A method and system for controlling delayed cold cracking in magnesium alloy hermetic die castings

Abstract

This application provides a method and system for controlling delayed cold cracking in magnesium alloy airtight die castings. The method includes the following steps: providing a magnesium alloy airtight die casting; heat-treating the magnesium alloy airtight die casting to obtain a first intermediate part; subjecting the first intermediate part to ultrasonic impact treatment to form a stress layer on at least a portion of the surface of the first intermediate part to obtain a second intermediate part; monitoring the hydrogen concentration in situ on the second intermediate part to obtain hydrogen concentration data; obtaining a leakage risk index based on the tensile stress, yield strength, and hydrogen concentration data of the magnesium alloy airtight die casting, and processing the magnesium alloy airtight die casting according to the leakage risk index. The method and system for controlling delayed cold cracking in magnesium alloy airtight die castings provided in this application can solve the problem that existing magnesium alloy airtight die castings may still experience delayed micro-leakage during the storage or service life period even after passing the end-stage leakage detection.

Description

Technical Field

[0001] This application relates to the fields of intelligent manufacturing and metal forming technology, specifically to a control method and system for preventing delayed cold cracking in magnesium alloy airtight die castings. Background Technology

[0002] As new energy vehicles increasingly demand lightweight, integrated, and efficient thermal management, magnesium alloys, due to their low density, high specific strength, and good casting properties, are being used for large, complex, airtight, thick-walled components such as motor housings, reducer housings, and transmission housings. These magnesium alloy airtight die-casting parts are typically formed using high-pressure casting processes and then undergo machining, cleaning, leak detection, and assembly before being put into storage or installed in vehicles.

[0003] In actual production, some magnesium alloy gas-tight die-cast parts, after passing the end-stage leakage test, may still experience micro-leakage of oil and water after several weeks to months of storage or early service. This type of leakage is often not caused by initial macroscopic casting defects, but is triggered by a combination of residual casting tensile stress, processing stress, hydrogen atom segregation, grain boundary weakening, and the slow propagation of subcritical microcracks. It is characterized by its insidious nature, delayed effect, and batch risk.

[0004] Currently, the industry mostly uses single methods to prevent leakage in magnesium alloy gas-tight die-cast parts, including traditional T5 heat treatment, surface shot peening and shot blasting, conventional helium or water testing, and sealing ring compensation. However, these methods all have shortcomings. Traditional T5 heat treatment can only macroscopically reduce some residual tensile stress, and prolonged high-temperature aging may cause hydrogen to re-accumulate at defect sites; shot peening and shot blasting mainly act on the outer surface, making it difficult to cover complex internal cavities such as oil passages, water passages, and bearing holes, and unstable impact strength may cause new surface damage, easily generating new crack sources; conventional helium or water testing can only identify defects that have penetrated through the molding process, but cannot identify subcritical cracks that have not yet penetrated, nor can it provide early warning of inventory risks; sealing ring compensation can only compensate for assembly gaps and cannot solve leakage problems caused by the propagation of microcracks in the matrix. Summary of the Invention

[0005] In view of this, this application provides a method and system for controlling delayed cold cracking of magnesium alloy airtight die castings, which can solve the problem that existing magnesium alloy airtight die castings may still have delayed micro-leakage during the storage period or service life after the end leakage detection is qualified.

[0006] To address the aforementioned technical problems, this application provides a method for controlling delayed cold cracking in magnesium alloy gas-tight die-cast parts, comprising the following steps: Provides airtight die-cast magnesium alloy parts; The first intermediate part is obtained by heat treatment of the magnesium alloy airtight die casting; The first intermediate part is subjected to ultrasonic impact treatment to form a stress layer on at least a portion of the surface of the first intermediate part, thereby obtaining the second intermediate part; In-situ hydrogen concentration monitoring was performed on the second intermediate component to obtain hydrogen concentration data; Leakage risk index is obtained based on tensile stress, yield strength and hydrogen concentration data of magnesium alloy gas-tight die castings, and the magnesium alloy gas-tight die castings are treated according to the leakage risk index.

[0007] In one embodiment, the heat treatment includes three stages performed sequentially: First stage: Keep warm at the first temperature for 0.5h~2h, the first temperature is 280℃~360℃; Second stage: Keep warm at the second temperature for 1 to 4 hours. The second temperature is 40 to 80 degrees lower than the first temperature. The third stage: keep warm at the third temperature for 0.5h to 2h, and the third temperature is 20℃ to 50℃ higher than the second temperature.

[0008] In one embodiment, the heating rate of the heat treatment is 1°C / min to 5°C / min, and the cooling rate is 1°C / min to 3°C / min.

[0009] In one embodiment, the ultrasonic impact treatment uses an ultrasonic impact device to perform scanning treatment on the magnesium alloy airtight die casting. The ultrasonic impact device operates at a frequency of 20kHz-40kHz and an amplitude of 10μm-30μm.

[0010] In one embodiment, the ultrasonic impact device includes a force sensor, a flexible waveguide, and an impact probe, wherein the force sensor is used to control the contact force to be 20N~50N.

[0011] In one embodiment, the thickness of the stress layer is 0.3 mm to 1.2 mm, and the compressive stress of the stress layer is -80 MPa to -180 MPa.

[0012] In one embodiment, in-situ hydrogen concentration monitoring includes: Blind holes are set at the crack-sensitive locations of the magnesium alloy airtight die casting, and palladium film-FBG composite fiber optic hydrogen sensors are installed in the blind holes. Hydrogen concentration data at crack-sensitive locations were obtained using a palladium film-FBG composite fiber optic hydrogen sensor.

[0013] In one embodiment, the leakage risk index is calculated according to formula (1): LRI=α×(σr / σs)+β×(CH / Cth) formula (1) Wherein, LRI (Leakage Risk Index) is the leakage risk index, σr is the tensile stress, σs is the yield strength, CH is the hydrogen concentration, Cth is the critical hydrogen concentration, α and β are weighting coefficients, α+β=1, α is 0.4~0.7, and β is 0.3~0.6.

[0014] In one embodiment, processing the magnesium alloy hermetic die-casting part according to the leakage risk index includes: When the leakage risk index is ≤0.75, it is determined that there is no leakage risk in the magnesium alloy airtight die casting, and the magnesium alloy airtight die casting is allowed to be circulated normally. When 0.75 < Leakage Risk Index < 0.90, it is determined that there is a potential risk of delayed leakage in the magnesium alloy airtight die casting. At least one of the following processes, namely heat treatment, ultrasonic impact treatment, and in-situ hydrogen concentration monitoring, should be repeated on the magnesium alloy airtight die casting until the leakage risk index of the magnesium alloy airtight die casting is ≤ 0.75. When the leakage risk index is ≥0.90, the leakage risk of the magnesium alloy airtight die casting is deemed to exceed the standard, and the magnesium alloy airtight die casting is isolated and its assembly and use are prohibited.

[0015] In one embodiment, after obtaining the leakage risk index based on the tensile stress, yield strength, and hydrogen concentration data of the magnesium alloy hermetic die casting, and processing the magnesium alloy hermetic die casting according to the leakage risk index, an adaptive sealing compensation step is further included. The adaptive sealing compensation step includes: assembling an adaptive sealing ring at the sealing position of the magnesium alloy hermetic die casting. The adaptive sealing ring includes a NiTi shape memory alloy substrate and an elastic metal ring disposed on the outside or inside of the NiTi shape memory alloy substrate.

[0016] In one embodiment, before heat-treating the magnesium alloy airtight die casting to obtain the first intermediate part, the process further includes a filing and preliminary inspection step for the magnesium alloy airtight die casting.

[0017] This application also provides a control system for preventing delayed cold cracking in magnesium alloy airtight die castings, including: The initial inspection module is used to establish a unique identifier for magnesium alloy airtight die castings, record process parameter information, and perform initial defect detection. A heat treatment module is used to heat treat magnesium alloy airtight die-cast parts to obtain the first intermediate part; A stress treatment module is used to perform ultrasonic impact treatment on a first intermediate part to form a stress layer on at least a portion of the surface of the first intermediate part, thereby obtaining a second intermediate part; The hydrogen concentration monitoring module is used to perform in-situ hydrogen concentration monitoring on the second middleware and obtain hydrogen concentration data. The risk assessment module is used to obtain the leakage risk index based on the tensile stress, yield strength and hydrogen concentration data of magnesium alloy airtight die castings, and to process the magnesium alloy airtight die castings according to the leakage risk index. A sealing compensation module is used to provide adaptive sealing at the sealing positions of magnesium alloy hermetic die-cast parts. The final inspection traceability module is used to perform terminal leakage detection on magnesium alloy airtight die-cast parts and upload the full-process data to the database after binding it with a unique identifier.

[0018] The beneficial effects of this application are as follows: By combining heat treatment, ultrasonic impact treatment, in-situ hydrogen concentration monitoring, and treatment of magnesium alloy gas-tight die castings based on leakage risk index, it is possible to provide early warning and control for delayed micro-leakage during the storage or service life of magnesium alloy gas-tight die castings that may still occur after the end-stage leakage detection has passed, thereby improving the long-term airtightness and service reliability of magnesium alloy gas-tight die castings. Firstly, by heat-treating the magnesium alloy gas-tight die castings to obtain a first intermediate part, the tensile stress in the magnesium alloy gas-tight die castings can be reduced, significantly reducing the mechanical driving force for delayed crack propagation, thereby reducing the risk of delayed micro-leakage during the storage or service life of magnesium alloy gas-tight die castings due to stress after the end-stage leakage detection has passed. Secondly, by subjecting the first intermediate component to ultrasonic impact treatment, a stress layer is formed on at least a portion of its surface. This stress layer can cover high-risk locations in complex internal cavities such as oil passages, water passages, and bearing holes, which are difficult to reach through processes like shot peening. The stress layer can counteract the promoting effect of external loads and residual tensile stress on crack initiation and propagation, thereby reducing the risk of delayed micro-leakage during the storage or service life due to stress after the end-of-life leak detection has passed. Thirdly, by monitoring the hydrogen concentration in situ of the second intermediate component and obtaining hydrogen concentration data, in-situ information on the hydrogen concentration in the second intermediate component can be obtained. This provides a basis for identifying the risk of hydrogen-induced delayed cracking, overcoming the limitation of end-of-life leak detection, which only reflects the airtightness at the time of detection and is difficult to predict delayed micro-leakage during the storage or service life. Finally, based on the tensile stress, yield strength, and hydrogen concentration data of magnesium alloy hermetic die castings, a leakage risk index is obtained. The magnesium alloy hermetic die castings are then processed according to the leakage risk index. This allows for the comprehensive quantification of mechanical state and hydrogen concentration factors, enabling the classification and closed-loop control of delayed microleakage risks. Potentially risky parts can be dealt with in a timely manner, reducing the risk that existing magnesium alloy hermetic die castings may still experience delayed microleakage during the inventory or service life even after passing the end-of-life leakage detection. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the three-stage evolution mechanism of delayed cold cracking in magnesium alloy airtight die castings; Figure 2 This is a flowchart of a method for controlling delayed cold cracking of magnesium alloy airtight die castings provided in this application embodiment; Figure 3 This is a comparison chart of the gradient heat treatment temperature curve provided in the embodiments of this application and the traditional isothermal heat treatment temperature curve; Figure 4 This is a schematic diagram of the structure of an ultrasonic impact device and its operation on the inner wall of an oil passage; Figure 5 This is a schematic diagram of the structure of a palladium film-FBG composite fiber optic hydrogen sensor; Figure 6 This is a schematic diagram of the principle of a palladium film-FBG composite fiber optic hydrogen sensor for measuring hydrogen concentration. Figure 7 This is a flowchart of the leakage risk index calculation and decision-making logic; Figure 8 This is a schematic diagram of the adaptive sealing ring in a contracted state; Figure 9 This is a schematic diagram of the adaptive sealing ring in a pressure-triggered expansion state; Figure 10 This is an overall layout diagram of the control method and system for preventing delayed cold cracking of magnesium alloy airtight die castings provided in this application; Figure 11 This is a curve comparing the cumulative leakage rate of magnesium alloy airtight die castings treated with the method of this application and magnesium alloy airtight die castings treated with conventional processes during the inventory period.

[0021] Explanation of key figure labels: 100 Magnesium alloy airtight die casting, 101 Residual tensile stress zone, 102 Hydrogen atoms, 103 Grain boundary / phase boundary, 104 Subcritical microcracks, 105 Through-leakage channel, 110 Initial inspection module, 120 Heat treatment module, 130 Stress treatment module, 140 Hydrogen concentration monitoring module, 150 Risk assessment module, 160 Sealing compensation module, 170 Final inspection traceability module, 180 Full-process data linkage control module, 190 Quality cloud platform, 200 Gradient heat treatment temperature curve, 210 Traditional isothermal heat treatment temperature curve, 220 Ultrasonic impact device, 221 Ultrasonic transducer, 222 Force sensor, 223 Flexible waveguide, 224 Impact probe, 300 Palladium film-FBG composite fiber optic hydrogen sensor, 301 Blind hole, 302 Fiber optic cable, 303 FBG grating, 304 Palladium film, 305 Fiber optic demodulator, 400 Adaptive sealing ring, 410 NiTi shape memory alloy matrix, 420 elastic metal ring, 430 microcrack exit. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0023] The terms "first," "second," and "third" in this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationships and movements between components in a specific orientation (as shown in the figures). If the specific orientation changes, the directional indications also change accordingly. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0024] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0025] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0026] In the description of the embodiments of this application, the technical terms "vertical", "horizontal", "inner" and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0027] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0028] In actual production, some magnesium alloy gas-tight die-cast parts, even after passing end-leak testing, may still experience minor oil and water leaks after several weeks to months of storage or early service. These leaks are triggered by a combination of factors, including residual casting tensile stress, processing stress, hydrogen atom segregation, grain boundary weakening, and the slow propagation of subcritical microcracks.

[0029] Please see Figure 1 , Figure 1This diagram illustrates the three-stage evolution mechanism of delayed cold cracking in magnesium alloy gas-tight die castings. The delayed cold cracking of the magnesium alloy gas-tight die casting 100 can be summarized into three stages. In the first stage, during high-pressure casting and rapid solidification, the shrinkage of the magnesium alloy gas-tight die casting 100 is hindered, resulting in residual tensile stress zones 101 at locations such as areas of abrupt wall thickness changes, bearing seats, water or oil passage intersections, and mounting bosses, generating residual tensile stresses of 50MPa to 250MPa. Subsequent machining (such as milling and boring) further introduces machining stress, leading to a redistribution of the stress field within the magnesium alloy gas-tight die casting 100. In the second stage, during the melting, die casting, and cleaning processes of the magnesium alloy, moisture or organic contaminants decompose to produce hydrogen atoms 102. These hydrogen atoms 102 dissolve and aggregate towards grain boundaries / phase boundaries 103 and dislocation trap sites, leading to a decrease in grain boundary bonding energy and a reduction in local bonding strength. Furthermore, under stress, the magnesium alloy hermetically sealed die-cast part 100 is more prone to developing microcracks (i.e., hydrogen-induced hysteresis cracking). In the third stage, under normal storage or early service conditions, the residual tensile stress and hydrogen segregation work together to cause subcritical microcracks 104, which are less than 10 μm in size, to gradually expand to penetrate the wall thickness, forming micron-sized through-thickness leakage channels 105, ultimately leading to oil and water leakage.

[0030] To resolve the above technical issues, please refer to Figure 2 , Figure 2 This is a flowchart of a method for controlling delayed cold cracking in magnesium alloy gas-tight die castings provided in this application, including the following steps: S100: Provides airtight die-cast magnesium alloy parts.

[0031] In this embodiment, the magnesium alloy material may be AZ91D, AM60B, AE44, or other magnesium alloys suitable for die-casting motor housings, reducer housings, transmission housings, and other die-casting parts.

[0032] S200: File and conduct preliminary inspection of magnesium alloy airtight die castings.

[0033] By conducting an initial inspection of the magnesium alloy hermetic die casting 100, its initial state can be identified before it undergoes heat treatment and ultrasonic impact treatment. This allows for the timely removal of die castings with obvious defects or high initial risks, avoiding resource waste caused by processing die castings with existing macroscopic defects in subsequent processes. For example, X-ray flaw detection, dimensional inspection, and initial leakage detection can be used to eliminate macroscopic shrinkage porosity, air holes, through holes, and assembly defects.

[0034] By establishing a file for each magnesium alloy airtight die casting 100, a unique identifier can be created for each part, recording the alloy grade, die casting batch, wall thickness distribution, hot spot location, oil and water passage structure, machining allowance, and designed sealing location. This file system enables full traceability recording of all process parameters, testing data, and risk levels for each individual casting. This facilitates precise tracking of heat treatment parameters, ultrasonic strengthening status, hydrogen concentration data, and risk management results for each die casting during mass production. It provides data support for batch process optimization and anomaly tracing, thereby improving process consistency and quality control in mass production.

[0035] S300: The first intermediate part is obtained by heat treatment of the magnesium alloy airtight die casting.

[0036] By heat-treating the magnesium alloy airtight die casting 100 to obtain the first intermediate part, the tensile stress in the magnesium alloy airtight die casting 100 can be reduced, the mechanical driving force for delayed crack propagation can be reduced, thereby reducing the risk of delayed micro-leakage of the magnesium alloy airtight die casting 100 due to stress during the storage period or service period after the end leakage detection is qualified.

[0037] Specifically, the heat treatment includes three stages performed sequentially: First stage: Keep warm at the first temperature for 0.5h~2h, the first temperature is 280℃~360℃; Second stage: Keep warm at the second temperature for 1 to 4 hours. The second temperature is 40 to 80 degrees lower than the first temperature. The third stage: keep warm at the third temperature for 0.5h to 2h, and the third temperature is 20℃ to 50℃ higher than the second temperature.

[0038] The first stage involves holding the magnesium alloy gas-tight die casting at a temperature of 280℃ to 360℃ for 0.5h to 2h. This allows the magnesium alloy gas-tight die casting 100 to receive sufficient thermal action, which helps reduce tensile stress in the magnesium alloy gas-tight die casting 100 and promotes hydrogen diffusion and escape, thereby weakening the mechanical driving force for delayed cold crack initiation and propagation and reducing hydrogen-induced risks. Specifically, the holding time at the first temperature can be 0.5h, 1h, 1.5h, 2h, or any range of two of the above values, such as 0.5h~1h, 1h~1.5h, 1.5h~2h, etc.; the first temperature can be 280℃, 300℃, 330℃, 360℃, or any range of two of the above values, such as 280℃~300℃, 300℃~330℃, 330℃~360℃, etc. The second stage involves holding the material at a temperature 40°C to 80°C lower than the first temperature for 1 to 4 hours. This allows for continued release of tensile stress and further hydrogen escape under more moderate temperature conditions than the first stage, reducing the risk of introducing new thermal stress due to a sudden temperature drop. Specifically, the holding time at the second temperature can be 1 hour, 2 hours, 3 hours, or 4 hours, or any range of two of these values, such as 1 hour to 2 hours, 2 hours to 3 hours, or 3 hours to 4 hours. The second temperature can be 40°C, 60°C, or 80°C lower than the first temperature, or any range of two of these values, such as 40°C to 60°C or 60°C to 80°C. The third stage involves holding the material at a temperature 20°C to 50°C higher than the second temperature for 0.5 to 2 hours. This stabilizes the first intermediate component, consolidating the effects of the first two stages in reducing tensile stress and promoting hydrogen escape, suppressing the rebound of tensile stress, and resulting in a lower and more stable stress state for the first intermediate component. The three heat treatment stages described above work together to reduce tensile stress while ensuring hydrogen escape and stable performance of the die-cast parts. Specifically, the third temperature is maintained for 0.5h, 1h, 1.5h, 2h, or any range of two of the above values, such as 0.5h~1h, 1h~1.5h, 1.5h~2h, etc.; the third temperature is 20℃, 30℃, 40℃, 50℃ higher than the second temperature, or any range of two of the above values, such as 20℃~30℃, 30℃~40℃, 40℃~50℃, etc.

[0039] Please see Figure 3 , Figure 3This is a comparison diagram between the gradient heat treatment temperature curve provided in this application embodiment and the traditional isothermal heat treatment temperature curve. In this application embodiment, the gradient heat treatment temperature curve 200 can be determined by using the solidus temperature Tm, yield strength σs, and die casting wall thickness of the magnesium alloy as parameters. The gradient heat treatment temperature curve 200 used in this application includes three stages: the first stage: heating from the initial temperature to the first temperature and holding at the first temperature for initial stress release; the second stage: subsequently cooling to the second temperature and holding at the second temperature for low-diffusion relaxation, wherein the second temperature is lower than the first temperature; the third stage: heating to the third temperature and holding at the third temperature for microstructure equilibrium, and finally cooling to room temperature. The traditional isothermal heat treatment temperature curve 210 adopts a single isothermal holding and simple heating and cooling process mode. The temperature parameters are fixed throughout the process, which easily leads to insufficient internal stress release and large residual tensile stress in the magnesium alloy airtight die casting 100, which can easily induce subsequent hydrogen-induced delayed cold cracking and leakage defects.

[0040] In this embodiment, the heating rate of the heat treatment is 1℃ / min to 5℃ / min, and the cooling rate is 1℃ / min to 3℃ / min. By setting the heating rate within the above range, the magnesium alloy hermetic die casting 100 can be heated more uniformly during the heating process, reducing the risk of new thermal stress caused by excessive temperature difference between the inside and outside of the magnesium alloy hermetic die casting 100 due to excessively rapid heating, and facilitating the stable diffusion and escape of hydrogen, thereby reducing the risk of delayed cold crack initiation and propagation. By setting the cooling rate within the above range, the first intermediate part can release thermal stress slowly and uniformly during the cooling process, reducing the risk of reintroducing tensile stress or causing local stress concentration due to excessively rapid cooling, which helps to consolidate the effect of heat treatment in reducing tensile stress and suppress the initiation and propagation of delayed cold cracks. The heating rate of the heat treatment is 1℃ / min, 3℃ / min, 5℃ / min, or any range of two of the above values, such as 1℃ / min~3℃ / min, 3℃ / min~5℃ / min, etc.; the cooling rate is 1℃ / min, 2℃ / min, 3℃ / min, or any range of two of the above values, such as 1℃ / min~2℃ / min, 2℃ / min~3℃ / min, etc.

[0041] S400: The first intermediate part is subjected to ultrasonic impact treatment to form a stress layer on at least a portion of the surface of the first intermediate part, thereby obtaining the second intermediate part.

[0042] By subjecting the first intermediate component to ultrasonic impact treatment, a stress layer is formed on at least a portion of the surface of the first intermediate component. This stress layer can cover high-risk locations in complex internal cavities such as oil passages, water passages, and bearing holes that are difficult to reach by shot peening. The stress layer can offset the promoting effect of external loads and residual tensile stress on crack initiation and propagation, thereby reducing the risk of delayed micro-leakage during the storage period or service period due to stress after the end-leakage detection is qualified.

[0043] In this embodiment of the application, ultrasonic impact treatment is performed by using an ultrasonic impact device 220 to scan the magnesium alloy airtight die casting 100. The ultrasonic impact device 220 operates at a frequency of 20kHz-40kHz and has an amplitude of 10μm-30μm.

[0044] The scanning process allows the ultrasonic impact to be continuously applied to at least a portion of the surface of the first intermediate part, which is beneficial for forming a continuous and uniform stress layer on the surface of the first intermediate part. By setting the operating frequency within the aforementioned range, the impact frequency and energy output by the ultrasonic impact device 220 can be adapted to the magnesium alloy airtight die-casting part 100. This is beneficial for promoting plastic deformation of the surface layer of the first intermediate part and forming a stress layer to offset or balance tensile stress, while also reducing the risk of insufficient stress layer formation due to inappropriate frequency. By setting the amplitude within the aforementioned range, the energy of a single impact can be kept within an appropriate range, which is beneficial for obtaining a stress layer with a certain depth and continuity, and reduces the risk of insufficient amplitude for effective stress layer formation or excessive amplitude causing surface microcracks or localized damage. The ultrasonic impact device 220 operates at frequencies of 20kHz, 30kHz, 40kHz, or any range of two of the above values, such as 20kHz~30kHz or 30kHz~40kHz. The amplitude of the ultrasonic impact device 220 is 10μm, 20μm, 30μm, or any range of two of the above values, such as 10μm~20μm or 20μm~30μm.

[0045] Please see Figure 4 , Figure 4This is a schematic diagram of the structure of the ultrasonic impact device and its operation on the inner wall of an oil passage. The ultrasonic impact device 220 includes an ultrasonic transducer 221, a force sensor 222, a flexible waveguide 223, and an impact probe 224. The force sensor 222 is used to control the contact force to be 20N~50N. The ultrasonic transducer 221, force sensor 222, flexible waveguide 223, and impact probe 224 are connected in sequence. The impact probe 224 is used to extend into the oil passage of the magnesium alloy airtight die-cast part 100 and to perform ultrasonic impact treatment on the inner wall of the oil passage. The force sensor 222 is used to control the contact force so that the contact force between the impact probe 224 and the surface of the magnesium alloy airtight die-cast part 100 is 20N~50N. The flexible waveguide 223 can adapt to the shape changes of the magnesium alloy hermetic die-casting 100 surface during the scanning process, maintaining a good fit between the impact probe 224 and the surface of the magnesium alloy hermetic die-casting 100. This allows the impact probe 224 to adapt to the geometry of complex internal cavities such as oil passages, water passages, bearing seat holes, and sealing grooves. Combined with the precise control of the contact force by the force sensor 222, the impact probe 224 can maintain a stable contact force even in complex internal cavities. By setting the contact force to 20N~50N, sufficient contact can be maintained between the impact probe 224 and the surface of the magnesium alloy hermetic die-casting 100 to ensure effective transfer of impact energy. At the same time, it reduces the risk of excessive deformation or microcracks on the surface of the magnesium alloy hermetic die-casting 100 due to excessive contact force, and the risk of insufficient impact energy transfer and insufficient stress layer depth due to insufficient contact force. The impact probe 224 can be configured with different end geometries according to the cross-sectional shape of the oil passage, the curvature of the water passage, and the diameter of the bearing hole, and can be scanned using a robot, a multi-axis platform, or a manually assisted fixture. Specifically, the impact probe 224 includes at least one of a cylindrical probe, a ball-shaped probe, and a flat probe, and the probe end of the impact probe 224 is provided with a hard alloy impact element. The force sensor 222 is used to control the contact force to be 20N, 30N, 40N, 50N, etc., or a range of any two of the above values, such as 20N~30N, 30N~40N, 40N~50N, etc.

[0046] The thickness of the stress layer is 0.3mm to 1.2mm, and the compressive stress of the stress layer is -80MPa to -180MPa. By adjusting the thickness of the stress layer within the above range, the stress layer can have sufficient depth to cover the stress concentration areas and micro-defects on the surface and near the surface, which is beneficial to suppressing the initiation and propagation of delayed cold cracks. By adjusting the compressive stress of the stress layer within the above range, the stress layer can have sufficient compressive stress to offset the promoting effect of external load and residual tensile stress on crack initiation and propagation, thereby reducing the risk of delayed micro-leakage during the storage period or service life due to stress after the end-leakage detection is qualified. The thickness of the stress layer is 0.3mm, 0.6mm, 0.9mm, 1.2mm, etc., or any two of the above values ​​within a range, such as 0.3mm~0.6mm, 0.6mm~0.9mm, 0.9mm~1.2mm, etc. The compressive stress of the stress layer is -80MPa, -120MPa, -180MPa, etc., or a range of any two of the above values, such as -80MPa to -120MPa, -120MPa to -180MPa, etc.

[0047] S500: Performs in-situ hydrogen concentration monitoring on the second intermediate component to obtain hydrogen concentration data.

[0048] By monitoring the hydrogen concentration in situ of the second intermediate component and obtaining hydrogen concentration data, in-situ information on the hydrogen concentration in the second intermediate component can be obtained, providing a basis for identifying the risk of hydrogen-induced delayed cracking and making up for the shortcomings of end-of-line leakage detection, which can only reflect the airtightness at the time of detection and is difficult to predict the delayed micro-leakage during the storage period or service life.

[0049] Please see Figure 5 and Figure 6 , Figure 5 This is a schematic diagram of the structure of a palladium film-FBG composite fiber optic hydrogen sensor. Figure 6This is a schematic diagram of a palladium film-FBG composite fiber optic hydrogen sensor for measuring hydrogen concentration. The palladium film-FBG composite fiber optic hydrogen sensor 300 includes an optical fiber 302, an FBG grating 303, a palladium film 304, and a fiber optic demodulator 305. Specifically, the blind hole 301 is arranged at the location of maximum wall thickness in the hermetic die-casting part, near a hot spot, at the bottom of an oil passage, near a bearing housing hole, or other crack-sensitive locations. The palladium film-FBG composite fiber optic hydrogen sensor 300 is installed within the blind hole 301 and fixed with a heat-resistant sealing material. Specifically, one end of the optical fiber 302 is inserted into the blind hole 301, and the FBG grating 303 is disposed on the optical fiber 302 within the blind hole 301, with the outer surface of the FBG grating 303 covered by the palladium film 304. The other end of the optical fiber 302 extends outward and connects to the external fiber optic demodulator 305. When hydrogen gas is present in the local environment within the blind hole 301, the palladium film 304 adsorbs the hydrogen gas, resulting in lattice expansion. The expansion effect directly acts on the FBG grating 303, causing tensile strain and resulting in a wavelength shift in its reflection (denoted as Δλ). The fiber optic demodulator 305 receives and demodulates this reflected wavelength signal, converting the wavelength shift Δλ into a local hydrogen concentration (CH). Figure 6 It can be seen that there is a positive correlation between wavelength drift Δλ and hydrogen concentration CH, and quantitative detection of hydrogen concentration can be achieved through calibration.

[0050] Furthermore, to eliminate the influence of ambient temperature on wavelength drift, a temperature compensation grating can be set on the optical fiber 302. The wavelength drift caused by temperature can be compensated and corrected by the wavelength drift of the temperature compensation grating, thereby improving the accuracy of hydrogen concentration detection. In this embodiment, the measurement accuracy of the palladium film-FBG composite fiber optic hydrogen sensor 300 is not less than 0.1 ppm.

[0051] In one specific implementation, in-situ hydrogen concentration monitoring includes: A blind hole 301 is provided at the crack-sensitive location of the magnesium alloy airtight die casting 100, and a palladium film-FBG composite fiber hydrogen sensor 300 is installed in the blind hole 301. Hydrogen concentration data at crack-sensitive locations were obtained using a palladium film-FBG composite fiber optic hydrogen sensor 300.

[0052] By placing a blind hole 301 at the crack-sensitive location, the palladium film-FBG composite fiber optic hydrogen sensor 300 can be placed directly close to or at the location of delayed cold cracks, thereby specifically acquiring hydrogen concentration data at the crack-sensitive location and improving the correlation between hydrogen concentration data and delayed cold crack risk. Installing the palladium film-FBG composite fiber optic hydrogen sensor 300 within the blind hole 301 utilizes the hydrogen response characteristics of the palladium film 304 and the optical sensing characteristics of the FBG to achieve in-situ hydrogen concentration monitoring at the crack-sensitive location. This facilitates continuous acquisition of hydrogen concentration changes at the crack-sensitive location during storage or service life, providing temporal data support for subsequent leak risk index acquisition based on hydrogen concentration data. Furthermore, the palladium film-FBG composite fiber optic hydrogen sensor 300 uses fiber optic 302 sensing, which features electromagnetic interference resistance and suitability for installation within the blind hole 301, facilitating stable acquisition of hydrogen concentration data in complex locations and improving the reliability of in-situ hydrogen concentration monitoring.

[0053] The palladium film-FBG composite fiber optic hydrogen sensor 300 can also be installed near the threaded hole, in the area adjacent to the sealing groove, or attached to the protective cavity outside the housing. The palladium film 304 in the palladium film-FBG composite fiber optic hydrogen sensor 300 can also be replaced with a hydrogen-sensitive palladium alloy film or other equivalent hydrogen-sensitive materials.

[0054] S600: Based on the tensile stress, yield strength and hydrogen concentration data of magnesium alloy gas-tight die castings, a leakage risk index is obtained, and the magnesium alloy gas-tight die castings are treated according to the leakage risk index.

[0055] Leakage risk index is obtained based on the tensile stress, yield strength, and hydrogen concentration data of the magnesium alloy hermetic die-casting 100. The magnesium alloy hermetic die-casting 100 is then processed according to this leakage risk index. This allows for the comprehensive quantification of mechanical state and hydrogen concentration factors, enabling the classification and closed-loop control of delayed micro-leakage risk. Potentially risky components can be addressed promptly, reducing the risk of delayed micro-leakage during the storage or service life of existing magnesium alloy hermetic die-castings 100 even after passing end-stage leakage detection. Tensile stress can be detected using methods such as X-ray diffraction, blind hole 301 method, and ultrasonic residual stress method.

[0056] In this embodiment of the application, the leakage risk index is calculated according to formula (1): LRI=α×(σr / σs)+β×(CH / Cth) formula (1) Wherein, LRI is the leakage risk index, σr is the tensile stress, σs is the yield strength, CH is the hydrogen concentration, Cth is the critical hydrogen concentration, α and β are weighting coefficients, α+β=1, α is 0.4~0.7, and β is 0.3~0.6.

[0057] Formula (1), by coupling two core variables—the ratio of tensile stress to yield strength and the ratio of real-time hydrogen concentration to critical hydrogen concentration—can simultaneously characterize both stress-driven cracking and hydrogen-induced cracking failure mechanisms, which is beneficial for matching the composite failure characteristics of delayed cold cracking in magnesium alloy gas-tight die castings. Compared with single stress evaluation or single hydrogen content evaluation, this evaluation method can effectively avoid the risk omission and misjudgment caused by the one-sidedness of single parameter evaluation, and can truly reflect the overall long-term gas-tightness failure risk of the casting. Among them, the leakage risk index (LRI) can be calibrated based on batch historical data using linear weights, piecewise functions, logistic regression, random forests, or other machine learning models.

[0058] Furthermore, to improve the comprehensiveness and accuracy of risk assessment, the leakage risk index of this application supports multi-dimensional parameter correction and optimization. Based on actual production conditions, one or more of the following can be selectively superimposed on the hydrogen escape rate correction term, wall thickness mutation coefficient correction term, and historical batch failure rate correction term on the basis of formula (1) to further reduce the risk assessment error and adapt to the leakage risk determination needs under complex production scenarios.

[0059] In this embodiment of the application, the treatment of the magnesium alloy airtight die-cast part 100 according to the leakage risk index includes: When the leakage risk index is ≤0.75, the magnesium alloy airtight die casting 100 is deemed to have no leakage risk and is allowed to be circulated normally. When 0.75 < Leakage Risk Index < 0.90, it is determined that the magnesium alloy airtight die casting 100 has a potential risk of delayed leakage, and at least one of the following processes, namely heat treatment, ultrasonic impact treatment, and in-situ hydrogen concentration monitoring, is re-executed on the magnesium alloy airtight die casting 100 until the leakage risk index of the magnesium alloy airtight die casting 100 is ≤ 0.75. When the leakage risk index is ≥0.90, the leakage risk of the magnesium alloy airtight die casting 100 is determined to be excessive. The magnesium alloy airtight die casting 100 is isolated and its assembly and use are prohibited.

[0060] By setting a three-level judgment standard based on the leakage risk index, the magnesium alloy airtight die casting 100 is classified and treated in a graded manner, forming a closed-loop process. This effectively controls the risk of occasional micro-leakage caused by hydrogen-induced delayed cracking in the subsequent storage and service life of the die casting that has passed the end-of-life leakage test.

[0061] Please see Figure 7 , Figure 7 This is a flowchart illustrating the leakage risk index calculation and decision-making logic. The leakage risk index calculation and decision-making logic is executed by the end-to-end data linkage control module, and specifically includes the following steps: S610: Basic data reading.

[0062] The unique identification (such as a shell QR code) of the magnesium alloy airtight die casting 100 is read by the identification identification reader / writer device, and the alloy grade, production batch and key wall thickness of the magnesium alloy airtight die casting 100 are automatically obtained from the database.

[0063] S620: Mechanical parameter acquisition.

[0064] The residual tensile stress of the magnesium alloy airtight die casting 100 was collected. And read its corresponding yield strength. .

[0065] S630: Hydrogen concentration data acquisition.

[0066] The hydrogen concentration of the magnesium alloy airtight die-cast part 100 was collected during the current monitoring period. and hydrogen escape rate .

[0067] S640: Leakage Risk Index Calculation.

[0068] The leakage risk index is calculated using the formula (1) above. To further improve the accuracy of the assessment, the leakage risk index (LRI) can also be supplemented with correction terms, including but not limited to: hydrogen escape rate correction term, wall thickness mutation coefficient correction term, and historical batch failure rate correction term.

[0069] S650: Based on the calculated leakage risk index, the corresponding decision branch is automatically triggered.

[0070] When the leakage risk index is ≤0.75, the magnesium alloy airtight die casting 100 is deemed to have no leakage risk and is allowed to be processed normally. When 0.75 < leakage risk index <0.90, the magnesium alloy airtight die casting 100 is deemed to have a potential risk of delayed leakage, and at least one of the following processes—heat treatment, ultrasonic impact treatment, and in-situ hydrogen concentration monitoring—must be re-executed on the magnesium alloy airtight die casting 100 until the leakage risk index of the magnesium alloy airtight die casting 100 is ≤0.75. When the leakage risk index is ≥0.90, the leakage risk of the magnesium alloy airtight die casting 100 is deemed to exceed the standard, and the magnesium alloy airtight die casting 100 is isolated and its assembly and use are prohibited.

[0071] S700: An adaptive sealing ring is fitted at the sealing position of the magnesium alloy hermetic die casting.

[0072] After obtaining the leakage risk index based on the tensile stress, yield strength and hydrogen concentration data of the magnesium alloy airtight die casting 100, and processing the magnesium alloy airtight die casting 100 according to the leakage risk index, an adaptive sealing compensation step is also included. The adaptive sealing compensation step includes: assembling an adaptive sealing ring 400 at the sealing position of the magnesium alloy airtight die casting 100. The adaptive sealing ring 400 includes a NiTi shape memory alloy substrate 410 and an elastic metal ring 420 disposed on the outside or inside of the NiTi shape memory alloy substrate 410.

[0073] By assembling a specially structured adaptive sealing ring 400 at the sealing position of the magnesium alloy hermetic die casting 100, a post-treatment hermetic protection reinforcement can be formed for the magnesium alloy hermetic die casting 100. This synergistic effect with the aforementioned stress regulation, ultrasonic strengthening, hydrogen concentration monitoring, and risk closed-loop management processes further offsets the leakage risks caused by minor aging deformation and micro-cracks, thereby improving the long-term service reliability and service life of the mass-produced magnesium alloy hermetic die casting 100. The adaptive sealing ring 400 is composed of a NiTi shape memory alloy matrix 410 and an elastic metal ring 420, possessing excellent deformation adaptive compensation capabilities. The NiTi shape memory alloy matrix 410, relying on its shape memory properties, can generate restoring force or adaptive deformation when the dimensions or fit of the sealing position of the magnesium alloy hermetically sealed die-cast part 100 undergoes minor changes due to factors such as temperature variations, residual stress release, hydrogen-induced micro-deformation, or vibration during storage or service life. This allows the adaptive sealing ring 400 to continue to maintain contact and seal with the sealing position, thereby compensating for the decrease in sealing performance caused by delayed cold cracking or delayed micro-leakage. The elastic metal ring 420, located inside or outside the NiTi shape memory alloy matrix 410, can work synergistically with the NiTi shape memory alloy matrix 410 to provide initial elastic contact force and springback compensation capability. This ensures that the adaptive sealing ring 400 maintains a stable fit with the sealing position after assembly and maintains the seal through elastic deformation when minor deformation or gap changes occur at the sealing position, further improving the reliability and adaptability of the sealing compensation.

[0074] The adaptive sealing ring 400 can adopt an internal expansion, external expansion, lip, or combined structure, and the NiTi shape memory alloy matrix 410 can be combined with stainless steel, elastic alloy, or oil-resistant polymer sealing materials.

[0075] In one specific embodiment, the elastic metal ring 420 includes an S-shaped elastic metal ring 420. Because the S-shaped elastic metal ring 420 has an S-shaped elastic structure, it has a large elastic deformation stroke and rebound compensation capability within a limited installation space.

[0076] Please see Figure 8 and Figure 9 , Figure 8 This is a schematic diagram of the adaptive sealing ring in a contracted state; Figure 9 This is a schematic diagram of the adaptive sealing ring in a pressure-triggered expansion state. (See diagram below.) Figure 8 As shown, under normal conditions where the die-cast part does not leak or reaches the trigger temperature, the adaptive sealing ring 400 maintains its initial contracted state; Figure 9 As shown, when a microcrack develops in the magnesium alloy hermetic die-casting 100 and forms a microcrack outlet 430, the penetration of this microcrack will cause pressure to act on the adaptive sealing ring 400, causing the adaptive sealing ring 400 to expand radially under pressure. When the operating temperature of the magnesium alloy hermetic die-casting 100 is between 80℃ and 120℃, the NiTi shape memory alloy matrix 410 returns to its expanded state. Together, these two components increase the outer diameter of the sealing ring or the radial direction of the sealing lip by 0.2mm to 0.5mm, thereby providing pressure-responsive sealing for the crack outlet or micro-leakage channel.

[0077] S800: Final inspection, warehousing, and traceability of magnesium alloy airtight die castings.

[0078] The magnesium alloy hermetic die-casting part 100 undergoes terminal helium testing or pressure decay testing, and is placed into storage after passing the test. The heat treatment curve, ultrasonic impact parameters, tensile stress data, hydrogen concentration data, leakage risk index (LRI), adaptive sealing ring 400 installation torque, and final inspection results of the magnesium alloy hermetic die-casting part 100 are all bound to a unique identifier and uploaded to the quality database for subsequent batch process optimization and after-sales traceability.

[0079] This application, through the combined use of heat treatment, ultrasonic impact treatment, in-situ hydrogen concentration monitoring, and treatment of magnesium alloy gas-tight die castings 100 based on leakage risk index, can provide early warning and control for potential delayed micro-leakage during the storage or service life of magnesium alloy gas-tight die castings 100 even after the end-leakage detection has passed, thereby improving the long-term gas-tightness and service reliability of magnesium alloy gas-tight die castings 100.

[0080] This application also provides a control system for preventing delayed cold cracking of magnesium alloy airtight die castings, including: a preliminary inspection module 110, a heat treatment module 120, a stress treatment module 130, a hydrogen concentration monitoring module 140, a risk assessment module 150, a sealing compensation module 160, a final inspection traceability module 170, and a full-process data linkage control module 180.

[0081] The initial inspection module 110 is used to establish a unique identifier for the magnesium alloy airtight die casting 100, record process parameter information, and perform initial defect detection. The initial inspection module 110 can associate data generated by subsequent processes with the same die casting, solving the problems of scattered data and difficulty in traceability throughout the entire process, and providing a data foundation for subsequent batch process optimization.

[0082] The heat treatment module 120 is used to heat treat the magnesium alloy hermetic die casting 100 to obtain a first intermediate part. In one specific embodiment, the heat treatment module 120 includes a zoned temperature-controlled furnace, a material rack, a temperature sensor, a furnace temperature PID control unit, and a heat treatment curve storage unit. The heat treatment module 120 can achieve precise control of the heat treatment temperature and traceable storage of the heat treatment curve, which can reduce the tensile stress in the magnesium alloy hermetic die casting 100, further reduce the mechanical driving force for delayed crack propagation, thereby reducing the risk of delayed micro-leakage of the magnesium alloy hermetic die casting 100 due to stress during the storage period or service life after passing the end-leakage detection.

[0083] The stress treatment module 130 is used to perform ultrasonic impact treatment on the first intermediate part to form a stress layer on at least a portion of the surface of the first intermediate part, thereby obtaining a second intermediate part. The stress treatment module 130 includes an ultrasonic transducer 221, a force sensor 222, a flexible waveguide 223, an impact probe 224, and a multi-axis motion mechanism. The stress treatment module 130 can introduce a controllable stress layer on the surface of the die-casting to counteract or balance the tensile stress in the magnesium alloy hermetic die-casting 100, thereby suppressing the initiation and propagation of delayed cold cracks.

[0084] The hydrogen concentration monitoring module 140 is used to perform in-situ hydrogen concentration monitoring on the second intermediate device and acquire hydrogen concentration data. The hydrogen concentration monitoring module 140 includes a palladium film-FBG composite fiber optic hydrogen sensor 300, which includes an optical fiber 302, an FBG grating 303, a palladium film 304, and an optical fiber demodulator 305.

[0085] The risk assessment module 150 is used to obtain a leakage risk index based on the tensile stress, yield strength, and hydrogen concentration data of the magnesium alloy hermetic die casting 100, and to process the magnesium alloy hermetic die casting 100 according to the leakage risk index. The risk assessment module 150 includes a data acquisition unit, a feature extraction unit, a leakage risk index (LRI) calculation unit, a threshold judgment unit, and a process correction suggestion unit. The risk assessment module 150 can quantitatively integrate parameters such as tensile stress, yield strength, and hydrogen concentration to obtain a leakage risk index, and perform graded judgment and intelligent decision-making based on this index, improving the accuracy of risk assessment and processing efficiency.

[0086] The sealing compensation module 160 is used to perform adaptive sealing at the sealing position of the magnesium alloy hermetic die casting 100. The sealing compensation module 160 includes a NiTi shape memory alloy substrate 410, an elastic metal ring 420, a groove positioning structure, and a torque acquisition device. The sealing compensation module 160 can provide post-installed hermetic protection reinforcement for the magnesium alloy hermetic die casting 100, creating a synergistic effect with the aforementioned stress regulation, ultrasonic strengthening, hydrogen concentration monitoring, and risk closed-loop management processes. This further offsets the leakage risks caused by minor aging deformation and micro-cracks, thereby improving the long-term service reliability and service life of the mass-produced magnesium alloy hermetic die casting 100.

[0087] The final inspection traceability module 170 is used to perform terminal leakage detection on the magnesium alloy airtight die casting 100, and uploads the full-process data to the database after binding it with a unique identifier.

[0088] The end-to-end data linkage control module 180 includes a PLC, an industrial edge gateway, a formula database, a quality cloud platform interface 190, and a casting identification reader / writer. The end-to-end data linkage control module 180 can automatically call up process formulas based on batch data of die-cast parts and perform linkage control on at least one of the following: heat treatment temperature, holding time, ultrasonic frequency, amplitude, feed speed, contact force threshold, and hydrogen monitoring duration. When the baseline hydrogen concentration of a batch of die-cast parts rises or the leakage risk index approaches the warning threshold, the end-to-end data linkage control module 180 can automatically extend the holding time of the low-temperature relaxation section of the heat treatment or increase the number of ultrasonic impact coverages, thereby achieving closed-loop control from detection to process correction.

[0089] By setting up a filing and initial inspection module 110, a heat treatment module 120, a stress treatment module 130, a hydrogen concentration monitoring module 140, a risk assessment module 150, a sealing compensation module 160, a final inspection traceability module 170, and a full-process data linkage control module 180, a closed-loop control system for the entire process from die casting entering the factory to final delivery can be formed. This system can systematically control the risk of delayed micro-leakage of magnesium alloy airtight die castings 100 during the storage period and service life, and significantly improve product batch consistency and long-term service stability.

[0090] Please see Figure 10 , Figure 10This is an overall layout diagram of the control method and system for preventing delayed cold cracking in magnesium alloy gas-tight die castings provided in this application. The control method includes steps S200 to S800 executed sequentially, and the system includes modules corresponding to the above steps: a preliminary inspection module 110, a heat treatment module 120, a stress treatment module 130, a hydrogen concentration monitoring module 140, a risk assessment module 150, a sealing compensation module 160, and a final inspection traceability module 170. Specifically, the preliminary inspection module 110 executes step S200, the heat treatment module 120 executes step S300, the stress treatment module 130 executes step S400, the hydrogen concentration monitoring module 140 executes step S500, the risk assessment module 150 executes step S600, the sealing compensation module 160 executes step S700, and the final inspection traceability module 170 executes step S800.

[0091] Furthermore, the system also includes a full-process data linkage control module 180, which is connected to the initial inspection module 110, heat treatment module 120, stress treatment module 130, hydrogen concentration monitoring module 140, risk assessment module 150, sealing compensation module 160, and final inspection traceability module 170. The full-process data linkage control module 180 is also connected to a quality cloud platform 190 to upload data from each process to the platform for subsequent batch process optimization and after-sales traceability.

[0092] Please see Figure 11 , Figure 11 This is a graph comparing the cumulative leakage rate of magnesium alloy gas-tight die castings treated with the method of this application and those treated with conventional processes during the inventory period. Solid lines represent die castings treated with conventional T5, shot peening, and helium peening processes, while dashed lines represent die casting samples treated with the method of this application. Figure 11 As can be seen, with the increase of the storage time, the cumulative leakage rate of die castings treated by traditional processes continues to rise, reaching approximately 3% to 5% at the end of the 180-day storage cycle. This indicates that traditional processes can only detect formed defects before leaving the factory and cannot effectively suppress delayed leakage failures caused by the release of residual compressive stress and the propagation of hydrogen-induced microcracks during the storage stage. In contrast, the die castings treated by the method of this application maintain a cumulative leakage rate of ≤0.1% during the 180-day storage cycle, significantly suppressing the leakage growth trend. This comparative result confirms that the control method and system for preventing delayed cold cracking of magnesium alloy airtight die castings 100 provided in this application can significantly reduce the risk of delayed cold cracking and microleakage during the storage stage of magnesium alloy airtight die castings 100, and improve the long-term quality stability of batch products.

[0093] It should be noted that, Figure 11The curves and specific data shown are mainly used to express the trend of the technical effect of this application. The specific values ​​of the curves can be replaced according to the measured statistical data of different alloy grades and different test batches.

[0094] Example 1 Example 1 provides a complete process for the processing of AE44 magnesium alloy motor housing.

[0095] A certain type of new energy magnesium alloy motor housing was selected, made of AE44 magnesium alloy, with a wall thickness of 3mm~8mm and a single piece weight of approximately 12kg. The blank was prepared by high-pressure casting. After X-ray inspection to eliminate macroscopic shrinkage porosity, gas holes, and inclusion defects, the bearing holes, mounting surfaces, and oil passage areas were rough-machined. A φ3mm blind hole was reserved for the subsequent installation of a palladium film-FBG composite fiber optic hydrogen sensor.

[0096] The shell was placed in a special rack and fed into a gradient aging furnace for gradient aging heat treatment. The aging program was set as follows: heating to 320℃ at 3℃ / min and holding for 1 hour; cooling to 260℃ at 2℃ / min and holding for 2 hours; then heating to 290℃ at 3℃ / min and holding for 1.5 hours; followed by furnace ventilation cooling to room temperature. After heat treatment, the residual tensile stress in key areas was detected by X-ray diffraction. The test results showed that the original residual tensile stress of the casting was approximately 210 MPa. After the gradient aging heat treatment of this application, the residual tensile stress was reduced to 78 MPa, which meets the safety standard that the residual tensile stress is less than 0.6 times the yield strength of the material. In this embodiment, the yield strength σs of AE44 magnesium alloy is taken as 180 MPa.

[0097] Subsequently, an ultrasonic impact device was used to scan and impact the outer surface of the housing, the inner wall of the bearing housing bore, and the inner wall of the oil passage. The ultrasonic frequency was 28 kHz, the amplitude was 20 μm, and the contact force was controlled within 45 N in a closed loop. A ball-shaped probe was used for the bearing bore, and a flat probe was used for the oil passage plane. After treatment, the key areas were all in a state of residual compressive stress. The measured thickness of the stress layer was 0.7 mm, and the compressive stress was -95 MPa to -135 MPa. The surface roughness Ra increased from 0.6 μm to 1.9 μm, meeting the assembly requirement of Ra ≤ 2.5 μm for the sealing surface.

[0098] A palladium film-FBG composite fiber optic hydrogen sensor was installed inside a φ3mm blind hole in the housing and fixed with high-temperature resistant epoxy resin. The fiber optic cable was connected to a fiber optic demodulator with a wavelength resolution of 1 pm. The housing was placed in a constant temperature warehouse at 25±2℃ and approximately 50% relative humidity for continuous monitoring for 7 days, resulting in an average hydrogen concentration CH=1.8ppm. Taking Cth=2.5ppm, α=0.6, and β=0.4, the LRI was calculated as 0.6×(78 / 180)+0.4×(1.8 / 2.5)=0.548. This LRI value is less than the safety threshold of 0.75, indicating that the leakage risk of the motor housing after this embodiment is within a safe range, allowing it to proceed normally to the subsequent assembly process.

[0099] An adaptive sealing ring, composed of a NiTi shape memory alloy and an S-shaped elastic outer ring, is assembled inside the groove of the oil passage end cap. The outer diameter of the sealing ring forms a 0.05mm interference fit with the assembly groove. A torque-controlled assembly process is used to tighten the end cap bolts with a torque of 25±1 N·m, and the torque data is recorded.

[0100] After assembly, a helium gas tightness test was performed on the casing under a pressure of 0.6 MPa for 5 minutes. The test results showed that the casing leakage rate was less than 1 × 10⁻⁶. -6 Pa·m 3 / s, meeting the factory airtightness standards, the product is deemed qualified and stored in the warehouse.

[0101] Example 2 Example 2 is an accelerated inventory simulation verification.

[0102] Ten AE44 magnesium alloy motor housings from the same batch were also taken. Five of them were treated according to the method described in Example 1, while the other five were treated with conventional T5 aging and shot peening. All housings were placed in an environment of 80°C and 95% relative humidity for 30 days of accelerated aging to simulate approximately 6 months of natural storage. After aging, all housings underwent helium testing.

[0103] The test results show that the leakage rate of all five shells in the test group treated with the process of this application is consistently less than 1×10⁻⁶. - 6 Pa·m 3 / s; Among the five shells in the control group treated with conventional processes, two shells had leakage rates that seriously exceeded the standard, with leakage rates of 3.5×10 -6 Pa·m 3 / s, 4.2×10 -6 Pa·m 3 / s. Upon disassembly and observation of the substandard samples, through-cracks were found at the points of abrupt change in shell wall thickness. This result indicates that the process proposed in this application can effectively reduce the initiation and propagation of delayed microcracks during the storage of magnesium alloy hermetic die-cast parts, significantly reducing the risk of delayed leakage.

[0104] Example 3 Example 3 is an adaptive linkage control for mass production lines.

[0105] During mass production, a unique electronic identification tag is attached to each magnesium alloy motor housing to achieve full life cycle traceability of individual products. All process data, such as heat treatment parameters of die castings, ultrasonic impact parameters, hydrogen concentration monitoring data, residual tensile stress data, and leakage risk index (LRI) calculation results, are uploaded in real time to the full-process data linkage control module and simultaneously stored in the quality cloud platform.

[0106] During mass production monitoring, when the system identified a batch of shells with a baseline hydrogen concentration (CH) greater than 2.2 ppm, the full-process data linkage control module automatically triggered a process adaptive calibration mechanism. This automatically extended the holding time of the low-temperature relaxation phase in the gradient aging process from the original 2 hours to 2.5 hours, and simultaneously increased the ultrasonic shock scan coverage from 2 times to 3 times. After the system's adaptive process adjustment, the leakage risk index (LRI) of all shells in this batch was controlled below 0.70, and no delay / leakage complaints occurred during subsequent inventory and assembly stages.

[0107] The above are merely embodiments of this application and do not limit the scope of this patent application. Any equivalent structural or procedural changes made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of this application.

Claims

1. A method for controlling delayed cold cracking in magnesium alloy airtight die-cast parts, characterized in that, Includes the following steps: Provides airtight die-cast magnesium alloy parts; The magnesium alloy airtight die-casting part is heat-treated to obtain the first intermediate part; The first intermediate part is subjected to ultrasonic impact treatment to form a stress layer on at least a portion of the surface of the first intermediate part, thereby obtaining a second intermediate part; The second intermediate component is subjected to in-situ hydrogen concentration monitoring to obtain hydrogen concentration data; Based on the tensile stress, yield strength, and hydrogen concentration data of the magnesium alloy airtight die casting, a leakage risk index is obtained, and the magnesium alloy airtight die casting is processed according to the leakage risk index.

2. The method for controlling delayed cold cracking of magnesium alloy airtight die-cast parts according to claim 1, characterized in that, The heat treatment comprises three stages performed sequentially: First stage: Keep warm at the first temperature for 0.5h~2h, the first temperature being 280℃~360℃; Second stage: Keep warm at the second temperature for 1 hour to 4 hours, the second temperature being 40°C to 80°C lower than the first temperature; The third stage involves maintaining the temperature at a third temperature for 0.5 to 2 hours, where the third temperature is 20 to 50 degrees Celsius higher than the second temperature.

3. The method for controlling delayed cold cracking of magnesium alloy airtight die-cast parts according to claim 1, characterized in that, The heating rate of the heat treatment is 1℃ / min to 5℃ / min, and the cooling rate is 1℃ / min to 3℃ / min.

4. The method for controlling delayed cold cracking of magnesium alloy airtight die-cast parts according to claim 1, characterized in that, The ultrasonic impact treatment uses an ultrasonic impact device to perform scanning treatment on the magnesium alloy airtight die casting. The ultrasonic impact device operates at a frequency of 20kHz to 40kHz and has an amplitude of 10μm to 30μm.

5. The method for controlling delayed cold cracking of magnesium alloy airtight die-cast parts according to claim 4, characterized in that, The ultrasonic impact device includes a force sensor, a flexible waveguide rod, and an impact probe. The force sensor is used to control the contact force to be 20N~50N.

6. The method for controlling delayed cold cracking of magnesium alloy airtight die-cast parts according to claim 1, characterized in that, The thickness of the stress layer is 0.3mm to 1.2mm, and the compressive stress of the stress layer is -80MPa to -180MPa.

7. The method for controlling delayed cold cracking of magnesium alloy airtight die-cast parts according to claim 1, characterized in that, The in-situ hydrogen concentration monitoring includes: Blind holes are provided at the crack-sensitive locations of the magnesium alloy airtight die casting, and palladium film-FBG composite fiber optic hydrogen sensors are installed in the blind holes. The hydrogen concentration data at the crack-sensitive location is obtained using the palladium film-FBG composite fiber optic hydrogen sensor.

8. The method for controlling delayed cold cracking of magnesium alloy airtight die-cast parts according to claim 1, characterized in that, The leakage risk index is calculated according to formula (1): LRI=α×(σr / σs)+β×(CH / Cth) formula (1) Wherein, LRI is the leakage risk index, σr is the tensile stress, σs is the yield strength, CH is the hydrogen concentration, Cth is the critical hydrogen concentration, α and β are weighting coefficients, α+β=1, α is 0.4~0.7, and β is 0.3~0.

6.

9. The method for controlling delayed cold cracking of magnesium alloy airtight die-cast parts according to claim 1, characterized in that, The treatment of the magnesium alloy airtight die-casting based on the leakage risk index includes: When the leakage risk index is ≤0.75, it is determined that the magnesium alloy airtight die casting has no leakage risk and the magnesium alloy airtight die casting is allowed to be circulated normally. When 0.75 < the leakage risk index < 0.90, it is determined that the magnesium alloy airtight die casting has a potential risk of delayed leakage, and at least one of the heat treatment, ultrasonic impact treatment, and in-situ hydrogen concentration monitoring is re-executed on the magnesium alloy airtight die casting until the leakage risk index of the magnesium alloy airtight die casting is ≤ 0.

75. When the leakage risk index is ≥0.90, it is determined that the leakage risk of the magnesium alloy airtight die casting exceeds the standard, and the magnesium alloy airtight die casting is isolated and its assembly and use are prohibited.

10. The method for controlling delayed cold cracking of magnesium alloy airtight die-cast parts according to claim 1, characterized in that, After obtaining the leakage risk index based on the tensile stress, yield strength, and hydrogen concentration data of the magnesium alloy airtight die casting, and processing the magnesium alloy airtight die casting according to the leakage risk index, an adaptive sealing compensation step is further included. The adaptive sealing compensation step includes: assembling an adaptive sealing ring at the sealing position of the magnesium alloy airtight die casting. The adaptive sealing ring includes a NiTi shape memory alloy substrate and an elastic metal ring disposed on the outside or inside of the NiTi shape memory alloy substrate.

11. The method for controlling delayed cold cracking of magnesium alloy airtight die-cast parts according to claim 1, characterized in that, Before heat treatment of the magnesium alloy airtight die casting to obtain the first intermediate part, the process also includes a filing and preliminary inspection step for the magnesium alloy airtight die casting.

12. A control system for preventing delayed cold cracking in magnesium alloy airtight die-cast parts, characterized in that, include: The initial inspection module is used to establish a unique identifier for magnesium alloy airtight die castings, record process parameter information, and perform initial defect detection. A heat treatment module is used to heat treat the magnesium alloy airtight die casting to obtain a first intermediate part. A stress treatment module is used to perform ultrasonic impact treatment on the first intermediate part to form a stress layer on at least a portion of the surface of the first intermediate part, thereby obtaining a second intermediate part. The hydrogen concentration monitoring module is used to perform in-situ hydrogen concentration monitoring on the second middleware and obtain hydrogen concentration data; The risk assessment module is used to obtain a leakage risk index based on the tensile stress, yield strength and hydrogen concentration data of the magnesium alloy airtight die casting, and to process the magnesium alloy airtight die casting according to the leakage risk index. A sealing compensation module is used to perform adaptive sealing at the sealing position of the magnesium alloy airtight die casting. The final inspection traceability module is used to perform terminal leakage detection on the magnesium alloy airtight die casting and upload the full-process data to the database after binding it with the unique identifier.

Images