High frequency pulsed anodising of pure aluminium was investigated with an aim to understand the effect of the anodising parameters on the growth kinetics of the anodic layer and optical appearance of the anodised surface. Anodising was performed in sulphuric acid, and the effect of the pulse duty cycle, applied potential offset, and pulse frequency was investigated. Optical properties of the anodised surfaces are improved upon lowering the anodising potential and by increasing the frequency of the applied potential pulses. Temperature evolution of the samples during anodising was investigated by employing a special flat cell setup equipped with a thermocouple close to the sample. The effect of high frequency pulsing of the anodising potential on the anodising kinetics is presented, which is related to the temperature evolution and dielectric losses, and the effect is compared to the traditional DC anodising process. From the observations, it is postulated that the dominant factor responsible for the improved growth kinetics during high frequency pulsed anodising might not be dielectric losses instead a thickness reduction in the Gouy-Chapman/Helmholtz layers.
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 potential 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 potential and increasing the pulse frequency. Improved kinetics under pulse mode allows for getting good anodic layers even with voltage levels lower than 10V, 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.
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