Low temperature gradient mechanical strengthening of alloy surfaces

Abstract

The application discloses a kind of alloy surface low-temperature gradient mechanical strengthening method, comprising the following steps: after cleaning treatment, the alloy surface is treated at low temperature, the temperature of the low-temperature treatment is-160~‑196 ℃;Alloy surface is sequentially treated by first shot blasting, low-temperature treatment, second shot blasting, low-temperature treatment and third shot blasting.The application is treated at low temperature before each shot blasting treatment, to reduce the alloy temperature to below-160 ℃, when first shot blasting, random high strain rate shear deformation is generated on the surface of alloy material, dynamic recovery in alloy deformation process is inhibited, modified layer grain refinement is realized, and the thickness of modified layer is increased, when second shot blasting, Almen strength in shot blasting process is reduced, and crack is inhibited on the surface in later shot blasting, finally, through third shot blasting treatment, the surface of alloy is repaired, protrusions and burrs on the surface of material are removed, the surface roughness of alloy is reduced, and the surface quality of aluminum alloy is improved.

Description

Technical Field

[0001] This invention relates to the field of alloy surface treatment technology, and in particular to a method for low-temperature gradient mechanical strengthening of alloy surfaces. Background Technology

[0002] Mechanical shot peening utilizes shot to mechanically impact materials, inducing high-strain-rate deformation on the material surface. This allows for the accumulation of high-density deformed structures within the grains, promoting recrystallization and forming a fine-grained modified layer. Mechanical shot peening technology effectively improves the fatigue strength, wear resistance, toughness, and corrosion resistance of parts, and is widely used in aerospace, automotive, shipbuilding, bridge construction, and pressure vessel industries.

[0003] To improve the thickness of the modified layer and the grain refinement effect, methods such as increasing the almen intensity, surface coverage, gas pressure, and shot diameter in mechanical shot peening are commonly used to increase the impact energy of the shot, causing the material to undergo higher strain rate deformation and greater deformation. However, high-energy shot impact can lead to over-deformation of the surface material, resulting in uneven distribution of the modified layer structure, localized pits, microcracks, and other defects, which compromise the smoothness and performance stability of the component. Therefore, the contradiction between modified layer construction and surface quality improvement has become one of the bottleneck problems in the application of mechanical shot peening.

[0004] The prior art discloses a technical solution that first uses a low-temperature medium to cool the surface of the workpiece, and then performs rolling strengthening, shot peening strengthening and laser strengthening on the surface. Although this method can increase the hardness of the material to a certain extent and suppress the formation of microcracks during the surface treatment process, the actual manufacturing process requires the use of high-energy shot to impact strengthen the material surface and to improve the thickness of the modified layer and the degree of microstructure refinement through long-term plastic deformation. The above methods can only suppress the formation of defects in the early stage of deformation. The effect of shot peening in suppressing local protrusions, depressions and cracks is weak. Therefore, there is a technical problem of poor surface quality. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a low-temperature gradient mechanical strengthening method for alloy surfaces with good modified layer thickness and surface roughness and no cracks.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for low-temperature gradient mechanical strengthening of alloy surfaces includes the following steps:

[0008] S1. The alloy surface after cleaning is subjected to low-temperature treatment, and the temperature of the low-temperature treatment is -160 to -196℃.

[0009] S2. The alloy surface is subjected to a first shot peening treatment, a low-temperature treatment, a second shot peening treatment, a low-temperature treatment, and a third shot peening treatment in sequence.

[0010] The Almen intensities of the first, second, and third shot peening treatments are A1, A2, and A3, respectively, satisfying A1 > A2 > A3. The diameters of the projectiles in the first, second, and third shot peening treatments are D1, D2, and D3, respectively, satisfying D1 ≥ D2 > D3.

[0011] As a further improvement to the above technical solution:

[0012] A1 is 0.15–0.2 mmA, A2 is 0.15–0.2 mmA, and A3 is 0.02–0.1 mmN.

[0013] D1 is 0.5–0.8 mm, D2 is 0.5–0.8 mm, and D3 is 0.05–0.1 mm.

[0014] During the first shot peening process, the distance between the nozzle and the alloy surface is 100-200 mm, the shot type is ceramic shot or cast steel shot, and the surface coverage is 500%-1000%.

[0015] During the second shot peening process, the distance between the nozzle and the alloy surface is 100-200 mm, the shot type is ceramic shot or cast steel shot, and the surface coverage is 500%-1000%.

[0016] During the third shot peening process, the distance between the nozzle and the alloy surface is 100-200 mm, the shot type is glass shot, and the surface coverage is 1500%-2500%.

[0017] During the first, second, and third shot peening processes, the alloy surface rotates relative to the nozzle.

[0018] During the cryogenic treatment, the cooling medium is liquid nitrogen or liquid helium.

[0019] The surface cleaning includes the following steps: first, sandpaper is used to polish the alloy surface, and then alcohol is used to clean away the debris on the alloy surface.

[0020] The alloy surface was polished using sandpaper of different grits.

[0021] Compared with the prior art, the advantages of the present invention are as follows:

[0022] The method of the present invention includes performing multiple cooling and shot peening treatments on a cleaned alloy surface, with the cooling and shot peening treatments alternating. Before each shot peening treatment, a low-temperature cooling treatment is performed to reduce the alloy temperature to below -160°C. During the first shot peening treatment, random high strain rate shear deformation occurs on the alloy material surface, suppressing dynamic recovery during alloy deformation, refining the grains of the modified layer, and increasing the thickness of the modified layer. During the second shot peening treatment, the Almen intensity is reduced during the shot peening process to suppress surface cracking in the later stages of shot peening. Finally, the alloy surface is repaired through a third shot peening treatment to remove surface protrusions and burrs, reduce the surface roughness of the alloy, and improve the surface quality of the aluminum alloy. Attached Figure Description

[0023] Figure 1 The fine grain layer thickness and surface roughness of the alloys after treatment in Example 1 and the comparative example of this invention are shown.

[0024] Figure 2 This is an electron microscope scan image of Embodiment 1 of the present invention.

[0025] Figure 3 This is a metallographic image of Comparative Example 1 of the present invention.

[0026] Figure 4 This is the metallographic image of Comparative Example 2 of the present invention. Detailed Implementation

[0027] The present invention will be further described in detail below. Unless otherwise specified, the instruments or materials used in the present invention are commercially available.

[0028] Example 1

[0029] This embodiment of a method for low-temperature gradient mechanical strengthening of alloy surfaces includes the following steps:

[0030] (1) Surface cleaning

[0031] Take a cylindrical (φ30×10mm) workpiece made of 6061 aluminum alloy. Use #600 and #1000 sandpaper to grind the surface of the workpiece in turn to remove the oxide layer on the material surface. Then use a non-layered cloth soaked in 60% volume concentration alcohol solution to wipe the surface repeatedly to remove surface impurities.

[0032] Cleaning the surface of aluminum alloy materials is to prevent impurities present on the surface from embedding into the aluminum matrix during shot peening, causing contamination of the modified layer and affecting the performance of the workpiece. Different grit sandpapers are used to polish the surface to be shot peened, and the debris left from the sandpaper polishing is removed by wiping with alcohol.

[0033] (2) Workpiece clamping

[0034] Transfer the workpiece to the SP1200 pneumatic shot peening machine, fix the workpiece with a cylindrical cast iron clamp, expose only the surface to be processed to the air, and wrap the other surfaces with a cylindrical mold. Fix the workpiece with φ10mm screws, and adjust the distance between the shot peening test machine nozzle and the workpiece surface to 150mm.

[0035] (3) Low temperature cooling

[0036] The material surface was cooled by liquid nitrogen spraying. The flow control valve of the self-pressurized liquid nitrogen container was adjusted to make the spray pressure of the nozzle 1.5 bar. The surface temperature of the material was monitored by a contact thermocouple. After the surface temperature was reduced to -160℃, cooling continued for 5 minutes.

[0037] To improve the grain refinement effect during the shot peening process of aluminum alloy, this embodiment uses a low-temperature medium to cool the workpiece, thereby suppressing the dynamic recovery that occurs during the deformation of the aluminum alloy. The cooling medium can be liquid nitrogen or liquid helium, and the cooling method is to directly spray the sample surface. Alternatively, other methods can be used as needed, such as equipping a low-temperature chamber in the test environment and controlling the temperature by vaporizing liquid nitrogen to absorb heat.

[0038] (4) Gradient shot peening:

[0039] 4-1: High-energy shot peening treatment (first shot peening treatment) is performed on the cooled material surface. The shot type is ceramic shot with a diameter of 0.5mm. The pressure of the pneumatic shot peening machine is adjusted to achieve an Almen intensity of 0.25mmA and a surface coverage of 500%. During the shot peening process, the workpiece rotates at 20 revolutions per minute.

[0040] 4-2: The surface of the material after high-energy shot peening is subjected to low-temperature cooling treatment again (the process parameters are the same as in step (3)), and then a second shot peening treatment is performed: the pressure of the pneumatic shot peening machine is reduced, the mechanical shot peening Almen intensity is adjusted to 0.15mmA, so that the surface coverage of the material is increased from 500% to 1000%, and the parameters such as shot type and shot diameter are the same as in step (4).

[0041] 4-3: Perform low-temperature cooling treatment on the surface of the material after the second shot peening treatment (process parameters are the same as in step (3)), and then perform the third shot peening treatment: change the shot type to glass shot with a diameter of 0.05mm, adjust the pressure of the pneumatic shot peening machine to make the Almen strength 0.05mmN and the surface coverage 1500%, and the surface repair is completed.

[0042] (5) Remove the workpiece and clean the surface with a high-pressure air gun.

[0043] The gradient shot peening of this invention comprises three parts: high-energy shot peening (first shot peening treatment), conventional shot peening (second shot peening treatment), and surface repair (third shot peening treatment). High-energy shot peening achieves sufficient grain refinement of the material through high strain rate shear deformation, combined with the low recovery characteristics of the material under ultra-low temperature conditions. Conventional shot peening reduces the impact energy of the shot, suppressing the formation of defects such as microcracks and micropores in the later stages of shot peening. Surface repair utilizes low-energy, small-scale shot to remove burrs and local protrusions from the workpiece surface, reducing the surface roughness of the material. This invention solves the problems of shallow modified layer thickness, insufficient grain refinement, and high surface roughness in mechanical shot peening, and also suppresses the generation of microcracks, thereby improving the performance of aluminum alloy components.

[0044] Comparative Example 1

[0045] This comparative example describes a low-temperature gradient mechanical strengthening method for alloy surfaces. Steps (1), (2), and (3) are the same as in the example. In step (4), the same shot peening treatment is performed twice, and no further surface repair treatment (third shot peening treatment) is performed. The shot peening parameters for steps 4-1 and 4-2 are as follows: the shot type is ceramic shot, the shot diameter is 0.5 mm, the surface coverage is 1000%, the mechanical shot peening Almen intensity reaches 0.25 mmA, and the workpiece rotates at 20 revolutions per minute during the shot peening process.

[0046] Comparative Example 2

[0047] This comparative example describes a low-temperature gradient mechanical strengthening method for alloy surfaces. Steps (1) and (2) are the same as in the example, except that steps (3) and (4) do not include low-temperature cooling treatment. The temperatures during the first shot peening treatment, the second shot peening treatment, and the third shot peening treatment are at room temperature.

[0048] Figure 1 The fine grain layer thickness and surface roughness of the alloys after shot peening in Examples 1, 1, and 2 show that the fine grain layer thicknesses after shot peening in Examples 1, 1, and 2 are 120 μm, 117 μm, and 110 μm, respectively, and the surface roughnesses are 5 μm, 10 μm, and 8 μm, respectively. The above results prove that the method in Example 1 can effectively increase the thickness of the modified layer and significantly reduce the surface roughness.

[0049] like Figure 2 , 3 As shown in Figures 4 and 5, the alloy prepared by the method of the present invention does not have microcracks, while Comparative Examples 1 and 2 both have microcracks.

[0050] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the present invention, should fall within the protection scope of the present invention.

Claims

1. A method for low-temperature gradient mechanical strengthening of alloy surfaces, characterized in that: Includes the following steps: S1. The alloy surface after cleaning is subjected to low-temperature treatment, and the temperature of the low-temperature treatment is -160 to -196℃. S2. The alloy surface is subjected to a first shot peening treatment, a low-temperature treatment, a second shot peening treatment, a low-temperature treatment, and a third shot peening treatment in sequence. The Almen intensities of the first, second, and third shot peening treatments are A1, A2, and A3, respectively, satisfying A1 > A2 > A3. The diameters of the projectiles in the first, second, and third shot peening treatments are D1, D2, and D3, respectively, satisfying D1 ≥ D2 > D3.

2. The low-temperature gradient mechanical strengthening method for alloy surfaces according to claim 1, characterized in that: A1 is 0.15–0.2 mmA, A2 is 0.15–0.2 mmA, and A3 is 0.02–0.1 mmN.

3. The low-temperature gradient mechanical strengthening method for alloy surfaces according to claim 2, characterized in that: D1 is 0.5–0.8 mm, D2 is 0.5–0.8 mm, and D3 is 0.05–0.1 mm.

4. The method for low-temperature gradient mechanical strengthening of alloy surfaces according to any one of claims 1 to 3, characterized in that: During the first shot peening process, the distance between the nozzle and the alloy surface is 100-200 mm, the shot type is ceramic shot or cast steel shot, and the surface coverage is 500%-1000%.

5. The low-temperature gradient mechanical strengthening method for alloy surfaces according to claim 4, characterized in that: During the second shot peening process, the distance between the nozzle and the alloy surface is 100-200 mm, the shot type is ceramic shot or cast steel shot, and the surface coverage is 500%-1000%.

6. The low-temperature gradient mechanical strengthening method for alloy surfaces according to claim 5, characterized in that: During the third shot peening process, the distance between the nozzle and the alloy surface is 100-200 mm, the shot type is glass shot, and the surface coverage is 1500%-2500%.

7. The method for low-temperature gradient mechanical strengthening of alloy surfaces according to any one of claims 1 to 3, characterized in that: During the first, second, and third shot peening processes, the alloy surface rotates relative to the nozzle.

8. The method for low-temperature gradient mechanical strengthening of alloy surfaces according to any one of claims 1 to 3, characterized in that: During the cryogenic treatment, the cooling medium is liquid nitrogen or liquid helium.

9. The method for low-temperature gradient mechanical strengthening of alloy surfaces according to any one of claims 1 to 3, characterized in that: The surface cleaning includes the following steps: first, sandpaper is used to polish the alloy surface, and then alcohol is used to clean away the debris on the alloy surface.

10. The low-temperature gradient mechanical strengthening method for alloy surfaces according to claim 9, characterized in that: The alloy surface was polished using sandpaper of different grits.

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