Effect of Al Oxide Layer on Frictional Properties of Hot Dip Galvanized Steel Sheet

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/m 2 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.

Segregation Mechanism of Al-based Oxides on Surface of Zn-0.2mass%Al Hot-dip Galvanized Steel Sheets

“…However, a significant difference was observed in the analytical results for Al ( After aging in air at 20°C, Al-based oxides were observed in the hollows formed by contact with the temper roll, as well as in the area on the grain boundaries of the Zn, whereas the intensities of Al and O on the HDG held in liquid nitrogen for the same time were low. This behavior was also similar to that observed in previous reports [16][17][18][19][20] investigating the segregation behavior of the Al-based oxides on the temperrolled HDG surface.…”

“…In order to understand the segregation behavior of the Al-based oxides on the area of contact with the temper and temper rolling was about 2.5 mg/m 2 and increased to approximately 7.0 mg/m 2 after aging for 1 680 h in air at 20°C. This behavior was similar to that observed in previous reports [16][17][18][19][20] investigating the segregation behavior of the Al-based oxides on the temper-rolled HDG surface. As in the result for HDG without temper rolling, the amount roll, the surfaces of the HDG without temper rolling and the temper-rolled HDG after aging for 1 680 h in air at 20°C were observed with the BSE detector.…”

“…15,16) Hoshino et al investigated the effect of these Al-based oxides on the friction coefficient of HDG and reported that the friction coefficient decreased due to Al-based oxides on the surface. [17][18][19][20] The Al-based oxides that originally existed on the HDG surface were removed by the sliding tool and adhered to the tool surface, and these adhering Al-based oxides prevented direct contact of the sliding tool with the Zn coating layer, thereby reducing the friction coefficient. [18][19][20] These segregated Al-based oxides presumably also affect other quality properties required in products, such as weldability.…”

“…[17][18][19][20] The Al-based oxides that originally existed on the HDG surface were removed by the sliding tool and adhered to the tool surface, and these adhering Al-based oxides prevented direct contact of the sliding tool with the Zn coating layer, thereby reducing the friction coefficient. [18][19][20] These segregated Al-based oxides presumably also affect other quality properties required in products, such as weldability. However, the segregation mechanism of Al-based oxides on the HDG surface with increasing aging time in air at room temperature has not yet been clarified.…”

Diffusion Behavior of Al in Zn Coating Layer of Zn-0.2mass%Al Hot-dip Galvanized Steel Sheets with and without Temper Rolling during Aging after Production

“…[3][4][5][6][7] It is well known that Al-based oxides exist on the surface of HDG, 8) and the effect of these oxides on the frictional characteristics of HDG has been investigated. [9][10][11] It has been reported that Al-based oxides had the effect of reducing the friction coefficient by adhering to the tool surface during sliding. [9][10][11] A new highlubricity HDG was developed by applying this mechanism, by which a thin oxide layer reduces the friction coefficient, and is used practically to stabilize press formability in mass production of automotive body parts.…”