 | 2009 |
Abstract:
This article presents the joining technologies investigated in the Collaborative Research Centre TR10. They are able to join modern aluminium alloys as well as novel aluminium-based reinforced composite materials. Therefore, the joining characteristics of the pure aluminium alloy, being the matrix material for the reinforcing elements, as well as the composite material are under consideration. To assemble composite aluminium profiles, joining processes and strategies have to be developed which take into account the special characteristics of the basic aluminium alloy and the composite material. The joining technologies in focus are Friction Stir Welding (FSW), Bifocal Hybrid Laser Welding (BHLW), joining by hydroforming and joining by electromagnetic expansion. FSW is a solid state joining process, combining friction and deformation heating to obtain defect-free high quality joints. The BHLW system incorporates an Nd:YAG laser and a high power diode laser. Both lasers are combined in one process zone by a dedicated optical head. This arrangement allows for a hot crack-free joining of aluminium alloys which generally are not weldable by fusion welding. To join using forming processes, the necessary forming pressure was applied by a medium (hydroforming) and by a magnetic field (electromagnetic expansion). The feasibility of joining by forming has been shown experimentally both for conventionally extruded and reinforced profiles. To generate high-quality joints by forming the milling of the connecting elements (nodes) and the preparation of contact areas is necessary. The machined contact areas affect the joint characteristics through surface quality, burr formation, dimensional accuracy and influence of the peripheral zone. Metallurgical investigations and characterization of the mechanical properties of all produced joints were accomplished in order to evaluate the individual welding joints and joints produced by forming. In conclusion, the experimental investigations and the influences of the different materials on the joining processes are outlined and discussed.