8.5 Dynamic Dilution Behavior of Moving Weld Pools …
233
Table 8.12 Concentration and behavior characteristics of the alloy element
Wire chemical composition (%) Parent metal chemical
composition (%)
Behavior characteristics of alloy
element
Wire as a kind of element 100
0
Such special element does not
exist in the parent metal and is
diluted by the parent metal
Si 20
0
Wire Si has a higher concentration
than parent metal and is diluted by
the parent metal
Ti 10
80
Wire Ti has a lower concentration
than parent metal, and parent
metal is diluted
Al 62
6
Wire Al has a higher
concentration than parent metal,
and is diluted by the parent metal
Figure 8.26b–f show the transient dilution process of the wire composition to the
moving weld pool on the upper surface of the moving weld pool. As it can be seen
from the figure that, when the wire composition is in transition to the weld pool at
1.6 ms, the concentration on both sides of the surface moving weld pool is relatively
high according to the concentration cloud chart, while the isoconcentration lines
in the middle position are almost parallel. By comparing the concentration cloud
charts when t = 1.6 and t = 3.2 ms, it shows that on the weld pool surface, the
wire composition moves gradually from the front of the surface weld pool to the
rear of the weld pool, and during the process, the weld pool is also gradually diluted
by the wire composition. It is observed by comparing the figure at 1.6 ms with the
figure at 6.4 ms that, the wire composition on both sides is relatively high, and the
isoconcentration lines at the rear of the surface moving weld pool tend to concave
towards the front of the weld pool. However, when the quasi-steady state is reached,
the isoconcentration lines in the middle of the surface moving weld pool are almost
parallel with the cross section direction, and the middle part of the isoconcentration
lines at the rear still tends to concave, but not that obvious anymore. It shows that
the concentration gradient of the wire composition close to the moving weld pool
surface becomes less apparent, but the wire composition in the weld pool micro area
is still uneven.
The reason for the above phenomenon is closely correlated to the convection and
diffusion factors in the weld pool. At the beginning of the dynamic dilution, due
to severe convection and high speed on both sides of the moving weld pool in the
upper part, the concentration of the wire composition on both sides of the weld pool
in the upper part is high, resulting in concave of the isoconcentration lines in the
middle of the upper surface of the weld pool towards the front of the weld pool.
Since the speed direction of the weld pool at the rear of the keyhole is from the front
to the back as a whole, the wire composition also moves gradually from the front
to the rear of the weld pool through convective motion. During the dilution process,
233
Table 8.12 Concentration and behavior characteristics of the alloy element
Wire chemical composition (%) Parent metal chemical
composition (%)
Behavior characteristics of alloy
element
Wire as a kind of element 100
0
Such special element does not
exist in the parent metal and is
diluted by the parent metal
Si 20
0
Wire Si has a higher concentration
than parent metal and is diluted by
the parent metal
Ti 10
80
Wire Ti has a lower concentration
than parent metal, and parent
metal is diluted
Al 62
6
Wire Al has a higher
concentration than parent metal,
and is diluted by the parent metal
Figure 8.26b–f show the transient dilution process of the wire composition to the
moving weld pool on the upper surface of the moving weld pool. As it can be seen
from the figure that, when the wire composition is in transition to the weld pool at
1.6 ms, the concentration on both sides of the surface moving weld pool is relatively
high according to the concentration cloud chart, while the isoconcentration lines
in the middle position are almost parallel. By comparing the concentration cloud
charts when t = 1.6 and t = 3.2 ms, it shows that on the weld pool surface, the
wire composition moves gradually from the front of the surface weld pool to the
rear of the weld pool, and during the process, the weld pool is also gradually diluted
by the wire composition. It is observed by comparing the figure at 1.6 ms with the
figure at 6.4 ms that, the wire composition on both sides is relatively high, and the
isoconcentration lines at the rear of the surface moving weld pool tend to concave
towards the front of the weld pool. However, when the quasi-steady state is reached,
the isoconcentration lines in the middle of the surface moving weld pool are almost
parallel with the cross section direction, and the middle part of the isoconcentration
lines at the rear still tends to concave, but not that obvious anymore. It shows that
the concentration gradient of the wire composition close to the moving weld pool
surface becomes less apparent, but the wire composition in the weld pool micro area
is still uneven.
The reason for the above phenomenon is closely correlated to the convection and
diffusion factors in the weld pool. At the beginning of the dynamic dilution, due
to severe convection and high speed on both sides of the moving weld pool in the
upper part, the concentration of the wire composition on both sides of the weld pool
in the upper part is high, resulting in concave of the isoconcentration lines in the
middle of the upper surface of the weld pool towards the front of the weld pool.
Since the speed direction of the weld pool at the rear of the keyhole is from the front
to the back as a whole, the wire composition also moves gradually from the front
to the rear of the weld pool through convective motion. During the dilution process,