Metal Additive Manufacturing Conference 2018

Anodizing is the most common electrochemical surface treatment applied to aluminium and its alloys for protection against corrosion. Due to the special conditions during the metal additive manufacturing process, the formation of unique microstructures with fine internal phase distributions can be achieved. These microstructures have been shown to have a considerable influence on the corrosion behavior and the mechanisms of surface treatments to improve corrosion resistance, such as anodizing. In order to understand the microstructure influence on the anodizing mechanism of these materials, additive manufactured AlSi10Mg specimens were galvanostatically anodized in H2SO4 electrolyte. As a reference, a cast alloy of approximately the same chemical composition as that of the AM specimens was used. In the cast alloy, eutectic structures are present and the silicon is distributed in large precipitates while in the AM alloy the silicon is more finely distributed. As the silicon seems to hinder the growth of the oxide layer during anodizing, the difference in phase distribution leads to differences in the anodizing behavior. Significant differences were found in the anodizing voltage–time characteristics and the resulting anodic film structure. In the additive manufactured specimens the anodic oxide growth is much more obstructed than for the cast alloy and the porous layer features look very different, following the local silicon distribution. The average oxide film thickness is significantly lower for the same anodic charge input, but a more continuous layer is formed.