Reduction of friction coefficient of magnesium alloy sheet by DLC coating with low-temperature plasma

Magnesium alloys have become of interest as promising light metals for various applications. Regardless of their good properties, however, Mg alloys cannot be processed through press-forming because of seizing on the surface of the material. In order to prevent the seizing, we coated diamondlike carbon (DLC) on Mg alloy sheets to reduce the surface friction using low-temperature plasma. We analyzed the surface properties with cross-cut test, friction test, deep drawing along with X-ray photoelectron spectroscopy and scanning electron microscopic observation. DLC has the nature of low friction, which could reduce the friction coefficient of the surface, but it was found that the adhesivity between DLC and Mg alloy sheet was not strong enough. Therefore, silicon interlayer was formed with tetraethoxysilane (TEOS) by plasma between Mg alloy sheet and DLC. The coated DLC on the silicon interlayer in some conditions exhibited very tight and patterned shape, which fairly improved the adhesivity and sustained lower friction. The formability of Mg alloy sheet by deep drawing was also improved.