Ball-on-plate testing of nanopore fillers for tribologically effective anodized alumina coatings

Aluminum alloys are often anodized (i.e. oxidized electrochemically) to increase surface hardness. However, their tribological properties become very poor mainly due to the abundance of narrow nanopores. Al alloy 1050A was anodized to produce ~ 70 µm thick coatings. Coefficients of Friction (COF) were measured using reciprocal ball-on-plate method against steel leading to COF of 0.7-1. Then anodized specimens were coated with either fluoropolymer PTFE or melted stearic acid, which led to improved wear resistance and reduced COF. In some cases stearic a. was more effective tribologically than PTFE and showed COF of 0.05-0.2 along with better inhibition of rapid wear propagation. Established tendencies could help in developing technologies for the manufacture of tribologically effective anodized Al coatings