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

Abstract

The invention discloses a high-toughness flame-retardant magnesium alloy and a preparation method and application thereof. The invention belongs to the field of flame-retardant magnesium alloys. The problems that in the prior art, magnesium alloy is poor in flame retardance and low in obdurability are solved. The prepared high-toughness flame-retardant magnesium alloy is a novel Mg-Yb-Zn-Zr series flame-retardant alloy, and is a flame-retardant alloy which does not contain conventional elements such as Ca, Be, Gd and Y. According to the flame-retardant magnesium alloy developed by the invention, the flame-retardant point is higher than 1050 DEG C, the flame-retardant property is not lower than that of a flame-retardant magnesium alloy added with Ca in the prior art, and the flame-retardant magnesium alloy has excellent casting property and mechanical property, can meet various casting process conditions such as conventional gravity casting and semi-continuous casting, and can be further subjected to deformation processes such as extrusion to prepare a proper sample; the alloy can be applied to the fields of aerocars, aerospace and the like, does not contain Be, is harmless to human bodies and is suitable for large-scale industrial production and application.

Description

Technical Field

[0001] The invention belongs to the field of flame retardant magnesium alloys, and in particular relates to a high-strength and toughness 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. Mg-Zn series is one of the commercialized deformable magnesium alloys, which has a huge application market in rail transportation, aerospace, national defense and military industries. With the gradual development of low-altitude areas and the rapid development of flying cars, flying cars have also put forward an urgent demand for weight reduction. While achieving lightweight structure, lightweight materials are also required to have higher safety, especially flame retardant properties. Magnesium and magnesium alloys usually have very active physical properties. Therefore, for magnesium alloys used in aviation, flame retardant properties have become the biggest obstacle to their application, especially for commercial manned aircraft, which have very high requirements for the flame retardant properties of lightweight materials and need to be able to meet the flame retardant standards of civil aviation. However, the current commercial magnesium alloys have a low ignition point and poor flame retardant properties, which cannot meet the aviation flame retardant standards. Mg-Zn alloy is one of the commercialized deformable magnesium alloys, which has a huge application market in rail transportation, aerospace and other fields. However, in the prior art, the ignition point of Mg-Zn alloy is usually lower than 760℃, and the flame retardant performance is poor. In order to improve the flame retardant performance of Mg-Zn alloy, researchers have also developed a variety of methods, which mainly focus on adding rare earth elements Gd and Y, alkaline earth elements Be and Ca, etc., among which the most effective is to add Ca and Be. However, Be is harmful to the human body and is generally not recommended for practical application. Although Ca is harmless to the human body, its addition often needs to exceed 2wt.% to have good flame retardant performance. However, the addition of Ca exceeding 2wt.% will increase the thermal cracking tendency of the alloy, resulting in the inability to prepare large-sized or complex-structured components with Ca-added flame-retardant magnesium alloys. In addition, the addition of Ca will also seriously affect the subsequent deformation process, resulting in a large number of hot cracks in the alloy during extrusion or forging, and the formability and mechanical properties are significantly reduced, especially plasticity. Therefore, Ca-added flame-retardant Mg-Zn alloys are usually unable to be cast to produce large-sized and complex-structured components, and are also difficult to apply to the mass production of deformable magnesium alloy components, resulting in the Ca-added flame-retardant Mg-Zn alloys having no high practical value.

[0003] Therefore, the development of a magnesium alloy with high toughness and high flame retardancy is of great significance in promoting fields such as rail transportation, aerospace, and flying cars. Summary of the invention

[0004] The purpose of the present invention is to solve the problems of poor flame retardancy and low strength and toughness of magnesium alloys in the prior art. The present invention provides a high-strength and tough 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-strength and tough flame-retardant magnesium alloy, wherein the alloy has the following components in weight percentage:

[0007] Yb: 0.5-15%, Zn: 0.5-12%, Zr: 0.03-0.8%, M: 0-3%, and the balance is magnesium and inevitable impurities.

[0008] It is further defined that M is one of La, Ce, Nd, Sm, Sc, Cu and Si.

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

[0010] S1: weighing raw metals of magnesium ingot, zinc ingot, Mg-Yb master alloy, Mg-Zr master alloy and Mg-M master alloy according to the weight percentage of the alloy, descaling the raw metals and preheating them;

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

[0012] S3: Heat up, add zinc ingot after the raw metal in S2 is completely melted, and stir;

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

[0014] S5: heating, allowing the melt to stand, and casting to obtain a high-strength, tough, and flame-retardant magnesium alloy ingot;

[0015] S6: preheating the high-strength, toughness and flame-retardant magnesium alloy ingot obtained in S5, and completing extrusion to obtain a high-strength, toughness and 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 700-800° C. and the stirring time is 5-10 min.

[0019] It is further defined that the temperature in S5 is 650-750° C. and the casting mold is a water-cooled cast iron mold.

[0020] It is further defined that the preheating temperature of S6 is 280-360°C, the preheating time is 2-3h, the extrusion temperature is 280-360°C, the extrusion ratio is 7-28, and the extrusion speed is 0.1-1mm / s.

[0021] A third object of the present invention is to provide an application of the high-strength, toughness and flame-retardant magnesium alloy in a flying car.

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

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

[0024] (1) In view of the deficiencies of the prior art, the present invention proposes a novel flame-retardant magnesium alloy that does not contain conventional flame-retardant alloy elements such as Ca, Be, Gd, and Y, and a preparation method thereof. The flame-retardant magnesium alloy developed by the present invention has a flame-retardant performance that is not lower than that of the flame-retardant magnesium alloy with Ca added in the prior art, and a flame-retardant point that is higher than 1050°C. It also has excellent casting performance and mechanical properties, and can meet various casting process conditions such as conventional gravity casting and semi-continuous casting. It can also be further subjected to deformation processes such as extrusion to prepare suitable samples. The alloy of the present invention does not contain Be, is harmless to the human body, and is suitable for large-scale industrial applications.

[0025] (2) The present invention does not refer to any publicly reported flame-retardant magnesium alloys, and does not consider conventional flame-retardant alloying elements of magnesium alloys such as Ca, Be, Y, Sr, Nb, etc., but creatively develops a Mg-Yb-Zn-Zr series of flame-retardant alloys.

[0026] (3) The present invention adds Yb to the magnesium alloy, and Yb reacts with oxygen on the surface of the magnesium alloy melt to form a dense oxide film layer. The oxide film has a high melting point, excellent high temperature resistance and low thermal cracking properties, and the oxide film layer will not crack or burn at high temperatures. In addition, Yb diffuses quickly in the magnesium alloy and has surface diffusion characteristics. Therefore, when the present invention is burned, as time goes by, the thicker the Yb oxide film layer on the surface of the magnesium alloy, the more effectively it can isolate the contact between magnesium and oxygen, increase the ignition temperature of the magnesium alloy, and achieve a better flame retardant effect. The addition of Zn can not only improve the fluidity of the magnesium alloy melt, improve the casting performance of the alloy, and refine the grains, but also further improve the density and toughness of the film layer on the surface of the magnesium alloy melt, thereby reducing the cracking tendency of the flame retardant film layer formed on the surface and improving the protective effect of the film layer. The extrusion process used in the present invention can also further improve the toughness of the flame retardant magnesium alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1a is the SEM image of the high-strength and flame-retardant magnesium alloy ingot of Example 1, Figure 1 b is the SEM image of the high-strength and flame-retardant magnesium alloy ingot of Example 2, Figure 1 c is the SEM image of the high-strength and flame-retardant magnesium alloy ingot of Example 3, Figure 1 d is the SEM image of the high-strength and flame-retardant magnesium alloy of Example 1, Figure 1 e is the SEM image of the high-strength and flame-retardant magnesium alloy of Example 2, Figure 1 f is the SEM image of the high-strength, toughness and flame-retardant magnesium alloy of Example 3. 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 the alloy components Yb: 2%, Zn: 6%, Zr: 0.5%, 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 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 zinc ingot is added and stirred for 5 minutes. Then, after the melt temperature reaches 730°C, the Mg-30Zr master alloy is added and stirred for 10 minutes. Then, the furnace temperature is adjusted to 690°C and kept at a constant temperature for 30 minutes. A cylindrical water-cooled cast iron mold with a length of 1000 mm and a diameter of 90 mm is selected as the mold for casting, and finally a Mg-Yb-Zn-Zr alloy ingot is obtained.

[0032] Preheat the Mg-Yb-Zn-Zr alloy ingot to 320°C for 2h, set the temperature of the extrusion barrel and the die to 320°C, the extrusion temperature to 320°C, the extrusion ratio to 7, the extrusion speed to 0.1mm / s, and start extrusion to obtain a high-strength, tough, flame-retardant magnesium alloy.

[0033] Embodiment 2:

[0034] According to the mass ratio of the alloy components Yb: 15%, Zn: 0.5%, Zr: 0.03%, 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 the Mg-30Yb master alloy are put into 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 zinc ingot is added and stirred for 5 minutes. Then, after the melt temperature reaches 730°C, the Mg-30Zr master alloy is added and stirred for 8 minutes. Then the furnace temperature is adjusted to 690°C and kept at a constant temperature for 30 minutes. A cylindrical water-cooled cast iron mold with a length of 1000 mm and a diameter of 90 mm is selected as the mold for casting, and finally a Mg-Yb-Zn-Zr alloy ingot is obtained.

[0035] Preheat the Mg-Yb-Zn-Zr alloy ingot to 360°C for 3 hours, set the extrusion barrel and die temperature to 360°C, set the extrusion temperature to 360°C, the extrusion ratio to 28, and the extrusion speed to 0.5 mm / s, and start extrusion to obtain a high-strength, tough, flame-retardant magnesium alloy.

[0036] Embodiment 3:

[0037] According to the mass ratio of the alloy components Yb: 3%, Zn: 0.5%, Zr: 0.8%, and the balance Mg, they are weighed, descaling is carried out by mechanical grinding, preheating at 250°C for 30 minutes, then the magnesium ingot and the Mg-30Yb master alloy are put into 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 zinc ingot is added and stirred for 5 minutes. Then, after the melt temperature reaches 730°C, the Mg-30Zr master alloy is added and stirred for 10 minutes. Then, the furnace temperature is adjusted to 690°C and kept at a constant temperature for 30 minutes. A cylindrical water-cooled cast iron mold with a length of 1000 mm and a diameter of 90 mm is selected as the mold for casting, and finally a Mg-Yb-Zn-Zr alloy ingot is obtained.

[0038] Preheat the Mg-Yb-Zn-Zr alloy ingot to 280°C for 2 hours, preheat the extrusion barrel and die to 280°C, set the extrusion temperature to 280°C, the extrusion ratio to 7, the extrusion speed to 0.1 mm / s, and start extrusion to obtain a high-strength, tough, flame-retardant magnesium alloy.

[0039] Embodiment 4:

[0040] According to the mass ratio of the alloy components Yb: 4.5%, Zn: 12%, Zr: 0.4%, and the balance Mg, they are weighed, descaling is carried out by mechanical grinding, preheating at 250°C for 30 minutes, then the magnesium ingot and the Mg-30Yb master alloy are put into 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 zinc ingot is added and stirred for 5 minutes. Then, after the melt temperature reaches 730°C, the Mg-30Zr master alloy is added and stirred for 10 minutes. Then, the furnace temperature is adjusted to 690°C and kept at a constant temperature for 30 minutes. A cylindrical water-cooled cast iron mold with a length of 1000 mm and a diameter of 90 mm is selected as the mold for casting, and finally a Mg-Yb-Zn-Zr alloy ingot is obtained.

[0041] Preheat the Mg-Yb-Zn-Zr alloy ingot to 300°C for 2h. Preheat the extrusion barrel and die temperature to 300°C. Set the extrusion temperature to 300°C, the extrusion ratio to 18, and the extrusion speed to 0.1mm / s. Start extrusion to obtain a high-strength, tough, flame-retardant magnesium alloy.

[0042] Embodiment 5:

[0043] According to the mass ratio of the alloy components Yb: 0.5%, Zn: 5%, Zr: 0.5%, Sm: 1.5%, and the balance Mg, they are weighed, descaling is carried out by mechanical grinding, and preheating is carried out 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 to raise the furnace temperature to 730°C. When the charge is completely melted, the zinc ingot is added and stirred for 5 minutes. Then, after the melt temperature reaches 730°C, the Mg-30Zr master alloy is added and stirred for 10 minutes. Then, the furnace temperature is adjusted to 690°C and kept at a constant temperature for 30 minutes. A cylindrical water-cooled cast iron mold with a length of 1000 mm and a diameter of 90 mm is selected as the mold for casting to finally obtain a Mg-Yb-Zn-Sm-Zr alloy ingot.

[0044] Preheat the Mg-Yb-Zn-Sm-Zr alloy ingot to 305°C for 2h. Preheat the extrusion barrel and die temperature to 305°C. Set the extrusion temperature to 305°C, extrusion ratio to 7, extrusion speed to 0.1mm / s, and start extrusion to obtain a high-strength, tough, flame-retardant magnesium alloy.

[0045] Embodiment 6:

[0046] According to the mass ratio of the alloy components Yb: 2.5%, Zn: 2%, Zr: 0.3%, Cu: 2%, 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, the Mg-30Yb master alloy and the Mg-30Cu master alloy are placed in a crucible furnace, and a protective gas of CO2+2vol.%SF6 is introduced to raise the furnace temperature to 730°C. When the charge is completely melted, the zinc ingot is added and stirred for 5 minutes. Then, after the melt temperature reaches 730°C, the Mg-30Zr master alloy is added and stirred for 10 minutes. Then, the furnace temperature is adjusted to 690°C and kept at a constant temperature for 30 minutes. A cylindrical water-cooled cast iron mold with a length of 1000 mm and a diameter of 90 mm is selected as the mold for casting to finally obtain a Mg-Yb-Zn-Cu-Zr alloy ingot.

[0047] Preheat the Mg-Yb-Zn-Cu-Zr alloy ingot to 2800°C for 2 hours. Preheat the extrusion barrel and die temperature to 280°C. Set the extrusion temperature to 280°C, the extrusion ratio to 7, and the extrusion speed to 0.1 mm / s. Start extrusion to obtain a high-strength, tough, flame-retardant magnesium alloy.

[0048] Comparative Example 1:

[0049] According to the mass ratio of the alloy components Zn: 6%, Zr: 0.5%, 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 is 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, a zinc ingot is added and stirred for 5 minutes. Then, after the melt temperature reaches 730°C, a Mg-30Zr intermediate alloy is added and stirred for 10 minutes. The furnace temperature is then adjusted to 690°C and kept at a constant temperature for 30 minutes. A cylindrical water-cooled cast iron mold with a length of 1000 mm and a diameter of 90 mm is selected as the mold for casting to finally obtain a Mg-Zn-Zr alloy ingot.

[0050] Preheat the Mg-Zn-Zr alloy ingot to 300°C for 2h, preheat the extrusion barrel and die to 300°C, set the extrusion temperature to 300°C, the extrusion ratio to 7, the extrusion speed to 0.1mm / s, start extrusion, and obtain a magnesium alloy.

[0051] Comparative Example 2:

[0052] According to the mass ratio of the alloy components Ca: 3%, Zn: 6%, Zr: 0.5%, 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 the Mg-30Ca 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 zinc ingot is added and stirred for 5 minutes. Then, after the melt temperature reaches 730°C, the Mg-30Zr master alloy is added and stirred for 10 minutes. Then the furnace temperature is adjusted to 690°C and kept at a constant temperature for 30 minutes. A cylindrical water-cooled cast iron mold with a length of 1000 mm and a diameter of 90 mm is selected for casting, and finally a Mg-Ca-Zn-Zr alloy ingot is obtained.

[0053] Preheat the Mg-Ca-Zn-Zr alloy ingot to 360°C for 2h, preheat the extrusion barrel and die to 360°C, set the extrusion temperature to 360°C, the extrusion ratio to 18, the extrusion speed to 0.1mm / s, start extrusion, and obtain a magnesium alloy.

[0054] The mechanical properties and ignition point tests were performed on the alloys in Examples 1-6 and Comparative Examples 1-2.

[0055] Mechanical properties test method:

[0056] The flame retardant finished magnesium alloys obtained in Examples 1-6 and Comparative Examples 1-2 were machined to produce dog bone-shaped tensile rods with a gauge length of 36 mm, a gauge diameter of 6 mm, and a clamping section thread of M10. The mechanical properties were tested in accordance with the standard of GB / T 228.1-2010 "Methods for Uniaxial Tension Test of Metallic Materials". The test results are shown in Table 1.

[0057] Fire point test:

[0058] The flame retardant finished magnesium alloys obtained in Examples 1-6 and Comparative Examples 1-2 were machined to form 60 mm × 80 mm × 4 mm thin plates. 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

[0059] Table 1 Mechanical properties and ignition point test results of flame retardant magnesium alloys of Examples 1-6 and Comparative Examples 1-2

[0060]

[0061] As can be seen from Table 1, the yield strength and elongation at break of Examples 1-6 prepared by the present invention are very superior, 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 toughness and high-temperature flame retardancy; while the Mg-Zn-Zr alloy of Comparative Example 1, although the yield strength and elongation at break are similar to those of Examples 1-6, violent combustion occurs at 800°C, the ignition point is low, and the flame retardancy is poor; the Mg-Ca-Zn-Zr alloy of Comparative Example 2, because of the addition of Ca, does not burn at 1050°C, has a high ignition point, and has good flame retardancy, but has an elongation at break of only 2.3%, poor toughness, and is not easy to process.

[0062] 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-strength and flame-retardant magnesium alloy, characterized in that: The alloy components by weight percentage are as follows: Yb: 0.5-15%, Zn: 0.5-12%, Zr: 0.03-0.8%, M: 0-3%, and the balance is magnesium and inevitable impurities.

2. The high-strength and tough flame-retardant magnesium alloy according to claim 1, characterized in that: M is one of La, Ce, Nd, Sm, Sc, Cu and Si.

3. The method for preparing the high-strength and tough flame-retardant magnesium alloy according to claim 1 or 2, characterized in that: The method: S1: weighing raw metals of magnesium ingot, zinc ingot, Mg-Yb master alloy, Mg-Zr master alloy and Mg-M master alloy according to the weight percentage of the alloy, descaling the raw metals and preheating them; S2: Put the raw metals other than zinc ingot and Mg-Zr master alloy into the crucible furnace, and introduce the protective gas of CO2+SF6; S3: Heat up, add zinc ingot after the raw metal in S2 is completely melted, and stir; S4: After the zinc ingot added in S3 is completely melted, the temperature is raised, and the Mg-Zr master alloy is added and stirred; S5: heating, allowing the melt to stand, and casting to obtain a high-strength, tough, and flame-retardant magnesium alloy ingot; S6: preheating the high-strength, toughness and flame-retardant magnesium alloy ingot obtained in S5, and extruding the ingot to obtain a high-strength, toughness and 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 700-800°C, and the stirring time is 5-10 min.

7. The method according to claim 3, characterized in that The temperature in S5 is 650-750°C, and the casting mold is a water-cooled cast iron mold.

8. The method according to claim 3, characterized in that The preheating temperature of S6 is 280-360°C, the preheating time is 2-3h, the extrusion temperature is 280-360°C, the extrusion ratio is 7-28, and the extrusion speed is 0.1-1mm / s.

9. Use of the high-strength, toughness and flame-retardant magnesium alloy according to claim 1 or 2 in flying cars.

10. Application of the high-strength, toughness and flame-retardant magnesium alloy according to claim 1 or 2 in aerospace.

Images