High frequency pulse anodising of recycled 5006 aluminium alloy for optimised decorative appearance

High frequency (HF) pulse anodising of a recycled AA5006 Aluminium alloy has been investigated to understand the effect of pulse anodising on improvements in optical quality of anodised surfaces in a sulphuric acid bath. The investigation includes the effect of applied voltage and pulse frequency on the anodising kinetics and optical properties of the recycled alloy with high number of intermetallic phases.

The effect is compared with anodised surfaces produced using conventional DC anodising. Both the anodising kinetics and optical properties are largely dependent on the applied pulse frequency and amplitude of the anodising voltage. Surface gloss of the layer is generally improved upon using pulses compared to DC and improved by lowering the anodising voltage and increasing the pulse frequency.

Improved kinetics under pulse mode allows for getting good anodic layers even with voltage levels lower than 10 V, however the surface gloss worsens when anodising below 10 V. The benefit from pulse anodising is found to be largely due to metal-oxide interface roughness rather than on the structure and composition of the anodised layer.