TWI Industrial Member Report Summary 990/2011
By K A Beamish
Background
There is an increasing industry need to join dissimilar materials, for example, steel chassis members to aluminium body panels to reduce vehicle weight; composite to metal components for aircraft structures and a range of dissimilar coatings to substrates. A wide range of joining techniques can potentially be applied to dissimilar welding applications, with the choice of approach depending on the combination of materials to be welded and the geometry of the components/joints involved.
Adhesive technology is currently applied to many dissimilar material combinations as are mechanical fastenings. Fusion welding technologies are also used, but must be applied with care due to the potential formation of brittle intermetallic compounds during welding, which can result in poor mechanical performance. Friction welding technology is, in general, one of the more successful approaches that can be applied to join dissimilar metals. Many material combinations can be directly joined using friction welding, with still more possible using a mutually compatible interlayer. The relative success of friction welding is due mainly to its solid phase nature (which limits overall heat input and minimises material melting), and the hot forging action of the process (which helps to expel the hottest material as weld flash in many cases).
This report provides a general introduction to the subject of dissimilar materials joining and the potential for use of friction welding, and begins by assessing current Industry needs. An overview of available joining methods is given, identifying those most likely to be successful and explaining why others are less successful for certain material combinations. This report is intended as an overview, and as such does not provide a detailed review of the application of individual processes to specific applications. The review does, however, identify a number of representative dissimilar joining applications, of interest to a range of industry sectors, where friction welding techniques may be of benefit. This report also outlines a number of test cases the will be investigated in detail in the next stage of this programme.
Objectives
- Establish the current status of dissimilar materials joining, including consideration of the materials, applications and technologies commonly involved.
- Identify a number of representative dissimilar joining applications suitable for practical investigation using friction welding techniques, of relevance to a wide range of industry sectors.