Fine-grain die-casting aluminum magnesium alloy prepared based on rare earth composite refiner Al-Ti-B-RE and preparation method of fine-grain die-casting aluminum magnesium alloy

Abstract

The invention belongs to the technical field of aluminum alloys, and particularly discloses a fine-grain die-casting aluminum-magnesium alloy prepared based on a rare earth composite refiner Al-Ti-B-RE and a preparation method of the fine-grain die-casting aluminum-magnesium alloy. The rare earth composite refiner Al-Ti-B-RE is prepared from the following components in percentage by mass: 4.0 to 6.5 percent of Ti, 0.5 to 2.0 percent of B, 2.1 to 9.0 percent of RE and the balance of Al and impurity elements. According to the fine grain die-casting aluminum prepared on the basis of the rare earth composite refiner Al-Ti-B-RE, the rare earth composite refiner Al-Ti-B-RE is prepared from the following components in percentage by mass: 5.00 to 8.50 percent of Mg, 1.50 to 4.50 percent of Si, 0.35 to 0.65 percent of Mn, 0.01 to 0.10 percent of Fe, 0.02 to 0.25 percent of Ti, 0.004 to 0.20 percent of B, 0.005 to 0.25 percent of RE and the balance of Al and impurity elements. According to the method, the composite refiner Al-Ti-B-RE is used for replacing a traditional Al-Ti-B refiner, and alloy component optimization is combined, so that effective refinement of die-casting aluminum magnesium alloy grains is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloys, and in particular to a fine-grained die-cast aluminum-magnesium alloy prepared based on a rare earth composite refiner Al-Ti-B-RE and a preparation method thereof. Background Art

[0002] With the continuous growth of the economy, automobile production has also increased year by year, accompanied by energy crisis and air pollution problems, so the lightweight of automobiles has been proposed. Al-Mg alloy has the advantages of high specific strength, good formability, good thermal conductivity and good electrical conductivity, so it has been widely used in the automotive field. Squeeze casting is a near-net forming technology with short fluidity and high efficiency, which combines the advantages of casting and forging. Squeeze casting pressure can improve the filling and shrinkage ability of liquid gold, and the casting performance of the alloy is low. Compact components can be obtained, and the mechanical properties are significantly improved. Compared with other casting methods, high-pressure die casting is more suitable for large-scale production in the automotive industry. This is due to its high production efficiency, ability to produce complex thin-walled parts and good comprehensive performance. Die-casting aluminum alloys are increasingly used in automotive parts. In addition, automotive structural parts require high-quality die-casting aluminum alloys with high strength and high ductility to meet safety standards. Al-Mg alloys with excellent ductility and high strength-to-weight ratio are increasingly attracting attention and are used for automotive structural parts produced by high-pressure die casting. In order to further improve the mechanical properties of die-casting aluminum-magnesium high alloys, we choose to achieve this by refining the alloy structure and grain.

[0003] Grain refinement is an important means to improve the toughness of aluminum alloys. It can improve strength and plasticity at the same time. In addition, grain refinement can also reduce the solidification defects of the alloy and improve the casting performance of the alloy. Therefore, the research on grain refinement has important practical significance. At present, the commonly used refiner is Al-5Ti-1B refiner, but there are still some problems with Al-Ti-B refiner, such as TiB2 particles are easy to aggregate and precipitate, which affects the grain refinement effect. And when Al-Ti-B refiner is used to refine aluminum alloys with high contents of Si, Zr, Cr, V, Mn and other elements, its refinement effect will be weakened or even fail, resulting in coarse grains and uneven structure. Therefore, the development of more efficient refiners has important research significance and practical significance.

[0004] The present invention takes die-cast aluminum-magnesium alloy as the object, and adds rare earth composite refiner Al-Ti-B-RE during the smelting process. After the die-cast aluminum-magnesium alloy is refined by the rare earth composite refiner Al-Ti-B-RE, the grain size is significantly reduced, thereby developing a fine-grained die-cast aluminum-magnesium alloy. Summary of the invention

[0005] The present invention provides a fine-grained die-cast aluminum-magnesium alloy prepared based on a rare earth composite refiner Al-Ti-B-RE and a preparation method thereof, wherein the element content of the rare earth composite refiner Al-Ti-B-RE is optimized, and the optimal element content and the optimal addition amount in the alloy are designed.

[0006] In order to achieve the above object, the specific technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present application provides a rare earth composite refiner Al-Ti-B-RE and a fine-grained die-cast aluminum-magnesium alloy prepared based on the rare earth composite refiner Al-Ti-B-RE. The rare earth composite refiner Al-Ti-B-RE comprises the following components by mass fraction: Ti 4.0-6.5%, B 0.5-2.0%, RE 2.1-9.0%, and the remainder is Al and impurity elements, and the total mass percentage of the impurity elements is less than or equal to 0.30%. Fine-grained die-cast aluminum prepared based on the rare earth composite refiner Al-Ti-B-RE. The rare earth composite refiner Al-Ti-B-RE includes the following components in mass fraction: Mg 5.00-8.50%, Si 1.50-4.50%, Mn 0.35-0.65%, Fe 0.01-0.10%, Ti 0.02-0.25%, B 0.004-0.20%, RE 0.005-0.25%, and the remainder is Al and impurity elements, and the total mass percentage content of the impurity elements is less than or equal to 0.30%.

[0008] Furthermore, the fine-grained die-cast aluminum-magnesium alloy includes the following components in mass fraction: Mg 5.00-8.00%, Si 1.50-4.00%, Mn 0.40-0.65%, Fe 0.01-0.08%, Ti 0.02-0.25%, B 0.004-0.20%, RE 0.005-0.20%, and the balance is Al and impurity elements.

[0009] Furthermore, the rare earth composite refiner Al-Ti-B-RE comprises the following components in mass fractions: Ti 4.0-6.0%, B 0.5-2.0%, RE 2.1-8.5%, and the remainder is Al and impurity elements.

[0010] Furthermore, the rare earth composite refiner Al-Ti-B-RE is added to the die-cast aluminum-magnesium alloy in an amount of 0.10 to 1.50%, preferably 0.10 to 1.20%.

[0011] Furthermore, the rare earth includes at least one of La, Ce, Y, Pm, Er, Nd, and Sm.

[0012] In a second aspect, the present invention provides the fine-grained die-casting aluminum-magnesium alloy prepared based on the rare earth composite refiner Al-Ti-B-RE, comprising the following steps:

[0013] S1. Provide prefabricated raw materials of pure aluminum, pure magnesium, aluminum-M master alloy, refining agent and Al-Ti-B-RE composite refiner, M includes Si, Fe, Mn; the component content of the Al-Ti-B-RE composite refiner is: Ti4.0-6.5%, B 0.5-2.0%, RE 2.1-9.0%, the balance is Al and impurity elements, and the total mass percentage of the impurity elements is less than or equal to 0.30%; the mass proportion of each element in the prefabricated raw material based on 100 parts by mass of all the above prefabricated raw materials is: Mg 5.00-8.50%, Si 1.50-4.50%, Mn 0.35-0.65%, Fe 0.01-0.10%, Ti 0.02-0.25%, B 0.004-0.20%, RE 0.005-0.25%, the balance being Al and impurity elements, the sum of the mass percentages of the impurity elements being less than or equal to 0.30%;

[0014] S2. Before smelting, pure aluminum, pure magnesium, aluminum-M master alloy, refining agent and Al-Ti-B-RE composite refiner are placed in a drying oven at a temperature of 150-250 ° C and dried for 1.5-2.5 hours for use;

[0015] S3. Adding a pure aluminum ingot into a smelting furnace, setting the furnace temperature to 720°C, and completely melting the aluminum ingot to obtain an aluminum melt;

[0016] S4. After sequentially adding aluminum-M master alloy and pure Mg to the aluminum melt to obtain an aluminum alloy melt;

[0017] S5. Raise the temperature of the aluminum alloy melt to 730°C-740°C, add a refining agent to the bottom of the melt, and stir the aluminum alloy melt for 5-10 minutes, and then let it stand for 5-10 minutes;

[0018] S6. After slagging, the temperature of the aluminum alloy melt is raised to 740°C-760°C, and an Al-Ti-B-RE rare earth composite refiner is added to the refined aluminum alloy melt, and the mixture is stirred for 3-5 minutes and then allowed to stand for 5-20 minutes;

[0019] S7. Then, the furnace temperature is lowered to 710°C-720°C, and the aluminum-silicon alloy melt is poured into a metal mold preheated to 150-200°C at 710-720°C, with a low speed of 0.10-0.6 m / s, a high speed of 1.5-5.0 m / s, and a casting pressure of 60-180 MPa to obtain a die-cast aluminum-magnesium alloy containing rare earth.

[0020] Furthermore, the refining agent is a fluoride salt refining agent, such as MgF2, AlF3, etc., which can be one or more.

[0021] The present invention has the following beneficial effects:

[0022] (1) RE can inhibit the aggregation of TiB2 particles in Al-Ti-B. TiB2 has the lowest nucleation energy and is a very effective nucleating agent for aluminum. Therefore, the addition of RE is beneficial to the refining effect of the composite rare earth refiner Al-Ti-B-RE.

[0023] (2) The addition of an appropriate amount of RE has a certain purification ability, which can reduce the hydrogen content in the aluminum melt and reduce harmful metal inclusions and oxides in the aluminum alloy, thereby playing a role in degassing and purifying the melt.

[0024] (3) The addition of rare earth composite refiner Al-Ti-B-RE greatly refines the alloy grain size and the size of the second phase, ensuring the uniformity of the structure. Grain refinement leads to a decrease in the porosity and pore size of the aluminum alloy, thereby improving the mechanical properties of the alloy.

[0025] (4) Adding a small amount of RE to the Al-Ti-B refiner can form Ti2Al 20 RE phase, Ti2Al 20 There are 8 matching relationships between RE phase and Al phase, so Ti2Al 20 RE has a better nucleation effect than TiAl3, so a small amount of rare earth can improve the refining effect of the composite rare earth refiner Al-Ti-B-RE. As the amount of RE added to the Al-Ti-B refiner increases, RE can form Ti2Al on the surface of the TiAl3 phase. 20 RE phase, Ti2Al 20 The TiAl3 phase surrounded by RE phase has a better nucleation effect.

[0026] (5) The content of RE in the composite rare earth refiner Al-Ti-B-RE cannot be too high. When the content of RE in the composite rare earth refiner Al-Ti-B-RE is too high, the excess RE will react with Ti2Al 20 RE phase reaction generates a large amount of network Al4RE phase, which will reduce the Ti2Al 20 RE phase nucleates particles, while the network Al4RE phase does not have a nucleation effect, so it is necessary to control the content of RE in the composite rare earth refiner Al-Ti-B-RE.

[0027] (6) The cooling rate of die-cast aluminum-magnesium alloy is very fast, so the amount of refiner added cannot be too high, otherwise it is easy to cause the refiner particles to aggregate at the grain boundaries and thus reduce the mechanical properties. An appropriate amount of RE element is beneficial to improving the corrosion resistance. In addition, the microstructure of the die-cast aluminum-magnesium alloy is significantly refined after being refined by an appropriate amount of rare earth composite refiner Al-Ti-B-RE, and the size of eutectic silicon is also significantly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art 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 paying any creative work.

[0029] Figure 1 This is the optical microstructure of the alloy of Example 1 of the present invention.

[0030] Figure 2 This is the optical microstructure of the alloy of Comparative Example 1 of the present invention.

[0031] Figure 3 This is the scanning microstructure of the rare earth composite refiner in Example 1 of the present invention.

[0032] Figure 4 This is the scanning microstructure of the refiner in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] The inventors found that the TiB2 particles of the Al-Ti-B grain refiner tend to aggregate, which results in a decrease in its aluminum alloy refinement effect. The addition of rare earth RE can make the TiB2 particles more evenly distributed in the Al-Ti-B structure, thereby improving the non-uniform nucleation effect of the TiB2 particles. 20 RE phase, and Ti2Al 20 The lattice matching degree between RE phase and α-Al is good, so Ti2Al 20RE phase can also serve as an effective nucleation site for α-Al. Based on this, the present invention combines the alloy z-basin and content optimization, so that the grain size of die-cast aluminum-magnesium is significantly reduced after being refined by the composite refiner Al-Ti-B-RE, the second phase in the structure is significantly refined, and the number of oxidation and metal inclusions in the structure is also reduced, which is beneficial to the improvement of mechanical properties and processing properties. In addition, the addition form of the composite refiner Al-Ti-B-RE of the present invention is also necessary. When Ti, B, and RE elements are added to the die-cast aluminum-magnesium alloy separately at the same content, the refinement effect when added as the composite refiner Al-Ti-B-RE and the improvement level of the alloy's mechanical properties and processing properties cannot be achieved.

[0035] The following describes the preparation method of aluminum alloy in combination with the embodiments and comparative examples, and the mass percentage of the impurity elements in each embodiment and comparative example is ≤0.30%. Those skilled in the art will understand that the preparation method described in the present invention is only an example, and any other suitable preparation method is within the scope of the present invention.

[0036] Example 1

[0037] A prefabricated raw material of pure aluminum, pure magnesium, aluminum-M master alloy, refining agent and Al-Ti-B-RE composite refiner is provided, wherein M comprises Si, Fe and Mn, and the mass proportion of each element in the prefabricated raw material based on 100 parts by mass of all the above prefabricated raw materials is as follows: Mg: 7.50%, Si: 2.50%, Mn: 0.55%, Fe: 0.06%, Ti: 0.026%, B: 0.006%, Ce: 0.023%, and the balance is Al and impurity elements.

[0038] The rare earth composite refiner Al-Ti-B-RE includes the following components in mass fractions: Ti: 5.3%, B: 1.2%, Ce: 4.5%, and the balance is Al and impurity elements.

[0039] Before smelting, pure aluminum, pure magnesium, aluminum-M master alloy, refining agent and Al-Ti-B-RE composite refiner are placed in a drying oven at a temperature of 200° C. and dried for 2.0 hours for use.

[0040] Add pure aluminum ingots into a smelting furnace, set the furnace temperature to 720°C, and completely melt the aluminum ingots to obtain aluminum melt.

[0041] An aluminum alloy melt is obtained by sequentially adding aluminum-M master alloy and pure Mg into the aluminum melt.

[0042] The temperature of the aluminum alloy melt was raised to 740°C, a refining agent was added to the bottom of the melt, and the aluminum alloy melt was stirred for 5 minutes and then allowed to stand for 5 minutes.

[0043] After slagging, the temperature of the aluminum alloy melt was raised to 750°C, and 0.5% by mass of Al-Ti-B-RE rare earth composite refiner was added to the refined aluminum alloy melt, and the mixture was stirred for 5 minutes and then allowed to stand for 10 minutes.

[0044] Subsequently, the furnace temperature was lowered to 710°C, and the aluminum-silicon alloy melt was poured into a metal mold preheated to 175°C at 710°C, with a low speed of 0.35 m / s, a high speed of 3.0 m / s, and a casting pressure of 140 MPa to obtain a fine-grained die-cast aluminum-magnesium alloy containing rare earths. The addition of the rare earth composite refiner reduced the grain size of the alloy, and its grain size was smaller than that of the die-cast aluminum-magnesium alloy after refinement by the Al-Ti-B refiner in Comparative Example 1.

[0045] Example 2

[0046] A prefabricated raw material of pure aluminum, pure magnesium, aluminum-M master alloy, refining agent and Al-Ti-B-RE composite refiner is provided, wherein M comprises Si, Fe and Mn, and the mass proportion of each element in the prefabricated raw material based on 100 parts by mass of all the above prefabricated raw materials is as follows: Mg: 7.30%, Si: 2.20%, Mn: 0.48%, Fe: 0.07%, Ti: 0.03%, B: 0.006%, La: 0.018%, and the balance is Al and impurity elements.

[0047] The rare earth composite refiner Al-Ti-B-RE includes the following components in mass fractions: Ti: 5.0%, B: 1.0%, La: 3.2%, and the balance is Al and impurity elements.

[0048] Before smelting, pure aluminum, pure magnesium, aluminum-M master alloy, refining agent and Al-Ti-B-RE composite refiner are placed in a drying oven at a temperature of 200° C. and dried for 2.0 hours for use.

[0049] Add pure aluminum ingots into a smelting furnace, set the furnace temperature to 720°C, and completely melt the aluminum ingots to obtain aluminum melt.

[0050] An aluminum alloy melt is obtained by sequentially adding aluminum-M master alloy and pure Mg into the aluminum melt.

[0051] The temperature of the aluminum alloy melt was raised to 730°C, a refining agent was added to the bottom of the melt, and the aluminum alloy melt was stirred for 8 minutes and then allowed to stand for 8 minutes.

[0052] After slagging, the temperature of the aluminum alloy melt was raised to 750°C, and an Al-Ti-B-RE rare earth composite refiner with a mass fraction of 0.6% was added to the refined aluminum alloy melt, and the mixture was stirred for 5 minutes and then allowed to stand for 10 minutes.

[0053] Subsequently, the furnace temperature was lowered to 720°C, and the aluminum-silicon alloy melt was poured into a metal mold preheated to 175°C at 720°C, with a low speed of 0.30 m / s, a high speed of 3.5 m / s, and a casting pressure of 120 MPa to obtain a fine-grained die-cast aluminum-magnesium alloy containing rare earths. The addition of the rare earth composite refiner reduced the grain size of the alloy, and its grain size was smaller than that of the die-cast aluminum-magnesium alloy after refinement by the Al-Ti-B refiner in Comparative Example 1.

[0054] Example 3

[0055] A prefabricated raw material of pure aluminum, pure magnesium, aluminum-M master alloy, refining agent and Al-Ti-B-RE composite refiner is provided, wherein M comprises Si, Fe and Mn, and the mass proportion of each element in the prefabricated raw material based on 100 parts by mass of all the above prefabricated raw materials is as follows: Mg: 6.90%, Si: 2.60%, Mn: 0.52%, Fe: 0.07%, Ti: 0.04%, B: 0.01%, Er: 0.03%, and the balance is Al and impurity elements.

[0056] The rare earth composite refiner Al-Ti-B-RE includes the following components in mass fractions: Ti: 5.2%, B: 1.3%, Er: 3.5%, and the balance is Al and impurity elements.

[0057] Before smelting, pure aluminum, pure magnesium, aluminum-M master alloy, refining agent and Al-Ti-B-RE composite refiner are placed in a drying oven at a temperature of 200° C. and dried for 2.0 hours for use.

[0058] Add pure aluminum ingots into a smelting furnace, set the furnace temperature to 720°C, and completely melt the aluminum ingots to obtain aluminum melt.

[0059] An aluminum alloy melt is obtained by sequentially adding aluminum-M master alloy and pure Mg into the aluminum melt.

[0060] The temperature of the aluminum alloy melt was raised to 730°C, a special refining agent for aluminum-magnesium alloy was added to the bottom of the melt, and the aluminum alloy melt was stirred for 10 minutes and then allowed to stand for 10 minutes.

[0061] After slagging, the temperature of the aluminum alloy melt was raised to 750°C, and 0.8% by mass of Al-Ti-B-RE rare earth composite refiner was added to the refined aluminum alloy melt, and the mixture was stirred for 5 minutes and then allowed to stand for 10 minutes.

[0062] Subsequently, the furnace temperature was lowered to 720°C, and the aluminum-silicon alloy melt was poured into a metal mold preheated to 175°C at 720°C, with a low speed of 0.40 m / s, a high speed of 3.3 m / s, and a casting pressure of 140 MPa to obtain a fine-grained die-cast aluminum-magnesium alloy containing rare earths. The addition of the rare earth composite refiner reduced the grain size of the alloy, and its grain size was smaller than that of the die-cast aluminum-magnesium alloy refined by the Al-Ti-B refiner in Comparative Example 1.

[0063] Comparative Example 1

[0064] A prefabricated raw material of pure aluminum, pure magnesium, aluminum-M master alloy, refining agent and Al-Ti-B refiner is provided, wherein M comprises Si, Fe and Mn, and the mass proportion of each element in the prefabricated raw material based on 100 parts by mass of all the above prefabricated raw materials is as follows: Mg: 7.40%, Si: 2.60%, Mn: 0.52%, Fe: 0.07%, Ti: 0.025%, B: 0.006%, and the balance is Al and impurity elements.

[0065] The refiner Al-Ti-B includes the following components in mass fractions: Ti: 5.2%, B: 1.2%, and the balance is Al and impurity elements.

[0066] Before smelting, pure aluminum, pure magnesium, aluminum-M master alloy, refining agent and Al-Ti-B refiner are placed in a drying oven at a temperature of 200° C. and dried for 2.0 hours for use.

[0067] Add pure aluminum ingots into a smelting furnace, set the furnace temperature to 720°C, and completely melt the aluminum ingots to obtain aluminum melt.

[0068] An aluminum alloy melt is obtained by sequentially adding aluminum-M master alloy and pure Mg into the aluminum melt.

[0069] The temperature of the aluminum alloy melt was raised to 730°C, a special refining agent for aluminum-magnesium alloy was added to the bottom of the melt, and the aluminum alloy melt was stirred for 8 minutes and then allowed to stand for 8 minutes.

[0070] After slagging, the temperature of the aluminum alloy melt was raised to 750°C, and an Al-Ti-B refiner with a mass fraction of 0.5% was added to the refined aluminum alloy melt. The mixture was stirred for 5 minutes and then allowed to stand for 10 minutes.

[0071] Then, the furnace temperature was lowered to 720°C, and the aluminum-silicon alloy melt was poured into a metal mold preheated to 175°C at 720°C, with a low speed of 0.30 m / s, a high speed of 3.5 m / s, and a casting pressure of 150 MPa to obtain a die-cast aluminum-magnesium alloy.

[0072] Examples 1-3 can all obtain uniform fine-grained structures, and the alloys have good mechanical properties and corrosion resistance. Among them, Example 1 has the smallest grain size and the best refinement effect. Comparing the optical microstructures of the alloys of Example 1 and Comparative Example 1, as shown in FIG. Figure 1-2 As shown, it can be seen that the degree of grain refinement in Example 1 is significantly higher; comparing the scanning microstructures of the refiners in Example 1 and Comparative Example 1, as shown in FIG. Figure 3-4 As shown in the figure, it can be seen that compared with comparative example 1, the aggregation phenomenon of TiB2 particles in Example 1 is improved, and the core-shell TiAl3 formed by RE i2 Al 20 RE phase and Al4RE phase are less, which are helpful to improve the grain refinement effect.

Claims

1. A fine-grained die-cast aluminum-magnesium alloy prepared based on a rare earth composite refiner Al-Ti-B-RE, characterized in that: The rare earth composite refiner Al-Ti-B-RE comprises the following components by mass fraction: Ti 4.0-6.5%, B 0.5-2.0%, RE 2.1-9.0%, and the remainder is Al and impurity elements, and the total mass percentage of the impurity elements is less than or equal to 0.30%; Fine-grained die-cast aluminum prepared based on the rare earth composite refiner Al-Ti-B-RE. The rare earth composite refiner Al-Ti-B-RE includes the following components in mass fraction: Mg 5.00-8.50%, Si 1.50-4.50%, Mn 0.35-0.65%, Fe0.01-0.10%, Ti 0.02-0.25%, B 0.004-0.20%, RE 0.005-0.25%, and the remainder is Al and impurity elements, and the total mass percentage content of the impurity elements is less than or equal to 0.30%.

2. The fine-grained die-cast aluminum-magnesium alloy according to claim 1, characterized in that: The invention comprises the following components in mass fraction: Mg 5.00-8.00%, Si 1.50-4.00%, Mn 0.40-0.65%, Fe 0.01-0.08%, Ti 0.02-0.25%, B 0.004-0.20%, RE 0.005-0.20%, and the balance is Al and impurity elements.

3. The fine-grained die-cast aluminum-magnesium alloy according to claim 1, characterized in that: The rare earth composite refiner Al-Ti-B-RE comprises the following components in mass fractions: Ti 4.0-6.0%, B 0.5-2.0%, RE 2.1-8.5%, and the balance is Al and impurity elements.

4. The fine-grained die-cast aluminum-magnesium alloy according to claim 1 or 3, characterized in that: The rare earth composite refiner Al-Ti-B-RE is added in an amount of 0.10-1.50% in the die-cast aluminum-magnesium alloy.

5. The fine-grained die-cast aluminum-magnesium alloy according to claim 4, characterized in that: The rare earth composite refiner Al-Ti-B-RE is added in an amount of 0.10-1.20% in the die-cast aluminum-magnesium alloy.

6. The fine-grained die-cast aluminum-magnesium alloy according to claim 1, characterized in that: The rare earth includes at least one of La, Ce, Y, Pm, Er, Nd, and Sm.

7. A method for preparing a fine-grained die-cast aluminum-magnesium alloy based on a rare earth composite refiner Al-Ti-B-RE, comprising the following steps: S1. Provide a prefabricated raw material of pure aluminum, pure magnesium, aluminum-M master alloy, refining agent and Al-Ti-B-RE composite refiner, M includes Si, Fe, Mn; the component content of the Al-Ti-B-RE composite refiner and the mass proportion of each element in the prefabricated raw material based on 100 parts by mass of all the above prefabricated raw materials are as shown in claim 1; S2. Before smelting, pure aluminum, pure magnesium, aluminum-M master alloy, refining agent and Al-Ti-B-RE composite refiner are placed in a drying oven at a temperature of 150-250 ° C and dried for 1.5-2.5 hours for use; S3. Adding a pure aluminum ingot into a smelting furnace, setting the furnace temperature to 720°C, and completely melting the aluminum ingot to obtain an aluminum melt; S4. After sequentially adding aluminum-M master alloy and pure Mg to the aluminum melt to obtain an aluminum alloy melt; S5. Raise the temperature of the aluminum alloy melt to 730°C-740°C, add a refining agent to the bottom of the melt, and stir the aluminum alloy melt for 5-10 minutes, and then let it stand for 5-10 minutes; S6. After slagging, the temperature of the aluminum alloy melt is raised to 740°C-760°C, and an Al-Ti-B-RE rare earth composite refiner is added to the refined aluminum alloy melt, and the mixture is stirred for 3-5 minutes and then allowed to stand for 5-20 minutes; S7. Then, the furnace temperature is lowered to 710°C-720°C, and the aluminum-silicon alloy melt is poured into a metal mold preheated to 150-200°C at 710-720°C, with a low speed of 0.10-0.6 m / s, a high speed of 1.5-5.0 m / s, and a casting pressure of 60-180 MPa to obtain a die-cast aluminum-magnesium alloy containing rare earth.

8. The preparation method according to claim 7, characterized in that: The refining agent is a fluoride salt refining agent.

9. A rare earth composite refiner Al-Ti-B-RE suitable for preparing fine-grained die-cast aluminum-magnesium alloy, characterized in that: The invention comprises the following components by mass fraction: Ti 4.0-6.5%, B 0.5-2.0%, RE 2.1-9.0%, and the remainder Al and impurity elements, wherein the total mass percentage of the impurity elements is less than or equal to 0.30%.

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