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

**Xuewei Yan 1, Bin Su 2,\*, Xuemei Yang 3, Qingdong Xu 2, Xiaopeng Zhang 2, Jing Wang <sup>2</sup> and Zhenhua Wen 1,\***


**Abstract:** 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 *α*-Mg dendrites and the intermetallic phases. A metastable *β* phase precipitated, followed by *α*-Mg dendrites that could be confirmed as Mg12Nd by X-ray diffraction (XRD) analysis. The amount of *β*-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 *α*-Mg matrix. The tertiary phase should be *β*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 *α*-Mg/*β*1-Mg3Nd eutectic growth. The simulated results of *α*-Mg/*β*1-Mg3Nd eutectic growth in Mg-3Nd presented that the growth of *α*-Mg dendrites was accompanied by the nucleation and growth of *β*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 *α*-Mg dendrite was a refinement, and the amount of *α*-Mg/*β*1-Mg3Nd eutectic was promoted, with increasing Nd content.

**Keywords:** Mg–Nd alloy; microstructure; precipitate; eutectic growth; modelling and simulation
