m. sajed

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 Al3Ni2, Al7Cu4Ni, and Cu3.8Ni 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.

In the present paper, two-stage refilled friction stir spot welding is used to join mild steel sheets with a thickness of 2 mm. Meanwhile, alumina and titanium oxide nanopowders are also introduced to the nugget to achieve superior mechanical properties. Two non-consumable tools are used with and without pins to weld and refill the keyhole, respectively. Before refilling, the keyhole is filled with nanopowders which are then distributed by the pinless refilling tool. Three parameters are investigated; the rotational speed of the welding tool and the rotational speed and dwell time of the refilling tool. The tensile test is used to evaluate the strength of the joints. The microhardness is measured in the welding zone to evaluate the powder distribution. The results suggest an increase in the joint strength by 42% and 18% with alumina and TiO2 as reinforcement, respectively. With a 31.94% contribution, the refilling tool rotational speed is the most effective input parameter affecting the joint strength. Considering the microstructure analysis and the microhardness test, the material flow pattern is mainly downward which results in the accumulation of the reinforcing powder in the lower sheet especially when a lower refilling tool rotational speed is used.