Effect of Fe-Rich Phases on Fracture Toughness of High Strength Al-Zn-Mg-Cu Alloy

In order to analyze the effect of insoluble Fe-rich phases on the fracture toughness of high-strength Al-Zn-Mg-Cu alloys, plane-strain fracture toughness test, scanning electron microscopy, finite element analysis and quantitative modeling were used to investigate the fracture toughness of three commercial high-strength Al-Zn-Mg-Cu alloys. The results show that the fracture mode of the three experimental alloys is strongly related to the Fe-rich phases, which are prone to initiate intergranular fracture of the experimental alloys. Finite element analysis proved that the larger the shape factor of the Fe-rich phases, the more sensitive it is to external stress and more prone to secondary cracking, which is consistent with the fracture morphology observation. Quantitative analysis shows that the size, volume fraction and morphology of the Fe-rich phases have a greater influence on the fracture toughness of the high-strength Al-Zn-Mg-Cu alloy. The fracture toughness of the alloy will be improved when the shape factor of the Fe-rich phases is small and close to circular and the volume fraction of the Fe-rich phases is small. The fracture toughness value of the Al-Zn-Mg-Cu alloys can be better predicted when the deviation of the shape and distribution of the Fe-rich phases is considered.