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Galvanized vs. Galvannealed Steel

What is the difference between Galvanized and Galvannealed steel?

They both are zinc coated at the mill and are designed for rust and corrosion resistance. Both are passed through a hot dip coating process; however Galvannealed steel goes through an additional annealing process, which induces diffusion alloying between the molten zinc coating and the steel.  This vastly improves the formability and paint adhesion of the Galvannealed material but leaves it with a duller matte surface compared to the spangle finish achieved with just Galvanized.

They both fall under ASTM A 653/A 653M. The Galvannealed is designated with an “A” (A40, A60); and Galvanized designated with a “G” (G40, G60).  The number call out for both is the weight of the coating; G60 or A60 is 0.60 ounces per square foot (resulting in an ‘average’ thickness of about 0.0005 inches).

So the question is: When is it worth the additional cost to create the zinc-iron alloy coating?  The general answer is if the parts will be formed significantly during manufacturing; and/or if the are to have a painted/powdercoated finish.

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