Thermal expansion studies on aluminium-matrix composites with different reinforcement architecture of SiC particles

The thermal expansion behaviour of different SiC particulate reinforced aluminium-matrix composites is investigated up to 500 °C using a thermal mechanical analysis equipment. The aim is to explain abnormalities in the thermal expansion behaviour of 70 vol% SiC particulate reinforced aluminium-matrix composites (Al/SiC) used as base plate material for high power electronic modules. Composites with different SiC contents (10, 20, 55, 70 vol%), various matrix-alloy compositions (Al99.5, A356, A359), and different fabrication routes are investigated. The instantaneous coefficient of linear thermal expansion (CTE) as a function of temperature is compared with predictions from thermo-elastic models according to Schapery and Turner using the expansion data determined for the ingredients.The expansion behaviour is correlated to the microstructure, the deformation of the matrix, and the internal stress conditions. The temperature dependence of the solubility of Si in Al influences the CTE of Al–Si matrix alloys significantly. Composites with isolated ceramic particles (10–55 vol%) show similar thermal behaviour as the matrix alloy just reduced by the volume fraction of SiC-particles. The CTE of highly reinforced Al/SiC(>55 vol% SiC), where the reinforcement is interconnected, drops above 250 °C. Such anomalies in the CTE are explained qualitatively by visco-plastic matrix deformations and changing void volume fractions. Although the matrix deforms non-elastic, the effects are reversible during reproduced thermal cycling.