Anodizing is an electrochemical process in which aluminium is converted into aluminium oxide (Al2O3) in a controlled environment. This is done with electricity and an electrolyte (sulphuric acid). By continuously dissolving aluminium, a layer is formed containing a large amount of pores. An anodized layer is hard and brittle, with properties that can be compared to glass or ceramics; the layer will also ‘break’ during strong bending.
It is a material-specific layer, with an exceptional adhesion to the substrate (aluminium). Practical anodic layers are between 5 – 60 µm, depending on alloy and application. The physical law for the anodizing process is Ohm’s law: U = I x R, or Voltage (V) = Current (A) x Resistance (Ω).
During anodizing, the resistance of the formed layer increases and influences the anodizing process / build-up speed. This is controlled by programmed process steps. Anodizing is a galvanic process, but with a reversed pole. The workpiece is connected to the anode in contrast to standard galvanic processes (such as silver plating).