Die-casting aluminum alloy free from heat treatment, product prepared from same, and preparation method therefor

Abstract

The present invention relates to a die-casting aluminum alloy free from heat treatment, a product prepared from same, and a preparation method therefor. The die-casting aluminum alloy further comprises, in addition to Al and unavoidable impurity elements, the following chemical components in percentages by mass: Si: 6.5-9.5%, Fe: 0.1-0.3%, Mn: 0.4-0.85%, Mg: 0.1-0.6%, Ti: 0.02-0.12% and Sb: 0.05-0.15%; in addition, the die-casting aluminum alloy satisfies the following expressions: Fe+Mn≥0.65%, and Mn / Fe＝2.0-6.6, wherein each element symbol in the expressions is substituted into the mass percentage content of the corresponding element. In the present invention, the alloy die casting can obtain a structure having no obvious hole loosening defects throughout the inside, thereby ensuring that the tensile strength is greater than 200 MPa, the yield strength is greater than 120 MPa, and the elongation throughout the component is greater than 10%.

Description

Heat-treatment-free die-cast aluminum alloy, products made therefrom, and preparation method thereof Technical Field

[0001] The present invention belongs to the technical field of die-cast aluminum alloys, and in particular relates to a heat-treatment-free die-cast aluminum alloy, a product made therefrom, and a preparation method thereof. Background Art

[0002] The development of the modern automobile industry has driven the demand for high-strength and toughness die-cast aluminum alloys. Since the 1990s, researchers at home and abroad have been committed to developing high-strength and toughness die-cast aluminum alloy materials based on high vacuum die-casting technology, mainly based on Al-Si-Mg alloys (typical alloy composition AlSi10MnMg). This is because Mg and Si in Al-Si-Mg alloys can form Mg2Si. During heat treatment, Mg2Si can be dissolved into the matrix and then precipitated during aging, playing a role in strengthening the alloy. At the same time, Si particles can spheroidize and passivate during the solution process, thereby improving the plasticity of the alloy.

[0003] To achieve high elongation performance, traditional aluminum die-cast body parts typically require heat treatment. However, as the size of integrated castings increases, deformation during heat treatment is more likely to occur, resulting in a decrease in yield rate. Therefore, heat-treatment-free materials have become the optimal choice for the implementation of integrated die-casting technology. The as-cast tensile mechanical properties requirements for large, integrated, thin-walled parts are: yield strength ≥120MPa, tensile strength ≥200MPa, and elongation ≥10%.

[0004] In view of the insufficient performance of existing die-cast aluminum alloys without heat treatment, many manufacturers or research institutions have disclosed some patents for die-cast aluminum alloys without heat treatment.

[0005] Chinese patent publication number CN115505795A discloses a heat-treatment-free aluminum alloy material, comprising the following components: Si, Fe, Cu, Mn, Mg, Zn, Ti, Sr, Zr, Cr, B, rare earth La+Y, Al and inevitable impurity elements, wherein the components are proportioned in percentage as follows: Si: 7.0-10.5%, Fe: 0.1-0.8%, Cu: 0.95-4.0%, Mn: 0.2-0.7%, Mg: 0.4-1.44%, Zn: 0.1-1.2%, Ti: 0.036-0.1%, Sr: 0.02-0.06%, Zr: 0.002-0.06%, Cr: 0≤Cr<0.008%, B: 0≤B<0.002%, rare earth La+Y: 0≤La+Y<0.2%, and the balance is Al and inevitable impurity elements. The advantages of this invention are: in terms of composition design, Si is controlled within the range of 7-10% hypoeutectic series, which can greatly improve the fluidity and filling capacity of the aluminum alloy. Through the synergistic effect of other elements, while ensuring a certain elongation, the yield strength is improved, the grain size of the die-cast structural parts is significantly refined, and a double refinement effect is achieved.

[0006] Chinese Patent Publication No. CN115094281A discloses a heat-treatment-free, bake-hardenable die-cast aluminum-silicon alloy, as well as a preparation method and bake-hardening method. The die-cast aluminum alloy contains the following elements by mass: Si: 5.5-8.0%, Mg: 0.2-0.9%, Cu: 0.1-0.6%, Fe ≤ 0.2%, Mn ≤ 0.4%, Mo ≤ 0.4%, Ni ≤ 0.1%, Sn ≤ 0.1%, Ti ≤ 0.1%, Sr: 0.01-0.02%, with the remainder being Al and unavoidable impurities. The mass ratio of Cu to Mg is ≤ 0.65, the mass ratio of Mn to Mo is 1.0-2.0, and the mass ratio of the sum of Mn and Mo to Fe is 3.0-6.0. This die-cast aluminum-silicon alloy is prepared through material preparation, smelting, refining, and die-casting. It exhibits excellent tensile strength, yield strength, and good ductility without requiring heat treatment.

[0007] Chinese Patent No. 3 (Publication No. CN114717455A) discloses a heat-treatment-free, high-strength and toughness die-cast aluminum alloy and its preparation method. The alloy comprises: Si 7.5-9.5 wt.%, Ni 0-1.5 wt.%, Mn 0.4-0.8 wt.%, Mg 0-0.4 wt.%, Cr 0.08-0.3 wt.%, Zr 0.01-0.15 wt.%, Ti 0.03-0.1 wt.%, Sr 0.005-0.025 wt.%, with the remainder being aluminum and unavoidable impurities. This die-cast aluminum alloy exhibits excellent thermal stability, with mechanical properties changing by no more than 10% after being held at or below 150°C for 1000 hours. It exhibits excellent mechanical properties with a die-cast yield strength exceeding 120 MPa and an elongation exceeding 14%. It meets the performance requirements of die-cast structural parts for vehicle bodies without subsequent heat treatment, significantly improving the yield rate of thin-walled die-cast structural parts and reducing the cost of automotive parts.

[0008] The Chinese patent application number CN114164362A discloses a heat-treatment-free, high-strength and tough aluminum alloy and a forming method thereof. The aluminum alloy comprises Si 8.5-1.5%, Cu 0.05-0.5%, Mg 0.05-0.5%, Mo 0.1-0.5%, Sr 0.005-0.1%, B 0.005-0.1%, Cd 0.05-0.3%, and Zr 0.05`-0.25% by mass, with the remainder being Al and unavoidable impurities. During the forming of the aluminum alloy of the present invention, boronization treatment is used to refine the grains, and strontium modification is used to refine the eutectic silicon. The addition of Mo not only avoids the poisoning phenomenon caused by the simultaneous addition of B and Sr, but also refines the eutectic silicon to a submicron size, significantly improving the strength and toughness of the alloy. At the same time, the alloy is given excellent mechanical properties by combining solid solution strengthening and dispersion strengthening. The alloy has good fluidity and excellent casting performance, and does not require heat treatment to strengthen it, which saves production processes and reduces production costs, and has a bright application prospect.

[0009] Chinese patent publication number CN105316542A discloses a high-strength, high-toughness die-cast aluminum alloy and its products. This alloy belongs to the Al-Si-Mn-Mg-Re system and is composed of the following components by mass percentage: silicon 7.5-8.5%, manganese 0.3-0.4%, magnesium 0.2-0.3%, rare earth 0.1-0.2%, strontium 0.01-0.02%, iron ≤0.15%, titanium ≤0.10%, copper ≤0.05%, and the remainder being aluminum and unavoidable trace impurities, wherein the content of each individual trace impurity is ≤0.05%, and the total amount of trace impurities is ≤0.15%. The products are made from this high-strength, high-toughness die-cast aluminum alloy. This die-cast aluminum alloy exhibits high strength and toughness, and achieves good mechanical properties in the as-cast state without T6 heat treatment. T6 heat treatment further improves the material's mechanical properties. This alloy material can meet the development needs of lightweight cars and is used in the manufacture of key components such as car chassis subframes and door pillars.

[0010] The heat-treatment-free die-casting alloys disclosed in the aforementioned patents ensure fluidity, strength, and toughness by adding alloying elements such as Si, Mg, Cu, V, Zr, rare earth elements, and Sr. All alloys contain 0.01-0.06% Sr (strontium). The addition of Sr makes the aluminum melt particularly susceptible to air absorption, making it difficult to ensure melt purity. Even after refining and degassing, the hydrogen content exceeds 0.18 ml / 100 g Al. Furthermore, in large-scale industrial production, the aluminum melt remains in the holding furnace for a long time. During subsequent vacuum die-casting production trials, the high hydrogen content in the melt causes numerous porosity defects in various locations within the casting, resulting in localized porosity exceeding the typical die-casting porosity requirement of less than 5%. This results in significant fluctuations in the elongation of the actual trial products, making it difficult to achieve elongation above 10% in some areas.

[0011] Summary of the Invention

[0012] The present invention aims to provide a heat-treatment-free die-cast aluminum alloy, products made therefrom, and a method for preparing the same. This invention addresses the problem of Sr element deterioration in such heat-treatment-free die-cast alloys, leading to melt inhalation and unstable elongation. This invention enables the aluminum alloy die-cast parts to have a microstructure free of significant porosity defects, thereby ensuring a tensile strength greater than 200 MPa, a yield strength greater than 120 MPa, and an elongation greater than 10% at all locations.

[0013] To achieve the above object, the technical solution of the present invention is:

[0014] A first aspect of the present invention provides a die-cast aluminum alloy. In addition to Al and unavoidable impurity elements, the die-cast aluminum alloy further comprises the following chemical composition, in percentage by mass: Si 6.5-9.5%, Fe 0.1-0.3%, Mn 0.4-0.85%, Mg 0.1-0.6%, Ti 0.02-0.12%, and Sb 0.05-0.15%; and simultaneously satisfies the following formula: Fe+Mn≥0.65%, Mn / Fe=2.0-6.6, where the symbols of the elements are substituted into the corresponding percentage by mass of the elements.

[0015] Preferably, the die-casting aluminum alloy of the present invention contains the following chemical components in mass percentage: Si 6.5-9.5%, Fe 0.1-0.3%, Mn 0.4-0.85%, Mg 0.1-0.6%, Ti 0.02-0.12%, Sb 0.05-0.15%, and the balance is Al and unavoidable impurity elements.

[0016] Preferably, the content of each element in the inevitable impurity elements is ≤0.075% by mass, and the total amount is ≤0.3%; preferably, the inevitable impurity elements include one or more of Cr, V, Ni, Sn, and Zn.

[0017] Preferably, the chemical composition of the die-cast aluminum alloy further includes at least one selected from Sr, Mo and Zr, wherein: Sr≤0.01%, Mo≤0.15%, Zr≤0.15%.

[0018] Preferably, Fe is 0.1-0.15%; and / or Mn is 0.55-0.65%; and / or Mg is 0.1-0.4%; and / or Ti is 0.05-0.1%; and / or Sb is 0.08-0.13%.

[0019] Preferably, the microstructure of the die-cast aluminum alloy of the present invention is α-Al+(α+Si) eutectic; wherein the eutectic silicon is in the form of round particles with a size of submicron level; preferably, the average size of the eutectic silicon is 0.1-1 μm, more preferably 0.63-0.80 μm.

[0020] Preferably, the die-cast aluminum alloy of the present invention has no needle-shaped iron-containing phase with a size larger than 20 μm in its microstructure, and no pore with a size larger than 50 μm.

[0021] Preferably, the porosity of the die-cast aluminum alloy of the present invention is less than 0.5%.

[0022] Preferably, the die-cast aluminum alloy of the present invention has a tensile strength greater than 200 MPa, preferably greater than 265 MPa, a yield strength greater than 120 MPa, and an elongation greater than 10%, preferably greater than 14%.

[0023] In the composition design of the die-casting aluminum alloy of the present invention, the design principle of each chemical element is as follows: In this article, unless otherwise explicitly stated, the element content is calculated in mass percentage.

[0024] Si: The element Si in aluminum alloys significantly improves die-casting fluidity and strength. A higher Si content results in a greater eutectic structure, improved fluidity, and increased strength, but also reduced toughness. Therefore, the present invention controls the Si content to 6.5-9.5%, which not only ensures the fluidity of the aluminum alloy but also reduces the proportion of eutectic silicon phase, thereby improving the plasticity of the aluminum alloy.

[0025] Fe: The maximum solid solubility of Fe in Al is only 0.052%. In wrought aluminum alloys, Fe is generally treated as an impurity. However, in die-cast aluminum alloys, Fe's mold release function is, in some cases, almost irreplaceable, while also improving the alloy's high-temperature mechanical properties and hot cracking resistance. However, Fe tends to form coarse, needle-like β-Al5FeSi phases in die-cast aluminum alloys, resulting in reduced strength and toughness. Therefore, the present invention controls the Fe content to 0.1-0.3%.

[0026] Mn: Mn has little effect on the strength of die-cast aluminum alloys. However, it can transform the β-Al5FeSi phase into a massive or shaped AlFeMnSi phase, thereby increasing the alloy's toughness and improving its die-sticking properties. However, excessive Mn content can form large manganese-containing phases, affecting the alloy's toughness. To ensure excellent mold release properties, the combined Fe and Mn contents should be controlled to ≥ 0.65%. To improve the morphology of the iron-containing phase, the present invention controls the Mn to Fe ratio to 2.0 to 6.6.

[0027] Mg: Mg, when added to die-cast aluminum alloys, forms the Mg2Si phase, which increases the tensile strength, hardness, and corrosion resistance of aluminum alloy die-castings. However, excessive Mg content can reduce the alloy's toughness and fluidity, increasing shrinkage and hot cracking tendencies, particularly affecting large castings. Therefore, the present invention limits the Mg content to 0.1-0.6%.

[0028] Ti: Ti refines the aluminum matrix and is typically added to the alloy along with boron. During solidification, it preferentially precipitates fine TiB2 and Al3Ti phases, which serve as heterogeneous nucleation sites and refine the grain size. However, excessive Ti can easily cause TiB2 particles to agglomerate, affecting the alloy's toughness. Therefore, in this invention, the Ti content is controlled to 0.02-0.12%.

[0029] Mo: Mo is a more effective Fe neutralizer than Mn, transforming the β-Al5FeSi phase into a fine α-Al(Mo,Fe)Si phase. Adding Mo together with Mn completely modifies both the pre-eutectic and eutectic β-Fe phases. This phase is evenly dispersed in the aluminum matrix, effectively blocking dislocation motion and improving alloy strength and toughness. To control alloy costs, the Mo content in this invention is controlled to ≤ 0.15%.

[0030] Zr: Zr forms the Al3Zr phase in aluminum alloys, which has a similar crystal structure to the Al3Ti phase. It exhibits a low lattice mismatch with the α-Al solid solution and also refines grain size. Furthermore, Zr forms a nanoscale dispersed phase uniformly distributed within the aluminum matrix, pinning dislocations and improving the strength of the cast aluminum alloy at both room and elevated temperatures. To control alloy costs, the present invention limits the Zr content to ≤ 0.15%.

[0031] Sr: Sr is widely used in die-cast aluminum alloys to modify eutectic silicon, transforming coarse, elongated eutectic silicon into short fibers, reducing its cracking effect on the matrix and preventing stress concentration that can reduce plasticity. However, excessive Sr content can increase the alloy's gas absorption and gas content. To control the purity of the alloy melt and consistently improve the elongation of the casting, the present invention limits the Sr content to ≤ 0.01%.

[0032] Sb: Sb element can produce AlSb phase in aluminum alloy. This phase precipitates before α-Al in the melt, promoting the nucleation and growth of α-Al. As the Si phase precipitates from the melt, it adheres to the AlSb phase. At the same time, α-Al grows and wraps the Si phase and AlSb phase. Therefore, Sb element can effectively modify eutectic silicon, and can effectively change eutectic silicon from coarse flakes to fine flakes and even round particles. The size of eutectic silicon can reach submicron level, and it can also refine the aluminum matrix, making the dendritic aluminum matrix rods thinner and more uniform.

[0033] Figure 1 shows the as-cast structure of a poorly modified hypoeutectic aluminum-silicon alloy, Figures 2 and 3 show the as-cast structures of a modified hypoeutectic aluminum-silicon alloy containing 0.02% Sr, and Figures 4 and 5 show the as-cast structures of a modified hypoeutectic aluminum-silicon alloy containing 0.1% Sb. The aluminum-silicon alloys used in Figures 1-5 have basically the same composition, with the main components being Si 10%, Fe 0.2%, Cu 2.1%, Mg 0.4%, and Ti 0.02% in mass percentage; the only difference is that 0.02% Sr is mixed into the aluminum-silicon alloys in Figures 2-3, and 0.1% Sb is mixed into the aluminum-silicon alloys in Figures 4-5.

[0034] The alloy melts in Figures 1-5 were all degassed at 720-730°C using a rotary degasser. 4m 3 / h of argon, a rotor speed of 400 rpm, and a degassing time of 10 minutes. After degassing, the surface slag was scraped off. A 178 mm diameter ingot was obtained using a semi-continuous casting process. Samples were taken from the core of the ingot for metallographic analysis. The results show that the eutectic silicon within the circle in Figure 1 is poorly modified, with elongated strips exceeding 10 microns in size. The eutectic silicon of the alloy with a 0.02% Sr content in Figures 2 and 3 is well modified, with punctate eutectic silicon appearing with a maximum size of approximately 7 microns, but with numerous pores ranging in size from 70 to 140 microns. The eutectic silicon of the alloy with a 0.1% Sb content in Figures 4 and 5 demonstrates comparable modification, with punctate eutectic silicon appearing with a maximum size of approximately 8 microns, but without pores and only slight porosity, with a porosity size of less than 25 microns. This microstructure is achieved through a semi-continuous casting process, which uses a cooling rate much lower than that of die casting. Die casting further refines the eutectic silicon to submicron size. Furthermore, the Sb addition process is simple, and the modification effect lasts long. Even after remelting, the modified alloy retains its good modification effect. However, excessive Sb content can produce flocculent or even coarse, needle-like AlSb phases, leading to a sharp decline in mechanical properties. Therefore, the present invention controls the Sb content to 0.05-0.15%.

[0035] A second aspect of the present invention further provides a method for preparing a die-cast aluminum alloy, the method comprising the following steps performed in sequence:

[0036] (1) preparing raw materials according to the chemical composition of the die-cast aluminum alloy and smelting them to obtain an alloy melt, and controlling the temperature of the alloy melt to be 720-730° C.;

[0037] (2) adding a sodium-free slag remover to the alloy melt, wherein the weight of the sodium-free slag remover accounts for 0.1 to 0.5% of the total weight of the alloy melt, and controlling the temperature of the alloy melt at 720 to 730° C.; adding a sodium-free covering agent to the alloy melt after slag removal, wherein the weight of the sodium-free covering agent accounts for 0.05 to 0.1% of the total weight of the alloy melt;

[0038] (3) Degassing the alloy melt from step (2), controlling the alloy melt temperature at 720-730°C, and removing the surface slag. The degassing is carried out under the following conditions: using a mixed gas of argon and chlorine, with an argon flow rate of 3.5-4.5 m 3 / h, chlorine flow rate is 0.05~0.15m 3 / h, degassing time is 10 to 20 minutes; the hydrogen content in the alloy melt after degassing is ≤0.14ml / 100gAl;

[0039] (4) The alloy melt after degassing is subjected to composition detection and hydrogen content detection, and the alloy melt that passes the detection is allowed to stand and cool to 690-720° C. to obtain the die-cast aluminum alloy.

[0040] Preferably, in step (1): first, the required aluminum raw material is put into a smelting furnace for melting and heated to 760-790°C; then, silicon, manganese, antimony, molybdenum, and zirconium raw materials are added and after they are completely melted, the temperature is controlled at 730-750°C; then, magnesium raw material is added and stirred until completely melted, and the temperature is controlled at 720-730°C; finally, titanium and strontium raw materials are added and stirred until completely melted to obtain an alloy melt, and the temperature of the alloy melt is controlled at 720-730°C.

[0041] The iron element in the present invention is derived from the aluminum raw material used in the present invention and exists as an impurity element in the aluminum raw material.

[0042] Preferably, in step (2): a sodium-free slag remover is added to the alloy melt by powder spray refining, and in the powder spray refining process, argon is used as a carrier with an argon flow rate of 0.1 to 0.3 m 3 / h, refining time 5 to 10 minutes; the sodium-free slag remover and sodium-free covering agent are both powdery, with a particle size of ≤2mm.

[0043] Preferably, in step (3): the degassing is performed using a rotary degasser, and the rotor speed of the rotary degasser is 400-450 r / min.

[0044] Preferably, the aluminum raw material is pure aluminum or recycled aluminum that meets the alloy composition requirements; the silicon raw material is aluminum-silicon master alloy or industrial silicon or quick-dissolving silicon; the manganese raw material is aluminum-manganese master alloy or manganese agent; the antimony raw material is aluminum-antimony master alloy; the molybdenum raw material is aluminum-molybdenum master alloy; the strontium raw material is aluminum-strontium master alloy; the zirconium raw material is aluminum-zirconium master alloy; the titanium raw material is aluminum-titanium-boron master alloy rod or aluminum-titanium-carbon-boron master alloy rod; and the magnesium raw material is pure magnesium.

[0045] Preferably, the aluminum-silicon master alloy is Al20Si; the aluminum-manganese master alloy is Al10Mn; the aluminum-antimony master alloy is Al10Sb; the aluminum-molybdenum master alloy is Al5Mo; the aluminum-strontium master alloy is Al10Sr; the aluminum-zirconium master alloy is Al10Zr; the aluminum-titanium-boron master alloy is Al5TiB; and the aluminum-titanium-carbon-boron master alloy is Al2Ti0.2C0.2B.

[0046] In the method for preparing the die-cast aluminum alloy of the present invention:

[0047] When using a rotary degasser for rotary degassing, a mixed gas of argon and chlorine is used, and the argon flow rate is 3.5 to 4.5 m 3 / h, chlorine flow rate is 0.05~0.15m 3 / h, and the degassing time is 10 to 20 minutes. The present invention improves the degassing capacity by mixing a small amount of chlorine with argon as the degassing medium, while utilizing dispersed argon bubbles to absorb hydrogen in the melt and also utilizing the chemical reaction between chlorine and hydrogen in the melt, thereby controlling the hydrogen content in the alloy melt to ≤0.14ml / 100gAl.

[0048] Hydrogen is removed from molten aluminum alloys by reacting hydrogen atoms to generate hydrogen gas, which is transferred to the gas phase. The reaction process is controlled by the hydrogen partial pressure difference between the melt and the gas phase. When the hydrogen partial pressure in the melt is higher than that in the gas phase, hydrogen gas is released from the melt. Argon gas is introduced into the melt. The hydrogen partial pressure in the argon bubbles is lower than that in the melt. The hydrogen in the melt diffuses into the argon bubbles and generates hydrogen gas, which floats up with the argon bubbles and is carried out of the melt.

[0049] During the degassing step, the high-speed rotation of the rotor in the rotary degasser breaks the argon gas flowing out of the rotor outlet into very fine bubbles, increasing the surface area and dispersion of the bubbles in the melt, allowing the argon bubbles to more fully contact the hydrogen atoms in the melt, thereby improving the degassing efficiency. The speed of the rotor determines the effectiveness of bubble crushing and dispersion during the degassing process. The higher the rotor speed, the better the bubble crushing and dispersion effect, and the better the degassing effect. However, too high a rotation speed causes equipment instability and can easily lead to rotor fracture and failure; too low a rotation speed will cause the bubbles in the melt to be too large, and the range of action will be limited to a very small area around the rotor. The bubbles will float up quickly in the melt, with a short residence time and poor hydrogen capture effect. Therefore, the present invention preferably controls the rotor speed to 400-450r / min.

[0050] The argon flow rate into the rotor is related to the rotor speed. Too low an argon flow rate results in fewer bubbles in the melt, while too high an argon flow rate results in the rotor being unable to fully break up and disperse the bubbles. The excess bubbles cause the small bubbles to re-aggregate into large bubbles, which float near the rotor and cause the liquid surface to churn, resulting in a decrease in degassing efficiency. Therefore, the argon flow rate is controlled at 3.5 to 4.5 m / s. 3 / h.

[0051] The present invention enhances the degassing ability by adding a small amount of chlorine to argon and utilizing the reaction of chlorine in the melt. The main reactions are as follows: Cl2+H2=2HCl↑ and 2Al+3Cl2=2AlCl3↑. Chlorine directly reacts chemically with hydrogen to remove hydrogen. At the same time, AlCl3 and HCl generated by the reaction of chlorine and aluminum float in the melt in a gaseous state, which also brings about the adsorption degassing effect. However, due to the direct reaction of chlorine with Al, excessive chlorine will cause the melt to slag. Therefore, the chlorine flow rate is controlled to 0.05-0.15m 3 / h. Rotary degassing introduces argon into the melt to absorb hydrogen. This requires controlling the hydrogen content of the melt to a low level, thus ensuring a sufficient degassing time. Too short a degassing time will obviously result in incomplete degassing, and equilibrium will be reached when the hydrogen content in the melt continues to decrease. Excessively long degassing times will fail to further reduce the hydrogen content in the melt and may instead cause slagging and oxidation of the melt. Therefore, the degassing time should be controlled between 10 and 20 minutes.

[0052] The sodium-free deslagging agent and sodium-free covering agent used in the present invention are not particularly limited, and those commonly used in the art can be used. The sodium-free deslagging agent, for example, includes but is not limited to the following components by mass percentage: KCl 42%, MgCl2 46%, BaCl2 6%, CaF2 6%, and the sodium-free covering agent includes but is not limited to the following components by mass percentage: (KCl+MgCl2) 80%, CaF2 20%.

[0053] The qualified alloy melt of the present invention refers to an alloy melt having the above composition of the present invention and a hydrogen content of ≤0.14 ml / 100 gAl.

[0054] A third aspect of the present invention provides a product made from the die-cast aluminum alloy, such as an aluminum alloy die-casting. The aluminum alloy die-casting may be an automobile component.

[0055] Compared with the prior art, the advantages of the present invention are:

[0056] 1. Existing alloys commonly modify eutectic silicon by adding Sr. Sr reduces the liquid-filling capacity of the alloy during solidification, making it prone to shrinkage cavities and porosity defects. To ensure the modification effect of eutectic Si, the Sr addition amount is usually 0.02%. However, high Sr content leads to severe air absorption in the alloy melt. The existing degassing process in the die-casting industry makes it difficult to control the hydrogen content of the melt to below 0.18ml / 100gAl. As a result, subsequent vacuum die-cast parts are more prone to porosity defects, and some porosity defects can reach a size of more than 100 microns.

[0057] The heat treatment-free die-cast aluminum alloy of the present invention adds Sb element to replace Sr element for the first time, and performs a modification treatment on eutectic silicon, which can effectively avoid the problem of high hydrogen content caused by gas absorption of high Sr content melt, thereby avoiding the problem of coarse needle-shaped eutectic silicon in the alloy structure of hypoeutectic Al-Si die-cast aluminum alloy, which seriously deteriorates the mechanical properties of the alloy.

[0058] 2. The present invention modifies eutectic silicon by adding Sb element, which can effectively change eutectic silicon from coarse flakes to fine flakes or even round particles, reaching the submicron level (0.1-1μm), and can refine the aluminum matrix, making the dendritic aluminum matrix rods thinner. Compared with the existing method of adding Ti element alone, the composite refining effect is better, and the aluminum matrix dendrites are evenly distributed, thereby significantly improving the mechanical properties, especially the elongation.

[0059] 3. The present invention uses Sb element to modify and refine the alloy, and its process is simple and the modification effect lasts for a long time. Even if the alloy is remelted, it does not need to be treated again and still maintains a good modification effect. However, the modification process of adding Sr element is relatively complicated because Sr is easily volatile in high-temperature melts and the addition yield is low. Sr element needs to be added again when the alloy is remelted.

[0060] 4. The present invention improves the morphology of the iron-containing phase and enhances the mechanical properties and demoulding properties of the alloy by controlling the total amount and ratio of the two elements Fe and Mn.

[0061] 5. In the melt degassing process in the preparation method of the present invention, an argon-chlorine mixed gas is used as a degassing medium for the first time in heat-treatment-free die-cast aluminum alloy, which improves the melt degassing efficiency and ensures that the hydrogen content in the melt can be controlled below 0.14ml / 100gAl, providing a prerequisite for vacuum die-casting of low-porosity components, thereby steadily improving the elongation of the components. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] FIG1 is a photo of the as-cast structure of a poorly modified hypoeutectic aluminum-silicon alloy;

[0063] FIG2 is a photo of the as-cast structure of a modified hypoeutectic Al-Si alloy containing 0.02% Sr;

[0064] FIG3 is an enlarged photograph of the as-cast structure of a modified hypoeutectic Al-Si alloy containing 0.02% Sr;

[0065] FIG4 is a photo of the as-cast structure of a modified hypoeutectic Al-Si alloy containing 0.1% Sb;

[0066] FIG5 is an enlarged photograph of the as-cast structure of a modified hypoeutectic Al-Si alloy containing 0.1% Sb;

[0067] FIG6 is a photograph of a typical cross-section of a vacuum die-cast test piece in Example 5 of the present invention;

[0068] FIG7 is an enlarged photograph of a typical cross-sectional metallographic structure of a vacuum die-cast test piece in Example 5 of the present invention;

[0069] FIG8 is a typical metallographic structure photograph of the cross section of the vacuum die-casting test piece in Comparative Example 1. DETAILED DESCRIPTION

[0070] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate the present invention and are not intended to limit the present invention.

[0071] The performance parameters of the present invention are measured as follows.

[0072] The chemical composition of the alloy melt was determined using an ARL 4460 direct reading spectrometer.

[0073] Hydrogen content in alloy melt: measured using ABB-Alscan hydrogen analyzer.

[0074] The tensile strength, yield strength and elongation of die-cast aluminum alloy were measured using an AG-xPlus-100kN electronic tensile testing machine.

[0075] Microstructure of die-cast aluminum alloy: photographed and observed using a Leica Sereozoom S9i metallographic microscope.

[0076] Average size of eutectic silicon particles in the microstructure of die-cast aluminum alloy: Based on scanning electron microscopy images, the size and number of eutectic silicon particles were identified using ImageJ software, and the average size was calculated.

[0077] Porosity of die-cast aluminum alloy: Based on metallographic photographs, the pore area was identified using ImageJ software, and the measured area ratio was calculated.

[0078] The compositions of the aluminum alloys of the embodiments of the present invention and the comparative examples are shown in Table 1, and the remainder of the compositions includes Al and unavoidable impurities.

[0079] The preparation process parameters of the embodiments of the present invention and the comparative examples are shown in Table 2.

[0080] The performance parameters of the embodiments of the present invention and the comparative examples are shown in Table 3.

[0081] Example 1

[0082] The heat treatment-free die-cast aluminum alloy of Example 1 comprises the following chemical composition, in percentage by mass: Si 6.5%, Fe 0.22%, Mn 0.45%, Mg 0.38%, Ti 0.08%, Sb 0.15%, with the remainder being Al and unavoidable impurity elements, wherein the content of each of the unavoidable impurity elements is ≤0.075% and the total amount is ≤0.3%. The preparation method thereof comprises:

[0083] (1) preparing raw materials of pure aluminum, pure Mg, Al20Si, Al10Mn, Al10Sb and Al2Ti0.2C0.2B according to the chemical composition weight ratio of the above die-cast aluminum alloy, and preheating and drying the raw materials to remove moisture;

[0084] (2) The required aluminum raw material is put into a smelting furnace for melting and heated to 770°C, wherein the iron element is introduced through the aluminum raw material and exists as an impurity component in the aluminum raw material, and then Al20Si, Al10Mn and Al10Sb are added. After the raw materials are completely melted, the temperature is controlled at 740°C, and then Mg raw material is added and stirred. After the raw materials are completely melted, the temperature is controlled at 730°C, and then Al2Ti0.2C0.2B is added and stirred. After the raw materials are completely melted, an alloy melt is obtained, and the temperature of the alloy melt is controlled at 730°C;

[0085] (3) The alloy melt is subjected to a composition test. After the composition is qualified, a sodium-free slag remover is added to the melt by powder spray refining. The weight of the sodium-free slag remover accounts for 0.2% of the total weight of the alloy melt. The temperature of the alloy melt is controlled at 730°C. After slag removal, a sodium-free covering agent is added to the alloy melt. The weight of the sodium-free covering agent is determined according to the size of the melt surface and accounts for about 0.05% of the total weight of the alloy melt. Argon is used as a carrier in powder spray refining, and the argon flow rate is 0.1m 3 / h, refining time 10min, sodium-free slag remover and sodium-free covering agent are both powdery, with particle size ≤2mm;

[0086] (4) The alloy melt was degassed using a rotary degasser, the alloy melt temperature was controlled at 730°C, and the surface slag was scraped off; the degassing was carried out under the following conditions: rotor speed 400 r / min, argon + chlorine mixed gas, argon flow rate 3.5m 3 / h, chlorine flow rate 0.05m 3 / h, degassing time 10min;

[0087] (5) The alloy melt after refining and degassing is subjected to composition detection and hydrogen content detection, and the qualified alloy melt is allowed to cool to 690°C to obtain a heat-treatment-free die-cast aluminum alloy, wherein the alloy melt is judged to be qualified when it meets the following requirements: the composition of the alloy melt meets the requirements of the present invention, and the hydrogen content of the alloy melt measured by an ABB-Alscan hydrogen meter is ≤0.14ml / 100gAl.

[0088] The heat-treatment-free die-cast aluminum alloy was then fabricated into tensile bars or die-cast test pieces using vacuum die-casting for performance testing. The die-casting temperature was 690°C, the mold temperature was 200°C, the injection speed was 2.5 m / s, the casting pressure was 65 MPa, and the vacuum level was 200 mbar.

[0089] Examples 2-9

[0090] Examples 2-9 of the present invention were prepared using methods substantially identical to those of Example 1, except that the aluminum alloy composition and preparation process parameters were adjusted within the limits of the present invention. For details, see Tables 1 and 2. Unless otherwise specified, the molybdenum raw material in Examples 7-9 was Al5Mo, the strontium raw material was Al10Sr, and the zirconium raw material was Al10Zr.

[0091] Comparative Example 1

[0092] The heat treatment-free die-cast aluminum alloy of Comparative Example 1 comprises the following components, by mass percentage: Si 8.01%, Fe 0.12%, Mn 0.56%, Mg 0.35%, Ti 0.11%, Sr 0.025wt.%, and the balance is aluminum and unavoidable impurity elements, wherein the content of each element in the unavoidable impurity elements is ≤0.075%, and the total amount is ≤0.3%; the preparation method thereof comprises:

[0093] (1) preparing pure aluminum, pure Mg, Al20Si, Al10Mn, Al10Sr and Al2Ti0.2C0.2B according to the chemical composition weight ratio of the above die-cast aluminum alloy, and preheating and drying the raw materials to remove moisture;

[0094] (2) The required aluminum raw material is put into a smelting furnace for melting and heated to 770°C, wherein the iron element is introduced through the aluminum raw material and exists as an impurity component in the aluminum raw material, and then Al20Si and Al10Mn are added. After the raw materials are completely melted, the temperature is controlled at 740°C, and then Mg raw material is added and stirred. After the raw materials are completely melted, the temperature is controlled at 730°C, and then Al2Ti0.2C0.2B and Al10Sr are added and stirred. After the raw materials are completely melted, an alloy melt is obtained, and the temperature of the alloy melt is controlled at 730°C;

[0095] (3) The alloy melt is subjected to a composition test. After the composition is qualified, a sodium-free slag remover is added to the melt by powder spray refining. The weight of the sodium-free slag remover accounts for 0.25% of the total weight of the alloy melt. The temperature of the alloy melt is controlled at 725°C. After slag removal, a sodium-free covering agent is added to the alloy melt. The weight of the sodium-free covering agent is determined according to the size of the melt surface and accounts for about 0.1% of the total weight of the alloy melt. In the powder spray refining, argon is used as a carrier, and the argon flow rate is 0.12m 3 / h, refining time 9.5min, sodium-free slag remover and sodium-free covering agent are both powdery, with particle size ≤2mm;

[0096] (4) The alloy melt was degassed using a rotary degasser, the alloy melt temperature was controlled at 728°C, and the surface slag was scraped off; the degassing was carried out under the following conditions: rotor speed 425 r / min, argon + chlorine mixed gas, argon flow rate 4m 3 / h, chlorine flow rate 0.08m3 / h, degassing time 15min;

[0097] (5) The alloy melt after refining and degassing is subjected to composition testing, and the qualified alloy melt is allowed to cool to 695°C to obtain a heat treatment-free die-cast aluminum alloy.

[0098] Tensile bars or test pieces were then fabricated from the heat-treatment-free die-cast aluminum alloy using vacuum die-casting for performance testing. The die-casting temperature was 690°C, the mold temperature was 200°C, the shot speed was 2.5 m / s, the casting pressure was 65 MPa, and the vacuum level was 200 mbar.

[0099] Comparative Example 2

[0100] Comparative Example 2 was prepared using substantially the same main alloy components and preparation method as Example 1 of the present invention, except that the total amount and ratio of Fe and Mn did not meet the requirements of the present invention. For details, see Tables 1 and 2.

[0101] Table 1 (Unit: weight percentage)

[0102] Table 2

[0103] Table 3

[0104] The mechanical properties and average size of eutectic silicon of the die-cast test pieces made of the aluminum alloy of the present invention and the die-cast test pieces made of the comparative alloy are compared in Table 3. Microstructure photographs of Example 5 and Comparative Example 1 are shown in Figures 6, 7 and 8.

[0105] Figures 6 and 7 are typical optical micrographs of the cross-section of the die-cast test piece in Example 5 obtained using an optical microscope. The results show that the microstructure of the aluminum alloy material in Example 5 is α-Al+(α+Si) eutectic, its internal structure is fine and uniform, there is no coarse needle-shaped iron-containing phase with a size greater than 20 microns, the eutectic silicon modification effect is good, the eutectic silicon is point-shaped, and the size is less than 1 micron (the average size of the eutectic silicon particles in Figure 7 is calculated to be 0.75 micron using ImageJ software, reaching the submicron level); and there are no obvious holes with a size greater than 50 microns in the interior, only a small amount of looseness (porosity <0.5%), thereby ensuring high elongation.

[0106] Figure 8 is a typical optical micrograph of the cross-section of the die-cast specimen in Comparative Example 1. The results show that the internal structure of the material is fine and uniform, without coarse needle-shaped iron-containing phases larger than 20 microns in size. The eutectic silicon modification effect is also good, and the average size of the eutectic silicon particles is 0.81 microns, which can also reach the submicron level; however, there are obvious hole defects with a size larger than 50 microns, and the size of the aggregation area reaches more than 100 microns, which reduces the elongation.

[0107] As shown in Table 3, the die-cast specimens of the present invention exhibited a tensile strength exceeding 265 MPa, a yield strength exceeding 120 MPa, and an elongation exceeding 14%. While the die-cast specimens of Comparative Examples 1 and 2 also met the strength requirements, their elongations were only 8.8% and 9.4%, respectively.

[0108] In summary, the present invention uses a Sb element modification / refinement process combined with optimization of the alloy composition (for example, controlling the Fe and Mn content and ratio) to achieve good eutectic silicon modification effects, effectively avoiding the problem of high hydrogen content caused by high Sr content melt aspiration. The hydrogen content of the alloy is controlled to below 0.14ml / 100gAl by the rotary degassing process. After die-casting, the internal structure is fine and uniform, without coarse needle-shaped iron-containing phases larger than 20 microns in size. The eutectic silicon is spherical and granular, with an average size reaching the submicron level, and without obvious loose pores larger than 50 microns in size. Excellent mechanical properties such as a die-cast yield strength greater than 120MPa and an elongation greater than 14% can be obtained, making it suitable for vacuum die-casting of large-scale integrated automotive parts. This large-scale integrated automotive part can meet the industry's automotive parts usage requirements (porosity <5%, elongation of more than 10%) while also meeting subsequent connection requirements.

[0109] It should be noted that all technical features described in this application can be freely combined or combined in any way unless there is a contradiction between them. Various modifications and variations can be made to the present invention without departing from the scope of the present invention, which will be apparent to those skilled in the art. For example, a feature shown or described as part of one embodiment can be used together with another embodiment to produce another embodiment. Therefore, the present invention is intended to encompass these modifications and variations that fall within the scope of the appended claims and their equivalents.

Claims

1. A die-cast aluminum alloy, characterized in that: The die-casting aluminum alloy contains, in addition to Al and unavoidable impurity elements, the following chemical components in mass percentage: Si 6.5-9.5%, Fe 0.1-0.3%, Mn 0.4-0.85%, Mg 0.1-0.6%, Ti 0.02-0.12%, Sb 0.05-0.15%; and at the same time satisfies the following formula: Fe+Mn≥0.65%, Mn / Fe=2.0-6.6, where the symbols of the elements are substituted into the corresponding mass percentage content of the elements.

2. The die-cast aluminum alloy according to claim 1, characterized in that: The die-casting aluminum alloy contains the following chemical components in mass percentage: Si 6.5-9.5%, Fe 0.1-0.3%, Mn 0.4-0.85%, Mg 0.1-0.6%, Ti 0.02-0.12%, Sb 0.05-0.15%, and the balance is Al and unavoidable impurity elements.

3. The die-cast aluminum alloy according to claim 1 or 2, characterized in that: The content of each element in the inevitable impurity elements in terms of mass percentage is ≤0.075%, and the total amount is ≤0.3%; preferably, the inevitable impurity elements include one or more of Cr, V, Ni, Sn, and Zn.

4. The die-cast aluminum alloy according to any one of claims 1 to 3, characterized in that: The die-casting aluminum alloy further comprises at least one selected from Sr, Mo and Zr, wherein: Sr≤0.01%, Mo≤0.15%, Zr≤0.15%.

5. The die-cast aluminum alloy according to any one of claims 1 to 4, characterized in that: Fe 0.1-0.15%; and / or, Mn 0.55-0.65%; and / or, Mg 0.1-0.4%; and / or, Ti 0.05-0.1%; and / or, Sb 0.08-0.13%.

6. The die-cast aluminum alloy according to any one of claims 1 to 5, characterized in that: The microstructure of the die-cast aluminum alloy is α-Al+(α+Si) eutectic, wherein the eutectic silicon is in the form of spherical particles with a size of submicron level. Preferably, the average size of the eutectic silicon is 0.1-1 μm, more preferably 0.63-0.80 μm. Preferably, the microstructure of the die-cast aluminum alloy does not contain needle-shaped iron-containing phases with a size greater than 20 μm, and does not contain pores with a size greater than 50 μm. Preferably, the porosity of the die-cast aluminum alloy is <0.5%.

7. The die-cast aluminum alloy according to any one of claims 1 to 6, characterized in that: The die-cast aluminum alloy has a tensile strength greater than 200 MPa, preferably greater than 265 MPa, a yield strength greater than 120 MPa, and an elongation greater than 10%, preferably greater than 14%.

8. A method for preparing a die-cast aluminum alloy as claimed in any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps performed sequentially: (1) preparing raw materials according to the chemical composition of the die-casting aluminum alloy and smelting them to obtain an alloy melt, and controlling the temperature of the alloy melt to be 720 to 730° C.; (2) adding a sodium-free slag remover to the alloy melt, wherein the weight of the sodium-free slag remover accounts for 0.1-0.5% of the total weight of the alloy melt, and controlling the temperature of the alloy melt at 720-730° C.; adding a sodium-free covering agent to the alloy melt after slag removal, wherein the weight of the sodium-free covering agent accounts for 0.05-0.1% of the total weight of the alloy melt; (3) Degassing the alloy melt from step (2), controlling the alloy melt temperature at 720-730° C., and removing the surface scum. The degassing is performed under the following conditions: using a mixed gas of argon and chlorine, with an argon flow rate of 3.5-4.5 m / s; 3 / h, chlorine gas flow rate is 0.05~0.15m 3 / h, degassing time is 10-20min; hydrogen content in the alloy melt after degassing is ≤0.14ml / 100gAl; (4) The alloy melt after degassing is subjected to composition detection and hydrogen content detection, and the alloy melt that passes the detection is allowed to stand and cool down to 690-720° C. to obtain the die-cast aluminum alloy.

9. The preparation method according to claim 8, characterized in that: In step (1): firstly, the required aluminum raw material is put into a smelting furnace for melting and heated to 760-790°C; then, silicon, manganese, antimony, molybdenum and zirconium raw materials are added and after they are completely melted, the temperature is controlled at 730-750°C; then, magnesium raw material is added and stirred until completely melted, and the temperature is controlled at 720-730°C; finally, titanium and strontium raw materials are added and stirred until completely melted to obtain an alloy melt, and the temperature of the alloy melt is controlled at 720-730°C.

10. The preparation method according to claim 8, characterized in that: In step (2), a sodium-free slag remover is added to the alloy melt by powder spray refining. During the powder spray refining process, argon gas is used as a carrier with an argon gas flow rate of 0.1 to 0.3 m / s. 3 / h, refining time 5 to 10 min; the sodium-free slag remover and sodium-free covering agent are both in powder form with a particle size of ≤2 mm.

11. The preparation method according to claim 8, characterized in that: In step (3), the degassing is performed by a rotary degasser, and the rotor speed of the rotary degasser is 400-450 r / min.

12. The preparation method according to claim 9, characterized in that: The aluminum raw material is pure aluminum or recycled aluminum that meets the alloy composition requirements; the silicon raw material is aluminum-silicon master alloy or industrial silicon or quick-dissolving silicon; the manganese raw material is aluminum-manganese master alloy or manganese agent; the antimony raw material is aluminum-antimony master alloy; the molybdenum raw material is aluminum-molybdenum master alloy; the strontium raw material is aluminum-strontium master alloy; the zirconium raw material is aluminum-zirconium master alloy; the titanium raw material is aluminum-titanium-boron master alloy rod or aluminum-titanium-carbon-boron master alloy rod; and the magnesium raw material is pure magnesium.

13. The preparation method according to claim 12, characterized in that: The aluminum-silicon master alloy is Al20Si; the aluminum-manganese master alloy is Al10Mn; the aluminum-antimony master alloy is Al10Sb; the aluminum-molybdenum master alloy is Al5Mo; the aluminum-strontium master alloy is Al10Sr; the aluminum-zirconium master alloy is Al10Zr; the aluminum-titanium-boron master alloy is Al5TiB; the aluminum-titanium-carbon-boron master alloy is Al2Ti0.2C0.2B.

14. A product made of the die-cast aluminum alloy according to any one of claims 1 to 7, characterized in that: The product is an aluminum alloy die casting.

15. The article of claim 14, wherein: The aluminum alloy die-casting is an automobile component.

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