Pertinent Facts of Nickel Plating

Plating baths each provide specific benefits that, regardless of cost, have become necessary for various on demand finishes. These include: decorative, functional, wear resistance, and corrosion protection. Nickel encompasses many plating systems, each of which is very important to many aspects of metal finishing. Even though the prices of nickel anodes and related salts have been very volatile, the importance of nickel in plated finishes is still of great significance.

For industrial purposes, almost any metal can be nickel plated. The inherent properties of nickel can be combined with the unique properties of other metals. Some examples of metals commonly plated with nickel are: steel (high strength), brass (easily bent and formed), aluminum (impact extrusion), and die castings (design flexibility). Plastics, which have been treated for conductivity, are also commonly nickel plated. Nickel can be directly plated over several metals. This is typically performed directly over steel, brass, and copper. In some cycles, appropriate immersion treatments or pre plate deposits precede nickel. This is especially prevalent when plating a copper strike and copper plate over zinc parts before nickel. Aluminum, because of it’s unique electropositive nature, must first be conditioned by immersion zincating, before plating either electrolytic or electroless nickel.

The application of a suitable nickel deposit can be of significant benefit to the parts, ultimate quality of the finish, and meet or exceed specifications. These advantages can actually reduce related manufacturing costs, improve marketability, and increase production throughput. Depending on the finishing requirements or service life of parts, nickel contributes the following advantages:
Good electrical conductivity, low coefficient of thermal expansion, magnetic, and good heat conduction. Nickel can be plated as a soft deposit (not far off from copper) or almost as hard as chrome. In fact, nickel can be plated to almost any desired deposit hardness in between this wide range. Aesthetically, nickel can be plated in decorative applications to achieve a wide range of brightness and leveling, still retaining sufficient deposit ductility.

Finished parts can be assembled or mechanically formed into selected commercial products. Along with these benefits, duplex nickel forms an excellent corrosion barrier, especially in the plating of exterior automotive parts. Nickel forms an important barrier to prevent the migration of zinc on tin plated parts. In engineered finishes, nickel decreases contact, resistance and friction, improves solder ability and brazing, and improves resistance to galling and wear. Plating with nickel can salvage worn or miss-machined parts. Almost all nickel deposits can be machined. Incorporating nickel into the deposit, in place of solid metal, reduces some manufacturing costs.

As mentioned previously, nickel can be plated to provide rapid leveling, filling voids, eliminating microscopic “peaks and valleys”, while plating a relatively thin deposit. For this reason the base metal may not have to be mechanically polished, buffed, or mass finished. If this is acceptable, cost savings to prepare the surface for plating may be realized. Nickel can be plated from a variety of specific bath formulations (usually Watts and sulfamate types), to develop deposits that range from flat to dull to semi bright to bright. This affords the finisher the capability to provide nickel deposits that meet engineering requirements, corrosion protection, and aesthetic preferences. The Woods strike effectively activates stainless steel for subsequent nickel plating. Duplex nickel, as mentioned earlier, promotes exceptional corrosion protection, by plating a balanced ratio of a special semi bright and bright nickels. The Step Test is a specific quality control procedure for this application. In recent years Watts baths containing modified organic additives, have successfully replaced cyanide copper strikes over zincated aluminum. Decorative chrome, either trivalent or hexavalent, continues to be a specified finish over nickel. The chrome topcoat enhances overall appearance and maintains an excellent scratch resistant, hard finish. Although we commonly refer to the bright chrome finish, it is primarily nickel (usually bright) with a thin chrome flash. The combination of these deposits give the assembled parts a preferred pleasing appearance, along with exceptional corrosion and wear resistance. For several decades, the combination of bright nickel and flash chrome has been the best selection for plating parts subject to outdoors exposure.
Nickel can be plated as a very ductile deposit. In combination with a proper base metal conditioning and any preplate deposits, the finished items can be stamped, drawn, or formed in a variety of shapes. This is very common in the strip plating of continuous coils that will be used in the manufacture of different types of consumer and industrial goods. In this application, the organic brightener and leveling additives may be kept at lower levels, to achieve the required ductility. Final aesthetic appearance of nickel occurs in a short buffing cycle before optional chrome plating. Parts that require exceptional brightness and leveling may be stamped before the plating cycle.

Nickel can be plated to meet any thickness requirement. Industrial based coatings usually require 0.005 – 0.020 inch. For decorative purposes, nickel thickness may range from 0.0003 – 0.001 inch (or up to one mil). As indicated by the application ranges, there is a minimum that should be plated to meet the intended use of finished parts. As a guide, 1 lb of plated nickel is required for every 22 ft2 of intended parts coverage. Depending on the nickel bath and plating parameters, the deposit tensile strength can range from 50 to 220 thousand lb / inch2.

Nickel anodes, as we are aware, are quite expensive. Be certain a certificate of analysis confirms the quality. Anything less than sufficient purity material could result in severe contamination of the nickel bath. A typical assay is: Nickel (99.950%), Cobalt (0.03%), Copper (0.005%), Carbon (0.001%), Iron (0.001%), Sulfur (0.01). Anodes are provided in various shapes, including: spears, buttons, rounds (sulfur containing S and sulfur free R), and chunks.

There are many applications for plating nickel, using several types of process baths. The demand for nickel plating continues to be relatively strong. Although the prices for nickel anodes and salts have markedly risen, the consumer market for plated finishes keeps this plating service very active. Original and after market automotive finishes have “re-discovered” bright nickel / chrome finishes. The decorative plumbing industry is very positive on nickel / chrome and brushed nickel finishes. Clothing and apparel manufacturers now feature nickel finishes (ex. oxidized, brushed, under flash brass or gold). Nickel anodes and salts may not be cheap (compared to a few years ago), but decorative and industrial finishes for nickel are still in strong demand.