Preparation method of high-toughness cast Al-Mg-Zn-Sc-Zr alloy

Abstract

The invention belongs to the field of aluminum alloy preparation, and particularly relates to a preparation method of a high-toughness cast Al-Mg-Zn-Sc-Zr alloy. The specific alloy component design is adopted, the use amount of Zn and the use amount of Mn + Sc + Zr are increased, and the structure and performance of the alloy are remarkably improved under the cooperation of the technology. According to the method, as-cast alloy is subjected to pre-aging (300-350 DEG C / 4-8 h) + solution treatment (420-490 DEG C / 12-36 h) and final low-temperature aging (120-180 DEG C / 8-72 h) treatment. The casting stress can be eliminated through pre-aging, a nanophase Al3 (Sc, Zr) can be separated out, intermetallic compounds are dissolved through solution treatment, and dendritic segregation is eliminated. And finally, the microstructure of the alloy is finely regulated and controlled through aging treatment, and the hardness of the product is improved as much as possible on the premise that it is guaranteed that the product has enough strength.

Description

Technical Field

[0001] The present invention belongs to the field of aluminum alloy preparation, and particularly relates to a preparation method of a high-strength and tough cast Al-Mg-Zn-Sc-Zr alloy. Background Art

[0002] With the rapid development of modern industry, aluminum alloy, as a lightweight and high-strength metal material, has been widely used in the fields of aerospace, automotive manufacturing, ship transportation, etc. Among them, Al-Mg series aluminum alloys have become the preferred materials in many industrial fields due to their excellent mechanical properties, corrosion resistance and good weldability. However, with the continuous increase in the strength requirements of engineering practical applications, the performance of traditional Al-Mg series aluminum alloys has been difficult to meet the needs of some high-end fields. Zn is one of the commonly used alloying elements in aluminum alloys. Adding an appropriate amount of Zn element to Al-Mg alloys can significantly improve the mechanical properties of the alloy through solid solution strengthening and aging strengthening mechanisms.

[0003] In the Al-Mg-Zn series aluminum alloy, the composite addition of Sc and Zr elements can form micron-sized Al3(Sc, Zr) primary phases and nano-sized secondary Al3(Sc, Zr) particles. The Al3(Sc, Zr) primary phase can be used as a nucleation site to increase the nucleation rate and refine the grains, thereby improving the alloy properties through fine grain strengthening. In addition, the uniformly distributed nano-sized Al3(Sc, Zr) particles can produce dispersion strengthening. On the basis of maintaining the advantages of the original Al-Mg-Zn series aluminum alloy, the Al-Mg-Zn-Sc-Zr alloy further improves its mechanical properties. However, the preparation process of this alloy is relatively complex, and it is necessary to precisely control various links such as alloy composition, melting process and heat treatment process to ensure the final performance of the alloy.

[0004] The present invention proposes a preparation method of a high-strength and tough cast Al-Mg-Zn-Sc-Zr alloy, aiming to prepare an Al-Mg-Zn-Sc-Zr alloy with excellent mechanical properties by precisely controlling various links such as alloy composition, melting process and heat treatment process, so as to meet the application requirements of higher-end fields. Summary of the Invention

[0005] The purpose of the present invention is to provide a reasonable preparation method of cast Al-Mg-Zn-Sc-Zr alloy. The provided pre-aging treatment eliminates the casting stress and dendritic segregation in the ingot, and promotes the precipitation of nano-sized Al3(Sc, Zr) particles. The solution treatment promotes the dissolution of coarse and continuous second phases. Finally, the aging treatment precisely regulates the precipitation of T-Mg 32 (Al, Zn) 49 phase, improves the comprehensive performance of the alloy, especially improves the hardness of the product as much as possible on the premise of ensuring that the product has sufficient strength.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A preparation method of a high-strength and tough cast Al-Mg-Zn-Sc-Zr alloy. The alloy raw materials are high-purity Al, high-purity Mg, high-purity Zn, Al-Mn, Al-Sc and Al-Zr master alloys respectively. The mass percentages of the alloy components are as follows: Mg 5.0-9.0%, Zn 0.5-4.0%, Mn 0.4-1.0%, Sc 0.2-0.3%, Zr 0.1-0.15%, unavoidable impurities ≤ 0.1%, and the rest is Al.

[0007] Preferably, the mass percentages of the alloy components are as follows: Mg 5.0-9.0%, Zn 3.0-4.0%, Mn 0.6-1.0%, Sc 0.2-0.3%, Zr 0.1-0.15%, unavoidable impurities ≤ 0.1%, and the rest is Al.

[0008] Preferably, in the alloy, by mass percentage, it is composed of the following components: Mg 7.0-9.0%, Zn 3.0-4.0%, Mn 0.6-1.0%, Sc 0.25-0.3%, Zr 0.12-0.15%, unavoidable impurities ≤ 0.1%, and the rest is Al.

[0009] Preferably, in the alloy, by mass percentage, Mn + Sc + Zr is greater than or equal to 0.9%; more preferably 1.0-1.45%.

[0010] As one of the further preferred solutions, when the alloy, by mass percentage, is composed of the following components: Mg 8%, Zn 3.0%, Mn 0.6%, Sc 0.25%, Zr 0.15%, unavoidable impurities ≤ 0.1%, and the rest is Al, with an appropriate process, the tensile strength of the obtained aged product is 477-497 MPa, the yield strength is 318-332 MPa, the elongation is 9.8-12.4%, and the hardness is 145-149 HV.

[0011] As one of the further preferred solutions, when the alloy, by mass percentage, is composed of the following components: Mg 9%, Zn 4.0%, Mn 1.0%, Sc 0.3%, Zr 0.15%, unavoidable impurities ≤ 0.1%, and the rest is Al, with an appropriate process, the average tensile strength of the obtained aged product is 562 MPa, the average yield strength is 423 MPa, the average elongation is 5.2%, and the hardness is 176 HV.

[0012] As one of the further preferred solutions, when the alloy consists of the following components in mass percentage: Mg 7%, Zn 3.5%, Mn 0.6%, Sc 0.3%, Zr 0.15%, unavoidable impurities ≤ 0.1%, and the rest is Al, with appropriate processes, the average tensile strength of the aged product is 506 MPa, the average yield strength is 362 MPa, the average elongation is 7.4%, and the hardness is 162 HV.

[0013] A preparation method of a high-strength and high-toughness cast Al-Mg-Zn-Sc-Zr alloy according to the present invention is carried out according to the following steps:

[0014] Step 1: Raw material preparation: Weigh pure aluminum ingots, pure magnesium ingots, pure zinc ingots, Al-Mn master alloy, Al-Sc master alloy, and Al-Zr master alloy according to the mass ratio of the alloy components, and preheat them.

[0015] Step 2: Melting: Melt Al and then add Al-Mn, Al-Sc, and Al-Zr master alloys, and then add pure Mg and Zn ingots. Wait for all the raw materials to melt and stir evenly to form an aluminum alloy melt.

[0016] Step 3: Refining: Remove gas by passing argon, add C2Cl6 for refining, and remove the surface scum after standing.

[0017] Step 4: Casting: Pour the aluminum alloy melt into an iron mold and rapidly cool to obtain an alloy ingot.

[0018] A preparation method of a high-strength and high-toughness cast Al-Mg-Zn-Sc-Zr alloy is processed successively through the following steps:

[0019] Step A: Pre-aging treatment: Carry out pre-aging treatment on the alloy ingot at a temperature of 300 - 360 °C for 4 - 8 h.

[0020] Step B: Solution treatment: Continue to carry out solution treatment on the alloy obtained from the pre-aging treatment at a temperature of 420 - 490 °C for 12 - 36 h, and then rapidly quench and cool to room temperature.

[0021] Step C: Aging treatment: Keep the alloy after the solution quenching treatment at a temperature of 120 - 180 °C for 8 - 72 h.

[0022] Preferably, in Step A, carry out pre-aging treatment on the alloy ingot at a temperature of 320 - 355 °C for 4 - 8 h. As a further preference, carry out pre-aging treatment on the alloy ingot at a temperature of 345 - 355 °C, which includes 350 °C, for 4 - 6 h.

[0023] Preferably, in step B, the alloy obtained by the pre-aging treatment is further heat-insulated at 420-465°C, more preferably at 450-465°C, for 18-36 h for solution treatment, and then rapidly quenched and cooled to room temperature.

[0024] Preferably, in step C, the alloy after the solution quenching treatment is heat-insulated at 120-150°C for 20-72 h.

[0025] Through the collaborative composition design of appropriate amounts of manganese, light rare earths Sc and Zr, and combined with the innovative pre-aging - high-temperature solution - low-temperature final aging process, the present invention realizes the composite strengthening of Al3(Sc,Zr) particles and nano-T-Mg 32 (Al,Zn) 49 phase. A large amount of zinc in the present invention can modify the high-density nano-T phase formed in the high-magnesium aluminum alloy to provide coherent strain strengthening; an appropriate amount of manganese element can refine the microstructure and improve stability; Sc-Zr generates thermally stable core-shell structure particles to pin dislocations and grain boundaries. The particles pre-implanted by pre-aging provide nucleation sites for the precipitation of the T phase, solution treatment eliminates segregation and dissolves primary phases, and final aging realizes the co-precipitation of two phases. The superposition of modulus difference strengthening, thermal stability improvement and anti-plastic deformation ability significantly enhances the comprehensive mechanical properties of the alloy, especially helps to greatly improve the hardness of the product on the premise of ensuring sufficient strength of the product.

[0026] The benefits of the present invention compared with the prior art are as follows:

[0027] 1. The present invention adds more Zn and Mn elements on the basis of the high-magnesium Al-Mg series alloy, and prepares a true Al-Mg(-Zn-Sc-Zr) alloy by compounding Sc and Zr elements. The primary Al3(Sc, Zr) phase, nano-scale secondary Al3(Sc, Zr) particles and T-Mg 32 (Al, Zn) 49 phase generated in the alloy bring the composite strengthening of fine grain strengthening and precipitation strengthening, which significantly improves the strength of the alloy.

[0028] 2. The pre-aging + high-temperature solution treatment adopted by the present invention has more advantages compared with the conventional single-stage solution treatment. The pre-aging treatment eliminates casting stress and precipitates nano-phases, and the subsequent high-temperature solution treatment dissolves the second phase and eliminates dendritic segregation. Finally, the microstructure of the alloy is finely regulated by aging treatment at a lower but appropriate temperature, which significantly synergistically improves the mechanical properties of the alloy, especially improves the hardness of the alloy.

[0029] 3. The cast Al-Mg-Zn-Sc-Zr alloy of the present invention finely regulates the microstructure through heat treatment, greatly improving the mechanical properties of the alloy. The hardness value is greater than 140 HV, the tensile strength is greater than or equal to 470 MPa, the yield strength is greater than or equal to 300 MPa, and the elongation is greater than or equal to 5.2%. The hardness of the optimized product is greater than or equal to 160 HV, the tensile strength is greater than or equal to 500 MPa, and the yield strength is greater than or equal to 360 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Microstructure images of the samples obtained from Comparative Example 1 and Examples 1, 2, and 3;

[0031] Among them Figure 1 (a) is the IPF color map of Example 1, Figure 1 (d) and (g) are the low-magnification and high-magnification SEM images of Example 1, and Figure (j) is the corresponding EDS analysis result of the high-magnification SEM of Example 1; Figure 1 (b) is the IPF color map of Example 2, Figure 1 (e) and (h) are the low-magnification and high-magnification SEM images of Example 2, and Figure (k) is the corresponding EDS analysis result of the high-magnification SEM of Example 2; Figure 1 (c) is the IPF color map of Example 3 and Comparative Example 1, Figure 1 (f) and (i) are the low-magnification and high-magnification SEM images of Example 3 and Comparative Example 1, and Figure (l) is the corresponding EDS analysis result of the high-magnification SEM of Example 3 and Comparative Example 1;

[0032] Figure 2 TEM images of the samples obtained from Example 4, Example 2, and Example 3;

[0033] Among them Figure 2 (a) and (b) are the dark-field TEM images of Al3(Sc, Zr) particles in Example 2 and Example 3, respectively; Figure 2 (c) is T-Mg 32 (Al, Zn) 49 phase image in Example 4, Figure 2 (d) is the STEM image of the precipitated phase in Example 4 and the corresponding EDS analysis result. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below in combination with the specific embodiments, the explanatory drawings, and the examples. It should be emphasized that the protection scope of the present invention is not limited to the following specific embodiments. The test methods used in the following embodiments are all conventional methods unless otherwise specified; the materials, reagents, instruments, etc. used are all commercially available unless otherwise specified.

[0035] Example 1

[0036] This example presents an Al-Mg-Zn-Sc-Zr alloy composition. The mass percentages of the alloy composition are as follows: 8.0% Mg, 3% Zn, 0.6% Mn, 0.25% Sc, 0.15% Zr, unavoidable impurities ≤ 0.1%, and the rest is Al.

[0037] The preparation method includes the following steps:

[0038] 1. Raw material preparation: Weigh pure aluminum ingots, pure magnesium ingots, pure zinc ingots, Al-Mn master alloy, Al-Sc master alloy, and Al-Zr master alloy according to the mass ratio of the alloy composition and preheat them.

[0039] 2. Melting: When melting the aluminum ingots at 750 - 760 °C, add RJ-2 type covering agent, then add Al-Mn, Al-Sc, and Al-Zr master alloys. Subsequently, cool down to 700 - 710 °C and then add pure Mg and Zn ingots. Wait for all the raw materials to melt and stir evenly to form an aluminum alloy melt.

[0040] 3. Refining: Remove gas by passing argon, add C2Cl6 for refining, let it stand and then remove the surface scum. Refine once before adding the rare earth master alloy and refine again after adding all the alloy elements. After refining, let it stand for 20 - 25 minutes.

[0041] 4. Casting: Pour the aluminum alloy melt into an iron mold at 690 - 700 °C for rapid cooling to obtain alloy ingots.

[0042] Finally, as-cast samples are obtained.

[0043] Example 2

[0044] The as-cast samples obtained in Example 1 are kept at 350 °C for 4 hours for pre-aging treatment.

[0045] Example 3

[0046] The as-cast samples obtained in Example 1 are first kept at 350 °C for 4 hours, then heated to 460 °C and kept at 460 °C for 20 hours to achieve pre-aging + high-temperature solution treatment.

[0047] In Example 1, the grain morphology of the samples was observed by backscattered electron diffraction at 200 times magnification, as shown in Figure 1 (a). It is mainly equiaxed grains with little anisotropy. The intergranular phases that are difficult to analyze can be observed by scanning electron microscopy at 200 times and 600 times magnification, as shown in Figure 1 (d), (g), and (j). The grayish-white phase continuously distributed along the grain boundaries is T-Mg 32 (Al,Zn) 49The phases are as follows: the bright white phase is the Al6Mn phase rich in manganese, and the square phase is the primary Al3(Sc, Zr) phase. The tensile strength, yield strength, and elongation of the alloy in Example 1 are 268 MPa, 237 MPa, and 2.3% respectively, and the hardness is 105 HV.

[0048] Compared with Example 1, after an additional heat treatment at 350 °C for 4 hours in Example 2, as shown in Figures (b), (e), (h), and (k), there are no obvious changes in the grain morphology and the morphology and distribution of the coarse intermetallic phases in the alloy. According to Figure 2 (a), a large number of fine and dispersed secondary Al3(Sc, Zr) particles are precipitated within the grains. The tensile strength, yield strength, and elongation of the alloy in Example 2 are 293 MPa, 265 MPa, and 2.1% respectively, and the hardness is 120 HV.

[0049] In Example 3, a solution treatment at 460 °C for 20 hours is carried out on the basis of Example 2. As can be seen from Figures (c), (f), (i), and (l), after the solution treatment, the continuous coarse T phase between the grains disappears and dissolves back into the matrix, which makes the zero resolution between the grains disappear in the IPF color image, but some primary Al3(Sc, Zr) phases and Al6Mn phases are still retained. In addition, as Figure 2 (b) shows, the precipitated Al3(Sc, Zr) particles within the grains coarsen to a certain extent. The tensile strength, yield strength, and elongation of the alloy in Example 3 are 312 MPa, 205 MPa, and 7.7% respectively, and the hardness is 119 HV.

[0050] Example 4

[0051] Example 4 is subjected to an aging treatment at 150 °C for 24 h on the basis of Example 3, that is, after cooling the sample obtained from the pre-aging + high-temperature solution treatment in Example 3 to room temperature, it is then heated to 150 °C and held at 150 °C for 24 h.

[0052] The microstructure characteristics of the alloy in the product obtained in Example 4 are not changed compared with those in the product obtained in Example 3 at the micron scale. At the nanoscale, combining Figure 2 (c) and (d), it can be found that a large number of fine and dispersed T-Mg 32 (Al,Zn) 49 phases are precipitated within the grains. The tensile strength, yield strength, and elongation of the alloy in Comparative Example 1 reach 487 MPa, 325 MPa, and 11.1% respectively, and the hardness is 147 HV.

[0053] Example 5

[0054] This embodiment proposes an Al-Mg-Zn-Sc-Zr alloy composition. The mass percentages of the alloy composition are as follows: 5.0% Mg, 0.5% Zn, 0.4% Mn, 0.2% Sc, 0.1% Zr, unavoidable impurities ≤ 0.1%, and the rest is Al. The process and parameters of melting-casting are exactly the same as those in Example 1. After obtaining the as-cast product, it is first held at 350 °C for 4 hours, then heated to 460 °C and held at 460 °C for 20 hours, so as to achieve pre-aging + high-temperature solution treatment. Then, after cooling the obtained sample to room temperature, it is heated to 150 °C and held at 150 °C for 24 h; the aged product is obtained, and the mechanical properties of the aged product are shown in Table 1.

[0055] Example 6

[0056] Other conditions are the same as those in Example 5, and the differences are as follows:

[0057] The mass percentages of the alloy composition are as follows: 9.0% Mg, 4.0% Zn, 1.0% Mn, 0.3% Sc, 0.15% Zr, unavoidable impurities ≤ 0.1%, and the rest is Al; the mechanical properties of the aged product are shown in Table 1.

[0058] Example 7

[0059] Other conditions are the same as those in Example 5, and the differences are as follows:

[0060] The mass percentages of the alloy composition are as follows: 7.0% Mg, 3.5% Zn, 0.6% Mn, 0.3% Sc, 0.15% Zr, unavoidable impurities ≤ 0.1%, and the rest is Al; the mechanical properties of the aged product are shown in Table 1.

[0061] Example 8

[0062] Other conditions are the same as those in Example 5, and the differences are as follows:

[0063] The mass percentages of the alloy composition are as follows: 8.0% Mg, 3% Zn, 0.6% Mn, 0.25% Sc, 0.15% Zr, unavoidable impurities ≤ 0.1%, and the rest is Al.

[0064] The process and parameters of melting-casting are exactly the same as those in Example 1. After obtaining the as-cast product, it is first held at 300 °C for 8 hours, then heated to 420 °C and held at 420 °C for 36 hours, so as to achieve pre-aging + high-temperature solution treatment. Then, after cooling the obtained sample to room temperature, it is heated to 180 °C and held at 180 °C for 8 h; the aged product is obtained, and the mechanical properties of the aged product are shown in Table 1. Through the exploration of this example and other examples, it is found that the temperatures of pre-aging treatment and solution treatment cannot be too low, otherwise it will greatly affect the strength of the product, and the increase in its hardness is not significant.

[0065] Example 9

[0066] Other conditions are the same as those in Example 8, except that:

[0067] After obtaining the as-cast product, it is first held at 320 °C for 6 hours, then heated to 450 °C and held at 450 °C for 24 hours to achieve pre-aging + solution heat treatment at high temperature; then after cooling the obtained sample to room temperature, it is heated to 120 °C and held at 120 °C for 72 h; an aged product is obtained, and the mechanical properties of the aged product are shown in Table 1.

[0068] ...... If there are data with better performance, supplement them into the examples according to the listing method of the above examples

[0069] Comparative Example 1

[0070] The mass percentages of the alloy components are respectively: 8.0% Mg, 3% Zn, 0.6% Mn, 0.25% Sc, 0.15% Zr, unavoidable impurities ≤ 0.1%, and the rest is Al.

[0071] The process and parameters of melting-casting are exactly the same as those in Example 1. After obtaining the as-cast product, it is held at 420 °C for 44 hours, then cooled to room temperature, and then heated to 180 °C and held at 180 °C for 8 h; an aged product is obtained, and the mechanical properties of the aged product are shown in Table 1.

[0072] Comparative Example 2

[0073] The mass percentages of the alloy components are respectively: 8.0% Mg, 3% Zn, 0.5% Mn, 0.1% Sc, 0.1% Zr, unavoidable impurities ≤ 0.1%, and the rest is Al.

[0074] The process and parameters of melting-casting are exactly the same as those in Example 1. After obtaining the as-cast product, it is first held at 360 °C for 8 hours, then heated to 420 °C and held at 420 °C for 36 hours; then after cooling the obtained sample to room temperature, it is heated to 180 °C and held at 180 °C for 8 h; an aged product is obtained, and the mechanical properties of the aged product are shown in Table 1.

[0075]

Claims

1. A preparation method of a high-strength and tough cast Al-Mg-Zn-Sc-Zr alloy, characterized in that: The alloy consists of the following components by mass percentage: Mg 5.0 - 9.0%, Zn 0.5 - 4.0%, Mn 0.4 - 1.0%, Sc 0.2 - 0.3%, Zr 0.1 - 0.15%, unavoidable impurities ≤ 0.1%, and the balance is Al; The alloy is prepared by the following steps: Step A: Pre-aging treatment: The alloy ingot is heat-preserved at 300 - 360 °C for 4 - 8 h for pre-aging treatment; Step B: Solution treatment: The alloy obtained from the pre-aging treatment is continuously heat-preserved at 420 - 490 °C for 12 - 36 h for solution treatment, and then rapidly quenched and cooled to room temperature; Step C: Aging treatment: The alloy after solution quenching treatment is heat-preserved at 120 - 180 °C for 8 - 72 h.

2. The preparation method of a high-strength and tough cast Al-Mg-Zn-Sc-Zr alloy according to claim 1, characterized in that: The alloy ingot is prepared by the following steps; Step 1: Raw material preparation: Pure aluminum ingots, pure magnesium ingots, pure zinc ingots, Al-Mn master alloy, Al-Sc master alloy, and Al-Zr master alloy are weighed according to the mass ratio of the alloy components and preheated; Step 2: Melting: After melting Al, add Al-Mn, Al-Sc, and Al-Zr master alloys, and then add pure Mg and Zn ingots. Wait for all the raw materials to melt and stir evenly to form an aluminum alloy melt; Step 3: Refining: Remove gas by passing argon, add C2Cl6 for refining, and remove the surface scum after standing; Step 4: Casting: Pour the aluminum alloy melt into an iron mold and rapidly cool to obtain an alloy ingot.

3. The preparation method of a high-strength and tough cast Al-Mg-Zn-Sc-Zr alloy according to claim 1, characterized in that: In Step A, the alloy ingot is heat-preserved at 320 - 355 °C for 4 - 8 h for pre-aging treatment. As a further preference, the alloy ingot is heat-preserved at 345 - 355 °C, including 350 °C, for 4 - 6 h for pre-aging treatment.

4. The preparation method of a high-strength and tough cast Al-Mg-Zn-Sc-Zr alloy according to claim 1, characterized in that: In Step B, the alloy obtained from the pre-aging treatment is continuously heat-preserved at 420 - 465 °C, preferably 450 - 465 °C, for 18 - 36 h for solution treatment, and then rapidly quenched and cooled to room temperature.

5. The preparation method of a high-strength and tough cast Al-Mg-Zn-Sc-Zr alloy according to claim 1, characterized in that: In Step C, the alloy after solution quenching treatment is heat-preserved at 120 - 150 °C for 20 - 72 h.

6. A method for preparing a high-strength and tough cast Al-Mg-Zn-Sc-Zr alloy according to claim 1, characterized in that: The alloy consists of the following components by mass percentage: Mg 5.0 - 9.0%, Zn 3.0 - 4.0%, Mn 0.6 - 1.0%, Sc 0.2 - 0.3%, Zr 0.1 - 0.15%, unavoidable impurities ≤ 0.1%, and the balance is Al.

7. A method for preparing a high-strength and tough cast Al-Mg-Zn-Sc-Zr alloy according to claim 6, characterized in that: The alloy consists of the following components by mass percentage: Mg 7.0 - 9.0%, Zn 3.0 - 4.0%, Mn 0.6 - 1.0%, Sc 0.25 - 0.3%, Zr 0.12 - 0.15%, unavoidable impurities ≤ 0.1%, and the balance is Al.

8. The preparation method of a high-strength and tough cast Al-Mg-Zn-Sc-Zr alloy according to claim 1, characterized in that: In terms of mass percentage, the alloy is composed of the following components: in the alloy, in terms of mass percentage, Mn + Sc + Zr is greater than or equal to 0.9%; more preferably 1.0 - 1.45%.

9. The preparation method of a high-strength and tough cast Al-Mg-Zn-Sc-Zr alloy according to claim 1, characterized in that: In terms of mass percentage, the alloy is composed of the following components: when in the alloy, in terms of mass percentage, it is composed of the following components, Mg 8%, Zn 3.0%, Mn 0.6%, Sc 0.25%, Zr 0.15%, unavoidable impurities ≤ 0.1%, and the rest is Al, with appropriate processes, the tensile strength of the aged product is 477 - 497 MPa, the yield strength is 318 - 332 MPa, the elongation is 9.8 - 12.4%, and the hardness is 145 - 149 HV.

10. The preparation method of a high-strength and tough cast Al-Mg-Zn-Sc-Zr alloy according to claim 1, characterized in that: In terms of mass percentage, the alloy is composed of the following components: when in the alloy, in terms of mass percentage, it is composed of the following components, Mg 9%, Zn 4.0%, Mn 1.0%, Sc 0.3%, Zr 0.15%, unavoidable impurities ≤ 0.1%, and the rest is Al, with appropriate processes, the average tensile strength of the aged product is 562 MPa, the average yield strength is 423 MPa, the average elongation is 5.2%, and the hardness is 176 HV; or when in the alloy, in terms of mass percentage, it is composed of the following components, Mg 7%, Zn 3.5%, Mn 0.6%, Sc 0.3%, Zr 0.15%, unavoidable impurities ≤ 0.1%, and the rest is Al, with appropriate processes, the average tensile strength of the aged product is 506 MPa, the average yield strength is 362 MPa, the average elongation is 7.4%, and the hardness is 162 HV.

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