A lightweight magnesium-based alloy with low thermal expansion, excellent strength and plasticity and a preparation method thereof

Abstract

The present invention discloses a lightweight magnesium-based alloy with low thermal expansion, excellent strength and plasticity and a preparation method thereof: First, preparation of negative thermal expansion material Mn x Ge powder, wherein 2.5≦x≦3.5; 2. Prepared by vacuum hot pressing sintering (Mn x Ge+Al) / metal-based material: 1) the negative thermal expansion material Mn obtained in step 1 is added x Ge is mixed with aluminum powder and metal matrix powder in proportion and fully ground until the powders are mixed evenly to obtain (Mn x Ge+Al) / metal matrix mixed powder; 2) (Mn x The mixed powder of Ge+Al) / metal matrix is kept in a hot pressing furnace for 0.5 to 1.5 hours and cooled to obtain (Mn x Ge+Al) / metal-based materials. Mn x The composite addition of Ge and Al not only reduces the thermal expansion coefficient of the original WE43 magnesium alloy to match that of the copper alloy, but also improves its strength and plasticity.

Description

Technical Field

[0001] The present invention relates to the technical field of metal composite materials, and in particular to a lightweight magnesium-based alloy with low thermal expansion, excellent strength and plasticity, and a preparation method thereof. Background Art

[0002] Compared with other structural materials, magnesium and magnesium alloys have the advantages of low density, high specific strength, good vibration damping, and excellent casting performance. They have broad application prospects in the fields of automobiles, electronics, military industry, aerospace, etc., and are the third type of metal structural materials developed after steel and aluminum alloys.

[0003] However, in the fields of precision instruments and mechanical engineering, the high coefficient of thermal expansion (CTE) of magnesium alloy materials causes the workpiece to deform slightly when the temperature changes. The thermal stress generated inside it can easily cause information transmission distortion, accelerate the aging of the workpiece, and even produce microcracks that directly cause the workpiece to fail. When used in combination with other materials (such as aluminum alloy, copper alloy, steel, etc.), the thermal expansion coefficient of magnesium alloy with a higher CTE does not match that of other materials, resulting in inconsistent contraction between different materials when the external temperature changes. At the very least, internal stress will be generated to reduce the precision and life of the instrument, and at worst, it will cause material breakage and lead to safety accidents.

[0004] Introducing negative / low thermal expansion second-phase particles into the magnesium matrix is currently an effective way to reduce the thermal expansion coefficient of magnesium alloys. However, blindly introducing negative / low thermal expansion particles often sacrifices the original mechanical properties of the magnesium alloy, especially its plasticity. How to minimize the thermal expansion coefficient of magnesium alloys while maintaining their original mechanical properties or even improving their plasticity has become a pressing issue in the field of high-temperature magnesium alloy research. Summary of the Invention

[0005] The object of the present invention is to provide a lightweight magnesium-based alloy with low thermal expansion, excellent strength and plasticity and a preparation method thereof in view of the above problems.

[0006] In order to achieve its purpose, the present invention adopts the following technical solutions:

[0007] A method for preparing a lightweight magnesium-based alloy with low thermal expansion, excellent strength and plasticity comprises the following steps:

[0008] 1. Preparation of negative thermal expansion material Mn x Ge powder, wherein 2.5≦x≦3.5;

[0009] 2. Preparation by vacuum hot pressing sintering (Mn x Ge+Al) / metal-based materials:

[0010] 1) The negative thermal expansion material Mn obtained in step 1x Ge is mixed with aluminum powder and metal matrix powder in proportion and fully ground until the powders are mixed evenly to obtain (Mn x Ge+Al) / metal matrix mixed powder, in which Mn x The mass ratio of Ge powder, Al powder and metal matrix powder is 3-30:0-6:70-97, and the metal matrix powder is pure magnesium or magnesium alloy powder;

[0011] 2) The (Mn x The mixed powder of Ge+Al) / metal matrix is put into the mold, and vacuum is drawn in the hot pressing sintering furnace. The temperature is raised from room temperature to 500-550℃ at a rate of 15-25℃ / min, and the pressure is increased to 15-25MPa. The heat and pressure are kept for 0.5-1.5h, and finally cooled to room temperature with the furnace to obtain (Mn x Ge+Al) / metal-based materials.

[0012] Preferably, in step 1) of step 2, the Mn x The mass ratio of Ge powder, Al powder and metal matrix powder is 3-30:2-6:64-95 or 3-20:2-6:74-95 or 4-15:2-6:79-94 or 4-10:2-6:84-94 or 4-6:2-6:88-94 or 4-6:2.5-5.5:89-94 or 4-6:2.5-5.5:89-93 or 5:3-5:90-92 or 5:4-5:90-91 or 5:5:90.

[0013] Preferably, in the preparation method, the metal matrix is WE43 magnesium alloy.

[0014] Preferably, in the preparation method, the Mn x Ge powder, wherein x=3.

[0015] Preferably, in the preparation method, in step 1) of step 2, the negative thermal expansion material Mn x Ge, aluminum powder and metal matrix powder are put into a planetary ball mill in proportion and ball milled at a ball-to-material ratio of 8 to 12:1, a ball milling time of 2 to 3 hours, and a ball mill speed of 60 to 100 r / min.

[0016] Preferably, in the preparation method, in step 2), in the hot pressing sintering furnace, vacuum is drawn, and the temperature is raised from room temperature to 510-530°C at a heating rate of 20°C / min, while the pressure is increased to 18-22 MPa, and the heat and pressure holding time is 0.8-1.2 h.

[0017] Preferably, in the preparation method, the negative thermal expansion material Mn x The preparation of Ge includes the following steps:

[0018] 1) Weigh Mn powder and Ge powder according to the molar ratio, mix the weighed powders, and grind them thoroughly until the powders are evenly mixed;

[0019] 2) The mixed powder is put into a mold, and in a hot pressing sintering furnace, vacuum is applied, and the temperature is raised from room temperature to 850-950°C at a heating rate of 15-25°C / min, while the pressure is increased to 80-120 MPa, and the heat and pressure are kept for 5-7 hours, and then cooled to room temperature to obtain the negative thermal expansion material Mn x Ge block;

[0020] 3) The negative thermal expansion material Mn obtained in step 2) is x The Ge block is crushed and ground into powder to obtain the negative thermal expansion material Mn x Ge powder.

[0021] Preferably, in the preparation method, the negative thermal expansion material Mn x The sintering conditions of Ge in the hot pressing sintering furnace are: heating from room temperature to 900°C at a heating rate of 20°C / min, while pressurizing to 100 MPa, and keeping the temperature and pressure for 6 hours.

[0022] Preferably, in the preparation method, in step 1), the weighed Mn powder and Ge powder are mixed and placed in a planetary ball mill for 4 to 6 hours, with a ball-to-material ratio of 8 to 12:1 and a ball mill speed of 220 to 280 r / min.

[0023] The present invention provides a lightweight magnesium-based alloy with low thermal expansion, excellent strength and plasticity, which is prepared by any of the preparation methods described above.

[0024] The beneficial effects of the present invention are:

[0025] The negative thermal expansion material Mn was prepared by vacuum sintering. x Ge, the preparation method has the characteristics of simple operation and high synthetic purity, and is suitable for large-scale industrial production.

[0026] The present invention uses WE43 magnesium alloy as the metal matrix, and uses negative thermal expansion material Mn x The (Mn x Ge+Al) / WE43 alloy material. Mn x The combined addition of Ge and Al not only reduces the thermal expansion coefficient of the original WE43 magnesium alloy to match that of copper alloys, but also improves its strength and ductility. This magnesium-based alloy with low thermal expansion, excellent compressive strength and ductility is lightweight, easy to prepare and operate, and inexpensive, making it suitable for a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The X-ray diffraction analysis results of the negative thermal expansion material Mn3Ge prepared in Example 1 of the present invention;

[0028] Figure 2 This is a thermal expansion curve of the negative thermal expansion material Mn3Ge prepared in Example 1 of the present invention;

[0029] Figure 3 The X-ray diffraction analysis results of the x% Mn3Ge / WE43 alloy materials (x=3, 5, 7, 10, 15, 30) prepared in Example 1 of the present invention;

[0030] Figure 4 This is a scan of the energy spectrum of the x% Mn3Ge / WE43 alloy material (x=3, 5, 7, 10, 15, 30) prepared in Example 1 of the present invention;

[0031] Figure 5 (a) thermal expansion curve and (b) thermal expansion coefficient histogram of the x% Mn3Ge / WE43 alloy material (x=0, 3, 5, 7, 10, 15, 30) prepared in Example 1 of the present invention;

[0032] Figure 6 (a) Compression curves and (b) compression performance analysis data of the x% Mn3Ge / WE43 alloy materials (x=0, 3, 5, 7, 10, 15, 30) prepared in Example 1 of the present invention;

[0033] Figure 7 (a) Thermal expansion curves and (b) thermal expansion coefficient histograms of the Mn3Ge / WE43 material and the (5%Mn3Ge+y%Al) / WE43 alloy material (y=0, 3, 5) prepared in Example 1 of the present invention;

[0034] Figure 8 (a) Compression curve diagram and (b) compression performance analysis data of the Mn3Ge / WE43 material and (5%Mn3Ge+y%Al) / WE43 alloy material (y=0, 3, 5) prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0036] The experimental methods in the following examples are conventional methods unless otherwise specified; the materials used are conventional materials in the art and can be obtained commercially unless otherwise specified.

[0037] WE43 magnesium alloy is a Mg-RE alloy with the chemical composition of Mg-4%Y-3%RE(Nd, Gd)-0.5%Zr and a purity of 99.9%.

[0038] Example 1

[0039] 1. Preparation of Negative Thermal Expansion Material Mn3Ge Powder

[0040] Preparation of negative thermal expansion material Mn3Ge powder: First, weigh Mn powder (purity 99.98%) and Ge powder (purity 99.9999%) in molar ratio. Place the weighed powder in a planetary ball mill and ball mill for 5 hours, the ball mill speed is 250r / min, and the ball-to-material ratio is 10:1. The mixed powder is loaded into a graphite mold, vacuumed in a hot pressing sintering furnace, pressurized to 100MPa, heated to 900℃ and kept warm for 6 hours, and then cooled to room temperature to obtain a negative thermal expansion material Mn3Ge block. Smash the obtained Mn3Ge block, then place it in a mortar and grind it into powder to obtain the negative thermal expansion material Mn3Ge powder for later use. 2. Preparation of x% Mn3Ge / WE43 alloy material

[0041] The negative thermal expansion material Mn3Ge powder was weighed at a mass fraction of 0%, 3%, 5%, 7%, 10%, 15%, and 30% with the metal matrix WE43 powder (200 mesh), and mixed evenly in a planetary ball mill to obtain a Mn3Ge / WE43 mixed powder. The ball-to-material ratio of the ball milling mixture was 10:1, the ball milling time was 2.5 hours, and the ball mill speed was 80r / min. The mixed Mn3Ge / WE43 powder was placed in a graphite mold and the preparation of the x% Mn3Ge / WE43 alloy material was completed in a vacuum hot pressing sintering furnace: the mixed powder was placed in a hot pressing sintering furnace and vacuumed to 1×10 -5 Pa, heating from room temperature to 520℃ at a rate of 20℃ / min, while pressurizing to 20MPa, holding time 1h, cooling method is furnace cooling.

[0042] 3. Preparation of (5%Mn3Ge+y%Al) / WE43 Alloy

[0043] Al powder with a purity of 99.5% (particle size 1-3μm) was weighed at 0%, 3%, 5% by mass and 5% by mass of Mn3Ge powder and metal matrix WE43 powder (200 mesh), and mixed evenly in a planetary ball mill to obtain (5% Mn3Ge + y% Al) / WE43 mixed powder. The ball-to-material ratio of the ball milling mixture was 10:1, the ball milling time was 2.5h, and the ball mill speed was 80r / min. The mixed (5% Mn3Ge + y% Al) / WE43 powder was placed in a graphite mold and the preparation of the (5% Mn3Ge + y% Al) / WE43 alloy material was completed in a vacuum hot pressing sintering furnace: the mixed powder was placed in a hot pressing sintering furnace and vacuumed to 1×10 -5 Pa, heating from room temperature to 520℃ at a rate of 20℃ / min, while pressurizing to 20MPa, holding time 1h, cooling method is furnace cooling.

[0044] Example 2: Product Testing

[0045] 1. Negative thermal expansion material Mn3Ge

[0046] (1) X-ray diffraction analysis

[0047] The negative thermal expansion material Mn3Ge prepared in Example 1 was subjected to X-ray diffraction analysis, and the results were as follows: Figure 1 As shown. Figure 1 It can be seen that the X-ray diffraction peak of the prepared negative thermal expansion material coincides with the diffraction peak of Mn3Ge, and the sample also contains a small amount of Mn element.

[0048] (2) Thermal expansion curve

[0049] Draw the thermal expansion curve of the negative thermal expansion material Mn3Ge prepared in Example 1, as shown in FIG. Figure 2 As shown in the figure, it can be seen that Mn3Ge has negative thermal expansion in the temperature range of 60-120℃, and its corresponding thermal expansion coefficient is α2=-4.25×10 -6 K -1 , and exhibits low thermal expansion in the temperature ranges from room temperature to 60°C and from 120 to 220°C.

[0050] 2. x%Mn3Ge / WE43 alloy material

[0051] (1) X-ray diffraction analysis

[0052] X-ray diffraction analysis was performed on the negative thermal expansion material x% Mn3Ge / WE43 alloy material (x=3, 7, 10, 15, 30) prepared in Example 1. The results are as follows: Figure 3As shown in Figure 4, there is an obvious Mg diffraction peak in x% Mn3Ge / WE43, and Mg2Ge phase is generated due to the reaction between Mn3Ge and the metal matrix.

[0053] (2) Energy spectrum scanning component analysis

[0054] Figure 4 This is a scanned image of the energy spectrum of the x% Mn3Ge / WE43 alloy materials (x = 3, 5, 7, 10, 15, 30) prepared in Example 1. Combined with the SEM image and the scanned image, the metal matrix of the x% Mn3Ge / WE43 alloy material is composed of equiaxed Mg grains surrounded by a fine, continuous network of material. Large, irregularly sized second-phase particles contain a significant amount of Mn. During hot pressing, a significant amount of Ge diffuses from the Mn3Ge into the Mg matrix, forming Mg2Ge. The Gd element in the WE43 alloy powder shows a slight tendency to diffuse into the second-phase particles, and the Y element tends to be slightly enriched at the Mg grain boundaries.

[0055] (3) Thermal expansion coefficient analysis

[0056] Figure 5 (a) is a thermal expansion curve of the x% Mn3Ge / WE43 alloy material (x=0, 3, 5, 7, 10, 15, 30) prepared in Example 1, Figure 5 (b) is the corresponding thermal expansion coefficient bar graph. The thermal expansion coefficient (CTE) of the WE43 sample without Mn3Ge addition is α = 29.48 × 10 -6 K -1 With the continuous increase of Mn3Ge content, the CTE of Mn3Ge / WE43 alloy material continues to decrease. When the addition of Mn3Ge reaches 30%, its CTE decreases to α=20.83×10 -6 K -1 However, when the content of Mn3Ge / WE43 is 5%, the thermal expansion coefficient shows an abnormal phenomenon: the thermal expansion coefficient of 5% Mn3Ge / WE43 drops sharply, reaching the lowest value in this composition system, α = 15.66×10 -6 K -1 .

[0057] (4) Compression performance analysis

[0058] The metal compressive properties of the prepared samples were tested using conventional methods for metal sample performance testing, and their ultimate compressive strength, compressive yield strength and compressive strain were analyzed.

[0059] Figure 6 (a) is a compression curve diagram of the x% Mn3Ge / WE43 alloy material (x=0, 3, 5, 7, 10, 15, 30) prepared in Example 1, Figure 6 (b) is the corresponding compression performance analysis data.

[0060] from Figure 6 As can be seen from the figure, the ultimate compressive strength of the x% Mn3Ge / WE43 alloy gradually increases with increasing Mn3Ge content. When 30% Mn3Ge is added, the ultimate compressive strength of the material increases from 343MPa without Mn3Ge to 501MPa, an increase of 46.1%. However, the plasticity of the material shows a gradual deterioration trend with increasing Mn3Ge content. The compressive strain of the 30% Mn3Ge / WE43 alloy decreases from 16.7% without Mn3Ge to 9.9%. This shows that adding Mn3Ge alone to the WE43 alloy will increase the ultimate compressive strength of the material, but will lead to a decrease in the plasticity of the material.

[0061] 3. (5%Mn3Ge+y%Al) / WE43 alloy material

[0062] (1) Thermal expansion coefficient analysis

[0063] Figure 7 (a) is a thermal expansion curve diagram of the Mn3Ge / WE43 material and the (5%Mn3Ge+y%Al) / WE43 alloy material (y=0, 3, 5) prepared in Example 1. Figure 7 (b) is the corresponding thermal expansion coefficient bar graph. Adding 5% Mn3Ge to WE43 alloy can reduce the thermal expansion coefficient of WE43 from α=29.48×10 -6 ·K -1 Reduced to α = 15.66 × 10 -6 ·K -1 On this basis, the thermal expansion coefficient does not change much after adding 3% Al; however, after adding 5% Al, the thermal expansion coefficient of the material is further reduced, and the thermal expansion coefficient of (5% Mn3Ge + 5% Al) / WE43 is α = 14.76×10 -6 ·K -1 The thermal expansion coefficient of WE43 is 49.9% lower than that of the metal matrix, which is comparable to that of copper alloy. This shows that the composite addition (5% Mn3Ge + 5% Al) in WE43 has a significant effect on reducing the thermal expansion coefficient.

[0064] (2) Compression performance analysis

[0065] Figure 8 (a) is a compression curve diagram of the Mn3Ge / WE43 material and the (5%Mn3Ge+y%Al) / WE43 alloy material (y=0, 3, 5) prepared in Example 1. Figure 8(b) The corresponding compression performance analysis data. Adding 5% Mn3Ge to the WE43 alloy has a certain effect on improving its strength, but at the expense of plasticity. Adding Al in combination with 5% Mn3Ge can further improve the strength and plasticity of the material. With the increase of the Al content, the compressive strength and compressive strain of the (5% Mn3Ge + y% Al) / WE43 alloy material continue to increase. The best effect is achieved when the (5% Mn3Ge + 5% Al) composite is added, with its compressive strength reaching 454 MPa and the compressive strain as high as 17.8%. Compared with the metal matrix, its compressive strength increased by 32.4% and the compressive strain increased by 6.6%. Compared with the 5% Mn3Ge / WE43 alloy material, the addition of 5% Al increased the compressive strength by 28.6% and the compressive strain by 21.2%. Therefore, Al has a significant reinforcing and plasticizing effect on the WE43 alloy.

[0066] 4. Density of alloy materials

[0067] Table 1 shows the calculated density values of the materials involved in Example 1. According to the mixing rule of composite materials, the density calculation formula of (5% Mn3Ge + y% Al) / WE43 alloy material is given as follows:

[0068]

[0069] In formula (I), ρ mix , m, V are the density, total mass, and total volume of the alloy material, respectively; ω and ρ are the mass fraction and density of the corresponding substances. Mn3Ge =7.38g / cm 3 ,ρ Al =2.70g / cm 3 ,ρ WE43 =1.82g / cm 3 .

[0070] As can be seen from Table 1, the (Mn3Ge+Al) / WE43 alloy material still maintains the excellent lightweight properties of magnesium alloy, and its density is much lower than that of copper alloy (ρ Mn3Ge =7.38g / cm 3 ). Combined Figure 6 and Figure 7 , a magnesium-based alloy ((5%Mn3Ge+5%Al) / WE43) with a thermal expansion coefficient matching that of copper alloys, excellent strength and plasticity, and the advantage of being lighter than copper alloys.

[0071] Table 1

[0072]

Claims

1. A method for preparing a lightweight magnesium-based alloy with low thermal expansion, excellent strength and plasticity, comprising the following steps:

1. Preparation of negative thermal expansion material Mn x Ge powder, wherein 2.5≤x≤3.5； 2. Preparation by vacuum hot pressing sintering method (Mn x Ge+Al) / metal-based materials: 1) The negative thermal expansion material Mn obtained in step 1 x Ge is mixed with aluminum powder and metal matrix powder in proportion and fully ground until the powders are mixed evenly to obtain (Mn x Ge+Al) / metal matrix mixed powder, in which Mn x The mass ratio of Ge powder, Al powder and metal matrix powder is 3-30: 2-6: 70-97, and the metal matrix powder is WE43 magnesium alloy; 2) The (Mn x The mixed powder of Ge+Al) / metal matrix was loaded into a mold, and vacuum was applied to the hot pressing sintering furnace. The temperature was raised from room temperature to 500-550°C at a rate of 15-25°C / min, and the pressure was increased to 15-25 MPa. The temperature and pressure were kept at this temperature for 0.5-1.5 h, and the mixture was cooled to room temperature. x Ge+Al) / metal-based materials.

2. The preparation method according to claim 1, wherein: The Mn x Ge powder, where x=3.

3. The preparation method according to claim 1, wherein: In step 1) of step 2, the negative thermal expansion material Mn x Ge, aluminum powder and metal matrix powder are placed in a planetary ball mill in proportion and ball-to-material ratio is 8-12:

1. The ball milling time is 2-3 h and the ball mill speed is 60-100 r / min.

4. The preparation method according to claim 1, wherein: In step 2) of step 2, in a hot pressing sintering furnace, vacuum is drawn, and the temperature is raised from room temperature to 510-530°C at a heating rate of 20°C / min, while the pressure is increased to 18-22 MPa, and the holding time is 0.8-1.2 h.

5. The preparation method according to claim 1, wherein: The negative thermal expansion material Mn x The preparation of Ge includes the following steps: 1) Weigh Mn powder and Ge powder according to the molar ratio, mix the weighed powders, and grind them thoroughly until the powders are mixed evenly; 2) The mixed powder is placed in a mold, and in a hot pressing sintering furnace, vacuum is applied, and the temperature is raised from room temperature to 850-950°C at a heating rate of 15-25°C / min, while the pressure is increased to 80-120 MPa, and the temperature is kept at this temperature for 5-7 hours, and then cooled to room temperature to obtain the negative thermal expansion material Mn x Ge block; 3) The negative thermal expansion material Mn obtained in step 2) x The Ge block is crushed and ground into powder to obtain the negative thermal expansion material Mn x Ge powder.

6. The preparation method according to claim 5, characterized in that: Negative thermal expansion material Mn x The sintering conditions of Ge in the hot pressing furnace are: heating from room temperature to 900 °C at a rate of 20 °C / min, while pressurizing to 100 MPa, and holding time for 6 h.

7. The preparation method according to claim 5, characterized in that: In step 1), the weighed Mn powder and Ge powder are mixed and placed in a planetary ball mill for 4 to 6 hours, with a ball-to-material ratio of 8 to 12:1 and a ball mill speed of 220 to 280 r / min.

8. A lightweight magnesium-based alloy having low thermal expansion, excellent strength and ductility, characterized in that: The product is prepared by the preparation method according to any one of claims 1 to 7.

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