Electrode temperature evolution during anodic oxidation of AlSi(Cu) alloys studied in the wall-jet reactor

Anodic oxidation in the wall-jet electrode reactor was performed for three different cast aluminum substrates (i.e. Al 99.80 wt.%, Al-10 wt.% Si, Al-10 wt.% Si-3 wt.% Cu) in order to assess the evolution of electrode temperature under a broad range of current densities (i.e. 3.0–40 A dm−2). Anodizing was carried out in 2.25 M H2SO4 electrolyte at 25 °C under free and forced convection regimes. At current densities between 3.0 and 15 A dm−2, corresponding to electrode temperatures lower than 60 °C, the temperature evolution showed the highest values for the AlSi alloy followed closely by the AlSiCu and Al substrates. At larger current densities and temperatures, the temperature sequence changed with the highest values recorded for Al followed by AlSi and AlSiCu alloys. In addition, under these conditions, the oxide layer thickness could not be further increased for any of the three compositions probably due to the severe effects of thermally enhanced field-assisted and chemical oxide dissolution. The changes observed in the thermal effects associated with anodizing of Al at large current densities (i.e. 15≥A dm−2) were related to the higher rates of conductive heat transfer for Al relative to the other two compositions. The forced convection regime determined a significant decrease in electrode temperature and an increase in oxide layer thickness and anodizing voltage for all three compositions investigated.