A high temperature resistant brazable die-casting aluminum alloy and its preparation method and application

Abstract

The invention relates to a high-temperature resistant brazed die-casting aluminum alloy and a preparation method and application thereof. The alloy comprises Si: 0.05-0.8wt%; Fe: 0.8-3.0wt%; Ni: 0.005-1.5wt%; Mn: 0.3-1.5wt%; Mg: 0.005-2.50wt%; Zn: 0.005-3.0wt%; Cu: 0.005-1.0wt%; Ce: 0.005-0.20wt%; Cr: 0.01-0.5wt%; Ti: 0.01-0.25w%; B: 0.001wt%-0.1wt%; the sum of the weight percentages of other impurities is controlled to be less than 0.5wt%, and the remainder is Al; and the mass ratio P value of Fe to (Ni+Mn+Cr) is controlled to be 0.3-3:1. Compared with the prior art, the die-casting aluminum alloy prepared by the present invention has excellent die-casting property, high temperature resistance and brazing property.

Description

Technical Field

[0001] The invention relates to the technical field of die-casting aluminum alloys, and in particular to a high-temperature resistant brazable die-casting aluminum alloy and a preparation method and application thereof. Background Art

[0002] In the modern automotive industry, heat exchanger systems are important components to ensure the normal operation and high efficiency of vehicles. Heat exchangers achieve key functions such as engine cooling and air conditioning refrigeration through heat transfer. As the core material of heat exchangers, aluminum alloys are widely used in the manufacture of heat exchangers due to their excellent thermal conductivity, light weight and corrosion resistance. Aluminum alloy sheets and profiles are made through extrusion, rolling and other processes, and have good mechanical properties and thermal conductivity. In automotive heat exchangers, these materials are usually used as components such as heat sinks, flow channels and housings.

[0003] Aluminum alloy has high thermal conductivity, which can conduct heat quickly and effectively, improving the efficiency of heat exchangers. Compared with traditional alloy materials, aluminum alloy has low density, which helps to reduce the overall weight of the vehicle and improve fuel economy. In addition, aluminum alloy materials have good forming properties during processing and are suitable for manufacturing heat exchanger components with complex shapes.

[0004] Although aluminum alloys have significant advantages in heat exchanger manufacturing, their manufacturing costs are relatively high. The production process of aluminum alloy heat exchange modules is complex, involving stamping and CNC processing of plates, which leads to rising costs. In order to reduce costs, some companies have tried to use aluminum alloy die-castings to replace traditional stampings and forgings to reduce process costs. However, the application of aluminum alloy die-castings in heat exchanger manufacturing faces some key problems: aluminum alloys suitable for die-casting, such as ADC12 / A380, have high Si elements, and their solidus lines are lower than the brazing temperature (590-610℃), and high-temperature brazing processes are key processes for achieving component connection and sealing. They cannot be avoided, and traditional die-casting materials are not suitable for the production of this type of product. The raw materials used in the production of traditional forgings and plates have poor die-casting properties due to the characteristics of the materials themselves, making it difficult to achieve reliable die-casting production. Defects such as pores and shrinkage cavities are prone to occur during the die-casting process, resulting in unstable product quality, affecting the sealing and reliability of the heat exchanger, and unable to achieve large-scale mass production. At present, there is a lack of aluminum alloys for die-casting that have both good die-casting properties and excellent brazing properties on the market.

[0005] Patent CN116334454B discloses a brazable heat-treatment-free die-cast aluminum alloy material and a preparation method thereof. The material is composed of the following components in mass percentage: Si: 0.05wt%-1.0wt%; Fe: 0.05wt%-0.60wt%; Mn: 0.6wt%-1.9wt%; Ce: 0.05wt%-2.0wt%; Mg: ≤0.5wt%; Cs: ≤0.3wt%; Sc+Zr: ≤0.5wt%; Zn: ≤0.3wt%; Ti: ≤0.25wt%; B: 0.002wt%-0.03wt%; Sr: 0.001wt%-0.1wt%; the remaining impurities are controlled below 0.3wt%, and the balance is Al. The patent contains rare and expensive elements such as Sc, Cs and Ce, and the intermediate alloy is added in the form of amorphous nanopowder, which will undoubtedly greatly increase the production cost of enterprises. At this stage, enterprises are increasingly interested in reducing costs and increasing efficiency. At the same time, the patent is mainly based on Mn, and the Mn content belongs to a relatively high content range, but too much Mn is prone to produce blocky large-sized precipitation phases, which hinder the flow of aluminum liquid and lead to loose organization and pores. After brazing, the material is prone to bulging and leakage defects, so the patent involves product costs and parts with high airtightness requirements, which have great limitations in application.

[0006] In view of the above challenges, it is necessary to develop new aluminum alloy materials that can adapt to the current needs of brazing die-cast aluminum alloy materials and provide better solutions for the development of the automotive industry. Summary of the invention

[0007] In view of the above problems, the purpose of the present invention is to provide a high temperature resistant brazed die-casting aluminum alloy material and a preparation method and application thereof in order to overcome the above defects of the prior art.

[0008] The object of the present invention can be achieved by the following technical scheme: a high temperature resistant brazed die-casting aluminum alloy, the alloy comprises Si: 0.05-0.8wt%; Fe: 0.8-3.0wt%; Ni: 0.005-2.0wt%; Mn: 0.3-1.5wt%; Mg: 0.005-3.0wt%; Zn: 0.005-3.0wt%; Cu: 0.005-1.0wt%; Ce: 0.005-0.20wt%; Cr: 0.01-0.5wt%; Ti: 0.01-0.25w%; B: 0.001wt%-0.1wt%; the sum of the weight percentages of the remaining impurities is controlled to be below 0.5wt%, and the balance is Al; the mass ratio of Fe to (Ni+Mn+Cr) is controlled to have a P value of 0.3~3:1.

[0009] Preferably, the following components are included in mass percentage: Si: 0.05-0.5wt%; Fe: 0.8-2.0wt%; Ni: 0.005-1.5wt%; Mn: 0.3-0.8wt%; Mg: 0.005-2.50wt%; Zn: 0.005-2.0wt%; Cu: 0.005-0.5wt%; Ce: 0.005-0.15wt%; Cr: 0.01-0.3wt%; Ti: 0.01-0.25w%; B: 0.001wt%-0.1wt%; the sum of the weight percentages of the remaining impurities is controlled below 0.5wt%, and the balance is Al; the mass ratio P value of Fe to (Ni+Mn+Cr) is controlled at 0.5~1.6:1.

[0010] The present invention also provides a method for preparing a die-cast aluminum alloy, comprising the following steps:

[0011] Step S1: first weigh pure Al raw material, Al-Si, Al-Fe, Al-Ni, Al-Mn, Al-Cr, Al-Ti-B and Al-Ce alloy according to the mass ratio.

[0012] Step S2: firstly, pure Al raw material is put into a heating furnace, heated to 680°C to obtain molten aluminum liquid, and after the aluminum metal is completely melted, it is kept at the temperature for 20-30 minutes;

[0013] Step S3: Raise the temperature to 780°C, add Al-Fe, Al-Ni, Al-Cr, Al-Mn, Al-Si, and pure Cu to the aluminum liquid in proportion, and wait for them to be completely dissolved;

[0014] Step S4: Cooling to 750°C, adding Al-Ce and Al-Ti-B master alloys, and keeping the temperature for 20-30 minutes;

[0015] Step S5: cooling to 720°C, adding pure Mg and pure Zn, keeping the temperature for 15-20 minutes and then performing degassing and refining;

[0016] Step S6: The casting sample is subjected to component analysis. If the sample is qualified, the refined melt is melted and poured into the vacuum die-casting machine again for high-pressure die-casting to obtain the high-temperature resistant brazable die-casting aluminum alloy.

[0017] Furthermore, the die-casting process comprises the following steps:

[0018] The refined melt is melted again at 720-740℃ and kept warm. During the heat preservation, protective gas is introduced to isolate it from the air. Then, it is injected into the die-casting mold by injection. After vacuuming, vacuum molding is performed to obtain a die-cast aluminum alloy product.

[0019] Furthermore, the injection adopts a filling method of first low speed and then high speed. The low speed of injection is controlled at 0.10~0.40m / s. The die-casting mold is temperature-controlled by the oil temperature machine, water temperature machine and chiller. The oil temperature machine is set at 180~250℃, the water temperature machine is 100~130℃, the cooling water is kept at 15~30℃, and the cooling water is passed through the mold core cooling pipeline at a water pressure of 0.8~1.2MPa. After the injection is completed, the pressure is maintained for 5~10 seconds.

[0020] Furthermore, the die-cast aluminum alloy product can withstand high-temperature brazing above 600°C. After brazing, the product has a yield strength greater than 50 MPa, an elongation greater than 10%, and a hardness greater than 50 HV.

[0021] Furthermore, the alloy structure of the die-cast aluminum alloy includes α-Al and eutectic structure;

[0022] Wherein, the eutectic structure includes α-Al phase, Al3Ni phase, Al3(Fe, Ni)Si phase, Al9FeNi phase, Mg2Si, AlCuMg phase and Al3(Fe, Re) phase;

[0023] In the eutectic structure, the precipitated phase is distributed in the form of dispersed particles, including short rods, spheres and blocks.

[0024] The present invention also provides an application of a die-cast aluminum alloy product, wherein the die-cast aluminum alloy product is used for brazing a heat exchanger mold assembly, specifically comprising the following steps:

[0025] Step (1): preparing raw materials, and obtaining a die-casting aluminum alloy by the above method;

[0026] Step (2): cleaning the surface of the die-cast aluminum alloy to remove oil stains and oxides on the surface of the workpiece;

[0027] Step (3): After applying brazing material to the brazing surface, assembling the workpieces and fixing them;

[0028] Step (4): brazing in a tunnel brazing furnace / vacuum brazing furnace at a temperature of 595°C-610°C;

[0029] Step (5): Obtain an aluminum alloy heat exchanger component with a dense brazing seam.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The material in the present invention is mainly Fe-based. By increasing Fe, the affinity between the aluminum liquid and the die-casting mold can be reduced, the wetting angle can be improved, the risk of product sticking to the mold can be reduced, and the die-casting performance of the material can be improved. However, the addition of Fe is easy to generate a needle-like Al3Fe phase during the solidification process. This long needle-like Fe phase is easy to split the matrix and produce cracks. And because the Fe content is high, the addition of Mn is easy to produce coarse AlFeMn phases, which is not conducive to the fluidity of the material. The amount of Mn added must be limited to a lower range. The innovative joint supplementary addition of Ni and Cr in the present invention plays a role in the deterioration and neutralization of the morphology of the Fe element. Through the deposition of Ni and Cr on the surface of the Fe phase, the diffusion of Fe atoms is hindered, and the growth of the Al3Fe phase is restricted, so that the Fe phase is transformed from a long needle to a short rod, thereby improving the fluidity of the aluminum liquid. Among them, there is a certain adaptation range for the ratio of Ni, Mn and Cr to Fe phase. If it is too little, the Fe phase will not be fully modified, and if it is too much, a coarse phase will be generated and the cost will increase. The inventors have verified many times that the mass ratio P of Fe to (Ni+Mn+Cr) is most suitable to be controlled at 0.3~3:1;

[0032] Considering the high brazing temperature (590-610℃), the mechanical properties and hardness of aluminum alloy materials will be significantly attenuated after the brazing process, and the strengthening phase and work hardening effect in the material before welding cannot be retained. The alloy of the present invention ensures that the solidus line is higher than 610℃, and by adding a small amount of Si and Cu, after brazing, Si, Cu and Mg dissolved in the matrix are complexed with each other to produce Mg2Si and AlCuMg aging phases at room temperature, thereby improving the mechanical properties and hardness of the material. At the same time, the addition of a small amount of Zn improves the distribution density and precipitation rate of the GP zone corresponding to the aging phase, effectively avoiding the problem of mechanical property attenuation of the material after brazing.

[0033] The alloy of the present invention ensures that the alloy liquidus is lower than 700°C through element design, which means that the casting temperature can be lower than 720°C. The lower melting and holding temperatures can significantly reduce the amount of gas absorption by the aluminum liquid. At the same time, the alloy of the present invention further removes gas and impurities in the aluminum liquid through the addition of Ce rare earth elements, reduces the gas content of the product after die casting, avoids pore temperature, and thus reduces the risk of bulging and leakage of the product during brazing. At the same time, Ce can be combined with Al3Ti and TiB2 as a heterogeneous core nucleation point to play a role in grain refinement, enhance the toughness of the alloy, and reduce the thermal cracking sensitivity of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the microstructure of the die-cast aluminum alloy of Example 2 of the present invention (1000 times).

[0035] Figure 2 This is the microstructure of the die-cast aluminum alloy of Example 7 of the present invention (1000 times).

[0036] Figure 3 This is the microstructure of the die-cast aluminum alloy of comparative example 1 of the present invention (1000 times).

[0037] Figure 4 This is the microstructure (1000 times) of the die-cast aluminum alloy of Comparative Example 2 of the present invention.

[0038] Figure 5 This is the microstructure (1000 times) of the die-cast aluminum alloy of Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0039] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0040] The raw materials used in the present invention are all commercially available raw materials. During the preparation process, Al, Mg, Zn, and Cu are added in the form of pure metal raw materials, and other raw materials are added in the form of commercially available alloys. For example, in the following embodiments, commercially available Al-Si, Al-20Fe, Al-10Ni, Al-10Mn, Al-10Cr, Al-5Ti-1B, and Al-10Ce alloys are used to add and control the amount of each element.

[0041] Examples 1-10 and Comparative Examples 1-3

[0042] A high-temperature resistant brazed die-casting aluminum alloy comprises Si: 0.05-0.8wt%; Fe: 0.8-3.0wt%; Ni: 0.005-2.0wt%; Mn: 0.3-1.5wt%; Mg: 0.005-3.0wt%; Zn: 0.005-3.0wt%; Cu: 0.005-1.0wt%; Ce: 0.005-0.20wt%; Cr: 0.01-0.5wt%; Ti: 0.01-0.25w%; B: 0.001wt%-0.1wt%; the sum of the weight percentages of other impurities is controlled to be below 0.5wt%, and the balance is Al; the mass ratio of Fe to (Ni+Mn+Cr) is controlled to have a P value of 0.3-3:1.

[0043] The ingredients of each embodiment and comparative example are shown in Table 1

[0044] Table 1 is the aluminum alloy content of the embodiment and the comparative example

[0045]

[0046] The present invention also provides a method for preparing the high temperature resistant brazed die-casting aluminum alloy, which specifically comprises:

[0047] Step S1: first weigh pure Al raw material, Al-Si, Al-20Fe, Al-10Ni, Al-10Mn, Al-10Cr, Al-5Ti-1B and Al-10Ce alloy according to the mass ratio.

[0048] Step S2: firstly, pure Al raw material is put into a heating furnace, heated to 680°C to obtain molten aluminum liquid, and after the aluminum metal is completely melted, it is kept at the temperature for 20 minutes;

[0049] Step S3: Raise the temperature to 780°C, add Al-20Fe, Al-10Ni, Al-10Cr, Al-10Mn, Al-Si, and pure Cu to the aluminum liquid in proportion, and wait for them to be completely dissolved;

[0050] Step S4: cooling to 750°C, adding Al-10Ce and Al-5Ti-B master alloys, and keeping the temperature for 20 minutes;

[0051] Step S5: cooling to 720°C, adding pure Mg and pure Zn, and performing degassing and refining after keeping the temperature for 20 minutes;

[0052] Step S6: Cast a small sample for component analysis. If it is qualified, melt it again at 720-740℃ and keep it warm. During the heat preservation, introduce protective gas to isolate it from the air. Then, inject it into the die-casting mold of the air die-casting machine by injection. The injection adopts a filling method of first low speed and then high speed. The low speed of injection is controlled at 0.35m / s. The die-casting mold is temperature-controlled by an oil temperature machine, a water temperature machine, and a chiller. The oil temperature machine is set at 185℃, and the water temperature machine is set at 110℃. The cold spot cooling water passes through the mold core spot cooling pipeline with a water pressure of 1.1MPa. After the injection is completed, the pressure is maintained for 6 seconds, and high-pressure die-casting is performed to obtain the high-temperature resistant brazed die-casting aluminum alloy.

[0053] The obtained die-cast aluminum alloy was subjected to the following performance tests: wherein, the mechanical properties, tensile strength, yield strength and elongation were tested in accordance with the national standard GB / T 228.1-2010; and the hardness was tested in accordance with GB / T4340.1-2009.

[0054] As shown in the example in Table 2, the material state refers to the state of the die-cast aluminum alloy without any heat treatment after high-pressure die-casting; after brazing refers to the experimental results of the die-cast aluminum alloy sample being heated from room temperature to 610℃ at a heating rate of 3.5℃ / min, kept at 610℃ for 10 minutes, and then taken out and the sample being cooled to room temperature in air. Customers can adjust this process according to their own needs; hardness refers to the Vickers hardness measured on the sample material.

[0055] Table 2 Performance results of Examples 1-10 and Comparative Examples 1-3

[0056]

[0057] From Table 2 above, we can see that:

[0058] Compared with Example 1, the main difference between Example 7 and Comparative Example 1 is that the content of Mn and Cr in the comparative example is significantly increased, and its Fe / (Mn+Cr+Ni) value is less than 0.3. Figure 2 This is the microstructure of the die-cast aluminum alloy of Example 7 (1000 times), Figure 3 Microstructure of die-cast aluminum alloy in Comparative Example 1 (1000 times), combined with Figure 2-3 By comparing the microstructures of the die castings, it can be found that the excessive addition of Mn and Cr in Comparative Example 1 leads to a significant increase in the number of large precipitates in the matrix, and the size of the precipitates is coarse, resulting in a non-dense die casting structure, low elongation, and poor mechanical properties.

[0059] The main difference between Example 2 and Comparative Example 2 is that more Ni element is added in Comparative Example 2, and its Fe / (Mn+Cr+Ni) value is less than 0.3. Figure 1 This is the microstructure of the die-cast aluminum alloy in Example 2 (1000 times), Figure 4 For the microstructure of die-cast aluminum alloy in comparative example 2 (1000 times), combined with Figure 1 and 4 The microstructure comparison shows that excessive addition of Ni leads to a significant increase in the number of large precipitates in the matrix. Although it can still have a metamorphic effect, excessive addition significantly increases the size of the Ni-based precipitates in the matrix. The difference in performance between the precipitates and the matrix easily leads to microcracks and stress concentration, which shows low elongation and poor mechanical properties on a macro scale.

[0060] The main difference between Example 2 and Comparative Example 3 is that the Ni element in Comparative Example 3 is lower, and its Fe / (Mn+Cr+Ni) value is greater than 3.0. Figure 1 This is the microstructure of the die-cast aluminum alloy in Example 2 (1000 times), Figure 5 For the microstructure of die-cast aluminum alloy in comparative example 3 (1000 times), combined with Figure 1 and 3 From the comparison of the microstructures, it can be found that the Ni content is insufficient, the modification effect of the Fe-based phase is poor, and a dispersed and rounded Fe-based structure cannot be obtained. The large Fe-based precipitated phase that is insufficiently modified will hinder the flow and shrinkage of the aluminum liquid during the die-casting process, which is easy to cause tissue shrinkage and holes, resulting in a decrease in mechanical properties. It can be seen from the above data that the heat-resistant brazed die-casting aluminum alloys of Examples 1-10 have excellent mechanical properties and brazing capabilities, while although the tensile strength of the material body of Example 2 and the elongation of Example 3 of Comparative Examples 1-3 are better, the overall comprehensive performance is poor, and once brazing is performed, the performance decreases significantly. It can be seen that the product of the present invention is very suitable for the production of products such as automotive cooling module components, and the specific application method includes the following steps:

[0061] Step (1): preparing raw materials, and obtaining a die-casting aluminum alloy by the above method;

[0062] Step (2): cleaning the surface of the die-cast aluminum alloy to remove oil stains and oxides on the surface of the workpiece;

[0063] Step (3): After applying brazing material to the brazing surface, assembling the workpieces and fixing them;

[0064] Step (4): brazing in a tunnel brazing furnace / vacuum brazing furnace at a temperature of 595°C-610°C;

[0065] Step (5): Obtain an aluminum alloy heat exchanger component with a dense brazing seam.

[0066] The die-casting aluminum alloy of the present invention has good economic benefits and application scope for various production enterprises.

[0067] The above is a preferred implementation mode of the present invention, but the protection scope of the present invention is not limited to the above implementation. All technical solutions under the concept of the present invention belong to the protection scope of the present invention.

Claims

1. A high temperature resistant brazable die casting aluminum alloy, characterized in that: The die-cast aluminum alloy includes Si: 0.09wt%; Fe: 1.49wt%; Ni: 0.81wt%; Mn: 0.58wt%; Mg: 2.48wt%; Zn: 0.08wt%; Cu: 0.01wt%; Ce: 0.13wt%; Cr: 0.12wt%; Ti: 0.11w%; B: 0.021wt%; the sum of the weight percentages of other impurities is controlled below 0.5wt%, and the remainder is Al; the mass ratio P value of Fe to (Ni+Mn+Cr) is controlled at 0.99:1; the obtained die-cast aluminum alloy product can withstand high-temperature brazing above 600°C, and the product after brazing has a yield strength of 108Mpa, an elongation of 10.2%, and a hardness of 82HV.

2. A high temperature resistant brazable die casting aluminum alloy according to claim 1, characterized in that: The alloy structure of the die-cast aluminum alloy includes α-Al and eutectic structure; Wherein, the eutectic structure includes α-Al phase, Al3Ni phase, Al3(Fe, Ni)Si phase, Al9FeNi phase, Mg2Si, AlCuMg phase and Al3(Fe, Re) phase; In the eutectic structure, the precipitated phase is distributed in the form of dispersed particles, including short rods, spheres and blocks.

3. A method for preparing a high temperature resistant brazable die casting aluminum alloy as claimed in claim 1, characterized in that: The preparation method comprises: Step S1: first weigh pure Al raw material, Al-Si, Al-Fe, Al-Ni, Al-Mn, Al-Cr, Al-Ti-B and Al-Ce alloy according to mass ratio; Step S2: Put the pure Al raw material into a heating furnace, heat it to 680°C to obtain molten aluminum liquid, and keep it at this temperature for 20-30 minutes after the aluminum metal is completely melted; Step S3: Raise the temperature to 780°C, add Al-Fe, Al-Ni, Al-Cr, Al-Mn, Al-Si, and pure Cu to the aluminum liquid in proportion, and wait for them to be completely dissolved; Step S4: Cooling to 750°C, adding Al-Ce and Al-Ti-B master alloys, and keeping the temperature for 20-30 minutes; Step S5: cooling to 720°C, adding pure Mg and pure Zn, keeping the temperature for 15-20 minutes and then performing degassing and refining; Step S6: Melting and pouring the obtained refined melt into a vacuum die-casting machine again for high-pressure die-casting to obtain the high-temperature resistant brazable die-casting aluminum alloy.

4. The method for preparing a high temperature resistant brazable die casting aluminum alloy according to claim 3, characterized in that: The die-casting molding comprises the following steps: re-melting the refined melt at 720-740° C. and keeping the temperature, introducing a protective gas to isolate the melt from the air during the heat preservation, injecting the melt into a die-casting mold by injection, and performing vacuum molding after evacuation to obtain a die-cast aluminum alloy product.

5. The method for preparing a high temperature resistant brazable die casting aluminum alloy according to claim 4, characterized in that: The injection adopts a filling method of first low speed and then high speed. The low speed of injection is controlled at 0.10~0.40m / s. The temperature of the die-casting mold is controlled by the oil temperature machine, water temperature machine and chiller. The oil temperature machine is set at 180~250℃, the water temperature machine is 100~130℃, the cooling water is kept at a constant temperature of 15~30℃, and the cooling water is passed through the mold core cooling pipeline at a water pressure of 0.8~1.2MPa. The pressure is maintained for 5~10 seconds after the injection is completed.

6. An application of a high temperature resistant brazable die casting aluminum alloy, characterized in that: The die-casting aluminum alloy obtained by any method of claims 3-5 is used for brazing heat exchanger mold components.

7. The use of a high temperature resistant brazable die casting aluminum alloy as claimed in claim 6, characterized in that: It is characterized in that The brazing temperature is 595℃-610℃.

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