Effect of Submerged Multi-pass Friction Stir Process on the Mechanical and Microstructural Properties of Al7075 Alloy

The friction stir process (FSP) is a solid-state process which is used for severe plastic deformation of materials and modification in microstructure. The microstructure evolution, which iscaused by dynamic recrystallization, changes the mechanical properties of the material. In this study, the FSP of the surface of Al7075 alloy is carried out using 0% overlapping of passes. The FSP caused the non-uniform structure of the raw material with an average grain size of 18 micrometers to change into a uniform structure. This process refined the structure to the grain size of about 8.2 and 12.1 micrometersfor overlapped regions in water and air respectively. In order to study the mechanical properties, the tensile specimens were prepared in both parallel and perpendicular directions to the pin motion. Results showed an improvement in the yield stress, ultimate stress, and elongation of the specimens after FSP. Furtheremore, Vickers hardness of the overlapping specimens decreased compared to the raw materials after applying the FSP.