Zinc electroplating is a method of depositing zinc metal on the surface of another metal such as steel by immersing it in a plating bath and passing an electric current through it.
A zinc coating provides corrosion protection to steel because it corrodes in preference to the steel; it is what is known as a sacrificial coating.
When zinc corrodes it develops a white powdery appearance commonly known as white rust. To delay the appearance of white rust a chromate surface treatment is usually applied to the zinc.
There are a number of types of chromate conversion coatings, each with a different appearance and offering differing levels of corrosion protection.
Zinc plated commercial fasteners in Australia are usually stocked in either a clear chromate finish (also known as blue or bright zinc) or yellow iridescent (known as yellow zinc or dichromate).
There are several other chromate conversion coatings specified for certain applications including olive drab, commonly used in the defence industry and black, which is often specified in the automotive industry.
All zinc plated fasteners in the Exafast range are plated in accordance with Australian Standards; AS4397 for imperial products and AS1897 for metric.
Coating thickness is typically between 4 and 8 microns. Although the chromate conversion coatings outlined above usually impart a pleasing luster to a zinc plated fastener, it should be remembered that in performing its function of protecting the fastener from red rust, the zinc will corrode and its appearance deteriorate over time.