Thermal effects associated with hard anodizing of cast aluminum alloys

Hard anodizing of three different cast aluminum substrates (i.e. Al99.8 wt%, Al-10 wt% Si, Al-10 wt% Si-3.5 wt% Cu) was performed in 2.25 M H2SO4 electrolyte at 0 °C. The effects of substrate composition, current density and convection regime on electrode temperature evolution were investigated. Temperature transients followed the voltage transients during anodizing. At a current density of 6.0 A dm−2, the electrode temperatures increased with alloying whereas at 30 A dm−2 the temperature reached a steady value around 65 °C and severe oxide dissolution effects were visible on the surface of the anodized specimens. Further, at this current density and under forced convection regime, highest temperature values were recorded for the Al99.8 wt% substrate and were accompanied by fluctuations. Forced convection significantly reduced the electrode temperatures during the non-uniform oxide growth for all three compositions and increased the oxide layer thickness.