Researchers from Shanghai Institute of Optics and Fine Mechanics (SIOM) of the Chinese Academy of Sciences (CAS) have developed a new hybrid resistance spot-laser welding process to join aluminum to steel. The process, described in an open-access paper in the journal Materials & Design, first conducts resistance spot welding of aluminum and steel dissimilar materials, followed by laser spot welding.
Application of aluminum-steel dissimilar materials body structure is one of key solutions in the automotive industry to reduce vehicle weight and improve fuel economy. Therefore, many research works have been conducted in order to achieve high-quality joints using aluminum to steel dissimilar materials in the past decades. However, there are two main challenging impediments for welding of aluminum to steel dissimilar materials.
One is that the extremely low solubility of iron in aluminum (∼0.03 %) leads to easy formation of brittle intermetallic compound (IMC: e.g. FeAl3 and Fe2Al5) in the weld instead of solid solution phases during the welding process; the other impediment relates to large thermal and residual stress produced in the welds due to different thermophysical properties between aluminum and steel such as thermal expansion coefficient, which results in the crack formation in the IMC layer and/or the weld, thus lowering the plastic deformation capacity and fatigue performance of the weld.
… Resistance spot welding (RSW) is one of the mainstream joining methods for car body-in-white (BIW) manufacturing because of its high efficiency and low cost. … Despite advantages of joining homogenous materials, it is still difficult for the conventional RSW process to directly joining of aluminum-steel dissimilar metals.
… In recent years, laser welding has shown many advantages such as high production efficiency and low heat input, and its application has gradually increased in the automotive industry. … However, laser welding of aluminum to steel still presents great challenge due to the formation of many cracks and brittle IMC, which prevent it from being widely used in joining aluminum-steel.
The purpose of this work is to fully take the advantages of RSW and laser welding to connect aluminum and steel dissimilar metals. A hybrid resistance-laser spot welding (HRLW) process is proposed combining a specially designed RSW process with laser welding in an innovative way.—Li et al.
Li et al.
The spot welds are made by resistance spot welding connection technology; circular welds are then made around the spot welds by laser flight welding technology.
The researchers found that significant improvements in the mechanical properties of aluminum/steel joints were achieved by changing the joint structure and controlling the thickness of brittle intermetallic compounds. The resistance spot weld had a considerable tensile-shear load but poor ductility and energy absorption due to the presence of a weak bonding area around the periphery of the joint, which facilitated the crack initiation and rapid propagation.
The following laser spot welding process was conducted in the weak bonding area of the resistance spot welding joint, which inhibited rapid propagation of the cracks along the faying interface (a faying surface is one of the surfaces in contact at a joint) avoiding interface fracture.
Compared with resistance spot welding joints, the tensile-shear peak load and energy absorption were increased by 18.2% and 424.8% for hybrid welding joints, respectively.
Mingfeng Li et al. (2022) “Hybrid resistance-laser spot welding of aluminum to steel dissimilar materials: Microstructure and mechanical properties,” Materials & Design doi: 10.1016/j.matdes.2022.111022