Effect of rice-husk ash on properties of laminated and functionally graded Al/SiC composites by one-step pressureless infiltration

The quantitative effect of the following parameters on the one single step pressureless infiltration characteristics of bilayer SiCp/rice-husk ash (RHA) porous preforms by aluminum alloys was investigated using the Taguchi method and analysis of variance (ANOVA): infiltration temperature and time, SIC particle size, RHA percentage, percentage porosity in the preforms, and magnesium content in the alloy. The contributions of each of the parameters and their interactions to the retained porosity, hardness and modulus of elasticity of the resulting bilayer composites were determined. The parameters that most significantly impact the modulus of elasticity (E) of the resulting composites are infiltration time and SiO2 phase type (from RHA), with contribution of 27% and 21%, respectively. They are followed by preform porosity, Mg concentration and process temperature, with contributions of 13%, 12% and 11%, correspondingly. Verification tests conducted using the established optimum parameters show a good agreement with the projected values of modulus of elasticity (169 +/- 9 GPa) and retained porosity (1.9 +/- 0.8). The in-situ formation of MgAl2O4 and MgO phases with the unique morphology of RHA in the microstructure, was manifested as exothermic peaks in the heat flow curves and identified by XRD and SEM analyses of the composites. A reaction pathway for MgAl2O4 and MgO formation was outlined. (C) 2015 Elsevier B.V. All rights reserved.