Fatigue Crack Growth Performance in Refilled Friction Stir Spot Welding and Friction Stir Welding of Aluminum Alloy Joints

Friction stir weld (FSW) is a novel solid-state welding technique that has gained significant attention in recent years due to its many advantages over conventional welding techniques. One of the potential applications of FSW is in the aerospace industry, where it could replace riveting as a joining method. In this study, we investigated the fatigue crack growth behavior of four different aerospace materials in three different joining methods, including Refilled friction stir spot weld (FSSW) and FSW, and were compared with those of riveted joints. The experiments were performed using MTS fatigue testing machine. The four aerospace materials investigated in this study were 2A12/2A12, 2A12/7A09, 2024/2024, and 2024/7075. The experiments were conducted in three different joining methods, including FSSW, FSW, and riveting. The fatigue crack growth (FCG) rate was determined for each material and joining method by analyzing the relationship between the crack growth rate and the stress intensity factor. The results showed that the crack growth rate decreased significantly when the crack extended to the welding area and riveted hole in the spot and riveting experiments. However, the crack growth rate did not change significantly in the FSW experiment. In terms of different forms of samples, the crack growth rate was higher in the FSSW samples at lower values of stress intensity factor, but it was equal to or greater than the crack growth rate of the FSW samples as stress intensity factor increased. The crack growth rate of the riveting form was relatively stable and higher than the FSSW and FSW samples.