IMPACT AND ABRASION RESISTANCE

      Hardness, ductility and adherence combine to provide the galvanized coating with unmatched protection against damage caused by rough handling during transportation to and/or at the job site as well during its service life. The toughness of the galvanized coating is extremely important since barrier protection is dependent upon coating integrity.
      Other coatings damage easily during shipment or through rough handling on the job site. Experts will argue that all organic forms of barrier protection (such as paint) by their nature are permeable to some degree. Correctly applied galvanized coatings are impermeable.
      If the galvanized coating is physically damaged, it will continue to provide cathodic protection to the exposed steel. If individual areas of underlying steel or iron become exposed by up to 1/4" diameter spot, the surrounding zinc will provide these areas with cathodic protection for as long as the coating lasts.

Below the name of each layer in the figure appears its respective hardness, expressed by a Diamond Pyramid Number (DPN). The DPN is a progressive measure of hardness. The higher the number the greater the hardness. Typically, the Gamma, Delta, and Zeta layers are harder than the underlying steel. The hardness of these inner layers provides exceptional protection against coating damage through abrasion. The Eta layer of the galvanized coating is quite ductile, providing the coating with some impact resistance.

PERFORMANCE AT ELEVATED TEMPERATURES

Galvanized coatings perform well under continuous exposure to temperatures up to 392^o F (200^o C). Exposure to temperatures above this can cause the outer free zinc layer to peel from the underlying zinc-iron alloy layer. However, the remaining zinc-iron alloy layer will provide good corrosion resistance and will continue to protect the steel for a long time, depending upon its thickness.

CORNER AND EDGE PROTECTION

The galvanizing process naturally produces coatings that are at least as thick at the corners and edges as the coating on the rest of the article. As coating damage is most likely to occur at edges, this is where added protection is needed most. Brush-applied or spray-applied coatings have a natural tendency to thin at corners and edges.

A photomicrograph of a cross-section
of an edge of a piece of galvanized steel.