A bimodal ZnCu / ZnMg layered composite material, a preparation method and application thereof

Abstract

The present invention discloses a bimodal ZnCu / ZnMg layered composite material, and a preparation method and application thereof. A ZnMg alloy plate is placed between two ZnCu alloy plates for lamination to obtain a composite plate, the composite plate is subjected to a single-pass cold rolling to obtain a cold-rolled plate, the cold-rolled plate is cut into two pieces from the middle, the plates are stacked, and then single-pass cold rolling is performed again. The cutting-stacking-single-pass cold rolling cycle is repeated, and finally annealing is performed to obtain the obtained material. The present invention utilizes the difference in change of recrystallization annealing grains between the ZnMg alloy plate and the ZnCu alloy plate to obtain a ZnCu / ZnMg layered composite material with different grain sizes (bimodal) by annealing after rolling. The ZnCu / ZnMg layered composite material provided by the present invention exhibits significant work hardening ability at room temperature, has a strength improvement of 115%-260% compared to the strength of pure Zn plate after the same rolling pass, and maintains good room-temperature plasticity.

Description

Technical Field

[0001] The present invention belongs to the technical field of biodegradable zinc alloys, and in particular relates to a bimodal ZnCu / ZnMg layered composite material with work hardening capability, a preparation method and an application thereof. Background Art

[0002] Zinc alloys have good biocompatibility and a moderate degradation rate, and are considered to be the most promising biodegradable implant materials. However, in terms of mechanical properties, pure Zn has poor hardness, strength, and plasticity. The tensile strength of cast pure Zn is only 30 MPa, and the elongation at break is only 2%. After plastic deformation treatments such as extrusion and rolling, the strength and plasticity of pure Zn are improved to a certain extent, but there is still a large gap between them and the mechanical properties requirements of degradable implant materials. Alloying is undoubtedly an effective way to improve the mechanical properties of alloys. Through alloy design, zinc alloys can have excellent comprehensive mechanical properties, suitable degradation rates and degradation patterns, while also considering matching the physiological process of tissue repair and reconstruction at the implant site and good biocompatibility. In recent years, binary Zn alloys such as Zn-Cu, Zn-Ag, Zn-Mn, Zn-Mg, and Zn-Li, as well as multi-component Zn alloys such as Zn-Cu-Mg, Zn-Cu-Li, Zn-Cu-Ag, Zn-Ag-Mg, Zn-Ag-Mn, and Zn-Cu-Mn-Mg, have been studied and reported. Research results indicate that alloying combined with appropriate plastic deformation treatments, such as hot extrusion and rolling, can refine the grain size of zinc alloys and fragment and disperse the secondary phase, significantly improving the strength and plasticity of Zn alloys. Some alloys have already met or exceeded the mechanical property requirements for biodegradable implants.

[0003] As research on zinc alloys deepens, two inherent deficiencies in the mechanical properties of zinc alloy materials have been exposed. Most current zinc alloys exhibit work-softening behavior or insufficient work-hardening capacity. There is also a self-aging phenomenon (i.e., the plasticity of the alloy decreases significantly with prolonged storage at room temperature). This has become the biggest challenge facing zinc alloys in clinical applications as vascular stents.

[0004] The insufficient work softening or work hardening capacity of zinc alloy is related to the low melting point of zinc. Pure zinc shows a high elongation at break, but the uniform plastic deformation stage is no more than 15%, and then it shows work softening. It is known that the mutual entanglement and pinning of high-density dislocations in the grain during deformation is an important source of the work hardening capacity of the metal after yielding. The low melting point of Zn allows dynamic recrystallization (DRX) to occur directly during cold deformation. On the one hand, DRX leads to grain refinement, thereby increasing the yield strength, but this makes the yield strength close to the tensile strength, thereby reducing the work hardening capacity. On the other hand, DRX leads to a decrease in the dislocation density within the grain, thereby causing the resistance to plastic deformation to continue to decrease, so that the zinc alloy can continue to deform, but it is difficult to harden and strengthen. The problem of work softening of zinc alloy may cause the stent to not be firmly fixed on the balloon during crimping, and the stent is easily displaced during implantation and delivery, so that the stent cannot be delivered to the correct lesion site where it is to be released. During stent expansion, the weak work hardening capacity may cause uneven deformation, and even cause the stent to break at a local position.

[0005] One of the solutions to the problem of work softening is to introduce a bimodal microstructure material with fine and coarse grains into the zinc alloy through microstructure control. The fine grains provide strength through back stress strengthening mechanism, and the coarse grains provide necessary work hardening rate and uniform elongation. However, these works are still in the initial stage, and there are few successful cases reported.

[0006] Accumulative roll bonding (ARB) is a unique process that can realize large deformation of metal materials. It combines the characteristics of interfacial bonding, continuous solid-phase diffusion, and continuous strain generation and accumulation. During the ARB process, the mechanical alloying effect gradually appears as the cumulative strain increases, which not only significantly enhances the bonding strength between the heterogeneous interfaces, but also effectively refines the grain structure of the component metal layers. Thus, the strength and plasticity of the alloy can be significantly improved. Compared with other severe plastic deformation (SPD) processes, ARB has relatively low cost, simple process flow, and can prepare large-size materials, and is easy to realize industrial production.

[0007] As summarized above, although there are reports on the use of ARB to prepare layered composites to improve the strength of zinc alloy or other metals, there is no report on the use of ARB to prepare zinc-based layered composites with a bimodal layered structure, especially the use of the deformation characteristics of layered composites with a bimodal structure to improve the work hardening capacity of zinc alloy. SUMMARY

[0008] In view of the deficiencies of the prior art, a first object of the present application is to provide a preparation method of a bimodal ZnCu / ZnMg layered composite material with high strength, good plasticity and significant work hardening capacity, wherein the ZnCu / ZnMg layered composite material is obtained by only using the method of accumulative roll bonding, and the prepared composite material has the characteristic of high strength.

[0009] A second object of the present application is to provide a bimodal ZnCu / ZnMg layered composite material with high strength, good plasticity and significant work hardening capacity prepared by the above preparation method.

[0010] A third object of the present application is to provide the application of a bimodal ZnCu / ZnMg layered composite material with high strength, good plasticity and significant work hardening capacity prepared by the above preparation method.

[0011] In order to achieve the above objects, the present application adopts the following technical solutions:

[0012] The preparation method of the bimodal ZnCu / ZnMg layered composite material comprises the following steps: placing a ZnMg alloy plate between two ZnCu alloy plates to obtain a composite plate; cold rolling the composite plate in a single pass to obtain a cold-rolled plate; cutting the cold-rolled plate from the middle into two pieces, stacking them, and then cold rolling them in a single pass; repeating the cutting-stacking-single pass cold rolling; and finally performing annealing treatment to obtain the ZnCu / ZnMg layered composite material.

[0013] The inventor found that the strength of Zn-Cu alloy decreases with the increase of the number of accumulative roll bonding, but the plasticity increases; while the Zn-Mg alloy shows the opposite result, in addition, the grain size of Zn-Cu alloy remains about 1 μm after annealing; while the grain size of Zn-Mg alloy grows significantly after annealing. Therefore, the ZnMg alloy plate is combined with the Zn-Mg alloy after accumulative roll bonding, and the difference in the change of grain size of Zn-Cu and Zn-Mg alloys during annealing can be used to construct a bimodal layered heterostructure material, in addition, a large number of soft and hard interfaces are generated in the ZnCu / ZnMg layered composite material after annealing, and HDI (Hetero-deformation induced) stress is formed at the soft and hard interfaces during tensile deformation, so that the obtained composite material exhibits excellent work hardening capacity, and the strength and plasticity of zinc alloy are complementary.

[0014] The preparation method of the application realizes alloying by laminating and cold rolling of ZnCu / ZnMg alloy plates, and then annealing to obtain Zn-based composite materials with high strength, good plasticity and significant work hardening capacity. The above method mainly improves the mechanical properties of the composite materials through mixed strengthening and heterogeneous deformation induced (HDI) strengthening, and the HDI strengthening can accumulate a large number of geometrically necessary dislocations (GNDs) at the interface, which is beneficial to improve the work hardening rate of the material. In addition, the addition of Cu can also make the composite material have excellent antibacterial performance.

[0015] However, the inventors found that the mechanical properties are better when a ZnMg alloy plate is placed between two ZnCu alloy plates. If a ZnCu alloy plate is placed between two ZnMg alloy plates, the improvement in mechanical properties is limited.

[0016] In a preferred embodiment, the ZnCu alloy plates are obtained by conventional smelting and rolling of metal raw materials. The purity of Zn, Cu and Mg required for smelting is ≥ 99.99%.

[0017] In a preferred embodiment, the mass fraction of Mg in the ZnMg alloy plate is 0.4-0.6%.

[0018] In a preferred embodiment, the mass fraction of Cu in the ZnCu alloy plate is 3-5%.

[0019] The inventors found that to obtain ZnCu / ZnMg layered composite materials with bimodal distribution and excellent mechanical properties, it is crucial to control the mass fraction of Mg in the ZnMg alloy plate and the mass fraction of Cu in the ZnCu alloy plate within the range of the application. On the one hand, some combinations cannot obtain bimodal ZnCu / ZnMg layered composite materials, and on the other hand, some combinations can obtain bimodal distribution but the mechanical properties are not as good as the application.

[0020] In a preferred embodiment, the thickness of the ZnCu alloy plate and the ZnMg alloy plate is 1-1.1 mm. The inventors found that by controlling the thickness of the alloy plate within the above range, the performance of the finally obtained ZnCu / ZnMg layered composite material is optimal.

[0021] In actual operation, the ZnCu and ZnMg alloy plates are cleaned in alcohol for 10 minutes using ultrasonic waves to remove surface grease. After air drying, the four corners of the alloy plate are drilled to facilitate fixing the composite plate using copper wire before rolling. Then, a circular stainless steel brush is used to polish the adjacent contact surface of the alloy plate in the direction parallel to the rolling direction to remove surface oxides and impurities. After polishing, the alloy plate is cleaned in acetone using ultrasonic waves to remove residual powder and other impurities.

[0022] Preferably, the composite sheet is single-pass cold-rolled, and the deformation amount is controlled to be 65-70%.

[0023] The inventors have found that, when the composite sheet is single-pass cold-rolled, and the deformation amount is controlled to be within the above range, the ZnCu and ZnMg alloy sheets can be combined metallurgically, while avoiding cracking, which would occur if the deformation amount were too low.

[0024] Preferably, the cold-rolled sheet is cut into two pieces in the middle, stacked, and then single-pass cold-rolled, and the cutting-stacking-single-pass cold-rolling process is repeated, with the deformation amount of any single-pass cold-rolling process being controlled to be 50-60%. The inventors have found that, when the composite sheet is single-pass cold-rolled, and the deformation amount is controlled to be within the above range, the alloy sheets can be combined tightly, while avoiding cracking, and the final bimodal ZnCu / ZnMg layered composite material has optimal performance.

[0025] Preferably, the cutting-stacking-single-pass cold-rolling process is repeated 1-8 times, preferably 4-8 times. The inventors have found that, when the cutting-stacking-single-pass cold-rolling process is repeated 4-8 times, the final composite material has optimal performance.

[0026] Preferably, the annealing temperature is 100-200℃, and the annealing time is 10-30 min.

[0027] The inventors have found that, when the annealing temperature and time are controlled to be within the above range, a bimodal ZnCu / ZnMg layered composite material can be obtained, and if the annealing temperature is too low, the Zn-Mg alloy grains grow only a limited amount, and if the annealing temperature is too high, the Zn-Mg alloy grains grow too much, and in both cases, an ideal bimodal structure cannot be obtained, so that the final composite material has reduced plasticity at too high an annealing temperature, and reduced work hardening capacity at too low an annealing temperature.

[0028] The application also provides a ZnCu / ZnMg layered composite material prepared by the above preparation method.

[0029] The application also provides a use of the ZnCu / ZnMg layered composite material prepared by the above preparation method, and the ZnCu / ZnMg layered composite material is used as a biodegradable implant material. The application also provides a new approach to preparing a degradable Zn-based alloy having work hardening capacity.

[0030] Advantages

[0031] The preparation method of the present invention comprises compounding a ZnMg alloy plate with a Zn-Mg alloy and then performing roll-bonding, and utilizing the difference in grain size change between the Zn-Cu and Zn-Mg alloys during annealing to construct a layered heterogeneous structure material with a bimodal structure. In addition, after annealing of the layered structure, a large number of soft-hard interfaces are generated in the ZnCu / ZnMg layered composite material. During tensile deformation, heterogeneous deformation induced (HDI) stress is formed at the soft-hard interfaces. The strength of the composite material is improved through hybrid strengthening and HDI strengthening, especially HDI strengthening, thereby obtaining a Zn-based composite material with high strength, good plasticity and significant work hardening ability.

[0032] The invention only realizes alloying by laminating ZnCu / ZnMg alloy plates and then cold rolling, and then combines annealing treatment to obtain the ZnCu / ZnMg layered composite material. The preparation process is simple and controllable, and is easy to industrialize.

[0033] The ZnCu / ZnMg layered composite material prepared by the present invention has a performance improvement of 115%-260% in strength compared to the pure Zn plate after rolling. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, other drawings obtained based on these drawings still fall within the scope of the present invention.

[0035] Figure 1 This is a SEM backscattered electron image of the ZnCu / ZnMg layered composite material obtained in the example after annealing after 8 passes of rolling.

[0036] Figure 2 This is the XRD pattern of the ZnCu / ZnMg layered composite material obtained in the example after 8 annealing passes.

[0037] Figure 3 These are the tensile deformation curves of pure Zn plates after being directly rolled 4, 6, and 8 times in the manner of the embodiment. The blue curve is the tensile deformation curve of pure Zn after 4 passes, the green curve is the tensile deformation curve of pure Zn after 6 passes, and the red curve is the tensile deformation curve of pure Zn after 8 passes.

[0038] Figure 4Graph showing the tensile deformation curves after rolling in the embodiment, wherein the purple curve is the tensile deformation curve after annealing after 4 rolling passes, the blue curve is the tensile deformation curve after annealing after 6 rolling passes, and the red curve is the tensile deformation curve after annealing after 8 rolling passes. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0040] Example 1

[0041] The ZnCu and ZnMg alloy plates in this embodiment are Zn-4Cu and Zn-0.5Mg alloy plates, respectively.

[0042] 1mm thick ZnCu and ZnMg alloy sheets were cut into 55mm long and 30mm wide sheets using a wire cutting machine. The cut sheets were ultrasonically cleaned in alcohol for 10 minutes to remove surface grease. After air drying, the four corners of the alloy sheet were drilled to allow for fixation with copper wire. The contact surfaces of the ZnCu and ZnMg alloy sheets were then polished parallel to the rolling direction using a round stainless steel brush with a wire diameter of 0.3mm to remove surface oxides and impurities. The polished Zn sheet was ultrasonically cleaned in acetone for 5 minutes to remove residual powder and other impurities. After completion, the ZnMg alloy sheet was placed between two ZnCu alloy sheets and stacked to obtain a composite sheet. The composite sheet was then fixed with copper wire to prevent the metal sheets from sliding against each other. The sheet is then cold-rolled in a single pass using a two-roll mill, with the deformation of the first cold rolling pass controlled to 70%. The cold-rolled sheet is then cut into two pieces, stacked, and then cold-rolled in a single pass. This cutting-stacking-single-pass cold rolling cycle is repeated eight times, with the deformation of the single cold rolling pass being 55%. The sheet is then rolled into a composite sheet with a thickness of 1 mm. The composite sheet is then annealed at a controlled annealing temperature of 150° C. for 20 minutes. The present invention does not require any lubricant treatment and can be prepared by repeated cold rolling to form the final ZnCu / ZnMg layered composite material.

[0043] Specific data

[0044] 1. Figure 1 The SEM image of the ZnCu / ZnMg layered composite material obtained in the embodiment after annealing by 8 passes is shown in FIG. Figure 1 It can be seen that the ZnCu / ZnMg layered composite material after laminated rolling is mainly composed of gray striped ZnCu layer and white striped ZnMg layer. The regions of ZnCu layer and ZnMg layer can be clearly distinguished. The regions are continuous and uninterrupted, alternating and evenly distributed in a fibrous manner. It can be seen from the figure that the Zn-Cu alloy layer is fine-grained and the ZnMg layer is coarse-grained, thus forming a bimodal state.

[0045] 2. Figure 2 The XRD pattern of the embodiment after 8-pass annealing shows that Cu and Zn can be metallurgically bonded, and some CuZn5 second phase is generated to strengthen the matrix. Secondly, Zn and Mg also undergo metallurgical bonding to generate a very small amount of brittle Mg2Zn 11 The second phase has a strengthening effect on the matrix.

[0046] 3. Figure 3 The following table shows the true stress-strain curves and corresponding tensile property data for the pure Zn plate after 4, 6, and 8 rolling passes. After 8 passes of laminate rolling, the pure Zn plate exhibited work-softening characteristics with a tensile yield strength (YS), ultimate tensile strength (UTS), and elongation of 80 MPa, 115 MPa, and 68.5%, respectively.

[0047] 4. Figure 4 The true stress-strain curves and corresponding tensile property data for the ZnCu / ZnMg layered composite after 4, 6, and 8 annealing passes of laminated rolling are shown. Compared to the 8-pass laminated rolling of pure Zn plate, the mechanical properties are significantly improved, with the tensile yield strength (YS), ultimate tensile strength (UTS), and elongation reaching 343 MPa, 343 MPa, and 12.1%, respectively. The composite also exhibits work-hardening properties.

[0048] Comparative Example 1

[0049] Other conditions were the same as those in Example 1, except that a ZnCu alloy plate was placed between two ZnMg alloy plates for stacking. The obtained composite plate was rolled 8 times and then recrystallized annealed at the same temperature. Its tensile yield strength (YS) and tensile ultimate strength (UTS) were 268 MPa and 293 MPa, respectively.

[0050] Comparative Example 2

[0051] The other conditions were the same as those in Example 1, except that the mass fraction of Cu in the ZnCu alloy plate was 2%. Recrystallization annealing was performed after rolling, and the plasticity was reduced while the work hardening characteristics were not obvious.

[0052] Comparative Example 3

[0053] Other conditions were the same as in Example 1, except that the mass fraction of Mg in the ZnMg alloy plate was 1%. Recrystallization annealing was performed after rolling. Compared with the composite plate in Comparative Example 2, the plasticity was lower and brittle fracture occurred before reaching the yield point.

[0054] Comparative Example 4

[0055] Other conditions were the same as those in Example 1, except that the annealing temperature was 250° C. The tensile mechanical property curve showed work-softening characteristics and failed to achieve the expected work-hardening effect. At the same time, its strength was also lower than 343 MPa in the example.

Claims

1. A method for preparing a bimodal ZnCu / ZnMg layered composite material, characterized by: A ZnMg alloy plate is placed between two ZnCu alloy plates for lamination to obtain a composite plate, the composite plate is subjected to a single-pass cold rolling to obtain a cold-rolled plate, the cold-rolled plate is cut into two pieces from the middle, stacked, and then subjected to a single-pass cold rolling, the cutting-stacking-single-pass cold rolling cycle is repeated, and finally annealing is performed to obtain a ZnCu / ZnMg layered composite material.

2. The method for preparing a bimodal ZnCu / ZnMg layered composite material according to claim 1, characterized in that: The ZnCu alloy plate and the ZnCu alloy plate are both obtained by smelting and then rolling metal raw materials.

3. The method for preparing a bimodal ZnCu / ZnMg layered composite material according to claim 1, characterized in that: In the ZnMg alloy plate, the mass fraction of Mg is 0.4-0.6%; in the ZnCu alloy plate, the mass fraction of Cu is 3-5%.

4. The method for preparing a bimodal ZnCu / ZnMg layered composite material according to claim 1, characterized in that: The thickness of the ZnCu alloy plate and the ZnMg alloy plate are both 1-1.1 mm.

5. The method for preparing a bimodal ZnCu / ZnMg layered composite material according to claim 1, characterized in that: When the composite plate is subjected to single-pass cold rolling, the deformation is controlled to be 65-70%.

6. The method for preparing a bimodal ZnCu / ZnMg layered composite material according to claim 1, characterized in that: The cold-rolled plate is cut into two pieces from the middle, stacked, and then subjected to single-pass cold rolling. The cutting-stacking-single-pass cold rolling process is repeated, and the deformation of any single-pass cold rolling is controlled to be 50%-60% during the repeated process.

7. The method for preparing a bimodal ZnCu / ZnMg layered composite material according to claim 1, characterized in that: The number of repeated cutting-lamination-single-pass cold rolling is 1-8 times.

8. The method for preparing a bimodal ZnCu / ZnMg layered composite material according to claim 7, characterized in that: The annealing temperature is 100° C.-200° C., and the annealing time is 10-30 minutes.

9. The ZnCu / ZnMg layered composite material prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the ZnCu / ZnMg layered composite material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The ZnCu / ZnMg layered composite material is used for biodegradable implant materials.

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