Sequential Trends in Corrosion Behaviour of Surface-Ground Aluminium 7075 Thin Plates in 3.5 wt% NaCl Solution

The primary aim of this study is to assess the progressive trend in the corrosion behaviour of Aluminium 7075 plates in a 3.5 wt% NaCl solution. Aluminium 7075 plates were ground using the Elliot 921 hydraulic surface grinding machine according to a factorial design schedule, and their corrosion parameters were obtained using a CorrTest Electrochemical Workstation. The electrochemical performance assessment revealed generally consistent and reproducible corrosion characteristics, albeit with some irregularities. The anodic Tafel slopes primarily fell between 64.09 and 139.54 mV, although anomalies of 291.55 mV and 366.51 mV were noted in Run Orders 46 and 48, indicating potential experimental disturbances. The cathodic slopes remained largely stable, except for unrealistic spikes of roughly 4,115,900 mV and 2,970,800 mV recorded in Run Orders 4 and 49, which likely resulted from instrumental errors. The corrosion potential initially ranged from –0.63 V to –0.58 V, stabilised between –0.67 V and –0.60 V during the mid-runs, and later shifted to values between –0.59 V and –0.67 V, illustrating the dynamics of the passive film. The current density escalated from approximately 1 × 10⁻⁵ A/cm² to around 4 × 10⁻⁵ A/cm², peaking at nearly 5 × 10⁻⁵ A/cm² in Run 27 before recovering in Run 29. The polarisation resistance decreased from above 2900 Ω·cm², exhibiting a temporary repassivation increase (3611.11 Ω·cm²) in Run 28. In summary, Aluminium 7075 demonstrated reproducible corrosion behaviour that was sensitive to surface grinding conditions.