High-thermal-conductivity flame-retardant magnesium alloy as well as preparation method and application thereof

Abstract

The invention discloses a high-thermal-conductivity flame-retardant magnesium alloy and a preparation method and application thereof. The invention belongs to the field of flame-retardant magnesium alloys. The problem that in the prior art, high flame retardance and high thermal conductivity of magnesium alloy are difficult to consider at the same time is solved. According to the prepared high-thermal-conductivity flame-retardant magnesium alloy, Mg-Yb-Ag-Mn series flame-retardant alloys are creatively developed, the flame-retardant points are all higher than 1050 DEG C, the flame-retardant standard of civil aviation is met, and the alloy does not contain Ca, Be, Y, Sr, Nb and other conventional flame-retardant elements, has excellent casting performance and high thermal conductivity, and is suitable for industrial production. And various casting process conditions such as conventional gravity casting, high-pressure casting and semi-continuous casting can be met. The alloy can be applied to high-end devices needing flame retardance and heat dissipation, such as electronic 3C shells, battery box shells, power system case assemblies and the like, and can also be applied to the fields of rail transit and aerospace. The invention does not contain Be, is harmless to human body, and is suitable for industrial production and application.

Description

Technical Field

[0001] The present invention belongs to the field of flame retardant magnesium alloys, and in particular relates to a high thermal conductivity flame retardant magnesium alloy and a preparation method and application thereof. Background Art

[0002] As the lightest metal structural material, magnesium alloy has the advantages of light density, high specific strength, good damping and shock absorption performance, excellent electromagnetic shielding performance, good thermal conductivity, easy processing, recyclability, etc. It has received great attention in many industries such as rail transportation and aerospace, and is considered to be one of the green lightweight structural materials. However, magnesium and magnesium alloys usually have very active physical properties, and flammability has become the biggest obstacle to their widespread application. With the rapid development of electronic 3C and new energy vehicles, many parts require materials to have excellent thermal conductivity and heat dissipation performance while being lightweight, but conventional flame-retardant magnesium alloys, such as alloys containing conventional flame-retardant elements such as Ca and Y, have poor thermal conductivity and cannot meet application requirements. Although adding Be to magnesium alloys can improve the flame retardancy of the alloy, it is less harmful to the human body. Therefore, there is currently no safe magnesium alloy that can meet both flame retardancy and high thermal conductivity. Adding silver (Ag) elements to magnesium alloys can improve the material's oxidation resistance and corrosion resistance, thereby improving flame retardancy; in addition, the addition of Ag can improve the fluidity of the magnesium alloy melt, so that the Mg-Ag alloy has die-castability, excellent thermal conductivity, biocompatibility and damping properties, and therefore, has attracted much attention in the aerospace, automotive, electronics and medical fields. The most representative QE22 alloy in the Mg-Ag alloy series has a flash point below 850°C, and its flame retardancy still cannot meet the flame retardancy standards of civil aviation. In the prior art, the flame retardancy of the alloy can be improved by further adding elements such as Ca, Y and Gd, but the addition of these elements will reduce the thermal conductivity of the Mg-Ag alloy, making it difficult to meet the required thermal conductivity requirements.

[0003] Therefore, developing a magnesium alloy with both high thermal conductivity and high flame retardancy is of great significance in promoting the widespread application of magnesium alloys in fields such as rail transportation and aerospace. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that it is difficult to achieve both high flame retardancy and high thermal conductivity of magnesium alloys in the prior art. The present invention provides a high thermal conductivity flame retardant magnesium alloy and a preparation method and application thereof.

[0005] The technical solution of the present invention is as follows:

[0006] One of the purposes of the present invention is to provide a high thermal conductivity flame retardant magnesium alloy, the alloy has the following components in weight percentage:

[0007] Yb: 0.5-15%, Ag: 0.5-6%, Mn: 0.03-0.5%, M: 0-3%, and the balance is magnesium and inevitable impurities.

[0008] It is further defined that M is one of Al, Zn, La, Sm, Ce and Nd.

[0009] A second object of the present invention is to provide a method for preparing a high thermal conductivity flame retardant magnesium alloy, the method comprising:

[0010] S1: weighing magnesium ingots, silver ingots, Mg-Yb master alloys, Mg-Mn master alloys and Mg-M master alloy raw metals according to the weight percentage of the alloys, descaling the raw metals and preheating them;

[0011] S2: Put the raw metals other than the silver ingot and the Mg-Mn master alloy into the crucible furnace, and introduce the protective gas of CO2+SF6;

[0012] S3: Heating, adding Mg-Mn master alloy after the raw metal of S2 is completely melted, and stirring;

[0013] S4: After the Mg-Mn master alloy added in S3 is completely melted, the temperature is raised, and the silver ingot is added and stirred;

[0014] S5: heating up and allowing the melt to stand to obtain a high thermal conductivity flame retardant magnesium alloy melt;

[0015] S6: gravity casting or high pressure casting is performed on the high thermal conductivity flame retardant magnesium alloy melt obtained in S5 to obtain a high thermal conductivity flame retardant magnesium alloy.

[0016] It is further defined that the preheating temperature in S1 is 200-300° C., and the preheating time is 20-40 minutes.

[0017] It is further defined that the protective gas in S2 is CO2 + 1 to 10 vol.% SF6.

[0018] It is further defined that the temperature in S3 is 700-800°C, and the stirring time is 5-10 min; the temperature in S4 is 700-710°C, and the stirring time is 5-7 min; and the temperature in S5 is 670-750°C.

[0019] It is further defined that the melt temperature during high pressure casting in S6 is 685-695°C.

[0020] It is further defined that the high pressure casting parameters of S6 are: injection pressure 110-130 MPa, injection rate 7.5-8.5 m / s, pressurization time 14-16 s, holding pressure 50-60 MPa, and holding time 11-12 s.

[0021] A third object of the present invention is to provide an application of the above-mentioned high thermal conductivity flame retardant magnesium alloy in rail transportation.

[0022] A fourth object of the present invention is to provide an application of the above-mentioned high thermal conductivity flame retardant magnesium alloy in aerospace.

[0023] Compared with the prior art, the advantages of the present invention are as follows:

[0024] (1) The flame retardant magnesium alloy developed in the present invention has a flame retardant point higher than 1050°C, which meets the flame retardant standards of civil aviation, and has excellent casting performance and thermal conductivity. It can be used in high-end devices that require both flame retardancy and heat dissipation, such as electronic 3C housings, battery boxes, and power system chassis components, and can also meet various casting process conditions such as conventional gravity casting, high-pressure casting, and semi-continuous casting.

[0025] (2) The present invention does not use any publicly reported flame-retardant magnesium alloy as a reference, and does not consider conventional flame-retardant alloy elements of magnesium alloys such as Ca, Be, Y, Sr, Nb, etc. Instead, the present invention creatively develops a series of Mg-Yb-Ag-Mn flame-retardant alloys, and the developed alloys have excellent flame retardancy and thermal conductivity.

[0026] (3) The Yb added in the present invention will form a dense oxide film layer with high temperature resistance and low thermal cracking resistance on the surface of the magnesium alloy melt, which can significantly improve the flame retardancy of the magnesium alloy. Regarding thermal conductivity, the Yb added in the present invention can also significantly reduce the solubility of the magnesium alloy melt to gases such as N2 and CO2, and reduce the gas content of the alloy; Yb is easy to combine with Ag during solidification to form a second phase distributed at the grain boundary; Yb combines with Ag and Mn to form a ternary AgMnYb phase, further reducing the solid solution atoms in the magnesium matrix; Ag is easy to segregate to defects, which will also reduce the Ag atomic content of the magnesium matrix; so the flame-retardant magnesium alloy prepared by the present invention also has high thermal conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 a is the SEM image of the high thermal conductivity flame retardant magnesium alloy of Example 1, Figure 1 b is the SEM image of the high thermal conductivity flame retardant magnesium alloy of Example 2, Figure 1 c is the SEM image of the high thermal conductivity flame retardant magnesium alloy of Example 3, Figure 1 d is the SEM image of the high thermal conductivity and flame retardant magnesium alloy of Example 4. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

[0030] Embodiment 1:

[0031] According to the mass ratio of alloy components, Yb: 4.5%, Ag: 3.5%, Mn: 0.3%, and the balance is Mg, they are weighed, descaling is carried out by mechanical grinding, preheated at 250°C for 30 minutes, and then the magnesium ingot and the Mg-30Yb master alloy are placed in a crucible furnace, and a protective gas of CO2+2vol.%SF6 is introduced, and the furnace temperature is raised to 730°C. When the charge is completely melted, the Mg-5Mn master alloy is added, stirred for 10 minutes, and then the furnace temperature is adjusted to 710°C, and the silver ingot is added, stirred for 5 minutes, and then the furnace temperature is adjusted to 690°C, and the mixture is allowed to stand at a constant temperature for 30 minutes, and then cast to obtain a Mg-Yb-Ag-Mn alloy.

[0032] Embodiment 2:

[0033] According to the mass ratio of the alloy components, Yb: 2.5%, Ag: 2.1%, Mn: 0.3%, and the balance Mg, they are weighed, descaling is carried out by mechanical grinding, and the alloy is preheated at 250°C for 30 minutes. Then, the magnesium ingot and the Mg-30Yb master alloy are placed in a crucible furnace, and a protective gas of CO2+2vol.%SF6 is introduced. The furnace temperature is raised to 720°C. When the charge is completely melted, the Mg-5Mn master alloy is added, stirred for 5 minutes, and then the furnace temperature is adjusted to 710°C, the silver ingot is added, stirred for 10 minutes, and then the furnace temperature is adjusted to 690°C. The alloy is allowed to stand at a constant temperature for 30 minutes to obtain a Mg-Yb-Ag-Mn alloy melt.

[0034] The Mg-Yb-Ag-Mn alloy melt was subjected to high-pressure die casting, with a melt temperature of 690°C, an injection pressure of 120 MPa, an injection rate of 8 m / s, a pressurization time of 15 ms, a holding pressure of 55 MPa, a holding time of 12 s, a die-casting mold of 60 mm×80 mm×2.6 mm, and a mold temperature of 220°C. After die casting, it was heat treated at 200°C for 24 h to obtain the Mg-Yb-Ag-Mn alloy.

[0035] Embodiment 3:

[0036] According to the mass ratio of the alloy components, Yb: 3.5%, Ag: 6%, Mn: 0.03%, and the balance Mg, they are weighed, descaling is carried out by mechanical grinding, and the alloy is preheated at 250°C for 30 minutes. Then, the magnesium ingot and the Mg-30Yb master alloy are placed in a crucible furnace, and a protective gas of CO2+2vol.%SF6 is introduced. The furnace temperature is raised to 720°C. When the charge is completely melted, the Mg-5Mn master alloy is added, stirred for 5 minutes, and then the furnace temperature is adjusted to 710°C, the silver ingot is added, stirred for 10 minutes, and then the furnace temperature is adjusted to 690°C. The alloy is allowed to stand at a constant temperature for 30 minutes to obtain a Mg-Yb-Ag-Mn alloy melt.

[0037] The Mg-Yb-Ag-Mn alloy melt was subjected to high-pressure die casting, with a melt temperature of 690°C, an injection pressure of 120 MPa, an injection rate of 8 m / s, a pressurization time of 15 ms, a holding pressure of 55 MPa, a holding time of 12 s, a die-casting mold of 60 mm×80 mm×2.6 mm, and a mold temperature of 220°C. After die casting, it was heat treated at 200°C for 24 h to obtain the Mg-Yb-Ag-Mn alloy.

[0038] Embodiment 4:

[0039] According to the mass ratio of the alloy components, Yb: 15%, Ag: 0.5%, Mn: 0.5%, and the balance Mg, they are weighed, descaling is carried out by mechanical grinding, preheating is carried out at 250°C for 30 minutes, and then the magnesium ingot and the Mg-30Yb master alloy are placed in a crucible furnace, and a protective gas of CO2+2vol.%SF6 is introduced, and the furnace temperature is raised to 720°C. When the charge is completely melted, the Mg-5Mn master alloy is added, stirred for 10 minutes, and then the furnace temperature is adjusted to 710°C, and the silver ingot is added, stirred for 5 minutes, and then the furnace temperature is adjusted to 690°C, and the mixture is allowed to stand at a constant temperature for 30 minutes, and then cast to obtain a Mg-Yb-Ag-Mn alloy.

[0040] Embodiment 5:

[0041] According to the mass ratio of the alloy components Yb: 4.5%, Ag: 0.5%, Mn: 0.3%, Al: 3.5%, and the balance Mg, they are weighed, descaling is carried out by mechanical grinding, and the alloy is preheated at 250°C for 30 minutes. Then, the magnesium ingot and the Mg-30Yb master alloy are placed in a crucible furnace, and a protective gas of CO2+2vol.%SF6 is introduced. The furnace temperature is raised to 720°C. When the charge is completely melted, the Mg-5Mn master alloy is added, stirred for 5 minutes, and then the furnace temperature is adjusted to 710°C, and silver ingots and aluminum ingots are added, stirred for 5 minutes, and then the furnace temperature is adjusted to 690°C. The alloy is allowed to stand at a constant temperature for 30 minutes to obtain a Mg-Yb-Al-Ag-Mn alloy melt.

[0042] The Mg-Yb-Al-Ag-Mn alloy melt was subjected to high-pressure die casting, with a melt temperature of 690°C, an injection pressure of 120 MPa, an injection rate of 8 m / s, a pressurization time of 15 ms, a holding pressure of 55 MPa, a holding time of 12 s, a die-casting mold of 60 mm×80 mm×2.6 mm, and a mold temperature of 220°C. After die casting, it was heat treated at 200°C for 16 h to obtain the Mg-Yb-Al-Ag-Mn alloy.

[0043] Embodiment 6:

[0044] According to the mass ratio of the alloy components, Yb: 0.5%, Ag: 2.1%, Mn: 0.03%, Sm: 2.6%, and the balance Mg, they are weighed, descaling is carried out by mechanical grinding, and the alloy is preheated at 250°C for 30 minutes. Then, the magnesium ingot, Mg-30Yb master alloy and Mg-20Sm master alloy are put into a crucible furnace, and a protective gas of CO2+2vol.%SF6 is introduced. The furnace temperature is raised to 720°C. When the charge is completely melted, the Mg-5Mn master alloy is added, stirred for 10 minutes, and then the furnace temperature is adjusted to 710°C, and silver ingots and aluminum ingots are added, stirred for 10 minutes. Then, the furnace temperature is adjusted to 690°C, and the alloy is allowed to stand at a constant temperature for 30 minutes to obtain a Mg-Yb-Sm-Ag-Mn alloy melt.

[0045] The Mg-Yb-Sm-Ag-Mn alloy melt was subjected to high-pressure die casting with a melt temperature of 690°C, an injection pressure of 110 MPa, an injection rate of 8.5 m / s, a pressurization time of 16 ms, a holding pressure of 60 MPa, a holding time of 12 s, a die-casting mold of 60 mm × 80 mm × 2.6 mm, and a mold temperature of 220°C. After die casting, it was heat treated at 220°C for 24 h to obtain the Mg-Yb-Sm-Ag-Mn alloy.

[0046] Comparative Example 1:

[0047] According to the mass ratio of alloy components Y: 4.5%, Ag: 3.5%, Mn: 0.3%, and the balance Mg, they are weighed, descaling is carried out by mechanical grinding, preheated at 250°C for 30 minutes, and then the magnesium ingot and Mg-30Y master alloy are placed in a crucible furnace, and a protective gas of CO2+2vol.%SF6 is introduced, and the furnace temperature is raised to 730°C. When the charge is completely melted, the Mg-5Mn master alloy is added, stirred for 5 minutes, and then the furnace temperature is adjusted to 710°C, the silver ingot is added, stirred for 10 minutes, and then the furnace temperature is adjusted to 690°C, and the mixture is allowed to stand at a constant temperature for 30 minutes, and then cast to obtain a Mg-Y-Ag-Mn alloy.

[0048] Comparative Example 2:

[0049] According to the mass ratio of the alloy components Ag: 2.1%, Mn: 0.3%, Nd: 2.5%, and the balance Mg, they are weighed, descaling is carried out by mechanical grinding, and the alloy is preheated at 250°C for 30 minutes. Then, the magnesium ingot and the Mg-20Nd master alloy are placed in a crucible furnace, and a protective gas of CO2+2vol.%SF6 is introduced. The furnace temperature is raised to 730°C. When the charge is completely melted, the Mg-5Mn master alloy is added, stirred for 5 minutes, and then the furnace temperature is adjusted to 710°C, the silver ingot is added, stirred for 50 minutes, and then the furnace temperature is adjusted to 690°C. The alloy is allowed to stand at a constant temperature for 30 minutes to obtain a Mg-Nd-Ag-Mn alloy melt.

[0050] The Mg-Nd-Ag-Mn alloy melt was subjected to high-pressure die casting with a melt temperature of 690°C, an injection pressure of 120 MPa, an injection rate of 8 m / s, a pressurization time of 15 ms, a holding pressure of 55 MPa, a holding time of 12 s, a die-casting mold of 60 mm×80 mm×2.6 mm, and a mold temperature of 220°C. After die casting, it was heat treated at 200°C for 24 h to obtain a Mg-Nd-Ag-Mn alloy.

[0051] The mechanical properties and ignition point tests were performed on the alloys in Examples 1-6 and Comparative Examples 1-2.

[0052] Mechanical properties test method:

[0053] The magnesium alloys obtained in Examples 1-6 and Comparative Examples 1-2 were machined to produce original sheets with a diameter of 11.8 mm and a thickness of 2.6 mm for thermal conductivity testing. The thermal conductivity testing method was based on the ASTM-E1461 "Metallic Material Thermal Conductivity Test" standard to test the thermal conductivity at room temperature. The test results are shown in Table 1.

[0054] Fire point test:

[0055] The magnesium alloy obtained in Example 1, Example 4 and Comparative Example 1 was machined to form 60 mm × 80 mm × 2.6 mm thin sheets, which were tested for ignition point together with the metal thin sheets prepared in other Examples and Comparative Examples. The ignition point test method was in accordance with ASTM E659-17 "Standard Test Method for Autoignition Temperature of Liquid Chemicals". The test results are shown in Table 1

[0056] Table 1 Thermal conductivity and ignition point test results of magnesium alloys of Examples 1-6 and Comparative Examples 1-2

[0057]

[0058]

[0059] It can be seen from Table 1 that the thermal conductivity of Examples 1-6 prepared by the present invention is excellent, and no combustion occurs at a high temperature of 1050°C, which shows that the flame-retardant magnesium alloy prepared by the present invention has high thermal conductivity and high-temperature flame retardancy; while although the thermal conductivity of Comparative Example 2 is similar to that of Examples 1-6, it burns violently at 900°C, has a low ignition point, and has poor flame retardancy; Comparative Example 1 burns at 1000°C, has a low ignition point, and has relatively poor flame retardancy, and the thermal conductivity coefficient is only half of that of Examples 1-6, and the thermal conductivity is also not good.

[0060] The above are only preferred specific embodiments of the present invention, which are all different implementations based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A high thermal conductivity flame retardant magnesium alloy, characterized in that: The alloy components by weight percentage are as follows: Yb: 0.5-15%, Ag: 0.5-6%, Mn: 0.03-0.5%, M: 0-3%, and the balance is magnesium and inevitable impurities.

2. The high thermal conductivity flame retardant magnesium alloy according to claim 1, characterized in that: M is one of Al, Zn, La, Sm, Ce and Nd.

3. The method for preparing the high thermal conductivity flame retardant magnesium alloy according to claim 1 or 2, characterized in that: The method: S1: weighing magnesium ingots, silver ingots, Mg-Yb master alloys, Mg-Mn master alloys and Mg-M master alloy raw metals according to the weight percentage of the alloys, descaling the raw metals and preheating them; S2: Put the raw metals other than the silver ingot and the Mg-Mn master alloy into the crucible furnace, and introduce the protective gas of CO2+SF6; S3: Heating, adding Mg-Mn master alloy after the raw metal of S2 is completely melted, and stirring; S4: After the Mg-Mn master alloy added in S3 is completely melted, the temperature is raised, and the silver ingot is added and stirred; S5: heating up and allowing the melt to stand to obtain a high thermal conductivity flame retardant magnesium alloy melt; S6: gravity casting or high pressure casting is performed on the high thermal conductivity flame retardant magnesium alloy melt obtained in S5 to obtain a high thermal conductivity flame retardant magnesium alloy.

4. The method according to claim 3, characterized in that: The preheating temperature in S1 is 200-300°C, and the preheating time is 20-40 minutes.

5. The method according to claim 3, characterized in that: The protective gas in S2 is CO2 + 1~10vol.% SF6.

6. The method according to claim 3, characterized in that The temperature in S3 is 700-800°C, and the stirring time is 5-10 min; the temperature in S4 is 700-710°C, and the stirring time is 5-7 min; the temperature in S5 is 670-750°C.

7. The method according to claim 3, characterized in that The melt temperature during S6 medium and high pressure casting is 685~695℃.

8. The method according to claim 3, characterized in that The high pressure casting parameters of S6 are: injection pressure 110-130MPa, injection rate 7.5-8.5m / s, pressurization time 14-16s, holding pressure 50-60MPa, and holding time 11-12s.

9. Application of the high thermal conductivity flame retardant magnesium alloy according to claim 1 or 2 in rail transportation.

10. Application of the high thermal conductivity flame retardant magnesium alloy according to claim 1 or 2 in aerospace.

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