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Oil type, weight and storage time effects on formability of galvannealed sheet steels were examined in punch stretching (LDH) and friction (DBS) tests. The effects of oil weights between 1 and 8 g/m2 and storage times up to three months were examined. The results suggest that application of prelube or mill oil of about 3 g/m2 is desirable to maximize formability. Lower amounts of oil could lower punch stretchability somewhat from the maximum values. On the other hand, oil weights beyond 3 g/m2 did not appear to offer additional improvements in formability. DBS friction coefficients did not change with oil weight or storage time. Storage caused some variability in punch stretching test results for samples with the mill oil. The results indicate that prelube is beneficial for the formability of galvannealed sheet steels in the specific forming modes tested here, and the benefits continue after storage for up to three months.

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.

Galvanneal powdering was examined on a stabilized ultra low carbon steel substrate as a function of strain state using cup drawing and in-plane stretching experiments to simulate deformations encountered in production stampings. Significant powdering was encountered in drawing while minimal powdering occurred in in-plane stretching. Powdering was measured at specific locations and correlated with strains in those locations. A powdering map was generated in strain space using the experimental data. A few measurements of powdering on selected regions of an automotive stamped part are reported.