Regulation and control method for Fe phase in cast aluminum alloy

Abstract

The invention relates to a method for regulating and controlling a Fe phase in a cast aluminum alloy, which comprises the following steps of: (1) adding Mo and V into an Al-Si alloy, and smelting; wherein the content of the Mo is controlled to be 0.06 wt%-0.5 wt%, and the content of the V is controlled to be 0.06 wt%-0.5 wt%; the smelted alloy liquid is subjected to degassing; and (3) the degassed alloy liquid is subjected to pressure casting, the die-casting aluminum alloy is obtained, the cooling rate in the pressure casting process is controlled to be larger than 40 K / s, the temperature of a charging barrel is controlled to range from 110 DEG C to 200 DEG C, and the temperature of a die is controlled to range from 160 DEG C to 210 DEG C. According to the method, control over the morphology, size and distribution of the harmful Fe phase in the aluminum alloy is achieved, the morphology of the Fe phase is spherical or granular, and the Fe phase is evenly distributed and dispersed in an alloy matrix, so that the plasticity of the aluminum alloy is guaranteed, and the ductility and the service performance of the aluminum alloy are improved.

Description

Technical Field

[0001] The invention relates to the field of aluminum alloys, and in particular to a method for regulating Fe phase in a cast aluminum alloy. Background Art

[0002] This section is intended to provide a background or context to the embodiments of the invention recited in the claims. No description herein is admitted to be prior art by inclusion in this section.

[0003] In most cases, Fe is considered to be the main harmful element in aluminum alloys. Usually in cast aluminum alloys (Al-Si alloy system), Fe will form needle-shaped or flaky β-AlFeSi phases with another main alloying element Si, which will cut the matrix structure or form the source of crack initiation due to stress concentration at the "needle tip", thereby seriously damaging the plasticity of the alloy, reducing the elongation of the alloy, and destroying the service performance.

[0004] Therefore, it is necessary to regulate the Fe phase in aluminum alloy to eliminate its destructive effect on the comprehensive properties of the alloy.

[0005] There are usually two ways to eliminate Fe phase hazards:

[0006] One is to use higher purity raw materials and reduce the harm of flaky Fe phase by strictly controlling the Fe content. For example, most alloys control the Fe mass percentage below 0.15%. Specific measures are:

[0007] (1) Use higher purity raw materials, such as high-purity electrolytic aluminum or recycled aluminum after multiple purifications. The intermediate alloy also requires a lower Fe content.

[0008] (2) Strict control of the process, for example, the smelting temperature and holding time must be strictly controlled to avoid "iron increase";

[0009] (3) Melting tools and equipment need surface treatment. For example, crucibles, iron spoons, ladles, slag rakes, degassing pipes, etc. need to be painted.

[0010] All of the above measures will increase the cost of the alloy. In addition, they also limit the recycling of recycled aluminum with a high Fe content, which is not conducive to the green and low-carbon development of the aluminum processing industry.

[0011] The other is to use chemical modification. The most common method is to use Mn to change the morphology of the Fe phase. A certain amount of Mn is added to the alloy, and the Mn atoms replace the Fe atoms in the β-AlFeSi phase, transforming the needle-shaped β-AlFeSi phase into an α-Al(Mn,Fe)Si phase that has less effect on mechanical properties or inhibiting the formation of the β-AlFeSi phase, where the α-Al(Mn,Fe)Si phase is in the shape of "Chinese characters" or irregular polygons.

[0012] The disadvantage of this method is that it is almost impossible to completely suppress the needle-shaped (lamellar) β-AlFeSi phase by adding Mn. This is because the suppression of the β-Fe phase requires strict control of two factors, namely, the appropriate Mn / Fe ratio and the appropriate solidification cooling rate. However, due to the complexity of the working conditions in actual production, the above two factors are not well controlled. For example, studies have shown that the molar ratio of Mn to Fe is X Mn :X Fe Reaching 1:2 can well achieve β-Fe phase elimination, but other studies have shown that even if X Mn :X Fe Even when the ratio reaches 2:1, it is still difficult to completely eliminate the β-Fe phase in the alloy.

[0013] According to published reports, if the addition ratio of Mn is too low, it is not enough to completely transform the β-Fe phase into the α-Fe phase. If the addition ratio is too high, a large number of coarse primary Fe-rich phases (also called "Sludge" phase or "slag phase") will be formed in the alloy melt. These primary Fe-rich phases are formed and agglomerated before the α-Al solidifies and precipitates. The "slag phase" solidified in the melt will settle and segregate in gravity casting, and will be mixed into the casting in pressure casting and eventually endanger the performance of the casting. Moreover, the appropriate amount of Mn added is not fixed, but is also related to factors such as the temperature of the melt, the casting temperature when producing the casting, and the cooling rate. In simple terms, in order to transform the β-Fe phase into the α-Fe phase, the Mn content must be higher than a minimum critical value, which is determined by the cooling rate. The increase in Mn content will reduce the minimum cooling rate for the complete formation of the α-Fe phase and expand the appropriate cooling rate range for the formation of the α-Fe phase [here, the "appropriate solidification cooling rate range for the formation of the α-Fe phase" is mentioned because if the cooling rate is too low, even if the Mn element is added, a certain amount of lamellar β-Fe phase will still be formed, and if the cooling rate is too high, a lamellar δ-Fe phase will be formed (although the size of this phase is very small at extremely high cooling rates, and the harm is not great)]. However, the increase in Mn content also increases the formation tendency of the "slag phase" and the volume fraction of the "slag phase" in the alloy.

[0014] Through the above analysis, it is found that it is difficult to completely suppress the needle-shaped (plate-shaped) β-AlFeSi phase by adding Mn.

[0015] Therefore, there is still a need to provide a simple and effective Fe phase regulation method to solve the hazards caused by high Fe content in aluminum alloys. Summary of the invention

[0016] The purpose of the present invention is to provide a simple and effective method for regulating the Fe phase in a cast aluminum alloy, which effectively solves the harm caused by high Fe content in the cast aluminum alloy.

[0017] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0018] The present invention provides a method for regulating the Fe phase in a cast aluminum alloy, comprising the following steps:

[0019] (1) adding Mo and V to an Al-Si alloy and smelting the alloy; wherein the content of Mo is controlled to be 0.06wt% to 0.5wt% and the content of V is controlled to be 0.06wt% to 0.5wt%;

[0020] (2) Degassing the molten alloy;

[0021] (3) The degassed alloy liquid is pressure-casted to obtain a die-cast aluminum alloy, wherein the cooling rate of the pressure casting process is controlled to be greater than 40K / s, the barrel temperature is controlled to be 110°C to 200°C, and the mold temperature is controlled to be 160°C to 210°C.

[0022] According to some specific embodiments, the total content of the Mo and the V is ≤0.8 wt %.

[0023] According to some specific embodiments, the content of Mo is controlled to be 0.06wt% to 0.5wt%, for example 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt%, 0.2wt%, 0.21wt%, 0.22wt%, 0.23wt%, 0.24wt%, 0.25wt%, 0.26wt%, 0.27wt%, 0.28wt%, 0.29wt%, 0.3wt%, 0.31wt%, 0.32wt%, 0.33wt%, 0.34wt%, 0.35wt%, 0.36wt%, 0.37wt%, 0.38wt%, 0.39wt%, 0.4wt%, 0.41wt%, 0.42wt%, 0.43wt%, 0.44wt%, 0.45wt%, 0.46wt%, 0.47wt%, 0.48wt%, 0.49wt%, 0.5wt%. Further, the content of Mo is controlled to be 0.06wt% to 0.3wt%.

[0024] According to some specific embodiments, the content of V is controlled to be 0.06wt% to 0.5wt%, for example 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt%, 0.2wt%, 0.21wt%, 0.22wt%, 0.23wt%, 0.24wt%, 0.25wt%, 0.26wt%, 0.27wt%, 0.28wt%, 0.29wt%, 0.30wt%, 0.31wt%, 0.32wt%, 0.33wt%, 0.34wt%, 0.35wt%, 0.36wt%, 0.37wt%, 0.38wt%, 0.39wt%, 0.40wt%, 0.41wt%, 0.42wt%, 0.43wt%, 0.44wt%, 0.45wt%, 0.46wt%, 0.47wt%, 0.48wt%, 0.49wt%, 0.50wt%, 0.51wt%, 0.5 .26wt%, 0.27wt%, 0.28wt%, 0.29wt%, 0.3wt%, 0.31wt%, 0.32wt%, 0.33wt%, 0.34wt%, 0.35wt%, 0.36wt%, 0.37wt%, 0.38wt%, 0.39wt%, 0.4wt%, 0.41wt%, 0.42wt%, 0.43wt%, 0.44wt%, 0.45wt%, 0.46wt%, 0.47wt%, 0.48wt%, 0.49wt%, 0.5wt%. Further, the V content is controlled to be 0.06wt% to 0.25wt%.

[0025] Further, the total content of Mo and V is 0.15wt% to 0.4wt%, for example 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt%, 0.2wt%, 0.21wt%, 0.22wt%, 0.23wt%, 0.24wt%, 0.25wt%, 0.26wt%, 0.27wt%, 0.28wt%, 0.29wt%, 0.3wt%, 0.31wt%, 0.32wt%, 0.33wt%, 0.34wt%, 0.35wt%, 0.36wt%, 0.37wt%, 0.38wt%, 0.39wt%, 0.4wt%.

[0026] The content of Mo in this application refers to the percentage of the mass of the Mo element in the total mass of the prepared cast aluminum alloy. The content of V refers to the percentage of the mass of the V element in the total mass of the prepared cast aluminum alloy.

[0027] According to some specific embodiments, the Mo and the V are added in the form of a master alloy.

[0028] The intermediate alloys of Mo and V may be any intermediate alloys whose contents meet standard requirements. For example, the intermediate alloy of Mo is AlMo10 and / or AlMo5, and the intermediate alloy of V is AlV10 and / or AlV5.

[0029] Furthermore, the addition temperature of the intermediate alloy to which the Mo and the V are added is controlled to be 720°C to 770°C, for example, 720°C, 725°C, 730°C, 735°C, 740°C, 745°C, 750°C, 755°C, 760°C, 765°C, 770°C.

[0030] According to some specific embodiments, the Al-Si alloy refers to an aluminum alloy with aluminum and silicon as main components and containing a small amount of iron, magnesium, copper, nickel, strontium and other elements. During the smelting process of step (1), the Al-Si alloy can be fed in the form of raw materials such as pure Al ingots, quick-dissolving silicon and / or metallic silicon, Mg ingots, etc., or the finished Al-Si alloy can be fed for smelting. The Fe phase control method of the present application is applicable to various types of aluminum silicon alloys, such as aluminum silicon magnesium alloy, aluminum silicon magnesium copper alloy, aluminum silicon manganese alloy, etc.

[0031] According to some specific embodiments, step (1) and step (2) can be performed according to conventional methods in the art.

[0032] For example, the specific steps of step (1) are as follows: firstly add pure Al ingot into the melting furnace, raise the temperature until it is completely melted, then raise the temperature to 720°C to 770°C, add quick-dissolving silicon and / or metallic silicon, and after they are completely melted, add Mo intermediate alloy and V intermediate alloy, and after they are completely melted, lower the temperature to 700°C to 730°C, add magnesium ingot below the liquid surface, and wait for them to be completely melted.

[0033] The specific steps of step (2) are: cooling the alloy liquid after smelting in step (1) to 690°C to 720°C, adding AlSr10 master alloy, stirring until it is completely melted, and then heating to 720°C to 730°C to start degassing, adding refining agent according to 0.1% to 0.15% of the mass of the alloy liquid, degassing by using a rotor degasser, and controlling the refining agent addition speed to 450r / min

[0034] ~550r / min, degassing speed is 350r / min~450r / min, argon flow rate is 20~30L / min, and degassing time is 20~45min.

[0035] According to some specific implementations, after step (2) is completed, an alloy composition sample and a reduced pressure solidification gas measurement sample are taken, and step (3) is performed after the degassing meets the standard and the composition is qualified.

[0036] According to some specific embodiments, in step (3), the temperature of the alloy liquid after degassing is controlled to be 695°C to 710°C, and then the pressure casting is performed. The temperature of the alloy liquid is, for example, 695°C, 700°C, 705°C, or 710°C.

[0037] According to some specific embodiments, in step (3), when the pressure casting is performed, the filling degree of the barrel is controlled to be ≥30%, for example, the filling degree is 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, etc. Further, the filling degree of the barrel is controlled to be 30% to 60%.

[0038] The degree of fullness of the barrel refers to the percentage of the volume of the alloy liquid to the total volume of the barrel.

[0039] According to some specific embodiments, the specific steps of the regulation method include:

[0040] (1) According to the formula, melt the Al-Si alloy and add the Mo master alloy and the V master alloy, and stir to fully melt;

[0041] (2) degassing the alloy liquid after smelting in step (1);

[0042] (3) The temperature of the alloy liquid after degassing in step (2) is adjusted to 695°C to 710°C, and then pressure casting is carried out on a die casting machine. The parameters for controlling the pressure casting are: barrel temperature is 110°C to 200°C, mold temperature is 160°C to 210°C, barrel filling degree is 30% to 50%, vacuum degree is 50 to 80 mBar, low speed section injection speed is 0.1 to 0.3 m / s, high speed section injection speed is 3 to 10 m / s, casting pressure is 40 to 120 MPa, and mold holding pressure time is 5 to 50 s.

[0043] Further, the barrel temperature is controlled to be 110°C to 200°C, for example, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C. If the barrel temperature is too low, it is not conducive to controlling the uniformity of cooling and the formation of pre-crystallization cannot be avoided; if the barrel temperature is too high, it will cause serious mold sticking during the casting process, thereby causing serious corrosion to the metal mold, which not only reduces the life of the mold, but also seriously affects the surface quality of the aluminum alloy casting.

[0044] Further, the mold temperature is controlled to be 160°C to 210°C, for example, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C.

[0045] Furthermore, the injection speed in the low speed section can be a fixed injection speed or a gradually increasing gradient injection speed. Further, the injection speed in the high speed section is 3 to 10 m / s, for example, 3 m / s, 3.2 m / s, 3.4 m / s, 3.6 m / s, 3.8 m / s, 4 m / s, 4.2 m / s, 4.4 m / s, 4.6 m / s, 4.8 m / s, 5 m / s, 5.2 m / s, 5.4 m / s, 5.6 m / s, 5.8 m / s, 6 m / s, 6.2 m / s, 6.4m / s, 6.6m / s, 6.8m / s, 7m / s, 7.2m / s, 7.4m / s, 7.6m / s, 7.8m / s, 8m / s, 8. 2m / s, 8.4m / s, 8.6m / s, 8.8m / s, 9m / s, 9.2m / s, 9.4m / s, 9.6m / s, 9.8m / s, 10m / s.

[0046] Furthermore, the casting pressure is 40 to 120 MPa, for example, 40 MPa, 45 MPa, 50 MPa, 55 MPa, 60 MPa, 65 MPa, 70 MPa, 75 MPa, 80 MPa, 85 MPa, 90 MPa, 95 MPa, 100 MPa, 105 MPa, 110 MPa, 115 MPa, 120 MPa.

[0047] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0048] The present invention realizes the control of the morphology, size and distribution of harmful Fe phase in aluminum alloy by adding Mo and V and controlling the process parameters of pressure casting. The morphology of Fe phase is spherical or granular, and the distribution in the alloy matrix is ​​uniform and dispersed, thereby ensuring the plasticity of aluminum alloy and improving the elongation and service performance of aluminum alloy. In addition, the method of the present invention is simple and easy to implement, and does not require strict control of raw materials and process, so as not to increase the cost of aluminum alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 The microstructure of the alloy of Example 1, wherein (a) is an optical microscope image; (b) is a scanning electron microscope backscattered electron image;

[0050] Figure 2 The microstructure of the alloy of Example 2, wherein (a) is an optical microscope image; (b) is a scanning electron microscope backscattered electron image;

[0051] Figure 3 The microstructure of the alloy of Comparative Example 1, wherein (a) is an optical microscope image; (b) is a scanning electron microscope backscattered electron image;

[0052] Figure 4 The microstructure of the alloy of Comparative Example 2 (Scanning Electron Microscope Backscattered Electron Image);

[0053] Figure 5 The microstructure of the alloy of Comparative Example 3 (SEM backscattered electron image);

[0054] Figure 6 Metallographic photograph of the secondary dendrite arm spacing. DETAILED DESCRIPTION

[0055] To address the deficiencies of the prior art, the present invention achieves regulation of harmful Fe phases by adding Mo and V elements in specific amounts and combining the control of pressure casting process parameters, thereby reducing the harmful effects of Fe elements in aluminum alloys.

[0056] The specific principles are as follows:

[0057] The formation process of needle-shaped (lamellar) β-AlFeSi phase in aluminum alloy is as follows:

[0058] Liquid phase → Al+Al3Fe (about 930K) (1)

[0059] Liquid phase + Al3Fe→Al+α-Al8Fe2Si (about 900K) (2)

[0060] Liquid phase + α-Al8Fe2Si → Al + β-Al5FeSi (about 880K) (3)

[0061] From the above reaction process, it can be seen that the β-Al5FeSi phase is formed by the peritectic transformation of α-Al8Fe2Si, indicating that the α-Al8Fe2Si phase is a prerequisite for the formation of the needle-shaped (plate-shaped) β-Al5FeSi phase. If the occurrence of reaction (3) is restricted, the β-Al5FeSi phase will obviously be suppressed. For multi-component compounds, the larger the structural entropy (configurational entropy), the more stable it is. The order of configurational entropy per unit mole of compound is as follows: α-Al8Fe2Si<β-Al5FeSi<Al8(FeCr)Si<Al8(FeMo)Si<Al 12 (FeV)3Si. Therefore, α-Al8Fe2Si cannot exist stably and will transform into β-Al5FeSi with greater configuration entropy than it, but Al8(FeMo)Si and Al 12 (FeV)3Si is more stable than β-Al5FeSi.

[0062] Therefore, the present invention adopts the method of composite addition of alloy elements + control of cooling process to achieve the control of the morphology and size of the Fe phase in the cast aluminum alloy, so as to reduce its harm to the alloy properties. The detailed scheme is as follows:

[0063] 1. Stabilization of the α-Al8Fe2Si phase is achieved by adding Mo and V in combination. Because Mo, V and Fe have the same crystal structure, similar atomic size and similar electronegativity, they conform to the Hume-Rothery law for solid solution formation. Therefore, Mo and V atoms will replace some Fe atoms to form Al8(FeMo)Si, Al8(FeMoV)Si and Al with greater configuration entropy than β-Al5FeSi. 12 (FeV)3Si phases form granular or "Chinese character-shaped" phases, which achieves the thermodynamic inhibition of the needle-shaped (plate-shaped) β-Fe phase.

[0064] Second, by controlling the appropriate casting cooling process, including controlling the cooling rate and cooling uniformity (avoiding pre-crystallization), avoid Al8(FeMo)Si, Al8(FeMoV)Si and Al 12The growth or agglomeration of the (FeV)3Si phase achieves dynamic control of the size and distribution of the generated granular or "Chinese character-shaped" Fe phase. The cooling rate is >40K / s. The uniformity of cooling is to avoid the appearance of large-sized pre-crystallized structures during the alloy casting solidification process, because large-sized pre-crystallized structures will cause the pre-formation of large-sized α-Fe phases, which will remain in the final casting structure and will also have an adverse effect on performance. In production practice, the uniformity of the cooling process is mainly controlled by controlling the barrel temperature and the mold temperature. Further control of the melt casting temperature, barrel filling degree or the temperature of other heat transfer systems in contact with the melt can further improve the uniformity of cooling.

[0065] The present invention is further described below in conjunction with the examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0066] Unless otherwise specified herein, the preparation methods and detection methods involved in the following examples or comparative examples refer to the prior art. Unless otherwise specified in the following examples, all raw materials are commercially available or prepared by conventional methods in the art.

[0067] Example 1

[0068] (1) In an Al-Si alloy, the composition is Si: 9wt%, Mg: 0.3wt%, Fe: 0.15wt%, Sr: 0.02wt%. The addition amounts of Mo and V are: Mo: 0.2%; V: 0.15% respectively.

[0069] (2) Batching: Batching according to the melting amount, and weighing the pure Al ingot, 95% quick-dissolving silicon, pure Mg ingot, AlMo5 master alloy, AlV5 master alloy, and AlSr10 master alloy in sequence according to the calculated values ​​in the batching table for use;

[0070] (3) Melting: first add pure Al ingot to the melting furnace and heat it up; after it is completely melted, raise the melt temperature to 765°C, and add 95% instant silicon in batches; after the instant silicon is completely melted, add AlMo5 master alloy and AlV5 master alloy according to the actual alloy ingredients, and stir evenly; after the master alloy is completely melted, cool it to 720°C, press the Mg ingot below the melt surface with a bell jar, and stir evenly after it is completely melted;

[0071] (4) Modification and degassing: Lower the melt temperature to 710°C, add the weighed AlSr10 intermediate alloy, stir to melt it all, and keep warm for 5 minutes. Then raise the melt temperature to 720°C-730°C to start degassing. Weigh the refining agent (Pyroflux GRDR212 purchased from Pyroflux (Shenzhen) High Temperature Materials Co., Ltd.) according to 0.1%-0.15% of the melt mass, and add it to the refining agent automatic adding funnel of the rotor degasser. Use a rotor degasser for degassing, the refining agent addition speed is 500r / min, the degassing speed is 400r / min, the high-purity Ar flow rate of the degasser is 25L / min, and the degassing time is 25min. After the degassing is completed, let it stand for 10 minutes, take the alloy composition sample and the reduced pressure solidification gas measurement sample;

[0072] (5) Die casting: After the degassing meets the standard and the composition is qualified, the melt temperature is adjusted to 705℃ and die casting is performed on a 400-ton die casting machine. The die casting parameters are: barrel temperature 180℃, mold temperature 180℃, barrel filling degree 33%, vacuum degree 50mBar, low speed section injection speed 0.2m / s, high speed section injection speed 3.9m / s, casting pressure 80MPa, and mold holding time 6s. The microstructure of the casting is shown in Figure 1 The black arrows in the figure indicate some Fe phase particles. Figure 1 It can be seen that the method of the present invention achieves good control of the Fe phase. The Fe phase after control by the present invention is in the form of fine particles (small spheres) and is evenly distributed in the alloy matrix.

[0073] Example 2

[0074] (1) In an Al-Si alloy, the composition is Si: 8.5wt%, Mg: 0.24wt%, Fe: 0.2wt%, Sr: 0.02wt%. The addition amounts of Mo and V are: Mo: 0.08%; V: 0.08% respectively.

[0075] Steps (2) to (4) are the same as those in Example 1, and step (5) is specifically as follows:

[0076] (5) Die casting: After the degassing meets the standard and the composition is qualified, the melt temperature is adjusted to 700℃ and die casting is performed on a 4000-ton die casting machine. The die casting parameters are: barrel temperature 150℃, mold temperature 190℃, barrel filling degree 48%, vacuum degree 80mBar, low speed section injection speed is divided into three sections of 0.1m / s, 0.2m / s, and 0.3m / s, high speed section injection speed is 6m / s, casting pressure is 75MPa, and mold holding time is 40s. The microstructure of the casting is shown in Figure 2 The black arrows in the figure indicate some Fe phase particles. Figure 2It can be seen that the method of the present invention achieves good control of the Fe phase. The Fe phase after control by the present invention is in the form of fine particles (small spheres) and is evenly distributed in the alloy matrix.

[0077] Comparative Example 1

[0078] Steps (1) to (4) are the same as those in Example 1, and step (5) is specifically as follows:

[0079] (5) Die casting: After the degassing meets the standard and the composition is qualified, the melt temperature is adjusted to 705℃ and die casting is carried out on a 400-ton die casting machine. The die casting parameters are: barrel temperature is room temperature, mold temperature is 180℃, barrel filling degree is 33%, vacuum degree is 60mBar, low speed section injection speed is 0.2m / s, high speed section injection speed is 3.9m / s, casting pressure is 80MPa, and mold holding time is 6s. The microstructure of the casting is shown in Figure 3 The position of the red dotted circle in the figure is the pre-crystallization of primary α-Al. Pre-crystallization is often a large block of structure formed by uneven cooling and pre-crystallization. It is mixed into the casting during the subsequent solidification process and finally retained in the casting structure. It can be seen from the figure that a large block of Fe phase is formed along with the pre-crystallization structure (indicated by the black arrow).

[0080] The biggest difference between this comparative example and Example 1 is that the barrel starts die casting at room temperature, and the barrel is not subjected to constant temperature control. Therefore, although the overall cooling rate meets the standard, uniform cooling (avoiding pre-crystallization) is not achieved, so larger Fe phase particles ( Figure 3 ).Depend on Figure 3 It can be seen that although Mo and V were added and the cooling rate reached >40K / s, uniform cooling control was not achieved, and large pieces of pre-crystallized structure appeared, accompanied by the pre-crystallization of larger Fe phase particles.

[0081] Comparative Example 2

[0082] Steps (1) to (4) are the same as those in Example 1, and step (5) is specifically as follows:

[0083] (5) Gravity casting using a water-cooled copper mold. The water-cooled copper mold is a mold made of pure copper with a rectangular cavity. It is composed of two symmetrical half molds. When the molds are closed, the two half molds form a rectangular cavity with a size of 200mm×100mm×30mm, which is also the size of the casting. The two half molds are fixed together by bolts when the molds are closed. Hollow cooling water channels are arranged inside the two half molds, and each has a water inlet and a water outlet. Before casting, room temperature cooling water is passed through the mold, and the cooling water pressure is 0.3MPa. During casting, the temperature is adjusted to 695-700℃, and about 1.8kg of aluminum liquid is scooped with an aluminum liquid spoon and gently poured into the mold cavity. After casting is completed, wait for the casting to cool to room temperature before turning off the cooling water to obtain the desired casting. The microstructure of the casting can be seen in Figure 4 .

[0084] Since the cooling rate cannot reach 40K / s, large-sized Fe phase appears in the structure ( Figure 4 ).Depend on Figure 4 It can be seen that although Mo and V were added in combination, due to the low overall cooling rate, although the needle-like Fe phase was suppressed, the size of the blocky Fe phase was very large.

[0085] Comparative Example 3

[0086] (1) In an Al-Si alloy, the composition is Si: 9wt%, Mg: 0.3wt%, Fe: 0.15wt%, Sr: 0.02wt%.

[0087] (2) Batching: Batching according to the melting amount, and weighing the pure Al ingot, 95% quick-dissolving silicon, pure Mg ingot, and AlSr10 master alloy in sequence according to the calculated values ​​in the batching table for use;

[0088] Steps (3) to (5) are the same as those in Comparative Example 2. The microstructure of the casting is shown in Figure 5 .

[0089] Since the comparative example did not use Mo and V composite additions and the cooling rate did not reach 40K / s, a large number of needle-shaped Fe phases appeared in the structure. Figure 5 It can be seen that for alloys with the same composition and Fe content, without the Fe phase control method of the present application, most of the Fe phases in the alloy are distributed in needle-like (thin-flaky) form.

[0090] The cooling rate described in this application is determined by the empirical formula SDAS = a·(T) -b The SDAS is called the secondary dendrite arm spacing (when the alloy starts to crystallize and solidify from the liquid state, a "branch-like" dendrite will be formed, and the distance between the center lines of the two dendrites is called the secondary dendrite arm spacing), which can be measured on the metallographic photograph (see Figure 6). a and b are material constants. For cast aluminum alloy, a≈40-50 (unit: μm·(K / s)^b), b≈0.3-0.33. Then the value of SDAS measured from the metallographic photograph is substituted into the above formula to calculate the cooling rate T. The cooling rates of the above-mentioned Example 1, Example 2 and Comparative Example 1 are greater than 40K / s.

[0091] Combining the results of Example 1, Comparative Example 2 and Comparative Example 3, it can be seen that the synergistic effect of the composite addition of Mo and V, the control of the cooling rate and the control of uniform cooling is achieved to control the morphology, size and distribution of the harmful Fe phase in the aluminum alloy. The morphology of the Fe phase is spherical or granular, with a size of <10μm, and is evenly and dispersedly distributed in the alloy matrix.

[0092] The above detailed description of the present invention is intended to enable persons familiar with the art to understand the contents of the present invention and implement them. It does not limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for regulating Fe phase in a cast aluminum alloy, characterized in that: The steps include: (1) adding Mo and V to an Al-Si alloy and smelting the alloy; wherein the content of Mo is controlled to be 0.06wt% to 0.5wt% and the content of V is controlled to be 0.06wt% to 0.5wt%; (2) Degassing the molten alloy; (3) The degassed alloy liquid is pressure-casted to obtain a die-cast aluminum alloy, wherein the cooling rate of the pressure casting process is controlled to be greater than 40K / s, the barrel temperature is controlled to be 110°C to 200°C, and the mold temperature is controlled to be 160°C to 210°C.

2. The control method according to claim 1, characterized in that: The total content of the Mo and the V is ≤0.8 wt %.

3. The control method according to claim 1, characterized in that: The content of Mo is controlled to be 0.06 wt%~0.3wt%, and the V content is 0.06wt%~0.25wt%.

4. The control method according to claim 3, characterized in that: The total content of the Mo and the V is 0.15wt%~0.4wt%.

5. The control method according to claim 1, characterized in that: The Mo and the V are added in the form of a master alloy.

6. The control method according to claim 5, characterized in that: The Mo master alloy is AlMo10 and / or AlMo5, and the V master alloy is AlV10 and / or AlV5.

7. The control method according to claim 5, characterized in that: The addition temperature of the intermediate alloy to which the Mo and V are added is controlled to be 720°C to 770°C.

8. The control method according to claim 1, characterized in that: In step (3), the temperature of the alloy liquid after degassing is controlled to be 695° C. to 710° C., and then the pressure casting is performed.

9. The control method according to claim 1, characterized in that: In step (3), when performing the pressure casting, the filling degree of the barrel is controlled to be ≥30%.

10. The control method according to claim 1, characterized in that: The specific steps of the control method include: (1) According to the formula, melt the Al-Si alloy and add the Mo master alloy and the V master alloy, and stir to fully melt; (2) degassing the alloy liquid after smelting in step (1); (3) The temperature of the alloy liquid after degassing in step (2) is adjusted to 695°C to 710°C, and then pressure casting is carried out on a die casting machine. The parameters for controlling the pressure casting are: barrel temperature is 110°C to 200°C, mold temperature is 160°C to 210°C, barrel filling degree is 30% to 50%, vacuum degree is 50 to 80 mBar, low speed section injection speed is 0.1 to 0.3 m / s, high speed section injection speed is 3 to 10 m / s, casting pressure is 40 to 120 MPa, and mold holding pressure time is 5 to 50 s.

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