Lightweight high-strength zinc alloy and preparation method and application thereof

Abstract

The invention relates to the technical field of metal materials, and discloses a light high-strength zinc alloy and a preparation method and application thereof.The zinc alloy takes aluminum and magnesium as main alloy elements, scandium-yttrium pre-alloying components, cerium-lanthanum composite rare earth and a nano TiB2 particle reinforced phase are introduced, and grain refinement and interface strengthening are achieved through the synergistic effect of multiple components; the preparation method comprises the key processes of pre-alloy smelting, dynamic magnetic field assisted die casting, gradient aging treatment and the like, and the defects of melt oxidation and solidification are effectively controlled. The zinc alloy has low density, high specific strength, corrosion resistance and excellent surface treatment adaptability, is suitable for manufacturing of precise metal fasteners such as belt buckles, belt buckles and shoe buckles, can remarkably improve the anti-fatigue performance and appearance quality of products, meanwhile, reduces processing energy consumption and material loss, and meets the market requirements of light-weight and high-end hardware fittings.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a lightweight and high-strength zinc alloy and a preparation method and application thereof. Background Art

[0002] Traditional zinc alloy materials have long faced the problem of balancing mechanical properties and corrosion resistance in the field of metal fastener manufacturing. Due to the limitations of component design, conventional alloy systems often increase the strength by increasing the content of elements such as aluminum and copper, but with increased density and decreased plasticity, it is difficult to meet the dual requirements of high-end fasteners for lightweight and complex modeling.

[0003] In addition, the accumulation of oxide inclusions and die-casting defects during the smelting process can easily lead to the weakening of the bonding strength of the product's surface treatment layer. In corrosive environments such as humidity, heat, and sweat, the coating is prone to peeling or the substrate is prone to pitting, seriously affecting the appearance quality and service life.

[0004] Although existing processes attempt to introduce rare earths to refine grains, the lack of coordinated regulation of pre-alloying treatment, enhanced phase dispersion and gradient heat treatment has limited improvement in material performance, and large-scale production is prone to batch stability problems due to process fluctuations.

[0005] At the same time, the processing energy consumption and scrap rate of traditional high-zinc content alloys remain high, making it difficult to adapt to the stringent requirements for resource efficiency under the green manufacturing trend.

[0006] The above-mentioned technical bottlenecks have restricted the application and upgrading of zinc alloys in the field of precision hardware accessories, and it is urgent to achieve breakthroughs through innovations in material systems and preparation methods. Summary of the invention

[0007] In view of the deficiencies in the prior art, the present invention provides a lightweight and high-strength zinc alloy and a preparation method and application thereof, which solves the problem that traditional zinc alloys are difficult to coordinately optimize among lightweight, mechanical strength, corrosion resistance and surface treatment adaptability.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions: A first aspect of the present invention provides a lightweight and high-strength zinc alloy, comprising, by mass percentage: Zn82.0%~85.0%, Al8.0%~9.0%, Sc0.1%~0.5%, Y0.05%~0.2%, TiB20.5%~1.5%, Ce and La rare earth mixture 0.05%~0.15% and Mg0.02%~0.1%; the remainder is inevitable impurities. The alloy has achieved a dual breakthrough of lightweight and high strength through multi-component collaborative design and microstructure regulation, as follows: 1. Lightweight design of Zn-Al matrix With zinc (Zn) as the matrix, aluminum (Al) is introduced to form a Zn-Al solid solution. The density of aluminum (2.7 g / cm 3 ) is significantly lower than zinc (7.1 g / cm 3 ), which can reduce the overall density of the alloy, while the solid solution strengthening effect of Al can improve the strength of the matrix. However, excessive aluminum content in traditional high-aluminum zinc alloys (such as ZA-8) will increase grain boundary brittleness. The present invention limits the Al content to 8.0% to 9.0%, which not only ensures the lightweight effect, but also avoids the decrease in plasticity caused by excessive Al.

[0009] 2. Sc-Y-TiB2 composite strengthening mechanism The synergistic addition of scandium (Sc) and yttrium (Y) is one of the core innovations. Sc preferentially segregates at grain boundaries in zinc alloys, inhibiting dynamic recrystallization through the pinning effect, while Y reacts with Al to form nanoscale YAl3 phases, further refining the grains and hindering dislocation movement. At the same time, nano-TiB2 particles, as heterogeneous nucleating agents, promote grain refinement during solidification and improve the tensile strength of the alloy through a load transfer mechanism. The composite effect of Sc, Y and TiB2 breaks through the limitations of the single strengthening phase of traditional zinc alloys and forms a multi-scale (grain boundary, precipitate phase, nanoparticles) synergistic strengthening network.

[0010] 3. Melt purification and microalloying of rare earth (Ce / La) Mixed rare earths of cerium (Ce) and lanthanum (La) improve alloy properties through dual effects: Melt purification: Rare earth elements form high melting point compounds (such as Ce2O3, La2S3) with impurities such as oxygen and sulfur, which reduces the inclusion content during the smelting process and improves the density of the alloy; Microalloying: trace rare earth is dissolved in the matrix to reduce the grain boundary energy and inhibit crack initiation. The reasonable ratio of Ce and La can balance the purification effect and cost and avoid grain boundary embrittlement caused by excessive single rare earth.

[0011] 4. Grain boundary strengthening and corrosion inhibition of Mg The addition of magnesium (Mg) has a dual function: Grain boundary strengthening: Mg is concentrated at the grain boundary, which reduces the grain boundary mobility and inhibits grain coarsening at high temperature; Corrosion inhibition: Mg and Al work together to form a dense oxide film (MgAl2O4), which improves the alloy's resistance to salt spray corrosion. The Mg content needs to be controlled at 0.02% to 0.1%. Excessive Mg content will cause a decrease in melt fluidity and affect die casting.

[0012] Preferably, the Sc and Y are added in the form of a pre-alloyed Al-Sc-Y master alloy, and the mass ratio of Sc to Y is (2.5-4):1. This design achieves performance optimization through the following synergistic mechanisms: 1. Advantages of pre-alloyed master alloys In the traditional process, Sc and Y are usually added to the melt in the form of single substance or simple mixture, which easily leads to element segregation and burning. The pre-alloyed Al-Sc-Y master alloy of the present invention forms a uniform Al-Sc-Y solid solution by pre-dissolving Sc and Y in the aluminum matrix at high temperature (750-800°C). This form has the following advantages: Inhibit element segregation: Sc and Y are evenly distributed in the Al matrix and directly dissolved into nano-scale Sc / Y-rich phase during smelting, avoiding grain boundary embrittlement caused by excessive local concentration; Reduce oxidation and burning loss: Pre-alloying reduces the contact area between Sc / Y and the melt, and the oxidation loss rate is reduced by more than 50% compared with single element addition; Improve process stability: The composition of the master alloy is fixed, which simplifies the smelting and batching process and reduces batch performance fluctuations.

[0013] 2. The mass ratio of Sc to Y is limited to (2.5-4):1, and its design is based on the following: Sc-dominated grain boundary strengthening: The solid solubility of Sc in the zinc matrix is ​​extremely low, and excessive Sc will form coarse ScZn4 phase, reducing plasticity. By setting the Sc / Y ratio to >2.5, Sc is ensured to occupy the grain boundary sites first, inhibiting dynamic recrystallization; Y-assisted precipitation strengthening: Y combines with Al to form nano YAl3 phase, pinning dislocations and hindering grain boundary migration. When the Sc / Y ratio is less than 4, the amount of Y added is sufficient to form a dispersed YAl3 phase, avoiding the increase in melt viscosity caused by excessive Y.

[0014] Preferably, the particle size of the TiB2 is ≤500 nm, and it is pre-mixed with Zn powder by ball milling to form a TiB2 / Zn mixed powder, wherein the mass ratio of TiB2 to Zn is 1:(8-12). This design achieves performance breakthroughs through the following mechanisms: 1. Heterogeneous nucleation of nano-TiB2 TiB2, as a high melting point ceramic phase (melting point 2980°C), can provide a large number of heterogeneous nucleation sites during the solidification of zinc alloys when its particle size is ≤500 nm (preferably 200-400 nm), significantly refining the grains.

[0015] 2. Uniform dispersion mechanism of ball mill premixing TiB2 and Zn powder are pre-mixed by ball milling (mass ratio 1:8-12). The process advantages are: Prevent nanoparticle agglomeration: TiB2 nanoparticles tend to spontaneously agglomerate due to their high specific surface area. During the ball milling process, Zn powder (particle size 50 μm) is used as a dispersion medium to peel off the agglomerates through mechanical collision and shear force to achieve single TiB2 particle dispersion; Pre-alloying effect: The mechanical energy generated by ball milling causes part of TiB2 to embed into the surface of Zn powder, forming a "Zn-TiB2 core-shell structure", which accelerates the wettability of TiB2 and the melt during smelting and improves the dispersion uniformity; Optimization of process parameters: ball milling time 1-3 h, ball-to-material ratio 8-10:1, argon protection, balance between dispersion effect and production cost.

[0016] Preferably, the mass ratio of Ce to La in the rare earth mixture is (6-8): (2-4). This ratio design achieves a balance between melt purification, grain boundary strengthening and cost control through the following synergistic mechanisms: 1. Functional division of Ce and La The dominant role of Ce in melt purification: Cerium (Ce) has strong deoxidation and desulfurization capabilities, and preferentially reacts with O and S in the melt to generate high-melting point Ce2O3 (melting point 2315°C) and Ce2S3 (melting point 2450°C), significantly reducing the inclusion content of the melt.

[0017] The dominant role of La in grain boundary strengthening: Lanthanum (La) combines with Al to form nano-LaAl3 phase, which pins the grain boundaries and hinders dislocation movement. At the same time, La segregates at the grain boundaries, reduces the grain boundary energy, and inhibits crack propagation.

[0018] 2. Synergistic mechanism Purification-enhancement coupling effect: Melt purification of Ce reduces the interference of inclusions on the nucleation of LaAl3 phase, making the distribution of LaAl3 phase more uniform; Improved grain boundary stability: The trace solid solution of Ce at the grain boundary synergistically inhibits grain boundary migration with La, and the grain coarsening rate is reduced by 50% at high temperature.

[0019] The second aspect of the present invention provides a method for preparing the lightweight and high-strength zinc alloy according to the first aspect of the present invention, comprising the following steps: Step 1: Vacuum melting 1. Loading and sequence: Add the raw materials into the vacuum induction furnace in the following order: Zinc ingot (Zn, purity ≥99.995%); Aluminum ingot (Al, purity ≥99.9%); Pre-alloyed Al-Sc-Y master alloy (Sc:Y mass ratio = 3:1); TiB2 / Zn mixed powder (TiB2:Zn mass ratio = 1:10, TiB2 particle size ≤ 500 nm); Magnesium granules (Mg, purity ≥99.9%, aluminum foil package).

[0020] 2. Melting parameters: Melting temperature: 420~440℃; Vacuum degree: ≤10 -2 Pa; Shielding gas: a mixture of argon (Ar) and carbon dioxide (CO2) (CO2 volume ratio 3-8%, partial pressure 10-20kPa); Electromagnetic stirring: frequency 20 kHz, time 10 min.

[0021] 3. Melt purification: After standing for 5 min, remove the slag twice and the slag amount should be ≤0.1% of the total mass.

[0022] Step 2: Electromagnetic Assisted High Pressure Die Casting 1. Mould pretreatment: Mold preheating temperature: 150~200℃; Lubricant spraying: nanographite suspension (particle size ≤ 100 nm), coating thickness 5-10 μm.

[0023] 2. Die casting parameters: Injection pressure: 80~120 MPa; Filling speed: 4-5 m / s; Holding time: 3-5 s; Mold cooling water flow rate: 20~30 L / min.

[0024] 3. Dynamic control of electromagnetic field: Filling stage: Apply 10-25 kHz high-frequency alternating magnetic field with a magnetic field strength of 150-250 mT; Pressure holding stage: switch to 5-15 Hz low-frequency rotating magnetic field, magnetic field strength 40-60 mT; Switching delay time: ≤0.1 s.

[0025] Step 3: Gradient aging 1. Time limit for the first stage: Temperature: 100-130°C; Insulation time: 1 to 3 hours; Cooling method: Cool down to 70-90℃ at a rate of 0.5-1℃ / min.

[0026] 2. Second stage validity period: Temperature: 70-90℃; Insulation time: calculated according to the formula: t = k·d + c, where: t: time (h); d: workpiece thickness (mm, range 1 to 10 mm); k: proportionality coefficient (0.05-0.15); c: constant term (1 to 3).

[0027] Cooling method: air cooling to room temperature.

[0028] The third aspect of the present invention provides the use of the lightweight and high-strength zinc alloy described in the first aspect of the present invention in the production of metal fasteners, including but not limited to the following specific products: Clothing fasteners: belt buckles, shoe buckles, jeans buttons, zipper pullers; Luggage accessories: luggage locks, handle connectors, D-rings; Industrial hardware: sign rivets, electrical cabinet locks, mechanical fasteners; Outdoor equipment: tent pegs, carabiners, tool clips.

[0029] The present invention provides a lightweight and high-strength zinc alloy and a preparation method and application thereof. The invention has the following beneficial effects: 1. By optimizing the zinc alloy components and processes, the present invention greatly enhances the material's wear resistance and deformation resistance in long-term use. It is particularly suitable for belt buckles, shoe buckles and other frequently stressed parts. Even in a humid or sweat-contact environment, the structure remains stable, avoiding breakage and disengagement caused by corrosion or fatigue, and extending the product's service life.

[0030] 2. The zinc alloy of the present invention reduces material density while ensuring strength, and is particularly suitable for high-end belt buckles, labels and other scenes with strict requirements on lightweight. Its excellent fluidity and low shrinkage characteristics can support precision die-casting of complex textures (such as antique patterns and hollow carvings), reduce subsequent machining processes, and reduce production costs.

[0031] 3. The low internal defect characteristics of the material of the present invention make the surface treatment layers such as electroplating and spraying more uniform and dense. For the common nickel plating, imitation gold plating or oxidation coloring process of hardware fasteners, it can significantly reduce the undesirable phenomena such as pitting and blistering, improve the glossiness and color adhesion of the product, and meet the strict requirements of high-end brands for appearance consistency.

[0032] 4. The present invention uses the synergistic effect of the components to keep the surface smooth in harsh environments such as salt spray, humidity and heat, avoiding the white rust and black spots that are easy to produce in traditional zinc alloys. This feature is particularly suitable for outdoor signs, marine hardware accessories and other scenes, reducing the frequency of repair or replacement due to corrosion and reducing the maintenance cost throughout the life cycle.

[0033] 5. The process optimization of the present invention reduces energy consumption and waste slag emissions during the smelting process, while high material utilization reduces waste of scraps. For small metal parts such as shoe buckles and buttons produced in large quantities, it can significantly reduce resource consumption per unit product, meet environmental protection regulations, and enhance the sustainable competitiveness of enterprises. DETAILED DESCRIPTION

[0034] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Embodiment 1: Alloy composition (mass percentage): Zn: 83.5% Al: 8.5% Sc: 0.35% Y: 0.1% TiB2: 1.0% Ce / La mixed rare earth (7:3): 0.08% Mg: 0.05% Total impurities: ≤0.3%; The preparation steps are as follows: 1. Vacuum melting Raw material pretreatment: The zinc ingot (Zn) and aluminum ingot (Al) were immersed in a 5% nitric acid solution for pickling for 30 seconds to remove surface oxides; TiB2 nanopowder (particle size ≤ 500 nm) and zinc powder were loaded into a ball mill at a mass ratio of 1:10 and ball milled for 2 hours under argon protection to form a uniform TiB2 / Zn premixed powder.

[0036] Charging and smelting: Add zinc ingot, aluminum ingot, Al-2%Sc-0.7%Y master alloy, TiB2 / Zn premixed powder and magnesium particles (Mg) into the vacuum induction furnace in sequence. Start the vacuum system and draw the vacuum degree in the furnace to 5×10 -3 Pa, the temperature was raised to 435 ° C for melting. During the melting process, a mixed gas of argon and 5% CO2 (partial pressure 15 kPa) was introduced, and electromagnetic stirring at 20 kHz was performed for 10 minutes to ensure uniform melt composition.

[0037] Melt purification: After smelting, let it stand for 5 minutes and remove the surface slag twice. The slag amount should be controlled within 0.08% of the total mass.

[0038] 2. Electromagnetic assisted high pressure die casting Mold pretreatment: The die-casting mold was preheated to 170 °C and sprayed with nanographite suspension (coating thickness 8 μm) as a release agent.

[0039] Die casting: Inject the molten alloy into the die casting machine, set the injection pressure to 100 MPa, the filling speed to 4.8 m / s, and the holding time to 4 seconds. Apply a 20 kHz high-frequency alternating magnetic field during the filling stage (initial intensity 200 mT, linearly decreasing to 50 mT as the filling progresses), and immediately switch to a 10 Hz low-frequency rotating magnetic field (intensity 50 mT) after filling is completed, with a switching delay time of ≤0.05 seconds.

[0040] Cooling and demoulding: After the pressure holding is completed, cooling water (flow rate 25 L / min) is introduced to quickly cool the mold, and the mold is opened to take out the casting.

[0041] 3. Gradient aging treatment The first stage of aging: the casting is placed in an aging furnace, kept at 125°C for 2 hours, and then slowly cooled to 80°C at a rate of 0.5°C / min.

[0042] Second stage aging: Keep warm at 80℃ for 2.5 hours (calculated according to the formula t=0.1d+2, casting thickness d=5 mm), and then air cool to room temperature.

[0043] Embodiment 2: Alloy composition (mass percentage): Zn: 82.8% Al: 8.2% Sc: 0.25% Y: 0.08% TiB2: 1.5% Ce / La mixed rare earth (6:4): 0.1% Mg: 0.07% Total impurities: ≤0.3%; The preparation steps are as follows: 1. Vacuum melting TiB2 pretreatment: TiB2 nanopowder (1.5%) and zinc powder were ball-milled at a mass ratio of 1:12 for 2.5 hours (argon protection, ball-to-material ratio of 10:1) to obtain a uniformly dispersed premixed powder.

[0044] Melting operation: zinc ingot, aluminum ingot, Al-Sc-Y master alloy (Sc:Y=3:1), TiB2 / Zn mixed powder and magnesium particles were added in sequence. The melting temperature was controlled at 425°C, 6% CO2 argon mixed gas (partial pressure 12 kPa) was introduced, and 18 kHz electromagnetic stirring was applied for 12 minutes.

[0045] Slag removal and testing: After standing, remove the slag three times to ensure that the slag volume is ≤0.06%. Take samples to test the oxygen content of the melt to be ≤25ppm.

[0046] 2. Electromagnetic assisted high pressure die casting Dynamic magnetic field control: A 25 kHz high-frequency magnetic field (intensity 250 mT linearly decreasing to 60 mT) was used in the filling stage, and the filling speed was increased to 5.0 m / s; in the pressure holding stage, it was switched to a 15 Hz low-frequency rotating magnetic field (intensity 60 mT) to suppress shrinkage cavity formation.

[0047] Process optimization: The mold is preheated to 190°C, the injection pressure is 110 MPa, and the holding time is 3 seconds to ensure complete filling of the complex groove structure.

[0048] 3. Gradient aging treatment High temperature stage: keep at 130℃ for 1.5 hours, then cool to 90℃ at a rate of 0.8℃ / min.

[0049] Low temperature stage: keep at 90℃ for 4.2 hours (d=8 mm, t=0.15×8+3=4.2 h) to strengthen the distribution of precipitated phase.

[0050] Embodiment 3: Alloy composition (mass percentage): Zn: 84.7% Al: 8.0% Sc: 0.1% Y: 0.05% TiB2: 0.5% Ce / La mixed rare earth (8:2): 0.05% Mg: 0.02% Total impurities: ≤0.3%; The preparation steps are as follows: 1. Vacuum melting Raw material ratio: low-cost rare earth ratio (Ce:La=8:2) is adopted to reduce the amount of La. Zinc ingots and aluminum ingots are simply pickled and then added into the furnace together with Al-Sc-Y master alloy (Sc:Y=2:1), TiB2 / Zn mixed powder (0.5%) and magnesium particles.

[0051] Melting control: melting temperature 420℃, 3% CO2 argon mixed gas (partial pressure 10 kPa), 15 kHz electromagnetic stirring for 8 minutes, melt oxygen content ≤35 ppm.

[0052] 2. Electromagnetic assisted high pressure die casting Filling process: preheat the mold to 150°C, injection pressure 80 MPa, filling speed 4.0 m / s.

[0053] Magnetic field configuration: A 10 kHz high-frequency magnetic field (intensity 150 mT decreasing to 40 mT) was used in the filling stage, and a 5 Hz low-frequency magnetic field (intensity 40 mT) was switched to in the pressure holding stage.

[0054] 3. Gradient aging treatment Aging parameters: After keeping at 100℃ for 3 hours, cool to 70℃ at a rate of 1.0℃ / min and keep at 70℃ for 1.15 hours (d=3 mm, t=0.05×3+1=1.15 h).

[0055] Comparative Example 1: Compared with Example 1, the difference is that no Al-Sc-Y intermediate alloy is added, and instead, single substances Sc and Y (Sc:Y mass ratio 3:1) are directly added, and the other preparation steps are the same.

[0056] Comparative Example 2: Compared with Example 1, the difference is that no CO2 mixed gas is introduced during smelting, and only pure argon gas is used for protection, and the remaining preparation steps are the same.

[0057] Comparative Example 3: Compared with Example 2, the difference is that the particle size of TiB2 is 1.2 μm, and the other preparation steps are the same.

[0058] Comparative Example 4: Compared with Example 2, the difference is that the low-frequency rotating magnetic field in the pressure holding stage is cancelled, and the other preparation steps are the same.

[0059] Comparative Example 5: Compared with Example 3, the difference is that the mass ratio of Ce to La in the mixed rare earth is adjusted to 5:5, and the other preparation steps are the same.

[0060] Comparative Example 6: Compared with Example 3, the difference is that the gradient aging treatment is changed to single-stage aging (100°C×4 h), and the other preparation steps are the same.

[0061] Comparative Example 7: Compared with Example 1, the difference is that the mass ratio of Sc to Y is adjusted to 1:1, and the other preparation steps are the same.

[0062] Comparative Example 8: Compared with Example 1, the difference is that the mixing mass ratio of TiB2 and Zn is adjusted to 1:5, and the other preparation steps are the same.

[0063] Test Example 1: The test steps are as follows: 1. Sample Preparation Example group: According to the preparation processes of Example 1, Example 2 and Example 3, 3 groups of alloy ingots were prepared respectively. The 3 groups of alloy ingots of Example 1 were respectively denoted as 1-1, 1-2 and 1-3, and the same was true for Examples 2 and 3 (size Φ50 mm×100 mm).

[0064] Comparative Example Group: Alloy ingots of Comparative Example 1, Comparative Example 3 and Comparative Example 5 were prepared, 3 groups each. The 3 groups of alloy ingots of Comparative Example 1 were respectively recorded as C1-1, C1-2 and C1-3, and the same applies to Comparative Examples 3 and 5 (size Φ50 mm×100 mm).

[0065] Standardization treatment: All sample surfaces were polished with sandpaper (800#→2000#) to remove the oxide layer.

[0066] 2. Tensile strength test Equipment: Instron 5967 universal testing machine, loading rate 2 mm / min; Specimen: Processed into standard tensile specimen according to GB / T 228.1 (gauge length section Φ6 mm × 30 mm); Data collection: Record the maximum load before fracture and calculate the tensile strength (MPa).

[0067] 3. Grain size analysis Corrosion liquid: 5% HNO3 + 95% ethanol, corrosion time 15 s; Equipment: Olympus GX53 metallographic microscope, 500 times field of view; Method: The average grain size (μm) of three fields of view was measured by the intercept method.

[0068] 4. Melt oxygen content detection Equipment: LECO ON836 oxygen and nitrogen analyzer; Sampling: After smelting, take a sample (10 g) from the center of the melt and quickly quench it with water; Conditions: high temperature pulse melting method, helium carrier gas, detection accuracy ±1 ppm.

[0069] The test results are shown in Table 1: Table 1 Test data of the influence of core components on the mechanical properties and melt cleanliness of zinc alloy

[0070] From the test data in Table 1, we can get: By comparing the optimization scheme of the core components (pre-alloyed Sc-Y, nano-TiB2, Ce / La=8:2) and the deterioration scheme (single element addition, coarse particle TiB2, Ce / La=5:5), the inherent mechanism of the component limitation in the claims is revealed. Sc-Y pre-alloying significantly reduces the oxidation and burning of Sc and Y elements during the smelting process (oxygen content ≤28 ppm in Example 1 vs ≥47 ppm in Comparative Example 1). Its essence lies in the fact that the Al3(Sc,Y) phase formed by pre-alloying preferentially dissolves in the melt and releases active Sc / Y atoms, rather than direct oxidation of single metal. This process not only improves the utilization rate of Sc / Y, but also inhibits grain boundary migration through the pinning effect of nano-scale Al3(Sc,Y) phase (size 50-80 nm), making the grain size of Example 1 (10.2 μm) nearly 50% finer than that of Comparative Example 1 (18.3 μm). At the same time, the dispersion strengthening of nano-TiB2 depends on the particle size control (≤500 nm) and the Zn powder premixing process: the ball milling pretreatment of TiB2 / Zn forms a Zn coating on the particle surface through mechanical alloying, which avoids the agglomeration of TiB2 in the melt (the dispersion spacing of TiB2 in Example 2 is ≤1 μm), thereby acting as a heterogeneous nucleation core to refine the grains and bear the load; while in Comparative Example 3, the coarse TiB2 (1.2 μm) has insufficient specific surface area and weakened interface bonding, resulting in grain coarsening (25.3 μm) and cracks preferentially initiating at the TiB2 / matrix interface (tensile strength is only 318 MPa).

[0071] The coordinated regulation of Ce / La ratio achieves the dual gains of melt purification and grain boundary strengthening through functional division of labor. The high Ce ratio of Ce:La=8:2 in Example 3 makes it react preferentially with O and S in the melt to form Ce2O3 / Ce2S3 high melting point inclusions (oxygen content ≤37 ppm), and the residual La is segregated to the grain boundary during solidification, combining with Al to form LaAl3 phase (size 80-120 nm), which not only reduces the grain boundary energy but also hinders dislocation movement; while in Comparative Example 5 (Ce:La=5:5), due to excessive La occupying the purification capacity of Ce, the oxygen content of the melt surges (≥48 ppm), and the excessive LaAl3 phase is excessively coarsened at the grain boundary (size ≥200nm), which becomes the crack propagation path instead, and finally manifests as a simultaneous decrease in strength and corrosion resistance (tensile strength 358 MPa, salt spray time 72 h). The above data confirm the inseparability of component optimization and process adaptation: only when Sc / Y pre-alloying, TiB2 nano-sizing and Ce / La functionalization ratio work synergistically can the invention goals of light weight, high strength and corrosion resistance be achieved.

[0072] Test Example 2: The test steps are as follows: 1. Sample Preparation Example group: Die-casting specimens (size 50 mm×20 mm×5 mm) were prepared according to the process parameters of Examples 1, 2, and 3, with 3 specimens in each group. The 3 specimens of Example 1 were respectively denoted as 1-4, 1-5, and 1-6, and the same applies to Examples 2 and 3.

[0073] Comparative Example Group: Prepare samples (size 50 mm×20 mm×5 mm) of Comparative Example 2, Comparative Example 4, and Comparative Example 6, 3 in each group, where the 3 samples of Comparative Example 2 are respectively recorded as C2-1, C2-2, and C2-3, and the same applies to Comparative Examples 4 and 6.

[0074] Post-treatment: All samples were electropolished (voltage 12 V, time 3 min) to remove the surface oxide layer.

[0075] 2. Porosity test Equipment: ZEISS Xradia 520 Versa X-ray tomography scanner, resolution 1 μm; Method: Scan the central area of ​​the sample (5 mm × 5 mm) and calculate the pore volume percentage (%).

[0076] 3. Plating adhesion test Plating process: Pulse electroplating nickel layer (thickness 10 μm), current density 2 A / dm 2 ; Standard: ISO 2409 cross-cut method, blade spacing 2 mm, evaluation of coating peeling area (0-5B grade).

[0077] 4. High temperature creep test Conditions: Constant load tensile (stress 80 MPa, temperature 80°C), record the strain rate (s -1 ); Equipment: Gotech GT-7005 high temperature creep testing machine.

[0078] The test results are shown in Table 2: Table 2 Test data of the impact of key processes on zinc alloy defect control and service performance

[0079] From the test data in Table 2, we can get: By comparing the key processes (CO2 partial pressure protection, dynamic magnetic field switching, gradient aging) with the simplified processes (pure Ar protection, cancellation of magnetic field, single-stage aging), the core role of process parameters in alloy defect control and long-term service performance is revealed. CO2 partial pressure protection significantly reduces the oxygen exchange rate between the melt and the furnace gas by forming a dense Al2O3-CO2 composite oxide film (thickness ≤50 nm) (oxygen content ≤28 ppm in Example 1 vs. ≥48 ppm in Comparative Example 2). Its essence lies in the preferential reaction of CO2 with Al on the surface of the melt to form an Al-OC transition layer, rather than the rupture tendency of a single Al2O3 film under traditional pure Ar protection. This mechanism reduces the amount of melt slag by more than 60% (slag amount 0.08% in Example 1 vs. slag amount 0.25% in Comparative Example 2), thereby improving the integrity of die casting filling (porosity ≤0.5%). The dynamic magnetic field switching induces laminar flow of the melt in the filling stage through the skin effect (penetration depth 0.5-1 mm) of the high-frequency magnetic field (20-25 kHz) to suppress turbulent air entrainment; while the low-frequency rotating magnetic field (10-15 Hz) in the pressure holding stage drives the directional shrinkage of the residual melt between the dendrites through the Lorentz force, so that the shrinkage rate (1.5%) of the comparative example 4 (without magnetic field) is 5 times higher than that of the embodiment 2 (0.3%), which confirms the necessity of staged regulation of the magnetic field.

[0080] The gradient aging process optimizes the distribution of precipitated phases through the synergistic effect of temperature and time in two stages: the first stage of high temperature aging (125-130℃) promotes the rapid diffusion of Sc / Y atoms to form a high-density Al3(Sc,Y) phase (size 30-50 nm), and the second stage of slow cooling to medium and low temperatures (70-90℃) induces the precipitation of Mg2Zn 11 The phase grows epitaxially around Al3(Sc,Y) (coating thickness 5-8 nm), forming a "core-shell" composite strengthening structure. However, due to the lack of temperature gradient, the single-stage aging of comparative example 6 resulted in uneven size of precipitated phases (50-200 nm) and large spacing (≥2 μm), which led to the failure of the dislocation bypass mechanism (Orowan mechanism), and the creep rate surged to 15×10 -6 s -1 (Example 2 is 2.3×10 -6 s -1 ). This difference highlights the ability of gradient aging to precisely control the topological structure of the precipitated phase.

[0081] Furthermore, the difference in coating bonding strength is directly related to the residual stress of the substrate: Examples 1-3 release the lattice distortion caused by rapid cooling of die casting through gradient aging (residual stress ≤ 80 MPa), while Comparative Example 6 causes microcracks at the coating / substrate interface (bonding strength ≤ 2B level) due to the residual stress (≥ 150 MPa) of single-stage aging. The synergistic effect of process parameters is essentially the optimization of the spatiotemporal distribution of energy input - from oxidation inhibition in the smelting stage, flow field control in the die-casting stage to phase change guidance in the aging stage. Only the coupling regulation of the entire process can achieve the comprehensive performance of high density, low stress and long life of the alloy.

[0082] Test Example 3: The test steps are as follows: Example group: Die-casting specimens (size 100 mm×10 mm×3 mm) were prepared according to the process of Example 1, 3 specimens in each group, respectively denoted as 1-7, 1-8, and 1-9; Comparative Example Group: Prepare samples (size 100 mm×10 mm×3 mm) of Comparative Example 7 (Sc / Y=1:1) and Comparative Example 8 (TiB2:Zn=1:5), 3 samples in each group, the 3 samples of Example 7 are respectively recorded as C7-1, C7-2, and C7-3, and the same is true for Example 8; Surface treatment: All samples were chemically polished (HNO3:H3PO4=1:3, time 30 s) and then ultrasonically cleaned.

[0083] 2. Elongation test Equipment: MTS Criterion 43 universal testing machine, loading rate 1 mm / min; Standard: GB / T 228.1, measure the elongation (%) of the gauge length after fracture.

[0084] 3. Salt spray corrosion resistance test Conditions: neutral salt spray (5% NaCl, pH 6.5-7.2, temperature 35°C), observe corrosion points every 24 hours; End point determination: the time (h) when the first corrosion point with a diameter ≥ 1 mm appears on the sample surface.

[0085] 4. Fatigue life test Parameters: high-frequency vibration table (frequency 50 Hz, stress amplitude ±150 MPa), record the number of cycles (times) when the sample breaks; Equipment: Instron 8874 servo-hydraulic fatigue testing machine.

[0086] The test results are shown in Table 3: Table 3 Test data on the effect of component ratio deviation on the comprehensive service performance of zinc alloy

[0087] From the test data in Table 3, we can get: By comparing the extreme performance differences between the Sc / Y mass ratio (3:1 vs 1:1) and the TiB2 / Zn mixing ratio (1:10 vs 1:5), the scientific basis for the ratio limitation in the claims is revealed. The synergistic ratio of Sc / Y = 3:1 optimizes the lattice distortion energy of the Al3(Sc,Y) phase through atomic radius matching (Sc: 0.164 nm, Y: 0.180 nm), allowing it to precipitate uniformly in the matrix (size 50-80 nm, spacing ≤1 μm), hindering dislocation movement through the Orowan mechanism (elongation ≥5.1%), and improving corrosion resistance (salt spray time ≥118 h) due to the synergistic passivation of Sc / Y oxides (Sc2O3-Y2O3 composite film). In contrast, in comparative example 7 (Sc / Y=1:1), excessive Y formed coarse YAl3 phase (size ≥200 nm), which not only reduced the grain boundary bonding strength (elongation ≤3.8%), but also caused pitting corrosion (salt spray time ≤88 h) due to local rupture of the Y2O3 film, confirming the sensitive regulation of the Sc / Y ratio on the mechanical-corrosion synergistic performance.

[0088] The Zn coating of TiB2 nanoparticles (≤500 nm) was achieved by ball milling energy adaptation (speed 200 rpm, time 4 h) with a mixing ratio of TiB2 / Zn=1:10. The mechanism of action includes two aspects: on the one hand, the Zn coating layer (thickness 5-10 nm) reduces the interfacial energy difference between TiB2 and molten Al, promoting dispersion (TiB2 spacing ≤1.5 μm in Example 1); on the other hand, the microgalvanic effect of TiB2 as a cathode phase (electrode potential -0.8 V vs SCE) and the matrix (-1.2 V) is buffered by the Zn layer, avoiding a surge in local corrosion current density (salt spray time 126 h in Example 1). However, in Comparative Example 8 (TiB2 / Zn=1:5), the coating is incomplete due to insufficient Zn content, and TiB2 is directly exposed to the melt (agglomerate size ≥5 μm), which becomes a fatigue crack source (fatigue life ≤2.1×10 5 times), and galvanic corrosion accelerates the dissolution of the matrix (salt spray time ≤ 72 h).

[0089] Furthermore, the fracture analysis of fatigue life shows that the crack propagation path of Example 1 shows typical dimple characteristics (depth 2-5 μm), while the fracture of Comparative Examples 7 / 8 shows intergranular fracture (Comparative Example 7) and cleavage steps caused by TiB2 agglomerates (Comparative Example 8). This difference stems from the regulation of the multi-level structure of the material by the component ratio: the Sc / Y ratio controls the distribution of the grain boundary precipitation phase, and the TiB2 / Zn ratio determines the dispersion of the reinforcement phase. Only within the ratio range defined in the claims can the synergistic strengthening of intragranular-grain boundary-reinforcement phase be achieved, thereby meeting the comprehensive requirements of high elongation, corrosion resistance, and fatigue resistance.

[0090] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lightweight and high-strength zinc alloy, characterized in that: Included by mass percentage: Zn 82.0%~85.0%, Al 8.0%~9.0%, Sc 0.1%~0.5%, Y 0.05%~0.2%, TiB2 0.5%~1.5%, Ce and La rare earth mixture 0.05%~0.15% and Mg 0.02%~0.1%; the balance is unavoidable impurities.

2. The lightweight and high-strength zinc alloy according to claim 1, characterized in that: The Sc and Y are added in the form of a pre-alloyed Al-Sc-Y master alloy, and the mass ratio of Sc to Y is (2.5-4):

1.

3. The lightweight and high-strength zinc alloy according to claim 1, characterized in that: The particle size of the TiB2 is ≤500 nm, and is premixed with Zn powder by ball milling to form a TiB2 / Zn mixed powder, wherein the mass ratio of TiB2 to Zn is 1:(8-12).

4. The lightweight and high-strength zinc alloy according to claim 1, characterized in that: The mass ratio of Ce to La in the rare earth mixture is (6-8): (2-4).

5. A method for preparing a lightweight and high-strength zinc alloy as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Vacuum melting: add Zn, Al, Al-Sc-Y master alloy, TiB2 / Zn mixed powder and Mg in sequence, with the melting temperature at 420-440°C; (2) Electromagnetic assisted high pressure die casting: Electromagnetic assisted high pressure die casting, injection pressure 80-120 MPa, mold preheating temperature 150-200 °C; (3) Gradient aging treatment: In the first stage, the temperature is kept at 100-130℃ for 1-3 h, then the temperature is reduced to 70-90℃ at a rate of 0.5-1℃ / min. In the second stage, the temperature is kept at 70-90℃ for a period of time of t=k·d+c, where t is time in h; d is workpiece thickness in mm; k is the proportional coefficient, k=0.05-0.15; c is a constant term, c=1-3.

6. The preparation method according to claim 5, characterized in that: In the vacuum melting step, a mixed gas of argon and CO2 is introduced during melting, with CO2 accounting for 3-8% by volume and a partial pressure of 10-20 kPa.

7. The preparation method according to claim 5, characterized in that: In the electromagnetic assisted high pressure die casting step, the electromagnetic assistance includes: During the filling stage, a high-frequency alternating magnetic field is applied with a frequency of 10 to 25 kHz and an intensity of 150 to 250 mT; During the pressure holding stage, the magnetic field is switched to a low-frequency rotating magnetic field with a frequency of 5 to 15 Hz and an intensity of 40 to 60 mT.

8. Use of the lightweight and high-strength zinc alloy according to any one of claims 1 to 4 in the production of metal fasteners.

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