Correlation Between the Accelerated-Rate Decay Mechanism in Neutral Salt Spray Tests and the Atmospheric Corrosion Kinetics Model of a 7075 Aluminum Alloy in Marine Environments

This study established a marine atmospheric corrosion prediction model by comparing the corrosion behavior of 7075 aluminum alloy in neutral salt spray tests and outdoor exposure tests conducted in the coastal atmosphere of Hainan. The results show that severe rusting occurred after 96 h of neutral salt spray testing, with loose white cluster-like corrosion products mainly composed of Al(OH)3 and Al2O3. The thickening of the corrosion product layer slowed down the corrosion process, following a nonlinear power-law kinetic relationship. In the later stage, potential dropped sharply due to product layer spallation, and recovered as new corrosion products formed, confirming that the stability of the product layer is critical for protection. Under coastal atmospheric exposure, the composition of corrosion products was similar to that observed in the salt spray test, but the actual corrosion rate was affected by environmental dynamic equilibrium. The acceleration factor of the neutral salt spray test corresponding to the same corrosion amount in the Hainan marine atmosphere exhibited a declining trend, reflecting that differences in the protective nature of the corrosion product layer were influenced by environmental factors. Electrochemical analysis indicated that both tests showed similar current–potential synergistic variation mechanisms dominated by product layer stability. In summary, while the neutral salt spray test effectively simulates the chloride-induced corrosion mechanism in marine atmospheres, its kinetic model cannot directly predict real corrosion behavior through a simple acceleration factor, as environmental complexity must be considered.