The application to the surfaces of metal objects (mainly steel) of a layer of brass several microns thick and consisting, for example, of 70 percent copper and 30 percent zinc.
Hardcoated items usually have a dark gray to a black finish. This can vary depending on the aluminum alloy.
The coating is usually applied electrolytically by deposition of brass from an electroplating bath. Brass plating is used to protect objects from corrosion, to provide strong bonds between steel and aluminum articles and rubber in the hot pressing process, and to create an intermediate layer (called the substratum) in nickel plating or tin plating of steel articles (which is more effective than direct coating with nickel or tin).
Brass plating is a means of improving the antifriction properties of titanium and its alloys.