Magnesium and its alloys have become increasingly attractive in the automotive, 3 C products and aerospace industries because of their advantages such as low density and high specific strength. In recent years, rare earth-Mg alloys have attracted much attention due to their high mechanical properties at room and elevated temperatures. Adjusting the microstructures by deformation treatment is a common method to improve the mechanical properties of Mg alloys. The microstructure especially the size, volume fraction and distribution of second phases in rare earth-Mg alloys will be changed during deformation treatment, which has a great effect on the corrosion resistance of Mg alloys. However, the studies on the effect of deformation treatment on the corrosion resistance of rare earth-Mg alloys are far away from sufficient. In this work, the corrosion behavior of cast and forged Mg-5 Y-7 Gd-1 Nd-0.5 Zr（EW75） alloys were studied by using SEM, XRD, mass loss measurements and electrochemical tests. The results indicate that the second phases are distributed along the grain boundaries of cast and forged EW75 alloys. Meanwhile, the second phases in forged EW75 alloy are finer and lower volume fraction than that in cast EW75 alloy. The micro-galvanic corrosion of the forged EW75 alloy is weaker in comparison with the cast EW75 alloy owing to the smaller size and lower volume fraction of second phases as well more compact surface film, resulting in the better corrosion resistance.
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