Effect of co-modification by Ba and Sb on the microstructure of Mg2Si/Mg–Zn–Si composite and mechanism

• Addition of Ba and Sb transforms the Chinese-script Mg2Si to fine polygonal particles finer than 15 μm.
• The combined effect of Ba+Sb is better than that obtained by only adding Ba or Sb.
• No over-modification phenomenon appeared.
• Ba2Sb are found inside Mg2Si. These particles act as heterogenous nucleation sites for Mg2Si.

Mg2Si/Mg–Zn–Si composite was in situ synthesized and modified by the addition of Ba and Sb; the microstructure and tensile properties of the resulting composites were investigated. Results show that the co-modification with Ba and Sb effectively refined the morphology of Mg2Si as follows: The primary Mg2Si particles were modified to fine polygonal particles <15 μm; when the Ba content was 1.0 wt.%, the average size of primary Mg2Si particles decreased with increasing Sb mass fraction. The ultimate tensile strength and elongation values of the composites increased with increasing Sb content. This was attributed to the formation of fine Ba2Sb particles that acted as the heterogeneous nucleation sites for the primary Mg2Si particles, resulting in a refined distribution of these precipitates. The dispersion of the refined Mg2Si particles strengthened the composite and improved the ductility.