Formability Performance of Prephosphated Galvannealed Sheet Steel

An experiment to determine the effects of mill oil weight, phosphate coating type and weight, surface roughness, and blank wash on the formability of prephosphated galvannealed steel was conducted. Limiting dome height, limiting drawing ratio and draw bead simulator friction tests were run on bare galvannealed and galvannealed coated with a conventional process phosphate and with three Dried-in-Place (DIP) phosphate products. Formability performance of both the conventional and DIP phosphate coated products was significantly better than that of oil-only coated galvannealed steel. Phosphate coating weights heavier than about 0.6 g/m² per side did not significantly improve formability. The formability improvement from phosphate coating was about equal for the four products tested, with optimum oil weight for formability in the 1.3 to 1.9 g/m² range. Surface roughness (within the testing range) and blank washing had no significant effects on formability.