Microstructural and X-ray tomographic analysis of damage in extruded aluminium weld seams

Abstract

In the present study, X-ray computer tomography is used to determine damage evolution in extrusion weld seams loaded close to failure for two comparable AlSiMg alloys with distinctively different grain structures. In the dispersoid free alloy, recrystallisation occurs upon extrusion and the weld seam has no effect on mechanical properties. No preferential void formation in the weld seam region was detected. In the non-recrystallising dispersoid rich alloy, the weld seam leads to a reduced ductility. There are no signs of internal void formation, and damage initiation was found to be close to the surface. It is argued that for the non-recrystallising alloy, the effect of the weld seam on the ductility is related to a sharp texture gradient across the weld seam.

Keywords:

• Tomography
• Weld seams
• Mechanical characterisation
• Aluminium alloys
• Thermomechanical processing
• Fracture
• Damage evolution

Acknowledgements

This research was carried out under project numbers MA10196 and MA10128 in the framework of the Research Program of the Materials innovation institute M2i.

The assistance of Norbert Grittner and Marcus Engelhardt of the Institut für Werkstoffkunde of the Leibniz Universität Hannover in assisting with the extrusion trials is gratefully acknowledged.

The support of Kees Kwakernaak in the SEM analysis of the grain structures is gratefully acknowledged.

Ranjita Bose of the Novel Aerospace Materials Department in the Faculty of Aerospace Engineering of Delft University of Technology is gratefully acknowledged for the preparation of the X-ray CT images.

The support of Tommaso Pinter of Almax Mori SRL in the design and supply of the extrusion tooling is greatly acknowledged.