Evaluation of the damping behaviour of Al-Mg-Si alloy based composites reinforced with steel, steel and graphite, and silicon carbide particulates

Metallic materials known for their good toughness and ductility are now contemplated as replacements to the inherently brittle ceramics which are typically used as reinforcements in aluminium based composites (AMCs), because of the growing structural applications of AMCs. However, the good damping properties offered by the ceramic reinforced AMCs have not been well studied in their metallic reinforced counterparts. The present study investigates and compares the damping behaviour of Al-Mg-Si alloy based composites reinforced with 6 and 8 wt% steel particles to that reinforced with a hybrid mix of 6 wt% steel and 2 wt% graphite, and 8 wt% SiC particles. The aluminium based composites were produced using stir casting process and the microstructures characterised with backscattered electron mode imaging. A dynamic mechanical analyser was used to evaluate the damping properties of the composites produced. The results show that the storage modulus of the composites containing 8 and 6 wt% steel particles were higher than that of the other composite grades with the 8 wt% SiC reinforced composite composition recording the lowest value. The Aluminium based composite containing 8 wt% steel particles also had the highest loss modulus over the test temperature range (70-250 °C) but because of its relatively higher storage modulus, it did not record the best damping capacity which was obtained with the 8 wt% SiC reinforced composite. The effect of the test frequencies 5 Hz and 10 Hz on the damping properties was on the average marginal, while significant variation in damping properties with test temperature were observed in the study.