激光除漆对铝合金飞机蒙皮微观组织的影响

Influence of Laser Paint Removal on Microstructure of Aluminum Alloy Aircraft Skin

目的探究激光除漆对铝合金飞机蒙皮基体近表层(15μm)微观组织的影响规律,阐明近表层微观组织变化与显微硬度的内在联系。方法采用纳秒脉冲红外激光去除2024-T3铝合金飞机蒙皮表面漆层,通过调节激光能量密度,分别除漆至基体阳极氧化层、铝合金、铝合金表面熔融。利用激光扫描共聚焦显微镜(LSCM)表征漆层的剥离程度及基体的表面形貌。通过超景深三维显微镜(OM)、扫描电子显微镜(SEM)、Image-Pro Plus软件表征Keller试剂腐蚀后铝合金基体近表层的微观组织。采用数显显微维氏硬度计测量基体剖面的显微硬度。结果在激光能量密度为4.26 J/cm^(2)时,相较于原始基体,阳极氧化层较完整,其基体的表面粗糙度接近于原始基体(未除漆),近表层的微观组织无明显改变,近表层的显微硬度增加了1.6%。当除漆至铝合金基体表面完整时(15.25 J/cm^(2)),相对于原始基体,其表面粗糙度降低,近表层的微观组织无明显改变,近表层的显微硬度增加了4.8%。在激光能量密度为27.79 J/cm^(2)时,铝合金表面熔融,其表面粗糙度相对于原始基体增大,近表层的晶粒显著细化,其显微硬度增加了17.3%。结论采用合适的激光能量密度对铝合金飞机蒙皮进行激光除漆,不会显著改变其基体近表层的微观组织。在较高能量密度下,铝合金近表层会发生晶粒细化,导致显微硬度显著增加。

The objective of this study is to investigate the influence of laser paint removal on the microstructure of the near-surface layer(15μm)of the aluminum alloy aircraft skin.Consequently,the internal relationship between the microstructural changes in the near-surface layer and the corresponding microhardness variations would be elucidated.To achieve the research objectives,a comprehensive experimental methodology was employed.A nanosecond-pulsed infrared laser was utilized to remove the surface paint layer from the 2024-T3 aluminum alloy aircraft skin firstly.The laser energy density was precisely adjusted to selectively remove the paint layer to different depths,including the anodized layer,the aluminum alloy substrate,and the molten aluminum alloy surface.And then,the extent of paint removal and the surface morphology of the substrate were evaluated using advanced techniques such as laser scanning confocal microscopy(LSCM).Furthermore,state-of-the-art imaging techniques,including high-resolution three-dimensional optical microscopy(OM),scanning electron microscopy(SEM),and Image-Pro Plus software,were employed to characterize the microstructural changes in the near-surface layer of the aluminum alloy substrate after corrosion with Keller's reagent.Finally,the microhardness profiles of the substrate were analyzed with a digital micro Vickers hardness tester.The results showed that compared with the original substrate,at a low laser energy density of 4.26 J/cm^(2),the anodized layer remained intact,exhibiting preserved structural integrity.The surface roughness and maximum height of the aluminum alloy substrate closely resembled those of the unpainted substrate,indicating minimal surface alteration.Microstructural analysis of the near-surface layer revealed no significant changes compared with the initial state.However,a slight increase in microhardness of approximately 1.6%was observed,suggesting a marginal improvement in the material's resistance to indentation.At a relatively high laser energy density of 15.25 J/cm^(2),the aluminum alloy surface remained undamaged,displaying reduced surface roughness and maximum height compared with the original substrate.Microstructural analysis confirmed that the near-surface layer exhibited similar characteristics to those of the unpainted substrate,indicating negligible microstructural modifications.However,a notable enhancement in microhardness of approximately 4.8%was observed,indicating an improvement in the material's hardness and strength.Increasing the laser energy density to 27.79 J/cm^(2)resulted in localized melting of the aluminum alloy surface,leading to amplified surface roughness and maximum height compared to the initial state.The laser paint removal process induced grain refinement within the near-surface region,resulting in a significant increase in microhardness of approximately 17.3%.This substantial enhancement in microhardnesscould be attributed to the refined microstructure,which enhanced the material's resistance to deformation and improved its mechanical properties.In conclusion,when the paint was removed down to the anodized layer,no significant changes were observed in the microstructure of the near-surface layer,but a slight increase in microhardness could be detected.With the increasing laser energy density,the paint removal extended to the aluminum alloy substrate,resulting in a more complete preservation of the near-surface microstructure without significant changes,and a further increase in microhardness.Therefore,it can be indicated that laser paint removal of aluminum alloy aircraft skin under appropriate parameters will not significantly change the microstructure of the near surface layer of the matrix material.However,when the paint removal reaches the aluminum alloy and causes surface melting,the refinement of the near-surface grain structure and a consequently significant increase in microhardness will occur,which will result in the skin not being able to meet the requirements of safe service after laser paint removal.