Abstract
Anodic oxide layers formed on three cases of 7075 Al alloy substrate were investigated. The effects of substrate microstructure on the anodic oxide layer were assessed. The 7075 Al alloy substrates were produced by superheated slurry casting of Gas Induced Semi-Solid (GISS) type, from initial solids fractions of 9% (SSM3), 22% (SSM10), and 33% (SSM20). They varied in the number and size of secondary phase particles in the microstructure. The anodizing was performed in sulphuric acid solution sealed by hot water. The thickness of the anodic oxide layer was similar (∼13 μm) across all cases. The SSM3 had rather linear substrate/oxide interface, while the other cases had irregular interfaces disturbed by the secondary phase particles. The SSM3 had smaller secondary particles embedded in the anodic oxide layer than the other cases that had higher secondary phase fraction. This resulted in the lowest hardness of the anodic oxide layer for the SSM3 case.
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