The Influence of Sealing Processes and Machining Operations on the Scratch and Wear Resistance of Anodized AlSi9Cu3(Fe) Diecasting Alloy

The effects of hydrothermal and cold sealing processes on the scratch and wear resistance of the anodic layer have been studied. High-pressure diecast AlSi9Cu3(Fe) alloy plates were anodized in a sulfuric acid electrolyte at 16°C and further sealed in boiled water or in a NiF2 solution at 25°C. To analyze the influence of pre-anodizing machining operations, the plates were studied in the as-diecast condition and after milling. Metallographic investigations and image analysis techniques were carried out to study the morphology and thickness of the anodic layer. Hardness, wear, and scratch measurements were also performed to characterize the surface mechanical properties. The results showed that the sealing processes enhanced the wear and scratch resistance of the anodized surfaces because of the precipitation of hydrates that sealed the surface porosity. The thicker oxide layer formed on the milled substrate led to a greater wear resistance compared to the as-diecast surface, owing to reduced wear of the underlying aluminum substrate. Finally, a cracked mechanically mixed layer, which was enriched with fragmented intermetallics and anodic layer debris, was formed on the anodized surfaces at the end of the wear tests.