Effect of the Interlocked Element Structure on REW Joining Properties of Aluminum Sheets/Steel Sheets

The automotive industry's ecosystem is rapidly shifting from internal combustion engine (ICE) vehicles to electric vehicles (EVs). This transition significantly increases vehicle weight due to added batteries and numerous convenience features. As a result, the use of aluminum in vehicles is rising. However, joining dissimilar materials like aluminum and steel remains a challenge because of their different mechanical and thermal properties. Resistance Element Welding (REW) is widely used for joining dissimilar materials such as aluminum and steel, due to its strong bonding capability and compatibility with existing equipment. This hybrid technique combines mechanical pressing with the thermal properties of resistance spot welding. However, when applied to aluminum sheets, the joint quality often deteriorates compared to die-cast or extruded aluminum. This study analyzes how the element's interlocked structure affects the joining behavior of aluminum sheets. The developed REW process produced a robust interlock, significantly improving both push-out force and bonding strength. Interestingly, although weld nugget size decreased with distance from the element’s center, bonding strength increased, likely due to element deformation and intermetallic compound formation. Ultimately, the robustly formed interlock also ensured watertightness performance.