Corrosion resistance improvement of Mg alloy AZ31 by combining bilayer amorphous DLC:H/SiNx film with N+ ions implantation

Highlights: • N⁺ ions implantation changes the Mg alloy surface into amorphous state. • Bilayer amorphous hydrogenated diamond-like carbon/silicon nitride film forms a good dielectric barrier. • N⁺ ions implantation and the bilayer amorphous film improve the anti-corrosion property of Mg alloy AZ31. Bilayer amorphous hydrogenated diamond-like carbon (DLC:H)/SiN_x film was successfully deposited onto Mg alloy AZ31 by reactive magnetron sputtering. Etching Mg alloy AZ31 in Ar and N₂ atmosphere by radio frequency bias (Ar&N/AZ31), not only implanted N⁺ ions into the substrate but also changed its crystal structure into amorphous state. DLC:H/SiN_x/Ar&N/AZ31 shows an increase in corrosion resistance during 120 h immersion in 3.5 wt% NaCl solution. The high corrosion resistance is attributed to combination of good barrier effect of the bilayer DLC:H/SiN_x film, the self-stabilized and self-sealed ability of SiN_x, and the amorphous layer of Mg alloy AZ31 surface.