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Advanced Materials for Transportation (AMT TCP)

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Building lighter vehicles with multiple materials

Activities of the AMT TCP are focused on improving vehicle energy efficiency without compromising safety, durability, performance or comfort. While promising lighter-weight materials could reduce consumption, studies of welding methods must be performed to ensure vehicle safety, integrity and durability. 

Computer image of a strong, solid-state metallurgical bond between different types of materials.*

In 2013 the transport sector accounted for 65% of world oil consumption.** Replacing vehicle chassis with lighter weight materials is an efficient way to reduce fuel consumption. Combining high-strength steels with lighter materials reduces consumption while maintaining safety standards and vehicle performance. Yet permanently and effectively joining these different materials into vehicle structures and systems is a very complex task.

The AMT TCP set out to examine the technical challenges in processing and joining multiple, dissimilar materials, as well as the testing and inspection techniques that would enable assembly and production of vehicles composed of multiple materials, while maintaining or increasing their structural integrity.

The AMT TCP examined the most efficient welding methods to join dissimilar materials. While fusion spot welding processes are commonly used in vehicle production today for mild steels, and corrosion-resistant galvanised steels are used for unibody vehicle structures, friction stir spot welds (FSSW) were shown to hold greater promise in joining multiple, dissimilar materials.

FSSW is used to join traditional steels with high-strength steels, or high-strength steels with lightweight materials such as aluminium, magnesium, polymers or carbon fibre reinforced plastics. Thus development of the FSSW technique for multi-materials was chosen for initial study.

Vehicle design relies on detailed knowledge of, and guidelines for, the performance of materials and the processes for manufacturing and assembling components. Of particular interest in the study of FSSW was the recession caused when the welding tool is inserted into the material substrates and the metal mixes with the components being joined. By using a refill technique the recession could be eliminated, resulting in improved joint strength and resistance to fatigue. Experiments evaluated the effects of tool rotation speed, tool plunge depth and weld time on the tensile properties of three combinations of materials: aluminium-aluminium, aluminium-steel and magnesium-steel.

The results show that it is possible to fabricate sound joints with all three material combinations using FSSW. In particular, no brittle intermetallic compound layers were detected at the interface between aluminium-aluminium and aluminium-steel, signalling a high level of joint strength. Further work will be done to enhance the joint properties.

The AMT TCP study will continue to expand, including activities on joining technologies which may include mechanical joints based on advanced riveting techniques and adhesives and fusion processes such as hybrid welding brazing. In the near term, the AMT TCP plans to further examine the performance of metal joints and detecting damage accumulation in polymers.

* Computer image courtesy of Charles David Warren, Oak Ridge National Laboratory
 
** IEA, Paris (2015), Key World Energy Statistics

Activities

  • International standards and testing for low-cost carbon fibres
  • Integrated surface technology to reduce engine friction
  • Model-based design of coating systems
  • Multiple-material joining for lightweight vehicles
  • Technology assessment and policy implications
  • Thermoelectric materials for waste heat recovery

Participants

  IEA member 
countries
 Partner 
 countries 
Reg./Int. 
orgs.
Contracting Parties  3  -
Sponsors -  -

For more information: www.iea-amt.org

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