A high-strength and ductile magnesium alloy material with discontinuous yielding behavior and its preparation method

Abstract

This invention relates to a high-strength, high-ductility magnesium alloy material with discontinuous yielding behavior and its preparation method, belonging to the field of magnesium alloy preparation technology. First, based on an AZ-based magnesium alloy, two types of refining elements (RE elements) are added via a Mg-RE master alloying process. Al ingots, Zn ingots, and the Mg-RE master alloy are added to the molten magnesium. After complete melting, the mixture is stirred, refined, and slag removed before casting to obtain a magnesium alloy ingot. Second, the magnesium alloy ingot is extruded into a magnesium alloy sheet. Third, the extruded sheet undergoes homogenization treatment. Finally, the homogenized sheet is rolled to obtain a high-strength, high-ductility magnesium alloy sheet with a thickness of less than 3 mm and discontinuous yielding behavior. This invention achieves matrix grain refinement through particle-induced recrystallization, while simultaneously promoting nano-Mg... 17 Al 12 The dispersed precipitation of the phase not only improves the mechanical properties of the material, but also enables the material to exhibit a clear yield plateau during the elastoplastic transition stage; it can meet the stringent requirements of high-end equipment fields for clear monitoring of material deformation behavior.

Description

Technical Field

[0001] This invention relates to a high-strength and ductile magnesium alloy material with discontinuous yielding behavior and its preparation method, belonging to the field of magnesium alloy preparation technology. Background Technology

[0002] Magnesium and magnesium alloys, with their outstanding advantages such as low density, high specific strength, high specific stiffness, and excellent vibration damping properties, have shown broad application prospects in high-end manufacturing fields such as aerospace, high-speed rail transportation, and electronic information, and have become one of the key materials driving the lightweight development of equipment. For metallic structural materials, in addition to core mechanical indicators such as strength and plasticity, yield behavior is a key performance characteristic that determines their engineering applicability. Once a material yields, its load-bearing capacity and deformation stability will change fundamentally. Therefore, yield strength is usually used as a design reference for allowable stress in engineering. However, unlike the discontinuous yielding behavior that traditional steel usually exhibits under tension, magnesium alloys, due to the limited number of operable slip systems, mostly exhibit continuous yielding characteristics. This continuous yielding behavior results in a lack of obvious signs when the material enters plastic deformation, making it difficult to provide effective warnings for overload, thereby increasing the risk of sudden fracture of components during service and limiting the large-scale application of magnesium alloys in critical components with high safety and reliability requirements.

[0003] With the deepening of magnesium alloy research, discontinuous yielding phenomena have been observed in magnesium alloys with certain microstructures. For example, by controlling the subsequent heat treatment process of rolled Mg-1.96Zn-0.62Mn-0.48Y-0.35Ca alloy, a microstructure with precipitate-free zones (PFZ) at grain boundaries was obtained. This type of material exhibits discontinuous yielding behavior during tensile testing (Xuet al., Impact of aging-induced precipitate-free zones on yielding mechanisms in a low-alloyed Mg-Zn-Ca-Mn-Y alloy, Scripta Materialia, 272 (2026) 117067). However, PFZ easily induces ductile instability, which is generally detrimental to the synergistic improvement of alloy strength and plasticity. Another study (Li et al., Discontinuous yielding phenomena triggered by Zn addition in low-alloyed Mg-Al-Ca-Mn alloys, Scripta Materialia, 221 (2022) 114967) induced discontinuous yielding by adding Zn to the Mg-Al-Ca-Mn system to form high-volume-fraction solute clusters, which then induced discontinuous yielding through the weak pinning effect of the clusters on dislocations. However, this method has limitations on the types of alloying elements and a narrow heat treatment process window, resulting in significant limitations in engineering applications. Previously, we introduced uniformly distributed Al2RE phase and Al... 11 Although the RE3 phase significantly promotes recrystallization during hot extrusion, the sample did not exhibit discontinuous yielding during tensile testing, possibly due to insufficient grain refinement and elemental distribution (Zhang et al., Bi-directional dynamic recrystallization behavior of AZ31 alloy by Al-RE precipitation control, International Journal of Plasticity, 187 (2025) 104289). Furthermore, extrusion-based sheets often exhibit significant differences in microstructure between the core and edges, and this method is difficult to apply to the production of thin-gauge sheets.

[0004] In conclusion, developing magnesium alloy sheets that combine discontinuous yielding characteristics with high strength and ductility, and their corresponding universally applicable preparation processes, remains a key technical problem that urgently needs to be solved in the field of magnesium alloys. Summary of the Invention

[0005] This invention addresses the problems of ambiguous yield points and insufficient mechanical properties in tensile tests of existing magnesium alloys by providing a high-strength, high-ductility magnesium alloy material with discontinuous yielding behavior and its preparation method. This method achieves matrix grain refinement through particle-induced recrystallization and simultaneously promotes the dispersed precipitation of nano-second phases. While significantly improving the material's mechanical properties, it also enables the material to exhibit a clear yield plateau during the elastoplastic transition stage. This effectively enhances the reliability of safety warnings during material service and meets the stringent requirements of high-end equipment for clear monitoring of material deformation behavior.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a high-strength, high-ductility magnesium alloy material with discontinuous yielding behavior, comprising stirring casting, hot extrusion blanking, homogenization treatment, and hot rolling forming. Specific steps are as follows: Step 1: First, determine the raw materials: Based on AZ-based magnesium alloys, add two types of RE elements, specifically through a Mg-RE master alloy. The AZ-based magnesium alloy uses commercially pure Mg, Al, and Zn ingots as raw materials. Second, melt the Mg ingots. Finally, add Al, Zn, and the Mg-RE master alloy to the molten Mg. After the raw materials are completely melted, stir, refine, and remove slag before casting to obtain a magnesium alloy ingot. In this step, Mg is formed... 17 Al 12 Phase, Al2RE phase and Al 11 RE3 phase.

[0007] Furthermore, the two types of RE elements include a first type of RE element and a second type of RE element. The first type of RE element is selected from Nd, La, or Ce (if Nd is selected, it is added as a Mg-Nd master alloy); the second type of RE element is selected from Y, Gd, or Sm (if Y is selected, it is added as a Mg-Y master alloy). Furthermore, based on 100% of the total mass of the magnesium alloy ingot, the Al content is 3.0~6.0 wt.%, the Zn content is controlled at 0.8~1.2 wt.%, the first type of RE element addition is 0.8~1.5 wt.%, and the second type of RE element addition is 0.2~0.5 wt.%. The unavoidable Fe, Cu, Ni, and Si impurities content is less than 0.05 wt.%, with the balance being Mg.

[0008] Furthermore, the Mg ingot is melted at a temperature of 700~720℃ for a time of 20~40 min; Furthermore, the remelting temperature is 730~750℃, and the time is 10~20min; Furthermore, the melt can be formed by ingot casting or continuous casting. When using continuous casting, the magnesium melt in the crystallizer needs to be protected with a mixture of CO2 and SF6 gas. Step 2: Place the magnesium alloy ingot in an extrusion press and extrude it into a magnesium alloy sheet at a temperature range of 250~350℃. In this step, Mg... 17 Al 12 Phase fragmentation helps to shorten the re-dissolution time during the subsequent homogenization process.

[0009] Furthermore, in the extrusion process, the extrusion ratio is selected according to the extrusion temperature range: when the extrusion temperature is not higher than 310℃, the extrusion ratio should not be greater than 10; when the extrusion temperature exceeds 310℃, an extrusion ratio greater than 10 is used for extrusion forming.

[0010] Step 3: The magnesium alloy plate obtained in Step 2 is subjected to homogenization treatment. The homogenization temperature is 350~400℃, and the holding time is 2~6 hours. In this step, Mg... 17 Al 12 The phase is dissolved in the magnesium matrix, increasing the Al content in the matrix, which facilitates subsequent nano-Mg... 17 Al 12 The dynamic precipitation of phase forms creates the conditions for this process.

[0011] Step 4: The homogenized sheet is rolled at 275~325℃ to obtain a high-strength, high-ductility magnesium alloy sheet with a thickness of less than 3mm and discontinuous yielding behavior. In this step, Al2RE phase and Al... 11 The RE3 phase significantly accelerated the recrystallization process, refined the matrix grain size, and promoted the formation of nano-Mg. 17 Al 12 Dynamic precipitation of phases.

[0012] Furthermore, the deformation amount of each rolling pass is 10-30%, the holding time between passes is controlled between 5-15 minutes, and the cumulative rolling deformation amount is 70-90%.

[0013] A high-strength, high-ductility magnesium alloy material with discontinuous yielding behavior is prepared by the above-described method.

[0014] The beneficial effects of this invention are as follows: (1) By screening the types of RE elements and controlling their addition amounts, this invention forms Al2RE and Al with high hardness and high thermal stability in various AZ-based magnesium alloy matrices. 11 RE3 phase. Hot extrusion can effectively break down Mg. 17 Al 12This approach not only significantly shortens the dissolution time of the phase during subsequent homogenization treatment, but also synergistically promotes the uniform diffusion of Al elements in the magnesium matrix, thereby facilitating the rolling process of nano-Mg. 17 Al 12 The diffuse precipitation of the phase laid the foundation.

[0015] (2) This invention prepares magnesium alloy thin sheets by hot rolling a homogenized extruded plate. During this process, Al2RE and Al... 11 The RE3 phase strongly stimulated recrystallization nucleation, resulting in the precipitation of nano-Mg. 17 Al 12 The phase hinders recrystallization and grain coarsening. The combined effect of these two factors significantly refines the matrix grain size and improves the uniformity of the microstructure.

[0016] (3) The thin plate prepared by this invention exhibits discontinuous yielding characteristics during the tensile process, which is mainly due to the nano-Mg 17 Al 12 The relatively weak pinning effect of dislocations; at the same time, the uniform fine-grained structure gives the plate both good strength and plasticity.

[0017] (4) The present invention uses conventional smelting, hot extrusion and hot rolling methods, which are easy to implement. In addition, the total addition of the two types of RE elements does not exceed 2%, which has the characteristics of low production cost and simple process, and is conducive to large-scale commercial production.

[0018] In summary, the magnesium alloy sheet prepared by this invention using conventional processes exhibits a uniform microstructure and demonstrates significant discontinuous yielding characteristics while achieving high strength and good plasticity. This material can meet the stringent service requirements for strength, plasticity, and safety reliability, and possesses promising application prospects. Attached Figure Description

[0019] Figure 1 The room temperature tensile curve and microstructure of the rolled AZ31-RE alloy in Example 1 are shown. Figure 1 (a) in the figure is the engineering stress-strain curve; Figure 1 (b) in the figure is a magnified view of the engineering stress-strain curve; Figure 1 (c) in the diagram is the corresponding metallographic structure diagram; Figure 1 (d) in the figure is the morphology diagram of the precipitated phase.

[0020] Figure 2 This is a room temperature tensile curve of the rolled AZ41-RE alloy in Example 2; Figure 2 (a) in the figure is the engineering stress-strain curve; Figure 2 (b) in the figure is a magnified view of the engineering stress-strain curve.

[0021] Figure 3 This is a room temperature tensile curve of the rolled AZ61-RE alloy in Example 3; Figure 3 (a) in the figure is the engineering stress-strain curve; Figure 3 (b) in the figure is a magnified view of the engineering stress-strain curve. Detailed Implementation

[0022] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It is obvious that the described embodiments are only one type of embodiment of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Example 1: The chemical composition (mass percentage) of the alloy is: 3.0% Al, 0.8% Zn, 1.5% Nd, 0.5% Y, with the total amount of impurity elements Fe, Cu, Ni, and Si being 0.04%, and the balance being Mg.

[0024] Step 1: Using commercially pure Mg ingots, Al ingots, Zn ingots, Mg-Nd master alloys, and Mg-Y master alloys as raw materials, the magnesium ingots are completely melted at 700℃ for 40 minutes under the protection of a covering agent. After raising the temperature of the molten magnesium to 730℃, pure Al, pure Zn, Mg-Nd master alloys, and Mg-Y master alloys are added sequentially, and the mixture is held at this temperature for 20 minutes. The mixture is then thoroughly stirred and refined by introducing high-purity argon gas. Once the melt temperature drops to 690℃, it is allowed to stand, slag is removed, and finally, the mixture is cast into magnesium alloy ingots in a metal mold.

[0025] Step 2: The ingot is placed in an extruder and extruded into a magnesium alloy sheet at an extrusion temperature of 250℃ and an extrusion ratio of 4.

[0026] Step 3: Homogenize the extruded sheet. The homogenization temperature is 350℃, and the holding time is 2 hours.

[0027] Step 4: The homogenized extruded sheet is rolled at 275℃, with a deformation of 30% per pass and a 5-minute holding period between passes, resulting in a cumulative deformation of 90%. This yields a 2mm thick high-strength, high-ductility magnesium alloy sheet exhibiting discontinuous yielding behavior. Analysis Figure 1 It can be seen that the thin plate has a uniform and fine recrystallized structure, and nano-sized Mg is dispersed in the matrix. 17 Al 12 The strain width of its tensile yield plateau is about 0.4%, and its yield strength, tensile strength and elongation are 263 MPa, 331 MPa and 21.8%, respectively.

[0028] Example 2: The chemical composition (mass percentage) of the alloy is: 4.1% Al, 1.1% Zn, 0.8% La, 0.2% Gd, with the total amount of impurity elements Fe, Cu, Ni, and Si being 0.02%, and the balance being Mg.

[0029] Step 1: Using commercially pure Mg ingots, Al ingots, Zn ingots, Mg-La master alloy, and Mg-Gd master alloy as raw materials, the magnesium ingots are completely melted at 710℃ for 30 minutes under the protection of a covering agent. After raising the temperature of the molten magnesium to 740℃, pure Al, pure Zn, Mg-La master alloy, and Mg-Gd master alloy are added sequentially and held for 15 minutes. Then, the mixture is thoroughly stirred and refined by introducing high-purity argon gas. Once the melt temperature drops to 690℃, a billet is prepared using an acoustic-magnetic coupling continuous casting process. Specific continuous casting process parameters are as follows: electromagnetic field power of 30kW, frequency of 2500Hz; ultrasonic field power of 1500W, frequency of 2000Hz; cooling water flow rate controlled at 0.75m³ / min. 3 / h, the casting speed is 50mm / min.

[0030] Step 2: The ingot is placed in an extruder and extruded into a magnesium alloy sheet at an extrusion temperature of 300℃ and an extrusion ratio of 9.

[0031] Step 3: Homogenize the extruded sheet. The homogenization temperature is 375℃, and the holding time is 4 hours.

[0032] Step 4: The homogenized extruded sheet is rolled at 300℃, with a deformation of 20% per pass and a holding time of 10 minutes between passes, resulting in a cumulative deformation of 80%. This yields a 2mm thick high-strength, high-ductility magnesium alloy sheet with discontinuous yielding behavior. The sheet exhibits a uniform, fine recrystallized structure with dispersed nano-sized Mg atoms. 17 Al 12 Phase. By Figure 2 It can be seen that the strain width of its tensile yield plateau is about 0.3%, and the yield strength, tensile strength and elongation are 274MPa, 341MPa and 19.7%, respectively.

[0033] Example 3: The chemical composition (mass percentage) of the alloy is: 6.0% Al, 1.2% Zn, 1.3% Ce, 0.4% Sm, with the total amount of impurity elements Fe, Cu, Ni and Si being 0.04%, and the balance being Mg.

[0034] Step 1: Using commercially pure Mg ingots, Al ingots, Zn ingots, Mg-Ce master alloy, and Mg-Sm master alloy as raw materials, the magnesium ingots are heated to 720℃ for 20 minutes under the protection of a covering agent to completely melt them. After raising the temperature of the molten magnesium to 750℃, pure Al, pure Zn, Mg-Ce master alloy, and Mg-Sm master alloy are added sequentially, and the mixture is held at this temperature for 10 minutes. The mixture is then thoroughly stirred and refined by introducing high-purity argon gas. Once the melt temperature drops to 690℃, it is allowed to stand, slag is removed, and finally, the mixture is cast into magnesium alloy ingots in a metal mold.

[0035] Step 2: The ingot is placed in an extruder and extruded into a magnesium alloy sheet at an extrusion temperature of 350℃ and an extrusion ratio of 16.

[0036] Step 3: Homogenize the extruded sheet. The homogenization temperature is 400℃, and the holding time is 6 hours.

[0037] Step 4: The resulting extruded sheet is rolled at 325℃, with a deformation of 10% per pass and a holding time of 15 minutes between passes, resulting in a cumulative deformation of 70%, thus obtaining a high-strength, ductile magnesium alloy sheet with a thickness of 2.4 mm and discontinuous yielding behavior. This sheet exhibits a uniform and fine recrystallized structure with a large amount of nano-Mg... 17 Al 12 Precipitated phase. From Figure 3 It can be seen that the strain width of its tensile yield plateau is about 0.5%, and the yield strength, tensile strength and elongation are 296MPa, 345MPa and 17.8%, respectively.

[0038] The above embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-strength, high-ductility magnesium alloy material with discontinuous yielding behavior, characterized in that, The preparation method includes stirring casting, hot extrusion blanking, homogenization treatment, and hot rolling forming; the specific steps are as follows: First step: firstly, determine raw materials: based on AZ series magnesium alloy, add two types of RE elements, the two types of RE elements are added by Mg-RE intermediate alloy, the AZ series magnesium alloy takes commercial pure Mg ingot, Al ingot and Zn ingot as raw materials; secondly, melt the Mg ingot; finally, add the Al ingot, the Zn ingot and the Mg-RE intermediate alloy into the Mg melt, after the raw materials are completely melted, the magnesium alloy cast ingot is obtained by pouring after stirring, refining and slagging, the cast ingot contains Mg 17 Al 12 phase, Al2RE phase and Al 11 RE3 phase; Step 2: Place the magnesium alloy ingot in an extruder and extrude the ingot into a magnesium alloy plate at a temperature range of 250~350℃. Step 3: Homogenize the magnesium alloy plate obtained in step 2 at a temperature of 350-400℃. Step 4: The sheet material after homogenization treatment in step 3 is rolled at 275~325℃ to finally obtain a high-strength ductile magnesium alloy sheet with a thickness of less than 3mm and discontinuous yielding behavior.

2. The method for preparing a high-strength, ductile magnesium alloy material with discontinuous yielding behavior according to claim 1, characterized in that, In the first step, the two types of RE elements include a first type of RE element and a second type of RE element; wherein, the first type of RE element is selected from Nd, La or Ce; and the second type of RE element is selected from Y, Gd or Sm.

3. The method for preparing a high-strength, ductile magnesium alloy material with discontinuous yielding behavior according to claim 1, characterized in that, In the first step, based on 100% of the total mass of the magnesium alloy ingot, the Al content is 3.0~6.0 wt.%, the Zn content is controlled at 0.8~1.2 wt.%, the first type of RE element addition is 0.8~1.5 wt.%, and the second type of RE element addition is 0.2~0.5 wt.%; the unavoidable Fe, Cu, Ni, and Si impurities content is less than 0.05 wt.%, and the balance is Mg.

4. The method for preparing a high-strength, ductile magnesium alloy material with discontinuous yielding behavior according to claim 1, characterized in that, In the first step, the Mg ingot is melted at a temperature of 700~720℃ for 20~40 minutes.

5. The method for preparing a high-strength, ductile magnesium alloy material with discontinuous yielding behavior according to claim 1, characterized in that, In the first step, the remelting temperature is 730~750℃ and the time is 10~20min.

6. The method for preparing a high-strength, ductile magnesium alloy material with discontinuous yielding behavior according to claim 1, characterized in that, In the first step, the melt is cast using either die casting or continuous casting. When using continuous casting, the magnesium melt in the crystallizer needs to be protected with a mixture of CO2 and SF6 gas.

7. The method for preparing a high-strength, ductile magnesium alloy material with discontinuous yielding behavior according to claim 1, characterized in that, In the second step, the extrusion process selects the extrusion ratio according to the extrusion temperature range: when the extrusion temperature is not higher than 310℃, the extrusion ratio should not be greater than 10; when the extrusion temperature exceeds 310℃, an extrusion ratio greater than 10 is used for extrusion forming.

8. The method for preparing a high-strength, ductile magnesium alloy material with discontinuous yielding behavior according to claim 1, characterized in that, In the third step, the homogenization treatment requires a heat treatment time of 2-6 hours, during which Mg... 17 Al 12 The phase is dissolved in the magnesium matrix.

9. The method for preparing a high-strength, ductile magnesium alloy material with discontinuous yielding behavior according to claim 1, characterized in that, In the fourth step, the deformation per pass is 10-30%, the holding time between passes is controlled between 5-15 minutes, and the cumulative deformation is 70-90%; during the rolling process, Al2RE phase and Al 11 RE3 phase accelerates the recrystallization process, refines the matrix grain size, and promotes nano-Mg 17 Al 12 Dynamic precipitation of phases.

10. A high-strength, high-ductility magnesium alloy material exhibiting discontinuous yielding behavior, characterized in that, It is prepared by any one of the preparation methods described in claims 1-9.

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