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First Edition: Oct. 2021 01-00235-EN
Table 1 Result of Quantitative Analysis of IMC Layers
Conclusion
In analysis of the cross sections of FSSW welds, it is possible to
investigate the changes in the composition of the weld zone and
the stirred portion by a macroscopic analysis. Microscopically, the
EPMA technique can also be applied to research on bond
strength by investigating the film thickness, element distribution,
and composition ratio of the IMC layers.
EPMA is a trademark of Shimadzu Corporation or its affiliated companies in Japan and/or other countries.
Analysis of Intermetallic Compound Layer
As one distinctive feature of FSSW, formation of IMC, which
affect bond strength, is slight due to the small heat input during
welding. The IMC layer is thicker in the central area than at the
edge, and it is generally thought that high bond strength is
obtained when an IMC layer with a thickness on the order of
1 μm is formed uniformly over a wide area.
Figs. 2, 3, and 4 show enlarged mapping images of the FSSW
weld center, the weld intermediate region between the center
and the weld edge, and edge, respectively. The film thickness of
the IMC layer is several μm in the weld center and intermediate
region, the IMC consists of multiple IMC layers, and virtually all
of the Zn contained in the coating layer has been expelled.
However, at the weld edge, the Zn coating layer was not
completely expelled and appearance of a new surface was
difficult, and as a result, it is thought that the film thickness of
the IMC layer was thin and the crack formed.
Fig. 5 shows an enlarged mapping image of the IMC layer in the
central part of the weld. The IMC layer consists of three layers
(shown by A, B, and C from the steel sheet side). The
approximate film thicknesses of layers A, B, and C are 0.4 μm,
1.7 μm, and 0.7 μm, respectively. From the element distributions
of Al, Si, Fe, and Zn in each layer, the existence of different IMC
layers and related elements can be identified, and it can be
understood that a slight amount of residual Zn has remained.
Quantitative Analysis of Intermetallic
Compound Layer
Table 1 shows the result of a quantitative analysis of the IMC
layers in the central part of the weld. From the quantitative values,
it is estimated that layer A on the steel sheet side consists of
Fe
2
Al
5
(η phase) and the intermediate layer B is FeAl
3
(θ phase),
while layer C on the aluminum alloy side contains about 4 wt% of
Zn in the coating layer which was not expelled from the weld.
(wt%)
Fig. 2 Mapping of Weld Center
Fig. 5 Mapping of IMC Layer in Weld Center
COMPO 15.0 kV ×5000 Al Ka 15.0 kV ×5000 Si Ka 15.0 kV ×5000 Zn Ka 15.0 kV ×5000 Fe Ka 15.0 kV ×5000
COMPO 15.0 kV ×5000 Al Ka 15.0 kV ×5000 Si Ka 15.0 kV ×5000 Zn Ka 15.0 kV ×5000 Fe Ka 15.0 kV ×5000
COMPO 15.0 kV ×5000 Al Ka 15.0 kV ×5000 Si Ka 15.0 kV ×5000 Zn Ka 15.0 kV ×5000 Fe Ka 15.0 kV ×5000
COMPO 10.0 kV ×20000 Si Ka 10.0 kV ×20000 Zn La 10.0 kV ×20000 Fe Ka 10.0 kV ×20000 Al Ka 10.0 kV ×20000
Steel A B C Al alloy
Fig. 3 Mapping of Weld Intermediate Region (1.56 mm from Center)
Fig. 4 Mapping of Weld Edge (3.87 mm from Center)
5 µm
5 µm
5 µm
1 µm
5 µm
5 µm
5 µm
1 µm
5 µm
5 µm
5 µm
1 µm
5 µm
5 µm
5 µm
1 µm
5 µm
5 µm
5 µm
1 µm
<Reference>
Materia Japan, Vol. 53, No. 12 (2014).
Hiroshi Tokisue, Friction Stir Welding (Fundamentals and Applications of FSW (Friction Stir Welding)), Nikkan Kogyo Shimbun, Ltd. (2005).
Layer \ Element Al Si Fe Zn
IMC layer A 51.2 1.6 45.3 2.0
IMC layer B 58.5 1.3 38.7 1.5
IMC layer C 60.8 5.0 30.2 3.9
