Growth Pattern of Hard Anodic Film of Al Alloy 6061 in Low Concentration H₂SO₄

The growth pattern of hard anodic film on Al alloy 6061 in low concentration H2SO4 was studied by SEM. The results showed that the hard anodic oxide film was point-like growth on the surface of substrate at first. As the reaction progressed, the point-like oxide film grew up and spread out on the surface of substrate. At the same time, some new point-like oxide film grew on the non-oxidized surface area of substrate. In this way, oxide film grew up gradually until all the surface of substrate was covered with oxide film. After that the growth pattern of hard anodic film was almost the same as the traditional pattern. Under the same oxidation time and temperature conditions, the hardness and thickness of the oxide film in low concentration H2SO4 were higher than those of the traditional ones.