Corrosion behavior of Al/AlNp composite in alkaline solution

The corrosion behavior of Al/AlNp composite in alkaline solution is investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The potentiodynamic anodic polarization cyclic voltammetry curves exhibit an active/passive transition. An anodic current peak PI appears in the active dissolution region, which is correlated to the precipitation of Al2O3 and the attack of hydroxide ions. With the increase of immersion time, the peak PI increasingly vanishes, implying the slow down of the electrochemical dissolution of the Al/AlNp composite. Bolt plots for the composite reveals a shift of phase angle peaks towards low frequencies with the increase of immersion time. The Nyquist plot shows an ideal Warburg tail following a semi-circle in the high frequency range in the late time, suggesting that the corrosion of Al/AlNp composite is completely controlled by a diffusion process. In addition, in different corrosion stage, the hydrolysis of AlN particle is observed to play different roles. In the initial time, it makes the passive layer of the Al/AlNp composite poorly protective by causing crevices within the passive layer. While, in the late time, the hydrolysis of AlN particle increases corrosion resistance of the composite by limiting the formation and mass transfer of Al(OH)4− and preventing hydroxide ions from invasion.