LAUSR

The effect of the Al-based oxide layer which segregates on the surface of hot-dip galvanized steel sheets (GI) with aging on the frictional properties of the GI was investigated. Conventional GI with the Zn coating weight of 67 g/m including 0.36 mass% Al were used as test specimens. It was found that an Al-based oxide layer grew on the GI surface with aging after production, and the friction coefficient tended to decrease due to the existence of these Al-based oxides. However, this tendency was clearer under the sliding conditions of shorter tool length and higher contact pressure than of longer tool length and lower contact pressure. In order to understand this behavior, surface observation and analysis of both the test specimens and the tools after sliding were carried out by SEM, EDX and EPMA. Both Al-based oxides and metallic Zn were detected as adhered materials on the tool surface after sliding, and the surfaces of adhered materials were covered with Al-based oxides. This suggests that the adhered materials on the tool have the effects of reducing the adhesion force between the metallic Zn of the GI and the tool and reducing the tool roughness. These effects led to a lower friction coefficient because both shearing and plowing resistance were decreased. In addition, the area on the tool which were covered by the adhered materials depended on the tool length. This is thought to be the reason why the effect of the Al-based oxide layer depended on the sliding conditions.