Copper can be applied in a variety of finishes from matte to shiny. It has good corrosion resistance when used as undercoat. A number of copper processes are available, each designed for a specific purpose:
- Brightness, to eliminate the need for buffing
- High speed for electroforming
- Fine grain for masking to prevent case hardening
Chrome plating provides excellent hardness (HRc68-74) and wear resistance. Chrome plating has a low coefficient of friction, and is resistant to heat and chemicals.
Zinc plating is a widely used coating for the corrosion protection of steel. It is used on stampings, fasteners, and automotive components, providing an excellent base for painting. Zinc is usually provided in a chromated condition, which ranges from blue bright, clear to yellow iridescent, to black. Corrosion resistance is good with the yellow chromates reaching 96 hours neutral salt spray to white corrosion. The new generation of clear, trivalent chromates perform equally as well. Older formulations of clear chromates can be expected to reach 12 hours of salt spray resistance before white corrosion. Red rust remains a function of thickness.
Nickel plating is a versatile process that satisfies a wide range of needs. Depending on the process and conditions, nickel can be deposited as a soft or hard finish, ranging from 150-500 Vickers. The color ranges from a bright finish similar to stainless steel in color, to a dull grey or light grey (almost white) color. Corrosion resistance is a function of thickness. Nickel also has a low coefficient of thermal expansion and is magnetic. All steel parts having a hardness of Rc-40 or greater require a post bake 375 25F for 3 hours.
Silver plating offers several advantages as a finish. It is one of the best electrical conductors and is easily soldered, although that capability of silver plating decreases with age. Silver plating also has excellent lubricity and smear characteristics for anti-galling fuses on static seals, bushings, etc. The color ranges of silver plating from white matte to very bright in appearance, but it will tarnish easily. Silver plating offers good corrosion resistance, depending on the base metal. Hardness varies from about 90 Brinnell to about 135 Brinnell, based on the process and plating conditions.
Tin plating is both soft and very ductile. The color of matte tin is gray-white and bright tin has a very high luster in fused condition and is silver in appearance. Corrosion resistance is fair, with coated items meeting 24 hour 5% salt spray requirement; solderability is excellent. Tin is not good for low temperature applications because it changes structure and loses adhesion when exposed to temperatures below -40C.