Low-alloying high-speed extrusion flame-retardant magnesium alloy as well as preparation method and application thereof

Abstract

The invention discloses a low-alloying high-speed extrusion flame-retardant magnesium alloy as well as a preparation method and application thereof. The alloy is prepared from the following components in percentage by mass: 0.3 to 1.5 percent of Al, 0.3 to 0.7 percent of Mn, 0.1 to 0.5 percent of Ca, 0.3 to 1.5 percent of Ce, 0.2 to 1.0 percent of Y and the balance of Mg and inevitable impurities. According to the low-alloying high-speed extrusion flame-retardant magnesium alloy provided by the invention, a trace amount of mixed rare earth elements Ce and Y and a trace amount of non-rare earth elements Al, Mn and Ca are added, so that the low-alloying high-speed extrusion flame-retardant magnesium alloy has the remarkable advantage of low cost. The aluminum alloy can be extruded at 250-450 DEG C at the highest extrusion speed of 60m / min, and shows extrudability comparable to that of aluminum alloy. The ultimate tensile strength at the room temperature in the extrusion state is 240 MPa or above, the yield strength is 200 MPa or above, the ductility is 10% or above, the ignition point is 800 DEG C or above, and excellent comprehensive mechanical property and flame retardant property are shown; the method has important significance in further promoting the application of the magnesium alloy extruded profile in the fields of rail transit, aerospace and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloys, and in particular to a low-alloyed high-speed extruded flame-retardant magnesium alloy and a preparation method and application thereof. Background Art

[0002] As a lightweight and high-strength metal material, magnesium alloy has shown broad application prospects in high-tech fields such as rail transportation and aerospace due to its low density, high specific strength, high specific stiffness, excellent machinability and good recyclability. However, despite the many advantages of magnesium alloy, it still faces some technical difficulties in its actual application, which limits its further promotion and application.

[0003] First, the plastic deformation capacity of magnesium alloys is relatively weak. Due to the close-packed hexagonal structure of magnesium, its plastic deformation capacity is difficult to compare with that of aluminum with a face-centered cubic structure. This characteristic makes it difficult to achieve high-speed extrusion during the extrusion process of most magnesium alloys, thus limiting the application of magnesium alloys in fields that require high-efficiency production.

[0004] Secondly, magnesium alloys pose safety risks during smelting and use. Magnesium has a low ignition point and is prone to spontaneous combustion. Once ignited, the fire is extremely difficult to extinguish. This characteristic requires additional safety measures during the smelting and processing of magnesium alloys, increasing production costs and complexity.

[0005] In addition, after high-speed extrusion, magnesium alloys are prone to defects such as overburning, cracks, and peeling on the alloy surface. Moreover, during the high-speed extrusion process, the temperature rise generated will cause the alloy structure to coarsen significantly, which in turn leads to a decrease in the mechanical properties of the magnesium alloy. At the same time, the commonly used commercial Mg-Al and Mg-Zn alloys contain a large amount of low-melting-point Mg-Al phase and Mg-Zn phase. During the high-speed extrusion process, the second phase is prone to decomposition, forming local melting, thereby forming defects such as cracks on the alloy surface. These problems make it difficult for these two types of alloys to achieve high-speed extrusion.

[0006] In order to overcome these technical difficulties, at present, there are two main methods for achieving high-speed extrusion of magnesium alloys: one is low alloying. For example, CN 106756365 B discloses a low-cost, low-alloyed Mg-Zn-Ca-Mn alloy, which can be produced at an extrusion speed of not less than 24m / min. The second is to contain a high melting point phase. For example, CN 105154734A discloses a Mg-Bi-Al-Zn-Mn alloy that can be extruded at high speed, which contains a large amount of high-melting point Mg3Bi2 phase, so that the alloy can be extruded at a speed of 20m / min. However, while achieving high-speed extrusion, the alloy is often difficult to take into account the high mechanical properties and flame retardant properties of the alloy, and it is difficult to meet the current requirements for the safety of magnesium alloys in fields such as rail transportation and aerospace.

[0007] In summary, developing a new low-cost magnesium alloy material that can be extruded at high speed and has excellent mechanical properties and flame retardant properties has become a technical problem that needs to be solved urgently by technicians in this field. This technological breakthrough is expected to promote the application of magnesium alloys in more fields and contribute to lightweight design and energy conservation and emission reduction. Summary of the invention

[0008] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a low-alloyed, high-performance, flame-retardant magnesium alloy material suitable for high-speed extrusion, so as to solve the problem that the existing magnesium alloys are difficult to achieve both high mechanical properties and flame retardant properties of the alloy while achieving high-speed extrusion, and cannot meet the new demands for magnesium alloy materials in the fields of rail transportation, aerospace, etc.

[0009] To achieve the above purpose, the present invention adopts the following technical solutions:

[0010] A low-alloy high-speed extrusion flame-retardant magnesium alloy, the magnesium alloy consists of the following components in percentage by mass: Al: 0.3-1.5%, Mn: 0.3-0.7%, Ca: 0.1-0.5%, Ce: 0.3-1.5%, Y: 0.2-1.0%, the remainder being Mg and inevitable impurities, the inevitable impurity content being less than 0.02wt.%; the flame-retardant magnesium alloy is obtained under the condition of an extrusion speed of 30-60m / min, and the extruded structure contains nano-sized Al2Ce, Al2Y, Al8Mn5 and Al8Mn4Ce second phases.

[0011] Furthermore, the sum of the contents of the three elements Al, Mn and Ca is ≤3.0 wt. %; and the sum of the contents of Ce and Y is ≤1.5 wt. %.

[0012] Furthermore, at high temperatures of 500°C to 800°C, a dense Y2O3-CeO2-CaO-MgO multi-component composite oxide film can be formed on the alloy surface.

[0013] Furthermore, the low-alloyed high-speed extruded flame-retardant magnesium alloy has an ultimate tensile strength of more than 240 MPa at room temperature in the extruded state, a yield strength of more than 200 MPa, an elongation of more than 10%, and a flash point of more than 800°C.

[0014] The present invention also provides a method for preparing the low-alloyed high-speed extrusion flame-retardant magnesium alloy, which comprises the following steps according to the above-mentioned components:

[0015] 1) Mechanically grinding the surfaces of raw materials of pure Mg, pure Al, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Ce master alloy and Mg-Y master alloy to remove the oxide layer and attached impurities on the surface of the raw materials; then preheating the raw materials at a temperature of 150 to 350° C. for 10 to 60 minutes; at the same time, cleaning the crucible with tap water and drying the residual water in the crucible;

[0016] 2) Preheating pure Mg and pure Al into a crucible, and then placing them together at 720-740°C, in a CO2 and SF6 mixed protective atmosphere for 30-90 minutes to obtain a liquid alloy; then heating the liquid alloy to 740-760°C, adding Mg-Ca master alloy and Mg-Mn master alloy, and heating for 20-40 minutes to ensure that all the master alloys are melted; after the heating is completed, stirring for 2-10 minutes; then heating the melt to 760-800°C, adding Mg- Y master alloy and Mg-Ce master alloy, continue to keep warm for 20 to 40 minutes; after the heat preservation is completed, stir for 2 to 10 minutes; after the stirring is completed, keep it still for 2 to 10 minutes; then, add 0.5 to 2.5g of refining agent, and refine for 10 to 30 minutes; after the refining is completed, stir for 2 to 10 minutes; remove the scum on the surface of the melt during the stirring process, and finally keep it still for 10 to 20 minutes to obtain a magnesium alloy melt; the entire smelting process is carried out under a mixed protective atmosphere of CO2 and SF6;

[0017] 3) taking out the magnesium alloy melt and the crucible obtained in step 2) together, and slowly putting the crucible into tap water for water cooling; taking out the melt after it is completely solidified, and air cooling it to room temperature; then, cutting off the impure alloy with a thickness of 2 to 5 mm on the upper and lower surfaces of the crucible and the magnesium alloy, and then turning it into an alloy ingot with a diameter of 75 to 85 mm and a height of 40 to 80 mm;

[0018] 4) The alloy ingot obtained in step 3) is kept at 350-400° C. for 8-48 hours, and then kept at 450-520° C. for 1-4 hours for homogenization annealing; after the treatment is completed, it is cooled to room temperature with tap water, and the oxide layer on the surface is polished off;

[0019] 5) preheating the alloy ingot obtained in step 4) at a temperature of 250 to 450° C. for a time of 20 to 60 min;

[0020] 6) hot extruding the alloy ingot preheated in step 5) at an extrusion ratio of 10:1 to 83:1; at an extrusion temperature of 250 to 450° C. and at an extrusion speed of 30 to 60 m / min, to obtain an extruded magnesium alloy.

[0021] Furthermore, in the step 2), the volume proportion of SF6 in the mixed protective atmosphere of CO2 and SF6 is 0.5-1.5%, and the rest is CO2.

[0022] The present invention also provides an application of the low-alloyed high-speed extrusion flame-retardant magnesium alloy for preparing flame-retardant magnesium alloy profiles in the fields of rail transportation, automobiles, 3C and aerospace.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention has developed a new type of magnesium alloy material with good mechanical properties, flame retardant properties and high extrusion forming properties by rationally adjusting the addition amounts of Ce, Y, Al, Mn and Ca elements. The magnesium alloy material can be hot extruded in a temperature range of 250-450°C and at an extrusion speed of up to 60m / min, showing extrudability comparable to that of aluminum alloys; the ultimate tensile strength at room temperature in the extruded state is above 240MPa, the yield strength is above 200MPa, the elongation is above 10%, and the ignition point is above 800°C, showing good comprehensive mechanical properties and flame retardant properties; it is of great significance to further promote the application of magnesium alloy extruded profiles in the fields of rail transportation and aerospace. In addition, the amount of alloying elements added in the magnesium alloy material of the present invention is relatively small, and compared with traditional magnesium alloys, it has a significant low-cost advantage.

[0025] 2. The low-alloyed high-speed extrusion flame-retardant magnesium alloy prepared by the present invention has little effect on the flame-retardant properties of the alloy by different heat treatment processes and deformation processes, and has good flame-retardant effects in the cast, annealed and extruded states.

[0026] 3. The method for preparing a low-alloyed high-speed extrusion flame-retardant magnesium alloy provided by the present invention adopts a conventional gravity casting method to prepare alloy ingots; and adopts a bipolar homogenization heat treatment system developed by the present invention, which is a long-term medium temperature of 350-400°C and a short-term high-temperature of 450-520°C, to ensure that the alloy does not have a low-melting point phase that deteriorates the extrusion speed before hot extrusion; at the same time, the high-melting point phase in the structure is dispersed in the matrix, thereby significantly improving the extrusion processing performance of the alloy and the comprehensive mechanical properties of the final product. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Macroscopic photographs and metallographic photographs of extruded bars of Examples 1-3;

[0028] Figure 2 The following are macroscopic photographs and metallographic photographs of the extruded bars of Comparative Examples 1-5. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto.

[0030] 1. A low alloyed high speed extrusion flame retardant magnesium alloy

[0031] The element contents are shown in Table 1:

[0032] Table 1 Content of each element in magnesium alloy in Examples 1-3 and Comparative Examples 1-4 (wt.%)

[0033] Example Al Mn Ca Ce Y Mg Impurities Example 1 0.32 0.35 0.17 0.38 0.21 98.56 0.01 Example 2 0.74 0.49 0.27 0.65 0.52 97.31 0.02 Example 3 1.07 0.31 0.43 0.32 0.85 97.01 0.01 Comparative Example 1 0.25 0.22 0.08 0.27 0.19 98.98 0.01 Comparative Example 2 0.82 0.64 0.25 1.24 - 97.03 0.02 Comparative Example 3 1.22 0.34 0.39 - 0.94 97.09 0.02 Comparative Example 4 2.55 0.74 0.66 1.55 1.32 93.16 0.02

[0034] In addition, Comparative Example 5 is a commercial AZ31B alloy, and the actual composition is: Al: 3.12wt.%, Zn: 0.97wt.%, Mn: 0.58wt.%, and the balance is Mg and unavoidable impurities;

[0035] It can be seen from Table 1 that the contents of Al, Mn, Ca, Ce and Y elements in Examples 1-3 are all controlled within the designed range, the Al, Mn, Ca, Ce and Y elements in Comparative Example 1 are all lower than the design requirements, no Y element is added in Comparative Example 2, no Ce element is added in Comparative Example 3, various alloy elements in Comparative Example 4 exceed the design requirements, and Comparative Example 5 is a commercial AZ31B alloy.

[0036] The total mass percentage of the inevitable impurities such as Fe, Si and Ni is less than 0.02%. The pure Mg and pure Al are both commercially available products, and the corresponding purities of Mg and Al are: Mg≥99.95wt.%, Al≥99.95wt.%.

[0037] Among them, Y, Ce and Ca elements can form a dense composite Y2O3-CeO2-CaO-MgO oxide film on the alloy surface at 500-800℃, which effectively blocks the contact between the magnesium matrix and oxygen, inhibits the internal oxidation of the magnesium alloy, and thus improves the flame retardant properties of the magnesium alloy; and Y2O3, CeO2 and CaO all have a PBR (Pilling-Bedworth ratio) value of 1 to 2, which can significantly improve the loose and porous structure of MgO, help to form a dense and continuous oxide film layer, and thus improve the material's antioxidant properties. However, the content of alloying elements cannot be increased arbitrarily to increase the ignition point, because this will increase the cost of the alloy and deteriorate the extrudability, which cannot meet actual needs.

[0038] The introduction of Al and Mn elements is mainly to form second phases that play a role in precipitation strengthening and grain refinement, such as Al8Mn5 phase, Al8Mn4Ce phase, Al2Y phase and Al2Ce phase; these second phases are broken into fine particles during the extrusion process, which effectively hinders the growth of grains and ensures that the grains of the alloy after high-speed extrusion are still relatively small; at the same time, these granular second phases can also play a good precipitation strengthening effect. Due to the introduction of Al and Mn elements, the Al8Mn5 phase, Al8Mn4Ce phase, Al2Y phase and Al2Ce phase precipitated in the alloy are all high melting point phases; during the extrusion process, the extrusion formability of the alloy will not be deteriorated. After high-speed extrusion at 60m / min, the alloy surface will not produce defects such as peeling and cracking. A small amount of Mn element added to the matrix can not only form Al8Mn5 phase and Al8Mn4Ce phase, but also refine the cast grains and the recrystallized grains after extrusion; in addition, it can also effectively reduce the Fe-containing compounds in the structure, thereby improving the corrosion resistance of the alloy.

[0039] The low-alloyed high-speed extrusion flame-retardant magnesium alloy prepared by the present invention has all added alloy elements designed within a reasonable range, will not significantly reduce the solidus temperature of the alloy, deteriorate the extrusion formability of the alloy, and can ensure that the alloy can be extruded at an extrusion speed of 60m / min.

[0040] 2. A method for preparing a low alloy high speed extruded flame retardant magnesium alloy

[0041] Example 1

[0042] The ingredients are prepared according to the composition ratio shown in Example 1 in Table 1, and the preparation steps of the low-alloyed high-speed extrusion flame-retardant magnesium alloy are as follows:

[0043] ① Mechanically polish the surfaces of the raw materials pure Mg, pure Al, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Ce master alloy and Mg-Y master alloy to remove the surface oxide layer and attached impurities of the raw materials; then place the raw materials in a resistance furnace for preheating at a temperature of 150°C for 10 min; at the same time, use room temperature tap water to clean the stainless steel crucible and dry the residual water in the crucible.

[0044] ②Put the fully preheated pure Mg ingot and pure Al ingot into a crucible and place them together in a pit-type resistance furnace preheated to 720°C; keep the mixture warm for 30 minutes under a mixed protective atmosphere of CO2 and SF6 (the volume proportion of SF6 is 0.5%) to obtain a liquid alloy; then heat the melt to 740°C, add Mg-Ca master alloy and Mg-Mn master alloy, and keep the mixture warm for 20 minutes to ensure that all the master alloys are melted; after the heat preservation is completed, perform the first stirring for 2 minutes; then heat the melt to 760°C, and then add The Mg-Y intermediate alloy and the Mg-Ce intermediate alloy are kept warm for 20 minutes; after the insulation is completed, a second stirring is carried out, and the stirring time is 2 minutes; after the stirring is completed, the alloy is kept still for 5 minutes; then, 0.5g of refining agent is added and refined for 10 minutes; after the refining is completed, a third stirring is carried out, and the stirring time is 2 minutes, and the scum on the surface of the melt is removed during the stirring process, and finally a magnesium alloy melt is obtained after being kept still for 10 minutes; it should be noted that the entire smelting process is carried out under the protective atmosphere of CO2 and SF6.

[0045] ③ Take out the magnesium alloy melt and crucible obtained in step ②, and slowly put the crucible into the prepared room temperature tap water for water cooling; take out the melt after it is completely solidified, and air cool it to room temperature; then, use a chain saw to cut off the stainless steel crucible, and at the same time cut off the impure alloy with a thickness of 2 mm on the upper and lower surfaces, and then turn it into an alloy ingot with a diameter of 75 mm and a height of 80 mm;

[0046] ④ The alloy ingot obtained in step ③ is subjected to homogenization annealing treatment using a bipolar heat treatment system; the heat treatment system is to keep it at 350°C for 8 hours and then keep it at 450°C for 1 hour; after the heat treatment is completed, it is cooled to room temperature using tap water, and the oxide layer formed on the surface during the heat treatment process is polished off using a grinding wheel.

[0047] ⑤ Preheat the alloy ingot after homogenization annealing in step ④ in a resistance furnace at a preheating temperature of 250° C. for 20 min.

[0048] ⑥ The alloy ingot preheated in step ⑤ is hot extruded with an extrusion ratio of 10:1; the extrusion temperature is 250° C. and the extrusion speed is 30 m / min.

[0049] ⑦ Take tensile samples from the center part of the extruded rod and 4mm×6mm×8mm cuboids from random positions for OM observation (optical microscope observation) and flame retardant performance test; perform tensile mechanical property test and ignition point test, with a heating rate of 20℃ / min and a tensile rate of 2mm / min.

[0050] Example 2

[0051] The ingredients are prepared according to the composition ratio shown in Example 2 in Table 1, and the preparation steps of the low-alloyed high-speed extrusion flame-retardant magnesium alloy are as follows:

[0052] ① Mechanically polish the surfaces of the raw materials pure Mg, pure Al, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Ce master alloy and Mg-Y master alloy to remove the surface oxide layer and attached impurities of the raw materials; then place the raw materials in a resistance furnace for preheating at a temperature of 250°C for 30 minutes; at the same time, use room temperature tap water to clean the stainless steel crucible and dry the residual water in the crucible.

[0053] ②Put the fully preheated pure Mg ingot and pure Al ingot into a crucible and place them together in a pit-type resistance furnace preheated to 730°C; keep the mixture warm for 60 minutes under a mixed protective atmosphere of CO2 and SF6 (the volume proportion of SF6 is 1.0%) to obtain a liquid alloy; then heat the melt to 750°C, add Mg-Ca master alloy and Mg-Mn master alloy, and keep the mixture warm for 30 minutes to ensure that all the master alloys are melted; after the heat preservation is completed, perform the first stirring for 6 minutes; then heat the melt to 780°C, add Mn master alloy, and heat the mixture to 780°C. g-Y intermediate alloy and Mg-Ce intermediate alloy, continue to keep warm for 30 minutes; after the insulation is completed, carry out the second stirring, the stirring time is 6 minutes; after the stirring is completed, keep it still for 8 minutes; then, add 1.5g refining agent and refine for 20 minutes; after the refining is completed, carry out the third stirring, the stirring time is 6 minutes, and remove the scum on the surface of the melt during the stirring process, and finally take it out after keeping it still for 15 minutes to obtain a magnesium alloy melt; it should be noted that the entire smelting process is carried out under the protective atmosphere of CO2 and SF6.

[0054] ③ Take out the magnesium alloy melt and crucible obtained in step ② together, and slowly put the crucible into the prepared room temperature tap water for water cooling; take out the melt after it is completely solidified, and air cool it to room temperature; then, use a chain saw to cut off the stainless steel crucible, and at the same time cut off the impure alloy with a thickness of 4 mm on the upper and lower surfaces, and then turn it into an alloy ingot with a diameter of 80 mm and a height of 60 mm;

[0055] ④ The alloy ingot obtained in step ③ is subjected to homogenization annealing treatment using a bipolar heat treatment system; the heat treatment system is to keep it at 380°C for 24 hours and then keep it at 500°C for 2 hours; after the heat treatment is completed, it is cooled to room temperature using tap water, and the oxide layer formed on the surface during the heat treatment process is polished off using a grinding wheel.

[0056] ⑤ Preheat the alloy ingot after homogenization annealing in step ④ in a resistance furnace at a preheating temperature of 350° C. for 40 minutes.

[0057] ⑥ The alloy ingot preheated in step ⑤ is hot extruded with an extrusion ratio of 46:1; the extrusion temperature is 350° C. and the extrusion speed is 45 m / min.

[0058] ⑦ Take tensile samples from the center part of the extruded rod and take 4mm×6mm×8mm cuboids at random positions for OM observation and flame retardant performance test; perform tensile mechanical property test and ignition point test, with a heating rate of 20℃ / min and a tensile rate of 2mm / min.

[0059] Example 3

[0060] The ingredients are prepared according to the composition ratio shown in Example 3 in Table 1, and the preparation steps of the low-alloyed high-speed extrusion flame-retardant magnesium alloy are as follows:

[0061] ① Mechanically polish the surfaces of the raw materials pure Mg, pure Al, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Ce master alloy and Mg-Y master alloy to remove the surface oxide layer and attached impurities of the raw materials; then place the raw materials in a resistance furnace for preheating at a temperature of 350°C for 60 minutes; at the same time, use room temperature tap water to clean the stainless steel crucible and dry the residual water in the crucible.

[0062] ②Put the fully preheated pure Mg ingot and pure Al ingot into a crucible and place them together in a pit-type resistance furnace preheated to 740°C; keep the mixture warm for 90 minutes under a mixed protective atmosphere of CO2 and SF6 (the volume proportion of SF6 is 1.5%) to obtain a liquid alloy; then heat the melt to 760°C, add Mg-Ca master alloy and Mg-Mn master alloy, and keep the mixture warm for 40 minutes to ensure that all the master alloys are melted; after the heat preservation is completed, perform the first stirring for 10 minutes; then heat the melt to 800°C, and then add M g-Y intermediate alloy and Mg-Ce intermediate alloy, continue to keep warm for 40 minutes; after the insulation is completed, carry out the second stirring, the stirring time is 10 minutes; after the stirring is completed, keep it still for 10 minutes; then, add 2.0g refining agent and refine for 30 minutes; after the refining is completed, carry out the third stirring, the stirring time is 10 minutes, and remove the scum on the surface of the melt during the stirring process, and finally keep it still for 20 minutes to obtain a magnesium alloy melt; it should be noted that the entire smelting process is carried out under the protective atmosphere of CO2 and SF6.

[0063] ③ Take out the magnesium alloy melt and crucible obtained in step ②, and slowly put the crucible into the prepared room temperature tap water for water cooling; take out the melt after it is completely solidified, and air cool it to room temperature; then, use a chain saw to cut off the stainless steel crucible, and at the same time cut off the impure alloy with a thickness of 5 mm on the upper and lower surfaces, and then turn it into an alloy ingot with a diameter of 85 mm and a height of 40 mm;

[0064] ④ The alloy ingot obtained in step ③ is subjected to homogenization annealing treatment using a bipolar heat treatment system; the heat treatment system is to keep it at 400°C for 48 hours and then keep it at 520°C for 4 hours; after the heat treatment is completed, it is cooled to room temperature using tap water, and the oxide layer formed on the surface during the heat treatment process is polished off using a grinding wheel.

[0065] ⑤ Preheat the alloy ingot after homogenization annealing in step ④ in a resistance furnace at a preheating temperature of 450° C. for 60 minutes.

[0066] ⑥ The alloy ingot preheated in step ⑤ is hot extruded with an extrusion ratio of 83:1; the extrusion temperature is 450° C. and the extrusion speed is 60 m / min.

[0067] ⑦ Take tensile samples from the center part of the extruded rod and take 4mm×6mm×8mm cuboids at random positions for OM observation and flame retardant performance test; perform tensile mechanical property test and ignition point test, with a heating rate of 20℃ / min and a tensile rate of 2mm / min.

[0068] Comparative Example 1:

[0069] The ingredients were prepared according to the ingredient ratio shown in Comparative Example 1 in Table 1. The preparation process and process of Comparative Example 1 were consistent with those of Example 1, except that the amount of raw materials added, pure Al, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Ce master alloy and Mg-Y master alloy, was less; at the same time, the steps and methods of OM observation, mechanical and flame retardant performance testing of Comparative Example 1 were consistent with those of Example 1.

[0070] Comparative Example 2:

[0071] The ingredients were prepared according to the ingredient ratio shown in Comparative Example 2 in Table 1. The preparation process and process of Comparative Example 2 were consistent with those of Example 1, except that the raw materials did not contain Mg-Y master alloy. At the same time, the steps and methods of OM observation, mechanical and flame retardant performance testing of Comparative Example 2 were consistent with those of Example 1.

[0072] Comparative Example 3:

[0073] The ingredients are prepared according to the ingredient ratio shown in Comparative Example 3 in Table 1. The preparation process and process of Comparative Example 3 are consistent with those of Example 1, except that the raw materials do not contain Mg-Ce intermediate alloy; at the same time, the steps and methods of OM observation, mechanical and flame retardant performance testing of Comparative Example 3 are consistent with those of Example 1.

[0074] Comparative Example 4:

[0075] The ingredients are prepared according to the ingredient ratio shown in Comparative Example 4 in Table 1. The preparation process and process of Comparative Example 4 are consistent with those of Example 1, except that the added amounts of raw materials pure Al, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Ce master alloy and Mg-Y master alloy are greater, all exceeding the requirements of the patent; at the same time, the steps and methods of OM observation, mechanical and flame retardant performance testing of Comparative Example 4 are consistent with those of Example 1.

[0076] Comparative Example 5:

[0077] The magnesium alloy in this comparative example is made of commercial AZ31B alloy, and the homogenization annealing heat treatment system and extrusion parameters are consistent with those in Example 1.

[0078] The room temperature tensile and flame retardant tests of the magnesium alloy in this comparative example, as well as the OM specimen are consistent with those in Example 1.

[0079] 3. Performance Test

[0080] Table 2 is a comparison table of room temperature mechanical properties and ignition points of the magnesium alloys obtained in Examples 1-3 and Comparative Examples 1-5, as well as extrusion speeds.

[0081] Table 2 Comparison of room temperature mechanical properties, ignition point and extrusion speed of magnesium alloys in Examples 1-3 and Comparative Examples 1-5

[0082]

[0083] It can be seen from Table 2 that Examples 1-3 are extruded at a speed of 30-60m / min, have excellent extrudability, and both mechanical properties and flame retardant properties can meet the design requirements; while Comparative Example 1 is extruded at a speed of 60m / min, but the mechanical and flame retardant properties of the alloy are much different from those of Examples 1-3; Comparative Example 2 cannot meet the design requirements for mechanical and flame retardant properties, and it is also difficult to achieve high-speed extrusion exceeding 30m / min; Comparative Example 3 is also difficult to achieve high-speed extrusion exceeding 30m / min, and the mechanical properties cannot meet the design requirements; Comparative Example 4 cannot achieve high-speed extrusion, even if the strength and flame retardant properties are good, but the shaping is low; and it does not meet the low-cost design requirements; Comparative Example 5 Commercial AZ31B alloy is also difficult to achieve high-speed extrusion at an extrusion speed of more than 30m / min, and the mechanical and flame retardant properties are lower than those of Examples 1-3. It can be seen that the present invention can achieve high-speed extrusion of magnesium alloys by reasonably designing the composition ratio of magnesium alloys, while ensuring the mechanical properties and flame retardant properties of magnesium alloys, which is beneficial to the application of magnesium alloys in fields requiring high-efficiency production.

[0084] The macroscopic photos and metallographic images of the extruded bars of Examples 1 to 3 of the present invention are as follows: Figure 1 As shown. Figure 1 It can be seen that the surfaces of the extruded rods of Examples 1 to 3 are bright, without defects such as burrs, peeling and cracking; and the extruded alloys of Examples 1 to 3 have fine grains, with the grain size being all below 10 microns; at the same time, the second phase is distributed in the organization in the form of dispersed fine particles, which has a good precipitation strengthening effect.

[0085] The macroscopic photos and metallographic images of the extruded bars of Comparative Examples 1 to 5 of the present invention are as follows: Figure 2 As shown. Figure 2 It can be seen that the surface of the extruded rod of Comparative Example 1 is bright, without defects such as burrs, peeling and cracking; but the grain structure is coarse and lacks a dispersed second phase, which leads to poor mechanical properties of the alloy after high-speed extrusion; the surface quality of the extruded rods of Comparative Examples 2 to 3 is poor, and there are a large number of annular cracks; in addition, compared with Examples 1 to 3, they have a coarser grain structure, which leads to low mechanical properties of the alloy; the surface quality of the extruded rod of Comparative Example 4 is poor, and there are a large number of annular cracks. Although the grain size is small, the high alloy content and phase content make the alloy plasticity low; the surface quality of the extruded rod of Comparative Example 5 is poor, and there are a large number of peeling defects; in addition, the grain structure is coarse and lacks a dispersed second phase, which makes the mechanical properties of the AZ31 alloy poor after high-speed extrusion.

[0086] pass Figure 1 and Figure 2By comparison, it can be found that the extruded bars of Examples 1 to 3 not only have good surface quality, but also the fine grain structure and dispersed second phase make the alloy have good mechanical properties after high-speed extrusion; in contrast, it is difficult to achieve an effective balance in the surface quality, microstructure, mechanical properties and extrusion speed of the extruded bars of Comparative Examples 1 to 5.

[0087] It should be noted that in the preparation method of the present invention, the Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy and Mg-Ce master alloy are all commercially available products, and the mass percentages of Mn, Ca, Y and Ce in the corresponding master alloys are: Mn: 5-10wt.%, Ca: 10-25wt.%, Y: 15-30wt.%, Ce: 15-30wt.%. The CO2 and SF6 are both commercially available products. The refining agent is hexachloroethane, HT-MJ magnesium refining agent or HZ-MFG magnesium refining agent.

[0088] The present invention uses an alloying method to add a small amount of light rare earth element Ce and heavy rare earth element Y, as well as a small amount of non-rare earth elements Al, Mn and Ca to pure Mg, and by rationally adjusting the addition amount of each alloy element, a new type of magnesium alloy material with good mechanical properties, flame retardant properties and high extrusion forming properties is developed. The magnesium alloy material can be hot extruded at a temperature range of 250-450°C and an extrusion speed of up to 60m / min, showing extrudability comparable to that of aluminum alloys; the ultimate tensile strength at room temperature in the extruded state is above 240MPa, the yield strength is above 200MPa, the elongation is above 10%, and the ignition point is above 800°C, showing good comprehensive mechanical properties and flame retardant properties.

[0089] At the same time, the flame retardant properties of the magnesium alloy prepared by the present invention have good flame retardant effects under different test methods; and the alloy has good flame retardant properties in the cast state, homogenization annealing state and extruded state. In addition, the low-alloyed high-speed extrusion flame-retardant magnesium alloy prepared by the present invention has a wide extrudable temperature range and extrusion speed range. After hot extrusion at a temperature range of 250-450°C and an extrusion speed of up to 60m / min, the recrystallized grain size in the extruded state is less than 10μm; this is mainly due to the high-density second phase contained in the organization, which effectively hinders the growth of recrystallized grains.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A low alloyed high speed extrusion flame retardant magnesium alloy, characterized in that: The magnesium alloy comprises the following components in percentage by mass: composition: Al: 0.3-1.5%, Mn: 0.3-0.7%, Ca: 0.1-0.5%, Ce: 0.3-1.5%, Y: 0.2-1.0%, the balance is Mg and inevitable impurities, the content of inevitable impurities is <0.02wt.%; The flame retardant magnesium alloy is obtained under the condition of an extrusion speed of 30 to 60 m / min, and the extruded state organization contains nano-sized Al2Ce, Al2Y, Al8Mn5 and Al8Mn4Ce second phases.

2. The low alloyed high speed extrusion flame retardant magnesium alloy according to claim 1, characterized in that: The sum of the contents of the three elements Al, Mn and Ca is ≤3.0wt.%.

3. The low alloyed high speed extrusion flame retardant magnesium alloy according to claim 1, characterized in that: 0.5wt.%≤the sum of the contents of Ce and Y≤1.5wt.%.

4. The low alloyed high speed extrusion flame retardant magnesium alloy according to claim 1, characterized in that: At high temperatures of 500℃ to 800℃, a dense Y2O3-CeO2-CaO-MgO multi-component oxide film can be formed on the alloy surface.

5. The low alloyed high speed extrusion flame retardant magnesium alloy according to any one of claims 1 to 4, characterized in that: The ultimate tensile strength of the extruded state at room temperature is above 240MPa, the yield strength is above 200MPa, the elongation is above 10%, and the ignition point is above 800℃.

6. A method for preparing a low-alloyed high-speed extruded flame-retardant magnesium alloy, characterized in that: The raw materials are prepared according to the components of claim 1, 2 or 3, comprising the following steps: 1) Mechanically grinding the surfaces of raw materials of pure Mg, pure Al, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Ce master alloy and Mg-Y master alloy to remove the oxide layer and attached impurities on the surface of the raw materials; then preheating the raw materials at a temperature of 150 to 350° C. for 10 to 60 minutes; at the same time, cleaning the crucible with tap water and drying the residual water in the crucible; 2) Preheating pure Mg and pure Al into a crucible, and then placing them together at 720-740°C, in a CO2 and SF6 mixed protective atmosphere for 30-90 minutes to obtain a liquid alloy; then heating the liquid alloy to 740-760°C, adding Mg-Ca master alloy and Mg-Mn master alloy, and heating for 20-40 minutes to ensure that all the master alloys are melted; after the heating is completed, stirring for 2-10 minutes; then heating the melt to 760-800°C, adding Mg- Y master alloy and Mg-Ce master alloy, continue to keep warm for 20 to 40 minutes; after the heat preservation is completed, stir for 2 to 10 minutes; after the stirring is completed, keep it still for 2 to 10 minutes; then, add 0.5 to 2.5g of refining agent, and refine for 10 to 30 minutes; after the refining is completed, stir for 2 to 10 minutes; remove the scum on the surface of the melt during the stirring process, and finally keep it still for 10 to 20 minutes to obtain a magnesium alloy melt; the entire smelting process is carried out under a mixed protective atmosphere of CO2 and SF6; 3) taking out the magnesium alloy melt and the crucible obtained in step 2) together, and slowly putting the crucible into tap water for water cooling; taking out the melt after it is completely solidified, and air cooling it to room temperature; then, cutting off the impure alloy with a thickness of 2 to 5 mm on the upper and lower surfaces of the crucible and the magnesium alloy, and then turning it into an alloy ingot with a diameter of 75 to 85 mm and a height of 40 to 80 mm; 4) The alloy ingot obtained in step 3) is kept at 350-400° C. for 8-48 hours, and then kept at 450-520° C. for 1-4 hours for homogenization annealing; after the treatment is completed, it is cooled to room temperature with tap water, and the oxide layer on the surface is polished off; 5) preheating the alloy ingot obtained in step 4) at a temperature of 250 to 450° C. for a time of 20 to 60 min; 6) hot extruding the alloy ingot preheated in step 5) at an extrusion ratio of 10:1 to 83:1; at an extrusion temperature of 250 to 450° C. and at an extrusion speed of 30 to 60 m / min, to obtain an extruded magnesium alloy.

7. The method for preparing a low-alloyed high-speed extrusion flame-retardant magnesium alloy according to claim 6, characterized in that: In step 2), the volume proportion of SF6 in the CO2 and SF6 mixed protective atmosphere is 0.5-1.5%, and the rest is CO2.

8. An application of a low alloyed high speed extruded flame retardant magnesium alloy, characterized in that: The magnesium alloy according to any one of claims 1 to 7 is used to prepare flame-retardant magnesium alloy profiles in the fields of rail transportation, automobiles, 3C and aerospace.

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