Different Microgalvanic Corrosion Behavior of Cast and Extruded EW75 Mg Alloys

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.