A novel organic-reinforced zirconium-based composite conversion coating with long-term corrosion resistance property for ADC12 aluminum alloy

Zirconium-based conversion coatings (ZCC) have emerged as an environmentally sustainable alternative to traditional chromate conversion coatings (CCC) for aluminum alloy corrosion protection. However, their corrosion resistance remains inferior to CCC, limiting widespread adoption. In this study, we introduce a novel organic-reinforced ZCC incorporating ethylenediamine-tetramethyl phosphonic acid (EDTMP) on ADC12 aluminum alloy, significantly enhancing the corrosion resistance. Systematic electrochemical tests, copper sulfate test, and neutral salt spray (NSS) test demonstrated that the optimized coating with 1.0 g/L EDTMP exhibits outstanding performance, achieving a remarkably low corrosion current density ( i corr = 0.45 μA/cm²) and high total resistance ( R sum = 202,028.50 Ω·cm²). The ZCC-EDTMP-1.0 coating maintained a corrosion resistance efficiency ( η ) exceeding 91 % over 72 h of immersion in 3.5 wt. % NaCl solution, highlighting its long-term stability. NSS and copper sulfate tests further validate its robustness in harsh environments. This superior performance is attributed to EDTMP's ability to chelate metal ions, forming a densely interlocked and stable protective barrier. This work presents a promising strategy to enhance ZCC performance, offering a viable pathway for the industrial-scale adoption of eco-friendly, chromium-free conversion technologies.