Electron Microscope Observation of Fracture Surface in Al-Zn Polycrystalline Alloys

Abstract

An electron microscope observation of tensile fracture surface has been made on some heat-treated alloys of Al-10 wt%Zn and 20 wt%Zn. Specimens for the electron microscope observation were made by the one-stage carbon replica method. The results obtained are as follows: (1) In all cases, tensile fracture occurs in or near grain boundaries. (2) The main characteristic of tensile fracture is common to both room temperature aged and furnace-cooled alloys. In both cases, cracks occur at first between the matrix and the thin layer at boundaries in which solute atoms preferably segregate or precipitate and they propagate until intergranular fracture occurs. (3) As for the alloys aged at 200°C, the main characteristic of fracture is that the materials fractionate in the denude zone at the grain boundaries or between the denuded zone and the matrix.