A type of ultrafine-grained Mg subjected to secondary extrusion and large plastic deformation 97 Preparation method of Y2Zn1 magnesium alloy

Abstract

The application discloses a kind of secondary extrusion large plastic deformation ultra-fine grain Mg 97 The application discloses a preparation method of Y2Zn1 magnesium alloy, and belongs to the technical field of magnesium alloy preparation.The alloy is smelted first: raw materials are prepared according to the atomic percentage of each component element of the alloy;the raw metal of Mg, Y and Zn is mixed and smelted by a smelting method, and then cast into a cast alloy;then, the cast alloy is extruded at an extrusion temperature of 450 DEG C for the first time, and the angle of the concave die for the first time is 45 DEG;finally, the cast alloy is extruded at an extrusion temperature of 390-450 DEG C for the second time, and the angle of the concave die for the second time is 30 DEG;by changing the extrusion temperature for the second time, the microstructure of the Mg 97 Y2Zn1 magnesium alloy is controlled, and a high-strength and high-toughness Mg 97 Y2Zn1 magnesium alloy with submicron grain size is obtained. 97 The strength and plasticity of the Y2Zn1 magnesium alloy are improved.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy preparation technology, and relates to a secondary extrusion large plastic deformation ultrafine crystalline Mg alloy. 97 Preparation method of Y2Zn1 magnesium alloy. Background Technology

[0002] To improve the overall mechanical properties of magnesium alloys, extrusion deformation is often used to refine the grain size. According to the Hall-Petch relationship: σ=σ 0 +kd^ (-1 / 2) The finer the grain size, the higher the strength. Simultaneously, grain refinement reduces dislocation stacking at grain boundaries, lowers stress concentration, allows for greater deformation before fracture, and improves toughness. Therefore, grain refinement can simultaneously improve both strength and toughness.

[0003] Currently, numerous studies have reported the effects of primary extrusion process parameters (extrusion temperature, extrusion ratio, extrusion angle, extrusion speed, etc.) on the microstructure and properties of magnesium alloys. Primary extrusion results in problems such as coarse non-recrystallized grains, incomplete dynamic recrystallization, and severe texture. For example, a higher extrusion ratio leads to greater lattice distortion at grain boundaries and higher stored energy, providing favorable conditions for dynamic recrystallization nucleation, significantly refining grains and increasing the recrystallization fraction. Furthermore, primary extrusion results in the precipitation of a second phase. Researchers at Harbin Engineering University, including Zhang Jinghuai, discovered through extruding Mg-4Er-2Y-3Zn-0.4Mn alloys that the second phase can serve as a nucleation site for dynamic recrystallization grains and also plays a positive role in inhibiting grain growth, thereby refining the grains.

[0004] While primary extrusion significantly improves strength, it offers only a minor boost to toughness, failing to achieve a synergistic improvement in both strength and toughness. Compared to primary extrusion, secondary extrusion results in more complete dynamic recrystallization and smaller grain sizes. Dynamic recrystallization produces randomly oriented equiaxed grains with a weak texture. During random-direction deformation, more grains are in a soft orientation, which facilitates matrix slippage and thus enhances the material's toughness. Secondary extrusion is a commonly used method for obtaining high-strength, high-toughness magnesium alloys; the first extrusion significantly improves the alloy's strength, while the second extrusion significantly improves its toughness.

[0005] Furthermore, rare earth elements have high solubility in magnesium, and their addition can strengthen magnesium through solid solution. Rare earth element Y (Y) is a commonly used rare earth element, with a solid solubility of 3.35% (mole fraction) in magnesium. In particular, adding Zn to Mg-Y alloys can yield unique structures. When the Y to Zn atomic ratio is greater than 2, a Long Period Stacking Ordered (LPSO) structure is easily formed. The main LPSO structures are 6H, 10H, 14H, 18R, and 24R, with 18R and 14H being the two most common. Although 18R can be obtained in the as-cast state, it is an unstable structure and can be transformed into 14H through appropriate heat treatment. 14H possesses excellent mechanical properties and high-temperature stability, significantly improving the mechanical properties of magnesium alloys. Therefore, rare earth Mg-Y-Zn alloys containing the 14H-LPSO structure have become a hot topic in the research of high-strength and high-toughness magnesium alloys. Secondary extrusion is an effective method to obtain magnesium alloys with synergistic improvement in strength and toughness. However, there are far fewer reports on Mg-Y-Zn alloys with large plastic deformation secondary extrusion than primary extrusion. The mechanism of secondary extrusion in synergistically improving strength and toughness is still unclear, and it is impossible to effectively and accurately control the microstructure of magnesium alloys. Summary of the Invention

[0006] This invention overcomes the shortcomings of existing technologies and proposes a method for secondary extrusion of large plastic deformation ultrafine-grained Mg 97 Preparation method of Y2Zn1 magnesium alloy.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] A type of ultrafine-grained Mg subjected to secondary extrusion and large plastic deformation 97 The preparation method of Y2Zn1 magnesium alloy includes the following steps:

[0009] 1) Alloy smelting: according to Mg 97 Prepare the metal raw materials by determining the atomic percentage of each constituent element of the Y2Zn1 alloy; mix and melt the raw metal materials of Mg, Y, and Zn by flux-covered protective melting method and then cast them into a cast alloy.

[0010] 2) Single extrusion: The cast alloy is extruded at an extrusion temperature of 450℃ in a single extrusion, and the die angle for the single extrusion is 45°.

[0011] 3) Secondary extrusion: The cast alloy after primary extrusion is subjected to secondary extrusion at an extrusion temperature of 390-450℃, and the die angle of the secondary extrusion is 30°.

[0012] Preferably, the extrusion speed for a single extrusion is 0.4 mm / s and the extrusion ratio is 4:1.

[0013] More preferably, the cast alloy produced in step 1) is cut into cylindrical specimens, and the primary extrusion die is heated to 450°C and the cylindrical specimens are preheated to 450°C and held for 1 hour; then a second extrusion is performed.

[0014] Preferably, the extrusion speed of the secondary extrusion is 0.4 mm / s and the extrusion ratio is 25:1.

[0015] Even better, the secondary extrusion die is heated to 390-450℃, and the cylindrical sample after the first extrusion is preheated to 390-450℃ and kept at that temperature for 1 hour; then the secondary extrusion is performed.

[0016] Preferably, the extrusion temperature for the secondary extrusion is 400℃.

[0017] Preferably, the metal raw materials are magnesium ingots with a purity of 99.99 wt%, Mg-30Y master alloy, zinc blocks with a purity of 99.99 wt%, as well as covering agents and refining agents.

[0018] Preferably, the alloy smelting process involves first heating a preheated magnesium ingot to 720°C and holding it for 20 minutes; then adding a preheated Mg-30Y master alloy and zinc blocks, and applying a covering agent, heating to 750°C, and holding for 10 minutes; after the holding time is completed, lowering the temperature to 730°C, skimming off the slag from the liquid surface, adding a preheated refining agent and stirring evenly, applying a covering agent, and holding at 750°C for 20 minutes; after the holding time is completed, lowering the temperature to 730°C, skimming off the slag from the liquid surface, and pouring the molten liquid into a mold. The casting process is carried out under gas protection, and the mixture is air-cooled to room temperature to obtain the as-cast alloy.

[0019] Preferably, after the first extrusion in step 2) is completed, the extruded sample is taken out and air-cooled to room temperature to obtain a first extrusion bar, and then a second extrusion is performed.

[0020] Even better, after the secondary extrusion is completed in step 3), the secondary extrusion rod is quickly placed in water for water cooling to obtain the secondary extrusion rod.

[0021] The beneficial effects of this invention compared to the prior art are as follows:

[0022] This invention employs a large deformation secondary extrusion process, by changing the secondary extrusion temperature, to control the deformation of Mg. 97 By controlling the microstructure of Y2Zn1 magnesium alloy, a high-strength and high-toughness Mg alloy with submicron grain size was obtained. 97Y2Zn1 magnesium alloy. This invention involves a secondary extrusion process for high plastic deformation of Mg-Y-Zn magnesium alloy. By using specific extrusion parameters (extrusion temperature and extrusion angle), a fully recrystallized, ultrafine-grained magnesium alloy with a grain size less than 1 μm was obtained. Increasing the extrusion temperature improves atomic activity and accelerates atomic diffusion, leading to complete recrystallization. A lower die angle reduces deformation heat, bringing the actual sample temperature close to the set extrusion temperature, controlling rapid grain growth, and achieving a grain size less than 1 μm. By adjusting the balance between recrystallization degree and grain size, a synergistic improvement in strength and toughness is achieved, overcoming the strength-ductility mismatch problem of high strength / low toughness or high toughness / low strength in magnesium alloys. A tensile strength of 332.6 MPa, elongation of 26.1%, and a strength-ductility product of 8.68 GPa% are obtained, exceeding the average level (6-8 GPa%).

[0023] This invention investigates the effects of different secondary extrusion temperatures and lower die angles on the microstructure evolution and mechanical properties of Mg-Y-Zn magnesium alloys. It elucidates the influence of extrusion temperature on recrystallization behavior and grain refinement, reveals the correlation between microstructure and mechanical properties, and produces high-strength, high-toughness Mg alloys with synergistic improvements in strength and plasticity. 97 Y2Zn1 magnesium alloy. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the secondary extrusion process in the embodiment;

[0025] Figure 2 The extruded Mg in the example 97 SEM microstructure images of Y2Zn1 alloy under different secondary extrusion temperature parameters; among which

[0026] (a), (b), (c), and (d) are 390℃, 400℃, 420℃, and 450℃, respectively; (e), (f), (g), and (h) are magnified views of the regions in (a), (b), (c), and (d), respectively.

[0027] Figure 3 The extruded Mg in the example 97 Room temperature tensile stress-strain curves of Y2Zn1 alloy under different secondary extrusion parameters. Detailed Implementation

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

[0029] This embodiment proposes a method for secondary extrusion and large plastic deformation of ultrafine-grained Mg. 97 The preparation method of Y2Zn1 magnesium alloy specifically includes the following steps:

[0030] Alloy composition design: This invention uses magnesium ingots with a purity of 99.99 wt%, Mg-30Y master alloy, zinc with a purity of 99.99 wt%, as well as covering agents and refining agents. A single smelting operation yields 1500g of alloy, including 1120.35g of Mg, 37.65g of Zn, 342g of Mg-30Y master alloy, a small amount of covering agent and refining agent, and Mg... 97 The composition of Y2Zn1 alloy is shown in Table 1.

[0031]

[0032] Step 1: Alloy Melting

[0033] 1) Add the preheated magnesium block to a crucible preheated to 500℃, sprinkle with a covering agent and pass in high-purity argon gas for protection, and heat to 720℃ and hold for 20 minutes.

[0034] 2) After the magnesium blocks have completely melted, remove the slag, add the preheated Mg-30Y master alloy and zinc blocks, and sprinkle a covering agent to protect the liquid surface. Heat to 750℃ and hold for 10 minutes.

[0035] 3) After the heat preservation time is over, lower the temperature to 730℃, skim off the slag on the liquid surface, add the preheated refining agent and stir evenly, sprinkle on the covering agent, and keep it at 750℃ for 20 minutes.

[0036] 4) Install the preheated metal mold on the mechanical vibration table, and at the same time install a foam ceramic filter screen at the pouring port. To enhance the adhesion of the filter to impurities, coat the surface of the foam ceramic filter screen with a special coating, and turn on the machine.

[0037] 5) After the heat preservation time is over, the temperature is reduced to 730℃ and the slag on the liquid surface is removed. The molten liquid is then poured into the mold. The casting process requires gas protection and air cooling to room temperature. Finally, a sample with a diameter of Ø80mm is obtained.

[0038] To reduce impurities in castings, this embodiment uses a refining agent to remove gases from the melt and adsorbs impurities, causing them to sink to the bottom or float to the surface, thus purifying the melt. Simultaneously, foam ceramics with stronger adsorption capacity are used to filter impurities in the melt, reducing the introduction of impurities during the casting process. Furthermore, mechanical vibration is used during the casting process to reduce shrinkage porosity and promote dendrite fracture, resulting in a denser microstructure and finer grains.

[0039] Step 2: One squeeze

[0040] 1) Cut the cast sample into cylinders with a diameter of Ø80×50mm, and polish the cut cylinders with gauze to obtain cylinders with a diameter of Ø78.5×50mm;

[0041] 2) Heat the extrusion die to 450℃, and preheat the extrusion sample to 450℃ and hold for 1 hour;

[0042] 3) Place the extrusion sample in the mold, place a shim underneath, and extrude at an extrusion speed of 0.4 mm / s, an extrusion ratio of 4:1, and an extrusion angle of 45°.

[0043] 4) Remove the extrusion sample and air-cool it to room temperature to obtain a primary extrusion bar with a diameter of Ø40mm.

[0044] The primary extrusion die uses a 45° angle and an extrusion temperature of 450°C. This ensures complete recrystallization after the first extrusion, while minimizing recrystallized grain growth and ensuring complete precipitation of the second phase, thus preparing for the secondary extrusion to obtain ultrafine grains. This is because as the extrusion angle increases, the sample strain increases, leading to increased extrusion heat, which promotes both recrystallization and grain growth. Similarly, as the extrusion temperature increases, it promotes both recrystallization and second phase precipitation, while also causing grain growth. Considering all factors, a 45° die angle and an extrusion temperature of 450°C are the most suitable for the primary extrusion.

[0045] Step 3: Secondary extrusion

[0046] 1) Cut the primary extrusion bar into cylinders with a diameter of Ø40×30mm, and use gauze to remove the surface oxide layer, reducing the diameter to 38.5mm;

[0047] 2) Heat the mold to the extrusion temperature (390℃, 400℃, 420℃, 450℃) using an electric resistance furnace, and at the same time heat the extruded sample to the extrusion temperature (390℃, 400℃, 420℃, 450℃) using a heat treatment furnace and keep it at that temperature for 1 hour;

[0048] 3) After the heat preservation time is 1 hour and the mold temperature reaches the extrusion temperature, quickly take out the extrusion sample and place it in the extrusion mold, put in the shim, and put on the extrusion rod;

[0049] 4) Adjust the extrusion parameters to an extrusion speed of 0.4 mm / s, an extrusion ratio of 25:1, and an extrusion angle of 30°.

[0050] 5) After extrusion, quickly immerse the secondary extrusion bar in water for water cooling to obtain a secondary extrusion bar with a diameter of Ø8mm. The extrusion process is as follows: Figure 1 As shown.

[0051] Figure 1Before the first extrusion, sample 1 is extruded through a first mold 5, which includes a first punch 2, a first gasket 3, and a first die 4 arranged sequentially from top to bottom; in the figure, the angle of the first die 4 is 45°. The first extrusion bar obtained after the first extrusion is polished to obtain sample 6 before the second extrusion. Sample 6 before the second extrusion is extruded through a second mold 7, which includes a second punch 8, a second gasket 9, and a second die 10 arranged sequentially from top to bottom; in the figure, the angle of the second die 10 is 30°. After the second extrusion, a second extrusion sample 11 is obtained, and the second extrusion sample 11 is water-cooled to obtain a second extrusion bar.

[0052] Temperature is a major factor affecting rapid grain growth during extrusion. Lowering the extrusion temperature is essential for preparing ultrafine grains. During extrusion deformation, different extrusion process parameters ultimately translate into temperature effects on microstructure evolution. For example, a smaller die angle results in less sample deformation during extrusion, leading to less deformation heat and ultimately, a sample temperature closer to the set extrusion temperature. Therefore, by selecting a lower extrusion temperature and a lower die angle (30°) to minimize deformation heat generation in the secondary extrusion process, this invention successfully prepared ultrafine-grained Mg with a grain size less than 1 μm. 97 Y2Zn1 magnesium alloy achieves a synergistic improvement in strength and toughness, overcoming the strength-ductility mismatch problem of high strength and low toughness or high toughness and low strength in magnesium alloys.

[0053] As the secondary extrusion temperature increases from 390℃ to 400℃, 420℃, and 450℃, recrystallization becomes more complete, and the grain size gradually increases. Complete recrystallization is achieved at 420℃, while significant grain growth is observed at 450℃. The alloy microstructure is as follows: Figure 2 As shown.

[0054] Mg obtained after secondary extrusion 97 The room temperature tensile stress-strain curves, tensile strength, and elongation of Y2Zn1 magnesium alloy are shown below. Figure 3 And Table 2.

[0055]

[0056] As the extrusion temperature increases from 390℃ to 400℃, 420℃, and 450℃, Mg 97The tensile strengths of the Y2Zn1 wrought magnesium alloy were 296.4 MPa, 352.7 MPa, 332.6 MPa, and 289.0 MPa, respectively, with elongations of 18.2%, 23.3%, 26.1%, and 29.1%, and strength-ductility products of 5.39 GPa%, 8.22 GPa%, 8.68 GPa%, and 8.41 GPa%, respectively. The experimental results show that the highest tensile strength (352.7 MPa) was achieved at a secondary extrusion temperature of 400℃, and the highest elongation (29.1%) was achieved at a secondary extrusion temperature of 420℃. The strength-ductility product, often used to measure the comprehensive mechanical properties of a material, was 8.68 GPa% at 420℃, indicating the best overall performance.

[0057] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. It should not be considered that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the present invention, and all of these should be considered to fall within the scope of patent protection determined by the submitted claims.

Claims

1. A type of ultrafine-grained Mg subjected to secondary extrusion and large plastic deformation 97 The method for preparing Y2Zn1 magnesium alloy is characterized by, Includes the following steps: 1) Alloy smelting: according to Mg 97 Prepare the metal raw materials by determining the atomic percentage of each constituent element of the Y2Zn1 alloy; mix and melt the raw metal materials of Mg, Y, and Zn by flux-covered protective melting method and then cast them into a cast alloy. 2) Single extrusion: The cast alloy is extruded at an extrusion temperature of 450℃, the die angle of the single extrusion is 45°, the extrusion speed of the single extrusion is 0.4mm / s, and the extrusion ratio is 4:1; 3) Secondary extrusion: The cast alloy after primary extrusion is subjected to secondary extrusion at an extrusion temperature of 390-450℃. The die angle for secondary extrusion is 30°. The extrusion speed for secondary extrusion is 0.4 mm / s and the extrusion ratio is 25:

1.

2. The ultrafine-grained Mg subjected to secondary extrusion and large plastic deformation as described in claim 1 97 The method for preparing Y2Zn1 magnesium alloy is characterized by, Cut the cast alloy from step 1) into cylindrical specimens, heat the primary extrusion die to 450°C, preheat the cylindrical specimens to 450°C and hold for 1 hour; then perform another extrusion.

3. The ultrafine-grained Mg subjected to secondary extrusion and large plastic deformation as described in claim 1 97 The method for preparing Y2Zn1 magnesium alloy is characterized by, Heat the secondary extrusion die to 390-450℃, preheat the cylindrical sample after the first extrusion to 390-450℃ and keep it at that temperature for 1 hour; then perform the second extrusion.

4. The ultrafine-grained Mg subjected to secondary extrusion and large plastic deformation as described in claim 1 97 The method for preparing Y2Zn1 magnesium alloy is characterized by, The extrusion temperature for the secondary extrusion is 400℃.

5. The ultrafine-grained Mg subjected to secondary extrusion and large plastic deformation according to claim 1. 97 The method for preparing Y2Zn1 magnesium alloy is characterized by, The metal raw materials used are magnesium ingots with a purity of 99.99 wt%, Mg-30Y master alloy, zinc blocks with a purity of 99.99 wt%, as well as covering agents and refining agents.

6. A secondary extrusion, high plastic deformation, ultrafine-grained Mg as described in claim 1 or 5 97 The method for preparing Y2Zn1 magnesium alloy is characterized by, The alloy smelting process involves first heating a preheated magnesium ingot to 720℃ and holding it for 20 minutes; then adding a preheated Mg-30Y master alloy and zinc blocks and covering them with a covering agent, heating the ingot to 750℃ and holding it for 10 minutes; after the holding time is over, the temperature is lowered to 730℃, the slag is skimmed off the surface of the liquid, a preheated refining agent is added and stirred evenly, a covering agent is added, and the ingot is held at 750℃ for 20 minutes. After the holding time is over, the temperature is lowered to 730℃ and the slag on the liquid surface is removed. The molten liquid is then poured into a mold. The casting process is carried out under gas protection and air-cooled to room temperature to obtain the cast alloy.

7. The ultrafine-grained Mg subjected to secondary extrusion and large plastic deformation according to claim 1. 97 The method for preparing Y2Zn1 magnesium alloy is characterized by, After the first extrusion in step 2) is completed, the extruded sample is taken out and air-cooled to room temperature to obtain a first extrusion bar, and then a second extrusion is performed.

8. The ultrafine-grained Mg subjected to secondary extrusion and large plastic deformation according to claim 7 97 The method for preparing Y2Zn1 magnesium alloy is characterized by, After the secondary extrusion is completed in step 3), the secondary extrusion rod is quickly placed in water for water cooling to obtain the secondary extrusion rod.

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