Heat-resistant and wear-resistant aluminum alloy-based composite material for coal feeder and preparation method thereof

Abstract

The invention discloses a heat-resistant and wear-resistant aluminum alloy-based composite material for a coal feeder and a preparation method of the heat-resistant and wear-resistant aluminum alloy-based composite material, the material takes Al-Zn-Mg-Cu-Ni-RE as a matrix, and a three-layer protection system is formed by micron SiC and nano dual-phase enhancement and combination with a surface WC / CoCr gradient coating. The high-temperature performance is outstanding, the tensile strength at 350 DEG C is greater than or equal to 220MPa, and the erosion wear rate of pulverized coal is low; the interface stability is good, the interface reaction is reduced through in-situ nanometer, and the high-temperature performance and the wear resistance are better; the whole material has the characteristics of low density, high strength, good wear resistance, excellent thermal fatigue resistance and the like, can effectively solve the problems of large dead weight, poor high-temperature performance, easiness in wear and the like of a traditional material applied to a coal feeder, has good corrosion resistance and impact damage resistance, and can meet the use requirements under complex working conditions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal matrix composites, and particularly relates to a high-performance aluminum alloy matrix composite specially designed for coal throwers of thermal power plants and a preparation method thereof. The material is mainly used for manufacturing key wear-resistant parts (such as conveying grooves and scrapers) of the coal thrower, and can solve the problems of easy softening and short service life of traditional materials in high-temperature (300-400℃) and high-wear environments. BACKGROUND

[0002] The coal thrower is the core equipment of the coal conveying system of the thermal power plant, and the working parts thereof are subjected to high-temperature coal powder scouring (temperature 300-400℃) and frequent friction for a long time, and therefore have extremely high requirements for the heat resistance and wear resistance of the material. At present, two types of materials are mainly used: traditional metal materials (such as 304 stainless steel and low-alloy steel): although the strength is relatively high, the density is large (≥7.8 g / cm³), resulting in high energy consumption of the equipment; and the materials are prone to thermal fatigue at high temperatures, and have a short service life; and aluminum alloy matrix composites: the density is low (about 2.7 g / cm³) and the thermal conductivity is good, but there are three major bottlenecks in the existing technology: poor high-temperature performance: the strength of ordinary aluminum alloys (such as Al-Si and Al-Cu systems) decreases greatly (<100 MPa) at 350℃, and cannot meet the working condition requirements of the coal thrower; interface reaction out of control: the reinforcing phase (such as SiC particles) is prone to generate brittle phases with the aluminum matrix at high temperatures, accelerating wear; high manufacturing cost: the powder metallurgy process is complex, and it is difficult to mass-produce large parts. Therefore, it is urgent to develop a new type of composite material which has the advantages of lightweight, high-temperature resistance, wear resistance and controllable cost. SUMMARY

[0003] In view of the deficiencies in the prior art, the present application provides a heat-resistant and wear-resistant aluminum alloy matrix composite material for a coal thrower and a preparation method thereof. The problem of easy softening and short service life of the material in the prior art in high-temperature (300-400℃) and high-wear environments is solved.

[0004] In order to solve the above technical problems, the present application adopts the following technical solutions: A heat-resistant and wear-resistant aluminum alloy matrix composite material for a coal thrower comprises the following components and structures: The base alloy contains Zn 6.0-8.0%, Mg 2.0-3.0%, Cu 1.5-2.5%, Ni 0.5-1.2%, Sc 0.3-0.5%, Zr 0.2-0.4%, Yb 0.3-0.6%, Sr 0.05-0.1% by mass, and the balance is Al and impurity elements (Fe <0.2%, Si <0.15%); The reinforcing phase comprises micron SiC particles (20-30vol%, particle size 3-5 μm) and nano Particles (3-5 vol%, particle size 50-100 nm); The grain structure is a bimodal grain structure, wherein the fine grain area (≤1 μm) accounts for 15±2%, and the coarse grain area (4-8 μm) accounts for 80±5%.

[0005] Preferably, the nano The particles are generated in situ by breaking the original surface oxide film (thickness 5-10 nm) of the flaky aluminum alloy powder through hot pressing.

[0006] Preferably, in the bimodal grain structure, the fine grain area is distributed at the coarse grain boundary, and the size ratio of fine grain / coarse grain is ≤1:4.

[0007] Preferably, the composite material has a tensile strength ≥220 MPa at 350℃, and a coal powder erosion wear rate ≤0.8 mm³ / 50h.

[0008] A preparation method of a heat-resistant and wear-resistant aluminum alloy-based composite material for a coal feeder, comprising the following steps: S1, mixing flaky aluminum alloy powder with a mass percentage of 23%-25%, spherical aluminum powder with a mass percentage of 49%-51%, SiC particles with a mass percentage of 15%-17%, and ball milling under argon protection to obtain a mixed powder; then triggering in-situ reaction of the mixed powder under high temperature and high pressure to obtain a sintered body containing nano particles; and then performing equal-channel angular extrusion on the sintered body containing nano particles to obtain a preform with a bimodal grain structure; S2, processing the preform obtained in S1 to near net shape, then performing sand blasting treatment, preheating to 500℃ to obtain a casting mold containing the preform; pouring a base alloy into the casting mold containing the preform after refining and deslagging, and cooling after stirring to obtain a composite material blank; The base alloy contains Zn 6.0-8.0%, Mg 2.0-3.0%, Cu 1.5-2.5%, Ni 0.5-1.2%, Sc 0.3-0.5%, Zr 0.2-0.4%, Yb 0.3-0.6%, Sr 0.05-0.1% by mass percentage, and the balance is Al and impurity elements (Fe <0.2%, Si <0.15%); S3, performing spray bonding layer and spray functional layer on the surface of the composite material blank obtained in S2 to obtain a heat-resistant and wear-resistant aluminum alloy-based composite material for a coal feeder.

[0009] Preferably, S1 specifically comprises flaky Al-6Zn-2Mg-1.5Cu with a thickness of 1-2 μm, spherical aluminum powder with a particle size of 20-50 μm, SiC particles of 3 μm, and The reactants are mixed in a mass ratio of 3:6:2:1, ball-milled under argon protection for 6h at a ball-to-material ratio of 10:1 and a rotation speed of 300rpm to obtain mixed powders; the mixed powders are hot-pressed at 450 DEG C and 300MPa for 1h to trigger in-situ reaction: , to obtain a sintered body containing nano ; and then the sintered body containing nano is subjected to equal-channel angular pressing (ECAP) at a path Bc for 4 passes to form a preform with a bimodal grain structure.

[0010] Preferably, the oxygen content of the mixed powders obtained after ball-milling in S1 is controlled at 0.8-1.2wt%.

[0011] Preferably, S2 specifically comprises processing the preform obtained in S1 to near net shape, then performing sand blasting treatment on the preform with 24-mesh corundum sand at a pressure of 0.6MPa to obtain a mold containing the preform; and then pouring the base alloy after refining and slag removal into the mold containing the preform at a temperature of 750 DEG C, applying electromagnetic stirring at a frequency of 15Hz for 3min, and cooling after stirring to obtain a composite blank.

[0012] Preferably, the magnetic field strength of the electromagnetic stirring in S2 is 0.5-0.8T.

[0013] Preferably, S3 specifically comprises plasma spraying an Al-bonded Ni powder on the working surface of the composite blank to form a bonding layer with a thickness of 80μm; and then plasma spraying a WC / 12Co-6Cr powder to form a functional layer with a thickness of 150μm, a porosity of ≤1.5% and a bonding strength of ≥50MPa, to obtain the heat-resistant and wear-resistant aluminum alloy matrix composite for a coal thrower.

[0014] Compared with the prior art, the present application has the following technical effects: (1) The heat-resistant and wear-resistant aluminum alloy matrix composite for a coal thrower has an Al-Zn-Mg-Cu-Ni-RE matrix, is reinforced by micro-SiC and nano , and forms a three-layer protective system in combination with a WC / CoCr gradient coating on the surface; and has the characteristics of low density, high strength, good wear resistance and excellent thermal fatigue resistance, etc., can effectively solve the problems of heavy weight, poor high-temperature performance and easy wear of traditional materials in the application of coal throwers, and has good corrosion resistance and impact damage resistance, and can meet the use requirements under complex working conditions.

[0015] (2) The preparation method of the heat-resistant and wear-resistant aluminum alloy matrix composite for a coal thrower comprises the following steps: firstly, mixing flaky aluminum powder, spherical aluminum powder, SiC particles and The preform with bimodal grain structure is formed by processes such as hot-press sintering and ECAP extrusion, so that the combination of high strength and good toughness is realized; secondly, the preform is combined with the base alloy by using the gravity casting composite process, so that the two are tightly combined, and the casting quality is ensured by controlling process parameters such as pouring temperature and electromagnetic stirring frequency; finally, the surface strengthening technology is used, the bonding performance and the comprehensive performance such as surface hardness and wear resistance of the material are improved respectively through the bonding layer spraying and the functional layer spraying, and the wear resistance of the material can be significantly improved.

[0016] (4) The preparation method of the heat-resistant and wear-resistant aluminum alloy-based composite material for a coal feeder has outstanding high-temperature performance, the tensile strength at 350 DEG C is greater than or equal to 220 MPa, the coal powder erosion wear rate is low, the interface stability is good, in-situ nano The interface reaction is reduced, the high-temperature performance and wear resistance are better, the manufacturing cost is optimized, the gravity casting is replaced by powder metallurgy, the service life of the WC coating is prolonged, the comprehensive benefits are good, and the method is suitable for high-temperature and high-wear working conditions. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 : Schematic diagram of the three-layer structure of the composite material Figure 2 : TEM photo of the bimodal grain structure, showing that the fine grain zone (1-2 mu m) is distributed at the grain boundary of the coarse grain (8-10 mu m). DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, any other embodiments obtained by any person of ordinary skill in the art belong to the scope of protection of the present application.

[0019] It should be noted that all raw materials in the present application are known raw materials in the art without special instructions. The present application provides a heat-resistant and wear-resistant aluminum alloy-based composite material for a coal feeder, which comprises the following components and structures: the base alloy comprises Zn 6.0-8.0%, Mg 2.0-3.0%, Cu 1.5-2.5%, Ni 0.5-1.2%, Sc 0.3-0.5%, Zr 0.2-0.4%, Yb 0.3-0.6%, Sr 0.05-0.1% by mass percentage, and the balance is Al and impurity elements (Fe <0.2%, Si <0.15%); the reinforcing phase comprises micron SiC particles (20-30vol%, particle size 3-5 mu m) and nano The particles (3-5 vol%, particle size 50-100 nm) exhibit a bimodal grain structure, with fine-grained regions (≤1 μm) accounting for 15±2% and coarse-grained regions (4-8 μm) accounting for 80±5%. The key steps in material preparation are described below: (1) Preform preparation: Raw material ratio: 30% flake aluminum alloy powder (Al-6Zn-2Mg-1.5Cu, thickness 1-2μm), 60% spherical aluminum powder, 20% SiC particles (3μm), Reactant 10%; ball milling: ball milling for 6 hours (300 rpm) under argon protection, controlling oxygen content to 1.0 wt%, so that... Uniformly coated with aluminum powder; hot-pressed sintering: hot-pressed at 450℃ and 300MPa for 1 hour to trigger in-situ reaction to generate nanoparticles. (Approximately 80nm); ECAP extrusion: Four extrusion passes using the Bc path are used to form a bimodal structure of fine grains (1-2μm) and coarse grains (8-10μm).

[0020] (2) Gravity casting composite: Preform treatment: Machining to scraper shape, sandblasting (24 mesh corundum sand, pressure 0.6MPa) and preheating to 500℃; Melting and casting: After melting the matrix alloy (composition same as the preform), it is poured into the mold at 750℃ and electromagnetic stirring (frequency 15Hz) is used to avoid SiC segregation.

[0021] (3) Surface strengthening: Adhesive layer: Plasma sprayed Al / Ni powder (Ni:Al=66:34), thickness 80μm; Functional layer: Sprayed WC / 12Co-6Cr coating, thickness 150μm, bonding strength ≥50MPa.

[0022] (4) Performance verification: High temperature tensile test (350℃): tensile strength 225MPa, elongation 8.5%; coal powder erosion test (60m / s, 30% concentration): wear rate 0.75mm³ / 50h; thermal shock test (1000 cycles): WC coating no peeling.

[0023] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0024] Example 1: This embodiment provides a preform preparation method that achieves the objectives of material pretreatment and microstructure optimization. (1) Raw material ratio: flake aluminum alloy powder (Al-6Zn-2Mg-1.5Cu, thickness 1.5 μm): 30 kg; spherical aluminum powder (particle size 30 μm): 60 kg; SiC particles (3 μm): 20 kg; Reagent: 10 kg (the oxygen content of the mixed powder obtained after ball milling in S1 is controlled at 0.8-1.2 wt% to regulate the nanometer yield) (2) Ball milling mixing: mixing in a planetary ball mill under argon protection; ball-to-material ratio 10:1, rotation speed 300 rpm, time 6 h; the oxygen content of the powder after mixing 1.0 wt%.

[0025] (3) Hot-pressing sintering: temperature 450℃, pressure 300 MPa, holding time 1 h; triggering reaction: , generating nanometer (approximately 80 nm).

[0026] (4) ECAP extrusion: path Bc, 4 passes, the relative density after extrusion ≥99.5%; forming a bimodal grain structure (fine grain 1.5 μm / coarse grain 8 μm).

[0027] Example 2: This example provides a gravity casting composite, achieving the purposes of macrostructure forming and defect control : (1) Preform pretreatment: processing to the near-net shape of the scraper; sandblasting treatment (24-mesh corundum sand, 0.6 MPa); preheating to 500℃ and holding for 2 h.

[0028] (2) Melting of the base alloy: batching according to Al-6Zn-2Mg-1.5Cu-1Ni-0.4Sc-0.2Zr-0.1Yb; refining and deslagging (rotary spraying of Ar+0.5% Cl2 mixed gas for 10 min).

[0029] (3) Pouring and stirring: pouring temperature 750℃, mold preheating 300℃; electromagnetic stirring: frequency 15 Hz, magnetic field strength 0.6 T, to avoid SiC particle segregation, time 3 min; the roughcast after cooling has no shrinkage holes, and the SiC segregation zone is ≤40 μm.

[0030] Example 3: This example provides a surface strengthening treatment, achieving the purpose of improving the wear resistance: (1) Spraying the bonding layer: the process is atmospheric plasma spraying (APS), current 500 A, argon flow rate 45 L / min; the material is Al-coated Ni powder (Ni:Al=66:34), thickness 80 μm → enhancing the bonding force between the coating and the substrate.

[0031] (2) Spraying the functional layer: the process is the same as APS, current 550 A, argon flow rate 50 L / min; Material: WC / 12Co-6Cr tungsten carbide powder, thickness 150 μm → superhard wear-resistant layer, porosity only 1.2%, bonding strength ≥ 55 MPa.

[0032] Example 4: This example provides a performance test (1) High temperature tensile (GB / T 228.2-2015): test the elongation under the condition of tensile strength of 225±5 MPa (Instron 5982 test) at 350℃ temperature, and the elongation under this condition is 8.5%.

[0033] (2) Pulverized coal erosion wear (ASTM G76): test for 50 h under the condition of particle speed 60 m / s and concentration 30%, and the wear rate is 0.75±0.05 mm³, which shows that the invention can reduce the wear of the coal feeding machine.

[0034] (3) Thermal shock test: 1000 thermal shock test cycles under room temperature ↔ 400℃ environment found that the WC coating had no peeling, and the bonding strength retention rate was > 90%, which showed that the invention could reduce the peeling of the WC coating.

[0035] Comparative example: The performance test results of example 4 were compared with 304 stainless steel and existing aluminum alloy-based composite material (see CN109576697B-A kind of aluminum base coating and preparation method, aluminum alloy composite material prepared by using the coating and preparation method), and it can be seen from table 1 that the heat-resistant and wear-resistant aluminum alloy-based composite material for coal feeding machine prepared by the invention has significantly better wear resistance and sulfur corrosion resistance than the comparative example.

[0036] Table 1 Performance comparison of composite material of the invention, 304 stainless steel and aluminum alloy-based composite material in actual coal feeding machine operating environment

Claims

1. A heat-resistant and wear-resistant aluminum alloy-based composite material for a coal feeder, characterized in that, It includes the following components and structures: The matrix alloy contains, by mass percentage, 6.0-8.0% Zn, 2.0-3.0% Mg, 1.5-2.5% Cu, 0.5-1.2% Ni, 0.3-0.5% Sc, 0.2-0.4% Zr, 0.3-0.6% Yb, and 0.05-0.1% Sr, with the balance being Al and impurity elements (Fe < 0.2%, Si < 0.15%). The reinforcing phase comprises micron-sized SiC particles (20-30 vol%, particle size 3-5 μm) and nano-sized SiC particles. Particles (3-5 vol%, particle size 50-100 nm); The grain structure is bimodal, with the fine-grained region (≤1μm) accounting for 15±2% and the coarse-grained region (4-8μm) accounting for 80±5%.

2. The heat-resistant and wear-resistant aluminum alloy-based composite material for coal feeders as described in claim 1, characterized in that, The nano The particles are generated in situ by hot pressing and crushing the original oxide film (5-10nm thick) on the surface of the sheet-like aluminum alloy powder.

3. The heat-resistant and wear-resistant aluminum alloy-based composite material for coal feeders as described in claim 1, characterized in that, In the bimodal grain structure, the fine grain region is distributed at the coarse grain boundary, and the fine grain / coarse grain size ratio is ≤1:

4.

4. The heat-resistant and wear-resistant aluminum alloy-based composite material for coal feeders as described in any one of claims 1-3, characterized in that, The composite material has a tensile strength ≥220MPa at 350℃ and a coal powder erosion wear rate ≤0.8mm³ / 50h.

5. A method for preparing a heat-resistant and wear-resistant aluminum alloy-based composite material for a coal feeder, characterized in that, Includes the following steps: S1 consists of 23%-25% by weight of flake aluminum alloy powder, 49%-51% by weight of spherical aluminum powder, 15%-17% by weight of SiC particles, and 5%-7% by weight of... The mixture was then ball-milled under argon protection to obtain a mixed powder; subsequently, the mixed powder was subjected to an in-situ reaction triggered under high temperature and high pressure to obtain a product containing nanoparticles. The sintered body; then containing nano The sintered body is subjected to equal channel angular extrusion to obtain a preform with a bimodal grain structure; S2, the preform obtained in S1 is processed to near-net shape, then sandblasted and preheated to 500℃ to obtain a mold containing the preform; the matrix alloy is refined and slag removed and poured into the mold containing the preform, stirred and cooled to obtain a composite material blank; The matrix alloy comprises, by mass percentage, 6.0-8.0% Zn, 2.0-3.0% Mg, 1.5-2.5% Cu, 0.5-1.2% Ni, 0.3-0.5% Sc, 0.2-0.4% Zr, 0.3-0.6% Yb, and 0.05-0.1% Sr, with the balance being Al and impurity elements (Fe < 0.2%, Si < 0.15%). S3, the surface of the composite material blank obtained in S2 is coated with an adhesive layer and a functional layer to obtain a heat-resistant and wear-resistant aluminum alloy-based composite material for coal feeders.

6. The preparation method of the heat-resistant and wear-resistant aluminum alloy-based composite material for coal feeders as described in claim 5, characterized in that, Specifically, S1 consists of flake-shaped Al-6Zn-2Mg-1.5Cu with a thickness of 1-2 μm, spherical aluminum powder with a particle size of 20-50 μm, and SiC with a particle size of 3 μm. The reactants were mixed in a mass ratio of 3:6:2:1 and ball-milled for 6 hours at a ball-to-particle ratio of 10:1 and a speed of 300 rpm under argon protection to obtain a mixed powder. The mixed powder was hot-pressed at 450℃ and 300MPa for 1 hour to trigger an in-situ reaction. To obtain nano-sized sintered body; Then, containing nano The sintered body is subjected to equal channel corner extrusion (ECAP) in path Bc, 4 passes, to form a preform with a bimodal grain structure.

7. The preparation method of the heat-resistant and wear-resistant aluminum alloy-based composite material for coal feeders as described in claim 6, characterized in that, The oxygen content of the mixed powder obtained after ball milling as described in S1 is controlled at 0.8-1.2 wt%.

8. The method for preparing the heat-resistant and wear-resistant aluminum alloy-based composite material for coal feeders as described in claim 5, characterized in that, S2 specifically involves processing the preform obtained in S1 to near-net-shape, and then performing sandblasting treatment with 24-mesh corundum sand at a pressure of 0.6 MPa to obtain a mold containing the preform. After refining and removing slag from the matrix alloy, it is poured into a mold containing the preform at a temperature of 750°C. Electromagnetic stirring at a frequency of 15Hz is applied for 3 minutes. After stirring, it is cooled to obtain a composite material blank.

9. The method for preparing the heat-resistant and wear-resistant aluminum alloy-based composite material for coal feeders as described in claim 8, characterized in that, The magnetic field strength of the electromagnetic stirrer in S2 is 0.5-0.8T.

10. The method for preparing the heat-resistant and wear-resistant aluminum alloy-based composite material for coal feeders as described in claim 5, characterized in that, Specifically, S3 involves applying an Al-coated Ni powder plasma-sprayed bonding layer with a thickness of 80 μm to the working surface of the composite material blank; followed by a WC / 12Co-6Cr powder plasma-sprayed functional layer with a thickness of 150 μm, a porosity ≤1.5%, and a bonding strength ≥50 MPa, to obtain a heat-resistant and wear-resistant aluminum alloy-based composite material for coal feeders.

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