The Effects of Zr Addition on the Microstructure and Mechanical Properties of A356-SiC Composites

The influences of Zr on the microstructure of A356-15 vol% SiC composites, such as the distribution of SiC particles in the matrix, the grain size and the hardness and impression creep between 225 and 275 degrees C, were examined. These composites were prepared using the stir casting technique. The addition of Zr forms Al3Zr phases, which can act as heterogeneous nucleation sites, thus resulting in grain refinement. Furthermore, Zr leads to a more uniform distribution and an increased area fraction of SiC particles. Moreover, the addition of only 0.1 wt% Zr significantly increased the Brinell hardness by approximately 18% when compared to the composite without added Zr. The addition of a small amount of Zr (0.1 wt%) is sufficient to increase the Vickers microhardness by approximately 34% when compared to the composite without added Zr, indicating the effect of solid solution strengthening on the composite matrix. The high-temperature stability test using the impression creep technique demonstrated that the A356-15 vol% SiC composite with 0.1 wt% added Zr shows improved creep resistance. However, the creep resistance of composite samples with higher than 0.1 wt% added Zr decreases due to grain boundary sliding occurring in the A356-15vol% SiC composites with too much added Zr.