WO2020082846A1 - 一种激光冲击强化方法 - Google Patents

一种激光冲击强化方法 Download PDF

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Publication number
WO2020082846A1
WO2020082846A1 PCT/CN2019/099029 CN2019099029W WO2020082846A1 WO 2020082846 A1 WO2020082846 A1 WO 2020082846A1 CN 2019099029 W CN2019099029 W CN 2019099029W WO 2020082846 A1 WO2020082846 A1 WO 2020082846A1
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area
strengthened
laser
surface roughness
treatment
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French (fr)
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卢国鑫
张永康
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Guangdong University of Technology
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Guangdong University of Technology
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D10/00—Modifying the physical properties by methods other than heat treatment or deformation
    • C21D10/005—Modifying the physical properties by methods other than heat treatment or deformation by laser shock processing

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  • the invention belongs to the technical field of surface strengthening treatment of metal materials, and particularly relates to a laser impact strengthening method.
  • Laser shock is a new technology that uses strong laser-induced shock waves to strengthen metals, which can greatly enhance the durability of metal materials. Consistent with the traditional surface strengthening technology, the laser impact treatment also achieves the strengthening effect through the surface strong plastic deformation. However, for the parts to be strengthened with low surface finish, laser shock treatment often cannot achieve a better surface strengthening effect.
  • the processing method of laser shock for parts to be strengthened with low surface finish is to change the process parameters of laser shock. However, it is a relatively costly task to improve the laser impact strength by changing the laser impact process parameters. How to achieve better surface strengthening of the metal parts with low surface finish to be processed without changing the conditions of the established laser impact process The effect is a problem that technicians currently need to solve.
  • the present invention provides a laser shock strengthening method for solving the problem of parts to be strengthened whose surface finish is not high, and the laser shock treatment often fails to achieve a better surface strengthening effect.
  • a laser shock strengthening method includes the following steps:
  • the finishing treatment is polishing treatment.
  • step a) further includes: determining the region to be strengthened of the metal part to be processed.
  • the arithmetic mean deviation Ra of the contour of the surface of the area to be strengthened after the finishing treatment is less than 1 ⁇ m.
  • the laser shock processing method is point-by-point processing.
  • the surface of the area to be strengthened after the smoothing treatment is coated with an absorption layer and a constraining layer in sequence.
  • the absorption layer is black tape or black paint.
  • the constraining layer is deionized water curtain or K9 glass.
  • the present invention provides a laser shock strengthening method, which includes the following steps: a) Finishing the area to be strengthened of the metal part to be processed to reduce the surface roughness of the area to be strengthened to the arithmetic mean deviation of the contour Ra is less than 3 ⁇ m; b) Laser-shocked the area to be strengthened after the finishing treatment to obtain a strengthened area.
  • the surface to be strengthened of the metal parts to be processed is smoothed to reduce the surface roughness of the area to be strengthened to an arithmetic mean deviation Ra of the contour less than 3 ⁇ m, and then laser shock can be performed without changing the laser shock process parameters , To achieve a significant surface strengthening effect.
  • FIG. 1 is a schematic diagram of the actual effect area change of a pulsed laser on the surface of a metal part to be processed with different surface roughness in an embodiment of the present invention
  • 3 is the surface state of the area to be strengthened by 800 # sandpaper grinding treatment in the embodiment of the present invention.
  • FIG. 5 is a reinforced area obtained by laser impacting the area to be strengthened after mechanical polishing in an embodiment of the present invention
  • FIG. 6 is the reinforced area obtained by laser impacting the area to be strengthened by 800 # sandpaper grinding in the embodiment of the present invention
  • the invention provides a laser impact strengthening method for solving the problem of parts to be strengthened whose surface finish is not high, and the laser impact treatment often cannot achieve a better surface strengthening effect.
  • a laser shock strengthening method includes the following steps:
  • FIG. 1 is a schematic diagram of the actual effect area change of the pulse laser on the surface of the metal part to be processed with different surface roughness in the embodiment of the present invention.
  • the pulse laser 2 can form a high temperature and high pressure plasma 3 in a very short time under the action of a special coating.
  • the high temperature and high pressure plasma 3 explodes on the surface of the metal part 1 to be processed and forms a shock wave propagating into the metal part 1 to be processed 4.
  • the magnitude of the shock wave 4 induced by the pulse laser 2 and the action time determine the intensity of the laser shock treatment, and the actual area of the pulse laser on the part directly affects the magnitude of the shock wave 4 by changing the laser power density. For the areas to be strengthened with different surface roughnesses, the actual active area of the pulsed laser is different.
  • the first surface roughness is less than the second surface roughness
  • the pulsed laser acts on the area to be strengthened 5 with the first surface roughness and the area to be strengthened 7 with the second surface roughness
  • Area 5 has a pulse laser area that is approximately equal to the beam size.
  • the actual area of the pulse laser for the area to be strengthened on the second surface roughness 8 is due to the presence of surface undulations compared to the pulse laser for the area to be strengthened on the first surface roughness.
  • the actual active area 6 showed a certain increase.
  • the principle of the laser shock strengthening method of the present invention is that: the irradiation area of the laser beam on the surface of the metal part 1 to be processed during the laser shock is an important index that determines the actual laser power density, and the laser power density and the laser-induced shock wave in the metal to be processed
  • the force on the surface of part 1 is directly related.
  • the irradiated area of the laser beam is the actual effective area of the laser shock wave, while for the area with high surface roughness to be strengthened, the actual area of the laser shock wave exceeds the laser beam's Irradiated area.
  • the laser shock strengthening method of the present invention enables the metal part 1 to be processed to introduce a residual compressive stress distribution with a large depth and a high surface amplitude through laser shock treatment after a simple surface treatment, effectively improves the residual compressive stress field strength, and is suitable for various types of Laser shock processing of metal parts 1.
  • the area to be strengthened of the metal part 1 to be processed is smoothed to reduce the surface roughness of the area to be strengthened to an arithmetic mean deviation Ra of the contour of less than 3 ⁇ m, and then the laser shock is applied. Decreasing to increase the laser power density can achieve a significant surface strengthening effect without changing the laser shock process parameters.
  • the laser shock strengthening method is simple and easy, without the need to determine new laser shock process parameters, the surface residual pressure of the strengthened area The depth of the stress and residual compressive stress layers are significantly increased, with a higher residual compressive stress field strength, which helps to reduce processing costs and improve strengthening quality and strengthening efficiency.
  • the polishing treatment is polishing treatment
  • the polishing treatment is preferably mechanical polishing treatment.
  • the area to be strengthened of the metal part 1 to be processed needs to be determined according to actual needs, and then the area to be strengthened is polished or polished according to the surface strengthening requirements, and then the area to be strengthened after the polishing treatment Use the established laser impact process to strengthen the laser impact.
  • step a) before step a), it further includes: determining a region to be strengthened of the metal part 1 to be processed.
  • the area to be strengthened is determined according to the specific failure form of the part 1 to be processed in service, etc., and the area to be strengthened that requires a more obvious strengthening effect is determined.
  • the surface strengthening treatment is performed on all locations or only the most prone to failure, there will be failure location transfer, etc., need to pass the failure analysis Experiment to determine the best reinforced area.
  • Failure analysis tests include tensile tests and / or fatigue tests.
  • the failure analysis tests are used to determine the failure location of the parts to be processed during service, that is, the areas that require the most strengthening treatment.
  • the areas with high surface roughness to be strengthened will get relatively poor strengthening effect.
  • the surface roughness needs to be significantly reduced by finishing treatment; for the local areas where the strengthening effect is slightly reduced due to the high surface roughness, A relatively low degree of surface roughness reduction is required.
  • the area where the strengthening effect is slightly weakened can be reduced by grinding to reduce the surface roughness of the area to be strengthened to Ra to 2 ⁇ m, and the strengthening effect is greatly reduced
  • the surface roughness of the area to be strengthened can be reduced to 1 ⁇ m Ra by grinding and polishing; if the initial surface roughness Ra of the area to be strengthened of the metal part 1 to be processed is 3 ⁇ m, the area where the strengthening effect is slightly weakened can be passed
  • the mechanical polishing process reduces the surface roughness of the area to be strengthened to Ra of 1 ⁇ m, and the area where the strengthening effect is relatively greatly weakened can be reduced to Ra of 0.5 ⁇ m by electrolytic polishing.
  • the embodiment of the present invention needs to characterize the surface strengthening effect of the region to be strengthened of the metal part 1 to be processed, and determine the gap between the region to be strengthened and the target strengthening effect at different positions.
  • the surface to be strengthened is subjected to a finishing treatment according to the surface strengthening requirements, and the surface roughness of the area to be strengthened is reduced by grinding treatment and / or polishing treatment.
  • the surface strengthening requirement specifically refers to the degree of improvement of the surface strengthening effect when the actual strengthening effect obtained under the existing surface quality conditions of the area to be strengthened is not the same as the target strengthening effect.
  • the surface strengthening effect refers to the indicators of the residual compressive stress field inside the metal part 1 to be processed and the microstructure changes within a certain depth of the surface layer.
  • the surface strengthening effect needs to be determined according to actual requirements. Polishing treatment is easier than grinding treatment to obtain better surface quality in the area to be strengthened. Relative to the grinding treatment, polishing the area with high surface roughness to be strengthened can make the laser impact strength more greatly improved.
  • the average arithmetic deviation Ra of the contour of the surface of the area to be strengthened after sandpaper grinding treatment is greater than 3 ⁇ m, and the average arithmetic deviation Ra of the contour of the surface of the area to be strengthened after mechanical polishing treatment is less than 1 ⁇ m.
  • the laser shock processing method is point-by-point processing, and the point-by-point processing specifically adopts a processing method in which a mechanical arm moves and the laser shock is processed.
  • step a) and before step b), the method further includes:
  • the surface of the area to be strengthened after the finishing treatment is coated with an absorption layer and a constraining layer in sequence.
  • the absorption layer is black tape or black paint.
  • the constraining layer is deionized water curtain or K9 glass.
  • the metal parts to be processed in the embodiment of the present invention are 304 stainless steel materials. Please refer to FIG. 2 to FIG. 4, which are the regions to be strengthened by mechanical polishing treatment, 800 # sandpaper grinding treatment and 200 # sandpaper grinding treatment in the embodiment of the present invention.
  • the surface roughness Ra of the to-be-strengthened area is 0.822 ⁇ m , 3.243 ⁇ m and 3.749 ⁇ m.
  • the above-mentioned areas to be strengthened with different surface treatments are subjected to laser shock.
  • the laser shock treatment is carried out on a pulsed laser.
  • the laser beam diameter is 3 mm
  • the laser energy is 8.5 J
  • the pulse width is 18 ns
  • the absorption layer is black tape
  • the constraining layer is deionized water curtain.
  • FIG. 5 to FIG. 7 are the strengthened area obtained by laser impact on the area to be strengthened after mechanical polishing, 800 # sandpaper grinding and 200 # sandpaper grinding in the embodiment of the present invention, and the surface of the strengthened area
  • the roughness Ra is 4.073 ⁇ m, 3.397 ⁇ m and 3.835 ⁇ m in sequence
  • the surface roughness increment ⁇ Ra is 3.332 ⁇ m, 0.154 ⁇ m and 0.086 ⁇ m in order compared with the area to be strengthened.
  • the change of surface roughness directly reflects the plastic deformation degree of the metal parts to be processed under the action of external force.
  • the incremental change of surface roughness before and after laser shock treatment can qualitatively characterize the degree of change of the plastic deformation of the metal parts to be processed, and also shows the different actual processing strength of laser shock treatment.
  • the surface roughness of the area to be strengthened is greater than 3 ⁇ m, and the laser impact treatment makes the surface roughness increment ⁇ Ra less than 0.2 ⁇ m; for the mechanical polishing metal parts to be processed, the area to be strengthened
  • the surface roughness is reduced to Ra 1 ⁇ m or less, and the laser impact treatment makes the surface roughness increase ⁇ Ra higher than 3.3 ⁇ m.
  • the introduction of residual compressive stress is the most important reason for laser shock treatment to improve service performance such as material fatigue.
  • the half-height width of the diffraction peak of the metal material reflects the changes in the microstructure of the material. For example, the results of microstructure changes such as dislocation configuration, elastic energy storage density and stacking faults will cause diffraction lines. Widening.
  • Example 1 After the laser shock is applied to the area to be strengthened after mechanical polishing, 800 # sandpaper grinding and 200 # sandpaper grinding, the strengthened area is obtained, and the surface residual stress (RS) and X-ray are detected by an X-ray stress meter For FWHM, no less than 3 positions should be taken for each enhanced area, and the results should be averaged. The results are shown in Table 1.
  • Table 1 The residual stress and X-ray diffraction half-height data of the strengthened area obtained by laser impact of the area to be strengthened after different surface treatments
  • the stainless steel sample with a surface roughness Ra of 0.822 ⁇ m was obtained after mechanical polishing.
  • the surface roughness increment ⁇ Ra was 3.332 ⁇ m; and 800 # sandpaper after mechanical grinding
  • the stainless steel sample with a surface roughness Ra of 3.243 ⁇ m has a surface roughness increment ⁇ Ra of only 0.154 ⁇ m after laser shock treatment with the same parameters.
  • the laser impact strength of samples with higher surface roughness was improved by changing the laser impact process parameters, and the following results were obtained: after mechanical grinding of 800 # sandpaper, stainless steel samples with a surface roughness Ra of 3.243 ⁇ m were obtained by laser The energy of 9J is used to increase the laser power density of the laser shock treatment to increase the intensity of the laser shock.
  • the surface roughness is increased to Ra of 4.012 ⁇ m, and the surface roughness can be calculated
  • the degree increment ⁇ Ra is 0.769 ⁇ m, indicating that the degree of plastic deformation on the surface of the material has increased, but the increase is much lower than the effect of reducing the initial surface roughness of the sample by mechanical polishing; in addition, for 800 #
  • the samples after mechanical grinding of sandpaper were subjected to laser impact treatment to increase the laser energy.
  • the ablation phenomenon of the black tape absorption layer on the surface of stainless steel samples was obvious, indicating that it is not practical to increase the laser impact intensity by increasing the laser power density.

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Abstract

一种激光冲击强化方法，包括以下步骤：a)对待加工金属零件的待强化区域进行光洁化处理将所述待强化区域的表面粗糙度降低至轮廓算术平均偏差Ra小于3μm；b)对经所述光洁化处理的待强化区域进行激光冲击，得到强化区域。对待加工金属零件的待强化区域进行光洁化处理将待强化区域的表面粗糙度降低至轮廓算术平均偏差Ra小于3μm，再进行激光冲击，能够在不改变激光冲击工艺参数的条件下，实现显著的表面强化效果。

Description

一种激光冲击强化方法 技术领域
本发明属于金属材料表面强化处理技术领域，尤其涉及一种激光冲击强化方法。
背景技术
激光冲击是一种利用强激光诱导的冲击波来强化金属的新技术，能够大幅度增强金属材料的耐久性。与传统表面强化技术一致，激光冲击处理也通过表面强烈塑性变形的方式来实现强化效果。但是，对于表面光洁度不高的待强化零件，激光冲击处理往往不能达到较好的表面强化效果。目前，针对表面光洁度不高的待强化零件的激光冲击的处理方式是变更激光冲击的工艺参数。然而，通过激光冲击工艺参数的变更以提高激光冲击强度是一项成本较高的工作，如何在不改变既定激光冲击工艺的条件下使得表面光洁度不高的待加工金属零件达到较好的表面强化效果是技术人员目前需要解决的问题。
发明内容
有鉴于此，本发明提供了一种激光冲击强化方法，用于解决表面光洁度不高的待强化零件，激光冲击处理往往不能达到较好的表面强化效果的问题。
本发明的具体技术方案如下：
一种激光冲击强化方法，包括以下步骤：
a)对待加工金属零件的待强化区域进行光洁化处理将所述待强化区域的表面粗糙度降低至轮廓算术平均偏差Ra小于3μm；
b)对经所述光洁化处理的待强化区域进行激光冲击，得到强化区域。
优选的，所述光洁化处理为抛光处理。
优选的，步骤a)之前，还包括：确定所述待加工金属零件的所述待强化区域。
优选的，经所述光洁化处理后的待强化区域表面的轮廓算术平均偏差Ra小于1μm。
优选的，所述激光冲击的处理方式为逐点加工。
优选的，步骤a)之后，步骤b)之前，还包括：
在经所述光洁化处理后的待强化区域表面依次涂覆吸收层和约束层。
优选的，所述吸收层为黑色胶带或黑漆。
优选的，所述约束层为去离子水幕或K9玻璃。
综上所述，本发明提供了一种激光冲击强化方法，包括以下步骤：a)对待加工金属零件的待强化区域进行光洁化处理将所述待强化区域的表面粗糙度降低至轮廓算术平均偏差Ra小于3μm；b)对经所述光洁化处理的待强化区域进行激光冲击，得到强化区域。本发明中，对待加工金属零件的待强化区域进行光洁化处理将待强化区域的表面粗糙度降低至轮廓算术平均偏差Ra小于3μm，再进行激光冲击，能够在不改变激光冲击工艺参数的条件下，实现显著的表面强化效果。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍。
图1为本发明实施例中脉冲激光在不同表面粗糙度待加工金属零件表面的实际作用面积变化示意图；
图2为本发明实施例中经机械抛光处理的待强化区域的表面状态；
图3为本发明实施例中经800#砂纸研磨处理的待强化区域的表面状态；
图4为本发明实施例中经200#砂纸研磨处理的待强化区域的表面状态；
图5为本发明实施例中经机械抛光处理的待强化区域进行激光冲击后得到的强化区域；
图6为本发明实施例中经800#砂纸研磨处理的待强化区域进行激光冲击后得到的强化区域；
图7为本发明实施例中经200#砂纸研磨处理的待强化区域进行激光冲击后得到的强化区域；
图示说明：1.待加工金属零件；2.脉冲激光；3.高温、高压等离子体；4.冲击波；5.具有第一表面粗糙度的待强化区域；6.脉冲激光对于第一表面粗糙度待强化区域的实际作用面积；7.具有第二表面粗糙度的待强化区域；8.脉冲激光对于第二表面粗糙度待强化区域的实际作用面积。
具体实施方式
本发明提供了一种激光冲击强化方法，用于解决表面光洁度不高的待强化零件，激光冲击处理往往不能达到较好的表面强化效果的问题。
下面将对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
一种激光冲击强化方法，包括以下步骤：
a)对待加工金属零件的待强化区域进行光洁化处理将待强化区域的表面粗糙度降低至轮廓算术平均偏差Ra小于3μm；
b)对经光洁化处理的待强化区域进行激光冲击，得到强化区域。
请参阅图1，为本发明实施例中脉冲激光在不同表面粗糙度待加工金属零件表面的实际作用面积变化示意图。
脉冲激光2在特殊涂层作用下可于极短时间内形成高温、高压等离子体3，高温、高压等离子体3在待加工金属零件1表面发生爆炸并形成向待加工金属零件1内部传播的冲击波4。脉冲激光2诱导冲击波4的大小与作用时间共同决定了激光冲击处理的强度大小，而脉冲激光对零件的实际作用面积通过改变激光功率密度直接影响了冲击波4的大小。对于具有不同表面粗糙度的待强化区域，脉冲激光的实际作用面积有所区别。第一表面粗糙度小于第二表面粗糙度，脉冲激光分别作用于具有第一表面粗糙度的待强化区域5和具有第二表面粗糙度的待强化区域7，具有第一表面粗糙度的待强化区域5具有近似等同于光束尺寸的脉冲激光作用面积，脉冲激光对于第二表面粗糙度待强化区域的实际作用面积8则由于表面波纹状起伏的存在较脉冲激光对于第一表面粗糙度待强化区域的实际作用面积6呈现一定程度的增加。
本发明激光冲击强化方法的原理是：激光冲击过程中的激光光束在待加工金属零件1表面的辐照面积是决定实际激光功率密度的重要指标，而激光功率密度与激光诱导冲击波在待加工金属零件1表面的作用力大小直接相关。对于表面完全平整的待强化区域，激光光束的辐照面积为激光冲击波的实际作用面积，而对于表面粗糙度较高的待强化区域，激光冲击波的实际作用面 积在不同程度上超过了激光光束的辐照面积。由于实际作用面积的增大必然引起激光功率密度的降低，因此高表面粗糙度区域在激光冲击过程中将获得较弱的强化效果。对具有较高表面粗糙度的待强化区域进行平整化处理以减小激光功率密度的损失程度，可有效提高实际激光冲击强度。本发明激光冲击强化方法可使待加工金属零件1在简单的表面处理后通过激光冲击处理引入深度大且表面幅值高的残余压应力分布，有效提高残余压应力场强度，适用于各类待加工金属零件1的激光冲击处理。
本发明实施例中，对待加工金属零件1的待强化区域进行光洁化处理将待强化区域的表面粗糙度降低至轮廓算术平均偏差Ra小于3μm，再进行激光冲击，借助脉冲激光2实际作用面积的降低来增加激光功率密度，能够在不改变激光冲击工艺参数的条件下，实现显著的表面强化效果，该激光冲击强化方法简便易行，无需确定新的激光冲击工艺参数，强化区域的表面残余压应力与残余压应力层深度均有明显增大，具有更高的残余压应力场强度，有助于降低加工成本，提高强化质量和强化效率。
本发明实施例中，光洁化处理为抛光处理，抛光处理优选为机械抛光处理。
本发明实施例中，需根据实际需要确定待加工金属零件1的待强化区域，然后根据表面强化需求选择研磨处理或者抛光处理对待强化区域进行光洁化处理，再对经光洁化处理的待强化区域采用既定激光冲击工艺进行激光冲击的强化处理。
本发明实施例中，步骤a)之前，还包括：确定待加工金属零件1的待强化区域。
本发明实施例中，根据待加工零件1在服役过程中的具体失效形式等确定待强化区域，并确定需要更明显强化效果的待强化区域。当存在多处失效位置或不同区域均发生失效但失效的难易程度不同时，若对所有位置或只针对最易失效的位置进行表面强化处理，会出现失效位置转移等情况，需通过失效分析试验以确定最佳强化区域。
失效分析试验包括拉伸试验和/或疲劳试验，通过失效分析试验确定待加工零件在服役过程中会出现的失效位置，即最需进行强化处理的区域。相同 的激光冲击强化参数条件下，表面粗糙度高的待强化区域会获得相对较差的强化效果。对于因较高表面粗糙度导致强化效果有较大幅度降低的局部区域，需通过光洁化处理使表面粗糙度实现明显减小；而对于因高表面粗糙度导致强化效果有小幅减低的局部区域，则需要相对低的表面粗糙度减小程度。比如，若待加工金属零件1的待强化区域的初始表面粗糙度Ra为5μm，强化效果小幅减弱的区域可通过研磨处理将待强化区域的表面粗糙度降低至Ra为2μm，而强化效果大幅减弱的区域则可通过研磨加抛光处理将待强化区域的表面粗糙度降低至Ra为1μm；若待加工金属零件1的待强化区域的初始表面粗糙度Ra为3μm，强化效果小幅减弱的区域可通过机械抛光处理将待强化区域的表面粗糙度降低至Ra为1μm，而强化效果相对大幅减弱的区域则可通过电解抛光处理将待强化区域的表面粗糙度降低至Ra为0.5μm。对待加工金属零件1的全部待强化区域进行相同工艺参数的激光冲击处理后，不同位置表面质量的不同会导致激光冲击强化效果出现差异。本发明实施例需要对待加工金属零件1的待强化区域进行表面强化效果表征，确定不同位置待强化区域与目标强化效果的差距。
本发明实施例中，根据表面强化需求对待强化区域进行光洁化处理，通过研磨处理和/或抛光处理降低待强化区域的表面粗糙度。表面强化需求具体指待强化区域在现有表面质量条件下获得的实际强化效果与目标强化效果存在差距时，表面强化效果的提高程度。而表面强化效果则指待加工金属零件1内部残余压应力场的各项指标以及表层一定深度内的显微组织变化等方面，表面强化效果需要根据实际要求进行确定。抛光处理比研磨处理更容易使待强化区域获得较优的表面质量。相对于研磨处理，对高表面粗糙度待强化区域进行抛光处理，可使得激光冲击强度有更大幅度的提高。
经砂纸研磨处理后的待强化区域表面的轮廓算术平均偏差Ra大于3μm，而经机械抛光处理后的待强化区域表面的轮廓算术平均偏差Ra小于1μm。
本发明实施例中，激光冲击的处理方式为逐点加工，逐点加工具体为采用机械臂移动一下，激光冲击一下的处理方式。
本发明实施例中，步骤a)之后，步骤b)之前，还包括：
在经光洁化处理后的待强化区域表面依次涂覆吸收层和约束层。
本发明实施例中，吸收层为黑色胶带或黑漆。
本发明实施例中，约束层为去离子水幕或K9玻璃。
为了进一步理解本发明，下面结合具体实施例对本发明进行详细阐述。
实施例1
本发明实施例的待加工金属零件为304不锈钢材料。请参阅图2至图4，依次为本发明实施例中经机械抛光处理、经800#砂纸研磨处理和经200#砂纸研磨处理的待强化区域，待强化区域的表面粗糙度Ra依次为0.822μm、3.243μm和3.749μm。将上述经不同表面处理的待强化区域进行激光冲击，激光冲击处理在脉冲激光器上进行，激光光束直径为3mm，激光能量为8.5J，脉冲宽度为18ns，激光光束的横/纵搭接率为30％，吸收层为黑胶带，约束层为去离子水幕。请参阅图5至图7，依次为本发明实施例中经机械抛光处理、经800#砂纸研磨处理和经200#砂纸研磨处理的待强化区域进行激光冲击后得到的强化区域，强化区域的表面粗糙度Ra依次为4.073μm、3.397μm和3.835μm，与待强化区域相比，表面粗糙度增量△Ra依次为3.332μm、0.154μm和0.086μm。
表面粗糙度的变化直接反映了待加工金属零件在外力作用下的塑性变形程度。通过表面粗糙度在激光冲击处理前后的增量变化可以定性表征待加工金属零件的塑性变形量的变化程度，也表明了激光冲击处理的不同的实际加工强度。对于研磨处理的待加工金属零件，待强化区域的表面粗糙度均大于3μm，激光冲击处理使其表面粗糙度增量△Ra低于0.2μm；对于机械抛光处理的待加工金属零件，待强化区域的表面粗糙度降低至Ra 1μm以下，激光冲击处理使其表面粗糙度增量△Ra高于3.3μm。上述结果表明采用机械抛光降低待强化区域的表面粗糙度，可显著增大激光冲击处理的实际作用强度。
实施例2
引入残余压应力是激光冲击处理提高材料疲劳等服役性能的最主要原因，残余压应力值越大说明激光冲击处理的强度越高。在X射线检测过程中，金属材料衍射峰的半高宽反映了材料内部显微组织变化，例如，位错组态、弹性储能密度及层错等显微组织变化结果均会导致衍射谱线的宽化。实施例1经机械抛光处理、经800#砂纸研磨处理和经200#砂纸研磨处理的待强化区域 进行激光冲击后，得到强化区域，采用X射线应力仪检测其表面残余应力(RS)和X射线衍射半高宽(FWHM)，每个强化区域取不少于3个位置进行检测，并对结果取平均值。结果如表1所示，结果表明相对于800#砂纸研磨处理和200#砂纸研磨处理，对304不锈钢材料进行机械抛光处理后，待强化区域获得较小的表面粗糙度，再进行激光冲击处理，引入相对高的残余压应力并产生更明显的X射线衍射谱线的宽化，结果从残余压应力与显微组织变化方面证实了采用机械抛光降低待强化区域的表面粗糙度能够提高激光冲击的实际作用强度。
表1 经不同表面处理的待强化区域进行激光冲击后得到的强化区域的残余应力和X射线衍射半高宽数据
光洁化处理方式 表面残余应力(RS) X射线衍射半高宽(FWHM)
机械抛光 -330MPa 1.81°
800#砂纸研磨 -298MPa 1.72°
200#砂纸研磨 -233MPa 1.67°
对比例1
实施例中机械抛光后获得表面粗糙度Ra为0.822μm的不锈钢试样在进行实施例1中所述的激光冲击处理后的表面粗糙度增量△Ra为3.332μm；而800#砂纸机械研磨后获得表面粗糙度Ra为3.243μm的不锈钢试样在相同参数的激光冲击处理后的表面粗糙度增量△Ra仅为0.154μm。采用改变激光冲击工艺参数的方式来提高具有较高表面粗糙度的试样的激光冲击强度，得到以下结果：针对800#砂纸机械研磨后获得表面粗糙度Ra为3.243μm的不锈钢试样，通过激光能量为9J的方式来提高激光冲击处理的激光功率密度以提高激光冲击的作用强度，对其进行改变激光能量的激光冲击处理之后，其表面粗糙度提高至Ra为4.012μm，计算可得表面粗糙度增量△Ra为0.769μm，表明材料表面的塑性变形程度有增大，但增大程度远低于通过机械抛光方法对试样进行降低初始表面粗糙度带来的效果；另外，对800#砂纸机械研磨后的试样进行提高激光能量的激光冲击处理，不锈钢试样表面的黑胶带吸收层的烧蚀现象明显，表明通过增加激光功率密度来提高激光冲击强度的方法不实用。
以上所述仅是本发明的优选实施方式，应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明原理的前提下，还可以做出若干改进和润饰，这些改进和润饰也应视为本发明的保护范围。

Claims (8)

  1. 一种激光冲击强化方法，其特征在于，包括以下步骤：
    a)对待加工金属零件的待强化区域进行光洁化处理将所述待强化区域的表面粗糙度降低至轮廓算术平均偏差Ra小于3μm；
    b)对经所述光洁化处理的强化区域进行激光冲击，得到强化区域。
  2. 根据权利要求1所述的方法，其特征在于，所述光洁化处理为抛光处理。
  3. 根据权利要求1所述的方法，其特征在于，步骤a)之前，还包括：确定所述待加工金属零件的所述待强化区域。
  4. 根据权利要求1所述的方法，其特征在于，经所述光洁化处理后的待强化区域表面的轮廓算术平均偏差Ra小于1μm。
  5. 根据权利要求1所述的方法，其特征在于，所述激光冲击的处理方式为逐点加工。
  6. 根据权利要求1所述的方法，其特征在于，步骤a)之后，步骤b)之前，还包括：
    在经所述光洁化处理后的待强化区域表面依次涂覆吸收层和约束层。
  7. 根据权利要求6所述的方法，其特征在于，所述吸收层为黑色胶带或黑漆。
  8. 根据权利要求6所述的方法，其特征在于，所述约束层为去离子水幕或K9玻璃。
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