Differences between the untreated and treated diffusion zone in the Alclad 2024-T3 aluminum alloy and hard anodic films

Chemical treatment with NaOH, followed by HNO3 is commonly performed during the surface preparation of aluminum alloys for their subsequent anodization. In the present work, the properties of the diffusion zone of Alclad 2024-T3 aluminum alloy and its hard anodic films without/with preliminary chemical treatment were examined. The studied surfaces were characterized morphologically, compositionally, and electrochemically to determine the changes caused by the treatment procedure. The obtained results revealed that the untreated diffusion zone exhibited a heterogeneous surface distribution of intermetallic compounds mostly containing silicon, copper, and magnesium elements, due to the presence of 1230 cladding and 2024-T3 core in the diffusion zone of Alclad 2024-T3 aluminum alloy. Furthermore, the non-treated hard anodic films had pores with angular shape and contained additional corundum and diasporic crystalline structures. While chemical treatment with NaOH, followed by HNO3 removed many intermetallic compounds or partially dissolved them, silicon atoms were preferentially eliminated making the alloy magnesium-rich, and the hard anodic films had pores with circular shape and completely amorphous. Finally, both films possessed a predominance of dielectric behavior, with minor p-type semiconducting contributions due to Al-Si-O intermetallic compounds.

Automated summary

This study examines the effects of chemical treatment on the surface properties of Alclad 2024-T3 aluminum alloy. The results show that the treatment removes intermetallic compounds and improves the surface homogeneity. Additionally, it enriches the alloy with magnesium and leads to the formation of completely amorphous hard anodic films.