| Summary: | In this article, the modification effects on Al–Mg<sub>2</sub>Si before and after heat treatment were investigated with Ca, Sb, and (Ca + Sb). In comparison with single Ca or Sb, the samples with composition modifiers (Ca + Sb) had the optimal microstructure. The sample with a molar ratio for Ca-to-Sb of 1:1 obtained relatively higher properties, for which the Brinell hardness values before and after heat treatment were remarkably increased by 31.74% and 28.93% in comparison with bare alloy. According to differential scanning calorimetr<b>y</b> analysis (DSC), it was found that the nucleation behavior of the primary Mg<sub>2</sub>Si phase could be significantly improved by using chemical modifiers. Some white particles were found to be embedded in the center of Mg<sub>2</sub>Si phases, which were deduced to be Ca<sub>5</sub>Sb<sub>3</sub> through X-ray diffraction (XRD) and field-emission scanning electron microscope (FESEM) analyses. Furthermore, Ca<sub>5</sub>Sb<sub>3</sub> articles possess a rather low mismatch degree with Mg<sub>2</sub>Si particles based on Phase Transformation Crystallography Lab software (PTCLab) calculation, meaning that the efficient nucleation capability of Ca<sub>5</sub>Sb<sub>3 </sub>for Mg<sub>2</sub>Si particles could be estimated.
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