A vacuum brazable aluminum alloy suitable for extrusion casting, its preparation method, and a method for preparing flow channel plates.

Abstract

This invention provides a vacuum brazable aluminum alloy suitable for extrusion casting, its preparation method, and a method for preparing a flow channel plate, relating to the technical field of aluminum alloy casting. The aluminum alloy, by mass fraction, comprises the following chemical composition: La: 9-12%, Cu: 0.1-1.2%, Zn: 1-2%, Mg: 0.2-0.7%, Zr: 0.15-0.4%, Fe≤0.5%, Si≤0.3%, with the balance being Al and unavoidable impurities. This invention solves at least one of the technical problems of existing technologies, namely, high tendency to hot cracking, low strength of castings, and easy melting and collapse during brazing. It reduces the tendency to hot cracking by adding Cu to Al-La eutectic alloy to form a specific microstructure and using continuous pressure from extrusion casting. Cu and Zr synergistically improve the strength of castings after brazing. At the same time, it prevents brazing collapse by ensuring that the solid phase temperature of the alloy exceeds 615°C. In addition, Zn and Mg vaporize and break the Al2O3 film formed on the surface of the aluminum alloy during vacuum brazing and protect the newly exposed base material from further oxidation. The final flow channel plate is compatible with R744 refrigerant and meets the requirements.

Description

Technical Field

[0001] This invention relates to the technical field of aluminum alloy casting, and more particularly to an aluminum alloy suitable for extrusion casting that can be vacuum brazed, its preparation method, and a method for preparing flow channel plates. Background Technology

[0002] The flow channel plates of the thermal management system of new energy vehicles are mostly manufactured by casting, which has the advantages of high processing efficiency and low cost compared with forging. Its typical structure is a pre-cast U-shaped flow channel plus a deformed aluminum cover plate. The two need to be vacuum brazed to form a closed flow channel cavity. Vacuum brazing is a key connection process for this type of flow channel plate because of its large connection area and strong pressure bearing capacity of the flow channel cavity.

[0003] However, cast aluminum alloys suitable for vacuum brazing present significant hot cracking problems. From the perspective of hot cracking causes, when liquid metal solidifies to near the solidus line, a small amount of unsolidified liquid metal remains between grains and forms a liquid film. When the shrinkage of the casting is hindered, tensile stress and deformation will concentrate on the liquid film. Once the stress of the liquid film exceeds the limit, it will crack and form hot cracks (intergranular cracks, as shown in Figure 6). From the perspective of temperature requirements, vacuum brazing needs to be carried out at a brazing temperature of 600℃. Considering the temperature uniformity of the vacuum brazing furnace, the solidus temperature of the aluminum alloy used in the casting needs to exceed 615℃. However, 615℃ is a relatively high temperature for aluminum alloys, which exceeds the liquidus temperature of commonly used cast aluminum alloys. Moreover, the strength of metal materials decreases with increasing temperature. Therefore, cast aluminum alloys used for brazing will exhibit a greater tendency to hot crack.

[0004] Existing technologies have not yet resolved the aforementioned core contradictions and have significant shortcomings: Firstly, when using certain casting brazing materials to manufacture highly integrated large flow channel plates, thermal cracking defects are prone to occur at the high-temperature fillet roots of the casting mold (e.g., Figure 5 Firstly, while commercially available Al-Ni-Mn brazing casting alloys can produce flow channel plates without hot cracking, the castings have low strength, affecting both the pressure resistance of the flow channel plates and causing excessive flatness deviations during welding surface machining, thus affecting the quality of vacuum brazing. Secondly, another technical solution designed with a higher Si content to improve casting performance, but the formation of Al-Si-Mg2Si ternary eutectic lowers the alloy solid phase temperature to below 600℃, causing the castings to melt and collapse during high-temperature hard brazing and fail. All of these measures fail to meet the actual application requirements of vacuum brazed flow channel plates. Summary of the Invention

[0005] The purpose of this invention is to provide an aluminum alloy suitable for extrusion casting that can be vacuum brazed, and its preparation method and flow channel plate preparation method, which solves at least one of the technical problems of high hot cracking tendency, low casting strength and easy melting and collapse during brazing in the prior art.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a vacuum brazable castable aluminum alloy suitable for extrusion casting, wherein the chemical composition of the aluminum alloy, by mass fraction, includes: La: 9-12%, Cu: 0.1-1.2%, Zn: 1-2%, Mg: 0.2-0.7%, Zr: 0.15-0.4%, Fe≤0.5%, Si≤0.3%, with the balance being Al and unavoidable impurities.

[0008] Secondly, the present invention also provides a method for preparing a vacuum brazable cast aluminum alloy suitable for extrusion casting, comprising the following steps:

[0009] a) Melting industrial pure aluminum ingots;

[0010] b) Heat the melt to 790-800℃ and hold it at that temperature. Add Al-La master alloy, Al-Zr master alloy and pure Cu in proportion. Stir and melt the mixture and then hold it at that temperature.

[0011] c) Cool the melt, add zinc and magnesium ingots in proportion, and ensure that the magnesium ingots are pressed under the surface of the melt and completely melted;

[0012] d) The melt is degassed and refined, stirred and allowed to stand, then the slag is removed to obtain a clean melt;

[0013] e) The clean melt is extruded and cast to obtain an aluminum alloy part blank.

[0014] Furthermore, the aluminum alloy is characterized in that it is prepared based on an Al-La eutectic alloy, with Cu added to form Al 11 Al-La-Cu alloy of La3 eutectic + Al7CuLa2.

[0015] Furthermore, the feature is that, in step b), the Al-La master alloy is Al-20La, and the Al-Zr master alloy is Al-10Zr.

[0016] Furthermore, the feature is that, in step d), high-purity argon and refining agent are used for degassing and refining, and the graphite rotor speed is not less than 400 r / min during refining.

[0017] Furthermore, the feature is that, in step e), the casting temperature of the extrusion casting is 750-765°C, the casting pressure is 105 MPa, and the holding time is 80 s.

[0018] Furthermore, the feature is that, in step e), during extrusion casting, pressure is continuously applied to the alloy still in the liquid phase through the gating system during the solidification process of the casting to counteract the tensile stress on the intergranular liquid metal film and reduce the tendency of the casting to hot crack.

[0019] Thirdly, the present invention also provides a method for preparing a flow channel plate, which first obtains a part blank using the above method, and then prepares a flow channel plate based on the part blank, specifically including the following steps:

[0020] After machining and cleaning the obtained flow channel plate blank, it is assembled with the composite plate and then placed in a vacuum brazing furnace for welding at a vacuum degree of 3×10⁻⁶. -3 The flow channel plate is prepared by holding it at 600℃ for 30 minutes under the conditions of Pa and temperature, and then cooling it to room temperature in the furnace.

[0021] Furthermore, during vacuum brazing, the pressure inside the vacuum brazing furnace is lower than the saturated vapor pressure of Zn and Mg elements in the blank of the part. Zn and Mg elements will vaporize and overflow from the surface of the blank of the part, which is used to break the Al2O3 film formed on the surface of the aluminum alloy to eliminate the brazing filler metal wetting barrier. At the same time, Mg vapor is also used to protect the newly exposed base material from further oxidation.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] This invention effectively solves the problem of hot cracking and improves the strength of castings: based on Al-La eutectic alloy, Cu is added to form Al 11 La3 eutectic + Al7CuLa2 reduces the shrinkage range of the alloy solidification line; combined with the extrusion casting process, continuous pressure is applied to the liquid phase alloy during solidification to offset the tensile stress of the liquid film between grains and significantly reduce the tendency for hot cracking; at the same time, Cu's Al7CuLa2 and Zr's ZrAl3 (high temperature stable) synergistically improve the strength of the casting after brazing, solving the problem of low strength of commercial Al-Ni-Mn alloys.

[0024] This invention also ensures brazing performance and improves brazing quality: by strictly limiting Si to ≤0.3%, it avoids the formation of ternary eutectic with low solid-state temperature, while ensuring that the alloy solid-state temperature exceeds 615℃ to meet the requirements of 600℃ vacuum brazing and prevent melting and collapse; at the same time, Zn and Mg in the alloy vaporize and overflow during vacuum brazing, which not only breaks the naturally formed Al2O3 film on the surface of the aluminum alloy (eliminating the brazing filler metal wetting barrier), but also protects the newly exposed base material from oxidation. The final flow channel plate is compatible with R744 refrigerant and meets the requirements of the thermal management system of new energy vehicles. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is an enlarged view of the metallographic structure of the aluminum alloy casting in Experiment Example 3;

[0027] Figure 2 A further enlarged view of the metallographic structure of the aluminum alloy casting in Experiment Example 3;

[0028] Figure 3 Diagram showing the high-temperature section of the runner plate mold;

[0029] Figure 4 A diagram showing the thermal crack location of the runner plate component;

[0030] Figure 5 The image shows the macroscopic morphology of hot cracks in the aluminum alloy casting of Comparative Example 1.

[0031] Figure 6 (6a, 6b) shows the microscopic morphology of hot cracks in the aluminum alloy casting of Comparative Example 1, where traces of tearing of the liquid metal film can be seen between the crack gaps.

[0032] Figure label:

[0033] 1-Al7CuLa2;2-Al 11 La3 eutectic. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0036] Example 1

[0037] This embodiment provides a vacuum brazable cast aluminum alloy suitable for extrusion casting. The chemical composition and mass fraction range of the aluminum alloy are as follows: La: 9-12%, Cu: 0.1-1.2%, Zn: 1-2%, Mg: 0.2-0.7%, Zr: 0.15-0.4%, Fe≤0.5%, Si≤0.3%, with the balance being Al and unavoidable impurities. La, based on an 11.03% Al-La eutectic composition, can narrow the temperature range where linear shrinkage occurs during alloy solidification. Cu is used to form a high-temperature stable Al7CuLa2, which can improve the strength after brazing. However, if the Cu content is too high, the solid phase temperature of the alloy will drop significantly, and the brazable characteristics of the parts cannot be maintained. Therefore, the amount of Cu added needs to be limited. Zn and Mg are high vapor pressure elements, which are used to break the Al2O3 film formed on the surface of the aluminum alloy during subsequent vacuum brazing and to protect the newly exposed base material from oxidation. Zr is a grain refiner, and the formed ZrAl3 has good high-temperature stability, which allows the casting to maintain higher strength after high-temperature brazing. Si will strongly reduce the solid phase temperature of the alloy, making the casting unsuitable for brazing. Therefore, its content needs to be limited. Si ≤ 0.3% can avoid the alloy solid phase temperature being too low and melting and collapsing during brazing. Addressing the shortcomings of existing technologies (aluminum alloys are prone to hot cracking, commercial Al-Ni-Mn systems have low strength, and brazing is prone to collapse), this invention solves the problems of hot cracking, insufficient strength, and brazing failure through the synergistic design of specific components. It can be adapted to R744 refrigerant flow channel plates with higher pressure, thus breaking through the existing technological bottlenecks.

[0038] Example 2

[0039] This embodiment also provides a method for preparing a vacuum brazable castable aluminum alloy suitable for extrusion casting, comprising the following steps: a) melting industrial pure aluminum ingots; b) heating the melt to 790-800℃ and holding for 10 min, adding Al-La master alloy, Al-Zr master alloy and pure Cu in proportion, stirring and melting, and then holding for 30 min to ensure uniform composition; c) cooling to 760℃, adding zinc ingots and magnesium ingots in proportion, and pressing the magnesium ingots below the liquid surface with a bell-shaped pressure hood until completely melted; d) degassing and refining with high-purity argon and refining agent for 15 min, with the graphite rotor speed ≥400 r / min during stirring, and removing slag after standing for 20-30 min to obtain a clean melt; e) casting part blanks using an extrusion casting machine (such as SCHB1300). This solution addresses the problems of uneven composition and high gas content in the melt that are common in conventional processes by using step-by-step temperature control (melting the master alloy at 790-800℃ and adding Zn / Mg at 760℃) and precise degassing parameters. It also adapts to the alloy composition to reduce the tendency for hot cracking.

[0040] This embodiment clarifies that the aluminum alloy is based on an Al-La eutectic alloy (e.g., 11.03% eutectic composition), with the addition of Cu (0.1-1.2%) to form an Al-containing alloy. 11Al-La-Cu alloys consisting of La3 eutectic phase and Al7CuLa2. Compared to existing Al-Ni-Mn-Fe alloys and commercially available Al-Ni-Mn alloys, this alloy has lower solidification and liquidation temperatures, reducing the temperature range where linear shrinkage occurs during solidification. This results in higher strength in the casting to resist shrinkage stress and improves the alloy's resistance to hot cracking. Simultaneously, the high-temperature stability of Al7CuLa2 enhances the strength after brazing, specifically addressing the problem of balancing hot cracking and strength in existing alloys.

[0041] This embodiment specifies that the Al-La master alloy in step b is Al-20La and the Al-Zr master alloy is Al-10Zr. Specifically, the amount of master alloy added can be determined through material calculations (e.g., Al-20La contains 20% La) based on the target content of La (9-12%) and Zr (0.15-0.4%), thus precisely controlling the composition. Directly adding pure La and Zr can easily lead to uneven composition due to dissolution difficulties. However, Al-20La and Al-10Zr master alloys ensure uniform dissolution of La and Zr, solving the problems of low precision and uneven composition in existing batching methods, and providing a guarantee for stable alloy performance.

[0042] This embodiment specifies that in step d, high-purity argon and refining agent are used for degassing and refining for 15 minutes, and the graphite rotor speed is ≥400 r / min. This can fully remove the gas in the melt (avoiding porosity in the casting), and after settling, slag is removed to obtain a clean melt. This avoids insufficient degassing and refining, which can lead to inadequate degassing, resulting in a melt with high gas content that affects the extrusion casting quality and subsequent brazing performance. By specifying the rotation speed parameters, the degassing and refining effect is ensured, providing a guarantee for the alloy's mechanical properties and brazing quality.

[0043] This embodiment specifies the parameters for squeeze casting in step e: temperature 750–765°C, pressure 105 MPa, and holding time 80 s. Operating according to these parameters, the tensile stress of the liquid film between grains during solidification is counteracted by continuous pressure, reducing the tendency for hot cracking. Compared to Comparative Example 4 (which has the same composition as Example 4 but a casting pressure of 75 MPa), hot cracking occurred. However, the 105 MPa pressure in this solution, combined with specific temperature and holding time, significantly reduces the tendency for hot cracking, solving the problem of hot crack control during squeeze casting.

[0044] This embodiment clarifies that during the squeeze casting process in step e, continuous pressure is applied to the liquid phase alloy through the gating system to counteract the tensile stress of the liquid film between grains and reduce the tendency for hot cracking (the causes of hot cracking include cracking of the liquid film under tensile stress), thereby effectively avoiding intergranular cracks and breaking through the bottleneck of hot cracking control in existing casting processes.

[0045] Example 3

[0046] This embodiment also provides a method for preparing a flow channel plate. First, a part blank is prepared using the above-mentioned method for preparing vacuum brazable cast aluminum alloys suitable for extrusion casting. Then, after machining and cleaning, it is assembled with a 6063 / 4004 composite plate and placed in a vacuum brazing furnace for welding at a vacuum degree of 3×10⁻⁶. -3 The flow channel plate was obtained by holding the plate at 600℃ for 30 minutes and then cooling it in the furnace. Existing flow channel plates are unsuitable for R744 refrigerant due to alloy defects (hot cracking, low strength) or improper brazing processes (such as melting and collapse of castings during high-temperature hard brazing). This solution uses high-quality blanks prepared by the above method, combined with the synergistic effect of Zn and Mg vaporization during vacuum brazing (as high vapor pressure elements, the pressure inside the vacuum brazing furnace is lower than the saturated vapor pressure of Zn and Mg, causing Zn and Mg to vaporize and overflow from the casting surface), breaking the Al2O3 film (breaking the Al2O3 film formed on the surface of the aluminum alloy casting to allow the liquid brazing filler metal to contact the casting), and protecting the newly exposed base material from oxidation (Mg vapor has a greater affinity for O2 than Al and reacts with the CO2 / O2 / H2O remaining in the furnace, protecting the surface of the newly exposed aluminum alloy base material in the vacuum furnace from oxidation and improving brazing quality). The resulting flow channel plate exhibits excellent pressure resistance and brazing quality, solving the technical problem of adapting existing flow channel plates to high-pressure refrigerants.

[0047] Comparative analysis of experimental cases and comparative examples (with appendix) Figure 1 -6)

[0048] Table 1 - Chemical composition and mass fraction range of aluminum alloys in experimental and comparative examples

[0049] Experimental Example 1 0.09 0.66 1.91 0.16 <0.01 0.01 11.03 0.16 0.24 0.01 0.01 Experiment Example 2 0.08 0.45 1.29 0.15 <0.01 0.01 10.19 0.14 0.22 <0.01 0.01 Experimental Example 3 0.08 0.46 1.27 0.45 <0.01 0.01 10.05 0.14 0.22 <0.01 0.01 Experiment Example 4 0.08 0.43 1.24 0.84 <0.01 0.01 9.89 0.14 0.21 <0.01 0.01 Comparative Example 1 0.06 <0.01 2.47 0.02 1.79 2.04 <0.01 0.96 0.25 0.07 0.27 Comparative Example 2 0.06 <0.01 3.11 0.01 2.12 1.82 <0.01 0.93 0.24 0.07 0.25 Comparative Example 3 0.06 <0.01 0.03 0.01 1.88 2.92 <0.01 0.14 <0.01 0.08 <0.01 Comparative Example 4 0.08 0.43 1.24 0.84 <0.01 0.01 9.89 0.14 0.21 <0.01 0.01 Comparative Example 5 0.08 0.40 1.22 1.22 <0.01 0.01 9.72 0.13 0.21 <0.01 0.01

[0050] Among them, Experimental Examples 1-4 are examples of the chemical composition and mass fraction range of the aluminum alloy of the present invention, and Comparative Examples 1-5 are examples used for comparison; among them, Comparative Example 4 has the same alloy composition as Experimental Example 4, the casting pressure used in Comparative Example 4 is 75 MPa, and Comparative Example 5 has increased Cu content compared with Experimental Example 4.

[0051] Table 2 - Solid and liquid phase temperatures and hot cracking of aluminum alloys in experimental and comparative examples.

[0052] Experimental Example 1 619.5 627.7 No heat cracking Experiment Example 2 624.8 630.0 No heat cracking Experimental Example 3 622.9 629.6 No heat cracking Experiment Example 4 617.7 627.9 No heat cracking Comparative Example 1 639.6 667.9 thermal cracking Comparative Example 2 634.3 659.5 thermal cracking Comparative Example 3 627.6 653.6 No heat cracking Comparative Example 4 617.7 627.9 thermal cracking Comparative Example 5 614.5 627.1 No heat cracking

[0053] The solid and liquid phase temperatures of each comparative example and experimental example were measured using a DSC 204F1 differential calorimeter at a heating rate of 5K / min. The solid phase temperatures of comparative examples 1 to 4 were all above 615℃, which can meet the requirements for high-temperature brazing at 600℃.

[0054] No hot cracking occurred in Experiment 1-4, while hot cracking occurred in the castings of Comparative Example 1-2 at the higher temperature of the mold. Experiment 4 had the same alloy composition as Comparative Example 4, and the hot cracking of the actual parts was alleviated after increasing the casting pressure.

[0055] In Comparative Example 5, after increasing the Cu content, the measured solid phase temperature of the casting dropped to below 615℃.

[0056] Table 3 - Mechanical Properties Tested by Tensile Testing Machine (XBD5105)

[0057]

[0058] The above tests on the flow channel plate parts in the as-cast and brazed states show that the strength of the castings increases after brazing as the Cu content in the alloy increases.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A vacuum brazable cast aluminum alloy suitable for extrusion casting, characterized in that, The chemical composition of the aluminum alloy, by mass fraction, includes: La: 9-12%, Cu: 0.1-1.2%, Zn: 1-2%, Mg: 0.2-0.7%, Zr: 0.15-0.4%, Fe≤0.5%, Si≤0.3%, with the balance being Al and unavoidable impurities; the aluminum alloy is prepared based on an Al-La eutectic alloy, with Cu added to form Al 11 Al-La-Cu alloy consisting of La3 eutectic + Al7CuLa2.

2. A method for preparing a vacuum brazable castable aluminum alloy suitable for extrusion casting as described in claim 1, comprising the following steps: a) Melting industrially pure aluminum ingots; b) Heat the melt to 790~800℃ and hold it at that temperature. Add Al-La master alloy, Al-Zr master alloy and pure Cu in proportion. Stir and melt the mixture and then hold it at that temperature. c) Cool the melt, add zinc and magnesium ingots in proportion, and ensure that the magnesium ingots are pressed under the surface of the melt and completely melted; d) The melt is degassed and refined, stirred and allowed to stand, then the slag is removed to obtain a clean melt; e) The clean melt is extruded and cast under a casting pressure of 105 MPa to obtain an aluminum alloy part blank.

3. The method for preparing a vacuum brazable castable aluminum alloy suitable for extrusion casting according to claim 2, characterized in that, In step b), the Al-La master alloy is Al-20La, and the Al-Zr master alloy is Al-10Zr.

4. The method for preparing a vacuum brazable castable aluminum alloy suitable for extrusion casting according to claim 2, characterized in that, In step d), high-purity argon and refining agent are used for degassing and refining, and the graphite rotor speed is not less than 400 r / min during refining.

5. The method for preparing a vacuum brazable castable aluminum alloy suitable for extrusion casting according to claim 2, characterized in that, In step e), the casting temperature of the extrusion casting is 750~765℃, and the holding time is 80s.

6. The method for preparing a vacuum brazable castable aluminum alloy suitable for extrusion casting according to claim 2, characterized in that, In step e), during squeeze casting, pressure is continuously applied to the alloy still in the liquid phase through the gating system during the solidification process of the casting to counteract the tensile stress on the intergranular liquid metal film and reduce the tendency of the casting to hot crack.

7. A method for preparing a flow channel plate, characterized in that, First, a part blank is obtained using the method described in claim 2, and then a flow channel plate is fabricated based on the part blank, specifically including the following steps: After machining and cleaning the obtained part blanks, they are assembled with the composite plate and then placed in a vacuum brazing furnace for welding at a vacuum degree of 3×10⁻⁶. -3 The flow channel plate is prepared by holding it at 600℃ for 30 minutes under the conditions of Pa and temperature, and then cooling it to room temperature in the furnace.

8. The method for preparing a flow channel plate according to claim 7, characterized in that, During vacuum brazing, the pressure inside the vacuum brazing furnace is lower than the saturated vapor pressure of Zn and Mg elements in the blank of the part. Zn and Mg elements will vaporize and overflow from the surface of the blank of the part, which is used to break the Al2O3 film formed on the surface of the aluminum alloy to eliminate the brazing filler metal wetting barrier. At the same time, Mg vapor is also used to protect the newly exposed base material from further oxidation.

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