Uniaxial tension and microstructure of a short alumina fibre-reinforced Al2Mg alloy

A metal matrix composite was manufactured with the squeeze casting technique. The composite is based on an Al2%Mg alloy and fibre preform with 10% alumina fibres. Mechanical testing was performed revealing that the elongation to fracture was unusually high compared with literature data. The composite was extensively investigated by means of optical microscopy, scanning electron microscopy and transmission electron microscopy equipped for microanalysis. A strong reaction between the amorphous silica binder and the liquid alloy during the fabrication of the composite was observed. The binder transforms to spinel MgAl₂O₄ and Mg₂Si precipitates in the matrix during cooling. Most of the precipitates form far away from the fibre-matrix interface. We suggest that the formation of Mg₂Si far away from rather than close to the fibre is responsible for the high elongation values.