As carmakers increasingly adopt aluminium to reduce the weight of their vehicles, they must adapt their bodyshops in order to join components made from this lightweight metal – both with other aluminium parts and those made from different materials.  

The use of resistance spot welding (RSW) is ubiquitous in the automotive industry, but using this technology to join aluminium structures presents a number of challenges. Compared with steel, the melting point of aluminium is significantly lower, but it demonstrates a higher thermal conductivity. It possesses roughly twice the thermal expansion of steel, which can lead to it cracking. Meanwhile the electrical resistance of aluminium drops rapidly during the spot-welding process.

As a result of these factors, the welding current must be two-to-three times higher than is needed for steel and the welding time must be cut by two thirds. This means the electric parameters (current and voltage) must be controlled more precisely in a narrower time window, and per-weld energy costs are increased. Furthermore, the fact that aluminium forms a corrosion-resistant oxide on its surface becomes a disadvantage when it comes to welding, as the reaction of the oxide during the welding process quickly contaminates the spot-welding tip, reducing its life. These problems are not insurmountable, though…