Friction spot welding multilayer thin Al alloy: Welding mode optimization, microstructure and mechanical properties

In this work, multilayer thin 2024 Al alloy sheets are joined by friction spot welding (FSpW). The effects of welding mode on the microstructure and mechanical properties of the joints are mainly studied. Results show that numerous tiny cracks are observed in the bonding ligament in the joint by single side FSpW, while these cracks can be eliminated by double side FSpW. In the double side FSpW joint, the grains are coarse in the joint center. The grain size increases from the top to the bottom of the joint by single side FSpW. The double side FSpW joints have obviously higher failure loads that the single side FSpW joints. The highest failure strength of 395.6 MPa is obtained at 1200 rpm by double side FSpW.