CN113130019B - Simulation method for solid phase transition of TC4 titanium alloy welding pool - Google Patents
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- 238000003466 welding Methods 0.000 title claims abstract description 85
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Abstract
The invention discloses a simulation method of solid phase transformation of a TC4 titanium alloy welding pool, which comprises the steps of firstly establishing a welding transient temperature field model by using a finite element method, then converting a macroscopic temperature field model into a microscopic temperature field model suitable for microscopic structure and phase transformation by using a linear interpolation method, carrying out proper simplification on some simulation conditions in the simulation process, establishing a calculation model of the solid phase transformation of the TC4 titanium alloy welding pool, and finally realizing visual calculation and analysis on simulation software Matlab. The model can calculate the evolution condition of a temperature field in the TC4 titanium alloy welding process under different time and different welding process parameters, and calculates the solid phase change condition of weld metal in the highly dynamic temperature field change process through macro-micro coupling of the temperature field, so that a brand new, efficient and reliable research means is provided for researching the solid phase change process in the TC4 titanium alloy welding process.
Description
Technical Field
The invention belongs to the technical field of simulation of welding pools, and relates to a simulation method of solid phase transformation of a TC4 titanium alloy welding pool.
Background
Titanium alloy is widely used in various fields because of the characteristics of high strength, good corrosion resistance, high heat resistance and the like, TC4 (Ti-6 Al-4V) titanium alloy is the most widely used titanium alloy so far, and is 'Wang alloy' in the titanium alloy industry; as a common connecting method, welding has the advantages of good flexibility, strong adaptability, good material connection performance and the like, and becomes the most main connecting method of the titanium alloy, so that the welding method has great significance on how to improve the quality of a welding joint in the welding process of the titanium alloy.
In the welding process, the solid phase transformation process of the weld metal has an important influence on the composition and the content of the final generated phase of the weld, so that the mechanical property and the service life of the welded joint are determined. The traditional metallographic experimental method is only used for observing and researching the phase composition of the weld metal completely cooled to room temperature, and is difficult to observe and analyze the solid phase transformation process generated by the action of high temperature after the weld metal is completely solidified, so that a research method capable of observing and analyzing the solid phase transformation process of the weld metal in real time is urgently needed. In recent years, computer technology is rapidly developed, and a new research thought is provided for students by adopting numerical simulation technology to research the processes of welding, casting and the like of metal materials.
Therefore, it is important to establish a simulation method of solid phase transformation of a TC4 titanium alloy welding pool.
Disclosure of Invention
The invention aims to provide a simulation method for solid phase transformation of a TC4 titanium alloy welding pool, which solves the problem that a weld metal solid phase transformation research method is lacked in the prior art.
The technical scheme adopted by the invention is that the simulation method of the solid-state phase transition of the TC4 titanium alloy welding pool is implemented according to the following steps:
step 1, constructing a welding transient temperature field model based on a finite element method;
step 2, constructing a microcosmic temperature field model by utilizing an interpolation principle;
step 3, constructing a solid phase change model of the weld metal;
and 4, calculating the numerical value and analyzing the calculation result.
The invention is also characterized in that:
the step 1 is specifically implemented according to the following steps:
step 1.1, establishing a finite element geometric model in finite element simulation software according to the size and the dimension of an actual weldment;
step 1.2, according to the welding material selected during welding, giving material properties to the finite element geometric model to obtain a finite element geometric material model;
step 1.3, setting an analysis step of welding simulation according to an actual welding process;
step 1.4, setting initial conditions and boundary conditions according to the actual condition of the welding process, wherein the initial conditions comprise setting initial temperature, and the boundary conditions comprise determining the heat exchange relation between the simulation area and the environment;
step 1.5, setting a load according to the actual condition of a welding pool, wherein the load comprises boundary constraint setting, surface heat flux setting, namely selecting a heat source model, wherein the heat source model selects a double-ellipsoid heat source model, and a specific calculation formula is as follows:
when x is more than or equal to 0, the functional expression of the first half of the model is:
when x < 0, the functional expression of the second half of the model is:
in the formulas (1) and (2): a, a f ，a r B and c are the axial lengths of the front and rear subareas of the ellipsoid respectively; f (f) 1 Coefficients that are the first half of the model; f (f) 2 Q is the effective heat input of the welding heat source, which is the coefficient of the latter half of the model;
and 1.6, forming a finite element model by adding initial conditions, boundary conditions and loads to the finite element geometric material model, carrying out grid division on the finite element model to obtain a finite element calculation model, and calculating a welding transient macroscopic temperature field model by utilizing finite element simulation software.
The step 2 is specifically implemented according to the following steps:
step 2.1, selecting a proper simulation area, and extracting a thermal cycle curve of finite element nodes of the selected simulation area, namely an instant-temperature curve;
step 2.2, fitting a thermal cycle curve by using simulation software Matlab to obtain a temperature-time function of the finite element node, and obtaining a macroscopic temperature field model of the selected simulation area;
2.3, converting the macroscopic temperature field model into a microscopic temperature field model for microscopic solid-state phase change calculation by adopting a linear interpolation method, wherein a specific calculation formula is represented by a formula (3):
in the formula (3): t (T) O The temperature of the microcell O; t (T) i Is the macro-cell temperature near the O-point; l (L) i Is the distance from the O-point to the surrounding macro-cells; n is the number of macro-cells surrounding the micro-cells, where N has a value of 8.
The step 3 is specifically implemented according to the following steps:
step 3.1, simplifying the construction conditions of a weld metal solid-state phase change model;
and 3.2, constructing a model of balance phase composition change of the weld metal in the heating and cooling processes.
Step 3.2 is carried out by the following steps:
step 3.3, according to the lever law, during the heating process of the TC4 titanium alloy, the change of the balance phase component is represented by the formula (4):
F(β)＝(F α (T)-6.0)/(F α (T)-F β (T)) (4)
in the formula (4), F (beta) represents the equilibrium phase volume fraction of the beta phase during heating; f (F) α (T) represents the equilibrium phase volume fraction of the alpha phase at a temperature T; f (F) β (T) represents the equilibrium phase volume fraction of the beta phase at a temperature T;
and 3.4, when the titanium alloy is rapidly cooled at a high temperature, adopting JMPRO software to calculate a macroscopic phase transformation process after solidification, adopting Matlab software to construct an alloy microscopic phase transformation model according to the macroscopic phase transformation model, and establishing a mathematical model of temperature-phase transformation, wherein a specific calculation formula is represented by a formula (5):
F α' (i,j)＝a*T(i,j)+b (5)
wherein: f (F) α' (i, j) represents the content of the alpha' martensite phase of the microcosmic unit (i, j); t (i, j) represents the temperature of the microcolumn (i, j); a and b represent real constants, and the values of a and b are related to the temperature of the weld metal.
The construction conditions for simplifying the weld metal solid-state phase transformation model comprise:
(1) Simplifying the main components of the multi-element alloy TC4 titanium alloy into Ti-6Al;
(2) Only the generation of the primary phase is considered in the solid-state phase transformation process of the alloy, and the generation of the secondary phase is ignored.
Step 4 is specifically implemented according to the following steps:
step 4.1, the welding transient temperature field model, the microcosmic temperature field model and the solid phase transformation model of the weld metal constructed in the steps 1 to 3 are imported into simulation software Matlab to form a calculation model of the solid phase transformation of the TC4 titanium alloy welding pool;
and 4.2, inputting the thermophysical performance parameters and specific welding process parameters of the TC4 titanium alloy into a calculation model of the solid-state transformation of the TC4 titanium alloy welding pool, calculating to obtain a simulation result image, and carrying out brief analysis.
The beneficial effects of the invention are as follows:
1. the invention provides a simulation method of solid phase transformation of a TC4 titanium alloy welding pool, which provides a high-efficiency and reliable research means for researching the solid phase transformation process of weld metal;
2. compared with the traditional test method, the method has the advantages of high calculation speed, high calculation precision and the like, and greatly improves the research efficiency;
3. the invention also has the advantages of safety, green, environmental protection and the like.
Drawings
FIG. 1 is a flow chart of a method of simulating solid state phase transition of a TC4 titanium alloy weld puddle in accordance with the present invention;
FIG. 2 is a finite element geometry model of a simulation method of solid state transformation of a TC4 titanium alloy weld puddle of the present invention;
FIG. 3 is a schematic diagram of a dual-ellipsoid heat source model of a simulation method of solid state transformation of a TC4 titanium alloy weld puddle of the present invention;
FIG. 4 is a schematic diagram of a geometric model mesh division of a simulation method of solid state transformation of a TC4 titanium alloy weld puddle of the present invention;
FIG. 5 is a schematic illustration of linear interpolation of a simulation method of solid state transformation of a TC4 titanium alloy weld puddle in accordance with the present invention;
FIG. 6 is a simulation result of solid state transformation at different times in the TC4 titanium alloy weld puddle of example 1;
FIG. 7 is a simulation result of solid state transformation at different welding currents for the TC4 titanium alloy weld puddle of example 2;
fig. 8 is a simulation result of solid state transformation at different welding speeds of the TC4 titanium alloy weld puddle of example 3.
Detailed Description
The invention will be described in detail below with reference to the drawings and the detailed description.
Example 1
The technical scheme adopted by the invention is that the simulation method of the solid-state phase transition of the TC4 titanium alloy welding pool is implemented as shown in figure 1, and specifically comprises the following steps:
step 1, constructing a welding transient temperature field model based on a finite element method;
step 2, constructing a microcosmic temperature field model by utilizing an interpolation principle;
step 3, constructing a solid phase change model of the weld metal;
and 4, calculating the numerical value and analyzing the calculation result.
The step 1 is specifically implemented according to the following steps:
step 1.1, establishing a finite element geometric model in finite element simulation software according to the size and the dimension of an actual weldment, wherein the dimension of the finite element geometric model is a cuboid of 50mm multiplied by 6mm multiplied by 100mm, as shown in fig. 2;
step 1.2, according to the welding materials selected during welding, endowing the finite element geometric model with material properties, obtaining a finite element geometric material model, and endowing the finite element geometric model with material properties of TC4 titanium alloy;
step 1.3, setting an analysis step of welding simulation according to an actual welding process;
step 1.4, setting initial conditions and boundary conditions according to the actual condition of the welding process, wherein the initial conditions comprise setting initial temperature, the boundary conditions comprise determining the heat exchange relation between the simulation area and the environment, and the selected boundary conditions prescribe free heat exchange on the surface of the object;
step 1.5, setting a load according to the actual condition of a welding pool, wherein the load comprises boundary constraint setting, surface heat flux setting, namely selecting a heat source model, wherein the heat source model selects a double-ellipsoid heat source model, and a specific calculation formula is as follows:
when x is more than or equal to 0, the functional expression of the first half of the model is:
when x < 0, the functional expression of the second half of the model is:
in the formulas (1) and (2): a, a f ，a r B and c are the axial lengths of the front and rear subareas of the ellipsoid respectively; f (f) 1 Coefficients that are the first half of the model; f (f) 2 Q is the effective heat input of the welding heat source, which is the coefficient of the first half part of the model;
step 1.6, adding initial conditions, boundary conditions and loads to a finite element geometric material model to form a finite element model, carrying out grid division on the finite element model to obtain a finite element calculation model, dividing a simulation area into hexahedral units with the same shape and size as 1mm multiplied by 1mm, counting 30000 units in total, as shown in fig. 4, and calculating a welding transient macroscopic temperature field model by utilizing finite element simulation software.
The step 2 is specifically implemented according to the following steps:
2.1, selecting a proper simulation area, extracting a thermal cycle curve of a finite element node of the selected simulation area, namely a time-temperature curve, wherein the selected simulation area is an area which is 30mm away from a welding starting point and contains weld metal and is 4mm multiplied by 11mm on the cross section of a weldment;
step 2.2, fitting a thermal cycle curve by using simulation software Matlab to obtain a temperature-time function of the finite element node, and obtaining a macroscopic temperature field model of the selected simulation area;
2.3, converting the macroscopic temperature field model into a microscopic temperature field model for microscopic solid-state phase change calculation by adopting a linear interpolation method, wherein a linear interpolation schematic diagram is shown in fig. 5, and a specific calculation formula is represented by a formula (3):
in the formula (3): t (T) O The temperature of the microcell O; t (T) i Is the macro-cell temperature near the O-point; l (L) i Is the distance from the O-point to the surrounding macro-cells; n is the number of macro-cells surrounding the micro-cells, where N has a value of 8.
The step 3 is specifically implemented according to the following steps:
step 3.1, simplifying the construction conditions of a weld metal solid-state phase change model;
and 3.2, constructing a model of balance phase composition change of the weld metal in the heating and cooling processes.
Step 3.2 is carried out by the following steps:
step 3.3, according to the lever law, during the heating process of the TC4 titanium alloy, the change of the balance phase component is represented by the formula (4):
F(β)＝(F α (T)-6.0)/(F α (T)-F β (T)) (4)
in the formula (4), F (beta) represents the equilibrium phase volume fraction of the beta phase during heating; f (F) α (T) TableShowing the equilibrium phase volume fraction of the alpha phase at temperature T; f (F) β (T) represents the equilibrium phase volume fraction of the beta phase at a temperature T;
and 3.4, when the titanium alloy is rapidly cooled at a high temperature, adopting JMPRO software to calculate a macroscopic phase transformation process after solidification, adopting Matlab software to construct an alloy microscopic phase transformation model according to the macroscopic phase transformation model, and establishing a mathematical model of temperature-phase transformation, wherein a specific calculation formula is represented by a formula (5):
F α' (i,j)＝a*T(i,j)+b (5)
wherein: f (F) α' (i, j) represents the content of the alpha' martensite phase of the microcosmic unit (i, j); t (i, j) represents the temperature of the microcolumn (i, j); a and b represent real constants, and the values of a and b are related to the temperature of the weld metal.
The construction conditions for simplifying the weld metal solid-state phase transformation model comprise:
(1) Simplifying the main components of the multi-element alloy TC4 titanium alloy into Ti-6Al;
(2) Only the generation of the primary phase is considered in the solid-state phase transformation process of the alloy, and the generation of the secondary phase is ignored.
Step 4 is specifically implemented according to the following steps:
step 4.1, the welding transient temperature field model, the microcosmic temperature field model and the solid phase transformation model of the weld metal constructed in the steps 1 to 3 are imported into simulation software Matlab to form a calculation model of the solid phase transformation of the TC4 titanium alloy welding pool;
and 4.2, inputting the thermophysical performance parameters and specific welding process parameters of the TC4 titanium alloy into a calculation model of the solid-state transformation of the TC4 titanium alloy welding pool, calculating to obtain a simulation result image, and carrying out brief analysis.
Example 1
And inputting the thermophysical performance parameters and welding process parameters of the TC4 titanium alloy into a calculation model of the solid phase transition of the TC4 titanium alloy welding pool to obtain a visual simulation result of the solid phase transition of the TC4 titanium alloy welding pool, wherein the visual simulation result is shown in FIG. 6. It can be observed from fig. 6 that, as the cooling process proceeds, the α ' martensite content in the weld joint rapidly increases, although the final weld joint structure is α ' martensite, the transformation processes of the regions in the weld joint are not synchronous, there is a significant difference in transformation rate, the α ' martensite phase transformation does not proceed immediately after the weld joint is solidified, and when the temperature drops to the transformation point (825 ℃), the α ' martensite phase transformation rapidly starts, and the β phase is completely transformed into α ' martensite phase in a very short time due to the large cooling rate of the welding temperature field, and the transformation process exhibits a significant difference due to the difference in heat dissipation and heat conduction conditions at different positions in the weld joint, and the upper phase transformation start time of the weld joint is earlier than the bottom of the weld joint.
Example 2
The thermophysical performance parameters of the TC4 titanium alloy are input into a calculation model of the solid phase transition of the TC4 titanium alloy welding pool, other conditions are kept unchanged, the solid phase transition condition of weld metal is respectively researched when the welding current is 60A, 75A and 90A, and the simulation result is shown in figure 7.
As can be seen from fig. 7, the effect of the welding current is mainly reflected on the change of the molten pool morphology, but the solid phase transformation is closely related to the post-welding cooling rate, and although the peak temperature of the welding molten pool increases with the increase of the welding current, the post-welding cooling rate is at a higher level, and the transformation temperature of the TC4 titanium alloy alpha 'martensite phase is far lower than the peak temperature of the molten pool, so that the formation structure is all alpha' martensite phase.
Example 3
Inputting the thermal physical performance parameters of the TC4 titanium alloy into a calculation model of the solid phase transition of the TC4 titanium alloy welding pool, keeping other conditions unchanged, and respectively researching the solid phase transition conditions of weld metal when the welding speed is 1mm/s, 1.5mm/s and 2mm/s, wherein the simulation result is shown in figure 8.
As can be seen from fig. 8, the microstructure after the solid phase transformation is the α ' martensite phase at different welding speeds, which is consistent with the law of the solid phase transformation at different welding currents, and the analysis is based on the fact that the higher cooling rate in the molten pool after the welding is completed and the transformation temperature of the α ' martensite phase structure are lower, and the strength of the α ' martensite phase structure is higher than that of the TC4 parent metal of the α+β two-phase structure, so that the high-strength welding quality can be obtained when the TC4 titanium alloy is welded under the condition of reasonably selecting the welding process parameters.
According to the three embodiments, the alpha' martensitic transformation condition of the weld metal at any moment in the TC4 titanium alloy welding process can be calculated, and meanwhile, the transformation condition of the weld metal under different welding process parameters can be researched, so that a new research means is provided for researching the solid phase transformation condition of the molten pool metal in the titanium alloy welding process.
Claims (1)
1. The simulation method of the solid phase transition of the TC4 titanium alloy welding pool is characterized by comprising the following steps of:
step 1, constructing a welding transient temperature field model based on a finite element method, and specifically implementing the method according to the following steps:
step 1.1, establishing a finite element geometric model in finite element simulation software according to the size and the dimension of an actual weldment;
step 1.2, according to the welding material selected during welding, giving material properties to the finite element geometric model to obtain a finite element geometric material model;
step 1.3, setting an analysis step of welding simulation according to an actual welding process;
step 1.4, setting initial conditions and boundary conditions according to the actual condition of the welding process, wherein the initial conditions comprise setting initial temperature, and the boundary conditions comprise determining the heat exchange relation between the simulation area and the environment;
step 1.5, setting a load according to the actual condition of a welding pool, wherein the load comprises boundary constraint setting, surface heat flux setting, and a heat source model is selected by setting the surface heat flux, and the heat source model selects a double-ellipsoid heat source model, and the specific calculation formula is as follows:
when x is more than or equal to 0, the functional expression of the first half of the model is:
when x < 0, the functional expression of the second half of the model is:
in the formulas (1) and (2): a, a f ，a r B and c are the axial lengths of the front and rear subareas of the ellipsoid respectively; f (f) 1 Coefficients that are the first half of the model; f (f) 2 Q is the effective heat input of the welding heat source, which is the coefficient of the latter half of the model;
step 1.6, forming a finite element model by adding initial conditions, boundary conditions and loads to the finite element geometric material model, carrying out grid division on the finite element model to obtain a finite element calculation model, and calculating a welding transient macroscopic temperature field model by utilizing finite element simulation software;
step 2, constructing a microcosmic temperature field model by utilizing an interpolation principle, and specifically implementing the steps as follows:
step 2.1, selecting a proper simulation area, and extracting a thermal cycle curve of finite element nodes of the selected simulation area, namely an instant-temperature curve;
step 2.2, fitting a thermal cycle curve by using simulation software Matlab to obtain a temperature-time function of the finite element node, and obtaining a macroscopic temperature field model of the selected simulation area;
2.3, converting the macroscopic temperature field model into a microscopic temperature field model for microscopic solid-state phase change calculation by adopting a linear interpolation method, wherein a specific calculation formula is represented by a formula (3):
in the formula (3): t (T) O The temperature of the microcell O; t (T) i Is the macro-cell temperature near the O-point; l (L) i Is the distance from the O-point to the surrounding macro-cells; n is the number of macro-cells surrounding the micro-cells, where N has a value of 8;
step 3, constructing a solid phase change model of weld metal, and specifically implementing the method according to the following steps:
step 3.1, simplifying construction conditions of a weld metal solid state transformation model, wherein the construction conditions of the simplified weld metal solid state transformation model comprise:
(1) Simplifying the main components of the multi-element alloy TC4 titanium alloy into Ti-6Al;
(2) Only the generation of a main phase is considered in the solid-state phase transformation process of the alloy, and the generation of a secondary phase is ignored;
step 3.2, constructing a model of balance phase composition change of weld metal in the heating and cooling processes, wherein the method comprises the following steps of:
step 3.3, according to the lever law, during the heating process of the TC4 titanium alloy, the change of the balance phase component is represented by the formula (4):
F(β)＝(F α (T)-6.0)/(F α (T)-F β (T)) (4)
in the formula (4), F (beta) represents the equilibrium phase volume fraction of the beta phase during heating; f (F) α (T) represents the equilibrium phase volume fraction of the alpha phase at a temperature T; f (F) β (T) represents the equilibrium phase volume fraction of the beta phase at a temperature T;
and 3.4, when the titanium alloy is rapidly cooled at a high temperature, adopting JMPRO software to calculate a macroscopic phase transformation process after solidification, adopting Matlab software to construct an alloy microscopic phase transformation model according to the macroscopic phase transformation model, and establishing a mathematical model of temperature-phase transformation, wherein a specific calculation formula is represented by a formula (5):
F α' (i,j)＝a*T(i,j)+b (5)
wherein: f (F) α' (i, j) represents the content of the alpha' martensite phase of the microcosmic unit (i, j); t (i, j) represents the temperature of the microcolumn (i, j); a and b represent real constants, and the numerical values of a and b are related to the temperature of weld metal;
and 4, numerical calculation and analysis of calculation results are carried out according to the following steps:
step 4.1, the welding transient temperature field model, the microcosmic temperature field model and the solid phase transformation model of the weld metal constructed in the steps 1 to 3 are imported into simulation software Matlab to form a calculation model of the solid phase transformation of the TC4 titanium alloy welding pool;
and 4.2, inputting the thermophysical performance parameters and specific welding process parameters of the TC4 titanium alloy into a calculation model of the solid-state transformation of the TC4 titanium alloy welding pool, calculating to obtain a simulation result image, and carrying out brief analysis.
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