High-thermal-conductivity aluminum-based composite die material and preparation process thereof

Abstract

The high-thermal-conductivity aluminum-based composite die material comprises, by weight, 70%-80% of matrix alloy, 15%-20% of silicon carbide particles, 5%-8% of rare earth oxide coated aluminum nitride powder, 2%-4% of graphene nanosheets, 1%-3% of cubic boron nitride powder, 0.3%-0.8% of Sn powder and 0.1%-0.3% of rare earth, and the thickness of rare earth oxide is 2-3 microns. A composite coating is further arranged on the inner surface of the forming die and comprises a micro-arc oxidation layer, a transition bonding layer, a nano-silver-containing diamond-like carbon antibacterial layer and a CrN / TiAlN multi-layer composite wear-resistant layer. According to the high-heat-conductivity aluminum-based composite die material and the preparation process thereof, the problems that a traditional die material is slow in heat conduction, large in weight and short in service life are solved.

Description

Technical Field

[0001] This invention relates to the field of metal matrix composite technology, specifically to a high thermal conductivity aluminum-based composite mold material and its preparation process, which is particularly suitable for the manufacture of high and low temperature resistant polyethylene blown film molds. Background Technology

[0002] In the production of polyethylene anti-slip packaging materials, the thermal conductivity and thermal stability of the mold directly affect product quality and production efficiency. Traditional mold materials, such as mold steels (e.g., P20, 718), while possessing high hardness and good wear resistance, have the following inherent defects: (1) Low thermal conductivity (usually 15-40 W / (m·K)) results in slow cooling speed, which affects production efficiency; (2) High density (approximately 7.8 g / cm³), making the mold bulky and increasing the load on the equipment; (3) It has no antibacterial properties and is not suitable for the production of packaging materials with strict hygiene requirements; Conventional aluminum alloys (such as 6061 and 7075) have improved thermal conductivity (approximately 150-180 W / (m·K)), but insufficient hardness (approximately 60-100 HV), poor wear resistance, and are easily worn under long-term scouring by polyethylene melt; they also have a high coefficient of thermal expansion (approximately 23×10⁻⁶). -6 / K), which is incompatible with the shrinkage characteristics of polyethylene, easily leading to uneven product wall thickness; it has limited corrosion resistance and is easily oxidized in humid production environments; Existing composite materials: Although some properties have been improved by adding reinforcing phases, the following problems still exist: Poor bonding between the reinforcing phase and the matrix affects the continuity of the heat conduction path; the preparation process is complex and costly; it is difficult to simultaneously achieve high thermal conductivity, low expansion, high hardness and good wear resistance; especially for the production of high and low temperature resistant polyethylene anti-slip packaging materials, the mold needs to maintain dimensional stability in a wide temperature range of -40℃ to 120℃ and be able to quickly conduct heat to control the crystallization process, which places extremely high demands on the mold material. Summary of the Invention

[0003] The purpose of this invention is to provide a high thermal conductivity aluminum-based composite mold material and its preparation process, which solves the technical problems of slow thermal conductivity, poor interface bonding and short life of traditional mold materials.

[0004] A high thermal conductivity aluminum-based composite mold material, by weight fraction, comprises 70-80% matrix alloy, 15-20% silicon carbide particles, 5-8% rare earth oxide-coated aluminum nitride powder, 2-4% graphene nanosheets, 1-3% cubic boron nitride powder, 0.3%-0.8% Sn powder, and 0.1%-0.3% rare earth, wherein the thickness of the rare earth oxide is 2-3 μm; The inner surface of the molding die is also provided with a composite coating, which includes a micro-arc oxidation layer, a transition bonding layer, a diamond-like carbon antibacterial layer containing nano-silver, and a CrN / TiAlN multilayer composite wear-resistant layer.

[0005] By weight fraction, silicon carbide / (rare earth oxide coated aluminum nitride + cubic boron nitride) = 1.5-3.0.

[0006] The matrix alloy is a modified 6061 aluminum alloy, the silicon carbide particles have a particle size of 10-30 μm, the graphene nanosheets have a sheet thickness of 3-8 nm and a lateral dimension of 5-15 μm, serving as a thermally conductive network framework, the aluminum nitride powder has a particle size of 0.5-2 μm, used to adjust the coefficient of thermal expansion and improve interfacial bonding, and the cubic boron nitride has a particle size of 1-3 μm, used to improve thermal conductivity.

[0007] A process for preparing a high thermal conductivity aluminum-based composite mold material includes the following steps: Step S1: Raw material pretreatment, preparation of matrix alloy powder and reinforcement phase pretreatment; Step S2: Multi-stage mixing, followed by spray granulation; Step S3: Densification is achieved through cold isostatic pressing followed by hot extrusion. Step S4: Perform solution treatment and aging heat treatment; Step S5: Surface treatment, first precision machining, then micro-arc oxidation, and finally physical vapor deposition of a multi-layer coating.

[0008] In step S1, when preparing the base alloy powder, modified 6061 aluminum alloy powder is prepared by atomization. The composition is: Al-1.0Mg-0.6Si-0.3Cu-0.2Cr (wt%), the powder particle size is controlled at 20-50μm, and the oxygen content is <0.1%. During the pretreatment of the reinforcing phase, the silicon carbide particles were acid-washed (HF:HNO3=1:3) to remove surface oxides, and then vacuum heat-treated at 800℃ for 2 hours. Graphene nanosheets were prepared by liquid phase exfoliation and surface modified by silane coupling agent (KH550); Aluminum nitride powder was heat-treated at 600℃ for 1 hour under nitrogen protection to remove surface adsorbed water.

[0009] In step S2, during the primary mixing, the pretreated silicon carbide particles are mixed with a portion of aluminum powder (accounting for 30% of the total aluminum powder) in a planetary ball mill with a ball-to-material ratio of 3:1, a rotation speed of 200 rpm, a time of 2 hours, and argon protection, to form a core-shell structure premixed powder of "aluminum-coated silicon carbide". During the secondary mixing process, the primary mixed powder, the remaining aluminum powder, graphene nanosheets, rare earth oxide-coated aluminum nitride powder, cubic boron nitride powder, and rare earth are placed into a V-type mixer and mixed for 8-12 hours to ensure uniform distribution of the multiphase. In spray granulation, the mixed powder is made into a slurry, spray-dried, and the granulated particle size is 80-120μm.

[0010] In step S3, during cold isostatic pressing, the granulated powder is loaded into the rubber mold, the pressure is 200-250 MPa, and the pressure is held for 3-5 minutes to obtain a compact with a relative density of 60-65%. Hot extrusion densification: The compact is heated to 500-520℃, the extrusion ratio is 16:1, and the extrusion speed is 1-2 mm / s to obtain fully densified bars or plates.

[0011] In step S4, the solution treatment is carried out at 530℃ for 2 hours, followed by water quenching, and the aging treatment is carried out at 175℃ for 8 hours, followed by air cooling.

[0012] In step S5, during precision machining, the material is machined to the required size of the mold, with a surface roughness Ra≤0.8μm; Subsequently, micro-arc oxidation is used to form a porous ceramic layer. The electrolyte is a sodium silicate system with a concentration of 15-20 g / L, voltage of 400-450 V, frequency of 500 Hz, duty cycle of 30%, and processing time of 20-30 minutes. Finally, a physical vapor deposition (PVD) multilayer coating is applied: a. Transition layer deposition: Cr / CrN multilayers (100 nm per layer) were deposited using magnetron sputtering. b. Antibacterial layer deposition: Ag-DLC composite film was prepared by co-sputtering with silver and graphite targets in an argon and methane atmosphere; c. Wear-resistant layer deposition: Multi-arc ion plating is used to alternately deposit CrN and TiAlN nano-multilayer films.

[0013] Micro-arc oxidation layer: 20-30μm thick; transition bonding layer: 2-3μm thick; antibacterial functional layer: 1-2μm thick; wear-resistant working layer: 3-5μm thick.

[0014] The rare earth elements and rare earth oxides mentioned in this scheme are different components. The rare earth elements can be La and Ce. The rare earth elements are rare earth metal powders with a particle size of 5-10 μm. This is hereby noted.

[0015] For any technical details not described in detail in this solution, please refer to the conventional understanding and operation of those skilled in the art and implement this solution with reference to existing technologies. They will not be described in detail here.

[0016] The beneficial effects of this invention are as follows: (1) The problem of agglomeration of the reinforcing phase is solved by using the "aluminum-coated silicon carbide" core-shell structure premixed powder; a dual thermal conductivity enhancement mechanism of "graphene thermal conductive network + aluminum nitride interface adjustment" is constructed; the longitudinal thermal conductivity is improved by forming fibrous structure through hot extrusion; and the interface thermal resistance is reduced by forming a clean interface through in-situ reaction. (2) The micro-arc oxidation layer provides basic corrosion resistance and coating adhesion; the Ag-DLC antibacterial layer achieves long-lasting antibacterial function, with silver ion slow release period > 2 years; the hardness of the CrN / TiAlN nano multilayer wear-resistant layer can reach more than 3000 HV; (3) By combining the processes of "multi-stage mixing + cold isostatic pressing + hot extrusion densification", high-density and high-performance composite materials are prepared. The surface treatment adopts the composite technology of "micro-arc oxidation + PVD multilayer deposition" to solve the problem of easy peeling of single coating. The thermal conductivity is 1-2 times that of traditional mold steel, which significantly shortens the cooling time and improves the production efficiency by more than 20%. The coefficient of thermal expansion is matched with that of polyethylene, and the uniformity of product thickness is improved (deviation ≤5%). (4) The wear resistance is improved by at least 20%, and the mold life is extended; the surface antibacterial rate is ≥99.9%, which meets the hygiene requirements of medical and food packaging; although the material cost is high, the overall cost can be greatly reduced by improving production efficiency, extending mold life and reducing energy consumption. Detailed Implementation

[0017] To more clearly illustrate the technical features of this solution, the following detailed implementation method will be used to explain the solution. Example

[0018] A high thermal conductivity aluminum-based composite mold material, by weight fraction, comprises 70-80% matrix alloy, 15-20% silicon carbide particles, 5-8% rare earth oxide-coated aluminum nitride powder, 2-4% graphene nanosheets, 1-3% cubic boron nitride powder, 0.3%-0.8% Sn powder, and 0.1%-0.3% rare earth, wherein the thickness of the rare earth oxide is 2-3 μm; The inner surface of the molding die is also provided with a composite coating, which includes a micro-arc oxidation layer, a transition bonding layer, a diamond-like carbon antibacterial layer containing nano-silver, and a CrN / TiAlN multilayer composite wear-resistant layer.

[0019] By weight fraction, silicon carbide / (rare earth oxide coated aluminum nitride + cubic boron nitride) = 1.5-3.0.

[0020] The matrix alloy is a modified 6061 aluminum alloy, the silicon carbide particles have a particle size of 10-30 μm, the graphene nanosheets have a sheet thickness of 3-8 nm and a lateral dimension of 5-15 μm, serving as a thermally conductive network framework, the aluminum nitride powder has a particle size of 0.5-2 μm, used to adjust the coefficient of thermal expansion and improve interfacial bonding, and the cubic boron nitride has a particle size of 1-3 μm, used to improve thermal conductivity.

[0021] In Example 1, the effects of varying the contents of silicon carbide, rare earth oxide-coated aluminum nitride, and cubic boron nitride on the properties of composite mold materials were investigated, and the following multiple experimental groups were designed: Experimental Group 1: 15% silicon carbide particles, 8% rare earth oxide-coated aluminum nitride powder, and 3% cubic boron nitride powder; Experimental Group 2: 17% silicon carbide particles, 7% rare earth oxide-coated aluminum nitride powder, and 2% cubic boron nitride powder; Experimental Group 3: 20% silicon carbide particles, 5% rare earth oxide-coated aluminum nitride powder, and 1% cubic boron nitride powder; Control group: 15% silicon carbide particles, 5% rare earth oxide-coated aluminum nitride powder, and 1% cubic boron nitride powder; In the above-mentioned experimental and control groups, other components include 2% graphene nanosheets, 0.3% Sn powder, 0.1% rare earth elements, a rare earth oxide thickness of 2-3 μm, and a matrix alloy content of 70-80%. In each experimental group, the matrix alloy content is the balance, and the specific value is calculated based on the above-mentioned reinforcing phase ratio. Table 1 is a comparison table of the mold material properties obtained under each experimental group.

[0022] Table 1 shows the comparison of mold material properties obtained under each experimental group. As can be seen from Table 1, the changes in the content of silicon carbide, rare earth oxide coated aluminum nitride, and cubic boron nitride have a significant impact on the performance of mold materials. Among them, silicon carbide has a greater impact on high-temperature hardness, tensile strength, and wear resistance, and the wear amount is reduced at this time. As the coating of aluminum nitride and cubic boron nitride with rare earth oxides decreases, the high-temperature hardness and tensile strength actually increase to a certain extent. This indicates that the coating of aluminum nitride and cubic boron nitride with rare earth oxides has little effect on high-temperature hardness and tensile strength. However, the thermal conductivity decreases, which suggests that the coating of aluminum nitride and cubic boron nitride with rare earth oxides helps to reduce thermal conductivity.

[0023] All three test groups achieved high antibacterial properties; the contact angle with the polyethylene melt was measured to be ≥100°, which facilitates demolding. Example

[0024] This second embodiment is derived from the first embodiment.

[0025] A process for preparing a high thermal conductivity aluminum-based composite mold material includes the following steps: Step S1: Raw material pretreatment, preparation of matrix alloy powder and reinforcement phase pretreatment; Step S2: Multi-stage mixing, followed by spray granulation; Step S3: Densification is achieved through cold isostatic pressing followed by hot extrusion. Step S4: Perform solution treatment and aging heat treatment; Step S5: Surface treatment, first precision machining, then micro-arc oxidation, and finally physical vapor deposition of a multi-layer coating.

[0026] In step S1, when preparing the base alloy powder, modified 6061 aluminum alloy powder is prepared by atomization. The composition is: Al-1.0Mg-0.6Si-0.3Cu-0.2Cr (wt%), the powder particle size is controlled at 20-50μm, and the oxygen content is <0.1%. During the pretreatment of the reinforcing phase, the silicon carbide particles were acid-washed (HF:HNO3=1:3) to remove surface oxides, and then vacuum heat-treated at 800℃ for 2 hours. Graphene nanosheets were prepared by liquid phase exfoliation and surface modified by silane coupling agent (KH550); Aluminum nitride powder was heat-treated at 600℃ for 1 hour under nitrogen protection to remove surface adsorbed water.

[0027] In step S2, during the primary mixing, the pretreated silicon carbide particles are mixed with a portion of aluminum powder (accounting for 30% of the total aluminum powder) in a planetary ball mill at a ball-to-material ratio of 3:1, a rotation speed of 200 rpm, a time of 2 hours, and under argon protection to form a core-shell structured premixed powder of "aluminum-coated silicon carbide". During the secondary mixing process, the primary mixed powder, the remaining aluminum powder, graphene nanosheets, rare earth oxide-coated aluminum nitride powder, cubic boron nitride powder, and rare earth are placed into a V-type mixer and mixed for 8-12 hours to ensure uniform distribution of the multiphase. In spray granulation, the mixed powder is made into a slurry, spray-dried, and the granulated particle size is 80-120μm.

[0028] In step S3, during cold isostatic pressing, the granulated powder is loaded into the rubber mold, the pressure is 200-250 MPa, and the pressure is held for 3-5 minutes to obtain a compact with a relative density of 60-65%. Hot extrusion densification: The compact is heated to 500-520℃, with an extrusion ratio of 16:1 and an extrusion speed of 1-2 mm / s, to obtain fully densified bars or sheets. It should be noted that the hot extrusion process simultaneously completes densification and sintering.

[0029] In step S4, solution treatment: 530℃×2 hours, water quenching, aging treatment: 175℃×8 hours, air cooling.

[0030] In step S5, during precision machining, the material is machined to the required dimensions of the mold, with a surface roughness Ra≤0.8μm; Subsequently, micro-arc oxidation is used to form a porous ceramic layer. The electrolyte is a sodium silicate system with a concentration of 15-20 g / L, voltage of 400-450 V, frequency of 500 Hz, duty cycle of 30%, and processing time of 20-30 minutes. Finally, a physical vapor deposition (PVD) multilayer coating is applied: a. Transition layer deposition: Cr / CrN multilayers (100 nm per layer) were deposited using magnetron sputtering. b. Antibacterial layer deposition: Ag-DLC composite film was prepared by co-sputtering with silver and graphite targets in an argon and methane atmosphere; c. Wear-resistant layer deposition: Multi-arc ion plating is used to alternately deposit CrN and TiAlN nano-multilayer films.

[0031] Micro-arc oxidation layer: 20-30μm thick; transition bonding layer: 2-3μm thick; antibacterial functional layer: 1-2μm thick; wear-resistant working layer: 3-5μm thick.

[0032] It should be noted that the parameter values ​​in this embodiment 2 are generally minimum values ​​in order to reduce costs, and are applied in embodiment 1. Example

[0033] Mold Manufacturing and Application A blown film die head with a diameter of 200 mm was manufactured using the material from Example 1. In actual production, it was compared with a P20 steel die: Cooldown time: reduced from 45 seconds to 28 seconds, efficiency increased by 38%; Product thickness uniformity: deviation decreased from 8.2% to 4.1%; Mold weight: reduced from 15.2 kg to 5.8 kg, a reduction of 62%; After 2000 hours of continuous operation, the wear of the die lip is only 1 / 4 of that of a P20 steel die. Industrial application prospects: This material is not only suitable for polyethylene blown film dies, but can also be extended to injection molds, die-casting molds, hot runner systems, and other fields. It is particularly suitable for precision molding applications with high requirements for thermal conductivity, lightweight, and hygiene.

[0034] Comparative Example 1 Comparative Example 1 is derived from Example 1. Sn powder and rare earth elements were omitted; other conditions were the same, but Sn powder and rare earth elements were not added. Compared with test group 1 in Example 1, the thermal conductivity decreased to 246 W / (m·K) and the tensile strength decreased to 349 MPa.

[0035] Comparative Example 2 Comparative Example 2 is derived from Example 1, with all other conditions remaining the same. Micro-arc oxidation and physical vapor deposition multilayer coating treatment were not performed. Using test group 1 from Example 1 as a comparison, after a thermal shock test (200℃⇄room temperature, 100 cycles), the wear resistance (dry sliding friction, load 50 N) was 1.58 × 10⁻⁶. -6 m³ / (N·m).

[0036] The technical features of this invention not described can be implemented by or using existing technology, and will not be repeated here. Of course, the above description is not a limitation of this invention, and this invention is not limited to the examples above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of this invention should also be within the protection scope of this invention.

Claims

1. A high thermal conductivity aluminum-based composite mold material, characterized in that, By weight fraction, it includes 70-80% matrix alloy, 15-20% silicon carbide particles, 5-8% rare earth oxide-coated aluminum nitride powder, 2-4% graphene nanosheets, 1-3% cubic boron nitride powder, 0.3%-0.8% Sn powder, and 0.1%-0.3% rare earth, with a thickness of 2-3 μm for the rare earth oxides; The inner surface of the molding die is also provided with a composite coating, which includes a micro-arc oxidation layer, a transition bonding layer, a diamond-like carbon antibacterial layer containing nano-silver, and a CrN / TiAlN multilayer composite wear-resistant layer.

2. The high thermal conductivity aluminum-based composite mold material according to claim 1, characterized in that, By weight fraction, silicon carbide / (rare earth oxide coated aluminum nitride + cubic boron nitride) = 1.5-3.

0.

3. The high thermal conductivity aluminum-based composite mold material according to claim 1, characterized in that, The matrix alloy is a modified 6061 aluminum alloy, the silicon carbide particles have a particle size of 10-30 μm, the graphene nanosheets have a sheet thickness of 3-8 nm and a lateral dimension of 5-15 μm, serving as a thermally conductive network framework, the aluminum nitride powder has a particle size of 0.5-2 μm, used to adjust the coefficient of thermal expansion and improve interfacial bonding, and the cubic boron nitride has a particle size of 1-3 μm, used to improve thermal conductivity.

4. A preparation process for a high thermal conductivity aluminum-based composite mold material as described in any one of claims 1-3, characterized in that, Includes the following steps: Step S1: Raw material pretreatment, preparation of matrix alloy powder and reinforcement phase pretreatment; Step S2: Multi-stage mixing, followed by spray granulation; Step S3: Densification is achieved through cold isostatic pressing followed by hot extrusion. Step S4: Perform solution treatment and aging heat treatment; Step S5: Surface treatment, first precision machining, then micro-arc oxidation, and finally physical vapor deposition of a multi-layer coating.

5. The preparation process of the high thermal conductivity aluminum-based composite mold material according to claim 4, characterized in that, In step S1, when preparing the base alloy powder, modified 6061 aluminum alloy powder is prepared by atomization. The composition is: Al-1.0Mg-0.6Si-0.3Cu-0.2Cr, wt%, with the powder particle size controlled at 20-50μm and the oxygen content <0.1%. During the pretreatment of the reinforcing phase, the silicon carbide particles are acid-washed to remove surface oxides, and then vacuum heat-treated at 800℃ for 2 hours. Graphene nanosheets were prepared by liquid-phase exfoliation and surface modification with silane coupling agents. Aluminum nitride powder was heat-treated at 600℃ for 1 hour under nitrogen protection to remove surface adsorbed water.

6. The preparation process of the high thermal conductivity aluminum-based composite mold material according to claim 4, characterized in that, In step S2, during the primary mixing, the pretreated silicon carbide particles are mixed with a portion of aluminum powder accounting for 30% of the total aluminum powder in a planetary ball mill at a ball-to-material ratio of 3:1, a rotation speed of 200 rpm, a time of 2 hours, and under argon protection to form a core-shell structured premixed powder of "aluminum-coated silicon carbide". During the secondary mixing process, the primary mixed powder, the remaining aluminum powder, graphene nanosheets, rare earth oxide-coated aluminum nitride powder, cubic boron nitride powder, and rare earth are placed into a V-type mixer and mixed for 8-12 hours to ensure uniform distribution of the multiphase. In spray granulation, the mixed powder is made into a slurry, spray-dried, and the granulated particle size is 80-120μm.

7. The preparation process of the high thermal conductivity aluminum-based composite mold material according to claim 4, characterized in that, In step S3, during cold isostatic pressing, the granulated powder is loaded into the rubber mold, the pressure is 200-250 MPa, and the pressure is held for 3-5 minutes to obtain a compact with a relative density of 60-65%. Hot extrusion densification: The compact is heated to 500-520℃, the extrusion ratio is 16:1, and the extrusion speed is 1-2 mm / s to obtain fully densified bars or plates.

8. The preparation process of the high thermal conductivity aluminum-based composite mold material according to claim 4, characterized in that, In step S4, the solution treatment is carried out at 530℃ for 2 hours, followed by water quenching, and the aging treatment is carried out at 175℃ for 8 hours, followed by air cooling.

9. The preparation process of the high thermal conductivity aluminum-based composite mold material according to claim 4, characterized in that, In step S5, during precision machining, the material is machined to the required size of the mold, with a surface roughness Ra≤0.8μm; Subsequently, micro-arc oxidation is used to form a porous ceramic layer with a thickness of 20-30 μm. The electrolyte is a sodium silicate system with a concentration of 15-20 g / L. The voltage is 400-450 V, the frequency is 500 Hz, the duty cycle is 30%, and the processing time is 20-30 minutes. Finally, a multilayer physical vapor deposition coating is performed: a. Transition layer deposition: Cr / CrN multilayers with a thickness of 2-3 μm were deposited by magnetron sputtering; b. Antibacterial layer deposition: Ag-DLC composite film with a thickness of 1-2 μm was prepared by co-sputtering with a silver target and a graphite target in an argon and methane atmosphere; c. Wear-resistant layer deposition: Multi-arc ion plating is used to alternately deposit CrN and TiAlN nano-multilayer films with a thickness of 3-5μm.