Friction Stir Additive Manufacturing—A Review
23
The heat required for the development of the third body region is generated by
the frictional resistance between the shoulder and the workpiece in addition to the
heat generated by the pin; severe plastic deformation is caused by the rotating and
translating motion of the pin. The geometry of the pin affects the macroshape of the
weld which is generated by the movement of the material from the front end to the
rear of the pin. This is a solid-state welding process, and by the virtue of it, there is
no melting involved [74].
The microstructural characterization is of specific interest for type 2 FSAM
because of intricacies associated in terms of heat exposures, deformation and material flow from the bottommost to the topmost layer. During FSAM, the material is
vigorously stirred, plastically deformed, and then, it undergoes dynamic recrystallization (DRX). Further, considering the pin length not to be greater than twice the
thickness of the plates that are subsequently being welded on top each other, all
the plates undergo the phenomenon of dynamic recrystallization twice except the
topmost and bottommost plate. This understanding of this phenomenon is vital to
understand and interpret the macro- and microstructure of the new weld. Due to
multiple recrystallizations, the weld nugget has a finer grain structure and imposes a
higher resistance to deformation because of Hall–Petch strengthening [75, 76]. This
signifies the capability of the FSAM process to manipulate microstructures.
In their study of FSAM of AA 5083, Palanivel et al. [77] reported an increase in
the mechanical properties of the weld as compared to the base metal. The hardness
increased by 18 percent and yield strength (YS) of 267 MPa and ultimate tensile
strength (UTS) of 362 are reported after FSAM compared to the YS of 190 MPa and
UTS of 336 MPa of the base metal.
The process of FSAM is not immune to the defects of FSW welding. The complex
process influences the material flow in the additively manufactured structure that
involves a series of lap welds on top of each other and results in various kinds
of defects. Most of the defects are analogous to the defects observed in a normal
FSW lap and butt welds and have characterized in FSW process parameters [78–83].
Furthermore, the complexity increases due to (a) difference of grain structure in the
bottom and top layers during every succeeding weld, (b) defects already present from
the previous welds and (c) overlapping of the new weld nuggets on top of the old
weld nuggets.
4 Scope of Friction Based Additive Technologies
4.1 Advantages of Friction-Based Additive Technologies
Over Fusion AM
The potential utility and capability of FSAM to penetrate the commercial market
stem out from the shortcomings of the conventional techniques. Unique properties
23
The heat required for the development of the third body region is generated by
the frictional resistance between the shoulder and the workpiece in addition to the
heat generated by the pin; severe plastic deformation is caused by the rotating and
translating motion of the pin. The geometry of the pin affects the macroshape of the
weld which is generated by the movement of the material from the front end to the
rear of the pin. This is a solid-state welding process, and by the virtue of it, there is
no melting involved [74].
The microstructural characterization is of specific interest for type 2 FSAM
because of intricacies associated in terms of heat exposures, deformation and material flow from the bottommost to the topmost layer. During FSAM, the material is
vigorously stirred, plastically deformed, and then, it undergoes dynamic recrystallization (DRX). Further, considering the pin length not to be greater than twice the
thickness of the plates that are subsequently being welded on top each other, all
the plates undergo the phenomenon of dynamic recrystallization twice except the
topmost and bottommost plate. This understanding of this phenomenon is vital to
understand and interpret the macro- and microstructure of the new weld. Due to
multiple recrystallizations, the weld nugget has a finer grain structure and imposes a
higher resistance to deformation because of Hall–Petch strengthening [75, 76]. This
signifies the capability of the FSAM process to manipulate microstructures.
In their study of FSAM of AA 5083, Palanivel et al. [77] reported an increase in
the mechanical properties of the weld as compared to the base metal. The hardness
increased by 18 percent and yield strength (YS) of 267 MPa and ultimate tensile
strength (UTS) of 362 are reported after FSAM compared to the YS of 190 MPa and
UTS of 336 MPa of the base metal.
The process of FSAM is not immune to the defects of FSW welding. The complex
process influences the material flow in the additively manufactured structure that
involves a series of lap welds on top of each other and results in various kinds
of defects. Most of the defects are analogous to the defects observed in a normal
FSW lap and butt welds and have characterized in FSW process parameters [78–83].
Furthermore, the complexity increases due to (a) difference of grain structure in the
bottom and top layers during every succeeding weld, (b) defects already present from
the previous welds and (c) overlapping of the new weld nuggets on top of the old
weld nuggets.
4 Scope of Friction Based Additive Technologies
4.1 Advantages of Friction-Based Additive Technologies
Over Fusion AM
The potential utility and capability of FSAM to penetrate the commercial market
stem out from the shortcomings of the conventional techniques. Unique properties