Al-mg-si alloy with micro-nano composite structure and preparation method thereof

Abstract

The application discloses an Al-Mg-Si alloy with micro-nano composite structure and a preparation method thereof. The Al-Mg-Si alloy comprises Mg, Mn, Si, Cu, Fe, Zn, Sc, Zr, Hf and Al. The Al-Mg-Si alloy of some examples of the application contains nano-sized strengthening phases, wherein the average diameter of the Mg2Si phase is 8-10 nm, and the average diameter of the Al3(Sc, Zr, Hf) phase is 15-20 nm. These fine nano second phases can hinder dislocation movement through the Orowan mechanism, thereby strengthening the alloy matrix. The Al3(Sc, Zr, Hf) phase has a coherent interface relationship with the aluminum matrix, and can further improve the mechanical properties of the Al-Mg-Si alloy through the cutting mechanism. The fine grains of double-size grains have obvious strengthening effect, and the coarse / fine distributed grains can coordinate strain and improve the plasticity and toughness of the alloy. The yield strength of the alloy at room temperature is 343-355 MPa, the tensile strength is 368-392 MPa, and the elongation is 11.2-14.6%, so that the alloy can be used as a light structure material for large load requirements.

Description

Technical Field

[0001] This invention belongs to the field of new materials, specifically relating to an Al-Mg-Si alloy with a micro-nano composite structure and its preparation method. Background Technology

[0002] Aluminum alloys are promising lightweight structural materials, especially Al-Mg-Si alloys. Due to their high specific strength, low density, excellent weldability, and good machinability, they are widely used in automotive structural components, building materials, and marine parts. To improve the safety of structural components, Al-Mg-Si alloys require high strength to meet heavy loads, while also possessing high ductility and toughness for subsequent processing and to prevent sudden instability failure. However, Al-Mg-Si alloys have moderate strength, making it difficult to significantly increase their strength through ordinary processing deformation and heat treatment. Furthermore, a substantial increase in the strength of Al-Mg-Si alloys leads to a significant decrease in ductility and toughness, meaning poorer machinability and lower part yield. Al-Mg-Si alloys face a "strength-toughness mismatch" problem, severely limiting their further applications. Therefore, there is an urgent need for an Al-Mg-Si alloy material with both high strength and high toughness.

[0003] Traditional strengthening mechanisms for metallic materials mainly include work hardening, solid solution strengthening, second-phase strengthening, and grain refinement strengthening. Based on these mechanisms, increasing the processing rate, increasing the content of solid solution elements, and introducing nano-precipitates can significantly improve the strength of Al-Mg-Si alloys. However, these methods all increase the strength of the alloy at the expense of toughness and cannot obtain Al-Mg-Si alloys with high strength and toughness.

[0004] CN113430428A discloses an Al-Mg-Si aluminum alloy with the following mass percentage composition: Er: 0.01wt%–0.2wt%, Zr: 0.01wt%–0.06wt%, Si: 0.9wt%–1.05wt%, Mg: 0.9wt%–1.2wt%, Mn: 0.5wt%–0.8wt%, Zn: 0.01wt%–0.2wt%, Ti: 0.01wt%–0.1wt%, Cr: 0.01wt%–0.2wt%, with the balance being Al and unavoidable impurities. The addition of Zr to the Al-Mg-Si aluminum alloy significantly inhibits recrystallization, increases the recrystallization temperature, refines the recrystallized grains, and improves the alloy's strength and plasticity. Er is an effective microalloying element, capable of forming an Al3Er phase with an L12 structure with Al, and when combined with Zr, it can form Al3(Zr) phase with even better thermal stability. x Er -xThese strengthening phases can effectively improve the microstructure and properties of aluminum alloys, thereby enhancing their overall performance.

[0005] CN106350713A discloses an Al-Mg-Si alloy, composed of the following components by weight percentage: Mg, Mn, Si, Cr, Cu, Fe≤0.32%, Zn≤0.25%, Ti≤0.1%, with the remainder being Al and some unavoidable impurity elements. By optimizing the alloy composition and adjusting the second-phase structure to suppress abnormal grain growth, while rationally controlling the Mg and Si content, the strength of the alloy sheet is effectively improved. Furthermore, hot-top casting and high-temperature homogenization heat treatment reduce component segregation and fully precipitate the second phase that suppresses abnormal grain growth. Moreover, the hot rolling process of this invention controls the final rolling temperature and the reduction rate of each rolling pass, effectively improving the internal structure and energy storage of the alloy. A multi-stage solution quenching process ensures uniform grain growth, ultimately refining the grains, improving the strength and plasticity of the alloy sheet, and reducing bending cracks. Through the step-by-step interaction and influence of the method of this invention, grain size can be effectively controlled, eliminating the orange peel texture phenomenon on the surface of the alloy sheet after stretching, and improving the surface quality of the sheet.

[0006] Existing Al-Mg-Si alloys primarily rely on grain refinement to improve material properties. While adding grain refiners to achieve fine grains can produce alloys with certain strength and toughness, Al-Mg-Si alloys are commonly used as wrought aluminum alloys, and their grain size is directly related to subsequent processing, deformation, and heat treatment. When the grain size is reduced to below 1 μm, forming ultrafine or nanocrystalline grains, the alloy's strength increases significantly, but its plasticity deteriorates. Therefore, it is necessary to control the appropriate grain size and dispersed strengthening phases to overcome the "strength-toughness mismatch" problem, thereby obtaining high-strength and high-toughness Al-Mg-Si alloy materials.

[0007] Heterogeneous structures are an effective alloy design strategy for addressing the strength-toughness mismatch problem in alloy materials. The aim is to design and fabricate alloys with multi-scale or differently sized "non-homogeneous" structures. Designed "non-homogeneous" structures can generate geometrically necessary dislocations to coordinate interfacial strain gradients, increasing new non-uniform deformation and thus leading to additional strain hardening and strengthening. Specifically, when the alloy grains exhibit a dual-size distribution (i.e., a certain amount of grains with significantly different sizes), large grains can store dislocations and hinder crack propagation, while small grains can absorb energy and act as grain refiners, resulting in an alloy with excellent overall performance. Furthermore, increasing the variety of dispersed strengthening phases in the alloy and precipitating nanoscale second phases of different sizes can achieve synergistic strengthening effects. Dispersed strengthening phases of various sizes can strengthen the alloy matrix using shear and Orowan mechanisms, further improving the alloy's mechanical properties. However, achieving a satisfactory heterogeneous structure by adjusting the alloy composition remains extremely difficult. Summary of the Invention

[0008] The purpose of this invention is to overcome at least one deficiency of the prior art and provide an Al-Mg-Si alloy with a micro-nano composite structure and its preparation method.

[0009] The technical solution adopted in this invention is:

[0010] The first aspect of the present invention provides:

[0011] A micro / nano composite Al-Mg-Si alloy has the following mass composition: Mg 0.7-1.3%, Mn 0.15-0.3%, Si 0.6-1.1%, Cu 0.1-0.3%, Fe 0.2-0.4%, Zn 0.2-0.3%, Sc 0.1-0.2%, Zr 0.1-0.2%, Hf 0.3-0.45%, with the balance being unavoidable impurities and Al.

[0012] In some examples of Al-Mg-Si alloys, the mass ratio of Hf:Sc:Zr is (2-4):1:1.

[0013] In some examples of Al-Mg-Si alloys, two nanoscale reinforcing phases are contained: Mg2Si phase and Al3(Sc,Zr,Hf) phase. The average diameter of the Mg2Si phase is 8–10 nm, and the average diameter of the Al3(Sc,Zr,Hf) phase is 15–20 nm.

[0014] In some examples of Al-Mg-Si alloys, there are micron-sized dual-grain structures, with core grains of 15–30 μm and surface grains of 100–135 μm.

[0015] In some examples of Al-Mg-Si alloys, the mass ratio of Hf:Sc:Zr is (2-4):1:1, and it contains two nanoscale reinforcing phases: Mg2Si phase and Al3(Sc,Zr,Hf) phase. The average diameter of the Mg2Si phase is 8-10 nm, and the average diameter of the Al3(Sc,Zr,Hf) phase is 15-20 nm.

[0016] In some examples of Al-Mg-Si alloys, the mass ratio of Hf:Sc:Zr is (2-4):1:1, containing two nanoscale reinforcing phases: Mg2Si phase and Al3(Sc,Zr,Hf) phase. The Mg2Si phase has an average diameter of 8-10 nm, and the Al3(Sc,Zr,Hf) phase has an average diameter of 15-20 nm. The alloys contain micron-sized dual-size grains, with the core grain size being 15-30 μm and the surface grain size being 100-135 μm.

[0017] In some examples of Al-Mg-Si alloys, the amount of unavoidable impurities does not exceed 0.1%.

[0018] A second aspect of the present invention provides:

[0019] The method for preparing the Al-Mg-Si alloy according to the first aspect of the present invention includes the following steps:

[0020] S1) Ingredients: Weigh the raw materials according to the composition of the Al-Mg-Si alloy and clean them thoroughly;

[0021] S2) Melting and casting: The prepared raw materials are heated and melted, mixed, degassed and refined, slag removed and then cast, and cooled to obtain alloy ingots.

[0022] S3) Extrusion molding: The alloy ingot is heated to 540-550℃ and then directly hot extruded. The extrusion ratio is 35-42. After cooling, the hot extruded material is obtained.

[0023] S4) Heat treatment: The hot extruded material is heated to 350-540℃ for solution treatment, held at the temperature and then water-cooled, followed by aging treatment to obtain Al-Mg-Si alloy.

[0024] In some examples of preparation methods, a three-stage variable speed extrusion is used during extrusion molding, with extrusion speeds of 3–5 mm / s, 6–7 mm / s, and 8–10 mm / s, respectively.

[0025] In some examples of preparation methods, during extrusion molding, the temperature is heated to 540–550°C and then held for 8–10 hours.

[0026] In some examples of preparation methods, during extrusion molding, the temperature is heated to 540–550°C and held for 8–10 hours. During extrusion molding, a three-stage variable speed extrusion is used, with extrusion speeds of 3–5 mm / s, 6–7 mm / s, and 8–10 mm / s, respectively.

[0027] In some examples of preparation methods, the solution treatment is carried out in stages, with the first stage being 350–400 °C for 40 min and the second stage being 530–540 °C for 25 min.

[0028] In some examples of preparation methods, the aging temperature is 165–180℃ and the aging time is 6–8 hours.

[0029] In some examples of preparation methods, the solution treatment is carried out in stages: the first stage solution treatment is carried out at 350-400℃ for 40 min, the second stage solution treatment is carried out at 530-540℃ for 25 min, the aging temperature is 165-180℃, and the aging time is 6-8 h.

[0030] The beneficial effects of this invention are:

[0031] Some examples of the Al-Mg-Si alloys of this invention contain nanoscale reinforcing phases. After aging, the average diameter of the Mg2Si phase is 8–10 nm, and the average diameter of the Al3(Sc,Zr,Hf) phase is 15–20 nm. These fine nanoscale second phases can hinder dislocation movement through the Orowan mechanism, thereby strengthening the alloy matrix. Moreover, the Al3(Sc,Zr,Hf) phase has a coherent interface relationship with the aluminum matrix, which can further improve the mechanical properties of the Al-Mg-Si alloy through the shearing mechanism. The fine grains of the dual-size grains have a significant strengthening effect, and the coarse / fine grain distribution can coordinate strain and improve the alloy's ductility and toughness. In addition to the strengthening effect of the nanoscale Al3(Sc,Zr,Hf) and Mg2Si second phases, the Al-Mg-Si alloy of this invention has high strength and ductility and toughness.

[0032] The Al-Mg-Si alloys of some examples of this invention have a yield strength of 343–355 MPa, a tensile strength of 368–392 MPa, and an elongation of 11.2–14.6% at room temperature. This Al-Mg-Si alloy combines high strength with good toughness, making it suitable as a lightweight structural component material for heavy load applications.

[0033] In some examples of the Al-Mg-Si alloys of this invention, trace amounts of rare earth elements Sc, Zr, and Hf are contained, with the mass ratio of Hf / Sc / Zr controlled at (2–4):1:1. The micron-sized Al3Hf phase (>1 μm) and the nano-sized Al3(Sc,Zr,Hf) phase (15–20 nm) formed therein influence the recrystallization process of the alloy through a "particle-induced nucleation mechanism" and a "particle pinning mechanism," respectively, resulting in a heterostructure with dual-size grain distribution characteristics. The smaller grain size is 15–30 μm, while the larger grain size is 100–135 μm. The formation of small grains is mainly due to two factors: First, this invention controls the Hf content to be greater than the Sc and Zr content, aiming to form a certain volume fraction of micron-sized Al3Hf phase after solidification. Recrystallization nuclei can be generated on specific crystal faces of these micron-sized phases, thereby promoting recrystallization and the formation of fine new grains. Second, this invention preferably adds trace amounts of equiproportional Sc and Zr elements, which can precipitate nano-sized Al3(Sc,Zr,Hf) phases during subsequent hot extrusion and heat treatment. These nano-phases can exert a Zener pinning effect on the grain boundaries of recrystallized grains, hindering grain growth and thus regulating fine grains. The formation of large grains is mainly related to the uneven distribution of the micron-sized Al3Hf phase. After hot extrusion, the micron-sized Al3Hf phase exists discontinuously along the extrusion direction, forming Al3Hf-rich and Al3Hf-poor phase regions. Because the grains in the Al3Hf-poor phase region undergo more severe deformation during extrusion, the recrystallization driving force in this region is greater, making grains more prone to growth or even abnormal growth. Ultimately, the Al-Mg-Si alloy forms a micron-sized dual-grain structure through the interaction of the micron-sized Al3Hf phase and the nano-sized Al3(Sc,Zr,Hf) phase.

[0034] The Al-Mg-Si alloy preparation method of some examples of this invention employs a three-stage variable-speed hot extrusion process, with extrusion speeds of 3–5 mm / s, 6–7 mm / s, and 8–10 mm / s, respectively. At lower extrusion speeds, the deformation energy storage is lower, leading to localized dynamic recovery and recrystallization. Increasing the extrusion speed means a higher deformation rate and greater deformation energy storage; moreover, some energy is converted into heat during extrusion, promoting recrystallization. The variable-speed extrusion method results in uneven deformation energy storage within the extruded microstructure, which affects the nucleation and growth of subsequent recrystallized grains. Areas with high energy storage are prone to recrystallization and grain growth, ultimately forming coarse grains of 100–135 μm. Areas with low energy storage exhibit insufficient recrystallization, making it difficult for the formed recrystallized grains to grow, resulting in fine grains of 15–30 μm. Furthermore, different extrusion speeds lead to uneven distribution of the micron-sized Al3Hf phase (>1 μm), with localized enrichment and depletion, also promoting the formation of dual-size grains.

[0035] The Al-Mg-Si alloy preparation method of some examples of this invention employs a staged solution treatment. The first stage of solution treatment is set at 350–400℃ for 40 min, aiming to precipitate fine and dispersed Al3(Sc, Zr, Hf) phases. These nanophases can hinder grain boundary migration, affect the recrystallization of the alloy, and promote the formation of fine recrystallized grains. The second stage of solution treatment is set at 530–540℃ for 25 min, which can fully dissolve Mg and Si back into the aluminum matrix to form a supersaturated solid solution, so that the Mg2Si strengthening phase can precipitate during the subsequent aging process. In addition, the high-temperature solution treatment time is controlled at 25 min, which can ensure that Mg and Si are fully dissolved into the matrix and avoid the large-scale release of deformation energy stored during extrusion, thus preserving the uneven microstructure after extrusion and promoting uneven recrystallization behavior. Attached Figure Description

[0036] Figure 1 This is an EBSD image of the Al-Mg-Si alloy prepared in Example 3. Detailed Implementation

[0037] The technical solution of the present invention will be further illustrated below with examples.

[0038] The chemical composition of the following embodiments, by elemental mass percentage, is as follows: Mg 0.7-1.3%, Mn 0.15-0.3%, Si 0.6-1.1%, Cu 0.1-0.3%, Fe 0.2-0.4%, Zn 0.2-0.3%, Sc 0.1-0.2%, Zr 0.1-0.2%, Hf 0.3-0.45%, with unavoidable impurity elements totaling ≤0.1%, and the balance being Al.

[0039] The raw materials for the Al-Mg-Si alloy of the present invention are industrial pure Al, Mg, and Zn ingots, as well as Al-10Mn, Al-20Si, Al-20Fe, Al-50Cu, Al-2Sc, Al-5Zr, and Al-2Hf master alloys.

[0040] Unless otherwise specified, all instruments, equipment, and raw materials involved in the following embodiments and comparative examples can be obtained through legitimate commercial channels.

[0041] Unless otherwise specified, the experimental and testing methods used in the following examples and comparative examples are conventional experimental and testing methods in the prior art. The room temperature tensile test was performed according to GB / T228.1-2010, the average grain size was obtained by EBSD testing, and the average sizes of the Al3(Sc,Zr,Hf) and Mg2Si phases were obtained by statistical analysis of TEM images using ImageJ software.

[0042] The following examples are merely preferred embodiments of the present invention and are not intended to limit the invention. It should be understood that any modifications, equivalent substitutions, partial improvements, etc., made without departing from the spirit and principles of the present invention are considered to be within the scope of protection of the present invention.

[0043] Example 1

[0044] S1) According to the weight percentage of the constituent elements, take Mg: 0.7%, Mn: 0.25%, Si: 0.6%, Cu: 0.15%, Fe: 0.3%, Zn: 0.25%, Sc: 0.1%, Zr: 0.1%, Hf: 0.3%, with the balance being Al; first clean the raw materials and place them in a drying oven to preheat at 160℃ for 30 minutes;

[0045] S2) Melting and casting: Preheated industrial pure aluminum, aluminum master alloy and rare earth alloy ingots are placed in a high-purity graphite crucible in a melting furnace and heated to 780℃ to melt. Then the temperature is reduced to 740℃ and pure magnesium and pure zinc are added. After all the ingots are melted, they are stirred evenly. High-purity argon gas is used to degas and refine the ingots at 730℃. After removing the slag and letting it stand for 20 minutes, the ingots are cast. After cooling to room temperature, the mold is opened to obtain the alloy ingot.

[0046] S3) Extrusion molding: The ingot is heated to 545℃ and held for 9 hours, and then hot extrusion molding is carried out directly. The diameter of the hot extruded material is 120 mm, the extrusion ratio is 35, and the three-stage extrusion speeds are 4, 6.5 and 9 mm / s, respectively. Each stage speed lasts for 2 minutes, and the extrusion outlet is water-cooled online.

[0047] S4) Heat treatment: The obtained board is first heated to 350℃ and held for 40 minutes, then heated to 530℃ and held for 25 minutes, and then water-cooled for aging treatment. The aging temperature is 180℃ and the aging time is 6 hours.

[0048] Example 2

[0049] S1) According to the weight percentage of the constituent elements, take Mg: 0.9%, Mn: 0.15%, Si: 1%, Cu: 0.1%, Fe: 0.35%, Zn: 0.2%, Sc: 0.15%, Zr: 0.15%, Hf: 0.35%, with the balance being Al; first clean the raw materials and place them in a drying oven to preheat at 150℃ for 30 minutes;

[0050] S2) Melting and casting: Preheated industrial pure aluminum, aluminum master alloy and rare earth alloy ingots are placed in a high-purity graphite crucible in a melting furnace and heated to 790℃ to melt. Then the temperature is reduced to 745℃ and pure magnesium and pure zinc are added. After all the ingots are melted, they are stirred evenly. High-purity argon gas is used to degas and refine the ingots at 735℃. After removing the slag and letting it stand for 15 minutes, the ingots are cast. After cooling to room temperature, the mold is opened to obtain the alloy ingot.

[0051] S3) Extrusion molding: The ingot is heated to 540℃ and held for 10 hours, and then hot extrusion molding is carried out directly. The diameter of the hot extruded material is 140 mm, the extrusion ratio is 38, and the three-stage extrusion speeds are 4, 6.5 and 9 mm / s respectively. Each stage speed lasts for 2 minutes, and the extrusion outlet is water-cooled online.

[0052] S4) Heat treatment: The obtained board is first heated to 380℃ and held for 40 minutes, then heated to 535℃ and held for 25 minutes, and then water-cooled for aging treatment. The aging temperature is 165℃ and the aging time is 8 hours.

[0053] Example 3

[0054] S1) According to the weight percentage of the constituent elements, take Mg: 1%, Mn: 0.3%, Si: 1.1%, Cu: 0.3%, Fe: 0.4%, Zn: 0.3%, Sc: 0.15%, Zr: 0.15%, Hf: 0.4%, with the balance being Al; first clean the raw materials and place them in a drying oven at 170℃ for 30 minutes.

[0055] S2) Melting and casting: Preheated industrial pure aluminum, aluminum master alloy and rare earth alloy ingots are placed in a high-purity graphite crucible in a melting furnace and heated to 800℃ to melt. Then the temperature is reduced to 750℃ and pure magnesium and pure zinc are added. After all the ingots are melted, they are stirred evenly. High-purity argon gas is used to degas and refine the ingots at 740℃. After removing the slag and letting it stand for 10 minutes, the ingots are cast. After cooling to room temperature, the mold is opened to obtain the alloy ingot.

[0056] S3) Extrusion molding: The ingot is heated to 550℃ and held for 8 hours, and then hot extrusion molding is carried out directly. The diameter of the hot extruded material is 170 mm, the extrusion ratio is 40, and the three-stage extrusion speeds are 4, 6.5 and 9 mm / s respectively. Each stage speed lasts for 2 minutes, and the extrusion outlet is water-cooled online.

[0057] S4) Heat treatment: The obtained board is first heated to 400℃ and held for 40 minutes, then heated to 540℃ and held for 25 minutes, and then water-cooled for aging treatment. The aging temperature is 175℃ and the aging time is 7 hours.

[0058] Example 4

[0059] S1) According to the weight percentage of the constituent elements, take Mg: 1.3%, Mn: 0.2%, Si: 0.9%, Cu: 0.2%, Fe: 0.2%, Zn: 0.2%, Sc: 0.2%, Zr: 0.2%, Hf: 0.45%, with the balance being Al; first clean the raw materials and place them in a drying oven at 160℃ for 30 minutes;

[0060] S2) Melting and casting: Preheated industrial pure aluminum, aluminum master alloy and rare earth alloy ingots are placed in a high-purity graphite crucible in a melting furnace and heated to 800℃ to melt. Then the temperature is reduced to 740℃ and pure magnesium and pure zinc are added. After all the ingots are melted, they are stirred evenly. High-purity argon gas is used to degas and refine the ingots at 740℃. After removing the slag and letting it stand for 15 minutes, the ingots are cast. After cooling to room temperature, the mold is opened to obtain the alloy ingot.

[0061] S3) Extrusion molding: The ingot is heated to 545℃ and held for 9 hours, and then hot extrusion molding is carried out directly. The diameter of the hot extruded material is 180 mm, the extrusion ratio is 42, and the three-stage extrusion speeds are 4, 6.5 and 9 mm / s, respectively. Each stage speed lasts for 2 minutes, and the extrusion outlet is water-cooled online.

[0062] S4) Heat treatment: The obtained board is first heated to 350℃ and held for 40 minutes, then heated to 535℃ and held for 25 minutes, and then water-cooled for aging treatment. The aging temperature is 175℃ and the aging time is 7 hours.

[0063] Comparative Example 1

[0064] S1) According to the weight percentage of the constituent elements, take Mg: 0.8%, Mn: 0.15%, Si: 0.9%, Cu: 0.15%, Fe: 0.3%, Zn: 0.25%, and the balance is Al; first clean the raw materials and place them in a drying oven at 150℃ for 30 minutes.

[0065] S2) Melting and casting: Preheated industrial pure aluminum and aluminum master alloy ingots are placed in a high-purity graphite crucible in a melting furnace and heated to 780°C to melt. Then the temperature is lowered to 740°C and pure magnesium and pure zinc are added. After all the ingots are melted, they are stirred evenly. High-purity argon gas is used to degas and refine the ingots at 740°C. After removing the slag and letting it stand for 15 minutes, the ingots are cast. After cooling to room temperature, the mold is opened to obtain the alloy ingot.

[0066] S3) Extrusion molding: The ingot is heated to 540℃ and held for 10 hours, and then hot extrusion molding is carried out directly. The diameter of the hot extruded material is 170 mm, the extrusion ratio is 40, and the three-stage extrusion speeds are 4, 6.5 and 9 mm / s respectively. Each stage speed lasts for 2 minutes, and the extrusion outlet is water-cooled online.

[0067] S4) Heat treatment: Heat the obtained board to 530℃ and hold for 30 min. After water cooling, perform aging treatment at 175℃ for 7 h.

[0068] Comparative Example 2

[0069] S1) According to the weight percentage of the constituent elements, take Mg: 1.3%, Mn: 0.3%, Si: 1%, Cu: 0.25%, Fe: 0.3%, Zn: 0.2%, and the balance is Al; first clean the raw materials and place them in a drying oven at 160℃ for 30 minutes.

[0070] S2) Melting and casting: Preheated industrial pure aluminum and aluminum master alloy ingots are placed in a high-purity graphite crucible in a melting furnace and heated to 780°C to melt. Then the temperature is lowered to 740°C and pure magnesium and pure zinc are added. After all the ingots are melted, they are stirred evenly. High-purity argon gas is used to degas and refine the ingots at 740°C. After removing the slag and letting it stand for 15 minutes, the ingots are cast. After cooling to room temperature, the mold is opened to obtain the alloy ingot.

[0071] S3) Extrusion molding: The ingot is heated to 540℃ and held for 9 hours, and then hot extrusion molding is carried out directly. The diameter of the hot extruded material is 140 mm, the extrusion ratio is 38, the extrusion speed is constant at 7 mm / s, the speed is maintained for 6 minutes, and the extrusion outlet is cooled online with water.

[0072] S4) Heat treatment: The obtained board is heated to 540℃ and held for 30 min. After water cooling, it is subjected to aging treatment at 175℃ for 7 h.

[0073] Comparative Example 3

[0074] S1) According to the weight percentage of the constituent elements, take Mg: 0.9%, Mn: 0.2%, Si: 1.1%, Cu: 0.15%, Fe: 0.2%, Zn: 0.3%, Sc: 0.15%, Zr: 0.15%, Hf: 0.15%, with the balance being Al; first clean the raw materials and place them in a drying oven to preheat at 160℃ for 30 minutes;

[0075] S2) Melting and casting: Preheated industrial pure aluminum and aluminum master alloy ingots are placed in a high-purity graphite crucible in a melting furnace and heated to 790℃ to melt. Then the temperature is reduced to 740℃ and pure magnesium and pure zinc are added. After complete melting, the mixture is stirred evenly. High-purity argon gas is used to degas and refine the alloy at 740℃. After removing the slag and letting it stand for 15 minutes, the alloy ingot is cast. After cooling to room temperature, the mold is opened to obtain the alloy ingot.

[0076] S3) Extrusion molding: The ingot is heated to 545℃ and held for 9 hours, and then hot extrusion molding is carried out directly. The diameter of the hot extruded material is 120 mm, the extrusion ratio is 35, and the three-stage extrusion speeds are 4, 6.5 and 9 mm / s, respectively. Each stage speed lasts for 2 minutes, and the extrusion outlet is water-cooled online.

[0077] S4) Heat treatment: The obtained board is first heated to 350℃ and held for 40 minutes, then heated to 535℃ and held for 25 minutes, and then water-cooled for aging treatment. The aging temperature is 175℃ and the aging time is 7 hours.

[0078] Performance testing

[0079] The room temperature mechanical properties of Examples 1-4 and Comparative Examples 1-3 were tested according to GB / T 228.1-2010, and the test results are shown in Table 1 below.

[0080] Table 1

[0081]

[0082] As shown in Table 1, the Al-Mg-Si alloy of the present invention possesses both high strength and high toughness, with a tensile strength greater than 368 MPa and an elongation of not less than 11.2%. Compared with Comparative Examples 1-3, the Al-Mg-Si alloy of the present invention, after microalloying Sc, Zr, and Hf rare earth elements and adopting a three-stage variable speed extrusion process, contains micron-sized dual-size grains and nano-sized Mg2Si and Al3(Sc,Zr,Hf) phases in its microstructure. This is beneficial for coordinating plastic deformation and strengthening the alloy matrix, thereby improving the strength and toughness of the alloy.

[0083] The average grain size and second phase size of Examples 1-4 and Comparative Examples 1-3 were statistically analyzed, and the results are shown in Table 2 below.

[0084] Table 2

[0085]

[0086] As shown in Figure 2, the Al-Mg-Si alloy of this invention exhibits a distinct micro-nano composite structure. The grain size in the alloy displays a dual-size distribution: coarse grains range from 100 to 135 μm, while fine grains range from 15 to 30 μm. Coarse grains can accommodate more dislocation structures, absorb energy, and improve the alloy's ductility and toughness. Fine grains, being smaller, exhibit better strengthening effects according to the Hall-Patch relation, thus enhancing the alloy's strength. Furthermore, the nanoscale Mg2Si phase in the Al-Mg-Si alloy of this invention strengthens the matrix through the Orowan mechanism, while the coherent nanoscale Al3(Sc,Zr,Hf) phases, which are coherent with the aluminum matrix, generate coherent strain that hinders dislocation movement, further enhancing the alloy's strength and toughness.

[0087] Figure 1 The image shows an EBSD image of the Al-Mg-Si alloy prepared in Example 3. As can be seen from the image, the alloy exhibits a heterogeneous structure with dual-size grain distribution characteristics, where the small grain size is 15–30 μm and the large grain size is 100–135 μm.

[0088] The above is a further detailed description of the present invention and should not be considered as a limitation on the specific implementation of the present invention. For those skilled in the art, simple deductions or substitutions without departing from the concept of the present invention are all within the protection scope of the present invention.

Claims

1. A micro / nano composite Al-Mg-Si alloy, the alloy having the following mass composition: Mg 0.7–1.3%, Mn 0.15–0.3%, Si 0.6–1.1%, Cu 0.1–0.3%, Fe 0.2–0.4%, Zn 0.2–0.3%, Sc 0.1–0.2%, Zr 0.1–0.2%, Hf 0.3–0.45%, with the balance being unavoidable impurities and Al. The mass ratio of Hf:Sc:Zr is (2–4):1:

1. It contains two nanoscale reinforcing phases: Mg2Si phase and Al3(Sc,Zr,Hf) phase, wherein the average diameter of the Mg2Si phase is 8–10 nm and the average diameter of the Al3(Sc,Zr,Hf) phase is 15–20 nm. nm, containing micron-sized dual-size grains, with core grain size of 15–30 μm and surface grain size of 100–135 μm, is prepared by the following steps: S1) Ingredients: Weigh the raw materials according to the composition of the Al-Mg-Si alloy and clean them thoroughly; S2) Melting and casting: The prepared raw materials are heated and melted, mixed, degassed and refined, slag removed and then cast, and cooled to obtain alloy ingots. S3) Extrusion molding: The alloy ingot is heated to 540-550℃ and then directly hot extruded. The extrusion ratio is 35-42. After cooling, the hot extruded material is obtained. S4) Heat treatment: The hot extruded material is heated to 350-540℃ for solution treatment, held at the temperature and then water-cooled, followed by aging treatment to obtain Al-Mg-Si alloy.

2. The Al-Mg-Si alloy according to claim 1, characterized in that, The amount of unavoidable impurities shall not exceed 0.1%.

3. The Al-Mg-Si alloy according to claim 1, characterized in that, The extrusion molding process employs a three-stage variable speed extrusion system, with extrusion speeds of 3–5 mm / s, 6–7 mm / s, and 8–10 mm / s, respectively.

4. The Al-Mg-Si alloy according to claim 1, characterized in that, During extrusion molding, heat to 540-550℃ and hold for 8-10 hours.

5. The Al-Mg-Si alloy according to claim 1, characterized in that, The solution treatment was carried out in stages: the first stage was at 350-400℃ for 40 min, and the second stage was at 530-540℃ for 25 min.

6. The Al-Mg-Si alloy according to claim 1, characterized in that, The aging temperature is 165–180℃, and the aging time is 6–8 hours.

Images