Spot welding of aluminium and steel sheet with an insert of aluminium clad steel sheet: Dissimilar metal joining of aluminium and steel sheet (1st Report)

Summary

This paper describes an investigation of the dissimilar metal spot welding of aluminium and steel sheet with an aluminium clad steel sheet insert. The study relates to application of this system in automotive fabrication in an effort to reduce motor vehicle weight. To ascertain the mechanical properties of the intermetallic compounds formed at the steel and aluminium bond interface, measurements were performed using four types of Fe‐Al binary system intermetallic compound. The mechanical properties of spot‐welded joints in aluminium and steel sheet with and without insertion of an aluminium clad steel sheet were measured by the cross tension test, and the microstructures of the welded joints then formed were observed.

The intermetallic compounds FeAl and Fe₃Al have a relatively high ductility, and Fe₂Al₅ and FeAl₃ have a high hardness and low ductility. Fe₂Al₅ intermetallic compounds were formed in the spot‐welded zones of the aluminium and steel sheet, resulting in loss of strength. The dissimilar metal spot‐welded joints produced with an aluminium clad steel sheet insert show an excellent tensile strength in the cross tension test and fracture in the aluminium alloy base metal. Two nuggets of Al/Al and steel/steel were independently obtained by this process. These two nuggets and the clad interface contribute to maintenance of joint strength. The results show that dissimilar metal spot‐welded joints of aluminium and steel have a strength equivalent to that of similar metal aluminium alloy joints in this process.