High-toughness cast aluminum alloy and preparation method thereof

Abstract

The invention discloses a high-toughness cast aluminum alloy and a preparation method thereof. The aluminum alloy is prepared from the following components in percentage by mass: 7-9.5% of Si, 0.1-2% of Bi, 0.1-2% of Zn, 0.1-0.55% of Mg, 0.1-0.6% of Mn, 0.2-0.5% of Fe, less than or equal to 0.2% of Ti, less than or equal to 0.2% of Zr, less than or equal to 0.2% of other impurities and the balance of Al. The preparation method comprises the processes of secondary refining, cooling sedimentation, component adding sequence, temperature control and the like. According to the method, double-layer film defects can be effectively reduced, double-layer films are passivated, formation of hole defects such as air holes and shrinkage cavities can be inhibited, rich-Fe phases and eutectic silicon can be effectively regulated and controlled, then the strength and toughness of the cast aluminum alloy are effectively improved, and the consistency of mechanical properties is remarkably improved. And meanwhile, the tolerance limit of the cast aluminum alloy to the Fe content can be improved, the high-toughness cast aluminum alloy is allowed to be prepared from the regenerated aluminum alloy, and the production cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy casting, and relates to a cast aluminum alloy with high strength and toughness mechanical properties and its preparation method. Background Technology

[0002] Driven by global demands for low-carbon, energy-saving, and environmentally friendly practices, the automotive, rail transportation, and aerospace industries are experiencing increasingly strong demand for high-performance, lightweight mechanical products and components. This necessitates the extensive use of lightweight aluminum alloys in components, and complex parts are trending towards integration. Integrated complex aluminum alloy castings offer significant advantages such as high integration, lightweight design, and low cost. However, these castings are structurally complex and large in size, and their mechanical properties cannot be improved through heat treatments like T6 and T7 (as solution treatment easily leads to deformation, and quenching results in high internal stress). The key to successful integrated complex aluminum alloy castings lies in achieving high comprehensive mechanical properties under as-cast conditions. The core of this development is the creation of high-strength, high-toughness cast aluminum alloy materials and their preparation methods.

[0003] Currently, some high-strength and high-toughness cast aluminum alloys (Alcoa C611 cast aluminum alloy, CN105316542A, CN111139381A, CN114164362A, CN115003832A, CN115161520A, CN110079712A, CN115198149A, CN115418537A, CN110079712A, CN114411020A, etc.) have been disclosed by enterprises, universities and research institutes. However, the following main problems still exist: (1) High-strength and high-toughness cast aluminum alloys are formed by vacuum die casting technology, but there are a large number of casting defects such as double film, porosity and shrinkage cavities in the castings, which damage the mechanical properties of the castings. In particular, the mechanical properties of vacuum die-cast high-strength and high-toughness cast aluminum alloys have high dispersion and poor consistency. (2) The overall mechanical properties of cast aluminum alloys currently used in the as-cast state are still relatively low. For example, it is difficult for the tensile strength of vacuum die casting to reach 300 MPa stably, and it is also difficult for the yield strength to reach 150 MPa stably, and the elongation to reach 12% stably. (3) It is limited to high pressure casting and it is difficult to use gravity casting and anti-gravity casting. (4) In order to obtain higher toughness, most of the cast aluminum alloys currently used in the as-cast state strictly limit the Fe content in the alloy (typically less than 0.2 wt.%), requiring the use of primary aluminum, which greatly limits the use of recycled aluminum.

[0004] Therefore, it is essential to develop a high-strength and high-toughness cast aluminum alloy and its preparation method. Under the premise of effectively controlling the microstructure, it can effectively reduce casting defects such as double film, porosity and shrinkage cavity, improve the tolerance to Fe content, and have high comprehensive mechanical properties and high mechanical property consistency, so as to meet the urgent needs of the automotive, rail transportation, aerospace and other fields for high-performance, lightweight, low-cost and integrated complex aluminum alloy castings. Summary of the Invention

[0005] The purpose of this invention is to provide a high-strength and high-toughness cast aluminum alloy and its preparation method, which can significantly reduce casting defects and control microstructure, and can significantly improve the strength and toughness of castings and reduce production costs under as-cast conditions.

[0006] This invention is achieved through the following technical solutions.

[0007] The high-strength and high-toughness cast aluminum alloy of the present invention is composed of the following components in the following proportions: 7-9.5 wt.% Si, 0.1-2 wt.% Bi, 0.1-2 wt.% Zn, 0.1-0.55 wt.% Mg, 0.1-0.6 wt.% Mn, 0.2-0.5 wt.% Fe, Ti≤0.2 wt.%, Zr≤0.2 wt.%, other impurities ≤0.2 wt.%, and the balance being Al.

[0008] The solidification temperature range of the high-strength and high-toughness cast aluminum alloy is ≤60°C. ℃.

[0009] The high-strength and high-toughness cast aluminum alloy has an Fe to Mn ratio ranging from 1 to 3 when the Fe content is >0.4 wt.%.

[0010] Of the other impurities, the Sr content is <0.01 wt.%.

[0011] The service environment temperature of the high-strength and high-toughness cast aluminum alloy is not higher than 255℃.

[0012] The present invention discloses a method for preparing a high-strength and high-toughness cast aluminum alloy, comprising the following steps.

[0013] (1) Weigh the raw materials according to the weight percentage, remove contaminants and oxide scale from the surface of the raw materials, and preheat and dry them at a temperature of 150-180℃ for 30-120 min. The raw materials include: pure Al, crystalline Si, Al-Si recycled aluminum ingots, Bi, pure Zn, pure Mg, Al-Mn master alloy, Al-Ti master alloy, and Al-Zr master alloy.

[0014] (2) Melt Al-Si recycled aluminum ingots at a melting temperature of 720-735℃ and perform the first refining.

[0015] (3) Add pure Al, Al-Mn master alloy, Al-Zr master alloy, crystalline Si and pure Zn to the aluminum alloy melt obtained in step (2); add pure Mg after melting; the melting temperature is 720-735℃, and the melt is completely melted for a second refining.

[0016] (4) Heat the aluminum alloy melt obtained in step (3) to 800-880℃, add Al-Ti master alloy, and after it is completely dissolved, cool it down to settle, that is, reduce the temperature of the aluminum alloy melt to 630-660℃, keep it at the temperature, and then raise the temperature of the alloy melt to 690-720℃.

[0017] (5) Add Bi to the aluminum alloy melt obtained in step (4) and keep it at a constant temperature.

[0018] (6) Cast the aluminum alloy melt obtained in step (5) to obtain a high-strength and high-toughness cast aluminum alloy.

[0019] In the method of the invention, the amount of Al-Si recycled aluminum ingot added is 20-50% of the total cast aluminum alloy, the Sr content in the Al-Si recycled aluminum ingot is ≤0.05wt.%, the ingot density equivalent is ≤2.5%, and the hydrogen content is ≤0.18ml / 100g.

[0020] In the method described above, the first refining in step (2) and the second refining in step (3) both involve using a rotary jetting device to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. The refining process lasts 20-30 minutes, followed by settling and slag removal. Before refining, the graphite rotor should be thoroughly dried. During the refining process, the surface of the aluminum alloy melt should be kept stable, preventing vortices, splashes, and surface turbulence.

[0021] In step (3) of the method described in the invention, stirring can be applied during the melting process of the raw materials, preferably electromagnetic stirring, to accelerate the melting speed of the raw materials and promote uniform composition. During the stirring process, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0022] In step (4) of the invention method, the total cooling and settling time is ≥60 min. Throughout the entire cooling and settling process, the molten aluminum alloy remains in a static state.

[0023] In the method of the invention, the Al-Ti master alloy is an alloy wire or an alloy rod with a diameter ≤8mm.

[0024] In the method of the invention, Bi can be pure Bi or Al-Bi master alloy, and preferably Bi is wire or bar with a diameter ≤ 8mm.

[0025] In step (6) of the invention method, the cooling rate of the aluminum alloy melt in the mold cavity is ≥5℃ / s.

[0026] Optionally, in step (6) of the method of the invention, the casting is performed by gravity casting or anti-gravity casting, the casting temperature is 690-720℃, and the ingate speed is ≤1m / s, preferably ≤0.5m / s.

[0027] Optionally, in step (6) of the method, the casting is performed by vacuum high-pressure casting, and the pouring temperature is 690-720°C. At ℃, the vacuum degree inside the mold cavity during injection is ≥10mbar.

[0028] The mechanical properties of castings are primarily determined by casting defects. Porosity, shrinkage cavities, and double-layer films are the main forms of casting defects in gravity casting, anti-gravity casting, and pressure casting technologies, severely damaging the mechanical properties (especially toughness) of castings and being the root cause of low consistency in casting mechanical properties. The formation of these casting defects is closely related to alloy composition and casting process. This invention has found that the double-layer film, besides constituting a casting defect itself, is also the optimal starting point for casting defects such as porosity and shrinkage cavities. This invention mainly regulates casting defects through two pathways: firstly, inhibiting the formation of casting defects; secondly, passivating existing casting defects, thereby reducing their harmfulness. The inventors have discovered that Ti and Al form AlTi high-melting-point intermetallic compound particles, which precipitate at high temperatures and adhere to the double-layer film. This invention utilizes the high-density characteristics of AlTi particles to promote the precipitation of the double-layer film through a cooling precipitation method, greatly reducing the number of double-layer films in the aluminum alloy melt, improving the purity of the alloy melt, and thus inhibiting the formation of casting defects such as porosity and shrinkage cavities, effectively improving the strength and toughness of castings. Bi has a melting point of approximately 271.4℃ and is immiscible with Al. This invention reveals that during surface turbulence, liquid Bi is folded within a double-layer film, forming a sandwich with a viscous core. This effectively inhibits the double-layer film from unfolding into pores and shrinkage cavities, promoting the passivation of double-layer film defects. During solidification and shrinkage, Bi remains liquid, and the expansion during solidification facilitates feeding. This invention, by adding Bi to cast aluminum alloys, effectively passivates double-layer film defects, reduces the harm of shrinkage cavities, and effectively improves the strength and toughness of castings.

[0029] Another major factor influencing the mechanical properties of castings is their microstructure, which mainly includes primary solid solution phases, eutectic silicon, and solidified crystalline phases. In the cast aluminum alloy of this invention, Si, Mg, Zn, Mn, Fe, Ti, and Zr elements can all dissolve in the aluminum lattice to form solid solutions. Furthermore, these elements have significant differences in valence, atomic radius, and electronegativity compared to Al, resulting in excellent solid solution strengthening effects. Ti and Zr in the cast aluminum alloy of this invention can form effective heterogeneous nucleation particles. Under the cooling rate achieved by the preparation method of this invention, they can effectively refine the primary solid solution phase, producing excellent fine-grain strengthening effects. On the other hand, these particles have high melting points, precipitate at high temperatures, are fine, and ultimately remain at grain boundaries, producing excellent second-phase particle strengthening. This invention reveals that eutectic silicon has a significant impact on the strength and toughness of castings, especially toughness. Specifically, eutectic silicon primarily grows via a bilayer film, ultimately forming lath-like structures. While Bi has a refining effect on eutectic silicon under low Sr content conditions, its modifying effect is poisoned when Sr content exceeds 0.01 wt%. This invention reduces the number of bilayer films in the aluminum alloy melt, allowing eutectic Si to form only at higher undercooling conditions. Simultaneously, the addition of Bi, under the cooling rate achieved by this method, effectively refines the eutectic silicon size and modifies its morphology, thus significantly improving the strength and toughness of the casting. The use of recycled aluminum results in higher Fe content in the cast aluminum alloy, forming a Fe-rich phase, which is beneficial for demolding but greatly impairs the strength and toughness of the casting. This invention finds that the main nucleation substrate for the Fe-rich phase is the bilayer film, and the growth of the bilayer film leads to its expansion and the formation of cracks. This invention reduces the number of double-layer films in the aluminum alloy melt, so that the Fe-rich phase can only precipitate at a greater degree of supercooling, thus refining the size of the Fe-rich phase. At the same time, the addition of Mn element further regulates the morphology of the Fe-rich phase. Under the cooling rate formed by the method of this invention, Fe element is dissolved in the matrix in the form of elemental substance or precipitates in the form of fine Fe-rich phase, effectively improving the strength and toughness of the casting.

[0030] Compared with the prior art, the present invention has the following beneficial effects.

[0031] (1) The present invention can combine composition design and preparation method, effectively reduce double film defects, passivate double film, inhibit the formation of pore-type defects such as pores and shrinkage cavities, effectively regulate the Fe-rich phase and eutectic silicon, and thus effectively improve the strength and toughness of cast aluminum alloys. In particular, the mechanical properties are significantly improved compared with the prior art.

[0032] (2) The present invention can improve the tolerance limit of cast aluminum alloy to Fe content, allow the use of recycled aluminum alloy to prepare high strength and toughness cast aluminum alloy, reduce carbon emissions and reduce production costs. Attached Figure Description

[0033] Figure 1 This is the microstructure of Embodiment 1 of the present invention, characterized by a primary solid solution phase.

[0034] Figure 2 These are the microstructure characteristics, eutectic structure, and Fe-rich phase characteristics of Embodiment 1 of the present invention.

[0035] Figure 3 This is the tensile fracture feature of Embodiment 1 of the present invention.

[0036] Figure 4 This is the microstructure feature of Embodiment 3 of the present invention.

[0037] Figure 5 This is the tensile fracture feature of Embodiment 3 of the present invention.

[0038] Figure 6 This is the characteristic of the casting defect with holes in Embodiment 4 of the present invention.

[0039] Figure 7 This describes the casting defect characteristics of holes in Comparative Example 3 of the present invention.

[0040] Figure 8 This is the double-layer film defect feature of Embodiment 4 of the present invention.

[0041] Figure 9 This is the double-layer membrane trapping feature of Comparative Example 4 of the present invention. Detailed Implementation

[0042] To better understand the technical solutions, features, and advantages of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described are only for further explanation of the present invention and are not intended to limit the present invention. Example 1

[0043] In this embodiment, the proportions of each component in the high-strength and tough cast aluminum alloy are as follows: 7.8 wt.% Si, 1.2 wt.% Bi, 0.8 wt.% Zn, 0.35 wt.% Mg, 0.35 wt.% Mn, 0.25 wt.% Fe, 0.11 wt.% Ti, 0.1 wt.% Zr, and the total amount of other impurities ≤ 0.2 wt.%, with the balance being Al.

[0044] (1) Weigh out pure Al, crystalline Si, Al-Si recycled aluminum ingot, Al-10Bi, pure Zn, pure Mg, Al-10Mn master alloy, Al-10Ti master alloy, and Al-5Zr master alloy according to their weight percentages. Remove contaminants and oxide scale from the surface of the raw materials. Preheat and dry at 160°C for 90 minutes. In this example, the weight percentage of Al-Si recycled aluminum ingot is 25%.

[0045] (2) Place the Al-Si recycled aluminum ingot into the melting furnace, heat to 730℃, and hold for 30 minutes after complete melting. Skim off the slag, and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then skim off the slag. Before refining, the graphite rotor should be thoroughly dried. During the refining process, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0046] (3) Add pure Al, Al-10Mn master alloy, Al-5Zr master alloy, crystalline Si, and pure Zn to the aluminum alloy melt at 730℃. After melting, add pure Mg and mechanically stir for 5 minutes to ensure uniform composition. Hold at this temperature for 30 minutes. Remove slag and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then remove slag. Before refining, the graphite rotor should be thoroughly dried. During mechanical stirring and refining, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0047] (4) Heat the aluminum alloy melt to 860°C and add Al-10Ti master alloy wire. After it is completely melted, perform a cooling and settling treatment, that is, lower the temperature of the aluminum alloy melt to 640°C, hold it for 20 minutes, and then raise the temperature of the aluminum alloy melt to 695°C. The entire cooling and settling treatment takes about 120 minutes.

[0048] (5) Add a 6mm diameter Al-10Bi intermediate alloy rod to the 695℃ aluminum alloy melt, keep it at the temperature for 10 minutes, and perform a pre-furnace composition test.

[0049] (6) Vacuum die casting of the qualified aluminum alloy melt at 695℃. The mold is a 4mm×80mm×200mm flat mold, the vacuum degree in the mold cavity is 10mbar, and the mold preheating temperature is 135℃.

[0050] In this embodiment, 30 tensile specimens were prepared according to ASTM B557-06 and subjected to room temperature tensile testing. Room temperature tensile properties: average tensile strength 321 MPa, average yield strength 159 MPa, average elongation 14.2%, and tensile strength Weibull modulus 31. Example 2

[0051] In this embodiment, the proportions of each component in the high-strength and tough cast aluminum alloy are as follows: 7.8 wt.% Si, 1.2 wt.% Bi, 0.8 wt.% Zn, 0.35 wt.% Mg, 0.21 wt.% Mn, 0.40 wt.% Fe, 0.11 wt.% Ti, 0.1 wt.% Zr, and the total amount of other impurities ≤ 0.2 wt.%, with the balance being Al.

[0052] (1) Weigh out pure Al, crystalline Si, Al-Si recycled aluminum ingot, Al-10Bi, pure Zn, pure Mg, Al-10Mn master alloy, Al-10Ti master alloy, and Al-5Zr master alloy according to their weight percentages. Remove contaminants and oxide scale from the surface of the raw materials. Preheat and dry at 160°C for 90 minutes. In this example, the weight percentage of Al-Si recycled aluminum ingot is 35%.

[0053] (2) Place the Al-Si recycled aluminum ingot into the melting furnace, heat to 730℃, and hold for 30 minutes after complete melting. Skim off the slag, and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then skim off the slag. Before refining, the graphite rotor should be thoroughly dried. During the refining process, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0054] (3) Add pure Al, Al-10Mn master alloy, Al-5Zr master alloy, crystalline Si, and pure Zn to the aluminum alloy melt at 730℃. After melting, add pure Mg and mechanically stir for 5 minutes to ensure uniform composition. Hold at this temperature for 30 minutes. Remove slag and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then remove slag. Before refining, the graphite rotor should be thoroughly dried. During mechanical stirring and refining, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0055] (4) Heat the aluminum alloy melt to 860°C and add Al-10Ti master alloy wire. After it is completely melted, perform a cooling and settling treatment, that is, lower the temperature of the aluminum alloy melt to 640°C, hold it for 20 minutes, and then raise the temperature of the aluminum alloy melt to 695°C. The entire cooling and settling treatment takes about 120 minutes.

[0056] (5) Add a 6mm diameter Al-10Bi intermediate alloy rod to the 695℃ aluminum alloy melt, keep it at the temperature for 10 minutes, and perform a pre-furnace composition test.

[0057] (6) Vacuum die casting of the qualified aluminum alloy melt at 695℃. The mold is a 4mm×80mm×200mm flat mold, the vacuum degree in the mold cavity is 10mbar, and the mold preheating temperature is 135℃. ℃.

[0058] In this embodiment, 30 tensile specimens were prepared according to ASTM B557-06 and subjected to room temperature tensile testing. Room temperature tensile properties: average tensile strength 308 MPa, average yield strength 154 MPa, average elongation 10.6%, and tensile strength Weibull modulus 29. Example 3

[0059] The chemical composition of the high-strength and high-toughness cast aluminum alloy in this embodiment is as follows: 9.2 wt.% Si, 0.8 wt.% Bi, 1.3 wt.% Zn, 0.3 wt.% Mg, 0.2 wt.% Mn, 0.25 wt.% Fe, 0.11 wt.% Ti, 0.1 wt.% Zr, with other impurities totaling ≤0.2 wt.% and the balance being Al.

[0060] (1) Weigh out pure Al, crystalline Si, Al-Si recycled aluminum ingot, Al-10Bi, pure Zn, pure Mg, Al-10Mn master alloy, Al-10Ti master alloy, and Al-5Zr master alloy according to their weight percentages. Remove contaminants and oxide scale from the surface of the raw materials. Preheat and dry at 160°C for 90 minutes. In this example, the weight percentage of Al-Si recycled aluminum ingot is 25%.

[0061] (2) Place the Al-Si recycled aluminum ingot into the melting furnace, heat to 730℃, and hold for 30 minutes after complete melting. Skim off the slag, and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then skim off the slag. Before refining, the graphite rotor should be thoroughly dried. During the refining process, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0062] (3) Add pure Al, Al-10Mn master alloy, Al-5Zr master alloy, crystalline Si, and pure Zn to the aluminum alloy melt at 730 °C. After melting, add pure Mg and mechanically stir for 5 minutes to ensure uniform composition. Hold at this temperature for 30 minutes. Remove slag and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then remove slag. Before refining, the graphite rotor should be thoroughly dried. During mechanical stirring and refining, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0063] (4) Heat the aluminum alloy melt to 860°C and add Al-10Ti master alloy wire. After it is completely melted, perform a cooling and settling treatment, that is, lower the temperature of the aluminum alloy melt to 640°C, hold it for 20 minutes, and then raise the temperature of the aluminum alloy melt to 700°C. The entire cooling and settling treatment takes about 120 minutes.

[0064] (5) Add a 6mm diameter Al-10Bi intermediate alloy rod to the 700℃ aluminum alloy melt, keep it at the temperature for 10 minutes, and perform a pre-furnace composition test.

[0065] (6) The aluminum alloy melt with qualified composition is subjected to low-pressure casting in a metal mold with an inlet gate speed of 0.5 m / s. Two 8 mm diameter round bar samples are made in one mold. The temperature of the aluminum alloy melt is 700 ℃ and the mold preheating temperature is 200 ℃.

[0066] In this embodiment, 30 tensile specimens were prepared and subjected to room temperature tensile testing according to ASTM B557-06. Room temperature tensile properties: average tensile strength 257 MPa, average yield strength 153 MPa, average elongation 15.7%, and tensile strength Weibull modulus 48. Example 4

[0067] The chemical composition of the high-strength and high-toughness cast aluminum alloy in this embodiment is as follows: 9.2 wt.% Si, 0.8 wt.% Bi, 1.3 wt.% Zn, 0.3 wt.% Mg, 0.2 wt.% Mn, 0.25 wt.% Fe, 0.11 wt.% Ti, 0.1 wt.% Zr, with other impurities totaling ≤0.2 wt.% and the balance being Al.

[0068] (1) Weigh out pure Al, crystalline Si, Al-Si recycled aluminum ingot, Al-10Bi, pure Zn, pure Mg, Al-10Mn master alloy, Al-10Ti master alloy, and Al-5Zr master alloy according to their weight percentages. Remove contaminants and oxide scale from the surface of the raw materials. Preheat and dry at 160°C for 90 minutes. In this example, the weight percentage of Al-Si recycled aluminum ingot is 25%.

[0069] (2) Place the Al-Si recycled aluminum ingot into the melting furnace, heat to 730℃, and hold for 30 minutes after complete melting. Skim off the slag, and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then skim off the slag. Before refining, the graphite rotor should be thoroughly dried. During the refining process, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0070] (3) Add pure Al, Al-10Mn master alloy, Al-5Zr master alloy, crystalline Si, and pure Zn to the aluminum alloy melt at 730℃. After melting, add pure Mg and mechanically stir for 5 minutes to ensure uniform composition. Hold at this temperature for 30 minutes. Remove slag and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then remove slag. Before refining, the graphite rotor should be thoroughly dried. During mechanical stirring and refining, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0071] (4) Heat the aluminum alloy melt to 860°C and add Al-10Ti master alloy wire. After it is completely melted, perform a cooling and settling treatment, that is, lower the temperature of the aluminum alloy melt to 640°C, hold it for 20 minutes, and then raise the temperature of the aluminum alloy melt to 700°C. The entire cooling and settling treatment takes about 120 minutes.

[0072] (5) Add a 6mm diameter Al-10Bi intermediate alloy rod to the 700℃ aluminum alloy melt, keep it at the temperature for 10 minutes, and perform a pre-furnace composition test.

[0073] (6) The aluminum alloy melt with qualified composition is subjected to gravity casting in a metal mold. Two 8mm diameter round bar samples are prepared in one mold. The pouring temperature is 700℃ and the mold preheating temperature is 200℃. The gating system is a bottom pouring suitable gating system. A swirling decoy is set at the extended end of the horizontal runner. A 20-mesh foam ceramic filter is set at the bottom of the ingate. The ingate velocity is 0.5m / s.

[0074] In this embodiment, 30 tensile specimens were prepared and subjected to room temperature tensile testing according to ASTM B557-06. Room temperature tensile properties: average tensile strength 249 MPa, average yield strength 154 MPa, average elongation 15.1%, and tensile strength Weibull modulus 40. Example 5

[0075] The chemical composition of the high-strength and high-toughness cast aluminum alloy in this embodiment is as follows: 9.2 wt.% Si, 1.2 wt.% Bi, 1.3 wt.% Zn, 0.3 wt.% Mg, 0.2 wt.% Mn, 0.25 wt.% Fe, 0.11 wt.% Ti, 0.1 wt.% Zr, with other impurities totaling ≤0.2 wt.%, and the balance being Al.

[0076] (1) Weigh out pure Al, crystalline Si, Al-Si recycled aluminum ingot, Al-10Bi, pure Zn, pure Mg, Al-10Mn master alloy, Al-10Ti master alloy, and Al-5Zr master alloy according to their weight percentages. Remove contaminants and oxide scale from the surface of the raw materials. Preheat and dry at 160°C for 90 minutes. In this example, the weight percentage of Al-Si recycled aluminum ingot is 25%.

[0077] (2) Place the Al-Si recycled aluminum ingot into the melting furnace, heat to 730℃, and hold for 30 minutes after complete melting. Skim off the slag, and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then skim off the slag. Before refining, the graphite rotor should be thoroughly dried. During the refining process, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0078] (3) Add pure Al, Al-10Mn master alloy, Al-5Zr master alloy, crystalline Si, and pure Zn to the aluminum alloy melt at 730℃. After melting, add pure Mg and mechanically stir for 5 minutes to ensure uniform composition. Hold at this temperature for 30 minutes. Remove slag and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then remove slag. Before refining, the graphite rotor should be thoroughly dried. During mechanical stirring and refining, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0079] (4) Heat the aluminum alloy melt to 860℃ and add Al-10Ti master alloy wire. After it is completely melted, perform a cooling and settling treatment, that is, lower the temperature of the aluminum alloy melt to 640℃, hold for 20 minutes, and then raise the temperature of the aluminum alloy melt to 700℃. ℃. The entire cooling and settling process took approximately 120 minutes.

[0080] (5) Add a 6mm diameter Al-10Bi intermediate alloy rod to the 700℃ aluminum alloy melt, keep it at the temperature for 10 minutes, and perform a pre-furnace composition test.

[0081] (6) The aluminum alloy melt with qualified composition is subjected to gravity casting in a metal mold. Two 8mm diameter round bar samples are cast in one mold. The pouring temperature is 700℃. The mold is an ASTM B108 metal mold with a preheating temperature of 200℃ and an ingate speed of 1.0m / s.

[0082] In this embodiment, 30 tensile specimens were prepared and subjected to room temperature tensile testing according to ASTM B557-06. Room temperature tensile properties: average tensile strength 242 MPa, average yield strength 143 MPa, average elongation 10.4%, and tensile strength Weibull modulus 31.

[0083] Comparative Example 1.

[0084] The weight percentages of each component in this comparative high-strength and high-toughness cast aluminum alloy are as follows: 7.8 wt.% Si, 1.2 wt.% Bi, 0.8 wt.% Zn, 0.25 wt.% Mg, 0.15 wt.% Mn, 0.25 wt.% Fe, 0.1 wt.% Zr, with other impurities totaling ≤0.2 wt.%, and the balance being Al.

[0085] (1) Weigh out pure Al, crystalline Si, Al-Si recycled aluminum ingot, Al-10Bi, pure Zn, pure Mg, Al-10Mn master alloy, Al-10Ti master alloy, and Al-5Zr master alloy according to their weight percentages. Remove contaminants and oxide scale from the surface of the raw materials. Preheat and dry at 160°C for 90 minutes. In this example, the weight percentage of Al-Si recycled aluminum ingot is 25%.

[0086] (2) Place the Al-Si recycled aluminum ingot into the melting furnace, heat to 730℃, and hold for 30 minutes after complete melting. Skim off the slag, and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then skim off the slag. Before refining, the graphite rotor should be thoroughly dried. During the refining process, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0087] (3) To 730 Pure Al, Al-10Mn master alloy, Al-5Zr master alloy, crystalline Si, and pure Zn are added to molten aluminum alloy at a temperature of ℃. After melting, pure Mg is added, and the mixture is mechanically stirred for 5 minutes to ensure uniform composition. The mixture is then held at this temperature for 30 minutes. Slag is skimmed off, and solid granular refining agent and dry argon gas are injected into the molten aluminum alloy using a rotary jet nozzle. Refining is carried out for 20 minutes, followed by standing for 15 minutes, and then slag is skimmed off again. The graphite rotor should be thoroughly dried before refining. During mechanical stirring and refining, the surface of the molten aluminum alloy should be kept stable, preventing vortices, splashing, and surface turbulence.

[0088] (4) Cool the aluminum alloy melt to 695°C, add an Al-10Bi intermediate alloy rod with a diameter of 6 mm, keep it at the temperature for 10 minutes, and perform a pre-furnace composition test.

[0089] (5) Vacuum die casting of the qualified aluminum alloy melt at 695℃. The mold is a 4mm×80mm×200mm flat mold, the vacuum degree in the mold cavity is 10mbar, and the mold preheating temperature is 135℃. ℃.

[0090] Compared with the examples, this comparative example did not contain Ti and did not undergo cooling sedimentation treatment. Thirty tensile specimens were prepared according to ASTM B557-06 and subjected to room temperature tensile testing. Room temperature tensile properties: average tensile strength 272 MPa, average yield strength 143 MPa, average elongation 10.2%, and tensile strength Weibull modulus 27.

[0091] Comparative Example 2.

[0092] The weight percentages of each component in the high-strength and high-toughness cast aluminum alloy of this embodiment are as follows: 7.8 wt.% Si, 0.8 wt.% Zn, 0.25 wt.% Mg, 0.15 wt.% Mn, 0.25 wt.% Fe, 0.11 wt.% Ti, 0.1 wt.% Zr, and the total amount of other impurities ≤ 0.2 wt.%, with the balance being Al.

[0093] (1) Weigh out pure Al, crystalline Si, Al-Si recycled aluminum ingot, Al-10Bi, pure Zn, pure Mg, Al-10Mn master alloy, Al-10Ti master alloy, and Al-5Zr master alloy according to their weight percentages. Remove contaminants and oxide scale from the surface of the raw materials. Preheat and dry at 160°C for 90 minutes. In this example, the weight percentage of Al-Si recycled aluminum ingot is 25%.

[0094] (2) Place the Al-Si recycled aluminum ingot into the melting furnace, heat to 730℃, and hold for 30 minutes after complete melting. Skim off the slag, and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then skim off the slag. Before refining, the graphite rotor should be thoroughly dried. During the refining process, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0095] (3) Add pure Al, Al-10Mn master alloy, Al-5Zr master alloy, crystalline Si, and pure Zn to the aluminum alloy melt at 730℃. After melting, add pure Mg and mechanically stir for 5 minutes to ensure uniform composition. Hold at this temperature for 30 minutes. Remove slag and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then remove slag. Before refining, the graphite rotor should be thoroughly dried. During mechanical stirring and refining, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0096] (4) Heat the aluminum alloy melt to 860℃ and add Al-10Ti master alloy wire. After it is completely melted, perform a cooling and settling treatment, that is, lower the temperature of the aluminum alloy melt to 640℃, hold it for 20 minutes, and then raise the temperature of the aluminum alloy melt to 695℃. ℃. The entire cooling and settling process took approximately 120 minutes. Compositional analysis was performed before the furnace.

[0097] (5) Vacuum die casting of the qualified aluminum alloy melt at 695℃. The mold is a 4mm×80mm×200mm flat mold, the vacuum degree in the mold cavity is 10mbar, and the mold preheating temperature is 135℃. ℃.

[0098] This comparative example is compared to the previous example; Bi was not added to this comparative example. Thirty tensile specimens were prepared according to ASTM B557-06 and subjected to room temperature tensile testing. Room temperature tensile properties: average tensile strength 257 MPa, average yield strength 134 MPa, average elongation 7.7%, and tensile strength Weibull modulus 21.

[0099] Comparative Example 3.

[0100] The weight percentages of each component in the high-strength and high-toughness cast aluminum alloy of this embodiment are as follows: 7.8 wt.% Si, 0.8 wt.% Zn, 0.25 wt.% Mg, 0.15 wt.% Mn, 0.25 wt.% Fe, 0.1 wt.% Zr, with other impurities totaling ≤0.2 wt.% and the balance being Al.

[0101] (1) Weigh out pure Al, crystalline Si, Al-Si recycled aluminum ingot, Al-10Bi, pure Zn, pure Mg, Al-10Mn master alloy, Al-10Ti master alloy, and Al-5Zr master alloy according to their weight percentages. Remove contaminants and oxide scale from the surface of the raw materials. Preheat and dry at 160°C for 90 minutes. In this example, the weight percentage of Al-Si recycled aluminum ingot is 25%.

[0102] (2) Place the Al-Si recycled aluminum ingot into the melting furnace, heat to 730℃, and hold for 30 minutes after complete melting. Skim off the slag, and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then skim off the slag. Before refining, the graphite rotor should be thoroughly dried. During the refining process, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0103] (3) Add pure Al, Al-10Mn master alloy, Al-5Zr master alloy, crystalline Si, and pure Zn to the aluminum alloy melt at 730℃. After melting, add pure Mg and mechanically stir for 5 minutes to ensure uniform composition. Hold at this temperature for 30 minutes. Remove slag and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then remove slag. Before refining, the graphite rotor should be thoroughly dried. During mechanical stirring and refining, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0104] (4) Reduce the temperature of the aluminum alloy melt to 695°C and perform pre-furnace composition testing.

[0105] (5) Vacuum die casting of the qualified aluminum alloy melt at 695℃. The mold is a 4mm×80mm×200mm flat mold, the vacuum degree in the mold cavity is 10mbar, and the mold preheating temperature is 135℃.

[0106] Compared with the examples, this comparative example did not contain Ti, did not undergo cooling sedimentation treatment, and did not contain Bi. Thirty tensile specimens were prepared according to ASTM B557-06 and subjected to room temperature tensile testing. Room temperature tensile properties: average tensile strength 257 MPa, average yield strength 133 MPa, average elongation 6.4%, and tensile strength Weibull modulus 14.

[0107] Comparative Example 4.

[0108] The chemical composition of the high-strength and high-toughness cast aluminum alloy in this embodiment is: 9.2 wt.% Si, 1.3 wt.% Zn, 0.3 wt.% Mg, 0.2 wt.% Mn, 0.25 wt.% Fe, 0.1 wt.% Zr, with other impurities totaling ≤0.2 wt.% and the balance being Al.

[0109] (1) Weigh out pure Al, crystalline Si, Al-Si recycled aluminum ingot, pure Zn, pure Mg, Al-10Mn master alloy, and Al-5Zr master alloy according to their weight percentages. Remove contaminants and oxide scale from the surface of the raw materials. Preheat and dry at 160°C for 90 minutes. In this example, the weight percentage of Al-Si recycled aluminum ingot is 25%.

[0110] (2) Place the Al-Si recycled aluminum ingot into the melting furnace, heat to 730℃, and hold for 30 minutes after complete melting. Skim off the slag, and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then skim off the slag. Before refining, the graphite rotor should be thoroughly dried. During the refining process, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0111] (3) Add pure Al, Al-10Mn master alloy, Al-5Zr master alloy, crystalline Si, and pure Zn to the aluminum alloy melt at 730℃. After melting, add pure Mg and mechanically stir for 5 minutes to ensure uniform composition. Hold at this temperature for 30 minutes. Remove slag and use a rotary jet to inject solid granular refining agent and dry argon gas into the aluminum alloy melt. Refine for 20 minutes, let stand for 15 minutes, and then remove slag. Before refining, the graphite rotor should be thoroughly dried. During mechanical stirring and refining, the surface of the aluminum alloy melt should be kept stable, and vortices, splashes, and surface turbulence should not occur.

[0112] (4) Reduce the temperature of the aluminum alloy melt to 700°C and perform pre-furnace composition testing.

[0113] (5) The aluminum alloy melt with qualified composition is subjected to gravity casting in a metal mold. Two 8mm diameter round bar samples are cast in one mold. The pouring temperature is 700℃. The mold is an ASTM B108 metal mold with a preheating temperature of 200℃ and an ingate speed of about 1.0m / s.

[0114] Compared with the examples, this comparative example did not contain Ti, did not undergo cooling sedimentation treatment, and did not contain Bi. Thirty tensile specimens were prepared and subjected to room temperature tensile testing according to ASTM B557-06. Room temperature tensile properties: average tensile strength 228 MPa, average yield strength 126 MPa, average elongation 5.4%, and tensile modulus 22.

[0115] Figures 1-2The microstructure of Example 1 is shown. The primary solid solution has fine grain size and a morphology close to granular, with an average grain size of 16 μm; the eutectic Si is fine fibrous, reaching the micrometer scale, which is a good metamorphic state; the Fe-rich phase is fine granular, with a size of about 1 μm; the tensile fracture surface shows a large number of dimples, which is a typical characteristic of ductile fracture, and there are very few casting defects on the fracture surface, such as... Figure 3 As shown. The above features further support the mechanical properties under the conditions of Example 1: average tensile strength of 321 MPa, average yield strength of 159 MPa, and average elongation of 14.2%, with excellent comprehensive mechanical properties, which can meet the manufacturing requirements of high-pressure die-casting integrated castings.

[0116] Figures 4-5 The microstructure and tensile fracture characteristics of Example 3 are shown. Compared with Example 1, the cooling rate under low-pressure casting conditions is slower. The primary solid solution is dendritic with a small secondary dendrite spacing of approximately 15 μm. The eutectic Si size increases but still exhibits a fibrous structure. The Fe-rich phase is fine-grained, with a size of approximately 15 μm. The tensile fracture surface shows numerous dimples, a typical characteristic of ductile fracture, and almost no casting defects were found on the fracture surface. These characteristics further support the mechanical properties under the conditions of Example 3: average tensile strength 257 MPa, average yield strength 153 MPa, average elongation 16.7%, and tensile strength Weibull modulus 48. Although the tensile strength decreases significantly, the elongation is further improved, and the consistency of mechanical properties reaches 48, which meets the manufacturing requirements of integrated castings produced by low-pressure casting.

[0117] Figure 6 The hole-like defect detected in Example 4 was filled with Bi; Figure 7 The hole-like defect detected in Comparative Example 3 is hollow. Hollow-like defects are a major type of defect in casting, significantly impacting strength, toughness, and consistency of mechanical properties. Comparative Example 4 and Comparative Example 3 demonstrate that Bi can be folded within the hole-like defect, forming a sandwich-like entity with a sticky core, effectively mitigating the harmful effects of hole-like defects and improving the consistency of strength, toughness, and mechanical properties.

[0118] Figure 8 The double-layer membrane defect detected in Example 4 was filled with Bi. Figure 9 To compare with the double-layer film defect detected in Example 4, where there is an air gap between the two oxide layers of the double-layer film. Double-layer film defects are a major defect in casting, significantly impacting strength, toughness, and mechanical property consistency. Comparing Example 4 and Comparative Example 4, it can be concluded that Bi can effectively fill the local air gaps in the double-layer film, forming an oxide-Bi-oxide sandwich structure, effectively passivating the harmful effects of the double-layer film and improving the consistency of strength, toughness, and mechanical properties.

[0119] The above embodiments and comparative embodiments show that the cast aluminum alloy and its preparation method proposed in this invention can combine composition design and preparation methods, effectively reduce casting defects, effectively control the Fe-rich phase and eutectic silicon, and thus effectively improve the strength and toughness of the cast aluminum alloy, especially the consistency of mechanical properties.

[0120] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any modifications to the equivalent structure or process described in the present invention, or direct or indirect applications to other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A high-strength and high-toughness cast aluminum alloy, characterized by being composed of the following components in the following proportions: 7-9.5 wt.% Si, 0.1-2 wt.% Bi, 0.1-2 wt.% Zn, 0.1-0.55 wt.% Mg, 0.1-0.6 wt.% Mn, 0.2-0.5 wt.% Fe, Ti≤0.2 wt.%, Zr≤0.2 wt.%, total amount of other impurities≤0.2 wt.%, balance Al; The solidification temperature interval of the high-strength and high-toughness cast aluminum alloy is ≤60℃; When the Fe content is >0.4 wt.%, the ratio of Fe to Mn in the high-strength and high-toughness cast aluminum alloy is 1-3; The content of Sr in the other impurities is <0.01 wt.%; The service environment temperature of the high-strength and high-toughness cast aluminum alloy is ≤255℃.

2. The method of claim 1, wherein the high strength and toughness cast aluminum alloy is prepared by the steps of: The method comprises the following steps: ​ (1) The raw materials are weighed according to the weight percentage, the surface contaminants and oxide skins of the raw materials are removed, and preheating and drying treatment is performed at a temperature of 150-180℃ for 30-120 min; the raw materials comprise pure Al, crystalline Si, Al-Si recycled aluminum ingot, Bi, pure Zn, pure Mg, Al-Mn intermediate alloy, Al-Ti intermediate alloy, and Al-Zr intermediate alloy; The addition amount of the Al-Si recycled aluminum ingot is 20-50% of the total cast aluminum alloy, and the content of Sr in the Al-Si recycled aluminum ingot is ≤0.05 wt.%; the ingot blank density equivalent is ≤2.5%, and the hydrogen content is ≤0.18 ml / 100 g; (2) The Al-Si recycled aluminum ingot is melted, and the melting temperature is 720-735℃, and the first refining is performed; (3) The pure Al, Al-Mn intermediate alloy, Al-Zr intermediate alloy, crystalline Si, and pure Zn are added to the aluminum alloy melt obtained in step (2); after melting, the pure Mg is added; the melting temperature is 720-735℃, and the second refining is performed after complete melting; (4) The aluminum alloy melt obtained in step (3) is heated to 800-880℃, the Al-Ti intermediate alloy is added, and after complete dissolution, the temperature of the aluminum alloy melt is reduced and settled, the temperature of the aluminum alloy melt is reduced to 630-660℃, and the alloy melt is heated to 690-720℃; (5) The Bi is added to the aluminum alloy melt obtained in step (4), and the temperature is kept constant; (6) The aluminum alloy melt obtained in step (5) is cast to form the high-strength and high-toughness cast aluminum alloy.

3. The method for preparing a high-strength and high-toughness cast aluminum alloy according to claim 2, characterized in that: In step (4), the total time of temperature reduction and settlement is ≥60 min; during the whole temperature reduction and settlement process, the aluminum alloy melt is in a static state.

4. The method for preparing a high-strength and high-toughness cast aluminum alloy according to claim 2, characterized in that: The Al-Ti intermediate alloy is an alloy wire or an alloy rod with a diameter ≤8 mm.

5. The method of claim 2 wherein Bi is present in an amount of 0.0005 to 0.005 wt. %. It is pure Bi or an Al-Bi intermediate alloy.

6. The method of claim 2, wherein Bi is present in an amount of 0.0005 to 0.005 wt. %. It is a wire or a rod with a diameter ≤8 mm.

7. The method for preparing a high-strength and high-toughness cast aluminum alloy according to claim 2, characterized in that: In step (6), the casting is metal mold gravity casting or counter-gravity casting, and the casting temperature is 690-720℃, and the inner gate speed is ≤1 m / s.

8. The method for preparing a high-strength and high-toughness cast aluminum alloy according to claim 7, characterized in that: In step (6), the inner gate speed is ≤0.5 m / s.

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