• Chinese Journal of Lasers
  • Vol. 48, Issue 18, 1802004 (2021)
Wei Wang1, Jie Shen1, Weijun Liu1、*, Hongyou Bian1, Qiang Li1, and Yu Zhou2
Author Affiliations
  • 1School of Mechanical Engineering, Shenyang University of Technology, Shenyang, Liaoning 110870, China
  • 2Shenyang Pakalaijing Co., Ltd., Shenyang, Liaoning 110042, China
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    DOI: 10.3788/CJL202148.1802004 Cite this Article Set citation alerts
    Wei Wang, Jie Shen, Weijun Liu, Hongyou Bian, Qiang Li, Yu Zhou. Effect of Scanning Speed of Galvanometer on Surface Oxide Layer of TA15 Titanium Alloy in Pulsed Laser Cleaning[J]. Chinese Journal of Lasers, 2021, 48(18): 1802004 Copy Citation Text show less

    Abstract

    Objective TA15 titanium alloy is often used to manufacture aircraft partitions, wall plates, welding bearing frames, and aircraft engine parts. These parts often need to withstand high temperatures and various stresses. However, the oxide layer on the surface of such parts reduces its welding performance, electrical conductivity, and bonding with the coating; therefore, it is necessary to clean the oxide layer film regularly. Compared with the traditional cleaning methods, laser cleaning technology has the advantages of high precision, broad applicability, simple process, and clean and green. As a new type of laser, pulsed fiber laser has the advantages of high photoelectric conversion efficiency, good beam quality, and high reliability compared with other lasers. This can solve the problems of poor consistency and low efficiency for cleaning some parts of the existing aircraft. This laser cleaning breaks the technical bottleneck of the traditional aircraft cleaning process regarding the cleaning mechanism, which is conducive to improving aircraft re-service safety and service life. It provides the scientific basis and technical support for the popularization and application of laser cleaning technology in aviation and other major equipment. This also ensures the safety of equipment in service to promote the green and high-quality development of Chinese industries including aviation, marine equipment, and rail transit.

    Methods In this study, a TA15 titanium alloy plate with oil stain and an oxide layer on the original surface was used. First, we used an IPG pulsed fiber laser and different scanning speeds of galvanometers to clean the original surface of TA15. Then, the surface morphologies of TA15 before and after the laser cleaning were observed using an ultra-depth three-dimensional field microscope to determine the feasibility of laser cleaning the oil stain and oxide layer on the TA15 surface. Then, a scanning electron microscope, an energy spectrum analyzer, and an X-ray diffractometer were used to observe and analyze the effect of different scanning speeds of galvanometers on the surface morphology, surface-element content, and surface composition of the cleaned TA15 surface. Simultaneously, the removal mechanism of the oil stain and oxide layer on the TA15 surface was studied. Finally, the hardness of the TA15 surface before and after the cleaning was tested using Vickers hardness tester to explore the influence of laser cleaning on the TA15 surface and the relationship between the scanning speed of the galvanometer and hardness during the laser cleaning.

    Results and Discussions After pulsed laser cleaning, the original black surface of TA15 becomes white and bright. The scanning speed of the galvanometer has a certain influence on the cleaning effect [Fig.1(a) and Fig.4]. When other laser cleaning process parameters remain unchanged, the overlap ratio of galvanometer spot increases with the decrease of scanning speed. This leads to an increase in the laser energy absorbed by the cleaning surface so that the porous and loose oxide layer on the TA15 surface can be removed. Moreover, the surface cleaned with the small scanning speed of the galvanometer is smoother than the surface cleaned with the large scanning speed, and the removal effect of the oxide layer is also more obvious [Fig.1(b) and Fig.5]. Combined with the principle of laser cleaning and the oxide debris observed on the surface of the TA15 alloy, it can be inferred that gasification and phase-explosion mechanisms are followed during the laser cleaning process for the oxide layer and oil stain on the TA15 surface. Because the air and moisture contained in the porous structure of the original oxide layer explode under the irradiation of the laser, phase-explosion is caused in the cleaning surface. Additionally, some oil stain can be attached to the oxide layer debris generated by the phase-explosion and removed together (Fig.6). Due to the element content changes on the cleaning surface, as the scanning speed of the galvanometer increases from 7000 mm·s -1 to 10000 mm·s -1, the Ti-element content on the TA15 surface first increases and then decreases, while the O-element content first decreases and then increases (Fig.7). The oil stain and oxide layer on the TA15 surface cannot be well cleaned when very high scanning speed is used. However, very low scanning speed can easily cause thermal oxidation of the cleaned surface and generate new Al2O3 and TiO2 layers that adhere to the cleaned surface (Fig.8). Through the analysis of the change of the hardness of the cleaned surface, it is concluded that the plasma and phase-explosions can cause the plastic deformation of the TA15 surface and the refinement of the grain, which can produce the effect of laser shock strengthening and improve the surface hardness of TA15. With the decrease of scanning speed, the effect of laser shock strengthening is also improved (Fig.9).

    Conclusions The scanning speed of the galvanometer in pulsed laser cleaning is an important factor influencing the cleaning effect of oil stain and oxide layer on the TA15 surface, and the removal mechanisms of the oil stain and oxide layer on the TA15 surface are mainly gasification and phase-explosion mechanisms. When the scanning speed increases from 7000 mm·s -1 to 10000 mm·s -1, the surface cleaning effect of TA15 is the best at the scanning speed of 8000 mm·s -1. At this time, the Ti-element content of the cleaned surface reaches the highest value of 79.47%, and the O-element content reaches the lowest value of 8.62%; the surface Al2O3 is almost removed, and the TiO2 content is low. Laser cleaning can strengthen the TA15 surface by laser shock and improve the hardness of the cleaning surface. Reducing the scanning speed of the galvanometer will enhance the effect of laser shock strengthening and increase the hardness of the cleaned surface.

    Wei Wang, Jie Shen, Weijun Liu, Hongyou Bian, Qiang Li, Yu Zhou. Effect of Scanning Speed of Galvanometer on Surface Oxide Layer of TA15 Titanium Alloy in Pulsed Laser Cleaning[J]. Chinese Journal of Lasers, 2021, 48(18): 1802004
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