Introduction

DECORATIVE CHROMIUM PLATING is different from hard chromium plating in terms of thickness and the type of undercoating used. The average thickness of decorative plating is actually very thin, usually not more than 1.25 ^m (50 ^in.). A decorative chromium deposit is used primarily for its pleasing blue-white color. Its highly reflective appearance is maintained in service because chromium can resist tarnish, chemicals, scratches, and wear. If the deposit is defect-free, then a level of corrosion resistance also is provided, because the deposit acts as a physical barrier to the environment. Decorative chromium is applied over undercoatings, such as nickel or copper and nickel, which give the chromium bright, semibright, or satin cosmetic appearances. Corrosion protection depends on the choice of undercoating, as well as the type of chromium being applied. Parts made from steel, copper and its alloys, zinc, stainless steel, and aluminum are typically plated with nickel-chromium or copper-nickel-chromium.

Most decorative chromium coatings have been applied using hexavalent chromium processes that are based on chromic anhydride. However, since 1975, trivalent chromium processes have become available commercially. They are increasing in importance because of their increased throwing and covering powers and because they offer environmental advantages. Both systems are considered in detail in this article.

0 0

Post a comment