High-strength and high-toughness rare earth magnesium alloy, forming method and application thereof

Abstract

The application discloses a high-strength and high-toughness rare earth magnesium alloy, a forming method and application thereof, and a light metal material and precision forming technical field; the alloy comprises the following components: Al: 7.3% to 7.7%, Zn: 0.6% to 0.9%, Mn: 0.3% to 0.5%, mixed rare earth RE: 1.4% to 1.7%, and the balance of Mg and inevitable impurities; the mixed rare earth RE comprises Ce, La, Nd and Pr; Nd is greater than or equal to 0.4%, the mass ratio of La / Ce is 1:2 to 2:1, and the mass ratio of RE / Al is 0.15 to 0.40; after raw materials are smelted and refined, high-pressure die casting forming is carried out; the application is used for manufacturing a large die casting wire reel; the application realizes the synergistic regulation of a crystal boundary Al-RE phase and a matrix Mg 17 Al 12 phase, under the premise of ensuring casting fluidity, significantly improves the strength and toughness matching of the alloy, solves the problem that the strength and toughness of the magnesium alloy cannot be compatible in a die casting state, and improves the overall die casting formability of a large and complex structure magnesium alloy part and the yield of finished products.

Description

Technical Field

[0001] This invention relates to the field of lightweight metal materials and precision forming technology, specifically to a high-strength, high-toughness rare-earth magnesium alloy, its forming method, and its applications. This invention is particularly applicable to fields with high requirements for large size, lightweight, and high toughness of materials, such as winding and unwinding reels in the wire and cable industry, yarn reels in textile machinery, and special turnover reels in the manufacture of special equipment. Background Technology

[0002] Cable reels are widely used in the cable and fiber optic industries for winding, unwinding, and storage. They withstand complex tensile, compressive, bending, and torsional stresses during cable winding and unwinding, and may also be subjected to impact loads during hoisting and transportation. The larger the reel, the more complex the stresses it experiences. Therefore, cable reels must possess both strength and toughness, especially toughness. A reel with good toughness can buffer complex stresses, prevent crack initiation and propagation, improve the reel's safety, and extend its service life. Traditional cable reels are mostly made of steel, wood, or plastic. While steel reels have high strength, a single reel weighs hundreds of kilograms, resulting in high transportation costs and significant difficulties in loading and unloading. Wooden and plastic reels have poor toughness and limited load-bearing capacity. Currently, with the continuous increase in cable winding capacity, the industry's demand for lightweight, large-size, and highly tough cable reels has grown significantly. Against this backdrop, the development of high-performance lightweight cable reels has become an urgent need.

[0003] Magnesium alloys have the lowest density (approximately 1.74–1.85 g / cm³). 3 Magnesium alloys are practical metallic structural materials, renowned as "green engineering materials of the 21st century" due to their extremely high specific strength, specific stiffness, excellent vibration damping and noise reduction capabilities, as well as outstanding casting fluidity and recyclability. They are an ideal choice to replace traditional materials in the manufacture of lightweight wire reels. Using magnesium alloys to manufacture wire reels can achieve a weight reduction of 50%-60%, significantly reducing transportation and handling loads and improving operational efficiency. Die casting is a core process in the field of magnesium alloy forming, characterized by its fast production pace, precise product dimensions, and suitability for forming complex thin-walled structures. However, commonly available die-cast magnesium alloys, such as AZ and AM series magnesium alloys, share a common drawback: it is difficult to achieve both strength and toughness simultaneously. This severely limits their application in large die-cast wire reels. This is because AZ and AM series magnesium alloys mainly rely on Al element solid solution strengthening and the formation of Mg... 17 Al 12 (β phase) precipitation strengthening is used to obtain higher strength. However, a high Al content will lead to the formation of a large number of continuous or semi-continuous coarse network β phases at the grain boundaries, which will severely disrupt the matrix and reduce the plasticity of the material. Reducing the Al content to reduce the number of β phases can improve toughness, but the effect of β phase precipitation strengthening will be significantly reduced, making it difficult to meet the strength requirements of the coil.

[0004] In addition, the preparation of large die-cast magnesium alloy coils also faces a series of technical challenges, mainly in the two major stages of forming and joining.

[0005] 1. Die-casting in one piece is challenging: The coil structure is complex and large, featuring reinforcing ribs, shaft holes, flanges, and other characteristics. Using large molds for integral die casting results in complex molds and extremely high costs. Furthermore, ensuring that molten metal instantly fills a huge cavity during die casting while maintaining a uniform temperature and preventing turbulence at the flow front is extremely difficult. Moreover, large molds often lack air permeability, making it difficult for air to escape during filling, easily leading to defects such as air entrapment and shrinkage cavities, resulting in low yields.

[0006] 2. Poor performance of traditional welding: To avoid the difficulties of integral die casting, a split casting and reassembly approach can be adopted. Decomposing the complex mold into smaller parts can significantly reduce the difficulty of mold design and manufacturing costs. Furthermore, the simple structure of individual components ensures smooth metal flow and uniform solidification, greatly reducing defects such as porosity, shrinkage, and incomplete filling. However, traditional joining techniques (such as argon arc welding) have inherent drawbacks: magnesium alloys are highly susceptible to oxidation at high temperatures, resulting in coarse grains and hot cracks. These factors cause the welded joint strength to be typically only 50%-70% of the base material, with a sharp decrease in ductility and toughness, making it a weak point in the structure and unable to meet the service requirements of the coil.

[0007] In recent years, friction stir welding (FSW), as an advanced solid-state joining technology, has provided a new solution to the aforementioned problems. Unlike traditional fusion welding, FSW achieves material bonding by mechanically stirring and generating heat through friction to plastically deform and fuse the joining materials. Its welding temperature is below the material's melting point, fundamentally avoiding fusion welding defects. In the manufacturing of complex thin-walled components such as the housings of new energy vehicle motors, FSW has demonstrated significant advantages: its joint tensile strength can reach over 90% of the base material, far exceeding that of traditional fusion welding; the weld has good density, low heat input, and minimal product deformation, which is beneficial for precise dimensional control; it is particularly suitable for the reliable joining of lightweight materials such as aluminum alloys and magnesium alloys.

[0008] Therefore, overcoming the dual constraints of existing materials and processes, and developing die-cast magnesium alloy coils with both high strength and high toughness through synergistic innovation in composition and processes, is not only a response to the needs of industry development, but also an inevitable way to promote related technological progress and industrial upgrading. Summary of the Invention

[0009] This invention addresses the problems existing in the prior art by proposing a high-strength, high-toughness rare-earth magnesium alloy, its forming method, and its application. It solves the problems that magnesium alloys cannot simultaneously achieve both strength and toughness in the die-cast state, and that large and complex magnesium alloy parts have poor overall die-casting formability and low yield.

[0010] This invention is achieved through the following technical solution: A high-strength, high-toughness rare-earth magnesium alloy comprises the following components by weight percentage: Al: 7.3%–7.7%, Zn: 0.6%–0.9%, Mn: 0.3%–0.5%, mixed rare earth RE: 1.4%–1.7%, with the balance being Mg and unavoidable impurities; mixed rare earth RE includes Ce, La, Nd, and Pr; Nd ≥ 0.4%, La / Ce mass ratio = 1:2–2:1, RE / Al mass ratio = 0.15–0.40.

[0011] Preferably, the impurities are Si≤0.05%, Fe≤0.005%, Cu≤0.01%, Ni≤0.001%, other single impurities≤0.01%, and total impurities≤0.15%.

[0012] A method for forming a high-strength and high-toughness rare earth magnesium alloy involves melting and refining the raw materials and then performing high-pressure die casting. After entering the fast injection stage, the high-pressure die casting drives the melt to be injected into the mold cavity at a high speed of 4-5 m / s, with the pressure boosting position at 630-670 mm. The entire injection stage is maintained for 10-30 seconds.

[0013] Preferably, before the die-casting operation, the high-pressure die-casting mold is uniformly heated to a working temperature of 240-280℃.

[0014] Preferably, the die-casting specific pressure is 60-80 MPa.

[0015] Preferably, the pressure holding stage is immediately initiated, applying a pressure of 40-60 MPa and maintaining it for 10-30 seconds.

[0016] Preferably, high-pressure die casting is performed while maintaining the melt temperature within 640-700℃.

[0017] Preferably, a slag collection bag is arranged in the final filling area of ​​the molten metal at the bottom of the product and at the confluence of multiple molten metal streams.

[0018] Large die-cast wire spools are manufactured using the aforementioned rare-earth magnesium alloy forming method.

[0019] Preferably, the coil halves are obtained by split die casting, then the two coil halves are overlapped, and a support ring is used inside the mating surface to bear the welding load. Finally, the coil halves are connected by friction stir welding.

[0020] This invention, through the synergistic effect of rare earth magnesium alloy composition optimization, die-casting mold structure improvement, orthogonal experimental process parameter optimization, and split friction stir welding assembly, has the following outstanding advantages compared to existing technologies: 1. Achieving a breakthrough in alloy strength and toughness, breaking the constraints of traditional material properties: The rare earth magnesium alloy designed in this invention optimizes the distribution morphology of the β phase by controlling the proportion of Nd, La, Ce, and Pr multi-element rare earth elements, achieving a balance between the grain boundary Al-RE phase and the matrix Mg. 17 Al 12 With coordinated regulation, while retaining excellent casting fluidity, the tensile strength can reach 275-294 MPa, the elongation after fracture is 9.74%-13.5%, and the strength-ductility product is up to 3713 MPa%, which is more than 5 times that of commercial AZ91D alloy. At the same time, it is superior to AZ31 alloy in terms of comprehensive performance and is suitable for the complex stress service requirements of wire coil.

[0021] 2. Significantly optimize casting quality and reduce product defect rate: By optimizing the arrangement of slag collection bags in the final filling area of ​​molten metal and at the confluence of multiple liquid flows, cold molten metal, oxide inclusions, and entrapped gas are precisely discharged; through a four-factor, three-level orthogonal experiment, the optimal combination of die-casting parameters is selected, reducing the casting density from 1.77 g / cm³. 3 Increased to 1.79 g / cm³ 3 (Increase of 1.1%), porosity decreased from ≤5% to ≤3% (a decrease of 40%), effectively solving the problems of defects such as porosity and inclusions in castings.

[0022] 3. Significantly reduce production costs and improve product yield: The split die casting process greatly simplifies the mold structure and reduces the design and manufacturing costs of large molds; after the optimal combination of process parameters stabilizes production, the product scrap rate drops from 14% to below 5%, a reduction of 64%, and the economic efficiency of large-scale production is significantly improved.

[0023] 4. Improve product performance consistency and stability: After multi-dimensional process coordination and control, the mechanical properties of different positions of the wire reel body and reel surface are greatly improved, and the performance fluctuation is significantly reduced. The overall mechanical performance fluctuation range is reduced from 40MPa to 25MPa, with a fluctuation reduction of 37.5%, and the batch stability and service reliability of the product are greatly improved.

[0024] 5. Overcoming the challenges of connecting large components and ensuring overall structural strength: By adopting friction stir welding solid-state joining technology, the problems of hot cracking and oxidation defects in traditional fusion welding are avoided. The strength of the welded joint can reach about 90% of the base material, taking into account both structural integrity and mechanical properties, while significantly reducing the difficulty of forming large and complex coils. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0026] Figure 1 Comparison charts of (a) tensile strength and yield strength, (b) elongation after fracture, and (c) strength-ductility product of Examples 1-5 and Comparative Examples 1 and 2; Figure 2 A comparative schematic diagram of slag collection bag design schemes; (a) No slag bag around the bottom of the product; (b) Slag collection bag installed at the bottom of the product; Figure 3 This is a schematic diagram of the welding of separate coils; Figure 4 Metallographic image of the AE81 die-cast part; Figure 5 Micrograph of the metallographic structure of the weld nugget area of ​​AE81 die-cast magnesium alloy wire coil (after etching).

[0027] Explanation of reference numerals in the attached diagram: 1-Spindle half, 2-Support ring, 3-Weld. Detailed Implementation

[0028] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0029] This invention provides a high-strength, high-toughness rare-earth magnesium alloy and its forming method, as well as a die-casting forming method for wire coils, wherein: I. Chemical composition of rare earth magnesium alloy (wt.%) Al: 7.3%–7.7%, Zn: 0.6%–0.9%, Mn: 0.3%–0.5%, mixed rare earth RE (Ce, La, Nd, Pr): 1.4%–1.7%, balance being Mg and unavoidable impurities; Impurities are strictly limited: Si≤0.05%, Fe≤0.005%, Cu≤0.01%, Ni≤0.001%, other single impurities≤0.01%, total impurities≤0.15%.

[0030] The key restrictions on the rare earth element ratios are: Nd ≥ 0.4%, La / Ce mass ratio = 1:2 to 2:1, RE / Al mass ratio = 0.15 to 0.40; After molding, the β phase exhibits an irregular network distribution at the grain boundaries, with some parts showing a discontinuous and diffuse distribution within the grains, thus achieving the integration of the grain boundary Al-RE phase with the matrix Mg. 17 Al 12 Synergistic regulation of phases significantly improves the strength-toughness balance of the alloy while ensuring casting fluidity.

[0031] II. Preparation method of high-strength and high-toughness AE81 magnesium alloy by die casting, including the following steps: S1. Batching and Pretreatment: Accurately weigh high-purity raw materials according to the designed composition, including pure magnesium ingots, pure aluminum, pure zinc, Mg-Mn master alloy, Mg-Nd master alloy, Mg-Ce master alloy, Mg-La master alloy, etc. All raw materials must be cleaned before use to remove oil and oxide scale, and preheated at 100-150℃ to remove moisture.

[0032] S2. Melting: Preheat a graphite or steel crucible (lined with a protective coating) to 300-400℃ in a resistance furnace, then add pure magnesium ingots. Immediately introduce a protective atmosphere (high-purity Ar or SF6 / CO2 mixture), raise the temperature to 700-720℃, and hold for a period of time to completely melt the magnesium ingots. Once the magnesium melt is clear, add preheated pure aluminum and pure zinc in sequence. After they have completely melted, add intermediate alloys such as Mg-Mn and Mg-Nd.

[0033] S3. Refining: Stabilize the melt temperature at 730–750℃, add an appropriate amount of refining agent (such as hexachloroethane or RJ series magnesium alloy refining agent, generally 0.5%–1.0% of the melt mass), and perform degassing and slag removal treatment. Let it stand for 10–20 minutes to allow the reaction products and inclusions to fully float or sink. Use a preheated slag skimmer to thoroughly remove the oxide scale and slag from the surface of the melt to obtain a clean and pure alloy melt.

[0034] S4, High-pressure die casting: 1. Melt Transfer and Mold Pretreatment: After refining, the magnesium alloy melt is transferred to a holding furnace for receiving and maintaining the melt temperature within the range of 640-700℃. It is then smoothly poured into the injection sleeve of the cold chamber die casting machine. The die casting mold is made of H13 hot work die steel. Before die casting, the mold should be uniformly heated to a working temperature of 240-280℃. Then, a water-based release agent is uniformly sprayed into the cavity, and any remaining liquid release agent is immediately blown away with compressed air to form a uniform film on the mold surface.

[0035] 2. Die Casting Process: The die casting process relies on a series of precisely controlled parameters. The entire process employs a high-speed, high-pressure method: In the slow injection stage, the punch moves at a low speed to ensure the melt smoothly fills the pressure chamber; upon entering the fast injection stage, the punch speed increases dramatically, driving the melt to inject into the mold cavity at a high speed of 4-5 m / s, with the pressure boosting position at 630-670 mm. This injection stage is maintained for 10-30 seconds. This high speed ensures that the melt completely fills the complex mold cavity before solidification, accurately replicating mold details and contributing to the formation of a dense, fine-grained surface layer. During filling, the die casting specific pressure acting on the melt is typically controlled at 60-80 MPa. Higher specific pressure effectively increases the density of the casting and forces the melt to compensate for solidification shrinkage under pressure, thereby significantly reducing internal defects such as shrinkage porosity and gas bubbles. This is crucial for ensuring the mechanical properties of the final part. After filling, the system immediately enters the holding pressure stage, applying a pressure of 40-60 MPa and maintaining it for 10-30 seconds. Under this sustained pressure, the undiluted melt continues to compensate for solidification shrinkage, further eliminating internal shrinkage cavities. The casting is then ejected from the mold after cooling for 10 seconds within the cavity. The entire die-casting cycle must be controlled within 60 seconds. After ejection, the gating system, overflow channels, and venting channels are removed by sawing or other methods. Then, burrs and flash are removed by grinding to achieve the desired surface finish.

[0036] Slag collection bags are placed in the final filling area of ​​the molten metal at the bottom of the product and at the confluence of multiple molten metal streams to collect cold molten metal, oxide inclusions and entrapped air, thereby eliminating defects in key forming areas.

[0037] III. This invention also provides a method for preparing a large die-cast wire spool using the aforementioned high-strength, high-toughness AE81 magnesium alloy as raw material. The core of this method lies in obtaining the spool halves through a split die-casting process, then overlapping the two halves, using a support ring inside the mating surface to bear the welding load, and finally connecting the spools using friction stir welding—a composite process route. An AE81 magnesium alloy spool with a rim diameter of Ф300mm and a wall thickness of 10mm was prepared.

[0038] S1, Die-casting of split-type coils See Figure 2 For die-casting the wire reel, simply replace the mold used to prepare AE81 with a wire reel mold (or remelt AE81 and die-cast it again using the same process). According to the design, only half of the wire reel needs to be die-cast (all half-reels are identical; the mating surfaces of two half-reels are welded together to form a complete reel), therefore the mold is a half-reel mold. Each half-mold includes a roll, a wall structure (such as reinforcing ribs), a side flange, and a connecting structure integrated into the flange end face (such as a shaft hole).

[0039] S2, Pretreatment of the support ring The AZ61 magnesium alloy support ring 2 combines strength and ductility, with an inner diameter of 205mm, a width of 20mm, and a wall thickness of 25mm. Support ring 2 is an independent intermediate connector, its cross-section designed as an annular support or other shape that matches the inner diameter of the rim of the coil half 1, allowing for mechanical interlocking. It undergoes machining and surface cleaning to ensure the mating surfaces are flat, clean, and free of oil and oxide layers.

[0040] S3, High-precision assembly and positioning of components One coil half 1 is fixed to the fixture base. The support ring 2 is precisely embedded into the corresponding slot of the coil half 1. To ensure support strength, the support ring 2 can be spot welded to the coil half 1. Then, the other coil half 1 is attached and positioned to the predetermined position of the inner wall of the rim of the first coil half 1. Finally, the fixture is used to clamp it from both ends to form the assembly to be welded.

[0041] S4. Friction stir welding of circumferential welds 1. Selection of stirring head: Select a threaded conical stirring needle, and use moving shaft shoulder friction stir welding to ensure the strength of the welded joint; 2. Welding parameters: Select a stirring head with a shoulder diameter of 30mm, a stirring head speed of 600 rpm, a welding speed of 45mm / min, and a shoulder pressing amount of 0.1mm.

[0042] 3. Welding process: A ring-shaped friction stir welding machine is used. After the stirring head is preheated, it is inserted at the starting point of weld seam 3. After the heat generation is stable, the worktable is rotated and the stirring head is fed laterally. At this time, the stirring head rotates at high speed and moves along the ring seam. Its shoulder presses against the surface of the component, and the stirring needle is inserted into the inside of the component to stir, rub and mix the material, thereby achieving a firm connection between the two half-coils. In order to ensure the aesthetics and strength of the weld seam, a retraction technique is used at the end to eliminate the keyhole.

[0043] S5. Post-weld treatment and finishing 1. After welding, place the entire wire coil in a heat treatment furnace for 2-4 hours of stress-relief annealing, and cool it with the furnace to eliminate residual welding stress.

[0044] 2. Final finishing: On a CNC lathe, using the integral axis as a reference, finish-machine the outer edges and end faces of both flanges, and bore the center shaft hole to ensure that the final dimensional accuracy and geometric tolerances meet the drawing requirements. Dynamic balancing tests and corrections may be performed if necessary. Depending on product requirements, surface treatments such as passivation, spraying, and anodizing can be performed to improve corrosion resistance or appearance.

[0045] To make the technical solution of the present invention clearer, the technical solution of the present invention will be further described in detail below with reference to the performance test data of the embodiments and comparative examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Unless otherwise specified in the embodiments, the purity of the raw materials used meets the foregoing requirements, and the performance tests are all conducted at room temperature (25±2℃) in accordance with relevant national standards (GB / T) or international standards (ASTM).

[0046] Referring to the above content, multiple AE81 die-cast magnesium alloy coils were obtained, numbered Examples 1-5, and their performance test data are shown in the table below. Example 1

[0047] Alloy composition: Al 7.5%, Zn 0.7%, Mn 0.4%, Ce 0.6%, La 0.45%, Nd 0.42%, Pr 0.08%, total RE content 1.55%, RE / Al=0.21, La / Ce=0.75; Parameters for wire coil die casting preparation method: S1. Raw material pretreatment: Accurately weigh pure magnesium ingots, pure aluminum, pure zinc and various magnesium alloy intermediates, remove surface oil and oxide scale from all raw materials, and preheat at 150℃ to remove water. S2. Melting process: Preheat the crucible to 350°C, introduce Ar gas, add magnesium ingots and heat to 720°C to melt, then add aluminum, zinc and intermediate alloy in sequence and stir evenly. S3. Refining and impurity removal: Heat the melt to 740℃, add 0.5% refining agent, remove gas and slag, let stand for 15 minutes, remove surface slag, and obtain pure melt; S4. Die casting: The melt is kept at 640℃, the mold is preheated to 240℃ and a release agent is sprayed. The die casting parameters are as follows: pressure boosting position: 670mm, filling speed: 5m / s, die casting specific pressure: 80MPa, holding pressure: 50MPa, holding time: 20s, single cycle cooling time: 10s, total die casting cycle: ≤60s.

[0048] S5. Separate assembly and welding: The coil half is assembled and positioned with the AZ61 support ring, and the butt joint is completed by annular friction stir welding. After welding, stress relief annealing, precision machining, and dynamic balance correction are performed.

[0049] Friction stir welding parameters: tapered threaded stirring pin and moving shoulder welding, shoulder diameter 30mm, stirring head speed 600rpm, welding speed 45mm / min, shoulder pressing amount 0.1mm; stress relief annealing at 300℃ for 3h after welding.

[0050] The density of the spool casting after molding is 1.79 g / cm³. 3 Porosity 2.8%, scrap rate 4.2%; Mechanical properties: tensile strength 293MPa, yield strength 164MPa, elongation after fracture 12.54%, strength-ductility product 3674MPa·; tensile strength of the coil body 201MPa, tensile strength of the coil surface 218MPa, overall performance fluctuation 22MPa.

[0051] For the die casting process, this embodiment adopts the optimal die casting process, which is obtained through orthogonal experimental design: the three process parameters with the greatest impact on the casting quality are selected, each with three levels, and an L9(34) orthogonal array is used: ; Using casting density (or porosity) as the evaluation index, the influence of various factors is studied: ; Range analysis: Factor A (Boost Location): Range R = 0.00641 Factor B (mold temperature): Range R = 0.00504 Factor C (magnesium bath temperature): Range R = 0.00717 (most influential) Factor D (holding time): Range R = 0.00637 Analysis conclusion: The temperature of the molten magnesium has the greatest impact, followed by the pressure boosting position and holding time, while the mold temperature has a relatively smaller impact. Lowering the temperature of the molten magnesium and the mold, setting the pressure boosting position appropriately (earlier or later), and appropriately increasing the holding time can all reduce the overall porosity. Based on a comprehensive range analysis and practical production feasibility, the optimal combination of process parameters is determined: Magnesium bath temperature: 640°C Boost position: 670 mm Mold temperature: 240℃ Pressure holding time: 20s; Using the above optimal process parameters, combined with alloy ratio optimization and slag collection / diversion bag design, the effects before and after optimization are compared: ; Mechanical properties were tested by sampling at different locations (edge, middle, center) of the coil: ; Example 2

[0052] Alloy composition: Al 7.4%, Zn 0.8%, Mn 0.35%, Ce 0.58%, La 0.48%, Nd 0.40%, Pr 0.07%, total RE content 1.53%, RE / Al=0.207, La / Ce=0.83; The process parameters are the same as in Example 1.

[0053] The density of the casting after molding is 1.789 g / cm³. 3 Porosity 2.9%, scrap rate 4.5%; Mechanical properties: tensile strength 285MPa, yield strength 160MPa, elongation after fracture 10.8%, strength-ductility product 3078MPa·; tensile strength of the coil body 196MPa, tensile strength of the coil surface 212MPa, overall performance fluctuation 24MPa. Example 3

[0054] Alloy composition: Al 7.6%, Zn 0.65%, Mn 0.45%, Ce 0.62%, La 0.42%, Nd 0.45%, Pr 0.09%, total RE content 1.5%, RE / Al=0.208, La / Ce=0.68; The process parameters are the same as in Example 1.

[0055] The density of the casting after molding is 1.791 g / cm³. 3 Porosity 2.7%, scrap rate 3.8%; Mechanical properties: tensile strength 275MPa, yield strength 152MPa, elongation after fracture 13.5%, strength-ductility product 3713MPa·; tensile strength of the coil body 203MPa, tensile strength of the coil surface 220MPa, overall performance fluctuation 21MPa. Example 4

[0056] Alloy composition: Al 7.7%, Zn 0.9%, Mn 0.3%, Ce 0.65%, La 0.50%, Nd 0.43%, Pr 0.07%, total RE content 1.65%, RE / Al=0.214, La / Ce=0.77; The process parameters are the same as in Example 1.

[0057] The density of the casting after molding is 1.788 g / cm³. 3 Porosity 2.9%, scrap rate 4.3%; Mechanical properties: tensile strength 294MPa, yield strength 157MPa, elongation after fracture 12.1%, strength-ductility product 3557MPa·; tensile strength of the coil body 198MPa, tensile strength of the coil surface 215MPa, overall performance fluctuation 23MPa. Example 5

[0058] Alloy composition: Al 7.3%, Zn 0.6%, Mn 0.5%, Ce 0.55%, La 0.40%, Nd 0.40%, Pr 0.06%, total RE content 1.41%, RE / Al=0.193, La / Ce=0.73; The process parameters are the same as in Example 1.

[0059] The density of the casting after molding is 1.787 g / cm³. 3 Porosity 3.0%, scrap rate 4.8%; Mechanical properties: tensile strength 281MPa, yield strength 154MPa, elongation after fracture 9.74%, strength-ductility product 2737MPa·; tensile strength of the coil body 195MPa, tensile strength of the coil surface 210MPa, overall performance fluctuation 25MPa.

[0060] Comparative Example 1 (Conventional Commercial AZ91D Magnesium Alloy) Commercially available AZ91D magnesium alloy ingots were used, with a typical composition of: Al 9.0%, Zn 0.7%, Mn 0.3%, Si 0.05%, Fe 0.015%, and the balance being Mg; the process parameters were the same as in Example 1.

[0061] The density of the casting after molding is 1.76 g / cm³. 3 Porosity 5.2%, scrap rate 14.2%; Mechanical properties: tensile strength 230MPa, yield strength 130MPa, elongation after fracture 3.0%, strength-ductility product 690MPa·; overall performance fluctuation of the coil 41MPa.

[0062] Comparative Example 2 (Conventional Commercial AZ31 Magnesium Alloy) Commercially available AZ31 magnesium alloy ingots were used, with a typical composition of: Al 3.0%, Zn 1.0%, Mn 0.2%, and the balance Mg; the process parameters were the same as in Example 1.

[0063] The density of the casting after molding is 1.75 g / cm³. 3 Porosity 4.8%, scrap rate 12.8%; Mechanical properties: tensile strength 215MPa, yield strength 125MPa, elongation after fracture 10.0%, strength-ductility product 2150MPa·; overall performance fluctuation of the coil 38MPa.

[0064] ; The alloys in this group of examples exhibited excellent overall mechanical properties. As shown in the table, their data almost universally surpassed those of the commercial magnesium alloys AZ91D (Comparative Example 1) and AZ31 (Comparative Example 2). In terms of strength, the tensile strength (275-294 MPa) and yield strength (152-164 MPa) of all examples were significantly higher than those of the two comparative examples (tensile strength 215-230 MPa, yield strength 125-130 MPa).

[0065] Furthermore, the elongation after fracture of the embodiments (9.74%-13.5%) is significantly higher than that of AZ91D (3%), and generally superior to that of AZ31 (10%). The "strength-ductility product," a key indicator for comprehensively evaluating the material's strength and toughness, is even more outstanding. Example 3 reaches 3713 MPa%, more than five times that of Comparative Example 1 (690 MPa%), and the other examples also exhibit extremely high levels, indicating that the alloy of this invention successfully overcomes the contradiction between strength and ductility that is difficult to achieve simultaneously in traditional die-cast magnesium alloys. In summary, AE81 provides excellent toughness while maintaining high strength, perfectly meeting the core requirements of "high strength, high toughness," reliability, and durability for structural components such as cable reels. Moreover, its die-casting-based implementation path ensures good formability and production efficiency.

[0066] Comparative Example 3 The alloy ratio of Example 1 was used, the mold had no slag-collecting structure, and the remaining process steps were completely consistent with Example 1. See also... Figure 2 This is a comparative schematic diagram of slag collection bag design schemes. Comparative Example 3 has no slag collection bag, while Example 1 has a slag collection bag at the bottom. The slag collection bag is arranged in the final filling area of ​​the molten metal and at the confluence of multiple molten metal streams. The density of the casting after molding is 1.77 g / cm³. 3 The porosity is 4.9%, the scrap rate is 13.5%; the tensile strength of the coil body is 172MPa, the tensile strength of the coil surface is 190MPa, and the overall performance fluctuation is 39MPa.

[0067] Comparative Example 4 The alloy ratio and mold structure of Example 1 were adopted; The traditional die-casting process is adopted: magnesium liquid temperature 700℃, mold temperature 260℃, holding time 30s, and pressure increase position 650mm.

[0068] The density of the casting after molding is 1.772 g / cm³. 3 The porosity is 4.5%, the scrap rate is 11.7%; the tensile strength of the coil body is 168MPa, the tensile strength of the coil surface is 185MPa, and the overall performance fluctuation is 36MPa.

[0069] Comparative Example 5 Tensile tests were conducted on samples taken from the weld seam of the AE81 magnesium alloy coil prepared in Example 1. The performance test results (average) were as follows: tensile strength 167 MPa, yield strength 87 MPa.

[0070] The AE81 wire reel was die-cast using an integral wire reel mold, and all other aspects were the same as in Example 1. Tensile specimens were obtained at the same locations on the wire reel. Performance test results (average): tensile strength 187 MPa, yield strength 113.75 MPa.

[0071] It can be observed that the strength of the coil produced by this method can reach almost 90% of that of the base material. This is because the weld nugget area undergoes significant secondary recrystallization, resulting in fine and uniform grains and excellent weld joint performance. More importantly, while significantly reducing mold costs and process difficulty, it solves the technical bottleneck of poor overall die-casting formability and low yield of large and complex magnesium alloy parts, and obtains a high-strength weld joint that can meet the requirements of tensile, compressive, bending, and torsional combined stresses and impact loads that the coil can withstand during dynamic cable winding and unwinding and hoisting transportation.

[0072] In summary, the high-strength, high-toughness large magnesium alloy die-cast coil and its preparation method provided by this invention, through multi-element microalloying composition design and preparation process, successfully break through the constraint of the traditional trade-off between strength and toughness in die-cast magnesium alloys. Under the premise of controllable cost, it achieves comprehensive mechanical properties that are superior to existing commercial alloys. This technical solution is mature and reliable, easy to implement in industrial applications, and provides an ideal material solution for the lightweight upgrading of a large number of structural components such as cable reels, possessing extremely high industrial application value and broad market prospects.

[0073] The foregoing has shown and described the basic principles, main features, and advantages of this disclosure. Those skilled in the art should understand that this disclosure is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this disclosure. Various changes and modifications can be made to this disclosure without departing from its spirit and scope, and all such changes and modifications fall within the scope of this disclosure as claimed.

Claims

1. A high-strength, high-toughness rare-earth magnesium alloy, characterized in that, Includes the following ingredients by weight percentage: Al: 7.3%–7.7%, Zn: 0.6%–0.9%, Mn: 0.3%–0.5%, mixed rare earth RE: 1.4%–1.7%, with the balance being Mg and unavoidable impurities; mixed rare earth RE includes Ce, La, Nd, and Pr; Nd ≥ 0.4%, La / Ce mass ratio = 1:2–2:1, RE / Al mass ratio = 0.15–0.

40.

2. The high-strength, high-toughness rare-earth magnesium alloy according to claim 1, characterized in that, Impurities: Si≤0.05%, Fe≤0.005%, Cu≤0.01%, Ni≤0.001%, other single impurities≤0.01%, total impurities≤0.15%.

3. A method for forming a high-strength, high-toughness rare-earth magnesium alloy according to claim 1 or 2, characterized in that, After the raw materials are melted and refined, they are subjected to high-pressure die casting. After entering the fast injection stage, the high-pressure die casting drives the melt to be injected into the mold cavity at a high speed of 4-5m / s. The pressure boosting position is 630~670mm, and the entire injection stage is maintained for 10~30s.

4. The forming method of a high-strength, high-toughness rare-earth magnesium alloy according to claim 3, characterized in that, The die-casting pressure is 60-80 MPa.

5. The forming method of a high-strength, high-toughness rare-earth magnesium alloy according to claim 3, characterized in that, After filling is complete, immediately proceed to the pressure holding stage, apply a pressure of 40-60 MPa and maintain it for 10-30 seconds.

6. The forming method of a high-strength, high-toughness rare-earth magnesium alloy according to claim 3, characterized in that, After filling, the melt temperature is maintained within 640-700℃ for high-pressure die casting.

7. The forming method of a high-strength, high-toughness rare-earth magnesium alloy according to claim 3, characterized in that, After the filling process is completed, before the die casting operation, the high-pressure die casting mold should be uniformly heated to a working temperature of 240-280℃.

8. The forming method of a high-strength, high-toughness rare-earth magnesium alloy according to claim 3, characterized in that, Slag collection bags are placed in the final filling area of ​​the molten metal at the bottom of the product and at the confluence of multiple molten metal streams.

9. A large die-cast wire spool is manufactured using the rare earth magnesium alloy forming method as described in claim 3.

10. The method for manufacturing large die-cast wire reels according to claim 9, characterized in that, The coil halves are obtained by split die casting, then the two coil halves are overlapped, and a support ring is used inside the mating surface to bear the welding load. Finally, the coil halves are connected by friction stir welding.

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