A high-performance Fe-based laser cladding treatment method for the surface of a nodular cast iron die-casting machine template

Abstract

This invention belongs to the field of die casting technology, specifically relating to a high-performance Fe-based laser cladding treatment method for the surface of a ductile iron die casting machine template. The method includes the following steps: selecting a substrate and a metal powder to be laser clad; the substrate is a QT500-7 ductile iron die casting machine template, and the metal powder is Fe60 alloy powder; setting parameters for the laser cladding system, including laser power, scanning speed, spot diameter, defocusing amount, powder feeding speed, and overlap rate; performing cladding; and selecting a corresponding tempering process based on the actual service conditions of the QT500-7 ductile iron die casting machine template. This invention, for QT500-7 ductile iron, uses lower-cost Fe-based alloy powder to replace expensive Ni-based alloy powder, and after tempering, the cladding layer exhibits excellent comprehensive performance, with a bonding strength close to that of the substrate and excellent corrosion resistance, significantly reducing the remanufacturing cost of the die casting machine template.

Description

Technical Field

[0001] This invention belongs to the field of metal die casting technology, specifically relating to a high-performance Fe-based laser cladding treatment method for the surface of die casting machine templates for ductile iron. Background Technology

[0002] Die casting, as a core process for the efficient forming of precision metal components, is a crucial support for integrated die casting in new energy vehicles and the manufacturing of lightweight components for aerospace. The die casting machine template, as the core component that bears the mold and transmits the clamping force, is generally made of QT500-7 ductile iron and can withstand alternating clamping forces of 1600~2500 tons over long periods. - SO4² - The corrosive media release agent erosion and fretting wear multiple loads make the surface prone to pitting corrosion, wear and deformation failure. Traditional electric arc welding and thermal spraying repair processes have defects such as large heat-affected zone, low bonding strength and poor repair accuracy, which cannot meet the remanufacturing requirements of high-end die casting equipment.

[0003] Laser cladding technology, with its advantages of high energy density, small heat-affected zone, and high metallurgical bonding strength, has become a preferred solution for strengthening metal surfaces. However, existing Fe-based laser cladding processes are mainly developed for hot work die steels such as H13. When applied to ductile iron templates, the following problems exist: First, the interface is prone to forming a ledeburite white brittle structure, which is the core source of crack initiation, requiring additional nickel plating pretreatment. Second, the cladding layer prepared by the existing process has a uniform single structure, which cannot simultaneously meet the multiple requirements of high interface toughness to ensure bonding strength and high surface hardness to resist wear and corrosion. Third, the tempering process of general steel does not match the martensite and carbide microstructure characteristics of the Fe-based cladding layer of ductile iron, which easily leads to cracking and peeling of the cladding layer.

[0004] This application addresses the aforementioned problems in the metal die casting process by applying laser cladding technology. Summary of the Invention

[0005] I. Technical problems to be solved This invention addresses the aforementioned deficiencies in existing technologies by proposing a high-performance Fe-based laser cladding treatment method for the surface of ductile iron die-casting machine templates. This method solves the problem that existing die-casting machine templates are prone to failure due to complex working environments by using laser cladding technology.

[0006] II. Technical Solution To address the aforementioned technical problems, this invention provides a high-performance Fe-based laser cladding treatment method for the surface of die-casting machine templates for ductile iron, comprising the following steps: S1: Select the substrate and the metal powder to be laser cladding. The substrate is a QT500-7 ductile iron die casting machine template, and the metal powder is Fe60 alloy powder. S2: Set parameters for the laser cladding system, including laser power, scanning speed, spot diameter, defocusing amount, powder feeding speed, and overlap rate; S3: Perform cladding; S4: Select the appropriate tempering process based on the actual service conditions of the QT500-7 ductile iron die-casting machine template.

[0007] In S2, the laser power value is set in the range of 1000W~3000W, the scanning speed value is set in the range of 3mm / s~12mm / s, the spot diameter is 3.6mm, the defocusing amount is 8mm, the powder feeding speed is 10g / min, and the overlap rate is 50%.

[0008] S1 includes grinding the oxide layer off the substrate surface to be clad, cleaning it with anhydrous ethanol, and then drying it with cold air.

[0009] In S3, argon is used as a protective gas during the cladding process.

[0010] In S1, the chemical composition of the Fe60 iron-based alloy powder by weight percentage is: Cr 16~18%, C 0.8~1.2%, B 3.8~4.2%, Si 1~2%, Ni 9~12%, with the balance being Fe.

[0011] In S4, tempering at 450~550℃ is selected for high wear resistance conditions.

[0012] In S4, the corrosion-resistant matching condition is selected by tempering at a temperature of 650~750℃.

[0013] In S4, the tempering and holding time is 1~2 hours, and the furnace is cooled to below 200℃ before being taken out and air-cooled.

[0014] After cladding, the main phase of the Fe60 cladding layer is BCC-Fe, and the cladding layer exhibits a gradient structure from bottom to top: cellular crystals, dendritic crystals, and equiaxed crystals.

[0015] In S2, the laser power is 2000W and the scanning speed is 7mm / s.

[0016] III. Beneficial Effects Compared with existing technologies, this invention targets QT500-7 ductile iron, using Fe60 iron-based alloy powder. It eliminates the need for pretreatment such as nickel plating / carburizing, requiring only grinding and cleaning before direct cladding. Through optimized process parameter matching, the cladding interface is free of ledeburite white iron structure, cracks, and porosity, with a bonding strength approaching the tensile strength of the matrix. Specifically, through the synergistic effect of parameters such as laser power of 2000W and scanning speed of 7mm / s, a gradient structure cladding layer is generated in situ: the interface region has a cellular crystalline structure with good toughness to ensure bonding strength; the central region has a dendritic structure balancing strength and toughness; and the surface layer has an equiaxed crystalline structure with high hardness, wear resistance, and corrosion resistance. Cr, C, Si, and B elements are precisely segregated at the grain boundaries, achieving a synergistic effect of fine grain strengthening and dispersion strengthening, simultaneously meeting the multiple requirements of high interface toughness and high surface hardness and corrosion resistance.

[0017] Furthermore, a two-stage gradient tempering process was developed for different working conditions. For high wear-resistant conditions, tempering at 500°C was used, resulting in a significant improvement in overall hardness, especially at the interface between the bottom of the cladding layer and the substrate, where the hardness reached 1200 HV. 0.2 For corrosion-resistant applications, tempering at 700°C is used, resulting in an overall hardness of 400 HV. 0.2 Up to 500HV 0.2 The optimal choice is one that matches the mold hardness, and in the electrochemical parameter fitting analysis, the cladding layer tempered at 700°C exhibits the highest charge transfer resistance (Rct) and the best corrosion resistance, effectively addressing the main failure mode of the cladding layer, which is Cl in the release agent. - The problem of corrosion.

[0018] Overall, this application uses lower-cost Fe-based alloy powder to replace expensive Ni-based alloy powder, and after tempering at 700°C, the cladding layer exhibits excellent comprehensive performance, with bonding strength close to that of the matrix and excellent corrosion resistance, which can significantly reduce the remanufacturing cost of die-casting machine templates. Attached Figure Description

[0019] Figure 1 The images show the microstructure of the Fe60 cladding layer, including (a) the overall morphology of the cladding layer; (b) the middle part of the cladding layer; (c) the top of the cladding layer; (d) the overlap area; and (e) the bottom of the cladding layer. Figure 2 This is a schematic diagram of the cladding layer growth model; Figure 3 This is a schematic diagram of the microstructure model of the Fe60 cladding layer; Figure 4 This is a schematic diagram of the cladding tempering process; Figure 5 Microhardness diagrams of the cladding layer after tempering at different temperatures; Figure 6Nyquist plots of Fe60 cladding layers under different tempering processes; Figure 7 Bode plots-modulus plots of Fe60 cladding layers under different tempering processes; Figure 8 Bode plots-phase diagrams of Fe60 cladding layers under different tempering processes. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0021] This embodiment focuses on the surface laser cladding treatment of die-casting machine templates under high wear-resistant conditions. The specific steps are as follows: S1: Substrate pretreatment: A QT500-7 ductile iron die-casting machine template is used as the substrate. The oxide layer on the surface to be clad is removed by grinding. After cleaning with anhydrous ethanol, it is dried with cold air. No additional nickel plating or carburizing pretreatment is required. Fe60 alloy powder is used as the cladding material. Its chemical composition by weight percentage is: Cr 17%, C 1.0%, B 4.0%, Si 1.5%, Ni 10%, with the balance being Fe.

[0022] S2: Laser cladding parameter settings: A coaxial powder feeding laser cladding system is adopted, and the parameters are set as follows: laser power 2000W, scanning speed 7mm / s, spot diameter 3.6mm, defocusing amount 8mm, powder feeding speed 10g / min, and overlap rate 50%.

[0023] S3: Cladding process: Argon gas is used as the protective gas, and multiple laser cladding processes are performed according to the set parameters. The thickness of the cladding layer is controlled between 0.5 and 1.5 mm.

[0024] S4: Tempering Treatment: Select the appropriate tempering process based on the actual service conditions of the QT500-7 ductile iron die-casting machine template, specifically as follows: Figure 4 As shown; for high wear-resistant conditions, tempering at 500°C is used, with a holding time of 1 hour, followed by furnace cooling to 200°C and then air cooling; for corrosion-resistant matching conditions, tempering at 700°C is selected, with a holding time of 1 hour, followed by furnace cooling to below 200°C and then air cooling.

[0025] The performance of the cladding layer prepared in this embodiment was tested: Table 1 shows the open-circuit potential of the cladding layer after heat treatment at different temperatures. As can be seen from the table, the open-circuit potential E of the cladding layer... 700℃ >E C2 =E 500℃ >E 900℃Therefore, the cladding layer tempered at 700℃ exhibits the lowest electrochemical activity and the least tendency to self-corrosion. The cladding layer tempered at 500℃ has the same open-circuit potential as the untreated cladding layer, while the cladding layer tempered at 900℃ shows the highest electrochemical activity and the greatest tendency to self-corrosion. C2 represents the untreated state under laser power of 2000W and scanning speed of 7mm / s. C2 That is the corresponding open circuit potential, E 700℃ This is the open circuit potential of the cladding layer tempered at 700℃, and so on.

[0026]

[0027] Table 1: Open circuit potential of cladding layer after tempering at different temperatures The effect of the tempering process on the corrosion resistance of the cladding layer was further tested using electrochemical impedance spectroscopy, such as... Figure 6 As shown, Figure 6 The Nyquist plots show the Fe60 cladding layers under different tempering temperatures. A larger capacitive arc radius in the Nyquist plot indicates better corrosion resistance. The plots show that the capacitive arc radius for each sample is: 700℃ tempered cladding layer > C2 cladding layer > 500℃ tempered cladding layer > 900℃ tempered cladding layer. The 700℃ tempered cladding layer exhibits the best corrosion resistance, while the C2 cladding layer and the 500℃ tempered cladding layer are quite similar.

[0028] like Figure 7 and Figure 8 As shown, Figure 7 and Figure 8 Bode diagrams of Fe60 cladding layers under different tempering processes are shown. Figure 7 This is a modulus plot, where the vertical axis |Z| represents the impedance modulus. The modulus value near 0.01 Hz directly corresponds to the material's corrosion resistance: the larger the modulus, the more difficult charge transfer, the less likely corrosion will occur, and the better the corrosion resistance. Figure 8 The phase diagram shows the phase angle on the vertical axis. A wider peak and a peak value closer to 90° indicate better corrosion resistance; a narrower peak indicates poorer corrosion resistance. Therefore, the phase diagram shows that only the 900℃ tempered cladding layer has a narrow peak, indicating that its fitting circuit is an R(QR) type system with one time constant. The peaks of other samples are wider, and the fitting circuit uses an R(Q(R(QR))) type system with two time constants. The fitting data are shown in Table 2. (Clad layer) 2 All values ​​were less than 5%, indicating reliable fitting results. The Rct values ​​for each sample were: 700℃ tempered cladding layer > C2 cladding layer > 500℃ tempered cladding layer > 900℃ tempered cladding layer, indicating that the 700℃ tempered cladding layer had the best corrosion resistance.

[0029]

[0030] Table 2: Electrochemical parameters of Fe60 cladding layers after tempering at different temperatures like Figure 5 As shown, Figure 5 The microhardness of the cladding layer after tempering at different temperatures was measured. At a tempering temperature of 500℃, the hardness of the cladding layer increased, reaching 1200 HV at the interface between the bottom of the cladding layer and the substrate. 0.2 This is because at a tempering temperature of 500℃, the cementite in the martensite is released, the martensite volume decreases, and the pressure on the retained austenite decreases, transforming it into martensite. Simultaneously, carbon elements in the matrix diffuse to the bottom of the cladding layer, forming a hard phase, leading to an increase in the hardness of the bottom of the cladding layer. As the heat treatment temperature increases, the hardness of the cladding layer decreases. The hardness of the cladding layer tempered at 700℃ is mainly around 400 HV. 0.2 Up to 500HV 0.2 Between these values, the hardness of the cladding layer tempered at 900℃ is even lower, at 300HV. 0.2 Up to 400HV 0.2 Between these two temperatures. This is because the main microstructures within the cladding layer tempered at 700℃ and 900℃ are tempered troostite and tempered sorbite, respectively. Die-casting molds are typically forged from H13 steel, which usually has a hardness of 450 HV. 0.2 Up to 550HV 0.2 After surface hardening, it can reach 550HV. 0.2 Up to 600HV 0.2 Therefore, from the perspective of hardness matching, 700℃ is the optimal tempering temperature for the template laser cladding Fe60 cladding layer.

[0031] In this embodiment, as Figures 1-3 As shown, where Figure 1 The image shows the microstructure morphology of the Fe60 cladding layer. Figure 2 This is a schematic diagram of the cladding layer growth model; Figure 3 This is a schematic diagram of the microstructure model of the Fe60 cladding layer. The interface region of the gradient structure cladding layer exhibits a cellular crystalline structure with good toughness and strong bonding. The central region consists of a dendritic structure balancing strength and toughness, while the surface layer displays an equiaxed crystalline structure with high hardness and resistance to wear and corrosion. Cr, C, Si, and B elements are precisely segregated at the grain boundaries, achieving a synergistic effect of fine-grain strengthening and dispersion strengthening, simultaneously meeting the multiple requirements of high interface toughness and high surface hardness and corrosion resistance. Regarding the microstructure of the Fe60 alloy powder cladding layer, a cladding layer growth model was established based on the influence of temperature gradient G and solidification rate R on the cladding layer microstructure, as shown below. Figure 2 As shown, and in combination Figure 1 The microstructure morphology of the Fe60 cladding layer was drawn as follows: Figure 3The microstructure model of the Fe60 cladding layer shown depicts the interface between the cladding layer and the substrate. Matrix elements, especially Fe and C, enter the molten pool in large quantities through this interface, and elements from the powder also diffuse into the substrate through the interface. In the initial stage of laser cladding, the large temperature gradient and low growth rate result in a high G / R ratio, leading to the formation of cellular crystals at the bottom of the cladding layer. As the distance from the substrate surface increases, G decreases, R increases, and the G / R ratio decreases, causing the grains to grow parallel to the heat dissipation direction, forming dendrites. When the distance from the substrate surface is even greater, the heat dissipation of the molten pool becomes non-directional, resulting in the formation of equiaxed crystals.

[0032] This invention targets QT500-7 ductile iron, using Fe60 iron-based alloy powder. It eliminates the need for pretreatment such as nickel plating / carburizing; after grinding and cleaning, it can be directly clad. Through optimized process parameter matching, the clad interface is free of ledeburite white iron structure, cracks, and porosity, exhibiting excellent metallurgical bonding with a bonding strength close to the tensile strength of the matrix. This effectively solves the technical problems of easily forming ledeburite white iron structure at the Fe-based laser cladding interface of ductile iron, requiring additional pretreatment costs and causing significant pollution, as well as the problem of low bonding strength of the cladding layer, which fails to meet the mechanical performance requirements of die-casting machine templates.

[0033] Furthermore, a two-stage gradient tempering process was developed for different working conditions. For high wear-resistant conditions, tempering at 500°C was used, resulting in a significant improvement in overall hardness, especially at the interface between the bottom of the cladding layer and the substrate, where the hardness reached 1200 HV. 0.2 For corrosion-resistant applications, tempering at 700°C is used, resulting in an overall hardness of 400 HV. 0.2 Up to 500HV 0.2 The optimal choice is one that matches the mold hardness, and in the electrochemical parameter fitting analysis, the cladding layer tempered at 700°C exhibits the highest charge transfer resistance (Rct) and the best corrosion resistance, effectively addressing the main failure mode of the cladding layer, which is Cl in the release agent. - The corrosion problem can be solved; at the same time, using lower-cost Fe-based alloy powder instead of expensive Ni-based alloy powder can significantly reduce the remanufacturing cost of die-casting machine templates.

[0034] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for high-performance Fe-based laser cladding treatment of the surface of a die-casting machine template for ductile iron, characterized in that, The high-performance Fe-based laser cladding treatment method for the surface of the die-casting machine template of ductile iron includes the following steps: S1: Select the substrate and the metal powder to be laser cladding. The substrate is a QT500-7 ductile iron die casting machine template, and the metal powder is Fe60 alloy powder. S2: Set parameters for the laser cladding system, including laser power, scanning speed, spot diameter, defocusing amount, powder feeding speed, and overlap rate; S3: Perform cladding; S4: Select the appropriate tempering process based on the actual service conditions of the QT500-7 ductile iron die-casting machine template.

2. The method for high-performance Fe-based laser cladding treatment of the surface of a die-casting machine template for ductile iron according to claim 1, characterized in that, In S2, the laser power value is set in the range of 1000W~3000W, the scanning speed value is set in the range of 3mm / s~12mm / s, the spot diameter is 3.6mm, the defocus amount is 8mm, the powder feeding speed is 10g / min, and the overlap rate is 50%.

3. The method for high-performance Fe-based laser cladding treatment of the surface of a die-casting machine template for ductile iron according to claim 1, characterized in that, S1 also includes grinding the oxide layer off the substrate surface to be clad, cleaning with anhydrous ethanol, and then drying with cold air.

4. The method for high-performance Fe-based laser cladding treatment of the surface of a die-casting machine template for ductile iron according to claim 1, characterized in that, In S3, argon is used as a protective gas during the cladding process.

5. A method for high-performance Fe-based laser cladding treatment of the surface of a die-casting machine template for ductile iron according to claim 1, characterized in that, In S1, the chemical composition of the Fe60 iron-based alloy powder by weight percentage is: Cr 16~18%, C 0.8~1.2%, B 3.8~4.2%, Si 1~2%, Ni 9~12%, with the balance being Fe.

6. The method for high-performance Fe-based laser cladding treatment of the surface of a die-casting machine template for ductile iron according to claim 1, characterized in that, In S4, tempering at 450~550℃ is selected for high wear resistance conditions.

7. The method for high-performance Fe-based laser cladding treatment of the surface of a die-casting machine template for ductile iron according to claim 1, characterized in that, In S4, the corrosion-resistant matching condition is selected by tempering at a temperature of 650~750℃.

8. The method for high-performance Fe-based laser cladding treatment of the surface of a die-casting machine template for ductile iron according to claim 1, characterized in that, In S4, the tempering and holding time is 1~2 hours, and the furnace is cooled to below 200℃ before being taken out and air-cooled.

9. A method for high-performance Fe-based laser cladding treatment of the surface of a die-casting machine template for ductile iron according to claim 1, characterized in that, After cladding, the main phase of the Fe60 cladding layer is BCC-Fe, and the cladding layer exhibits a gradient structure from bottom to top: cellular crystals, dendritic crystals, and equiaxed crystals.

10. A method for high-performance Fe-based laser cladding treatment of the surface of a die-casting machine template for ductile iron according to claim 2, characterized in that, In S2, the laser power is 2000W and the scanning speed is 7mm / s.

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