Aluminum alloys are used in different areas from the automobile to the white appliances due to their high strength compared to their weight, high corrosion resistance, high electrical and thermal conductivity, and easy formability 1. However, problems such as difficulties in weldability, losses in alloying elements in the weld zone, porosity, and crack/tunnel defects in the fusion weld zone create problems in the joints made with fusion welding 2–4. In order for the materials to be combined with the fusion welding, the melting temperatures must be close to each other. Therefore, materials which have different melting temperatures cannot be welded with fusion welding techniques 5. Therefore, innovative welding methods have been focused on 6.
Friction stir welding (FSW) which the solid-state welding methods, is forcing two materials to friction by using a shoulder and a pin profile and combining them by converting mechanical energy into heat at the welding interface 7–9. The FSW method includes a shoulder and a pin profile, a fixture to bind materials so they don't move, a pair of materials, and a machine. In addition, materials are combined below their melting temperatures and no consumables are used 10. During FSW, the shoulder rubs with the material pair. Thus, heat is generated in the weld area, and softening occurs in the material pair. Meanwhile, the pin mixes the materials together along the weld line. Thus, severe plastic deformation and material flow occur in the weld area 11. In recent years, many researchers have focused on FSW because of its advantages. The studies carried out include the joining of different material pairs (AA6063/AA5052 10, AA6082-T6 2, Al5083/Cu 12, Al/mild steel 13, 14, 304 austenitic stainless steel/ Q235 low carbon steel 15, Al-Cu-Li 16, AA7075/AZ31B 17, the effects of process parameters and tools: shoulder 18, 19, pin geometry 20–22, rotational speed 4, 23–29) on the weld quality in FSW, and microstructure investigations.
Guo et al; The effects of process parameters (rotational speed 1200 rpm and travel speed 1, 3, and 5 mm/sec) on the friction stir welding method of AA 7075-T6 and AA 6061-T6 alloys were investigated. They found that when the best weld quality is at the highest feed rate and the AA 6061-T6 alloy is placed on the advancing side, better mixing is achieved and the weld seam becomes more efficient 30.
Quintana et al.; analyzed the effects of process parameters ( tool pin, tool shoulder, and complete tool) on the axial force by joining 5052-H34 aluminum plates using FSW. They reported that the correct design of the pin significantly reduces the effect of the shoulder on the axial force, while the welding speed does not affect the axial force 31.
Hasan et al; The mechanical characteristics of the weld zone were examined by combining AA 7075-T651 and AA 2024-T351 aluminum alloys with the FSW process. In addition, the effects on the weld quality were investigated by changing the positions of the alloys relative to each other as advancing and receding edges 32.
Palanivel et al.; The effect of the pin profile on the tensile strength of AA 6351-T6 and AA 5083-H11 aluminum alloys using FSW was investigated. As FSW parameters, tool rotational speed (600–1300 rpm) and 5 types of pin profiles as straight square, tapered square, straight hexagon, straight octagon, and tapered octagon were used. They concluded that the highest strength joint was obtained with a tool rotation speed of 950 rpm and a square type profile 33. In another study, it was stated that the microhardness was the lowest, the weld zone temperature was the highest, and the square pin provided sufficient material flow 34.
Khan et al. investigated the defects occurring in the welded region in the joining of AA 5083 H-116 and AA 6063-T6 alloys. In order to eliminate the tunnel-type gap defect occurring in the weld area, the plunge depth of the pin was increased and they observed that the strength values increased as well. They also concluded that the tunnel defects were completely eliminated by shifting the pin towards the softer of the two plates 35. In another study, the effects on microstructure and mechanical properties were investigated by positioning the pin 0.1, 0.2, 0.3, and 0.4 mm eccentrically. Better weld interface, finer grain structures, and high mechanical properties were obtained in pins with 0.2 mm eccentricity 36. Sameer et al. attempted to bond dual-phase (DP) 600 steel and AA6082-T6 Aluminum (Al) alloy with an intermetallic compound (IMC) layer by the FSW process. Five different tool tilt angles of 0°, 0.5°, 1°, 1.5°, and 2° were chosen for the welding. Welded with a 0.5° tilt angle, the joint achieved its highest ultimate tensile strength (UTS) of 240 MPa 37.
When the previous studies are examined, it is seen that the weldability of the material pairs and the effects of the process parameters on the weld quality and microstructure are examined. In particular, the tensile test, which is one of the destructive testing methods, is used in examining the effects of process parameters. This method is both costly and time-consuming.
In the study, the mechanical responses of AA5083/AA6061 alloys combined with FSW were investigated. Three different pin geometries, three different rotational speeds, and two different feed rates were used in the FSW process. The evaluation was made by using a tensile test and microhardness measurements to determine the weld quality. Vibration characteristics of an FSW welded Al alloys are investigated experimental. The effects of FSW process parameters on the mechanical properties (yield stress, ultimate stress, etc.) and modal properties in the weld zone were investigated. The utility of modal analysis in determining weld quality in FSW welded specimens has been discussed.