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

• Published in: Surface & coatings technology 2022-01, Vol.429, p.127939, Article 127939
• Main Authors: García Rueda, Francy Catalina, Torres González, Julieta, Hernández-López, Juan Manuel
• Format: Article
• Language: English
• Subjects: AA2024-T3; Alloys; Aluminum alloys; Aluminum base alloys; Chemical treatment; Corundum; Diffusion; Diffusion zone; Hard anodic film; Intermetallic compound; Intermetallic compounds; Magnesium; P-type semiconductors; Silicon compounds; Surface preparation
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2021.127939

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. •Chemical treatment with NaOH followed by HNO3 enriches the surface with Mg and eliminates Si in the diffusion zone.•The diffusion zone of Alclad 2024-T3 alloy favors the incorporation of Si, Mg, Fe, Zn to anodic film surfaces.•Avoiding the chemical treatment gives angular pores and more crystalline hard anodic films.•Chemical treatment favors higher charge and capacitance in the anodizing process and a more orderly porous layer.