5 Welding of Dissimilar Metals—Challenges and a Way Forward …
185
The significant dissimilarity in the melting point of these metals makes the combination very challenging for joining by using fusion welding [44, 45]. Moreover, the
dissimilarity in different properties of the metals adds to the challenge in the joining
process. Additionally, the formidable norms of the industries in terms of higher
productivity and lower cost without compromising the product quality becomes a
very difficult task for the manufacturers to produce a component from dissimilar
materials. Because of the advantages mentioned above, FSW is one of the potent
solutions for welding dissimilar metals. In FSW, the rotational speed of the tool (ω),
the speed with which the tool traverses (v), the tilt angle of the tool (α), depth of the
tool shoulder inserted into workpiece (pd), and the profile of the tool are the major
variables that greatly affect the weld quality. Amongst these variables, ω and v have
been identified as the key parameters affecting the joint quality [18].
The following subsections discuss the details of the case study where AA6061
is welded with AISI 304 steel using FSW. The FSW experiments were carried out
in lap configuration using a 3-axis NC FSW machine (ETA Pvt. Ltd., WS004). A
cylindrical tool made of tungsten carbide of 16 mm of shoulder diameter, 5 mm of
pin diameter, and 1 mm of pin length was used for experimentation. To determine
the lap shear load, rectangular-shaped samples of 172.6 mm length and 30 mm width
were fabricated. Scanning electron microscopy (SEM) observation was carried out
to study the fracture surface of samples. The specimens for microstructural studies of
the welded samples were prepared by considering ASTM E3 standard. The samples
were prepared using a hot mounting process; and these were then polished using
different grades of polishing papers with varying grit size varying within the range
of 120–2000 μm. The polished samples were then etched using Keller’s reagent
for AA6061. The weld cross-section microstructure was captured with the help of
optical microscopy (Leica, DMILM). Furthermore, to identify IMCs near the joint
interface, the weld line was characterized under the X-ray diffraction (Panalytical,
Empyrean).
The discussed attributes include joint strength, IMCs, and interfacemicrostructure. The obtained results have also been qualitatively compared with
the fusion welding methods. This helps in understanding the differences among the
two. A process parametric combinations of ω of 1600 rpm and v of 50, 100, and
200 mm/min was selected by considering constant α and pd of 2° and 0.2 mm,
respectively.
5.6.1 Joint Strength of Welds
The highest joint strength values of the sample welded using FSW is found to be
5950 N which is approximately 87.5% of base AA6061-T6 Al alloy, as shown in
Fig. 5.15. A similar work [46], has reported the joint strength as 64.35%. This
difference accounts for the selection of optimum parameters. In case of the fusion
weldingof Al alloy and steel, the strength has been found to be varying in the range
of 45–75% [9, 10]. This is significantly lower than the strength obtained by FSW.
185
The significant dissimilarity in the melting point of these metals makes the combination very challenging for joining by using fusion welding [44, 45]. Moreover, the
dissimilarity in different properties of the metals adds to the challenge in the joining
process. Additionally, the formidable norms of the industries in terms of higher
productivity and lower cost without compromising the product quality becomes a
very difficult task for the manufacturers to produce a component from dissimilar
materials. Because of the advantages mentioned above, FSW is one of the potent
solutions for welding dissimilar metals. In FSW, the rotational speed of the tool (ω),
the speed with which the tool traverses (v), the tilt angle of the tool (α), depth of the
tool shoulder inserted into workpiece (pd), and the profile of the tool are the major
variables that greatly affect the weld quality. Amongst these variables, ω and v have
been identified as the key parameters affecting the joint quality [18].
The following subsections discuss the details of the case study where AA6061
is welded with AISI 304 steel using FSW. The FSW experiments were carried out
in lap configuration using a 3-axis NC FSW machine (ETA Pvt. Ltd., WS004). A
cylindrical tool made of tungsten carbide of 16 mm of shoulder diameter, 5 mm of
pin diameter, and 1 mm of pin length was used for experimentation. To determine
the lap shear load, rectangular-shaped samples of 172.6 mm length and 30 mm width
were fabricated. Scanning electron microscopy (SEM) observation was carried out
to study the fracture surface of samples. The specimens for microstructural studies of
the welded samples were prepared by considering ASTM E3 standard. The samples
were prepared using a hot mounting process; and these were then polished using
different grades of polishing papers with varying grit size varying within the range
of 120–2000 μm. The polished samples were then etched using Keller’s reagent
for AA6061. The weld cross-section microstructure was captured with the help of
optical microscopy (Leica, DMILM). Furthermore, to identify IMCs near the joint
interface, the weld line was characterized under the X-ray diffraction (Panalytical,
Empyrean).
The discussed attributes include joint strength, IMCs, and interfacemicrostructure. The obtained results have also been qualitatively compared with
the fusion welding methods. This helps in understanding the differences among the
two. A process parametric combinations of ω of 1600 rpm and v of 50, 100, and
200 mm/min was selected by considering constant α and pd of 2° and 0.2 mm,
respectively.
5.6.1 Joint Strength of Welds
The highest joint strength values of the sample welded using FSW is found to be
5950 N which is approximately 87.5% of base AA6061-T6 Al alloy, as shown in
Fig. 5.15. A similar work [46], has reported the joint strength as 64.35%. This
difference accounts for the selection of optimum parameters. In case of the fusion
weldingof Al alloy and steel, the strength has been found to be varying in the range
of 45–75% [9, 10]. This is significantly lower than the strength obtained by FSW.