In magnesium alloys, the rare-earth (RE) elements first react with the impurities in the alloy, then with alloying elements, and finally form an intermetallic compound with magnesium. Therefore, RE elements play the key role in removing impurity and purifying the matrix in Mg alloys so as to enhance the corrosion resistance. The RE elements have a lower electrode potential resulting in a decrease in the electrode potential of the intermetallic compound in which they participate. The reaction results lead to reduced electrode potential difference between the matrix and second phase. It will play an important role in reducing galvanic corrosion.