The size, distribution, and volume fraction of second phases are altered during extrusion deformation. As a result, the microgalvanic corrosion of Mg alloys will change. The corrosion behaviors of cast and extruded EW75 (Mg-5Y-7Gd-1Nd-0.5Zr) were studied by scanning electron microscopy observations, hydrogen evolution and weight loss measurements, and electrochemical tests. Extruded EW75, which has a lower volume fraction, smaller size, and more uniform distribution of second phases, is found to exhibit better corrosion resistance than cast EW75; the difference can be attributed to weaker microgalvanic corrosion and a more protective surface film. (C) The Author(s) 2016. Published by ECS. All rights reserved.