Structure and properties of DLC films deposited by mixed carbon on the surface of AZ31

To improve the corrosion resistance and wear resistance of magnesium alloys, expand the application of Mg alloy, save energy, reduce emissions and protect the environment, green and environmentally friendly magnetron sputtering technology was used to prepare a strong protective DLC film on the surface of AZ31. The phase structure of the film was studied by small-angle grazing incidence of X-ray, the surface morphology, cross-section morphology and corrosion morphology of the film were observed by scanning electron microscope, and bonding properties of film-to-substrate were tested by a nano-indenter. The electrochemical workstation, friction and wear tester were employed to investigate the corrosion resistance and wear resistance of the film, and the bonding performance was evaluated by scratch test. The results showed that the DLC film had an amorphous structure. With the increase of the active gas flow rate, the DLC film tended to change from amorphous to nanocrystalline. The film was well bonded to the substrate with a bonding force of 19～25 N. The surface of the DLC film had irregularly distributed particles, and the surface roughness was significantly affected by the flow of active gas. The thickness of the film was 1.15～1.18 μm, and the active gas flow appeared little effect on the thickness. With the increase of the active gas flow rate, the hardness and Young’s modulus of the DLC film increased with the maximum values of 17.35 GPa and 94 GPa, respectively, and the friction coefficient and wear rate decreased with the minimum values of 0.103 and 6.45×10-10 mm3/(N·m), respectively. The corrosion resistance of the film was the best when the active acetylene flow rate was 5 mL/min, whereas the wear resistance was the best when the active acetylene flow rate was 10 mL/min.Highlights: (1) DLC films with high bonding strength were prepared on soft substrates.(2) Hybrid carbon source was used to prepare DLC films, which increased plasma density in vacuum chamber and deposition rate of films.(3) Nonmetallic Si was used as the substrate transition layer to improve the film-base bonding performance.(4) Effect of acetylene flow rate on structure and properties of films was studied.