Influences of Ca and Y Addition on the Microstructure and Corrosion Resistance of Vacuum Die-Cast AZ91 Alloy

The influences of Ca and Y additions on the microstructure and corrosion resistance of vacuum die-cast AZ91 alloys were investigated by optical microscope, electron scanning microscope, weight-loss test, and electrochemical corrosion experiment. The results indicate that the Ca or Ca and Y additions refined the microstructure and decreased the amount of Mg17Al12phase on grain boundaries in the alloys. Meanwhile, the addition of Ca and Y led to the formation of network Al2Ca phase and rod-like Al2Y phase, improved the corrosion resistance of AZ91 magnesium alloy. Compared with AZ91 alloy, the corrosion rate of AZ91–1.5Ca–1.0Y alloy was decreased to 16.2%, and its corrosion current density was dropped by one order of magnitude after immersion in 3.5 wt% NaCl solution for 24 h.