Pulsed current effect on hard anodizing process of 2024-T3 aluminium alloy

This work focused on studying the effects of different electrical parameters on the hard anodizing process (in sulphuric acid bath) of AA 2024-T3, an important heat treated aluminium alloy which has several engineering applications in aerospace, motorsport and automotive fields due to its significant combination of high mechanical properties and low density. Hard anodizing treatment is here crucial for increasing both corrosion and abrasion resistance, but the presence of typical intermetallic precipitates makes the obtainment of a performing non-defective oxide difficult. Different anodizing procedures in direct current (DC), multistep direct current (MSDC), pulsed current (PC) (slow square pulse mode) and their appropriate combination (DC&PC) were studied aiming at obtaining the optimal mechanical properties/thickness/defectiveness compromise. DC and MSDC results showed good hardness values while their optical microscopy characterization indicated a poor defectiveness state; PC modality induced a moderate loss in mechanical performances in all the different duty cycles experimented, while an extremely low defected oxide was obtained with a duty cycle of 50%. Proper merge of a soft and long initial DC current step followed by a suitable balanced final stage in PC allowed to obtain an interesting combination of significant hardness (> 340 HV) in parallel with a good oxide defectiveness state.