Microstructure and Impression Creep Characteristics of A356-SiC Composites Containing Zr

The influences of Zr on the microstructures and impression creep behavior of A356-SiC composites were investigated. An optical microscope and a scanning electron microscopy were used to examine the microstructure. An impression creep test was conducted in a temperature range of 225-275 degrees C under a stress range of 350-450 MPa. The addition of 0.14 wt% Zr can significantly improve the creep resistance of the A356-SiC composite. The stress exponent (n) and creep activation energy (Q) reveal that the lattice diffusion climb-controlled creep is a dislocation climb in the A356-SiC composite, and with the addition of Zr in the A356-SiC composite, grain boundary sliding is the dominant creep mechanism. The activation energy for creep is obtained in a range of 112-173 kJ/mol, which is close to the value for the lattice self-diffusion of aluminum (142 kJ/mol). The addition of Zr alters the creep mechanism of the A356-SiC composite. The creep resistance of A356-SiC composites with added Zr higher than 0.14 wt% decreases due to grain boundary sliding.