High-performance magnesium alloy laminated plate and preparation method thereof

Abstract

The invention discloses a high-performance magnesium alloy laminated plate and a preparation method thereof, and belongs to the technical field of metal materials. The preparation method of the high-performance magnesium alloy laminated plate comprises the following steps: selecting a plurality of magnesium alloys with different aluminum contents as raw materials, uniformly annealing and cooling the magnesium alloys, and polishing and degreasing the surfaces of the magnesium alloys; the magnesium alloy raw materials are arranged in a low-medium-high-medium-low continuous symmetrical distribution mode from the surface layer to the core part according to the aluminum content to form a blank pile; carrying out hot extrusion treatment on the blank pile to form a laminated plate; and the extruded laminated plate is subjected to annealing treatment for 1 min to 60 min at the temperature of 250 DEG C to 350 DEG C, and the high-performance magnesium alloy laminated plate is obtained. According to the magnesium alloy laminated plate with the heterostructure is constructed through the aluminum content gradient design in combination with the extrusion and short-time annealing processes.

Description

Technical Field

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

[0002] As the lightest metal structural material, magnesium alloys have significant application potential in aerospace, new energy vehicles, and other fields. However, magnesium alloys generally face the challenge of balancing strength and ductility. Traditional strengthening methods (such as alloying, grain refinement, and texture control) often improve material strength at the expense of ductility, making it difficult to achieve a synergistic improvement in both strength and ductility.

[0003] In recent years, heterostructure designs (such as layered heterostructures and gradient structures) have emerged as an emerging strategy to overcome these challenges. By incorporating mechanisms such as backstress strengthening, heterogeneous deformation-induced (HDI) strengthening, and HDI work hardening, these novel structural designs have demonstrated significant advantages in simultaneously improving both strength and ductility. However, existing research has largely focused on heterostructures with step-step compositions between adjacent components (e.g., AZ31 / ZK60, AZ31 / Mg-xGd, and AZ31 / GW103K). These heterostructured magnesium alloys with step-step compositions suffer from the following drawbacks: 1) In step-step heterostructures, the composition and properties of adjacent components differ significantly, and this sudden change can lead to insufficient interfacial bonding strength; 2) unstable compounds or phases may form at the interface between the different components, affecting interfacial stability; and 3) during processing, such as rolling and extrusion, the different properties of the layers in the step-step heterostructure can lead to different deformation behaviors and processing defects. In summary, the main defects of the traditional composition-step heterostructure design are concentrated on insufficient interface bonding strength, interface compatibility problems and uneven processing performance. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems in the prior art and provide a high-performance magnesium alloy laminate and a preparation method thereof. The present invention is based on an aluminum content gradient design and combines an extrusion and a short-time annealing process to prepare a heterogeneous structure magnesium alloy laminate, realizing the synergistic effect of element diffusion-induced solid solution strengthening, nano-precipitation strengthening and heterogeneous deformation-induced strengthening. Not only does it overcome the problem of difficulty in balancing strength and plasticity, but the laminate of the present invention also has high interface bonding strength, good interface compatibility, and uniform processing performance.

[0005] A high-performance magnesium alloy laminate of the present invention comprises the following steps: Selecting multiple magnesium alloys with different aluminum contents as raw materials, uniformly annealing and cooling the magnesium alloys, and then grinding and degreasing the surface; stacking the magnesium alloy raw materials to form a billet stack, wherein the aluminum content of the billet stack presents a continuous and symmetrical distribution of "low-medium-high-medium-low" from the surface to the core; The blank stack is subjected to hot extrusion to form a laminate; The laminate is annealed at 250°C-350°C for 1 min-60 min to obtain a high-performance magnesium alloy laminate.

[0006] Preferably, the magnesium alloy raw material is pure Mg, AZ31 and AZ91.

[0007] Preferably, the pure Mg layer accounts for 5%-15%, the AZ31 layer accounts for 15%-35%, and the AZ91 layer accounts for 45%-65%.

[0008] Preferably, the temperature of the hot extrusion treatment is 200° C. to 400° C., and the extrusion ratio is 3.9-12.8.

[0009] Preferably, the annealing treatment time is 30 minutes.

[0010] Preferably, graphite is used as a lubricant during the extrusion process, the extrusion speed is 6 mm / s, and the extrusion ratio is 12.8.

[0011] A second object of the present invention is to provide a high-performance magnesium alloy laminate prepared by the above-mentioned method for preparing the high-performance magnesium alloy laminate.

[0012] Preferably, the high-performance magnesium alloy laminate is characterized by a tensile strength of 321.1 MPa and an elongation of 12.1%.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The preparation method of the present invention utilizes an aluminum content gradient design combined with extrusion and short-time annealing processes to construct a magnesium alloy laminate with a heterogeneous structure. The extrusion process induces dynamic recrystallization, resulting in cross-scale heterogeneity in grain size / texture gradients, dislocation density, and precipitate distribution. Short-time annealing further promotes the diffusion of Al and Zn elements from the high-Al layer to the low-Al layer, forming a solid solution and significantly improving interfacial bonding strength. During annealing, the high-Al layer precipitates a high-density nanoscale β-MgAl phase (size 8nm-90nm), effectively hindering dislocation motion. Interlayer differences in grain size, dislocation density, and texture gradients induce synergistic deformation, with a heterogeneous deformation-induced stress contribution rate of ≥50%. The resulting magnesium alloy laminate exhibits an ultimate tensile strength (UTS) of 321.1 MPa and an elongation (EL) of 12.1%, surpassing conventional magnesium alloy laminates in comprehensive mechanical properties. Compared with existing heterogeneous magnesium alloys with cross-composition designs, it also exhibits high interfacial bonding strength, good interfacial compatibility, and uniform processing properties.

[0014] The gradient heterostructure design of this invention, combined with multi-mechanism synergistic strengthening, provides a new paradigm for the development of high-strength and toughness magnesium alloys. The short annealing time (≤60 minutes) of this invention combines low energy consumption with high efficiency, breaking through the softening limitations of traditional annealing and achieving an "annealing strengthening" effect. The preparation process is simple, operational, and controllable, making the finished product performance suitable for large-scale industrial production. It also provides ideas for the large-scale industrial production of other metal laminates.

[0015] The present invention achieves defect-free interface bonding, strain coordination optimization and cost control through the innovation of "continuous composition gradient design + short process technology", providing a new paradigm for the engineering application of magnesium alloy laminates. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the extrusion preparation of a laminate with gradient Al content according to an embodiment of the present invention.

[0017] Figure 2 Schematic diagram of the microscopic morphology of the laminate after extrusion according to an embodiment of the present invention.

[0018] Figure 3 Schematic diagram of the microscopic morphology of the laminate after annealing according to an embodiment of the present invention.

[0019] Figure 4 The figure shows a comparison of the mechanical properties of magnesium alloy laminates under different conditions according to the embodiments of the present invention. DETAILED DESCRIPTION

[0020] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described 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.

[0021] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by persons of ordinary skill in the art to which the invention pertains. The terms "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are merely used to distinguish different components. The terms "include" or "comprise" and similar words mean that the elements or objects appearing before "include" or "comprise" encompass the elements or objects listed after "include" or "comprise" and their equivalents, and do not exclude other elements or objects. The terms "connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms "upper", "lower", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0022] A high-performance magnesium alloy laminate of the present invention comprises the following steps: Multiple magnesium alloys with different aluminum contents are selected as raw materials, and the magnesium alloys are uniformly annealed and cooled before the surfaces are polished and degreased. The purpose of uniformly annealing the magnesium alloy raw materials in the present invention is to eliminate the composition segregation, residual stress and coarse / inhomogeneous structure that may exist in the original cast or processed magnesium alloy, so as to provide a uniform and consistent initial microstructural foundation for subsequent gradient stacking and uniform deformation.

[0023] This method thoroughly removes surface oxide layers, oil stains, and impurities, ensuring a clean, tight, and metallurgically bonded interface between layers during the subsequent hot extrusion process. This is a key prerequisite for achieving a high-quality laminate interface, directly impacting interlayer bonding strength and element diffusion pathways. This pretreatment process provides clean, uniform, and controllable raw materials.

[0024] The magnesium alloy raw materials are stacked to form a billet stack, wherein the aluminum content of the billet stack is continuously and symmetrically distributed in a "low-medium-high-medium-low" manner from the surface to the core; the billet stack is hot extruded to form a laminate; and the laminate is annealed at 250°C to 350°C for 1 min to 60 min to obtain a high-performance magnesium alloy laminate.

[0025] The present invention creates a continuous gradient of strength and plasticity from the surface layer to the core and back to the surface layer, forming a laminate after hot extrusion of the billet stack. The significant aluminum concentration difference between adjacent layers provides a strong thermodynamic driving force for the interdiffusion of aluminum atoms during subsequent hot extrusion and annealing. Different aluminum contents correspond to different microstructures (such as grain size, phase composition, and deformation behavior), forming heterogeneous layered structures with significant microstructural differences. The symmetrical distribution design of the present invention helps to balance the overall performance of the material. By establishing compositional gradients and potential microstructural gradients, the present invention provides conditions for the introduction of strain gradients and heterogeneous deformation during subsequent extrusion deformation, and provides a driving force for elemental diffusion during annealing.

[0026] The extrusion process of the present invention induces dynamic recrystallization, resulting in heterogeneity across scales in grain size / texture gradients, dislocation density, and precipitate distribution. The short-term annealing treatment further promotes the diffusion of Al and Zn elements from the high-Al layer to the low-Al layer, forming a solid solution and significantly improving interfacial bonding strength. During annealing, the high-Al layer precipitates a high-density nanoscale β-MgAl phase (8-90 nm in size), effectively hindering dislocation motion. Differences in grain size, dislocation density, and texture gradients between layers trigger cooperative deformation.

[0027] The key to raw material selection and layering in this invention is ensuring a continuous, symmetrical distribution of aluminum content from the surface to the core: "low-medium-high-medium-low." For example, a low-aluminum alloy such as Mg-1Al, Mg-2Al, or pure magnesium can be selected for the surface layer; a medium-aluminum alloy such as AZ31, AZ61, or AM30 can be selected for the transition layer; and a high-aluminum alloy such as AZ91, AZ80, AZ61, or AM60 can be selected for the core layer. In this embodiment, a composition of pure Mg (0% Al) / AZ31 (3% Al) / AZ91 (9% Al) is used to achieve a continuous, symmetrical distribution of aluminum content from the surface to the core: "low-medium-high-medium-low." However, it should be understood that any combination of magnesium alloys for the surface, transition, and core layers that adheres to the principle of a "low Al-medium Al-high Al-medium Al-low Al" gradient and symmetrical stacking is within the scope of this invention.

[0028] As a preferred embodiment, the magnesium alloy raw materials are pure Mg, AZ31 and AZ91.

[0029] As a preferred embodiment, the pure Mg layer accounts for 5%-15% of the total thickness of the billet stack, the AZ31 layer accounts for 15%-35% of the total thickness of the billet stack, and the AZ91 layer accounts for 45%-65% of the total thickness of the billet stack. This embodiment achieves high plasticity in the surface layer and high strength in the core through composition gradients and thickness gradients, while the thickness of the transition layer is designed to balance the deformation compatibility of both sides.

[0030] In this embodiment, the pure Mg layer (5%-15%) serves as a soft matrix, mainly providing plastic deformation capability; the AZ31 layer (15%-35%) serves as an intermediate transition layer to balance strength and plasticity; the AZ91 layer (45%-65%) serves as a high-strength bearing layer to enhance the overall structural strength; this ratio in this embodiment is achieved by regulating the volume fraction of each layer to form a gradient distribution of the soft phase (pure Mg) and the hard phase (AZ91) to avoid stress concentration. Secondly, the principle of process formability is considered. During extrusion molding, it is necessary to ensure that the thickness ratio of each layer meets the fluidity requirements. A too thin pure Mg layer may lead to poor interface bonding, and an overly thick AZ91 layer may cause defects due to poor fluidity. Thirdly, the principle of thermodynamic stability is considered. The difference in thermal expansion coefficients of different magnesium alloy layers needs to be compensated by a thickness gradient to avoid interface cracking due to thermal stress. More specifically, the thickness ratio in this embodiment has the following advantages:

[0031] 1) The thickness ratio in this embodiment can take into account both strength and shaping In this embodiment, the greater the thickness of the core layer (AZ91), the higher the overall sheet strength and hardness, but plasticity (elongation) may be reduced; too thin a layer may result in insufficient strength. The surface layer (pure Mg) contributes less to overall strength and hardness (due to its low strength) and primarily affects plasticity. Too thin a layer may reduce its corrosion protection, while too thick a layer may excessively dilute the overall strength. The thickness of the intermediate layer (AZ31) affects deformation coordination and stress distribution. Too thin a layer may lead to stress concentration, poor interfacial bonding, or premature cracking; too thick a layer may occupy an excessive proportion, weakening the core layer's contribution to strength. In this embodiment, the pure Mg layer accounts for 5%-15% of the total thickness of the billet stack, the AZ31 layer accounts for 15%-35%, and the AZ91 layer accounts for 45%-65%. This thickness design achieves a balance between strength and plasticity.

[0032] 2) The thickness ratio in this embodiment can enhance the interlayer bonding strength: The AZ31 layer in this embodiment serves as a transition layer, crucial for relieving interfacial stress and promoting good bonding. A mismatch in thickness (especially one that is too thin) can weaken the bond and easily lead to delamination during subsequent processing (such as bending) or service. The AZ31 layer in this embodiment (15%-35%) ensures interlayer bonding strength.

[0033] 8) The thickness ratio in this embodiment can meet the forming process performance: In this embodiment, the plastic deformation capacity (rheological stress) of each layer of material during extrusion varies. The appropriate thickness ratio (especially the cushioning effect of the middle layer) is key to ensuring a smooth extrusion process (good sheet shape, no wrinkles, and no delamination). This avoids problems such as uneven extrusion force distribution, warping, and even delamination and cracking during extrusion.

[0034] 9) The thickness ratio in this embodiment can reduce residual stress: Due to the different thermal expansion coefficients of the various layers, thermal residual stresses are generated during the cooling process after extrusion. The thickness ratio directly affects the degree to which each layer constrains the overall thermal mismatch, thereby affecting the magnitude and distribution of residual stresses. The thickness ratios employed in this embodiment can reduce residual stresses, preventing excessive residual stresses from causing sheet warping or reducing fatigue performance.

[0035] It should be noted that when raw materials change, the thickness ratio needs to be re-optimized. The optimized thickness ratio must also consider the strength-ductility trade-off, interface matching optimization, and deformation coordination optimization. Furthermore, due to the varying deformation resistance of different materials, the deformation coordination of each layer will change during the extrusion process, potentially leading to warping, delamination, or uneven thickness. Therefore, the optimized thickness ratio must ensure uniform deformation.

[0036] Example 1 This embodiment uses pure Mg (0% Al), AZ31 (3% Al) and AZ91 (9% Al) as the magnesium alloy raw material combination. This embodiment provides a method for preparing a high-performance magnesium alloy laminate, which includes the following steps:

[0037] S1, material pretreatment: pure Mg (99.9wt.%), AZ31 (Mg-3Al-1Zn) and AZ91 (Mg-9Al-0.7Zn) ingots were cut into 35×15×1.5mm 3 (pure Mg), 35×15×3mm 3 (AZ31), 35×15×6mm 3 (AZ91) blocks were preheated at 400°C for 12 hours. In this example, homogenization annealing primarily provided a uniform, ductile matrix for subsequent extrusion deformation. Pure Mg and AZ31 samples were cooled in air, while AZ91 samples were quenched in water. Each sample was then surface-brushed and degreased using a wire brush.

[0038] S2, stacking and hot extrusion: The pretreated materials are stacked in the order of pure Mg-AZ31-AZ91-AZ31-pure Mg to form a billet with a total thickness of about 15 mm, see Figure 1 . After the temperature of the extrusion cylinder stabilizes at 260°C, the billet is placed in the extrusion cylinder and kept warm for 8 minutes before extrusion molding to obtain a magnesium alloy laminate with a thickness of about 1.5 mm. Graphite is used as a lubricant during the extrusion process, the extrusion speed is 6 mm / s, and the extrusion ratio is 12.8. In this embodiment, the extrusion die can control the final thickness of the extruded product. In order to ensure a good interface bonding between the components of the laminate, the width of the sizing band of the extrusion die is between 1-5 mm; and the extrusion cylinder is approximately square and is mainly used for plate extrusion.

[0039] See also Figure 2 , observing the grain morphology between the layers of each component after extrusion, it is found that after hot extrusion, a grain gradient change is achieved from the surface to the core.

[0040] In step S3, the extruded laminates were placed in a box furnace for annealing at 250°C, held at that temperature for 30 minutes, and then air-cooled. Annealing was used to manipulate the microstructural heterogeneity of the component layers, element diffusion at the layer interfaces, and the presence of nano-precipitates, thereby achieving control over the mechanical properties of the laminates.

[0041] Example 2 The extruded laminate was annealed at a temperature of 300° C., and the rest was the same as in Example 1.

[0042] In the third embodiment, the extruded laminate is annealed at a temperature of 350° C., and the rest is the same as in the first embodiment.

[0043] Comparative Example 1 The specific method of Comparative Example 1 differs from that of Example 1 only in that no annealing treatment is performed.

[0044] Mechanical properties of Examples 1 to 3 were tested respectively, and the results are shown in Table 1.

[0045] Table 1 Mechanical properties of magnesium alloy laminates under different processing conditions See also Figure 2 In the first comparative example, a magnesium alloy laminate with a heterogeneous structure was constructed by designing an Al content gradient. The extrusion process induces dynamic recrystallization, resulting in heterogeneity in grain size and texture strength across scales.

[0046] See also Figure 3 and Figure 4 The plates of Examples 1 to 3 were subjected to a short-term annealing treatment, which promoted the diffusion of aluminum and zinc elements from the AZ91 and AZ31 layers into the pure magnesium layer, inducing solid solution strengthening. The number of nano-precipitated phases in the AZ91 layer increased significantly during the annealing process, especially the large amount of nano-β phase, which effectively hindered dislocation movement and strengthened the laminate. At the same time, the heterogeneous deformation-induced strengthening effect of the laminate was enhanced, and the proportion of HDI stress increased after annealing. All annealed laminates showed abnormal strengthening characteristics compared to the extruded state. Among them, the laminate annealed at 300℃ / 30min had a yield strength increased by 15.4% and a tensile strength increased by 8.1% compared to the extruded state, while the elongation still reached 12.1%.

[0047] While 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 these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-performance magnesium alloy laminate, characterized in that: include: Selecting multiple magnesium alloys with different aluminum contents as raw materials, uniformly annealing and cooling the magnesium alloys, and then grinding and degreasing the surface; stacking the magnesium alloy raw materials to form a billet stack, wherein the aluminum content of the billet stack presents a continuous and symmetrical distribution of "low-medium-high-medium-low" from the surface to the core; The blank stack is subjected to hot extrusion to form a laminate; The laminate is annealed at 250°C-350°C for 1 min-60 min to obtain a high-performance magnesium alloy laminate.

2. The method for preparing a high-performance magnesium alloy laminate according to claim 1, wherein: The magnesium alloy raw materials are pure Mg, AZ31 and AZ91.

3. The method for preparing a high performance magnesium alloy laminate according to claim 2, wherein: The pure Mg layer accounts for 5%-15% of the total thickness of the billet stack, the AZ31 layer accounts for 15%-35% of the total thickness of the billet stack, and the AZ91 layer accounts for 45%-65% of the total thickness of the billet stack.

4. The method for preparing a high performance magnesium alloy laminate according to claim 1, wherein: The temperature of the hot extrusion treatment is 200° C. to 400° C., and the extrusion ratio is 3.9-12.

8.

5. The method for preparing a high performance magnesium alloy laminate according to claim 1, wherein: The annealing time is 30 min.

6. The method for preparing a high performance magnesium alloy laminate according to claim 1, wherein: Graphite was used as lubricant during the extrusion process, and the extrusion speed was 6 mm / s.

7. A high performance magnesium alloy laminate obtained by the method for preparing a high performance magnesium alloy laminate according to any one of claims 1 to 6.

8. The high performance magnesium alloy laminate according to claim 7, wherein: The tensile strength is 321.1MPa and the elongation is 12.1%.

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