Study on Tribological Properties of Duplex Coating Formed on Magnesium Alloy Using Micro-Arc Oxidation and Magnetron Sputtering under Different Power

Abstract

For further improving the tribological properties of magnesium alloy micro-arc oxidation (MAO) coating，a carbon film was deposited on such coating by magnetron sputtering (MS) technology under different sputtering power to prepare duplex MAO/MS coating with different carbon contents.The carbon structure in the coating was tested by Raman spectrometer.Scanning electron microscope (SEM) and energy spectrum (EDS) were employed to analyze the micro morphology and the elemental composition，distribution and content of coatings before and after friction and wear test.Additionally，the tribological properties of the coatings were studied by the ball-on-disk friction tester.Results showed that the carbon film deposited on the surface of the magnesium alloy MAO coating by MS technology partly sealed the micropores of MAO coating，and reduced the size and number of micro-pores as well as the coating’s surface roughness.During the friction and wear process，the duplex coatings exhibited a low friction coefficient，narrow and shallow wear scars，and a small wear rate，indicating that they possessed excellent tribological properties.Moreover，sputtering power had a significant effect on the duplex MAO/MS coatings.The duplex coating prepared under high sputtering power possessed better tribological properties due to lower friction coefficient，narrower and shallower wear scars as well as smaller wear rate，which were attributed to a smoother surface and a larger quantity of C with self-lubricating characteristic.The as-prepared coating could provide a better protection on the substrate especially under high load.

Keywords

• magnesium alloy|micro-arc oxidation|magnetron sputtering|carbon film|sputtering power|tribological property