International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Corrosion remains a major limitation for the long-term use of aluminum alloys such as A356, particularly in chloride-rich environments. Although traditional chromate coatings provide effective protection, their toxicity necessitates environmentally friendly alternatives. In this study, a composite ZrO2–Al2O3–Sm2O3 coating was synthesized via a sol-gel method and deposited on A356 alloy using dip-coating. The precursor system was formulated from zirconyl chloride, samarium oxide, and aluminum oxide, stabilized with acetylacetone and acetic acid at pH 0.5 to ensure homogeneous film formation. The coated samples were thermally treated at 400 °C to obtain dense oxide layers. Corrosion resistance was assessed under neutral salt spray conditions (5% NaCl, 35 °C, 648 h) according to BDS EN ISO 9227:2023. Comparison between uncoated A356, binary Al–Zr (ADZ), and ternary Sm–Al–Zr (SADZ) coatings demonstrated a clear performance improvement with increasing film complexity. While ADZ coatings reduced surface damage relative to the bare alloy, the SADZ films exhibited the lowest amount of corrosion products, minimal surface darkening, and significantly reduced pitting. The enhanced performance is attributed to the synergistic effect of the three oxides: ZrO₂ provides chemical stability, Al2O3 increases layer density, and Sm₂O₃ contributes active corrosion inhibition.
Overall, the ZrO2–Al2O3–Sm2O3 composite film offers a promising non-chromate protective system for improving the long-term corrosion resistance of A356 aluminum alloy.

Thin coatings of aluminum oxide (Al2O3), zirconium oxide (ZrO2) and samarium oxide (Sm2O3) on aluminum alloy Al7SiMg (A356) were prepared by sol-gel method and immersion technique. The materials were characterized in detail by X-ray diffraction. The luminescent properties at room temperature were also investigated. Luminescence analysis showed that the Al2O3 coating containing ZrO2 exhibits broad excitation and emission bands, peaking at 328 nm and 392 nm, respectively. Photoluminescence data for the Al2O3 coating containing ZrO2 and Sm2O3 indicated effective excitation at 404 nm and strong broadband emission, which is due to the co-emission of ZrO2 and Sm2O3. Chromaticity coordinate analysis revealed that Al2O3 coating containing ZrO2 and Al2O3 coating containing ZrO2 and Sm₂ O₃ emit in the blue-purple and pale pink regions, respectively.The chromaticity coordinates, color purity and CIE (Commission Internationale de L’Eclairage) color-correlated temperature were determined.