Ultrasonic vibration enhanced friction stir welding process of aluminum/steel dissimilar metals

A novel ultrasonic vibration enhanced friction stir welding (UVeFSW) process was employed to join the 6061-T6 aluminum alloy and QP980 high-strength steel. The macro morphology, microstructure and tensile shear properties of the joint with or without ultrasonic energy were compared and analyzed. Meanwhile, the effects of ultrasonic energy on the welding load were studied. The results show that the ultrasonic vibration applied to the base metal before welding can soften the base metal, promote the plastic flow of the material, expand interface zone and nugget zone of the aluminum/steel, make more steel particles rotate into the aluminum alloy side with the stirring needle, forming a hook structure at the edge of the interface zone which can improve the failure load of the joint. The fracture position and fracture morphology of FSW joint are changed by ultrasonic, and the mechanical properties of FSW joint are improved. Under the welding parameters conducted in the experiment, the maximum average failure load of the joint is 4.99 kN. Under the conditions of a welding rate of 90 mm/min and a depth of 0. 1 mm, the application of ultrasonic vibration makes the average failure load of the joint increase by 0. 98 kN and the tensile shear performance increase by 28. 24%. After applying ultrasonic vibration, the axial force F-z, the tool torque M-1 and the spindle power decrease by 2. 46%, 6. 44% and 4. 59% respectively.