MICROSTRUCTURAL AND MECHANICAL CHARACTERIZATION OF ALUMINUM-MATRIX COMPOSITES REINFORCED WITH NI AND NIP COATED SIC PARTICLES VIA LIQUID PROCESSING

The microstructure and the mechanical properties of A357 aluminium alloys reinforced with Ni and NiP coated SiC particles produced via addition of particles into liquid metal are described. Ingots solidified under pressure and subsequently extruded, and centrifugally cast parts were used in this investigation. Microstructural observations show that the coating is dissolved during fabrication of the composites leading to NiAl3 phase formation. For the NiP coated particles, AlP phases are also observed together with some Mg segregation around the particles. Mechanical property evaluation shows the materials to be age hardenable, leading to good mechanical properties in the T6 condition. Strain to failure, however, is much smaller than that of the unreinforced alloy. In situ tensile tests carried out via scanning electron microscopy show that fracture of the SiC particles is the main failure mechanism and that the NiAl3 phases have a weak influence. (C) 1994 The Institute of Materials.