Benefits of Zinc

Zinc plating is a valuable tool which is used to combat corrosion of steel. A metal bond is formed between the zinc and the steel, which allows the zinc itself to corrode before the steel. This way the zinc will be sacrificed allowing the steel to remain intact.

The basic principle behind electroplating is the process of depositing a metal layer on a metal base using a direct current through an electrolyte solution. Zinc is one of the easiest metals to plate, giving good corrosion protection without using exotic chemicals. The finish can be polished to give a shiny lustre almost as good as chromium.

Zinc plated components are attractive when new providing a bright, smooth surface. Hot dip galvanized coating is dull and does not provide as smooth a surface. The duller, galvanized surface requires more zinc and typically lasts longer than the bright, shiny surface.

Alkaline zinc has good brightness and produces a reliable and consistent coverage. Chloride zinc produces an outstanding brightness. Zinc plating is extensively used by the automotive industry. Many space and military products also use zinc plating. Colors are usually offered in clear, yellow, or green and can be applied to steel, aluminum, copper, or brass. Zinc plating can be done by a professional but if you follow careful instructions and precautions it can also be done at home with great results.

Cleaning The Surface

The first and probably most important requirement for plating is proper cleaning of the components you intend to plate. It is best to use a degreaser, solvent, or even scrubbing with caustic soda. This should be followed by a solution known as "pickle". Common vinegar is not strong enough. Iron mongers offer a solution known as hydrochloric acid which can be used when diluted. When using this acid it is important to know that it is very corrosive so every precaution should be used to protect the handler. After the components are soaked for four minutes they will need to be rinsed with water. After rinsing take care not to touch the components again or you will be required to repeat the process.

Zinc Plating Set-up

You will need a plastic or stainless steel container which is appropriately sized. You will also need an electrical source such as a car battery or charger and a meter to check current levels. Iron mongers or non-ferrous scrap yards will be able to supply you with either pure or perforated zinc. The electrolyte, zinc chloride and ammonium chloride, can be found at chemistry suppliers, pharmacies, or chemical suppliers. It will take 120 grams of ammonium chloride mixed with 750 ms of tap water to produce one litre of electrolyte.

This should then be mixed with 20 grams of zinc chloride and 250 ml of warm water. Keep in mind this solution is corrosive so precaution should be taken to protect your skin.

You will need a way to control the current going to your plating bath. If you are using a car battery a rheostat can help you to keep the current to about 100 milliamps per square inch of your plating surface. If your current is set too high it will produce a rough surface which is not acceptable. The zinc serves as the anode and should be connected to the positive terminal. The component you are working on is the cathode and is connected to the negative terminal. You should soon see your component turn grey which indicates to you the zinc layer is forming. The grey layer becomes thicker the longer you leave it. When the plating is complete you will need to scrub the component under regular tap water before allowing it to dry. Once the component is dry you can polish it. You should be able to achieve a shiny finish which closely resembles chrome but will be much more durable.

Supply House Kits

Zinc plating kits with directions are available from some electroplating supply houses. The kits can include a power supply, made up solutions, cleaners and acid dips, chromate passivate dips to protect the coating and full directions. These can be listed under hobby plating or electroplating kits.

A salt spray test is used to determine the capability of the zinc plating and to measure the quality of the finish. A continuous solution of salt is either sprayed or fogged onto the surface which will accelerate the corrosion process. This test can determine the effectiveness of the plated finish when left out in the elements. Typically the plated surface will hold up better if protected from moisture.

Twice The Protection

You can get double protection with zinc electroplating and passivation. Most types of steel can be protected including castings. Passivation, or conversion coatings, are applied to zinc deposits in order to improve the life of the plated component. These coatings provide extended surface corrosion resistance in extreme environmental conditions. With continued research platers have developed a wide range of sealants which improves performance and extends the range of finishes which are available.

Full yellow passivation is well known and has proven to provide a high level of protection. Clear blue passivation will provide a shiny, chrome-like finish. Olive and black can be decorative and also provide corrosion resistance. A clear corrosion resistant topcoat will improve the surface appearance while adding additional protection.

While there has been some adverse reaction to traces of hexavalent chromium in passivate coatings it is also well known that as little as 0.1 gram of hexavalent chromium per square meter can provide outstanding corrosion resistance. Zinc platers are now using passivate coatings that do not have hexavalent chrome.

There are many variables when trying to choose the type of zinc plating which is right for you. You need to know what the component is being used for and what type of elements it will be exposed to. Also you will need to decide what type of finish you desire. If you choose to have a high gloss, shiny finish you will need to take extra precaution to protect the finish from harsh elements since this can cause the finish to corrode. Cost is always a consideration. If you are plating an inexpensive object you may choose to do the plating yourself whereas a bigger, more expensive project may require a professional. Whatever your need, zinc plating can be a cost effective way to protect your components.