Enhancement of the interface of friction welded steel-aluminium joints

Abstract

Lightweight multi-material components are of great importance for the transport industry. Not only the component’s weight can be decreased, but also its local properties can be adapted to different loading profiles. Tailored Forming is a novel concept for producing multi-material components. By using a joining process, the creation of a bond between different materials takes place in the first step of the process chain. In the subsequent steps, multi-material workpieces are processed in their joined state while maintaining or improving the joint strength. This study focuses on steel-aluminium joints, which were created by friction welding and further processed by induction heating and impact extrusion. A counter pressure superposition mechanism was implemented in the extrusion tooling to control the stress state during plastic deformation. Flow behaviours of steel and aluminium are largely different at a given temperature, which necessitates a near step-function temperature distribution in the hybrid billet to obtain matching flow stresses. An inductive heating strategy was developed which led to a temperature gradient in the billets before extrusion. Extruded billets were analysed by destructive testing methods and metallography. The bond could be maintained after extrusion when counter pressure superposition was used; but no improvement could be obtained. Without counter force superposition, however, cracks were observed in the joining interface and the joint strength decreased. This paper discusses the aforementioned findings in the current process design and makes suggestions on how the involved processes should be reconfigured to improve the joint strength.

Investigation of the joining zone formation of impact extruded hybrid components by varied forming sequence and partial cooling

“…The process chain of Tailored Forming has already been used in earlier work to create customised, hybrid machine parts in serial and coaxial arrangements like axial bearing washers or bevel gears [10]. The parameters were chosen according to the previous work [18] and are designed to prevent unnecessary shortening and to set low temperatures in order to keep the emerging intermetallic phase as small as possible. The steel rotates at a speed of n = 1500 rpm on the spindle side, while on the sledge side the aluminium is rubbed against it with a relative friction path of sR = 4 mm at a friction pressure of pF = 120 MPa.…”

Process Chain-Oriented Design Evaluation of Multi-Material Components by Knowledge-Based Engineering

“…In contrast to other manufacturing technologies for solid multi-material components, a forming process takes place with previously joined semi-finished products so that two different materials are formed simultaneously. This has the advantage that, on the one hand, load-adapted material topologies can be achieved locally and, on the other hand, the joining zone can be influenced both geometrically and thermally during the forming process, resulting in a longer service life of the components [10]. With the use of tailored forming, the number of necessary manufacturing steps usually increases, which also increases the complexity of the corresponding process chain [11].…”

“…The geometry of the joining zone of a tailored forming shaft is significantly influenced by the impact extrusion process. The main factors influencing this are the geometry of the previously joined surface α (e.g., flat or pointed), the degree of forming η, the shoulder angle of the extrusion die β, and the process parameters p i (e.g., temperature or back pressure) [48]. In order to obtain the knowledge about the forming behavior of the joining zone, parameter studies are carried out in advance with the aid of a finite element simulation of the impact extrusion.…”