Mechanism of macro-segregation formation in SiC whisker reinforced aluminum alloys composites fabricated by squeeze casting

Mechanism of macro-segregation formation in SiC whisker/pureAl, Al-Mg and Al-Li alloys composites formed during squeeze casting was investigated by using micro-Vickers hardness, X-ray diffraction, EPMA, SEM and TEM observations. The macro-segregated area is formed along the infiltration routes of molten metal from side walls and top surface of the SiCw preform at the center-low zone in the SiCw/aluminum alloys composites. It is the main reason for the formation of macro-segregation that the melt reduced active solute element (Mg or Li) due to the interface reaction between SiO2 contained in the preform and the matrix alloys squeezes toward the center-low zone which solidifies finally in the composite and solidifies as it is. The following compounds were detected as interface reaction products; Al2O3 in the SiCw/pureAl, spinel type of MgAl2O4 and Mg2Si in the SiCw/Al-Mg, and LiAlSi, lithium oxides in the SiCw/Al-Li alloy composites. Finally the sound composites without the macro-segregation can he obtained by using the specially designed fabrication method for this study.