The improved effects by the combinative addition of lanthanum and samarium on the microstructures and the tensile properties of high-pressure die-cast Mg-4Al-based alloy

The combinative addition of two rare earths of lanthanum and samarium, which have different solid solubilities in magnesium, has improved effects on the microstructures and the tensile properties of the high-pressure die-cast Mg-4Al-based alloy. The microstructural characterizations illustrate that the studied alloy has very fine dendrite cells and four kinds of Al-(La-Sm) intermetallic phases with different morphologies, in which different rare earths are preferred. In addition, the transmission electron microscopy observations reveal that most Al2(Sm-La) particles contain (111) twins, whose formation is probably related to the Al6(Sm-La)Mn6 phase which could act as nucleation substrates for the twins during solidification. Finally, the studied alloy has outstanding tensile properties at both room temperature and high temperatures, compared with the conventional heat-resistant die-cast magnesium alloys, due to the cell-refinement strengthening, the intermetallic phase strengthening, and possibly the solid-solution strengthening.