**2. Literature review**

*Aluminium Alloys and Composites*

on physical disturbance.

an effect on about the device shoulder.

due to the lack of parent metal melting.

*Schematic representation of FSW principle.*

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

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

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

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

without filler wire because it leads to solidification cracking.

**134**

**Figure 1.**

A brief literature review is presented based on the earlier publications on FSW, to start with:


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 chapter deals with experimentation on FSW.

**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

#### **Figure 2.**

*Different regions of FSW joint. A = unaffected metal base; B = Heat Affected Zone (HAZ); C = Thermo-Mechanically Affected Zone (TMAZ); D = Friction Stir Processed (FSP) zone.*

because of the heat produced by the friction and the metal flow through the stirring action. On the other hand, owing to incorrect metal flow and inadequate metal consolidation in the FSP region, FSW Joints are susceptible to other defects such as cracks, tunnel defect, kissing bond, piping defect, pin hole, etc. Existing literature focuses on the impact of welding parameters and tool profiles on the formation of defect-free FSP is very limited.

**Objectives of this present work**: a Solemn attempt is made in the present investigation to conquer the limitations identified and to conduct experimentation on AA6061 Al alloys with the objectives as given in the following:

