The most common and long-established method of decorative plating on steel is copper-nickel-chrome plating also known as ‘chrome plating’. In recent years, nickel-chrome plating (semi-bright + bright plating) is also common for its superior corrosion resistance and aesthetic properties. These are not only applied to metal substrates but also applied over plastic substrates. Chrome plating is the mainstream of decorative plating today. Since chrome plating provides various surface properties including satin, hairline, spin, diamond cut, semi-bright satin, velour, pearl pattern finishes in addition to a mirror finish, each type of finish is adopted for corresponding purposes. Chrome plating is a type of electroless plating that does not use any electrical sources to charge the plating bath. Check out the post on electroless plating here. Hard chrome plating can be found in a variety of products such as rollers, shafts, and linear guides.
Today’s automobile industry requires higher corrosion resistance to battle the various weather attacks, therefore, using dual plating consisting of electrochemically different nickels, triple plating with the medium layer made of tri-nickel, and micro-cracked chromium plating for the top layer to improve corrosion resistance. The other types of decorative plating include nickel plating adopted for the top layer instead of chrome plating to produce a reddish finish, and bright copper plating on the top for bronze finish.
There are different manufacturing processing methods for chrome plating. “1” indicating the industrial application is added before Cr (chrome plating) for plating symbols. This table summarizes the symbols representing pre/post plating processes.
Industrial Chrome Plating
The industrial chrome plating, also customarily called hard chrome plating, has been in wide usage in many areas in 10 ~ 100μm thickness due to its hardness, lubrication retention ability, and wear resistant properties.
The industrial chrome plating coating properties are as follows.
(1) High hardness. Hardest among the standard electroplating (Macro Vickers hardness approx. 1000). Much harder than heat treated or nitride steels.
(2) Wear resistance. The most importantly expected property for the chrome plating, and fully satisfies the requirements.
(3) Corrosion resistance. Good corrosion resistance against chemicals other than chlorides, and is stable in the atmosphere.
(4) Heat resistance. When heated, hydrogen occluded in the coating is released and the hardness lowers. When exceeding 300°C, the hardness rapidly lowers. Therefore, the wear resistance is also decreased.