Zinc and zinc-alloy coated steel is used to enhance a structureâs protection against corrosion degradation. For the purpose of this SAE Recommended Practice, a galvanized coating is defined as a zinc or zinc-alloy metallic coating. The selection of the optimum galvanized steel sheet product depends on many factors, the most important being: desired corrosion protection, formability, weldability, surface characteristics, and paintability. The trade-offs of these product characteristics are more complex than is the case with uncoated steel sheet products.