Effect of Graphite Content on the Conductivity, Wear Behavior, and Corrosion Resistance of the Organic Layer on Magnesium Alloy MAO Coatings

To impart electrical conductivity on magnesium alloy micro-arc oxidation coatings, a graphite/epoxy conductive layer was prepared on the surface of a ceramic layer in this work, focusing on wear behavior and corrosion resistance of the coating. At a graphite weight of 80 wt%, the square resistance of the coating decreased to 217.6 kΩ/□, and it exhibited good resistance. Combined with the distribution of graphite particles in the coating and the change in surface resistance, we determined that the conductive mechanism of the coating occurred through quantum tunneling when the graphite content was 60 wt%. When the graphite content increased from 60 to 80 and 100 wt%, the formation of conductive paths on the surface of the coating further improved the conductivity. The hardness of the organic coatings was positively related to the graphite content. Analysis of the wear scars and wear debris after dry friction and wear testing showed that the wear forms of the coating consisted of abrasive wear when the graphite content was in the range of 20–40 wt%. When the graphite content was in the range of 60–100 wt%, the wear forms of the coating consisted of abrasive wear and peeling wear.