A continuous extrusion preparation process for aluminum-based powder metallurgy materials

Abstract

This invention relates to a continuous extrusion process for preparing aluminum-based powder metallurgy materials, comprising: preparing several billets with a first cross-section from aluminum-based powder material by cold isostatic pressing; feeding the billets into the groove of a first continuous extruder in a continuous manner; continuously extruding the billets into a long, continuous intermediate product with a second cross-section; and feeding the intermediate product into a second continuous extruder for secondary continuous extrusion to obtain a product with a third cross-section. This invention utilizes the combined effects of friction and deformation heat during continuous extrusion, as well as the intense shear zone within the deformation zone, to improve the densification and mechanical properties of powder metallurgy products. It balances the densification of powder metallurgy products with the near-net-shape characteristics of powder metallurgy, reduces or avoids reliance on subsequent processing steps, shortens the process flow, lowers costs, and broadens the application scope of powder metallurgy technology.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy and its plastic processing technology, specifically to a continuous extrusion preparation process for aluminum-based powder metallurgy materials. Background Technology

[0002] Compared with casting (IM), aluminum alloys and composite materials prepared by powder metallurgy (PM) can not only avoid material composition segregation, but also improve solid solubility, obtain some aluminum alloy properties that cannot be obtained by IM process, and refine the microstructure, improve its morphology and distribution characteristics. Therefore, they have superior physical, chemical and mechanical properties and are widely used in advanced technology manufacturing fields such as aerospace, weaponry, and transportation. Powder metallurgy has become one of the main methods for preparing high-performance aluminum alloys and composite materials.

[0003] The preparation process of powder metallurgy aluminum alloys and composites can be roughly divided into three stages: powder preparation, densification forming, and post-processing. Because aluminum-based powders inevitably have a dense, non-reducible alumina film on their surface, this film hinders the formation of metallurgical bonds between particles during forming and sintering. Therefore, conventional powder metallurgy processes, i.e., pressing-sintering, often fail to produce aluminum alloys and composites with high density and clean interfaces, resulting in poor final material properties. To eliminate the adverse effects of the alumina film, improve material density, and obtain high-performance powder metallurgy aluminum alloys and composites, post-processing (rolling, extrusion, forging, etc.) after sintering becomes essential. Furthermore, machining is usually required after post-processing to obtain the final product with the desired shape and precise dimensions. These processes inevitably increase the preparation cost of powder metallurgy aluminum alloys and composites, limiting the application of powder metallurgy aluminum alloy technology. In conclusion, although powder metallurgy has become an important means of improving the performance of aluminum-based materials, its excessively long process flow and high cost are the main reasons limiting its widespread application.

[0004] In view of the above problems, the industry urgently needs to develop new forming technologies based on powder metallurgy, which can simplify or shorten the process flow and reduce the preparation cost of powder metallurgy aluminum-based materials while further improving the performance of aluminum-based materials, so that powder metallurgy aluminum-based materials can be more widely used. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a continuous extrusion preparation process for aluminum-based powder metallurgy materials. It mainly utilizes the combined effect of friction and deformation heat in the continuous extrusion process, as well as the intense shear band in the continuous extrusion deformation zone, to improve the densification degree and mechanical properties of powder metallurgy products, reduce dependence on subsequent processing steps, shorten the preparation process of powder metallurgy aluminum alloys and their composite materials, reduce the process cost of powder metallurgy aluminum alloys, and broaden the application range of powder metallurgy aluminum-based materials.

[0007] (II) Technical Solution

[0008] The main technical solutions adopted in this invention are as follows:

[0009] In a first aspect, the present invention provides a continuous extrusion preparation process for aluminum-based powder metallurgy materials, comprising: preparing a plurality of billets with a first cross section by cold isostatic pressing of aluminum-based powder materials; feeding the billets into a first continuous extruder for a single continuous extrusion to obtain an intermediate product with a second cross section; and feeding the intermediate product with the second cross section into a second continuous extruder for a second continuous extrusion to obtain a product with a third cross section.

[0010] The continuous feeding of the billets into the first continuous extruder for one continuous extrusion means that several billets are fed into the groove of the first continuous extruder one by one in a continuous manner, and are connected into a long continuous intermediate product through continuous extrusion.

[0011] Preferably, the product is a bar, profile, or plate. When producing bar, profile, or plate products of powder metallurgy aluminum alloys and their composites using the preparation process of this invention, only the extrusion die of the continuous extrusion press needs to be changed according to the product type to obtain round bars, profiles, or plates with high density and high mechanical properties. The entire process is very short. While improving the density and mechanical properties of powder metallurgy products, it can greatly simplify or shorten the powder metallurgy aluminum alloy process and reduce preparation costs, enabling wider application of powder metallurgy aluminum alloy technology. Preferably, the aluminum alloy profiles include profiles of various shapes such as flat plates, sharp corners, squares, and angle aluminum.

[0012] According to a preferred embodiment of the present invention, the aluminum-based powder material is at least one of aluminum alloy powder metallurgy material, aluminum-based particle-reinforced composite material, and aluminum-based fiber-reinforced composite material. The particle size of the aluminum-based powder material is selected based on a comprehensive consideration of proportion, performance, and other factors.

[0013] Among them, aluminum alloy powder metallurgy materials are aluminum alloy powders, including powders made from all deformable aluminum alloys. Aluminum-based particle-reinforced composite materials are aluminum alloy powders doped with inorganic reinforcing particles, such as SiC powder particles; aluminum-based fiber-reinforced composite materials are aluminum alloy powders doped with inorganic reinforcing fibers, such as SiC whiskers.

[0014] According to a preferred embodiment of the present invention, the aluminum-based powder material is prepared by a mixing process, which includes, but is not limited to, ball milling mixing.

[0015] According to a preferred embodiment of the present invention, when preparing bar blanks using cold isostatic pressing, the process pressure is 120-200 MPa, the holding time is 5-20 min, and the relative density is 75-95%; more preferably, the process pressure is 160-180 MPa; more preferably, the holding time is 10-15 min; and more preferably, the relative density is 85-90%. Compared with hot isostatic pressing, cold isostatic pressing has the advantages of low investment, high production efficiency, and low cost in preparing powder material blanks. Hot isostatic pressing, on the other hand, requires high vacuum and high temperature conditions, resulting in large equipment investment, extremely low production efficiency, and extremely high cost. It is mainly used for preparing some special products, and the blanks obtained from hot isostatic pressing also require cold isostatic pressing to prepare the blanks.

[0016] A higher relative density is more conducive to smooth feeding into the groove of the continuous extruder; otherwise, it is easy to cause feeding difficulties. Considering the exhaust of powder material during continuous extrusion, the relative density of cold isostatic pressing is limited to 75-95%.

[0017] According to a preferred embodiment of the present invention, the length-to-diameter ratio of the bar blank prepared by cold isostatic pressing is 10-25. This length-to-diameter ratio has good economy and applicability, which helps to reduce the difficulty of the process and avoid problems such as bending and poor diameter control caused by excessive length-to-diameter ratio. A more preferred length-to-diameter ratio is 15-20, the bar blank diameter is preferably 20 mm, and the bar blank length is preferably 450-455 mm.

[0018] According to a preferred embodiment of the present invention, the extrusion speed of the continuous extrusion is 1-3 rpm, and the extrusion roller groove temperature is 450-550°C, more preferably 480-520°C. Preferably, the first continuous extrusion press is a 400-type aluminum continuous extrusion press. During a single continuous extrusion, if the extrusion speed is too high, it will become difficult or even impossible to feed the billet prepared by the cold isostatic pressing method into the roller groove of the continuous extrusion press. Therefore, the speed of the continuous extrusion is 1-3 rpm. An extrusion roller groove temperature of 450-550°C is more conducive to the plastic deformation of the aluminum matrix and improves its densification.

[0019] According to a preferred embodiment of the present invention, the extrusion speed of the secondary continuous extrusion is 5-10 rpm, and the extrusion outlet temperature is 420-480℃, more preferably 430-460℃. Preferably, the second continuous extrusion press is a 350-type aluminum continuous extrusion press. Preferably, the diameter of the bar with a third cross-section obtained after the secondary continuous extrusion is 12mm. Increasing the secondary continuous extrusion speed to 5-10 rpm can achieve better plastic deformation effect, and there is no need to consider the difficulty of feeding material into the extruder wheel groove, so the speed can be increased to 5-10 rpm. The extrusion outlet temperature of 420-480℃ will help to obtain the optimal plastic deformation effect during continuous extrusion and to densify the powder metallurgy aluminum alloy product, and ensure the surface quality and performance of the final product.

[0020] According to a preferred embodiment of the present invention, after being extruded by a first continuous extruder, the product is cooled to obtain an intermediate product with the second cross section. The intermediate product is wound into a roll by a constant tension winding device. The roll is then fed into a second continuous extruder for a second continuous extrusion. After cooling, it is wound into a roll by a constant tension winding device to obtain a product (bar, profile, or sheet) with a third cross section.

[0021] This invention utilizes the combined effects of friction and deformation heat during continuous extrusion, as well as the intense shear bands within the continuous extrusion deformation zone, to transform cold isostatically pressed aluminum-based powder materials into large-roll, highly dense powder metallurgy aluminum alloy products with superior mechanical properties. The manufacturing process of this invention can be used to produce large-roll powder metallurgy aluminum alloy bars, profiles, or plates, particularly small and medium-sized aluminum alloy bars, profiles, or plates.

[0022] Preferably, if the first cross-sectional area is X, the second cross-sectional area is Y, and the third cross-sectional area is Z, where Y = (0.6-0.7)X and Z = (0.5-0.6)Y; preferably, the shape of the second cross-section is different from the shape of the third cross-section. Furthermore, depending on the selected extrusion die, there may be cases where Z > Y or Z = Y.

[0023] Preferably, Z is the cross-sectional area of ​​the target product of powder metallurgy aluminum alloy. If Z is still larger than the cross-sectional area of ​​the target bar product, another continuous extrusion can be performed to obtain a product with the required precise dimensions, and the densification degree and mechanical properties of the target product can be further improved by the second continuous extrusion.

[0024] (III) Beneficial Effects

[0025] This invention utilizes the combined effects of friction and deformation heat during continuous extrusion, as well as the intense shear band within the continuous extrusion deformation zone, to continuously feed cold isostatically pressed billets of powder metallurgy aluminum alloys and their composites (including aluminum-based particle-reinforced composites and aluminum-based fiber-reinforced composites) into continuous extrusion wheel grooves. Through two consecutive extrusions, the densification of powder metallurgy products and the improvement of mechanical properties are achieved. This provides a new process method for developing short-process, low-cost preparation of large-roll-weight, small- and medium-sized powder metallurgy aluminum alloys and their composites into bars, profiles, and plates.

[0026] This invention can take into account both the densification of powder metallurgy products and the near-net-shape process characteristics of powder metallurgy. It can reduce or avoid dependence on subsequent processing steps, thereby shortening the process flow, improving the cost-effectiveness of powder metallurgy aluminum alloys and their composites, and enabling aluminum alloy powder metallurgy technology to be more widely used.

[0027] The main contribution of this invention is that, while shortening and simplifying the preparation process of aluminum-based powder metallurgy materials, the mechanical properties and relative density of powder metallurgy products of the same substrate and specifications produced by hot pressing sintering-hot extrusion method are significantly improved. In addition, the process energy consumption and equipment costs of this invention are lower, making it particularly suitable for producing rods, strips and other products of large-roll weight, small-specification powder metallurgy aluminum alloys and their composites. Detailed Implementation

[0028] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below through specific embodiments.

[0029] Example 1

[0030] The steps for preparing round bars of powder metallurgy 6013 aluminum alloy in this embodiment are as follows:

[0031] (1) Commercially available 6013 aluminum alloy powder with an average particle size of 20μm was loaded into a cold isostatic pressing mold with a diameter of 21mm and a length of 500mm, and pressed into a bar blank with a diameter of 20mm and a length of 450mm on a cold isostatic press. The pressure was 160MPa, and the pressure was held for 10min. The relative density was 81.6%.

[0032] (2) The billets are fed one after another into the groove of the 400-type aluminum continuous extrusion press and continuously extruded into round bars with a diameter of 16mm. The speed of the extrusion wheel is set to 2rpm. The actual temperature of the extrusion wheel groove is about 500℃. After cooling, the product is wound up using a constant tension winding device.

[0033] (3) The 16mm diameter round bar is continuously extruded for the second time into a 12mm diameter round bar product on a 350 type aluminum continuous extrusion press. The extrusion roller speed is set to 8rpm, and the actual measured outlet temperature of the extruded product is about 460℃.

[0034] (4) Samples were taken from the head, middle and tail of the bars produced by the first continuous extrusion in step (2) and the second continuous extrusion in step (3), respectively. The samples were then subjected to solution treatment at 540℃ for 2 hours, followed by water quenching and artificial aging treatment at 175℃ for 10 hours (T6 state). The tensile properties and relative density of the samples were tested, and the results are shown in Table 1.

[0035] Comparative Example 1

[0036] This comparative example uses a hot pressing sintering-hot extrusion method to produce bars of the same specifications as in Example 1:

[0037] Commercially available 6013 aluminum alloy powder with an average particle size of 20 μm was pressed into extruded billets with a diameter of 80 mm and a length of 300 mm on a cold isostatic press. After vacuum sintering at 560 °C and 40 MPa for 20 min, the billets were extruded in one go on an 800T extruder into aluminum alloy rods with a diameter of 12 mm. The subsequent processing was carried out in the same way as in Example 1: solution treatment at 540 °C for 2 hours followed by water quenching and artificial aging treatment at 175 °C for 10 hours (T6 state). The tensile properties and relative density of the product were tested, and the results are shown in Table 1.

[0038] Table 1: Comparison of tensile properties and relative density of the T6 state bar stock of Example 1 and Comparative Example 1 bar stock in the T6 state.

[0039]

[0040] Comparative analysis revealed that the mechanical properties and relative density of the powder metallurgy 6013 aluminum alloy rods produced by the method in Example 1 of this invention are significantly superior to those produced by the vacuum sintering-hot extrusion process. Furthermore, compared to the comparative example, this invention eliminates the need for vacuum hot pressing sintering and uses a thinner billet to achieve the desired diameter through two consecutive extrusion processes, without requiring large-tonnage extrusion equipment. Therefore, this invention offers lower process energy and equipment costs, making it particularly suitable for producing large-coil, small-diameter powder metallurgy aluminum alloys and their composite materials, including rods and strips.

[0041] Example 2

[0042] The steps for preparing round bars of powder metallurgy 6061 aluminum alloy SiC powder reinforced composite material in this embodiment are as follows:

[0043] (1) Commercially available 6061 aluminum alloy powder with an average particle size of 20 μm and commercially available SiC powder with an average particle size of 10 μm were mixed by planetary ball milling.

[0044] (2) The mixture was loaded into a cold isostatic pressing mold with a diameter of 21 mm and a length of 500 mm, and pressed into a 15 wt.% SiC particle-reinforced 6061 aluminum matrix composite rod blank with a diameter of 20 mm and a length of 455 mm on a cold isostatic press. The pressure was 180 MPa, the holding pressure was 15 min, and the relative density was 81.6%.

[0045] (3) The billets are fed one after another into the groove of the 400-type aluminum continuous extrusion press and continuously extruded into round bars with a diameter of 16mm. The speed of the extrusion wheel is set to 1.5rpm. The actual temperature of the extrusion wheel groove is about 490℃. After cooling, the product is wound up using a constant tension winding device.

[0046] (4) The 16mm diameter round bar that was first continuously extruded into a coil was then continuously extruded into a 12mm diameter round bar product on a 350 type aluminum continuous extrusion press. The extrusion roller speed was set to 5rpm, and the measured outlet temperature of the extruded product was about 450℃.

[0047] (5) Samples were taken from the coiling head, middle and tail of the bars produced by the first continuous extrusion in step (3) and the second continuous extrusion in step (4). The samples were then subjected to solution treatment at 540℃ for 2 hours, followed by water quenching and artificial aging treatment at 175℃ for 10 hours (T6 state). The tensile properties and relative density of the samples were tested, and the results are shown in Table 2.

[0048] Comparative Example 2

[0049] This comparative example uses a hot pressing sintering-hot extrusion method to produce bars of the same specifications as in Example 2: The mixture prepared in step (1) of Example 2 was pressed into extruded billets with a diameter of 80 mm and a length of 300 mm on a cold isostatic press. After vacuum sintering at 560°C and 40 MPa for 60 min, it was extruded in one go on an 800T extruder into aluminum alloy bars with a diameter of 12 mm. Subsequently, it was processed in the same way as in Example 2: first, it was solution treated at 540°C for 2 hours, then water quenched and artificially aged at 175°C for 10 hours (T6 state). The tensile properties and relative density of the product were tested, and the results are shown in Table 2.

[0050] Table 2: Comparison of tensile properties and relative density of the T6 state bar stock of Example 2 and Comparative Example 2 bar stock in the T6 state.

[0051]

[0052] Comparative analysis revealed that the mechanical properties and relative density of the powder metallurgy 15% SiC particle-reinforced 6061 aluminum matrix composite rods produced by the method of Example 2 of this invention are significantly superior to those produced by the vacuum sintering-hot extrusion process. Furthermore, compared to Comparative Example 2, this invention eliminates the need for vacuum hot pressing sintering and uses a thinner diameter billet to obtain the desired diameter round rod through two consecutive extrusions, without requiring large-tonnage extrusion equipment. Therefore, the process energy consumption and equipment costs of this invention are lower.

[0053] 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 continuous extrusion production process of an aluminum-based powder metallurgical material, characterized in that, It includes: A number of billets with a first cross section are prepared by cold isostatic pressing of aluminum-based powder material. The billets are then fed into a first continuous extruder for continuous extrusion to obtain an intermediate product with a second cross section. The extrusion speed of the continuous extrusion is 1-3 rpm and the temperature of the extrusion wheel groove is 450-550℃. The intermediate product with the second cross section is fed into the second continuous extruder for a second continuous extrusion to obtain a product with the third cross section. The extrusion speed of the second continuous extrusion is 5-10 rpm, and the extrusion outlet temperature is 420-480℃. When preparing the billet using the cold isostatic pressing method, the process pressure is 120-200 MPa, the holding time is 5-20 min, and the relative density of the billet prepared by the cold isostatic pressing method is 75-95%, and the length-to-diameter ratio is 10-25. Feeding the billet into the first continuous extruder for continuous extrusion means feeding several billets into the groove of the first continuous extruder one by one in a continuous manner, and connecting them into a long continuous intermediate product through continuous extrusion.

2. The continuous extrusion preparation process for aluminum-based powder metallurgy materials according to claim 1, characterized in that, The aluminum-based powder material is at least one of aluminum alloy powder metallurgy material, aluminum-based particle reinforced composite material, and aluminum-based fiber reinforced composite material.

3. The continuous extrusion preparation process for aluminum-based powder metallurgy materials according to claim 1, characterized in that, When preparing bar blanks using the cold isostatic pressing method, the process pressure is 160-180 MPa; the holding time is 10-15 min; and the relative density is 85-90%.

4. The continuous extrusion preparation process for aluminum-based powder metallurgy materials according to claim 1, characterized in that, The length-to-diameter ratio of the bar blank prepared by cold isostatic pressing is 15-20.

5. The continuous extrusion preparation process for aluminum-based powder metallurgy materials according to claim 1, characterized in that, The temperature of the extrusion wheel groove during the continuous extrusion is 480-520℃.

6. The continuous extrusion preparation process for aluminum-based powder metallurgy materials according to claim 1, characterized in that, The extrusion outlet temperature of the secondary continuous extrusion is 430-460℃.

7. The continuous extrusion preparation process for aluminum-based powder metallurgy materials according to claim 1, characterized in that, After being extruded by the first continuous extruder and cooled, an intermediate product with the second cross section is obtained. The intermediate product is wound into a roll by a constant tension winding device. The roll is then fed into the second continuous extruder for a second continuous extrusion. After cooling, it is wound into a roll by a constant tension winding device to obtain a product with the third cross section.

8. The continuous extrusion preparation process for aluminum-based powder metallurgy materials according to claim 1 or 7, characterized in that, The product is a round bar, profile, or plate of powder metallurgy aluminum alloy or its composite material.

Images