A high temperature brazable Al-Fe-Mn low thermal conductivity die-casting aluminum alloy

Abstract

The present invention belongs to the technical field of aluminum alloy materials, and in particular relates to an Al-Fe-Mn series low thermal conductivity die-casting aluminum alloy capable of high-temperature brazing. The aluminum alloy comprises: Fe: 0.6-1.8wt%; Mn: 1.2-2.7wt%; Si: 0.1-0.6wt%; Cr: 0.22-0.68wt%; Ti: 0.15-0.45wt%; Sm: 0.01-0.05wt%; Mg≤0.6wt%; Mo≤0.4wt%; V≤0.4wt%; Zr≤0.4wt%; Ni≤1.0wt%; the content of a single element of trace impurities is ≤0.05wt%, and the total amount of trace impurities is ≤0.15wt%, and the balance is aluminum and unavoidable impurities, wherein the mass ratio of manganese to iron is 1.8-2.2, the mass ratio of chromium to titanium is 1.5-2.0, and the C value (C=(Mn-Fe) / Sm) control range is 50-90. Compared with the prior art, the beneficial effects of the present invention are that the mechanical properties, casting properties and physical properties of the material are comprehensively guaranteed, the material cost is reduced, and it is conducive to recycling and reuse.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy materials, and in particular to an Al-Fe-Mn series low thermal conductivity die-casting aluminum alloy capable of high-temperature brazing. Background Art

[0002] Aluminum heat transfer materials are widely used in heat exchange systems, and downstream industries include automobiles, air conditioners, power stations, and other fields. Taking new energy vehicles as an example, battery thermal management is the cornerstone of safe operation of new energy vehicles. A large amount of heat is generated during the operation of new energy batteries. Ensuring that the temperature of the battery pack is in the optimal operating temperature range (25-40°C) and the maximum temperature difference between cells does not exceed 5°C is of great significance for the performance of the power battery pack. When the temperature approaches 60°C, the active substances inside the battery will decompose and "thermal runaway" will occur, causing the temperature to rise sharply to 400-1000°C, which will lead to fire or even explosion.

[0003] Brazing is one of the three important welding processes and is suitable for the assembly of liquid cooling systems with complex structures. Brazing is a welding method that uses a filler metal (called brazing filler metal or solder) with a lower melting point than the parent material (the material being brazed) to wet the parent material and fill the contact gap between the workpieces with liquid brazing filler metal at a temperature lower than the melting point of the parent material and higher than the melting point of the brazing filler metal, and diffuse it with the parent material. Brazing has the advantages of small deformation and smooth and beautiful welding points, and is suitable for welding precise, complex components composed of different materials.

[0004] Liquid cooling plate substrates such as runner plates of thermal management systems of new energy vehicles are currently mostly produced by hot forging or machining, and then welded to the cover plate by brazing. This processing method has a long process, high cost and low efficiency. With the continuous maturity of vacuum die-casting, especially ultra-high vacuum die-casting technology, it is possible to use vacuum die-casting technology to replace hot forging or machining to produce substrates. However, due to the high Si content, the melting temperature of traditional die-casting aluminum alloys is generally lower than 590℃, which cannot meet the brazing requirements (the brazing temperature is generally 595-610℃). Therefore, the market urgently needs to develop new die-casting aluminum alloy materials that can meet the brazing requirements and have both casting performance and mechanical properties that meet the requirements.

[0005] CN113897519A discloses an Al-Mn-Mg-Si-Ti-Sn casting alloy for vacuum brazing by vacuum die casting and a preparation method thereof. The Al-Mn-Mg-Si-Ti-Sn casting alloy comprises the following components by mass percentage: Mn 1.6-2.4%, Mg 0.45-0.9%, Si 0.2-0.6%, Ti 0.1-0.2%, Sn 0.5-1.5%, and the remainder is Al and impurities, and the impurity Fe content is ≤0.5%. The room temperature tensile strength of the Al-Mn-Mg-Si-Ti-Sn casting alloy is ≥200MPa, and the yield strength is ≤100MPa. The Al-Mn-Mg-Si-Ti-Sn casting alloy can be vacuum brazed with 4004 clad fins to obtain an aluminum alloy water-cooled radiator; the patent contains 0.45-0.9wt% of Mg element. As is known to all, aluminum alloys with high Mg content can only be vacuum brazed and cannot be brazed by the Nocolok brazing process commonly used in the industry. This is because the brazing flux in the brazing will undergo a "poisoning reaction" with the Mg element at high temperature, making the brazing flux inactive and resulting in unsatisfactory brazing quality. Therefore, the brazing process of the product involved in the patent has great limitations.

[0006] CN116334454A discloses a brazable heat-treatment-free die-cast aluminum alloy material and its preparation method and application, which strictly controls the upper limit of the Mg content range to ≤0.5wt%, but adds the precious rare earth element Sc, and further supplements the technical solution of the present invention, in which Mn, Sc, Ce, Cs and Zr are added in the form of mesophase alloy amorphous nano powder. The preparation method of the amorphous nano powder is: Al-Mn, Al-Sc, Al-Ce, Al-Cs and Al-Zr are treated by a quenching block rotation technology combined with a high-energy ball mill to obtain a mesophase alloy amorphous nano powder. The mesophase alloy amorphous nano powder uses a quenching block rotation technology. The above alloy material composition and preparation process result in significantly high material cost and low performance. The room temperature tensile strength of the die-cast aluminum alloy is 130-180Mpa, the yield strength is ≥75Mpa, and the elongation is ≥16%.

[0007] CN116377262A discloses a method for making a high-pressure cast aluminum alloy that can be used for brazing. The alloy disclosed in the patent application contains 5-12% rare earth elements, and the rare earth is implemented as at least one selected from lanthanum or cerium. The high-pressure cast aluminum alloy has a tensile yield limit Rp0.2 of >110MPa in the cast state, a fracture elongation A of >5.0%, and a tensile strength Rm of >210MPa. The large amount of rare earth elements used in the alloy increases the material cost and is not conducive to the recycling of materials. The alloy does not disclose the thermal conductivity.

[0008] CN115679159A discloses an Al-Ni-Mn alloy material for high temperature brazing, wherein the Al-Ni-Mn alloy material is calculated by mass as follows: Ni3-3.5%, Mn1.0-1.2%, and the remainder is aluminum and inevitable impurity elements, wherein the content of each impurity element is ≤0.1%, and the total amount of impurity elements is ≤0.3%. The large amount of Ni element added can increase the material cost to a certain extent while improving the alloy casting performance to a limited extent. In order to further alleviate the shrinkage and thermal cracking problems of the material during the solidification process, the patent introduces a rheological die-casting process, and reduces the slurry temperature through external field treatment to alleviate the solidification shrinkage and thermal cracking problems. Summary of the invention

[0009] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an Al-Fe-Mn series low thermal conductivity die-cast aluminum alloy that can be brazed at high temperature. The problem that the existing high temperature brazed die-cast aluminum alloy has high cost, high thermal conductivity and cannot be used in low thermal conductivity occasions is solved, and a more cost-effective Al-Fe-Mn series low thermal conductivity die-cast aluminum alloy suitable for high temperature brazing is provided.

[0010] To achieve the above-mentioned purpose, the technical solution of the present invention is a low thermal conductivity die-casting aluminum alloy material that can be brazed at high temperature, which is composed of the following materials in mass percentage: Fe: 0.6-1.8wt%; Mn: 1.2-2.7wt%; Si: 0.1-0.6wt%; Cr: 0.22-0.68wt%; Ti: 0.15-0.45wt%; Sm: 0.01-0.05wt%; Mg≤0.6wt%; Mo≤0.4wt%; V≤0.4wt%; Zr≤0.4wt%; Ni≤1.0wt%; the content of a single element of trace impurities is ≤0.05wt%, and the total amount of trace impurities is ≤0.15wt%, and the balance is aluminum and unavoidable impurities, wherein the mass ratio of manganese to iron is 1.8-2.2, the mass ratio of chromium to titanium is 1.5-2.0, and the C value (C=(Mn-Fe) / Sm) is controlled in the range of 50-90.

[0011] The Al-Fe-Mn series low thermal conductivity die-casting aluminum alloy capable of high temperature brazing has a tensile strength of 200-240 MPa, a yield strength of 125-145 MPa, an elongation after fracture of 3.5-6%, and a Brinell hardness HB of 65-75 in the cast state; after brazing, the tensile strength is 150-190 MPa, the yield strength is 95-115 MPa, the elongation after fracture is 5-8%, and the Brinell hardness HB is 50-60.

[0012] The brazable Al-Fe-Mn low thermal conductivity die-cast aluminum alloy of the present invention has a thermal conductivity of 80-100 W / (mK) and is suitable for use in scenarios requiring low thermal conductivity.

[0013] The brazable Al-Fe-Mn low thermal conductivity die-casting aluminum alloy of the present invention has a solidus temperature of 625-640° C., can meet the high-temperature brazing temperature requirement of 595-610° C., and has a sufficient safety interval.

[0014] The brazable Al-Fe-Mn low thermal conductivity die-casting aluminum alloy of the present invention has a flow index of 540-600 and a thermal cracking index of 110-190.

[0015] More preferably, the mass ratio of manganese to iron is 1.85-2.15, and the mass ratio of chromium to titanium is 1.6-1.9.

[0016] The (Mn-Fe) / Sm ratio is 55-85.

[0017] Further preferably, the above-mentioned Al-Fe-Mn series low thermal conductivity die-casting aluminum alloy capable of high temperature brazing is prepared by: placing an aluminum ingot, an AlFe10 master alloy, an AlMn10 master alloy, an AlTi10 master alloy, an AlCr10 master alloy, an AlSi20 master alloy, and an AlSm10 master alloy into a smelting furnace, heating the furnace to 780-800°C, stirring the alloy after it is melted, keeping the temperature for 3-4 hours, and then cooling the furnace to 735-745°C, using a rotary degasser in the smelting furnace, connecting argon gas with a pressure of 0.2-0.3MPa, controlling the rotor speed to 370-390r / min, and the argon gas flow rate to 10-20m 3 / h, refining and degassing for 20-30min, to obtain a low thermal conductivity die-casting aluminum alloy melt with qualified composition that can be brazed at high temperature; a die-casting machine is used for vacuum high-pressure casting, the casting pressure is 110-1300bar, the slow injection speed is 0.1-0.3m / s; the fast injection speed is 4-6m / s; the mold temperature and barrel temperature are 16--200℃; the cavity vacuum degree is <30mbar.

[0018] More preferably, the casting pressure is 1200-1300 bar.

[0019] More preferably, the mold temperature and the barrel temperature are 180-200°C.

[0020] The brazable Al-Fe-Mn low thermal conductivity die-casting aluminum alloy of the present invention uses Fe and Mn as main alloying elements, mainly considering that: 1) the temperature range of the Al-Fe eutectic is 655°C, the temperature range of the Al-Mn eutectic is 657°C, and the addition of Fe and Mn will not significantly reduce the solidus temperature of the alloy; 2) Fe and Mn have good effects on preventing mold sticking and improving the life of the mold; 3) the eutectic points of Fe and Mn are both 1.8-1.9%, and the casting performance of the alloy can be effectively improved by reasonably controlling the addition ratio. The present invention tests the casting performance of the alloy through an N-Tec mold, and after a large number of experimental verifications, it is determined that the optimal mass ratio A value (Mn / Fe) of manganese and iron is 1.8-2.2. Within this ratio range, the alloy has a minimum hot cracking index while maintaining good fluidity; 4) the alloy is low-cost and recyclable.

[0021] The brazable Al-Fe-Mn low thermal conductivity die-casting aluminum alloy of the present invention uses Cr and Ti as secondary alloying elements, and controls their mass ratio B value (Cr / Ti) within the range of 1.5-2.0, mainly because: 1) Cr and Ti play an important role in reducing thermal conductivity in the alloy system of the present invention; 2) through a large number of tests and microstructure analysis, it is found that when the mass ratio B value of chromium and titanium (Cr / Ti) is 1.5-2.0, the best effect on the dissimilarity of AlFeMn phase and AlSiFeMn phase is achieved, and the best effect on reducing the thermal conductivity of the alloy is achieved.

[0022] The main reasons for using Si and rare earth element Sm as microalloying elements in the brazable Al-Fe-Mn low thermal conductivity die-casting aluminum alloy of the present invention are: 1) 0.1-0.6wt% Si can improve the casting performance of the alloy without significantly reducing the solidus temperature of the alloy; 2) the addition of a trace amount of rare earth element Sm can refine the α-Al phase to a limited extent, transform the AlFeMn phase and AlSiFeMn phase, and improve the mechanical properties of the alloy. In the present invention, the addition ratio of Sm is controlled to 0.01-0.03wt, and the C value (C=(Mn-Fe) / Sm) is controlled to 50-90, thereby achieving the best refinement and transformation effect.

[0023] The high temperature brazable Al-Fe-Mn low thermal conductivity die-casting aluminum alloy of the present invention controls Mg, V, Zr, and Ni as impurity elements and maintains them at a relatively high content range upper limit because: 1) Mg element is controlled as an impurity, and the upper limit range is controlled to be ≤0.6wt%. Under vacuum brazing conditions, it can be added according to the middle and upper limits to improve the material strength. When potassium fluoroaluminate brazing flux is used for brazing, the magnesium content is controlled according to the middle and lower limits or not added, and good mechanical performance indicators can also be obtained by relying on the dispersion strengthening effect of elements such as Mn, Ti, and Cr; 2) The upper limits of V and Zr content are controlled at 0.4wt%, and their main function is to adjust the thermal conductivity of the alloy within a narrow range for use; 3) The upper limit of Ni element content is controlled at 1%, as long as it is used to adjust the casting performance of the alloy. It should be particularly noted that the reason why these alloy elements are controlled as impurity elements is that they are not indispensable in the alloy system, that is, even if these elements are not added at all, they will not affect the application of the alloy of the present invention.

[0024] Advantages and beneficial effects of the present invention:

[0025] 1) Through the effective control of the content range of the main elements Fe and Mn, the secondary alloying elements Cr and Ti, the microalloying elements Si and Sm, and the element mass ratios A, B, and C, the optimal balance of the alloy solidus temperature, casting performance, mechanical properties before and after brazing, and thermal conductivity is achieved, which can meet the performance requirements of the liquid cooling plate substrate parts, the vacuum die-casting process requirements, and the high-temperature brazing process requirements.

[0026] 2) No precious rare earth elements such as Sc and Pr are added, which greatly reduces the material cost; Ni, Zr, V, etc. are not used as necessary added elements, which is conducive to recycling and reuse and reduces material costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a typical metallographic structure diagram of the vacuum die-casting test piece of the Al-Fe-Mn series low thermal conductivity die-casting aluminum alloy that can be brazed at high temperature prepared in Example 1.

[0028] Figure 2 This is a scanning electron microscope analysis of the AlFeMn phase of the vacuum die-casting test piece of the high-temperature brazable Al-Fe-Mn low thermal conductivity die-casting aluminum alloy prepared in Example 1. DETAILED DESCRIPTION

[0029] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0030] Example 1

[0031] The chemical composition is: Fe 1.2wt%; Mn 2.2wt%; Cr 0.45wt%; Ti 0.28wt%; Si 0.4wt%; Sm 0.015wt%; and the balance is Al.

[0032] 140 kg of A00 aluminum ingot, 29.8 kg of AlFe10 master alloy, 54.6 kg of AlMn10 master alloy, 6.9 kg of AlTi10 master alloy, 11.2 kg of AlCr10 master alloy, 5.0 kg of AlSi20 master alloy and 0.37 kg of AlSm10 master alloy were put into the melting furnace, heated to 790°C, stirred fully after the alloy was melted, kept warm for 3 hours, and then cooled to 740°C. The rotary degasser in the melting furnace was used, and argon gas with a pressure of 0.25 MPa was connected. The rotor was controlled to rotate at 380 r / min and the argon gas flow rate was 15 m 3 / h, refining and degassing for 20 minutes, to obtain a low thermal conductivity die-casting aluminum alloy melt with qualified composition that can be brazed at high temperature.

[0033] A LK IMPRESS-Ⅲ DCC500 die-casting machine was used for vacuum high-pressure casting, with a casting pressure of 1200 bar, a slow shot speed of 0.2 m / s, a fast shot speed of 5.0 m / s, a mold temperature and a barrel temperature of 180°C, a flat mold with a length of 200 mm and a width of 65 mm, and a wall thickness of 3 mm, and an AIGAYA HG600 vacuum machine with a cavity vacuum degree of <30 mbar.

[0034] Example 2

[0035] The difference from Example 1 is that the chemical composition is: Fe 1.4wt%; Mn 2.7wt%; Cr 0.57wt%; Ti 0.3wt%; Si 0.3wt%; Sm 0.015wt%; and the balance is Al.

[0036] Example 3

[0037] The difference from Example 1 is that the components are: Fe 0.65wt%; Mn 1.4wt%; Cr 0.65wt%; Ti 0.43wt%; Si 0.2wt%; Sm 0.015wt%; and the balance is Al.

[0038] Example 4

[0039] The difference from Example 1 is that the chemical composition is: Fe 0.65wt%; Mn 1.4wt%; Cr 0.65wt%; Ti 0.43wt%; Si 0.2wt%; Sm 0.015wt%; Mg 0.4wt%; and the balance is Al.

[0040] Example 5

[0041] The difference from Example 1 is that the chemical composition is: Fe 0.65wt%; Mn 1.4wt%; Cr 0.65wt%; Ti 0.43wt%; Si 0.2wt%; Sm 0.015wt%; Mg 0.4wt%; V 0.3wt%; Zr 0.3wt%; and the balance is Al.

[0042] Example 6

[0043] The difference from Example 1 is that the chemical composition is: Fe 0.65wt%; Mn 1.4wt%; Cr 0.65wt%; Ti 0.43wt%; Si 0.2wt%; Sm 0.015wt%; Mg 0.4wt%; Ni 0.8wt%; and the balance is Al.

[0044] Example 7

[0045] The difference from Example 1 is that the chemical composition is: Fe 0.65wt%; Mn 1.4wt%; Cr 0.65wt%; Ti 0.43wt%; Si 0.2wt%; Sm 0.015wt%; Mg 0.4wt%; La 2.8wt%; and the balance is Al.

[0046] Table 1

[0047]

[0048]

[0049] In Examples 1-7, the content of each component was changed and the mechanical properties of the prepared aluminum alloy specimens (3 mm) were tested. The results showed that when the content of each component, the Mn / Fe ratio, the Cr / Ti ratio and the C value (C = (Mn-Fe) / Sm) were all within the control range, the casting performance, physical properties and mechanical properties of the prepared aluminum alloy material achieved a good balance and could meet the casting process requirements, welding process requirements and final use requirements.

[0050] Comparative Example 1

[0051] The chemical composition of Comparative Example 1 is: Fe1.2wt%; Mn2.8wt%; Cr0.45wt%; Ti0.28wt%; Si0.4wt%; Sm 0.015wt%; the balance is Al. The main difference between the comparative example and Example 1 is that the manganese content is higher, the Mn / Fe ratio is higher, and the C value (C=(Mn-Fe) / Sm) is also higher. Compared with the performance of Comparative Example 1 and Example 1, the main difference is that the casting performance is deteriorated, especially the hot cracking index is significantly increased, resulting in a significant increase in the scrap rate when the vacuum die casting process is used to produce the flow plate and other related parts.

[0052] Comparative Example 2

[0053] The chemical composition of Comparative Example 2 is: Fe 1.2wt%; Mn 2.2wt%; Cr 0.25wt%; Ti 0.28wt%; Si 0.4wt%; Sm 0.015wt%; the balance is Al. The main difference between Comparative Example 2 and Example 1 is that the Cr content is lower and the B value (B = Cr / Ti) is lower. The main difference between the performance of Comparative Example 2 and Example 1 is that the thermal conductivity is higher and cannot meet the use requirements of low thermal conductivity parts.

[0054] Comparative Example 3

[0055] The chemical composition of Comparative Example 3 is: Fe 1.2wt%; Mn 2.2wt%; Cr 0.45wt%; Ti 0.28wt%; Si 0.4wt%; Sm 0.004wt%; the balance is Al. The main difference between Comparative Example 3 and Example 1 is that the Sm content is lower and the C value (C = (Mn-Fe) / Sm) is higher. The main difference between the performance of Comparative Example 3 and Example 1 is that the casting mechanical properties, especially the elongation after fracture, are significantly worse.

[0056] Table 2

[0057]

[0058] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept, which all belong to the protection scope of the present invention.

Claims

1. A high temperature brazable Al-Fe-Mn low thermal conductivity die-casting aluminum alloy, characterized in that: The aluminum alloy comprises: Fe: 1.2-1.8wt%; Mn: 2.2-2.7wt%; Si: 0.1-0.6wt%; Cr: 0.22-0.68wt%; Ti: 0.15-0.45wt%; Sm: 0.01-0.05wt%; Mg≤0.6wt%; Mo≤0.4wt%; V≤0.4wt%; Zr≤0.4wt%; Ni≤1.0wt%; the content of a single element of trace impurities is ≤0.05wt%, and the total amount of trace impurities is ≤0.15wt%, the balance is aluminum and unavoidable impurities, the mass ratio of manganese to iron is 1.8-1.9, the mass ratio of chromium to titanium is 1.5-2.0, the (Mn-Fe) / Sm ratio is 50-90, the tensile strength in the cast state is 200-240MPa, the yield strength is 125 -145MPa, elongation after fracture is 3.5-6%, Brinell hardness HB is 65-75; tensile strength after brazing is 150-190MPa, yield strength is 95-115MPa, elongation after fracture is 5-8%, Brinell hardness HB is 50-60, thermal conductivity is 80-100W / (m·K), solidus temperature is 625-640℃, flow index is 540-600, and hot cracking index is 110-190; The preparation method is as follows: put aluminum ingots, AlFe10 master alloy, AlMn10 master alloy, AlTi10 master alloy, AlCr10 master alloy, AlSi20 master alloy, and AlSm10 master alloy into a smelting furnace, heat it to 780-800°C, wait for the alloy to melt, stir it fully, keep it warm for 3-4 hours, then cool it to 735-745°C, use a rotary degasser in the smelting furnace, connect argon with a pressure of 0.2-0.3MPa, control the rotor speed to 370-390r / min, and the argon flow rate to 10-20m 3 / h, refining and degassing for 20-30min, to obtain a low thermal conductivity die-casting aluminum alloy melt with qualified composition that can be brazed at high temperature; a die-casting machine is used for vacuum high-pressure casting, the casting pressure is 1200-1300bar, the slow injection speed is 0.1-0.3m / s; the fast injection speed is 4-6m / s; the mold temperature and barrel temperature are 180-200℃; the cavity vacuum degree is <30mbar.

2. The Al-Fe-Mn low thermal conductivity die-casting aluminum alloy capable of high temperature brazing according to claim 1, characterized in that: The aluminum alloy comprises: Fe: 1.2-1.5wt%; Mn: 2.2wt%; Si: 0.1-0.4wt%; Cr: 0.32-0.58wt%; Ti: 0.25-0.40wt%; Sm: 0.01-0.03wt%; Mg≤0.5wt%; Mo≤0.3wt%; V≤0.3wt%; Zr≤0.3wt%; Ni≤0.8wt%; the content of a single element of trace impurities is ≤0.05wt%, and the total amount of trace impurities is ≤0.15wt%, and the balance is aluminum and unavoidable impurities.

3. The Al-Fe-Mn low thermal conductivity die-casting aluminum alloy capable of high temperature brazing according to claim 1, characterized in that: The mass ratio of chromium to titanium is 1.6-1.

9.

4. The Al-Fe-Mn low thermal conductivity die-casting aluminum alloy capable of high temperature brazing according to claim 1, characterized in that: The (Mn-Fe) / Sm ratio is 55-85.

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