Effects Of Surface Micro-Galvanic Corrosion And Corrosive Film On The Corrosion Resistance Of Az91-Xnd Alloys

The effects of surface micro-galvanic corrosion and corrosive film on the corrosion resistance of AZ91-xNd alloys was evaluated by scanning electron microscopy (SEM), scanning Kelvin probe force microscopy (SKPFM), and electrochemical measurements. The microstructural morphologies showed that the formations of Al2Nd and Al-Mn-Nd phases were observed in AZ91-Nd alloy. According to the results of SKPFM, the Nd-rich phases were slightly noble than the beta-Mg17Al12 phase but less than the Al-Mn phase. Consequently, AZ91-1.0Nd alloy with dispersed Nd-rich phases showed the largest polarization resistance values of 5129 Omega.cm(2), about 3.9 times than that of AZ91 (1313 Omega.cm(2)). The main factors affecting the corrosion resistance of AZ91-xNd alloys were as follows: (i) the suppression of surface micro-galvanic couple corrosion, since the Volta potential difference (secondary phases/alpha-Mg) was reduced after Nd addition, the effect of surface micro-galvanic corrosion was weakened, thereby enhancing the corrosion resistance of the tested alloy (AZ91); (ii) corrosive film, the uniform corrosive film containing Nd2O3 isolated the specimens and the electrolyte, which suppressed the penetration of harmful anions (OH(-)CO32) and inhibited the occurrence of surface micro-galvanic corrosion of AZ91-Nd alloys.