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What additive in an E-Coating provides the corrosion resistance?

Hi my Name is Terry Smith and I promote hot dip galvanizing in South Africa. I have been asked to compare an e-coating with hdg, so my question is this: What property in an E-Coat provides the so-called corrosion resistance that I have read in various articles and how is this corrosion resistance rated against a general hot dip galvanized coating of say 70um thick?

Terry Smith
Metallic Coating Consultant - Cape Town, South Africa
August 30, 2011

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September 1, 2011

Your question is similar to asking us to compare a Rolls Royce and a mini automobile--but here goes.
Both systems are used to slow down the attack from the surrounding elements, oxygen, and water and in some cases salt that would ultimately cause the metal substrate to rust/corrode. These two types of coating act as a sacrificial substance in that they offer themselves up to attack prior to the metal substrate.
However, the similarity ends there, the HDG is a one coat system whereas the e-coat will need a pre-treatment (Zinc Phos) if maximum protection is required. You are also talking of 25 microns max film weight for the EC. HDG is a stand alone treatment where EC would require a further top coat (Powder Coat) before one would specify it for use as a corrosion preventative coating system, otherwise, as a stand alone finish it would just be used purely as a decorative finish. If one talks about corrosion resistance then HDG will outlast a single coat of EC (correctly pre-treated) by a factor of >3.

Terry Hickling
Birmingham, United Kingdom