Modification effect of calcium-magnesia phosphate fertilizer on microstructure and mechanical properties of Mg2Si/Mg-4Si composite

In order to modify in-situ synthesized Mg2Si particles in Mg2Si/Mg-4Si composite, the modification effect of calcium-magnesia phosphate fertilizer on primary Mg2Si phase in Mg2Si/Mg-4Si composite was investigated by means of X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis. The results indicate that the morphology of the primary Mg2Si phase apparently changes from coarse dendrites to fine dispersive polygonal particles, and the mean size is decreased from 277 μm to 17 μm. With the addition of 4.0wt.% calcium-magnesia phosphate fertilizer as a modifier, the ultimate tensile strength and elongation of the Mg2Si/Mg-4Si composite are increased from 78.7 MPa and 2.1% to 105.2 MPa and 2.6%, as compared to those of the base composite, which is probably attributed to the formation of the phosphorous compound and the cluster of Ca compounds that acted as the heterogeneous nucleation substrates of the primary Mg2Si particles, resulting in a refined distribution of these precipitates.