CN109596800B - High-volume-fraction whisker reinforced 2024 aluminum-based composite sheath thermoforming method - Google Patents

High-volume-fraction whisker reinforced 2024 aluminum-based composite sheath thermoforming method Download PDF

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CN109596800B
CN109596800B CN201811580953.4A CN201811580953A CN109596800B CN 109596800 B CN109596800 B CN 109596800B CN 201811580953 A CN201811580953 A CN 201811580953A CN 109596800 B CN109596800 B CN 109596800B
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aluminum
blank
sheath
composite material
sic
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CN109596800A (en
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袁林
徐福昌
王磊
宗影影
成功
郑镇洙
单德彬
郭斌
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Harbin Institute of Technology
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Harbin Institute of Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/20—Metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
    • B21J5/00—Methods for forging, hammering, or pressing; Special equipment or accessories therefor
    • B21J5/002—Hybrid process, e.g. forging following casting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21K—MAKING FORGED OR PRESSED METAL PRODUCTS, e.g. HORSE-SHOES, RIVETS, BOLTS OR WHEELS
    • B21K29/00—Arrangements for heating or cooling during processing

Abstract

High volumeA fractional whisker reinforced 2024 aluminum matrix composite sheath thermoforming method relates to an aluminum matrix composite sheath thermoforming method, which comprises the following steps: firstly, observing the mechanical property and microstructure of an original blank: scanning electron microscope for original as-cast high-volume-fraction SiC by utilizing field emission environmentw+Al18B4O33wThe whisker reinforced 2024 aluminum matrix composite blank microscopic structure is observed and tensile test is carried out to test the mechanical property; secondly, testing the hot forgeability of the original blank; thirdly, sheath extruding the blank or sheath upsetting the blank to obtain the SiC with high volume fractionw+Al18B4O33wThe whisker reinforced 2024 aluminum-based composite material forging stock. The aluminum-based composite material bar and the forging stock which have good forming quality, no macroscopic cracks on the surface and remarkably improved forgeability are obtained by sheath extrusion and sheath upsetting-drawing at high temperature.

Description

High-volume-fraction whisker reinforced 2024 aluminum-based composite sheath thermoforming method
Technical Field
The invention relates to a thermal forming method for an aluminum-based composite sheath, in particular to a thermal forming method for a high-volume-fraction whisker reinforced 2024 aluminum-based composite sheath.
Background
The aluminum-based composite material has the advantages of light weight, high strength, high temperature resistance, wear resistance, low thermal expansion coefficient and the like, and becomes an indispensable lightweight structural material and functional material in the high-tech fields of military, national defense, aerospace and the like. However, the introduction of the brittle and hard reinforcement, which has a large difference from the aluminum alloy matrix in properties, hinders the long-range slip of dislocation in the matrix metal during deformation, and the brittle and hard reinforcement fracture strain is generally low. When the external strain is lower, the fracture occurs, and the matrix is induced to generate micro-cracks, and particularly when the reinforced volume fraction of the crystal whisker is higher, the cracks are easy to generate. For the particle-reinforced aluminum matrix composite material, when the volume fraction is small, the thermoplastic forming is easy, and when the volume fraction is high, the forging stock is difficult to prepare through the thermoplastic forming. For the whisker reinforced aluminum matrix composite, the reinforced phase has larger size, so that the thermal forming is more difficult. In addition, due to the non-uniformity of the distribution of the reinforcing phase material in the preparation of the aluminum matrix composite, the aluminum matrix composite with large size is more difficult to realize hot forming due to smaller size.
Disclosure of Invention
The invention provides high volume fraction SiC for improving the forgeability of an aluminum-based composite material and improving the forming quality of a forging stock to overcome the defects of the prior artw+Al18B4O33wA method for thermally forming a whisker reinforced 2024 aluminum-based composite material sheath.
According to one aspect of the invention, a high volume fraction SiC based jacket extrusion is providedw+Al18B4O33wA whisker reinforced 2024 aluminum-based composite material sheath thermoforming method; it comprises the following steps:
firstly, observing the mechanical property and microstructure of an original blank: scanning electron microscope for original as-cast high-volume-fraction SiC by utilizing field emission environmentw+Al18B4O33wThe whisker reinforced 2024 aluminum matrix composite blank microscopic structure is observed and tensile test is carried out to test the mechanical property;
secondly, testing the hot forgeability of the original blank: selecting original as-cast high volume fraction SiC with certain height and diameterw+Al18B4O33wPerforming a forgeability compression test on the whisker reinforced 2024 aluminum-based composite material blank to obtain a forgeability compression test temperature of 470-510 ℃;
thirdly, sheathing and extruding the blank: the original as-cast state high volume fraction SiCw+Al18B4O33wProcessing the whisker reinforced 2024 aluminum-based composite material into a blank with a certain height and diameter, coating the blank with a sheath, and covering the sheath at the temperature determined in the step two of 470-510 DEG CExtruding a blank;
fourthly, testing the forgeability of the sheath extrusion material: cutting a sample from the extruded material after sheath extrusion to perform an upsetting experiment, wherein the deformation temperature of the upsetting experiment is set to be 470-510 ℃, and the strain rate is set to be 0.01S-1Compressed along the axial direction and the radial direction in the upsetting and drawing process to obtain SiC with high volume fractionw+Al18B4O33wThe whisker reinforced 2024 aluminum-based composite material forging stock.
In accordance with another aspect of the invention, a high volume fraction SiC based on pack upset is providedw+Al18B4O33wA whisker reinforced 2024 aluminum-based composite material sheath thermoforming method; it comprises the following steps:
firstly, observing the mechanical property and microstructure of an original blank: scanning electron microscope for original as-cast high-volume-fraction SiC by utilizing field emission environmentw+Al18B4O33wThe whisker reinforced 2024 aluminum matrix composite blank microscopic structure is observed and tensile test is carried out to test the mechanical property;
secondly, testing the hot forgeability of the original blank: selecting original as-cast high volume fraction SiC with certain height and diameterw+Al18B4O33wPerforming a forgeability compression test on the whisker reinforced 2024 aluminum-based composite material blank to obtain a forgeability compression test temperature of 470-510 ℃;
thirdly, covering and upsetting the blank: the original as-cast state high volume fraction SiCw+Al18B4O33wProcessing the whisker reinforced 2024 aluminum-based composite material into a blank with a certain height and diameter, coating the blank with a sheath, performing multi-pass axial upsetting to axial 30% deformation at the temperature of 470-510 ℃ determined in the step two, turning over for 90 degrees, performing radial compression for 8-10%, rotating the blank, performing radial compression for 8-10%, repeating the radial compression process along the whole circumference, performing axial upsetting for 8-10% after completing, performing the radial compression process, performing the axial upsetting process again, and repeating the process for multiple passes; finally, the axial compression reaches 50-70 percent, the radial compression reaches 40-50 percent, and the high volume fraction SiC is obtainedw+Al18B4O33w whisker reinforced 2024 aluminum base composite material forging stock.
Further, the high volume fraction SiCw+Al18B4O33wSiC in whisker reinforced 2024 aluminium base composite materialw+Al18B4O33wThe volume fraction of the whiskers is 15-25%.
Compared with the prior art, the invention has the beneficial effects that
The method adopts samples with different specifications to carry out the forgeability test on the aluminum matrix composite; and high volume fraction SiC is proposedw+Al18B4O33wThe sheath extrusion forming technology for whisker reinforced composite material is characterized in that the tensile strength at room temperature of a bar manufactured by sheath extrusion reaches 350MPa, is far higher than the tensile strength of an original die-casting blank by 100MPa, has a room temperature elongation rate of 0.2 percent compared with an as-cast state, and the bar obtained by the sheath extrusion is about 2.0 percent. The surface of the forging stock obtained by sheath upsetting has no macrocracks. The invention overcomes the defects of poor forgeability and easy cracking of plastic forming of the current high volume fraction whisker reinforced composite material, and is an effective method for improving the forgeability and the mechanical property of the high volume fraction whisker reinforced composite material.
Drawings
FIG. 1 shows the original as-cast high volume fraction SiCw+Al18B4O33wA transverse tissue diagram of the whisker reinforced 2024 aluminum matrix composite;
FIG. 2 shows the original as-cast high volume fraction SiCw+Al18B4O33wA longitudinal structure diagram of the whisker reinforced 2024 aluminum matrix composite;
FIG. 3 shows the original as-cast high volume fraction SiCw+Al18B4O33wThe whisker reinforced 2024 aluminum matrix composite material has axial and radial room temperature tensile stress strain curve diagrams;
FIG. 4 is a chart showing the results of thermo-compression test of a test specimen having a diameter of 8mm × 12 mm;
FIG. 5 is a graph showing the results of the thermocompression test of a sample having a diameter of 60mm × 60 mm;
FIG. 6 is a graph showing the results of thermo-compression test of a test piece having a diameter of 190mm × 300 mm;
FIG. 7 is a cross-sectional view of the female die of the extrusion die;
FIG. 8 is a pictorial view of the female die of the extrusion die;
FIG. 9 is a schematic illustration of an extruded billet and a pure aluminum sheath;
FIG. 10 is a view of an uncoated extruded rod;
FIG. 11 shows the extruded rod after jacket extrusion;
FIG. 12 is a schematic illustration of an upset blank and an aluminum alloy wrap;
FIG. 13 is a blank after uncapping;
FIG. 14 is a blank after jacket upsetting;
FIG. 15 is a graph of room temperature tensile stress strain curves for an original as-cast aluminum-based composite and a jacket extrusion;
FIG. 16 is a graph of the results of the forgeability of a jacket extrudate bar compressed axially and radially by 20% each;
FIG. 17 is a graph of the results of the forgeability of a jacket extrudate bar compressed axially and radially by 30% each;
FIG. 18 is a microstructure view of an as-cast aluminum-based composite material;
FIG. 19 is a microstructure of the aluminum matrix composite after jacket extrusion.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
A high volume fraction SiC as illustrated in connection with FIGS. 1-19w+Al18B4O33wThe thermal forming process of whisker reinforced 2024 aluminum base composite material includes the following steps:
firstly, observing the mechanical property and microstructure of an original blank: scanning electron microscope for original as-cast high-volume-fraction SiC by utilizing field emission environmentw+Al18B4O33wThe whisker reinforced 2024 aluminum matrix composite blank microscopic structure is observed and tensile test is carried out to test the mechanical property;
second, original blank heatingAnd (3) forgeability testing: selecting original as-cast high volume fraction SiC with certain height and diameterw+Al18B4O33wPerforming a forgeability compression test on the whisker reinforced 2024 aluminum-based composite material blank to obtain a forgeability compression test temperature of 470-510 ℃;
thirdly, sheathing and extruding the blank: the original as-cast state high volume fraction SiCw+Al18B4O33wProcessing the whisker reinforced 2024 aluminum matrix composite into a blank with a certain height and diameter, coating the blank with a sheath, and extruding the sheathed blank at the temperature determined in the step two of 470-510 ℃;
fourthly, testing the forgeability of the sheath extrusion material: cutting a sample from the extruded material after sheath extrusion to perform an upsetting experiment, wherein the deformation temperature of the upsetting experiment is set to be 470-510 ℃, and the strain rate is set to be 0.01S-1Compressed along the axial direction and the radial direction in the upsetting and drawing process to obtain SiC with high volume fractionw+Al18B4O33wThe whisker reinforced 2024 aluminum-based composite material forging stock.
As-cast SiC of originw+Al18B4O33wThe transverse structure (shown in figure 1) and the longitudinal structure (shown in figure 2) of the microstructure of the whisker reinforced 2024 aluminum alloy composite material show that aluminum alloy molten metal cannot completely penetrate into gaps among the whiskers of the reinforcement body in the extrusion casting preparation process of the aluminum alloy composite material, and as-cast defects exist. The defects are easy to generate micro cracks in the subsequent deformation process, the deformability of the material is reduced, and the original aluminum-based composite material shown in FIG. 3 has an axial and radial room-temperature tensile stress-strain curve (the abscissa represents strain, and the ordinate represents stress), wherein ■ represents the axial original cast SiCw+Al18B4O33wThe elongation of the whisker reinforced 2024 aluminum alloy composite material is shown in the curve, wherein, the curve is tangle-solidup represents the original cast-state SiC in the radial directionw+Al18B4O33wThe whiskers enhance the elongation of the 2024 aluminum alloy composite. As can be seen, the original as-cast SiCw+Al18B4O33wThe elongation rate of the whisker reinforced 2024 aluminum alloy composite material at room temperature in the axial direction is lower than that of the composite materialThe radial room temperature elongation rate, which shows the plasticity difference of the original cast aluminum-based composite material in different directions, brings great difficulty to the thermoplastic forming.
Preferably, high volume fraction SiCw+Al18B4O33wSiC in whisker reinforced 2024 aluminium base composite materialw+Al18B4O33wThe volume fraction of the whiskers is 15-25%. Taking 20% volume fraction as an example:
testing 20% volume fraction SiCw+Al18B4O33wThe forgeability and the formability temperature of the whisker reinforced aluminum matrix composite, and because the reinforcing phase is not uniformly distributed in the preparation process of the high volume fraction aluminum matrix composite, the actual forming condition cannot be reflected by a small sample. This example presents forgeability and temperature tests using bars of three different dimensions phi 190 x 300mm, phi 60mm x 60mm, and phi 8mm x 12 mm. The test results are respectively shown in the compression test result of the small sample of phi 8mm multiplied by 12mm in fig. 4, the compression test result of the middle sample of phi 60mm multiplied by 60mm in fig. 5, and the compression test result of the large sample of phi 190mm multiplied by 300mm in fig. 6.
The left graph of fig. 4 shows that the compression surface has no macrocracks in the 470-510 ℃ high temperature region, the middle graph of fig. 4 shows that the compression surface has slight macrocracks in the 370-410 ℃ medium temperature region, and the right graph of fig. 4 shows that the compression surface has obviously deeper macrocracks in the 270-310 ℃ low temperature region, which shows that the high volume fraction aluminum-based composite material is suitable for forming at 470-510 ℃.
FIG. 5 shows that when a sample of the medium-sized aluminum-based composite material with the diameter of 60mm multiplied by 60mm is axially compressed at the temperature of 470-510 ℃ by 40%, the side surface of the blank forms shallow longitudinal cracks under the action of tangential tensile stress, and the medium-sized high volume fraction aluminum-based composite material shows strong compressive resistance. The left side of fig. 5 shows the original sample compressed at high temperature, and the right side of fig. 5 shows the sample compressed at high temperature to a degree of 40%.
In order to reduce the influence of uneven distribution of reinforcing phases on the forgeability test of the high volume fraction aluminum-based composite material in the preparation process, fig. 6 shows that the result of the thermal compression test of a large-size aluminum-based composite material sample with the diameter of 190mm multiplied by 300mm at the temperature of 470-510 ℃ shows that the side surface of the thermal compression sample has obvious deep macroscopic cracks, which indicates that for the large sample of the high volume fraction aluminum-based composite material, even if the large sample is formed in a higher temperature range, the large sample still has poor thermoplasticity, cracks are easy to generate, and the direct thermoplastic forming is difficult.
For this purpose, a three-step jacket extrusion technique was used, as described in the examples below: in order to ensure the extrusion stability and reliability and the stable performance of the obtained extruded blank, an extrusion die as shown in fig. 7 and 8 is used, and the extrusion die is the prior art. And extruding the aluminum matrix composite material at 470-510 ℃ by adopting a sheath extrusion forming process, wherein the extrusion ratio is 9: 1. The method specifically comprises the following steps: SiC of 20% volume fraction of original cast statew+Al18B4O33wCutting the whisker reinforced 2024 aluminum-based composite material into extruded bars with the diameter of 60mm and the height of 60mm, wherein the selected sheath material is pure aluminum or aluminum alloy, the sizes are 72mm of outer diameter, 60mm of inner diameter and 60mm of height, and the extruded blank and the pure aluminum sheath as shown in figure 9 and high volume fraction SiCw+Al18B4O33wGraphite is adopted for lubrication between the whisker reinforced 2024 aluminum matrix composite and the sheath, and the composite is put into a heating furnace for heating and is kept warm for 2 hours after reaching the temperature. And (3) extruding and forming the sample of the non-sheathed aluminum-based composite material with the diameter of 60mm and the height of 60mm of the extruded bar under the same forming condition. As shown in FIG. 10, the uncased extruded bar exhibited a large number of macrocracks on the surface, while the results of the jacket extrusion of FIG. 11 showed no macrocracks on the surface of the jacketed bar. Wherein the upper graph of FIG. 11 shows a bar graph without jacket stripping and the lower graph of FIG. 11 shows a bar graph with jacket stripping.
For the high volume fraction whisker reinforced 2024 aluminum alloy composite material with poor plasticity, easy crack generation in hot working and poor forgeability limiting the application of the aluminum matrix composite material, the bar obtained after extrusion through the pure aluminum sheath has no crack and has high surface forming quality, because the pure aluminum sheath outside the composite material can obstruct the direct contact between the composite material and the extrusion die in the extrusion deformation process, the friction force from the inner surface of the extrusion die is transferred to the pure aluminum sheath, and meanwhile, the temperature loss caused by the direct contact between the composite material and the extrusion die in the extrusion process is also reduced. Because the yield strength of the pure aluminum is less than that of the composite material at the same temperature, the pure aluminum sheath is preferentially subjected to plastic deformation in the extrusion deformation process of the material, and the pure aluminum has better plasticity and can bear deformation to a great extent, so that cracks perpendicular to the extrusion direction are not generated on the surface in the extrusion deformation process, and the friction force from the inner side surface of the extrusion die is not transferred to the surface of the composite material due to the graphite lubricant existing between the pure aluminum sheath and the composite material, so that the uniformity of plastic flow of the composite material at each position in the extrusion deformation process is ensured.
On the basis of the sheath extrusion molding, a tensile test is carried out on the 20% high volume fraction whisker reinforced aluminum matrix composite after the sheath extrusion deformation, and fig. 15 is a room temperature tensile stress strain curve of the original as-cast and sheath extruded material. Wherein the curve in which ■ is located represents the original as-cast SiCw+Al18B4O33wThe curve of the whisker reinforced 2024 aluminum alloy composite material is represented by the curve of a solidup-solidup part of SiC after sheath extrusion formingw+Al18B4O33wThe whisker reinforced 2024 aluminum alloy composite material has room temperature elongation of about 2.0% after extrusion deformation of an as-cast aluminum alloy composite material by a sheath with an extrusion ratio of 9:1, which is higher than the room temperature elongation of 0.2% in an as-cast state, and has obviously improved strength after extrusion deformation of the sheath, and the tensile strength is improved from 100MPa to 350 MPa. The tensile strength and the elongation percentage of the material after the extrusion deformation of the sheath are obviously improved,
in order to test the hot forgeability of the sheathed extruded bar, a block sample with the size of 14mm multiplied by 14mm is cut from the sheathed extruded bar for upsetting and drawing experiment, and the block sample is loaded along the axial direction and the radial direction in the upsetting and drawing process. The deformation temperature of the upsetting test is set to be 470-510 ℃, and the strain rate is set to be 0.01S-1. As shown in the figures 16 and 17, after the bar extruded by the sheath is respectively compressed by 20 percent in the axial direction and the radial direction and 30 percent in the axial direction and the radial direction, no macrocracks are generated, and the hot forgeability is obviously improved.
To further observe the original cast condition and the sheathAnd after the fourth step, a fifth step of observing the microstructure of the extruded bar after sheath extrusion is also set: high volume fraction SiC after jacket extrusion by using field emission environment scanning electron microscopew+Al18B4O33wAnd (4) observing the microstructure of the whisker reinforced 2024 aluminum-based composite material bar. The method specifically comprises the following steps: and observing and comparing the microstructure of the high volume fraction whisker reinforced aluminum matrix composite after the extrusion deformation of the sheath with that of the original as-cast high volume fraction whisker reinforced aluminum matrix composite. Fig. 18 and 19 are the microstructures of the aluminum matrix composite extruded through the sheath and the original cast state, respectively, and it can be observed from fig. 18 and 19 that the whiskers of the reinforcement rotate during the extrusion deformation of the composite, the orientation of the whiskers is changed from the free orientation in the cast state to the axial distribution along the extruded bar, and the distribution of the whiskers is more uniform than that of the composite in the cast state. The sheath extrusion deformation can improve more as-cast structure defects in as-cast materials, and further improve the mechanical properties of the composite material, for example, gaps among the agglomerated reinforcement whiskers with small sizes are difficult to infiltrate due to the fact that the surface tension of molten aluminum alloy molten metal is large, so that more gaps exist in the as-cast composite material, and the gaps can be reduced or welded in the extrusion deformation process of the composite material. In addition, the mechanical property of the composite material can be improved by refining coarse grains in the cast material in the extrusion deformation process of the composite material sheath. The second phase with larger size in the matrix is broken, the surface area is increased after elongation, more solute atoms are fused into the matrix, and the solid solution strengthening effect is enhanced, so that the ductility and the strength of the high volume fraction fiber reinforced composite material extruded by the sheath are obviously improved.
In another embodiment, there is provided a high volume fraction SiCw+Al18B4O33wThe sheath thermoforming method of the whisker reinforced 2024 aluminum-based composite material adopts sheath pier drawing forming and comprises the following steps:
firstly, observing the mechanical property and microstructure of an original blank: scanning electron microscope for original as-cast high-volume-fraction SiC by utilizing field emission environmentw+Al18B4O33wThe whisker reinforced 2024 aluminum matrix composite blank microscopic structure is observed and tensile test is carried out to test the mechanical property;
secondly, testing the hot forgeability of the original blank: selecting original as-cast high volume fraction SiC with certain height and diameterw+Al18B4O33wPerforming a forgeability compression test on the whisker reinforced 2024 aluminum-based composite material blank to obtain a forgeability compression test temperature of 470-510 ℃;
thirdly, covering and upsetting the blank: the original as-cast state high volume fraction SiCw+Al18B4O33wProcessing the whisker reinforced 2024 aluminum-based composite material into a blank with a certain height and diameter, coating the blank with a sheath, performing multi-pass axial upsetting to axial 30% deformation at the temperature of 470-510 ℃ determined in the step two, turning over for 90 degrees, performing radial compression for 8-10%, rotating the blank, performing radial compression for 8-10%, repeating the radial compression process along the whole circumference, performing axial upsetting for 8-10% after completing, performing the radial compression process, performing the axial upsetting process again, and repeating the process for multiple passes; finally, the axial compression reaches 50-70 percent, the radial compression reaches 40-50 percent, and the high volume fraction SiC is obtainedw+Al18B4O33wThe whisker reinforced 2024 aluminum-based composite material forging stock.
As-cast SiC of originw+Al18B4O33wThe transverse structure (shown in figure 1) and the longitudinal structure (shown in figure 2) of the microstructure of the whisker reinforced 2024 aluminum alloy composite material show that aluminum alloy molten metal cannot completely penetrate into gaps among the whiskers of the reinforcement body in the extrusion casting preparation process of the aluminum alloy composite material, and as-cast defects exist. The defects are easy to generate micro cracks in the subsequent deformation process, the deformation capability of the material is reduced, the original aluminum-based composite material in the figure 3 has an axial and radial room-temperature tensile stress-strain curve ((the abscissa represents strain, and the ordinate represents stress), the axial room-temperature elongation of the composite material is lower than the radial room-temperature elongation, and the original cast aluminum-based composite material shows plastic difference in different directions, so that great difficulty is brought to thermoplastic forming.
Preferably, high volume fraction SiCw+Al18B4O33wSiC in whisker reinforced 2024 aluminium base composite materialw+Al18B4O33wThe volume fraction of the whiskers is 15-25%. Taking 20% volume fraction as an example:
testing 20% volume fraction SiCw+Al18B4O33wThe forgeability and the formability temperature of the whisker reinforced aluminum matrix composite, and because the reinforcing phase is not uniformly distributed in the preparation process of the high volume fraction aluminum matrix composite, the actual forming condition cannot be reflected by a small sample. This example presents the forgeability tests using three different dimensional specifications of phi 190X 300mm, phi 60mm X60 mm, and phi 8mm X12 mm. The test results are respectively shown in the compression test result of the small sample of phi 8mm multiplied by 12mm in fig. 4, the compression test result of the middle sample of phi 60mm multiplied by 60mm in fig. 5, and the compression test result of the large sample of phi 190mm multiplied by 300mm in fig. 6.
The left graph of fig. 4 shows no macrocracks on the compression surface in the high temperature region of 470-510 c, the middle graph of fig. 4 shows slight macrocracks on the compression surface in the medium temperature region of 370-410 c, and the right graph of fig. 4 shows significantly deeper macrocracks on the compression surface in the low temperature region of 270-310 c, indicating that the high volume fraction aluminum-based composite is suitable for forming at 470-510 c.
FIG. 5 shows that when a sample of the medium-sized aluminum-based composite material with the diameter of 60mm multiplied by 60mm is axially compressed at the temperature of 470-510 ℃ by 40%, the side surface of the blank forms shallow longitudinal cracks under the action of tangential tensile stress, and the medium-sized high volume fraction aluminum-based composite material shows strong compressive resistance. The left side of fig. 5 shows the original sample compressed at high temperature, and the right side of fig. 5 shows the sample compressed at high temperature to a degree of 40%.
In order to reduce the influence of uneven distribution of reinforcing phases on the forgeability test of the high volume fraction aluminum-based composite material in the preparation process, fig. 6 shows that the result of the thermal compression test of a large-size aluminum-based composite material sample with the diameter of 190mm multiplied by 300mm at the temperature of 470-510 ℃ shows that the side surface of the thermal compression sample has obvious deep macroscopic cracks, which indicates that for the large sample of the high volume fraction aluminum-based composite material, even if the large sample is formed in a higher temperature range, the large sample still has poor thermoplasticity, cracks are easy to generate, and the direct thermoplastic forming is difficult.
For this purpose, a three-step jacket upsetting-drawing forming was used, as described in the examples below: SiC of 20% volume fraction of original cast statew+Al18B4O33wThe whisker reinforced 2024 aluminum alloy composite material is cut into blanks with the diameter of 60mm and the height of 60mm, and the cast aluminum matrix composite material is subjected to upsetting and drawing experiments on a 5000-ton extruder. The blank was heated and held for 2 hours before the experiment, with the furnace temperature set at 470-510 ℃. During forming, multi-pass axial upsetting is carried out to axial 30% deformation according to pass deformation amount of 8% -10%, the blank is turned over for 90 degrees and radially compressed for 8% -10%, the blank is rotated and radially compressed for 8% -10%, the radial compression process is repeated along the whole circumference, after the radial compression process is finished, axial upsetting is carried out for 8% -10%, the radial compression process is carried out again, the axial upsetting process is carried out again, and the process is repeated for multiple passes; finally, the axial compression reaches 50-70 percent, the radial compression reaches 40-50 percent, and the high volume fraction SiC is obtainedw+Al18B4O33wThe square forging stock of the whisker reinforced 2024 aluminum-based composite material is formed by selecting the sheath with the dimensions of 72mm of outer diameter, 60mm of inner diameter and 60mm of height when sheath forming, wherein the material is aluminum alloy or pure aluminum, and high volume fraction SiCw+Al18B4O33wGraphite lubrication is adopted between the whisker reinforced 2024 aluminum matrix composite and the sheath. FIG. 12 shows an upset blank and aluminum alloy clad. Setting an uncased upsetting-pulling control group (uncased forming is also according to the process), in the following embodiment, performing multi-pass axial upsetting to axially deform 30% at a pass deformation of 9%, turning 90 degrees, performing radial compression of 9%, rotating a blank, performing radial compression of 9%, repeating the radial compression process along the whole circumference, performing axial upsetting of 9% after the completion, performing the radial compression process again, performing the axial upsetting process again, and repeating the process for multiple passes, wherein the final axial compression reaches 60%, and the radial compression reaches 45%; obtaining high volume fraction SiCw+Al18B4O33wThe crystal whisker reinforced 2024 aluminum-based composite material square forging stock; the occurrence of upsetting without sheathSuch as the deep transverse crack shown in figure 13. The result of the upsetting of the sheath is shown in figure 14, the surface has no macrocracks, and SiC with high volume fraction is obtainedw+Al18B4O33wThe crystal whisker reinforced 2024 aluminum matrix composite square forging stock.
The present invention is not limited to the above embodiments, and any person skilled in the art can make many modifications and equivalent variations by using the above-described structures and technical contents without departing from the scope of the present invention.

Claims (1)

1. A method for thermally forming a high volume fraction whisker reinforced 2024 aluminum matrix composite sheath, wherein the whisker is SiCw+Al18B4O33wWhisker; the method is characterized in that: the sheath thermoforming method comprises the following steps:
firstly, observing the mechanical property and microstructure of an original blank: scanning electron microscope for original as-cast high-volume-fraction SiC by utilizing field emission environmentw+Al18B4O33wThe whisker reinforced 2024 aluminum matrix composite blank microscopic structure is observed and tensile test is carried out to test the mechanical property; SiC in the reinforced 2024 aluminum matrix compositew+Al18B4O33wThe volume fraction of the whisker is 15-20%;
secondly, testing the hot forgeability of the original blank: selecting original as-cast high volume fraction SiC with certain height and diameterw+Al18B4O33wPerforming a forgeability compression test on the whisker reinforced 2024 aluminum-based composite material blank to obtain a forgeability compression test temperature of 470-510 ℃;
thirdly, covering and upsetting the blank: the original as-cast state high volume fraction SiCw+Al18B4O33wThe whisker reinforced 2024 aluminum-based composite material is processed into a blank with the height of 60mm and the diameter of 60mm, and is usedThe blank is coated by a sheath, the sheath material is pure aluminum or aluminum alloy, and the volume fraction of SiC is highw+Al18B4O33wAdopting graphite lubrication between the whisker reinforced 2024 aluminum-based composite material and the sheath, firstly heating the blank at the temperature determined in the step two, keeping the temperature for 2 hours, then carrying out multi-pass axial upsetting to axial 30% deformation according to 9% of pass deformation, turning over 90 degrees, carrying out radial compression 9%, rotating the blank, then carrying out radial compression 9%, repeating the radial compression process along the whole circumference, carrying out axial upsetting 9% after the completion, then carrying out the radial compression process, carrying out the axial upsetting process again, repeating the process for multiple passes, finally enabling the axial compression to reach 60%, enabling the radial compression to reach 45%, and obtaining the high volume fraction SiCw+Al18B4O33wThe reinforced 2024 aluminum-based composite material forged blank with uniformly distributed whiskers.
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