**1. Introduction**

Hardenable aluminum alloy namely AA6061 has played a key role in the production arena, to meet not only the strength to weight ratio but also light in weight. Magnesium and silicon are AA6061 main alloy components and thus Al-Mg-Si aluminum alloy is of medium strength and is widely used due to its superior formability, weldability, machinability, and corrosion resistance compared to other aluminum alloys. Magnesium and silicon forms Mg2Si which in turn forms a simple eutectic system with aluminum. It is the precipitation of Mg2Si after artificial aging and then allows the alloys to reach their full strength. Therefore, AA6061 alloy is extensively employed in ship building, marine frames, pipelines, storage tanks and applications of aircraft. Even though Al-Mg-Si alloys are without difficulty weldable, owing to reversion (dissolution) of Mg2Si precipitates during the welding thermal cycle, they suffer from serious softening in the HAZ. This sort of mechanical deficiency poses a significant engineering issue. To enhance the mechanical

characteristics of welding, it will be more suitable to overcome or minimize HAZ softening. AA 6061 aluminum alloy cannot be Tungsten Inert Gas [TIG] welded without filler wire because it leads to solidification cracking.

Moreover, the weld fusion area of aluminum alloys typically has coarse columnar grains due to the prevailing heat circumstances during solidification of the welded metal. This often results in lower mechanical welding characteristics and bad cracking resistance to hot. Hence, such is particularly suited in accordance with monitoring solidification structure of welds, but such control is often tough because on higher temperatures then thermal gradients between welds between rapport in accordance with castings yet the epi-axial makeup about growth procedure. Further, into the past as inoculation with heterogeneous nucleants, micro-cooler additions, floor nucleation triggered by using gas impingement and commencement on physical disturbance.

So as to beat these troubles between the fusion welding tactics to that amount are mechanically chronic in imitation of be a part of structural alloys, the Friction Stir Welding (FSW) is an emerging solid-state joining process in which the metal is not softened and recast. In 1991, Friction Stir Welding (FSW) was created as a solidstate joining method at the United Kingdom's Welding Institute (TWI) and applied originally to aluminum alloys [1]. FSW's fundamental concept is remarkably easy. Friction Stir Welding is an uninterrupted, hot shear, auto-genous and environmentally friendly method with a non-consumable rotating tool of a harder material than the substrate. It is found that a contraption of onion circle structure during aluminum alloy FSW welds relies upon the extent of material mixing and between dispersion, whereas the thickness of twisted aluminum lamellae, and material stream designs exceptionally rely on the geometry of the apparatus [2]. Further the temperature of welding and the stress on the material flow are depending on the axial force. In additionally, opined so much at low axial force, the structure about non-symmetrical semi-circular capabilities at the top surface concerning the weld suggests poor plasticization yet consolidation on the material underneath the have an effect on about the device shoulder.

A non-consumable rotating tool along an exceptionally designed pin and shoulder is put into the edges of the sheets or plates in conformity to be joined and after that navigated along the joint line. **Figure 1** suggests the schematic sketch of FSW. The new FSW method is noted to offer several benefits over fusion welding due to the lack of parent metal melting.

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*Experimental Investigations on AA 6061 Alloy Welded Joints by Friction Stir Welding*

A brief literature review is presented based on the earlier publications on FSW,

• CFD analyses the pin profile and shows that it plays a vital part in the material flow and controls the welding speed of the FSW process and is concentrated for refining weld fusion zones on the basis of several experimental methods but with only partial success [3]. Since the FSW is also dependent on the temperature distribution, the micro-structural evolution of the FSW of 6061 aluminum alloy (T6-temper condition) to copper [4] has been analysed. In FSW, the shoulder force is directly accountable for plunging the tool pin's depth into the work piece and load characteristics of linear friction stir welds. At steady state, the shoulder force varies depending upon the rotational speed. Increase in rotational speed is results in drop in initial axial force with increasing time [5]. Different micro-structural zones have been identified which show the hardness distribution on single and overlapped layers [6]. The nugget region with severe plastic deformation and exposure to elevated temperatures being characterized by fine and equiaxed recrystallized grains. Further, the thermo-mechanically affected region experiencing medium temperature and deformation having deformed and un-recrystallized grains and the heataffected zone have been experienced based on temperature, characterized by precipitate coarsening. Transient and quasi-stationary phases of FSP are revealed by roughness mapping. Just as each high rotational rates could raise strain rate, and there by impact the recrystallization procedure; which thus

• The FSW is also extended to join the AA 6061 T-6 aluminum alloy and AZ31 alloy and to study hybrid laser FSW's microstructure and mechanical properties [8]. It is followed by the experimental study of butt joints of AA 6061 and ZRB2 metals in-situ Composite materials and studied the effect of those

The literature also shows that a number of modelling techniques are developed for the analysis of FSW process parameters and their influence on the joints. In this context, the optimization of process parameters is studied by Taguchi method on cast aluminum alloy A319, it is followed by the modelling of AA6061-T6 butt joints and studied the tensile properties [10–13]. Further, a case study is presented with a review on the optimization of process parameters of 6061 Al alloy using Taguchi method [14]. Though noted research has been taken place, the literature shows that there is no consideration on the effect of the various pin profiles on the joint geometry at various rotational speeds of FSW is still limping. Therefore the present

**Figure 2** shows the different regions of FSW joints. It consists of four elements: (a) unaffected base metal, (b) heat affected zone (HAZ), (c) thermo mechanically affected zone (TMAZ) and (d) friction stir processed (FSP) zone weld nugget zone. Structure of the above areas is influenced by the behaviour of the material stream under the activity of pivoting un-consumable instruments. Even though, the FSW tool profiles, FSW tool dimensions and FSW process parameters [5] predominantly influence the material flow behaviour. In fusion welding of aluminum amalgams, the imperfections like porosity, slag consideration, cementing splits and so on break down the weld quality and joint properties. Usually, FSW joints are free of such defects as there is no fusion during welding and the metals are joined by solid-state

*DOI: http://dx.doi.org/10.5772/intechopen.89797*

could impact the FSW procedure [7].

materials on sliding wear [9].

chapter deals with experimentation on FSW.

**2. Literature review**

to start with:

**Figure 1.** *Schematic representation of FSW principle.*

*Experimental Investigations on AA 6061 Alloy Welded Joints by Friction Stir Welding DOI: http://dx.doi.org/10.5772/intechopen.89797*
