Abstract <p>The present study investigates the formation efficiency of anodic aluminum oxide (AAO) films on AA2024 alloy in 15 vol% sulfuric acid (15SA) and 6 wt% oxalic acid (6OA) solutions. Thickness measurements indicated that the AAO growth rate in the 6OA solution was only 38% of that in the 15SA solution. Gravimetric measurements suggested that the mass of AAO films formed in the 6OA solution was approximately 40% of that in the 15SA solution. Gravimetric analysis also revealed that the fraction of anodic charge consumed for AAO film formation was 17.8% in the 6OA solution and 44.5% in the 15SA solution, confirming lower film formation efficiency in oxalic acid than in sulfuric acid. On the other hand, charge loss due to O₂ evolution was significantly higher in the 6OA solution (66.1%) than in the 15SA solution (11.2%), whereas the fraction of anodic charge consumed by anodic dissolution was 16.1% in the 6OA solution and 44.3% in the 15SA solution. Scanning electron microscope (SEM) observations further revealed that second-phase particles dissolved much more slowly in the 6OA solution than in the 15SA solution. The experimental results revealed that the slower dissolution of particles in the 6OA solution led to rapid O₂ evolution, thereby causing very low AAO film formation efficiency. In contrast, the faster particle dissolution in the 15SA solution suppressed O₂ evolution and resulted in an AAO film formation efficiency about 2.5 times higher than that in the 6OA solution.</p> Graphical Abstract <p></p>