What is Zinc Plating?
Zinc plating involves zinc metal being electrodeposited on to components. Zinc plating is passivated to give it corrosion resistance and the zinc plating protects the underlying material further by being sacrificial. Zinc electroplating is a form of electrochemical galvanization. The passivation on zinc plating determines its final colour - we can offer no passivation, clear passivation (blue tinted, trivalent) or colour passivation (yellow, iridescent, hexavalent). A clear passivate is close to a natural zinc finish in terms of appearance but will have considerably better corrosion resistance and appearance over time. Thicknesses of 5µm, 8µm, 12µm and 25µm are common, but other thickness are available on request. We offer bright zinc plating on components made of steel, stainless steel, copper, brass and bronze.
As well as a rack zinc plating, we can also perform barrel zinc plating as an economical way to handle high quantities of small parts.
Specifications Offered
- ISO 2081 (replaces BS 1706 and BS EN 12329)
- ASTM B633
- Def Stan 03-20 (replaces DTD 903D)
- MIL-STD-171 1.9.1, 1.9.2
We can work to many other specifications, but the above are our most popular. Please contact us with your requirements.
Information for Designers
Thickness and Growth
Zinc Plating is deposited on the surface of the component. So the growth per surface will be equal to the thickness per surface. Thicknesses for zinc plating are generally specified as minima (ISO 2081 and ASTM B633), although control within a range is possible. We have written some guidance for zinc plating thickness.
Sacrificial Anode
A coating of zinc on steel acts as a sacrificial anode because of its position in the galvanic series. This is very useful because even if the coating is scratched or damaged, the zinc will provide protection to the base metal by sacrificing itself.
Base Material Condition
The base material is very important to the quality of the plating. Best results will be obtained by using clean steel (as opposed to black steel). It is recommended that you ensure that material is not porous or pitted, because these will be corrosion sites despite the zinc plating. A common problem is when people use bar without mechanically abrading/machining the surface. ASTM B663-13 states:
Defects in the surface of the basis metal, such as scratches, porosity, pits, inclusions, cracks, roll marks, and die marks, may adversely affect the appearance and performance of coatings applied thereto despite the observance of the best electroplating practices.
Tensile Strength of Base Metal
Components with a tensile strength of over 1000 MPa are liable to hydrogen embrittlement and require de-embrittlement and stress relief. It is essential that parts that are high tensile strength and will require de-embrittlement and/or stress relief are clearly marked as requiring this when sent to us.
Throwing
This is not a concern for the majority of parts. The geometry of parts may make it difficult for the zinc to "throw" into certain areas (usually insides of tubes and the corners of deep boxes). For situations like this we can usually have an internal anode manufactured (for all over coverage) or if that is not economic or not possible, we can dip the part in a corrosion inhibitor that helps to protect the bare areas.