In the direct current (DC) sulphuric acid anodisation process, an artificial oxide layer is created on the treated aluminium. This layer has special characteristics. One of these is its porosity. The porosity of the layer enables, for example, the incorporation of coloured pigments and is thus an important criterion for a more or less intensive colouring of anodised surfaces.
How can the porosity of the aluminium oxide layer be influenced?
Especially this question is important in daily practice, as it enables quick intervention and optimization in case of unexpected results. The pore size can lead to both desired and undesired properties of an anodisation layer. For example, better colouring can be achieved with large-pored oxide layers (more colour can be deposited). Higher porosity, on the other hand, also means softer anodised layers, which reduces the resistance of the layer. In addition, large-pored aluminium oxide layers are also more difficult to compact, which can lead to quality problems (poor sealing quality values).
For this reason, in the anodisation process a suitable middle course is usually tried to be found that compensates for all properties to achieve a positive end result.
Which parameters can be varied for this purpose?
The following table shows a simple overview of measures and effects: