6 Microstructure and Texture in Welding: A Case Study on Friction Stir Welding
195
the solid-state itself. Phase change does not occur here, but the parent material is
heated up below its melting point temperature. Pressure is usually applied instead
of external heat for this category of welding process. A few examples in this category are roll welding, ultrasonic welding, friction welding, diffusion welding and
friction stir welding (FSW). A sufficient knowledge of physical metallurgy is crucial
to understand the welding metallurgy which includes the welding operation and the
effects of welding parameters on the properties of the metals to be joined [3].
Over the last few decades in metal industries, especially in aluminium industry,
FSW seems to be an important joining process. In FSW, the metals to be joined
undergo deformation, and the texture distribution in the stir zone (SZ) is very
complex. It may deteriorate the joint performance, if not controlled. Therefore, the
control of texture, either by controlling the welding parameters or by any post-weld
analysis in FSW, is crucial to optimize the mechanical properties of the joint. The
current chapter primarily highlights the fundamental principles which govern the
evolution of microstructure and texture in the weld zones of fusion and solid-state
welding processes. Towards the end, a case study has been presented which discusses
on the formation of microstructure and texture in FSW of aluminium to steel.
The success or failure of a welded joint depends upon several aspects such as
process parameters, type of filler material, heating and cooling cycles, compositional
variation with respect to percentage of alloying elements such as carbon, sulphur,
nitrogen, stress patterns around the weld because of thermal expansion during heating
and contraction during welding, environmental factors, formation of intermetallic
compounds, etc. These factors govern the final microstructure and texture of a welded
structure. Thus, it is highly essential to keep a track of the change in the microstructure
of the weld to preserve its properties by taking care of the aforementioned points.
6.2 Microstructure in Welding
The microstructure is affected by the way a welding process is performed, and the
details in this regard are discussed in the following subsections. The discussions have
been carried out for fusion and solid-state welding processes.
6.2.1 Microstructure in Fusion Welding
This section will give a brief overview of microstructural regions of fusion welding
processes, followed by various metallurgical processes that influence the welding.
195
the solid-state itself. Phase change does not occur here, but the parent material is
heated up below its melting point temperature. Pressure is usually applied instead
of external heat for this category of welding process. A few examples in this category are roll welding, ultrasonic welding, friction welding, diffusion welding and
friction stir welding (FSW). A sufficient knowledge of physical metallurgy is crucial
to understand the welding metallurgy which includes the welding operation and the
effects of welding parameters on the properties of the metals to be joined [3].
Over the last few decades in metal industries, especially in aluminium industry,
FSW seems to be an important joining process. In FSW, the metals to be joined
undergo deformation, and the texture distribution in the stir zone (SZ) is very
complex. It may deteriorate the joint performance, if not controlled. Therefore, the
control of texture, either by controlling the welding parameters or by any post-weld
analysis in FSW, is crucial to optimize the mechanical properties of the joint. The
current chapter primarily highlights the fundamental principles which govern the
evolution of microstructure and texture in the weld zones of fusion and solid-state
welding processes. Towards the end, a case study has been presented which discusses
on the formation of microstructure and texture in FSW of aluminium to steel.
The success or failure of a welded joint depends upon several aspects such as
process parameters, type of filler material, heating and cooling cycles, compositional
variation with respect to percentage of alloying elements such as carbon, sulphur,
nitrogen, stress patterns around the weld because of thermal expansion during heating
and contraction during welding, environmental factors, formation of intermetallic
compounds, etc. These factors govern the final microstructure and texture of a welded
structure. Thus, it is highly essential to keep a track of the change in the microstructure
of the weld to preserve its properties by taking care of the aforementioned points.
6.2 Microstructure in Welding
The microstructure is affected by the way a welding process is performed, and the
details in this regard are discussed in the following subsections. The discussions have
been carried out for fusion and solid-state welding processes.
6.2.1 Microstructure in Fusion Welding
This section will give a brief overview of microstructural regions of fusion welding
processes, followed by various metallurgical processes that influence the welding.