A step closer to implementing structural aluminium in the automotive sector.

Making vehicles lighter is an important part of reducing emissions from the transport sector. In her doctoral thesis, On aluminium transfer at high temperature – Mechanisms and control, Justine Decrozant-Triquenaux, doctoral student at Luleå University of Technology, has explored some of the tribological challenges associated with the use of aluminium as a lightweight structural material for the automotive industry.

“We see different lubrication mechanisms at work and some promising formulations and PVD coatings. The next step is to test the most relevant combinations in conditions closer to real production,” says Justine Decrozant-Triquenaux, doctoral student in Machine Elements at Luleå University of Technology.

The transport sector accounts for about a quarter of the European Union’s total greenhouse gas emissions. To meet climate targets, innovation in both materials and manufacturing processes is essential. One effective way to reduce emissions is to build lighter vehicles that require less energy to operate

Justine Decrozant-Triquenaux, doctoral student in machine elements at Luleå University of Technology. Photo: Petra Älvstrand

Towards understanding the hot forming contact

High-strength aluminium alloys are promising materials thanks to their combined low weight and high strength. They offer a good balance between weight reduction and passenger safety, but despite their advantages, large-scale use has been limited – especially in structural parts of car bodies. During high-temperature forming, aluminium tends to adhere to the tool steel, which complicates production. In her research, Justine Decrozant-Triquenaux has investigated why this happens and how the problem can be solved.

"Because of their poor formability at room temperature, high-strength aluminium alloys must be formed at high temperatures," she explains. "However, at these temperatures aluminium tends to stick to the tools, which currently prevents large-scale production."

Her results show that the combination of the right lubricants and surface engineering techniques is crucial to prevent aluminium transfer. The surface roughness of the tool steel also plays a dual role, both beneficial and detrimental.

"The surface roughness can lead to ploughing in the soft aluminium, but it also helps retain lubricants in the contact, especially under starved lubrication conditions," says Justine Decrozant-Triquenaux.

By combining lubricants and surface treatments, her research provides new insights on the synergistic impact of these parameters on aluminium transfer. In the long-term, this will help the development of production though hot forming of such aluminium alloys.

The next step is to test the most promising lubricants and surface engineering techniques in industrial environments to further investigate their behaviour under real conditions.

"I hope these results help the community better grasp the synergistic relationship between lubricant and surface engineering," says Justine Decrozant-Triquenaux

• Machine elements