<p>This study investigated the corrosion behaviors of Mg-9Al-1Zn (Al-modified alloy) and Mg-5Gd-4Y-1Zn (RE-modified alloy) from microstructural and electrochemical perspectives. The heterogeneous grain structure and dislocation distribution readily promoted galvanic corrosion, thereby accelerating the degradation of the RE-modified alloy. Furthermore, the potential difference induced by the LPSO phase was greater than that caused by the <i>β</i>-Mg₁₇Al₁₂ phase, leading to a highly non-uniform overall potential distribution and the pronounced micro-galvanic corrosion in the RE-modified alloy. Notably, compared to modification by Gd₂O₃/Y₂O₃, the formation of Al₂O₃/Al(OH)₃ was more effective in enhancing the stability of the protective film. Consequently, the Al-modified alloy demonstrated superior corrosion resistance relative to the RE-modified alloy.</p>