212
S. S. Nayak et al.
6.4.1 FSW Process and Microstructural Zones
FSW is an efficient, economic and eco-friendly joining process, which is accomplished in the solid-state without melting the base materials. A rotating and nonconsumable tool is inserted in the mid-line of two neighbouring edges of the BMs to
be joined. Heat is generated by the friction occurring between tool and BMs along
with plastic deformation of BMs. The BM gets heated up to an elevated temperature and material flows in the vicinity of FSW tool by stirring action leading to
joining. In FSW, various problems associated with the fusion welding are reduced
and high integrity joints are formed in solid state. The details have been mentioned
in a previous chapter.
Four microstructural zones are present in a FSWed sample. The first one is known
as the SZ, sometimes also called as the nugget zone (NZ). In this zone, the material
undergoes severe plastic deformation since this zone is directly under the influence
of the tool action. The grains in this zone undergo DRX, and the grain size gets
reduced in comparison to the parent material. The flow of the material starts with
the movement of the tool, extruding from the advancing side (AS) in NZ, and flows
around retreating side (RS). Surrounding the NZ, thermo-mechanically affected zone
(TMAZ) exists. Very little recrystallization is noticed here. It is often difficult to
observe the TMAZ in few materials (steels and titanium alloys) [37]. In FSW, the
third zone is the HAZ, which sometimes exhibits the same metallurgical reactions
as in fusion welding. The softening of HAZ in aluminium occurs because of overageing, both in fusion welds and FSW [38, 39]. In order to obtain a sound weld joint
in FSW, sufficient deformation of the BMs is to be ensured so that and they can flow
alongside the tool.
It is well understood that the material deformation occurs in FSW primarily due to
extrusion, forging and shear created by the FSW tool. The deformation mechanism
in the process can be understood through a detailed investigation of crystallographic
texture. The detailed experimental procedure of FSW for AA6061-T6 aluminium
alloy–AISI304 austenitic stainless steel has been given in Sect. 6.4.2. In the FSWed
joint, the authors have studied the microstructure and texture in the aluminium alloy
by using EBSD technique, and the results are shown in Sect. 6.4.3.
6.4.2 Experimental Details
The materials were austenitic stainless steel AISI304 and aluminium alloy AA6061T6 of 1 mm thickness each and were welded in the lap configuration, keeping the
aluminium sheet over the steel sheet. The tool used in this process was made with
bimetallic materials: tungsten carbide (WC) and H13 die steel. The tool pin material
was taken as WC to avoid tool wear and the rest of the tool parts were of H13 die steel.
The WC pin was inserted into the H13 die steel and assembled through interference
fit and supported through the grove screw. The tool has a flat shoulder, and cylindrical
S. S. Nayak et al.
6.4.1 FSW Process and Microstructural Zones
FSW is an efficient, economic and eco-friendly joining process, which is accomplished in the solid-state without melting the base materials. A rotating and nonconsumable tool is inserted in the mid-line of two neighbouring edges of the BMs to
be joined. Heat is generated by the friction occurring between tool and BMs along
with plastic deformation of BMs. The BM gets heated up to an elevated temperature and material flows in the vicinity of FSW tool by stirring action leading to
joining. In FSW, various problems associated with the fusion welding are reduced
and high integrity joints are formed in solid state. The details have been mentioned
in a previous chapter.
Four microstructural zones are present in a FSWed sample. The first one is known
as the SZ, sometimes also called as the nugget zone (NZ). In this zone, the material
undergoes severe plastic deformation since this zone is directly under the influence
of the tool action. The grains in this zone undergo DRX, and the grain size gets
reduced in comparison to the parent material. The flow of the material starts with
the movement of the tool, extruding from the advancing side (AS) in NZ, and flows
around retreating side (RS). Surrounding the NZ, thermo-mechanically affected zone
(TMAZ) exists. Very little recrystallization is noticed here. It is often difficult to
observe the TMAZ in few materials (steels and titanium alloys) [37]. In FSW, the
third zone is the HAZ, which sometimes exhibits the same metallurgical reactions
as in fusion welding. The softening of HAZ in aluminium occurs because of overageing, both in fusion welds and FSW [38, 39]. In order to obtain a sound weld joint
in FSW, sufficient deformation of the BMs is to be ensured so that and they can flow
alongside the tool.
It is well understood that the material deformation occurs in FSW primarily due to
extrusion, forging and shear created by the FSW tool. The deformation mechanism
in the process can be understood through a detailed investigation of crystallographic
texture. The detailed experimental procedure of FSW for AA6061-T6 aluminium
alloy–AISI304 austenitic stainless steel has been given in Sect. 6.4.2. In the FSWed
joint, the authors have studied the microstructure and texture in the aluminium alloy
by using EBSD technique, and the results are shown in Sect. 6.4.3.
6.4.2 Experimental Details
The materials were austenitic stainless steel AISI304 and aluminium alloy AA6061T6 of 1 mm thickness each and were welded in the lap configuration, keeping the
aluminium sheet over the steel sheet. The tool used in this process was made with
bimetallic materials: tungsten carbide (WC) and H13 die steel. The tool pin material
was taken as WC to avoid tool wear and the rest of the tool parts were of H13 die steel.
The WC pin was inserted into the H13 die steel and assembled through interference
fit and supported through the grove screw. The tool has a flat shoulder, and cylindrical