High-strength and high-plasticity low-melting-point aluminum alloy brazing material and preparation method and application thereof

Abstract

The invention discloses a high-strength and high-plasticity low-melting-point aluminum alloy brazing material and a preparation method and application thereof, and relates to the technical field of solder manufacturing. The low-melting-point aluminum alloy welding flux is prepared from the following components in percentage by weight: 10 to 14 percent of Si, 4 to 20 percent of Cu, 0.04 to 0.25 percent of Eu, 0.78 to 0.82 percent of Fe, 0.13 to 0.17 percent of Mn, 0.08 to 0.12 percent of Mg, 0.18 to 0.22 percent of Zn and the balance of aluminum and inevitable impurities. The Al-Si-Cu ternary alloy is constructed to form a low-melting-point eutectic phase, the melting point of the material is effectively reduced, meanwhile, Eu atoms are doped, the aluminum matrix is subjected to the pressure stress effect, the interplanar spacing is reduced, the grain size of the matrix aluminum phase is reduced, the elemental Si phase is refined, the eutectic Al-Si phase content is increased, and precipitation of the brittle Al2Cu phase is restrained; therefore, the aluminum alloy solder has high tensile strength and elongation after fracture under the condition that the melting point is low.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of solder manufacturing, in particular to a low-melting-point aluminum alloy brazing material with high strength and high plasticity and a preparation method and application thereof. BACKGROUND

[0002] Aluminum-silicon solder refers to a brazing filler material used for connecting aluminum alloy components, which takes aluminum-silicon alloy as a matrix. The melting point of the solder is lower than that of the aluminum alloy base material, so that the brazing process of "base material not melting and solder melting and filling the joint" is realized. Researchers found that Al-Si binary alloy forms eutectic structure when the silicon content is about 12%, and the melting point is fixed and low (~577℃), which provides a theoretical basis for the development of low-melting-point solder.

[0003] At present, the widely used 4047 aluminum alloy solder is an alloy material taking aluminum as the base and adding silicon, magnesium and other elements, which belongs to Al-Si series deformed aluminum alloy. In its chemical composition, the silicon content is about 11%-13%, the magnesium content is low (about 0.3%-0.7%), and a small amount of copper, iron and other elements are also contained. This ratio endows the 4047 aluminum alloy with excellent fluidity, which can be used for welding 2 series, 3 series and 6 series aluminum alloys and aluminum-silicon series forged aluminum. The melting point of 4047 aluminum solder is between 570-590℃, while the melting point of most aluminum alloy base materials is 600-630℃, resulting in a very small difference in melting point between the solder and the base material. When brazing is carried out, the base material is easily caused to be locally overheated or melted, which causes the deformation of the welded part or the oxidation of the aluminum base material grain boundary, affecting the mechanical properties and safety performance of the welded workpiece. It is necessary to adjust and improve the chemical composition and preparation process of the solder to ensure the fluidity of the solder, reduce the melting point of the solder, and improve the adaptability and compatibility of the solder in the application of aluminum alloy welding, so that it can be better applied to more kinds of welding scenes and welding work of different materials.

[0004] To solve the problem of too high melting point of the solder, 4047 aluminum alloy is used as raw material, and an appropriate amount of Cu is added to form a ternary eutectic alloy, which can further reduce the melting point of the material. However, the ternary eutectic alloy contains a large amount of coarse Al2Cu phase. Since Al2Cu itself is a brittle phase, and the Si phase is generally in the form of flake and long needle, the overall strength of the material is low and the plasticity is poor, so that this solder is only suitable for casting into strips, which limits its application in more welding scenes.

[0005] For example, a low melting point aluminum-based filler metal and its preparation and application in 6000 series aluminum alloy brazing of patent application CN114654127A, the filler metal composition is 6.0-8.0% silicon, 18.0-20.0% copper, 1.0-2.0% nickel, 0.05-0.12% strontium, and the balance is aluminum. By adjusting the Si content in the aluminum-silicon filler metal and adding a specific amount of Cu, Ni and Sr, the melting temperature of the filler metal is reduced to 515-535℃, but this scheme fails to overcome the defect of low strength and poor plasticity of the material caused by the introduction of Cu. SUMMARY

[0006] The purpose of the present application is to overcome the existing defects and deficiencies, and to provide a low melting point aluminum alloy solder with a lower melting point and higher tensile strength and elongation after fracture.

[0007] Another purpose of the present application is to provide a preparation method of a low melting point aluminum alloy solder.

[0008] Another purpose of the present application is the application of a low melting point aluminum alloy solder in aluminum alloy substrate welding.

[0009] The above purposes of the present application are achieved by the following technical solutions: The present application protects a low melting point aluminum alloy solder, which comprises the following components in weight percentage: Si 10-14%, Cu 4-20%, Eu 0.04-0.25%, Fe 0.78-0.82%, Mn 0.13-0.17%, Mg 0.08-0.12%, Zn 0.18-0.22%, and the balance is aluminum and unavoidable impurities.

[0010] In some embodiments, the following components are included in weight percentage: Si 10.5-13%, Cu 5-15%, Eu 0.05-0.23%, Fe 0.80%, Mn 0.15%, Mg 0.10%, Zn 0.20%, and the balance is aluminum and unavoidable impurities.

[0011] In some embodiments, the mass ratio of Cu and Eu atoms is (50-110): 1.

[0012] In some embodiments, the lattice constant of the aluminum matrix in the X-ray diffraction pattern is less than that of pure aluminum in standard card PDF #04-0787, and has diffraction peaks of α-Al at 38.46-38.70°, 44.76-44.92°, 65.14-65.32° and 78.36-78.46°.

[0013] Preferably, the lattice constant of the aluminum matrix is 4.037-4.048.

[0014] The lattice constant of the alpha-Al phase of the present application is less than the standard card of pure aluminum (PDF #04-0787), and the diffraction angle of alpha-Al is greater than that of pure aluminum, which indicates that the crystal is subjected to compressive stress, resulting in a decrease in atomic spacing, which is beneficial to the tensile strength and plasticity of the reinforced material.

[0015] Further, the peak width of the (111) crystal plane of the alpha-Al phase in the XRD spectrum is 0.74-1.14°, the peak width of the (200) crystal plane is 0.42-1.08°, the peak width of the (220) crystal plane is 0.61-1.10°, and the peak width of the (311) crystal plane is 0.52-1.10°; according to the Scherrer formula, the wider diffraction peak proves that the rare earth Eu can effectively reduce the grain size of the matrix aluminum phase; at the same time, according to the Hall-Petch formula, the smaller the grain size, the greater the yield strength σ of the material.

[0016] In some embodiments, the low-melting-point aluminum alloy solder has a melting point of 515-540℃, a spreading rate ≥100%, an elongation after fracture ≥5.96%, and a tensile strength ≥235.29MPa.

[0017] In some embodiments, the raw materials include the following components by weight: 4047 aluminum alloy 20-160 parts, Al-50Cu intermediate alloy 20-62 parts, Al-20Si-5Eu intermediate alloy 6-20 parts, Al-20Si intermediate alloy 0-112 parts, and pure aluminum 0-4 parts.

[0018] The present application protects a preparation method of a low-melting-point aluminum alloy solder, which comprises the following steps: mixing raw material components according to stoichiometric ratios and carrying out melting, the melting temperature is 790-850℃, casting forming, and water cooling, thereby obtaining the low-melting-point aluminum alloy solder.

[0019] The present application should be rapidly cooled after casting forming, and the cooling method can be selected from water cooling. The present application does not make special limitations on the water cooling means, and the conventional water cooling means of the present application can achieve the purpose of the present application. Preferably, the present application is copper mold static water cooling. Specifically, a sprue and a mold cavity are arranged in the copper mold, the sprue communicates with the mold cavity, and a plurality of cooling water flow channels are arranged in the copper mold, so that water cooling can be achieved after casting the aluminum alloy, further improving the rapid cooling of the aluminum alloy melt, inhibiting the growth of aluminum alloy precipitates Al2Cu, and thereby improving the strength of the material.

[0020] In some embodiments, 0.1-3wt% of a refining agent is further added before melting; preferably, the refining agent is selected from at least one of hexachloroethane and Na3AlF6.

[0021] The present application protects the application of a low-melting-point aluminum alloy solder in the welding of an aluminum alloy base material.

[0022] In some embodiments, the melting point of the aluminum alloy substrate is ≥ 550℃; preferably, the melting point is 570-660℃.

[0023] Compared with the prior art, the present application has the following advantages: The present application provides a low-melting-point aluminum alloy solder, which utilizes an Al-Si-Cu ternary alloy to form a low-melting-point eutectic phase, effectively reduces the melting point of the material, and simultaneously dopes Eu atoms, so that the aluminum matrix is subjected to a compressive stress, the interplanar spacing is reduced, the grain size of the aluminum phase of the matrix is reduced, the elemental Si phase is refined, the content of the eutectic Al-Si phase is increased, and the precipitation of the brittle Al2Cu phase is inhibited, so that the aluminum alloy solder has a lower melting point while having a higher tensile strength and elongation after fracture. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Al-Si-Cu ternary phase diagram of the prior art.

[0025] Figure 2 Mold used in the preparation method of the low-melting-point aluminum alloy solder described in embodiments 1-4 of the present application.

[0026] Figure 3 Microstructure morphology of the material of embodiment 3 and comparative example 3 of the present application; wherein (a) is embodiment 3; (b) is comparative example 3.

[0027] Figure 4 Microstructure morphology of the material of comparative example 5 and comparative example 6 of the present application; wherein (a) is comparative example 5; (b) is comparative example 6.

[0028] Figure 5 SEM and EDS results of the microstructure morphology of embodiment 3 of the present application.

[0029] Figure 6 EDS spectrum of embodiment 3 of the present application; wherein, (a) is the Al surface distribution map; (b) is the Si surface distribution map; (c) is the Cu surface distribution map; (d) is the Eu surface distribution map.

[0030] Figure 7 XRD spectrum of embodiment 1 and comparative example 1 of the present application.

[0031] Figure 8 XRD spectrum of embodiment 2 and comparative example 2 of the present application.

[0032] Figure 9 XRD spectrum of embodiment 3 and comparative example 3 of the present application.

[0033] Figure 10DSC curve diagram of the alloy of the present application comparative example 1~5.

[0034] Figure 11 DSC curve diagram of the alloy of the present application example 1~4.

[0035] Wherein, 1, gate; 2, copper mould; 3, cooling water channel; 4, mould cavity. DETAILED DESCRIPTION

[0036] The application will be further described in conjunction with specific embodiments, but the embodiments do not limit the application in any form. Unless otherwise specified, the raw materials used in the embodiments of the application are conventional commercially available raw materials.

[0037] From Al-Si-Cu ternary phase diagram (Fig. 1) Figure 1 It can be seen from the Al-Si-Cu ternary phase diagram (Fig. 1) that increasing the Cu content can significantly reduce the melting point of the Al-Si alloy. The principle is that Cu can promote the generation of ternary eutectic material Al-Al2Cu-Si; the melting point of Al2Cu is 548℃, and the Al-Si eutectic point is 577℃. When the Al-Si-Cu ternary phase melting temperature drops to 525℃, the required Cu weight percentage for the eutectic reaction is 26.7%, and the Si is 5.0%. Because the Al2Cu content in the low-melting ternary eutectic alloy is very high, Al2Cu is a brittle phase, so the ternary eutectic alloy is easy to break. Therefore, using Al-Si-Cu ternary eutectic material as the solder can effectively reduce the melting point of the solder, but the solder has the problems of low strength and poor plasticity.

[0038] To solve the above technical problems, the application uses 4047 alloy as the base material, introduces Cu to prepare an Al-Si-Cu alloy with a low melting point, and also dopes a specific amount of rare earth Eu to inhibit the precipitation of Al2Cu, so that the Si element preferentially forms a eutectic body with Al, effectively reducing the grain size of the base aluminum phase; the prepared aluminum alloy solder has a low melting point, and effectively improves the strength and plasticity of the solder.

[0039] Example 1 A low-melting-point aluminum alloy solder, comprising the following components in terms of weight percentage: Si 11.02%, Cu 5%, Eu 0.05%, Fe 0.80%, Mn 0.15%, Mg 0.10%, Zn 0.20%, and the balance being aluminum and unavoidable impurities.

[0040] The preparation method of the low-melting-point aluminum alloy solder comprises the following steps: S1, the reference Al burn rate is 5%, the Si burn rate is 3%, the Cu burn rate is 1%, the burn rate of Eu is negligible, and the raw materials are: 4047 aluminum ingot 160 parts, Al-50Cu intermediate alloy 20 parts and Al-20Si-5Eu intermediate alloy 20 parts, calculated by weight parts, placed in a graphite crucible, and 0.2wt% of hexachloroethane (C2Cl6) is added as a refining agent.

[0041] S2: the raw materials are placed in a resistance induction furnace for melting, heated to 800℃, melted, and kept for 30 minutes after continuous stirring, then the slag is removed, and cast into a copper mold, the copper mold is provided with a water cooling pipe, and the copper mold is cooled under water cooling conditions, and then demolded after solidification and cooling. Specifically, the mold structure schematic diagram is as shown in Figure 2 The copper mold 2 is provided with a sprue 1 and a mold cavity 4, the sprue 1 communicates with the mold cavity 4, and the copper mold 2 is provided with a plurality of cooling water channels, so that water cooling can be realized after casting the aluminum alloy, further improving the rapid cooling of the aluminum alloy melt, inhibiting the growth of the aluminum alloy precipitates Al2Cu, and thus improving the strength of the material.

[0042] Example 2 A low-melting-point aluminum alloy solder, comprising the following components by weight percentage: Si 10.97%, Cu 11.5%, Eu 0.18%, Fe 0.80%, Mn 0.15%, Mg 0.10%, Zn 0.20%, and the balance being aluminum and unavoidable impurities.

[0043] The preparation method of the low-melting-point aluminum alloy solder, comprising the following steps: S1, the reference Al burn rate is 5%, the Si burn rate is 3%, the Cu burn rate is 1%, the burn rate of Eu is negligible, and the raw materials are: 4047 aluminum ingot 160 parts, Al-50Cu intermediate alloy 20 parts and Al-20Si-5Eu intermediate alloy 20 parts, calculated by weight parts, placed in a graphite crucible, and 0.2wt% of hexachloroethane (C2Cl6) is added as a refining agent.

[0044] S2: the raw materials are placed in a resistance induction furnace for melting, heated to 800℃, melted, and kept for 30 minutes after continuous stirring, then the slag is removed, and cast into a copper mold, the copper mold is provided with a water cooling pipe, and the copper mold is cooled under water cooling conditions, and then demolded after solidification and cooling.

[0045] Example 3 A low-melting-point aluminum alloy solder comprises the following components in percentage by weight: Si 10.66%, Cu 13.87%, Eu 0.23%, Fe 0.80%, Mn 0.15%, Mg 0.10%, Zn 0.20%, and the balance being aluminum and inevitable impurities.

[0046] A preparation method of the low-melting-point aluminum alloy solder comprises the following steps: S1, referring to the Al burn rate of 5%, the Si burn rate of 3%, the Cu burn rate of 1%, and the Eu burn rate being negligible, the raw materials are 4047 aluminum ingot 85.87 parts, Al-50Cu intermediate alloy 60.6 parts, Al-20Si-5Eu intermediate alloy 9.82 parts, and Al-20Si intermediate alloy 60.0 parts in weight parts, which are placed in a graphite crucible and added with C2Cl6 (hexachloroethane) as a refining agent with a mass fraction of 0.2wt%.

[0047] S2: the raw materials are placed in a resistance induction furnace for smelting, heated to 830℃ for melting, and after 30 minutes of heat preservation under continuous stirring, the slag is removed, and cast into a copper mold, the copper mold is provided with a water cooling pipe, and the copper mold is allowed to stand and solidify under water cooling conditions, and then demolded after cooling.

[0048] Example 4 A low-melting-point aluminum alloy solder comprises the following components in percentage by weight: Si 10.66%, Cu 13.87%, Eu 0.23%, Fe 0.80%, Mn 0.15%, Mg 0.10%, Zn 0.20%, and the balance being aluminum and inevitable impurities.

[0049] A preparation method of the low-melting-point aluminum alloy solder comprises the following steps: S1, referring to the Al burn rate of 5%, the Si burn rate of 3%, the Cu burn rate of 1%, and the Eu burn rate being negligible, the raw materials are 4047 aluminum ingot 85.87 parts, Al-50Cu intermediate alloy 60.6 parts, Al-20Si-5Eu intermediate alloy 9.82 parts, and Al-20Si intermediate alloy 60.0 parts in weight parts, which are placed in a graphite crucible and added with C2Cl6 (hexachloroethane) as a refining agent with a mass fraction of 0.2wt%.

[0050] S2: the raw materials are placed in a resistance induction furnace for smelting, heated to 830℃ for melting, and after 30 minutes of heat preservation under continuous stirring, the slag is removed, and cast into a copper mold, the copper mold is provided with a water cooling pipe, and the copper mold is allowed to stand and solidify under water cooling conditions, and then demolded after cooling.

[0051] Comparative Example 1 A low-melting-point aluminum alloy solder, different from Example 1 in that: no rare earth Eu is contained in the present comparative example; and a traditional air cooling mode is adopted for solidification.

[0052] Specifically, the low-melting-point aluminum alloy solder comprises the following components in percentage by weight: Si 11.4%, Cu 5%, Fe 0.80%, Mn 0.15%, Mg 0.10%, Zn 0.20%, and the balance being aluminum and unavoidable impurities.

[0053] The preparation method of the low-melting-point aluminum alloy solder comprises the following steps: S1, referring to the Al burn loss rate of 5%, the Si burn loss rate of 3%, and the Cu burn loss rate of 1%, the raw materials are: 4047 aluminum ingot 160 parts, Al-50Cu intermediate alloy 20 parts, and Al-20Si intermediate alloy 20 parts, which are placed in a graphite crucible and added with C2Cl6 (hexachloroethane) as a refining agent with a mass fraction of 0.2wt%.

[0054] S2: the raw materials are placed into a resistance induction furnace for smelting, heated to 800℃ for melting, and after 30 minutes of heat preservation under continuous stirring, the slag is removed, and cast into a copper mold preheated to 300℃, and after standing, solidification, and cooling under room temperature conditions, the mold is demolded. Comparative Example 2 A low-melting-point aluminum alloy solder, different from Example 2 in that: no rare earth Eu is contained in the present comparative example; and a traditional air cooling mode is adopted for solidification.

[0055] Specifically, the low-melting-point aluminum alloy solder comprises the following components in percentage by weight: Si 11.07, Cu 11.5%, Fe 0.80%, Mn 0.15%, Mg 0.10%, Zn 0.20%, and the balance being aluminum and unavoidable impurities.

[0056] The preparation method of the low-melting-point aluminum alloy solder comprises the following steps: S1, referring to the Al burn loss rate of 5%, the Si burn loss rate of 3%, and the Cu burn loss rate of 1%, the raw materials are: 4047 aluminum ingot 160 parts, Al-50Cu intermediate alloy 20 parts, and Al-20Si intermediate alloy 20 parts, which are placed in a graphite crucible and added with C2Cl6 (hexachloroethane) as a refining agent with a mass fraction of 0.2wt%.

[0057] S2: the raw materials are placed into a resistance induction furnace for smelting, heated to 800℃ for melting, and after 30 minutes of heat preservation under continuous stirring, the slag is removed, and cast into a copper mold preheated to 300℃, and after standing, solidification, and cooling under room temperature conditions, the mold is demolded. Comparative Example 3 A low melting point aluminum alloy solder, different from example 3 in that: this comparative example does not contain rare earth Eu; and adopts the traditional air cooling method to solidify.

[0058] Specifically, the low melting point aluminum alloy solder comprises the following components in percentage by weight: Si 10.66%, Cu 13.87%, Fe 0.80%, Mn 0.15%, Mg 0.10%, Zn 0.20%, and the balance being aluminum and unavoidable impurities.

[0059] The preparation method of the low melting point aluminum alloy solder comprises the following steps: S1, referring to the Al burn rate of 5%, the Si burn rate of 3%, and the Cu burn rate of 1%, the raw materials are: 4047 aluminum ingot 85.87 parts, Al-50Cu intermediate alloy 60.60 parts, and Al-20Si intermediate alloy 69.82 parts, which are placed in a graphite crucible and added with C2Cl6 (hexachloroethane) as a refining agent with a mass fraction of 0.2wt%.

[0060] S2: the raw materials are placed in a resistance induction furnace for melting, heated to 830℃ for melting, and after 30 minutes of heat preservation under continuous stirring, the slag is removed, and cast into a copper mold preheated to 300℃, and then left to solidify and cool under room temperature conditions and demolded.

[0061] Comparative example 4 A low melting point aluminum alloy solder, different from example 4 in that: this comparative example does not contain rare earth Eu.

[0062] Specifically, the low melting point aluminum alloy solder comprises the following components in percentage by weight: Si 12.23, Cu 15%, Fe 0.80%, Mn 0.15%, Mg 0.10%, Zn 0.20%, and the balance being aluminum and unavoidable impurities.

[0063] The preparation method of the low melting point aluminum alloy solder comprises the following steps: S1, referring to the Al burn rate of 5%, the Si burn rate of 3%, and the Cu burn rate of 1%, the raw materials are: 4047 aluminum ingot 85.87 parts, Al-50Cu intermediate alloy 60.60 parts, and Al-20Si intermediate alloy 69.82 parts, which are placed in a graphite crucible and added with C2Cl6 (hexachloroethane) as a refining agent with a mass fraction of 0.2wt%.

[0064] S2: the raw materials are placed in a resistance induction furnace for melting, heated to 830℃ for melting, and after 30 minutes of heat preservation under continuous stirring, the slag is removed, and cast into a copper mold preheated to 300℃, and then left to solidify and cool under room temperature conditions and demolded. The structure of the copper mold is the same as that of example 1, and is not described again.

[0065] Comparative Example 5 A 4047 aluminum alloy solder, a preparation method thereof, comprising the following steps: S1, 200 parts of 4047 aluminum alloy ingot were placed in a graphite crucible, and C2Cl6 (hexachloroethane) with a mass fraction of 0.2wt% was added as a refining agent.

[0066] S2: The raw materials were placed in a resistance induction furnace for melting, heated to 830°C for melting, and after 30 minutes of continuous stirring, the slag was removed, and cast into a copper mold. The copper mold was provided with a water cooling pipe, and was allowed to stand and solidify under water cooling conditions, and then demolded after cooling. The structure of the copper mold was the same as that of Example 1, and will not be repeated here.

[0067] Comparative Example 6 A low-melting-point aluminum alloy solder, which is different from Example 3 in that the present comparative example does not contain Cu; Specifically, the low-melting-point aluminum alloy solder comprises the following components in terms of weight percentage: Si 11.39%, Eu 0.23%, Fe 0.80%, Mn 0.15%, Mg 0.10%, Zn 0.20%, and the balance being aluminum and unavoidable impurities.

[0068] The preparation method of the low-melting-point aluminum alloy solder comprises the following steps: S1, according to the Al burn rate of 5%, the Si burn rate of 3%, and the Eu burn rate being negligible, the raw materials are: 4047 aluminum ingot 146.47 parts, Al-20Si-5Eu intermediate alloy 9.82 parts, Al-20Si intermediate alloy 32 parts, and pure aluminum 28 parts, which are placed in a graphite crucible, and C2Cl6 (hexachloroethane) with a mass fraction of 0.2wt% is added as a refining agent.

[0069] S2: The raw materials were placed in a resistance induction furnace for melting, heated to 830°C for melting, and after 30 minutes of continuous stirring, the slag was removed, and cast into a copper mold. The copper mold was provided with a water cooling pipe, and was allowed to stand and solidify under water cooling conditions, and then demolded after cooling. The structure of the copper mold was the same as that of Example 1, and will not be repeated here.

[0070] The aluminum alloy component of the above Examples 1-4 and Comparative Examples 1-6 is summarized in Table 1 in terms of weight parts of raw material ratio.

[0071] Table 1

[0072] Performance test 1. Microstructure observation and analysis (1) Metallographic analysis: The low melting point aluminum alloy solder samples of Example 3 and Comparative Examples 3, 5 and 6 were observed for microstructure using a smart digital inverted metallurgical microscope (OM) of model DMi8C produced by Leica Microsystems, Germany, and the results are shown in Figs. 1-3. Figures 3-4

[0073] As can be seen from Figure 3 (a), the α-Al grains in the sample of Example 3 are equiaxed crystals, the ternary eutectic (Al-CuAl2-Si) is precipitated along the α-Al grain boundaries, and the inside of the grains is filled with fibrous Al-Si eutectic, and the primary Si is in the form of long lines.

[0074] As can be seen from Figure 3 (b), the white background in the sample of Comparative Example 3 is dendritic α-Al grains, the black irregularly shaped precipitates are ternary eutectic (Al-CuAl2-Si), and the primary Si is in the form of sharp-edged square blocks.

[0075] The above results show that the addition of rare earth Eu can reduce the amount of ternary eutectic (Al-CuAl2-Si) precipitation, refine the α-Al grains and part of the Al-Si eutectic.

[0076] In addition, there are a large number of sharp-edged block-shaped and sharp needle-shaped Si phases in the 4047 alloy of Comparative Example 5, which cut the aluminum matrix, resulting in a large brittleness of the material (a). Figure 4 However, in the 4047-0.23Eu alloy formed by adding 0.23% Eu in Comparative Example 6, the Si phase is in the form of rounded block-shaped, and the needle-shaped Si phase disappears, and the eutectic Si is refined (b). Figure 4 This shows that the addition of Eu can effectively refine the Si phase in the 4047 alloy, providing a technical basis for the 4047-Cu alloy.

[0077] (2) SEM and EDS analysis: The solder sample of Example 3 was analyzed for elemental composition using a high-resolution field emission scanning electron microscope of model (Apreo 2S HiVac), and the results are shown in Figs. 4-5. Figures 5-6

[0078] As can be seen from Fig. 5(a), in the SEM image of the alloy of Example 3, there is white material precipitated along the grain boundaries at the gray matrix. Dot spectrum analysis was performed on different phases, and the results are shown in Fig. 5(b). Figure 5 ​​(b) Spectrum 1, the black and gray tissue components in the region where Spectrum 1 is located are subjected to quantitative analysis, and the measurement results show that, in terms of mass percentage, the alloy contains 88.99% Al, 2.55% Cu, 0.89% Si, and C and O as impurities, indicating that the black matrix is an α-Al solid solution. The white substance region of Spectrum 2 contains 53.11% Al, 36.71% Cu, and C and Ag as impurities in terms of mass percentage, and it can be determined that the phase is CuAl2. Spectrum 3 contains 88.16% Si, which can be determined as the primary Si precipitated phase. The black point-like substance in the inner part of the Al2Cu phase (corresponding to the Spectrum 4 region) is subjected to micro-area composition analysis, and the detection data show that it contains 81.38% Al and 8.24% Cu, which indicates that the phase is a eutectic phase formed by Al / Al2Cu.

[0079] Referring to Figure 6 , the Al element distribution map (a graph of Figure 6 ) shows that the dark blue substance is an α-Al solid solution, and the α-Al solid solution is in the shape of a dendrite. The Si element distribution map (b graph of Figure 6 ) shows that the lake blue Si phase contains square-shaped and long needle-shaped substances, and the square-shaped substance is primary Si and the long needle-shaped substance is eutectic Si. The Cu element distribution map (c graph of Figure 6 ) shows that the yellow substance is a Cu-rich phase. The Eu element distribution map (d graph of Figure 6 ) shows that the magenta substance is Eu, and the Eu element is in a homogeneous distribution pattern.

[0080] 2. XRD phase analysis The low-melting-point aluminum alloy solder samples of Examples 1-3 and Comparative Examples 1-3 are detected by an Ultima-IV X-ray diffractometer, the scanning speed is 2° / min, and the scanning range is 10°-90°; the XRD spectrum obtained by testing is shown in Figures 7-9 , and the calculated lattice constant and lattice strain rate of α-Al are shown in Table 2.

[0081] As can be seen from Figure 7 , the materials prepared in Comparative Example 1 and Example 1 mainly contain α-Al, Si and CuAl2 three phases. Among them, the CuAl2 diffraction peak corresponding to Example 1 has only one, while the CuAl2 diffraction peak corresponding to Comparative Example 1 has six, indicating that the incorporation of Eu inhibits the formation of CuAl2.

[0082] The diffraction peaks corresponding to the α-Al phase in Example 1 are 38.70°, 44.92°, 65.32° and 78.46°, respectively. The diffraction peaks corresponding to Comparative Example 1 are 38.34°, 44.56°, 64.92° and 78.04°, respectively. The diffraction peaks corresponding to the α-Al phase in the standard card of pure aluminum are 38.47°, 44.74°, 65.13° and 78.23°, respectively. That is, the diffraction angles corresponding to the α-Al phase in Example 1 are all greater than those in the standard card, and the diffraction angles corresponding to the α-Al phase in Comparative Example 1 are all less than those in the standard card.

[0083] According to Bragg's equation 2dsinθ = nλ, where d is the lattice spacing corresponding to each diffraction peak, θ is the angle between the incident X-rays and the corresponding crystal plane (diffraction angle), λ is the wavelength of the X-rays, and n is the diffraction order. The larger θ is, the smaller the interplanar spacing in the crystal lattice is. Therefore, compared with pure aluminum, the interplanar spacing of the aluminum matrix in the material prepared in Example 1 is smaller, indicating that the addition of Eu causes the aluminum matrix to be under compressive stress; while the interplanar spacing of the aluminum matrix in the material prepared in Comparative Example 1 is larger, and the aluminum matrix is under tensile stress. Compressive stress can improve the mechanical properties of the material, including the tensile strength and plasticity of the material, and further provides evidence for the addition of rare earth Eu to improve the mechanical properties of Al-Si-Cu.

[0084] From Figure 8 It can be seen that Comparative Example 2 and Example 2 mainly contain α-Al, Si and CuAl2 three phases. Among them, the peak intensity corresponding to α-Al is the largest, indicating that the alloy is α-Al as the main phase of the matrix. It can be seen from the figure that the four α-Al diffraction peaks in the aluminum alloy in Example 2 are wider than those in Comparative Example 2. According to the Scherrer formula, the wider diffraction peak proves that the rare earth Eu can effectively reduce the grain size of the aluminum matrix; at the same time, according to the Hall-Petch formula, the smaller the grain size, the greater the yield strength σ of the material.

[0085] Among them, the Scherrer formula is D = Kλ / (β cosθ). Wherein, D is the grain size, K is the Scherrer constant, λ is the X-ray wavelength, β is the full width at half maximum (FWHM) of the diffraction peak, and θ is the diffraction angle. The larger the half width β of the diffraction peak, the wider the diffraction peak, and the smaller the grain size D. It shows that the rare earth Eu can effectively reduce the grain size of the aluminum matrix.

[0086] The Hall-Petch formula is σ = σ0 + k / √(D). Wherein σ is the yield strength of the material, σ0 is the material constant, k is the strengthening coefficient, and D is the average diameter of the grain. The formula shows that the smaller the grain, the greater the yield strength σ of the material.

[0087] Further, the alloy CuAl2 of the comparative example 2 has 7 diffraction peaks, indicating that the content of CuAl2 in the comparative example 2 is relatively high; while the CuAl2 of the example 2 has only one diffraction peak at a diffraction angle 2θ = 47.18°, indicating that the rare earth metal Eu can effectively inhibit the generation of CuAl2.

[0088] In addition, the diffraction peak at 2θ = 28.34° of the example 2 corresponds to elemental Si, and the peak width 2β of the elemental Si phase is 0.92°, while the peak width 2β of the elemental Si at 2θ = 28.44° in the comparative example 2 is 0.40°, further proving that Eu can refine the elemental Si.

[0089] From Figure 9 It can be seen that the alloys prepared in the comparative example 3 and the example 3 mainly contain α-Al, Si and CuAl2 three phases. The α-Al peak in the example 3 has 4 strong peaks, and 2θ is 38.60°, 44.32°, 65.28° and 78.42° respectively. Among them, the peak at 38.60° also includes the Si phase, indicating that this diffraction peak is a lamellar mechanical mixed eutectic phase of α-Al and Si. The diffraction peak at 2θ = 44.88° in the comparative example 3 is the first strong peak, and the diffraction peak at 2θ = 38.60° is the second strong peak, followed by the third and fourth strong peaks at 65.24° and 78.40°. It is proved that the rare earth Eu promotes the increase of the content of the eutectic Al-Si phase in the 4047-15Cu alloy.

[0090] In addition, the CuAl2 diffraction peak of the example 3 has 9 peaks, and the CuAl2 diffraction peak of the comparative example 3 has 10 peaks, and the intensity of the 8 CuAl2 diffraction peaks of the comparative example 3 is greater than that of the example (except 2θ = 47.36), indicating that the addition of Eu inhibits the amount of CuAl2 in the 4047-13.87Cu alloy to a certain extent.

[0091] Further, the lattice constants of the example 3 and the comparative example 3 are calculated by using JADE software, and the lattice constants of the example 3 and the comparative example 3 are smaller than that of pure aluminum, but the compressive stress of the example 3 is greater than that of the comparative example 3, indicating that 0.23% of Eu makes the compressive stress of the 4047-13.87Cu slightly larger, which is beneficial to improve the strength and plasticity of the material.

[0092] Table 2 Crystal lattice constant and lattice strain rate of α-Al of examples 1-3 and comparative examples 1-3

[0093] Among them, the crystal structure of pure aluminum in the standard card with index number 04-0787 is face-centered cubic (FCC) structure, and the crystal lattice constant of aluminum is 4.049Å.

[0094] The α-Al of the low-melting-point aluminum alloy solder of the present invention has a smaller lattice constant than that of pure aluminum. This means that the crystal is subjected to compressive stress, which leads to a shortening of the interatomic spacing. Therefore, a negative number indicates that the crystal is subjected to compressive stress, which is beneficial to enhancing the tensile strength and plasticity of the material. A positive number indicates that the crystal is subjected to tensile force.

[0095] Compared to Comparative Example 1, the addition of 0.05% rare earth metal Eu in Example 1 caused the Al matrix in 4047-5Cu to change from a tensile stress state to a compressive stress state. Compressive stress is beneficial to improving the mechanical properties of the material. Compared to Comparative Example 2, the addition of 0.18% rare earth metal Eu in Example 2 showed that the material was subjected to a compressive stress state, and compressive stress is more beneficial to improving mechanical properties than tensile force.

[0096] The lattice constants of both Example 3 and Comparative Example 3 are less than those of pure aluminum, but the compressive stress of Example 3 is greater than that of Comparative Example 3, indicating that 0.23% Eu causes the 4047-13.87Cu to experience slightly greater compressive stress, which is beneficial to improving the strength and plasticity of the material.

[0097] 3. Differential Scanning Calorimetry (DSC) Analysis Differential scanning calorimetry (DSC) tests were performed on the low-melting-point aluminum alloy solder samples from Examples 1-4 and Comparative Examples 1-5, and the obtained DSC curves are shown below. Figures 10-11 As shown.

[0098] from Figure 10 The DSC curves of the alloys prepared in Comparative Examples 1 to 5 show that Comparative Example 5 is alloy 4047, which has an endothermic peak at 590℃. According to the Al-Si phase diagram, it can be determined that this is an Al-Si eutectic. Extending the baseline on the low-temperature side of the curve to the high-temperature side, and intersecting the tangent line drawn from the point where the slope of the curve is the largest on the low-temperature side of the melting curve peak and valley, we can determine that its melting point is 579℃.

[0099] Unlike the DSC curve of the 4047 alloy in Comparative Example 5, the alloys of Comparative Examples 1-4, which incorporated a specific Cu element, showed two endothermic peaks, indicating that the addition of Cu resulted in two phases with different melting points. According to... Figure 1 As can be seen from the Al-Si-Cu ternary phase diagram, the endothermic peak near 525.5℃ in Comparative Example 1 is the heat of fusion required for the ternary eutectic material Al-Al2Cu-Si, while the peak near 562℃ is a mechanical mixture of Al2Cu and Si.

[0100] Meanwhile, as the amount of Cu increases, the melting point of the alloy decreases. When 15% copper is added to Comparative Example 4, its melting point drops to 519.62℃.

[0101] from Figure 11The DSC curves of the alloys prepared in Examples 1-4 show that, compared with Comparative Examples 1-4, the melting point of the 4047-xCu alloys prepared in Examples 1-4 is slightly reduced when the weight percentage of the Eu rare earth metal element is 0.05%-0.25%, which is related to the fact that the Eu rare earth metal element can refine the matrix aAl and part of the eutectic Si grains. It is particularly worth mentioning that only one endothermic melting peak appears near 574-579℃ in Example 1 and Example 2, indicating that the Al2Cu phase is inhibited by Eu at this time.

[0102] 4. Alloy performance characterization The low-melting-point aluminum alloy solder samples of Examples 1-4 and Comparative Examples 1-6 were subjected to the following performance tests, and the results are shown in Table 2.

[0103] (1) Tensile strength and elongation at break: According to the national standard GB / T 228.1-2010, a universal testing machine from Shanghai Huagong was used to test the strength of the prepared material, and the pulling rate was 0.6 mm / min.

[0104] (2) Hardness: According to the GB / T 4340.2:2012 standard, a TH750 Vickers hardness tester was used to test the hardness of the surface of the aluminum alloy.

[0105] (3) Melting point: A Q10 differential scanning calorimeter was used to measure the solder melting characteristics by differential scanning calorimetry (DSC). Nitrogen was used as the protective gas. The temperature was raised to 800℃ at a rate of 10℃ / min and held at this temperature for 10 min, and then the temperature was lowered to room temperature at a rate of 10℃ / min.

[0106] (4) Spread rate: Pure aluminum was used as the substrate, and after alkaline washing, 0.2 g of alloy solder was selected. The mass ratio of solder to flux was 9:1, and the flux was potassium fluoroaluminate, which was covered and completely coated on the surface of the solder, and then slowly sent into a 580℃ box furnace. After the solder completely solidified, a digital camera was used to take pictures of the spread sample after cooling, and professional image processing software was used to test the spread area. The spread rate is calculated as shown in formula (1): Formula (1); In the formula Spread rate %; H Height of the spread solder (mm); D Diameter of the solder used in the test (mm), D = 1.24 V 1 / 3 ; V - mass / density of the solder sample used in the test. H= Spread solder volume / Average spreading area. The prepared solder is weighed using an electronic balance, and its volume is measured using a graduated cylinder to calculate the density of various solders. Given the mass of the spread solder, the volume of solder used for spreading can be calculated, and this volume can be divided by the average spreading area to obtain the density. H And the result was obtained from the solder volume. D Substitute the values ​​into formula (1) to obtain the spreading rate.

[0107] Table 3

[0108] As shown in Table 3, this invention utilizes an Al-Si-Cu ternary alloy to form a low-melting-point eutectic phase, effectively reducing the melting point of the material. Simultaneously, the doping with Eu atoms suppresses the precipitation of the brittle Al₂Cu phase, thus enabling the aluminum alloy solder to possess both a low melting point and high tensile strength and elongation at fracture. Specifically, the alloy of this invention has a melting point ≤538.27℃, a spread rate ≥100%, a hardness ≥74.1HV, an elongation at fracture ≥5.96%, and a tensile strength ≥235.29MPa.

[0109] Comparing the alloys of Comparative Examples 1-4 with those of Examples 1-4, it can be seen that the addition of Eu in this invention can refine the microstructure, lower the melting point, and simultaneously improve the spread, elongation after fracture, and tensile strength.

[0110] Comparing Example 3 and Comparative Examples 5-6, in Example 3, the addition of Cu and Eu directly to the 4047 alloy resulted in a reduction in melting point difference of over 50°C. Furthermore, the addition of Eu rare earth elements further improved the solder's spreadability, reduced the material's hardness and brittleness, and significantly increased its elongation after fracture.

[0111] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A low-melting-point aluminum alloy solder, characterized in that, The composition includes the following components by weight percentage: Si 10-14%, Cu 4-20%, Eu 0.04-0.25%, Fe 0.78-0.82%, Mn 0.13-0.17%, Mg 0.08-0.12%, Zn 0.18-0.22%, with the balance being aluminum and unavoidable impurities.

2. The low-melting-point aluminum alloy solder according to claim 1, characterized in that, It includes the following components by weight percentage: Si 10.5-13%, Cu 5-15%, Eu 0.05-0.23%, Fe 0.80%, Mn 0.15%, Mg 0.10%, Zn 0.20%, with the balance being aluminum and unavoidable impurities.

3. The low-melting-point aluminum alloy solder according to claim 1 or 2, characterized in that, The mass ratio of Cu to Eu atoms is (50-110):

1.

4. The low-melting-point aluminum alloy solder according to claim 1, characterized in that, The aluminum matrix has a lattice constant less than that of pure aluminum in the standard card PDF#04-0787 in the X-ray diffraction pattern, and has α-Al diffraction peaks at 38.46-38.70°, 44.76-44.92°, 65.14-65.32° and 78.36-78.46°.

5. The low-melting-point aluminum alloy solder according to claim 1, characterized in that, The low-melting-point aluminum alloy solder has a melting point of 515-540℃, a spread rate of ≥100%, an elongation after fracture of ≥5.96%, and a tensile strength of ≥235.29MPa.

6. The low-melting-point aluminum alloy solder according to claim 1, characterized in that, The raw materials consist of the following components by weight: 20-160 parts of 4047 aluminum alloy, 20-62 parts of Al-50Cu master alloy, 6-20 parts of Al-20Si-5Eu master alloy, 0-112 parts of Al-20Si master alloy, and 0-4 parts of pure aluminum.

7. A method for preparing a low-melting-point aluminum alloy solder according to any one of claims 1-6, characterized in that, The process includes the following steps: mixing and melting raw material components according to stoichiometric ratio at a melting temperature of 790~850℃, casting into shape, and water cooling to obtain the low melting point aluminum alloy solder.

8. The method for preparing low-melting-point aluminum alloy solder according to claim 7, characterized in that, Before smelting, 0.1-3 wt% of refining agent is added; the refining agent is selected from at least one of hexachloroethane and Na3AlF6.

9. The application of a low-melting-point aluminum alloy solder according to any one of claims 1-6 in the welding of aluminum alloy substrates.

10. The application according to claim 9, characterized in that, The aluminum alloy substrate has a melting point ≥550℃.

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