Analysis of solid-state welding in extruding wide aluminium hollow profiles using a new three-container extrusion system

A novel multi-container extrusion has recently been proposed to extrude multiple billets simultaneously for manufacturing thin-walled wide engineering components with greatly reduced force. The metal flow behaviour and solid-state welding in the process are crucial factors that influence the final product quality and industrial application. In this study, thin-walled wide AA6063 hollow profiles were extruded by three-container extrusion technology under different combinations of extrusion temperature and speed. The bonding quality of the welds that formed between the adjacent billets during the extrusion process was experimentally evaluated via tensile tests of specimens at different positions of the extrudates. A three-dimensional numerical model was established and validated to characterise the metal flow behaviour and the solid-state welding. Ten points in the first 140 mm of the weld of the extrudate were traced to investigate the flow paths and the related physical information such as pressure, effective stress, velocity and strain rate to reveal the weld formation mechanism. The simulated results showed that the whole three-container extrusion process includes five stages, i.e. separation stage, smooth flow stage, welding chamber filling stage, die bearing breakthrough stage and steady extrusion stage. By evaluating the simulated results and the tensile testing results, the pressure-time (Q) criterion was found able to evaluate the welding quality individually for each extrusion condition, while the pressure-time-flow (K) criterion appeared suitable to predict the welding quality for various extrusion conditions within a small range of critical limits.