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R ecently, metal matrix composites (MMCs) have attracted extensive attention in automobile industry, in order to meet the demands of weight reduction and fuel economization [1][2][3] . The hypereutectic Mg-Si particulate metal matrix composites (PMMCs) have high potential as structural materials because the reinforcing particulate Mg 2 Si intermetallic exhibits a low density of, a high elastic modulus of 120 GPa, a high melting temperature of 1,085 °C, a high hardness of 4.5×10 9 N • m -2 and a low thermal expansion coefficient of. However, as in-situ Mg 2 Si reinforced PMMCs, hypereutectic Mg-Si alloys do not have satisfactory mechanical properties in general, due to the exhibition of coarse dendritic primary Mg 2 Si particles and the brittle Chinese script shape eutectic Mg 2 Si phases [5,6] . It was proposed that a modification process seems to be the Abstract: In order to modify in-situ synthesized Mg 2 Si particles in Mg 2 Si/Mg-4Si composite, the modification effect of calcium-magnesia phosphate fertilizer on primary Mg 2 Si phase in Mg 2 Si/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 Mg 2 Si 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 Mg 2 Si/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 Mg 2 Si particles, resulting in a refined distribution of these precipitates.

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The development history and social contribution of cement were briefly described. The physical and chemical indexes of P.O42.5 cement were tested according to GB 175-2007 standard. The correlation of coagulation time, strength and chemical index was analyzed. The results showed that the final coagulation time was closely and positively correlated with the initial coagulation time, and the correlation coefficient was 0.9572. The 28-day compressive strength doesn’t have obvious correlation with final setting time, loss on ignition, MgO content and SO3 content.