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The growth of coated sheet steels in automotive applications continues to require new application technology in joining, finishing, painting and forming. The formability of zinc-coated steels depends on both the character of the substrate and nature of the coating. By eliminating the substrate as a variable in this study, the effect of various coatings (one-side electrogalvanized, hot-dip zinc and iron-zinc alloy) on formability was determined using simulative laboratory tests. Under conditions of plane strain and stretch, all coated and uncoated steels performed comparably and can be considered interchangeable with each other. However, for drawing conditions, the drawability parameter, rm, of the hot-dip iron-zinc alloy coated steels was inferior to that of both free zinc coatings and uncoated steels.

Sheet metal automotive components are developed in several stages, including “soft tool” (zinc alloy) prototype development and “hard” final tool tryout. Increased use of zinc and zinc-alloy coated steels for these stampings has raised concern about the reaction of metallic coatings on steels with the “soft” prototype die materials. Choice of forming lubricant adds further complications. To investigate this, a variety of hot-dip and electro-galvanized zinc and zinc-alloy coated mild steels were tested in several forming modes using both “hard” steel and “soft” prototype tools and several different lubricants. The zinc coating interaction with the prototype tooling depends on the nature of the coating on the steel, the deformation mode, and the lubricant. Therefore, proper selection of lubricant for soft tool tryout may be difficult. Hot-dip, alloy-coated steels pose special problems in this respect.