The intergranular fracture of AlMgSi alloys

The fracture behavior of an Al  Mg  Si alloy has been investigated as a function of both the magnitude of precipitation hardening and the grain size. For coarse-grained samples the fracture mode at peak hardness is intergranular in nature and the results show that both yield stress and fracture stress can be expressed as a function of the inverse square root of the grain diameter.Both the occurrence of intergranular fracture and the magnitude of the grain size deoendence of the yield stress can be correlated with the coarse slip mode which occurs at peak hardness and a simple quantitative model is advanced to describe this behavior. It is shown that by promoting more dispersed slip modes or by grain refinement the intergranular fracture mode is replaced by conventional ductile rupture in which void formation and shear failure become energetically more favourable than grain boundary decohesion.