Artificial aging of thixocast ZA27 alloy and particulate ZA27/SiCp composites

Thixocast ZA27 alloy and particulate ZA27/SiCp composites were subjected to artificial aging at 80, 120 and 160 degrees C (T5 regime). Composites with 5 and 10 vol.% SiC particles were produced via the compocasting method. The influence of the aging was investigated using different techniques. Differential scanning calorimetry was performed to reveal the presence of phases created in the thixocast ZA27 alloy and the composites. Microstructures and fracture behavior were examined by means of optical microscopy, scanning electron microscopy and X-ray diffraction. Aging processes in the matrix alloy and composites were followed using hardness measurements. A decrease in the hardness values was noticed with the increase in the aging temperature. At higher temperatures diffusion of zinc atoms from supersaturated phases in the matrix alloy was enhanced, which resulted in faster changes in the hardness. Aging processes in the composites were significantly accelerated compared to the matrix alloy, due to the presence of particulate reinforcements. The maximum in hardness was achieved for shorter time in the ZA27/SiCp composite with higher volume fraction of SiC particles.