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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.

A comparison of the cosmetic corrosion performance of zinc and zinc-iron alloy coated steels is made. Cosmetic corrosion can be defined in terms of paint creepage/blistering, red rust, and paint adhesion. Traditional scribe-type tests adequately address creepage and rusting, but do not adequately address paint adhesion. A new lab procedure called the Chipping Corrosion Test was used to assess paint adhesion of coated steels processed under various phosphate conditions. A review of the relative performance of zinc and zinc alloy coated steels in traditional scribed panel corrosion tests and the new chipping corrosion lab procedure is presented. Results of the Chipping Corrosion Tests showed significant differences in material performance when processed under plant conditions that were not evident under laboratory process conditions, or in traditional scribe-type tests.