**2. Working principle of FSW**

Friction stir welding (FSW) is a solid-state welding process created and patented by The Welding Institute (TWI) in 1991 [17]. It is a relatively novel joining technology, which has caught the interest of many industrial sectors, including automotive, aeronautic and transportation due to its many advantages and clear industrial potential. The process adds new possibilities within component design and allows more economical and environmentally efficient use of materials [18, 19]. FSW can produce low-cost and high-quality joints of heat-treatable aluminum alloys without

#### **Figure 2.**

*Schematic diagram of the friction stir welding process [22].*

#### **Figure 3.**

*The schematic diagram showing heat energy generation and distribution during FSW process [25].*

use of consumable filler materials, no special preparation of the welding sample is required and can eliminate welding defects, little waste or pollution is generated during the welding process [20, 21]. Friction stir welding offers distinguish advantages like ease of handling by precise external process control and can create homogeneous welds with high levels of repeatability [21]. The working principle of FSW is shown in **Figure 2**.

In FSW, cylindrical rotating tool consisting of a concentric threaded pin and tool shoulder are used for welding the parts. A non-consumable rotating tool along with specially designed pin and shoulder is attached at the faying edges of the plates to be joined and traversed along the welded joint. The clamps are used to fix the two sheets on the bed and force is applied vertically to fix the tool on the collect of vertical milling machine. The friction between the welding tool i.e. rotating tool and workpiece is generated due to rotation of rotation tool on the plated to be welded which leads to plastic deformation of work piece. The plates get soften at the around the pin due to generation localized heat from the friction and the combination of tool rotation and translation leads the movement of the soften material from front of the pin to back of the pin. The welded joint is formed by deforming the material at temperatures below the melting point of parent material. If the direction of tool rotation and translation of the welding tool in same direction, then it is called advancing side whereas both the motions in opposite direction then it is

**11**

*Recent Advances in Joining of Aluminum Alloys by Using Friction Stir Welding*

highly depends on deciding the quality levels of joint obtained.

area [24]. The heat distribution is clearly shown in **Figure 3**.

called retreating side. In FSW process, geometry of the tool is very important which

During the FSW process, the temperature distribution is a function of the heat generated by the friction between the workpiece and tip and shoulder of the tool [4]. The heat generation is depending on the physical properties of the workpiece and the tool [23]. And the generated heat equal distribution is crucial for the quality of the weldment and heat distribution is depends on the thermal conductivities of the tools and workpieces, thermal capacities, the relative speed, and the intersection

As mentioned earlier that fusion based welding of aluminum alloys is difficult because of limited weldability. Some aluminum alloys can be resistance welded but the surface preparation is problematic, and time consuming and surface oxide is being a major problem during welding [26] On the other hand, FSW can be used join most of the aluminum alloys without any surface oxide problems and no special cleaning is required prior to welding. Some of the research publications which reported to literature based on friction stir welding of aluminum alloys are

Rhodes et al. [26] had been made an experimental analysis to study the significance of welding process on weld nugget (WN), heat affected zone (HAZ) and microstructural changes of FSWed 7075 aluminum alloy material. They stated from the study that friction stir welding process was useful to join unweldable aluminum alloys without introducing a cast microstructure and it was not influencing much on WN, HAZ and microstructure of welded joint compared to fusion welding techniques. Jata et al. [27] were investigated the effects of FSW method on microstructure and mechanical properties of friction stir welded aluminum alloy 7050- T7451. Researchers observed from analysis that FSW process transforms the initial millimeter sized pancake-shaped grains in the parent work-material to fine 1 to 5 micrometer dynamically recrystallized grains and it also redissolves the strengthening precipitates in the weld-nugget area. The fatigue strength of welded specimen depends on the bonding between the intergranular mechanism. Frigaard et al. [4] had been studied the microstructure evolution and its effects on hardness distribution of FSWed samples of AA6082-T6 and AA7108-T79 aluminum alloys with the use of numerical three-dimensional heat flow model. They observed that thermal effects were main reasons behind the strength losses of welded samples during FSW of age hardening aluminum alloys. This was because of high level welding speeds which introduces plastic deformation resulting initiation of the dissolution of hardening precipitates. The grain structure within the plastically deformed region was analyzed by electron backscattered diffraction (EBSD) technique in the scanning electron microscope (SEM) and stated that dynamic recovery is significant softening procedure for FSW of age hardening aluminum alloys. Lee et al. [28] had made an investigation-based on experiments study to enhance welding process performance of FSW of A356 Al alloy. Liu et al. [20] had made an experimental investigation to study, analyze the effects of process welding parameters on tensile properties of friction stir welded 2017-T351 aluminum alloy and optimum welding parameters to attain better quality response of weldment. They observed from analysis that tensile properties and fracture locations of the welded joints are significantly affected by the friction stir process parameters. Peel et al. [21] had made a research analysis on welded samples of aluminum AA5083 in friction stir welds process. They studied the influences of varied process conditions

*DOI: http://dx.doi.org/10.5772/intechopen.89382*

**3. Literature review**

discussed as follows:

#### *Recent Advances in Joining of Aluminum Alloys by Using Friction Stir Welding DOI: http://dx.doi.org/10.5772/intechopen.89382*

called retreating side. In FSW process, geometry of the tool is very important which highly depends on deciding the quality levels of joint obtained.

During the FSW process, the temperature distribution is a function of the heat generated by the friction between the workpiece and tip and shoulder of the tool [4]. The heat generation is depending on the physical properties of the workpiece and the tool [23]. And the generated heat equal distribution is crucial for the quality of the weldment and heat distribution is depends on the thermal conductivities of the tools and workpieces, thermal capacities, the relative speed, and the intersection area [24]. The heat distribution is clearly shown in **Figure 3**.
