2015 Volume 101 Issue 11 Pages 584-589
The effect of iron content of zinc layer and lubricated layer on sliding performance of the galvannealed steel sheets (GA) was investigated.
The effect of iron content on friction coefficient for lubricated GA was dependent on the sliding condition. For the condition in which the contact pressure is high, the friction coefficient increased with the increase of iron content of GA. However, for the condition in which the pressure is low, the friction coefficient decreased with the increase of iron content. This tendency of the friction coefficient was also observed in the fender model press forming test.
When the contact pressure is high, more oil pockets were formed on the surface due to the increase of the plateau area. Therefore, the friction coefficient decreased since the partial pressure was sustained in the oil pockets. Since the GA coating with low iron content is softer than that with high iron content, the friction coefficient of lubricated GA increased with the increase of iron content.
On the other hand, when the contact pressure is low, the oil pocket was not formed on the surface. In addition, the lubricated layer is easily worn since the tool length is long and the lubricant surface is more damaged than in the case of short length tool. Therefore, the friction coefficient is affected by the adhesion between tool and GA surface. This is why the tendency of iron content on friction coefficient for GA and lubricated GA is similar.
