*2.2. Friction Stir Welding Procedure*

The welding process was performed on the friction stir welding machine (EG-FSW-M1) at Suez University. This machine has been locally designed and manufactured in Egypt. The main motor power of this machine is 30 HP (22 kW) and can deliver torque up to 100 N·m, rotational speed up to 3000 rpm and tilt angel up to ±5◦. The travel speed of the table up to 1000 mm/min. The tool design is an important parameter in FSW processes, which influences the heat generation, plastic flow, the resulting microstructure and mechanical properties of the welded material. The used rotating tool was of a cylindrical threaded pin with scrolled shoulder made of H13 tool steel that heat treated to obtain hardness of 50 HRC. The shoulder diameter was 25 mm, the pin (probe) diameter was 8 mm, and pin height was 9.8 mm, which is slightly less than the material thickness (10 mm). The angle between the edge of shoulder and the pin was 3◦. The configuration of the tool used in this study is shown in Figure 1.

The hardness of the as-received tool steel was 25.3 HRC. After manufacturing the FSW tool, it has been hardened by heating to 950 ◦C and holding for 30 min then oil quenched, then tempered by heating to 550 ◦C and holding for one hour then air-cooled to room temperature. The heat treatment process was carried out using an electric resistant furnace of type Nabertherm-1200 ◦C. The hardness of the hardened tool steel was measured as 61 HRC. The tempering process has decreased the tool hardness to 54 HRC. Al alloy plates were prepared to obtain the required dimensions of 200 mm length and 100 mm width. The plates were clamped properly on the FSW machine table as shown in Figure 2a, b shows the butt joint after completing the FSW process.

For the system AA5083/AA5754, the plate of the alloy AA5083 was positioned in the AS, while the AA5754 plate was in the RS as illustrated in Figure 2a. Workpieces were rigidly clamped, to prevent the plates from lifting apart during the welding process. For the system AA5083/AA7020, the plate of the alloy AA5083 was positioned in the AS, while the AA7020 plate was in the RS for a set of welding conditions. For the same set of the welding conditions, the plate of the AA7020 was reversed to be positioned in the AS and

the plate of the AA5083 was in the RS, as shown in Table 3. The welding process progressed as follows: The tool was rotated and slowly plunged into the workpiece with speed of 0.1 mm/s until the shoulder of the tool forcibly contacts the upper surface of the material. After that, the tool was traversed along the weld line for a single pass weld. The tool was tilted by a constant angle of 3◦ against the vertical axis, so that the rear of the tool is lower than the front. This has been found to assist the forging process and the material flow during FSW. Table 3 summarizes the different combinations of operating conditions parameters investigated in this work during FSW. The desired welding parameters are based on the ongoing research at the authors laboratory in FSW of the different aluminum alloys of 10 mm thick.
