A low-cost high-strength high-thermal-conductivity magnesium alloy without heat treatment and a preparation method thereof

Abstract

The application provides a heat treatment-free low-cost high-strength high-thermal-conductivity magnesium alloy and a preparation method thereof, and relates to the field of metal materials. The components and mass percentages of the alloy are as follows: Mn: 0.43-0.6 wt.%, Ca: 0.11-0.2 wt.%, an additive element, the additive element being any one or two of Zn, La or Ce, wherein Zn: 0-0.6 wt.%, Ce: 0-0.8 wt.%, La: 0-0.7 wt.%, the balance being Mg, unavoidable impurities being less than or equal to 0.1 wt.%, and the total amount of alloy elements being less than or equal to 2.3 wt.%. The high-strength high-thermal-conductivity magnesium alloy is obtained through smelting, pouring, turning processing and low-temperature extrusion treatment under the condition of omitting a heat treatment process, the strength and the thermal conductivity of the alloy are simultaneously improved, the thermal conductivity coefficient of the alloy at room temperature is greater than or equal to 130 W / Km, the yield strength is greater than or equal to 357 MPa, the alloy has excellent comprehensive performance and low-cost advantages, and is suitable for large-scale production of aerospace electronic heat dissipation components.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing, specifically relating to a low-cost, high-strength, and high-thermal-conductivity magnesium alloy that requires no heat treatment and its preparation method. Background Technology

[0002] Magnesium and magnesium alloys, as the lightest metallic structural materials, possess high specific strength, high specific stiffness, good dimensional stability, excellent damping performance, and machinability. They have become an important research direction in the field of lightweight high-performance structural materials and have shown broad application prospects in transportation, aerospace, and 3C products.

[0003] Pure magnesium has a room temperature thermal conductivity of approximately 158 W / km, but its strength is extremely low, making it difficult to meet the requirements of engineering applications that demand both high mechanical and thermal conductivity. Furthermore, alloying can improve the strength of magnesium alloys, but it significantly reduces thermal conductivity. For example, commercial AM60 magnesium alloy has a yield strength of 212 MPa and a thermal conductivity of 61 W / km; commercial ZK61 magnesium alloy has a yield strength of 220 MPa and a thermal conductivity of 96.4 W / km; and rare-earth magnesium alloy WE43 has a yield strength of 250 MPa and a thermal conductivity of 51.3 W / km. Therefore, it is evident that increasing the strength of magnesium alloys reduces thermal conductivity, and vice versa. In other words, it is difficult to simultaneously improve both mechanical and thermal properties, thus limiting the application of magnesium alloys in industrial heat dissipation devices.

[0004] To simultaneously improve the mechanical properties and thermal conductivity of magnesium alloys, existing technologies typically employ methods such as increasing the alloy content (generally >6%), multi-pass rolling with large reductions, and other large deformation processes combined with multi-stage high-temperature heat treatment. However, this leads to increased alloying costs, more complex processes, higher energy consumption, and lower yields, making it difficult to apply to industrial production. Therefore, how to simultaneously improve the mechanical properties and thermal conductivity of magnesium alloys and achieve industrial-scale production while reducing energy consumption, controlling alloy production costs, and simplifying processes is a pressing technical challenge that needs to be addressed. Summary of the Invention

[0005] To address the aforementioned technical challenges, this invention provides a heat-treasure-free, low-cost, high-strength, and high-thermal-conductivity magnesium alloy. The alloy, by mass percentage, comprises the following components: Mn: 0.43-0.6 wt.%, Ca: 0.11-0.2 wt.%, and additives, wherein the additives are any one or two of Zn, La, or Ce, with Zn: 0-0.6 wt.%, Ce: 0-0.8 wt.%, La: 0-0.7 wt.%, balance Mg, unavoidable impurities ≤0.1 wt.%, and total alloy element content ≤2.3 wt.%.

[0006] The preparation method of the magnesium alloy includes the following steps:

[0007] (1) Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 97-99:3-1, pure Mg, Mg-Mn, Mg-Ca, Mg-Ce, Mg-La master alloys and pure Zn are melted at 700-720℃, stirred for 15-20 minutes, and refined by blowing with argon gas. After standing and holding at the temperature for 25-40 minutes, magnesium alloy ingots are obtained by gravity casting into a preheated mold at 200-250℃.

[0008] (2) The magnesium alloy ingot obtained in step (1) is machined and extruded to obtain a low-cost, high-strength, and high-thermal-conductivity magnesium alloy that does not require heat treatment. The extrusion process involves holding the ingot at 250-260℃ for 2-3 hours, with an extrusion speed of 2.7-3.5 mm / s and an extrusion ratio of 6-7:1. The average grain size of the low-cost, high-strength, and high-thermal-conductivity magnesium alloy that does not require heat treatment is ≤1.6 μm, and the thermal conductivity at room temperature is ≥130 W / Km and the yield strength is ≥357 MPa.

[0009] Furthermore, the alloy is composed of the following components: Mn: 0.45-0.5 wt.%, Ca: 0.12-0.15 wt.%, Zn: 0.1-0.5 wt.%, Ce: 0.1-0.6 wt.%, La: 0.1-0.5 wt.%, balance Mg, and unavoidable impurities ≤0.09 wt.%.

[0010] Furthermore, the average grain size of the heat-free, low-cost, high-strength, and high-thermal-conductivity magnesium alloy obtained in step (2) is ≤1.4μm.

[0011] Compared with existing technologies that struggle to simultaneously improve alloy strength and thermal conductivity, this invention achieves the following superior effects through the synergistic regulation of component interactions, component ratios, processes, and process parameters:

[0012] (1) The total mass percentage of alloying elements in the existing technology is >6wt.%, resulting in high raw material costs; the total mass percentage of alloying elements added in this invention is ≤2.3wt., which significantly reduces raw material costs while achieving material lightweighting.

[0013] (2) Existing technologies mainly use multi-stage large deformation processes combined with multi-stage heat treatment processes, but this leads to high production costs and long production cycles. This invention reduces the number of large deformation processes and eliminates the need for high-temperature heat treatment processes. It only uses casting and low-temperature (≤260℃) extrusion processes, which significantly improves production efficiency by streamlining the process and is suitable for large-scale production.

[0014] (3) Existing technologies mainly produce high thermal conductivity alloys with relatively uniform microstructures and an average grain size ≥10μm. However, this invention achieves simultaneous improvement in alloy strength and thermal conductivity through multiple effects such as grain size, texture, grain boundaries, and second phase. The alloy has an average grain size ≤1.6μm and a layered heterogeneous microstructure with interwoven coarse and fine grains, achieving a synergistic improvement in strength and thermal conductivity. This includes fine recrystallized grains in the fine-grained region, which play a role in grain strengthening; the coarse-grained region consists of unrecrystallized grains containing a large number of residual dislocations and small-angle grain boundaries, contributing to dislocation strengthening and grain boundary strengthening effects; the fine-grained region has a weak basal texture, which helps to improve plasticity, while the coarse-grained region has a strong basal texture, which helps to improve strength. At the same time, a large number of nanoscale second-phase particles precipitate in the alloy, which can pin grain boundaries and reduce the concentration of solute atoms in the matrix, thus simultaneously enhancing the strength and thermal conductivity of the alloy. The resulting magnesium alloy possesses both high thermal conductivity and high strength, with a thermal conductivity of ≥130W / Km and a yield strength of ≥357MPa at room temperature. Compared with existing technologies, this invention has significant advantages in saving production costs, simplifying the process, and reducing energy consumption, while simultaneously improving the strength and thermal conductivity of the magnesium alloy, making it suitable for industrial production. Detailed Implementation

[0015] Example 1

[0016] The Mg-0.48Mn-0.11Ca-0.8Ce alloy, by mass percentage, consists of the following components: Mn: 0.48 wt.%, Ca: 0.11 wt.%, Ce: 0.8 wt.%, unavoidable impurities ≤ 0.08%, and the balance being Mg; the preparation method includes the following steps:

[0017] (1) Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 97:3, pure Mg, Mg-Mn, Mg-Ca and Mg-Ce master alloys were melted at 700℃, stirred for 20 minutes, and refined by blowing argon gas. After standing and holding at the temperature for 25 minutes, the magnesium alloy ingots were obtained by gravity casting into a mold at 200℃.

[0018] (2) The alloy ingot obtained in step (1) is machined and extruded to obtain a low-cost, high-strength, and high-thermal-conductivity magnesium alloy that does not require heat treatment. The extrusion process is carried out at 260°C for 2.7 hours, with an extrusion speed of 2.7 mm / s and an extrusion ratio of 7:1. The average grain size of the low-cost, high-strength, and high-thermal-conductivity magnesium alloy that does not require heat treatment is 1.2 μm, and the thermal conductivity of the alloy at room temperature is 135 W / Km and the yield strength is 361 MPa.

[0019] Example 2

[0020] The Mg-0.6Mn-0.2Ca-0.7La alloy, by mass percentage, consists of the following components: Mn: 0.6 wt.%, Ca: 0.2 wt.%, La: 0.7 wt.%, unavoidable impurities ≤ 0.1%, and the balance being Mg; the preparation method includes the following steps:

[0021] (1) Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 99:1, pure Mg, Mg-Mn, Mg-Ca and Mg-La master alloys were melted at 710℃, stirred for 15 minutes, and refined by blowing argon gas. After standing and holding at the temperature for 30 minutes, magnesium alloy ingots were obtained by gravity casting into a mold at 250℃.

[0022] (2) The alloy ingot obtained in step (1) is machined and extruded to obtain a low-cost, high-strength, and high-thermal-conductivity magnesium alloy that does not require heat treatment. The extrusion process is carried out at 250°C for 2.5 hours, with an extrusion speed of 3 mm / s and an extrusion ratio of 6.5:1. The average grain size of the low-cost, high-strength, and high-thermal-conductivity magnesium alloy that does not require heat treatment is 1.4 μm, and the thermal conductivity of the alloy at room temperature is 135 W / Km and the yield strength is 357 MPa.

[0023] Example 3

[0024] The Mg-0.43Mn-0.6Zn-0.12Ca-0.15La alloy, by mass percentage, consists of the following components: Mn: 0.43 wt.%, Zn: 0.6 wt.%, Ca: 0.12 wt.%, La: 0.15 wt.%, unavoidable impurities ≤ 0.1%, and the balance being Mg; the preparation method includes the following steps:

[0025] (1) Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 98:2, pure Mg, Mg-Mn, Mg-Ca, Mg-La master alloy and pure Zn were melted at 720℃, stirred for 15 minutes, and argon gas was introduced for refining. After standing and holding at the temperature for 40 minutes, the magnesium alloy ingot was obtained by gravity casting into a mold at 230℃.

[0026] (2) The alloy ingot obtained in step (1) is machined and extruded to obtain a low-cost, high-strength, and high-thermal-conductivity magnesium alloy that does not require heat treatment. The extrusion process is carried out at 255°C for 3 hours, with an extrusion speed of 3.5 mm / s and an extrusion ratio of 6:1. The average grain size of the low-cost, high-strength, and high-thermal-conductivity magnesium alloy that does not require heat treatment is 1.6 μm, and the thermal conductivity of the alloy at room temperature is 130 W / Km and the yield strength is 365 MPa.

[0027] Comparative Example 1

[0028] The publicly published paper (Shi, Hailong, et al., “Tailoring Microstructure via Rolling to Achieve Concurrent High Strength and Thermal Conductivity in Mg-Zn-Nd-Zr Alloys”, Materials, 2025, ISSN: 1996-1944) reports on Mg-Zn-Nd-Zr alloys, among which the best-performing Mg-5Zn-2Nd-0.4Zr alloy has the following mass percentages: Zn: 5.88 wt.%, Nd: 2.18 wt.%, Zr: 0.39 wt.%, with the balance being Mg. The preparation process of this comparative alloy includes the following steps: melting and casting into ingots at 760-780℃, followed by multi-pass rolling at 450℃ at a rolling speed of 20 m / min and a total reduction of 87.5%, with each pass followed by a 10-minute holding period in the furnace, and then homogenization treatment. The obtained Mg-5Zn-2Nd-0.4Zr alloy has an average grain size of 2.23 μm, a room temperature thermal conductivity of 123.1 W / Km, and a yield strength of 294 MPa.

[0029] Compared with Comparative Example 1, the present invention has the following advantages: In terms of cost, the total content of alloying elements in the present invention (≤2.3wt.%) is much lower than that in Comparative Example 1 (8.45wt.%), reducing production costs; in terms of process, the present invention adopts a process of direct low-temperature (≤260℃) extrusion after casting, eliminating the complex process of "multi-pass rolling + homogenization treatment" required in Comparative Example 1. In comparison, the process is shorter, energy consumption is lower, and efficiency is higher, making it suitable for continuous industrial production of large-size profiles; in terms of performance, the alloy structure obtained in the present invention is finer, with an average grain size ≤1.6μm (smaller than that disclosed in Comparative Example 1), and the thermal conductivity and yield strength of all embodiments are higher than those of Comparative Example 1, achieving a good match between thermal conductivity and strength, and showing excellent prospects for industrial application.

[0030] In summary, this invention replaces traditional thermally conductive magnesium alloys with low-alloy (total content ≤2.3 wt.%) high-strength, high-thermal-conductivity magnesium alloys, significantly reducing raw material costs and suppressing the negative impact of alloying elements on thermal conductivity. The use of a direct low-temperature (≤260℃) extrusion process after casting eliminates the need for a long-term high-temperature (>300℃) heat treatment step, shortening the process, saving energy, and making it suitable for large-scale production. All embodiments of this invention have different compositions, proportions, and process parameters, and the alloy properties obtained in each embodiment also differ. This demonstrates that the superior effects obtained by this invention are not determined by any single element, proportion, or process parameter, but are achieved through the interaction of components, proportions, processes, and the synergistic regulation of process parameters. This invention employs low-temperature (≤260℃) extrusion to obtain a layered heterogeneous structure with interwoven coarse and fine grains. Through a multi-level gradient design of "grain size-texture-grain boundary-second phase," a synergistic improvement in strength and thermal conductivity is achieved. Within the scope of protection of the claims of this invention, the average grain size of the alloy is ≤1.6μm, the thermal conductivity at room temperature is ≥130W / Km, and the yield strength is ≥357MPa, thereby breaking through the existing bottleneck of strength-thermal conductivity trade-off in magnesium alloys and realizing lightweight, low cost, high strength and high thermal conductivity integration.

Claims

1. A low-cost, high-strength, high-thermal-conductivity magnesium alloy that requires no heat treatment, characterized in that: The alloy consists of the following components by weight percentage: Composition: Mn: 0.43-0.6 wt.%, Ca: 0.11-0.2 wt.%, additives, wherein the additives are any one or both of La and Ce, wherein Ce: 0.8 wt.%, La: 0.7 wt.%, balance Mg, unavoidable impurities ≤0.1 wt.%, total alloying elements ≤2.3 wt.%; The preparation method of the magnesium alloy includes the following steps: (1) Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 97-99:3-1, pure Mg, Mg-Mn, Mg-Ca, Mg-Ce and Mg-La master alloys are melted at 700-720 ℃, stirred for 15-20 minutes, and refined by blowing with argon gas. After standing and holding at the temperature for 25-40 minutes, magnesium alloy ingots are obtained by gravity casting into a preheated mold at 200-250 ℃. (2) The magnesium alloy ingot obtained in step (1) is machined and extruded to obtain a low-cost, high-strength, and high-thermal-conductivity magnesium alloy that does not require heat treatment. The extrusion process is carried out at 250-260 ℃ for 2-3 hours, with an extrusion speed of 2.7-3.5 mm / s and an extrusion ratio of 6-7:

1. The average grain size of the low-cost, high-strength, and high-thermal-conductivity magnesium alloy that does not require heat treatment is ≤1.6 μm, and the thermal conductivity at room temperature is ≥130 W / (m·K) and the yield strength is ≥357 MPa.

2. The heat-treasure-free, low-cost, high-strength, and high-thermal-conductivity magnesium alloy according to claim 1, characterized in that: The average grain size of the heat-free, low-cost, high-strength, and high-thermal-conductivity magnesium alloy obtained in step (2) is ≤1.4 μm.