Fracture behavior of thixoformed A356 alloy produced by SIMA process

There are various methods for production of thixoforming stock. One of these methods is strain induced melt activation (SIMA) process. In the present study, the effect of thixoforming process on morphological properties of silicon particles that affect fracture mode of A356 alloy was investigated. Microstructure and fracture surfaces of thixoformed samples were investigated by image analyzing technique and scanning electron microscopy. A new combination parameter, called silicon particle appearance (SPA) index, was introduced. SPA index approximates the collective effects of silicon particles morphological characteristics on microstructure transparency of alloy in crossing the dislocation. It is suggested that samples with lower SPA index have superior mechanical properties, especially tensile elongation, and consequently intergranular fracture mode. On the contrary, samples with higher SPA index have inferior mechanical properties and fracture path tends to propagate along the cell boundaries leading to transgranular fracture.