Magnesium alloy ignition point coupling judgment method and system under flame condition

Abstract

The invention provides a magnesium alloy ignition point coupling judgment method and system under a flame condition, and belongs to the technical field of material performance testing. The method comprises the following steps: heating a magnesium alloy sample under a flame heating condition; driving a temperature measuring probe to penetrate into the sample at a preset moment so as to penetrate through a surface oxidation film of the sample, and obtaining the real temperature of the melt in the sample; and performing space-time coupling matching on the change of the real temperature and the visual information of the sample state so as to determine the ignition point of the magnesium alloy. The invention also provides a system for realizing the method. The system comprises a flame heating unit, a dynamic temperature measurement unit and a signal acquisition and judgment unit. The real temperature of the melt is obtained by dynamically puncturing the oxide film, so that the problem of temperature measurement distortion caused by heat insulation of the oxide film is fundamentally solved; and in combination with a time-space coupling judgment criterion of temperature jump and combustion expansion behaviors, dual confirmation of the ignition point is realized, interference is effectively eliminated, and accuracy, reliability and repeatability of ignition point data are ensured.

Description

Technical Field

[0001] This invention relates to the field of material performance testing technology, and in particular to a method and system for determining the ignition point of magnesium alloys under flame conditions. Background Technology

[0002] Magnesium alloys, with their excellent specific strength and lightweight properties, are widely considered one of the most promising structural materials in aerospace, transportation, and electronic communications. However, their flammability at high temperatures has become a key bottleneck restricting their engineering applications. To meet the dual demands of high performance and high safety in high-end manufacturing sectors such as new energy vehicles and aerospace, the development of fire-resistant magnesium alloys has become a research focus. Ignition point, as a core parameter for measuring the fire resistance of magnesium alloys, is directly related to the material's service safety under extreme thermal environments. Establishing a high-precision, reproducible ignition point testing method not only helps to accurately assess the fire resistance of fire-resistant magnesium alloys but also provides crucial information for alloy composition design and process optimization, which is of great significance for promoting the development and standardized evaluation of high-performance fire-resistant magnesium alloys.

[0003] In actual service, over 90% of magnesium alloy ignition accidents occur under the influence of external flames, where the material is simultaneously subjected to multiple effects, including high-temperature radiation, airflow impact, and thermal stress. Under such conditions, the molten zone is prone to deformation under gravity, leading to instability and accelerated rupture of the surface oxide film, thus altering the alloy's actual ignition point. This makes traditional testing methods based on crucible heating or resistance furnace temperature control ineffective in reflecting the ignition behavior under these dynamic conditions, potentially deviating from the alloy's true ignition point in a fire.

[0004] Furthermore, temperature measurement distortion is a major technical challenge in ignition point testing under flame conditions. In the initial heating stage, the magnesium alloy matrix conducts heat quickly (thermal conductivity approximately 156 W / m·K), and the temperature difference between the interior and surface is small, allowing surface temperature measurement by thermocouples to reflect the overall temperature change. However, as the heating process progresses, an oxide film with significantly reduced thermal conductivity (<50 W / m·K) rapidly forms on the sample surface, creating a thermal resistance layer that causes a significant deviation between the measured temperature and the internal temperature of the melt. Traditional contact thermocouples, due to the insulation of the oxide film and interference from flame radiation, cannot accurately reflect the true temperature of the melt even when in close contact with the surface. While non-contact temperature measurement methods such as infrared thermometry, laser-induced fluorescence (LIF), and coherent anti-Stokes Raman scattering (CARS) avoid contact interference, they are still susceptible to changes in the emissivity of the magnesium alloy surface, flame radiation, and smoke interference in high-temperature combustion environments, resulting in relatively large measurement errors.

[0005] To address the aforementioned issues, existing research has attempted to improve accuracy by refining temperature measurement methods. For example, patent CN201210387221.X uses colorimetry for non-contact temperature measurement, but the signal is easily interfered with under strong flame radiation, resulting in limited stability and applicability. CN202410485953.5 and CN201811241784.1 utilize resistance furnace heating to control the stability of the testing environment, but their operating conditions differ significantly from the dynamic flame action during actual service, making it difficult to accurately reflect the true temperature changes throughout the entire process from melting to ignition. Therefore, current technologies cannot accurately capture the true ignition point of magnesium alloys under complex thermal environments, hindering the scientific evaluation and standardized determination of fire resistance performance.

[0006] In summary, there is an urgent need to establish a method for testing the ignition point of magnesium alloys in dynamic flame environments. This method should be able to simultaneously capture the coupling process between the actual melt temperature and combustion behavior, accurately identify the temperature jump characteristics at the moment of ignition, and thus achieve dynamic, accurate, and repeatable determination of the ignition point of magnesium alloys. The proposed method will provide reliable technical support for the performance evaluation, material design, and safe application of fire-resistant magnesium alloys. Summary of the Invention

[0007] The purpose of this invention is to provide a method and system for determining the ignition point of magnesium alloys under flame conditions. This invention aims to solve the technical problems in the prior art where the ignition point test conditions of magnesium alloys deviate from the actual working conditions and the temperature measurement is biased due to the heat insulation effect of the oxide film on the sample surface, making it impossible to accurately measure the true temperature inside the melt, thus resulting in distorted and unreliable ignition point determination results.

[0008] The technical solution provided by this invention is as follows: <First Aspect> This invention provides a method for determining the ignition point coupling of magnesium alloys under flame conditions, comprising the following steps: A magnesium alloy sample was heated under flame heating conditions; A dynamic temperature measurement strategy is employed, in which a temperature probe is driven to penetrate the sample at a preset time to penetrate its surface oxide film, thereby obtaining the true temperature of the melt inside the sample; and, The spatiotemporal coupling criterion is used to match the change in the actual temperature with the visual information of the sample state in order to determine the ignition point of the magnesium alloy. The preset time is when a continuous melting zone is detected on the surface of the sample, and the temperature-time curve of the actual temperature changes from a rapid rising phase to a flat phase.

[0009] Furthermore, the displacement of the driving temperature probe into the sample is 1 / 4 to 3 / 4 of the sample thickness.

[0010] Furthermore, the spatiotemporal coupling determination criterion is specifically as follows: the temperature jump point on the temperature-time curve of the actual temperature is matched with the combustion expansion start point observed through the visualization information in time. When the two occur synchronously, the temperature corresponding to the temperature jump point is determined to be the ignition point.

[0011] Furthermore, the method includes at least one of the following: (A) The temperature jump point is identified by calculating the maximum point of the first derivative or the zero crossing point of the second derivative of the temperature-time curve; (B) The combustion extension initiation point is automatically identified by an algorithm based on a brightness threshold or contour change.

[0012] In one embodiment of the present invention, the temperature probe is a K-type thermocouple.

[0013] <Second aspect> This invention also provides a magnesium alloy ignition point coupling determination system under flame conditions, comprising: A flame heating unit is used to heat magnesium alloy samples; The dynamic temperature measurement unit includes a temperature probe and a driving mechanism. The driving mechanism is used to drive the temperature probe to penetrate the sample at a preset time to penetrate its surface oxide film, thereby obtaining the true temperature of the melt inside the sample. The signal acquisition and judgment unit is electrically connected to the dynamic temperature measurement unit and is configured to acquire the real temperature and the visualization information of the sample state, and to match the change of the real temperature and the visualization information based on the spatiotemporal coupling judgment criterion to determine the ignition point of the magnesium alloy.

[0014] Optionally, the drive mechanism is a precision linear motor, a servo electric actuator, or a linear drive device.

[0015] Optionally, the signal acquisition and judgment unit is configured to control the drive mechanism to perform an insertion action when a continuous melting zone is detected on the surface of the sample and the temperature-time curve of the actual temperature turns to a flat phase.

[0016] Optionally, the signal acquisition and determination unit includes: a signal analysis module for identifying temperature jump points in the actual temperature change, and an image analysis module for identifying the combustion expansion start point in the visualized information.

[0017] Optionally, the signal acquisition and determination unit is configured to simultaneously acquire the temperature signal of the real temperature and the visualization information at an acquisition frequency of not less than 10 Hz.

[0018] The key features of this invention are: Based on the dynamic ignition mechanism of magnesium alloys under flame, the ignition point of magnesium alloys is accurately measured by coupling the melt temperature evolution with the combustion behavior. Magnesium alloys exhibit three typical characteristics in a flame environment: (1) rapid oxidation of the surface to form an oxide film; (2) melting before ignition; and (3) combustion gradually expanding along the temperature gradient. The ignition process is essentially a continuous thermal reaction evolution of oxide film formation, local melting, and film rupture. In the initial stage of flame heating, the temperature of the magnesium alloy rises rapidly, and the surface oxidizes rapidly. When the temperature reaches the alloy liquidus line, the surface begins to melt locally and is covered by an oxide film to form a closed molten pool, and the heating rate slows down. As the melting area expands, the oxide film ruptures locally under the action of stress accumulation and airflow disturbance, triggering a violent oxidation reaction and releasing a large amount of heat, causing the temperature to jump instantaneously. When the temperature begins to rise rapidly, the corresponding temperature is the ignition point of the magnesium alloy. Subsequently, the heat generated by combustion is conducted to the unburned area along the temperature gradient, and the flame gradually expands until the entire sample is burned out.

[0019] This invention utilizes a thermocouple insertion strategy to pierce the oxide film, enabling dynamic measurement of the true temperature of the melt, and combines this with synchronous combustion imaging for ignition point determination. After the sample melts, the thermocouple tip, controlled by a drive mechanism, pierces the oxide film and directly contacts the melt, effectively eliminating the insulating effect of the oxide film and ensuring the temperature measurement accurately reflects the internal temperature of the melt. Simultaneously, the combustion imaging synchronously records the alloy's ignition behavior; when self-sustaining combustion forms on the surface and occurs synchronously with a temperature jump, that temperature is determined to be the magnesium alloy's ignition point. Furthermore, to ensure measurement accuracy and repeatability, this invention employs a synchronous sampling frequency of at least 10 Hz to record temperature signals and combustion images, and adjusts the thermocouple insertion depth according to the sample thickness to ensure the tip accurately enters the molten region without penetrating the sample's main structure.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention is applicable to the ignition point test of magnesium alloys under dynamic flame conditions. It can realistically simulate the complex thermal environment faced by materials in fire conditions, including airflow disturbance, flame fluctuation and local thermal shock, etc., making the test results more representative of engineering and providing a reliable scientific basis for the evaluation of the fire resistance performance of magnesium alloys.

[0021] (2) This invention overcomes the technical bottleneck of traditional surface temperature measurement, which is affected by the heat insulation of the oxide film and is difficult to obtain the true temperature of the melt, by actively puncturing the oxide film during the melting stage. This method ensures that the ignition point determination is based on the true thermal response of the melt and couples the temperature change with the combustion expansion behavior to achieve accurate identification of the ignition point, effectively eliminate the temperature measurement deviation during the melting stage, and significantly improve the authenticity, reliability and repeatability of the ignition point test.

[0022] (3) This invention achieves objective determination of the ignition point of magnesium alloys by synchronously coupling the melt temperature signal with the combustion expansion behavior. Combined with systematic flame heat flux density calibration, heating control and determination criteria, a standardized test process that is repeatable and comparable is constructed, which effectively reduces the impact of differences in test conditions on the results and significantly improves the accuracy and applicability of the ignition point test. Attached Figure Description

[0023] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the temperature measurement principle provided by the present invention; Figure 2 This is a schematic diagram of the magnesium alloy ignition point coupling determination system under flame conditions provided in Embodiment 1 of the present invention. Figure 3 A flowchart of the magnesium alloy ignition point coupling determination method under flame conditions provided in the embodiments of this application; Figure 4 This is a timing diagram illustrating the signaling interaction between the main units in the embodiments of this application; Figure 5 This is a temperature-time curve of the Mg-4Y alloy measured in Example 1 of this application; Figure 6 This is a temperature-time curve of the Mg-4Y alloy measured in Example 2 of this application; Figure 7 This is a temperature-time curve of the commercial AZ91D alloy measured in Example 4 of this application; Figure 8 This is a temperature-time curve of the magnesium alloy ignition point test in Comparative Example 1 of the present invention. Figure 9 This is a temperature-time curve of the magnesium alloy ignition point test in Comparative Example 2 of the present invention.

[0024] Explanation of reference numerals in the attached figures: 10-Magnesium alloy sample; 20-Sample clamping device; 30-Flame gun; 40-Dynamic temperature measurement unit; 41-Thermocouple; 42-Drive mechanism; 50-Image acquisition device; 60-Signal acquisition and judgment unit. Detailed Implementation

[0025] The present invention will be described in detail below with reference to embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0026] Example 1 This invention provides a method for determining the ignition point of magnesium alloys under flame conditions and a system for implementing this method. The solution involves constructing an integrated testing system. In a simulated dynamic flame environment, a controlled driving mechanism drives a temperature probe to penetrate the melt inside the magnesium alloy sample after melting to obtain its true temperature. Combined with visualized information on the combustion behavior of the sample surface, the temperature change characteristics and combustion expansion characteristics are spatiotemporally coupled for determination, thereby achieving accurate determination of the ignition point of the magnesium alloy.

[0027] Please see Figure 2 The diagram illustrates a structural schematic of a magnesium alloy ignition point coupling determination system under flame conditions used in this embodiment. The system includes a flame heating unit, a sample carrying unit, a dynamic temperature measurement unit 40, and a signal acquisition and determination unit 60.

[0028] In this embodiment, the flame heating unit includes a flame torch 30, a gas source device for providing fuel gas (e.g., a gas cylinder containing a propyne-propadiene mixture), and a mass flow controller installed in the gas path. The flame heating unit generates a stable and controllable flame to continuously heat the magnesium alloy sample 10, simulating a real flame environment. The mass flow controller precisely adjusts and maintains the heat flux density and temperature of the flame, thereby ensuring the stability of the flame state and the repeatability of the test conditions.

[0029] The sample carrying unit can be a sample clamping device 20, such as a three-dimensional adjustable platform, which is used to firmly fix the magnesium alloy sample 10 to be tested, and adjust the position so that the sample 10 is located in a predetermined area (such as the center of the flame) where the flame is generated by the flame gun 30, so as to ensure the consistency of the sample heating conditions.

[0030] The dynamic temperature measurement unit 40 includes a temperature probe and a driving mechanism. In this embodiment, the temperature probe is a K-type thermocouple 41, and the driving mechanism 42 is used to drive the thermocouple 41 to move. As an exemplary implementation, the driving mechanism 42 can be a precision linear motor to provide stable and controllable insertion displacement. Under the control of the signal acquisition and judgment unit 60, the dynamic temperature measurement unit 40 drives the thermocouple 41 to penetrate the magnesium alloy sample 10 at a preset time, allowing it to penetrate the oxide film formed on the sample surface during heating and directly contact the internal melt, thereby obtaining the true temperature inside the melt.

[0031] The signal acquisition and judgment unit 60 serves as the core of the system's data acquisition and control, and is electrically or signal-connected to the dynamic temperature measurement unit 40 and the image acquisition device 50. The image acquisition device 50 is used to acquire the surface state changes of the sample during heating, and can be an industrial camera, high-speed camera, or other imaging device capable of meeting the time resolution requirements of the combustion expansion process. The signal acquisition and judgment unit 60 is configured to simultaneously acquire temperature signals and visualized image information, and control the insertion time of the temperature measuring probe and perform ignition point coupling judgment according to preset judgment logic.

[0032] Please combine Figure 3 The flowchart illustrates the magnesium alloy ignition point coupling determination method under flame conditions described in this embodiment. The following is in conjunction with... Figure 2 The system shown illustrates the specific implementation process of this method.

[0033] Step S1, Sample Preparation. A piece of Mg-4Y (yttrium content 4% by weight) magnesium alloy was selected as the test object and machined into a rectangular magnesium alloy sample 10 with dimensions of 20 mm long × 5 mm wide × 100 mm high. The sample surface was mechanically ground to achieve a surface roughness R. a The sample was then ultrasonically cleaned with anhydrous ethanol to remove surface oil and debris, and subsequently dried. The sample was designed to be less than 0.8 μm to minimize the impact of surface defects and irregular oxide layers.

[0034] Step S2, Flame Calibration. Before testing, calibrate the flame heating unit. Start the flame torch 30 and adjust the fuel gas and combustion-supporting gas flow rates using the mass flow controller to stabilize the flame center temperature at 1450±50 ℃. Simultaneously measure and confirm that the heat flux density at the sample placement location is stable at 250±20 kW / m³. 2 This is to ensure the consistency of test conditions.

[0035] Step S3, Installation and Positioning. Fix the magnesium alloy sample 10 onto the sample clamping device 20 and adjust its position so that the sample body is located in the calibrated flame center region. Install the thermocouple 41 to its initial position, with its tip in contact with the non-directly flame-exposed surface of the magnesium alloy sample 10, and put the drive mechanism 42 in standby mode. Adjust the shooting angle and focal length of the image acquisition device 50 to clearly record the surface condition changes of the heated area of ​​the sample.

[0036] Step S4, Synchronous Acquisition. The test process is initiated, and the flame gun 30 is controlled to heat the sample 10. The signal acquisition and judgment unit 60 begins to synchronously acquire temperature signals from the thermocouple 41 and visual information from the image acquisition device 50. The acquisition frequency is not lower than 10 Hz to ensure that the time-resolved information required for ignition point determination can be obtained; in this embodiment, the acquisition frequency is exemplarily set to 10 Hz.

[0037] Step S5, dynamic insertion. During the heating process, the signal acquisition and judgment unit 60 analyzes the acquired temperature-time curve and video images in real time. For example... Figure 1 As shown, in the initial stage of heating, because thermocouple 41 is attached to the surface of sample 10, the temperature it measures will be lower than the actual temperature of the internal melt due to the heat insulation effect of the surface oxide film. This corresponds to... Figure 1 The "temperature measurement distortion" curve is shown in the figure. When heating has proceeded for approximately 80 seconds, the signal acquisition and judgment unit 60 determines that the preset time has been reached when the following conditions are met: (1) Through image analysis, it was observed that the magnesium alloy sample 10 exhibited melting characteristics such as the formation of a continuous melting zone and deformation on its surface; (2) Through temperature data analysis, it was found that the slope of the temperature-time curve decreased significantly, that is, the heating rate changed from a rapid rising stage to a relatively flat stage.

[0038] The simultaneous fulfillment of the above two conditions indicates that the sample has formed a sufficient amount of internal melt, which is the preset time for performing dynamic temperature measurement.

[0039] Please see Figure 4 This demonstrates the signaling interaction timing of each unit in the system. Upon detecting the melting plateau, the signal acquisition and judgment unit 60 immediately sends a "trigger insertion command" to the drive mechanism 42 (precision linear motor) of the dynamic temperature measurement unit 40. Upon receiving the command, the drive mechanism 42 precisely drives the thermocouple 41 to penetrate the magnesium alloy sample 10 horizontally, with the displacement precisely controlled to 3 mm. Since the sample thickness is 5 mm, the 3 mm insertion depth ensures that the tip of the thermocouple 41 can effectively penetrate the surface oxide layer and stably contact the internal melt, while avoiding penetration of the sample and contact with the flame on the other side. It can be understood that this insertion depth is within the range of 1 / 4 to 3 / 4 of the sample thickness (i.e., 1.25 mm to 3.75 mm). After the tip of the thermocouple 41 enters the melt, the measured temperature will no longer be affected by the insulating effect of the oxide film, but will instead reflect the true temperature inside the melt, which corresponds to... Figure 1 The "precise temperature measurement" curve in the middle.

[0040] Step S6, ignition observation, and step S7, coupling determination. After thermocouple 41 is successfully inserted into the melt, the system continues to heat sample 10 and simultaneously acquires the actual melt temperature and surface visualization information. At this time, the signal acquisition and determination unit 60 begins to execute the spatiotemporal coupling determination criteria: on the one hand, it reads the "temperature jump behavior" from the temperature sensor through the signal analysis module; on the other hand, it identifies the "combustion expansion behavior" from the visual sensor through the image analysis module.

[0041] Specifically, the signal analysis module inside the signal acquisition and judgment unit 60 calculates the first or second derivative of the temperature-time curve in real time. When the magnesium alloy undergoes self-sustaining combustion, it releases a large amount of heat due to the intense oxidation reaction, causing the melt temperature to rise sharply. This is manifested as an inflection point on the temperature-time curve with a sharply increasing slope, i.e., the "temperature jump point." Mathematically, this point corresponds to the maximum value of the first derivative (heating rate) of the temperature-time curve, or the zero-crossing point of its second derivative. The signal analysis module accurately identifies the moment of the temperature jump by finding the zero-crossing point of the second derivative.

[0042] Meanwhile, the image analysis module inside the signal acquisition and judgment unit 60 processes video frames from the image acquisition device 50 in real time. This module analyzes the number and distribution of bright pixels in the image using a brightness threshold-based algorithm. When the first flame capable of detaching from the external flame heat source and beginning to spread appears on the surface of the sample 10—the "combustion propagation initiation point"—a sudden change occurs in the area or average brightness of the bright region in the image. The image analysis module detects this sudden change to accurately identify the initiation time of combustion propagation.

[0043] When the temperature jump characteristic and the combustion expansion initiation characteristic appear synchronously in time, the signal acquisition and judgment unit 60 determines that the moment is the ignition point of the magnesium alloy and records the corresponding actual melt temperature value.

[0044] Please see Figure 5 The diagram shows the temperature-time curve of the Mg-4Y magnesium alloy measured in this embodiment. The temperature change indicates that after the thermocouple is inserted into the melt, the temperature continues to rise steadily. At approximately 142.4 s, a significant temperature jump occurs in the temperature-time curve. Based on the aforementioned spatiotemporal coupling criterion, the temperature corresponding to this jump point, 820.08 ℃, is determined to be the true ignition point of the Mg-4Y magnesium alloy under dynamic flame conditions.

[0045] Therefore, this embodiment effectively overcomes the thermal resistance effect of the oxide film by using dynamic insertion temperature measurement, obtains the true internal temperature of the melt, and establishes an objective and reliable basis for judging the ignition point by combining the spatiotemporal coupling of temperature and visualization information, thereby achieving accurate measurement of the ignition point of magnesium alloy.

[0046] Example 2 As an optional implementation, this embodiment illustrates that in the system used to implement the present invention, the driving mechanism 42 of the dynamic temperature measuring unit 40 and the control logic for triggering its action can adopt other equivalent or simplified forms. The overall system structure, test object, and ignition point determination approach of this embodiment are basically the same as those of Embodiment 1. The main difference lies in the specific form of the driving mechanism in the dynamic temperature measuring unit 40 and the implementation method of inserting the trigger control logic.

[0047] In this embodiment, the drive mechanism 42 in the dynamic temperature measurement unit 40 adopts a servo electric actuator instead of the precision linear motor in Embodiment 1. The servo electric actuator can also achieve stable and controllable linear displacement output, which can meet the requirements of driving the temperature measurement probe 41 to perform millimeter-level insertion displacement control. At the same time, it has the advantages of simple structure and low cost, and is suitable for engineering applications.

[0048] Correspondingly, the control logic in the signal acquisition and judgment unit 60 used to determine the "preset time" and trigger the insertion action has also been appropriately simplified. This embodiment no longer uses a triggering and judgment method based on visual information, but instead adopts a control strategy based on temperature change characteristics as the basis for insertion triggering judgment, in order to further reduce system complexity. Specifically, during the flame heating process, the signal acquisition and judgment unit 60 calculates the first derivative of the temperature-time curve in real time, i.e., the heating rate, and presets a heating rate threshold, for example, 3 ℃ / s. When the heating rate is detected to gradually decrease from a higher value in the initial heating stage (e.g., >10 ℃ / s) and stabilize below the threshold, and the duration exceeds a preset duration (e.g., 8 s), the system determines that the sample has entered the stable melting platform stage, and a sufficient amount of continuous melt region has been formed inside.

[0049] After the above conditions are met, the signal acquisition and judgment unit 60 sends a trigger command to the servo electric push rod, driving the temperature probe 41 to penetrate the melt inside the sample with a preset insertion displacement, for example, an insertion depth of 3 mm, thereby penetrating the surface oxide film and obtaining the true temperature inside the melt.

[0050] The subsequent testing steps, including the continued synchronous acquisition of the actual temperature of the melt and video images after penetration, and the process of using the spatiotemporal coupling judgment criterion (i.e., matching the temperature jump point and the combustion expansion start point) to finally determine the ignition point, are exactly the same as in Example 1.

[0051] By adopting the method of this embodiment, a Mg-4Y magnesium alloy sample of the same specifications as in Example 1 was tested, and the obtained temperature-time curve is shown below. Figure 6As shown, after heating to approximately 137.5 s, a significant temperature jump was observed in the temperature-time curve, and the expansion of combustion behavior on the sample surface was simultaneously observed. Based on this, the temperature of 817.31 ℃ at this moment was determined to be the true ignition point of the Mg-4Y magnesium alloy under dynamic flame conditions. This result is similar to the ignition point value measured in Example 1, verifying the effectiveness and reliability of the scheme in this embodiment.

[0052] Therefore, it is evident that the core technical concept of this invention does not rely on a specific type or high-cost driving device, nor is it limited to complex insertion trigger control logic. By employing linear driving devices such as servo electric actuators, combined with a simplified triggering strategy based on temperature change characteristics, the dynamic insertion temperature measurement and ignition point coupling determination process can be reliably completed, demonstrating the good universality and engineering applicability of this invention.

[0053] Example 3 In another embodiment of the present invention, the determination algorithm for implementing the "spatiotemporal coupling determination" can adopt a feature fusion determination method based on machine learning, so as to further improve the adaptability and robustness of the ignition point determination under different alloy systems and complex combustion conditions.

[0054] The hardware system configuration, sample preparation method, flame calibration process, dynamic piercing temperature measurement steps, and the method of obtaining the true temperature by contacting the thermocouple with the melt in this embodiment are exactly the same as those in Embodiment 1. The only difference is the implementation method of the software algorithm used to perform the ignition point determination in the signal acquisition and determination unit 60.

[0055] In Example 1, the ignition point is determined by extracting the temperature jump features from the temperature-time curve and the combustion expansion initiation features from the image, and then explicitly matching their temporal correspondence. As an equivalent implementation, in this example, the signal acquisition and determination unit 60 is configured to use a machine learning-based feature fusion determination model to jointly analyze the temperature signal acquired by the dynamic temperature measurement unit 40 and the sample surface state image acquired by the image acquisition device 50, thereby determining the moment of ignition.

[0056] Specifically, the signal acquisition and determination unit 60 integrates a pre-obtained feature fusion determination model. This model takes as input continuously acquired melt temperature time-series data within a set time window and time-synchronized sample surface state image data, and outputs a determination result characterizing whether the current sample has entered the ignition stage. The determination result can be characterized using probability values, confidence indices, or other equivalent forms.

[0057] In one feasible implementation, the feature fusion judgment model may include two functional modules: temperature feature extraction and image feature extraction. The temperature feature extraction module extracts features characterizing changes in the melt state, such as the rate of temperature change and trends in temperature jumps. The image feature extraction module extracts features characterizing the evolution of combustion behavior, such as changes in image brightness and the appearance and expansion of combustion areas. These two types of features are fused within the model to output a comprehensive judgment result. The model may be implemented using a convolutional neural network, a temporal neural network, or a combination of both, and the specific network structure is not limited by this invention.

[0058] The feature fusion judgment model can be trained based on historical ignition test data or experimental data. Its training process is only used to form the judgment model itself and does not constitute a necessary technical step in the actual testing process of the method of the present invention, nor does it affect the implementation of the method of the present invention without model training.

[0059] During actual testing, once thermocouple 41 penetrates the melt inside the sample and begins to stably acquire the true melt temperature, signal acquisition and judgment unit 60 combines and processes the continuously acquired temperature data and image data within the corresponding time period according to a predetermined time window (e.g., 0.5 s), and sends the data to the feature fusion judgment model for real-time analysis. When the judgment result output by the model first reaches or exceeds the preset ignition judgment threshold (e.g., 0.95), signal acquisition and judgment unit 60 determines that this moment is the ignition point occurrence time and records the true melt temperature corresponding to this moment as the ignition point value of the magnesium alloy.

[0060] It should be noted that the feature fusion judgment method based on machine learning does not change the basic technical idea of ​​the present invention, "spatiotemporal coupling judgment based on temperature change features and combustion expansion features". Its judgment basis is essentially still derived from the co-evolution features of temperature signal and image signal near the ignition point.

[0061] Through the above implementation methods, without changing the test hardware structure and temperature measurement method, a stable determination of the ignition point can be achieved, improving the versatility and engineering applicability of the method of the present invention under different magnesium alloy materials and different flame conditions.

[0062] Example 4 This embodiment is used to illustrate that the ignition point coupling determination method proposed in this invention is not only applicable to rare earth flame-retardant magnesium alloys (such as the Mg-4Y magnesium alloy described in Example 1), but also applicable to traditional commercial magnesium alloy systems, thereby demonstrating the good applicability of the technical solution of this invention in magnesium alloy materials with different combustion characteristics.

[0063] The hardware of the ignition point coupling determination system used in this embodiment is exactly the same as that in Embodiment 1, including a flame gun 30, a sample clamping device 20, a dynamic temperature measurement unit 40 composed of a K-type thermocouple 41 and a precision linear motor, an image acquisition device 50, and a signal acquisition and determination unit 60.

[0064] The test object was changed to a commonly used commercial magnesium alloy, AZ91D, whose chemical composition meets the composition requirements of the AZ91D grade in GB / T 5153-2016. The AZ91D magnesium alloy was processed into a cuboid sample with the same dimensions as the magnesium alloy sample in Example 1, measuring 100 mm × 20 mm × 5 mm, and underwent the same surface polishing and cleaning treatment.

[0065] During the test, the flame torch 30 continuously heats the sample, and the signal acquisition and judgment unit 60 monitors the surface temperature changes of the sample and the corresponding video image information in real time. At the preset judgment time, following the same triggering method as in Example 1, the dynamic temperature measurement unit 40 drives the thermocouple 41 to penetrate the sample surface at a predetermined insertion speed. The insertion depth is set to 3 mm, which is within the effective range of 1 / 4 to 3 / 4 of the sample thickness, thereby piercing the surface oxide film and directly contacting the internal melt to obtain the true melt temperature. The subsequent ignition point determination process is completely consistent with Example 1. The system continues to synchronously acquire temperature signals and video images, and determines the ignition point of AZ91D magnesium alloy under dynamic flame conditions based on the spatiotemporal coupling relationship between the temperature jump characteristics appearing in the temperature-time curve and the combustion expansion initiation characteristics in the video image.

[0066] By following the steps above, the ignition point test results of AZ91D magnesium alloy can be obtained reliably. Figure 7 The temperature change curve of the AZ91D magnesium alloy measured in this embodiment shows a significant temperature jump, indicating that the AZ91D magnesium alloy ignited, with a corresponding ignition point of approximately 661 °C. These results demonstrate that the ignition point coupling determination method proposed in this invention is applicable not only to flame-retardant magnesium alloys but also to traditional flammable magnesium alloy systems, exhibiting good versatility and engineering applicability.

[0067] Comparative Example 1 Taking the same Mg-4Y alloy sample as in Example 1 as an example, the experimental conditions (including gas type and device arrangement) of this comparative example are consistent with those of Example 1, with the only difference being the thermocouple insertion conditions.

[0068] Unlike Example 1, where the thermocouple was driven to penetrate 3 mm (an effective depth within the range of 1 / 4 to 3 / 4 of the sample thickness), in this comparative example, the displacement by which the driving mechanism moves the thermocouple toward the sample was set to 1 mm. Since the magnesium alloy sample thickness was 5 mm, the thermocouple did not reach the predetermined effective insertion depth, resulting in the thermocouple failing to form stable direct contact with the molten material inside the sample.

[0069] The temperature-time curve obtained in this comparative example is as follows: Figure 8 As shown in the figure. The results indicate that the temperature recorded by the thermocouple rises rapidly in the initial stage of heating, with little difference from Example 1. However, after the sample melts, the temperature-time curve enters a clear plateau phase, only slowly rising to above 600 °C, which is significantly lower than the internal temperature of the melt obtained under the same test conditions in Example 1. This plateau temperature cannot reflect the true heating process of the melt, resulting in a significantly lower temperature inflection point at the occurrence of combustion. The ignition temperature value obtained is approximately 664.91 °C, which is significantly lower than the ignition point value measured by the method of this invention in Example 1, with a difference of approximately 155 °C.

[0070] Comparative Example 2 Taking the same Mg-4Y alloy sample as in Example 1 as an example, the experimental conditions (including gas type and device arrangement) of this comparative example are consistent with those of Example 1, with the only difference being the thermocouple insertion conditions.

[0071] Unlike Example 1, where the thermocouple was driven to penetrate 3 mm (an effective depth within the range of 1 / 4 to 3 / 4 of the sample thickness), in this comparative example, the displacement by which the driving mechanism moves the thermocouple toward the sample direction is set to 4.5 mm. That is, the thermocouple exceeds the predetermined insertion depth requirement.

[0072] The temperature-time curve obtained in this comparative example is as follows: Figure 9 As shown in the figure. The results indicate that the temperature recorded by the thermocouple rises rapidly in the initial stage of heating, similar to that in Example 1; however, due to the excessive insertion depth, the thermocouple is more susceptible to the influence of the external flame environment, causing an abnormal surge in the temperature signal at the moment of insertion, resulting in an premature ignition point determination before stable combustion has occurred. At this time, the sample has not yet undergone self-sustaining combustion, and the ignition time is advanced to 82.6 s, with a corresponding temperature inflection point of only 578.85 ℃, which is significantly lower than the ignition point result obtained in Example 1 using the method of this invention.

[0073] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for determining the ignition point of magnesium alloys under flame conditions, characterized in that, include: A magnesium alloy sample was heated under flame heating conditions; A dynamic temperature measurement strategy is adopted, in which a temperature probe is driven to penetrate the sample at a preset time to penetrate the oxide film on its surface, thereby obtaining the true temperature of the melt inside the sample. as well as The spatiotemporal coupling criterion is used to match the change in the actual temperature with the visual information of the sample state in order to determine the ignition point of the magnesium alloy. The preset time is when a continuous melting zone is detected on the surface of the sample, and the temperature-time curve of the actual temperature changes from a rapid rising phase to a flat phase.

2. The method according to claim 1, characterized in that, The displacement of the driving temperature probe into the sample is 1 / 4 to 3 / 4 of the sample thickness.

3. The method according to claim 1, characterized in that, The spatiotemporal coupling determination criterion is as follows: the temperature jump point on the temperature-time curve of the actual temperature is matched with the combustion expansion start point observed through the visualization information in time. When the two occur synchronously, the temperature corresponding to the temperature jump point is determined to be the ignition point.

4. The method according to claim 3, characterized in that, Includes at least one of the following: (A) The temperature jump point is identified by calculating the maximum point of the first derivative or the zero crossing point of the second derivative of the temperature-time curve; (B) The combustion extension initiation point is automatically identified by an algorithm based on a brightness threshold or contour change.

5. A coupled system for determining the ignition point of magnesium alloys under flame conditions, characterized in that, include: A flame heating unit is used to heat magnesium alloy samples; The dynamic temperature measurement unit includes a temperature probe and a driving mechanism. The driving mechanism is used to drive the temperature probe to penetrate the sample at a preset time to penetrate its surface oxide film, thereby obtaining the true temperature of the melt inside the sample. as well as The signal acquisition and judgment unit is electrically connected to the dynamic temperature measurement unit and is configured to acquire the real temperature and the visualization information of the sample state, and to match the change of the real temperature and the visualization information based on the spatiotemporal coupling judgment criterion to determine the ignition point of the magnesium alloy.

6. The system according to claim 5, characterized in that, The drive mechanism is a precision linear motor, a servo electric actuator, or a linear drive device.

7. The system according to claim 5 or 6, characterized in that, The signal acquisition and judgment unit is configured to control the drive mechanism to perform an insertion action when a continuous melting zone is detected on the surface of the sample and the temperature-time curve of the actual temperature turns to a flat phase.

8. The system according to claim 5, characterized in that, The signal acquisition and determination unit includes: a signal analysis module for identifying temperature jump points in the actual temperature change, and an image analysis module for identifying the combustion expansion start point in the visualized information.

9. The system according to claim 5, characterized in that, The signal acquisition and determination unit is configured to simultaneously acquire the temperature signal of the real temperature and the visualization information at an acquisition frequency of not less than 10 Hz.

10. The system according to claim 5, characterized in that, The flame heating unit includes a flame gun, a gas supply device, and a mass flow controller installed in the gas path, which is used to precisely adjust the composition, flow rate, and stability of the flame.

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