Heat-treatment-free die-casting Al-Si alloy as well as preparation method and application thereof

Abstract

The invention provides a heat-treatment-free die-casting Al-Si alloy and a preparation method and application thereof. The heat treatment-free die-casting Al-Si alloy comprises the following components in percentage by weight: 8.10 to 10.30 percent of Si, 0.50 to 0.57 percent of Mn, 0 to 0.5 percent of Fe, 0.26 to 0.35 percent of Mg, 0.0045 to 0.0083 percent of B, 0.10 to 0.30 percent of Ti, less than or equal to 0.005 percent of Na, less than or equal to 0.005 percent of K, less than or equal to 0.005 percent of P and the balance of Al. The preparation method of the heat-treatment-free die-casting Al-Si alloy is low in cost and short in process, the obtained alloy is few in structure defect and excellent in mechanical property, and the tensile strength, the yield strength and the ductility are 310 MPa-340 MPa, 170 MPa-200 MPa and 10%-15% respectively.

Description

Technical Field

[0001] The invention relates to Al-Si alloy technology, and in particular to a heat treatment-free die-casting Al-Si alloy, a preparation method and application thereof. Background Art

[0002] At present, the global demand for energy conservation and environmental protection is becoming increasingly urgent, and the development of highly integrated lightweight structural parts is a hot spot of competition in the automotive field. Large-integrated high-pressure die-casting technology has the unique advantages of short process, high efficiency and high integration, and is the mainstream solution for net forming preparation of large-sized complex thin-walled body structural parts. Due to its good filling performance, load-bearing capacity and low cost, hypoeutectic Al-Si alloy is currently the preferred material for large thin-walled die-casting structural parts.

[0003] However, since high-pressure die casting is a process in which rapid solidification and high-speed flow of the melt are completed simultaneously in a short time, the inherent endogenous defects that are difficult to eliminate in high-pressure die casting are caused by the entrainment of the melt during the flow process and the insufficient filling of the cavity, which will deteriorate the mechanical properties of the casting. Due to the large and thin walls of the parts, traditional solid solution and aging heat treatment methods will cause deformation of the components, and the molded components cannot be strengthened by deformation. Therefore, the regulation of the die-casting state organization is crucial for the optimization of the performance of heat-treatment-free aluminum alloys. In order to control the defects of castings, the current methods are mainly based on the die-casting process, such as increasing the injection speed, melt temperature, and using high vacuum technology. These methods are often costly, and at the same time, the loss and energy consumption of the equipment will increase, which cannot meet the further demand of die casting, a low-cost, short-process technology. Al-Si alloy is the mainstream die-casting alloy, and the morphology of eutectic Si has a significant effect on the performance of die-casting parts, especially the needle-shaped Si particles will significantly deteriorate the plasticity of the alloy.

[0004] Therefore, providing a low-cost, short-process method for reducing defects and microstructure of heat-treatment-free aluminum alloy die castings has become a technical problem that needs to be urgently solved in the field. Summary of the invention

[0005] The purpose of the present invention is to provide a heat-treatment-free die-cast Al-Si alloy in view of the above-mentioned problems of the existing Al-Si alloy, which has excellent mechanical properties and fewer structural defects.

[0006] It should be noted that, in the present invention, unless otherwise specified, the specific meaning of "including" in relation to composition limitations and descriptions includes both open-ended "including", "comprising", etc. and similar meanings, as well as closed-ended "composed of", "composed of", etc. and similar meanings.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a heat-treatment-free die-cast Al-Si alloy, comprising: Si: 8.10-10.30wt.%, Mn: 0.50-0.57wt.%, Fe: 0-0.5wt.%, Mg: 0.26-0.35wt.%, B: 0.0045-0.0083wt.%, Ti: 0.10-0.30wt.%, Na: ≤0.005wt.%, K: ≤0.005wt.%, P: ≤0.005wt.%, and the balance is Al.

[0008] Furthermore, the composition of the heat treatment-free die-casting Al-Si alloy is preferably: Si: 8.50-9.10wt.%, Mn: 0.50-0.52wt.%, Fe: 0.1-0.3wt.%, Mg: 0.26-0.28wt.%, B: 0.005-0.007wt.%, Ti: 0.10-0.24wt.%, Na: ≤0.005wt.%, K: ≤0.005wt.%, P: ≤0.005wt.%, and the balance is Al.

[0009] Furthermore, the tensile strength, yield strength and elongation of the heat treatment-free die-cast Al-Si alloy are 310MPa-340MPa, 170MPa-200MPa and 10%-15% respectively.

[0010] Another object of the present invention is to disclose a method for preparing a heat-treatment-free die-cast Al-Si alloy, which has low cost and short process and can reduce defects of the heat-treatment-free die-cast Al-Si alloy, and specifically comprises the following steps:

[0011] Step (1) smelting: melting pure aluminum, adding Al-Mn, Al-Si, Al-Ti and Al-Mg master alloys in sequence after the aluminum ingot is completely melted, refining under the condition of passing inert gas, and after the refining is completed, slag is removed and heat preservation is carried out;

[0012] Step (2): adding TiB2 nanocrystalline seed alloy online during the process of feeding the alloy liquid to the die casting machine;

[0013] Step (3) high pressure die casting: heating the mold and the blank, pouring the alloy liquid into the barrel, and after the die casting is completed, taking the casting out of the separated mold and air cooling it to prepare a heat treatment-free die-cast Al-Si alloy.

[0014] Further, step (1) smelting: melt the pure aluminum ingot at 750-800°C, then add Al-Mn, Al-Si, Al-Ti in sequence, and keep it at 720-760°C for 0.5-2h, preferably the holding temperature and holding time are 740-750°C and 1-1.5h respectively, to ensure uniform diffusion of the elements, then reduce the aluminum liquid temperature to 700-730°C, and refine it under the condition of rotating the rotor and introducing inert gas, the refining time is 10-25min, when the rotary blowing is carried out for 5-10min, add Al-Mg intermediate alloy for refining, this addition sequence can ensure the impurity removal effect and avoid burning, adopt auxiliary process for melt treatment, after refining, carry out slag removal, then the alloy liquid is kept for 10-30min, and cooled to the pouring temperature for die casting.

[0015] Furthermore, the content of Mn in the Al-Mn is 5%-30%, preferably 10%.

[0016] Furthermore, the content of Si in the Al-Si is 5%-30%, preferably 10%.

[0017] Furthermore, the content of Ti in the Al-Ti is 5%-30%, preferably 10%.

[0018] Furthermore, the content of Mg in the Al-Mg is 5%-30%, preferably 10%.

[0019] Furthermore, in step (1), the rotor speed is 250-500 r / min, and the rotor speed is preferably 358 r / min.

[0020] Unless otherwise specified, % in the present invention refers to mass percentage.

[0021] Furthermore, the refining time in step (1) is preferably 15 minutes.

[0022] Furthermore, the insulation time in step (1) is preferably 15 minutes.

[0023] Furthermore, the inert gas in step (1) is nitrogen and / or argon, and the gas is preferably argon.

[0024] Furthermore, in step (1), the inert gas flow rate is 4-8 L / min, and the preferred value of the inert gas flow rate is 6-7 L / min.

[0025] Furthermore, the auxiliary process in step (1) is ultrasonic melt vibration, and the ultrasonic time is 5-20 minutes, preferably 10-20 minutes. The use of ultrasonic vibration technology can promote the degassing effect and element dissolution.

[0026] Furthermore, the TiB2 seed alloy in step (2) is nanoparticles with an average particle size of 50nm-400nm.

[0027] Furthermore, in step (2), the nano-TiB2 seed alloy is added online: the weighed TiB2 seed alloy is heated to 300-350° C. in an induction coil, and then placed in a spoon with the alloy liquid, and stirred in the spoon for 10-15 seconds.

[0028] Furthermore, in step (3), the alloy liquid pouring temperature is 680-720°C, preferably 700-710°C.

[0029] Furthermore, in step (3), the mold is heated to maintain a mold temperature of 180-220°C, preferably 195°C-205°C.

[0030] Furthermore, the die-casting parameters of step (3) are: slow injection speed is 0.2-0.5 m / s, slow injection speed is preferably 0.25-0.4 m / s, fast injection speed is 1 m / s-4 m / s, fast injection speed is preferably 1.5-3.0 m / s, and holding pressure is 100-120 MPa.

[0031] Another object of the present invention is to disclose the use of the heat-treatment-free die-casting Al-Si alloy in heat-treatment-free die-casting structural parts for automobiles.

[0032] The heat-treatment-free die-cast Al-Si alloy, the preparation method and the use thereof of the present invention have the following advantages compared with the prior art:

[0033] 1) The present invention successfully achieves the refinement of α-Al grains in Al-Si alloy by selecting appropriate TiB2 seed alloy, addition amount and addition process, thereby reducing the defects of die-casting structure. The formation of defects in die-casting parts is closely related to the rheological shear behavior of the solid-liquid mixed phase in the holding stage. The smaller the solid phase grain size in the solid-liquid mixed phase system, the smaller its resistance to rheological shear, so it can coordinate the deformation of the grains in the local area through rotation, thereby reducing the gaps and holes caused by the cooling and shrinkage of the melt. Therefore, introducing a certain amount of particles that can play a heterogeneous nucleation role into the solidification process under die-casting conditions is a feasible means to achieve the reduction of die-casting parts by refining the grains of die-casting parts. However, most of the Al-Ti-B seed alloys commonly used in industry, such as Al-3Ti-B and Al-5Ti-B, are micron-sized, and the effect is not obvious under high-pressure casting conditions, so it is necessary to use particles suitable for solidification conditions with high cooling rates. Since the increase of B element will significantly increase the viscosity of the melt, thereby deteriorating the filling performance of the alloy in the die-casting process, the addition amount of particles is crucial. In addition, in Al-Si alloy, Si atoms will destroy the pseudomorphic layer on the surface of TiB2 particles, thereby reducing the nucleation ability of the particles, that is, Si poisoning. Therefore, the existence time of TiB2 particles in the melt cannot be too long. At the same time, TiB2 particles will interact with Sr in the melt. Therefore, the traditional furnace addition method cannot give full play to the effect of particles. Taking a suitable addition method is crucial for the actual nucleation effect of particles. This patent application has been verified through a large number of experiments: for the target component aluminum alloy, when the TiB2 particle size is 50-300nm, and the B and Ti contents in the alloy are 0.005-0.007% and 0.10-0.24% respectively, the online addition method in a spoon has the most obvious refinement effect.

[0034] 2) The present invention achieves a synergistic improvement in the strength and plasticity of the alloy by matching the changes in the solidification behavior of the melt caused by the Si and Mg contents and TiB2. During the die-casting process, coarse α-Al grains are formed in the area near the inner wall of the barrel due to heat loss, which is called pre-crystallization. Pre-crystallization hinders the filling of the liquid phase in the cavity and causes looseness. For hypoeutectic Al-Si alloys, the higher the Si content, the lower the liquidus line, and thus the less pre-crystallization. However, too high a Si content will lead to an increase in the eutectic structure content and thus reduce plasticity. Mg is a commonly used strengthening element in AlSi alloys, and its precipitated phase can significantly improve the strength of aluminum alloys, but too high a content will lead to reduced plasticity. At the same time, the die-casting process parameters that match the target alloy composition are the guarantee for preparing high-performance die-casting Al-Si alloys. This patent application has been verified through a large number of experiments: when the Si content is 8.50-9.10% and the Mg content is 0.26-0.34%, the mold temperature is maintained at 195℃-205℃, the slow injection speed is 0.25-0.3m / s, the fast injection speed is 1.5-2.0m / s, and the holding pressure is 100-120MPa. The use of the TiB2 seed alloy can effectively refine the grain size of the die-casting, reduce defects, and achieve a synergistic improvement in alloy strength and plasticity.

[0035] 3) The present invention aims at the problem of regulating the morphology of Si particles in Al-Si alloys, strictly controls the three impurity elements Na, K and P introduced in the process of adding conventional raw materials, refiners and refining agents, and optimizes the removal of impurity elements by ultrasonic treatment. In the conventional preparation process of die-cast Al-Si alloys, most of them are modified by Sr to ensure the plasticity of the castings. However, the addition of Sr has the following three problems: 1. Sr is easy to burn in the aluminum liquid. Since Sr is more active, it is very easy to oxidize and burn in the aluminum liquid. Therefore, in actual production, Sr needs to be added to the aluminum liquid every once in a while, which undoubtedly increases the cost and interferes with the production rhythm; 2. Sr will accelerate the air absorption of aluminum liquid, deteriorate the quality of the melt, and increase the porosity of the casting; 3. Sr will interact with Ti and B in the alloy to generate products such as SrB6, weaken the refinement effect, and deteriorate the organization. Therefore, finding a modifier that can replace Sr is crucial to optimize the morphology of the eutectic organization of Al-Si alloys and improve the performance of Al-Si alloys. The three alloying elements Na, K, and P will react with Al in the Al melt to form compounds, thereby providing nucleation sites for eutectic Si and increasing the nucleation temperature of eutectic Si. Extremely small amounts of these alloying elements can significantly promote the formation of coarse eutectic Si. The preparation of Al-Si alloys has always ignored the control of these extremely small amounts of alloying elements. The present invention has found through a large number of experimental studies that when the contents of Na, K, and P exceed 0.005% respectively, it is easy to cause the formation of coarse eutectic Si and agglomerated eutectic Si, thereby deteriorating the plasticity of the alloy. In conventional preparation processes, due to the use of raw materials, refiners, and refining agents, these three trace elements are extremely difficult to control below 0.005%. Therefore, the regulation of the morphology of eutectic Si in Al-Si alloys has always been the key to limiting the further improvement of its plasticity. Furthermore, the present invention, after adding the refining agent, ultrasonically treats the melt, combined with rotary blowing, to promote the reaction of the three trace alloying elements in the alloy with Al, thereby accelerating its slag formation speed, floating to the surface of the melt with the gas, thereby achieving the regulation of trace alloying elements, and then achieving the regulation of the eutectic Si morphology without the use of the modifier Sr, significantly improving the alloy performance. The Al-Si eutectic alloy prepared by the method of the present invention has Na, K, and P contents all lower than 0.005%, the eutectic Si morphology is short rod-shaped, and the cluster aggregation of the eutectic structure is significantly reduced. Compared with the Al-Si alloy of the same composition with Na, K, and P exceeding 0.005%, the mechanical properties are significantly improved, and the tensile strength, yield strength, and elongation are 310MPa-340MPa, 170MPa-200MPa, and 10%-15%, respectively, which are increased by 12%, 16%, and 54%, respectively.

[0036] In summary, the present invention can reduce the defects of heat-treatment-free die-casting aluminum alloys at low cost by synergistically regulating four aspects: alloy composition, online addition of TiB2 nanocrystalline seed alloy, ultrasonic-assisted refining treatment and die-casting process parameters, thereby optimizing performance and being suitable for mass industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The optical microstructures of the die-casting structures of the comparative examples and the examples, wherein (a), (b), (c) and (d) are comparative example 1, comparative example 2, example 1 and example 2, respectively;

[0038] Figure 2 3D reconstruction of holes based on micrometer CT, where (a) and (d) are comparative example 2, (b) and (e) are comparative example 4, and (c) and (f) are example 2;

[0039] Figure 3 The mechanical properties of the comparative examples and embodiments are shown in FIG. DETAILED DESCRIPTION

[0040] The present invention is further described below with reference to the examples. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0041] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0042] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0043] In the present specification, a numerical range expressed using "above" or "below" means a numerical range including the number.

[0044] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0045] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0046] In this specification, when "normal temperature" or "room temperature" is used, the temperature may be 15-25°C.

[0047] In this manual, the reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0048] Comparative Example 1

[0049] Comparative Example 1 discloses a die-cast aluminum alloy, comprising the following components in mass percentage: Si: 7.1%, Mn: 0.52%, Fe: 0.11%, Mg: 0.28%, B: 0.006%, Ti: 0.103%, Na: 0.002%, K: 0.003%, P: 0.001%, and the balance is Al. The preparation method thereof comprises the following steps:

[0050] (1) Melting: Melt the pure aluminum ingot at 800°C, then add Al-10Mn, Al-10Si, and Al-10Ti in sequence, keep the temperature at 800°C for 1 hour to ensure uniform diffusion of the elements, and then reduce the aluminum liquid temperature to 720°C.

[0051] (2) Ultrasonic refining: refining was carried out under the condition of argon gas passing through the rotating rotor, with a gas flow rate of 6 L / min and a rotation speed of 358 r / min. Refining agent was added and the melt was ultrasonically treated at the same time. The ultrasonic refining time was 15 min. Al-10Mg was added when the rotary blowing was carried out for 5 min. After refining, slag was removed and the alloy liquid was left to stand for 15 min and cooled to the pouring temperature for die casting. The pouring temperature was 710 °C.

[0052] (3) Adding nano-TiB2 seed alloy with an average particle diameter of 300 nm: The TiB2 nano-crystalline seed alloy was heated to 320°C in an induction coil, then placed in a spoon with aluminum liquid and stirred in the spoon for 10 seconds.

[0053] (4) High-pressure die casting: Heat the mold to keep the mold temperature at 200°C, pour the molten aluminum into the barrel, the slow injection speed is 0.3m / s, the fast injection speed is 3m / s, and the boost pressure is 100MPa. After the die casting is completed, the casting is taken out of the separated mold and air-cooled.

[0054] Comparative Example 2

[0055] Comparative Example 2 discloses a die-cast aluminum alloy, comprising the following components in mass percentage: Si: 10.2%, Mn: 0.52%, Fe: 0.11%, Mg: 0.28%, B: 0.006%, Ti: 0.103%, Na: 0.002%, K: 0.003%, P: 0.001%, and the balance is Al. The preparation method thereof comprises the following steps:

[0056] (1) Melting: Melt the pure aluminum ingot at 800°C, then add Al-10Mn, Al-10Si, and Al-10Ti in sequence, keep the temperature at 800°C for 1 hour to ensure uniform diffusion of the elements, and then reduce the aluminum liquid temperature to 720°C.

[0057] (2) Ultrasonic refining: refining was carried out under the condition of argon gas passing through the rotating rotor, with a gas flow rate of 6 L / min and a rotation speed of 358 r / min. Refining agent was added and the melt was ultrasonically treated at the same time. The ultrasonic refining time was 15 min. Al-10Mg was added when the rotary blowing was carried out for 5 min. After refining, slag was removed and the alloy liquid was left to stand for 15 min and cooled to the pouring temperature for die casting. The pouring temperature was 710 °C.

[0058] (3) High-pressure die casting: Heat the mold to keep the mold temperature at 200°C, pour the molten aluminum into the barrel, the slow injection speed is 0.3m / s, the fast injection speed is 3m / s, and the boost pressure is 100MPa. After the die casting is completed, the casting is taken out of the separated mold and air-cooled.

[0059] Comparative Example 3

[0060] Comparative Example 3 discloses a die-cast aluminum alloy, comprising the following components in mass percentage: Si: 10.2%, Mn: 0.52%, Fe: 0.10%, Mg: 0.28%, B: 0.006%, Ti: 0.103%, Na: 0.002%, K: 0.003%, P: 0.001%, and the balance is Al. The preparation method thereof comprises the following steps:

[0061] (1) Melting: Melt the pure aluminum ingot at 800°C, then add Al-10Mn, Al-10Si, and Al-10Ti in sequence, keep the temperature at 800°C for 1 hour to ensure uniform diffusion of the elements, and then reduce the aluminum liquid temperature to 720°C.

[0062] (2) Ultrasonic refining: refining was carried out under the condition of argon gas passing through the rotating rotor, with a gas flow rate of 6 L / min and a rotation speed of 358 r / min. Refining agent was added and the melt was ultrasonically treated at the same time. The ultrasonic refining time was 15 min. Al-10Mg was added when the rotary blowing was carried out for 5 min. After refining, slag was removed and the alloy liquid was left to stand for 15 min and cooled to the pouring temperature for die casting. The pouring temperature was 710 °C.

[0063] (3) A conventional Al-5Ti-B seed alloy was heated to 320 °C in an induction coil and then placed in a spoon with molten aluminum and stirred in the spoon for 10 seconds.

[0064] (4) High-pressure die casting: Heat the mold to keep the mold temperature at 200°C, pour the molten aluminum into the barrel, the slow injection speed is 0.3m / s, the fast injection speed is 3m / s, and the boost pressure is 100MPa. After the die casting is completed, the casting is taken out of the separated mold and air-cooled.

[0065] Comparative Example 4

[0066] Comparative Example 4 discloses a die-cast aluminum alloy, including the following components in mass percentage: Si: 10.2%, Mn: 0.52%, Fe: 0.11%, Mg: 0.28%, B: 0.006%, Ti: 0.103%, Na: 0.006%, K: 0.0055%, P: 0.007%, and the balance is Al. Among them, the composition of Na, K, and P is different from that of Example 2, which is due to the fact that no ultrasonic treatment is added during the preparation process, and the raw materials, refiners, and refining agents are left, but no artificial additions are made. The preparation method thereof comprises the following steps:

[0067] (1) Melting: Melt the pure aluminum ingot at 800°C, then add Al-10Mn, Al-10Si, and Al-10Ti in sequence, keep the temperature at 800°C for 1 hour to ensure uniform diffusion of the elements, and then reduce the aluminum liquid temperature to 720°C.

[0068] (2) Refining treatment: Refining was carried out under the condition of argon gas passing through the rotating rotor, with a gas flow rate of 6 L / min and a rotation speed of 358 r / min. Refining agent was added and the refining time was 15 min. Al-10Mg was added when the rotary blowing was carried out for 5 min. After the refining was completed, the slag was removed and the alloy liquid was allowed to stand for 15 min and then cooled to the pouring temperature for die casting. The pouring temperature was 710 °C.

[0069] (3) Adding nano-TiB2 seed alloy: The TiB2 nano-crystalline seed alloy with an average particle diameter of 300 nm was heated to 320°C in an induction coil, then placed in a spoon with molten aluminum and stirred in the spoon for 10 seconds.

[0070] (4) High-pressure die casting: Heat the mold to keep the mold temperature at 200°C, pour the molten aluminum into the barrel, the slow injection speed is 0.3m / s, the fast injection speed is 3m / s, and the boost pressure is 100MPa. After the die casting is completed, the casting is taken out of the separated mold and air-cooled.

[0071] Example 1

[0072] This embodiment 1 discloses a heat-treatment-free die-cast Al-Si alloy, comprising the following components in mass percentage: Si: 10.2%, Mn: 0.52%, Fe: 0.11%, Mg: 0.28%, B: 0.006%, Ti: 0.103%, Na: 0.002%, K: 0.003%, P: 0.001% and the balance is Al. The preparation method thereof comprises the following steps:

[0073] (1) Melting: Melt the pure aluminum ingot at 800°C, then add Al-10Mn, Al-10Si, and Al-10Ti in sequence, keep the temperature at 800°C for 1 hour to ensure uniform diffusion of the elements, and then reduce the aluminum liquid temperature to 720°C.

[0074] (2) Ultrasonic refining: refining was carried out under the condition of argon gas passing through the rotating rotor, with a gas flow rate of 6 L / min and a rotation speed of 358 r / min. Refining agent was added and the melt was ultrasonically treated at the same time. The ultrasonic refining time was 15 min. Al-10Mg was added when the rotary blowing was carried out for 5 min. After refining, slag was removed and the alloy liquid was left to stand for 15 min and cooled to the pouring temperature for die casting. The pouring temperature was 710 °C.

[0075] (3) Adding TiB2 nanocrystalline seed alloy with an average particle diameter of 300 nm, the TiB2 nanocrystalline seed alloy was heated to 320°C in an induction coil, then placed in a spoon with aluminum liquid and stirred in the spoon for 10 seconds.

[0076] (4) High-pressure die casting: Heat the mold to keep the mold temperature at 200°C, pour the molten aluminum into the barrel, the slow injection speed is 0.3m / s, the fast injection speed is 1.5m / s, and the boost pressure is 100MPa. After the die casting is completed, the casting is taken out of the separated mold and air-cooled.

[0077] Example 2

[0078] This embodiment 2 discloses a heat-treatment-free die-cast Al-Si alloy, comprising the following components in mass percentage: Si: 10.2%, Mn: 0.52%, Fe: 0.10%, Mg: 0.28%, B: 0.006%, Ti: 0.103%, Na: 0.002%, K: 0.003%, P: 0.001%, and the balance is Al. The preparation method thereof comprises the following steps:

[0079] (1) Melting: Melt the pure aluminum ingot at 800°C, then add Al-10Mn, Al-10Si, and Al-10Ti in sequence, keep the temperature at 800°C for 1 hour to ensure uniform diffusion of the elements, and then reduce the aluminum liquid temperature to 720°C.

[0080] (2) Ultrasonic refining: refining was carried out under the condition of argon gas passing through the rotating rotor, with a gas flow rate of 6 L / min and a rotation speed of 358 r / min. Refining agent was added and the melt was ultrasonically treated at the same time. The ultrasonic refining time was 15 min. Al-10Mg was added when the rotary blowing was carried out for 5 min. After refining, slag was removed and the alloy liquid was left to stand for 15 min and cooled to the pouring temperature for die casting. The pouring temperature was 710 °C.

[0081] (3) Adding nano-TiB2 seed alloy: The TiB2 nano-crystalline seed alloy with an average particle diameter of 300 nm was heated to 320°C in an induction coil, then placed in a spoon with molten aluminum and stirred in the spoon for 10 seconds.

[0082] (4) High-pressure die casting: Heat the mold to keep the mold temperature at 200°C, pour the molten aluminum into the barrel, the slow injection speed is 0.3m / s, the fast injection speed is 3m / s, and the boost pressure is 100MPa. After the die casting is completed, the casting is taken out of the separated mold and air-cooled.

[0083] Combined with the comparative examples and embodiments, the microstructure characteristics and mechanical properties are as follows Figure 1-3 As shown:

[0084] Figure 1 The optical microstructures of the die-cast alloys corresponding to the comparative examples and the embodiments are shown in Figures (a), (b), (c) and (d) respectively, which are the optical microstructures of the die-cast aluminum alloys prepared in Comparative Example 1, Comparative Example 2, Embodiment 1 and Embodiment 2. It can be seen from Figure (a) that when Si is 7%, this component is not within the preferred Si content range (8.10-10.30%). Even if the preparation process consistent with that of Embodiment 2 is adopted, the obtained die-cast structure contains a large number of coarse α-Al grains. It can be seen from Figure (b) that when the online addition of TiB2 nano-seed process is not implemented, the obtained die-cast structure contains a large number of dendritic coarse α-Al grains and eutectic clusters, and the structure uniformity is poor. It can be seen from Figure (c) that when the injection speed is 1.5m / s and the online addition of TiB2 nano-seed process is implemented, the grain size is significantly reduced, the coarse α-Al grains are reduced, and the structure uniformity is significantly improved. It can be seen from Figure (d) that when the injection speed is 3m / s and the online addition of TiB2 nano-seed process is implemented, the coarse α-Al grains are further reduced compared with Figure (c) and the organizational uniformity is further improved.

[0085] Figure 2 It is a three-dimensional reconstruction of the holes by micron CT. It can be seen from the figure that the hole size and volume fraction of Comparative Example 2, Comparative Example 4 and Example 2 are reduced successively, and the hole volume fractions are 3.24%, 1.13% and 0.35% respectively. When nano-TiB2 particles are not added, even if the preparation process consistent with Example 2 is adopted, the holes in the die-casting alloy are still relatively obvious, as shown in Figures (a) and (d). When TiB2 seed alloy is added online but not ultrasonically treated, the holes are improved to a certain extent, but there are still many, as shown in Figures (b) and (e). Further increasing the injection speed within the preferred injection speed range, i.e. 3m / s, while adding TiB2 nano-seed alloy online, the hole content can be further reduced during ultrasonic refining treatment, as shown in Figures (c) and (f). This shows that the use of ultrasound to treat the melt can significantly reduce the content of Na, K, and P while reducing the macroscopic agglomeration of eutectic Si, thereby reducing holes.

[0086] Figure 3The mechanical properties are shown in Table 1, Table 2, Table 3, Table 4, Example 1 and Example 2. It can be seen that the tensile strength, yield strength and elongation of Example 1 are 256MPa, 128MPa and 3.30% respectively, the tensile strength, yield strength and elongation of Example 2 are 284MPa, 158MPa and 4.52% respectively, the tensile strength, yield strength and elongation of Example 3 are 295MPa, 166MPa and 6.78% respectively, the tensile strength, yield strength and elongation of Example 4 are 290MPa, 160MPa and 7.32% respectively, the tensile strength, yield strength and elongation of Example 1 are 318MPa, 178MPa and 10.23% respectively, and the tensile strength, yield strength and elongation of Example 2 are 326MPa, 186MPa and 11.34% respectively. It shows that as the void content decreases, the mechanical properties increase. When the alloy in the preferred composition range is not used, even if the preferred process is used, the die-casting structure obtained contains a large number of coarse α-Al grains, which are prone to stress concentration during tensile deformation, inducing the initiation and expansion of cracks, that is, Comparative Example 1. When the preferred composition is used and the process of adding nano-seed alloy online is not used, the die-casting alloy still contains a large number of coarse dendritic α-Al grains and contains obvious eutectic groups, resulting in poor plasticity of the alloy, that is, Comparative Example 2. When conventional Al-5Ti-B seed alloy is added, the performance is slightly improved, that is, Comparative Example 3. When ultrasonic assisted refining and degassing are not used, the Na, K, and P contents are significantly increased, the eutectic Si segregation is obvious, and there are many holes in the casting, and the performance is still poor, that is, Comparative Example 4. When nano-TiB2 particles are added online and ultrasonic assisted refining is used to adjust Na, K, and P to less than 0.005%, the regulation of eutectic Si can be achieved, and the coarse α-Al grains are significantly reduced, and the holes are also reduced, and the strength and plasticity of the die-casting alloy are improved, that is, Example 1. When the injection speed is increased to 3m / s on the basis of Example 1, the strength and plasticity of the alloy are further improved. The above results show that the type of TiB2 seed alloy and the regulation of trace elements Na, K, and P in the melt have an important influence on the performance of the die-casting alloy. The use of the preferred nano-TiB2 seed alloy and ultrasonic-assisted refining to regulate Na, K, and P is the guarantee for obtaining excellent Al-Si die-casting alloys. This fully demonstrates that the present invention can reduce the defects of heat-free die-casting aluminum alloys, optimize the organization, and thus improve the performance by synergistically regulating the four aspects of alloy composition, online addition of TiB2 nano-seed alloys, ultrasonic-assisted refining treatment, and die-casting process parameters.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A heat treatment-free die-casting Al-Si alloy, characterized in that: Its composition is: Si: 8.10-10.30wt.%, Mn: 0.50-0.57wt.%, Fe: 0-0.5wt.%, Mg: 0.26-0.35wt.%, B: 0.0045-0.0083wt.%, Ti: 0.10-0.30wt.%, Na: ≤0.005wt.%, K: ≤0.005wt.%, P: ≤0.005wt.%, and the balance is Al.

2. A method for preparing the heat treatment-free die-casting Al-Si alloy according to claim 1, characterized in that: The following steps are involved: Step (1) smelting: melting pure aluminum, adding Al-Mn, Al-Si, Al-Ti and Al-Mg master alloys in sequence after the aluminum ingot is completely melted, refining under the condition of passing inert gas, and after the refining is completed, slag is removed and heat preservation is carried out; Step (2): adding TiB2 nanocrystalline seed alloy online during the process of feeding the alloy to the die casting machine; Step (3) high pressure die casting: heating the mold and the blank, pouring the alloy liquid into the barrel, and after the die casting is completed, taking the casting out of the separated mold and air cooling it to prepare a heat treatment-free die-cast Al-Si alloy.

3. The method for preparing the heat treatment-free die-casting Al-Si alloy according to claim 2, characterized in that: Step (1) smelting: melt the pure aluminum ingot at 750-800°C, then add Al-Mn, Al-Si and Al-Ti in sequence, keep the temperature at 720-760°C for 0.5-2h, then reduce the temperature of the aluminum liquid to 700-730°C, and refine it under the condition of rotating the rotor and introducing inert gas, the refining time is 10-25min, when the rotary blowing is carried out for 5-10min, add Al-Mg intermediate alloy for refining, adopt auxiliary process for melt treatment, and after refining, skim the slag, then keep the alloy liquid for 10-30min, and cool it to the pouring temperature for die casting.

4. The method for preparing the heat treatment-free die-cast Al-Si alloy according to claim 2 or 3, characterized in that: The content of Mn in the Al-Mn is 5%-30%; And / or, the content of Si in the Al-Si is 5%-30%; And / or, the content of Ti in the Al-Ti is 5%-30%; And / or, the content of Mg in the Al-Mg is 5%-30%.

5. The method for preparing the heat treatment-free die-casting Al-Si alloy according to claim 2 or 3, characterized in that: The inert gas in step (1) is nitrogen and / or argon; And / or, the inert gas flow rate in step (1) is 4-8 L / min.

6. The method for preparing heat-treatment-free die-casting Al-Si alloy according to claim 3, characterized in that: The auxiliary process in step (1) is ultrasonic melt vibration, and the ultrasonic time is 5-20 minutes.

7. The method for preparing heat-treatment-free die-casting Al-Si alloy according to claim 2, characterized in that: The TiB2 seed alloy in step (2) is nanoparticles with an average particle size of 50nm-400nm; And / or, in step (2), the nano-TiB2 seed alloy is added online: the weighed TiB2 seed alloy is heated to 300-350° C. in an induction coil, then placed in a spoon with the alloy liquid, and stirred in the spoon for 10-15 seconds.

8. The method for preparing heat-treatment-free die-casting Al-Si alloy according to claim 2, characterized in that: The alloy liquid pouring temperature in step (3) is 680-720°C; And / or, step (3) heats the mold to maintain the mold temperature at 180-220°C.

9. The method for preparing heat-treatment-free die-cast Al-Si alloy according to claim 2, characterized in that: The die-casting parameters of step (3) are: slow injection speed is 0.2-0.5 m / s, fast injection speed is 1 m / s-4 m / s, and holding pressure is 100-120 MPa.

10. Use of the Al-Si alloy according to claim 1 in die-casting structural parts for automobiles without heat treatment.

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