Preparation method of high-conductivity and high-toughness Mg-Zn-Cu wrought magnesium alloy

Abstract

The application discloses a preparation method of high-conductivity high-toughness Mg-Zn-Cu wrought magnesium alloy and belongs to the technical field of non-ferrous metal plastic deformation processing. Metal raw materials are prepared according to the mass percentage content proportion of each component element of the Mg-xZn-xCu alloy, the mass ratio of Zn and Cu is 1:1, and x=1, 2 or 3. Then, alloy smelting, multi-stage progressive solid solution treatment and hot extrusion deformation are sequentially carried out. The Mg-Zn-Cu magnesium alloy is subjected to low-alloying modification treatment, the original alpha-Mg grain refinement and MgZnCu eutectic phase generation can be promoted under specific conditions, and the conductivity of the alloy is improved. After the solid solution treatment, the MgZnCu phase precipitated along the grain boundary is reduced, and the grain grows. The initial grain size of the magnesium alloy is greatly refined through the hot extrusion deformation, the comprehensive mechanical properties of the magnesium alloy are improved, and the magnesium alloy is suitable for the manufacturing of wearable electronic equipment.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal plastic deformation processing technology, and relates to a method for preparing a high-conductivity, high-strength and high-toughness Mg-Zn-Cu deformed magnesium alloy. Background Technology

[0002] With the rapid development of technology, portable wearable devices, such as Bluetooth headsets and smartwatches, have become an important part of daily life. The main materials used in these devices are not only crucial for their portability but also must possess excellent electrical conductivity. Currently, titanium alloys and aluminum alloys are the primary metal materials used. Compared to titanium alloys, magnesium alloys have advantages such as lower cost and easier processing; compared to aluminum alloys, they are lighter and have higher specific strength, while also possessing excellent electrical conductivity. Therefore, magnesium alloys are considered the most promising lightweight structural material for wearable electronic devices.

[0003] Pure magnesium has a conductivity of 22.6 MS / m, second only to copper and aluminum. However, its tensile strength and elongation are only 11.5 MPa and 6.1%, respectively, and due to its close-packed hexagonal structure, its plastic deformation and processing properties are poor, insufficient to meet the requirements of wearable electronic devices for tensile strength (150-280 MPa) and elongation (3%-12%). Studies have shown that although alloying can improve the mechanical properties of magnesium alloys, it leads to a decrease in conductivity. This is attributed to the introduction of solute atoms during alloying, which causes lattice distortion in the magnesium matrix, increases electron scattering, and leads to a decrease in conductivity. For example, the AZ91D alloy prepared by Yuan Guangyu of Chongqing University has a tensile strength of 240 MPa and an elongation of 6%, but its conductivity drops to less than 10 MS / m.

[0004] Among the four major magnesium alloy systems, Mg-Zn alloys, compared to Mg-Al, Mg-Mn, and Mg-RE alloys, exhibit the greatest potential for meeting conductivity requirements due to the smaller lattice distortion caused by zinc (Zn) when dissolved in the Mg matrix, resulting in less negative impact on conductivity. Furthermore, zinc can enhance alloy properties through solid solution strengthening. However, simple Mg-Zn binary alloys are insufficient for industrial applications, necessitating the introduction of a third alloying element to improve their mechanical properties. Research has shown that adding copper (Cu) significantly refines the grain size of Mg-Zn alloys, improving their mechanical properties. Copper possesses good conductivity and exhibits low solid solubility in Mg-Zn alloys (approximately 0.03 at%). Simultaneously, the MgZnCu phase formed after copper addition reduces zinc atoms in the matrix, minimizing lattice distortion and thus increasing conductivity. For example, Zhang Wanpeng of the China General Research Institute of Nonferrous Metals prepared Mg-2Zn-xCu (x=0, 0.5, 1) alloys. With increasing copper content, the conductivity increased from 17.3 MS / m for Mg-2Zn to 18.1 MS / m for Mg-2Zn-0.5Cu, and finally reached 18.7 MS / m for Mg-2Zn-1Cu. Therefore, Mg-Zn-Cu magnesium alloys are an alloy system with the potential to meet conductivity requirements.

[0005] To further improve the mechanical properties of as-cast alloys, hot deformation processing allows magnesium alloys to achieve dynamic recrystallization, refining their microstructure and improving their mechanical and formability properties. During extrusion processing, the alloy is subjected to triaxial compressive stress, which helps prevent instability and cracking during processing. This processing method not only achieves greater plastic deformation but also effectively refines the alloy's microstructure. Furthermore, extrusion processing helps eliminate defects in the ingot, such as porosity, shrinkage cavities, and shrinkage pits, thereby further enhancing the material's mechanical and formability properties. Magnesium alloys, due to their lightweight properties and excellent electrical conductivity, can be used as the main material for portable wearable devices. However, there is a contradictory relationship: alloying can improve mechanical properties but negatively impact electrical conductivity. To address this, this invention selects Zn and Cu elements with minimal impact on conductivity for alloying and precisely sets the Zn / Cu ratio to optimize the alloy composition. In addition, low-temperature, low-speed extrusion deformation technology effectively improves the alloy's mechanical properties. Through these methods, a high-conductivity, high-strength, and high-toughness Mg-Zn-Cu wrought magnesium alloy suitable for wearable electronic devices has been successfully prepared. Summary of the Invention

[0006] This invention overcomes the shortcomings of the prior art and proposes a method for preparing a high-conductivity, high-strength and high-toughness Mg-Zn-Cu wrought magnesium alloy.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: A method for preparing a high-conductivity, high-strength, and high-toughness Mg-Zn-Cu wrought magnesium alloy includes the following steps: 1) Prepare metal raw materials according to the mass percentage of each constituent element of the Mg-xZn-xCu alloy, with the mass ratio of Zn to Cu being 1:1 and x = 1, 2, 3; 2) Alloy smelting: The raw materials Mg, Zn and Cu are mixed and smelted by flux covering and protected smelting method and then cast into as-cast alloy; 3) Solution treatment: The as-cast alloy is subjected to a multi-stage progressive solution treatment, which involves first heating the as-cast alloy to 200℃ and holding it for 10 minutes, then raising the temperature to 300℃ and holding it for 10 minutes, and finally raising the temperature to 430℃ for 60 hours of solution treatment. 4) Hot extrusion deformation: The solution-treated Mg-xZn-xCu alloy is subjected to hot extrusion deformation at a temperature of 230-240 ℃ and a speed of 0.3-0.6 mm / s.

[0008] Preferably, the extrusion ratio for hot extrusion deformation is 25:1.

[0009] Even better, the hot extrusion deformation is performed at an extrusion temperature of 240 ℃ and an extrusion speed of 0.4 mm / s.

[0010] Preferably, the Mg-xZn-xCu alloy is preheated in a holding furnace at 240°C for 1 hour before hot extrusion deformation.

[0011] Even better, after solution treatment, the Mg-xZn-xCu alloy is cooled by water and then preheated.

[0012] Preferably, the alloy smelting includes sequentially melting magnesium blocks, adding alloying element Zn, adding alloying element Cu, alloy refining, and casting.

[0013] Preferably, the molten magnesium block is first added to a crucible after preheating, and then a dry covering agent is sprinkled on the magnesium block for melt protection. High-purity argon gas is then introduced for gas protection; once the resistance furnace temperature reaches 720°C, constant temperature holding is initiated and continued for 30 minutes.

[0014] Preferably, the addition of alloying elements Zn and Cu involves adding a preheated zinc block into the resistance furnace, sprinkling a dried covering agent on the zinc block, closing the furnace lid, and heating to melt the zinc block. When the temperature reaches 750°C, the furnace lid is opened to remove slag, then copper sheets that have been cleaned with alcohol and preheated are added and stirred. Afterward, a covering agent is sprinkled on, the furnace lid is closed, and the temperature is maintained for 5 minutes after the resistance furnace temperature returns to 750°C.

[0015] More preferably, the alloy refining process involves lowering the resistance furnace temperature to 730°C, opening the resistance furnace, opening the furnace cover to remove slag, adding refining agent for refining, then moving the mechanical stirring device above the resistance furnace, inserting the stirring head into the melt until the melt just submerges the stirring head, stirring at a speed of 60 r / min for 1 min, removing the stirrer, evenly sprinkling a covering agent, closing the furnace cover, raising the temperature to 750°C, and maintaining the temperature for 20 min.

[0016] Even better, the casting process involves holding the magnesium alloy at 750°C for 20 minutes, then reducing the temperature of the resistance furnace to 730°C, removing the slag, and pouring the molten magnesium alloy into a mold preheated to 200°C. After the mold temperature naturally cools to room temperature, the sample is knocked out of the mold to obtain a cast alloy test bar.

[0017] The beneficial effects of this invention compared to the prior art are as follows: This invention optimizes the alloy composition by selecting Zn and Cu elements with minimal impact on conductivity and precisely setting the Zn / Cu ratio. During the smelting stage, the process flow is optimized, and the solution treatment method is innovated. Furthermore, a low-temperature, low-speed extrusion deformation technique is employed to effectively improve the alloy's mechanical properties. Through these methods, a highly conductive, high-strength, and high-toughness Mg-Zn-Cu wrought magnesium alloy suitable for wearable electronic devices has been successfully prepared.

[0018] This invention relates to a low-alloying modification treatment of Mg-Zn-Cu magnesium alloys. Under specific conditions (Zn and Cu content, Zn / Cu ratio, Cu addition method, and smelting process), the refinement of the original α-Mg grains and the formation of the MgZnCu eutectic phase can be promoted. This reduces the number of Zn atoms dissolved in the Mg matrix, decreases lattice distortion, reduces electron scattering, and improves the alloy's electrical conductivity. After solution treatment, the amount of MgZnCu phase precipitated along the grain boundaries decreases, and the grains grow. Through hot extrusion deformation, MgZnCu reprecipitates and is distributed in an island-like pattern along the extrusion direction. Simultaneously, hot extrusion deformation greatly refines the initial grain size of the magnesium alloy, improving its overall mechanical properties.

[0019] By studying the effects of Zn and Cu content on the microstructure and properties of Mg-Zn-Cu magnesium alloys, this invention elucidates the influence of Zn and Cu content on the α-Mg matrix and the MgZnCu phase. Through hot extrusion, the changes in the eutectic structure and grain size within the matrix are clarified, and the relationship between mechanical properties, electrical conductivity, and microstructure changes is revealed, thereby preparing a conductive, high-strength, and highly ductile Mg-Zn-Cu wrought magnesium alloy. Attached Figure Description

[0020] Figure 1These are scanning electron microscope (SEM) images of the Mg-xZn-xCu (x=1,2,3) extruded alloys prepared in the examples; wherein, (a) is Mg-1Zn-1Cu, (b) is a magnified view of (a); (c) is Mg-2Zn-2Cu, (d) is a magnified view of (c); (e) is Mg-3Zn-3Cu, and (f) is a magnified view of (e). Figure 2 The mechanical properties of the Mg-xZn-xCu (x=1,2,3) extruded alloys prepared in the examples are shown. Figure 3 The conductivity is the conductivity of the Mg-xZn-xCu (x=1,2,3) extruded alloy prepared in the examples. Detailed Implementation

[0021] 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.

[0022] This embodiment proposes a method for preparing a high-conductivity, high-strength, and high-toughness Mg-Zn-Cu wrought magnesium alloy, specifically including the following steps: Step 1: Ingredient Design To achieve high conductivity, the Mg-Zn-Cu alloy needs to form as much of the MgZnCu phase as possible, with a Zn to Cu ratio of 1:1. Therefore, the mass ratio of Zn to Cu is set to 1:1. This embodiment designs three Mg-xZn-xCu (x=1,2,3) magnesium alloy systems with different Zn and Cu contents but a Zn / Cu ratio of 1: Mg-1Zn-1Cu, Mg-2Zn-2Cu, and Mg-3Zn-3Cu. Metal raw materials are prepared according to the atomic percentage of each component element in the Mg-Zn-Cu alloy.

[0023] Step 2: Alloy Melting This embodiment uses high-purity Mg, Zn, and Cu as raw materials, and prepares three sets of magnesium alloy test bars—Mg-1Zn-1Cu, Mg-2Zn-2Cu, and Mg-3Zn-3Cu—using an electric resistance furnace with argon as the protective gas. The specific steps are as follows: (1) To melt pure magnesium, place the crucible in a resistance furnace and raise the furnace temperature to 500°C. Add pure magnesium preheated at 200°C for 30 minutes to the crucible and sprinkle a preheated covering agent (at 200°C) on its surface. Close the furnace lid and introduce Ar2 into the furnace for protection. Since Mg is a very reactive metallic element, it is easily oxidized at high temperatures. The resulting oxides will reduce the quality and performance of the magnesium alloy. Therefore, a salt covering agent + Ar2 protection method is used for protection. When the resistance furnace temperature reaches 720°C, maintain the temperature for 30 minutes to ensure that the pure magnesium is completely melted.

[0024] (2) Add zinc. After the magnesium ingots have completely melted, open the furnace cover to remove the slag, then add the preheated pure zinc, sprinkle the covering agent evenly, close the furnace cover and start heating.

[0025] (3) Add copper sheets. When the temperature rises to 750°C, open the furnace cover to remove slag. Then add copper sheets that have been cleaned with alcohol and preheated, and stir. After that, sprinkle a covering agent and close the furnace cover. After the resistance furnace temperature rises back to 750°C, keep it warm for 5 minutes.

[0026] (4) Refining: Reduce the temperature of the resistance furnace to 730°C, open the resistance furnace, open the furnace cover to remove slag, and add refining agent for refining. Then move the mechanical stirring device above the resistance furnace, insert the stirring head into the melt until the melt just submerges the stirring head, stir at 60 r / min, stir for 1 min, remove the stirrer, evenly sprinkle the covering agent, close the furnace cover, raise the temperature to 750°C, and keep it at a constant temperature for 20 min.

[0027] (5) Casting: After holding the furnace at 750℃ for 20 minutes, the temperature of the resistance furnace is reduced to 730℃. After removing the slag, the magnesium alloy melt is poured into a mold preheated to 200℃. After the mold temperature cools naturally to room temperature, the sample is knocked out of the mold to obtain a cast alloy test bar.

[0028] To achieve uniform microstructure and composition and reduce impurities, mechanical stirring is performed during refining. During mechanical stirring, the melt is agitated, allowing the metals to mix more evenly. Simultaneously, mechanical stirring enables the refining agents to react fully with the melt, causing impurities to precipitate to the bottom of the crucible. This achieves uniform microstructure and composition, as well as melt purification.

[0029] Step 3: Solution treatment Solution treatment was performed on three alloys: Mg-1Zn-1Cu, Mg-2Zn-2Cu, and Mg-3Zn-3Cu. Differential thermal analysis (DTA) was conducted on the as-cast alloy samples before solution treatment. The DSC curve of this alloy showed only one endothermic peak, which was the endothermic peak of the second phase melting at 470℃. Therefore, to avoid overheating of the second phase, the solution temperature was set at 430℃. Subsequently, a multi-stage progressive solution treatment was performed on the as-cast alloys in a vacuum tube furnace for 60 hours. Specifically, the alloys were first heated to 200℃ and held for 10 minutes, then heated to 300℃ and held for 10 minutes, and finally heated to 430℃ for 60 hours of solution treatment. Water cooling was used.

[0030] Traditional solution treatment typically involves heating the alloy to a fixed temperature and holding it for a period of time. This invention divides the solution treatment into multiple stages, with the temperature gradually increasing in each stage. This gradual heating helps to distribute the alloying elements more evenly and reduces internal stress caused by rapid heating.

[0031] Step 4: Hot extrusion deformation Cylindrical specimens with dimensions of Φ40mm × 45mm were cut from three groups of solid solution-treated Mg-1Zn-1Cu, Mg-2Zn-2Cu, and Mg-3Zn-3Cu samples for hot extrusion deformation. This invention employs low-temperature, low-speed extrusion, with an extrusion temperature of 240℃, an extrusion speed of 0.4mm / s, and an extrusion ratio of 25 / 1. Before extrusion, the three groups of samples were preheated in a 240℃ holding furnace for 1 hour, and then hot-extruded according to the set parameters. The extruded samples were then water-cooled.

[0032] Low-temperature, low-speed extrusion helps refine the grain structure because the lower temperature slows down the growth rate of dynamically recrystallized grains. A refined grain structure improves the material's mechanical properties. Simultaneously, low-speed extrusion reduces thermal stress during processing, contributing to a more uniform stress distribution. The magnesium alloy prepared in this embodiment is suitable for manufacturing wearable electronic devices.

[0033] In this embodiment, the extruded alloy consists of an α-Mg matrix, a MgZnCu phase, and nanoscale precipitates dispersed within the matrix. The volume fraction of the MgZnCu phase gradually increases with increasing Zn and Cu content. After hot extrusion deformation, all three alloys undergo dynamic recrystallization, resulting in a significant reduction in grain size. Simultaneously, the nanoscale precipitates have a pinning effect on the Mg matrix. Under the combined effect of these two factors, the mechanical properties of the alloys are significantly improved. The extruded Mg-1Zn-1Cu alloy has a tensile strength of 241 MPa, a yield strength of 148 MPa, and an elongation of 40%; the extruded Mg-2Zn-2Cu alloy has a tensile strength of 280 MPa, a yield strength of 179 MPa, and an elongation of 38%; and the extruded Mg-3Zn-3Cu alloy has a tensile strength of 249 MPa, a yield strength of 169 MPa, and an elongation of 34%. (See also...) Figure 1 , Figure 2 See Table 1.

[0034] After extrusion deformation, the grain size decreases and the number of grain boundaries increases. Simultaneously, nanoscale precipitates are dispersed throughout the matrix, both enhancing electron scattering. Therefore, the electrical conductivity of extruded Mg-1Zn-1Cu, Mg-2Zn-2Cu, and Mg-3Zn-3Cu are 16.43 MS / m, 21.14 MS / m, and 19.54 MS / m, respectively. (See also...) Figure 3 And Table 2.

[0035] 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 method for preparing a high-conductivity, high-strength, and high-toughness Mg-Zn-Cu wrought magnesium alloy, characterized in that, Includes the following steps: 1) Prepare metal raw materials according to the mass percentage of each constituent element of the Mg-xZn-xCu alloy, with the mass ratio of Zn to Cu being 1:1 and x = 1, 2, 3; 2) Alloy smelting: The raw materials Mg, Zn and Cu are mixed and smelted by flux covering and protected smelting method and then cast into as-cast alloy; 3) Solution treatment: The as-cast alloy is subjected to a multi-stage progressive solution treatment, which involves first heating the as-cast alloy to 200℃ and holding it for 10 minutes, then raising the temperature to 300℃ and holding it for 10 minutes, and finally raising the temperature to 430℃ for 60 hours of solution treatment. 4) Hot extrusion deformation: The solution-treated Mg-xZn-xCu alloy is subjected to hot extrusion deformation at a temperature of 240 ℃ and a speed of 0.4 mm / s; the extrusion ratio of hot extrusion deformation is 25:

1.

2. The method for preparing a high-conductivity, high-strength, and high-toughness Mg-Zn-Cu wrought magnesium alloy according to claim 1, characterized in that, Before hot extrusion deformation, the Mg-xZn-xCu alloy is preheated in a holding furnace at 240℃ for 1 hour.

3. The method for preparing a high-conductivity, high-strength, and high-toughness Mg-Zn-Cu wrought magnesium alloy according to claim 2, characterized in that, After solution treatment, the Mg-xZn-xCu alloy is cooled by water and then preheated.

4. The method for preparing a high-conductivity, high-strength, and high-toughness Mg-Zn-Cu wrought magnesium alloy according to claim 1, characterized in that, The alloy smelting process includes, in sequence, melting magnesium blocks, adding alloying element Zn, adding alloying element Cu, alloy refining, and casting.

5. The method for preparing a high-conductivity, high-strength, and high-toughness Mg-Zn-Cu wrought magnesium alloy according to claim 4, characterized in that, The process of melting magnesium blocks involves first adding preheated magnesium blocks into a crucible and then sprinkling a dry covering agent on the magnesium blocks for melt protection; then introducing high-purity argon gas for gas protection; and finally, when the resistance furnace temperature reaches 720°C, maintaining the temperature for 30 minutes.

6. The method for preparing a high-conductivity, high-strength, and high-toughness Mg-Zn-Cu wrought magnesium alloy according to claim 4, characterized in that, The addition of alloying elements Zn and Cu involves adding a preheated zinc block into a resistance furnace, sprinkling a dried covering agent on the zinc block, closing the furnace lid, and heating the furnace to melt the zinc block. When the temperature reaches 750°C, the furnace lid is opened to remove slag, and then copper sheets that have been cleaned with alcohol and preheated are added and stirred. After that, a covering agent is sprinkled on the furnace, the furnace lid is closed, and the furnace is kept at 750°C for 5 minutes.

7. The method for preparing a high-conductivity, high-strength, and high-toughness Mg-Zn-Cu wrought magnesium alloy according to claim 6, characterized in that, The alloy refining process involves lowering the resistance furnace temperature to 730°C, opening the furnace, opening the furnace cover to remove slag, adding refining agent for refining, then moving the mechanical stirring device above the resistance furnace, inserting the stirring head into the melt until the melt just submerges the stirring head, stirring at a speed of 60 r / min for 1 min, removing the stirrer, evenly sprinkling a covering agent, closing the furnace cover, raising the temperature to 750°C, and maintaining the temperature for 20 min.

8. The method for preparing a high-conductivity, high-strength, and high-toughness Mg-Zn-Cu wrought magnesium alloy according to claim 7, characterized in that, The casting process involves maintaining a constant temperature of 750℃ for 20 minutes, then lowering the temperature of the resistance furnace to 730℃, removing the slag, and then pouring the molten magnesium alloy into a mold that has been preheated to 200℃. After the mold temperature naturally cools to room temperature, the sample is knocked out of the mold to obtain a cast alloy test bar.

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