High-temperature protective composite coating for die-casting die as well as preparation method and application of high-temperature protective composite coating

Abstract

The invention relates to the technical field of die-casting die surface treatment, in particular to a high-temperature protection composite coating for a die-casting die and a preparation method and application of the high-temperature protection composite coating. The composite coating sequentially comprises a nitrogenous diffusion layer, a Cr bonding layer, a CrN transition layer and an AlCrWSiN working layer from a die base body to the surface. The nitride composite coating with the element content in continuous gradient change is efficiently prepared through the arc ion plating multi-target co-deposition technology, the high-temperature protective coating material suitable for the aluminum alloy die-casting die is rapidly screened out, the high hardness, high abrasion resistance and excellent molten aluminum corrosion resistance of the surface of the die-casting die are effectively improved, and the research and development efficiency is improved. The method is simple, controllable, good in repeatability, high in practicability and capable of being applied to the field of aluminum alloy die-casting dies.

Description

Technical Field

[0001] The present invention relates to the technical field of die-casting mold surface treatment, and particularly relates to a high-temperature protection composite coating for die-casting molds, a preparation method thereof, and an application thereof. Background Art

[0002] Lightweight has become the development direction of energy conservation and emission reduction in the automotive and communication industries. Lightweight and high-strength aluminum alloys are often used as lightweight materials to replace traditional materials for manufacturing structural components. Precision die-casting integrates high-performance alloy preparation and precise forming of products, and has become the mainstream manufacturing method for future lightweight components. Die-casting machines, molds, and alloy materials are collectively referred to as the three elements of die-casting, which jointly determine the quality, efficiency, and performance of die-cast parts. Among them, the long service life of die-casting molds under harsh service environments has become an international industry problem. During the die-casting process, the mold is subjected to the erosion of high-temperature and high-speed aluminum liquid and alternating stresses, and is prone to failure problems such as erosion, thermal wear, thermal fatigue, and welding, resulting in premature failure of the mold. Therefore, the quality and life of the mold have become the key factors restricting die-casting efficiency. Traditional mold surface treatment methods, such as ion nitriding, TD surface super-hardening treatment, laser quenching, etc., although improve the surface hardness of the mold, the mold directly contacts the high-temperature aluminum liquid, inevitably reacts to form Fe-Al intermetallic compounds, forms an aluminum adhesion layer, and causes mold damage under repeated pulling.

[0003] Physical vapor deposition (PVD) coatings are an effective measure to improve the service performance of industrial tools and molds. PVD coatings mainly composed of transition metal nitrides form a continuous and dense protective layer with strong wear and friction reduction ability, stable chemical properties, and no reaction with aluminum melt, avoiding direct contact between the hot melt and the mold, thereby playing a role in protecting the mold. In particular, the addition of elements such as Cr and Al significantly improves the high-temperature resistance, wear resistance, corrosion resistance, and oxidation resistance of the mold. However, the high friction coefficient and relatively low oxidation resistance of binary nitride coatings are difficult to meet the high-temperature performance requirements. The development trend of PVD hard coatings is diversification, compositeization, and nanometerization. However, the performance of multi-component coatings directly depends on the element content and microstructure in the coatings.

[0004] Traditional "stir-frying method" and "trial-and-error method" need to explore the coating material formula and optimal process parameters through a large number of repeated experiments, which have disadvantages such as low efficiency, high cost, and uncertainty. The complexity of the multi-component and multi-scale interface combination makes it difficult for the empirical trial-and-error R & D mode to quickly obtain a coating system with the best comprehensive performance, and it is impossible to efficiently construct the "component-structure-property" relationship. Applying the high-throughput screening and optimization method of materials gene engineering is an inevitable choice for the R & D and application of high-temperature protective composite coatings for new die-casting molds. However, the multi-target co-sputtering and mask method commonly used in high-throughput coating preparation mainly focus on the target coating area, which is difficult to ensure the uniformity of the coating and is not suitable for large-size workpieces such as die-casting molds. And the element composition content and structure regulation of a single multi-component alloy target are relatively complex, and alloy targets with different components and contents need to be prefabricated, resulting in an increase in R & D costs and low production efficiency.

[0005] In view of the above defects, the inventors of the present invention have finally obtained the present invention through long-term research and practice. Summary of the Invention

[0006] The purpose of the present invention is to solve the problem that the complexity of the multi-component and multi-scale interface combination makes it difficult for the empirical trial-and-error R & D mode to quickly obtain a coating system with the best comprehensive performance and it is impossible to efficiently construct the "component-structure-property" relationship, and provides a high-temperature protective composite coating for die-casting molds, a preparation method thereof, and an application thereof.

[0007] To achieve the above purpose, the present invention discloses a high-temperature protective composite coating for die-casting molds, which sequentially includes a nitrogen-containing diffusion layer, a Cr bonding layer, a CrN transition layer, and an AlCrWSiN working layer from the mold substrate to the surface. The thickness of the nitrogen-containing diffusion layer is 50-200 μm, the thickness of the Cr bonding layer is 0.3-0.5 μm, the thickness of the CrN transition layer is 0.3-0.7 μm, and the thickness of the AlCrWSiN working layer is 3-8 μm. The AlCrWSiN working layer is a nano-composite multi-layer structure. The element composition range of the AlCrWSiN working layer is calculated by atomic percentage and includes: Al: 5-30%, Cr: 20%-45%, W: 0.5-15%, Si: 0.5-7%, and the rest is N.

[0008] The nitrided layer contains a high-toughness α-Fe(N) phase structure.

[0009] The present invention also discloses a preparation method of the above high-temperature protective composite coating for die-casting molds, which includes the following steps:

[0010] S1. Perform plasma nitriding treatment on the surface of die steel: Introduce nitrogen and hydrogen into the plasma nitriding furnace. The nitrogen flow rate is 100 - 300 sccm, the hydrogen flow rate is 500 - 700 sccm, the nitriding pressure is 200 Pa, the nitriding temperature is 450 - 550 °C, and the nitriding time is 6 - 10 h to prepare a nitrided layer, then cool it to room temperature and take out the sample;

[0011] S2. Etch and clean the nitrided die steel: Place the sample obtained in step S1 on the turntable of the arc ion plating equipment. The turntable rotation speed is 1 - 5 rpm, the chamber heating temperature is 400 - 500 °C. After pumping to the base vacuum, introduce argon and maintain the pressure at 1 - 4 Pa. The glow cleaning time is 5 - 30 min; then turn on the arc-assisted glow discharge to enhance etching, adjust the column arc current to 70 - 120 A. Stage 1: The negative bias voltage and ion source current increase gradually from low to high for etching; Stage 2: Etch with a high negative bias voltage and ion source current continuously;

[0012] S3. Prepare a Cr bonding layer and a CrN transition layer: After etching, introduce argon to adjust and maintain the deposition pressure at 1 - 4 Pa. Set the Cr arc target current to 100 - 150 A, the substrate negative bias voltage to 40 - 80 V, turn on the Cr target, and deposit the Cr bonding layer for 10 - 40 min. Then keep the target current and substrate negative bias voltage unchanged, turn off argon, introduce nitrogen to adjust the vacuum degree in the chamber to 1 - 5 Pa, and deposit the CrN transition layer for 20 - 40 min;

[0013] S4. Prepare an AlCrWSiN working layer: After the CrN transition layer is prepared, turn off the Cr target current, keep the pressure, temperature, and substrate negative bias voltage unchanged, and at the same time turn on and set the CrW alloy target and the AlCrSi alloy target. The arc target current is 100 - 150 A, and deposit the AlCrWSiN working layer for 100 - 250 min.

[0014] In step S2, the arc ion plating equipment arranges two rows of targets, A and B, with 2 targets arranged in each row. Among them, a high-purity Cr target is arranged in row A, and a CrW alloy target and an AlCrSi alloy target are arranged in row B.

[0015] In step S2, the samples are placed at equal-proportion heights on the turntable of the arc ion plating equipment.

[0016] In step S2, in stage 1, the etching negative bias voltage is 50 - 200 V, the ion source current is 30 - 80 A, the etching time is 5 min, and the etching negative bias voltage and ion source current increase gradually within five minutes; in stage 2, the etching negative bias voltage is 200 - 400 V, and the etching time is 20 - 40 min.

[0017] In step S4, the W content in the CrW alloy target is 10-20 at.%, and the AlCrSi alloy target contains 60 at.% Al, 30 at.% Cr, and 10 at.% Si.

[0018] In step S4, for the obtained AlCrWSiN working layer, the Al element content gradually decreases from 27.0 at.% near the AlCrSi alloy target to 5.0 at.% far from the AlCrSi alloy target; the Si element content gradually decreases from 5.0 at.% near the AlCrSi alloy target to 0.5 at.% far from the AlCrSi alloy target; the W element content gradually decreases from 5.0 at.% near the CrW alloy target to 0.5 at.% far from the CrW alloy target.

[0019] The present invention also discloses the application of the above high-temperature protective composite coating in an aluminum alloy die-casting mold for a die-casting mold.

[0020] Die-casting molds need to have complete surface working properties such as good wear resistance, anti-adhesion, easy demolding, oxidation resistance, and corrosion resistance to molten metal. The diversification of components and the multi-layer composite design of the structure have become the main means to enhance the high strength and toughness of nitride ceramic protective coatings. Through the combined design of multi-factor and multi-performance coating components and preparation process parameters, the present invention realizes the simultaneous deposition of coatings of multiple component systems in the same furnace, the linear gradient distribution of regional components, and the preparation of uniformity. Before the deposition of the multi-alloying coating, a plasma nitriding layer with high toughness is prefabricated to increase the hardness of the mold substrate and form a gradient hardness, improve the load-bearing capacity of the mold substrate for the coating, and greatly improve the film-substrate adhesion and fatigue resistance of the coating. By using a combination of alloy targets, an AlCrWSiN coating with continuously gradient-changing elemental composition is prepared with high throughput, improving the screening efficiency of high-temperature protective coatings for die-casting molds. The prepared coating has a hardness higher than 25 GPa and an aluminum liquid corrosion resistance performance of more than 10 hours, ensuring the long-term stable service of aluminum alloy die-casting molds and promoting the application of high-temperature protective coatings in the industrial production of aluminum alloy die-casting molds.

[0021] The beneficial effects of the present invention compared with the prior art are as follows:

[0022] 1. The present invention uses the arc ion plating multi-target co-deposition technology to prepare the AlCrWSiN multi-layer structure composite coating with high throughput, efficiently deposits a coating with continuously gradient-changing elemental content, and the prepared coating is flat and smooth, and the film layer is denser; the high-throughput preparation method can accurately control the coating thickness, accurately adjust the proportion of elemental components in the coating, and obtain the best coating;

[0023] 2. The present invention utilizes the solid solution strengthening of elements such as Al and W and CrN and Si 3 N 4Two-phase modulated decomposition forms a composite structure, and a nano-structured multi-element multi-layer composite coating mainly composed of multi-element nitride nanocrystals and Si 3 N 4 amorphous phase is prepared. The ratio of nanocrystals to amorphous phase is appropriate. At the same time, the high-temperature self-lubricating element W is added, which greatly improves the coating hardness and high-temperature wear resistance. At the same time, the co-action of amorphous-wrapped nanocrystals and nano-multilayer structure inhibits the rapid outward diffusion of W element and prevents high-temperature friction loss; and the nano-scale multi-layer structure effectively hinders the penetration of aluminum melt and improves the corrosion resistance;

[0024] 3. The high-temperature protection composite coating prepared by the present invention forms a gradient hardness distribution that gradually decreases from the surface to the subsurface, effectively alleviating the "eggshell effect", enhancing the film-substrate bonding force between the coating and the substrate. The bonding force of the deposited coatings is all at HF1 level, which is beneficial to improving the anti-fatigue performance of the coating;

[0025] 4. The high-throughput preparation process of the high-temperature protection composite coating developed by the present invention is simple and controllable, has good repeatability, wide application range, and strong practicability. Brief Description of the Drawings

[0026] Figure 1 is a schematic diagram of the high-throughput preparation principle based on arc ion plating multi-target co-deposition of the present invention;

[0027] Figure 2 is a schematic diagram of the structure of the high-temperature protection composite coating of the present invention;

[0028] Figure 3 is the XRD pattern of the composite coating samples at different positions in Example 1;

[0029] Figure 4 is the cross-sectional TEM image of the composite coating prepared at position 11 in Example 1;

[0030] Figure 5 is the nano-hardness and elastic modulus of the composite coating samples at different positions in Example 1;

[0031] Figure 6 is the friction coefficient diagram of the composite coating sample and alumina grinding ball under high-temperature friction at 600 °C in Example 1;

[0032] Figure 7 is the Rockwell indentation morphology of the composite coating sample in Example 2;

[0033] Figure 8 is the wear rate diagram of the composite coating sample in Example 1 and the coating samples of Comparative Example 1 and Comparative Example 2 and alumina grinding ball under high-temperature friction at 600 °C;

[0034] Figure 9Cross-sectional morphology of the composite coating sample after being immersed in molten aluminum for 10 hours in Example 1;

[0035] Figure 10 Cross-sectional morphology of the composite coating sample after being immersed in molten aluminum for 10 hours in Comparative Example 2.

[0036] The numbers in the figure represent:

[0037] 1 - Cr target; 2 - CrW alloy target; 3 - CrAlSi alloy target; 4 - 12 - sample positions; 13 - die steel substrate; 14 - nitrided layer; 15 - Cr bonding layer; 16 - CrN transition layer; 17 - AlCrWSiN working layer. Specific embodiments

[0038] The above and other technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings.

[0039] Figure 1 Schematic diagram of the principle for high-throughput preparation of multi-target co-deposition by arc ion plating adopted in the present invention. The arc ion plating equipment arranges two rows of targets, A and B. Each row arranges 2 targets. Among them, a high-purity Cr target is arranged in row A, and a CrW alloy target and a CrAlSi alloy target are arranged in row B. The substrate sample positions are placed at equal-proportion heights. 1 - Cr target; 2 - CrW alloy target; 3 - CrAlSi alloy target; 4 - 12 - sample positions.

[0040] Figure 2 Schematic diagram of the scheme for preparing a high-temperature protective composite coating in Examples 1 - 2. The high-temperature protective composite coating includes: die steel substrate 13, nitrogen-containing diffusion layer 14, Cr bonding layer 15, CrN transition layer 16, and AlCrWSiN working layer 17. The die steel substrate used in the specific embodiments part is H13 hot work die steel.

[0041] Example 1

[0042] A high-temperature protective composite coating for die-casting molds, which sequentially includes a nitrogen-containing diffusion layer, a Cr bonding layer, a CrN transition layer, and an AlCrWSiN working layer from the die steel substrate to the surface. The CrW alloy target used contains 90 at.% Cr and 10 at.% W. Its specific preparation steps are as follows:

[0043] S1. Perform plasma nitriding treatment on the die steel surface. Introduce nitrogen and hydrogen into the plasma nitriding furnace. The nitrogen flow rate is 100 sccm, the hydrogen flow rate is 700 sccm, the nitriding pressure is 200 Pa, the nitriding temperature is 520 °C, and the nitriding time is 8 h to prepare a nitrided layer. Then cool to room temperature and take out the sample.

[0044] S2. Etch and clean the nitrided die steel. Place the sample obtained in step S1 on the turntable of the arc ion plating equipment. The turntable rotates at 3 rpm, the chamber heating temperature is 450 °C, and it is pumped to a base vacuum of 5×10 -4 Pa, then argon is introduced, and the gas pressure is maintained at 3 Pa. The glow cleaning time is 10 min. Then, arc-assisted glow discharge is turned on to enhance etching. Adjust the column arc current to 90 A. In the first stage, the etching negative bias voltage and ion source current gradually increase, reaching 50 - 200 V and 30 - 80 A respectively. The total etching time is 5 min, and the duty cycles of the negative bias voltage and ion source current are 70% and 75% respectively. Then, in the second stage, a high negative bias voltage of 250 V and an ion source current of 80 A are maintained for 25 min of etching.

[0045] S3. Prepare the Cr bonding layer and CrN transition layer. After etching, argon is introduced to adjust and maintain the deposition pressure at 3 Pa. Set the Cr arc target current to 120 A and the substrate negative bias voltage to 60 V. Turn on the Cr target to deposit the Cr bonding layer for 20 min. Then, keep the target current and substrate negative bias voltage unchanged, turn off the argon, introduce nitrogen to adjust the vacuum in the chamber to 3 Pa, and deposit the CrN transition layer for 20 min.

[0046] S4. Prepare the AlCrWSiN working layer. After the CrN transition layer is prepared, turn off the Cr target current, keep the gas pressure, temperature, and substrate negative bias voltage unchanged. At the same time, turn on and set the CrW alloy target (90 at.% Cr, 10 at.% W) and the AlCrSi alloy target, with the arc target current of both being 120 A, and deposit the AlCrWSiN working layer for 120 min.

[0047] After the high-temperature protection composite coating AlCrWSiN for die-casting molds is prepared, the elemental content of the coating is analyzed. As shown in Table 1, it can be seen that the component content of the coatings prepared in the same furnace and synchronously shows a continuous gradient change.

[0048] Table 1 Elemental content of the AlCrWSiN coating at different positions prepared in Example 1

[0049]

[0050] Figure 3 is the XRD pattern of the composite coating samples at different positions in Example 1. The phase structure of the composite coating mainly includes fcc-AlCrWN and α-Fe(N). With the change of the coating component composition, the phase structure does not change significantly. In addition to the high-toughness α-Fe(N) nitrogen-containing martensite structure characteristics, a nitride crystal structure with multi-element solid solution strengthening is mainly formed in the coating.

[0051] Figure 4It is the cross-sectional TEM image of the composite coating sample at position 11 in Example 1. It can be clearly seen that the composite coating mainly consists of a nitrogen-containing diffusion layer, a Cr bonding layer, a CrN transition layer, and an AlCrWSiN working layer. Among them, AlCrWSiN exhibits the characteristics of a nanocomposite multi-layer structure, forming a nanomultilayer structure rich in Al layer and Cr layer. At the same time, alloying forms a nanocrystalline Cr(Al,W)N solid solution phase and an amorphous a-SiN x phase. Under the synergistic effect of the multi-layer structure at the nanoscale and the composite structure of amorphous wrapping nanocrystals, it is beneficial to improve the strength and toughness of the composite coating. In addition, it gives full play to the self-lubricating characteristics of the W element during high-temperature friction, while preventing the rapid loss of the W element.

[0052] Figure 5 It is the nano-hardness and elastic modulus of the composite coating samples at different positions in Example 1. The hardness of the prepared composite coatings all exceeds 26.8 GPa, and with the increase of the Si element content, the hardness and elastic modulus of the coatings increase, indicating that the nano-composite structure characteristics formed by the Si element are more obvious, which is beneficial to the improvement of mechanical properties.

[0053] Figure 6 It is the friction coefficient of the composite coating sample and alumina grinding ball under high-temperature friction at 600 °C in Example 1. When the W element content is relatively high, more self-lubricating Magnéli phase is generated during the friction process, which is beneficial to reducing the friction coefficient.

[0054] Example 2

[0055] The preparation method of this example is the same as that of Example 1, except that the composition of the CrW alloy target and the arc target current are changed. The CrW alloy target contains 80 at.% Cr and 20 at.% W, and the arc target current is adjusted to 130 A.

[0056] After the high-temperature protective composite coating AlCrWSiN for die-casting molds is prepared, the element content of the coating is analyzed. As shown in Table 2, it can be seen that the component content of the coatings prepared synchronously in the same furnace still shows a continuous gradient change.

[0057] Table 2 Element content of AlCrWSiN coatings at different positions prepared in Example 2

[0058]

[0059] Figure 7 It is the Rockwell indentation morphology of the composite coating sample in Example 2, indicating that the prepared composite coating has excellent interfacial bonding strength, and the bonding force reaches HF1 level, ensuring the stable service of the composite coating under harsh working conditions of high load and alternating hot and cold.

[0060] Example 3

[0061] This example has the same preparation method as Example 1, with the difference that the plasma nitriding time is 4 h.

[0062] The test results of the prepared composite coating are as follows: the thickness of the nitrogen-containing diffusion layer is 60 μm, and the hardness values of the composite coating at different positions are 26 - 32 GPa.

[0063] Example 4

[0064] This example has the same preparation method as Example 1, with the difference that the column arc current is 70 A during the arc-assisted glow discharge enhanced etching process.

[0065] The test results of the prepared composite coating are as follows: the bonding strength of the composite coating is HF1 level, and the anti-aluminum melt erosion time exceeds 10 hours.

[0066] Comparative Example 1

[0067] In this Comparative Example 1, a CrN multi-layer coating is prepared by the infiltration plating composite technology. The coating includes a die steel substrate, a nitrogen-containing diffusion layer, a Cr bonding layer, and a CrN coating working layer from bottom to top in sequence. The specific preparation steps are as follows:

[0068] S1. Perform plasma nitriding treatment on the die steel surface. Introduce nitrogen and hydrogen into the plasma nitriding furnace. The nitrogen flow rate is 100 sccm, the hydrogen flow rate is 700 sccm, the nitriding pressure is 200 Pa, the nitriding temperature is 520 °C, and the nitriding time is 8 h to prepare a nitrided layer. Then cool it to room temperature and take out the sample.

[0069] S2. Etch and clean the nitrided die steel. Place the sample obtained in step S1 on the turntable of the arc ion plating equipment. The turntable rotation speed is 3 rpm, the chamber heating temperature is 450 °C, evacuate to the base vacuum of 5×10 -4 Pa, then introduce argon, keep the pressure at 3 Pa, and the glow cleaning time is 10 min. Then turn on the arc-assisted glow discharge enhanced etching, adjust the column arc current to 90 A. In the first stage, the etching negative bias voltage and ion source current gradually increase, which are 50 - 200 V and 30 - 80 A respectively. The total etching time is 5 min, and the duty cycles of the negative bias voltage and ion source current are 70% and 75% respectively. Then in the second stage, a high negative bias voltage of 250 V and an ion source current of 80 A are used for continuous etching for 25 min.

[0070] S3. Prepare the Cr bonding layer. After the etching is completed, introduce argon to adjust and keep the deposition pressure at 3 Pa. Set the Cr arc target current to 120 A, the substrate negative bias voltage to 60 V, turn on the Cr target, and deposit the Cr bonding layer. The deposition time is 20 min.

[0071] S4. Prepare the CrN working layer. Adjust the current of the Cr arc target to 130 A, keep the gas pressure, temperature, and substrate negative bias voltage unchanged, deposit the CrN working layer, and the deposition time is 210 min.

[0072] The thickness of the prepared CrN coating is 5.06 μm, and the coating hardness is 22.9 GPa.

[0073] Comparative Example 2

[0074] In this Comparative Example 2, an arc ion plating method is used to prepare an AlCrWN multi-layer composite coating. The coating includes a die steel substrate, a nitrogen-containing diffusion layer, a Cr bonding layer, a CrN transition layer, and an AlCrWN working layer from bottom to top. The specific preparation steps are as follows:

[0075] S1. Perform plasma nitriding treatment on the surface of the die steel. Introduce nitrogen and hydrogen into the plasma nitriding furnace. The nitrogen flow rate is 100 sccm, the hydrogen flow rate is 700 sccm, the nitriding gas pressure is 200 Pa, the nitriding temperature is 520 °C, the nitriding time is 8 h, prepare the nitrided layer, then cool it to room temperature, and take out the sample.

[0076] S2. Etch and clean the nitrided die steel. Place the sample obtained in Step S1 on the turntable of the arc ion plating equipment. The turntable rotation speed is 3 rpm, the chamber heating temperature is 450 °C, evacuate to the base vacuum of 5×10 -4 Pa, then introduce argon gas, keep the gas pressure at 3 Pa, and the glow cleaning time is 10 min. Then turn on the arc-assisted glow discharge to enhance etching. Adjust the column arc current to 90 A. In the first stage, the etching negative bias voltage and ion source current gradually increase, which are 50 - 200 V and 30 - 80 A respectively. The total etching time is 5 min, and the duty cycles of the negative bias voltage and ion source current are 70% and 75% respectively. Then in the second stage, a high negative bias voltage of 250 V and an ion source current of 80 A are maintained for etching for 25 min.

[0077] S3. Prepare the Cr bonding layer and the CrN transition layer. After the etching is completed, introduce argon gas to adjust and keep the deposition gas pressure at 3 Pa. Set the Cr arc target current to 120 A, the substrate negative bias voltage to 60 V, turn on the Cr target, deposit the Cr bonding layer, and the deposition time is 20 min. Then keep the target current and substrate negative bias voltage unchanged, turn off the argon gas, introduce nitrogen gas to adjust the vacuum degree in the chamber to 3 Pa, and deposit the CrN transition layer, and the deposition time is 20 min.

[0078] S4. Prepare the AlCrWN working layer. After the preparation of the CrN transition layer is completed, turn off the Cr target current, keep the gas pressure, temperature, and substrate negative bias voltage unchanged. At the same time, turn on and set the CrW alloy target (90 at.% Cr, 10 at.% W) and the AlCr alloy target (70 at.% Al, 30 at.% Cr), with the arc target current of both being 120 A, and deposit the AlCrWN working layer for 120 min.

[0079] The thickness of the prepared AlCrWN coating is 5.6 μm, and the coating hardness is 25 GPa.

[0080] Figure 8 The wear rates of the composite coating sample in Example 1, the coating samples in Comparative Example 1 and Comparative Example 2, and the alumina grinding balls under high-temperature friction at 600 °C are shown. The nano-composite multi-layer structure coating in Example 1 has a lower wear rate compared with the traditional binary coating in Comparative Example 1 and the composite coating with solid solution strengthening effect in Comparative Example 2, and its wear resistance is better, which is beneficial to the service life of die-casting molds.

[0081] Figure 9 and Figure 10 The cross-sectional morphology diagrams of the composite coating sample at position 9 in Example 1 and the composite coating sample in Comparative Example 2 after being immersed in molten aluminum for 10 hours are shown. It can be seen that the composite coating in Example 1 is still intact after long-term corrosion, while the composite coating in Comparative Example 2 shows corrosion pits and the coating has failed, indicating that the coating in Example 1 has excellent molten aluminum corrosion resistance, which is beneficial to extending the service life of die-casting molds.

[0082] The above are only the preferred embodiments of the present invention, which are illustrative rather than restrictive to the present invention. Those skilled in the art understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, but all will fall within the protection scope of the present invention.

Claims

1. A high temperature protective composite coating for die casting molds, characterized in that: The mold substrate includes a nitrogen diffusion layer, a Cr bonding layer, a CrN transition layer and an AlCrWSiN working layer in sequence from the mold substrate to the surface. The thickness of the nitrogen diffusion layer is 50-200 μm, the thickness of the Cr bonding layer is 0.3-0.5 μm, the thickness of the CrN transition layer is 0.3-0.7 μm, the thickness of the AlCrWSiN working layer is 3-8 μm, and the AlCrWSiN working layer is a nano-composite multilayer structure. The element composition range of the AlCrWSiN working layer includes, in terms of atomic percentage, Al: 5-30%, Cr: 20%-45%, W: 0.5-15%, Si: 0.5-7%, and the rest is N.

2. A high temperature protective composite coating for die casting mold according to claim 1, characterized in that: The nitrogen-containing diffusion layer includes a high-toughness α-Fe(N) phase structure.

3. A method for preparing a high temperature protective composite coating for a die casting mold as claimed in claim 1 or 2, characterized in that: The following steps are involved: S1, plasma nitriding treatment is performed on the surface of the mold steel: nitrogen and hydrogen are introduced into the plasma nitriding furnace, the nitrogen flow rate is 100-300sccm, the hydrogen flow rate is 500-700sccm, the nitriding pressure is 200Pa, the nitriding temperature is 450-550℃, the nitriding time is 6-10h, the nitriding layer is prepared, and then cooled to room temperature and the sample is taken out; S2, etching and cleaning the nitriding die steel: placing the sample obtained in step S1 on the rotating rack of the arc ion plating equipment, the rotating rack speed is 1-5rpm, the chamber heating temperature is 400-500℃, and after the vacuum is evacuated to the background degree, argon gas is introduced, and the gas pressure is maintained at 1-4Pa, and the glow cleaning time is 5-30min; then the arc-assisted glow discharge enhanced etching is turned on, and the column arc current is adjusted to 70-120A, stage one: negative bias voltage and ion source current are gradually increased from low to high etching; stage two: high negative bias voltage and ion source current are continuously etched; S3, preparation of Cr bonding layer and CrN transition layer: after etching, introduce argon gas to adjust the deposition pressure to 1-4 Pa, set the Cr arc target current to 100-150A, the substrate negative bias voltage to 40-80V, turn on the Cr target, deposit the Cr bonding layer, and the deposition time is 10-40 minutes. Then, keep the target current and substrate negative bias voltage unchanged, turn off the argon gas, introduce nitrogen gas to adjust the vacuum degree in the chamber to 1-5 Pa, and deposit the CrN transition layer for 20-40 minutes; S4, preparing AlCrWSiN working layer: after the preparation of CrN transition layer is completed, the Cr target current is turned off, the gas pressure, temperature and substrate negative bias voltage are kept unchanged, and the CrW alloy target and AlCrSi alloy target are turned on and set at the same time, the arc target current is 100-150A, and the AlCrWSiN working layer is deposited for 100-250min.

4. The method for preparing a high temperature protective composite coating for a die casting mold according to claim 3, characterized in that: In step S2, the arc ion plating equipment arranges two columns of targets, A and B, with two targets arranged in each column, wherein column A is arranged with high-purity Cr targets, and column B is arranged with CrW alloy targets and AlCrSi alloy targets.

5. The method for preparing a high temperature protective composite coating for a die casting mold according to claim 3, characterized in that: In the step S2, the samples are placed at equal heights on a rotating rack of the arc ion plating equipment.

6. The method for preparing a high temperature protective composite coating for a die casting mold according to claim 3, characterized in that: In step S2, in stage one, the etching negative bias voltage is 50-200V, the ion source current is 30-80A, the etching time is 5min, and the etching negative bias voltage and ion source current gradually increase within five minutes; in stage two, the etching negative bias voltage is 200-400V, and the etching time is 20-40min.

7. The method for preparing a high temperature protective composite coating for a die casting mold according to claim 3, characterized in that: In the step S4, the W content in the CrW alloy target is 10-20 at.%, and the AlCrSi alloy target contains 60 at.% Al, 30 at.% Cr and 10 at.% Si.

8. The method for preparing a high temperature protective composite coating for a die casting mold according to claim 3, characterized in that: In the step S4, the AlCrWSiN working layer obtained has an Al element content gradually decreasing from 30.0 at.% close to the AlCrSi alloy target to 5.0 at.% far away from the AlCrSi alloy target; the Si element content gradually decreasing from 7.0 at.% close to the AlCrSi alloy target to 0.5 at.% far away from the AlCrSi alloy target; and the W element content gradually decreasing from 15.0 at.% close to the CrW alloy target to 0.5 at.% far away from the CrW alloy target.

9. Use of the high temperature protective composite coating for die casting molds as claimed in claim 1 or 2 in aluminum alloy die casting molds.

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