Damage by the cracking of silicon particles in an Al-7Si-0.4Mg casting alloy

The cracking of Si particles during plastic deformation has been studied for different microstructures produced by varying the solidification rate and length of solution treatment. The number of cracked particles increases with the applied strain. The larger and longer particles are more prone to cracking. In coarser structures particle cracking occurs at low strains, while in finer structures the progression of damage is more gradual. Between 3 and 10% of the particles crack prior to fracture. The stresses in the particles can be calculated using current models of dispersion hardening and the particle cracking can be described by Weibull statistics. Assuming that fracture occurs when a critical level of damage is attained, the ductility of the alloy can be expressed as a function of the dendrite cell size and the average size and aspect ratio of the cracked Si particles.