Coat with alloy is a process used to protect metal surfaces from corrosion. It involves applying a thin layer of metal, usually an alloy of tin and lead, to the surface of the metal. The process is also known as plating or terne coating. Plating is the process of depositing a thin layer of metal onto the surface of another metal, while terne coating is the process of applying a thin layer of tin and lead alloy to the surface of the metal. Both processes are used to protect the metal from corrosion and to improve its appearance.