A transient ultrasonic treatment method for rapidly generating an aluminum oxide-rich protective layer in situ on the surface of a rare earth magnesium alloy and application thereof

Abstract

The application discloses a kind of in-situ generation of rich alumina protective layer on the surface of rare earth magnesium alloy fast transient ultrasonic processing method and its application, belong to metal material surface engineering and modification technical field.Method includes: providing magnesium alloy workpiece containing aluminum and rare earth element, using ultrasonic tool head to workpiece surface in oxygen-containing environment Mechanical contact and high-frequency vibration irradiation;Through ultrasonic friction heat and the coupling effect of severe plastic deformation, induce surface layer aluminum element rapid diffusion and oxidation, in 5-15 seconds in-situ growth with alumina as main dense protective layer.The protective layer presents black, with amorphous-nanocrystalline composite structure of size increasing from surface to heart.This application does not need electrolyte and external heat source, process green environmental protection and extremely efficient, the obtained oxide layer and matrix form firm metallurgical bonding, significantly improve the surface hardness, wear resistance and corrosion resistance of magnesium alloy, suitable for industrialization online processing.

Description

Technical Field

[0001] This invention relates to a corrosion-resistant and wear-resistant strengthening treatment technology for the surface of magnesium alloy parts, and more particularly to an instantaneous ultrasonic treatment method for rapidly generating an alumina-rich protective layer on the surface of rare-earth magnesium alloys and its application, belonging to the field of surface engineering and modification technology of metallic materials. This invention is particularly suitable for surface modification of industrial parts that are weight-sensitive and require high strength and high corrosion resistance, such as automotive bogies, aircraft engine casings, drone frames, and portable electronic product housings. Background Technology

[0002] The poor corrosion resistance of magnesium alloys is a major bottleneck in their application. Traditional surface protection technologies such as micro-arc oxidation and anodizing, while effectively improving performance, generally suffer from drawbacks such as complex processes, long processing times (typically 10 to 60 minutes), high energy consumption, and reliance on chemical electrolytes. These methods fail to meet the urgent demands of modern industry for high-efficiency, low-energy, green manufacturing, and online processing. In existing technologies, ultrasonic vibration is mainly used for auxiliary cleaning, grain refinement, or promoting coating adhesion, but the processing time is also relatively long. The direct and rapid initiation of specific component oxidation reactions on metal surfaces using ultrasonic energy has not yet been reported. In particular, achieving in-situ growth of functional oxide layers within seconds, without relying on external heat sources and chemical reagents, presents a significant technical challenge.

[0003] Existing technologies have several drawbacks: Traditional electrolytic oxidation methods (micro-arc oxidation, anodic oxidation) have long processes, are time-consuming, and energy-intensive, making rapid surface treatment impossible. Existing surface treatment technologies struggle to balance high efficiency and speed with high-quality protection. 2. Rapid treatment often only yields a loose, amorphous, or poorly bonded surface layer. 3. Conventional technologies cannot trigger the selective oxidation of alloying elements and form a dense, well-bonded oxide layer within seconds. 4. There is a lack of a simple, convenient, and near-one-click high-efficiency surface strengthening technology for magnesium alloys. Based on these issues, there is an urgent need for an instantaneous ultrasonic treatment method for rapidly generating an alumina-rich protective layer on the surface of rare-earth magnesium alloys and its application. Summary of the Invention

[0004] The present invention aims to solve the technical problems of existing magnesium alloy surface treatment technologies (such as micro-arc oxidation and anodizing), such as long process flow, high energy consumption, dependence on chemical electrolytes, and difficulty in achieving rapid online processing.

[0005] This invention provides a rapid, in-situ ultrasonic treatment method for generating an alumina-rich protective layer on the surface of aluminum-rare-earth magnesium alloys. This method requires no external heat source or electrolyte, and can induce the formation of a dense black protective layer with an amorphous-nanocrystalline composite structure on the workpiece surface in just a few seconds. This layer contains a unique amorphous Al₂O₃ reinforcing phase, with an amorphous content of approximately 35-50%. The formation mechanism of this amorphous phase is as follows: the intense plastic deformation induced by ultrasonic vibration and frictional thermal coupling promote the rapid migration of Al atoms in the nanocrystalline boundaries (as diffusion channels), and they undergo a non-equilibrium oxidation reaction with oxygen to form highly active amorphous Al₂O₃ particles. These particles are compacted in-situ by the ultrasonic "micro-forging" effect and embedded in a gradient nanocrystalline matrix, significantly improving the surface hardness and wear and corrosion resistance of the magnesium alloy.

[0006] Meanwhile, this invention provides an application of an instantaneous ultrasonic treatment method for rapidly generating an alumina-rich protective layer on the surface of rare earth magnesium alloys. It is particularly suitable for surface modification of industrial parts that are weight-sensitive and require high strength and high corrosion resistance, such as automotive bogies, aircraft engine casings, drone frames, and portable electronic product housings.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: This invention provides a method for rapidly generating an alumina-rich protective layer in situ on the surface of rare-earth magnesium alloys using instantaneous ultrasonic treatment, comprising the following steps: S1, a magnesium alloy workpiece is provided, the base chemical composition by mass percentage is: Y: 5.8-7.5%, Gd: 4.5-5.8%, Zn: 2.0-3.2%, Al: 0.8-1.5%, with the balance being Mg and unavoidable impurities; the core limiting condition for this specific composition range is the mass ratio of Al to RE (Gd + Y) K = Al / (Gd + Y), with the K value controlled between 0.06 and 0.15. Only under this K value, combined with the ultrasonic process of this invention, can a black alumina protective layer be instantaneously generated through the synergistic effect of "non-equilibrium selective oxidation": when RE elements Gd and Y are at K of 0.06-0.15, they synergistically regulate the selective diffusion of Al atoms (as an oxidation source), inhibiting crystallization and promoting high strain rates (10). 3 -10 4 s -1 Amorphous Al2O3 particles are formed under the oxide layer (amorphous content 35-50%, volume ratio). If K < 0.06 (too little Al), the oxide source is insufficient and a continuous film cannot be formed; if K > 0.15 (too little RE), the oxide layer is severely crystallized and has poor density.

[0008] S2, clean and dry the surface of the workpiece to be processed to ensure that the surface is free of oil, oxide scale and obvious scratches; S3, in an air environment, a high-energy-density ultrasonic vibration device (the ultrasonic vibration device is an ultrasonic plastic welding machine produced by Shenzhen Hongri Ultrasonic Equipment Co., Ltd. (Shenzhen, China), mainly composed of a pressure device, ultrasonic generator, transducer, amplitude modulator, titanium alloy punch, stamping die and other testing equipment) is used to make the tool head directly contact the surface of the workpiece to be treated with a preset static pressure (50–200 N), and start ultrasonic vibration for instantaneous treatment; in: 1) The ultrasonic vibration frequency is 15-60 kHz, and the amplitude of the tool head end face is 10-100 μm; the ultrasonic output power density is controlled at 1000-5000 W / cm². 2 The processing employs a multi-stage dynamic control mode: initial low amplitude (10-30 μm) and low power density (1000-2000 W / cm²). 2 Pre-vibrate for 1-2 seconds to establish stable contact and initially induce plastic deformation; then gradually increase to the target amplitude (30-100 μm) and peak power density (3000-5000 W / cm²). 2 Simultaneously, frequency sweeping (gradually changing from 15-30 kHz to 40-60 kHz) is activated during the main processing phase (60-80% of the total time) to promote the non-equilibrium rapid oxidation of Al and the formation of amorphous phases; finally, low amplitude (10-30 μm) and decreasing power density (2000-1000 W / cm²) are used. 2 The low-pressure termination lasts for 1-2 seconds, promoting interlayer densification and stress release. This mode ensures gradient structure optimization and avoids inhomogeneities caused by a single parameter.

[0009] 2) During the processing, maintain a stable contact pressure between the tool head and the workpiece surface, and flexibly adjust the relative movement trajectory or scanning method of the tool head according to the workpiece geometry to achieve uniform coverage of the surface to be processed. 3) The total processing time should be controlled within 5-15 seconds, preferably 5-7 seconds; 4) Optionally, the surface temperature of the processing area can be monitored in real time using an infrared thermometer or thermocouple to keep its peak temperature within the range of 600-750℃.

[0010] S4. After the process is completed, the ultrasonic device is removed immediately. Without any subsequent heat treatment, cleaning or coating process, a magnesium alloy workpiece with a continuous, dense, black aluminum oxide protective layer on the surface is obtained.

[0011] The dense protective layer is black, 0.5-5μm thick, and forms a metallurgical bond with the substrate.

[0012] A magnesium alloy workpiece obtained by the method of the present invention has a continuous and dense black alumina protective layer with a thickness of 0.5-5 μm on its surface. The protective layer has an amorphous-nanocrystalline composite structure, with the surface grain size being nanoscale and gradually transitioning to micron-scale matrix grains as the depth increases.

[0013] The magnesium alloy workpiece with an alumina protective layer of the present invention has a hardness of 796.4-851.6 HV. 0.05 The wear rate is 3.2 × 10⁻⁶. -6 -5.5×10 -6 mm 3 · N -1 ·m -1 The corrosion current density is 1.2 × 10⁻⁶. -7 -2.7×10 -7 A·cm -2 .

[0014] The magnesium alloy workpieces of the present invention are used in industrial parts that are sensitive to weight and require high strength and high corrosion resistance, such as automobile bogies, aircraft engine casings, drone frames and portable electronic product housings.

[0015] The application of the magnesium alloy workpiece of the present invention in the automotive, aerospace and 3C electronics fields.

[0016] In the automotive field, this includes steering wheel frames, wheel hubs, and brackets.

[0017] In the aerospace field, this includes cabin shells and accessory housings; The 3C electronics field includes laptop mid-frames and camera frames, among others.

[0018] Using the instantaneous ultrasonic treatment method of the present invention, a dense alumina protective layer can be generated in situ on the parts to be protected of these complex-shaped components.

[0019] A portable magnesium alloy surface treatment apparatus for carrying out the method of the present invention includes: an ultrasonic generator for generating an electrical signal of 15-60 kHz; a transducer and an amplitude transformer for converting the electrical signal into mechanical vibration and amplifying it; a tool head connected to the end of the amplitude transformer, the end face of which is configured to withstand direct frictional contact with a metal surface; and a force application mechanism configured to apply a predetermined contact pressure to the tool head during treatment.

[0020] The inventiveness of this invention is prominently reflected in the introduction of the mass ratio K = Al / (Gd+Y) (0.06-0.15). This constraint ensures the synergy between Al as a minority of oxidation sources and RE (Gd+Y) as the majority of stabilizers, achieving "non-equilibrium selective oxidation" under high-energy acoustic fields (ultrasonic vibration): Al is selectively activated by RE under K optimization, achieving instantaneous diffusion and oxidation (cooling rate > 10). 6 (K / s) to generate amorphous-nanocrystalline reinforced alumina films. Without this K limit, although the ultrasonic parameters can be adjusted, the synergistic effect cannot be produced, leading to film formation failure or insufficient performance. This unpredictability stems from the regulation of Al oxidation kinetics by the RE, which is not obtainable through conventional experiments.

[0021] The beneficial effects achieved by this invention are as follows: Extremely fast and efficient: The processing time is only 5-15 seconds, which is more than 100 times more efficient than traditional micro-arc oxidation (10-60 minutes), making it suitable for large-scale production on assembly lines.

[0022] Green and environmentally friendly: The entire process takes place in the air, without the need for electrolytes or strong acids and alkalis, achieving truly green and pollution-free manufacturing.

[0023] Excellent film-substrate adhesion: The in-situ generated oxide layer achieves metallurgical bonding with the substrate through an "amorphous-nanocrystalline composite structure", which solves the problem of easy peeling of traditional coatings. It is also dense and non-porous, which significantly improves wear and corrosion resistance.

[0024] Simple process: The equipment is portable, easy to operate, requires no complicated pre-treatment or post-treatment, and has extremely low energy consumption.

[0025] Comparison of the protective layer obtained by this invention with traditional ceramic films: 1. Microstructure The protective layer of this invention is a black alumina film: it adopts an amorphous-nanocrystalline composite gradient structure, wherein the surface grain size is approximately 20-50 nm, gradually transitioning to the micrometer scale towards the interior of the substrate. This gradient design originates from the intense plastic deformation and rapid cooling process induced by ultrasound, resulting in the mixing of the amorphous phase (approximately 35-50%) and the nanocrystalline phase, forming a continuous, non-porous protective layer. This structure enhances the stress buffering between layers and reduces the risk of brittle failure.

[0026] Existing general ceramic films typically exhibit a highly crystalline monocrystalline structure with relatively uniform grain sizes (often ranging from hundreds of nanometers to micrometers). This structure is formed through conventional thermodynamic equilibrium processes, making it prone to grain boundary weaknesses and microscopic defects such as micropores or cracks, and it also lacks toughness.

[0027] 2. Color formation mechanism The black alumina film of this invention is black primarily due to the presence of numerous intrinsic defects (such as oxygen vacancies, dislocations, or vacancy clusters) in its amorphous structure. These defects create intermediate energy levels between the valence and conduction bands, effectively narrowing the band gap. This causes the material to shift from transparent / white to gray or black because the defects enhance the absorption of visible light, rather than simply reflecting or refracting it. Furthermore, the rare earth elements Y and Gd can modulate the oxidation kinetics of Al, forming a more stable amorphous phase, thereby enhancing defect density and light absorption.

[0028] Existing general ceramic films are typically white, transparent, or light-colored (such as silvery-white or light gray), with the color originating from the reflection and refraction of light within the crystal structure, rather than absorption. The electronic structure of pure crystalline Al₂O₃ results in high transparency, with light-colored variations only appearing when specific impurities (such as iron or chromium) are present. This mechanism relies on an equilibrium oxidation process, resulting in relatively simple optical properties.

[0029] Technical principle: The key to achieving second-level in-situ film formation and significantly superior performance in this invention lies in the strong synergistic effect of a specific rare-earth magnesium alloy composition (containing 0.8-1.5 wt% Al and a high proportion of rare-earth elements Y and Gd, and K=Al / (Gd+Y) (0.06-0.15)) and ultra-high energy density ultrasonic pulses in a multi-stage dynamic control mode. In an air environment, through a transient thermo-mechanical coupling process, this induces the selective and rapid oxidation of surface aluminum elements, forming a unique amorphous-nanocrystalline Al2O3 reinforcing phase (amorphous content approximately 35-50%). The formation of this amorphous phase originates from an ultra-high strain rate (10... 3 -10 4 s -1 Non-equilibrium oxidation driven by extreme rapid cooling conditions (cooling rate > 10) 6 This non-equilibrium selective oxidation (K / s) is significantly different from the crystalline Al₂O₃ formed by traditional thermodynamic equilibrium oxidation. This non-equilibrium selective oxidation is highly dependent on the mass ratio K = Al / (Gd + Y): when K is 0.06-0.15, the RE elements Gd and Y selectively enhance the migration of Al in the nanograin boundaries (avoiding interference from non-target elements) through solid solution and phase stabilization mechanisms, and "freeze" the amorphous phase under ultrasonically induced transient high temperatures (>600°C). If K < 0.06, Al is insufficient to provide an oxidation source, resulting in the absence of the non-equilibrium effect; if K > 0.15, RE is relatively insufficient, oxidation transitions to equilibrium, the crystallization temperature decreases (<600°C), the film transforms into crystalline Al₂O₃ (amorphous <5%), and corrosion resistance decreases by >50%.

[0030] The specific formation mechanism is as follows: 1. Ultra-high strain rate induces surface nanostructuring and amorphization tendency: The ultrasonic tool head applies tens of thousands of high-frequency micro-impacts per second at a frequency of 15-60 kHz and an amplitude of 10-100 μm, generating an extremely high strain rate (10 μm) on the surface. 3 -10 4 s -1 This intense plastic deformation instantly breaks down the original grains, forming a surface nanocrystalline structure (grain size 20-50 nm), while simultaneously introducing numerous defects such as grain boundaries, dislocations, and vacancies. These defects serve as rapid diffusion channels and provide the structural basis for amorphization. Under extreme shear stress and localized transient high temperatures, atomic arrangement struggles to maintain long-range order, resulting in localized amorphous regions (similar to high strain rate-induced shear band amorphization).

[0031] 2. Gradient Energy Distribution Constructs an Amorphous-Nanocrystalline Composite Gradient Structure: The ultrasonic impact energy decays exponentially from the surface to the interior, causing the degree of plastic deformation to decrease with depth, thus forming a unique gradient structure: the outermost layer is dominated by Al2O3 with a high amorphous content (35-50% amorphous), the second layer is a composite of nanocrystalline Al2O3 and a small amount of amorphous phase, gradually transitioning inward to micron-sized matrix grains. This gradient design effectively alleviates stress concentration and improves the overall toughness and anti-stripping ability of the coating. Thermo-mechanical coupling drives the non-equilibrium rapid oxidation of Al elements, and high-frequency friction generates local transient high temperatures (>600°C, locally reaching even higher), which, combined with intense plastic deformation, activates the ultra-fast outward diffusion of Al atoms in a large number of nanocrystalline boundaries (the diffusion coefficient is several orders of magnitude higher than conventional). Al atoms undergo a non-equilibrium oxidation reaction with oxygen in the environment, and due to the extremely high cooling rate (>10), 6 (At the K / s level, determined by the transient nature of the ultrasonic pulse), the oxidation products do not have time to nucleate and grow into crystals, and are directly "frozen" into highly reactive amorphous Al2O3 particles. Rare earth elements (Y, Gd) further promote the selective oxidation of Al and stabilize the amorphous phase, inhibiting the tendency to crystallize.

[0032] 3. The ultrasonic "micro-forging" effect achieves dynamic densification and metallurgical bonding: Continuous high-frequency micro-impact generates a dynamic "micro-forging" effect: each impact is equivalent to a micrometer-level high-frequency hammer blow, repeatedly squeezing, compacting, and plastically flowing the newly generated amorphous Al2O3 particles and nano-oxides in situ. This process effectively eliminates defects such as micropores and cracks common in traditional oxidation processes, forming a continuous, dense, and pore-free protective layer. Simultaneously, the amorphous phase and the substrate achieve atomic-level metallurgical bonding through intense deformation, significantly improving the interfacial bonding strength. The resulting amorphous-nanocrystalline composite alumina protective layer possesses extremely high hardness (approximately 800 HV), excellent wear resistance, and corrosion resistance. The synergistic effect of these mechanisms allows this invention to achieve a dense, amorphous strengthened oxide layer that is difficult to achieve with traditional micro-arc oxidation (requiring 10-60 minutes) within 5-15 seconds. This process requires no external heat source or electrolyte, is green and efficient, and offers performance improvements with significant unpredictability.

[0033] This invention discloses a rapid, in-situ ultrasonic treatment method for generating an alumina-rich protective layer on the surface of rare-earth magnesium alloys. The method includes: providing a magnesium alloy workpiece containing aluminum and rare-earth elements; applying mechanical contact and high-frequency vibration irradiation to the workpiece surface using an ultrasonic tool head in an oxygen-containing environment; and inducing rapid diffusion and oxidation of surface aluminum elements through the coupling effect of ultrasonic frictional heat and intense plastic deformation, resulting in the in-situ growth of a dense protective layer dominated by alumina within 5 to 15 seconds. This protective layer is black and has an amorphous-nanocrystalline composite structure with dimensions increasing from the surface to the core. This invention requires no electrolyte or external heat source, making the process green, environmentally friendly, and extremely efficient. The resulting oxide layer forms a strong metallurgical bond with the substrate, significantly improving the surface hardness, wear resistance, and corrosion resistance of the magnesium alloy, making it suitable for industrial online processing. Attached Figure Description

[0034] Figure 1 These are macroscopic comparison photos of the sample surface before and after processing for only 5 seconds in Example 1 of this invention (the left side is bright, and the right side has turned black). Figure 2 This is a high-magnification cross-sectional SEM image of the black oxide layer obtained in Example 1 of the present invention, showing its thin and dense morphology. Detailed Implementation

[0035] The following description, in conjunction with the accompanying drawings and embodiments of the present invention, will further clarify the objectives, technical solutions, and advantages of the present invention. The specific embodiments described are merely illustrative and are not intended to limit the scope of the invention.

[0036] The magnesium alloy workpieces described in this invention have broad industrial applicability. In actual production, the workpieces can be structural or functional components formed by casting (such as die casting, semi-solid casting), forging, or machining. Specifically, the workpieces can be steering wheel frames, wheel hubs, and brackets in the automotive industry; cabin shells and accessory housings in the aerospace industry; and laptop computer frames or camera frames in the 3C electronics industry, etc. Using the instantaneous ultrasonic treatment method of this invention, a dense alumina protective layer can be generated in situ on the parts of these complex-shaped components to be protected. Example 1

[0037] Substrate: Cast magnesium alloy with composition Mg-6.7Y-5Gd-2.5Zn-1Al (wt.%), K=0.085. The surface is cleaned and dried after degreasing treatment.

[0038] Processing: Parameter settings: amplitude 15-30 μm, contact static pressure 100 N, processing energy controlled at around 1000 J. Initial low amplitude 15 μm and power density 1500 W / cm². 2 Pre-vibrate for 1 second to establish contact; gradually increase to the target amplitude of 30μm and peak power density of 3000W / cm². 2 Simultaneously, frequency sweeping is initiated (gradually transitioning from 20 kHz to 40 kHz), with main processing lasting 3 seconds; low-voltage termination lasts 1 second, and power density decreases to 1500 W / cm². 2 The tail amplitude is 30μm and the tail ultrasonic vibration frequency is 40kHz.

[0039] Procedure: Press the tool head vertically into the surface of the test piece, start the vibration, and continue the treatment for 5 seconds.

[0040] Results: A uniform black layer was formed on the surface of the treated area. SEM analysis showed that the oxide layer was approximately 3.5 μm thick, dense, and non-porous. EDS analysis confirmed that the layer was rich in Al and O elements, while the Mg content of the matrix decreased significantly in this layer, indicating the formation of a protective layer dominated by alumina. The amorphous phase accounted for approximately 35% of this protective layer, and the grain size increased in a gradient from the surface to the center.

[0041] like Figure 1 As shown in the figure, the macroscopic comparison photos of the sample surface before and after processing in this embodiment are shown in only 5 seconds. The left side is bright before 5 seconds, and the right side has turned black after 5 seconds.

[0042] like Figure 2 The image shown is a high-magnification cross-sectional SEM image of the black oxide layer obtained in this embodiment, demonstrating its thin and dense morphology.

[0043] Example 2: Effect of different contact static pressures on the density and amorphous content of the protective layer Substrate: Cast magnesium alloy with composition Mg-6.7Y-5Gd-2.5Zn-1Al (wt.%). The surface is cleaned and dried after degreasing treatment.

[0044] Processing parameters: Amplitude 15-30μm, contact static pressure (trigger pressure) 200N, processing energy controlled at around 1000J. Initial low amplitude 15μm and power density 1500W / cm². 2 Pre-vibrate for 1 second to establish contact; gradually increase to the target amplitude of 30 μm and peak power density of 3000 W / cm². 2 Simultaneously, frequency sweeping is initiated (gradually transitioning from 20 kHz to 40 kHz), with main processing lasting 3 seconds; low-voltage termination lasts 1 second, and power density decreases to 1500 W / cm². 2 The tail amplitude is 30μm and the tail ultrasonic vibration frequency is 40kHz.

[0045] Procedure: Press the tool head vertically into the surface of the test piece, start the vibration, and continue the treatment for 5 seconds.

[0046] Results: A uniform black oxide layer with a thickness of approximately 3.8 μm was formed on the surface of the treated area. The layer was dense and non-porous. The amorphous phase accounted for approximately 42% of the protective layer, and the grain size increased in a gradient from the surface to the center.

[0047] Example 3: Effect of different processing energies on the density and amorphous content of the protective layer Substrate: Cast magnesium alloy with composition Mg-6.7Y-5Gd-2.5Zn-1Al (wt.%). The surface is cleaned and dried after degreasing treatment.

[0048] Processing: Parameter settings: amplitude 15-30μm, contact static pressure (trigger pressure) 100N. Energy regulation is achieved by adjusting the output power of the ultrasonic generator, with the processed energy controlled at around 2000J. Initial low amplitude 25μm and power density 2000W / cm². 2 Pre-vibrate for 1 second to establish contact; gradually increase to the target amplitude of 30μm and peak power density of 5000W / cm². 2 Simultaneously, frequency sweeping is initiated (gradually transitioning from 20kHz to 40kHz), with main processing lasting 3 seconds; low-voltage termination lasts 1 second, and power density decreases to 2000W / cm². 2 The tail amplitude is 30μm and the tail ultrasonic vibration frequency is 40kHz.

[0049] Procedure: Press the tool head vertically into the surface of the test piece, start the vibration, and continue the treatment for 5 seconds.

[0050] Results: A uniform black oxide layer with a thickness of approximately 5.1 μm was formed on the surface of the treated area. The layer was dense and non-porous. The amorphous phase accounted for approximately 50% of the protective layer, and the grain size increased in a gradient from the surface to the center.

[0051] Example 4: A method for rapidly generating an alumina-rich protective layer on the surface of a rare-earth magnesium alloy using instantaneous ultrasonic treatment includes the following steps: S1, a magnesium alloy workpiece is provided, the base chemical composition by mass percentage is: Y: 5.8%, Gd: 4.5%, Zn: 2.0%, Al: 0.8%, with the balance being Mg and unavoidable impurities; wherein, the mass ratio of Al to (Gd + Y) is K = Al / (Gd + Y) = 0.078; S2, clean and dry the surface of the magnesium alloy workpiece to be treated to ensure that the surface is free of oil, oxide scale and obvious scratches; S3, In an air environment, the tool head of an ultrasonic vibration device applies mechanical contact and ultrasonic vibration irradiation to the surface of a magnesium alloy workpiece to be treated. The tool head directly contacts the surface of the magnesium alloy workpiece to be treated with a static pressure of 50 N, and initiates ultrasonic vibration in a multi-stage dynamic control mode for instantaneous treatment. Initial ultrasonic vibration phase: with low amplitude of 10 μm and low power density of 1000 W / cm² 2 Pre-vibration for 2 seconds; ultrasonic vibration frequency is 15kHz; Main processing stage: followed by an amplitude of 100 μm and a peak power density of 5000 W / cm² 2 Ultrasound, with an ultrasonic vibration frequency of 60 kHz, is used in the main processing phase, which accounts for 80% of the total time, or 12 seconds, for a total time of 15 seconds. Final stage: A low amplitude of 10μm and a decreasing power density of 2000W / cm² were used. 2 The low-pressure termination lasts for 1 second, with a termination ultrasonic vibration frequency of 60kHz.

[0052] In S3, during the main processing stage, the surface temperature of the processing area is monitored in real time using an infrared thermometer or thermocouple to keep its peak temperature around 600℃.

[0053] After the S3 treatment is completed, the ultrasonic vibration device is immediately removed. Without any subsequent heat treatment, cleaning or coating process, a magnesium alloy workpiece with a continuous, dense, black aluminum oxide protective layer on the surface is obtained.

[0054] The magnesium alloy workpiece with an alumina protective layer obtained by the method of this embodiment has an alumina protective layer with a thickness of approximately 5.0 μm and forms a metallurgical bond with the substrate. The alumina protective layer has an amorphous-nanocrystalline composite gradient structure, with an amorphous content of approximately 50% by volume, a surface grain size of 20-50 nm, and gradually transitions to the micrometer scale with increasing depth.

[0055] In this embodiment, the magnesium alloy workpiece with an alumina protective layer has a hardness of 836.1 HV. 0.05 The wear rate was 3.9 × 10⁻⁶. -6 mm 3 · N -1 ·m -1 The corrosion current density is 2.0 × 10⁻⁶. -7 A·cm -2 .

[0056] This embodiment describes the application of magnesium alloy workpieces with an alumina protective layer in the automotive, aerospace, and 3C electronics fields. In the automotive field, these include steering wheel frames, wheel hubs, and brackets; in the aerospace field, they include cabin shells and accessory housings; and in the 3C electronics field, they include laptop computer frames and camera frames.

[0057] Example 5: A method for rapidly generating an alumina-rich protective layer on the surface of a rare-earth magnesium alloy using instantaneous ultrasonic treatment includes the following steps: S1, a magnesium alloy workpiece is provided, the base chemical composition by mass percentage is: Y: 7.5%, Gd: 5.8%, Zn: 3.2%, Al: 1.5%, with the balance being Mg and unavoidable impurities; wherein, the mass ratio of Al to (Gd + Y) is K = Al / (Gd + Y) = 0.113; S2, clean and dry the surface of the magnesium alloy workpiece to be treated to ensure that the surface is free of oil, oxide scale and obvious scratches; S3, In an air environment, the tool head of an ultrasonic vibration device applies mechanical contact and ultrasonic vibration irradiation to the surface of a magnesium alloy workpiece to be treated. The tool head directly contacts the surface of the magnesium alloy workpiece to be treated with a static pressure of 150 N, and initiates ultrasonic vibration in a multi-stage dynamic control mode for instantaneous treatment. Initial ultrasonic vibration phase: with low amplitude of 30 μm and low power density of 2000 W / cm² 2 Pre-vibration for 1 second; ultrasonic vibration frequency of 30kHz; Main processing stage: followed by an amplitude of 50 μm and a peak power density of 4000 W / cm² 2 Ultrasound, with an ultrasonic vibration frequency of 50 kHz, is used in the main processing phase, which accounts for 60% of the total time, or 4 seconds, for a total time of 7 seconds. Final stage: A low amplitude of 20μm and a decreasing power density of 1000W / cm² were used. 2 The low-pressure termination lasts for 2 seconds, with a termination ultrasonic vibration frequency of 50kHz.

[0058] In S3, during the main processing stage, the surface temperature of the processing area is monitored in real time using an infrared thermometer or thermocouple to keep its peak temperature around 750℃.

[0059] After the S3 treatment is completed, the ultrasonic vibration device is immediately removed. Without any subsequent heat treatment, cleaning or coating process, a magnesium alloy workpiece with a continuous, dense, black aluminum oxide protective layer on the surface is obtained.

[0060] The magnesium alloy workpiece with an alumina protective layer obtained by the method of this embodiment has an alumina protective layer with a thickness of approximately 4.0 μm and forms a metallurgical bond with the substrate. The alumina protective layer has an amorphous-nanocrystalline composite gradient structure, with an amorphous content of approximately 50% by volume, a surface grain size of 20-50 nm, and gradually transitions to the micrometer scale with increasing depth.

[0061] In this embodiment, the magnesium alloy workpiece with an alumina protective layer has a hardness of 801.5 HV. 0.05 The wear rate was 4.8 × 10⁻⁶. -6 mm 3 · N -1 ·m -1 The corrosion current density is 2.3 × 10⁻⁶. -7 A·cm -2 .

[0062] This embodiment describes the application of magnesium alloy workpieces with an alumina protective layer in the automotive, aerospace, and 3C electronics fields. In the automotive field, these include steering wheel frames, wheel hubs, and brackets; in the aerospace field, they include cabin shells and accessory housings; and in the 3C electronics field, they include laptop computer frames and camera frames.

[0063] Example 6: The only difference between this comparative example and Example 5 is that: The base chemical composition of the magnesium alloy workpiece, by mass percentage, is: Y: 7.5%, Gd: 5.8%, Zn: 3.0%, Al: 0.8%, with the balance being Mg and unavoidable impurities; wherein, the mass ratio of Al to (Gd + Y) is K = Al / (Gd + Y) = 0.06.

[0064] The magnesium alloy workpiece with an alumina protective layer obtained by the method of this embodiment has an alumina protective layer with a thickness of approximately 0.5 μm and forms a metallurgical bond with the substrate. The alumina protective layer has an amorphous-nanocrystalline composite gradient structure, with an amorphous content of approximately 35% by volume, a surface grain size of 20-50 nm, and gradually transitions to the micrometer scale with increasing depth.

[0065] In this embodiment, the magnesium alloy workpiece with an alumina protective layer has a hardness of 799.2 HV. 0.05The wear rate was 5.4 × 10⁻⁶. -6 mm 3 · N -1 ·m -1 The corrosion current density is 2.6 × 10⁻⁶. -7 A·cm -2 .

[0066] Example 7: The only difference between this comparative example and Example 5 is that: The base chemical composition of the magnesium alloy workpiece, by mass percentage, is: Y: 5.8%, Gd: 4.5%, Zn: 2.6%, Al: 1.5%, with the balance being Mg and unavoidable impurities; wherein, the mass ratio of Al to (Gd + Y) is K = Al / (Gd + Y) = 0.15.

[0067] The magnesium alloy workpiece with an alumina protective layer obtained by the method of this embodiment has an alumina protective layer with a thickness of approximately 4.8 μm and forms a metallurgical bond with the substrate. The alumina protective layer has an amorphous-nanocrystalline composite gradient structure, with an amorphous content of approximately 45% by volume, a surface grain size of 20-50 nm, and gradually transitions to the micrometer scale with increasing depth.

[0068] In this embodiment, the magnesium alloy workpiece with an alumina protective layer has a hardness of 815.6 HV. 0.05 The wear rate was 5.2 × 10⁻⁶. -6 mm 3 · N -1 ·m -1 The corrosion current density is 2.2 × 10⁻⁶. -7 A·cm -2 .

[0069] Comparative Example 1: Performance Testing of Untreated Rare Earth Magnesium Alloy Raw Substrate A cast magnesium alloy (Mg-6.7Y-5Gd-2.5Zn-1Al) with the exact same composition as in Example 1 was selected as a control sample. The surface of this sample underwent only routine mechanical polishing and alcohol cleaning, without any ultrasonic vibration treatment. Comparison of Examples 1-3 and Comparative Example 1 shows that the untreated raw magnesium alloy surface has extremely low hardness and extremely poor corrosion resistance (I...). corr =10 -5 A cm -2 After instantaneous ultrasonic treatment according to this invention, without the addition of any external chemical reagents, corrosion resistance can be improved by two orders of magnitude and wear resistance by approximately two orders of magnitude in just 5 seconds. This extremely rapid in-situ film formation effect fully demonstrates the uniqueness and inventiveness of the non-equilibrium oxidation induced by the coupling of ultrasonic frictional heat and intense plastic deformation in this invention.

[0070] Comparative Example 2: Alloys with K values ​​outside the range (K<0.06) Substrate: Cast magnesium alloy with composition Mg-6.7Y-5Gd-2.5Zn-0.5Al (wt.%, Gd + Y = 11.7%, K≈0.043<0.06). The surface is cleaned and dried after degreasing treatment.

[0071] Treatment: The same ultrasound parameters as in Example 1 were used.

[0072] Results: A black layer formed on the treated surface, but SEM showed that the oxide layer thickness was <0.5 μm and exhibited porosity. EDS analysis revealed insufficient Al-O elements, preventing the formation of a dense protective layer. Reason: The low Al content failed to provide a sufficient oxidation source, resulting in incomplete non-equilibrium oxidation and an amorphous phase ratio of <5%.

[0073] Comparative Example 3: Alloys with K values ​​outside the range (K>0.15) Substrate: Cast magnesium alloy with composition Mg-4.0Y-2.5Gd-2.5Zn-1Al (wt.%, Gd + Y = 6.5%, K≈0.154>0.15). The surface is cleaned and dried after degreasing treatment.

[0074] Treatment: The same ultrasound parameters as in Example 1 were used.

[0075] Results: A light gray layer, not black, formed on the treated surface. SEM showed a layer thickness of approximately 2 μm, but with obvious porosity and cracks. The amorphous phase accounted for less than 5%, indicating severe crystallization. Reason: Excessive K and relatively insufficient RE led to oxidation reaching equilibrium, resulting in a non-dense film.

[0076] Effect test Analysis of the magnesium alloys prepared in the examples and comparative examples using SEM / EDS, TEM, microhardness, wear tests, electrochemical tests, and UV-Vis DRS showed that the black protective layer had a high absorption rate in the visible light band, and the corresponding band gap was significantly narrower compared with wide bandgap alumina.

[0077] The wear and corrosion resistance results of Examples 1-7 and Comparative Examples 1-3 are shown in Table 1 below.

[0078] Table 1

[0079] It should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the above description of exemplary embodiments of the invention. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in fewer than all the features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0080] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0081] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for rapid in-situ generation of an alumina-rich protective layer on the surface of rare earth magnesium alloys using instantaneous ultrasonic treatment, characterized in that: Includes the following steps: S1, a magnesium alloy workpiece is provided, the base chemical composition by mass percentage is: Y: 5.8-7.5%, Gd: 4.5-5.8%, Zn: 2.0-3.2%, Al: 0.8-1.5%, with the balance being Mg and unavoidable impurities; wherein, the mass ratio of Al to (Gd + Y) is K = Al / (Gd + Y) = 0.06-0.15; S2, Clean and dry the surface of the magnesium alloy workpiece to be treated; S3, In an air environment, the tool head of an ultrasonic vibration device applies mechanical contact and ultrasonic vibration irradiation to the surface of a magnesium alloy workpiece to be treated. The tool head directly contacts the surface of the magnesium alloy workpiece to be treated with a static pressure of 50-200 N, and initiates ultrasonic vibration in a multi-stage dynamic control mode for instantaneous treatment. Initial ultrasonic vibration phase: low amplitude 10-30 μm and low power density 1000-2000 W / cm² 2 Pre-vibration for 1-2 seconds; ultrasonic vibration frequency of 15-30 kHz; Main processing stage: followed by amplitude of 30-100 μm and peak power density of 3000-5000 W / cm² 2 Ultrasound, with an ultrasonic vibration frequency of 40-60 kHz, is used in the main processing phase, which accounts for 60-80% of the total time, with a total time of 5-15 seconds. Final stage: Maintain low amplitude (10-30 μm) and decreasing power density (2000-1000 W / cm²) at the end. 2 The low-pressure termination lasts 1-2 seconds, with an ultrasonic vibration frequency of 40-60 kHz.

2. The method according to claim 1, characterized in that: In S3, the total time is 5-7 seconds.

3. The method according to claim 1, characterized in that: In S3, during the main processing stage, the surface temperature of the processing area is monitored in real time using an infrared thermometer or thermocouple, so that its peak temperature is controlled within the range of 600-750℃.

4. The method according to claim 1, characterized in that: After the S3 treatment is completed, the ultrasonic vibration device is immediately removed. Without any subsequent heat treatment, cleaning or coating process, a magnesium alloy workpiece with a continuous, dense, black aluminum oxide protective layer on the surface is obtained.

5. The method according to claim 4, characterized in that: The thickness of the alumina protective layer is 0.5-5 μm, and it forms a metallurgical bond with the substrate.

6. The method according to claim 4, characterized in that: The alumina protective layer has an amorphous-nanocrystalline composite gradient structure, with an amorphous content of 35-50% by volume, a surface grain size of 20-50 nm, and gradually transitions to the micron level with increasing depth.

7. A magnesium alloy workpiece with an alumina protective layer obtained by the method according to any one of claims 1-6.

8. The magnesium alloy workpiece with an alumina protective layer according to claim 7, characterized in that: The thickness of the alumina protective layer is 0.5-5μm, and it forms a metallurgical bond with the substrate. The alumina protective layer has an amorphous-nanocrystalline composite gradient structure, with an amorphous content of 35-50% by volume, a surface grain size of 20-50nm, and gradually transitions to the micron level with increasing depth.

9. The magnesium alloy workpiece with an alumina protective layer according to claim 7, characterized in that: Its hardness is 796.4-851.6 HV. 0.05 The wear rate is 3.2 × 10⁻⁶. -6 -5.5×10 -6 mm 3 · N -1 ·m -1 The corrosion current density is 1.2 × 10⁻⁶. -7 -2.7×10 -7 A·cm -2 .

10. The application of magnesium alloy workpieces with an alumina protective layer according to claim 7 in the automotive, aerospace, and 3C electronics fields, characterized in that: In the automotive sector, this includes steering wheel frames, wheel hubs, and brackets; in the aerospace sector, it includes cabin shells and accessory housings; and in the 3C electronics sector, it includes laptop mid-frames and camera frames.

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