Method for calculating residual stresses in dissimilar metal laser welded joints

Abstract

A method for calculating residual stress in a welded joint includes: establishing a finite element geometric model of an assembly comprising a first metallic alloy joined to a second metallic alloy by a weld fillet; and calculating the residual stress of the assembly by performing a finite element analysis (FEA) on the finite element geometric model within a predetermined heating and cooling temperature range for effectively forming the weld fillet by laser welding. The first and second metallic alloys are dissimilar metals. The finite element analysis includes incorporating the respective phase transformation properties and phase-specific properties of each of the first and second metallic alloys within a predetermined temperature range. The FEA can be performed by a solver, and the phase transformation properties and phase-specific properties of the alloys can be incorporated into the solver via user-defined subroutines (UMAT).

Description

[0001] Government funding

[0002] This disclosure was made with government funding under Agreement No. DE-AC05-00OR22725 granted by the Department of Energy. The government may have certain rights to this disclosure. Technical Field

[0003] This disclosure generally relates to calculating residual stress in an assembly, and more specifically, to a method for calculating residual stress in an assembly having a laser-welded joint of dissimilar metals. Background Technology

[0004] Automotive components, such as sun gear assemblies, may include workpieces joined together by laser welding, where dissimilar metals are joined together. Laser welding, or laser beam welding, is a welding technique that uses a laser beam to join sheets of metal. The laser beam provides a concentrated heat source, allowing for narrow, deep weld seams and high welding rates. Laser welding is commonly used in the automotive industry because the process can be automated for high-volume, precision welding.

[0005] Laser welding can be used to join various dissimilar base metals such as steel, aluminum, and titanium. However, due to the high power density of the laser beam and the rapid heating and cooling of the laser-welded joint, residual stress may concentrate in certain areas of the weld joint and adjacent heat-affected zones.

[0006] While current methods for welding components with dissimilar base metals have achieved their purpose, a method for determining residual stress in laser-welded joints of dissimilar metals is still needed to improve laser welding technology for joining dissimilar base metals. Summary of the Invention

[0007] According to several aspects, a method for calculating residual stress in a welded joint is provided. The method includes: establishing a finite element geometric model of an assembly including a first workpiece joined to a second workpiece by a weld joint; and calculating the residual stress of the assembly by performing a finite element analysis on the finite element geometric model within a predetermined heating and cooling temperature range for effectively forming the weld joint by laser welding. The finite element analysis includes incorporating the respective phase transformation properties and phase-specific properties of each of the first and second workpieces within the predetermined heating and cooling temperature range, at predetermined temperature increments.

[0008] In another aspect of this disclosure, the finite element analysis also includes, when representing the weld bead, incorporating the phase transformation properties and phase-specific properties of the mixture of the first and second workpieces.

[0009] In another aspect of this disclosure, the first workpiece is formed of a first metal alloy, while the second workpiece is formed of a second metal alloy different from the first metal alloy. The mixture of the first and second workpieces is a mixture of the first and second metal alloys.

[0010] In another aspect of this disclosure, the mixture of the first metal alloy and the second metal alloy comprises a homogeneous mixture of 50 wt% of the first metal alloy and 50 wt% of the second metal alloy.

[0011] In another aspect of this disclosure, the phase transformation properties and phase-specific properties include: thermal expansion of the first metal alloy, the second metal alloy, and mixtures of the first metal alloy and the second metal alloy; flow stress of the first metal alloy, the second metal alloy, and mixtures of the first metal alloy and the second metal alloy; and phase fraction of the first metal alloy, the second metal alloy, and mixtures of the first metal alloy and the second metal alloy within a predetermined temperature range.

[0012] In another aspect of this disclosure, the phase transformation properties and phase-specific properties also include the Young's modulus and Poisson's ratio of the first metal alloy, the second metal alloy, and mixtures of the first metal alloy and the second metal alloy within a predetermined heating and cooling temperature range.

[0013] In another aspect of this disclosure, by utilizing Abaqus TM The software is used to perform finite element analysis. User-defined subroutines (UMAT) are used to incorporate phase transitions and include phase-specific properties in Abaqus. TM middle.

[0014] In another aspect of this disclosure, UMAT is configured to: invoke a matrix material property database at a predetermined temperature increment to obtain the metallic properties of the workpiece at a temperature (T) below Tmelt; invoke a WELD material property database to obtain the metallic properties of the workpiece at a temperature (T) above Tmelt; update the phase fraction based on the workpiece; update the material phase transformation properties and phase-specific properties; calculate the elastic test stress; check the yield condition; in response to the predetermined yield condition, correct the stress and strain increments through plastic cycling; and update the stress and state variables.

[0015] In another aspect of this disclosure, the method also includes generating a visual representation based on the calculated residual stress of the component, and modifying at least one of the laser welding processes based on the visual representation to achieve the weld bead and component design, thereby mitigating the calculated residual stress.

[0016] According to several aspects, a method is provided for calculating residual stress in a welded joint of two workpieces having dissimilar base metals. The method includes establishing a finite element model of an assembly comprising a first workpiece connected to a second workpiece by a weld joint formed by laser welding, and calculating the residual stress of the weld joint by performing a finite element analysis of the finite element model within a heating and cooling temperature range effectively used to form the weld joint by laser welding. The first workpiece comprises a first base metal, and the second workpiece comprises a second base metal different from the first base metal. The finite element analysis includes incorporating phase transformation properties and phase-specific properties of the weld joint within a predetermined temperature increment over the heating and cooling temperature range.

[0017] In another aspect of this disclosure, the phase transformation properties and phase-specific properties of the weld fillet include: thermal expansion of the mixture of the first base metal and the second base metal within the heating and cooling temperature range; flow stress of the mixture of the first base metal and the second base metal within the heating and cooling temperature range; and phase fraction of the mixture of the first base metal and the second base metal within the heating and cooling temperature range.

[0018] In another aspect of this disclosure, the mixture of the first base metal and the second base metal comprises 50 wt% of the first base metal and 50 wt% of the second base metal.

[0019] In another aspect of this disclosure, the phase transformation properties and phase-specific properties of the weld fillet include: Young's modulus and Poisson's ratio of the mixture of the first base metal alloy and the second base metal alloy within the heating and cooling temperature range.

[0020] In another aspect of this disclosure, finite element analysis is performed using Abaqus. TM Software execution. Phase transition properties and phase-specific properties are incorporated into Abaqus through user-defined subroutines (UMAT). TM In the software.

[0021] According to several aspects, a method for calculating residual stress in a welded joint is provided. The method includes establishing a finite element geometric model of an assembly comprising a first workpiece joined to a second workpiece by a weld fillet, wherein the first workpiece comprises a first base metal and the second workpiece comprises a second base metal different from the first base metal; using Abaqus... TM The software calculates the residual stress of the component by performing finite element analysis on the finite element geometric model within a predetermined heating and cooling temperature range that effectively forms the weld corner by laser welding; and incorporates the phase transformation properties and phase-specific properties of the first metal, the second metal, and mixtures of the first metal and the second metal using user-defined subroutines (UMAT).

[0022] In another aspect of this disclosure, UMAT is configured to incorporate the phase transition properties and phase-specific properties of a first base metal, a second base metal, and a mixture of the first base metal and the second base metal within a predetermined temperature increment over a heating and cooling temperature range.

[0023] In another aspect of this disclosure, the phase transition properties and phase-specific properties include at least one of the following: thermal expansion of at least one of the first base metal, the second base metal, and a mixture of the first base metal and the second base metal; flow stress of at least one of the first base metal, the second base metal, and a mixture of the first base metal and the second base metal; phase fraction of at least one of the first base metal, the second base metal, and a mixture of the first base metal and the second base metal; Young's modulus of at least one of the first base metal, the second base metal, and a mixture of the first base metal and the second base metal; and Poisson's ratio of at least one of the first base metal, the second base metal, and a mixture of the first base metal and the second base metal.

[0024] In another aspect of this disclosure, the first metal is SAE-AISI 8620 steel, and the second metal is SAE-AISI 1020 steel.

[0025] In another aspect of this disclosure, the component is a sun gear assembly.

[0026] Other application areas will become clear from the description provided herein. It should be understood that the specification and specific examples are for illustrative purposes only and are not intended to limit the scope of this disclosure. Attached Figure Description

[0027] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of this disclosure in any way.

[0028] Figure 1 This is a cross-sectional perspective view of a sun gear assembly with a laser-welded joint according to an exemplary embodiment;

[0029] Figure 2 This is according to an exemplary embodiment. Figure 1 A detailed view of a portion;

[0030] Figure 3 This is a perspective view of a first workpiece adjacent to a second workpiece, according to an exemplary embodiment of laser welding;

[0031] Figure 4 This is a diagram illustrating the functional block diagram of finite element analysis (FEA) according to an exemplary embodiment;

[0032] Figure 5 This is an exemplary illustration of a finite element model (FEA) according to an exemplary embodiment;

[0033] Figure 6a , Figure 6b and Figure 6c These are thermal expansion diagrams showing the thermal expansion of weld metals of 8620, 1020, and those including 50% 8620 and 50% 1020, respectively.

[0034] Figure 7a , Figure 7b , Figure 7c and Figure 7d The flow stresses of 8620, 1020 and their mixtures are described at corresponding temperatures of 25°C, 300°C, 500°C and 900°C.

[0035] Figure 8a , Figure 8b , Figure 8c and Figure 8d Temperature-dependent flow stresses of austenite, ferrite, pearlite and martensite during cooling were depicted respectively.

[0036] Figure 8e The temperature- and cooling rate-dependent flow stresses of bainite were described;

[0037] Figure 9a and Figure 9b The phase fractions of 8620 and 1020 are depicted; and

[0038] Figure 10a and Figure 10b These are the continuous cooling transition (CCT) curves for 8620 and 1020. Detailed Implementation

[0039] The following description is merely exemplary in nature and is not intended to limit this disclosure, its application, or its use. The illustrated embodiments are disclosed with reference to the accompanying drawings, wherein the same numerals identify corresponding parts in the various drawings. The drawings are not necessarily drawn to scale, and some features may be exaggerated or reduced to show detail of a particular feature. The specific structural and functional details disclosed are not intended to be construed as limiting, but rather as a representative basis for teaching those skilled in the art how to practice the disclosed concepts.

[0040] The embodiments of this disclosure can be described herein in terms of functional and / or logical block components and various processing steps. It should be understood that such block components can be implemented by any number of hardware, software, and / or firmware components configured to perform the specified functions. For example, embodiments of this disclosure can employ various integrated circuit components, such as memory elements, digital signal processing elements, logic elements, lookup tables, etc., capable of performing various functions under the control of one or more microprocessors or other control devices. Furthermore, those skilled in the art will understand that embodiments of this disclosure can be incorporated into any number of systems for practice, and the systems described herein are merely exemplary embodiments of this disclosure.

[0041] The connecting lines shown in the figures included herein are intended to illustrate exemplary functional relationships and / or physical couplings between components. Conventional techniques may be used for signal processing, data transmission, signaling, control, and other functional aspects of the system (and individual operating components of the system) that may not be described in detail herein. It should be noted that many alternative or additional functional relationships or physical connections may exist in the embodiments of this disclosure.

[0042] Although the terms first, second, third, etc., may be used herein to describe various steps, elements, components, regions, layers, and / or sections, these steps, elements, components, regions, layers, and / or sections should not be limited by these terms unless otherwise indicated. These terms may be used only to distinguish one step, element, component, region, layer, or section from another. Terms such as “first,” “second,” and other numerical terms used herein do not imply order or sequence unless the context clearly indicates otherwise. Therefore, the first step, element, component, region, layer, or section discussed below may be referred to as the second step, element, component, region, layer, or section without departing from the teachings of the exemplary embodiments.

[0043] Residual stress induced by phase transformation contributes significantly to the final residual stress in laser welding used to join dissimilar base metals. Due to the phase fraction in the laser-welded joint of dissimilar metals, the flow stress during the heating and cooling of the dissimilar metals differs compared to laser welding the same base metal. A method 500 for calculating the residual stress in the laser-welded joint of dissimilar metals, as detailed below, incorporates the phase transformation properties and phase-specific properties of the dissimilar base metals during the heating and cooling cycles of laser welding. Method 500 utilizes Abaqus... TM Finite element analysis software (also known as Abaqus) TMUser-defined subroutines (UMAT) in the solver are used to capture the temperature-dependent material properties at each integration point (also known as a node) of the finite element geometry model. Due to the presence of dissimilar metals, the material properties of mixtures of dissimilar base metals are applied to the molten zone (e.g., weld joints or weld fillets). Method 500 can be applied to any laser welding process used to join dissimilar metals.

[0044] Figure 1 This is a cross-sectional perspective view of the sun gear assembly 100. The sun gear assembly 100 includes a hollow cylindrical member 102 assembled onto a housing 104. The cylindrical member 102 is formed of a first base metal, while the housing 104 is formed of a second base metal. The first and second base metals are different base metals (also referred to as dissimilar metals). Dissimilar metals are alloys with different dominant metal types or different alloying elements. In a non-limiting example, the first base metal is SAE-AISI 8620 steel (also referred to as 8620), and the second base metal is SAE-AISI 1020 steel (also referred to as 1020). Although 8620 and 1020 are steel alloys with 20% iron by weight, 8620 and 1020 have slightly different alloying elements (such as Cr), resulting in different mechanical and corrosion properties. The hollow cylindrical member 102 abuts against the housing 104 and is joined by a laser-welded joint 106.

[0045] Figure 2 yes Figure 1 A detailed view of part 200 shows a diagram of the hollow cylindrical member 102 being laser-welded to the housing 104. Figure 3 This is a perspective view of a first workpiece 102 adjacent to a second workpiece 104, which is laser-welded using 108 welding. The first workpiece 102 is a schematic representation of a hollow cylindrical member 102, and the second workpiece 104 is a schematic representation of a housing 104.

[0046] refer to Figures 1 to 3 Laser welding is a welding process that uses a laser 108 emitting a high-energy laser beam as the primary heat source to melt and join a first workpiece 102 and a second workpiece 104 at a welding interface 110. The laser moves relative to the assembly 100 along the direction of the welding interface 110. The high-energy laser beam is sufficient to cause the first and second base metals near the welding interface 110 to undergo a phase transition from solid to liquid, thereby allowing the first and second base metals to mix to form a relatively narrow and deep weld bead 112 upon cooling. The weld bead 112 is also referred to as the molten zone 112 of the first base metal 102 and the second base metal 104.

[0047] As the laser 108 moves relative to the assembly along the weld interface during welding, the earlier formed portion of the weld corner 112 is cooled as the laser beam continues to melt the base metal along the weld interface. The base metals 102 and 104 forming the weld corner 112, and the region adjacent to the weld corner 112, can undergo a temperature cycle from room temperature to 2,000°C and back to room temperature during laser welding. On either side of the weld corner 112 is a heat-affected zone (HAZ) 114, which is the region in the workpieces 102 and 104 that undergoes changes in mechanical properties due to exposure to the temperature cycle experienced during the laser welding process.

[0048] The stress components are calculated incrementally using the following equation.

[0049] dσ=(D e +D p )·dε-C T ·dT

[0050] Where dσ and dε are the increments of the stress and strain tensors, D e D p and C T Let be the elastic stiffness, plastic stiffness, and thermal expansion-induced stiffness matrices, and let be related to material properties, where T is the temperature, and dT is the temperature change in each simulation increment. These material properties can vary with material type, phase, and temperature. Residual stress refers to the stress state when the welded assembly cools to room temperature.

[0051] The residual stress resulting from the phase transformation of the base metal and its fusion in the weld fillet 112 (molten zone 112) contributes significantly to the final residual stress in laser welding, particularly in medium carbon steels such as 8620 and 1020. The flow stress during the heating and cooling cycles varies depending on the phase fraction. A method 500 for calculating residual stress using finite element analysis is disclosed below, which incorporates the phase transformation properties and phase-specific properties of these specific base metals, as well as the mixing (mixture) of these base metals, during the thermal cycle of laser welding.

[0052] Figure 4 An exemplary representation of the finite element geometric model (FEM 400) is shown. FEM 400 is a numerical model for solving partial differential equations that approximates complex problems by subdividing a large system into smaller parts called finite elements 402. Each finite element 402 is connected to directly adjacent finite elements via a common node 404, which transfers effects from one finite element 402 to another.

[0053] Figure 5A functional block diagram of a finite element analysis (FEA) method 500 is shown, which typically includes three stages 502, 504, and 524. The first stage 502 involves inputting a file containing an engineering design (e.g., FEM 400) for the finite element analysis into the solver. In the second stage 504 (presented in the box defined by dashed lines), the solver performs a finite element analysis on the finite element model (FEM 400). In a non-limiting example, FEM 400 is a model representing the sun gear assembly 100. The third stage 524 generates reports, images, animations, and other visual representations based on the output file from the second stage 504. The FEA output can be used to identify areas in FEM 400 with unwanted residual stresses. The laser welding process and / or design of the actual sun gear assembly 100 represented by FEM 400 can be modified to mitigate these unwanted residual stresses.

[0054] Methods for predicting residual stress 500 can be based on Abaqus TM Abaqus is a solver for this problem. TM The solver is commercially available software for FEA and has a large library of element and material models that can be used in FEA. However, Abaqus... TM The solver does not account for the phase transformation and phase-specific properties of dissimilar base metals and mixtures of dissimilar base metals within the inherent temperature cycle of laser welding. Method 500 incorporates a user material subroutine (also known as UMAT), which is configured to define custom material behavior that can more accurately represent the behavior of the dissimilar metals to be modeled by incorporating the phase transformation and phase-specific properties of different base metals and mixtures of different base metals.

[0055] The subroutine UMAT is incorporated in the second stage 504 of FEA. At box 502, UMAT is iterated over a temperature range typically associated with laser welding processes (from T0 to T). N The process begins with predetermined increments for each node-associated element of the FEM 400. T0 is the temperature of the assembly 100 at the welding interface 110 prior to the laser welding process, while T... N This is the highest temperature of component 100 at the weld interface 110 during the laser welding process. The weld bead 112 (melting zone 112), the heat-affected zone 114 (HAZ 114) adjacent to the weld bead 112, and the base metal are exposed from T0 to T10. N At a temperature within a predetermined temperature range, proceed to box 503.

[0056] At box 503, FEA is located from T0 to T... NThe process iterates over a predetermined heating and cooling temperature cycle to T0 in predetermined temperature increments (such as for every 5-degree temperature change). T0 is typically room temperature, while T... N This is the highest temperature experienced during laser welding. For a single iteration, proceed to box 505.

[0057] At box 505, it is determined whether the temperature of each base metal is greater than the melting temperature (also known as the liquidus) of the corresponding base metal. If the temperature of a particular base metal is higher than its melting temperature (Tmelt), method 500 proceeds to box 506 to retrieve the weld material properties from a user-filled material database. If the temperature of a particular base material is lower than its melting temperature, method 500 retrieves the weld material properties from Abaqus. TM The base material properties are retrieved from a standard material database. In other words, for each component, it is determined whether the material is a base material or a weld material based on its melting temperature. If the temperature is below the melting temperature, the base material properties are used. If the temperature is above the melting temperature, the weld material properties are used. From boxes 505 and / or 506, method 500 proceeds to box 508.

[0058] At box 508, the phase fraction of each base metal is updated based on the data obtained from boxes 505 and 506. In the FEM location where the base metal is at a temperature above its melting temperature, it is assumed that the base metal is in a 50 / 50 homogeneous mixture, and the phase fraction of the mixture is updated accordingly. The phase fractions include base metal (BM) wt%, austenite wt%, martensite wt%, ferrite wt%, bainite wt%, and pearlite wt%. Proceed to box 510.

[0059] Exemplary thermal profiles are presented in Figures 6a-6c , Figures 7a-7d , Figures 8a-8e , Figures 9a-9b and Figures 10a-10b The flow stress for each material is determined based on the thermal profile. If the thermal profile represents a heating process, the heating flow stress profile is used. If the thermal profile represents a cooling process, the cooling flow stress profile is used. Cooling flow stress data are calculated using phase-dependent flow stresses, including ferrite, pearlite, martensite, and matrix materials. Temperature-dependent and strain-rate-dependent properties of bainite are calculated during cooling.

[0060] At box 510, update the base metal properties and mixtures of base metal properties for the iterative input to the FEA. Update the material phases and their fractions based on the current temperature and cooling rate during cooling. Material properties include Young's modulus, Poisson's ratio, thermal expansion, and flow stress. Proceed to box 512.

[0061] At box 512, perform strain increment calculation and elastic test stress calculation. Proceed to box 514.

[0062] At box 514, the yield criterion is checked to determine whether the local stresses in the weld and heat-affected zone exceed the material's yield strength. If the material yields, it enters a plastic cycle to correct for stress and strain increments, and then updates the plastic strain, stress, and state variables. If "No," proceed to box 518; if "Yes," proceed to box 516.

[0063] At box 516, the plastic cycle is calculated to correct for stress and strain increments, and stress and state variables are calculated. Proceed to box 518.

[0064] At box 518, the Jacobian matrix is ​​calculated, and method 500 exits UMAT at box 520 and proceeds to box 522. If the variables do not converge, convergence is checked, and the process returns to box 503. Convergence means that the solution error between the two most recent time steps is below a predetermined set value. The solver then moves to the next time increment and repeats the process.

[0065] Figure 6a , Figure 6b , Figure 6c These are thermal expansion diagrams, representing the thermal expansion of 8620, 1020, and weld metals comprising 50 wt% of 8620 and 50 wt% of 1020, respectively. The corresponding diagrams show temperature-dependent thermal expansion during heating, temperature and cooling rate-dependent thermal expansion during cooling, and the effect of phase transformations on expansion, including (1) the base metal to austenite transformation during heating; and (2) the austenite to martensite and other phase transformations during cooling. The material properties at the molten zone 112 (weld fillet 112) are considered using a mixed material composition.

[0066] Figure 7a , Figure 7b , Figure 7c and Figure 7d This is a graph showing the relationship between strain (%) and stress (MPa), displaying the flow stress of 8620, 1020, and weld metals including 50 wt% 8620 and 50 wt% 1020 during heating at corresponding temperatures of 25°C, 300°C, 500°C, and 900°C. The corresponding graph shows the flow stress of the base material during the initial heating cycle and the flow stress of the base material during subsequent cycles (if the original base material is retained).

[0067] Figure 8a , Figure 8b , Figure 8c and Figure 8d Temperature-dependent flow stresses of austenite, ferrite, pearlite and martensite during cooling were depicted respectively. Figure 8e The temperature- and cooling rate-dependent flow stresses of bainite are depicted. If the material transforms into a new phase during a previous welding cycle, phase flow stresses are applied during cooling and subsequent cycles.

[0068] Temperature- and strain-rate-dependent material properties were considered. Flow stresses for each phase were considered separately during heating and cooling. The total flow stress σ is... f It is based on the specific flow stress σ of the phase. i and the weight or volume fraction f of each phase i Calculated using the following equation:

[0069]

[0070] in:

[0071] i = Independent matrix material, austenite, ferrite, bainite, pearlite, martensite; f i σ is the volume fraction of phase i. i For a specific i-phase flow stress, σ f This represents the total flow stress.

[0072] Figure 9a and Figure 9b The phase fractions of 8620 and 1020 are depicted. During heating, the matrix material transforms into austenite at Ac1 and completes the transformation at Ac3. Changes in material phases, Young's modulus, and thermal expansion at different temperatures during heating are also shown.

[0073] Figure 10a and Figure 10b The continuous cooling transformation (CCT) curves for AISI 8620 and AISI 1020 are shown for calculating the phase fractions of ferrite, bainite, pearlite, and martensite during cooling. CCT is used to apply node-based material properties.

[0074] The FEM can be executed by a computing module. Non-limiting examples of a computing module include at least one processor and a non-transitory computer-readable storage device or medium. The non-transitory computer-readable storage device or medium includes machine-readable instructions that, when executed by a processor, cause the processor to perform the method 500 as described herein. The non-transitory computer-readable storage device or medium may be programmed with computer-readable data representing instructions executable by a processor for performing the described method 500, as well as other contemplated but not specifically listed variations. Parts of method 500 can be executed by multiple distributed computing modules having the above configuration.

[0075] Method 500 determines the weld material properties for laser welding of dissimilar metal joints. Flow stresses of each phase are considered separately during heating and cooling. A mixture of material compositions is used to account for material properties at the molten zone. Temperature-dependent and strain-rate-dependent material properties are considered. The cooling profile is used to apply these node-based material properties. The output of Method 500 can be used to modify the laser welding process and / or the design of the assembly to mitigate this undesirable residual stress.

[0076] The description in this disclosure is merely exemplary in nature, and variations thereof without departing from the general meaning of this disclosure are intended to be within the scope of this disclosure. Such variations should not be considered as departing from the spirit and scope of this disclosure.

Claims

1. A method for calculating residual stress in a welded joint, comprising: A finite element geometric model of a component is established, the component including a first workpiece, which is joined to a second workpiece by a weld joint; The residual stress of the component is calculated by performing finite element analysis on the finite element geometric model within a predetermined heating and cooling temperature range that effectively forms the weld bead by laser welding; and The finite element analysis includes incorporating the phase transition properties and phase-specific properties of the first workpiece and the second workpiece within the predetermined heating and cooling temperature range and under predetermined temperature increments.

2. The method according to claim 1, wherein, The finite element analysis also includes incorporating the phase transformation properties and phase-specific properties of the mixture of the first workpiece and the second workpiece into the modeling of the weld corner formation.

3. The method according to claim 2, wherein, The first workpiece comprises a first metal alloy, the second workpiece comprises a second metal alloy different from the first metal alloy, and a mixture of the first workpiece and the second workpiece comprises a mixture of the first metal alloy and the second metal alloy.

4. The method according to claim 3, wherein, The mixture of the first metal alloy and the second metal alloy comprises a homogeneous mixture of 50 wt% of the first metal alloy and 50 wt% of the second metal alloy.

5. The method according to claim 3, wherein, The phase transition properties and phase-specific properties include: The thermal expansion of the first metal alloy, the second metal alloy, and the mixture of the first metal alloy and the second metal alloy within the predetermined heating and cooling temperature range; The flow stresses of the first metal alloy, the second metal alloy, and the mixture of the first metal alloy and the second metal alloy within the predetermined heating and cooling temperature range; and The phase fractions of the first metal alloy, the second metal alloy, and the mixture of the first metal alloy and the second metal alloy within the predetermined heating and cooling temperature range.

6. The method according to claim 5, wherein, The phase transformation properties and phase-specific properties also include the Young's modulus and Poisson's ratio of the first metal alloy, the second metal alloy, and mixtures of the first metal alloy and the second metal alloy within the predetermined heating and cooling temperature range.

7. The method according to claim 5, wherein, The finite element analysis is performed using a solver; and The phase transition properties and phase-specific properties are incorporated into the solver through the user-defined subroutine UMAT.

8. The method according to claim 7, wherein, The UMAT is configured as follows: The matrix material property database is invoked to obtain the metal alloy properties of the first metal alloy, the second metal alloy, and a mixture of the first metal alloy and the second metal alloy at a temperature T below the Tmelt of the respective alloys; as well as The welding material property database is invoked to obtain the metal alloy properties of the first metal alloy, the second metal alloy, and the mixture of the first metal alloy and the second metal alloy at a T value greater than the Tmelt of the respective alloy.

9. The method according to claim 8, wherein, For at least one of the first metal alloy, the second metal alloy, and a mixture of the first metal alloy and the second metal alloy, the UMAT is further configured to: The phase fraction is updated based on the obtained metal alloy properties; Update material phase transition properties and phase-specific properties; Calculate the stress in the elastic test; Check the yield condition; Plastic cycling in response to a predetermined yield condition to correct for stress and strain increments; and Update stress and state variables.

10. The method of claim 1, further comprising generating a visual representation based on the calculated residual stress of the component; and Based on the visual representation, the laser welding process is modified to achieve at least one of the weld bead and the design of the component, in order to reduce the calculated residual stress.

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