FABRICATION AND PROPERTIES OF METAL MATRIX COMPOSITES BASED ON SIC FIBER REINFORCED ALUMINUM-ALLOYS

Composite made with Al-7 wt-%Si alloys and discontinuous Nicalon SiC fibres were prepared by compocasting followed by squeeze casting. This technique gives rise to macroscopically homogeneous materials with, however, some segregation of the fibres in the eutectic phase, especially for the lowest volume fractions. The SiC fibres appreciably improve wear resistance, hardness, and compressive strength of the matrix, both in the as cast and heat treated conditions. An analysis of the compressive test results is given based on the mixture rule modified to apply for discontinuous randomly oriented fibre composites. However, it is shown that agreement between predictions and experimental results can only be obtained by considering the increase of the strength of the matrix as a result of the presence of the fibres. This increase is discussed in terms of structural changes and residual stresses created during cooling resulting from the difference in the coefficients of thermal expansion of the components.