Using High Field Model to Interpret Potentiodynamic Polarization Curves of AA7075 at High Scan Rates

Abstract

The drastic distortion of potentiodynamic polarization curves measured at high potential scan rates prevents the extraction of accurate kinetic parameters. By measuring potentiodynamic polarization curves of AA7075 at scan rates ranging from 0.167 mV/s to 100 mV/s, in an acidic solution of 0.62 M NaH2PO4 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 both the changing kinetics with scan rates, electrolytes, and the variance between the measurement performed at different sites. Figure 1