Carbon fiber reinforced aluminum silicate ceramic fiber casting nozzle material and preparation method thereof

Abstract

The invention discloses a carbon fiber reinforced aluminum silicate ceramic fiber casting nozzle material which is prepared by taking aluminum phosphate-nano zirconium oxide as a composite binding agent, forming a three-dimensional interlocking structure by using 5-15wt% of chopped carbon fibers and 50-70wt% of aluminum silicate fibers, and matching with 2-8wt% of a graphite powder pore forming agent and a gradient sintering process. The performance breakthrough that the porosity is 25-35%, the breaking strength is larger than or equal to 180 MPa, and the thermal shock cycle is larger than or equal to 50 times is achieved. And the surface boron nitride coating effectively inhibits high-temperature oxidation, and the high-efficiency cast rolling requirement of the magnesium alloy wide plate is met.

Description

Technical Field

[0001] The invention belongs to the technical field of metal processing, and in particular relates to a carbon fiber reinforced aluminum silicate ceramic fiber casting nozzle material and a preparation method thereof. Background Art

[0002] The traditional aluminum silicate fiber ceramic casting nozzle and runner have the following main problems in magnesium alloy casting and rolling:

[0003] 1. Chemical reaction with magnesium alloy melt

[0004] The high activity of the magnesium alloy melt causes a violent replacement reaction with aluminum silicate, leading to aluminum precipitation in the nozzle material and structural failure. Even with the use of boron nitride coating and graphite paper for protection, the difference in thermal expansion coefficient between the coating and the aluminum silicate at high temperatures can still cause the coating to crack, leading to magnesium leakage and serious disruption to production continuity.

[0005] 2. Low high temperature strength and insufficient stability

[0006] Alumina silicate fibers undergo a phase transition (e.g., from glassy to crystalline) when subjected to prolonged high temperatures (700-750°C), resulting in a loose fiber structure, abnormal grain growth, and a significant decrease in mechanical strength. Experiments have shown that after 500 hours of continuous operation at 1200°C, the tensile strength of alumina silicate fibers can decrease by 40%-60%, accompanied by the formation of numerous microcracks and pores. This degradation directly shortens the life of the casting nozzle.

[0007] 3. Thermal expansion coefficient mismatch

[0008] The significant difference in thermal expansion coefficients between aluminum silicate ceramics and metal components can easily lead to thermal stress concentration during the casting process, causing cracks or deformation in the casting nozzle and runners. For example, boron nitride coatings can crack at high temperatures due to the mismatch in thermal expansion coefficients, allowing the melt to directly contact the aluminum silicate substrate, accelerating material erosion.

[0009] 4. Thermal insulation performance leads to component segregation

[0010] The high thermal insulation properties of aluminum silicate slow down the cooling rate of magnesium alloy melts, causing alloying elements to concentrate towards the center during solidification, forming central segregation defects. This not only reduces the mechanical properties of the billet but also affects the uniformity of subsequent rolling processes.

[0011] 5. Uneven melt flow

[0012] The structural design of conventional aluminum silicate flow channels can easily lead to uneven melt flow rates, with the flow rate in the center significantly higher than at the edges, causing uneven temperature distribution. This can cause surface defects such as cracks, heat spots, and holes in the cast plate, while also exacerbating the unevenness of the solidification structure. While the addition of diversion units can partially improve this, the inherent limitations of the material's flow channel design remain.

[0013] 6. Insufficient antioxidant properties

[0014] Magnesium alloy melts are easily oxidized at high temperatures, forming a loose MgO layer. Alumina silicate ceramics cannot effectively prevent this oxidation process. Oxides may fall off and enter the melt, causing inclusions in the product and affecting the final quality.

[0015] 7. Difficulty in maintenance and cleaning

[0016] The porous structure of aluminum silicate fibers easily absorbs melt or oxides, forming difficult-to-remove deposits. This not only affects the purity of the melt in subsequent production, but can also cause abnormal flow channel pressure due to local blockage, further exacerbating equipment losses.

[0017] 8. Insufficient thermal shock resistance

[0018] Temperature fluctuations can easily lead to cracking;

[0019] 9. Poor wettability with magnesium melt (600-800℃)

[0020] It is easy to cause surface defects of the casting nozzle.

[0021] The combined effect of these problems makes it difficult for traditional aluminum silicate fiber ceramics to meet the efficient and stable production requirements in magnesium alloy casting and rolling. There is an urgent need to develop alternative material formulations and manufacturing methods to solve the above challenges. Summary of the Invention

[0022] 1. Purpose of the Invention

[0023] To address the aforementioned issues in the existing technology, the present invention aims to provide a nozzle material with high strength, high thermal shock resistance, and resistance to magnesium melt corrosion, thereby resolving the nine aforementioned deficiencies of conventional materials. This invention provides important theoretical guidance and practical significance for the development of efficient casting and rolling processes for magnesium alloy sheets.

[0024] 2. Technical Solution

[0025] In order to achieve the above-mentioned object of the invention, the present invention discloses the following technical solutions:

[0026] (1) Material composition (wt%)

[0027]

[0028]

[0029] (2) Preparation method:

[0030] Fiber dispersion: Aluminum silicate fibers and carbon fibers were dispersed in ethanol by ultrasonication at 40 kHz for 30 min.

[0031] Mixed molding: Add aluminum phosphate colloid, nano ZrO2, graphite powder, vacuum kneading (vacuum degree ≥ 0.095MPa)

[0032] Post-extrusion molding;

[0033] Gradient sintering:

[0034] Pre-burning stage: 200-400℃ for 1-3h (heating rate 5℃ / min);

[0035] High temperature sintering: sintering at 1400-1550℃ for 3-5h under N2 protection (heating rate 3℃ / min);

[0036] Post-treatment: Surface coating with 50-100μm boron nitride coating.

[0037] (3) Technical effects

[0038] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0039] 1. Mechanical properties:

[0040] 1) High strength and thermal shock resistance: Carbon fiber and aluminum silicate fiber interlocking reinforcement, combined with nano-ZrO2 reinforcement, achieve flexural strength ≥180MPa (increased by 40%+), thermal shock cycles ≥50 times (conventional ≤30 times), and long-term working strength attenuation at 1200°C ≤30% (conventional 40%-60%), significantly extending the life of the casting nozzle, reducing equipment replacement, and improving production continuity;

[0041] 2) Thermal expansion matching: Reduce thermal stress concentration, reduce magnesium leakage accident rate by ≥80%, solve the cracking problem of traditional coatings, and ensure casting and rolling stability;

[0042] 2. Improved corrosion and oxidation resistance

[0043] 1) Resistance to magnesium melt corrosion: Boron nitride coating blocks the reaction, the corrosion depth at 650℃ is ≤0.3mm (traditional ≥1mm), the risk of magnesium leakage is close to zero, and structural damage is avoided.

[0044] 2) Anti-oxidation and cleanliness: Inhibits the formation and shedding of MgO, reduces melt inclusions by ≥70%, reduces billet defect rate by 60%, and improves product quality.

[0045] 3. Optimization of melt flow and composition uniformity

[0046] 25-35% porosity + flow channel design, flow rate deviation ≤ 5% (conventional ≥ 15%), reduced surface defects (reduced by ≥ 50%); accelerated cooling (heat insulation reduced by 30%), center segregation ≤ 1.2 (conventional ≥ 1.5), improved billet performance uniformity (tensile strength fluctuation ≤ 5%);

[0047] 4. Lifespan improvement: continuous operation ≥100h without cracks, lifespan extended by 2-3 times.

[0048] 5. Process and maintenance advantages

[0049] 1) Preparation controllability: Gradient sintering (N2 protection), vacuum slurry kneading, and ultrasonic dispersion ensure a dense structure and high product consistency (batch deviation ≤ 3%).

[0050] 2) Easy to clean: Pore optimization reduces adsorption, sediment removal efficiency +40%, maintenance cycle extended by 30%, and operation and maintenance costs reduced.

[0051] 6. Application and benefit improvement

[0052] It supports efficient magnesium alloy casting and rolling, improves production efficiency and product quality, and has significant economic and social benefits, which is different from the narrow-width, low-performance applications of traditional materials.

[0053] 1) Wide-width adaptation: Supports casting and rolling of magnesium alloy plates ≥1000mm, and can run continuously for ≥100h without any faults, promoting the application of large-size magnesium alloys (in aviation, automobiles, etc.).

[0054] 2) Economic and environmentally friendly: The service life is extended by 2-3 times, production efficiency is increased by 20%, and energy consumption is reduced by 15%, achieving green and efficient manufacturing and significantly improving industry competitiveness.

[0055] Summary: This invention solves the nine major defects of traditional aluminum silicate casting nozzles through collaborative innovation of materials, processes and performance, provides high-performance, long-life and easy-to-maintain casting nozzle materials, lays the core foundation for the upgrading of magnesium alloy casting and rolling technology, and has significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0057] Figure 1 The process flow chart for preparing the new nozzle material is as follows:

[0058] 1. Raw material preparation: weigh each component in proportion;

[0059] 2. Ultrasonic dispersion: The fibers were treated in ethanol at 40 kHz for 30 min;

[0060] 3. Vacuum mud kneading: vacuum degree ≥ 0.095MPa, mix pore-forming agent and binder;

[0061] 4. Extrusion molding: 20-30MPa pressure molding;

[0062] 5. Gradient sintering: pre-sintering (200-400℃) → high temperature sintering (1400-1550℃, N2 protection);

[0063] 6. Coating treatment: spray / brush 50-100μm boron nitride layer. DETAILED DESCRIPTION

[0064] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0065] A specific embodiment of the present invention discloses a carbon fiber reinforced aluminum silicate ceramic fiber casting nozzle material and a preparation method thereof.

[0066] Example 1:

[0067] Material composition (wt%)

[0068] Aluminum silicate ceramic fiber (diameter 5μm, length 1mm): 60%

[0069] Chopped carbon fiber (length 0.8mm): 10%

[0070] Aluminum phosphate colloid (solid content 50%): 15%

[0071] Nano ZrO2 (particle size 50nm): 7%

[0072] Graphite powder (particle size 20 μm): 6%

[0073] Preparation method

[0074] 1. Fiber dispersion: Add 60 g of aluminum silicate fiber and 10 g of chopped carbon fiber to 200 mL of ethanol and disperse them ultrasonically at 40 kHz for 30 min to form a uniform slurry.

[0075] 2. Mixing molding: Add 15g aluminum phosphate colloid, 7g nano ZrO2, and 6g graphite powder, vacuum knead the clay (vacuum degree -0.095MPa, 30min), and extrude at 25MPa to obtain a Φ50mm×10mm green body.

[0076] 3. Pre-firing: Heat the green body to 300℃ at 5℃ / min and keep it at this temperature for 2h to remove organic matter.

[0077] 4. High temperature sintering: Under N2 protection, heat up to 1450℃ at 3℃ / min, keep warm for 4h, and cool naturally.

[0078] 5. Post-treatment: Surface coating with 75 μm boron nitride coating (spraying method, curing temperature 300°C).

[0079] Performance Testing

[0080] Flexural strength: 192 MPa (three-point bending test, span 40 mm, loading rate 0.5 mm / min)

[0081] Porosity: 30% (Archimedes drainage method)

[0082] Thermal shock cycle: 55 times (1000℃→room temperature water cooling, no cracks during the cycle)

[0083] Oxidation resistance: 800℃ in air atmosphere for 20h, weight gain ≤0.5% (thermogravimetric analysis)

[0084] Magnesium melt contact test: Immerse in 650℃ Mg-Al alloy melt for 24 hours, corrosion depth ≤ 0.2mm (SEM observation).

[0085] Example 2:

[0086] Material composition (wt%)

[0087] Aluminum silicate ceramic fiber (diameter 8μm, length 2mm): 50%

[0088] Chopped carbon fiber (length 1.2mm): 15%

[0089] Aluminum phosphate colloid (solid content 60%): 20%

[0090] Nano ZrO2 (particle size 30nm): 5%

[0091] Graphite powder (particle size 15μm): 8%

[0092] Preparation method

[0093] 1. Fiber dispersion: 50 g aluminum silicate fiber + 15 g chopped carbon fiber, ethanol ultrasonication (40 kHz, 30 min).

[0094] 2. Mixed molding: 20g aluminum phosphate colloid + 5g nano ZrO2 + 8g graphite powder, vacuum mud kneading (-0.095MPa, 40min), 30MPa extrusion molding (Φ50mm×10mm green body).

[0095] 3. Pre-burning: 400℃ for 3h (heating rate 5℃ / min).

[0096] 4. High temperature sintering: N2 protection, heating to 1500℃ at 3℃ / min, keeping warm for 5h.

[0097] 5. Post-treatment: Apply 100 μm boron nitride coating (brush coating method, curing temperature 350°C).

[0098] Performance Testing

[0099] Flexural strength: 185MPa

[0100] Porosity: 32%

[0101] Thermal shock cycles: 52 times

[0102] Magnesium melt corrosion depth: ≤0.3mm (650℃, 24h)

[0103] Flow channel simulation test: When magnesium alloy melt (700°C) passes through the flow channel, the flow velocity uniformity deviation is ≤5% (PIV particle velocity measurement), which is 15% higher than that of traditional materials.

[0104] Example 3:

[0105] Material composition (wt%)

[0106] Aluminum silicate ceramic fiber (diameter 10μm, length 3mm): 70%

[0107] Chopped carbon fiber (length 0.5mm): 5%

[0108] Aluminum phosphate colloid (solid content 40%): 10%

[0109] Nano ZrO2 (particle size 80nm): 10%

[0110] Graphite powder (particle size 25μm): 2%

[0111] Preparation method

[0112] 1. Fiber dispersion: 70 g aluminum silicate fiber + 5 g chopped carbon fiber, ethanol ultrasonication (40 kHz, 30 min).

[0113] 2. Mixed molding: 10g aluminum phosphate colloid + 10g nano ZrO2 + 2g graphite powder, vacuum mud kneading (-0.095MPa, 20min), 20MPa extrusion molding (CD50mm×10mm green body).

[0114] 3. Pre-burning: keep warm at 200℃ for 1h (heating rate 5℃ / min).

[0115] 4. High temperature sintering: N2 protection, heating to 1400℃ at 3℃ / min, keeping warm for 3h.

[0116] 5. Post-treatment: Apply 50 μm boron nitride coating (dip coating method, curing temperature 250°C).

[0117] Performance Testing

[0118] Flexural strength: 188MPa

[0119] Porosity: 28%

[0120] Thermal shock cycles: 58 times

[0121] Magnesium melt corrosion depth: ≤0.15mm (650℃, 24h)

[0122] Installation test: Magnesium alloy casting and rolling (plate width 1200mm, casting speed 0.8m / min) ran continuously for 120 hours with no cracks or magnesium leakage in the casting nozzle, and the surface defect rate of the billet was reduced by 60% (compared with traditional materials).

Claims

1. A carbon fiber reinforced aluminum silicate ceramic fiber casting nozzle material, characterized in that: By mass percentage, it is composed of the following components: (1) Aluminum silicate ceramic fiber: 50-70%, wherein the aluminum silicate ceramic fiber has a diameter of 3-10 μm and a length of 0.5-3 mm; (2) chopped carbon fiber: 5-15%, the length of the chopped carbon fiber is 0.5-1.5 mm; (3) aluminum phosphate colloid: 10-20%, wherein the solid content of the aluminum phosphate colloid is 40-60%; (4) Nano ZrO2: 5-10%, wherein the particle size of the nano ZrO2 is 30-80 nm; (5) Graphite powder: 2-8%, wherein the particle size of the graphite powder is 15-25 μm; The material has the following properties after sintering: porosity 25-35%, flexural strength ≥180MPa, thermal shock cycle (1000°C→room temperature water cooling) ≥50 times, and 650°C magnesium alloy melt erosion depth ≤0.3mm.

2. The carbon fiber reinforced aluminum silicate ceramic fiber nozzle material according to claim 1, characterized in that: The chopped carbon fibers and aluminum silicate ceramic fibers form a three-dimensional interlocking reinforcement structure inside the material. This structure works synergistically with nano ZrO2 and aluminum phosphate colloid to increase the material's flexural strength by ≥40% and the number of thermal shock cycles by ≥60% compared to traditional aluminum silicate casting nozzle materials.

3. A method for preparing the carbon fiber reinforced aluminum silicate ceramic fiber nozzle material according to claim 1 or 2, characterized in that: The following steps are involved: (1) Fiber dispersion: Aluminum silicate ceramic fibers and chopped carbon fibers were added to an ethanol solution and ultrasonically dispersed at a frequency of 40 kHz for 30 min to form a uniformly dispersed fiber mixed slurry; (2) Mixing and molding: adding aluminum phosphate colloid, nano ZrO2 and graphite powder to the fiber mixed slurry, performing vacuum mud kneading (vacuum degree ≥ -0.095 MPa, mud kneading time 20-40 min), and then extruding and molding at a pressure of 20-30 MPa to obtain a green body; (3) Gradient sintering: a. Pre-firing stage: Heat the green body to 200-400℃ at a heating rate of 5℃ / min and keep it at this temperature for 1-3h to remove organic matter and initially solidify the structure; b. High temperature sintering stage: The pre-sintered green body is heated to 1400-1500℃ in a N2 protective atmosphere at a heating rate of 3℃ / min and kept at this temperature for 3-5h to form a dense ceramic matrix; (4) Post-processing: coating the surface of the sintered ceramic substrate with a boron nitride coating of 50-100 μm in thickness, wherein the curing temperature of the coating is 250-350° C., and finally obtaining the casting nozzle material.

4. The preparation method according to claim 3, wherein: The N2 protective atmosphere of the gradient sintering can prevent the chopped carbon fibers from being oxidized at high temperatures. In the pre-sintering stage, the ethanol and other volatile components in the blank are completely removed by controlling the heating rate and the holding time. In the high-temperature sintering stage, a ZrO2-AIPO4 strengthening phase is formed by the solid solution reaction of ZrO2 and aluminum phosphate, and the porosity of the material is synergistically regulated to optimize the fluidity of the magnesium alloy melt (flow rate deviation ≤ 5%).

5. The preparation method according to claim 3, wherein: The vacuum degree of the vacuum mud kneading is -0.095MPa to -0.1MPa, the mud kneading time is 25-35min, and the extrusion molding pressure is 22-28MPa. The density and uniformity of the green body are controlled by the above parameters.

6. The preparation method according to claim 3, wherein: The boron nitride coating is applied by spraying, brushing or dipping. After curing, the bonding strength between the coating and the ceramic substrate is ≥15 MPa, which can effectively block the direct chemical reaction between the magnesium alloy melt and the ceramic substrate.

7. Use of the carbon fiber reinforced aluminum silicate ceramic fiber casting nozzle material according to claim 1 or 2 in casting and rolling of wide magnesium alloy plates, characterized in that: The material is used for preparing a casting nozzle or a runner for magnesium alloy casting and rolling, and is suitable for a casting and rolling process of magnesium alloy plates with a width of ≥1000 mm.

8. The use according to claim 7, characterized in that: The casting nozzle material has no cracks during continuous operation for ≥100h in the magnesium alloy casting and rolling process, and the surface defect rate of the cast and rolled billet is reduced by ≥50% compared with the traditional aluminum silicate casting nozzle material.

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