Method and system for preparing hard magnesium-aluminum alloy pressing cap through normal-temperature pulse

Abstract

The invention discloses a method and system for preparing a hard magnesium-aluminum alloy pressing cap through normal-temperature pulse, and belongs to the field of metal-based composite material preparation. The method comprises the following steps: mixing aluminum powder and magnesium oxide particles, and adding a dispersant for ball-milling treatment; applying a bipolar symmetric square-wave pulsed electric field to the mixed powder to achieve a synergistic effect with periodic pulse pressure, polarizing magnesium oxide particles by the electric field, breaking down an oxide layer and performing directional arrangement, and promoting mechanical occlusion of the particles and chemical bonding of an interface by the pressure; and the treated powder is subjected to normal-temperature static pressure forming, cleaning and polishing. The system comprises a raw material processing unit, a pulse compounding unit, a compression molding unit, a cleaning unit, a polishing unit and a control system. The method solves the problems of low interface strength, limited ceramic phase content, poor forming precision and the like of a traditional process, realizes interface chemical bonding and densification at normal temperature, improves the material hardness and structural stability, reduces energy consumption, supports large-scale production, and is suitable for preparation of complex structural members such as precise electronic shielding cases and aerospace fasteners.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of metal matrix composite materials, and in particular to a method and system for preparing a hard magnesium oxide aluminum alloy button cap by pulse processing at room temperature. Background Art

[0002] The magnesium oxide aluminum alloy button cap is a high-performance structural component composed of a metal aluminum matrix and a ceramic magnesium oxide reinforcement. It combines the lightness and thermal conductivity of aluminum with the high hardness, high temperature resistance and wear resistance of magnesium oxide. This type of button cap is often used in shielding covers of precision electronic equipment, aerospace fasteners and optical instrument connection parts. It needs to achieve high strength, low thermal expansion coefficient and complex surface forming in a small size. Because the application scenarios have strict requirements on dimensional accuracy (such as micron-level tolerances), surface finish and long-term stability, its preparation process needs to meet the multiple challenges of material densification, interface bonding strength and shape fidelity at the same time;

[0003] At present, the mainstream preparation processes of magnesium oxide aluminum alloy caps can be divided into two categories:

[0004] High-temperature sintering method: After mixing aluminum powder and magnesium oxide powder, sinter them under pressure in an inert atmosphere above 600°C, using high temperature to promote the plastic flow of aluminum and the interfacial diffusion bonding of magnesium oxide particles;

[0005] Cold pressing combined with post-processing: The mixed powder is first pressed at room temperature, and then heat treated (200-400℃) or mechanical surface treated (such as shot peening) to improve density and hardness.

[0006] In addition, some improved processes attempt to introduce external field assistance, such as unidirectional pulsed electric field or static high-voltage treatment, to enhance the bonding effect between particles.

[0007] However, the above method has significant defects in practical applications:

[0008] The high-temperature sintering method causes the aluminum matrix grains to coarsen and the magnesium oxide to be unevenly distributed due to long-term high-temperature environment. Complex-shaped parts are prone to warping and deformation, and the energy consumption is high.

[0009] Although the temperature is lowered by cold pressing and post-processing, the interface bonding between magnesium oxide and aluminum relies on physical interlocking, resulting in low interface strength and high ceramic content, which easily leads to internal cracks.

[0010] It is difficult to achieve simultaneous particle dispersion activation and densification with a single external field assist (such as only electric field or only pressure), and local density differences or electric field breakdown often occur.

[0011] These problems make it difficult for existing processes to meet the high hardness, high precision and complex structure forming requirements of magnesium oxide aluminum alloy press caps, especially restricting the increase in the content of ceramic phase (i.e. magnesium oxide particles) and large-scale production efficiency. Summary of the Invention

[0012] In order to solve the above technical problems, the present invention provides a method and system for preparing hard magnesium oxide aluminum alloy button caps by pulse processing at room temperature, which can take into account the high hardness, high precision and complex structure forming requirements of magnesium oxide aluminum alloy button caps, as well as improve the ceramic phase content and large-scale production efficiency.

[0013] The method for preparing a hard magnesium oxide aluminum alloy button cap by pulse forming at room temperature of the present invention comprises the following steps:

[0014] S1: Raw material pretreatment step, mixing aluminum powder and magnesium oxide particles and adding a dispersant for ball milling;

[0015] S2: pulse composite treatment step, applying a pulse electric field and pulse pressure synergistically to the mixed powder;

[0016] The synergistic effect of pulsed electric field and pulsed pressure is achieved through the following means:

[0017] Electric field activation and particle orientation: A pulsed electric field (bipolar symmetrical square wave) generates an instantaneous high electric field intensity (10-30kV) in the mixed powder, polarizing the surface of the magnesium oxide particles, breaking through the surface oxide layer and exposing active sites. At the same time, the electric field induces the aluminum powder and magnesium oxide particles to align along the direction of the electric field, reducing the interfacial gap.

[0018] Pressure densification and interface bonding: Pulse pressure (peak value 50-150MPa) compresses the powder in a periodic loading manner, promoting mechanical interlocking between particles. At the same time, the dynamic impact of the pulse pressure eliminates local pores. When the pulse pressure is applied synchronously with the electric field, the pressure forces the particles into close contact, and the electric field further promotes electron migration and chemical bonding at the aluminum-magnesium oxide interface.

[0019] Synergistic overheating prevention: The duty cycle (20-40%) and period (1-5 seconds) of the pulse parameters are designed to enable alternating action of the electric field and pressure, avoiding local temperature rise caused by continuous energy input (temperature control ≤ 50°C) and maintaining normal temperature process conditions.

[0020] S3: a compression molding step, wherein the treated mixed powder is statically pressure molded at room temperature;

[0021] S4: Surface treatment step, cleaning and polishing the formed body.

[0022] Furthermore, in the raw material pretreatment step, the mass ratio of aluminum powder to magnesium oxide particles is 8:2-6:4, the dispersant is stearic acid, oleic acid or polyethylene glycol, the addition amount is 0.5-1.5wt%, the ball milling speed is 300-500rpm, and the ball milling time is 2-4 hours.

[0023] Furthermore, in the pulse composite treatment step, the voltage of the pulse electric field is 10-30 kV, the frequency is 10-50 Hz, the duty cycle is 20-40%, the peak value of the pulse pressure is 50-150 MPa, the cycle is 1-5 seconds, and the treatment time is 5-15 minutes.

[0024] Furthermore, the aluminum powder has a particle size of 5-20 μm, the magnesium oxide particle has a particle size of 1-5 μm, and the surface of the magnesium oxide particle is pre-treated by nano-crystallization;

[0025] The specific steps of nano-pretreatment of the surface of magnesium oxide particles are as follows:

[0026] 1. Ball milling nano-crystallization: Magnesium oxide particles and nano-sized zirconium oxide grinding balls are loaded into a planetary ball mill at a mass ratio of 1:5. The milling is carried out under argon protection at a speed of 400 rpm for 6 hours to obtain a surface nano-scale rough structure with a surface roughness of Ra 50-100 nm.

[0027] 2. Chemical modification: The ball-milled magnesium oxide particles were immersed in a silane coupling agent ethanol solution (concentration 2 wt%), ultrasonically treated for 30 minutes, and dried at 60°C to form a nano-scale silane coating;

[0028] 3. High temperature stabilization: Annealing at 300°C in a nitrogen atmosphere for 1 hour to eliminate surface stress and enhance nanostructure stability.

[0029] Furthermore, the static pressure in the compression molding step is 50-100 MPa, the mold surface is coated with a boron nitride coating, the ultrasonic cleaning frequency in the surface treatment step is 20-60 kHz, and the time is 5-15 minutes. The coating technology of the boron nitride coating is specifically physical vapor deposition or plasma spraying.

[0030] Furthermore, in the pulse composite treatment step, the powder temperature is monitored in real time and controlled below 50°C. The pulse electric field is a bipolar symmetrical square wave with a rising edge time of ≤100ns and a falling edge time of ≤500ns. The design purpose of the pulse electric field being a bipolar symmetrical square wave is: charge neutralization, symmetrical activation and rapid response.

[0031] The system for pulse forming hard magnesium oxide aluminum alloy caps at room temperature includes:

[0032] Raw material processing unit, used to mix aluminum powder, magnesium oxide particles and dispersant;

[0033] A pulse compound device for applying a pulse electric field and pulse pressure to the mixed powder;

[0034] A compression molding unit is used to compress the processed mixed powder into a shape;

[0035] A cleaning unit is used to clean the molded body; the cleaning unit is specifically configured as a multi-band ultrasonic cleaning machine equipped with a 20-60kHz adjustable transducer array;

[0036] A polishing unit is used to polish the cleaned molded body; the polishing unit is specifically configured as a magnetorheological polishing device, and the polishing medium is a magnetorheological fluid of aluminum oxide / diamond micropowder;

[0037] Control system for monitoring pulse parameters and processing.

[0038] Furthermore, the raw material processing unit includes a ball mill, a weighing sensor and a mixing tank. The speed adjustment range of the ball mill is 0-800 rpm, and the inner wall of the mixing tank is provided with a polytetrafluoroethylene coating.

[0039] Furthermore, the pulse compounding device includes a processing chamber, a pulse power supply and a hydraulic pulse cylinder. The output voltage adjustment range of the pulse power supply is 0-50kV, the frequency adjustment range is 0-100Hz, and the duty cycle adjustment range is 0-50%. The peak pressure adjustment range of the hydraulic pulse cylinder is 0-200MPa and the period adjustment range is 0-10 seconds.

[0040] Furthermore, the control system integrates a PLC controller and a PID algorithm module, automatically adjusts pulse parameters according to powder temperature and pressure feedback, and supports remote data monitoring and cloud platform access;

[0041] The functions of the PLC controller include:

[0042] 1. Support 4-way analog input (temperature, pressure sensor signals) and 2-way analog output (pulse power supply, hydraulic cylinder control);

[0043] 2. Integrate Profinet communication protocol and be compatible with cloud platform access;

[0044] 3. The expansion module supports real-time operation of PID algorithm.

[0045] The PID algorithm module is specifically set to incremental digital PID, and the parameter setting adopts the critical proportionality method. The PID algorithm module matches the analog input and output (4-way input, 2-way output) interface of the PLC controller;

[0046] The control logic of the algorithm is:

[0047] 1. Input variables: powder temperature (infrared temperature measurement), real-time pressure (piezoelectric sensor);

[0048] 2. Output variables: adjust pulse frequency, duty cycle and pressure peak;

[0049] 3. Anti-integral saturation treatment: When the temperature approaches 50°C, the priority is to reduce the electric field duty cycle, and then reduce the pressure loading frequency.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] (1) Preparation of high-performance materials: Through the synergistic effect of pulsed electric field and pressure, the interface chemical bonding and densification between magnesium oxide particles and aluminum matrix are achieved, which significantly improves the material hardness, interface bonding strength and structural stability, and solves the problems of low interface strength and limited ceramic phase content in traditional processes.

[0052] (2) Room temperature precision molding: The temperature is controlled at ≤50℃ throughout the entire process to avoid grain coarsening and deformation caused by high temperature, support high-precision molding (micron-level tolerance) of small-sized and complex curved parts, and meet the stringent requirements of precision equipment for dimensional accuracy and surface finish.

[0053] (III) High-efficiency and low-consumption production: Pulse parameter optimization design reduces continuous energy input and lowers energy consumption; nano-pretreatment and intelligent control system (PLC-PID) realize real-time control of process parameters, improve production efficiency and support large-scale continuous production.

[0054] (IV) Adaptability to complex structures: Dynamic pulse pressure eliminates local pores and, combined with magnetorheological polishing technology, solves the molding defects (such as cracks and warping) of complex-shaped parts in traditional processes, expanding the application range of materials in aerospace fasteners, optical connection components and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a flow chart of the method implementation of the present invention;

[0056] Figure 2 It is a system architecture diagram of the present invention;

[0057] Figure 3 is a schematic diagram of the pulse synergy of the present invention;

[0058] Figure 4 This is a diagram of the nano-pretreatment process of the present invention; DETAILED DESCRIPTION

[0059] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0060] like Figures 1 to 4 As shown,

[0061] 1. Implementation of the Overall Technical Solution

[0062] The present invention provides a method and system for preparing a hard magnesium oxide aluminum alloy cap by pulse forming at room temperature, which realizes material densification and interface strengthening through the synergistic effect of pulse electric field and pulse pressure. The method specifically includes the following core steps:

[0063] Raw material pretreatment unit:

[0064] Aluminum powder and magnesium oxide particles are mixed in a mass ratio of 8:2-6:4, and 0.5-1.5 wt% of a dispersant, specifically stearic acid, oleic acid, or polyethylene glycol, is added. The mixture is then ball-milled in a planetary ball mill at 300-500 rpm for 2-4 hours. The magnesium oxide particles are pre-nanosized by first ball-milling them with nano-sized zirconium oxide balls at a mass ratio of 1:5 under argon for 6 hours to create a nanoscale surface roughness. The particles are then immersed in a 2 wt% silane coupling agent solution in ethanol and ultrasonically treated for 30 minutes. After drying at 60°C, the particles are then annealed in a nitrogen atmosphere at 300°C for 1 hour to enhance surface activity and structural stability.

[0065] Pulse compound processing unit:

[0066] The mixed powder is placed in a processing chamber, where a bipolar, symmetrical square-wave pulsed electric field and periodic pulsed pressure are simultaneously applied. Pulsed electric field parameters range from 10-30 kV, 10-50 Hz, a 20-40% duty cycle, a peak pulse pressure of 50-150 MPa, a period of 1-5 seconds, and a processing time of 5-15 minutes. A PLC controller with an integrated PID algorithm monitors the powder temperature in real time, ensuring it remains below 50°C during processing.

[0067] Compression molding unit:

[0068] The treated powder is formed at room temperature by a hydraulic press with a static pressure of 50-100 MPa. The mold surface is coated with a boron nitride coating with a thickness of 5-10 μm using physical vapor deposition or plasma spraying technology to improve demoulding performance and surface quality.

[0069] Surface treatment unit:

[0070] The formed body is first treated with a multi-band ultrasonic cleaning machine with a cleaning frequency of 20-60kHz and a cleaning time of 5-15 minutes to remove residual impurities on the surface; then, magnetorheological polishing equipment is used to precisely polish the complex curved surface using alumina or diamond micropowder magnetorheological fluid as the polishing medium to achieve micron-level dimensional accuracy and low surface roughness. 2. Specific embodiments

[0072] Example 1

[0073] Raw material pretreatment:

[0074] Aluminum powder with a particle size of 10 μm and magnesium oxide particles with a particle size of 1 μm were mixed in a mass ratio of 6:4, and 1.5 wt% stearic acid was added as a dispersant. A QM-3SP2 planetary ball mill with a polytetrafluoroethylene lining was used for ball milling at 300 rpm for 4 hours.

[0075] Ball milling nano-crystallization: Magnesium oxide particles and 0.5 mm diameter zirconium oxide grinding balls were loaded into a ball mill at a mass ratio of 1:5. Argon was passed through the mill and the particles were milled at 400 rpm for 6 h to obtain particles with a surface roughness of 50 nm Ra.

[0076] Chemical modification: The ball-milled particles were immersed in a 2 wt% γ-aminopropyltriethoxysilane ethanol solution, ultrasonically treated in a KQ-500DE ultrasonic cleaner for 30 minutes, and then dried in a DHG-9070A oven at 60°C for 2 hours.

[0077] High temperature stabilization: Heat to 300°C in a tube furnace at a heating rate of 5°C / min, keep at this temperature for 1 hour in a nitrogen atmosphere, and cool to room temperature with the furnace.

[0078] Pulse compounding:

[0079] A CTP-2000 pulse power supply outputs a 10kV bipolar symmetrical square wave electric field with a 10Hz frequency, a 20% duty cycle, an 80ns rise time, and a 400ns fall time. A YTD-200 hydraulic pulse cylinder applies a peak pulse pressure of 50MPa with a 5-second cycle, resulting in a 15-minute processing time. Powder temperature is monitored in real time using an infrared thermometer, reaching a maximum of 45°C, without triggering the temperature compensation mechanism.

[0080] Compression Molding:

[0081] Static pressure forming was performed on a Y32-200 hydraulic press. The mold was coated with a 5 μm thick boron nitride coating using PVD technology. A pressure of 50 MPa was applied and maintained for 30 seconds to obtain the initial green body.

[0082] Surface treatment:

[0083] The cleaning process uses a KS-2000 ultrasonic cleaning machine with a setting frequency of 20kHz for 15 minutes to remove residual dispersant on the surface; the polishing process uses an MRF-600 magnetorheological polishing equipment with a magnetorheological fluid of 15% volume fraction of alumina micropowder (particle size 10μm) and 5% volume fraction of diamond micropowder (particle size 5μm) as the medium. After polishing for 30 minutes, the surface roughness Ra is ≤ 0.1μm.

[0084] Example 2

[0085] Raw material pretreatment:

[0086] Aluminum powder with a particle size of 15 μm and magnesium oxide particles with a particle size of 3 μm were prepared in a mass ratio of 7:3. Oleic acid was used as the dispersant at a dosage of 1.0 wt%. The mixture was ball milled in a QM-3SP2 planetary ball mill at 400 rpm for 3 hours. The surface roughness Ra of the magnesium oxide after nano-crystallization was 75 nm. All other process parameters were the same as in Example 1.

[0087] Pulse compounding:

[0088] The pulsed electric field parameters were adjusted to 20kV, 30Hz, a 30% duty cycle, a peak pulse pressure of 100MPa, a 3-second cycle, and a processing time of 10 minutes. When infrared temperature measurement indicated the powder temperature reached 42°C, the PLC controller automatically fine-tuned the duty cycle to 28%, ensuring the temperature remained within the control range.

[0089] Compression Molding:

[0090] Plasma spraying technology was used to prepare an 8μm thick boron nitride coating on the mold surface. The static pressure was maintained at 75MPa for 20 seconds. The dimensional accuracy of the green body after molding was controlled within ±5μm.

[0091] Surface treatment:

[0092] The ultrasonic cleaning frequency was set at 40 kHz and the time was 10 minutes. The polishing medium was replaced with a magnetorheological fluid containing 10% alumina micropowder (particle size 5 μm) and 3% diamond micropowder (particle size 3 μm). After polishing, the surface roughness Ra was ≤ 0.08 μm, and the profile error of the complex curved surface was ≤ ± 3 μm.

[0093] The equipment or device used in this embodiment is the same as that in the first embodiment.

[0094] Example 3

[0095] Raw material pretreatment:

[0096] Aluminum powder with a particle size of 20 μm and magnesium oxide particles with a particle size of 5 μm were prepared in a mass ratio of 8:2. Polyethylene glycol was used as the dispersant at a dosage of 0.5 wt%. The mixture was ball-milled in a QM-3SP2 planetary ball mill at 500 rpm for 2 hours. The surface roughness Ra of the magnesium oxide after nanocrystallization was 100 nm. γ-methacryloxypropyltrimethoxysilane was used as the silane coupling agent.

[0097] Pulse compounding:

[0098] A 30kV pulsed electric field is applied at a frequency of 50Hz, a duty cycle of 40%, a peak pulse pressure of 150MPa, a cycle of 1 second, and a treatment time of 5 minutes. Real-time feedback from the pressure sensor ensures that the hydraulic pulse cylinder has a response time of ≤50ms, ensuring that pressure and electric field loading are synchronized.

[0099] Compression Molding:

[0100] The mold coating adopts PVD technology, with a static pressure of 100MPa maintained for 10 seconds. The mold temperature sensor is used to monitor the molding process to confirm that the mold surface temperature is maintained at 25℃±2℃.

[0101] Surface treatment:

[0102] The ultrasonic cleaning frequency is 60kHz and the time is 5 minutes. The polishing process uses a high-concentration diamond micropowder magnetorheological fluid (volume fraction 8%, particle size 2μm) to perform fixed-point polishing on the precision surface. The final surface roughness Ra is ≤ 0.12μm, and the dimensional tolerance is controlled at ±8μm.

[0103] The equipment or device used in this embodiment is the same as that in the first embodiment.

[0104] 3. Comparative Example

[0105] Comparative Example 1 (High-temperature sintering method)

[0106] Preparation steps:

[0107] Raw material mixing: aluminum powder (particle size 20 μm) and magnesium oxide particles (particle size 5 μm, mass ratio 6:4) were directly mixed without nano-processing or dispersant addition;

[0108] High temperature sintering: In a vacuum sintering furnace, heat up to 650°C at 10°C / min, introduce argon protection, apply 80MPa pressure and keep warm for 2 hours, then cool to room temperature with the furnace;

[0109] Machining: The sintered green body was roughly machined using a CNC milling machine, and no surface polishing was performed.

[0110] Performance drawbacks:

[0111] After sintering, the average grain size of the aluminum matrix reached 50 μm, the magnesium oxide particles showed significant agglomeration, and the density was only 92%. Complex structural parts (such as curved shields) warped after cooling, with a maximum deformation of 0.3 mm and a surface roughness of Ra 0.3 μm, which could not meet the requirements of precision instrument assembly.

[0112] Comparative Example 2 (cold pressing + post-processing)

[0113] Preparation steps:

[0114] Room temperature molding: Aluminum powder (particle size 15 μm) and magnesium oxide particles (particle size 3 μm, mass ratio 7:3) were mixed, 1.0 wt% oleic acid was added, and the mixture was cold-pressed at 80 MPa on a YJ32-100 hydraulic press.

[0115] Heat treatment strengthening: Place the formed body into a box-type resistance furnace, heat it to 400℃ at 5℃ / min, keep it at this temperature for 2 hours, and then air cool it.

[0116] Surface treatment: Shot peening process is adopted, and 0.5mm diameter glass shot is sprayed on the surface at a pressure of 0.3MPa for 3 minutes.

[0117] Performance drawbacks:

[0118] The interface between magnesium oxide and the aluminum matrix is only physically bonded, resulting in an interfacial shear strength of only 35 MPa, lower than the 85 MPa of Example 2. When the magnesium oxide content exceeds 40%, a network of cracks appears within the blank, with a crack rate of 15%. After shot peening, the surface roughness is Ra 0.5 μm, with localized depressions caused by excessive impact in complex curved areas. The dimensional accuracy error reaches ±15 μm.

[0119] 4. Key performance indicators are compared in Table 1:

[0120] Table 1:

[0121]

[0122]

[0123] Technical advantage analysis:

[0124] This method achieves chemical bonding between magnesium oxide particles and the aluminum matrix at room temperature by inducing particle orientation and interfacial activation through a pulsed electric field, combined with dynamic densification through pulsed pressure. This avoids the grain coarsening and deformation associated with high-temperature sintering. Nano-sizing pretreatment and silane coating significantly enhance particle dispersibility and interfacial adhesion, increasing the upper limit of the ceramic phase content to 40% without cracks. Compression molding and magnetorheological polishing techniques ensure micron-level dimensional accuracy and low surface roughness, significantly outperforming traditional processes in overall performance.

[0125] The testing instruments and methods corresponding to the key performance indicators are based on conventional testing standards and industry practices in the field of materials science and engineering, specifically:

[0126] 1. Material density (%)

[0127] Detection method:

[0128] The density of the sample was measured using the Archimedes drainage method. The calculation formula is: density = theoretical density / measured density × 100%

[0129] Measured density: Use an analytical balance with an accuracy of 0.0001g (such as Mettler Toledo ME204E) and measure the sample volume and mass by the distilled water immersion method in accordance with GB / T5060-1985 "Method for measuring the density of metallic materials" to calculate the density.

[0130] Theoretical density: According to the mixing law, aluminum (2.7g / cm 3) and magnesium oxide (3.58g / cm 3 ) is used to calculate the theoretical density.

[0131] 2. Interface shear strength (MPa)

[0132] Detection method:

[0133] The single lap shear test (Single Lap Shear Test) was used to prepare the specimen according to ASTM D1002 standard:

[0134] The magnesium oxide aluminum alloy was processed into a sheet specimen of 10 mm × 10 mm × 2 mm by pressing a cap, and a shear test area was prepared along the aluminum-magnesium oxide interface;

[0135] Use an electronic universal testing machine (such as Instron 5967) to load at a rate of 1 mm / min, record the maximum load when the interface breaks, and calculate the shear strength: τ = A / F,

[0136] Where F is the breaking load (N), A is the shear area (mm 2 ).

[0137] 3. Surface roughness Ra (μm)

[0138] Testing instruments and methods:

[0139] Use a stylus surface roughness measuring instrument (such as Japan's Mitutoyo SJ-210) or an optical profilometer (such as the American Veeco NT1100) in accordance with GB / T1031-2009 "Surface Roughness Parameters and Their Values":

[0140] Stylus method: The radius of the stylus tip is 2 μm, the sample surface is scanned at a speed of 0.5 mm / s, the sampling length is 4 mm, and the arithmetic average roughness Ra is calculated.

[0141] Optical method: The three-dimensional surface profile is obtained through white light interferometry or laser scanning, and the Ra value is output after software analysis.

[0142] 4. Upper limit of ceramic phase (magnesium oxide) content (%)

[0143] Detection method:

[0144] Quantitative metallographic method: Prepare the metallographic cross-section of the sample, mechanically polish and electrolytically etch (electrolyte: 10% perchloric acid ethanol solution, voltage 20V, time 30s), and observe using a scanning electron microscope (SEM, such as ZEISS Sigma300). Combined with Image-ProPlus software, the area ratio of magnesium oxide particles is calculated and converted into mass fraction.

[0145] X-ray diffraction (XRD) method: A Bruker D8 Advance X-ray diffractometer was used with CuKα radiation (λ = 0.154 nm), a scanning range of 10°-80°, and a step size of 0.02°. The relative contents of the aluminum matrix and the magnesium oxide phase were analyzed by Rietveld full spectrum fitting, referring to GB / T19500-2004 "X-ray quantitative analysis method for metals and alloys".

[0146] 5. Molding dimensional accuracy (μm)

[0147] Testing instruments and methods:

[0148] Use a coordinate measuring machine (CMM, such as the German Zeiss CONTURAG2) or an image measuring instrument (such as the Japanese Keyence VR-3200) in accordance with GB / T1958-2017 "Product Geometric Technical Specification (GPS) Shape and Position Tolerance Inspection Regulations":

[0149] Three-coordinate method: Use a ruby probe (2 mm in diameter) to contact-measure the key dimensions of the sample (such as pore diameter, wall thickness, and surface profile). Repeat the measurement three times and take the average value to calculate the deviation from the design dimension.

[0150] Imaging method: Scan the sample surface non-contactly, use sub-pixel edge detection technology to obtain contour coordinates, and compare them with the CAD model to calculate dimensional accuracy.

[0151] 6. Average grain size (μm)

[0152] Detection method:

[0153] Metallographic microscopy method: Prepare the metallographic cross-section of the sample, polish it, and etch it (aluminum matrix etching solution: 0.5% hydrofluoric acid aqueous solution, etching time 10s). Then, observe it using a Leica DM4000M metallographic microscope. Use the intercept method (GB / T6394-2017 “Method for determination of average grain size of metals”) to measure the intercept length of at least 50 grains and calculate the average grain size.

[0154] Scanning electron microscopy (SEM) method: Observe the grain boundaries under high-magnification SEM, analyze the grain orientation using EBSD (electron backscatter diffraction) technology, and automatically calculate the average grain size using statistical software.

[0155] Testing standards and instrument configuration instructions:

[0156] All tests are carried out in a standard environment (temperature 23°C ± 2°C, humidity 50% ± 5%), and the samples need to be placed in the test environment for 24 hours in advance for equilibrium.

[0157] At least five parallel specimens should be prepared for the interface shear strength and dimensional accuracy tests, and the results should be averaged to reduce errors.

[0158] Before XRD and EBSD testing, the sample surface needs to be ion thinned or electrolytically polished to avoid interference of mechanical damage on phase analysis.

[0159] By using the above method, the key properties of the magnesium oxide aluminum alloy button cap prepared by the present invention can be accurately quantified, providing data support for process optimization and quality control.

[0160] VII. Supplementary technical details

[0161] Pulsed electric field waveform design:

[0162] The bipolar symmetrical square wave eliminates charge accumulation by alternating between positive and negative (no DC bias observed on the oscilloscope), and the rising edge is ≤100ns to ensure that the instantaneous high electric field strength breaks through the oxide layer on the surface of the magnesium oxide (the Al2O3 layer is about 2nm thick and breaks down when the field strength is ≥10kV / mm).

[0163] Nano-crystallization of magnesium oxide surface:

[0164] The nano-rough structure (Ra50-100nm) provides mechanical biting sites, the silane coating (-Si-O-Al bond) promotes interfacial chemical bonding, and high-temperature stabilization eliminates surface hydroxyl groups (FTIR detection -OH absorption peak intensity is reduced by 60%), reducing interfacial defects caused by moisture adsorption.

[0165] Real-time adjustment of the control system:

[0166] The PLC controller collects temperature (infrared temperature measurement) and pressure (piezoelectric sensor) data every 50ms, and the PID algorithm uses incremental calculations:

[0167] Δu(k)=K p [e(k)-e(k-1)]+K i e(k)+K d [e(k)-2e(k-1)+e(k-2)],

[0168] Among them, Δu(k) is the control quantity increment at the kth moment;

[0169] K p is the proportionality coefficient, K i is the integral coefficient, K d is the differential coefficient;

[0170] e(k)=r(k)-y(k) is the deviation at the kth moment, r(k) is the set value, y(k) is the measured value, e(k-1) and e(k-2) are the deviations at the k-1st and k-2th moments respectively.

[0171] Through the above detailed steps, the process implementation details of the present invention under different magnesium oxide contents are fully presented, strictly adhering to the core technical points such as "pulsed electric field and pressure coordination", "normal temperature control", and "surface nano-pretreatment" in the specification. At the same time, the essential differences and advantages over the existing process are highlighted through comparative examples, meeting the patent specification's requirement that the specific implementation methods be "fully disclosed and repeatable".

[0172] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a hard magnesium oxide aluminum alloy button cap by pulse forming at room temperature, characterized in that: The following steps are involved: S1: Raw material pretreatment step, mixing aluminum powder and magnesium oxide particles and adding a dispersant for ball milling; S2: pulse composite treatment step, applying a pulse electric field and pulse pressure synergistically to the mixed powder; S3: a compression molding step, wherein the treated mixed powder is statically pressure molded at room temperature; S4: Surface treatment step, cleaning and polishing the formed body.

2. The method for preparing a hard magnesium oxide aluminum alloy button cap by pulse forming at room temperature according to claim 1, characterized in that: In the raw material pretreatment step, the mass ratio of aluminum powder to magnesium oxide particles is 8:2-6:4, the dispersant is stearic acid, oleic acid or polyethylene glycol, the added amount of the dispersant is 0.5-1.5wt%, the ball milling speed is 300-500rpm, and the ball milling time is 2-4 hours.

3. The method for preparing a hard magnesium oxide aluminum alloy button cap by pulse forming at room temperature according to claim 1, characterized in that: In the pulse composite treatment step, the voltage of the pulse electric field is 10-30 kV, the frequency is 10-50 Hz, the duty cycle is 20-40%, the peak value of the pulse pressure is 50-150 MPa, the cycle is 1-5 seconds, and the treatment time is 5-15 minutes.

4. The method for preparing a hard magnesium oxide aluminum alloy button cap by pulse forming at room temperature according to claim 1, wherein: The particle size of the aluminum powder is 5-20 μm, the particle size of the magnesium oxide particles is 1-5 μm, and the surface of the magnesium oxide particles is pre-treated by nano-processing.

5. The method for preparing a hard magnesium oxide aluminum alloy button cap by pulse forming at room temperature according to claim 1, wherein: The static pressure in the compression molding step is 50-100 MPa, the mold surface is coated with a boron nitride coating, and the ultrasonic cleaning frequency in the surface treatment step is 20-60 kHz and the time is 5-15 minutes.

6. The method for preparing a hard magnesium oxide aluminum alloy button cap by pulse forming at room temperature according to claim 1, characterized in that: In the pulse composite treatment step, the powder temperature is monitored in real time and controlled below 50° C. The pulse electric field is a bipolar symmetrical square wave with a rising edge time of ≤100 ns and a falling edge time of ≤500 ns.

7. A system for preparing hard magnesium oxide aluminum alloy button caps by pulse molding at room temperature, characterized in that: The system is used to implement the method according to any one of claims 1 to 6, specifically comprising: Raw material processing unit, used to mix aluminum powder, magnesium oxide particles and dispersant; A pulse compound device for applying a pulse electric field and pulse pressure to the mixed powder; A compression molding unit is used to compress the processed mixed powder into a shape; A cleaning unit is used to clean the blank after compression molding; A polishing unit, used for polishing the cleaned formed body; Control system for monitoring pulse parameters and processing.

8. The method and system for preparing hard magnesium oxide aluminum alloy button caps by pulse forming at room temperature according to claim 7, characterized in that: The raw material processing unit includes a ball mill, a weighing sensor and a mixing tank. The speed adjustment range of the ball mill is 0-800rpm, and the inner wall of the mixing tank is provided with a polytetrafluoroethylene coating.

9. The system for preparing hard magnesium oxide aluminum alloy button caps by pulse forming at room temperature according to claim 7, characterized in that: The pulse compound device includes a processing chamber, a pulse power supply and a hydraulic pulse cylinder. The output voltage adjustment range of the pulse power supply is 0-50kV, the frequency adjustment range is 0-100Hz, and the duty cycle adjustment range is 0-50%. The hydraulic pulse cylinder pressure peak adjustment range is 0-200MPa and the cycle adjustment range is 0-10 seconds.

10. The system for preparing hard magnesium oxide aluminum alloy button caps by pulse forming at room temperature according to claim 7, characterized in that: The control system integrates a PLC controller and a PID algorithm module, automatically adjusts pulse parameters according to powder temperature and pressure feedback, and supports remote data monitoring and cloud platform access.

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