Laser shock process for improving CrN coating deposition efficiency of aluminum alloy mold

Abstract

The invention relates to a laser shock process for improving the deposition efficiency of a CrN coating of an aluminum alloy die. The laser shock process comprises the following steps: (1) linearly cutting original die steel into a sample; (2) carrying out heat treatment on the sample, polishing, carrying out ultrasonic cleaning by using an organic solvent, and drying; (3) clamping the sample on a laser shock peening test platform, and carrying out laser shock treatment on the surface; and (4) the sample is placed in a multifunctional nitriding and metalizing furnace to be subjected to coating deposition treatment, and the sample is cooled to the room temperature along with the furnace. The laser shock treatment enables the surface of a sample to generate plastic deformation and increases the surface roughness, a nanocrystalline and high-density dislocation structure is formed, nanoscale grain boundaries and high-density dislocation defects provide a rapid channel for nitrogen atom diffusion, the rough surface provides more nucleation sites, initial nucleation and growth of the CrN coating are promoted, and the surface roughness of the CrN coating is improved. And the method has the advantages of energy conservation, high efficiency and the like.

Description

Technical Field

[0001] The invention relates to a laser shock process for improving the deposition efficiency of a CrN coating on an aluminum alloy die. Background Art

[0002] H13 steel, a typical hot-working die steel, is widely used in aluminum alloy extrusion dies and other fields due to its excellent high-temperature strength, thermal fatigue resistance, and hardenability. However, under extreme operating conditions of high temperature, high pressure, and cyclic loading, H13 steel surfaces often fail due to wear, corrosion, and thermal fatigue, directly affecting die life and machining accuracy. Therefore, surface modification technologies are needed to enhance its overall performance.

[0003] In recent years, laser shock processing has been widely used and developed for material surface strengthening. It can effectively inhibit crack initiation and propagation, while refining grains and improving the fatigue resistance of the substrate. Although the application of single laser shock processing is becoming more and more widespread, as mold working conditions become more complex and service conditions become more and more demanding, such as the need to withstand high loads and severe wear, single laser shock processing is becoming increasingly limited. Therefore, material surface treatment technology will develop in the direction of the coordinated development of multiple technologies. Through the rational combination of multiple surface strengthening methods, the shortcomings of single surface technologies can be compensated to obtain composite films with better overall performance.

[0004] A CrN coating was prepared using a laser shock treatment combined with a double-glow plasma surface alloying technique to extend the service life of the mold. Laser shock treatment refines the surface grains of the sample, introducing high-density dislocations that provide diffusion pathways for the deposited CrN coating, improving the coating's density and mechanical continuity. This technique, combined with laser shock treatment and double-glow plasma surface alloying, has not been previously reported. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: in response to the problem that aluminum alloy extrusion dies serve in harsh environments for a long time, resulting in mold failure, the present invention provides a laser shock process for improving the deposition efficiency of CrN coatings on aluminum alloy molds. Through laser shock treatment, the surface grains of the mold steel can be refined to the nanoscale, a large number of high-energy grain boundaries are formed on the surface, and a large number of dislocations are generated, thereby increasing the surface roughness, providing dense nucleation sites for CrN deposition, promoting its rapid nucleation and forming an equiaxed nanocrystalline structure, and improving the deposition efficiency of the CrN layer coating.

[0006] The present invention is achieved through the following technical solutions.

[0007] A laser shock process for improving the deposition efficiency of CrN coating on aluminum alloy molds comprises the following steps:

[0008] (1) Cut the original mold steel into samples. The original mold steel is a type of mold steel, preferably AISI H13 steel, and the sample size is 15mm×15mm×5mm.

[0009] (2) The samples were heat treated, polished, and then ultrasonically cleaned and dried in an organic solvent. The heat treatment was performed by first heating the sample to 1060°C, holding the temperature for 30 minutes, cooling it to room temperature with nitrogen, then heating it to 560°C, holding the temperature for 3 hours, and then cooling it to room temperature with the furnace. The polishing treatment was performed by grinding the sample with diamond sandpaper of 400 to 2000 mesh in stages, and then polishing it to a mirror surface with polishing paste of grit w2.5. Ultrasonic cleaning in an organic solvent was performed by first immersing the sample in an acetone solution for ultrasonic cleaning for 30 minutes, and then immersing the sample in alcohol for 15 minutes to remove oil stains.

[0010] (3) The sample is clamped onto the laser shock peening test platform and its surface is laser-shocked. Laser shock treatment uses a short-pulse laser beam with high power density to irradiate the sample surface. After the absorption layer on the sample surface absorbs the laser energy, it is rapidly vaporized under the action of the confinement layer, generating high-temperature, high-pressure plasma. This plasma expands rapidly, generating a high-intensity shock wave that propagates into the sample and acts on the sample surface.

[0011] (4) Place the sample in a multifunctional nitriding and metalizing furnace, and use the double glow plasma surface alloying technology to deposit the CrN coating, and then cool it to room temperature. The specific operation of the coating deposition process is: draw the vacuum degree in the furnace to 6×10 -4 Pa, introduce argon and nitrogen, the flow rates of argon and nitrogen are 300ml / min and 150ml / min respectively, adjust the current and voltage to generate glow discharge in the furnace, sputter the sample surface for 30min, then adjust the temperature to 520℃, and the deposition time is 6h.

[0012] In step (3), the laser shock treatment uses a laser wavelength of 1064nm, a pulse energy of 20-30J, a pulse width of 10-15ns, a circular spot shape, a spot diameter of 4.5mm, a spot overlap rate of 50%, 2-4 laser shock times, and the plasma shock wave is impacted according to the set grid path; the shock wave is impacted downward from the starting point of the sample surface, then displaced 2.25mm to the right, impacted upward, displaced 2.25mm to the right, and impacted downward, and this path is repeated until the entire sample is impacted.

[0013] In step (3), a 1 mm thick aluminum foil is used as the energy absorption layer, and a 1 mm thick deionized water film is used as the constraint layer.

[0014] In step (4), the target material is a chromium target with a purity of 99.9%, and the cooling method is furnace cooling. After cooling, an OLYMPUS-PMG3 optical microscope is used to measure the sample microstructure and coating thickness.

[0015] Compared with the prior art, the advantages of the present invention are:

[0016] 1. Laser shock treatment treats the material surface. After treatment, the surface grains of the sample are refined to the nanoscale, forming a large number of high-energy grain boundaries and increasing the surface roughness, which provides dense nucleation sites for CrN, promotes its rapid nucleation and forms an equiaxed nanocrystalline structure, and significantly improves the deposition rate of the CrN coating on the substrate;

[0017] 2. After the CrN coating is deposited, the residual stress gradient structure retained in the middle part after laser shock treatment enhances the bonding strength between the coating and the substrate. The existence of this gradient structure effectively alleviates the hardness difference between the hard CrN layer and the mold steel, enabling the substrate to provide more effective mechanical support for the CrN layer, thereby improving the CrN layer's carrying capacity for external loads. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic flow diagram of the present invention;

[0019] Figure 2 This is the microstructure of the CrN coating on H13 steel without laser shock.

[0020] Figure 3 is a microstructure diagram of the CrN coating obtained in Example 1;

[0021] Figure 4 is a microstructure diagram of the CrN coating obtained in Example 2;

[0022] Figure 5 It is the path diagram of the plasma shock wave acting on the sample surface; DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0024] Example 1

[0025] (1) Processing the original mold steel into a sample with a size of 15 mm × 15 mm × 5 mm; the original mold steel is a type of mold steel, and in this embodiment, it is AISI H13 steel;

[0026] (2) Heat the sample by heating it to 1060°C, keeping it warm for 30 minutes, cooling it to room temperature with nitrogen, then heating it to 560°C, keeping it warm for 3 hours, and cooling it to room temperature with the furnace. The cooling time with the furnace is about 3 hours.

[0027] (3) The samples were polished step by step with diamond sandpaper ranging from 400 to 2000 mesh, and then polished to a mirror surface with polishing paste of particle size w2.5. The samples were then immersed in acetone solution for ultrasonic cleaning for 30 minutes, and then immersed in alcohol for 15 minutes to remove oil stains.

[0028] (4) The sample was clamped onto the laser shock peening test platform, and the laser wavelength was set to 1064 nm, the pulse energy to 30 J, the pulse width to 15 ns, the spot shape to be circular, the spot diameter to be 4.5 mm, the spot overlap rate to be 50%, the laser shock number to be 4, and the plasma shock wave to be impacted according to the set grid path; the shock wave was impacted downward from the starting point of the sample surface, then moved 2.25 mm to the right, impacted upward, then moved 2.25 mm to the right, impacted downward, and repeated this path until the entire sample was impacted. Figure 5 After the absorption layer on the sample surface absorbs the laser energy, it is rapidly vaporized under the action of the confinement layer, generating high-temperature, high-pressure plasma. These plasmas expand rapidly, generating high-intensity shock waves that propagate into the interior of the sample and act on the sample surface.

[0029] (5) The sample was placed in a multifunctional nitriding and metallizing furnace, and the CrN coating was deposited using a double glow plasma surface alloying technique. The vacuum in the furnace was evacuated to 6×10-4 Pa, and argon and nitrogen were introduced at a flow rate of 300 ml / min and 150 ml / min, respectively. The current and voltage were adjusted to generate a glow discharge in the furnace, and the sample surface was sputtered for 30 minutes. The temperature was then adjusted to 520°C, and the deposition time was 6 hours. The target material was a chromium target with a purity of 99.9%, and the cooling method was furnace cooling. After cooling, the sample microstructure and coating thickness were measured using an OLYMPUS-PMG3 optical microscope.

[0030] Experimental results:

[0031] The sample surface was laser-shocked and then CrN was deposited. The thickness of the CrN coating reached about 22.86 μm, and the deposition rate was 3.81 μm / h. Figure 3 The coating thickness is increased, the coating interface is well bonded to the substrate, the coating structure is dense, and there are no defects such as holes and cracks. The coating thickness and deposition rate obtained by this process are increased by 45.6% and 45.42% respectively compared with the traditional single deposition CrN coating. The coating microstructure of the traditional single deposition CrN process is shown in Figure 2. Figure 2 .

[0032] Example 2

[0033] Example 2 is the same as Example 1, except that the pulse energy is 20 J, the pulse width is 10 ns, and the number of laser shocks is 2.

[0034] Experimental results:

[0035] The sample surface was laser-shocked and then CrN was deposited. The thickness of the CrN coating reached about 20.11 μm, and the deposition rate was 3.35 μm / h. Figure 4 The coating thickness is increased, the coating interface is well bonded to the substrate, the coating structure is dense, and there are no defects such as holes and cracks. The coating thickness and deposition rate obtained by this process are 28.1% and 27.86% higher than those of the traditional single deposition CrN coating. The coating thickness obtained by this process is about 40.79% of the traditional single deposition CrN coating. The coating microstructure of the traditional single deposition CrN process is shown in Figure 2. Figure 2 .

[0036] Comparative Example

[0037] Compared with Example 1, the comparative example lacks only step (4), and the other steps are the same. That is, the comparative example is implemented according to steps (1), (2), (3), and (5) in Example 1.

[0038] Experimental results:

[0039] After CrN deposition on the sample surface, the thickness of the CrN coating reached about 15.70 μm, and the deposition rate was 2.62 μm / h. Figure 2 There are a few holes at the interface between the coating and the substrate, the coating structure is dense, and no defects such as cracks are found.

[0040] The above description is only a preferred embodiment of the present invention and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A laser shock process for improving the deposition efficiency of CrN coating on aluminum alloy molds, characterized in that: The steps include: (1) Cut the original mold steel wire into samples; (2) heat-treating the sample obtained in step (1), polishing it, ultrasonically cleaning it with an organic solvent, and drying it; (3) Clamp the sample onto the laser shock peening test platform and perform laser shock treatment on the surface; specifically, irradiate the sample surface with a short pulse laser beam with high power density, so that the absorption layer on the sample surface absorbs the laser energy and then rapidly vaporizes under the action of the confinement layer, generating high-temperature, high-pressure plasma. These plasmas expand rapidly, generating high-intensity shock waves that propagate into the interior of the sample and act on the sample surface; the laser shock treatment uses a laser wavelength of 1064nm, a pulse energy of 20-30J, a pulse width of 10-15ns, a circular spot shape, a spot diameter of 4.5mm, a spot overlap rate of 50%, and 2-4 laser shock times; the plasma shock wave acts on the sample surface according to the set laser shock path; (4) Place the sample in a multifunctional nitriding and metalizing furnace, use double glow plasma surface alloying technology to deposit CrN coating, and cool to room temperature with the furnace; specifically: draw the vacuum degree in the furnace to 6×10 -4 Pa, introduce argon and nitrogen, the flow rates of argon and nitrogen are 300ml / min and 150ml / min respectively, adjust the current and voltage to generate glow discharge in the furnace, sputter the sample surface for 30min, then adjust the temperature to 520℃, and the deposition time is 6h.

2. The laser shock process for improving the deposition efficiency of CrN coating on aluminum alloy mold according to claim 1, characterized in that: In the step (1), the original mold steel is AISI H13 steel, and the sample size is 15 mm × 15 mm × 5 mm.

3. The laser shock process for improving the deposition efficiency of CrN coating on aluminum alloy mold according to claim 1, characterized in that: The heat treatment in step (2) is to first heat the sample to 1060°C, keep the temperature for 30 minutes, cool the sample to room temperature in nitrogen, then heat the sample to 560°C, keep the temperature for 3 hours, and cool the sample to room temperature in the furnace.

4. The laser shock process for improving the deposition efficiency of CrN coating on aluminum alloy mold according to claim 1, characterized in that: The grinding and polishing treatment in step (2) is as follows: the sample is polished step by step with diamond sandpaper of 400 to 2000 mesh, and then polished to a mirror surface with polishing paste of particle size W2.5; the ultrasonic cleaning in an organic solvent is as follows: the sample is first immersed in an acetone solution for ultrasonic cleaning for 30 minutes, and then the sample is immersed in alcohol for 15 minutes to remove oil stains.

5. The laser shock process for improving the deposition efficiency of CrN coating on aluminum alloy mold according to claim 1, characterized in that: In step (3), the pulse energy is 30 J and the pulse width is 15 ns.

6. The laser shock process for improving the deposition efficiency of CrN coating on aluminum alloy mold according to claim 1, characterized in that: In the laser shock treatment of step (3), a 1 mm thick aluminum foil is used as the energy absorption layer, and a 1 mm thick deionized water film is used as the constraint layer.

7. The laser shock process for improving the deposition efficiency of CrN coating on aluminum alloy mold according to claim 1, characterized in that: The laser shock path set in step (3) is a grid path; the laser shock is performed downward from the starting point of the sample surface, then displaced 2.25 mm to the right, and then the laser shock is performed upward, and then displaced 2.25 mm to the right, and then the laser shock is performed downward, and this path is repeated until the entire sample is shocked.

8. The laser shock process for improving the deposition efficiency of CrN coating on aluminum alloy mold according to claim 1, characterized in that: In step (4), the target material is a chromium target with a purity of 99.9%, and the cooling method is furnace cooling. After cooling, an OLYMPUS-PMG3 optical microscope is used to measure the sample microstructure and the coating thickness.

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