Intergranular crack during fatigue in Al-Mg-Si aluminum alloy thin extrusions

Abstract The fatigue properties and possible mechanisms of intergranular fatigue fracture were investigated in the Al-Mg-Si aluminum alloy. The fatigue fracture surface of the 6N01-T5 aluminum alloy exhibited thorough intergranular cracking and a “rock candy” morphology, where the stress amplitude had no effect on the fracture morphology. The three typical fracture regions were obtained after solution heat treatment, whereupon the crack paths changed from intergranular cracking to traditional brittle cracking. A chainlike continuous distribution of Mg-Si and Fe-Al-Si phases was observed by electron backscatter diffraction phase graph analysis. After solution heat treatment, the number of Mg-Si phases decreased sharply and the chainlike continuous distribution of the intermetallic phases transformed into an interrupted island distribution, which demonstrates that Mg-Si phases are the main cause of intergranular cracking.