The fabrication method of particulate reinforced magnesium matrix composites using spontaneous infiltration phenomenon was developed. By pre-mixing the infiltration agent to reinforcement powder, magnesium melt infiltrated into the powder spontaneously even under pure argon gas atmosphere at 973K. In this work, fundamental experiments were carried out to find out the conditions that the spontaneous infiltration can occur in the pure Mg-SiC
p system, using SiO
2 powder as an infiltration agent. Microstructure observation and XRD analysis were also carried out to make clear the infiltration mechanism. The spontaneous infiltration depends both on SiC
p diameter and on SiO
2 content. The threshold SiO
2 content decreases with increasing SiC
p diameter. Microstructure observation revealed no uninfiltrated part and the formation of two kinds of reaction products. In the composites MgO, Mg2Si and no SiO
2 were detected by XRD analysis. Since the reaction for producing MgO and Mg
2Si from magnesium and SiO
2 is exothermic (thermit reaction), it is predicted that the temperature becomes higher in the infiltration front than in other part, as temperature rise was actually confirmed during infiltration. It is predicted that the spontaneous infiltration is caused by the temperature rise due to the thermit reaction and/or the contribution of good wettability of magnesium to SiO
2.
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