In the present study, the corrosion behavior of AM magnesium alloys (AM50 and AM60) in 5% NaCl solution was examined. The corrosion rate was found to depend on the impurity concentration in the alloy, and increased with Fe/Mn ratio. Inclusions were present within the alloys, with compositions of 40–80% Al, 20–60% Mn, and 0–10% Fe. It was determined that these inclusions acted as initiation points for corrosion. In addition, corrosion preferentially occurred at inclusions with a high Fe content, and the Fe content of inclusions was found to be proportional to that in the alloy itself.