Coated Sheet 


Electrolytic Zinc Coated and Zinc-Iron Alloy Coated Sheet
U. S. Steel Electrolytic Zinc Coated and Zinc-Iron Alloy Coated Sheet is manufactured by electroplating either a pure zinc or a zinc-alloy (typically, 12-15% iron) coating on one or two sides of carbon steel sheet. This continuous electrolytic coating process can be used to apply either type of coating onto the surface of the steel sheet with an exceptionally uniform thickness. In addition, the coated sheet has a smooth, matte appearance similar to cold rolled sheet. Thus, the surface quality is exceptionally good for applications that require a high finish after painting, such as automotive exposed panels.

The excellent control of the coating thickness that is achieved with the electrolytic deposition process is beneficial to enhance forming and joining operations, especially by contributing to more reliable results from automatic and robotic welding systems.

The excellent control of the coating thickness that is achieved with the electrolytic deposition process is beneficial to enhance forming and joining operations, especially by contributing to more reliable results from automatic and robotic welding systems. 

Both the zinc and zinc-iron electrogalvanized coatings are readily paintable, but to achieve good resistance to corrosion, the coated-steel surface should be pretreated and primed prior to application of the finish paint coating.

The most common pretreatment is zinc phosphate. Both the pure zinc and the zinc-iron alloy coating provide sacrificial corrosion protection for the steel. However, the zinc-iron alloy corrodes more slowly than zinc, thus, the same amount of protection can be achieved with a thinner coating of the alloy than of pure zinc.

Both types of coatings exhibit very good adhesion during forming operations even though the bond is not a metallurgical bond like that attained during hot-dip coating. Because the zinc-iron alloy coating is harder than the pure zinc coating, the surface is more resistant to manufacturing damage during stamping and handling.

The mechanical properties of electrogalvanized sheet are approximately the same as those for the equivalent grade (steel designation) of cold rolled sheet because the steel coils are pre-annealed prior to processing on the electroplating line. For example, DDS cold rolled sheet and DDS electrogalvanized sheet have similar mechanical properties. This does not mean that electrogalvanized product will behave similarly during stamping/drawing.

The coating influences the behavior during forming; thus, special practices are required when stamping electrogalvanized products. With the correct type of die material, clearances, etc., the stamping performance of the two products are similar.

U. S. Steel Electrogalvanized Sheet can be roll- and brake-formed, lock-seamed, deep drawn, stretched, and joined using methods such as welding, soldering, and adhesive bonding. As a result, the designer and materials specifier have a good range of practical choices for matching electrogalvanized material to the end use, the degree of corrosion resistance required and the fabrication process.

Typical Applications Application Considerations Fabrication Considerations Tolerances