A high-fluidity, low-casting-defect, and high-strength-toughness Al-Zn alloy and its preparation method.

Abstract

This invention discloses a high-fluidity, low-casting-defect, and high-strength-toughness Al-Zn alloy and its preparation method, relating to the field of high-performance aluminum alloy materials in aerospace and transportation. The high-fluidity, low-casting-defect, and high-strength-toughness Al-Zn alloy, by mass percentage, comprises the following components: Zn: 5.3-7.3%, Mg: 2.4-3.3%, Cu: 1.4-2.0%, Ni: 0.3-1.3%, Ti: 0.05-0.5%, Zr: 0.03-0.3%, Mn: 0.01-0.2%, Si: ≤0.07%, with Ti and Zr added at a mass ratio of 1-1.5:1. The content of any single impurity is ≤0.03%, and the total impurity content is ≤0.1%, with the balance being aluminum and non-removable impurities. By controlling the content of the main alloying elements and microalloying, the fluidity of the alloy can be improved and casting defects reduced. High-strength and high-toughness alloys can be obtained through heat treatment. The invented alloy has an average spiral flow channel length of ≥700mm, tensile strength of ≥710MPa, yield strength of ≥630MPa, and elongation of ≥8%.

Description

Technical Field

[0001] This invention relates to the field of alloy design and development technology, and to the field of high-performance aluminum alloy materials in aerospace and transportation. Specifically, it relates to an Al-Zn alloy with high fluidity, low casting defects, and high strength and toughness, and its preparation method. Background Technology

[0002] With the high-quality development of my country's transportation industry, industries such as aerospace, road transportation, rail transportation, and water transportation have put forward high requirements for energy saving and weight reduction of components. Aluminum alloys have the characteristics of low density and high strength, and replacing steel with aluminum is an important choice to achieve a win-win situation of economic benefits and lightweight energy saving and weight reduction.

[0003] Al-Zn aluminum alloys are generally formed by forging, and there are few reports on their fluidity. Through literature review, the main approach to developing high-performance aluminum-to-steel alloys is composition optimization and process control. This involves optimizing the content of main alloying elements and microalloying, and developing aluminum alloys by adopting reasonable process control.

[0004] In the prior art, CN 115927933A provides an Al-Zn-Cu-Mg aluminum alloy ingot and its preparation method, which can stably control the ingot forming, with a hydrogen content ≤0.12ml / 100gAl, and the flaw detection of ultra-large-sized, large-deformation complex forgings meets Class A, satisfying the quality requirements of the final product; CN 108286001A describes a high-strength and high-toughness aluminum alloy prepared using semi-solid die casting technology, which consists of Si, Mg, Cu, Ti, V, Sb, Yb, Fe, Al, and other impurity elements. The high-strength and high-toughness aluminum alloy provided by this invention has high strength, good plasticity, and excellent semi-solid die casting process performance. CN 116590557A discloses an aluminum alloy whose raw materials consist of Si, Fe, Zn, Ti, Cu, Mn, Mg, Ni, Zr and the balance Al, and is used in a high-pressure casting process for high-temperature brazable aluminum alloys. This high-temperature brazable aluminum alloy can effectively suppress the formation of interface compounds during low-temperature diffusion reactions, and can also effectively suppress the formation of interface compounds during high-temperature brazing.

[0005] For high-performance aluminum alloys, properties such as fluidity, casting defects, and strength and toughness need to be considered. Existing technologies are insufficient in addressing these properties or fail to meet the requirements. This invention aims to improve the raw materials and processes to obtain alloys with high fluidity, low casting defects, and high strength and toughness, thereby solving the technical problems existing in the prior art. Summary of the Invention

[0006] The purpose of this invention is to provide a high-fluidity, low-casting-defect, and high-strength-toughness Al-Zn alloy and its preparation method. The prepared Al-Zn alloy has an average spiral channel length ≥700mm, tensile strength ≥710MPa, yield strength ≥630MPa, and elongation ≥8%, meeting the requirements of aerospace and transportation fields for high-performance aluminum alloy materials.

[0007] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0008] A highly fluid Al-Zn alloy with low casting defects and high strength and toughness, comprising the following components by mass percentage:

[0009] Zn: 5.3-7.3%, Mg: 2.4-3.3%, Cu: 1.4-2.0%, Ni: 0.3-1.3%, Ti: 0.05-0.5%, Zr: 0.03-0.3%, Mn: 0.01-0.2%, Si: ≤0.07%, Ti and Zr are added at a mass ratio of 1-1.5:1, the content of a single impurity is ≤0.03%, the total impurity content is ≤0.1%, and the balance is aluminum and non-removable impurities.

[0010] Furthermore, the Al-Zn alloy, characterized by high fluidity, low casting defects, and high strength and toughness, comprises the following components by mass percentage:

[0011] Zn: 5.6%, Mg: 2.6%, Cu: 1.7%, Ni: 0.4%, Ti: 0.12%, Zr: 0.1%, Mn: 0.15%, Si: ≤0.05%, Ti and Zr are added at a mass ratio of Ti:Zr = 1.2:1, the content of a single impurity is ≤0.03%, the total impurity content is ≤0.1%, and the balance is aluminum and non-removable impurities.

[0012] Furthermore, the Al-Zn alloy, characterized by high fluidity, low casting defects, and high strength and toughness, comprises the following components by mass percentage:

[0013] Zn: 5.6%, Mg: 2.5%, Cu: 1.6%, Ni: 0.5%, Ti: 0.1%, Zr: 0.1%, Mn: 0.1%, Si: ≤0.05%, Ti and Zr are added in a mass ratio of Ti:Zr = 1:1, the content of a single impurity is ≤0.03%, the total impurity content is ≤0.1%, and the balance is aluminum and non-removable impurities.

[0014] Another objective of this invention is to provide a method for preparing Al-Zn alloys with high fluidity, low casting defects, and high strength and toughness, comprising the following steps:

[0015] S1: Raw material preparation and pretreatment;

[0016] S2: Material feeding and smelting;

[0017] S3: Refining, impurity removal, and heat preservation of the smelted material.

[0018] After the molten metal is fully alloyed, perlite slag remover is added to the alloy melt to collect slag, and argon gas is introduced at the same time for 5-15 minutes. After standing and removing slag, the standing and slag removal steps are repeated twice. Then the aluminum alloy melt is kept at a constant temperature for more than 30 minutes.

[0019] S4: Casting

[0020] The aluminum alloy melt obtained from S3, which has been held at a temperature of 725±10℃ for more than 30 minutes, is poured into a prepared mold for solidification and flowability testing.

[0021] S5: Sampling

[0022] 40 minutes after casting is completed, the spiral casting is removed from the box to obtain the ingot. The length of the spiral flow is measured, and the corresponding casting of the sprue is cut off for later use.

[0023] S6: Homogenization

[0024] Heat the casting corresponding to the sprue in S5 to 350-450℃ and hold for 30-40 hours. Then heat it to 450-550℃ and hold for 30-40 hours. Remove the casting and air cool it.

[0025] S7: Hot Extrusion

[0026] The castings corresponding to the homogenized sprue in S6 are hot extruded at 400-450℃ for 1-3 hours, with a die temperature of 420-460℃ and an extrusion ratio of 20-30.

[0027] S8: Solution treatment

[0028] The extruded parts obtained by hot extrusion in S7 are heated to 435-455℃ and held for 1-3 hours, then heated to 455-475℃ and held for 1-3 hours, and finally heated to 475-495℃ and held for 1.5-2.5 hours, followed by water quenching at room temperature.

[0029] S9: Timeliness Processing

[0030] The extruded parts after solution treatment in S8 are subjected to first-stage aging by holding at 50-90℃ for 20-50 hours, followed by second-stage aging by holding at 100-150℃ for 8-30 hours.

[0031] Furthermore, the raw material preparation and pretreatment in S1 uses high-purity aluminum, high-purity zinc, high-purity magnesium, high-purity copper, high-purity nickel, high-purity manganese, aluminum-titanium master alloy, and aluminum-zirconium master alloy as raw materials. Among them, the purity of high-purity aluminum is ≥99.95%, the purity of high-purity zinc is ≥99.96%, the purity of high-purity magnesium is ≥99.95%, the purity of high-purity copper is ≥99.98%, the purity of high-purity manganese is ≥99.97%, the purity of high-purity zinc is ≥99.9%, the titanium content in the aluminum-titanium master alloy is ≥5.0%, and the zirconium content in the aluminum-zirconium master alloy is ≥5.0%. The surface oxide film of high-purity aluminum, high-purity zinc, and high-purity magnesium is polished and cleaned with sandpaper. After polishing and cleaning, the raw materials are weighed according to the proportion for later use, and a spiral flow mold is prepared.

[0032] Furthermore, the S2 material feeding and smelting process involves adding the raw materials from step S1 into a crucible in sequence for smelting. First, high-purity copper, high-purity nickel, high-purity manganese, aluminum-titanium master alloy, and aluminum-zirconium master alloy are added. The mixture is heated, and after all the metals have melted, it is kept at that temperature for 8 minutes. Then, high-purity aluminum is added, and after all the metals have melted again, it is kept at that temperature for 8 minutes. Finally, high-purity zinc and high-purity magnesium are added.

[0033] Another objective of this invention is to provide a high-performance aluminum alloy for the aerospace and transportation fields, wherein the aluminum alloy is prepared from the above-mentioned raw materials and preparation method.

[0034] The beneficial effects of this invention are as follows:

[0035] This invention reduces the solidification range and low-temperature viscosity of the alloy by adjusting the content of the main alloying elements and the microalloying content, which significantly improves the fluidity of the alloy, reduces the tendency to hot cracking, and reduces product defects. At the same time, high-strength and high-toughness alloys can still be obtained after subsequent processing.

[0036] This invention significantly reduces the tendency of castings to hot crack, reduces defects in ingots, and improves casting quality by adjusting casting process parameters.

[0037] This invention prepares an Al-Zn alloy with high fluidity, low casting defects, and high strength and toughness by homogenizing the ingot, hot pressurizing, three-stage solution treatment, and two-stage aging treatment. The alloy has an average spiral channel length of ≥700mm, tensile strength of ≥710MPa, yield strength of ≥630MPa, elongation of ≥8%, and good toughness.

[0038] The Al-Zn alloy prepared by this invention has high fluidity, low casting defects, and high strength and toughness, with an elongation of ≥8%, which is higher than the elongation of 6% in the prior art. The high fluidity has advantages in plastic deformation and hot working; and it has better formability and connectivity. At the same time, according to the metallographic results, compared with the coarse grains and obvious defects in the prior art, the metallographic images of this invention have fewer defects and finer grains.

[0039] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating the preparation method of the Al-Zn alloy with high fluidity, low casting defects, and high strength and toughness according to an embodiment of the present invention.

[0041] Figure 2 The results of the spiral flow test of the Al-Zn alloy with high fluidity, low casting defects and high strength and toughness in Example 1 of the present invention;

[0042] Figure 3 The results of the spiral flowability test of the Al-Zn alloy with high fluidity, low casting defects and high strength and toughness described in Example 2 of this invention;

[0043] Figure 4 The results of the spiral flowability test of the Al-Zn alloy with high fluidity, low casting defects and high strength and toughness described in Example 3 of this invention;

[0044] Figure 5 The metallographic structure of the Al-Zn alloy with high fluidity, low casting defects and high strength and toughness described in Example 1 of this invention;

[0045] Figure 6 The metallographic structure of the Al-Zn alloy with high fluidity, low casting defects and high strength and toughness described in Example 3 of this invention. Detailed Implementation

[0046] To more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings.

[0047] This invention provides a high-fluidity, low-casting-defect, and high-strength-toughness Al-Zn alloy and its preparation method. The prepared Al-Zn alloy has an average spiral channel length ≥700mm, tensile strength ≥710MPa, yield strength ≥630MPa, and elongation ≥8%. The development of this product can well meet the demand for aluminum to replace steel in many parts and components of the transportation industry.

[0048] The present invention will now be described in conjunction with specific embodiments:

[0049] like Figure 1-6 As shown:

[0050] Example 1 (Comparative Example)

[0051] In this embodiment, an Al-Zn-Mg-Cui aluminum alloy is composed of the following components by mass percentage: Zn: 5.7%, Mg: 2.5%, Cu: 1.6%, with individual impurity content ≤0.03%, total impurity content ≤0.1%, and the balance being aluminum and non-removable impurities.

[0052] The specific preparation method and steps are as follows:

[0053] S1: Preparation of experimental materials: High-purity aluminum, high-purity zinc, high-purity magnesium, and high-purity copper are used as raw materials, wherein the purity of high-purity aluminum is ≥99.95%, the purity of high-purity zinc is ≥99.96%, the purity of high-purity magnesium is ≥99.95%, and the purity of high-purity copper is ≥99.98%. The oxide film on the surface of high-purity aluminum, high-purity zinc, and high-purity magnesium is polished and cleaned with sandpaper. After polishing and cleaning, the raw materials are weighed according to the ratio for later use, and a spiral flow mold is prepared.

[0054] S2: Adding materials: Add the raw materials from step S1 to the crucible in sequence for melting. First, add high-purity copper, high-purity nickel, high-purity manganese, aluminum-titanium master alloy, and aluminum-zirconium master alloy. Heat and hold for 7 minutes after all the metals have melted. Then add high-purity aluminum and hold for 7 minutes after all the metals have melted again. Finally, add high-purity zinc and high-purity magnesium.

[0055] S3: Refining, impurity removal, and heat preservation: After the molten metal is fully alloyed, add the slag remover to the alloy melt to collect slag, and simultaneously introduce argon gas for 10 minutes. Let it stand, remove the slag, and repeat the standing and slag removal operation twice. Then, let the aluminum alloy melt stand and keep it at a constant temperature for more than 30 minutes.

[0056] S4: Casting: After the melt is kept at a certain temperature for a period of time, the melting power is turned off, the crucible is taken out, the melt temperature is kept at 725±10℃, and the melt is poured into the mold prepared in S1 for solidification and fluidity testing.

[0057] S5: Sampling: 40 minutes after casting is completed, open the mold and remove the spiral casting to obtain the ingot. Measure the spiral flow length and cut off the corresponding casting from the sprue for later use.

[0058] S6: Homogenization: Heat the casting corresponding to the sprue in S5 to 380±10℃, hold for 35h, then heat to 400±10℃, hold for 35h, then remove the casting and air cool it.

[0059] S7: Hot extrusion: The casting corresponding to the homogenized sprue in S6 is held at 420±10℃ for 2 hours and then hot extruded. The die temperature is 440℃ and the extrusion ratio is 20.

[0060] S8: Solution treatment: The extruded part obtained from S7 after hot extrusion is heated to 450℃ and held for 1.5h, then heated to 460℃ and held for 1.5h, and finally heated to 480℃ and held for 2h, and then water quenched at room temperature.

[0061] S9: Aging treatment: The extruded parts after solution treatment in S8 are subjected to long-term heat treatment at 50-60℃ for 35 hours for the first stage of aging, and then subjected to heat treatment at 100-120℃ for 15 hours for the second stage of aging.

[0062] The results are as follows: the average length of the spiral channel is 368.33 mm, the tensile strength is 515 MPa, the yield strength is 450 MPa, and the elongation is 6%.

[0063] The spiral flowability test results of the material prepared in Example 1 are as follows: Figure 2 As shown;

[0064] The metallographic structure of the high fluidity, low casting defects, and high strength and toughness Al-Zn alloy described in Example 1 is as follows: Figure 5 As shown, its defects are obvious, and the grains are coarse.

[0065] Example 2

[0066] In this embodiment, an Al-Zn alloy with high fluidity, low casting defects, and high strength and toughness is composed of the following components by mass percentage:

[0067] Zn: 5.6%, Mg: 2.6%, Cu: 1.7%, Ni: 0.4%, Ti: 0.12%, Zr: 0.1%, Mn: 0.15%, Si: ≤0.05%, Ti and Zr are added at a mass ratio of Ti:Zr = 1.2:1, the content of a single impurity is ≤0.03%, the total impurity content is ≤0.1%, and the balance is aluminum and non-removable impurities.

[0068] The specific preparation method and steps are as follows:

[0069] S1: Preparation of experimental materials: High-purity aluminum, high-purity zinc, high-purity magnesium, high-purity copper, high-purity nickel, high-purity manganese, aluminum-titanium master alloy, and aluminum-zirconium master alloy are used as raw materials. Among them, the purity of high-purity aluminum is ≥99.95%, the purity of high-purity zinc is ≥99.96%, the purity of high-purity magnesium is ≥99.95%, the purity of high-purity copper is ≥99.98%, the purity of high-purity manganese is ≥99.97%, the purity of high-purity zinc is ≥99.9%, the titanium content in the aluminum-titanium master alloy is ≥5.0%, and the zirconium content in the aluminum-zirconium master alloy is ≥5.0%. The surface oxide film of high-purity aluminum, high-purity zinc, and high-purity magnesium is polished and cleaned with sandpaper. After polishing and cleaning, the raw materials are weighed according to the proportions for later use, and a spiral flow mold is prepared.

[0070] S2: Adding materials: Add the raw materials from step S1 to the crucible in sequence for melting. First, add high-purity copper, high-purity nickel, high-purity manganese, aluminum-titanium master alloy, and aluminum-zirconium master alloy. Heat and hold for 8 minutes after all the metals have melted. Then add high-purity aluminum and hold for 8 minutes after all the metals have melted again. Finally, add high-purity zinc and high-purity magnesium.

[0071] S3: Refining, impurity removal, and heat preservation: After the molten metal is fully alloyed, add the slag remover to the alloy melt to collect slag, and simultaneously introduce argon gas for 10 minutes. Let it stand, remove the slag, and repeat the standing and slag removal operation twice. Then, let the aluminum alloy melt stand and keep it at a constant temperature for more than 30 minutes.

[0072] S4: Casting: After the melt is kept at a certain temperature for a period of time, the melting power is turned off, the crucible is taken out, the melt temperature is kept at 725±8℃, and the melt is poured into the mold prepared in S1 for solidification and fluidity testing.

[0073] S5: Sampling: 40 minutes after casting is completed, open the mold and remove the spiral casting to obtain the ingot. Measure the spiral flow length and cut off the corresponding casting from the sprue for later use.

[0074] S6: Homogenization: Heat the casting corresponding to the sprue in S5 to 380±10℃, hold for 35h, then heat to 400±10℃, hold for 35h, then remove the casting and air cool it.

[0075] S7: Hot extrusion: The casting corresponding to the homogenized sprue in S6 is held at 420±10℃ for 2.5h and then hot extruded. The die temperature is 450℃ and the extrusion ratio is 23.

[0076] S8: Solution treatment: The extruded part obtained from hot extrusion in S7 is heated to 450℃ and held for 2 hours, then heated to 460℃ and held for 2 hours, and finally heated to 480℃ and held for 2 hours, and then water quenched at room temperature.

[0077] S9: Aging treatment: The extruded parts after solution treatment in S8 are subjected to long-term heat treatment at 60-70℃ for 40 hours for the first stage of aging, followed by heat treatment at 100-120℃ for 20 hours for the second stage of aging.

[0078] The results are: average length of spiral channel ≥700mm, tensile strength ≥715MPa, yield strength ≥634MPa, elongation ≥8%.

[0079] like Figure 2 The figure shows the spiral flow test results of the Al-Zn alloy with high fluidity, low casting defects, and high strength and toughness described in Example 2.

[0080] Example 3

[0081] In this embodiment, an Al-Zn alloy with high fluidity, low casting defects, and high strength and toughness is composed of the following components by mass percentage:

[0082] Zn: 5.6%, Mg: 2.5%, Cu: 1.6%, Ni: 0.5%, Ti: 0.1%, Zr: 0.1%, Mn: 0.1%, Si: ≤0.05%, Ti and Zr are added in a mass ratio of Ti:Zr = 1:1, the content of a single impurity is ≤0.03%, the total impurity content is ≤0.1%, and the balance is aluminum and non-removable impurities.

[0083] The specific preparation method and steps are as follows:

[0084] S1: Preparation of experimental materials: High-purity aluminum, high-purity zinc, high-purity magnesium, high-purity copper, high-purity nickel, high-purity manganese, aluminum-titanium master alloy, and aluminum-zirconium master alloy are used as raw materials. Among them, the purity of high-purity aluminum is ≥99.95%, the purity of high-purity zinc is ≥99.96%, the purity of high-purity magnesium is ≥99.95%, the purity of high-purity copper is ≥99.98%, the purity of high-purity manganese is ≥99.97%, the purity of high-purity zinc is ≥99.9%, the titanium content in the aluminum-titanium master alloy is ≥5.0%, and the zirconium content in the aluminum-zirconium master alloy is ≥5.0%. The surface oxide film of high-purity aluminum, high-purity zinc, and high-purity magnesium is polished and cleaned with sandpaper. After polishing and cleaning, the raw materials are weighed according to the proportions for later use, and a spiral flow mold is prepared.

[0085] S2: Adding materials: Add the raw materials from step S1 to the crucible in sequence for melting. First, add high-purity copper, high-purity nickel, high-purity manganese, aluminum-titanium master alloy, and aluminum-zirconium master alloy. Heat and hold for 10 minutes after all the metals have melted. Then add high-purity aluminum and hold for 10 minutes after all the metals have melted again. Finally, add high-purity zinc and high-purity magnesium.

[0086] S3: Refining, impurity removal, and heat preservation: After the molten metal is fully alloyed, add the slag remover to the alloy melt to collect slag, and simultaneously introduce argon gas for 10 minutes. Let it stand, remove the slag, and repeat the standing and slag removal operation twice. Then, let the aluminum alloy melt stand and keep it at a constant temperature for more than 30 minutes.

[0087] S4: Casting: After the melt is kept at a certain temperature for a period of time, the melting power is turned off, the crucible is taken out, the melt temperature is kept at 725±5℃, and the melt is poured into the mold prepared in S1 for solidification and fluidity testing.

[0088] S5: Sampling: 40 minutes after casting is completed, open the mold and remove the spiral casting to obtain the ingot. Measure the spiral flow length and cut off the corresponding casting from the sprue for later use.

[0089] S6: Homogenization: Heat the casting corresponding to the sprue in S5 to 400±5℃, hold for 37h, then heat to 420±5℃, hold for 37h, then remove the casting and air cool it.

[0090] S7: Hot extrusion: The casting corresponding to the homogenized sprue in S6 is held at 430±5℃ for 2.5h and then hot extruded. The die temperature is 450℃ and the extrusion ratio is 25.

[0091] S8: Solution treatment: The extruded part obtained from hot extrusion in S7 is heated to 455℃ and held for 2.5h, then heated to 470℃ and held for 2.5h, and finally heated to 490℃ and held for 2.5h, and then water quenched at room temperature.

[0092] S9: Aging treatment: The extruded parts after solution treatment in S8 are subjected to long-term heat treatment at 60-65℃ for 45 hours for the first stage of aging, and then subjected to heat treatment at 100-110℃ for 25 hours for the second stage of aging.

[0093] The results are as follows: average length of spiral channel ≥720mm, tensile strength ≥700MPa, yield strength ≥635MPa, elongation ≥8%.

[0094] The spiral flowability test results of the material prepared in Example 3 are as follows: Figure 4 As shown;

[0095] The metallographic structure of the high-fluidity, low-casting-defect, and high-strength-toughness Al-Zn alloy described in Example 3 is as follows: Figure 6 As shown, it has few defects and fine grains.

[0096] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Many modifications and variations can be made based on the content of this specification. These embodiments have been selected and specifically described in this specification to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing an Al-Zn alloy with high fluidity, low casting defects, and high strength and toughness, characterized in that: The alloy comprises the following components by mass percentage: Zn: 5.3-7.3%, Mg: 2.4-3.3%, Cu: 1.4-2.0%, Ni: 0.3-1.3%, Ti: 0.05-0.5%, Zr: 0.03-0.3%, Mn: 0.01-0.2%, Si: ≤0.07%, Ti and Zr are added at a mass ratio of 1-1.5:1, the content of a single impurity is ≤0.03%, the total impurity content is ≤0.1%, and the balance is aluminum and non-removable impurities; The preparation method includes the following steps: S1: Raw material preparation and pretreatment; S2: Material feeding and smelting; S3: Refining, impurity removal, and heat preservation of the smelted material. After the molten metal is fully alloyed, perlite slag remover is added to the alloy melt to collect slag, and argon gas is introduced at the same time for 5-15 minutes. After standing and removing slag, the standing and slag removal steps are repeated twice. Then the aluminum alloy melt is kept at a constant temperature for more than 30 minutes. S4: Casting The aluminum alloy melt obtained from S3, which has been held at a temperature of 725±10℃ for more than 30 minutes, is poured into a prepared mold for solidification and flowability testing. S5: Sampling 40 minutes after casting is completed, the spiral casting is removed from the box to obtain the ingot. The spiral flow length is measured, and the corresponding casting of the sprue is cut off for later use. S6: Homogenization Heat the casting corresponding to the sprue in S5 to 350-450℃ and hold for 30-40 hours. Then heat it to 450-550℃ and hold for 30-40 hours. Remove the casting and air cool it. S7: Hot Extrusion The castings corresponding to the homogenized sprue in S6 are hot extruded at 400-450℃ for 1-3 hours, with a die temperature of 420-460℃ and an extrusion ratio of 20-30. S8: Solution treatment The extruded parts obtained by hot extrusion in S7 are heated to 435-455℃ and held for 1-3 hours, then heated to 455-475℃ and held for 1-3 hours, and finally heated to 475-495℃ and held for 1.5-2.5 hours, followed by water quenching at room temperature. S9: Timeliness Processing The extruded parts after solution treatment in S8 are subjected to first-stage aging by holding at 50-90℃ for 20-50 hours, followed by second-stage aging by holding at 100-150℃ for 8-30 hours.

2. The method for preparing a high-fluidity, low-casting-defect, and high-strength-toughness Al-Zn alloy as described in claim 1, characterized in that: The high-fluidity, low-casting-defect, and high-strength-toughness Al-Zn alloy comprises, by mass percentage, the following components: Zn: 5.6%, Mg: 2.6%, Cu: 1.7%, Ni: 0.4%, Ti: 0.12%, Zr: 0.1%, Mn: 0.15%, Si: ≤0.05%, Ti and Zr are added at a mass ratio of Ti:Zr = 1.2:1, the content of a single impurity is ≤0.03%, the total impurity content is ≤0.1%, and the balance is aluminum and non-removable impurities.

3. The method for preparing a high-fluidity, low-casting-defect, and high-strength-toughness Al-Zn alloy as described in claim 1, characterized in that: The high-fluidity, low-casting-defect, and high-strength-toughness Al-Zn alloy comprises, by mass percentage, the following components: Zn: 5.6%, Mg: 2.5%, Cu: 1.6%, Ni: 0.5%, Ti: 0.1%, Zr: 0.1%, Mn: 0.1%, Si: ≤0.05%, Ti and Zr are added in a mass ratio of Ti:Zr = 1:1, the content of a single impurity is ≤0.03%, the total impurity content is ≤0.1%, and the balance is aluminum and non-removable impurities.

4. The preparation method according to claim 1, characterized in that: The raw material preparation and pretreatment in S1 uses high-purity aluminum, high-purity zinc, high-purity magnesium, high-purity copper, high-purity nickel, high-purity manganese, aluminum-titanium master alloy, and aluminum-zirconium master alloy as raw materials. Among them, the purity of high-purity aluminum is ≥99.95%, high-purity zinc is ≥99.96%, high-purity magnesium is ≥99.95%, high-purity copper is ≥99.98%, high-purity manganese is ≥99.97%, high-purity zinc is ≥99.9%, the titanium content in the aluminum-titanium master alloy is ≥5.0%, and the zirconium content in the aluminum-zirconium master alloy is ≥5.0%. The surface oxide film of high-purity aluminum, high-purity zinc, and high-purity magnesium is polished and cleaned with sandpaper. After polishing and cleaning, the raw materials are weighed according to the proportion for later use, and a spiral flow mold is prepared.

5. The preparation method according to claim 1, characterized in that: The S2 material feeding and smelting process involves adding the raw materials from step S1 into a crucible in sequence for smelting. First, high-purity copper, high-purity nickel, high-purity manganese, aluminum-titanium master alloy, and aluminum-zirconium master alloy are added. The mixture is heated until all the metals have melted and then kept at that temperature for 8 minutes. Next, high-purity aluminum is added, and after the metals have melted completely again, the mixture is kept at that temperature for 8 minutes. Finally, high-purity zinc and high-purity magnesium are added.

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