Open Access
Add to BibSonomy
Abstract
After the aluminum alloy mirror machined by single point diamond turning (SPDT), the residual tool marks and surface accuracy of the aluminum alloy mirror cannot meet the requirements of visible or ultraviolet light system. In this study, a processing method combining magnetorheological finishing (MRF) and chemical mechanical polishing (CMP) is proposed to realize the polishing of aluminum alloy mirrors with high efficiency, high precision and high-quality. Firstly, the properties and composition of passivation layer after MRF were analyzed and the polishing performance of acidic, neutral and alkaline alumina polishing fluid on passivation layer were investigated based on the computer numerical control (CNC) polishing equipment. Based on the experimental results, a new acidic nano-silica polishing fluid which is suitable for the efficient and high-quality removal of passivation layers on aluminum alloy surfaces was developed. Finally, a combined approach of MRF-CMP was used to the directly polishing of a rapidly solidified aluminum mirror (RSA-6061) with a diameter of 100 mm after SPDT. With two iterative of MRF-CMP polishing in 220 minutes, the surface accuracy of the aluminum alloy mirror was improved from 0.1λ (λ=632.8 nm) to 0.024λ, and the surface roughness (Ra) decreased from 3.6 nm to 1.38 nm. The experiment results manifest that high precision, and high-quality aluminum alloy mirror can be achieved by MRF-CMP method with the new developed acid nano-silica polishing fluid and suitable MR polishing fluid. The research results will provide a new strategy for ultra-precision direct polishing of aluminum alloy mirrors and will also give the important technical support for the extensive use of aluminum alloy mirror in visible light and ultraviolet optical systems.
© 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Aluminum alloy optical components possess several advantages, including being lightweight, cost-effective, easy to machine, having good thermal conductivity, and exhibiting excellent corrosion resistance. These properties make them suitable for high-quality and high-performance optical systems [1–3]. Recently, aluminum alloy reflectors have been widely used in optical systems such as infrared warning systems, micro/nano satellites, high resolution cameras, navigation and guidance, space exploration, and optical remote sensing [4–7]. Single-point diamond turning (SPDT) is currently the most commonly used method for manufacturing aluminum alloy mirrors. However, due to its cutting mechanism, it inevitably leaves tool marks on the surface after the cutting process [8,9]. These tool marks can result in diffraction effects and scattering on the surface of the part, thereby diminishing the optical performance of the system. To meet the performance requirements of the optical system, post-polishing process is required to improve the surface accuracy and roughness. However, aluminum alloys are very soft and complex composite materials with multiple components, which makes it a challenge to polish them. To improve the accuracy and quality of aluminum alloy surfaces, surface modification treatments are typically applied, such as using nickel phosphorus alloy or pure aluminum. The difference in thermal expansion coefficients between aluminum alloy and the nickel phosphorus modification layer will introduce bimetallic effects [10–12]. On the other hand, modifying the surface with a pure aluminum layer will result in poor machining quality and a difficult polishing task. Therefore, direct polishing is an optimal solution for achieving high precision and quality fabrication of aluminum alloy mirrors.
The feasible methods for polishing aluminum alloy mirrors include chemical mechanical polishing (CMP), magnetorheological polishing (MRF), ion beam finishing (IBF) and bonnet polishing technology. CMP can improve the surface quality of mirrors and has been used for aluminum alloy mirrors polishing ranging from a few millimeters to nearly meters. The surface accuracy can reach several tens of nanometers and roughness reach several nanometers with special polishing fluid and process [13]. However, it suffers from issues such as unstable removal efficiency and edge effects, which result in low process convergence efficiency. This is particularly challenging when it comes to polishing complex curved surfaces, as it has limited surface accuracy and is difficult to meet the requirements of high-performance optical systems. [14,15]. IBF can achieve high precision aluminum alloy components. However, due to the processing mechanism of IBF and the multi-element nature of aluminum alloy materials, it often results in micro or sub-micron scale microstructures on the polished surface. As a result, balancing surface roughness and processing efficiency in the polishing process can be very challenging [16,17]. In order to address this issue, Du proposed a new polishing method for removing tool marks on aluminum alloy mirrors. The process combines ion beam sputtering and smooth polishing to obtain an aluminum alloy reflector with a surface roughness of Ra 3.7 nm [18]. However, the processing is relatively complex, and the surface quality may not meet the requirements of visible light systems. Therefore, high efficiency and high precision polishing of aluminum alloy mirrors is still an important research topic in the processing of metal mirrors.
Magnetorheological Finishing (MRF) technology is a deterministic polishing technique that can offer high determinism and polishing efficiency, making it capable of achieving high precision, high-quality surface for various materials. It can quickly eliminate surface tool marks resulting from SPDT and improve surface accuracy [19,20]. Different from IBF, the material removal MRF results from the shearing force between MR polishing fluid and workpiece, making it non-selective for doped composite materials like aluminum alloys and achieving better surface roughness. However, due to the composition and characteristics of the MR polishing fluid, a passivation layer is formed on the surface of aluminum alloy mirrors after MRF, which will reduce the reflectivity of the aluminum alloy mirror and make it unable to meet the optical system requirements [21,22]. The key to quickly eliminating the passivation layer on aluminum alloy surface after MRF has become a critical challenge. Du proposed to remove the passivation layer (or contamination layer) by using ion beam sputtering method. The composition and thickness of the passivation layer was analyzed and experiments was conducted. This method can eliminate the passivation layer on the polished surface while maintaining the surface roughness formed by MRF. However, a surface roughness in the tens of nanometers will be an arduous task for subsequent smoothing polishing processes.
The composition and characteristics of the passivation layer on the surface of an aluminum alloy result from MRF and are influenced by the composition of the MR polishing fluid and the process parameters. It is essential to optimize the MRF process parameters, particularly the composition of the MR polishing fluid, in order to achieve high precision and low roughness polishing of aluminum alloy mirrors. It also requires the development of an effective process for the rapid removal of the passivation layer and mid-to-high frequency errors on the surface. Although CMP cannot realize the high precision polishing of aluminum alloy surfaces, this method is still effective in removing mid-to-high frequency errors and reducing surface roughness on optical surfaces [23,24]. Through the optimization of the process and polishing fluid, it is expected to become an ideal processing method for eliminating the passivation layer on the aluminum surface after MRF.
Therefore, this study utilized a specially optimized MR polishing fluid to conduct polishing of RSA-6061 (Rapidly Solidified Aluminum 6061). The composition and characteristics of the passivation layer on the RSA-6061 surface after MRF are analyzed. The polishing performance of three different aluminum oxide polishing fluids was investigated using a computer numerically controlled (CNC) polishing machine, based on the CMP method. Subsequently, an acidic nano-silica dioxide polishing fluid was developed, taking into consideration the properties and composition of the passivation layer. This fluid is capable of efficiently removing the passivation layer and achieving high-quality surfaces made of aluminum alloy. Finally, polishing experiments were carried out on the RSA-6061 part after SPDT by combining MRF and CMP. The results demonstrate that the MRF-CMP composite polishing method can effectively and quickly remove the mid-to-high frequency and passivation layer on the surface of aluminum alloy. A high precision and high surface-quality aluminum alloy mirror was obtained, with a surface accuracy of 0.024λ and a surface roughness (Ra) of 1.38 nm.
The research results have significant implications for the polishing of aluminum alloy mirrors and the widespread application of these mirrors in visible or even ultraviolet optical systems.
2. Mechanism of passivation layer of magnetorheological polishing aluminum alloy mirror
2.1 RSA-6061
RSA-6061 is developed by RSP Technology company using the rapid solidification method, which can be utilized to enhance the mechanical properties of the alloy. Compared to standard AA-6061, RSA-6061 has a much finer structure of precipitated phases and higher hardness. As shown in Fig. 1, the largest particle size of RSA-6061 is in the range of 1µm and below, which is significantly smaller than AA6061, where the largest particles measure 10-20µm [25].
Fig. 1. Scanning electron microscope (SEM) result of the fine polished RSA-6061 surface microstructure result.
Therefore, the polishing performance of RSA-6061 is better than that of standard AA-6061, making it a promising material for optical applications in the visual or even ultraviolet spectral range. The composition of RSA-6061 is shown in Table 1.
Table 1. The composition of RSA-6061
2.2 MR polishing fluid for RSA-6061
The composition and performance of the MR polishing fluid determine its polishing effect on aluminum alloy materials. MR polishing fluid primarily consists of micrometer-sized iron powders, deionized water (or oil), chemical additives, and abrasives. To prevent the iron powders from rusting, the MR polishing fluid needs to be adjusted to an alkaline pH level. However, aluminum alloy materials are amphoteric metals, which means they can react with both acidic and alkaline fluids. The extent of the reaction depends on the pH level. As shown in Fig. 2, the potential-pH diagram of the aluminum alloy illustrates this relationship [26].
The pH value of typical MR polishing fluids commonly reaches 10 or higher. Therefore, in order to balance the mechanical and chemical effects during the polishing process and improve the polishing quality, orthogonal experiments were conducted to analyze the polishing efficiency and roughness. Different abrasives, including nano-alumina, nano-cerium oxide, nano-diamond, nano-silica, and nano-boron nitride, were used under various pH conditions (pH = 9-11). Based on the experimental results, it was found that nano-boron nitride has the highest removal rate at different pH levels but relatively poor roughness (20-80 nm Ra). The use of nano-cerium oxide, nano-alumina, and nano-silica will result in an extremely low removal rate, with a roughness Ra of about 3-6 nm. Therefore, nano-diamond was selected as the abrasive for the MR polishing fluid, which is suitable for polishing aluminum alloy materials. To ensure optimal corrosion resistance and stability during polishing, the pH of the water-based composite fluid is adjusted to 9.5. The MR polishing fluid contains 35vol% of carbonyl iron powders (CIPs) with a particle size of D50 = 3.5 µm. The scanning electron microscope (SEM) image of the used CIPs is shown in Fig. 3. Nano polycrystalline diamond with a particle size of D50 = 25 nm is used as the abrasive material, and the volume content is 0.05%.
2.3 MRF of RSA-6061
In order to analyze the passivation layer formed on the surface of RSA-6061 after MRF and validate its ability to rapidly improve the surface quality of aluminum alloy mirrors. The MRF experiments was carried out on aluminum alloy mirrors with the MR polishing fluid specifically developed for aluminum alloy materials, as mentioned earlier. The experimental material was a Φ100 mm RSA-6061 flat mirror. Figure 4 shows the MRF equipment used in the experiment, and specific parameters are shown in Table 2.
Table 2. Processing parameters of MRF
To mitigate the mutual interference between the mid and high frequency errors resulting from single-point diamond turning (SPDT) and the high frequency errors produced by magnetorheological finishing (MRF), this experiment utilized aluminum alloy mirrors that had undergone polishing after SPDT. After a 60-minute MRF process, the surface roughness Ra is reduced from 8.22 nm to 2.71 nm, as shown in Fig. 5. This indicates that the MRF can rapidly improve the surface roughness of aluminum alloy mirrors. However, as seen in Fig. 5(b), there are still some high frequency errors remaining after the MRF process. Additionally, as shown in Fig. 5(c), a noticeable passivation layer formed on the surface of the aluminum alloy mirror after MRF.
Fig. 5. Comparison of RSA-6061 surface roughness. (a) Initial surface roughness before MRF polishing. (b) Surface roughness after MRF. (c) The photo of surface passivation layer induced by MRF.
2.4 Properties of passivation layer on the surface of aluminum alloy
The surface chemical composition of RSA-6061 aluminum alloy before MRF polishing was analyzed using X-ray energy dispersive spectroscopy, and the results are shown in Fig. 6. According to the analysis results, the surface of RSA-6061 mainly consists of elements such as Al, Cu, Mg, Si, and O. Among them, Al element content is the highest, accounting for 95.45wt%, and the remaining elements such as Mg and Cu account for 0.19wt% and 0.172wt%.
In the actual polishing process, the quality of the results is also influenced by the physical properties of the workpiece. Moreover, the surface physical parameters of the workpiece will change before and after processing. The main physical parameters of the RSA-6061 aluminum alloy are shown in Table 3.
Table 3. Physical properties of RSA-6061
The passivation layer on the aluminum alloy reflective mirror is formed through the chemical reaction between the MR polishing fluid and the surface of the mirror. The MR polishing fluid consists of base liquid (usually water), iron powders, abrasives, and additives. Aluminum is a kind of metal with amphoteric properties, capable of reacting with both acids and bases. When using an alkaline MR polishing fluid for the polishing of aluminum alloy mirrors, the oxide layer on the surface of the aluminum alloy will initially react with the polishing fluid, resulting in the formation of water-soluble aluminum acid compounds. After removing the oxide layer, the surface of the aluminum alloy becomes exposed. The aluminum then reacts with oxygen and the polishing fluid, resulting in the formation of aluminum oxides and hydroxides. These substances adhere to the surface of the aluminum alloy mirror. Some of the oxide products react with OH- to form water-soluble aluminum acid salts, which are then carried away from the surface of the aluminum alloy mirror by the MR polishing fluid. Most of the oxide products are removed by the abrasive action of the particles in the MR polishing fluid, resulting in a cyclic process of oxidation, film formation, removal, and subsequent oxidation reactions. Therefore, MRF can achieve a good surface roughness for the RSA-6061 aluminum alloy.
However, unlike conventional CMP, the MR polishing fluid contains the corrosion inhibitor that prevents the rusting of iron powders. During polishing process, iron ions on the surface of the iron powders and corrosion inhibitor will react with the aluminum acid, resulting in the formation of aluminum hydroxide and small quantities of iron hydroxide. This process leads to the formation of a compact passivation layer on the surface, composed of iron oxide-doped aluminum oxide and aluminum-organic compounds. The chemical reaction process is as follows:
To achieve a fast and efficient removal of the passivation layer on the surface after MRF, Shimadzu DUH-211S dynamic ultra microhardness tester was used to analyze the hardness of the passivated surface. The results are shown in Fig. 7. The test results indicate that the Vickers hardness (Hv) of the polished aluminum alloy surface is approximately 150. Compared to the typical hardness values in Table 3, the passivation layer on the surface of the aluminum alloy exhibits a significantly higher hardness than the aluminum alloy substrate. This shows that the passivation layer formed by the chemical reaction on the surface of RSA-6061 aluminum alloy during the MRF process increases its surface hardness.
Meanwhile, X-ray photoelectron spectroscopy (XPS) analysis was performed on the passivation layer of the aluminum alloy surface after MRF. The results are shown in Fig. 8. It can be observed that there are peaks for aluminum and oxygen on the polished aluminum alloy surface, indicating the presence of an aluminum oxide layer. Additionally, there is a phosphorus peak, which is a result of the reaction between the corrosion inhibitor in the MR polishing fluid and Al (OH)4. The carbon peak in the Fig. 8 is attributed to the presence of a small amount of surface contamination.
Fig. 8. X-ray photoelectron spectroscopy analysis of passivation layer on aluminum alloy surface after MRF.
3. Removal of the passivation layer on aluminum alloy mirrors after MRF
3.1 Conventional aluminum oxide polishing slurry
CMP is an important method for correcting optical element surfaces and achieving surface smoothness. Its principle is illustrated in Fig. 9(a). The rapid and high-quality removal of the passivation layer largely depends on the specific polishing process. For aluminum alloys, a combination of a dampening cloth polishing pad and aluminum oxide polishing slurry is typically chosen for high precision polishing. The use of alkaline or neutral aluminum oxide polishing slurry can achieve a good polishing quality and surface roughness [27,28].
Fig. 9. CMP polishing process. (a) CMP polishing contact characteristics. (b) Polishing equipment used in the CMP experiment.
To investigate the performance of aluminum oxide polishing fluid, the polishing experiments were conducted using three kinds of aluminum oxide polishing fluid (acid, neutral and alkaline) on the mirror surface of an aluminum alloy after MRF. The size of aluminum oxide abrasives used in the polishing fluid is 800 nm with ellipsoidal shape and the concentration is 1.5% in mass ratio. The analysis focused on the time required for these three fluids to completely remove the surface passivation layer and high frequency errors, as well as the resulting surface roughness. The experiments were carried out using a CNC (Computer Numerical Control) polishing device (IRB 2600, ABB, Zurich, Switzerland), as depicted in Fig. 9(b). The process parameters followed the conventional parameters for mirror polishing aluminum alloy. The processing mode employed was a flat rotation pattern, with a speed of 200 rpm and a polishing pressure of 0.05 MPa. Surface quality and roughness variations were monitored during the polishing process using different aluminum oxide polishing fluid with the assistance of a white light interferometer (New View 9000, ZYGO, Connecticut, USA).
In this study, all experimental aluminum alloy parts were fabricated through mechanical machining and single point diamond turning (SPDT) using the same RSA-6061 aluminum alloy rod stock. These components, featuring a diameter of 100 mm and a thickness of 10 mm, underwent a uniform 1-hour MRF process. As illustrated in Fig. 5(b), the surface roughness of all experimental parts fell within the range of Ra values between 2.5 nm and 3 nm.
Furthermore, the time required to remove the passivation layer from the surface of the aluminum alloy parts and the resulting surface roughness were determined by monitoring changes in surface roughness and color during the polishing process. The results for the passivation layer removal time and the final surface roughness achieved with the aluminum oxide polishing fluids are presented in Fig. 10.
Fig. 10. Surface roughness and passivation layer removal time by using three type alumina polishing fluid.
As shown in Fig. 10, the acid polishing fluid can remove the passivation layer in 20 minutes. However, the surface roughness Ra reaches 19 nm, and the pits caused by the composite composition of RSA-6061 are more noticeable on the surface. This phenomenon also occurs when polishing using alkaline and neutral fluids. The difference is that the polishing time is about 80 minutes to remove the passivation layer, and the surface roughness Ra reaches 16 nm when using alkaline fluid. The polishing time required to eliminate the passivation layer using a neutral fluid is approximately 150 minutes, and the resulting surface roughness is 6 nm. From the results shown above, it can be observed that the passivation layer formed during the MRF process makes the surface of RSA-6061 harder and more difficult to remove. Moreover, the surface roughness will be higher than the initial surface after MRF. Therefore, the common aluminum polishing fluid will not be suitable for the removal of the passivation layer. It is necessary to develop a new fluid that can quickly and efficiently remove the passivation layer while maintaining high surface quality.
3.2 Acidic silicon dioxide polishing fluid
From the experimental results in Section 3.1, it can be observed that the acidic polishing slurry achieves rapid removal of the passivation layer. However, the surface roughness polished with aluminum oxide polishing fluid is relatively poor. On the other hand, neutral and alkaline aluminum oxide polishing fluids have excessively long polishing times, and their surface roughness is also suboptimal. Therefore, a new polishing fluid was chosen, replacing aluminum oxide abrasive particles with nano-silicon dioxide abrasives. In comparison to aluminum oxide abrasives, nano-silicon dioxide abrasives have lower hardness and smaller particle sizes, which can result in a higher surface quality. More importantly, the inclusion of halogenated organic acids in the polishing fluid aids in the penetration and softening of the passivation layer, thereby improving the effectiveness of passivation layer removal. The selected halogenated organic acid is trichloroacetic, and its reaction mechanism with the passivation layer on the surface of the aluminum alloy can be represented as follows:
The nano-silicon dioxide particles selected for the polishing fluid have a particle size of 100 nm. Additionally, based on the potential-pH behavior of the aluminum alloy shown in Fig. 2, the developed acidic nano-silicon dioxide polishing fluid was adjusted to a pH value of 4.
To validate the effectiveness of the acidic nano-silicon dioxide polishing fluid for removing the passivation layer, experiments were conducted on aluminum alloy parts after MRF. The experimental parts, process parameters, and equipment used were consistent with the previous experiments. The experimental results are presented in Fig. 11. Figure 11(a) shows the aluminum alloy mirror after MRF.it can be observed the presence of the yellow background resulting from passivation layer, which leads to poor imaging quality. Figure 11(b) presents the aluminum alloy mirror after 20 minutes of uniform full-aperture CMP using the new acidic silicon dioxide polishing fluid to remove the passivation layer. This demonstrates a notable enhancement in the imaging quality with the aluminum alloy mirror. Figure 11(c) displays the aluminum alloy mirror after 30 minutes of CMP, demonstrating the successful removal of the passivation layer introduced by MRF and good imaging quality can be obtained.
Fig. 11. Results of the passivation layer removal experiment. (a) Fuzzy imaged with a yellow background by aluminum mirror polishing after MRF. (b) Clear imaged by the aluminum mirror after 20 min of CMP. (c) Clear imaged by the aluminum mirror after 30 min of CMP.
4. Polishing of aluminum alloy mirrors
Based on the aforementioned research results, this paper proposes a method for the composite polishing of aluminum alloy mirrors. The high-precision manufacturing process of aluminum alloy mirrors was proposed as shown in Fig. 12.
Fig. 13. The experimental results and corresponding polishing process. (a) and (d) The surface accuracy and roughness after SPDT. (b) and (e) The surface accuracy and roughness after 90 min MRF + 30 min CMP. (c) and (f) The surface accuracy and roughness after 60 min MRF + 40 min CMP.
To realize the high-quality fabrication of aluminum alloy mirrors, a new process strategy is proposed as shown in Fig. 12. After the precision machining and SPDT on the aluminum blank. The polishing process adopt the method combing MRF with CMP to achieve the surface accuracy and quality improvement rapidly. This method adopted MRF to aluminum alloy mirrors after single point diamond turning to remove tool marks. This allows for rapid convergence of surface accuracy and improvement in surface quality. Subsequently, CMP is performed using CNC polishing equipment to remove the passivation layer and any remaining high frequency errors introduced by MRF. Through multiple iterations, it is possible to achieve high efficiency and high precision polishing of aluminum alloy mirrors.
Therefore, this paper conducted a combined polishing verification on a Φ100 mm RSA-6061 aluminum alloy mirror. The experimental process and results are presented in Fig. 13. Firstly, 90 minutes MRF process was performed on the aluminum alloy mirror after SPDT. Subsequently, 30 minutes uniform polishing was carried out using the equipment shown in Fig. 9(b) and the developed acidic nano-silicon dioxide polishing fluid. After polishing, the surface accuracy RMS of the aluminum alloy was improved from 0.1 λ (λ = 632.8 nm) to 0.056 λ, and the surface roughness (Ra) was improved from 3.63 nm to 2.21 nm. The tool marks introduced by SPDT were mostly removed, resulting in significant improvements in surface accuracy and surface roughness. Additionally, the passivation layer was completely removed from the aluminum alloy surface. Subsequently, 60 minutes high precision surface accuracy correction polishing was conducted using MRF, followed by 40 minutes uniform polishing with CMP. This further improved the surface accuracy RMS to 0.024λ, and the surface roughness (Ra) reached 1.38 nm. The experimental results demonstrated that by utilizing special MR polishing fluid and acidic nano-silicon dioxide polishing fluid, a two-iteration MRF-CMP combined polishing process for 220 minutes achieved high precision and high-quality polishing of a Φ100 mm aluminum alloy mirror. The surface accuracy and roughness can meet the requirements for visible light system. The research results have significant implications for the widespread use of aluminum alloy mirrors in visible light or even ultraviolet optical systems.
5. Conclusion
This paper studies the high-quality and high precision polishing of aluminum alloys mirrors. The aim is to improve surface accuracy and surface roughness after SPDT. The experimental results indicate that MRF polishing can rapidly improve surface shape accuracy and roughness. However, it introduces high frequency errors and a passivation layer on the polished surface, which will be a challenge for the further polishing. Therefore, a study was conducted on the mechanism of passivation layer formation on aluminum alloy mirrors after MRF. It was found that the primary components of the passivation layer are aluminum oxides and a complex formed by the aluminum alloy and corrosion inhibitors. Subsequently, experiments were conducted to investigate the effects of acidic, neutral, and alkaline aluminum oxide polishing fluids on the removal of the passivation layer and high frequency errors on the surface of the aluminum alloy mirrors after MRF.
The research indicates that the regular use aluminum oxide polishing fluid unable to realize the rapid removal of passivation layer and surface quality improvement. Therefore, based on the passivation layer properties and composition, a new acidic nano-silica polishing fluid was developed by using halogenated organic acid. The experiment results demonstrated that the new acidic nano-silica polishing fluid can significantly improved the removal efficiency of the passivation layer on aluminum alloy surfaces by adding acetic acid to the polishing fluid. This approach ensures the high efficiency and high-quality removal of the passivation layer on aluminum alloy surfaces after MRF, while also maintaining the polishing quality. At the same time, the developed acid aluminum oxide can also be used for polishing of other aluminum alloy materials such as AA-6061 or RSA-905.
Based on the research findings presented above, this paper proposes a method for the polishing of aluminum alloy mirrors by combining MRF with CMP. The feasibility and efficiency of this method were verified through the polishing of a flat aluminum alloy mirror with a diameter of Φ100 mm. The mirror had previously processed by single-point diamond turning. The polishing results demonstrate that after two-iteration of MRF-CMP composite polishing, the surface accuracy (RMS) of the mirror improved from 0.1λ (λ=632.8 nm) after turning to 0.024λ, and the surface roughness (Ra) improved from 3.6 nm after turning to 1.28 nm. The experiment results show that the tool marks from SPDT or high frequency errors introduced by MRF over the mirror surface is eliminated. These results confirm that the research presented in this paper introduces a novel approach for the high precision and high efficiency polishing of aluminum alloy mirrors.
Funding
National Natural Science Foundation of China (12203048); Natural Science Foundation of Jilin Province (SKL202302021); National Key Research and Development Program of China (2022YFB3403405).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. J. Paenoi, C. Bourgenot, C. Atkins, et al., “Lightweight, aluminum, mirror design optimization for conventional and additive manufacturing processes,” Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation V (SPIE, 2022), pp. 286–309.
2. D. Zaalberg, M. L. Maresca, E. Ruinemans, et al., “Development of an aluminium mirror with a novel integrated flexure-based mount for METIS cryogenic environment,” Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation V (SPIE, 2022), pp. 600–611.
3. F Liu, P Jia, H Shen, et al., “Optical performance of aluminum mirror for cryogenic applications,” Optik 231, 166282 (2021). [CrossRef]
4. M. L. Maresca, D. Zaalberg, E. Tabak, et al., “Development and verification of the largest cryogenic mid IR aluminium concave mirror for METIS showing excellent wavefront performance,” Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation V (SPIE, 2022), pp. 612–624.
5. J Zhang, X Zhang, S Tan, et al., “Design and manufacture of an off-axis aluminum mirror for visible-light imaging,” Curr. Opt. Photonics 1(4), 364–371 (2017). [CrossRef]
6. Z. Yin and Z. Yi, “Direct polishing of aluminum mirrors with higher quality and accuracy,” Appl. Opt. 54(26), 7835–7841 (2015). [CrossRef]
7. H. Li, D. D. Walker, X. Zheng, et al., “Mid-spatial frequency removal on aluminum free-form mirror,” Opt. Express 27(18), 24885–24899 (2019). [CrossRef]
8. X. Shi, Y. Sun, P. Li, et al., “Research on Scattering Characteristics of Ultra-precision Turned Aluminum Alloy Mirror Surface,” International Conference on Nanomanufacturing (Springer Singapore: Singapore, 2021), pp. 33–46.
9. H. Zhang, X. Zhang, Z. Li, et al., “Removing single-point diamond turning marks using form-preserving active fluid jet polishing,” Precis. Eng. 76, 237–254 (2022). [CrossRef]
10. J. Zhang, C. Wang, H. Qu, et al., “Design and Fabrication of an Additively Manufactured Aluminum Mirror with Compound Surfaces,” Materials 15(20), 7050 (2022). [CrossRef]
11. J. P. Schaefer, “Advanced metal mirror processing for tactical ISR systems,” Airborne Intelligence, Surveillance, Reconnaissance (ISR) Systems and Applications X (SPIE, 2013), pp. 18–27.
12. S. Risse, A. Gebhardt, C. Damm, et al., “Novel TMA telescope based on ultra precise metal mirrors,” Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter (SPIE, 2008), pp. 65–372.
13. T. Andrea, B. Anna, C. Rodolfo, et al., “Toward ARIEL’s primary mirror,” Proc. SPIE 12180, 1218040 (2022). [CrossRef]
14. J. Kinast, R. Schlegel, K. Kleinbauer, et al., “Manufacturing of aluminum mirrors for cryogenic applications,” Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation III (SPIE, 2018), pp. 1024–1030.
15. R. Horst, N. Tromp, M. Haan, et al., “Directly polished lightweight aluminum mirror,” Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation (SPIE, 2008), pp. 63–72.
16. J. Bauer, F. Frost, A. Lehmann, et al., “Finishing of metal optics by ion beam technologies,” Opt. Eng. 58(9), 092612 (2019). [CrossRef]
17. C. Du, Y. Dai, H. Hu, et al., “Surface roughness evolution mechanism of the optical aluminum 6061 alloy during low energy Ar+ ion beam sputtering,” Opt. Express 28(23), 34054–34068 (2020). [CrossRef]
18. C. Du, Y. Dai, C. Guan, et al., “High efficiency removal of single point diamond turning marks on aluminum surface by combination of ion beam sputtering and smoothing polishing,” Opt. Express 29(3), 3738–3753 (2021). [CrossRef]
19. M. Beier, S. Scheiding, A. Gebhardt, et al., “Fabrication of high precision metallic freeform mirrors with magnetorheological finishing (MRF),” Optifab 2013 (SPIE, 2013), pp. 139–152.
20. J. Seok, Y. J. Kim, K. I. Jang, et al., “A study on the fabrication of curved surfaces using magnetorheological fluid finishing,” Int. J. Mach. Tools Manuf. 47(14), 2077–2090 (2007). [CrossRef]
21. Y. Bai, Z. Zhang, D. Xue, et al., “Ultra-precision fabrication of a nickel-phosphorus layer on aluminum substrate by SPDT and MRF,” Appl. Opt. 57(34), F62–F67 (2018). [CrossRef]
22. C. Du, Y. Dai, C. Guan, et al., “Rapid fabrication technique for aluminum optics by inducing a MRF contamination layer modification with Ar+ ion beam sputtering,” Opt. Express 29(6), 8951–8966 (2021). [CrossRef]
23. T. Zhao, H. Hu, X. Q. Peng, et al., “Study on the surface crystallization mechanism and inhibition method in the CMP process of aluminum alloy mirrors,” Appl. Opt. 58(22), 6091–6097 (2019). [CrossRef]
24. A. Tozzi, A. Brucalassi, R. Canestrari, et al., “Toward ARIEL’s primary mirror,” Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave (SPIE, 2022) pp. 1494–1508.
25. G. P. H. Gubbels, B. W. H. Venrooy, A. J. Bosch, et al., “Rapidly solidified aluminium for optical applications,” Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation (SPIE, 2008), pp. 1145–1153.
26. M. M. El-Rabiei, G. M. A. El-Hafez, and A. H. Ali, “Effects of Alloying Elements (Ti and x Al) on the Electrochemical Corrosion Behaviour of Iron-Based Alloys in Corrosive Solutions of Different pH,” J. Bio. Tribocorros. 6, 27 (2020). [CrossRef]
27. T. Li, H. Sun, D. Wang, et al., “High-performance chemical mechanical polishing slurry for aluminum alloy using hybrid abrasives of zirconium phosphate and alumina,” Appl. Surf. Sci. 537, 147859 (2021). [CrossRef]
28. Y. Wang, Y. Chen, Y. Zhao, et al., “Chemical mechanical planarization of Al alloy in alkaline slurry at low down pressure,” J. Mater. Sci.: Mater. Electron. 28(1), 3364–3372 (2017). [CrossRef]
