Zk60 magnesium alloy crank forging forming process optimization method and forming method based on finite element simulation

Abstract

The application provides a ZK60 magnesium alloy crank forging forming process optimization method and forming method based on finite element simulation, relates to the magnesium alloy forging forming technical field, and comprises the following steps: drawing a geometric model of a forging forming process by using UG software, including a upsetting die, a finish forging die and a blank; importing the geometric model into Deform-3D finite element numerical simulation software to perform finite element numerical simulation; combining specific production scenes and equipment parameters to construct a finite element simulation model that is in line with actual working conditions; and simulating the forging forming process of forgings. The application combines finite element numerical simulation and test verification by using Deform finite element numerical simulation software, innovatively designs upsetting preforming and bending and flattening preforming procedures, effectively solves the cracking tendency, incomplete filling and folding defects and other problems in the ZK60 magnesium alloy forging process, and successfully obtains a magnesium alloy crank forging that meets the standards in size precision and mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy forging technology, and more specifically, to an optimization method and forming method for the forging process of ZK60 magnesium alloy crank based on finite element simulation. Background Technology

[0002] Magnesium alloys have become strategic materials for replacing aluminum alloys in the field of lightweighting due to their low density, high specific strength and excellent vibration damping performance. Among them, ZK60 magnesium alloy has great potential for application in key load-bearing components of automobiles. However, the inherent close-packed hexagonal structure of ZK60 magnesium alloy results in its room temperature plasticity being significantly lower than that of aluminum alloy. When forming forgings with complex geometric features such as abrupt cross-sections, stiffeners, and flanges, it is very easy to cause forming defects such as folding and cracking due to insufficient filling and stress concentration.

[0003] Currently, magnesium alloy forging research is mostly focused on laboratory exploration of simple structural components. Research on the forming process and stability control of complex load-bearing components such as crankshafts remains scarce. Furthermore, mature aluminum alloy forging technology cannot be directly applied due to the fundamental differences in crystal structure and plastic forming ability between magnesium and aluminum alloys. The current production of ZK60 magnesium alloy components largely relies on semi-solid casting or pressure casting processes. Components produced by these processes are prone to defects such as porosity, shrinkage porosity, and second-phase segregation, making it difficult to meet the stringent requirements of automotive crankshafts for high strength, high fatigue performance, and dimensional accuracy. In addition, existing magnesium alloy forging process research is mainly experimental, lacking systematic research combining finite element numerical simulation and experimental verification. This makes it difficult to accurately reveal the stress field, strain field, and microstructure evolution during the forming process, resulting in low process optimization efficiency and poor reliability, severely restricting the precision forging and large-scale application of complex magnesium alloy forgings. Therefore, it is necessary to propose a finite element simulation-based optimization method for the forging forming process of ZK60 magnesium alloy crankshafts to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to address the existing problems of defects such as porosity, shrinkage, and second-phase segregation in the forging process of complex magnesium alloy structural parts, and the lack of systematic research combining finite element numerical simulation and experimental verification. Therefore, this invention proposes an optimization method and forming method for the forging process of ZK60 magnesium alloy cranks based on finite element simulation.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The optimization method for the forging process of ZK60 magnesium alloy crank based on finite element simulation includes the following steps: S10: Use UG software to draw the geometric model of the forging process, including the upsetting die, the final forging die and the billet; S20: Import the geometric model established in step S10 into the Deform-3D finite element numerical simulation software for finite element numerical simulation. Combine the specific production scenario and equipment parameters to construct a finite element simulation model that fits the actual working conditions, simulate the forging process of the forging, and predict the forming of the die forging. S30: Based on the simulation of step S20, the equivalent stress distribution of each process under the forging forming process is obtained. The forming defects are analyzed by the equivalent stress distribution. The forging forming process includes upsetting and final forging. S40: Based on the forming defects obtained from step S30, the forging process is optimized to obtain an optimized forging process, which includes upsetting, bending and flattening, and final forging. S50: The optimized geometric model of the forging process is drawn using UG software, including the upsetting die, the final forging die, the composite die, and the billet; S60: Import the geometric model established in step S50 into the Deform-3D finite element numerical simulation software for finite element numerical simulation. Combine the specific production scenario and equipment parameters to construct a finite element simulation model that fits the actual working conditions, simulate the forging process of the forging, and predict the forming of the die forging. S70: Based on the simulation of step S60, the equivalent stress distribution of each process under the optimized forging forming process is obtained. The forming quality is analyzed through the equivalent stress distribution, and the design of ZK60 magnesium alloy crank forging process parameters is guided. S80: Based on the ZK60 magnesium alloy crank forging process parameters obtained in step S70, conduct trial production of forgings, record the forming quality of forgings during the production process, and compare it with the simulation results to verify the setting of the ZK60 magnesium alloy crank forging process parameters.

[0006] As a preferred technical solution of this application, step S20 includes constructing the constitutive equation of ZK60 magnesium alloy, comprising the following steps: S210: Select mold material from the Deform material library; S220: The ZK60 magnesium alloy was subjected to isothermal compression test using a thermal simulator to obtain typical peak stress data of the ZK60 magnesium alloy. S230: Based on the Arrhenius constitutive equation and the results of hot compression experiments on ZK60 magnesium alloy at different temperatures and strain rates, the constitutive equation of ZK60 magnesium alloy is obtained, and its expression is as follows: ε= 6.83×1011[sinh(0.02511σ)] 5.68 exp(-209844 / RT), where ε is the strain rate in seconds. -1σ represents the flow stress, in MPa; R is the gas constant, R = 8.314 J / mol·K. -1 T represents absolute temperature, measured in Kelvin (K).

[0007] As a preferred technical solution of this application, the finite element numerical simulation parameters in step S20 include: billet temperature of 400℃; die temperature of 400℃; and upsetting die speed of 2.1×10⁻⁶. -5 mms -1 The upsetting reduction is 40mm; the final forging reduction is 1.3mm; and the friction factor is 0.

[0008] As a preferred technical solution of this application, in step S30, the height-to-diameter ratio of the upsetting region in the forging process is controlled to be less than 3.

[0009] As a preferred technical solution of this application, the finite element numerical simulation parameters in step S60 include: billet temperature of 380℃; die temperature of 380℃; and upsetting die speed of 1×10⁻⁶. -5 mms -1 The bending reduction is 22mm; the flattening reduction is 22mm; and the friction factor is 0.7.

[0010] A forging process for a ZK60 magnesium alloy crankshaft includes the following steps: S10': Provides ZK60 magnesium alloy bars, which are sheared and have their surface oxide scale removed to provide magnesium alloy billets that meet the target forging volume requirements; S20': The billet is fed into a mesh belt heating furnace and heated to 400°C at a heating rate of 10°C / min, and held for 120 min to ensure that the internal temperature uniformity of the billet is ≤±10°C. S30': The heat-insulated billet is quickly transferred into the upsetting die cavity preheated to 400°C, and upsetting is completed by a press; S40': The upset billet is quickly transferred into the cavity of a composite mold preheated to 400°C, and the billet is simultaneously bent and flattened by a 400t press. S50': The bent and flattened billet is quickly transferred into the cavity of the final forging die, which is preheated to 400°C, and the final forging is quickly completed by an 830t press. S60': The corrected forgings are cooled to room temperature by air cooling at a rate of 5℃ / min, and then subjected to visual inspection, dimensional measurement and internal quality inspection.

[0011] As a preferred technical solution of this application, in step S30', upsetting is performed in an upsetting mold. The upsetting mold includes a lower upsetting mold, a height limiting block disposed on the top of the lower upsetting mold, and an upper upsetting mold. The lower upsetting mold is provided with a cavity for accommodating the billet rod and head.

[0012] As a preferred technical solution of this application, in step S40', the composite forming is continuously flattened and bent in the same set of composite molds. The composite mold is an open structure, including a composite upper mold and a matching composite lower mold. The composite upper mold includes an upper mold boss and an upper mold recess, and the composite lower mold includes a lower mold recess and a lower mold protrusion.

[0013] As a preferred technical solution of this application, in step S50', the final forging is carried out in the final forging mold, which is an open structure including an upper final forging mold and a lower final forging mold; the upper final forging mold and the lower final forging mold are provided with matching square locks.

[0014] As a preferred technical solution of this application, the ZK60 magnesium alloy crank includes a flange, reinforcing ribs, and a bent rod section.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention focuses on the ZK60 magnesium alloy crankshaft, a complex load-bearing component that has not been fully studied. It fills a gap in existing research on the forging and forming of complex magnesium alloy crankshafts. Addressing the issues of poor plasticity and difficulty in forming complex structural parts of ZK60 magnesium alloy, this invention innovatively combines finite element numerical simulation with experimental verification using Deform finite element numerical simulation software. It designs upsetting pre-forming and bending / flattening pre-forming processes and optimizes forging process parameters, overcoming the limitations of low efficiency and insufficient accuracy in traditional experimental optimization. This effectively solves problems such as cracking tendency, incomplete filling, and folding defects in the forging process of ZK60 magnesium alloy. Finally, through industrial-scale trial production verification, magnesium alloy crankshaft forgings with dimensional accuracy and mechanical properties meeting standards were successfully obtained. This provides a reliable technical solution for lightweighting and industrial applications in vehicles, promoting the large-scale application of magnesium alloys in key automotive components.

[0016] 2. In this invention, the crank forging rod has a curved arc structure. This is because when the billet is placed in the final forging die after upsetting, the billet slides from the upper die to the lower die, causing the billet to slide towards the large end of the crank, resulting in unstable positioning and material flowing towards the front end of the flash chamber. Therefore, two pre-forming processes, bending and flattening, are added after the upsetting process to pre-distribute and shape the material in each part of the billet, which facilitates the full filling of the complex parts of the crank forging in the subsequent final forging process and promotes better filling of the entire cavity with metal.

[0017] 3. This invention integrates the flattening and bending pre-forming processes into a single composite mold for continuous completion, reducing process transitions and secondary heating steps, shortening the production cycle, and improving production efficiency. Simultaneously, the optimized metal flow path and reasonable material pre-distribution reduce the forming load compared to traditional processes, alleviating equipment burden, extending mold life, and lowering production costs. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the optimization method provided by the present invention; Figure 2 This is an equivalent stress distribution diagram for the upsetting process in forging. Figure 3 This is an equivalent stress distribution diagram of the final forging process in the forging forming process; Figure 4 This is an equivalent stress distribution diagram of the bending and flattening processes in the optimized forging forming process; Figure 5 This is an equivalent stress distribution diagram of the final forging process in the optimized forging forming process. Figure 6 This is one of the optimized forging process flow diagrams provided by the present invention; Figure 7 This is a schematic diagram of the upsetting die. Figure 8 This is a schematic diagram of the composite mold. Figure 9 This is a schematic diagram of the final forging die. Figure 10 The second optimized forging process flow diagram provided by the present invention; Figure 11 A front view of the ZK60 magnesium alloy crank provided for this invention; Figure 12 A bottom view of the ZK60 magnesium alloy crank provided for this invention; Figure 13 A side view of the ZK60 magnesium alloy crank provided by the present invention; Figure 14 Physical images (front and back) of the ZK60 magnesium alloy crank provided for this invention; Figure 15 The sampling location diagram and tensile strain diagram of the ZK60 magnesium alloy crank provided for this invention. Figure 16 A cross-sectional view of the ZK60 magnesium alloy crank and a metallographic sample position diagram provided for this invention. Figure 17Metallographic images of sample 1#, sample 2#, sample 8#, and sample 15# of ZK60 magnesium alloy crank provided for this invention. Figure 18 EBSD images of sample 1#, sample 2#, sample 8#, and sample 15# of the ZK60 magnesium alloy crank provided for this invention. Figure 19 The internal metallographic image of the ZK60 magnesium alloy billet sample for multi-directional forging provided by the present invention.

[0019] Figure 20 EBSD image of a multi-directional forging specimen of ZK60 magnesium alloy billet provided by the present invention.

[0020] In the diagram: 110, lower upsetting die; 111, cavity; 120, height limiting block; 130, upper upsetting die; 210, composite upper die; 220, composite lower die; 310, final forging upper die; 320, final forging lower die; 410, flange; 420, reinforcing rib; 430, bending rod. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] like Figure 1 As shown, this embodiment proposes an optimization method M10 for the forging process of ZK60 magnesium alloy crank based on finite element simulation. M10 includes S10, S20, S30, S40 and S50.

[0023] A method M10 for optimizing the forging process of ZK60 magnesium alloy cranks based on finite element simulation includes: S10: Use UG software to draw the geometric model of the forging process, including the upsetting die, the final forging die, and the billet.

[0024] That is, using 3D modeling software, such as UG, to draw geometric models of the upsetting mold, the final forging mold, and the billet involved in the forging process.

[0025] It should be noted that, referring to Figure 11 , Figure 12 , Figure 13 , Figure 14The ZK60 magnesium alloy crank has a flange 410, reinforcing ribs 420, and a bent rod portion 430. The flange has four mounting holes, the center of which is only 52mm from the center of the forging. The aforementioned reinforcing rib structure is provided between the rod portion and the four flange claws. This integrated structure causes drastic changes in the crank's cross-sectional dimensions and shape, resulting in complex metal flow paths and uneven filling resistance during hot forging of the aluminum alloy. This makes it difficult to fully fill the mold cavity, easily leading to forming defects such as insufficient material in the flange claws and folding in the reinforcing rib area, becoming a core factor restricting the improvement of crank yield.

[0026] Based on the above method, further, S20: import the geometric model established in step S10 into the Deform-3D finite element numerical simulation software for finite element numerical simulation, combine the specific production scenario and equipment parameters to construct a finite element simulation model that fits the actual working conditions, simulate the forging process of the forging, and predict the forming of the die forging.

[0027] Specifically, the geometric models of the upsetting die, final forging die, and billet obtained in step S10 are imported into the Deform-3D finite element numerical simulation software. These models are then combined with specific production scenarios and equipment parameters, such as a billet temperature of 400℃, a die temperature of 400℃, and an upsetting die speed of 2.1 × 10⁻⁶. -5 mms -1 With an upsetting reduction of 40mm, a final forging reduction of 1.3mm, and a friction factor of 0.3, a finite element simulation model that closely matches the actual working conditions is constructed to simulate the forging process and predict the forming process of the die forging.

[0028] Furthermore, step S20 includes the construction of the constitutive equation for the ZK60 magnesium alloy, comprising the following steps: S210: Select mold material from the Deform material library.

[0029] Specifically, the mold materials are all H13 mold steel, which can be obtained from the Deform material library.

[0030] S220: The ZK60 magnesium alloy was subjected to isothermal compression test using a thermal simulator to obtain typical peak stress data of the ZK60 magnesium alloy.

[0031] Specifically, since the billet is ZK60 magnesium alloy, which is not available in the Deform material library, a Gleeble thermal simulator is needed to simulate it at 240-440℃ for 0.001-1s. -1 Isothermal compression tests were conducted on ZK60 magnesium alloy within a certain range to obtain typical peak stress data. Then, referring to the physical properties of ZK60 magnesium alloy, numerical simulations or empirical equations were obtained.

[0032] S230: Based on the Arrhenius constitutive equation and the results of hot compression experiments on ZK60 magnesium alloy at different temperatures and strain rates, the constitutive equation of ZK60 magnesium alloy is obtained, and its expression is as follows: ε= 6.83×1011[sinh(0.02511σ)] 5.68 exp(-209844 / RT), where ε is the strain rate in seconds. -1 σ represents the flow stress, in MPa; R is the gas constant, R = 8.314 J / mol·K. -1 T represents absolute temperature, measured in Kelvin (K).

[0033] Specifically, based on the Arrhenius constitutive equation and the results of hot compression experiments on ZK60 magnesium alloy at different temperatures and strain rates, the constitutive equation of ZK60 magnesium alloy is obtained, and its expression is as follows: ε= 6.83×1011[sinh(0.02511σ)] 5.68 The equation exp(-209844 / RT) should be used. It should be noted that sinh is a hyperbolic sine function, a core member of the hyperbolic function family. This constitutive equation can be used to characterize the correlation between strain rate and peak stress during hot deformation of ZK60 magnesium alloy across the entire stress range, providing theoretical support for optimizing stress levels and energy consumption parameters during hot working by controlling the strain rate.

[0034] As a preferred embodiment, based on the above method, further, S30: based on the simulation of step S20, the equivalent stress distribution of each process under the forging forming process is obtained, and the forming defects are analyzed by the equivalent stress distribution. The forging forming process includes upsetting and final forging.

[0035] Specifically, through the finite element simulation in step S20, the equivalent stress distribution of each process in the forging process is obtained. The equivalent stress distribution reflects the changing trend of internal stress in the material during the forging process, which helps to determine whether the material flow is uniform and whether there is local stress concentration. Therefore, forming defects can be analyzed based on the equivalent stress distribution. It should be noted that this forging process includes upsetting and final forging. The purpose of the upsetting process is to improve material utilization and reduce the problem of insufficient filling at the four cleats of the large end of the magnesium alloy crank. The upsetting process evenly concentrates the material of the bent rod 430 to the large end of the billet, forming a drumstick shape, which facilitates subsequent bending and flattening processes. The purpose of the final forging process is to meet the final design dimensions and realize the subsequent processing and assembly of the crank.

[0036] Upsetting is a forging process that achieves shaping by reducing the billet height and increasing the cross-sectional area. This process uses partial upsetting, primarily to increase the cross-sectional area of ​​the crank flange. Upsetting helps to: 1) break down the dendritic structure within the cast steel ingot; 2) refine the grain structure within the forging; 3) improve the transverse mechanical properties of magnesium alloy forgings; and 4) reduce material anisotropy. Its equivalent stress distribution is as follows: Figure 2 As shown.

[0037] Final forging is a crucial step in the forging process. It is defined as the process of completing the final forming in the final forging die cavity. The main purpose of this step is to precisely control the dimensional accuracy and surface quality of the forging, thereby meeting the requirements of product design and technical specifications. Figure 3 Simulation of the stress field distribution of the billet during the final forging process revealed that the rear claw cavity of the crank large-end flange was not fully filled, and excess material flowed towards the front end of the flash bin. This is because the crank forging has a curved arc structure in the rod section. When the billet is placed in the final forging die after upsetting, it slides along with the upper die to the lower die, causing the billet to slide towards the large end of the crank, resulting in unstable positioning. Consequently, material flows towards the front end of the flash bin, especially at the large-end flange area of ​​the crank, where the projected area is large. The drum-shaped round bar formed after local upsetting is difficult to place accurately, leading to a high scrap rate during production. See details for specific defects. Figure 3 As shown in the middle red circle.

[0038] Based on this, further, S40: Based on the forming defects obtained from step S30, the forging forming process is optimized to obtain an optimized forging forming process, which includes upsetting, bending and flattening, and final forging.

[0039] Specifically, after analyzing the forging defects and their causes during the final forging process, and considering both process feasibility and production efficiency, two pre-forming processes, bending and flattening, are added after the upsetting process to obtain the optimized forging process. Furthermore, the optimized forging process includes upsetting, bending and flattening, and final forging.

[0040] Based on the above method, further, S50: Use UG software to draw the optimized geometric model of the forging forming process, including upsetting die, final forging die, composite die and billet.

[0041] Specifically, 3D modeling software, such as UG, is used to create optimized geometric models of the upsetting dies, final forging dies, composite dies, and billets involved in the forging process.

[0042] Based on the above method, further, S60: import the geometric model established in step S50 into the Deform-3D finite element numerical simulation software for finite element numerical simulation, combine the specific production scenario and equipment parameters to construct a finite element simulation model that fits the actual working conditions, simulate the forging process of the forging, and predict the forming of the die forging.

[0043] Specifically, the geometric models of the upsetting die, final forging die, composite die, and billet obtained in step S50 are imported into the Deform-3D finite element numerical simulation software. Combined with specific production scenarios and equipment parameters, such as billet temperature, die temperature, upsetting upper die speed, upsetting reduction, final forging reduction, and friction factor, a finite element simulation model that fits the actual working conditions is constructed to simulate the optimized forging process and predict the forming process of the die forging under the optimized process.

[0044] As a preferred embodiment, based on the above method, further, S70: based on the simulation of step S60, the equivalent stress distribution of each process under the optimized forging forming process is obtained, the forming quality is analyzed through the equivalent stress distribution, and the design of ZK60 magnesium alloy crank forging process parameters is guided.

[0045] Specifically, step S60 simulation is used to obtain the equivalent stress distribution of each process under the optimized forging process, so as to reflect the changing trend of internal stress of the material during the optimized forging process.

[0046] Reference Figure 4 The bending and flattening processes are integrated into a single composite die, achieving process integration. This effectively improves the final forging positioning problem and significantly enhances production efficiency. Analysis of the equivalent stress distribution in the bending and flattening processes reveals that the flattening process initially employs an open die structure, with the upper composite die initially contacting the large end of the billet. At this point, the metal flow resistance in the transition area between the two ends of the billet and the cavity of the composite die is relatively low, resulting in a high metal flow velocity, reaching a maximum of approximately 650 mm / s. As the upper composite die continues to press down, the billet rod gradually contacts the protrusion of the lower composite die, the contact area gradually increases, and the metal begins to undergo plastic deformation. The flow velocity decreases accordingly, eventually dropping to approximately 100 mm / s, while the forging load gradually increases. Throughout the flattening process, the metal flow transitions from rapid free deformation to controlled plastic forming, ultimately requiring a maximum forging pressure of approximately 633 kN.

[0047] Reference Figure 5After bending and flattening processes, the material pre-distribution of various parts of the billet has been initially formed. Entering the final forging process, the main goal is to fully fill the long rod section and the four-jaw area of ​​the flange, and to squeeze excess metal into the flash groove, thereby promoting better filling of the entire cavity. After the process transition, the billet contacts the final forging cavity. As the upper die of the final forging continues to press down, the flash gradually flows outwards, with a metal flow velocity reaching up to 900 mm / s. At this time, the metal at the large end of the crank forging, driven by the flash on both sides, flows into the cavity, further completing the filling. Simultaneously, under the action of extrusion pressure, the inclined bottom skin formed in the pre-forging stage begins to flow into the skin compartment in the final forging process, helping to improve the overall forming quality of the forging. Figure 5 It can be seen that when the forming is nearing completion, most of the sloping bottom connecting skin has flowed into the connecting skin compartment of the final forging die cavity, while the flash on the outer periphery of the forging is still discharged outward at a relatively high speed.

[0048] As a preferred embodiment, based on the above method, further, S80: based on the ZK60 magnesium alloy crank forging process parameters obtained in step S70, conduct trial production of forging, record the forming quality of forging during the production process, and compare it with the simulation results to verify the setting of the ZK60 magnesium alloy crank forging process parameters.

[0049] Specifically, based on the finite element numerical simulation process and results of the above forming processes, the forging process parameters of ZK60 magnesium alloy crank were obtained. Forging production trial was carried out, the forming quality of the forging during the production process was recorded, and the results were compared with the simulation results to verify the setting of the forging process parameters of ZK60 magnesium alloy crank.

[0050] Reference Figure 6 , Figure 10 Based on the aforementioned optimized method for forging ZK60 magnesium alloy crankshafts, this application also provides a forging process, including the following steps: S10': Provides ZK60 magnesium alloy bars, which are sheared and have their surface oxide scale removed to provide magnesium alloy billets that meet the target forging volume requirements.

[0051] S20': The billet is fed into a mesh belt heating furnace and heated to 400℃ at a heating rate of 10℃ / min, and held at that temperature for 120min to ensure that the internal temperature uniformity of the billet is ≤±10℃.

[0052] S30': The heat-insulated billet is quickly transferred into the cavity of the upsetting mold preheated to 400°C, and upsetting is completed by a press.

[0053] S40': The upset billet is quickly transferred to the cavity of a composite mold preheated to 400°C, and the billet is simultaneously bent and flattened by a 400t press.

[0054] S50': The bent and flattened billet is quickly transferred to the cavity of the final forging die, which is preheated to 400°C, and the final forging is quickly completed by an 830t press.

[0055] S60': The corrected forgings are cooled to room temperature by air cooling at a rate of 5℃ / min, and then subjected to visual inspection, dimensional measurement and internal quality inspection.

[0056] Furthermore, refer to Figure 7 To address the structural characteristics of the crankshaft's large end, a specialized upsetting process was designed and developed. In step S30', upsetting is performed in an upsetting mold, which includes a lower upsetting mold 110, a height-limiting block 120 positioned at the top of the lower upsetting mold, and an upper upsetting mold 130. The lower upsetting mold 110 has a cavity 111 for accommodating the rod and head of the billet. This cavity 111 is used to accommodate the connection between the rod and head of the billet, so as to form the forging head during upsetting. The specific implementation process is as follows: the billet is precisely preheated to 400±20℃ in a chain furnace and held for 90 minutes to ensure that the material reaches the optimal plastic deformation state.

[0057] Subsequently, upsetting was performed on a 400t mechanical press. The corner radius of the upsetting die cavity was R15±2mm to achieve reasonable metal flow and finally obtain a preform shape that meets the requirements of die forging. This upsetting process fully considers the activation characteristics of the (0001)<11-20> slip system of magnesium alloy HCP structure at high temperature, which can effectively avoid cracking defects during the forming process and provide a high-quality blank with stable dimensions and uniform structure for subsequent die forging processes.

[0058] Furthermore, refer to Figure 8 To address the forming challenges of the large-end flange of magnesium alloy crankshafts, in step S40', composite forming involves continuous flattening and bending operations within the same composite mold. The composite mold has an open structure, comprising a composite upper mold 210 and a matching composite lower mold 220. The composite upper mold includes an upper mold boss 211 and an upper mold recess 212, while the composite lower mold includes a lower mold recess 221 and a lower mold protrusion 222. Thus, as the composite upper mold 210 and the composite lower mold 220 come into contact, radial flow of metal can be promoted during flattening, effectively solving the filling defects caused by abrupt changes in cross-sectional area.

[0059] It should be noted that the horizontal dimension of the upper die recess 211 of the composite upper die 210 is strongly related to the dimension of the ZK60 magnesium alloy crank bending rod 430. Specifically, in this embodiment, the horizontal dimension of the upper die recess 211 is set to three-fifths of the dimension of the ZK60 magnesium alloy crank bending rod 430. For example, if the horizontal dimension of the upper die recess 211 is 90mm and the dimension of the ZK60 magnesium alloy crank bending rod 430 is 150mm, the ratio of the two is 90 / 150=3 / 5. Furthermore, the horizontal dimension of the lower die protrusion 222 in the composite lower die 220 is strongly correlated with the vertical drop dimension between the ZK60 magnesium alloy crank bending rod 430 and the flange surface. Specifically, in this embodiment, the horizontal dimension of the lower die protrusion 222 is nine-tenths of the vertical drop dimension between the ZK60 magnesium alloy crank bending rod 430 and the flange surface. For example, if the horizontal dimension of the lower die protrusion 222 is 23.4 mm and the vertical drop dimension between the ZK60 magnesium alloy crank bending rod 430 and the flange surface is 26 mm, the ratio is 23.4 / 26 = 9 / 10. This structural design allows for simultaneous bending and flattening of the upset blank during a single pre-forming process.

[0060] Furthermore, refer to Figure 9 In step S50', the final forging is performed inside the final forging die. The final forging die has an open structure and is assembled at the center of the die frame of the press worktable, i.e., at the impact center of the press. This design can effectively improve the flow characteristics of metal inside the final forging cavity and promote the metal billet to fully fill the die cavity of the final forging die. Specifically, the final forging die includes an upper final forging die 310 and a lower final forging die 320, and the upper final forging die 310 and the lower final forging die 320 are provided with matching square latches. The latch gap is strictly controlled to be 0.1mm.

[0061] Based on the optimized finite element numerical simulation process and results of the forging forming process, the forging process parameters of ZK60 magnesium alloy crank were obtained. Forging production trials were then conducted. The key forming areas of the crank forging are the fork-shaped connection and the journal transition zone. These areas have complex shapes and large cross-sectional variations, making them prone to defects such as incomplete filling and corner collapse. Tensile specimens were cut longitudinally along the crank shaft. Mechanical property tests were performed at room temperature according to GB / T 228.1—2021 standard, with the tensile direction parallel to the main forging deformation direction. The stress-strain curve of the ZK60 magnesium alloy crank was obtained as follows: Figure 15 As shown, by Figure 15It is known that the forged magnesium alloy crank has a tensile strength of 337.2 MPa, a yield strength of 268.4 MPa, and an elongation after fracture of 10.8%. All these indicators are superior to the standard reference values ​​for ZK60 forgings and significantly higher than the tensile strength (310 MPa) of the replaced 6061 aluminum alloy forgings. Notably, the ZK60 magnesium alloy crank, while maintaining high strength, also achieves an elongation of 10.8%, demonstrating excellent plasticity matching. This synergistic improvement in strength and plasticity is mainly attributed to two aspects: firstly, the fine-grained structure effectively reduces stress concentration caused by dislocation pile-up, delaying the initiation and propagation of microcracks; secondly, the reasonable crystal orientation formed during forging weakens the basal surface texture strength, promotes the activation of non-basal surface slip systems, and improves deformation coordination.

[0062] Meanwhile, to verify the performance improvement brought about by the optimized forging process compared to the billet, the ZK60 magnesium alloy crankshafts were cut into pieces and numbered 1-16, such as... Figure 16 As shown. To clearly observe the internal microstructure of the product, key characteristic areas of the crankshaft in the final forged state were selected, namely, specimens 1#, 2#, 8#, and 15#, for optical microstructure analysis and backscattered electron diffraction analysis, respectively. The metallographic images and EBSD images of the above specimens 1#, 2#, 8#, and 15# are shown below. Figure 17 and Figure 18 As shown. Combining the metallographic diagram and EBSD diagram of the billet (e.g.) Figure 19 and Figure 20 ).observe Figure 17 It can be seen that the final forged microstructure exhibits typical dynamic recrystallization characteristics, and the original extruded grains have undergone sufficient fragmentation and refinement. The end region of the rod ( Figure 17-1 #) The recrystallized grains are uniform in size, with an average grain diameter of approximately 13.6 μm. The grain boundaries are clear and straight, and the number of twins is relatively small, indicating that the deformation in this region is relatively uniform and that relatively complete dynamic recrystallization has occurred. (Central region of the bar) Figure 17-8 #) The average grain diameter is approximately 11.1 μm, with clear and straight grain boundaries. Flange transition zone ( Figure 17-15 #) The grain size is slightly coarse, averaging about 13.4 μm. A small number of incompletely recrystallized elongated grains are visible in some areas. This is due to the drastic changes in cross-section and complex metal flow in this region, resulting in uneven strain distribution in different parts. Observation Figure 18It is evident that the final forged microstructure consists of fine equiaxed grains, with high-angle grain boundaries dominating (76% having an orientation difference angle >15°), indicating that dynamic recrystallization proceeded sufficiently. Simultaneously, a small number of low-angle subgrain boundaries (orientation difference angle 2°~5°) remain within the grains. These substructures represent transitional morphologies during dynamic recrystallization, reflecting incomplete dislocation rearrangement and annihilation during deformation. EBSD analysis further reveals the mechanism by which the forging process regulates crystal orientation: multi-directional deformation paths induce multi-axis grain rotation, effectively weakening the strong basal texture of the original extruded state. Simultaneously, the high-temperature condition (400℃) activates cylindrical and conical slip, reducing the dependence of deformation on twins and thus mitigating the risk of stress concentration at twin boundaries. This synergistic optimization of microstructure and texture allows the ZK60 magnesium alloy crank to achieve excellent plasticity while maintaining high strength.

[0063] Comprehensive analysis shows that the optimized four-step composite forming process successfully achieved grain refinement and texture weakening in ZK60 magnesium alloy. The combined effect of fine recrystallized grains and dispersed basal texture reduced stress concentration during deformation and suppressed microcrack initiation, effectively solving the problem of easy cracking during magnesium alloy forging. The formation of the fine-grained structure benefits from both the geometric dynamic recrystallization during the multi-step deformation process and the low stacking fault energy of magnesium alloy, which facilitates continuous dynamic recrystallization. This fine-grained structure lays the structural foundation for subsequent improvements in mechanical properties.

[0064] The actual production verification results are shown in Table 1 below.

[0065] Table 1 - Statistical Table of Verification Results for ZK60 Magnesium Alloy Forged Cranks Defect types Common locations Proportion fold Inner side of the arm claw, at the reinforcing ribs none Collapsed corner Flange and arm connection ≤1.1% Underfill Arm claw end, rod tail end none Production verification results show that, through the Deform finite element numerical simulation software, the upsetting preforming and bending and flattening preforming processes were creatively designed, and the forging process parameters were optimized. This solved problems such as cracking tendency, incomplete filling, and folding defects in the ZK60 magnesium alloy forging process. Therefore, the method of combining Deform numerical simulation software with experimental verification can accurately control the forming process parameters and obtain qualified ZK60 magnesium alloy forged cranks, providing a reliable technical solution for vehicle lightweighting and industrial applications.

[0066] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described herein. Although the present invention has been described in detail with reference to the above embodiments, the present invention is not limited to the specific embodiments described above. Therefore, any modifications or equivalent substitutions to the present invention, as well as all technical solutions and improvements that do not depart from the spirit and scope of the invention, are covered within the scope of the claims of the present invention.

Claims

1. An optimization method for the forging process of ZK60 magnesium alloy crank based on finite element simulation, characterized in that, Includes the following steps: S10: Use UG software to draw the geometric model of the forging process, including the upsetting die, the final forging die, and the billet; S20: Import the geometric model established in step S10 into the Deform-3D finite element numerical simulation software for finite element numerical simulation. Combine the specific production scenario and equipment parameters to construct a finite element simulation model that fits the actual working conditions, simulate the forging process of the forging, and predict the forming of the die forging. Step S20 includes constructing the constitutive equation of ZK60 magnesium alloy, comprising the following steps: S210: Select mold material from the Deform material library; S220: The ZK60 magnesium alloy was subjected to isothermal compression test using a thermal simulator to obtain typical peak stress data of the ZK60 magnesium alloy. S230: Based on the Arrhenius constitutive equation and the results of hot compression experiments on ZK60 magnesium alloy at different temperatures and strain rates, the constitutive equation of ZK60 magnesium alloy is obtained, and its expression is as follows: ε = 6.83 × 10 11 [sinh(0.02511σ)] 5.68 exp(-209844 / RT), where ε is the strain rate in seconds. -1 σ represents the flow stress, in MPa; R is the gas constant, R = 8.314 J / mol·K. -1 T represents absolute temperature, measured in Kelvin (K). S30: Based on the simulation of step S20, the equivalent stress distribution of each process under the forging forming process is obtained. The forming defects are analyzed by the equivalent stress distribution. The forging forming process includes upsetting and final forging. S40: Based on the forming defects obtained from step S30, the forging process is optimized to obtain an optimized forging process, which includes upsetting, bending and flattening, and final forging. S50: The geometric model of the optimized forging forming process is drawn using UG software, including upsetting die, final forging die, composite die and billet; the composite die is an open structure, including a composite upper die (210) and a matching composite lower die (220). The composite upper die includes an upper die boss (211) and an upper die recess (212). The composite lower die includes a lower die recess (221) and a lower die protrusion (222). The horizontal dimension of the upper die recess (212) is set to three-fifths of the dimension of the bending rod of the ZK60 magnesium alloy crank. The horizontal dimension of the lower die protrusion (222) is nine-tenths of the vertical drop dimension between the bending rod of the ZK60 magnesium alloy crank and the flange surface. S60: Import the geometric model established in step S50 into the Deform-3D finite element numerical simulation software for finite element numerical simulation. Combined with specific production scenarios and equipment parameters, construct a finite element simulation model that closely matches the actual working conditions to simulate the forging process of the forging and predict the forming of the die forging. The finite element numerical simulation parameters in step S60 include: billet temperature of 380℃; die temperature of 380℃; and upsetting die speed of 1×10⁻⁶. -5 mms -1 The bending reduction is 22mm; the flattening reduction is 22mm; the friction factor is 0.

7. S70: Based on the simulation of step S60, the equivalent stress distribution of each process under the optimized forging forming process is obtained. The forming quality is analyzed through the equivalent stress distribution, and the design of ZK60 magnesium alloy crank forging process parameters is guided. S80: Based on the ZK60 magnesium alloy crank forging process parameters obtained in step S70, conduct trial production of forgings, record the forming quality of forgings during the production process, and compare it with the simulation results to verify the setting of the ZK60 magnesium alloy crank forging process parameters.

2. The method for optimizing the forging process of ZK60 magnesium alloy crankshafts based on finite element simulation according to claim 1, characterized in that, The finite element numerical simulation parameters in step S20 include: billet temperature of 400℃; die temperature of 400℃; and upsetting die speed of 2.1×10⁻⁶. -5 mms -1 The upsetting reduction is 40mm; the final forging reduction is 1.3mm; and the friction factor is 0.

3.

3. The method for optimizing the forging process of ZK60 magnesium alloy crankshafts based on finite element simulation according to claim 2, characterized in that, In step S30, the height-to-diameter ratio of the upsetting region in the forging process is controlled to be less than 3.

4. A forging process for forging ZK60 magnesium alloy cranks based on the optimized method described in any one of claims 1-3, characterized in that, Includes the following steps: S10': Provides ZK60 magnesium alloy bars, which are sheared and have their surface oxide scale removed to provide magnesium alloy billets that meet the target forging volume requirements; S20': The billet is fed into a mesh belt heating furnace and heated to 400°C at a heating rate of 10°C / min, and held for 120 min to ensure that the internal temperature uniformity of the billet is ≤±10°C. S30': The heat-insulated billet is quickly transferred into the upsetting die cavity preheated to 400°C, and upsetting is completed by a press; S40': The upset billet is quickly transferred into the cavity of a composite mold preheated to 400°C, and the billet is simultaneously bent and flattened by a 400t press. S50': The bent and flattened billet is quickly transferred into the cavity of the final forging die, which is preheated to 400°C, and the final forging is quickly completed by an 830t press. S60': The corrected forgings are cooled to room temperature by air cooling at a rate of 5℃ / min, and then subjected to visual inspection, dimensional measurement and internal quality inspection.

5. The forging process according to claim 4, characterized in that, In step S30', upsetting is performed in an upsetting mold. The upsetting mold includes a lower upsetting mold (110), a height limiting block (120) set on the top of the lower upsetting mold, and an upper upsetting mold (130). The lower upsetting mold (110) is provided with a cavity (111) for accommodating the billet rod and head.

6. The forging process according to claim 5, characterized in that, In step S40', the composite forming process involves continuous flattening and bending operations within the same composite mold.

7. The forging process according to claim 6, characterized in that, In step S50', the final forging is carried out in the final forging mold. The final forging mold has an open structure and includes an upper final forging mold (310) and a lower final forging mold (320). The upper final forging mold (310) and the lower final forging mold (320) are provided with matching square locks.

8. The forging process according to claim 4, characterized in that, The ZK60 magnesium alloy crank includes a flange, reinforcing ribs, and a bent rod section.

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