The influence of the solid-state bonding process on the mechanical integrity of longitudinal weld seams

For production of complex hollow 6xxx series aluminium extrusions, porthole dies are the predominant tooling set up. In porthole dies, the billet is divided into multiple metal streams, which are rejoined in the weld chamber to form 'longitudinal weld seams'. Fundamental understanding of the solid state bonding process, as well as the ability to detect a well bonded (or a defective) weld seam are important for the production of high quality structural hollow extrusions. A study is being conducted to investigate the solid state bonding and weld seam formation processes during extrusion. The method chosen was to use a thermo-mechanical simulator (Gleeble 3500), thereby having the ability to vary process parameters such as strain, strain rate and temperature. The alloy investigated was primary and remelt AA6082. It was determined that the key parameter for bonding is surface stretching (creation of new surface at the interface) and bonding time.