Effect of AC Current Density on the PEO Film Formation of Al6061 Alloy

Al6061합금의 PEO 피막 형성에 미치는 AC 전류밀도의 영향

Abstract

In this work, PEO (Plasma Electrolytic Oxidation) film formation behavior of Al6061 alloy was investigated as a function of applied current density of AC at 310 Hz in the range from $120mA/cm^2$ to $300mA/cm^2$ in 0.5 M $Na_2SiO_3$ solution. When applied current density is lower than a critical voltage of about $132mA/cm^2$, voltage reaches a steady-state values less than 120 V without generation of arcs and metallic color of the alloy surface remains. On the other hand, when applied current density exceeds about $132mA/cm^2$, voltage increases continuously with time and arcs are generated at more than 175 V, resulting in the formation of PEO films with grey colors. Two different types of arcs, large size and small number of arcs with orange color, and small size and large number of arcs with white color, were generated at the same time when the PEO film thickness exceeds about $50{\mu}m$, irrespective of applied current density. Formation efficiency of the PEO films was found to increase with increasing applied current density and the growth rate was obtained to be about $5{\mu}m/min$ at $300mA/cm^2$. It was also found that surface roughness of the PEO films with $70{\mu}m$ thickness is not dependent on the applied current density.

Fig. 1. Schematic diagram of experimental setup for PEO treatment.

Fig. 2. V-t curves of Al6061 at various applied current densities of 310 Hz AC in 0.5 M Na₂SiO₃ solution.

Fig. 3. V-t curves of Al6061 at various applied current densities of 310 Hz AC in 0.5 M Na₂SiO₃ solution.

Fig. 4. Photographs of arcs generated during PEO of Al6061 alloy at 150 mA/cm² 310 Hz AC in 0.5 M Na₂SiO₃ solution.

Fig. 5. Photographs of arcs generated during PEO of Al6061 alloy at 200 mA/cm² 310 Hz AC in 0.5 M Na₂SiO₃ solution.

Fig. 6. Photographs of arcs generated during PEO of Al6061 alloy at 250 mA/cm² 310 Hz AC in 0.5 M Na₂SiO₃ solution.

Fig. 7. Photographs of arcs generated during PEO of Al6061 alloy at 300 mA/cm² 310 Hz AC in 0.5 M Na₂SiO₃ solution.

Fig. 8. PEO film thickness-t curves of Al6061 with treatment time at various current densities of 310 Hz AC in 0.5 M Na₂SiO₃ solution.

Fig. 9. PEO film growth rate on Al6061 with treatment time at various current densities of 310 Hz AC in 0.5 M Na₂SiO₃ solution.

Fig. 10. Surface roughness of PEO films with the same thickness of about 72±2 μm on Al6061 formed at various current densities of 310 Hz AC in 0.5 M Na₂SiO₃ solution.

Table 1. Chemical composition of Al6061