Preparation method of high-strength and high-thermal-conductivity Mg-Zn-Cu-Mn magnesium alloy

Abstract

This invention discloses a method for preparing a high-strength, high-thermal-conductivity Mg-Zn-Cu-Mn magnesium alloy, belonging to the field of magnesium alloy preparation technology. Metal raw materials are prepared according to the atomic percentage ratio of each constituent element in the Mg-3Zn-3Cu-xMn alloy (0≤x≤1). Then, alloy melting, homogenization treatment, and hot extrusion deformation are performed sequentially. The extrusion temperature is 260-270℃, and the extrusion speed is 0.3-0.6 mm / s. This invention achieves homogeneous dispersion of Mn to cluster precipitation in the Mg-Zn-Cu magnesium alloy through Mn alloying modification treatment. When 0.6 wt.% Mn is added, the alloy exhibits the best thermal conductivity and tensile strength. This invention refines the grain size of the Mg-Zn-Cu-Mn magnesium alloy and eliminates some casting defects, thereby further improving the alloy's strength and thermal conductivity.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy preparation technology, and relates to a method for preparing a high-strength, high-thermal-conductivity Mg-Zn-Cu-Mn magnesium alloy. Background Technology

[0002] Mg-Zn-Cu magnesium alloys are widely used in 3C products and 5G base stations due to their excellent thermal conductivity (110-120 W / (W·K)). However, due to their low strength, the yield strength of Mg-Zn-Cu magnesium alloys is usually difficult to exceed 100 MPa under as-cast conditions, making them unsuitable as structural materials to withstand high loads and limiting their further applications.

[0003] Currently, extrusion deformation is an effective method to improve the strength of alloys. However, the size and shape of the grains change after extrusion deformation, leading to the introduction of a large number of grain boundaries into the magnesium matrix, which inhibits heat conduction and thus affects thermal conductivity. For example, Zheng Mingyi from Harbin Institute of Technology, Liu Riping et al. from Yanshan University, and others found that after extrusion treatment, although the ultimate tensile strength of Mg-1Zn alloy increased from 99 MPa to 169 MPa, the thermal conductivity decreased from 138 W / (W·K) to 131 W / (W·K). Similarly, Bai Shilei et al. from Chongqing University developed Mg-9Al-Zn (AZ91) magnesium alloy, and after extrusion deformation, its ultimate tensile strength increased from 315 MPa to 382 MPa, but the thermal conductivity decreased from 51.2 W / (W·K) to 46.9 W / (W·K). This shows that extruded magnesium alloys face a significant challenge of an imbalance between strength and thermal conductivity.

[0004] However, Yuan Jiawei and others at the Beijing General Research Institute of Nonferrous Metals prepared a high-strength, high-thermal-conductivity Mg-5Zn-1Mn magnesium alloy. After Mn alloying and extrusion deformation, the alloy's strength increased from 217 MPa to 264 MPa. Simultaneously, the alloy's thermal conductivity increased from 102.9 W / (W·K) to 113.0 W / (W·K). Mn, as a common alloying element in extruded magnesium alloys, can significantly improve the alloy's strength. First, the addition of Mn can significantly refine the grain size of the magnesium alloy. Solute atoms can reduce grain boundary energy through a dragging effect, decreasing the grain boundary migration rate and thus improving the material's toughness. Second, Mn also forms atomic clusters during extrusion. These atomic clusters are dispersed at grain boundaries and within grains, producing a pinning effect, thereby restricting dislocation movement and improving the alloy's strength. The addition of Mn can also improve the alloy's thermal conductivity. On one hand, Mn atoms in the Mg matrix are affected by stress and temperature, precipitating in the matrix as nanoparticles. Therefore, the reduced Mn atom content in the matrix weakens the lattice distortion present in the matrix, thereby improving the thermal conductivity of the alloy. On the other hand, Mn atoms, through vacancy effects, can reduce the number of Zn and Cu atoms in the matrix, further weakening the lattice distortion present in the matrix while promoting the precipitation of the MgZnCu phase with high thermal conductivity.

[0005] Although researchers have made some progress in the study of Mg-Zn-Cu magnesium alloys and Mn-strengthened magnesium alloys, the methods of Mn addition and the mechanism by which Mn affects the thermal conductivity of Mg-Zn-Cu magnesium alloys remain unclear. While the addition of Mn improves the strength and thermal conductivity of Mg-Zn-Cu magnesium alloys, casting defects such as overheating and shrinkage cavities still occur during the casting process. Further improvements in the strength and thermal conductivity of these alloys are needed. Summary of the Invention

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

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: A method for preparing a high-strength, high-thermal-conductivity Mg-Zn-Cu-Mn magnesium alloy includes the following steps: 1) Prepare metal raw materials according to the atomic percentage of each constituent element of the Mg-3Zn-3Cu-xMn alloy, where x takes the value of 0≤x≤1; 2) Alloy smelting: The raw materials Mg, Zn, Cu and Mn are mixed and smelted by flux covering and protected smelting method and then cast into as-cast alloy; 3) Homogenization treatment: The as-cast alloy is homogenized at a temperature of 430-470℃ for 40-50 hours. 4) Hot extrusion deformation: The homogenized Mg-3Zn-3Cu-xMn is subjected to hot extrusion deformation at a temperature of 260-270 ℃ and a speed of 0.3-0.6 mm / s.

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

[0009] Preferably, the extrusion temperature for hot extrusion deformation is 260 ℃ and the extrusion speed is 0.5 mm / s.

[0010] Preferably, the homogenization temperature is 430℃ and the homogenization time is 48h.

[0011] Preferably, x is 0.6.

[0012] Preferably, the alloy smelting process includes, in sequence, melting magnesium blocks, adding alloying elements Zn, adding alloying elements Cu and Mn, converter, alloy refining, casting and cooling, and ultrasonic cleaning.

[0013] More 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, a constant temperature holding period is initiated for 20 minutes.

[0014] More preferably, the addition of alloying elements Zn, Cu, and Mn involves adding a preheated zinc block into the furnace, sprinkling a dried covering agent on the zinc block, closing the furnace lid, and heating to 750°C to melt the zinc block; then opening the furnace a second time to clean the surface of the solution with a slag scraper, adding preheated copper and manganese particles as needed for the experiment, stirring, sprinkling a covering agent, closing the furnace lid, and holding at that temperature for 5 minutes.

[0015] More preferably, the converter and alloy refining are carried out when the temperature rises to 750°C, the molten metal is transferred to a holding furnace and held for 5 minutes before refining; when the temperature of the holding furnace reaches 750°C, the slag on the surface of the molten metal is removed and the refining operation is carried out; after the refining is completed, a layer of covering agent is evenly sprinkled on the surface of the molten metal, the furnace temperature is kept constant at 750°C, and the temperature is held for 20 minutes.

[0016] Even better, the pouring and cooling process involves holding the metal at 750 °C for 20 minutes, then lowering the furnace temperature to 730 °C, pouring the molten metal into the funnel gate, and then removing the sample from the mold to obtain the as-cast alloy test bar after the mold temperature has naturally cooled to room temperature.

[0017] The beneficial effects of this invention compared to the prior art are as follows: This invention, based on the Mg-Zn-Cu alloy, designs a novel Mg-Zn-Cu-Mn magnesium alloy through Mn alloying modification treatment. First, during the smelting process, stirring the Mn particles combined with converter technology ensures a uniform distribution of Mn in the Mg-Zn-Cu alloy. Second, homogenization treatment further promotes the diffusion behavior of Mn in the alloy, transforming the high thermal conductivity MgZnCu phase from a continuous network structure into a spheroidized granular phase. Finally, after hot extrusion deformation, the volume fraction of the MgZnCu granular phase first increases and then decreases with increasing Mn content. Simultaneously, Mn precipitates in the form of nano-sized atomic clusters. Furthermore, the extruded magnesium alloy refines the grains and eliminates some casting defects, such as hot spots and shrinkage cavities, thereby further improving the alloy's strength and thermal conductivity.

[0018] This invention achieves homogeneous dispersion and cluster precipitation of Mn in Mg-Zn-Cu magnesium alloys through alloying modification treatment. Optimization was performed under specific conditions, including Mn content, Mn addition method, smelting process, homogenization treatment, and hot extrusion process. When 0.6 wt.% Mn was added, the alloy exhibited the best thermal conductivity (125.3 W / m·K) and tensile strength (278.9 MPa). After homogenization treatment, the MgZnCu phase underwent spheroidization. After hot extrusion deformation, these spheroidized MgZnCu phases were uniformly dispersed around the grain boundaries along the extrusion direction, effectively pinning the magnesium matrix and improving the overall mechanical properties of the magnesium alloy. Furthermore, the uniform precipitation of Mn in clusters after addition, and the significant increase in the volume fraction of the MgZnCu phase, reduced lattice distortion in the α-Mg matrix, synergistically improving the thermal conductivity of the alloy.

[0019] By studying the influence of Mn on the microstructure and properties of Mg-Zn-Cu alloys, this invention elucidates the effects of Mn on the α-Mg matrix and the MgZnCu phase, respectively. Through hot extrusion, the evolution law of the MgZnCu phase within the matrix was explored, and the relationship between mechanical properties, thermal conductivity, and microstructure changes was revealed, thereby preparing a novel high-performance Mg-Zn-Cu-Mn magnesium alloy. Attached Figure Description

[0020] Figure 1 This is the DSC spectrum of the Mg-3Zn-3Cu as-cast alloy prepared in the example.

[0021] Figure 2 The tensile properties are those of the as-cast alloys of Mg-3Zn-3Cu-xMn (x=0, 0.2, 0.6, 1, wt. %) prepared in the examples.

[0022] Figure 3 The tensile properties are those of the Mg-3Zn-3Cu-xMn (x=0, 0.2, 0.6, 1, wt. %) extruded alloys prepared in the examples.

[0023] Figure 4 The value is the thermal conductivity of the Mg-3Zn-3Cu-xMn (x=0, 0.2, 0.6, 1, wt. %) alloy prepared in the examples.

[0024] Figure 5 This is a low-magnification scanning micrograph of the Mg-3Zn-3Cu-xMn (x=0, 0.2, 0.6, 1, wt. %) extruded alloy prepared in the examples.

[0025] Figure 6 These are high-magnification scanning micrographs of the Mg-3Zn-3Cu-xMn (x=0, 0.2, 0.6, 1, wt. %) extruded alloys prepared in the examples; wherein, (a) is Mg-3Zn-3Cu, (b) is Mg-3Zn-3Cu-0.2Mn, (c) is Mg-3Zn-3Cu-0.6Mn, and (d) is Mg-3Zn-3Cu-1Mn.

[0026] Figure 7 This is the EDS spectrum of the Mg-3Zn-3Cu-0.6Mn extruded alloy prepared in the example.

[0027] Figure 8 yes Figure 7 Enlarged view of Mg, Zn, Cu, and Mn.

[0028] Figure 9 yes Figure 7 EDS spot scan pattern of Mg-3Zn-3Cu-0.6Mn extruded alloy. Detailed Implementation

[0029] 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.

[0030] This embodiment proposes a method for preparing a high-strength, high-thermal-conductivity Mg-Zn-Cu-Mn magnesium alloy, which specifically includes the following steps: Step 1: Ingredient Design This embodiment designed four magnesium alloy systems with different Mn contents: Mg-3Zn-3Cu-xMn (x=0, 0.2, 0.6, 1), namely: Mg-3Zn-3Cu, Mg-3Zn-3Cu-0.2Mn, Mg-3Zn-3Cu-0.6Mn, and Mg-3Zn-3Cu-1Mn. Metal raw materials were prepared according to the atomic percentage ratio of each constituent element in the above four magnesium alloys.

[0031] Step 2: Alloy Melting (1) Melting magnesium blocks: When the temperature of the box-type resistance furnace reaches 500℃, firstly, the preheated magnesium blocks are added to the crucible, and a covering agent dried at 200℃ is sprinkled on the magnesium blocks for melt protection. Secondly, high-purity argon gas is introduced into the box-type resistance furnace for gas protection to prevent oxidation of the alloy and affect the stability of the alloy properties. Finally, when the temperature of the resistance furnace reaches 720℃, constant temperature holding is started for 20 minutes to ensure that inclusions or impurities in the metal remain on the liquid surface, thereby improving the purity and quality of the alloy.

[0032] (2) Adding alloying element Zn: After the magnesium block has completely melted, first open the furnace lid and use a slag remover to clean the inclusions and impurities on the surface of the alloy solution. Then, add the preheated zinc block into the furnace and sprinkle a dried covering agent on the zinc block. Finally, close the furnace lid and heat to 750°C to ensure that the zinc block melts.

[0033] (3) Add alloying elements Cu and Mn: When the temperature rises to 750 ℃, the furnace is opened for the second time and the surface of the solution is cleaned with a slag scraper. Preheated copper particles and manganese particles are added according to the test requirements. After stirring, a covering agent is sprinkled on and the furnace lid is closed. Keep warm for 5 minutes.

[0034] (4) Converter: When the temperature rises to 750℃, the converter can be used to transfer the melt into the holding furnace and refine it after holding for 5 minutes.

[0035] (5) Alloy refining: When the furnace temperature reaches 750℃, remove the slag from the surface of the molten metal and perform refining operations to improve the purity and quality of the materials in the furnace. After refining, a layer of covering agent needs to be evenly sprinkled on the surface of the molten metal to prevent oxidation and contamination. After refining, keep the furnace temperature constant at 750℃ and maintain the temperature for 20 minutes.

[0036] (6) Mold assembly: Take out the preheated mold (200℃) and assemble a funnel on top of the mold. Assemble a copper mesh at the outlet of the funnel to ensure the purity of the alloy during casting and to ensure that the magnesium alloy liquid enters the mold smoothly to reduce splashing. Finally, introduce protective gas at the funnel to reduce the contact between the magnesium alloy and the air.

[0037] (7) Casting and cooling: After holding at 750 °C for 20 min, the furnace temperature is then reduced to 730 °C. The molten metal is poured into the funnel gate. After the mold temperature is naturally cooled to room temperature, the sample is taken out of the mold to obtain the cast alloy test bar.

[0038] (8) Ultrasonic Cleaning: Place the casting in an ultrasonic cleaning tank, ensuring it is completely submerged in the alcohol solution. Start the ultrasonic cleaner to generate high-frequency ultrasonic waves. The ultrasonic waves effectively separate and remove contaminants through the bursting of tiny bubbles in the cleaning solution, thus ensuring the accuracy of the sample.

[0039] Step 3: Homogenization Four alloys, Mg-3Zn-3Cu, Mg-3Zn-3Cu-0.2Mn, Mg-3Zn-3Cu-0.6Mn, and Mg-3Zn-3Cu-1Mn, were subjected to homogenization treatment before extrusion. Differential thermal analysis (DTA) was performed on the as-cast Mg-3Zn-3Cu alloy samples before homogenization. The 473 ℃ peak on the DSC curve corresponded to the endothermic melting peak of the second phase (MgZnCu phase). Therefore, to avoid the dissolution phase transformation of the second phase in the alloy, the homogenization temperature was set at 430 ℃. Finally, the as-cast Mg-3Zn-3Cu, Mg-3Zn-3Cu-0.2Mn, Mg-3Zn-3Cu-0.6Mn, and Mg-3Zn-3Cu-1Mn were subjected to a 48-hour homogenization treatment in a vacuum tube heat treatment furnace to ensure uniform dispersion of solute atoms and the second phase. Water cooling was used.

[0040] Step 4: Hot extrusion deformation Two cylindrical test bars with dimensions of Φ40 mm × 25 mm were cut from the homogenized Mg-3Zn-3Cu-xMn alloy test bars and subjected to hot extrusion deformation. Before extrusion, the two sets of Mg-3Zn-3Cu-xMn alloy test bars were respectively placed in a 260°C oven. o Preheat in the oven of C for 1 hour, and then perform hot extrusion deformation according to the set extrusion temperature (260 ℃), extrusion speed (0.5 mm / s) and extrusion ratio (25 / 1). The extruded test bar is then water-cooled.

[0041] When 0.6 wt.% Mn was added, the alloy exhibited the best thermal conductivity (125.3 W / m·K) and tensile strength (278.9 MPa). After homogenization treatment, the MgZnCu phase underwent spheroidization. Following hot extrusion deformation, these spheroidized MgZnCu phases were uniformly dispersed around the grain boundaries along the extrusion direction, effectively pinning the magnesium matrix and improving the overall mechanical properties of the magnesium alloy. Furthermore, the addition of Mn resulted in uniform precipitation in clusters, and the volume fraction of the MgZnCu phase significantly increased, reducing lattice distortion in the α-Mg matrix and synergistically enhancing the alloy's thermal conductivity.

[0042] After hot extrusion deformation, dynamic recrystallization occurred in the extruded Mg-3Zn-3Cu, Mg-3Zn-3Cu-0.2Mn, Mg-3Zn-3Cu-0.6Mn, and Mg-3Zn-3Cu-1Mn alloys. Dynamic recrystallization mainly occurred along the original grain boundaries and the MgZnCu phase interface, with average grain sizes of 3.2±0.5 μm, 2.5±0.3 μm, 1.9±0.4 μm, and 2.2±0.5 μm, respectively. Among them, Mg-3Zn-3Cu-0.6Mn exhibited the best mechanical properties, with tensile strength, yield strength, and elongation reaching 267.2 MPa, 173.8 MPa, and 18.3%, respectively. (See [reference needed]). Figure 2 , Figure 3 , Figure 5 , Figure 6 , as well as Tables 1 and 2.

[0043] After hot extrusion deformation, Mn elements are uniformly distributed in the matrix in a clustered manner. Furthermore, the volume fraction of the second phase (MgZnCu phase) first increases and then decreases with increasing Mn content. Specifically, at an Mn content of 0.6 wt%, the volume fraction of the MgZnCu phase is 16.43%. The precipitation of the MgZnCu phase weakens the lattice distortion in the α-Mg matrix, thereby improving the thermal conductivity of the alloy. Therefore, Mg-3Zn-3Cu-0.6Mn possesses the best thermal conductivity of 125.3 W / m·K. (See [reference needed]). Figure 4 , Figure 7 , Figure 8 and Figure 9 .

[0044] 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-strength, high-thermal-conductivity Mg-Zn-Cu-Mn magnesium alloy, characterized in that, Includes the following steps: 1) Prepare metal raw materials according to the atomic percentage of each constituent element of the Mg-3Zn-3Cu-xMn alloy, where x is 0.6; 2) Alloy smelting: The raw materials Mg, Zn, Cu and Mn are mixed and smelted by flux covering and protected smelting method and then cast into as-cast alloy; 3) Homogenization treatment: The as-cast alloy is homogenized at a temperature of 430℃ for 48 hours. 4) Hot extrusion deformation: The homogenized Mg-3Zn-3Cu-xMn was subjected to hot extrusion deformation at a temperature of 260℃ and a speed of 0.5mm / s; the extrusion ratio of hot extrusion deformation was 25:

1.

2. The method for preparing a high-strength, high-thermal-conductivity Mg-Zn-Cu-Mn magnesium alloy according to claim 1, characterized in that, The alloy smelting process includes, in sequence, melting magnesium blocks, adding alloying elements Zn, adding alloying elements Cu and Mn, converter, alloy refining, casting and cooling, and ultrasonic cleaning.

3. The method for preparing a high-strength, high-thermal-conductivity Mg-Zn-Cu-Mn magnesium alloy according to claim 2, 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 20 minutes.

4. A method for preparing a high-strength, high-thermal-conductivity Mg-Zn-Cu-Mn magnesium alloy according to claim 2, characterized in that, The addition of alloying elements Zn, Cu, and Mn involves adding a preheated zinc block into the furnace, sprinkling a dried covering agent on the zinc block, closing the furnace lid, and heating to 750°C to melt the zinc block. The furnace is then opened a second time to clean the surface of the solution with a slag scraper. Preheated copper and manganese particles are added as needed for the experiment. After stirring, a covering agent is sprinkled on top, the furnace lid is closed, and the furnace is kept warm for 5 minutes.

5. The method for preparing a high-strength, high-thermal-conductivity Mg-Zn-Cu-Mn magnesium alloy according to claim 4, characterized in that, The aforementioned converter and alloy refining process involves transferring the melt to a holding furnace when the temperature reaches 750°C. After holding for 5 minutes, refining is then performed. When the temperature of the holding furnace reaches 750°C, the slag on the surface of the melt is removed, and refining is carried out. After refining, a layer of covering agent is evenly sprinkled on the surface of the melt to maintain the furnace temperature at a constant 750°C for 20 minutes.

6. A method for preparing a high-strength, high-thermal-conductivity Mg-Zn-Cu-Mn magnesium alloy according to claim 5, characterized in that, The casting and cooling process involves holding the metal at 750 °C for 20 minutes, then lowering the furnace temperature to 730 °C. The molten metal is then poured into the funnel gate. After the mold temperature naturally cools to room temperature, the sample is removed from the mold to obtain a cast alloy test bar.

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