Mechanical properties and fracture behavior of thixoformed, rheocast and gravity-cast A356 alloy

In the research work presented here, effects of T6 treatment, microstructural features and defects and reheating temperature on mechanical properties and fracture behavior of thixoformed A356 samples were investigated. The results were then compared with mechanical properties and fracture behavior of rheocast and gravity-cast samples. Results obtained show that, in the case of thixoformed A356 samples, by increasing reheating temperature tensile strength increased and tensile fracture path was changed from trans-primary alpha phase to inter-primary alpha phase. In the case of rheocast A356 samples, tensile fracture path tended to shearing eutectic phase whereas, in the case of gravity-cast A356 samples, shrinkage porosities were seen in the tensile fracture side views. By T6 treatment, tensile strength increased while tensile elongation decreased. In the case of thixoformed A356-T6 samples, fracture path tended to shear the primary alpha phase. Differences observed in the tensile fracture path are attributed to microstructural changes as well as morphological aspects of silicon phase. The improvement in the tensile strength after T6 treatment appears to be related to the reduction of stress concentration at Si/eutectic matrix interface.