Structure and properties of different elements doped diamond-like carbon on micro-arc oxidation coated AZ31B Mg alloy

To further improve corrosion and wear protection of micro-arc oxidation (MAO) to magnesium (Mg) alloys, a pure diamond-like carbon (DLC), H-DLC, Si-DLC, and Cr-DLC film was deposited the MAO coated-Mg alloys using closed field unbalance magnetron sputtering system, respectively. The microstructure and properties of the coatings were investigated. Results indicated that DLC films cannot completely seal the surface micropores of MAO coatings but can reduce their number and pore size. The duplex MAO/DLC films significantly improved the tribological properties of the MAO coating. The MAO/Si/Si-DLC film showed the lowest friction coefficient (0.17) and wear rate (3.18 × 10−6 mm3/(m·N)). The electrochemical test results showed that the lowest corrosion current density (icorr)of the MAO/Si/H-DLC is 3.26 × 10−7 A/cm2 but the icorr of other duplex films is higher than that of the MAO (4.27 × 10−7 A/cm2) coated sample. This indicated that the H-DLC can enhance the anti-corrosion properties of the MAO coating on magnesium alloys. However, the NSS test results indicated that the long-term anti-corrosion properties of duplex H-DLC/MAO coating is not good as that of MAO coating due to the conductivity of the H-DLC.