METALLIC COATINGS

Metallic coatings change the surface properties of the workpiece from those of the substrate to that of the metal being applied. This process allows the workpiece to become a composite material with properties that generally cannot be achieved by either material alone. The coating's function is usually as a durable, corrosion-resistant protective layer, while the core material provides a load-bearing function. Common coating materials include aluminum, coated lead, tin, zinc, and combinations of these metals.
Metallic coatings often are referred to as diffusion coatings because the base metal is brought into contact with the coating metal at elevated temperatures, allowing the two materials to interlace. These systems include various metallic spraying applications, cladding (application using mechanical techniques), hot dipping, vapor deposition, and vacuum coating.
The main application for spray diffusion coatings is workpieces that are difficult to coat by other means because of their size, shape, or susceptibility to damage at high temperatures. Cladding uses a layer of metal that can be bonded to the workpiece using high-pressure welding or casting techniques. In some applications, cladding can be used as an alternative to plating.
Hot dipping is another diffusion process that involves partial or complete immersion of the workpiece in a molten metal bath. The facility applies the coating metal in a powdered form at high temperatures (800 to 1,100 degrees Celsius) in a mixture with inert particles such as alumina or sand, and a halide activator. Vapor deposition and vacuum coating produce high-quality pure metallic layers, and can sometimes be used in place of plating processes