A TiC particle-reinforced aluminum matrix composite material and a method for preparing the same

Abstract

The application provides a TiC particle reinforced aluminum matrix composite material and a preparation method thereof, and comprises the following steps: firstly, synthesizing a 7075-TiC alloy blank in situ; then, after artificially aging the 7075-TiC alloy blank, processing and milling the alloy blank through a numerical control lathe to obtain an extrusion sample; then, after coating a lubricant on the inner channel surface of an ECAP mold, the outer surface of the extrusion sample and the end surface of an extrusion rod, heating the ECAP mold, and placing the extrusion sample into the ECAP mold for heat preservation, performing ECAP treatment to obtain the TiC particle reinforced aluminum matrix composite material. The application adopts a composite process of "precise preparation of raw materials, targeted TiC particle pretreatment and 120 DEG C isothermal ECAP extrusion", so that the microstructure of the TiC particle reinforced aluminum matrix composite material can be optimized, the hardness of the composite material can be improved, and the thermal conductivity of the composite material can also be improved. The TiC particle reinforced aluminum matrix composite material has good comprehensive performance, so that the application scenarios of the composite material can be widened.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, and in particular to a TiC particle-reinforced aluminum matrix composite material and its preparation method. Background Technology

[0002] Currently, the preparation of TiC particle-reinforced Al-Zn-Mg-Cu (7075) alloys mainly employs powder metallurgy or direct casting processes. The TiC particle addition is typically 0.5~2 vol.%, with particle sizes mostly between 100 nm and 250 nm. During the preparation of TiC particle-reinforced 7075 alloys, mechanical stirring is relied upon to mix the TiC particles with the 7075 aluminum alloy matrix. If equal channel angle extrusion (ECAP) is subsequently used to optimize its properties, the die channel angle is typically between 90° and 110°. The preparation of TiC particle-reinforced 7075 alloys faces the following challenges:

[0003] 1. Poor dispersion of TiC particles: Mechanical stirring easily leads to collision and agglomeration of TiC particles (agglomeration size ≥ 500 nm). The particles cannot be evenly distributed in the 7075 aluminum alloy matrix, which not only makes it difficult to exert the dispersion strengthening effect, but also forms stress concentration in the agglomeration area, reducing the overall mechanical property stability of the alloy. 2. Weak bonding between TiC matrix and matrix: TiC particles lack effective bonding sites with matrix elements on their surface. During extrusion or stress, particles are prone to debonding from the matrix, which affects the mechanical properties and service life of the alloy. 3. Insufficient adaptability: Room temperature extrusion easily causes TiC particles to break due to high brittleness, while small channel angles and multiple extrusions exacerbate particle agglomeration and matrix work hardening, making it impossible to balance the strengthening effect of TiC with the matrix forming performance. 4. Poor Synergy: While existing technologies can improve the strength of aluminum alloys, the high-temperature (420℃) ECAP process and over-aging pretreatment used can lead to adverse reactions at the TiC / matrix interface in TiC particle-reinforced aluminum matrix composites (such as the formation of the Al4C3 brittle phase) and cause grain coarsening. For TiC particle-reinforced 7075 alloys, this type of process not only fails to improve thermal conductivity but also reduces it by 12%~15% compared to the matrix, failing to meet the requirements of applications demanding comprehensive performance. Summary of the Invention

[0004] The purpose of this invention is to provide a TiC particle-reinforced aluminum-based composite material, which has high hardness and thermal conductivity.

[0005] Another objective of this invention is to provide a method for preparing TiC particle-reinforced aluminum-based composite materials. Adding TiC particles to an aluminum matrix would normally reduce the thermal conductivity of the alloy. However, by combining the aging treatment and ECAP process of this invention, the overall performance of TiC particle-reinforced aluminum-based alloys, including thermal conductivity, can be improved. This method has controllable parameters and is suitable for large-scale industrial production.

[0006] The technical problem solved by this invention is achieved by the following technical solution.

[0007] This invention proposes a method for preparing TiC particle-reinforced aluminum-based composite materials, comprising the following steps: S1. 7075-TiC alloy billet is synthesized in situ using 7075 aluminum alloy and TiC particles; S2. After the 7075-TiC alloy billet is artificially aged, it is machined and milled by CNC lathe to obtain extruded samples; S3. Apply lubricant to the inner channel surface of the ECAP mold, the outer surface of the extruded sample, and the end face of the extrusion rod, then heat the ECAP mold, and then place the extruded sample into the ECAP mold for heat preservation. After ECAP treatment, TiC particle-reinforced aluminum-based composite material is obtained.

[0008] This invention proposes a TiC particle-reinforced aluminum-based composite material, which is prepared according to the above-described preparation method.

[0009] The beneficial effects of the TiC particle-reinforced aluminum matrix composite material and its preparation method in this invention are as follows: 1. Increased Hardness: The TiC particle-reinforced aluminum matrix composite material of this invention exhibits significantly improved hardness after ECAP treatment. The hardness of the 7075-1 vol.% TiC composite material after aging is 195.90 HV, while that of pure 7075 aged aluminum alloy is 177.71 HV. After one ECAP pass, the composite material maintains a high hardness; after two ECAP passes, the hardness of the 7075-1 vol.% TiC composite material reaches 198.8 HV, which is close to the performance of pure 7075 aluminum alloy (201.5 HV) under the same extrusion conditions. While retaining the advantages of TiC reinforcement, the hardness is further optimized through plastic deformation.

[0010] 2. Improved Thermal Conductivity: Contrary to the conventional understanding that adding ceramic particles reduces the thermal conductivity of the metal matrix, this invention, through the synergistic effect of "artificial aging interface modification + 120℃ isothermal ECAP," not only reverses the downward trend in thermal conductivity caused by TiC particles but also achieves an improvement. Taking 7075-1 vol.% TiC as an example, the thermal conductivity of the billet without the treatment in steps S2 and S3 of this invention is approximately 80 W / (m·K); while after treatment by this invention, the thermal conductivity of the first-pass ECAP sample reaches 133 W / (m·K), an improvement of over 30%. This is due to two factors. The first and main reason is that the aging treatment adsorbs solid solution atoms in the TiC particles, forming a MgZn2 precipitate phase on the surface, reducing the content of solid solution atoms in the matrix. The second is that the 120℃ isothermal ECAP constructs an oriented grain structure along the extrusion direction, allowing heat flow to preferentially conduct along the low-resistance path.

[0011] 3. Microstructure Optimization: After ECAP deformation, the grain size of the 7075-1 vol.% TiC composite material was significantly refined. The average grain width after one pass of ECAP was 333.2 ± 105 nm, and further optimization was achieved after two passes. The grain uniformity was also superior to that of pure 7075 aluminum alloy. Furthermore, the dislocation density of the aged 7075-1 vol.% TiC composite material was 2.60 × 10⁻⁶. 13 m -2 After one ECAP test, it dropped to 3.94 × 10⁻⁶. 14 m -2 After two passes, the result was 3.09 × 10⁻⁶. 14 m -2 By recrystallization, dislocation density can be effectively controlled to balance strength and plasticity. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of the ECAP mold structure and extrusion process; Figure 2 Dark-field image of 7075-1 vol.% TiC alloy after one pass of ECAP; Figure 3 Dark-field image of 7075-1 vol.% TiC alloy after two passes of ECAP; Figure 4 This is an energy dispersive spectroscopy (EDS) image of TiC particles and their surrounding components under high-resolution TEM. Figure 5 Figures showing the hardness and thermal conductivity of 7075-1 vol.% TiC alloy and 7075 aluminum alloy after different processing passes. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0015] The TiC particle-reinforced aluminum matrix composite material and its preparation method according to embodiments of the present invention will be described in detail below.

[0016] Reference Figure 1 As shown in the figure, an embodiment of the present invention provides a method for preparing a TiC particle-reinforced aluminum matrix composite material, comprising the following steps: S1. A 7075-TiC alloy billet is synthesized in situ using 7075 aluminum alloy and TiC particles, with the TiC particles being uniformly dispersed and free of agglomeration. This invention utilizes the online reaction between the mixed salt and aluminum to generate TiC ceramic particles through a process of "melting pure aluminum → melting mixed salt → electromagnetic stirring + ultrasonic treatment → settling to remove byproducts," thus preparing the in-situ 7075-TiC alloy billet. It should be noted that this 7075-TiC alloy billet is also commercially available.

[0017] Further, in a preferred embodiment of the present invention, the 7075 aluminum alloy, by mass fraction, comprises 2-2.5% Mg, 1-2% Cu, 5-6% Zn, 0.1-0.2% Cr, 0.05-0.1% Fe, with the balance being Al. Preferably, by mass fraction, the 7075 aluminum alloy comprises 2.36% Mg, 1.70% Cu, 5.86% Zn, 0.18% Cr, 0.09% Fe, with the balance being Al.

[0018] Furthermore, in a preferred embodiment of the present invention, the TiC particles have a particle size of 100~250nm and a purity of ≥99.5%.

[0019] S2. After artificial aging, the 7075-TiC alloy billet is machined and milled on a CNC lathe to obtain extruded samples. This invention designs a TiC particle pretreatment process based on the characteristics of TiC particles. Aging treatment promotes the precipitation of Mg and Zn atoms onto the TiC surface, forming a 5-10 nm MgZn2 precipitate phase on the TiC particle surface. This increases the interfacial bonding force by more than 35%, avoiding the debonding problem caused by the lack of pretreatment in existing technologies, and simultaneously achieving secondary strengthening.

[0020] Furthermore, in a preferred embodiment of the present invention, the artificial aging temperature is 110~130℃, and the artificial aging time is 22~26h. Preferably, the artificial aging temperature is 120℃, and the aging time is 24h.

[0021] Furthermore, in a preferred embodiment of the present invention, the roughness Ra of the extruded sample is ≤0.8μm.

[0022] S3. After applying lubricant to the inner channel surface of the ECAP mold, the outer surface of the extruded sample, and the end face of the extrusion rod, the ECAP mold is heated. Then, the extruded sample is placed in the ECAP mold and kept at a constant temperature to ensure that the temperature of the extruded sample matches that of the mold. After ECAP treatment, a TiC particle-reinforced aluminum-based composite material is obtained. The reason why this invention increases the thermal conductivity of the aluminum-based composite material through ECAP deformation is that it constructs a grain that elongates in one direction, reducing the collision between heat carriers and grain boundaries during heat conduction in that direction.

[0023] Furthermore, in a preferred embodiment of the present invention, the lubricant is a mixture of MoS2 and engine oil, the volume ratio of MoS2 to engine oil is 1:9 to 2:8, and the channel angle of the ECAP mold is 120° and the outer arc angle is 20°.

[0024] Further, in a preferred embodiment of the present invention, the step of heating the ECAP mold is as follows: activating the mold heating system to raise the temperature of the ECAP mold to 115~125℃ and holding it at that temperature for 25~35 minutes. Preferably, the ECAP mold is heated to 120℃ and held at that temperature for 30 minutes.

[0025] Furthermore, in a preferred embodiment of the present invention, the time for which the extruded sample is placed in the ECAP mold and kept at a constant temperature is 4-6 minutes. Preferably, the holding time is 5 minutes.

[0026] Further, in a preferred embodiment of the present invention, the ECAP treatment steps are as follows: A 1000kN hydraulic universal testing machine is used to apply downward pressure, the extrusion rate is controlled at 5 mm / min, the extruded sample is completely extruded into the lower die channel and held under pressure for 5 seconds. After completing one extrusion pass, the extruded sample is removed, cooled to room temperature, and residual lubricant is removed from the surface. The die loading, heat preservation, and extrusion steps are repeated for a second extrusion pass to obtain a TiC particle-reinforced aluminum matrix composite material. The extruded sample does not rotate after extrusion. In this invention, after each extrusion pass, the sample needs to be immediately removed from the die and air-cooled to room temperature, thus obtaining 7075-TiC samples after different ECAP treatment passes. This invention, by employing ECAP process parameters that match the characteristics of TiC particles, can balance the strengthening effect of TiC with its matrix forming properties.

[0027] This invention addresses the problems of poor TiC particle dispersion, weak interfacial bonding in the TiC matrix, insufficient adaptability, and insufficient synergy in existing TiC particle-reinforced 7075 alloys. It employs a composite process of "precise raw material preparation → targeted TiC particle pretreatment → 120℃ isothermal ECAP extrusion," thereby optimizing the microstructure of the TiC particle-reinforced aluminum matrix composite material, improving its hardness and thermal conductivity. The TiC particle-reinforced aluminum matrix composite material of this invention exhibits good comprehensive performance, thus broadening its application scenarios.

[0028] This invention provides a TiC particle-reinforced aluminum-based composite material, which is prepared according to the above-described preparation method.

[0029] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0030] Example 1 This embodiment provides a TiC particle-reinforced aluminum-based composite material, which is prepared according to the following steps: (1) Raw material preparation: 7075 aluminum alloy (mass fraction: Mg 2.36%, Cu 1.70%, Zn 5.86%, Cr 0.18%, Fe 0.09%, balance Al) and 1 vol.% TiC particles (particle size 100~250nm, purity ≥99.5%) were selected. Through the process of "melting pure aluminum → melting mixed salt → electromagnetic stirring + ultrasonic treatment → settling to remove by-products", TiC ceramic particles were generated by the online reaction of mixed salt and aluminum, and in-situ TiC particle-reinforced 7075 alloy billet (i.e. 7075-1 vol.% TiC alloy billet) was prepared.

[0031] (2) TiC matrix pretreatment: The 7075-1 vol.% TiC alloy billet was artificially aged at 120℃ for 24 hours. The pretreated 7075-1 vol.% TiC alloy billet was machined into cylindrical extrusion specimens with a diameter of φ10 and a length of 35 mm by CNC lathe, and the surface of the specimen was milled to a smooth surface (roughness Ra≤0.8μm).

[0032] (3) ECAP process adapted to TiC: First, select an ECAP mold with a channel angle of 120° and an outer arc angle of 20°. Then, use a mixture of MoS2 and machine oil in a 1:9 ratio as a lubricant, and apply it evenly to the inner channel surface of the ECAP mold, the outer surface of the cylindrical extrusion sample, and the end face of the extrusion rod to ensure sufficient lubrication during the extrusion process. Then, start the mold heating system to raise the temperature to 120°C and keep it at that temperature for 30 minutes to ensure uniform mold temperature (temperature difference ≤ 3°C). Then, place the lubricated cylindrical extrusion sample into the mold inlet channel and keep it at that temperature for 5 minutes to make the sample temperature consistent with the mold temperature. In the ECAP process, "Path A" (the sample does not rotate after each extrusion) is adopted. Pressure is applied downwards using a 1000kN hydraulic universal testing machine, with the extrusion rate controlled at 5 mm / min. The sample is completely extruded into the lower die channel and held under pressure for 5 seconds to complete one extrusion pass. After the first extrusion pass, the sample is removed, residual lubricant is cleaned from the surface, and the "mold loading → heat holding → extrusion" steps are repeated for the second extrusion pass, yielding a TiC particle-reinforced aluminum matrix composite material (i.e., a 7075-1 vol.% TiC sample). After each extrusion pass, the sample needs to be immediately removed from the mold and air-cooled to room temperature.

[0033] Experimental Example 1 In this experiment, transmission electron microscopy was used to observe the 7075-1 vol.% TiC sample after one pass of ECAP and the 7075-1 vol.% TiC sample after two passes of ECAP in Example 1.

[0034] like Figure 2 The image shown is a dark-field transmission electron microscope (TEM) image of a 7075-1 vol.% TiC alloy after one pass of ECAP. From... Figure 2 It can be seen that after 1ECAP, the dislocation density increases sharply, the interaction between dislocations intensifies, and dislocations are more prone to cross-cutting during slip, leading to a further increase in dislocation density, but the dislocation length decreases, such as... Figure 2 As shown in (b). Figure 2 As shown in (c), in regions far from the TiC particles, the density of fine, round precipitates in the matrix increases, and their distribution becomes more uniform. During deformation, larger impurity precipitates remain and are not broken by shear stress. Figure 2 The high-resolution image in (d) shows the semi-coherent state of the MgZn2 phase with the aluminum matrix.

[0035] Figure 3 This is a dark-field transmission electron microscopy (TEM) image of a 7075-1 vol.% TiC alloy after two passes of ECAP. From... Figure 3 A low dislocation density region surrounded by dislocations, i.e., dislocation cells, can be observed. During polycrystalline slip, dislocations can be randomly distributed or form a dislocation network. For high dislocation energy metallic polycrystalline materials, dislocations are prone to cross-slip, and different slip systems and numbers can lead to grain breakage, forming dislocation clusters and dislocation cells. Table 1 shows the average grain size L, average grain boundary angle θ, high-angle grain boundary ratio f, and average low-angle grain boundary θ of 7075-1vt%TiC and 7075 aluminum alloy after ECAP process in Example 1 of this invention. L and average high-angle grain boundary θ H Changes. As shown in Table 1, the average grain size L of both 7075 alloy and 7075-1 vol.% TiC alloy decreased after different ECAP passes, while the average grain boundary angle θ increased slightly. This is because the formation of new grains during recrystallization causes some grain boundaries to transform into high-angle grain boundaries.

[0036] Table 1. Grain boundary data variation of 7075-1vt%TiC and 7075 aluminum alloys after ECAP process.

[0037] Experimental Example 2 This experimental example studies the hardness and thermal conductivity of 7075-1 vol.% TiC alloy and 7075 aluminum alloy after different processing passes. The specific steps are as follows: During alloy hardness testing, the samples need to be polished with 240#, 400#, 800#, and 1200# sandpaper, followed by mechanical polishing until the surface is free of obvious scratches. After removing surface machining marks and oxide layers, an HV-1000 micro Vickers hardness tester is used. A load of 0.98 N (corresponding to 100 gf) is applied to the alloy surface and held for 10 seconds. It is important to note that 10 points should be selected from each sample for hardness testing, and the average value should be taken as the hardness value of that sample.

[0038] When testing the thermal conductivity of the alloy, the alloy sample needs to be processed into a circular disc with a diameter of φ10 mm and a thickness of approximately 2 mm. The surface is polished to a roughness Ra ≤ 1.6 μm to ensure uniform heat conduction. The sample is tested at room temperature using a German LFA-457 laser flare analyzer to obtain the thermal diffusivity α of the alloy, which is then calculated using the formula... λ = α × ρ × c p ( ρ Alloy density; c p The thermal conductivity of TiC can be calculated from the specific heat capacity of the alloy at constant pressure (7075-1 vol.%).

[0039] like Figure 4 The image shown is an energy dispersive spectroscopy (EDS) spectrum of a 7075-1 vol.% TiC alloy after two ECAP passes. From... Figure 4 It is known that a large number of Mg atoms precipitate around the TIC particles, forming the ŋ phase with Zn atoms. This significantly reduces the number of solid-solution atoms in the matrix, lowering the density of lattice distortion and thus reducing electron scattering during thermal conduction.

[0040] like Figure 5 The figures show the hardness and thermal conductivity of 7075-1 vol.% TiC alloy and 7075 aluminum alloy after different processing passes. From... Figure 5 It can be seen that the hardness of both materials increases with the number of ECAP passes. The solution-treated hardness of 7075 aluminum alloy is 166.1 HV, which increases to 193.6 HV after one ECAP pass and reaches 193.8 HV after two passes. The hardness increase is due to the synergistic effect of grain refinement, dislocation strengthening, and precipitation strengthening. The aged hardness of the 7075-1 vol.% TiC composite material is 182.8 HV, which reaches 197.1 HV after one ECAP pass and 194.2 HV after two ECAP passes. The difference between the hardness test results and those of 7075 aluminum alloy under the same conditions is not significant, indicating that the strengthening effect of TiC particles offsets part of the hardness increase caused by deformation. However, in the undeformed state, the hardness of 7075-1 vol.% TiC is higher than that of 7075 aluminum alloy. Regarding thermal conductivity, the thermal conductivity of the 7075-1 vol.% TiC alloy was 133 W / (m²) in the undeformed, 1-pass, and 2-pass processes, respectively. K), 125 W / (m K), 105 W / (m K). The thermal conductivity of 7075 aluminum alloy, after undeformed treatment and after one and two passes, is 130 W / (m²). K), 80W / (m K), 48 W / (m K).

[0041] It should be noted that the "improvement" in thermal conductivity described in this invention is relative to the "baseline state with added TiC particles but without the treatments S2 and S3 of this invention." Normally, adding 1 vol.% TiC particles to 7075 aluminum alloy results in a decrease in thermal conductivity of approximately 15% to 20% due to interfacial thermal resistance. However, after artificial aging (forming a MgZn2 semi-coherent interfacial layer) and isothermal ECAP at 120°C (constructing directional heat flow channels) according to this invention, the thermal conductivity of the composite material not only recovers but also exceeds that of pure 7075 aluminum alloy under the same deformation conditions (typically below 100 W / (m·K)). This effect of "enhancing without reducing thermal conductivity" is unexpected.

[0042] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a TiC particle-reinforced aluminum-based composite material, characterized in that, Includes the following steps: S1. 7075-TiC alloy billet is synthesized in situ using 7075 aluminum alloy and TiC particles; S2. After the 7075-TiC alloy billet is artificially aged, it is machined and milled by CNC lathe to obtain extruded samples; S3. Apply lubricant to the inner channel surface of the ECAP mold, the outer surface of the extruded sample, and the end face of the extrusion rod, then heat the ECAP mold, and then place the extruded sample into the ECAP mold for heat preservation. After ECAP treatment, TiC particle-reinforced aluminum-based composite material is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the 7075 aluminum alloy comprises, by mass fraction, 2-2.5% Mg, 1-2% Cu, 5-6% Zn, 0.1-0.2% Cr, 0.05-0.1% Fe, with the balance being Al.

3. The preparation method according to claim 1, characterized in that, In step S1, the TiC particles have a particle size of 100~250nm and a purity of ≥99.5%.

4. The preparation method according to claim 1, characterized in that, In step S2, the temperature for artificial aging is 110~130℃, and the artificial aging time is 22~26h.

5. The preparation method according to claim 1, characterized in that, In step S2, the roughness Ra of the extruded sample is ≤0.8μm.

6. The preparation method according to claim 1, characterized in that, In step S3, the lubricant is a mixture of MoS2 and engine oil, and the volume ratio of MoS2 to engine oil is 1:9 to 2:

8. The channel angle of the ECAP mold is 120° and the outer arc angle is 20°.

7. The preparation method according to claim 1, characterized in that, In step S3, the step of heating the ECAP mold is as follows: start the mold heating system to heat the ECAP mold to 115~125℃ and keep it at that temperature for 25~35 minutes.

8. The preparation method according to claim 1, characterized in that, In step S3, the extrusion sample is placed in the ECAP mold and kept warm for 4 to 6 minutes.

9. The preparation method according to claim 1, characterized in that, In step S3, the ECAP treatment steps are as follows: a 1000kN hydraulic universal testing machine is used to apply downward pressure, the extrusion rate is controlled at 5 mm / min, the extruded sample is completely extruded into the lower die channel and pressure is held for 5s. After completing one extrusion, the extruded sample is taken out, cooled to room temperature and the residual lubricant on the surface is removed. The mold loading, heat holding and extrusion steps are repeated to perform the second extrusion to obtain TiC particle-reinforced aluminum matrix composite material. The extruded sample does not rotate after extrusion.

10. A TiC particle-reinforced aluminum-based composite material, characterized in that, Prepared by the preparation method according to any one of claims 1 to 9.

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