Aluminum Exhibition | NTNU researchers find new technique using cold welding aluminium-copper to reduce EV weight
Researchers at the Norwegian University of Science and Technology (NTNU) have found that partially replacing copper in EV conductors with aluminium can reduce vehicle weight and improve energy efficiency. They propose using cold welding to combine the strengths of both metals without sacrificing conductivity.
In this process, aluminium and copper bond at the atomic level along the contact surface. While higher temperatures typically improve mixing, they also tend to produce brittle intermetallic phases—crystals that form between the metals and hinder conductivity. Cold welding helps avoid these, preserving electrical performance.
To prevent the formation of brittle crystals, researchers at NTNU have developed a new method called Hybrid Metal Extrusion and Bonding (HYB). PhD research fellow Jørgen A. Sørhaug explains that HYB is quite similar to friction stir welding, which relies on frictional heat generated by a rotating tool to join materials. However, HYB adds a unique twist: it incorporates continuous extrusion of a filler metal—specifically, an aluminium alloy rich in silicon and magnesium.
The processes’ involved
This continuous extrusion is driven by the rotating pin housed within a rigid structure. As the pin turns, it draws the filler wire into an extrusion chamber positioned above it. The wire then passes through a series of dies integrated into the pin, enabling precise control over the bonding process and enhancing the quality of the aluminium-copper joint.
The team then examined the welds using precision electron diffraction, high-resolution transmission electron microscopy, and X-ray analysis. Their findings suggest that the HYB technique outperforms traditional welding methods for joining aluminium and copper. This is due to the formation of thinner, slower-growing intermetallic layers at the metal interface, which helps maintain the mechanical strength and electrical conductivity of the conductors over time.
According to Sørhaug, the aluminium-copper conductors produced have a 50:50 ratio, leading to a weight reduction of approximately 35 per cent compared to pure copper conductors. He believes the weight reduction could potentially reach 50 per cent. However, since aluminium is mechanically weaker than copper, the team notes that further research is required before aluminium can fully replace copper. They propose that creating an aluminium alloy with additional elements and applying thermomechanical treatment could enhance its strength.
'But aluminium alloys are often sensitive to high temperatures, and their strength will generally be weakened by welding. We have therefore also investigated what causes this strength reduction at the atomic level and how we can improve the alloys to better withstand heat,' says Sørhaug.
NTNU will continue its research into cold welding of aluminium and copper through a new project in collaboration with SINTEF. The focus will be on better controlling temperature and tailoring plastic deformation at the nanoscale. Sørhaug also plans to further explore the impact of magnesium, silicon, and copper in the aluminium portion, investigating how these elements influence the strength and electrical conductivity of the conductors, as well as the effect of alloying elements on the weld interface properties.
Sørhaug points out that EVs typically contain 30-80kg of copper wiring, which represents about 1.5-4.5 per cent of a car's total weight (around 2,150kg). He estimates that using aluminium-copper hybrid wires could result in a weight reduction of approximately 1-3 per cent. However, the most significant benefit for the industry, he notes, lies in the cost savings. The HYB technology is currently being explored at SINTEF Manufacturing in Raufoss, where Sørhaug is investigating whether it can be integrated with industrial friction stir welding machines.
Source：AlCircle
