Please note - The information provided on this page is purely to inform you about some aspects of zinc plating as a surface finishing choice. A Class does not actually provide zinc plating processes here at A Class. For restorers - we will take in your job, do the preparation work then arrange the zinc plating for you through another supplier if you like (some of the zinc plating firms will not handle small jobs, or they have high minimum charges). For large batches and Manufacturers quantities you are advised to go direct to a firm that does this plating process on site (we can provide you the names of one or two firms to try).
About Zinc Plating
The primary purpose of zinc plating is to protect metals from the effects of corrosion or rust. Zinc Plated coatings are “sacrificial” coatings – meaning the coating sacrifices itself in order to protect the substrate beneath, as the coating oxidizes the corrosion itself continues to provide a level of protection to the substrate.
One of the criticisms of zinc plating is the use of chromates (Hex-valent Chromium) in the process, which, because the chromates are retained in the surface of the parts, can result in leaching of that toxic substance into the environment when it eventually breaks down and corrodes away. This does not occur in ‘chromium’ plating where, even though hex-valent chrome may be used in the application process, the plated coating does not retain the hexvalency (the coating is relatively pure, inert metal) and therefore cannot leach any toxins if it breaks down. The focus on environmental impacts has had an impact on developments for zinc plating and the industry is now beginning to see the substitution of hex-valent chrome with tri-valent chrome which is far less harmful. If environmental impacts are important to you it would be wise to investigate the type of plating process used by your supplier.
Zinc plating comes in different colours – but each of the colourscan result from the type of plating formulationused - meaning that they do not necessarily have the same resulting corrosion resistance properties as each other. Further, zinc plating types also vary in their ability to protect from both “red” (iron related) and “white” (alloy related) corrosion types – though we will not explore that any further here.
The following briefly describes some of the common zinc colours/types:
1) Zinc Gold Passivate
Yellow Zinc (Gold Zinc) is the most common type of zinc plating used in automotive parts finishing. Gold is its colour only – it does not contain actual gold. Of all the zinc types it retains a good average level of corrosion resistance.
2) Black Zinc
Some suppliers use a black oxide coating or dye over the surface of zinc plating (e.g. olive drab) and call it black zinc. Others use formulations that are actually black plated. The level of corrosion resistance of the latter will be somewhat lower than that of gold zinc – but better than clear passivate. The oxide-coated versions will tend to offer slightly better resistance due to the additional coating and depending on the underlying type of zinc used.
3) Blue or Clear Zinc
Though clear zinc, you would imagine, has no colour, often it is referred to as blue as it can result in a blue-ish hue. This type of coating is often achieved by tri-valent based processes which are more environmentally friendly than the hex-valent versions but offer lower corrosion resistance properties.
4) inc cobalt
Cobalt zinchas been said to offer more than 5 times the corrosion resistance of other zinc types and is very ductile. It is a plated alloy of the two metals and in some cases it can be provided in colours of olive, blue, black or gold.
5) Acid zinc
Acid zinc plating does not use cyanides in the process (sometimes used in alkaline types). It’s advantages as a finish (over other types) include brightness, ability to plate otherwise difficult to plate substrates, and lower levels of hydrogen embrittlement of parts.
Alternatives to Zinc Plating for Corrosion Resistance
Depending on the application, A Class can offer advice on alternatives to zinc plating for achieving corrosion resistant outcomes. One such alternative that offers many advantages is Electroless Nickel plating. Please call us if you require any further information.
Please note that the above information is provided as a general guide, for the general information of the reader only, and should not be relied or acted upon as accurate technical advice.
