Effect of Single and Co-addition of Rare Earth on the Microstructure, Mechanical Properties, and Corrosion Behavior of AZ31 Magnesium Alloys

In this work, AZ31 and AZ31-1 wt.% RE (RE = Nd, Dy, Nd+Dy) alloys were prepared by conventional casting. The effect of single and co-addition of rare earth (RE) on the microstructure, mechanical properties and corrosion behavior of as-cast AZ31 magnesium alloys were investigated at ambient temperature, and after heat treatment at 400 °C for 1 h. The addition of 1 wt.% RE (RE = Nd, Dy, Nd+Dy) preferentially formed the Al2RE phase and completely suppressed the formation of the intermetallic β-Mg17Al12 phase. An excellent ultimate tensile strength (UTS)/ductility combination of 209 MPa/21% and 192 MPa/17% with an adequate yield strength (YS) of 90 MPa was observed for AZ31+Nd sample in as-cast and annealed states, respectively. The work-hardening rate of the AZ31 alloy containing Nd and Dy increased significantly after annealing compared to those of the as-cast state. Fracture analysis indicated that the additive RE did not obviously change the fracture mechanism of the Mg alloy. All specimens exhibit a hybrid fracture with cleavages and dimples. The weight loss test showed that the corrosion resistance of the AZ31 Mg alloy was improved with added RE as it interacts with Al to form Al-RE phase, which upgraded the corrosion resistance of the alloys. The co-addition of RE (RE = Nd+Dy) was proven to enhance corrosion resistance, and also stabilized the corrosion rate. In brief, the co-addition of Nd and Dy significantly improved the corrosion resistance of the AZ31 magnesium alloys than the counterpart of the mechanical properties. Graphical Abstract