The effect of nickel powder and tool penetration depth on microstructure and mechanical properties of friction stir lap welded aluminum-copper joints

In this research, the effect of nickel powder as an interlayer and the tool penetration depth on the microstructure and mechanical properties of lap joints between aluminum 1050 (top sheet) and pure copper (bottom sheet), both with a thickness of 2 mm, was investigated.Nickel powder was added through a machined groove with a width and depth of 1 mm at the base of the aluminum sheet.Friction stir lap welding was performed using a hot work steel tool with a shoulder diameter of 16 mm, a pin diameter of 4 mm, a pin height of 2.1 mm, a rotational speed of 950 rpm, a feed rate of 85 mm/min, a tool tilt angle of 2, and varying tool penetration depths of 0, 0.05, and 0.1 mm.The results revealed that in the sample with a 0 mm penetration depth, due to insufficient heat generation, defects such as tunnel voids were formed.Increasing the penetration depth to 0.05 mm resulted in the formation of uniform and thin intermetallic layers, including Al 3 Ni 2 , Al 7 Cu 4 Ni, and Cu 3.8 Ni at the interface, which enhanced joint quality and increased tensile strength to 185.2 MPa with a fracture strain of 8.7%.In the sample with a 0.1 mm penetration depth, thicker and less uniform intermetallic layers were formed, which, despite locally increasing hardness, led to a decrease in tensile strength and fracture strain to 136.6 MPa and 6.7%, respectively.This study demonstrates that under the conditions of this research, a tool penetration depth of 0.05 mm provides the optimal conditions for FSLW of aluminum-copper alloys using nickel powder.