Layered isomeric Mg-Al-Ca-Zn magnesium alloy and preparation method thereof

Abstract

The invention relates to a layered isomeric Mg-Al-Ca-Zn magnesium alloy and a preparation method thereof, the alloy comprises the following components in percentage by mass: 0-0.6% of Zn, 1.0-1.4% of Al, 0.4-0.8% of Ca, and the balance of Mg and inevitable impurities, and has a layered isomeric structure in which coarse deformed grains and dynamic recrystallized grains are alternately distributed. The preparation method comprises the steps of burdening, crucible pretreatment, smelting, casting, homogenizing annealing and hot extrusion, and is simple in process and low in cost. According to the alloy, dynamic recrystallization is regulated and controlled through Zn grain boundary segregation, strong plasticity synergy is achieved, and the comprehensive mechanical property is excellent. Conventional equipment is adopted, and the method is environmentally friendly, easy to industrialize and suitable for the fields of aerospace, automobile lightweight and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials, and particularly relates to a layered heterogeneous Mg-Al-Ca-Zn magnesium alloy and a preparation method thereof. Background Art

[0002] With the increasingly severe energy and environmental problems and the continuous improvement of the performance requirements of lightweight materials in industrial applications, magnesium alloys have attracted much attention due to their low density, high specific strength, and good processing performance. The demand for magnesium alloys is growing rapidly at an unprecedented rate, and it has broad application prospects especially in the fields of aerospace, automotive lightweighting, new energy battery trays, etc.

[0003] Low-alloyed magnesium alloys have the advantages of high mechanical properties, low production cost, and excellent hot working performance, but their absolute strength is relatively low. Although traditional strengthening methods (such as solid solution strengthening and precipitation strengthening) can improve the strength to a certain extent, they often sacrifice plasticity and show an obvious strength-plasticity inversion relationship. In recent years, the proposal of heterogeneous deformation-induced (HDI) strengthening provides a new idea for solving the problem of the simultaneous improvement of strength and plasticity of magnesium alloys, and realizes the simultaneous improvement of strength and plasticity by constructing heterogeneous structures.

[0004] At present, the main technical solutions for preparing heterogeneous magnesium alloy structures include:

[0005] 1. Accumulative roll bonding and annealing treatment: The grain refinement is regulated to the sub-micron level through multi-pass rolling and heat treatment to form a layered composite structure, thereby improving strength and plasticity. However, this method requires multi-pass deformation and precise heat treatment control, with complex processes, high energy consumption, and high requirements for equipment, making it difficult to achieve large-scale industrial production.

[0006] 2. Ultrasonic treatment: An ultrasonic field is applied during the solidification process to regulate the grain structure through cavitation effects and acoustic streaming effects, improving the mechanical properties. However, the cost of ultrasonic equipment is high, the process parameters are difficult to precisely control, and its applicability to the preparation of large-sized components is limited, restricting its industrial application.

[0007] 3. Friction stir processing: Grain refinement and the formation of multi-scale structures are achieved through severe solid-state deformation, which is suitable for local modification of aerospace lightweight components, etc. However, this method has complex processes, low processing efficiency, it is difficult to achieve uniform tissue regulation of the overall component, and the equipment maintenance cost is relatively high.

[0008] Although the above methods can prepare heterogeneous magnesium alloy structures and improve mechanical properties to a certain extent, they all have significant limitations: First, the process is complex and difficult to operate, relying on special equipment or multi-pass processing, resulting in high production costs; Second, the synergistic effect of strength and plasticity is limited, making it difficult to simultaneously meet the industrial requirements of high strength and high plasticity; Third, industrial production is restricted, and it is difficult to achieve low-cost and large-scale production. These problems limit the wide application of heterogeneous magnesium alloys in high-end manufacturing fields. Therefore, there is an urgent need to develop a magnesium alloy preparation method with simple process, low cost, excellent synergistic effect of strength and plasticity, and easy industrialization to meet the needs of high-performance lightweight materials in fields such as aerospace and automotive lightweighting. Summary of the Invention

[0009] To solve the above problems, the purpose of the present invention is to provide a layered heterogeneous Mg-Al-Ca-Zn magnesium alloy and its preparation method. By regulating the dynamic recrystallization behavior through the grain boundary segregation of Zn element, a layered heterogeneous grain structure is constructed to achieve the simultaneous improvement of the strength and plasticity of the magnesium alloy, and it also has the advantages of simple process, low cost, easy industrialization, and environmental protection.

[0010] To achieve the above purpose, the present invention provides the following technical solutions:

[0011] A layered heterogeneous Mg-Al-Ca-Zn magnesium alloy, the content of each component of the material is calculated by mass percentage as follows: Zn: 0 - 0.6%; Al: 1.0 - 1.4%; Ca: 0.4 - 0.8%, and the rest is magnesium and inevitable impurities; the magnesium alloy has a layered heterogeneous grain structure, and the layered heterogeneous grain structure includes a structure in which coarse deformed grains and dynamically recrystallized grains are alternately distributed.

[0012] Preferably, the mass percentage of Zn is 0.4 - 0.6%.

[0013] A preparation method of the layered heterogeneous Mg-Al-Ca-Zn magnesium alloy as described above, characterized by including the following steps:

[0014] (1) Batching: Weigh industrial pure magnesium ingots, pure zinc grains, pure aluminum ingots, and Mg-25%Ca master alloy according to the designed alloy composition, consider the alloy burning loss rate for batching, and remove the oil stains and oxide skins on the surface of the raw materials.

[0015] (2) Crucible pretreatment: Coat the inner surface of the iron crucible with a mold release coating, which is prepared from water, boron nitride powder, and alcohol. After coating, dry and preheat the crucible to 250 ± 5 °C.

[0016] (3) Melting: Under a protective atmosphere of CO2 and SF6, place pure magnesium ingots, pure aluminum ingots, and Mg-25%Ca master alloy in a preheated iron crucible, heat to 750 ± 5 °C, hold until completely melted, stir for 5 - 10 minutes and then skim the slag; cool down to 720 ± 5 °C, add pure zinc granules, and stir for 5 - 10 minutes; continue to hold the temperature and stir once every 5 minutes, with each stirring lasting 3 minutes, for a total of 4 times, and skim the slag after each stirring; hold at 720 °C for 10 - 20 minutes, then stir and skim the slag again;

[0017] (4) Casting: Under a protective atmosphere, quickly pour the melt into an iron mold coated with a release coating to obtain an alloy ingot;

[0018] (5) Homogenization annealing: Wrap the alloy ingot with aluminum foil and bury it in graphite powder, perform homogenization annealing at 400 °C for 12 hours, and then water-cool;

[0019] (6) Hot extrusion: After holding the annealed alloy at 400 °C for 2 hours, perform forward extrusion. The extrusion temperature is 400 °C, the extrusion speed is 1.5 - 2 m·min-1, and the extrusion ratio is 25:1 to obtain a magnesium alloy with a layered heterogeneous grain structure.

[0020] Furthermore, in step (3), the protective atmosphere of CO2 and SF6 is a mixed gas of 99% CO2 and 1% SF6.

[0021] Furthermore, in step (1), the burning loss rate of the pure zinc granules is 10%.

[0022] Furthermore, in step (3), the stirring is carried out using an iron stirring rod with a release coating on its surface.

[0023] Furthermore, in step (4), the inner surface of the iron mold is coated with a release coating prepared from water, boron nitride powder, and alcohol.

[0024] Furthermore, in step (5), the homogenization annealing is carried out in a stainless-steel crucible.

[0025] Furthermore, before heat treatment of the alloy ingot obtained by casting, use sandpaper to polish off the oxide scale, remove the oil stain with NaOH solution, and then wash and dry with alcohol.

[0026] The beneficial effects of the present invention are as follows:

[0027] The present invention provides a layered heterogeneous Mg-Al-Ca-Zn magnesium alloy and its preparation method, which has significant technical advantages and application values. Its beneficial effects are as follows:

[0028] First, the present invention adds 0 to 0.6% Zn (preferably 0.4 to 0.6%) to the Mg-Al-Ca-based alloy, and utilizes the grain boundary segregation of Zn to regulate dynamic recrystallization, forming a lamellar heterogeneous structure with alternating distribution of coarse deformed grains and dynamically recrystallized grains. This structure significantly improves the strength and plasticity of the alloy through heterogeneous deformation-induced strengthening, overcomes the limitation of the strength-plasticity inversion of traditional magnesium alloys, and is particularly suitable for the requirements of high-performance materials in fields such as aerospace and automotive lightweighting.

[0029] Secondly, the preparation method adopts conventional melting and casting, homogenization annealing, and hot extrusion processes, which are simple to operate and low in cost. Using common raw materials such as industrial pure magnesium ingots and pure zinc grains, combined with a CO2+SF6 protective atmosphere and boron nitride release agent coating, the process is compatible with existing production lines and is easy to promote industrially. Compared with complex processes such as accumulative roll bonding and ultrasonic treatment, the present invention does not require special equipment, has low energy consumption, and high production efficiency.

[0030] In addition, the process of the present invention is green and environmentally friendly. The low Zn content reduces resource waste, and the protective atmosphere and water-cooled annealing reduce harmful emissions, meeting the requirements of green manufacturing. Stable process parameters ensure product quality consistency and are suitable for mass production.

[0031] In summary, the present invention has outstanding advantages in terms of strength-plasticity synergy, cost control, industrialization potential, and environmental protection, provides an innovative solution for the development of high-performance magnesium alloys, and has broad market prospects and academic value.

[0032] Other advantages, objectives, and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0034] Figure 1 is a scanning electron microscope (SEM) micrograph of the alloy material of the present invention.

[0035] Figure 2 is an electron backscatter diffraction (EBSD) photograph of the alloy material of the present invention.

[0036] Figure 3 is a transmission electron microscope (TEM) photograph of the alloy material of the present invention.

[0037] Figure 4 is the engineering stress-strain curve of the alloy material of the present invention. Specific Embodiments

[0038] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0039] Among them, the drawings are only for illustrative purposes, showing only schematic diagrams, not physical diagrams, and should not be construed as a limitation on the present invention; in order to better illustrate the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0040] In the drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and should not be construed as a limitation on the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0041] Embodiment 1

[0042] (1) Ingredients preparation: Prepare the required raw materials by mass percentage: 99% pure magnesium, 99% pure zinc, 99% pure aluminum, Mg-25% Ca master alloy. The burning loss rate of pure zinc is 10%.

[0043] (2) Melting: Place the iron mold filled with raw materials in a pit-type resistance furnace. Heat the resistance furnace to 750 ± 5 °C and hold for insulation until all the above raw materials are melted. Use an iron stirring rod with its surface coated with paint to stir evenly for 5 - 10 minutes and then skim the slag; when the temperature is reduced to 720 ± 5 °C, add pure zinc granules to the molten metal liquid in sequence; use the iron stirring rod coated with paint to stir evenly for 5 - 10 minutes; after all the raw materials are melted, stir once every 5 minutes for 3 minutes each time, stir a total of 4 times, and skim the slag after each stirring; hold for 10 - 20 minutes at 720 °C, stir the melt again and skim the slag; turn off the power supply, and quickly pour the melt into an iron mold with its inner surface coated with paint under the protection of a protective gas.

[0044] (3) Machining: Use sandpaper to grind off the oxide scale on the sample taken in step 2, remove the oil stain with NaOH solution, and then wash and dry it with alcohol.

[0045] (4) Wrap the alloy ingot obtained by melting with aluminum foil and then bury it completely with graphite powder in a stainless steel crucible. Place the crucible in a heat treatment furnace. The homogenization annealing process is: 400 °C × 12 h, cooling method: water cooling; then hold the alloy and the mold that have completed homogenization annealing at 400 °C for 2 h, and then put them into an extrusion cylinder for forward extrusion. The extrusion temperature is 400 °C, the extrusion speed is 1.5 - 2 m·min -1 , and the extrusion ratio is 25:1.

[0046] Example 2

[0047] (1) Batching: Prepare the required raw materials according to the mass percentage: 99% pure magnesium, 99% pure zinc, 99% pure aluminum, Mg - 25% Ca master alloy. The burn-off rate of pure zinc is 10%.

[0048] (2) Melting: Place the iron mold filled with raw materials in a pit-type resistance furnace. Heat the resistance furnace to 750 ± 5 °C and hold for insulation until all the above raw materials are melted. Use an iron stirring rod with its surface coated with paint to stir evenly for 5 - 10 minutes and then skim the slag; when the temperature is reduced to 720 ± 5 °C, add pure zinc granules to the molten metal liquid in sequence; use the iron stirring rod coated with paint to stir evenly for 5 - 10 minutes; after all the raw materials are melted, stir once every 5 minutes for 3 minutes each time, stir a total of 4 times, and skim the slag after each stirring; hold for 10 - 20 minutes at 720 °C, stir the melt again and skim the slag; turn off the power supply, and quickly pour the melt into an iron mold with its inner surface coated with paint under the protection of a protective gas.

[0049] (3) Machining: Use sandpaper to grind off the oxide scale on the sample taken in step 2, remove the oil stain with NaOH solution, and then wash and dry it with alcohol.

[0050] (4) Wrap the smelted alloy ingot with aluminum foil and then bury it in a stainless steel crucible with graphite powder. Place the crucible in a heat treatment furnace. The homogenization annealing process is: 400℃×12h, cooling method: water cooling; then, the alloy and mold that have completed homogenization annealing are kept at 400℃ for 2h, and then placed in the extrusion barrel for positive extrusion. The extrusion temperature is 400℃, and the extrusion speed is 1.5-2m·min -1 , the extrusion ratio is 25:1.

[0051] Example 3

[0052] (1) Ingredients: Prepare the required raw materials according to mass percentage: 99% pure magnesium, 99% pure zinc, 99% pure aluminum, and Mg-25% Ca master alloy. The burnout rate of pure zinc is 10%.

[0053] (2) Melting: Place the iron mold filled with raw materials in a pit-type resistance furnace, heat the resistance furnace to 750±5℃ and keep it warm until all the raw materials are melted, stir evenly with an iron stirring rod with a coating on the surface for 5 to 10 minutes and then remove the slag; when the temperature is lowered to 720±5℃, add pure zinc particles to the molten metal liquid in sequence; stir evenly with an iron stirring rod with a coating on the surface for 5 to 10 minutes; after all the raw materials are melted, stir once every 5 minutes, 3 minutes each time, for a total of 4 times, and remove the slag after each stirring; keep it warm at 720℃ for 10 to 20 minutes, stir the melt again and remove the slag; turn off the power, and under the protection of protective gas, quickly pour the melt into the iron mold with the inner surface coated with paint.

[0054] (3) Machining: Use sandpaper to remove the oxide scale from the sample taken in step 2, remove the oil stain with NaOH solution, and then wash and dry with alcohol.

[0055] (4) Wrap the smelted alloy ingot with aluminum foil and then bury it in a stainless steel crucible with graphite powder. Place the crucible in a heat treatment furnace. The homogenization annealing process is: 400℃×12h, cooling method: water cooling; then, the alloy and mold that have completed homogenization annealing are kept at 400℃ for 2h, and then placed in the extrusion barrel for positive extrusion. The extrusion temperature is 400℃, and the extrusion speed is 1.5-2m·min -1 , the extrusion ratio is 25:1.

[0056] Example 4

[0057] (1) Ingredients: Prepare the required raw materials according to mass percentage: 99% pure magnesium, 99% pure zinc, 99% pure aluminum, and Mg-25% Ca master alloy. The burnout rate of pure zinc is 10%.

[0058] (2) Melting: Place the iron mold filled with raw materials in a pit-type resistance furnace. Heat the resistance furnace to 750 ± 5 °C and hold for insulation until all the above raw materials are melted. Use an iron stirring rod with a coated surface to stir evenly for 5 - 10 minutes and then skim the slag; when the temperature is reduced to 720 ± 5 °C, add pure zinc granules to the molten metal liquid in sequence; use an iron stirring rod with a coated surface to stir evenly for 5 - 10 minutes; after all the raw materials are melted, stir once every 5 minutes for 3 minutes each time, stir a total of 4 times, and skim the slag after each stirring; hold for 10 - 20 minutes at 720 °C, stir the melt again and skim the slag; turn off the power supply, and quickly pour the melt into an iron mold with a coated inner surface under the protection of a protective gas.

[0059] (3) Machining: Use sandpaper to grind off the oxide scale of the sample taken in step 2, remove the oil stain with NaOH solution, and then wash and dry it with alcohol.

[0060] (4) Wrap the alloy ingot obtained by melting with aluminum foil and then bury it completely with graphite powder in a stainless steel crucible. Place the crucible in a heat treatment furnace. The homogenization annealing process is: 400 °C × 12 h, cooling method: water cooling; then keep the alloy and the mold after homogenization annealing at 400 °C for 2 h, and put them into an extrusion cylinder for forward extrusion. The extrusion temperature is 400 °C, the extrusion speed is 1.5 - 2 m·min -1 , and the extrusion ratio is 25:1.

[0061] Among them, the specific components and characteristics of the alloy after adding Zn element to Mg-1.2Al-0.6Ca in Examples 1 - 4:

[0062]

[0063] As Figures 1 to 4 shown, it can be seen from Example 1 that after the alloy does not add Zn element, the extruded Mg-Al-Ca presents a completely dynamically recrystallized structure. It can be seen from Example 2 that the grain size of the extruded alloy decreases significantly with the addition of Zn. When the Zn addition amount is 0.2 wt.%, some elongated deformed grains appear in the alloy; it can be seen from Example 3 that the alloy shows long strip-shaped elongated deformed grains, presenting a layered heterogeneous structure, including coarse deformed grains and sub-micron dynamically recrystallized grains. It can be seen from Example 4 that with the further addition of Zn element, the alloy still presents a layered heterogeneous structure, and its dynamically recrystallized grains are further refined.

[0064] The results of the examples show that the Mg-1.2Al-0.6Ca-0.4Zn magnesium alloy prepared by the present invention presents an obvious layered heterogeneous structure and has the best comprehensive mechanical properties.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A layered heterogeneous Mg-Al-Ca-Zn magnesium alloy, characterized in that: The content of each component of the material is by mass percentage: Zn: 0 - 0.6%; Al：1.0～1.4％； Ca: 0.4 - 0.8%, and the rest is magnesium and inevitable impurities; The magnesium alloy has a lamellar heterogeneous grain structure, and the lamellar heterogeneous grain structure includes a structure in which coarse deformed grains and dynamically recrystallized grains are alternately distributed.

2. The layered heterogeneous Mg-Al-Ca-Zn magnesium alloy according to claim 1, characterized in that, The mass percentage of the Zn is 0.4 - 0.6%.

3. A method for preparing a layered heterogeneous Mg-Al-Ca-Zn magnesium alloy as described in claim 1 or 2, characterized in that, It includes the following steps: (1) Batching: Weigh industrial pure magnesium ingots, pure zinc grains, pure aluminum ingots and Mg-25%Ca master alloy according to the designed alloy composition, batch after considering the alloy burning loss rate, and remove the oil stain and oxide skin on the surface of the raw materials; (2) Crucible pretreatment: Coat the inner surface of the iron crucible with a mold release coating, which is prepared from water, boron nitride powder and alcohol. After coating, dry and preheat the crucible to 250 ± 5 °C; (3) Melting: Under the protection atmosphere of CO2 and SF6, place the pure magnesium ingots, pure aluminum ingots and Mg-25%Ca master alloy in the preheated iron crucible, heat to 750 ± 5 °C and keep warm until completely melted, stir for 5 - 10 minutes and then skim the slag; cool down to 720 ± 5 °C, add pure zinc grains and stir for 5 - 10 minutes; continue to keep warm and stir once every 5 minutes, stir for 3 minutes each time, stir 4 times in total, and skim the slag after each stirring; keep warm at 720 °C for 10 - 20 minutes and then stir and skim the slag again; (4) Casting: Under the protection atmosphere, quickly pour the melt into an iron mold coated with a mold release coating to obtain an alloy ingot; (5) Homogenization annealing: Wrap the alloy ingot with aluminum foil and bury it in graphite powder, carry out homogenization annealing at 400 °C for 12 hours and then water-cool; (6) Hot extrusion: After keeping the annealed alloy at 400 °C for 2 hours, carry out forward extrusion, the extrusion temperature is 400 °C, the extrusion speed is 1.5 - 2 m·min-1, and the extrusion ratio is 25:1 to obtain a magnesium alloy with a lamellar heterogeneous grain structure.

4. The preparation method according to claim 3, characterized in that: In step (3), the protection atmosphere of CO2 and SF6 is a mixed gas of 99% CO2 and 1% SF6.

5. The preparation method according to claim 3, wherein: In step (1), the burning loss rate of the pure zinc grains is 10%.

6. The preparation method according to claim 3, characterized in that: In step (3), the stirring is carried out using an iron stirring rod with a mold release coating on the surface.

7. The preparation method according to claim 3, characterized in that: In step (4), the inner surface of the iron mold is coated with a mold release coating prepared from water, boron nitride powder and alcohol.

8. The preparation method according to claim 3, characterized in that: In step (5), the homogenization annealing is carried out in a stainless steel crucible.

9. The preparation method according to claim 3, wherein: Before heat treatment, the alloy ingot obtained by casting is polished with sandpaper to remove the oxide skin, the oil stain is removed with NaOH solution, and then washed and dried with alcohol.

Images