Abstract
The effect of the Al oxide layer which segregated on the surface of hot dip galvanized steel sheet (GI) with aging on the frictional properties of the GI was investigated.
Conventional GI with the Zn coating weight of 67 g/m2 including 0.36 mass% Al were used as test specimens. It was found that an Al oxide layer grew on the GI surface with aging after production, and the friction coefficient tended to decrease due to the existence of this Al oxide. However, the tendency was clearer under the sliding conditions with shorter tool length and higher contact pressure than with longer tool length and lower contact pressure.
In order to clarify the mechanism, surface observation and analysis of both the test specimens and the tools after sliding were carried out by SEM, EDX and EPMA. Both Al oxide and metallic Zn were detected as adhesions on the tool surface after sliding, and the surface of the adhesions was covered with Al oxide. It is thought that the adhesions on the tool had the effects of reducing the stickiness between metallic Zn of 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 was covered by the adhesions depended on the tool length. This is thought to be the reason why the effect of the Al oxide layer on the friction coefficient depended on the sliding conditions.
