Corrosion inhibitor from nature: Fundamentals of tannic acid inhibition for AA2024 alloy

• Tannic acid (TA) inhibition was evaluated for the first time on AA2024 alloy. • Short-term immersion in TA solutions reveals a mixed inhibition effect on AA2024 alloy. • Long-term immersion in TA solutions yields a tannate-rich layer on the AA2024 alloy. • A low tannate content in the oxide layer increases its stability and corrosion protection. This study addresses the fundamentals of corrosion inhibition of AA2024 alloy by tannic acid (TA), a Cr-free and eco-friendly natural product. To this end, the AA2024 alloy was immersed in NaCl solution (50 mM) with different TA concentrations (0.1–10 mM) for 7 days. Surface (SEM, Raman, and SKPFM) and electrochemical analyses (EIS, PDP, and SVET) revealed mixed inhibition after 1 day of immersion in TA solution. Long-term immersion tests in TA solutions produced a tannate-rich oxide film on the surface. The films with low tannate content (formed in 0.1 and 1 mM TA) showed the highest stability and corrosion resistance.