Plating Corrosion Resistant Coatings
Plating corrosion resistant coatings using electroless nickel plating (EN) have been an integral part of the metal finishing industry for years. Their protective surface properties against chemicals are widely documented for an array of industrial applications.
EN, also commonly referred to as autocatalytic plating or electroless plating, offers considerable advantage over electrolytic products, like chrome -- based on the ability to cover complex geometry, penetrate deep internal or recessed surfaces, using an aqueous bath without electrical energy.
Generally, plating corrosion resistant coatings gain greater performance using higher phosphorous content (greater than 10-12%) in the nickel bath. Depending on base metal, plating thickness, and surface finish, 1000 hour salt spray (ASTM B117) is achievable.
Corrosion phenomenon, like fretting, however, is often mitigated using composites of EN for increased hardness or enhanced dry lubrication.
Because EN is conformal by nature, surface finish is a large determinant in product life. Typically, there is a positive correlation between surface finish and resistance to corrosion. Consequently, cast surfaces, for best results, should be polished. And machined billet is far preferable.
For plating corrosion resistant coatings, base metal selection should also be considered. Homogeneous metals are far preferable over alloys, such as leaded steels, which are known to accelerate corrosion.