Potentiodynamic polarization curves of AA7075 at high scan rates interpreted using the high field model

Abstract

The drastic distortion of potentiodynamic polarization curves measured at high potential scan rates prevents the extraction of accurate kinetic parameters. In this work, we start by measuring potentiodynamic polarization curves of AA7075 at scan rates ranging from 0.167 mV·s⁻¹ to 100 mV·s⁻¹, in an acidic 0.62 M NaH₂PO₄ solution and a near-neutral 3.5 wt% NaCl solution. Changes in potentiodynamic polarization curves are observed not only at different scan rates and electrolytes but also between replicated experiments. Contrary to what was reported in previous studies, the disturbance of charging current associated with high scan rates does not satisfactorily explain the potentiodynamic polarization shape. Instead, the high field model that incorporates the kinetics of anodic oxide growth successfully captures the features of experimental potentiodynamic polarization curves. Compared to Tafel’s theory, the high field model explains remarkably the changing kinetics with scan rates, electrolytes, and the variance between measurements performed at different sites.