Mn–Fe–P–Si compounds are promising magnetocaloric materials for magnetic refrigeration. However, the microstructure evolution and solidification characteristics are rarely discussed in the literature. Here, we investigate the solidification characteristics and microstructure evolution of MnFeP_0·5Si_0.5 alloys under different undercooling and cooling rates based on droplet melting method. Results show that the alloy solidifies in the sequence of Fe₂P phases, (Fe₂P+(Mn,Fe)₅Si₃) eutectics and (Fe₂P+(Mn,Fe)₃Si eutectics. With the increase in undercooling and cooling rate, the (Fe₂P+(Mn,Fe)₅Si₃) and (Fe₂P+(Mn,Fe)₃Si) eutectic growth is divorced, and the Fe₂P phase experiences from coarse strips to fine dendrites, then fragmented dendrites, and finally to equiaxed dendrites. Besides, the volume fraction of the Fe₂P phase increases, and its atomic ratio approaches the nominal composition. As the droplet diameters decrease, we find a drop in Curie temperatures (228-210 K) and an increase in hysteresis (4–11 K). The magnetisation of the 500 μm droplet is also up to 51 Am²/kg. These results indicate that the magnetocaloric properties of the alloys strongly depend on the phase-type, morphology and composition evolution. Additionally, the operating temperature range and the refrigerant capacity of the 500 μm droplet are as high as 41 K and 112 J/kg, respectively, which will benefit the practical application of Mn–Fe–P–Si alloys.

Mn–Fe–P–Si化合物是用于磁制冷的有前途的磁热材料。但是，文献中很少讨论微观组织的演变和凝固特征。在此，我们基于熔滴法研究了在不同过冷和冷却速率下MnFeP _0·5 Si _0.5合金的凝固特性和组织演变。结果表明，合金以Fe ₂ P相，（Fe ₂ P +（Mn，Fe）₅ Si ₃）共晶和（Fe ₂ P +（Mn，Fe）₃ Si共晶的顺序凝固。 （Fe ₂ P +（Mn，Fe）₅Si ₃）和（Fe ₂ P +（Mn，Fe）₃ Si）共晶生长被离婚，Fe ₂ P相经历了从粗条状到细枝状，然后碎裂的枝状，最后到等轴枝状的转变。此外，Fe ₂ P相的体积分数增加，并且其原子比接近标称组成。随着液滴直径的减小，我们发现居里温度下降（228-210 K），磁滞上升（4-11 K）。500μm液滴的磁化强度也高达51 Am ²/公斤。这些结果表明，合金的磁热性能在很大程度上取决于相类型，形态和组成演变。此外，500μm液滴的工作温度范围和制冷剂容量分别高达41 K和112 J / kg，这将有利于Mn–Fe–P–Si合金的实际应用。