Abstract:

In order to eliminate the disadvantages of the keyhole in conventional friction stir spot welding joint and attain the high-strength lap joint of Al/Cu dissimilar metals, a novel welding technique, named as friction stir spot riveting (FSSR), was proposed. A pinless tool and an extra filling stud were employed. The Al/Cu spot joints without keyhole defect were achieved by the FSSR. A Cu anchor-like structure was formed, which greatly increased the mechanical interlocking between the upper Al sheet and lower Cu sheet. The thin intermetallic compounds containing CuAl₂ and CuAl at the Al/Cu interface strengthened the joining interface between the Al sheet and the Cu stud. Increasing rotating velocity increased frictional heat and plastic deformation and then eliminated the interfacial joining defects. The FSSR joint with the maximum tensile shear load of 3.50 kN was achieved at a rotating velocity of 1800 rpm and a dwell time of 20 s, whose fracture path passed through the softened region of upper Al sheet. In summary, the novel FSSR technique has the advantages of strong mechanical interlocking and metallurgical bonding between dissimilar materials, thereby attaining the high-strength spot joint.

Key words: Al/Cu dissimilar materials, Friction stir spot riveting, Intermetallic compounds, Microstructures, Tensile shear strength