Conclusions
We have succeeded in the development of a spontaneous in- filtration process within 100 seconds at 900C (1652F) in air in the Al-Si-Mg melt and SiC-preform system. The preform was fabricated using a water glass binder mixed with Fe2
powders for improvement of the wettability. The infiltration mechanism was confirmed based on the measurement of the preform weight change during the dipping with a load sensor. The onset of the infiltration occurs with a pressure drop in the preform due to the chemical reaction between the trapped gases in the preform and the Mg and Al in the melt, and the reaction allows the melt to be sucked into the pre- form. The pressure decrease causes the breaking of the oxide film on the aluminum melt surface and makes the surface fresh. This allows a significant chemical reaction between the trapped gases and the melt to occur and a pressure de- crease which accelerates the infiltration.
O3
If the sandwich process (namely, the small particles are en- closed between the outer large particle layers) is employed, where the outer layer acts as an oxide film remover, and the small particle preform fraction (such as 30 µm) can then be infiltrated without pressure.
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