Experimental and Simulation Investigation of Nd Additions on As-Cast Microstructure and Precipitate Development in Mg-Nd System Alloys

The microstructure and precipitate evolution of as-cast Mg-Nd alloys with different contents of Nd was investigated via experimental and simulation methods. The research showed that the as-cast microstructure of Mg-Nd alloy consisted of alpha-Mg dendrites and the intermetallic phases. A metastable beta phase precipitated, followed by alpha-Mg dendrites that could be confirmed as Mg12Nd by X-ray diffraction (XRD) analysis. The amount of beta-Mg12Nd presented a rising trend with increasing Nd additions. In addition, the tertiary phase was also observed in as-cast Mg-Nd alloy when Nd content was greater than 3 wt.%, which precipitated from the oversaturated alpha-Mg matrix. The tertiary phase should be beta(1)-Mg3Nd, which is also a metastable phase with a face-centered cubic lattice. However, it is a pity that the tertiary phase was not detected by the XRD technique. Moreover, an effective cellular automaton (CA) model was explored and applied to simulate the time-dependent alpha-Mg/beta(1)-Mg3Nd eutectic growth. The simulated results of alpha-Mg/beta(1)-Mg3Nd eutectic growth in Mg-3Nd presented that the growth of alpha-Mg dendrites was accompanied by the nucleation and growth of beta(1)-Mg3Nd precipitates and eventually formed a eutectic structure. The eutectic morphologies for Mg-Nd system alloys with different Nd contents were also simulated using the proposed model, and the results revealed that alpha-Mg dendrite was a refinement, and the amount of alpha-Mg/beta(1)-Mg3Nd eutectic was promoted, with increasing Nd content.