In Situ Investigations on the Ductility of an Al-Si-Mg Casting Alloy

This paper reports the results of an investigation into the damage mechanisms that occur during straining of the aluminum alloy A356-T6 using in situ tensile experiments in a scanning electron microscope. Quantitative stereological analyses of the microstructure and in situ studies of the damage mechanisms have been used to characterize the Si particles and their eutectic distribution that ultimately controls ductility. In situ testing has revealed that, at increasing applied strain, the damage begins with brittle fractures of the Si particles due to cleavage. In this way, adjacent microcracks are created. Subsequently, the joining of the Si microcracks gives rise to the nucleation of a microcrack on the dendrite boundaries. The final damage stage involves the growth of the crack along the dendrite boundaries, until instability is reached. The investigations have shown that, by means of in situ mechanical testing, it is possible to obtain quantitative data of the damage mechanisms which are useful to predict the engineering characteristics of casting alloys.