The deformation and fracture behaviour of an AlSiMg casting alloy

By changing the solidification rate, chemical modification and length of solution treatment we show that the ductility of the Al7Si0.4Mg casting alloy depends on the dendrite cell size and the size and shape of the silicon particles. For the strontium-modified alloy the ductility has a minimum at intermediate cell sizes, the fracture mode being transgranular for the larger cell sizes and intergranular for the finer cell sizes. For the unmodified alloy, the ductility also has a minimum at intermediate cell sizes and the fracture mode is, again, transgranular at large cell sizes and intergranular at fine cell sizes. The ductility of the large cell size unmodified materials is low, being dominated by the large elongated silicon particles. If the unmodified alloy is solution treated for shorter times it is more brittle because the silicon particles are more elongated.