Mg-Gd Alloy with Enhanced Mechanical Properties in Wide Temperature Range by Nanoparticles, Preparation Method and Application

Abstract

The present invention discloses an Mg-Gd alloy for enhancing mechanical properties in a wide temperature range by nanoparticles, a preparation method and an application thereof, comprising components in the following mass percentages: gadolinium 10-12 wt.%; aluminum nitride 0.3-1.0 wt.%; and the balance being magnesium; the magnesium is a mixture of pure magnesium and a magnesium-gadolinium master alloy. The present invention adopts the Mg-Gd alloy for enhancing mechanical properties in a wide temperature range by nanoparticles, the preparation method and the application thereof. By adding a nano AlN / Mg master alloy, nano AlN ceramic particles are introduced into a magnesium matrix. The nano AlN particles serve as heterogeneous nucleation sites for α-Mg to refine the alloy structure, improve the distribution of the Mg-Gd phase, and play a role in secondary phase strengthening, thereby improving the mechanical properties of the alloy and being conducive to further expanding the application of the magnesium alloy as key components in the fields of aerospace and automobile manufacturing.

Description

Technical Field

[0001] The present invention relates to the technical field of high-strength magnesium alloy preparation, and in particular to a Mg-Gd alloy for enhancing mechanical properties in a wide temperature range by nanoparticles, a preparation method thereof, and an application thereof. Background Art

[0002] As the lightest alloy among current metal structural materials, magnesium alloy not only has high specific strength and specific stiffness, but also has good vibration damping performance. In the automotive field, magnesium alloy can greatly reduce the weight of objects and thus reduce energy consumption. Therefore, achieving weight reduction through magnesium alloy materials has become an important trend in the automotive manufacturing industry. However, when an automobile experiences a low-temperature region, its components have to withstand long-term low temperature or high temperature during use. But when the temperature exceeds 175°C, the strength of the magnesium alloy will significantly decrease, unable to meet the use requirements of components at high temperatures. Therefore, it is necessary to improve the heat resistance of the magnesium alloy.

[0003] Mg-RE alloy is a high-strength magnesium alloy system that has been studied and applied more currently. Among them, the Mg-Gd alloy system has a simple composition and excellent high-temperature resistance, and can greatly reduce the mass of components in industrial production applications. However, at low temperatures, the plasticity of the Mg-Gd alloy system is general. When the temperature is higher than 200°C, the second phase still cannot effectively maintain the stability of the grain boundary. Therefore, the tensile strength of the alloy is weak, which greatly limits its application range, and it is necessary to explore relevant processes to regulate the microstructure of the Mg-Gd alloy system and improve the performance of the Mg-Gd alloy system.

[0004] In the prior art, the mechanical properties of magnesium alloys can be improved by methods such as adding external particles or in-situ particles to form magnesium matrix composites, heat treatment, hot extrusion, etc. Among them, AlN particles not only have the advantages of high melting point, high hardness, good thermal stability, etc., but also their crystal configuration and lattice parameters are similar to those of Mg, and they are very promising reinforcement phases in magnesium alloys. Therefore, introducing AlN particles into the Mg-Gd alloy and studying the regulation effect of AlN particles on the second-phase microstructure and matrix grains of the Mg-Gd alloy have important guiding significance and engineering application value for the development and application of high-strength magnesium alloys. Summary of the Invention

[0005] The purpose of the present invention is to provide a Mg-Gd alloy for enhancing mechanical properties in a wide temperature range by nanoparticles, a preparation method thereof, and an application thereof. By adding a nano AlN / Mg master alloy, nano AlN ceramic particles are introduced into the magnesium matrix. The nano AlN particles can serve as heterogeneous nucleation sites for α-Mg to refine the alloy microstructure, improve the distribution of the Mg-Gd phase, and play a role in second-phase strengthening, thereby improving the mechanical properties of the alloy, which is beneficial to further expanding the application of magnesium rare earth alloys as key components in the aerospace and automotive manufacturing fields.

[0006] To achieve the above object, the present invention provides a Mg-Gd alloy with enhanced mechanical properties over a wide temperature range by nanoparticles, comprising components in the following mass percentages:

[0007] Gadolinium 10 - 12 wt.%;

[0008] Aluminum nitride 0.3 - 1.0 wt.%;

[0009] The balance is magnesium;

[0010] The magnesium is a mixture of pure magnesium and a Mg-Gd master alloy.

[0011] Preferably, the aluminum nitride is an AlN / Mg master alloy containing 40 wt.% of nano-sized AlN ceramic particles, the purity of the pure magnesium is 99.8%, and the Mg-Gd master alloy is Mg-30 wt.% Gd with a purity of 99.9%.

[0012] Preferably, the average size of the nano-sized AlN ceramic particles is 350 nm, and the diameter of the nano-sized AlN ceramic particles is 150 - 500 nm.

[0013] To achieve the above object, the present invention also provides a method for preparing a Mg-Gd alloy with enhanced mechanical properties over a wide temperature range by nanoparticles, comprising the following steps:

[0014] S1. Raw material grinding: Grind the pure magnesium, the Mg-Gd master alloy, and the AlN / Mg master alloy.

[0015] S2. Alloy melting: Melt the ground pure magnesium obtained in S1 under a mixed gas protection, add the ground Mg-Gd master alloy obtained in S1 and melt it under the mixed gas protection, then add the ground AlN / Mg master alloy obtained in S1 and melt it under the mixed gas protection, and perform heat preservation stirring, slag removal, and casting to obtain an ingot.

[0016] S3. Homogenization treatment: Perform homogenization treatment on the ingot obtained in S2, and then air-cool the treated ingot to room temperature to obtain a billet.

[0017] S4. Extrusion treatment: Perform hot extrusion on the billet obtained in S3 to obtain an extruded bar.

[0018] Preferably, in S2, the mixed gas comprises 99% by volume of CO2 and 1% by volume of SF6.

[0019] Preferably, in S2, the melting temperature of the pure magnesium is 710 - 730 °C, the melting temperature of the Mg-Gd master alloy is 700 - 720 °C, and the melting temperature of the AlN / Mg master alloy is 790 - 800 °C.

[0020] Preferably, in S2, the temperature of the heat preservation and stirring is 780 - 800 °C. The heat preservation and stirring is first mechanical stirring and then ultrasonic stirring. The stirring speed of the mechanical stirring is 50 - 100 rpm, the stirring time is 5 - 7 min, the stirring frequency of the ultrasonic stirring is 19.5 - 20.7 kHz, and the stirring time is 3 - 5 min.

[0021] Preferably, in S3, the temperature of the homogenization treatment is 520 °C and the time is 12 h.

[0022] Preferably, in S4, the temperature of the hot extrusion is 430 °C and the extrusion ratio is 18:1.

[0023] To achieve the above object, the present invention also provides an application of a Mg - Gd alloy with enhanced wide - temperature mechanical properties by nanoparticles in key components in the fields of aerospace and automotive manufacturing in the north or the Arctic and Antarctic regions.

[0024] Therefore, the present invention adopts the above Mg - Gd alloy with enhanced wide - temperature mechanical properties by nanoparticles, its preparation method and application, and the beneficial effects are as follows:

[0025] (1) By adding nano - AlN ceramic particles to the alloy in the present invention, the nano - AlN ceramic particles have characteristics such as low density, high hardness, and high melting point. Introducing them into the magnesium alloy can strengthen the alloy by hindering dislocation movement and grain - boundary sliding. At the same time, the interface between the AlN ceramic particles and the Mg matrix is clean without inclusions, and there is a good lattice matching relationship with the magnesium matrix, which helps to reduce the α - Mg grain size during solidification and improve the mechanical properties of the alloy.

[0026] (2) In the melting process of the present invention, mechanical stirring and ultrasonic stirring are introduced to promote the uniform dispersion of nano - AlN ceramic particles, thereby significantly strengthening the high - temperature performance of the alloy and improving the low - temperature plasticity.

[0027] (3) By regulating the addition content of nano - AlN ceramic particles in the present invention, it is found that the second - phase structure in the alloy significantly increases, and the second - phase structure is evenly distributed in a dispersed manner within the grains. In the extruded state, when the addition amount of AlN is only 0.5 wt.%, the yield strength and tensile strength of the composite material at - 196 °C, 25 °C, and 250 °C are significantly higher than those of the Mg - Gd matrix alloy. Its low - temperature tensile performance has good strength and plasticity, and has excellent high - temperature mechanical properties, significantly improving the low - temperature, room - temperature, and high - temperature mechanical properties of the Mg - Gd alloy.

[0028] (4) By introducing low-content nano-AlN ceramic particles, the present invention can significantly improve the mechanical properties of Mg-Gd alloys. The mechanical properties in a wide temperature range (-196~250°C) can be applied not only in ordinary environments but also in colder conditions, such as in the north or even in the Arctic and Antarctic. The components prepared from this material solve the problems of heat generation and material property degradation caused by high temperature and continuous working conditions, and expand the application of magnesium alloys as key components in the fields of aerospace and automotive manufacturing.

[0029] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Description of the Drawings

[0030] Figure 1 is a scanning electron microscope image of the Mg-Gd alloy with improved mechanical properties in a wide temperature range by the nano-particles of the present invention. Among them, (a) is the scanning electron microscope image of the Mg-12Gd matrix alloy prepared in Comparative Example 1, and (b) is the scanning electron microscope image of the 0.5wt.% AlN / Mg-12Gd alloy prepared in Example 2.

[0031] Figure 2 is the tensile engineering stress-strain curve of the 0.5wt.% AlN / Mg-12Gd alloy prepared in Example 2 of the Mg-Gd alloy with improved mechanical properties in a wide temperature range by the nano-particles of the present invention. Detailed Embodiments

[0032] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0034] Example 1

[0035] A Mg-Gd alloy with improved mechanical properties in a wide temperature range by nano-particles, comprising the following components in mass percentage: gadolinium (Gd) 12wt.%, aluminum nitride (AlN) 0.3wt.%, and the balance being magnesium.

[0036] The preparation method includes the following steps:

[0037] S1. Raw material grinding: Grind pure magnesium, Mg-Gd master alloy, and AlN / Mg master alloy to remove surface stains and oxide scales, obtaining ground pure magnesium, ground Mg-Gd master alloy, and ground AlN / Mg master alloy.

[0038] Among them, the purity of pure magnesium is 99.8%; the purity of the magnesium-gadolinium master alloy (Mg-30wt.%Gd) is 99.9%, which is purchased from Chongqing Yuhua New Materials Technology Co., Ltd.; the AlN / Mg master alloy (40wt.% AlN / Mg master alloy) contains 40wt.% of nano-AlN ceramic particles, and its preparation method is as follows: Mg3N2 and pure aluminum powder with a mass ratio of 49.26:50.74 are ball-milled and then hot-pressed and sintered. The ball-milling speed is 280r / min; the ball-to-material ratio is 10:1; the hot-pressing and sintering temperature is 1000°C. Among them, Mg3N2 is purchased from Shanghai Xiangtian Nano Materials Co., Ltd., with a size of 2~8μm (average size of 5μm); pure aluminum powder is purchased from Beijing Xingrongyuan Technology Co., Ltd., with a size of 9~13μm (average size of 10μm), and the purity is 99.5%.

[0039] S2. Alloy melting: The polished pure magnesium obtained in S1 is melted in a resistance furnace at a temperature of 720°C under the protection of a mixed gas, then the polished magnesium-gadolinium master alloy obtained in S1 is added and melted again at a temperature of 700°C, and finally the polished AlN / Mg master alloy is added and melted again at a temperature of 800°C, and heat preservation and stirring are carried out. The heat preservation temperature is 790°C, and the stirring is first mechanical stirring (stirring speed is 50rpm, stirring time is 5min), and then ultrasonic stirring (ultrasonic frequency is 20.7kHz, stirring time is 5min); then slag is removed, and finally casting is carried out at a temperature of 700°C to obtain an 85mm diameter ingot.

[0040] Among them, the mixed gas is composed of 99% by volume of CO2 and 1% by volume of SF6; the mass ratio of pure magnesium, gadolinium content in the polished magnesium-gadolinium master alloy, and AlN content in the polished AlN / Mg master alloy in the ingot is 87.7:12:0.3, and the diameter of the nano-AlN ceramic particles is 150~500nm.

[0041] S3. Homogenization treatment: The ingot obtained in S2 is subjected to homogenization treatment at a temperature of 520°C for 12h, and the treated ingot is air-cooled to room temperature (25°C) to obtain a billet.

[0042] S4. Extrusion treatment: The billet obtained in S3 is hot-extruded at a temperature of 430°C, and the extrusion ratio is 18:1 to obtain an extrusion rod with a diameter of 20mm. The extrusion rod is a nano-particle reinforced Mg-Gd alloy, that is, 0.3wt.% AlN / Mg-12Gd.

[0043] Example 2

[0044] A Mg-Gd alloy with enhanced mechanical properties in a wide temperature range by nanoparticles, comprising the following components by mass percentage: gadolinium (Gd) 12 wt.%, aluminum nitride (AlN) 0.5 wt.%, and the balance being magnesium.

[0045] In this embodiment, the preparation method of the Mg-Gd alloy is exactly the same as that in Example 1. The difference lies in that in S2 of this embodiment, the mass ratio of pure magnesium in the ingot, the gadolinium content in the polished Mg-Gd master alloy, and the AlN content in the polished AlN / Mg master alloy is 87.5:12:0.5, and the diameter of the nano-AlN ceramic particles is 150 - 500 nm. The final alloy material obtained is 0.5 wt.% AlN / Mg-12Gd.

[0046] Example 3

[0047] A Mg-Gd alloy with enhanced mechanical properties in a wide temperature range by nanoparticles, comprising the following components by mass percentage: gadolinium (Gd) 12 wt.%, aluminum nitride (AlN) 1.0 wt.%, and the balance being magnesium.

[0048] In this embodiment, the preparation method of the Mg-Gd alloy is exactly the same as that in Example 1. The difference lies in that in S2 of this embodiment, the mass ratio of pure magnesium in the ingot, the gadolinium content in the polished Mg-Gd master alloy, and the AlN content in the polished AlN / Mg master alloy is 87:12:1, and the diameter of the nano-AlN ceramic particles is 150 - 500 nm. The final alloy material obtained is 1.0 wt.% AlN / Mg-12Gd.

[0049] Comparative Example 1

[0050] This comparative example is a Mg-12Gd matrix alloy, comprising the following components by mass percentage: gadolinium (Gd) 12 wt.%, and the balance being magnesium.

[0051] The preparation method includes the following steps:

[0052] S1. Raw material polishing: Both pure magnesium and the Mg-Gd master alloy are polished to remove surface stains and oxide scales, obtaining polished pure magnesium and polished Mg-Gd master alloy.

[0053] Among them, the purity of pure magnesium is 99.8%; the purity of the Mg-Gd master alloy (Mg-30 wt.% Gd) is 99.9%, purchased from Chongqing Yuhua New Material Technology Co., Ltd.

[0054] S2. Alloy Melting: The polished pure magnesium obtained in S1 is melted in a resistance furnace at 720 °C under the protection of a mixed gas, and then the polished magnesium-gadolinium master alloy obtained in S1 is added and melted again at 720 °C, and kept warm for 10 min, stirred to remove slag, and finally cast at 700 °C to obtain an ingot with a diameter of 85 mm.

[0055] Among them, the mixed gas is composed of 99% CO2 by volume fraction and 1% SF6 by volume fraction; the mass ratio of pure magnesium in the ingot to the gadolinium content in the polished magnesium-gadolinium master alloy is 88:12.

[0056] S3. Homogenization Treatment: The ingot obtained in S2 is homogenized at 520 °C for 12 h, and the homogenized ingot is air-cooled to room temperature (25 °C) to obtain a billet.

[0057] S4. Extrusion Treatment: The billet obtained in S3 is hot-extruded at 430 °C, and the extrusion ratio is 18:1 to obtain an extrusion bar with a diameter of 20 mm. The extrusion bar is Mg-12Gd alloy.

[0058] Experimental Tests

[0059] The alloy materials prepared in Examples 1-3 and Comparative Example 1 are analyzed for structure and properties.

[0060] Microstructural Analysis

[0061] As Figure 1 shown, Figure 1 in (a) is the scanning electron microscope image of the extruded Mg-12Gd matrix alloy prepared in Comparative Example 1, Figure 1 in (b) is the scanning electron microscope image of the extruded 0.5 wt.% AlN / Mg-12Gd alloy in Example 2. The introduction of nano-AlN ceramic particles can be observed that the volume fraction of micron-scale particulate Mg-rich rare earth phase in the alloy increases and the distribution becomes more uniform.

[0062] Mechanical Property Tests

[0063] By testing the low-temperature, room-temperature and high-temperature tensile properties of the alloy prepared in Example 2, the obtained tensile yield strength, tensile strength and fracture strain results are shown in Table 1.

[0064] Table 1 Performance Tests of Extruded Alloys at Different Temperatures

[0065]

[0066] Figure 2Engineering stress-strain curves of the 0.5 wt.% AlN / Mg-12Gd alloy prepared in Example 2 at different temperatures.

[0067] According to Table 1, compared with the room temperature yield strength and tensile strength of the 0.5 wt.% AlN / Mg-12Gd alloy prepared in Example 2, its yield strength and tensile strength at -196 °C are increased by 101 MPa and 156 MPa respectively, but its elongation only decreases by 3.2%; its yield strength at 250 °C only decreases by 6 MPa and its tensile strength only decreases by 17 MPa, but its elongation increases by 9.4%; indicating that the nano-AlN ceramic particles effectively improve the plasticity of the alloy while ensuring the strength of the Mg-Gd alloy, making it have excellent strength and plasticity at low and high temperatures.

[0068] Therefore, the present invention uses the above-mentioned nanoparticles to improve the mechanical properties of the Mg-Gd alloy with wide temperature range and its preparation method and application. By adding the nano-AlN / Mg master alloy, the nano-AlN ceramic particles are introduced into the magnesium matrix. The nano-AlN particles can act as heterogeneous nucleation sites of α-Mg to refine the alloy microstructure, improve the distribution of the Mg-Gd phase, and play a role in secondary phase strengthening, thereby improving the mechanical properties of the alloy, which is beneficial to further expanding the application of magnesium rare earth alloys as key components in the fields of aerospace and automotive manufacturing.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. Mg-Gd alloy with nanoparticles to improve mechanical properties over a wide temperature range, characterized in that: The following components are included in mass percentage: Gadolinium 10~12wt.%; Aluminum nitride 0.3~1.0wt.%; The balance is magnesium; The raw materials for preparing the nano-AlN ceramic particles include pure magnesium, an AlN / Mg master alloy containing 40 wt.% of nano-AlN ceramic particles, and a magnesium-gadolinium master alloy. The average size of the nano-AlN ceramic particles is 350 nm, and the diameter of the nano-AlN ceramic particles is 150-500 nm.

2. The Mg-Gd alloy with nanoparticles improving mechanical properties over a wide temperature range according to claim 1, characterized in that: The purity of the pure magnesium is 99.8%, and the magnesium-gadolinium master alloy is Mg-30wt.%Gd with a purity of 99.9%.

3. A method for preparing a Mg-Gd alloy with nanoparticles improving mechanical properties over a wide temperature range as claimed in any one of claims 1 to 2, characterized in that: The following steps are involved: S1. Raw material grinding: pure magnesium, magnesium-gadolinium master alloy and AlN / Mg master alloy are all ground; S2, alloy smelting: melting the polished pure magnesium obtained in S1 under the protection of a mixed gas, adding the polished magnesium-gadolinium master alloy obtained in S1 to melt under the protection of a mixed gas, and then adding the polished AlN / Mg master alloy obtained in S1 to melt under the protection of a mixed gas, and performing heat preservation stirring, slag removal, and casting to obtain an ingot; S3, homogenization treatment: homogenizing the ingot obtained in S2, and then air-cooling the treated ingot to room temperature to obtain an ingot; S4, extrusion treatment: hot extruding the billet obtained in S3 to obtain an extruded rod; In S2, the melting temperature of the pure magnesium is 710-730°C, the melting temperature of the magnesium-gadolinium master alloy is 700-720°C, and the melting temperature of the AlN / Mg master alloy is 790-800°C.

4. The method for preparing a Mg-Gd alloy with nanoparticles improving mechanical properties over a wide temperature range according to claim 3, characterized in that: In S2, the mixed gas includes 99% by volume of CO2 and 1% by volume of SF6.

5. The method for preparing a Mg-Gd alloy with nanoparticles improving mechanical properties over a wide temperature range according to claim 3, characterized in that: In S2, the temperature of the heat preservation stirring is 780~800℃, and the heat preservation stirring is first mechanical stirring and then ultrasonic stirring; the stirring speed of the mechanical stirring is 50~100rpm and the stirring time is 5~7min, and the stirring frequency of the ultrasonic stirring is 19.5~20.7kHz and the stirring time is 3~5min.

6. The method for preparing a Mg-Gd alloy with nanoparticles improving mechanical properties over a wide temperature range according to claim 3, characterized in that: In S3, the temperature of the homogenization treatment is 520° C. and the time is 12 hours.

7. The method for preparing a Mg-Gd alloy with nanoparticles improving mechanical properties over a wide temperature range according to claim 3, characterized in that: In S4, the hot extrusion temperature is 430° C. and the extrusion ratio is 18:

1.

8. A Mg-Gd alloy with nanoparticles as claimed in any one of claims 1 to 2 that improves mechanical properties over a wide temperature range, used as a key component in the aerospace and automobile manufacturing fields in the northern or southern polar regions.

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