3D printed double flow cell for local through-thickness anodisation in aluminium

• Localised anodisation of Al was achieved by use of 3D printed double flow cell.
• Double flow cell approach reduces process time for complete anodisation of Al.
• Fabricated ceramic windows made out of Al2O3 show promising optical properties.

Local through-thickness anodisation of aluminium sheets was performed in a specially designed double flow cell, which was realised by selective laser sintering. Hard anodisation (HA) conditions with voltages between 110 and 140 V including different pre-anodisations at mild conditions were tested employing oxalic acid as electrolyte. Partly transparent, porous alumina spots of 15 μm thickness and 3.5 mm diameter, predetermined by the cell geometry, were produced. The design of the presented cell allows tuning of electrolyte flow profile and electric field by adjusting the distance between counter electrode and aluminium specimen (working electrode) and therefore altering mass and heat transfer during the anodising process. As it enables localised oxide growth in HA regime from both sides of an aluminium sheet, process times for through-thickness anodisation can be reduced. Pore arrangement of the produced alumina spots was examined showing interpore distances in the range of 180 and 220 nm and pore diameters of 40 to 60 nm, both values increasing with applied HA voltage. Optical properties of the produced alumina spots were studied by means of UV-visible transmittance analysis.

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