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• The surface potential of the phases in AZ91–xGd alloys was characterized by AFM. • Nd–rich phases with lower surface potentials obviously improved corrosion resistance. • The polarization resistance of the AZ91–1.0Nd alloy is 3.9 times than that of matrix. • The effect of micro–galvanic corrosion was weakened after the addition of Nd. • Corrosive film containing Nd 2 O 3 inhibited the occurrence of micro–galvanic corrosion. 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 Al 2 Nd 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 β–Mg 17 Al 12 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 Ω·cm2, about 3.9 times than that of AZ91 (1313 Ω·cm2). 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/α–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 Nd 2 O 3 isolated the specimens and the electrolyte, which suppressed the penetration of harmful anions (OH–, C O 3 2 -) and inhibited the occurrence of surface micro–galvanic corrosion of AZ91–Nd alloys. [ABSTRACT FROM AUTHOR]