Method for preparing crack-free high-temperature brazing cast aluminum alloy casting, alloy and casting

Abstract

The invention discloses a method for preparing a crack-free high-temperature brazing cast aluminum alloy casting, an alloy and a casting, and the method comprises the following steps: A, calculating the thermophysical property of an alternative aluminum alloy, evaluating the fluidity, feeding property and volume shrinkage of the alloy, and screening the part meeting the following conditions as a pre-selected alloy; b, obtaining solid-phase fraction curves of the pre-selected alloy at different temperatures through thermodynamic calculation; and C, a gravity casting verification test: adding a proper amount of refined matrix elements M1 and reinforced matrix elements M2 after the alloy is molten, and verifying after degassing and deslagging. According to the method, the process that the high-temperature brazed aluminum alloy part is cast instead of forging is achieved, the preparation process and procedure of the high-temperature brazed aluminum alloy part are greatly shortened, and compared with a conventional forging process, the prepared crack-free high-temperature brazed cast aluminum alloy casting has the great advantages in the preparation procedure, period, cost and part structure design.

Description

Technical Field

[0001] The invention belongs to the technical field of nonferrous metal preparation, and in particular relates to a method for preparing a crack-free high-temperature brazing cast aluminum alloy casting, an alloy and a casting. Background Art

[0002] At present, high-temperature brazed aluminum alloy parts are mostly processed by forging technology. Although this method has the characteristics of good uniformity of organization, high strength and excellent welding performance, the forging process can only forge a simple blank outline, and the complex structure of the parts depends entirely on precision machining to complete, which undoubtedly brings about problems such as low production efficiency, high cost and large material loss. In order to reverse this unfavorable situation, many domestic foundry companies have invested in the research and development of parts instead of forging parts by casting. However, due to the high sealing requirements of high-temperature brazed cast alloy castings and the use of brazing technology for welding, traditional aluminum silicon alloys are difficult to be used as high-temperature brazed casting alloy materials due to their low eutectic temperature. Therefore, high-temperature brazed cast aluminum alloys mostly use high melting point near-pure aluminum alloys, but this type of aluminum alloy has the characteristics of high thermal conductivity, high thermal cracking tendency and large expansion coefficient. If the casting process and material are not properly selected, it is easy to cause irreparable casting defects, especially diffuse crack defects in the castings, which directly cause the castings to be scrapped and failed. At present, the solution to high temperature brazing cast aluminum alloy cracks is mostly improved from a single factor, for example: by adjusting the specific alloy composition, casting process and mold structure to improve the crack problem of high temperature brazing cast alloy. However, these methods are based on experience and trial and error, and it is difficult to fundamentally eliminate the problem of high temperature brazing cast aluminum alloy cracks.

[0003] Therefore, in view of the above technical problems, it is necessary to provide a method, alloy and casting for preparing crack-free high-temperature brazing cast aluminum alloy castings.

[0004] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a crack-free high-temperature brazing cast aluminum alloy casting, an alloy and a casting.

[0006] In order to achieve the above object, a technical solution provided by a specific embodiment of the present invention is as follows:

[0007] A method for preparing a crack-free high-temperature brazed cast aluminum alloy casting comprises:

[0008] A. For the candidate aluminum alloys, the main elements of the candidate aluminum alloys except aluminum are selected from Mn, Cr, Fe, and Ni. The thermophysical properties are calculated, and the fluidity, shrinkage compensation and volume shrinkage of the alloy are evaluated. The parts that meet the following conditions are selected as pre-selected alloys: the eutectic content is greater than 90%, the liquid-solid phase interval of the alloy is less than 5°C, the solid phase temperature is greater than 600°C, and the linear expansion coefficient of the alloy from liquid to room temperature is (25-32)×10 -6 / ℃;

[0009] B. For the pre-selected alloy, the solid phase fraction curve of the alloy at different temperatures is obtained by thermodynamic calculation. The alloy is integrated with the solid phase fraction in the temperature range of Tl and Ts using formula 1. When the integral area is less than M, the range of M is between 0.2 and 50 (its specific value is related to the specific alloy composition), and the high-temperature brazing alloy a with relatively small thermal cracking tendency is screened out. The integral area Where Tl is the liquidus temperature and Ts is the solidus temperature;

[0010] C. Gravity casting verification test: After the alloy is melted, add appropriate amount of refining matrix element M1 and strengthening matrix element M2, and verify after degassing and slag removal. The verification conditions are: the melt temperature is above 700℃ during casting, so that the overall cooling rate of the casting is controlled within 15℃ / s, and the temperature gradient is controlled within 10℃ / mm. After the sample is completely solidified, the sample is tested for cracks:

[0011] When the sample is tested and no crack defect exists, return to step B to adjust the integral area to increase by 5%, repeat the screening and casting verification until cracks appear, so as to determine that the alloy does not have cracks and obtain the final composition of the cast aluminum alloy, and prepare to enter the next step of sand casting; or

[0012] When the sample is detected to have crack defects, return to step B to adjust the integral area to reduce 5%, repeat screening and casting verification until the cracks disappear, so as to determine that the alloy has no cracks and the final composition is obtained to obtain the cast aluminum alloy, and prepare to enter the next step of sand casting.

[0013] In one or more embodiments of the present invention, the alloy after degassing and slag removal in step C meets the following requirements: the gas content is less than 0.15 mL / 100 g, and the slag content is controlled within 0.02 mm 2 / kg or less.

[0014] In one or more embodiments of the present invention, the refined matrix element M1 in step C is selected from Ti, Nb, B, C, and Sr.

[0015] In one or more embodiments of the present invention, in step C, the matrix strengthening element M2 is selected from Mo, Zr, Er, Sc, Y, and V.

[0016] In one or more embodiments of the present invention, the cooling rate in step C is controlled within 10° C. / s, and the temperature gradient is controlled within 5° C. / mm.

[0017] In one or more embodiments of the present invention, a cast aluminum alloy is obtained by a method for preparing a crack-free high-temperature brazed cast aluminum alloy casting.

[0018] In one or more embodiments of the present invention, the cast aluminum alloy includes the following components, measured in mass percentage:

[0019] Mn content 1-3%;

[0020] Cr content 2-4%;

[0021] Fe content 0.5-1%;

[0022] Ni content 0.1-3%;

[0023] M1 total amount 0.01 to 1%;

[0024] M2 total amount 0.02 to 1%;

[0025] The balance is aluminum and avoided impurities.

[0026] In one or more embodiments of the present invention, the casting is obtained by casting aluminum alloy through low-pressure sand casting.

[0027] In one or more embodiments of the present invention, the process conditions during low-pressure sand casting are: the melt temperature is above 750°C, the upper mold temperature is set to 300-350°C, the lower mold temperature is set to 350-400°C, and the overall cooling rate of the casting is controlled within 15°C / s, and the temperature gradient is controlled within 10°C / mm.

[0028] In one or more embodiments of the present invention, it is further subjected to a heat treatment after casting, under the conditions of: keeping warm at 200-350° C. for 5-12 hours.

[0029] Compared with the prior art, the method, alloy, and casting of the present invention for preparing crack-free high-temperature brazed cast aluminum alloy castings. First, effective hot cracking criteria are used to screen out brazed cast aluminum alloys with a lower tendency to hot cracking, and then high-temperature brazed cast aluminum alloy castings with no cracks and excellent mechanical properties are prepared by precisely controlling the low-pressure sand casting process and the heat treatment process. The present invention realizes the process of replacing forging with casting for high-temperature brazed aluminum alloy parts, greatly shortening the preparation process and procedures of high-temperature brazed aluminum alloy parts. Compared with conventional forging processes, the crack-free high-temperature brazed cast aluminum alloy castings prepared by the present invention have great advantages in preparation procedures, cycles, costs, and part structure design. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 It is an integral curve diagram of the solid phase fraction of Al1.4-2.%Mn alloy in the two-phase temperature range in one embodiment of the present invention;

[0032] Figure 2 This is a sample diagram showing a slight crack defect in one embodiment of the present invention;

[0033] Figure 3 This is a diagram of a sample without any crack defects in one embodiment of the present invention. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0035] In order to more clearly understand the method and application effect provided by the present invention, a specific embodiment is described below.

[0036] 1. First, the thermodynamic software is used to calculate the thermal properties of Al-Mn alloy, where the Mn content is 1-3%. After calculation, the eutectic content of Al1.4-2%Mn under the Scheil model is greater than 90%, the liquid-solid two-phase range of the alloy is less than 5°C, the solid phase temperature is greater than 600°C, and the linear expansion coefficient of the alloy from liquid to room temperature is between 26-31×10-6 / °C.

[0037] 2. Formula 1 is used to integrate the selected Al1.4-2%Mn alloy in the two-phase temperature range and the solid phase fraction. The specific values ​​are shown in Table 1. When the alloy composition is Al1.6-2%Mn within the composition range, it is calculated that the integral area of ​​the alloy needs to be less than M. The range of M is between 0.2 and 50. Here, 0.2 is used as an example. Figure 1 shown.

[0038] Integral area

[0039] 3. Carry out metal mold casting verification test, select Al1.6%Mn, Al1.7%Mn, Al1.8%Mn, Al1.9%Mn and Al2.0%Mn five samples for gravity casting verification test: after the sample alloy is melted, add 0.1%Ti and 0.1%Mo elements, after the melt is degassed and deslag treated, the gas content of the aluminum alloy melt reaches 0.14ml / 100g, and the slag content is 0.018mm 2 / kg, the test pouring temperature is 720℃, the metal mold heating and cooling pipes are adjusted to control the overall cooling rate of the casting at 15℃ / s, and the temperature gradient is controlled at 10℃ / mm. After the samples are completely solidified, the samples are tested for cracks. The gravity samples Al1.6%Mn, Al1.7%Mn, Al1.8%Mn, Al1.9%Mn and A2.0%Mn are tested and no crack defects are found.

[0040] 4. Increase the integral ratio by 5%, and the integral area is 0.21 at this time. Carry out metal mold casting verification test, and select Al1.5%Mn sample for gravity casting verification test: After the sample alloy is melted, add 0.1%Ti and 0.1%Mo elements. After the melt is degassed and deslag treated, the gas content of the aluminum alloy melt reaches 0.14ml / 100g, and the slag content is 0.018mm2 / kg. The test pouring temperature is 720℃. After adjusting the metal mold heating and cooling pipelines, the overall cooling rate of the casting is controlled at 15℃ / s, and the temperature gradient is controlled at 10℃ / mm. After the sample is completely solidified, the sample is tested for cracks. There is no crack defect in the gravity sample Al1.5%Mn. Repeat this process until the integral is adjusted to 0.25, and there is no crack in the gravity sample.

[0041] At this time, the integral is further increased to 0.26, and a gravity casting verification test of Al1.485%Mn samples is carried out: after the sample alloy is melted, 0.1% Ti and 0.1% Mo elements are added. After the melt is degassed and deslag treated, the gas content of the aluminum alloy melt reaches 0.14ml / 100g, and the slag content is 0.018mm2 / kg. The test pouring temperature is 720℃. After adjusting the heating and cooling pipes of the metal mold, the overall cooling rate of the casting is controlled at 15℃ / s, and the temperature gradient is controlled at 10℃ / mm. After the sample is completely solidified, the sample is tested for cracks. Obvious cracks appear in the gravity sample Al1.485%Mn. The integral area can be adjusted back to 0.25 through the test, indicating that the specific composition range of this type of high-temperature crack-free brazing casting aluminum alloy can be efficiently selected through the integral 0.25 criterion.

[0042] 5. Six alloys, Al1.5Mn, Al1.6Mn, Al1.7Mn, Al1.8Mn, Al1.9Mn and Al2.0Mn, were selected for low-pressure casting. After degassing and slag removal, the gas content of the aluminum alloy melt reached 0.13ml / 100g, and the slag content was 0.018mm2 / kg. The melt temperature during casting was 780℃. Before casting, the upper mold temperature of the low-pressure casting mold was set to 350℃, and the lower mold temperature was set to 400℃. After adjusting the heat exchange of the heating and cooling pipes in the metal mold, the cooling rate of the entire casting was controlled within 8℃ / s, and the temperature gradient was controlled within 4℃ / mm. After the castings were completely solidified, they were tested for cracks, and it was found that there were no cracks in the six component castings. Subsequently, the casting was subjected to solution treatment, and the treatment process was 250℃×3H (hours) heat treatment. Finally, the samples were sampled and analyzed. The six components showed certain improvements in performance compared with the cast state after heat treatment. The specific performance indicators are shown in Table 2, indicating that the six components can effectively improve the mechanical properties of the casting after heat treatment.

[0043] Table 1 Integral area of ​​different alloy compositions

[0044] Alloy composition Al1.4%Mn Al1.485%Mn Al1.5%Mn Al1.6%Mn Al1.7%Mn Al1.8%Mn Al1.9%Mn Al2.0%Mn area 0.34 0.26 0.25 0.17 0.1 0.06 0.02 0.01

[0045] Table 2 Comparison of mechanical properties of three alloys in cast and heat treated state

[0046]

[0047]

[0048] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0049] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing a crack-free high-temperature brazed cast aluminum alloy casting, comprising: A. For the candidate aluminum alloy, the main element composition of the candidate aluminum alloy other than aluminum is selected from Mn, Cr, Fe, and Ni. The thermophysical properties are calculated, and the fluidity, shrinkage compensation and volume shrinkage of the alloy are evaluated. The parts that meet the following conditions are selected as pre-selected alloys: the eutectic content is greater than 90%, the liquid-solid two-phase interval of the alloy is less than 5°C, the solid phase temperature is greater than 600°C, and the linear expansion coefficient of the alloy from liquid to room temperature is (25-32)×10 -6 / ℃; B. For the pre-selected alloy, the solid phase fraction curve of the alloy at different temperatures is obtained by thermodynamic calculation. The alloy is integrated with the solid phase fraction in the temperature range of Tl and Ts using formula 1. When the integral area is less than M, the range of M is between 0.2-50, and the high-temperature brazing alloy a with relatively small thermal cracking tendency is screened out. The integral area Where Tl is the liquidus temperature and Ts is the solidus temperature; C. Gravity casting verification test: After the alloy is melted, add appropriate amount of refining matrix element M1 and strengthening matrix element M2, and verify after degassing and slag removal. The verification conditions are: the melt temperature is above 700℃ during casting, so that the overall cooling rate of the casting is controlled within 15℃ / s, and the temperature gradient is controlled within 10℃ / mm. After the sample is completely solidified, the sample is tested for cracks: When the sample is tested and no crack defect exists, return to step B to adjust the integral area to increase by 5%, repeat the screening and casting verification until cracks appear, so as to determine that the alloy does not have cracks and obtain the final composition of the cast aluminum alloy, and prepare to enter the next step of sand casting; or When the sample is detected to have crack defects, return to step B to adjust the integral area to reduce 5%, repeat screening and casting verification until the cracks disappear, so as to determine that the alloy has no cracks and the final composition is obtained to obtain the cast aluminum alloy, and prepare to enter the next step of sand casting.

2. The method for preparing a crack-free high-temperature brazing cast aluminum alloy casting according to claim 1, characterized in that: The alloy after degassing and slag removal in step C meets the following requirements: the gas content is less than 0.15 mL / 100 g, and the slag content is controlled within 0.02 mm 2 / kg or less.

3. The method for preparing a crack-free high-temperature brazing cast aluminum alloy casting according to claim 1, characterized in that: The refined matrix element M1 in step C is selected from Ti, Nb, B, C, and Sr.

4. The method for preparing a crack-free high-temperature brazing cast aluminum alloy casting according to claim 1, characterized in that: The strengthening matrix element M2 in step C is selected from Mo, Zr, Er, Sc, Y, and V.

5. The method for preparing crack-free high-temperature brazing cast aluminum alloy casting according to claim 1, characterized in that: In step C, the cooling rate is controlled within 10°C / s, and the temperature gradient is controlled within 5°C / mm.

6. A cast aluminum alloy obtained according to the method for preparing a crack-free high-temperature brazing cast aluminum alloy casting according to any one of claims 1 to 5.

7. The cast aluminum alloy according to claim 6, characterized in that: It includes the following components, calculated by mass percentage: Mn content 1-3%; Cr content 2-4%; Fe content 0.5-1%; Ni content 0.1-3%; M1 total amount 0.01 to 1%; M2 total amount 0.02 to 1%; The balance is aluminum and avoided impurities.

8. A casting obtained by low-pressure sand casting of the cast aluminum alloy according to claim 6 or 7.

9. The casting according to claim 8, characterized in that The process conditions during low-pressure sand casting are: the melt temperature is above 750°C, the upper mold temperature is set to 300-350°C, the lower mold temperature is set to 350-400°C, and the overall cooling rate of the casting is controlled within 15°C / s, and the temperature gradient is controlled within 10°C / mm.

10. The casting according to claim 9, characterized in that After casting, the steel is subjected to a heat treatment at 200-350°C for 5-12 hours.

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