Patent ID: 8470452

Claim:
A wear resistant oxide coated aluminum alloy article in the form of a sprocket or gear, wherein the aluminum alloy substrate comprises 85 to 92 percent aluminum metal, 6 to 15 percent of metals selected from the group consisting of copper, magnesium, zinc and copper and less than 0.5 percent each of manganese, iron and silicon metals and the oxide coating comprises intertwined oxides of the alloy metals, said oxide coating being formed by: a) immersing the aluminum alloy article in an aqueous electrolyte comprising from about 1.5 to about 2.5 grams per liter of alkali metal hydroxide, from about 6.5 to about 9.5 grams per liter of alkali metal silicate, in the absence of significant amounts of other components and in the absence of more than 1 g per liter of alkali metal pyrophosphate and in the absence of more than 0.05 percent hydrogen peroxide; b) applying an alternating current through the electrolyte using the article as one electrode where a second electrode comprises at least one of an electrically conductive container or an immersed separate electrode, where applied EMF is selected to provide a current density of from about 15 to about 25 A/dm 2 , for a sufficient time to obtain a wear resistant ceramic coating having a thickness of from about 125 to about 150 μm, as measured on a flat face of the article; and c) stopping the applying of the alternating current when the article has a wear resistant ceramic coating having a thickness of from about 125 to about 150 μm, as measured on a flat face of the article.