*2.4. Mechanical Properties*

The materials were mechanically tested before and after FSW for comparison. To have an insight into the mechanical properties, hardness measurements and tensile testing were carried out. Vickers macro-hardness tests were performed on the transverse cross-sections

perpendicular to the welding direction with an interspacing distance of 2 mm using a test load of 1000 g force and dwell time of a 15 s. To evaluate the tensile properties of the welded stir zone, transverse flat tensile specimens were used. Specimens were machined perpendicular to the FSW direction to the dimensions: length of 80 mm, width of 15 mm, and thickness of 8.5 mm. The specimen's dimensions agree with the DIN EN10002-1 2001(D) standards. After machining, both surfaces of the samples were flushed to avoid any dimensional irregularity. Figure 3 shows the dimensions of the tensile specimen and an image of the sample after tensile testing. Tensile tests were carried out at room temperature with an initial crosshead speed of 0.1 mm/s using the universal testing machine Instron 4210, Norwood, MA, USA. The tensile data acquired were analyzed to determine tensile properties and joint efficiency. The fracture surface of the tension tested samples was examined using the Scanning Electron Microscope Type: Quanta 250 with a Field Emission Gun, FEI company (Hillsboro, OR, USA) to determine the failure mode of the welded samples.

**Figure 3.** The dimensions of the tensile specimen and an image of the sample after tensile testing.
