Galvanneal Powdering in Drawbeads

Coating mass losses occurring on two galvannealed sheet steel samples, one with and one without significant amounts of zeta in the coating, were measured in draw bead simulator tests at different bead penetrations, sliding speeds and with different amounts of oil on the surface. Coating mass losses were small relative to the coating weight. The galvanneal coating without zeta exhibited a greater mass loss than the coating with zeta. Bead penetration was an important variable affecting coating mass loss in both coils, and through an interaction with sliding speed in one coil. Compressive strains due to bending and unbending are the primary cause for coating mass loss; sliding friction did not enhance coating mass loss. The quantitative results are compared with coating mass losses that occur in other formability tests.