210
S. S. Nayak et al.
cooling direction is because of the temperature gradient change. In GMAW, higher
values of current increase the Lorenze force and reduces the Marangoni force [32].
This promotes a strong downward fluid flow force along the thickness direction of the
weld and thereby causes preferred grain growth along <001> and <101> directions.
The low electromagnetic force and high heat for a long period causes grain growth
along <101> and <111> directions.
6.3.1.3 Laser Beam Welding (LBW)
In LBW, the amount of heat input and time of heating largely affect the secondary
phase precipitates, size of the microstructure and orientations [33]. The existence
of the columnar and equiaxed grains is found in the LBW of aluminium. Columnar
grains orient along <100> plane, i.e. parallel to RD. LBW produces strong cube {001}
<100> textured microstructure in the welded regions which makes the material prone
to slip, preferentially aligns to {100} plane. Cube-oriented microstructure has a low
value of critically resolved shear stress. As a result, columnar grains with Cube {001}
<100> microstructure reduces the joint strength.
6.3.2 Texture in Solid-State Welding
In solid-state welding processes, texture develops mostly due to plastic deformation
(by glide or slip and twinning) and annealing (recrystallization/grain growth). As a
result, the solid-state welding techniques produce moderately textured grains in the
welded zone. Initially, due to dynamic recovery, the formation of low-angle boundaries occur. Then subgrain boundaries transform into grain boundaries followed by
local migration of newly formed grain boundaries. The complete mechanism is linked
with texture development. This section is limited to aluminium welding in all the
solid-state processes as discussed below and the reason for taking only aluminium
is found in one of the subsequent sections.
6.3.2.1 Ultrasonic Welding (UW)
It has been extensively applied in the welding of thin sheets of aluminium, copper, etc.
Oscillation amplitude and the falling height are the two important process parameters
of UW which affect the orientations of microstructure and the weldability. Large value
of oscillation amplitude and falling height weakens the texture intensity but yields fine
microstructures in UWed regions [34]. The UW at an increased value of ultrasonic
amplitude causes large deformation and heat in the build. Deformation leads to the
formation of strong deformation texture components such as Brass {011} <211>
, Cube {001} <100> and Rotated-cube {001} <110> at the cost of recrystallized
texture components. Similarly, UW at an increased value of the falling height (i.e.
S. S. Nayak et al.
cooling direction is because of the temperature gradient change. In GMAW, higher
values of current increase the Lorenze force and reduces the Marangoni force [32].
This promotes a strong downward fluid flow force along the thickness direction of the
weld and thereby causes preferred grain growth along <001> and <101> directions.
The low electromagnetic force and high heat for a long period causes grain growth
along <101> and <111> directions.
6.3.1.3 Laser Beam Welding (LBW)
In LBW, the amount of heat input and time of heating largely affect the secondary
phase precipitates, size of the microstructure and orientations [33]. The existence
of the columnar and equiaxed grains is found in the LBW of aluminium. Columnar
grains orient along <100> plane, i.e. parallel to RD. LBW produces strong cube {001}
<100> textured microstructure in the welded regions which makes the material prone
to slip, preferentially aligns to {100} plane. Cube-oriented microstructure has a low
value of critically resolved shear stress. As a result, columnar grains with Cube {001}
<100> microstructure reduces the joint strength.
6.3.2 Texture in Solid-State Welding
In solid-state welding processes, texture develops mostly due to plastic deformation
(by glide or slip and twinning) and annealing (recrystallization/grain growth). As a
result, the solid-state welding techniques produce moderately textured grains in the
welded zone. Initially, due to dynamic recovery, the formation of low-angle boundaries occur. Then subgrain boundaries transform into grain boundaries followed by
local migration of newly formed grain boundaries. The complete mechanism is linked
with texture development. This section is limited to aluminium welding in all the
solid-state processes as discussed below and the reason for taking only aluminium
is found in one of the subsequent sections.
6.3.2.1 Ultrasonic Welding (UW)
It has been extensively applied in the welding of thin sheets of aluminium, copper, etc.
Oscillation amplitude and the falling height are the two important process parameters
of UW which affect the orientations of microstructure and the weldability. Large value
of oscillation amplitude and falling height weakens the texture intensity but yields fine
microstructures in UWed regions [34]. The UW at an increased value of ultrasonic
amplitude causes large deformation and heat in the build. Deformation leads to the
formation of strong deformation texture components such as Brass {011} <211>
, Cube {001} <100> and Rotated-cube {001} <110> at the cost of recrystallized
texture components. Similarly, UW at an increased value of the falling height (i.e.