fixed at 2wt%, and Ni is fixed at 2wt%; b is the effect of Cu on the solid-liquid phase temperature of Al-based solder when Si is 7.5wt%, Zn is 2wt%, Mg is fixed at 2wt%, and Ni is fixed at 2wt%; c is the effect of Cu on the solid-liquid phase temperature of Al-based solder when Si is 7.5wt%, Zn is 4wt%, Mg is fixed at 2wt%, and Ni is fixed at 2wt%; d is the effect of Cu on the solid-liquid phase temperature of Al-based solder when Si is 7.5wt%, Zn is 6wt%, Mg is fixed at 2wt%, and Ni is fixed at 2wt%.

[0021] Figure 4Figure 3 is the effect of Sn on the solid-liquid phase temperature of Al-based solder, where a is the effect of Sn on the solid-liquid phase temperature of Al-based solder when Si is fixed at 7.5wt%, Cu is 14wt%, Mg is 2wt%, Ni is fixed at 2wt%, and Zn is 6wt%; b is the effect of Si at 7.5wt%, Sn at 2wt%, Mg at 2wt%, Zn at 6wt%, and Ni is fixed at 2wt% and Cu is affected on the solid-liquid phase temperature of Al-based solder; c is the effect of Si at 7.5wt%, Sn at 4wt%, Mg at 2wt%, Ni at 2wt%, Zn at 6wt% and Cu is affected on the solid-liquid phase temperature of Al-based solder.

[0022] Figure 5 1, 2, 3, 4, 5, comparative example 1, comparative example 2, and comparative example 3 are DSC curves of the Al-based solders in Example 1, Example 2, Example 3, Example 4, Example 5, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0023] Figure 6 Microstructure diagrams of brazed joints made by welding 3003 series aluminum alloy and 6061 series aluminum alloy with low-melting-point aluminum alloy brazing filler metals prepared in Example 1, Example 2, Example 3, Example 4, Example 5, Comparative Example 1, Comparative Example 2 and Comparative Example 3, wherein (a) is Al-7.5Si-6Cu-2Mg-4Sn-2Ni, (b) Al-7.5Si-6Cu-6Zn-2Ni, (c) Al-7.5Si-6Cu-2Mg-4Sn-6Zn-2Ni, (d) Al-7.5Si-10Cu-4Sn-6Zn-2Ni, (e) Al-7.0Si-5Cu-2Ni, (f) is Al-7.3Si-8Cu-1Mg-2Sn-3Zn-2Ni, (g) Al-7.5Si-6Cu, and (h) Al-7.5Si.

[0024] Figure 7 This is a graph showing the shear strength results of brazed joints made by welding 3003 series aluminum alloy and 6061 series aluminum alloy using the low-melting-point brazing filler metals of Example 1, Example 2, Example 3, Example 4, Example 5, Comparative Example 1, Comparative Example 2, and Comparative Example 3. DETAILED DESCRIPTION

[0025] The following is a detailed description of the technical solutions in the embodiments of the present invention, using preferred embodiments and accompanying drawings in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0026] It should be noted that all professional terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, the various raw materials, reagents, instruments, and equipment used in the following examples of this invention can be purchased from the market or prepared by existing methods. In the following examples, the purity of pure aluminum is ≥99.0%, the purity of pure magnesium is ≥99.5%, the purity of pure tin is ≥99.0%, and the purity of pure zinc is ≥99.0%.

[0027] The present invention provides a low-Cu content, low-melting-point aluminum-based solder, a preparation method and an application thereof. The low-Cu content, low-melting-point aluminum-based solder has low cost, high strength, high toughness, good spreadability and low melting point, and can prevent the problems of overburning and corrosion of the base material.

[0028] Based on the following weight percentage raw materials that can be used to make low-Cu content low-melting-point aluminum-based solder: silicon 7.5%-11%, copper 5.0%-10.0%, nickel 2.0%, magnesium 0%-2.0%, tin 0%-4.0%, zinc 0%-6.0%, and the balance being aluminum, a preferred method for giving the weight percentage values ​​of low-Cu content low-melting-point aluminum-based solder is given: Considering the influence of Ni and Mg contents on the strength and melting point of aluminum-based solder, Mg is controlled to be 2wt%, Ni is 2wt%, and Cu is 5wt%. The influence of Si content on the solid-liquid phase temperature is calculated using the Solidification software of JMatPro, and Al-11Si-5Cu-2Mg-2Ni is obtained, where the weight content of x is 7.5%~11%. The Si weight content was fixed at 7.5%, 8%, 9%, 10% and 11%, and the Cu content was changed. The effect of Cu content on the solid-liquid temperature of the solder was calculated using the Solidification software of JMatPro. It was found that Al-7.5Si-18Cu-2Mg-2Ni had a better liquidus temperature and solidification range. Based on Al-7.5Si-18Cu-2Mg-2Ni, with fixed Si and Cu contents, the effect of Mg content on the solidus-liquidus temperature was explored, and it was found that 2wt%Mg had the lowest solidus-liquidus temperature, but increased the solidification range, resulting in Al-7.5Si-18Cu-2Mg-2Ni; Taking Al-7.5Si-18Cu-2Mg-2Ni as the base, when the weight percentage of Zn changes in the range of 1% to 6%, the liquidus temperature continues to increase, the solidus temperature continues to decrease, and the solidification range gradually increases; when the Zn content is fixed at 2%, 4% and 6%, it is found that increasing the Zn content can reduce the proportion of Cu. When Zn = 6wt%, the optimal Cu content can be reduced to 14wt%, resulting in Al-7.5Si-14Cu-2Mg-2Ni-6Zn. Based on Al-7.5Si-14Cu-2Mg-6Zn-2Ni, varying the Sn weight percentage within the range of 0-4 significantly reduces the solidus temperature and slightly increases the liquidus temperature. When the Sn weight percentage is fixed at 2% and 4%, respectively, resulting in Sn = 4wt%, the Cu ratio can be further reduced to 12wt%, resulting in Al-7.5Si-12Cu-2Mg-6Zn-4Sn-2Ni. Combined with a liquidus temperature of 525°C, the liquidus temperature of Al-7.5Si-6Cu-2Mg-4Sn-6Zn-2Ni calculated using the Solidification module in JMatPro software also meets the requirements for low-melting-point aluminum-based solder.

[0029] The effects of Si and Cu on the solid-liquidus temperature of Al-based solder, the effects of Mg on the solid-liquidus temperature of Al-based solder, the effects of Zn on the solid-liquidus temperature of Al-based solder, and the effects of Sn on the solid-liquidus temperature of Al-based solder were verified, and the results are as follows: like Figure 1As shown in Figure 1, the Cu content is first fixed at 5wt.%, the Ni content is fixed at 2wt.%, and the Mg content is fixed at 2wt.%. As the Si content increases, the melting point of the Al alloy first decreases and then increases, while the solidus temperature remains unchanged, as shown in Figure (a). When the Si content is fixed at 7.5wt.%, the Ni content is fixed at 2wt.%, the Mg content is fixed at 2wt.%, and the Cu content is 14wt.%-19wt.%, an aluminum alloy brazing filler metal with a melting point below 550°C is obtained, and the Al-7.5Si-18Cu-2Mg-2Ni composition has the optimal solid-liquid phase temperature, as shown in Figure (b). When the Si content is fixed at 8wt.%, the Ni content is fixed at 2wt.%, the Mg content is fixed at 2wt.%, and the Cu content is 13wt.%-18wt.%, an aluminum alloy brazing filler metal with a melting point below 550°C is obtained, and the Al-8Si-16Cu-2Mg-2Ni composition has the optimal solid-liquid phase temperature, as shown in Figure (c). When the Si content is fixed at 9wt.%, the Ni content is fixed at 2wt.%, the Mg content is fixed at 2wt.%, and the Cu content is 11wt.%-16wt.%, an aluminum alloy brazing filler metal with a melting point below 550°C can be obtained, and the Al-9Si-14Cu-2Mg-2Ni composition has the optimal solid-liquid phase temperature, as shown in Figure (d). When the Si content is fixed at 10wt.%, the Ni content is fixed at 2wt.%, the Mg content is fixed at 2wt.%, and the Cu content is 9wt.%-11wt.%, an aluminum alloy brazing filler metal with a melting point below 550°C can be obtained, and the Al-10Si-10Cu-2Mg-2Ni composition has the optimal solid-liquid phase temperature, as shown in Figure (e). When the Si content is fixed at 11wt.%, the Ni content is fixed at 2wt.%, and the Mg content is fixed at 2wt.%, the alloy liquidus temperature is all above 550°C, as shown in Figure (f). The results show that when the Si content is 7.5wt.% and 8wt.%, and the Cu content is 16wt.%~18wt.%, the melting point of the alloy can be reduced to below 540℃. In this case, the Cu content is relatively high.

[0030] like Figure 2 As shown in Figure (b), when the Si content is fixed at 7.5wt.% and the Cu content is fixed at 18wt.%, as the Mg content increases, the alloy melting point first decreases and then increases, and the impact on the solidus temperature is greater. When the Mg content is fixed at 2wt.%, the Ni content is fixed at 2wt.%, and the Cu content is 14wt.%, an aluminum alloy brazing filler metal with a melting point below 550°C is obtained, and the solid-liquid phase interval is minimized, as shown in Figure (b). At the same time, the Cu content is reduced to 16wt.%, and the alloy melting point is guaranteed to be below 540°C. When the Mg content is fixed at 4wt.%, the Ni content is fixed at 2wt.%, and the Cu content is 14wt.%, an aluminum alloy brazing filler metal with a melting point below 540°C is obtained, as shown in Figure (c).

[0031] like Figure 3 As shown in Figure (a), when the Si content is fixed at 7.5wt.%, the Cu content is fixed at 18wt.%, the Mg content is fixed at 2wt.%, and the Ni content is fixed at 2wt.%, the liquidus temperature of the alloy increases, the solidus temperature decreases, and the solid-liquid range increases significantly, as shown in Figure (a). When the Si content is fixed at 7.5wt.%, the Zn content is fixed at 2wt.%, the Mg content is fixed at 2wt.%, and the Ni content is fixed at 2wt.%, the melting point of the alloy can be guaranteed to be within 550℃ within the range of Cu content from 14wt.% to 18wt.%, and the melting point is the lowest and the solid-liquid range is the smallest when the Cu content is 16wt.%, as shown in Figure (b). When the Si content is fixed at 7.5wt.%, the Zn content is fixed at 4wt.%, the Mg content is 2wt.%, and the Ni content is 2wt.%, the melting point of the alloy can be guaranteed to be within 540℃ when the Cu content is within the range of 13wt.%~17wt.%, as shown in Figure (c). When the Si content is fixed at 7.5wt.%, the Zn content is fixed at 6wt.%, the Mg content is 2wt.%, and the Ni content is 2wt.%, the melting point of the alloy can be guaranteed to be within 540℃ when the Cu content is within the range of 12wt.%~16wt.%, as shown in Figure (d). Figure 4 As shown in Figure (a), when the Si content is fixed at 7.5wt%, the Cu content is 14wt%, the Zn content is 6wt%, and the Mg content is 2wt%, as the Sn content increases to 2wt%, the liquidus temperature of the alloy hardly changes, the solidus temperature drops rapidly, and then remains unchanged. When the Si content is fixed at 7.5wt%, the Sn content is 2wt%, the Zn content is 6wt%, and the Mg content is 2wt%, the melting point of the alloy is guaranteed to be within 550℃ when the Cu content is within the range of 10wt% to 14wt%, but the solidus temperature range gradually increases with the Cu content, as shown in Figure (b). When the Si content is fixed at 7.5wt%, the Sn content is 4wt%, the Zn content is 6wt%, and the Mg content is 2wt%, the melting point of the alloy is guaranteed to be within 550℃ within the Cu content range of 7wt% to 14wt%. The solidus temperature range continues to gradually increase with the Cu content, as shown in Figure (c). Considering cost and achieving a lower liquidus temperature, the Cu content is selected here at 6wt%.

[0032] The following examples can be used to melt aluminum-based solder of any total mass. Here, an example is given of the total mass of the aluminum-based solder melted being 2 kg.

[0033] Example 1 A low-melting-point aluminum-based solder with low Cu content is prepared by using 7.5% silicon, 6.0% copper, 2.0% nickel, 2.0% magnesium, 4.0% tin, 0% zinc, and the balance being aluminum to obtain Al-7.5Si-6Cu-2Mg-4Sn-2Ni.

[0034] The method for preparing a low melting point aluminum-based solder with low Cu content comprises the following steps: The total mass of the aluminum-based solder melt is 2 kg. According to the above weight percentages, 0.49 kg of pure aluminum, 0.04 kg of pure magnesium, 0.08 kg of pure tin, 0.75 kg of Al-20Si, 0.24 kg of Al-50Cu, and 0.40 kg of Al-10Ni were weighed and cleaned to remove the surface oxide film and oil stains. The cleaned raw materials are charged into a crucible according to pure aluminum, Al-20Si, Al-50Cu and Al-10Ni, aluminum flux is charged into the crucible and heated and smelted at 750°C covered with a covering agent, Al-20Si, Al-50Cu and Al-10Ni are melted under the protection of the covering agent, stirred, descummed and allowed to stand for 5 minutes; the temperature is then lowered to 700°C, and the cleaned pure tin and pure magnesium are charged into a furnace for heating and melting, stirred, descummed and allowed to stand for 5 minutes; a refining agent is added and refined for 10 minutes, and the scum is removed after standing for 5 minutes; a refiner is added and melted, stirred, descummed to obtain a molten solution; the molten solution is cooled to obtain a casting, and the casting is cut to obtain a low-melting-point aluminum-based brazing filler metal with a low Cu content.

[0035] The covering agent is a binary molten salt composed of sodium chloride and potassium chloride in a mass ratio of 1:1.3. The mass of the covering agent is 4wt.% of the mass of the smelting solution of pure aluminum, Al-20Si, Al-50Cu and Al-10Ni; The refining agent is hexachloroethane, and the mass of the refining agent is 0.2 wt.% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10N, pure tin, pure magnesium and pure zinc smelting solution.

[0036] The refiner is aluminum titanium boron, in which the mass fraction of titanium is 5% and the mass fraction of boron is 1%. The mass of the aluminum titanium boron is 3% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10Ni, pure tin, pure magnesium and pure zinc smelting solution.

[0037] Example 2 A low-melting-point aluminum-based solder with low Cu content is prepared by using 7.5% silicon, 6.0% copper, 2.0% nickel, 0% magnesium, 0% tin, 6.0% zinc and the balance being aluminum to obtain Al-7.5Si-6Cu-2Ni-6Zn.

[0038] The method for preparing a low melting point aluminum-based solder with low Cu content comprises the following steps: The total mass of the aluminum-based solder melt is 2 kg. According to the above weight percentages, 0.49 kg of pure aluminum, 0.12 kg of pure zinc, 0.75 kg of Al-20Si, 0.24 kg of Al-50Cu, and 0.40 kg of Al-10Ni are weighed and cleaned to remove the surface oxide film and oil stains. The cleaned raw materials are loaded into a crucible according to pure aluminum, Al-20Si, Al-50Cu and Al-10Ni. Aluminum flux is loaded into the crucible and heated and smelted at 800°C covered with a covering agent. Under the protection of the covering agent, Al-20Si, Al-50Cu and Al-10Ni are melted, stirred, descummed and allowed to stand for 5 minutes; the temperature is then lowered to 720°C, pure zinc is added and melted, stirred, descummed and allowed to stand for 5 minutes; a refining agent is added and refined for 12 minutes, and after standing for 5 minutes, the scum is removed; a refiner is added and melted, stirred, descummed to obtain a molten solution; the molten solution is cooled to obtain a casting, and the casting is cut to obtain a low-Cu content low-melting-point aluminum-based brazing filler metal.

[0039] The covering agent is a binary molten salt composed of sodium chloride and potassium chloride in a mass ratio of 1:1.4. The mass of the covering agent is 3wt.% of the mass of the smelting solution of pure aluminum, Al-20Si, Al-50Cu and Al-10Ni; The refining agent is hexachloroethane, and the mass of the refining agent is 0.3wt.% of the mass of the pure aluminum, Al-20Si, Al-50Cu, and Al-10Ni smelting solution.

[0040] The refiner is aluminum titanium boron, in which the mass fraction of titanium is 4.5%, the mass fraction of boron is 1%, and the mass of the aluminum titanium boron is 3% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10Ni and pure zinc smelting solution.

[0041] Example 3 A low-melting-point aluminum-based solder with a low Cu content is prepared by using 7.5% silicon, 6.0% copper, 2.0% nickel, 2.0% magnesium, 4.0% tin, 6.0% zinc and the balance being aluminum to obtain Al-7.5Si-6Cu-2Mg-4Sn-6Zn-2Ni.

[0042] The method for preparing a low melting point aluminum-based solder with low Cu content comprises the following steps: The total mass of the aluminum-based solder melt is 2 kg. According to the above weight percentages, 0.37 kg of pure aluminum, 0.04 kg of pure magnesium, 0.08 kg of pure tin, 0.12 kg of pure zinc, 0.75 kg of Al-20Si, 0.24 kg of Al-50Cu, and 0.40 kg of Al-10Ni are weighed and cleaned to remove the surface oxide film and oil stains. The cleaned raw materials are charged into a crucible according to pure aluminum, Al-20Si, Al-50Cu and Al-10Ni, aluminum flux is charged into the crucible and heated and smelted at 850°C covered with a covering agent, Al-20Si, Al-50Cu and Al-10Ni are melted under the protection of the covering agent, stirred, descummed and allowed to stand for 5 minutes; the temperature is then lowered to 750°C, and the cleaned pure tin, pure magnesium and pure zinc are charged into a furnace for heating and melting, stirred, descummed and allowed to stand for 5 minutes; a refining agent is added and refined for 10 minutes, and the scum is removed after standing for 5 minutes; a refiner is added and melted, stirred and descummed to obtain a molten solution; the molten solution is cooled to obtain a casting, and the casting is cut to obtain a low-melting-point aluminum-based brazing filler metal with a low Cu content.

[0043] The covering agent is a binary molten salt composed of sodium chloride and potassium chloride in a mass ratio of 1:1.5. The mass of the covering agent is 4wt.% of the mass of the smelting solution of pure aluminum, Al-20Si, Al-50Cu and Al-10Ni; The refining agent is hexachloroethane, and the mass of the refining agent is 0.3 wt.% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10Ni, pure tin, pure magnesium and pure zinc smelting solution.

[0044] The refiner is aluminum titanium boron, in which the mass fraction of titanium is 5% and the mass fraction of boron is 1.2%. The mass of the aluminum titanium boron is 5% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10Ni, pure tin, pure magnesium and pure zinc smelting solution.

[0045] Example 4 A low-melting-point aluminum-based solder with a low Cu content is prepared by using 7.5% silicon, 10.0% copper, 2.0% nickel, 2.0% magnesium, 4.0% tin, 6.0% zinc and the balance being aluminum to obtain Al-7.5Si-10Cu-2Mg-4Sn-6Zn-2Ni.

[0046] The method for preparing a low melting point aluminum-based solder with low Cu content comprises the following steps: The total mass of the aluminum-based solder melt is 2 kg. According to the above weight percentages, 0.21 kg of pure aluminum, 0.04 kg of pure magnesium, 0.08 kg of pure tin, 0.12 kg of pure zinc, 0.75 kg of Al-20Si, 0.40 kg of Al-50Cu, and 0.40 kg of Al-10Ni are weighed and cleaned to remove the surface oxide film and oil stains. The cleaned raw materials are charged into a crucible according to pure aluminum, Al-20Si, Al-50Cu and Al-10Ni, aluminum flux is charged into the crucible and heated and smelted at 750°C covered with the covering agent, Al-20Si, Al-50Cu and Al-10Ni are melted under the protection of the covering agent, stirred, descummed and allowed to stand for 5 minutes; the temperature is then lowered to 700°C, and the cleaned pure tin, pure magnesium and pure zinc are charged into a furnace for heating and melting, stirred, descummed and allowed to stand for 5 minutes; a refining agent is added and refined for 10 minutes, and the scum is removed after standing for 5 minutes; a refiner is added and melted, stirred and descummed to obtain a molten solution; the molten solution is cooled to obtain a casting, and the casting is cut to obtain a low-Cu content low-melting-point aluminum-based brazing filler metal.

[0047] The covering agent is a binary molten salt composed of sodium chloride and potassium chloride in a mass ratio of 1:1.5. The mass of the covering agent is 5wt.% of the mass of the smelting solution of pure aluminum, Al-20Si, Al-50Cu and Al-10Ni; The refining agent is hexachloroethane, and the mass of the refining agent is 0.5wt.% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10N, pure tin, pure magnesium and pure zinc smelting solution.

[0048] The refiner is aluminum titanium boron, in which the mass fraction of titanium is 4.6%, the mass fraction of boron is 1.1%, and the mass of the aluminum titanium boron is 4% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10Ni, pure tin, pure magnesium and pure zinc smelting solution.

[0049] Example 5 A low-melting-point aluminum-based solder with low Cu content is prepared by using 7.3% silicon, 8.0% copper, 2.0% nickel, 1.0% magnesium, 2.0% tin, 3.0% zinc and the balance being aluminum to obtain Al-7.3Si-8Cu-1Mg-2Sn-3Zn-2Ni.

[0050] The method for preparing a low melting point aluminum-based solder with low Cu content comprises the following steps: The total mass of the aluminum-based solder melt is 2 kg. According to the above weight percentages, 0.43 kg of pure aluminum, 0.02 kg of pure magnesium, 0.06 kg of pure zinc, 0.04 kg of pure tin, 0.73 kg of Al-20Si, 0.32 kg of Al-50Cu, and 0.40 kg of Al-10Ni are weighed and cleaned to remove the surface oxide film and oil stains. The cleaned raw materials are charged into a crucible according to pure aluminum, Al-20Si, Al-50Cu and Al-10Ni, aluminum flux is charged into the crucible and heated and smelted at 750°C covered with a covering agent, Al-20Si, Al-50Cu and Al-10Ni are melted under the protection of the covering agent, stirred, descummed and allowed to stand for 5 minutes; the temperature is then lowered to 700°C, and the cleaned pure zinc, pure tin and pure magnesium are charged into a furnace for heating and melting, stirred, descummed and allowed to stand for 5 minutes; a refining agent is added and refined for 10 minutes, and the scum is removed after standing for 5 minutes; a refiner is added and melted, stirred and descummed to obtain a molten solution; the molten solution is cooled to obtain a casting, and the casting is cut to obtain a low-melting-point aluminum-based brazing filler metal with a low Cu content.

[0051] The covering agent is a binary molten salt composed of sodium chloride and potassium chloride in a mass ratio of 1:1.5. The mass of the covering agent is 4wt.% of the mass of the smelting solution of pure aluminum, Al-20Si, Al-50Cu and Al-10Ni; The refining agent is hexachloroethane, and the mass of the refining agent is 0.3 wt.% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10Ni, pure tin, pure magnesium and pure zinc smelting solution.

[0052] The refiner is aluminum titanium boron, in which the mass fraction of titanium is 5% and the mass fraction of boron is 1%. The mass of the aluminum titanium boron is 3% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10Ni, pure tin, pure magnesium and pure zinc smelting solution.

[0053] Comparative Example 1 An aluminum-based brazing filler metal is prepared by using 7.5% silicon, 6.0% copper, and the balance aluminum to obtain Al-7.5Si-6Cu. The total mass of the smelted aluminum-based brazing filler metal is 2 kg. According to the above weight percentages, 1.01 kg of pure aluminum, 0.75 kg of Al-20Si, and 0.24 kg of Al-50Cu are weighed.

[0054] The preparation method of the aluminum-based solder is the same as that in Example 3.

[0055] Comparative Example 2 An aluminum-based brazing filler metal, Al-7.5Si, was prepared with 7.5% silicon and the balance aluminum. The total mass of the smelted aluminum-based brazing filler metal was 2 kg. According to the above weight percentages, 1.25 kg of pure aluminum and 0.75 kg of Al-20Si were weighed. The preparation method for this aluminum-based brazing filler metal was the same as in Example 3.

[0056] Comparative Example 3 A low melting point aluminum-based solder with low Cu content is prepared by using 7.0% silicon, 5.0% copper, 2.0% nickel, 0% magnesium, 0% tin, 0% zinc and the balance being aluminum to obtain Al-7.0Si-5Cu-2Ni.

[0057] The method for preparing a low melting point aluminum-based solder with low Cu content comprises the following steps: The total mass of the aluminum-based solder melt is 2 kg. According to the above weight percentages, 0.70 kg of pure aluminum, 0.70 kg of Al-20Si, 0.20 kg of Al-50Cu, and 0.40 kg of Al-10Ni are weighed and cleaned to remove the surface oxide film and oil stains. The cleaned raw materials are loaded into a crucible according to pure aluminum, Al-20Si, Al-50Cu and Al-10Ni. Aluminum flux is loaded into the crucible and heated and melted at 750°C covered with a covering agent. Al-20Si, Al-50Cu and Al-10Ni are melted under the protection of the covering agent, stirred, descummed and allowed to stand for 5 minutes; the temperature is then lowered to 700°C, a refining agent is added and refined for 10 minutes, the refining agent is allowed to stand for 5 minutes, and the scum is removed; a refiner is added and melted, stirred, and descummed to obtain a molten solution; the molten solution is cooled to obtain a casting, and the casting is cut to obtain a low-Cu content, low-melting-point aluminum-based brazing filler metal.

[0058] The covering agent is a binary molten salt composed of sodium chloride and potassium chloride in a mass ratio of 1:1.5. The mass of the covering agent is 4wt.% of the mass of the smelting solution of pure aluminum, Al-20Si, Al-50Cu and Al-10Ni; The refining agent is hexachloroethane, and the mass of the refining agent is 0.3 wt.% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10Ni, pure tin, pure magnesium and pure zinc smelting solution.

[0059] The refiner is aluminum titanium boron, in which the mass fraction of titanium is 5% and the mass fraction of boron is 1%. The mass of the aluminum titanium boron is 3% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10Ni, pure tin, pure magnesium and pure zinc smelting solution.

[0060] The above-mentioned Examples 1 to 5 and Comparative Examples 1 to 3 can all prepare aluminum-based brazing filler metals, which can be used to weld 3003 series aluminum alloys and 6061 series aluminum alloys, respectively. The specific steps are as follows: (a) Cubes of 4 mm × 4 mm × 4 mm were prepared from 3003 aluminum alloy and 6061 aluminum alloy parent materials. The parent materials were polished with 320-2000 grit sandpaper and polished with polishing paste. The samples were ultrasonically cleaned in alcohol for 2-3 min and then dried. (b) The aluminum-based brazing filler metal has a size of 4 mm × 4 mm × 200 μm. The filler metal is polished on 320-2000 mesh sandpaper, then ultrasonically cleaned in alcohol for 2-3 min and blown dry. (c) Each aluminum-based brazing filler metal was sandwiched between the 3003 aluminum alloy and 6061 aluminum alloy base materials, placed in a fixed fixture, and QJ202 aluminum alloy brazing flux was spread. The materials were heated to 580°C and kept warm for 10 min. (d) After cooling to 400°C in the furnace, the brazed joint is obtained by air cooling to room temperature.

[0061] Examples 1 to 5 and Comparative Examples 1 to 3 can all prepare aluminum-based solders. The performance of the aluminum-based solders of Examples 1 to 5 and Comparative Examples 1 to 3 will be verified below.

[0062] Experimental characterization (1) Spreading area test The test results of the spreading area are shown in Table 1. Table 1 Spreading area per unit mass of solder (2) Differential scanning calorimetry test of aluminum-based solder like Figure 5 As shown, the melting points of the solders corresponding to Example 1, Example 2, Example 3, Example 4, Comparative Example 3, Example 5 and Comparative Example 1 to Comparative Example 2 are 550°C, 577.6°C, 546.3°C, 532.6°C, 591.5°C, 559°C, 592.5°C and 607.9°C, respectively.

[0063] Figure 5 (h) The melting point of the binary alloy Al-7.5Si given in Comparative Example 2 is the highest at 607.9°C. Figure 5 (g) The melting point of Al-7.5Si-6Cu given in Comparative Example 1 is the highest at 592.5°C. Compared with the two, adding 6% by weight of Cu will significantly reduce the melting point of Comparative Example 2, which also verifies the significant melting-reducing effect of copper. Figure 5 (c) is the DSC of the alloy of Example 3. Compared with the melting point of 577.6°C of Al-7.5Si-6Cu-2Ni-6Zn given in Example 2, the addition of Mg and Sn significantly reduces the melting point of the alloy. Figure 5 (e) shows the DSC of the alloy from Example 5. Compared to the Al-7.5Si-6Cu alloy from Comparative Example 1, which has a maximum melting point of 592.5°C, the addition of Ni reduces the Cu content to a certain extent, but also lowers the melting point, confirming that 2 wt.% Ni has a certain melting point-lowering effect. Adding 10 wt.% Cu (Al-7.5Si-10Cu) further lowers the melting point to 532.6°C. This clearly utilizes the formation of the Al-Al2Cu eutectic (548°C) and the Al-Si-Al2Cu ternary eutectic (525°C).

[0064] Zinc's auxiliary melting effect: comparison Figure 5 (g) Al-7.5Si-6Cu (592.5°C) and Figure 5 (b) Al-7.5Si-6Cu-6Zn (577.6°C), showing that the addition of 6% Zn lowers the melting point by about 15°C. Zn has a large solid solubility in Al, can lower the liquidus, and participate in the formation of a low-melting-point multicomponent eutectic.

[0065] Magnesium (Mg) melting / stabilization effect: comparison Figure 5 (g) Al-7.5Si-6Cu (592.5°C) and Figure 5 (a) Al-7.5Si-6Cu-2Mg (550°C). The addition of 2% Mg significantly lowers the melting point (by approximately 42.5°C). Mg promotes the formation of the Mg2Si phase, and the Al-Mg2Si eutectic has a relatively high temperature (595°C). The melting point drop in this case is more likely due to Mg altering the composition and temperature of the multicomponent eutectic or promoting the formation of other low-melting-point phases. Mg is crucial for preventing overburning / erosion.

[0066] Role of nickel (Ni): Ni usually forms high melting point intermetallic compounds (such as Al3Ni, melting point > 850°C), which tends to raise the liquidus.

[0067] Compare similar ingredients: Figure 5 (g) Al-7.5Si-6Cu (592.5℃) is close to Al-7.5Si-6Cu-2Ni Figure 5 (e) 591.5℃ for Al-7.0Si-5Cu-2Ni or Figure 5 (b) Al-7.5Si-6Cu-6Zn-2Ni (577.6°C) - The addition of Ni does not appear to significantly lower the melting point and may even slightly raise the liquidus. Its core value lies in inhibiting corrosion.

[0068] Multi-component synergistic effect: the most complex alloy Figure 5 (d) Al-7.5Si-10Cu-4Sn-6Zn-2Ni exhibits the lowest melting point (532.6°C). This demonstrates the synergistic melting-depressing effect of Cu, Sn, and Zn. Together, they form multicomponent eutectics with even lower melting points (e.g., Al-Si-Cu-Sn-Zn related eutectics), which are lower than any single binary or ternary eutectic. Figure 5 (f) Al-7.3Si-8Cu-1Mg-2Sn-3Zn-2Ni (559℃) is also a successful example of multi-element synergistic melting reduction.

[0069] The role of silicon (Si): Si is a core element in aluminum brazing filler metals. The melting point of the Al-Si eutectic (577°C) is lower than that of pure aluminum (660°C), providing essential low-melting properties, good fluidity, and wettability to the base metal. A commonly used Si content range of 7.0% to 7.5% provides a balance between melting point, fluidity, joint strength, and control of base metal corrosion.

[0070] These brazing filler metals achieve low melting points (as low as 532.6°C) through ingenious multi-element alloying design, particularly the synergistic formation of ultra-low-melting multi-element eutectics with Cu, Sn, and Zn. Simultaneously, by adding Mg and Ni and controlling their content, excessive dissolution (corrosion) of the base metal by the liquid brazing filler metal is effectively suppressed. More importantly, the precise setting of the melting point (well below the target base metal solidus) directly ensures that the base metal will not overheat at the appropriate brazing temperature. This compositional design successfully strikes a balance between a low melting point and excellent resistance to corrosion / overheating, making it the key to developing high-performance aluminum brazing filler metals.

[0071] (3) Microstructure of brazed joints made of 3003 series aluminum alloy and 6061 series aluminum alloy welded with aluminum alloy brazing filler metal like Figure 6 As shown, Figure 6 (a) The figure shows the microstructure of the Al-7.5Si-6Cu-2Mg-4Sn-2Ni brazing joint. There are discontinuously distributed large blocks of intermetallic compounds in the center of the brazing seam of the Al-7.5Si-6Cu-2Mg-4Sn-2Ni brazing filler metal. There is no significant change in the HAZ area of ​​3003 and 6061, and there is no grain boundary liquefaction. Figure 6 (b) The figure shows the microstructure of the Al-7.5Si-6Cu-6Zn-2Ni brazing joint. The Al-7.5Si-6Cu-6Zn-2Ni brazing filler metal has an Al-Si-Zn ternary eutectic dominant in the weld center. The flake Al2Cu and dot-like Al3NiZn dissolve in the α-Al matrix, lowering the liquidus but coarsening the eutectic (higher melting point). Figure 6 (c) The figure shows the microstructure of the Al-7.5Si-6Cu-2Mg-4Sn-6Zn-2Ni brazing joint. A small amount of discontinuously distributed bright white and grayish white intermetallic compounds exist in the center of the Al-7.5Si-6Cu-2Mg-4Sn-6Zn-2Ni brazing filler metal weld. Figure 6 (d) Figure 2 shows the microstructure of the Al-7.5Si-10Cu-4Sn-6Zn-2Ni brazed joint. The weld zone of the Al-7.5Si-10Cu-4Sn-6Zn-2Ni is mainly composed of α-Al matrix, with a small amount of small intermetallic compounds at the grain boundaries, corresponding to higher shear strength. Figure 6(e) Figure 2 shows the microstructure of the Al-7.0Si-5Cu-2Ni brazing joint. The weld zone of the Al-7.0Si-5Cu-2Ni brazing filler metal is wider, and the size of the bulk intermetallic compounds between the dendrites is larger than that of the Al-7.5Si-6Cu-6Zn-2Ni brazing filler metal. Figure 6 (f) Figure 2 shows the microstructure of the Al-7.3Si-8Cu-1Mg-2Sn-3Zn-2Ni brazing joint. The Al-7.3Si-8Cu-1Mg-2Sn-3Zn-2Ni brazing filler metal has a weld-affected zone on the 3003 side, while the base material on the 6061 side is not corroded. Figure 6 (g) Figure 2 shows the microstructure of the Al-7.5Si-6Cu brazing joint. The weld zone of the Al-7.5Si-6Cu brazing filler metal is wider than that of the Al-7.5Si-6Cu-2Mg-4Sn-6Zn-2Ni brazing filler metal, and the microstructure changes little, indicating that Mg inhibits Cu diffusion, Sn improves wetting, and Ni strengthens the interface. Figure 6 (h) Figure 3 shows the microstructure of the Al-7.5Si brazing joint. The Al-7.5Si brazing filler metal has a high melting point, and the solidified structure is coarse in the center of the weld. A non-linear weld is formed, and corrosion occurs between the interdendritic intermetallic compound phase and the matrix.

[0072] (IV) Shear strength results of brazed joints The shear strength test results of the brazed joints of Examples 1 to 5 and Comparative Examples 1 to 3 are as follows: Figure 7 As shown in the figure, under the same brazing process, the shear strengths of the welded joints are 42.43 MPa, 76.9 MPa, 65.7 MPa, 120.6 MPa, 78.1 MPa, 92.1 MPa, 63.7 MPa, and 47.2 MPa, respectively.

[0073] By comprehensively considering the spreading area test results, differential scanning calorimetry test, solder weld microstructure test results and cost, it was concluded that the low melting point aluminum-based solder with low Cu content was Al-7.5Si-6Cu-2Mg-4Sn-6Zn-2Ni prepared in Example 3.

[0074] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims and their equivalents, the present invention is intended to include such modifications and variations.

Claims

1. A low melting point aluminum-based brazing filler metal with low Cu content, characterized in that: Made from the following raw materials in percentage by weight: Silicon 7.5%-11%, copper 5.0%-10.0%, nickel 2.0%, magnesium 0%-2.0%, tin 0%-4.0%, zinc 0%-6.0%, and the balance is aluminum, wherein the weight percentage of at least one of magnesium, tin and zinc is greater than 0%.

2. The low melting point aluminum-based brazing filler metal with low Cu content according to claim 1, characterized in that: The silicon is 7.5%, the copper is 6.0%, the nickel is 2.0%, the magnesium is 2.0%, the tin is 4.0%, the zinc is 6.0%, and the balance is aluminum.

3. The low melting point aluminum-based brazing filler metal with low Cu content according to claim 1, characterized in that: The raw materials of low melting point aluminum-based solder are pure aluminum, pure magnesium, pure tin, pure zinc, aluminum-silicon master alloy, aluminum-copper master alloy, and aluminum-nickel master alloy; The aluminum-silicon master alloy is Al-20Si, the aluminum-copper master alloy is Al-50Cu, and the aluminum-nickel master alloy is Al-10Ni.

4. The method for preparing a low melting point aluminum-based solder with low Cu content according to claim 3, characterized in that: The steps include: Cleaning pure aluminum, pure magnesium, pure tin, pure zinc, Al-20Si, Al-50Cu and Al-10Ni; The cleaned pure aluminum, Al-20Si, Al-50Cu, and Al-10Ni are charged into a furnace and covered with a covering agent for heating and smelting. Under the protection of the covering agent, the Al-20Si, Al-50Cu, and Al-10Ni are melted, stirred, descummed, and allowed to stand. The temperature is then lowered, and the cleaned pure tin, pure magnesium, and pure zinc are charged into a furnace for heating and smelting. The mixture is stirred, descummed, and allowed to stand. A refining agent is added for refining, and the scum is removed after standing. A refiner is added for melting, stirred, and descummed to obtain a molten solution. The molten solution is cooled to obtain a casting, and the casting is cut to obtain a low melting point aluminum-based brazing filler metal with low Cu content.

5. The method for preparing a low melting point aluminum-based solder with low Cu content according to claim 4, characterized in that: The covering agent is a binary molten salt formed by mixing sodium chloride and potassium chloride in a mass ratio of 1: (1.3-1.5), and the mass of the covering agent is 3wt.%-5wt.% of the mass of the pure aluminum, Al-20Si, Al-50Cu and Al-10Ni smelting solution.

6. The method for preparing a low melting point aluminum-based solder with low Cu content according to claim 4, characterized in that: The pure aluminum, Al-20Si, Al-50Cu and Al-10Ni are heated and smelted at a temperature of 750°C to 850°C after being charged into a furnace, and the smelting temperature after being cooled is 700°C to 750°C.

7. The method for preparing a low melting point aluminum-based solder with low Cu content according to claim 4, characterized in that: The refining agent is hexachloroethane, and the mass of the refining agent is 0.2wt.%~0.5wt.% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10Ni, pure tin, pure magnesium and pure zinc smelting solution.

8. The method for preparing a low melting point aluminum-based solder with low Cu content according to claim 4, characterized in that: The refiner is aluminum titanium boron, in which the mass fraction of titanium is 4.5wt.%~5wt.%, the mass fraction of boron is 1wt.%~1.2wt.%, and the mass of the aluminum titanium boron is 3wt.%~5wt.% of the mass of the pure aluminum, Al-20Si, Al-50Cu, Al-10Ni, pure tin, pure magnesium and pure zinc smelting solution.

9. Use of the low melting point aluminum-based brazing filler metal with low Cu content according to claim 1 in welding 3003 aluminum alloy and 6061 aluminum alloy.

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