Study on Preparation and Properties of DLC Film on 7A04 Aluminum Alloy

In order to improve the surface properties of 7A04 aluminum alloy, a radio frequency assisted plasma is used to immerse ion implantation and deposition equipment to prepare a diamond-like carbon (DLC) film on the surface. Due to the large difference between the mechanical properties of the DLC film and the aluminum alloy substrate, the film substrate has poor bonding strength. In this study, unbalanced magnetron sputtering technology was used to deposit a layer of Si film in advance as a transition layer to improve the adhesion of the film base; laser Raman spectrometer, Vickers microhardness tester, nano-scratch tester, friction and wear tester and other equipment were used , Systematic analysis of film structure, micro-hardness, film base adhesion and wear resistance. The results show that the preparation of the Si transition layer improves the load-bearing capacity of the substrate and the bonding force of the film-base, thereby greatly improving the wear resistance.

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7A04 belongs to the Al-Zn-Mg-Cu super-hard aluminum alloy. Due to its low density, high specific strength, good ductility, easy processing, strong electrical and thermal conductivity, it is widely used in aerospace, transportation, and chemical industries. And other fields. However, 7A04 aluminum alloy has problems such as low hardness, poor wear resistance, and large thermal expansion coefficient, which restrict the application of aluminum alloy to some extent. In recent years, the use of surface treatment technology to modify the surface of aluminum alloy has attracted widespread attention. Researchers have used various technologies such as electroless plating, thermal spraying, and anodic oxidation to study the surface modification of aluminum alloy and have made certain progress. However, these methods also have shortcomings. For example, chemical plating technology has certain pollution to the environment, and the surface roughness of coatings prepared by anodic oxidation technology and spraying technology is too high and the uniformity is poor. Compared with conventional surface modification technologies, RF-assisted plasma immersion ion implantation and deposition (RF-PIII&D) technology has many advantages, such as high energy of deposited ions, low film formation temperature, and deposition It has many advantages, such as short time, good film uniformity, and ability to process workpieces with three-dimensional scale and complex profile. It is suitable for surface modification of temperature-sensitive materials such as aluminum alloy.

Diamond-Like Carbon (DLC, Diamond-Like Carbon) film combines the excellent properties of graphite and diamond, with high hardness, high resistivity, and good optical and wear resistance. It is widely used in machinery, optics, medicine and microelectronics. in. Researchers have successfully prepared DLC films on the surface of aluminum alloys. However, due to the large difference in mechanical properties between DLC films and aluminum alloy substrates, the film-base adhesion is poor, and it is difficult to prepare high-quality films on the aluminum alloy surface (film-base adhesion Strong, high wear resistance). Adding a transition layer between the substrate and the hard film is one of the effective ways to improve the matching of the mechanical properties of the DLC film and the substrate. Si and diamond have the same lattice structure and are used as a transition layer for the deposition of DLC films, which is conducive to the preparation of high-quality films. Yang Yishang et al. used the reactive sputtering method to study the influence of the Si transition layer on the adhesion characteristics of the F-DLC film. The results show that the introduction of the Si transition layer can significantly enhance the bonding strength of the F-DLC film and the stainless steel substrate. Wang Jing et al. studied and compared DLC films deposited on the Ti/TiC transition layer and Si/SiXNY transition layer, and the results showed that the DLC film with Si/SiXNY as the transition layer was more uniform and stable.

In this study, RF-PIII&D equipment was used to prepare DLC film on the surface of 7A04 aluminum alloy. In order to improve the bonding force of the film base, the unbalanced magnetron sputtering technology is used to deposit a layer of Si film between the aluminum alloy surface and the DLC film as a transition layer. The influence of the Si transition layer on the structure and performance of DLC films is systematically studied, which has certain research significance for the preparation of hard functional coatings on the surface of materials with lower hardness.

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The 7A04 aluminum alloy round bar is processed into a circular sample (Φ10mm×3mm) that is convenient for clamping, and the sample is polished to the mirror surface using a semi-automatic grinding and polishing machine produced by Bühler. Wash them in anhydrous ethanol for 5 minutes, and put them in a vacuum chamber for plating after drying.

First, use unbalanced magnetron sputtering equipment to prepare a Si transition layer (about 50nm) on the sample surface. The target material uses a pure Si target with a purity of 99.99%, and the working gas is Ar (purity ≥ 99.999%); then use RF -PIII&D equipment to prepare DLC film (about 245nm), using C2H2 (purity ≥99.999%) as the carbon source gas, the radio frequency is 13.56MHz, the specific parameters are shown in Table 1, the background vacuum of the vacuum chamber is 3.3× 10-3Pa. The samples with Si transition layer and DLC film deposited directly on the aluminum alloy surface are marked as DLC/Si/Al and DLC/Al, respectively.

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The Raman spectrometer (AIMEGA XR, U.S.) was used to analyze the microstructure of the DLC film; the digital microhardness meter (HXD-1000TM) was used to detect the Vickers microhardness of the test sample. The film-base binding force was analyzed with a nano-scratch tester (CSEM Nano-scratch Tester, Swiss) and an optical microscope (Axio Image A1m), using a linear loading mode, with a loading range of 0-50mN and a scratch length of 200μm. The friction and wear tester (CSEM Tribometer, Swiss) is used to analyze the wear resistance of the film. It adopts a pin-disc type, the friction pair is GCr15 ball (Φ6mm), the load is 0.49N, the wear speed and the wear radius are 3cm respectively /s and 3mm. Observe the morphology of the wear scar with a scanning electron microscope (SEM, QUANPA200), and use the energy dispersive X-ray spectroscopy (EDX) instrument that comes with the SEM to analyze the composition changes of the wear scar; scan the depth of the wear scar with a step meter (AMBIOS XP-2, US) And width, through friction coefficient, wear scar width, depth and wear scar composition analysis, comprehensively evaluate the wear resistance of the sample.

Using RF-PIII&D equipment, using C2H2 as carbon source and Ar as transport gas, DLC film was successfully prepared on the surface of 7A04 aluminum alloy; using unbalanced magnetron sputtering equipment, Si was added to the film base system formed by DLC film and aluminum alloy Transition layer. After testing and analyzing the film, the following conclusions are obtained:

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(1) The preparation of Si transition layer has no obvious influence on the structure of DLC film;

(2) The preparation of the Si transition layer improves the load-bearing capacity of the aluminum alloy substrate and improves the bonding force between the DLC film and the aluminum alloy substrate;

(3) Compared with the DLC/Al sample without the Si transition layer, the DLC/Si/Al sample with the Si transition layer has significantly improved wear resistance.

Founded in 2015,Zunhua Baorui Titanium Equipment Co.,Ltd. is a manufacturer specializing in pvd vacuum ion coating equipment. The company’s products mainly include large plate coating machine, large tube collating machine, tool coating machine and LOW-E glass production line. Mr.Wang baijiang ,general manager of the company ,has been engaged in vacuum coating industry for more than 30 years. He continuously improve production technology, improve product performance and devote himself to provide customers with better product experience and higher production efficiency.