A flame-retardant magnesium alloy for die casting with a high-temperature resistant composite oxide film and its preparation method.

Abstract

This invention discloses a flame-retardant magnesium alloy for die casting with a high-temperature resistant composite oxide film layer and its preparation method, relating to the field of magnesium alloy technology. The weight percentages of the components in the flame-retardant magnesium alloy for die casting of this invention are as follows: Al 4.5-9.5%, Zn 0.1-0.5%, Mn 0.1-0.3%, Ca 0.15-2.8%, La and Ce mixed rare earth 0.2-7.5%, Y 0.005-0.45%, Nd 0.001-0.35%, Er 0.001-0.3%; the total content of other impurities is ≤0.1%, with the balance being Mg. This invention significantly improves the performance of the flame-retardant magnesium alloy material through optimized composition design, achieving an ignition temperature higher than 750℃, while also possessing excellent die-casting performance, meeting the engineering requirements for automotive body structural components.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy technology, and in particular to a flame-retardant magnesium alloy for die casting with a high-temperature resistant composite oxide film layer and its preparation method. Background Technology

[0002] Magnesium alloys are the lightest metallic structural materials, possessing advantages such as high specific strength, high specific stiffness, and strong shock absorption. Their application in the automotive industry can significantly reduce vehicle weight, increase driving range, and reduce carbon emissions, making them a promising green material. However, magnesium alloys are reactive and prone to oxidation and continuous combustion, leading to burn-off during alloy preparation and limiting their application scope.

[0003] The ignition process of magnesium alloys involves the rapid oxidation of magnesium with oxygen. This oxidation and ignition process can be described as follows: In the initial stage, a thin and dense protective oxide film forms on the surface of the magnesium alloy. As oxidation continues, the oxide film thickens, increasing internal stress and promoting crack formation. The high vapor pressure of the magnesium alloy at high temperatures also promotes crack formation. Cracks act as channels for the rapid transport of magnesium and oxygen, accelerating the oxidation rate. Furthermore, magnesium can react with oxygen within the cracks, forming oxide ridges. Further growth of these ridges forms oxide nodules, and their aggregation results in a porous oxide film. Liquid magnesium and its vapor can saturate within the oxide nodules and porous oxide film, increasing the contact area with oxygen and leading to a vigorous oxidation process. A significant amount of heat is generated during this stage. If this heat is not sufficiently released, the local temperature will rise sufficiently, causing the magnesium alloy to burn. Therefore, the flame-retardant properties of magnesium alloys are related to the density of the surface oxide film.

[0004] Magnesium alloys are typically coated with MgO, but their Pilling-Bedworth ratio (PB ratio) is 0.64, meaning the MgO film surface is usually loose and porous. Therefore, upon continued heating, the magnesium alloy continues to oxidize and burn. Calculations of the Gibbs free energy of the reaction show that, under high-temperature reaction conditions, the ΔG(T) for MgO formation is always lower than that for Al₂O₃ and ZnO formation. Therefore, in the Mg-Al-Zn system, the oxide film tends to be composed of MgO. This indicates that magnesium alloys alloyed solely with Al and Zn do not possess flame-retardant properties.

[0005] To address the above issues, it is necessary to improve the flame retardant properties of magnesium alloys by alloying with other elements, develop new grades of flame-retardant magnesium alloys, and study their preparation and die-casting processes to meet the automotive industry's demand for lightweighting by replacing aluminum with magnesium, as well as safety requirements in practical applications. Summary of the Invention

[0006] The purpose of this invention is to provide a flame-retardant magnesium alloy for die casting with a high-temperature resistant composite oxide film layer and its preparation method, thereby solving the problems existing in the prior art. This invention discloses a flame-retardant magnesium alloy suitable for die casting processes, which significantly improves the overall performance of the material through optimized composition design. This alloy exhibits excellent flame-retardant properties, specifically: an ignition temperature higher than 750℃, and the ability to remain stable for 5 minutes without spontaneous combustion under continuous flame exposure at 1100℃; it also possesses good die-casting performance, ensuring the material's suitability for the die-casting process; its room-temperature mechanical properties in the die-cast state meet industrial application requirements: yield strength 150-210MPa, tensile strength 250-310MPa, and elongation >7%. The comprehensive achievement of these performance indicators can meet the engineering requirements for automotive body structural components.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] One of the technical solutions of this invention is to provide a flame-retardant magnesium alloy for die casting, wherein the weight percentage of each component in the flame-retardant magnesium alloy for die casting is: Al 4.5-9.5%, Zn 0.1-0.5%, Mn 0.1-0.3%, Ca 0.15-2.8%, La and Ce mixed rare earth 0.2-7.5%, Y 0.005-0.45%, Nd 0.001-0.35%, Er 0.001-0.3%, the total content of other impurities ≤0.1%, and the balance is Mg.

[0009] As a further preferred embodiment of the present invention, the weight percentage of each component in the flame-retardant magnesium alloy for die casting is as follows: Al 4.5-6.5%, Zn 0.1-0.5%, Mn 0.1-0.3%, Ca 0.15-1.2%, La and Ce mixed rare earth 0.2-2.8%, Y 0.005-0.15%, Nd 0.001-0.15%, Er 0.001-0.1%, the total content of other impurities ≤0.1%, and the balance being Mg.

[0010] As a further preferred embodiment of the present invention, the composition is: Al 6.5-8%, Zn 0.1-0.5%, Mn 0.1-0.3%, Ca 0.15-1.2%, La and Ce mixed rare earth 2.8-5%, Y 0.15-0.2%, Nd 0.15-0.2%, Er 0.15-0.2%, with the total content of other impurities ≤0.1%, and the balance being Mg.

[0011] As a further preferred embodiment of the present invention, the content is Al 8-9.5%, Zn 0.1-0.5%, Mn 0.1-0.3%, Ca 1.2-2.8%, La and Ce mixed rare earth 5-7.5%, Y 0.2-0.45%, Nd 0.2-0.35%, Er 0.2-0.3%, the total content of other impurities is ≤0.1%, and the balance is Mg.

[0012] As a further preferred embodiment of the present invention, the mass ratio of La to Ce in the La and Ce mixed rare earth is 1:2.

[0013] The second technical solution of this invention provides a method for preparing the above-mentioned flame-retardant magnesium alloy for die casting, comprising the following steps:

[0014] The raw materials are melted and cast according to the weight percentage of each component to obtain the flame-retardant magnesium alloy for die casting.

[0015] As a further preferred embodiment of the present invention, the preparation method includes the following steps:

[0016] (1) Pure Mg was melted at 650-660℃ and then pure Al, pure Zn, and Mg-Mn master alloy were added.

[0017] (2) Heat the system from step (1) to 740-760℃, add Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy and La and Ce mixed rare earth, stir and keep warm.

[0018] (3) Cool the system from step (2) to 680-700℃, and then add Mg-Ca master alloy for mixing;

[0019] (4) Add covering agent and refining agent to the system obtained in step (3), and refine and remove slag, let stand, keep warm, and cast to obtain the flame-retardant magnesium alloy for die casting.

[0020] Steps (1)-(4) are carried out under a protective atmosphere.

[0021] As a further preferred embodiment of the present invention, before performing step (1), the method further includes a step of preheating and drying pure Mg, pure Al, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Er master alloy, Mg-Nd master alloy, La and Ce mixed rare earth, as well as refining agent and covering agent.

[0022] As a further preferred embodiment of the present invention, the preheating temperature is 150-200°C.

[0023] As a further preferred embodiment of the present invention, the protective atmosphere is a mixture of SF6 and CO2. More preferably, the volume ratio of SF6 to CO2 is 1:3.

[0024] As a further preferred embodiment of the present invention, the raw material components and mass percentages of the covering agent are: 35% MgCl2, 30% KCl, 20% MgCO3, 10% NaCl, and 5% CaCl2; the raw material components and mass percentages of the refining agent are: 25% Na3AlF6, 25% NaF, 25% Na2SiF6, 15% NaCl, and 10% MgCO3.

[0025] As a further preferred embodiment of the present invention, in step (2), after adding Mg-Y master alloy, Mg-Er master alloy, Mg-Nd master alloy and La and Ce mixed rare earth, stir for 3-5 minutes until it is completely melted.

[0026] As a further preferred embodiment of the present invention, the heat preservation time in step (2) is 25-30 min; the standing time in step (4) is 25-30 min.

[0027] As a further preferred embodiment of the present invention, the specific process parameters for the die casting are as follows: magnesium alloy liquid temperature 700℃, mold temperature 150-250℃, injection speed 4-5m / s, die casting pressure 80-100MPa, and the ratio of release agent to water 1:90-1:120.

[0028] This invention introduces alkaline earth element Ca and rare earth elements La, Ce, Y, Nd, and Er for multi-element alloying without affecting the alloy die-casting performance (fluidity and demolding ability), further refining the solidification structure and improving mechanical properties; under the action of high-temperature flame, a dense oxide film layer composed of calcium oxide and rare earth oxides is spontaneously formed, exhibiting high flame retardant properties.

[0029] A higher Al content (≥4.5 wt.%) can effectively narrow the solid-liquid two-phase region, improve fluidity, and reduce solidification shrinkage; simultaneously, it strengthens the solid solution and the second phase (Mg) 17 Al 12Al content can improve alloy strength. However, excessively high Al content (>10 wt.%) will generate a continuous network of hard and brittle second phase, increasing alloy strength but decreasing alloy plasticity. Zn is a traditional solid solution alloying element, playing a role in solid solution strengthening. Current research shows that alkaline earth element Ca is one of the most effective alloying elements for improving flame retardancy: Ca will preferentially oxidize over Mg, and the resulting CaO film is dense, effectively protecting the matrix. The flame retardancy of the alloy increases with increasing Ca content. However, when Ca is added to Mg-Al-Zn magnesium alloys for die casting, excessively high Ca content (>3 wt.%) will form a hard and brittle Al2Ca phase, reducing the alloy's plasticity and significantly increasing the tendency for hot cracking during die casting. Therefore, the flame retardancy of the alloy cannot be improved by alloying with Ca alone. The role of rare earth elements in magnesium alloy systems is currently a research hotspot. Rare earth elements can effectively remove impurities from the melt during the solidification process. La, Ce, Y, Nd, and Er have high Q values ​​(growth limiting factors), making them prone to forming compositionally supercooled zones at the dendrite growth front during alloy solidification, promoting nucleation and effectively refining grains. Mechanical properties are improved through solid solution strengthening and second-phase strengthening. Under high-temperature flame conditions, similar to Ca, Y, Nd, and Er preferentially oxidize to form rare earth oxides, which accumulate at the oxide ends, forming a dense oxide film. However, magnesium-rare earth master alloys are expensive, and adding high amounts of rare earth elements would significantly increase costs, hindering commercial applications. Therefore, this invention chooses to add trace amounts of rare earth elements to meet cost requirements. Based on Mg-Al magnesium alloys, this invention achieves a novel magnesium alloy with high strength, die-casting properties, and flame-retardant performance by adding small amounts of alkaline earth element Ca and rare earth elements La, Ce, Y, Nd, and Er.

[0030] The present invention discloses the following technical effects:

[0031] This invention provides a flame-retardant magnesium alloy suitable for die casting. Through optimized composition design, the performance of the flame-retardant magnesium alloy material is significantly improved. Its ignition temperature is higher than 750℃, and it can remain stable for 5 minutes without spontaneous combustion under continuous burning environment at 1100℃. At the same time, it has good die casting performance, yield strength of 150-210MPa, tensile strength of 250-310MPa, and elongation >7%. The material properties are significantly superior and can meet the engineering requirements of automotive body structural components. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 Metallographic image of the as-cast microstructure of the flame-retardant magnesium alloy prepared in Example 1 of this invention.

[0034] Figure 2 The image shows a scanning electron microscope (SEM) image of the as-cast microstructure of the flame-retardant magnesium alloy prepared in Example 1 of this invention, including the morphology and composition distribution of the second phase.

[0035] Figure 3 In the figure, (a) shows the stress-strain curves of the die-cast tensile bars of the flame-retardant magnesium alloy prepared in Example 12 of the present invention and the flame-retardant magnesium alloy prepared in Comparative Example 1, and (b) and (c) show the SEM morphology of the fracture surface of the die-cast test bar of the flame-retardant magnesium alloy prepared in Example 12. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0041] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0042] One objective of this invention is to provide a flame-retardant magnesium alloy for die casting, wherein the weight percentages of its components are: Al 4.5-9.5%, Zn 0.1-0.5%, Mn 0.1-0.3%, Ca 0.15-2.8%, La and Ce mixed rare earth 0.2-7.5%, Y 0.005-0.45%, Nd 0.001-0.35%, Er 0.001-0.3%, the total content of other impurities ≤0.1%, and the balance being Mg.

[0043] As a further preferred embodiment of the present invention, the weight percentage of each component in the flame-retardant magnesium alloy for die casting is as follows: Al 4.5-6.5%, Zn 0.1-0.5%, Mn 0.1-0.3%, Ca 0.15-1.2%, La and Ce mixed rare earth 0.2-2.8%, Y 0.005-0.15%, Nd 0.001-0.15%, Er 0.001-0.1%, the total content of other impurities ≤0.1%, and the balance being Mg.

[0044] As a further preferred embodiment of the present invention, the weight percentage of each component in the flame-retardant magnesium alloy for die casting is as follows: Al 6.5-8%, Zn 0.1-0.5%, Mn 0.1-0.3%, Ca 0.15-1.2%, La and Ce mixed rare earth 2.8-5%, Y 0.15-0.2%, Nd 0.15-0.2%, Er 0.15-0.2%, the total content of other impurities ≤0.1%, and the balance being Mg.

[0045] As a further preferred embodiment of the present invention, the weight percentage of each component in the flame-retardant magnesium alloy for die casting is as follows: Al 8-9.5%, Zn 0.1-0.5%, Mn 0.1-0.3%, Ca 1.2-2.8%, La and Ce mixed rare earth 5-7.5%, Y 0.2-0.45%, Nd 0.2-0.35%, Er 0.2-0.3%, the total content of other impurities ≤0.1%, and the balance being Mg.

[0046] As a further preferred embodiment of the present invention, the mass ratio of La to Ce in the La and Ce mixed rare earth is 1:2.

[0047] The second objective of this invention is to provide a method for preparing the above-mentioned flame-retardant magnesium alloy for die casting, comprising the following steps:

[0048] The raw materials are melted and cast according to the weight percentage of each component to obtain the flame-retardant magnesium alloy for die casting.

[0049] As a further preferred embodiment of the present invention, the preparation method more specifically includes the following steps:

[0050] (1) Pure Mg was melted at 650-660℃ and then pure Al, pure Zn, and Mg-Mn master alloy were added.

[0051] (2) Heat the system from step (1) to 740-760℃, add Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy and La and Ce mixed rare earth, stir and keep warm.

[0052] (3) Cool the system from step (2) to 680-700℃, and then add Mg-Ca master alloy for mixing;

[0053] (4) Add covering agent and refining agent to the system obtained in step (3), and refine and remove slag, let stand, keep warm, and cast to obtain the flame-retardant magnesium alloy for die casting.

[0054] Steps (1)-(4) are carried out under a protective atmosphere.

[0055] As a further preferred embodiment of the present invention, before performing step (1), the method further includes a step of preheating and drying pure Mg, pure Al, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Er master alloy, Mg-Nd master alloy, La and Ce mixed rare earth, as well as refining agent and covering agent.

[0056] As a further preferred embodiment of the present invention, the preheating temperature is 150-200°C.

[0057] As a further preferred embodiment of the invention, the protective atmosphere is a mixture of SF6 and CO2. More preferably, the volume ratio of SF6 to CO2 is 1:3.

[0058] As a further preferred embodiment of the present invention, the raw material composition and mass percentage of the covering agent are: 35% MgCl2, 30% KCl, 20% MgCO3, 10% NaCl, and 5% CaCl2; the raw material composition and mass percentage of the refining agent are: 25% Na3AlF6, 25% NaF, 25% Na2SiF6, 15% NaCl, and 10% MgCO3.

[0059] As a further preferred embodiment of the present invention, in step (2), after adding Mg-Y master alloy, Mg-Er master alloy, Mg-Nd master alloy and La and Ce mixed rare earth, stir for 3-5 minutes until it is completely melted.

[0060] As a further preferred embodiment of the present invention, the heat preservation time in step (2) is 25-30 min; the standing time in step (4) is 25-30 min.

[0061] As a further preferred embodiment of the present invention, the specific process parameters for the die casting are as follows: magnesium alloy liquid temperature 700℃, mold temperature 150-250℃, injection speed 4-5m / s, die casting pressure 80-100MPa, and the ratio of release agent to water 1:90-1:120.

[0062] In this embodiment of the invention, the raw material composition and mass percentage of the covering agent are: 35% MgCl2, 30% KCl, 20% MgCO3, 10% NaCl, and 5% CaCl2; the raw material composition and mass percentage of the refining agent are: 25% Na3AlF6, 25% NaF, 25% Na2SiF6, 15% NaCl, and 10% MgCO3.

[0063] Example 1

[0064] In this embodiment, the weight percentages of each component in the die-casting flame-retardant magnesium alloy with a high-temperature resistant composite oxide film layer are as follows: Al: 4.5 wt.%; Zn: 0.25 wt.%; Mn: 0.25 wt.%; Ca: 0.15 wt.%; La and Ce mixed rare earth 0.25 wt.% (La and Ce mass ratio 1:2); Y: 0.005 wt.%; Nd: 0.001 wt.%; Er: 0.001 wt.%; the total amount of other impurities is 0.1 wt.%; and the balance is Mg.

[0065] The preparation method is as follows:

[0066] 1) Drying: The prepared raw materials, pure magnesium, pure aluminum, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy, and La and Ce mixed rare earth are preheated to 200℃ and dried.

[0067] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, and Mg-Mn master alloys are added. After melting, the temperature is raised to 750℃, and Mg-Y, Mg-Nd, and Mg-Er master alloys are added along with La and Ce mixed rare earth elements. The mixture is stirred for 3 minutes, and held at this temperature for 30 minutes after the master alloys are completely melted. The temperature is then lowered to 700℃, and Mg-Ca master alloys are added. The mixture is stirred for 2 minutes until the master alloys are completely melted. 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes to remove slag. 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes. Pre-furnace composition analysis is then performed. After the composition is deemed acceptable, high-pressure casting is performed at 700℃ with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test mold, and the resulting casting is designated as No. 1.

[0068] Steps 1) and 2) are carried out under a protective atmosphere (SF6 to CO2 volume ratio of 1:3).

[0069] Example 2

[0070] In this embodiment, the weight percentages of each component in the die-casting flame-retardant magnesium alloy with a high-temperature resistant composite oxide film layer are as follows:

[0071] Al: 7.5 wt.%; Zn: 0.25 wt.%; Mn: 0.25 wt.%; Ca: 0.15 wt.%; La and Ce mixed rare earth 0.25 wt.% (La and Ce mass ratio 1:2); Y: 0.005 wt.%; Nd: 0.001 wt.%; Er: 0.001 wt.%; other impurities total 0.1 wt.%; balance Mg.

[0072] The preparation method is as follows:

[0073] 1) Drying: The prepared raw materials, pure magnesium, pure aluminum, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy, and La and Ce mixed rare earth are preheated to 200℃ and dried.

[0074] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, and Mg-Mn master alloys are added. After melting, the temperature is raised to 750℃, and Mg-Y, Mg-Nd, and Mg-Er master alloys are added along with La and Ce rare earth elements. The mixture is stirred for 3 minutes, and held at this temperature for 30 minutes after the master alloys are completely melted. The temperature is then lowered to 700℃, and Mg-Ca master alloys are added. The mixture is stirred for 2 minutes until the master alloys are completely melted. 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes to remove slag. 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes, followed by pre-furnace composition analysis. After the composition is deemed acceptable, high-pressure casting is performed at 700℃ with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test mold, and the resulting casting is designated as No. 2.

[0075] Steps 1) and 2) are carried out under a protective atmosphere (SF6 to CO2 volume ratio of 1:3).

[0076] Example 3

[0077] In this embodiment, the weight percentages of each component in the die-casting flame-retardant magnesium alloy with a high-temperature resistant composite oxide film layer are as follows:

[0078] Al: 9 wt.%; Zn: 0.25 wt.%; Mn: 0.25 wt.%; Ca: 0.15 wt.%; La and Ce mixed rare earth 0.25 wt.% (La and Ce mass ratio 1:2); Y: 0.005 wt.%; Nd: 0.001 wt.%; Er: 0.001 wt.%; other impurities totaled 0.1 wt.%; balance Mg.

[0079] The preparation method is as follows:

[0080] 1) Drying: The prepared raw materials, pure magnesium, pure aluminum, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy and La and Ce mixed rare earth, are preheated to 200℃ and dried.

[0081] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, and Mg-Mn master alloys are added. After melting, the temperature is raised to 750℃, and Mg-Y, Mg-Nd, and Mg-Er master alloys are added along with La and Ce rare earth elements. The mixture is stirred for 3 minutes, and held at this temperature for 30 minutes after the master alloys are completely melted. The temperature is then lowered to 700℃, and Mg-Ca master alloys are added. The mixture is stirred for 2 minutes until the master alloys are completely melted. 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes to remove slag. 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes, followed by pre-furnace composition analysis. After the composition is deemed acceptable, high-pressure casting is performed at 700℃ with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test mold, and the resulting casting is designated as No. 3.

[0082] Steps 1) and 2) are carried out under a protective atmosphere (SF6 to CO2 volume ratio of 1:3).

[0083] Example 4

[0084] In this embodiment, the weight percentages of each component in the die-casting flame-retardant magnesium alloy with a high-temperature resistant composite oxide film layer are as follows:

[0085] Al: 9.5 wt.%; Zn: 0.25 wt.%; Mn: 0.25 wt.%; Ca: 1.2 wt.%; La and Ce mixed rare earth: 0.25 wt.% (La and Ce mass ratio 1:2), Y: 0.005 wt.%, Nd: 0.001 wt.%, Er: 0.001 wt.%, other impurities totaled 0.1 wt.%, balance Mg.

[0086] The preparation method is as follows:

[0087] 1) Drying: The prepared raw materials, pure magnesium, pure aluminum, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy, and La and Ce mixed rare earth are preheated to 200℃ and dried.

[0088] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, and Mg-Mn master alloys are added. After melting, the temperature is raised to 750℃, and Mg-Y, Mg-Nd, and Mg-Er master alloys are added along with La and Ce rare earth elements. The mixture is stirred for 3 minutes, and held at this temperature for 30 minutes after the master alloys are completely melted. The temperature is then lowered to 700℃, and Mg-Ca master alloys are added. The mixture is stirred for 2 minutes until the master alloys are completely melted. 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes to remove slag. 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes, followed by pre-furnace composition analysis. After the composition is deemed acceptable, high-pressure casting is performed at 700℃ with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test mold, and the resulting casting is designated as No. 4.

[0089] Steps 1) and 2) are carried out under a protective atmosphere (SF6 to CO2 volume ratio of 1:3).

[0090] Example 5

[0091] In this embodiment, the weight percentages of each component in the die-casting flame-retardant magnesium alloy with a high-temperature resistant composite oxide film layer are as follows:

[0092] Al: 9.5 wt.%; Zn: 0.25 wt.%; Mn: 0.25 wt.%; Ca: 2.8 wt.%; La and Ce mixed rare earth: 0.25 wt.% (La and Ce mass ratio 1:2); Y: 0.005 wt.%; Nd: 0.001 wt.%; Er: 0.001 wt.%; other impurities total 0.1 wt.%; balance Mg.

[0093] The preparation method is as follows:

[0094] 1) Drying: The prepared raw materials, pure magnesium, pure aluminum, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy, and La and Ce mixed rare earth are preheated to 200℃ and dried.

[0095] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, and Mg-Mn master alloys are added. After melting, the temperature is raised to 750℃, and Mg-Y, Mg-Nd, and Mg-Er master alloys, along with mixed rare earth elements, are added. The mixture is stirred for 3 minutes, and then held at this temperature for 30 minutes after the master alloys are completely melted. The temperature is then lowered to 700℃, and Mg-Ca master alloys are added. The mixture is stirred for 2 minutes until the master alloys are completely melted. 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes to remove slag. 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes, followed by pre-furnace composition analysis. After the composition is deemed acceptable, high-pressure casting is performed at 700℃ with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test mold, and the resulting casting is designated as number 5.

[0096] Steps 1) and 2) are carried out under a protective atmosphere (SF6 to CO2 volume ratio of 1:3).

[0097] Example 6

[0098] In this embodiment, the weight percentages of each component in the die-casting flame-retardant magnesium alloy with a high-temperature resistant composite oxide film layer are as follows:

[0099] Al: 9.5 wt.%; Zn: 0.25 wt.%; Mn: 0.25 wt.%; Ca: 1.5 wt.%; La and Ce mixed rare earth: 4.5 wt.% (La and Ce mass ratio 1:2); Y: 0.005 wt.%; Nd: 0.001 wt.%; Er: 0.001 wt.%; other impurities total 0.1 wt.%; balance Mg.

[0100] The preparation method is as follows:

[0101] 1) Drying: The prepared raw materials, pure magnesium, pure aluminum, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy, and La and Ce mixed rare earth are preheated to 200℃ and dried.

[0102] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, and Mg-Mn master alloys are added. After melting, the temperature is raised to 750℃, and Mg-Y, Mg-Nd, and Mg-Er master alloys are added along with La and Ce rare earth elements. The mixture is stirred for 3 minutes, and held at this temperature for 30 minutes after the master alloys are completely melted. The temperature is then lowered to 700℃, and Mg-Ca master alloys are added. The mixture is stirred for 2 minutes until the master alloys are completely melted. 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes to remove slag. 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes, followed by pre-furnace composition analysis. After the composition is deemed acceptable, high-pressure casting is performed at 700℃ with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test mold, and the resulting casting is designated as number 6.

[0103] Steps 1) and 2) are carried out under a protective atmosphere (SF6 to CO2 volume ratio of 1:3).

[0104] Example 7

[0105] In this embodiment, the weight percentages of each component in the die-casting flame-retardant magnesium alloy with a high-temperature resistant composite oxide film layer are as follows:

[0106] Al: 9.5 wt.%; Zn: 0.25 wt.%; Mn: 0.25 wt.%; Ca: 1.5 wt.%; La and Ce mixed rare earth: 7.5 wt.% (La and Ce mass ratio 1:2); Y: 0.005 wt.%; Nd: 0.001 wt.%; Er: 0.001 wt.%; other impurities total 0.1 wt.%; balance Mg.

[0107] The preparation method is as follows:

[0108] 1) Drying: The prepared raw materials, pure magnesium, pure aluminum, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy, and La and Ce mixed rare earth are preheated to 200℃ and dried.

[0109] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, and Mg-Mn master alloys are added. After melting, the temperature is raised to 750℃, and Mg-Y, Mg-Nd, and Mg-Er master alloys are added along with La and Ce rare earth elements. The mixture is stirred for 3 minutes, and held at this temperature for 30 minutes after the master alloys are completely melted. The temperature is then lowered to 700℃, and Mg-Ca master alloys are added. The mixture is stirred for 2 minutes until the master alloys are completely melted. 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes to remove slag. 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes, followed by pre-furnace composition analysis. After the composition is deemed acceptable, high-pressure casting is performed at 700℃ with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test mold, and the resulting casting is designated as number 7.

[0110] Steps 1) and 2) are carried out under a protective atmosphere (SF6 to CO2 volume ratio of 1:3).

[0111] Example 8

[0112] In this embodiment, the weight percentages of each component in the die-casting flame-retardant magnesium alloy with a high-temperature resistant composite oxide film layer are as follows:

[0113] Al: 9.5 wt.%; Zn: 0.25 wt.%; Mn: 0.25 wt.%; Ca: 1.5 wt.%; La and Ce mixed rare earth: 4.5 wt.% (La and Ce mass ratio 1:2); Y: 0.3 wt.%; Nd: 0.001 wt.%; Er: 0.001 wt.%; other impurities totaled 0.1 wt.%; balance Mg.

[0114] The preparation method is as follows:

[0115] 1) Drying: The prepared raw materials, pure magnesium, pure aluminum, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy, and La and Ce mixed rare earth are preheated to 200℃ and dried.

[0116] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, and Mg-Mn master alloys are added. After melting, the temperature is raised to 750℃, and Mg-Y, Mg-Nd, and Mg-Er master alloys are added along with La and Ce rare earth elements. The mixture is stirred for 3 minutes, and held at this temperature for 30 minutes after the master alloys are completely melted. The temperature is then lowered to 700℃, and Mg-Ca master alloys are added. The mixture is stirred for 2 minutes until the master alloys are completely melted. 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes to remove slag. 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes, followed by pre-furnace composition analysis. After the composition is deemed acceptable, high-pressure casting is performed at 700℃ with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test mold, and the resulting casting is designated as No. 8.

[0117] Steps 1) and 2) are carried out under a protective atmosphere (SF6 to CO2 volume ratio of 1:3).

[0118] Example 9

[0119] In this embodiment, the weight percentages of each component in the die-casting flame-retardant magnesium alloy with a high-temperature resistant composite oxide film layer are as follows:

[0120] Al: 9.5 wt.%; Zn: 0.25 wt.%; Mn: 0.25 wt.%; Ca: 1.5 wt.%; La and Ce mixed rare earth: 4.5 wt.% (La and Ce mass ratio 1:2); Y: 0.005 wt.%; Nd: 0.03 wt.%; Er: 0.001 wt.%; other impurities totaled 0.1 wt.%; balance Mg.

[0121] The preparation method is as follows:

[0122] 1) Drying: The prepared raw materials, pure magnesium, pure aluminum, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy, and La and Ce mixed rare earth are preheated to 200℃ and dried.

[0123] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, and Mg-Mn master alloys are added. After melting, the temperature is raised to 750℃, and Mg-Y, Mg-Nd, and Mg-Er master alloys are added along with La and Ce rare earth elements. The mixture is stirred for 3 minutes, and held at this temperature for 30 minutes after the master alloys are completely melted. The temperature is then lowered to 700℃, and Mg-Ca master alloys are added. The mixture is stirred for 2 minutes until the master alloys are completely melted. 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes to remove slag. 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes, followed by pre-furnace composition analysis. After the composition is deemed acceptable, high-pressure casting is performed at 700℃ with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test mold, and the resulting casting is designated as number 9.

[0124] Steps 1) and 2) are carried out under a protective atmosphere (SF6 to CO2 volume ratio of 1:3).

[0125] Example 10

[0126] In this embodiment, the weight percentages of each component in the die-casting flame-retardant magnesium alloy with a high-temperature resistant composite oxide film layer are as follows:

[0127] Al: 9.5 wt.%; Zn: 0.25 wt.%; Mn: 0.25 wt.%; Ca: 1.5 wt.%; La and Ce mixed rare earth: 4.5 wt.% (La and Ce mass ratio 1:2); Y: 0.005 wt.%; Nd: 0.001 wt.%; Er: 0.3 wt.%; other impurities totaled 0.1 wt.%; balance Mg.

[0128] The preparation method is as follows:

[0129] 1) Drying: The prepared raw materials, pure magnesium, pure aluminum, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy, and La and Ce mixed rare earth are preheated to 200℃ and dried.

[0130] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, and Mg-Mn master alloys are added. After melting, the temperature is raised to 750℃, and Mg-Y, Mg-Nd, and Mg-Er master alloys are added along with La and Ce rare earth elements. The mixture is stirred for 3 minutes, and held at this temperature for 30 minutes after the master alloys are completely melted. The temperature is then lowered to 700℃, and Mg-Ca master alloys are added. The mixture is stirred for 2 minutes until the master alloys are completely melted. 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes to remove slag. 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes, followed by pre-furnace composition analysis. After the composition is deemed acceptable, high-pressure casting is performed at 700℃ with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test mold, and the resulting casting is designated as number 10.

[0131] Steps 1) and 2) are carried out under a protective atmosphere (SF6 to CO2 volume ratio of 1:3).

[0132] Example 11

[0133] In this embodiment, the weight percentages of each component in the die-casting flame-retardant magnesium alloy with a high-temperature resistant composite oxide film layer are as follows:

[0134] Al: 9.5 wt.%; Zn: 0.25 wt.%; Mn: 0.25 wt.%; Ca: 1.5 wt.%; La and Ce mixed rare earth: 4.5 wt.% (La and Ce mass ratio 1:2); Y: 0.5 wt.%; Nd: 0.351 wt.%; Er: 0.001 wt.%; other impurities totaled 0.1 wt.%; balance Mg.

[0135] The preparation method is as follows:

[0136] 1) Drying: The prepared raw materials, pure magnesium, pure aluminum, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy, and La and Ce mixed rare earth are preheated to 200℃ and dried.

[0137] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, and Mg-Mn master alloys are added. After melting, the temperature is raised to 750℃, and Mg-Y, Mg-Nd, and Mg-Er master alloys are added along with La and Ce rare earth elements. The mixture is stirred for 3 minutes, and held at this temperature for 30 minutes after the master alloys are completely melted. The temperature is then lowered to 700℃, and Mg-Ca master alloys are added. The mixture is stirred for 2 minutes until the master alloys are completely melted. 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes to remove slag. 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes, followed by pre-furnace composition analysis. After the composition is deemed acceptable, high-pressure casting is performed at 700℃ with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test rod mold, and the resulting casting is designated as No. 11.

[0138] Steps 1) and 2) are carried out under a protective atmosphere (SF6 to CO2 volume ratio of 1:3).

[0139] Example 12

[0140] In this embodiment, the weight percentages of each component in the die-casting flame-retardant magnesium alloy with a high-temperature resistant composite oxide film layer are as follows:

[0141] Al: 9.5 wt.%; Zn: 0.25 wt.%; Mn: 0.25 wt.%; Ca: 1.5 wt.%; La and Ce mixed rare earth: 4.5 wt.% (La and Ce mass ratio 1:2); Y: 0.5 wt.%; Nd: 0.35 wt.%; Er: 0.3 wt.%; other impurities totaled 0.1 wt.%; balance Mg.

[0142] The preparation method is as follows:

[0143] 1) Drying: The prepared raw materials, pure magnesium, pure aluminum, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy, and La and Ce mixed rare earth are preheated to 200℃ and dried.

[0144] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, and Mg-Mn master alloys are added. After melting, the temperature is raised to 750℃, and Mg-Y, Mg-Nd, and Mg-Er master alloys are added along with La and Ce rare earth elements. The mixture is stirred for 3 minutes, and held at this temperature for 30 minutes after the master alloys are completely melted. The temperature is then lowered to 700℃, and Mg-Ca master alloys are added. The mixture is stirred for 2 minutes until the master alloys are completely melted. 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes to remove slag. 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes, followed by pre-furnace composition analysis. After the composition is deemed acceptable, high-pressure casting is performed at 700℃ with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test mold, and the resulting casting is designated as No. 12.

[0145] Steps 1) and 2) are carried out under a protective atmosphere (SF6 to CO2 volume ratio of 1:3).

[0146] Comparative Example 1

[0147] A commercial magnesium alloy was used as Comparative Example 1. The weight percentages of the components in the commercial magnesium alloy were: Al: 9.0 wt.%; Zn: 0.25 wt.%; Mn: 0.6 wt.%; other impurities totaled 0.1 wt.%; and the balance was Mg.

[0148] The preparation method of commercial magnesium alloys is as follows:

[0149] 1) Drying: Preheat the prepared raw materials, pure magnesium, pure aluminum, pure Zn, and Mg-Mn master alloy, to 200℃ and dry them;

[0150] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, and Mg-Mn master alloy are added. After melting, 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes before slag removal. Then, 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes, followed by pre-furnace composition analysis. After the composition is deemed acceptable, high-pressure casting is performed at 700℃, with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test mold, and the resulting casting is designated as No. 13.

[0151] Comparative Example 2

[0152] Based on the commercial magnesium alloy of Comparative Example 1, rare earth element Gd was added. The weight percentages of each component were: Al: 9.0 wt.%; Zn: 0.25 wt.%; Mn: 0.6 wt.%; Gd: 0.25%; other impurities totaled 0.1 wt.%; and the balance was Mg.

[0153] The preparation method is as follows:

[0154] 1) Drying: Preheat the prepared raw materials, pure magnesium, pure aluminum, pure Zn, Mg-Mn, and Mg-Gd master alloy, to 200℃ and dry them;

[0155] 2) Melting: The melting furnace is heated to 650℃ to melt pure magnesium. Then, pure Al, pure Zn, Mg-Mn master alloy, and Mg-Gd master alloy are added. After melting, 0.5% of the total melt weight of refining agent powder is added, and the mixture is stirred for 5 minutes before slag removal. 0.5% of the total melt weight of covering agent powder is added, and the mixture is held at this temperature for 25 minutes, followed by pre-furnace composition analysis. After the composition is deemed acceptable, high-pressure casting is performed at 700℃, with an injection speed of 4.5 m / s, a casting pressure of 90 MPa, a release agent ratio of 1:100, and a mold temperature of 210℃. The die-casting production mold is a die-casting test rod mold, and the resulting casting is designated as No. 14.

[0156] Figure 1 Metallographic image of the as-cast microstructure of the flame-retardant magnesium alloy prepared in Example 1 of this invention.

[0157] Figure 2 The image shows a scanning electron microscope (SEM) image of the as-cast microstructure of the flame-retardant magnesium alloy prepared in Example 1 of this invention, including the morphology and composition distribution of the second phase.

[0158] Figure 3 In the figure, (a) shows the stress-strain curves of the die-cast tensile bars of the flame-retardant magnesium alloy prepared in Example 12 of the present invention and the flame-retardant magnesium alloy prepared in Comparative Example 1, and (b) and (c) show the SEM morphology of the fracture surface of the die-cast test bar of the flame-retardant magnesium alloy prepared in Example 12.

[0159] The castings prepared in Examples 1-12 were subjected to mechanical property tests, ignition point tests, and high-temperature flame combustion tests at 1100℃, and the results are shown in Table 1.

[0160] Table 1

[0161] 1 151 251 18.0 770 302 2 162 277 12.9 761 311 3 172 290 9.2 766 308 4 180 300 7.6 850 441 5 193 310 7.1 950 535 6 201 309 8.5 889 412 7 215 325 7.1 902 406 8 185 310 9.2 913 455 9 183 293 8.7 887 439 10 179 290 9.4 890 447 11 192 303 8.6 934 490 12 193 320 8.2 967 545 13 170 288 8.5 605 30 14 174 291 9.0 610 35

[0162] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A flame-retardant magnesium alloy for die casting, characterized in that, The weight percentages of each component in the flame-retardant magnesium alloy for die casting are as follows: Al 6.5-9.5%, Zn 0.1-0.5%, Mn 0.1-0.3%, Ca 0.15-1.2%, La and Ce mixed rare earth 0.2-7.5%, Y 0.005-0.45%, Nd 0.001-0.35%, Er 0.001-0.3%, with the total content of other impurities ≤0.1%, and the balance being Mg; The preparation method of the flame-retardant magnesium alloy for die casting includes the following steps: (1) At 650-660℃, pure Mg is melted and then pure Al, pure Zn, and Mg-Mn master alloy are added; (2) Heat the system from step (1) to 740-760℃, add Mg-Y master alloy, Mg-Nd master alloy, Mg-Er master alloy and La and Ce mixed rare earth, and stir. (3) Cool the system from step (2) to 680-700℃, and then add Mg-Ca master alloy for mixing; (4) Add covering agent and refining agent to the system in step (3), and refine and remove slag, let stand, keep warm, and cast to obtain the flame-retardant magnesium alloy for die casting; Steps (1)-(4) are carried out under a protective atmosphere.

2. The flame-retardant magnesium alloy for die casting according to claim 1, characterized in that, Al 6.5~8%, Zn 0.1~0.5%, Mn 0.1-0.3%, Ca 0.15~1.2%, La and Ce mixed rare earth 2.8~5%, Y 0.15-0.2%, Nd 0.15-0.2%, Er 0.15-0.2%, other impurities ≤0.1%, balance Mg.

3. The flame-retardant magnesium alloy for die casting according to claim 1, characterized in that, Before step (1), the process includes preheating and drying of pure Mg, pure Al, pure Zn, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Y master alloy, Mg-Er master alloy, Mg-Nd master alloy, La and Ce mixed rare earth, as well as refining agent and covering agent; the preheating temperature is 150-200℃.

4. The flame-retardant magnesium alloy for die casting according to claim 1, characterized in that, The protective atmosphere is a mixture of SF6 and CO2.

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