Abstract: A treated rotor is provided by a method in which a surface of a ferrous rotor having cooling elements is heat-treated to produce a microporous, outermost surface layer, then the heat-treated rotor is coated by electrodepositing a coating layer of an electrocoat coating composition on the heat-treated the surface of to provide a electrocoat coating directed on the surface of the heat-treated rotor. The electrocoat coating layer has a throwpower of at least about 40% and the coating layer is continuous on cooling elements of the rotor. The microporous outermost layer is a controlled iron oxide layer.