Al-Mg-Lu aluminum alloy and preparation method thereof

Abstract

The embodiment of the invention discloses an Al-Mg-Lu aluminum alloy and a preparation method thereof, and relates to the technical field of aluminum alloy preparation. The Al-Mg-Lu aluminum alloy consists of the following components: 1.0 to 5.5 percent of Mg, 0.1 to 1.0 percent of Mn, 0.05 to 0.25 percent of Cr, less than or equal to 0.40 percent of Si, less than or equal to 0.40 percent of Fe, 0.01 to 0.15 percent of Ti, less than or equal to 0.15 percent of the total content of other impurity elements, less than 0.05 percent of Cu, 0.1 to 2.0 percent of Lu and the balance of Al. According to the Al-Mg-Lu aluminum alloy provided by some embodiments of the invention, the plasticity of the aluminum-magnesium alloy is greatly improved, it is indicated that Lu can make the aluminum alloy become a plasticized alloy, the engineering application range of the aluminum alloy is widened, and the performance and economic benefits of the alloy can be improved. The rare earth Lu element is added into the aluminum-magnesium alloy for microalloying, the novel Lu-containing aluminum-magnesium alloy is developed, the alloy can effectively balance the synergy problem of strength and corrosion resistance, and compared with a traditional Sc element for improving the alloy performance, the production cost of the alloy is reduced through addition of the rare earth Lu.

Description

Technical Field

[0001] The present application relates to the technical field of aluminum alloy preparation, and in particular to an Al-Mg-Lu aluminum alloy and a preparation method thereof. Background Art

[0002] Aluminum-magnesium alloy (Mg mass fraction of 1.0-5.5%) is a non-heat-treatable alloy with the characteristics of light weight, medium strength, good corrosion resistance and welding performance. It is widely used in the fields of ships, automobiles, aviation, etc. With the rapid development of global LNG trade and the increasing demand for LNG in China, the demand for LNG carrier tanks continues to expand, and the performance requirements are getting higher and higher. Aluminum-magnesium alloy is a common material for LNG tanks. However, the current performance of aluminum-magnesium alloy cannot fully meet the material standards used in the seaside receiving station of LNG carrier tanks. In addition, aluminum-magnesium alloy is becoming one of the materials used in extreme environments, such as deep space with strong magnetic fields and strong radiation, deep sea with high water pressure and strong currents, the South and North Poles with ultra-low temperature environments, and the high-altitude Tibetan Plateau. However, the research results of existing aluminum-magnesium alloys cannot fully meet the requirements for the use of materials in extreme environments, so it is urgent to modify the performance of this series of alloys. Summary of the invention

[0003] The embodiments of the present application provide an Al-Mg-Lu aluminum alloy and a preparation method thereof, which continuously balances the synergistic problem of the strength and corrosion resistance of the aluminum-magnesium alloy on the basis of reducing the production cost.

[0004] The present application embodiment is implemented by the following technical solutions:

[0005] On the one hand, the embodiment of the present application provides an Al-Mg-Lu aluminum alloy, which is composed of the following components: Mg 1.0-5.5%, Mn 0.1-1.0%, Cr 0.05-0.25%, Si≤0.40%, Fe≤0.40%, Ti 0.01-0.15%, the total content of other impurity elements ≤0.15%, Cu less than 0.05%, Lu content of 0.1-

[0006] 2.0%, and the balance is Al.

[0007] In some embodiments, the alloy is composed of the following components: Mg 3.8-5.0%, Mn 0.3-1.0%, Cr0.05-0.25%, Si≤0.40%, Fe≤0.40%, Ti 0.01-0.15%, the total content of other impurity elements ≤0.15%, Cu less than 0.05%, Lu 0.10-1.5%, and the balance is Al.

[0008] In some embodiments, the alloy is composed of the following components: Mg 4.0-4.9%, Mn 0.4-1.0%, Cr0.05-0.25%, Si≤0.40%, Fe≤0.40%, Ti 0.01-0.15%, the total content of other impurity elements ≤0.15%, Cu less than 0.05%, Lu 0.25-0.35%, and the balance is Al.

[0009] On the other hand, the present invention provides a method for preparing the Al-Mg-Lu aluminum alloy according to any one of the above embodiments, comprising the following steps:

[0010] Step 1: pre-treat pure aluminum ingots, pure magnesium ingots, Al-Mn, Al-Cr, Al-Fe, Al-Si, Al-Lu master alloys, and then weigh the corresponding alloys as ingredients according to the mass fraction ratio of each element; preheat the pure aluminum ingots, pure magnesium ingots, Al-Mn, Al-Cr, Al-Fe, Al-Si and other master alloys, and the smelting tools used;

[0011] Step 2: Preparation of Al 20%-Lu 80% master alloy. The master alloy composition is Al20%-Lu80% (the composition fluctuation range is Al 15-25%, Lu 75-85%. When mixing the ingredients, the composition of aluminum is controlled at 20% of the theoretical value, and the burnout of aluminum is calculated at 8-10%. The smelting can be carried out in a high-temperature medium-frequency induction furnace. First, Al is melted, and then Lu (irregular particles, purity 99.99%) is added when the temperature is raised to 1000-1200°C. After the Lu is melted, the temperature is lowered to 690-730°C and then cast into an intermediate strip or block Al-Lu master alloy. After the actual alloy content is tested, the aluminum ingot is supplemented to the preset composition according to the test results.

[0012] Step 3: When the crucible is heated to 740-760°C and turns red, put in the preheated pure aluminum ingot, and continue to keep warm until the aluminum ingot is completely melted; after the aluminum ingot is melted, heat it to 780-800°C and add Al-Mn, Al-Cr, Al-Fe, and Al-Si intermediate alloys. After the above intermediate or alloy elements are melted and stirred evenly, heat it to 800-820°C, add Al-Lu intermediate alloy, and after the Al-Lu intermediate alloy is melted and stirred evenly, cool it to 720-740°C and add Mg. At the same time, test the alloy composition in the furnace, add aluminum ingots to the preset composition according to the test results, and add Mg ingots to the preset composition after melting evenly. Then cool it to 685-715°C and cast it into the required alloy ingot.

[0013] Step 4: After refining, removing impurities and slag from the melt, it is cast using a preheated mold to obtain an alloy ingot.

[0014] The above-mentioned sequence of steps is only for the convenience of subsequent detailed description of the specific contents of each step and to be able to present it more clearly, but does not limit the sequence of the method. The technical personnel in this field perform different steps in different sequences within a reasonable range to obtain the method of Al-Mg-Lu aluminum alloy, which all fall within the scope of protection of this application.

[0015] In some embodiments, the ingredients in step 1 are calculated. The ingredients of Mn, Fe and other elements are calculated according to the normal burn-out value, and the normal burn-out value is as follows: Mn 0.5-1.5%, Fe 0.1-0.3%, Mg 2.0-4.0%, Al0.5-1.5%. According to the Al-Lu alloy phase diagram, Lu has a high melting point (1663°C) and aluminum will be severely burned during smelting. Therefore, when smelting Al-Lu master alloy, Lu burn-out is calculated as 7-8%, Mg element burn-out is calculated as 3-5%, and Al element burn-out is calculated as 8-10%; when adding Al-Lu master alloy, Lu burn-out is calculated as 2-3%, Mg is calculated as 3-5%, and Al element burn-out is calculated as 2-3%.

[0016] In some embodiments, the preheating temperature of the smelting tool in step 2 is 200-300° C. / 1h-2h;

[0017] In some embodiments, in step 2, different melting temperatures and casting temperatures are designed taking into account the melting point and burning conditions of the alloy components. When melting the Lu element, the temperature is 1000-1200°C; when melting the Al-Lu alloy, the temperature is 800-820°C.

[0018] In some embodiments, Al-Cu intermediate alloy is not added during the smelting process in step three, in order to strictly control the Cu content in the alloy to below 0.05%, thereby significantly improving the corrosion resistance and welding performance of the alloy, thereby achieving the theoretical optimal effect, and at the same time reducing production costs.

[0019] In some embodiments, in step three, since the Mg element is easily burned during the smelting process, magnesium ingots are added to a preset composition before the melt is decontaminated.

[0020] In some embodiments, an Al-Lu master alloy wrapped in aluminum foil is added in step three.

[0021] Compared with the prior art, the embodiments of the present application have the following advantages and beneficial effects:

[0022] The Al-Mg-Lu aluminum alloy provided in some embodiments of the present application greatly improves the plasticity of aluminum-magnesium alloy, indicating that Lu can make aluminum alloy a plasticized alloy, which not only broadens the engineering application scope of aluminum alloy, but also can improve the performance and economic benefits of the alloy. In addition, the addition of rare earth Lu improves the corrosion resistance of the alloy and extends the service life of the alloy. By adding rare earth Lu elements to aluminum-magnesium alloys for microalloying, a new type of Lu-containing aluminum-magnesium alloy is developed. The alloy can effectively balance the synergistic problem of strength and corrosion resistance, and compared with the traditional Sc element that improves the performance of the alloy, the addition of rare earth Lu reduces the production cost of the alloy.

[0023] In the method for preparing Al-Mg-Lu aluminum alloy provided in some embodiments of the present application, the Al-Mg-Lu aluminum alloy and its preparation method obtain a new aluminum-magnesium alloy by optimizing alloy smelting technology, adjusting smelting temperature, adding Al-Lu master alloy and controlling the Cu content in the alloy; and by adding rare earth Lu element for microalloying, the alloy grain size is refined, thereby improving the tensile strength of the aluminum alloy, reducing the tendency of the alloy material to fracture during use, and increasing the reliability of the aluminum-magnesium alloy material during use. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 It is a comparison chart of mechanical properties of Examples 1, 2, 3, and 4 of the present application and Comparative Examples 1, 2, and 3;

[0026] Figure 2 It is a comparison chart of the strength-plasticity products of Examples 1, 2, 3, and 4 of the present application and Comparative Examples 1, 2, and 3;

[0027] Figure 3 1 is a comparison chart of the properties of the cast and rolled states of Examples 1, 2, 3, and 4 of the present application;

[0028] Figure 4 is the EBSD grain size distribution diagram of Examples 1, 2, 3, and 4 of the present application;

[0029] Figure 5 EBSD grain size distribution diagram of comparative examples 1, 2, and 3 of the present application;

[0030] Figure 6 It is the polarization curve diagram of Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3 of the present application. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0032] The terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or device that includes a series of steps or modules is not limited to the listed steps or modules, but may optionally include steps or modules that are not listed, or may optionally include other steps or modules that are inherent to these processes, methods, products, or devices.

[0033] Microalloying is one of the common ways to improve the performance of aluminum-magnesium alloys. It aims to improve the overall performance of the alloy by adding one or more microalloying elements and optimizing the microstructure of the alloy using the microalloying mechanism. The addition of rare earth elements can increase the degree of supercooling, purify impurities, and effectively refine the alloy precipitation phase and cast structure, making a huge contribution to the coordinated optimization of the mechanical properties and corrosion resistance of aluminum-magnesium alloys.

[0034] The microalloying elements of aluminum-magnesium alloys are mainly concentrated in Sc, Zr, Er, Ce, La and other elements. At present, Sc element has the best optimization effect on alloy properties, but Sc element is relatively expensive. Therefore, it is necessary to explore economical and effective microalloying elements to optimize high-magnesium aluminum alloys. Lu, like Sc element, can form L1 2 The second phase of the structure (Al 3 Lu), and Al 3 Lu has strong thermal stability and can improve the hardness and high-temperature creep resistance of the alloy. Its addition has better economic performance than Sc. At the same time, it can balance the synergistic problem of strength and corrosion resistance of aluminum-magnesium alloys and meet the needs of extreme environments such as the high-altitude Tibetan Plateau and ultra-low temperature South and North Poles.

[0035] Example 1

[0036] This embodiment provides an Al-Mg-Lu aluminum alloy, whose composition is Mg 4.5%, Mn 0.4%, Cr 0.1%, Si 0.2%, Fe 0.2%, Ti 0.02%, the total content of other impurity elements is less than or equal to 0.15%, the trace element Cu is strictly controlled to be less than 0.05%, and the balance is Al. On this basis, the addition amount of element Lu is 0.10%.

[0037] Example 2

[0038] This embodiment provides an Al-Mg-Lu aluminum alloy, whose composition is Mg 4.5%, Mn 0.4%, Cr 0.1%, Si 0.2%, Fe 0.2%, Ti 0.02%, the total content of other impurity elements is less than or equal to 0.15%, the trace element Cu is strictly controlled to be less than 0.05%, and the balance is Al. On this basis, the addition amount of element Lu is 0.2%.

[0039] Example 3

[0040] This embodiment provides an Al-Mg-Lu aluminum alloy, whose composition is Mg 4.5%, Mn 0.4%, Cr 0.1%, Si 0.2%, Fe 0.2%, Ti 0.02%, the total content of other impurity elements is less than or equal to 0.15%, the trace element Cu is strictly controlled to be lower than 0.05%, and the balance is Al. On this basis, the addition amount of element Lu is Lu 0.3%.

[0041] Example 4

[0042] This embodiment provides an Al-Mg-Lu aluminum alloy, whose composition is Mg 4.5%, Mn 0.4%, Cr 0.1%, Si 0.2%, Fe 0.2%, Ti 0.02%, the total content of other impurity elements is less than or equal to 0.15%, the trace element Cu is strictly controlled to be lower than 0.05%, and the balance is Al. On this basis, the addition amount of element Lu is Lu 0.5%.

[0043] The method for preparing the Al-Mg-Lu aluminum alloy according to any one of the above embodiments comprises the following steps:

[0044] (1) Pre-treating pure aluminum ingots, pure magnesium ingots, Al-Mn, Al-Cr, Al-Fe, Al-Si, and Al-Lu master alloys, and then weighing corresponding alloys as ingredients according to the mass fraction ratio of each element; preheating pure aluminum ingots, pure magnesium ingots, Al-Mn, Al-Cr, Al-Fe, Al-Si and other master alloys, and smelting tools used;

[0045] (2) Preparation of Al 20%-Lu 80% master alloy. The master alloy composition is Al 20%-Lu 80% (the composition fluctuation range is Al 15-25%, Lu 77-83%. When mixing the materials, the aluminum composition is controlled at 20% of the theoretical value, and the aluminum burnout is calculated at 8-10%. The smelting adopts a high-temperature medium-frequency induction furnace. First, Al is melted, and then Lu (irregular particles, purity 99.99%) is added when the temperature is raised to 1000-1200°C. After the Lu is melted, the temperature is lowered to 690-730°C and then cast into an intermediate strip or block Al-Lu master alloy. After the actual alloy content is tested, the aluminum ingot is supplemented to the preset composition according to the test results.

[0046] (3) When the crucible is heated to 740-760°C and turns red, put in the preheated pure aluminum ingot and continue to keep it warm until the aluminum ingot is completely melted; after the aluminum ingot is melted, heat it to 780-800°C and add Al-Mn, Al-Cr, Al-Fe, and Al-Si intermediate alloys. After the above intermediate or alloy elements are melted and stirred evenly, heat it to 800-820°C and add Al-Lu intermediate alloy. After Lu is melted and stirred evenly, cool it to 720-740°C and add Mg. At the same time, test the alloy composition in the furnace, add aluminum ingots to the preset composition according to the test results, and add Mg ingots to the preset composition after melting evenly. Then cool it to 685-715°C and cast it into the required alloy ingot.

[0047] (4) After refining, removing impurities and slag from the melt, it is cast using a preheated mold to obtain an alloy ingot.

[0048] In addition to the as-cast samples obtained by alloy smelting, the ingots obtained in Examples 1-4 were rolled, and the rolling process was as follows (ie, Examples 1-4 had as-cast samples and rolled samples):

[0049] (5) The ingot was homogenized annealed at 500°C for 12 h, and surface treated. It was then kept at 450°C for 1 h and then hot rolled and cold rolled. After cold rolling, the ingot was subjected to a gold stabilization treatment at 250°C for 2 h and air cooled.

[0050] The cast and rolled samples of the aluminum-magnesium alloy prepared in Examples 1-4 were subjected to room temperature tensile tests. The size of the tensile specimens was designed according to GB / T228-2002, and the tensile rate was 2 mm / min.

[0051] Comparative Example

[0052] Comparative Example 1

[0053] In order to compare the effect of rare earth Lu on the performance of aluminum-magnesium alloy, 5083 aluminum alloy was prepared according to the same preparation method as in Example 1-4, except that the ingredients and proportions were different. Specifically, its composition was Mg 4.5%, Mn 0.4%, Cr 0.1%, Si 0.2%, Fe 0.2%, Ti 0.02%, the total content of other impurity elements was less than or equal to 0.15%, the trace element Cu was strictly controlled to be less than 0.05%, and the balance was Al.

[0054] The prepared aluminum alloy ingot was subjected to a room temperature tensile test in the same manner as the method for preparing the Al-Mg-Lu aluminum alloy.

[0055] Comparative Example 2

[0056] In order to compare the effect of rare earth Lu on the performance of aluminum-magnesium alloy, an aluminum-magnesium alloy was prepared according to the same preparation method as in Examples 1-4, except that the ingredients and proportions were different. Specifically, the composition was Mg 4.5%, Mn 0.4%, Cr 0.1%, Si0.2%, Fe 0.2%, Ti 0.02%, the total content of other impurity elements was less than or equal to 0.15%, the trace element Cu was strictly controlled to be less than 0.05%, and the balance was Al. On this basis, the addition amount of element Lu was 1.0%.

[0057] The prepared aluminum alloy ingot was subjected to a room temperature tensile test in the same manner as the method for preparing the Al-Mg-Lu aluminum alloy.

[0058] Comparative Example 3

[0059] In order to compare the effect of rare earth Lu on the performance of aluminum-magnesium alloy, 5083 aluminum alloy was prepared according to the same preparation method as in Examples 1-4, except that the ingredients and proportions were different. Specifically, its composition was Mg 4.5%, Mn 0.4%, Cr 0.1%, Si 0.2%, Fe 0.2%, Ti 0.02%, the total content of other impurity elements was less than or equal to 0.15%, the trace element Cu was strictly controlled to be less than 0.05%, and the balance was Al. On this basis, the addition amount of element Lu was 1.5%.

[0060] The prepared aluminum alloy ingot was subjected to a room temperature tensile test in the same manner as the method for preparing the Al-Mg-Lu aluminum alloy.

[0061] Performance testing

[0062] The room temperature tensile test was carried out on Examples 1-4 and Comparative Examples 1-3 at a tensile rate of 2 mm / min.

[0063] Table 1 Comparison of mechanical properties of cast alloys

[0064] Serial number Tensile strength / MPa Elongation / % Example 1 184.74 17.78 Example 2 185.20 20 Example 3 187.95 23.33 Example 4 185.77 22.22 Comparative Example 1 168.76 13.33 Comparative Example 2 183.52 22.22 Comparative Example 3 179.31 24.45

[0065] Combined with Table 1, Figure 1It can be concluded that after adding rare earth Lu, the tensile strength and elongation of the alloy are improved to varying degrees, and the tensile strength of the aluminum-magnesium alloy shows a trend of first increasing and then decreasing with the increase of Lu content. When the Lu content (mass fraction, the same below) is 0.3%, the alloy strength reaches the highest, and its tensile strength and elongation are increased by 11.37% and 24.97% respectively compared with the aluminum-magnesium alloy without rare earth addition; when the addition of rare earth Lu exceeds 0.3%, the tensile strength of the alloy begins to decrease, but it is higher than the aluminum-magnesium alloy without rare earth Lu. In particular, the addition of rare earth Lu greatly improves the plasticity of the alloy, indicating that the addition of Lu makes the alloy a plasticized alloy. In addition, the strength-plasticity product is a new indicator to characterize the comprehensive performance of materials, that is, the product of σ (tensile strength) and δ (plasticity), with the unit of MPa / %, expressed by Figure 2 It can be seen that after adding rare earth Lu, the strength-ductility product of the alloy is significantly improved, reaching the highest when Lu is 0.3%, an increase of 94.92%.

[0066] Table 2 Comparison of corrosion resistance of cast alloys

[0067] alloy <![CDATA[E corr (In SCE )]]> <![CDATA[I corr (A / cm -2 )]]> Example 1 -1.00195 <![CDATA[8.6497ⅹ10 -6 ]]> Example 2 -1.00849 <![CDATA[1.1299ⅹ10 -5 ]]> Example 3 -0.96721 <![CDATA[3.74973ⅹ10 -6 ]]> Example 4 -0.94943 <![CDATA[5.7016ⅹ10 -6 <!-- 5 -->]]> Comparative Example 1 -1.05292 <![CDATA[5.3456ⅹ10 -4 ]]> Comparative Example 2 -0.99638 <![CDATA[8.5114ⅹ10 -5 ]]> Comparative Example 3 -0.98305 <![CDATA[1.8365ⅹ10 -5 ]]>

[0068] From Table 2, Figure 4 , Figure 5 It can be seen that compared with aluminum-magnesium alloys without Lu addition, the self-corrosion potential of the alloys after adding rare earth Lu is higher, and their self-corrosion rates are lower than those of alloys without Lu addition. The more positive the self-corrosion potential, the lower the self-corrosion current, and the better the corrosion resistance of the material, it can be seen that the corrosion resistance of the alloys is improved after adding rare earth Lu.

[0069] Table 3 Comparison of mechanical properties of rolled alloys

[0070] alloy Tensile strength / MPa Elongation / % Example 1 246.42 24.44 Example 2 264.22 23.33 Example 3 296.57 23.33 Example 4 280.83 21.11

[0071] From Table 3, Figure 3 It can be seen that after rolling deformation of the cast ingots with Lu content of 0.1, 0.2, 0.3, and 0.5, the tensile strength of the alloy is greatly improved. This is mainly due to the presence of defects such as segregation and pores in the cast alloy. The addition of Lu improves the casting structure, and rolling deformation optimizes the microstructure, that is, through dynamic recrystallization and increased dislocation density, it has the effect of refining grains and eliminating defects, further improving the strength of the alloy.

[0072] Combination Figure 3 It can be seen that the average grain sizes of Examples 1, 2, 3, 4 and Comparative Examples 2 and 3 (corresponding to a, b, c, d, f, g, respectively) are all smaller than the average grain size of Comparative Example 1 (corresponding to e), indicating that the grain size of the aluminum-magnesium alloy is significantly refined after the addition of rare earth Lu, that is, the addition of rare earth Lu has a fine grain strengthening effect on the aluminum-magnesium alloy.

[0073] Combination Figure 3 As can be seen from the figure, during the anodic polarization process, the current density increases with the increase of potential. Once the passivation potential is reached, the process shifts to the passivation zone, which is characterized by a stable current density. The main reason for the formation of the passivation zone is the gradual formation of a passivation film (Al 2 O 3 ), forming a barrier between the matrix and the electrolyte solution. This film layer slows down the dissolution rate of the aluminum-magnesium alloy. pit When the passive film is destroyed, the slope of the polarization curve increases sharply, the corrosion current density increases significantly, and Cl - The continuous erosion of Lu caused the passive film to puncture and peel off, exposing the alloy to the corrosive medium again, and the sample was transformed from a passivated state to an active dissolved state. As Lu increased, the corrosion potential of the alloy increased significantly, and the corrosion current density decreased significantly, indicating that the alloy with Lu added had better corrosion resistance.

[0074] The above description is only a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modification or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. An Al-Mg-Lu aluminum alloy, characterized in that: It is composed of the following components: Mg 1.0-5.5%, Mn 0.1-1.0%, Cr 0.05-0.25%, Si≤0.40%, Fe≤0.40%, Ti 0.01-0.15%, the total content of other impurity elements ≤0.15%, Cu less than 0.05%, Lu content of 0.1-2.0%, and the balance is Al.

2. The Al-Mg-Lu aluminum alloy according to claim 1, characterized in that: It is composed of the following components: Mg 3.8-5.0%, Mn 0.3-1.0%, Cr 0.05-0.25%, Si≤0.40%, Fe≤0.40%, Ti 0.01-0.15%, the total content of other impurity elements ≤0.15%, Cu less than 0.05%, Lu 0.10-1.5%, and the balance is Al.

3. The Al-Mg-Lu aluminum alloy according to claim 1 or 2, characterized in that: It is composed of the following components: Mg 4.0-4.9%, Mn 0.4-1.0%, Cr 0.05-0.25%, Si≤0.40%, Fe≤0.40%, Ti 0.01-0.15%, the total content of other impurity elements ≤0.15%, Cu less than 0.05%, Lu 0.25-0.35%, and the balance is Al.

4. A method for preparing the Al-Mg-Lu aluminum alloy according to any one of claims 1 to 3, characterized in that: The following steps are involved: Pre-treating pure aluminum ingots, pure magnesium ingots, Al-Mn, Al-Cr, Al-Fe, Al-Si, and Al-Lu master alloys, and then weighing corresponding alloys as ingredients according to the mass fraction ratio of each element; preheating the pure aluminum ingots, pure magnesium ingots, master alloys, and smelting tools used; The components of Al-Lu master alloy are Al 15-25% and Lu 75-85%. The preparation of Al-Lu master alloy includes: When mixing the materials, the aluminum component is controlled at 20% of the theoretical value, and the aluminum burnout is calculated at 8-10%. First, melt Al, then heat it to 1000-1200°C and add Lu. After Lu is melted, cool it to 690-730°C and then cast it into an intermediate strip or block Al-Lu intermediate alloy. After testing the actual alloy content, add aluminum ingots to the preset composition according to the test results. When the crucible is heated to 740-760°C and turns red, put the preheated pure aluminum ingot in, and continue to keep the temperature until the aluminum ingot is completely melted; after the aluminum ingot is melted, heat it to 780-800°C, add Al-Mn, Al-Cr, Al-Fe, and Al-Si master alloys, and after the above master alloy elements are melted and stirred evenly, heat it to 800-820°C, add Al-Lu master alloy, and after the Al-Lu master alloy is melted and stirred evenly, cool it to 720-740°C, add pure magnesium ingot, and at the same time, test the alloy composition in the furnace, add aluminum ingot to the preset composition according to the test results, and after melting evenly, add Mg ingot to the preset composition, and then cool it to 685-715°C to cast into the required alloy ingot; After refining, removing impurities and deslagging the melt, it is cast using a preheated mold to obtain an alloy ingot.

5. The method for preparing Al-Mg-Lu aluminum alloy according to claim 4, characterized in that: The ingredient calculation includes: the Mn element burnout is calculated at 0.5-1.5%, the Fe element burnout is calculated at 0.1-0.3%, when smelting Al-Lu master alloy, the Lu element burnout is calculated at 7-8%, and the Al element burnout is calculated at 8-10%; when adding Al-Lu master alloy, the Lu burnout is calculated at 2-3%, Mg is calculated at 3-5%, and the Al element burnout is calculated at 2-3%.

6. The method for preparing Al-Mg-Lu aluminum alloy according to claim 4, characterized in that: The preheating temperature of the smelting tool is 200-300℃ / 1h-2h.

7. The method for preparing Al-Mg-Lu aluminum alloy according to claim 4, characterized in that: When smelting Lu element, the temperature is 1000-1200℃; when smelting Al-Lu alloy, the temperature is 800-820℃.

8. The method for preparing Al-Mg-Lu aluminum alloy according to claim 4, characterized in that: Al-Lu master alloy: Al-Lu master alloy wrapped in aluminum foil is used.

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