Mechanical Properties Enhancement in Friction Stir Processed AA2024 Alloy through Pin Profile Optimization

The current study investigates the impact of pin profiles, namely cylindrical pin tool (CT), cylindrical threaded pin tool (CTT), and tapered cylindrical threaded pin tool (TCTT), on microstructural features and mechanical and characteristics of friction stir processed (FSPed) AA2024. Comparing the experimental results to the AA2024 base metal, all assessed metrics show considerable improvements. In particular, the TCTT shows the greatest improvements, showing a decrease in grain size to 4.3 µm, an increase in hardness to 175 HV, and increases in both elongation to 31% and ultimate tensile strength (UTS) to 543 MPa. In comparison to the CT, the CTT shows significant benefits as well, including smaller grain size (6.5 µm), greater UTS (529 MPa), hardness (162 HV), and better elongation (28%). In addition, the CT exhibits improvements over the AA2024 base metal in terms of elongation (26%) hardness (155 HV), UTS (517 MPa), and grain size (7.9 µm). With the introduction of threaded pin profiles, the fracture morphologies of the friction stir-processed specimens show a shift towards more ductile failure modes. The microstructure and mechanical characteristics of the FSPed AA2024 alloy are significantly impacted by the pin profile geometry, as demonstrated by these findings. These findings offer important new information for improving material performance and processing parameter optimization in aluminum alloy applications.