Anodic dyeing of micro-arc oxidized aluminum with a cathodic pretreatment

Conventional anodized aluminum with diverse colors by surface dyeing has recently become widespread for consumer electronic appliances. Satisfactory performance, though, it failed to present good enough protection purpose. On the contrary, micro-arc oxidation (MAO) is a relatively new anodizing surface treatment to provide very high surface hardness and thus protection purpose but is incompatible with the dyeing process. In this study, we investigated a dyeing method for the MAO treated aluminum alloy by using a cathodic pretreatment to produce micropores over the MAO layer, as a result to absorb the anionic dye in a subsequent anodic treatment, thereby dyeing the MAO layer. The research results showed that the dyed MAO film achieved the optimal color saturation (L* a* b*) = (53.55, 1.17, − 29.16) when the specimen was immersed in a blue dye to undergo a dyeing process with an applied anodic current of 1 A subsequent to the pretreatment at an applied cathodic voltage of 30 V. Additionally, red and green dyes were also demonstrated to be feasible. Mechanism to make the MAO layer dyeable is proposed.