Lateral growth of PEO films on Al7050 alloy in 0.1 M NaAlO2

This paper investigated generation behavior of micro-arcs and growth behavior of PEO films on the AA7050 disc specimen in 0.1 M NaAlO2 solution under the application of 1200 Hz anodic pulse current. Morphologies, thickness and surface roughness of PEO films were examined at the edge part and central part separately. Micro-arcs were generated first at the edge part and then moved towards the central part with PEO treatment time, indicating lateral growth of PEO films. The lateral growth resulted in uniform PEO thickness of about 5 μm and surface roughness of about 0.5 μm. Moving of the arcs from the edge towards the central part appeared only one time and large size arcs were generated at the edge before completing the central part with small size micro-arcs. This suggests that vertical growth starts before completing the lateral growth. Large size arcs generated at the edge resulted in the formation of relatively large size pores within the PEO films on the AA7050 disc specimen.