Joining aluminum to steel dissimilar metals using novel resistance spot welding process

• Aluminum in the weld can be efficiently removed by the active-expulsion process. • A large nugget free of brittle compounds can be obtained in the aluminum-steel joint. • Aluminum-steel joints provide excellent mechanical properties and ductility. Reliable welding of aluminum to steel dissimilar metals is of great significance in the automotive industry, which promotes lightweight automobile body structure. Here we propose an innovative resistance spot welding process to weld the AA6016 aluminum alloy and press hardened steel. Experimental results shown that the expulsion pulse, intentionally set, can instantly pushed out the molten aluminum from the interface in the form of expulsion. Furthermore, the locking plate contacts the steel workpiece and/or even achieve micro-connection through forming a small steel weld nugget. After the welding current pulse was applied, the locking plate and the steel workpiece were strongly joined together and produce a large steel weld nugget with a diameter greater than 5 mm. Moreover, the aluminum workpiece was tightly locked between the locking plate and the steel, thus achieving an effective joint between aluminum and steel.