Metallographical investigations of ductile damage in aluminium alloys

During plastic deformation, the structure of metallic materials exhibits ch aracteristic signs of damage such as porosity and micro-cracking. In the wo rk presented here, various different aluminium wrought alloys are deformed in a series of tensile tests. By subsequently investigating the specimens u sing Scanning Electron Microscopy (SEM), it is shown that in these material s the damage which takes place is highly localised and occurs at the points of fracture of brittle precipitates. The voids formed lead to a decrease i n the density of the material which is measured according to Archimedes Pri nciple. From this, a porosity factor is derived, the value of which is corr elated with the area fraction of the pores contained within the structure. In the case of a high reduction of area at fracture (AIMsSi0.5), it is show n that a high multi-axial stress state predominates which promotes the form ation of voids. In this case, the macro-crack ultimately leading to fractur e forms at the centre of the narrowest cross-section of the specimen.