8.5 Dynamic Dilution Behavior of Moving Weld Pools …
237
process diagram of the wire composition concentration of the above two points over
time. It can be seen from the figure that, at the two points, the time of Point X
closer to the keyhole reaching the quasi-steady state is about 32 ms, while Point Y
further from the keyhole reaching the quasi-steady state is about 38 ms. Therefore,
the time of the wire composition reaching the quasi-steady state in the moving weld
pool is inconsistent. In addition, when the quasi-steady state is reached, the additive
concentration at PointX is 60%, while that at the right point is roughly 55%. It shows
that the concentration in the moving weld pool is also uneven when the quasi-steady
state is reached.
Based on the above discussion, the following conclusions can be made: ➀ In the
upper part of the moving weld pool, the wire composition moves gradually from
the front to the rear of the weld pool through convective motion and dilutes the
parent metal from the edge of the moving weld pool gradually to depth direction; ➁
Convection plays a primary role in the dynamic dilution process in the upper part
of the moving weld pool; ➂ At the places with flowing vortex in the moving weld
pool, the wire composition concentration is usually higher than that in the periphery;
➃ When the quasi-steady state is reached, the wire composition concentration at
different positions in the upper part of the moving weld pool is generally uneven,
and the time of reaching the quasi-steady state is also different.
8.5.2.3 Dynamic Dilution of Different Chemical Compositions
in the Quasi-Steady Moving Weld Pool
The section will mainly discuss the dynamic dilution behavior of different chemical
compositions in the quasi-steady moving weld pool through the numerical simulation. The mentioned chemical compositions in wire alloy are different from those in
parent metal alloy. Technical parameters and material parameters used in numerical
calculation are consistent with those stated in Sect. 8.5.2.2.
Figure 8.30 is the concentration distribution diagram for Ti chemical composition
on two sections of the moving weld pool when the quasi-steady state is reached.
Section A is the longitudinal section close to the edge on both sides of the moving
weld pool; Section B is the longitudinal section in the center of the moving weld pool.
It can be seen from the figure that the concentration distribution trend of Ti chemical
composition is just the opposite of the wire concentration trend, i.e., the higher the
wire composition is, the lower the Ti chemical composition will be. Therefore, the
concentration of Ti chemical composition in the moving weld pool is diluted, and
uneven in the moving weld pool, and will reach a local minimum at the vortex.
Figure 8.31 is the concentration distribution diagram of Ti chemical composition
in two sections of moving weld pool when the quasi-steady state is reached. Section
A is the longitudinal section close to the edge on both sides of the moving weld
pool; Section B is the longitudinal section in the center of the moving weld pool.
As known in the figure that, Al content in the wire is higher than that in the parent
metal, so the Al composition in the wire is diluted by the moving weld pool, and it
237
process diagram of the wire composition concentration of the above two points over
time. It can be seen from the figure that, at the two points, the time of Point X
closer to the keyhole reaching the quasi-steady state is about 32 ms, while Point Y
further from the keyhole reaching the quasi-steady state is about 38 ms. Therefore,
the time of the wire composition reaching the quasi-steady state in the moving weld
pool is inconsistent. In addition, when the quasi-steady state is reached, the additive
concentration at PointX is 60%, while that at the right point is roughly 55%. It shows
that the concentration in the moving weld pool is also uneven when the quasi-steady
state is reached.
Based on the above discussion, the following conclusions can be made: ➀ In the
upper part of the moving weld pool, the wire composition moves gradually from
the front to the rear of the weld pool through convective motion and dilutes the
parent metal from the edge of the moving weld pool gradually to depth direction; ➁
Convection plays a primary role in the dynamic dilution process in the upper part
of the moving weld pool; ➂ At the places with flowing vortex in the moving weld
pool, the wire composition concentration is usually higher than that in the periphery;
➃ When the quasi-steady state is reached, the wire composition concentration at
different positions in the upper part of the moving weld pool is generally uneven,
and the time of reaching the quasi-steady state is also different.
8.5.2.3 Dynamic Dilution of Different Chemical Compositions
in the Quasi-Steady Moving Weld Pool
The section will mainly discuss the dynamic dilution behavior of different chemical
compositions in the quasi-steady moving weld pool through the numerical simulation. The mentioned chemical compositions in wire alloy are different from those in
parent metal alloy. Technical parameters and material parameters used in numerical
calculation are consistent with those stated in Sect. 8.5.2.2.
Figure 8.30 is the concentration distribution diagram for Ti chemical composition
on two sections of the moving weld pool when the quasi-steady state is reached.
Section A is the longitudinal section close to the edge on both sides of the moving
weld pool; Section B is the longitudinal section in the center of the moving weld pool.
It can be seen from the figure that the concentration distribution trend of Ti chemical
composition is just the opposite of the wire concentration trend, i.e., the higher the
wire composition is, the lower the Ti chemical composition will be. Therefore, the
concentration of Ti chemical composition in the moving weld pool is diluted, and
uneven in the moving weld pool, and will reach a local minimum at the vortex.
Figure 8.31 is the concentration distribution diagram of Ti chemical composition
in two sections of moving weld pool when the quasi-steady state is reached. Section
A is the longitudinal section close to the edge on both sides of the moving weld
pool; Section B is the longitudinal section in the center of the moving weld pool.
As known in the figure that, Al content in the wire is higher than that in the parent
metal, so the Al composition in the wire is diluted by the moving weld pool, and it