Screening method and preparation method of Al-Si-Mg ternary intermediate alloy based on semi-solid state method

Abstract

The invention discloses an Al-Si-Mg ternary intermediate alloy screening method based on a semi-solid state method. The Al-Si-Mg ternary intermediate alloy screening method comprises the following steps: 1, setting phase diagram calculation and setting parameters of solidification simulation; 2, calculating a result and a solidification simulation result based on the phase diagram; and 3, intermediate alloy components meeting the screening requirements are confirmed. The screening conditions need to meet three screening conditions at the same time, the condition 1 is that the intermediate alloy comprises (0.25-0.45) d wt% of Mg, (6.5-7.5) d wt% of Si, the parameter d is larger than or equal to 4, and the balance is Al; condition 2: f (Si) > 30 wt.%; and the condition 3 is that the semi-solid temperature interval delta T in the solidification process is greater than or equal to 50 DEG C. The invention further discloses a preparation method of the Al-Si-Mg ternary intermediate alloy based on the semi-solid state method and a preparation method of a cast Al-Si-Mg alloy with the ternary intermediate alloy as a raw material.

Description

Technical Field

[0001] The present invention relates to the field of aluminum alloy material preparation, and in particular to a screening method and a preparation method of an Al-Si-Mg ternary master alloy based on a semi-solid process. Background Art

[0002] Cast Al-Si alloy, namely A356 alloy, has the casting characteristics of high fluidity and low shrinkage, as well as high wear resistance and corrosion resistance. Therefore, A356 alloy is suitable for the automotive industry and aerospace field. However, there is an energy consumption problem in the production process of cast aluminum alloy, which directly affects the production cost and production efficiency. Traditional Al-Si alloy ingot preparation often adopts the method of melting pure Al ingot and then adding pure Si and other alloying elements for smelting and casting to obtain alloy ingot. In the smelting process of multi-element alloy, due to the different melting points of various alloying elements, the traditional preparation method not only requires a long smelting time, but also easily causes uneven distribution of high-melting-point alloying elements such as Mn and Si, and burnout of low-melting-point alloying elements such as Mg, which increases production cost and energy consumption.

[0003] A common solution currently involves using master alloys instead of pure elements to prepare Al-Si alloys. Common master alloys include AlSi20 and AlMg50. The principle is that master alloys have a lower melting point than pure metals, effectively shortening the alloy's smelting time and promoting the uniform distribution of alloying elements in the cast Al-Si alloy. For example, in existing document 1 (Liu Shuji, CN118910444A, "An Improved Method for Melting and Preparing Aluminum-Silicon Alloy Castings," 2024-09-11), a near- / hypereutectic aluminum-silicon alloy Al-xSi (10≤x≤22) ingot is used as the aluminum-silicon master alloy. Pure aluminum is added in a specific ratio (1:a) and heated to melt. Pure Mg, Al-Ti-B, Al-Sr, and other elements are then added to adjust the aluminum liquid composition and transform the melt. Mg, a susceptible element to burning, is added as pure Mg blocks (≥99.5%) and placed in a launder between the melting furnace and the standing furnace, ultimately producing the desired Al-Si alloy melt. Although this technical solution proposes a method for preparing cast Al-Si alloy using an intermediate alloy, the elements in the intermediate alloy are single and the content is low, which does not effectively simplify the alloy preparation process. In addition, the direct contact of pure Mg with the high-temperature melt will cause oxidation and burning of Mg.

[0004] Designing and preparing multi-element master alloys can effectively simplify the preparation process of cast Al-Si alloys. However, the introduction of multiple elements into the master alloy increases the difficulty of controlling the element content during the master alloy preparation process. Different alloying elements may also react chemically or form intermetallic compounds. For example, in existing document 2 (Chen Weiping, CN107794419A, A Multi-element Master Alloy for Aluminum Alloy and Preparation Method Thereof, March 13, 2018), a multi-element master alloy containing 2-6% Mg, 0.2-0.8% Mn, 0.08-0.8% Sc, and 0.08-0.4% Zr was prepared by molten salt aluminothermic reduction. Although this technical solution increases the elemental composition of the master alloy, the low element content directly leads to a high amount of master alloy in subsequent use, failing to achieve the goal of reducing production difficulty. Moreover, this technical solution is not suitable for the production of cast Al-Si alloys. At the same time, this type of molten salt aluminothermic reduction method also has the technical problem of difficulty in separating the reaction products from the alloy melt during the preparation process and the generation of harmful gases.

[0005] According to existing documents 1 and 2, the existing technology is still unable to effectively increase the element content of the intermediate alloy. The reason is that increasing the element content of the intermediate alloy will directly lead to an increase in the melting point of the intermediate alloy, thereby reproducing the aforementioned technical problems represented by element segregation when the intermediate alloy is not used, which ultimately affects the composition accuracy and performance consistency of the cast Al alloy. The traditional smelting method for preparing the intermediate alloy is specifically to mix the metal elements in a certain proportion at a high temperature and homogenize the composition by stirring. The traditional smelting method has the characteristics of mature technology and low cost. However, the traditional smelting method has the technical problems of high smelting temperature, which leads to burn-out of low-melting-point metals, and segregation of high-melting-point metals during the cooling process. For example, in existing document 3 (Hao Yonggang, CN119194144A, a method for preparing a large deformation-assisted high-homogeneity aluminum-silicon master alloy, 2024-12-17), AlSi10, AlSi30 and AlSi60 master alloys were prepared by powder metallurgy combined with ultra-low temperature extrusion and large plastic deformation. Although this technical solution effectively increases the element content in the master alloy, it also obtains a uniform master alloy structure. However, compared with traditional smelting methods, the production process of powder metallurgy includes multiple steps such as powder preparation, uniform mixing, molding, sintering and post-processing. Each step requires a certain amount of time and process control, especially in the powder pressing and sintering links. The production cycle is relatively long. Compared with smelting, it is limited by conditions such as the size of the briquetting mold, and the production efficiency is low, which is also not conducive to large-scale industrial production. Summary of the Invention

[0006] The present invention aims to provide a method for screening and preparing an Al-Si-Mg ternary master alloy based on a semi-solid process. The basic principle is to screen the composition of the Al-Si-Mg alloy through phase diagram calculation. Furthermore, by introducing the Mg element in the semi-solid state, the Mg content in the prepared master alloy is essentially consistent with the actual added content, thus solving the problem of Mg loss during the smelting process. This is specifically reflected in the following two aspects:

[0007] 1. As the Si content continues to increase, the phase transformation process of the master alloy during solidification changes. Along with the formation of coarse primary Si phase, the melting point of the Al-Si alloy changes. The composition range and melting point interval of the Al-Si-Mg alloy can be screened through phase diagram calculation;

[0008] 2. During the alloy solidification process, when the solid phase ratio in the melt is between 20-80 mol%, the melt is in a semi-solid state. At this time, the viscosity of the melt is relatively high, which can effectively bury the master alloy, isolate oxygen, and reduce the burnout of Mg elements during the smelting process. Through solidification simulation, the semi-solid temperature range of solutions with different compositions can be obtained;

[0009] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0010] A method for screening an Al-Si-Mg ternary master alloy based on a semi-solid process comprises the following steps:

[0011] Step 1: Set up phase diagram calculation and solidification simulation parameters. Phase diagram calculation includes selecting the phase diagram type and setting the alloying element types. Solidification simulation includes selecting the calculation model and setting the alloying element types and compositions.

[0012] Step 2: Based on the phase diagram calculation results and the solidification simulation results, set the master alloy composition screening conditions, which include the composition range and the temperature range. The screening conditions must meet all three screening conditions at the same time.

[0013] Step 3: Confirm the composition of the intermediate alloy that meets the screening requirements. In the Al-Si-Mg alloy thermodynamic phase diagram, select the liquid phase projection surface and the phase composition area that meets the screening requirements in step 2 to confirm the phase composition area that meets the screening requirements.

[0014] In step 1, the phase diagram type is selected as follows: the calculated phase diagram is the liquid phase projection surface and liquidus temperature contour line of the ternary system, and the calculation is performed using Pandat software and Phase Projection in the PanPhaseDiagram phase diagram module;

[0015] The calculation step size of the liquidus temperature contour line is 100°C;

[0016] The alloy element types calculated in the phase diagram are set as follows: the alloy element types include Al, Si and Mg;

[0017] The calculation model of the solidification simulation is selected by using Pandat software and selecting the Scheil-Gulliver model in the PanPhaseDiagram phase diagram module for solidification simulation;

[0018] The composition setting in the solidification simulation is Si: 7d, Mg: 0.3d, and the balance is Al, where d≥4.

[0019] In step 2, the screening conditions for the intermediate alloy composition simultaneously meet the following three screening conditions:

[0020] The master alloy composition screening condition 1 is that the master alloy composition is Mg: (0.25-0.45) d wt.%, Si: (6.5-7.5) d wt.%, wherein the parameter d ≥ 4, and the balance is Al;

[0021] The intermediate alloy composition screening condition 2 is: f(Si)>30wt.%;

[0022] The intermediate alloy composition screening condition 3 is that the semi-solid temperature range ΔT during the solidification process is ≥ 50°C.

[0023] In the screening condition 3, the semi-solid range of the solidification process of the master alloy must meet the following conditions: solid phase ratio: f(s) = 0.2-0.8.

[0024] A method for preparing an Al-Si-Mg ternary master alloy based on a semi-solid process comprises the following steps: first, raw materials are prepared in a satisfactory mass ratio, pure Al, pure Si and an Al-20Si master alloy are placed in a crucible, then, the crucible and the master alloy are preheated at a preheating temperature to remove moisture in the crucible and the alloy, then, heating is performed at a smelting temperature, and after the pure Al, pure Si and Al-20Si master alloy are melted, surface slag and oxide scale are removed to obtain an aluminum alloy melt, then, the Al-50Mg master alloy is wrapped with aluminum foil and preheated at a preheating temperature, and the temperature of the aluminum alloy melt is lowered to a semi-solid temperature range, then, the preheated Al-50Mg master alloy is pressed into the semi-solid aluminum alloy melt, and finally, casting is performed at a casting temperature and solidified and cooled to obtain the Al-Si-Mg ternary master alloy prepared by the semi-solid process.

[0025] The preheating temperature of the crucible and the master alloy is 200-400°C;

[0026] The melting temperature of the master alloy is 900-1200°C;

[0027] The casting temperature of the master alloy is 800-1000°C.

[0028] A method for preparing a cast Al-Si-Mg alloy using a ternary master alloy as a raw material comprises the following steps: first, pure Al and a master alloy are weighed to meet a mass ratio condition, the pure Al is placed in a crucible, then, the crucible is preheated at a preheating temperature to remove moisture in the crucible and the alloy, then, the alloy is heated at a smelting temperature, and after the pure Al is melted, surface scum and oxide scale are removed, then, the master alloy is wrapped with aluminum foil and preheated at a preheating temperature, the preheated master alloy is pressed into the pure Al melt, fully stirred for a stirring time, then, the alloy is allowed to stand at the smelting temperature for 1 hour, fully stirred every 20 minutes during the standing period, then, the casting temperature is adjusted, and the melt is cast into a permanent mold preheated at the preheating temperature and solidified and cooled to obtain the cast Al-Si-Mg alloy.

[0029] The preheating temperature of the crucible and raw materials is 200-400°C;

[0030] The melting temperature of the cast Al-Si-Mg alloy is 750-850°C;

[0031] The casting temperature of the Al-Si-Mg alloy is 700-750°C.

[0032] The technical effects of the present invention have been tested and the specific contents are as follows:

[0033] Metallographic examination revealed that the Al-Si-Mg ternary master alloy contained α-Al, primary Si, eutectic Si, and Mg2Si phases. Statistical analysis of the area ratios of primary and eutectic Si revealed that the measured phase composition of the Al-42Si-1.8Mg alloy was 31.0 mol% primary Si and 10.2 mol% eutectic Si, while that of the Al-49Si-2.14Mg alloy was 36.3 mol% primary Si and 10.2 mol% eutectic Si. The measured total content of primary Si and eutectic Si was generally consistent with the calculated total content. These metallographic and statistical results demonstrate that the master alloy screening method can accurately predict the phase composition and content of the primary and eutectic phases in master alloys.

[0034] SEM-EDS analysis revealed uniform distribution of Mg and Si in the Al-Si-Mg ternary master alloy, with no elemental segregation. The Si and Mg contents of the Al-42Si-1.8Mg alloy were 40.8±2.8wt.% and 1.9±0.1wt.%, respectively, and those of the Al-49Si-2.1Mg alloy were 46.3±0.4wt.% and 2.3±0.1wt.%, respectively. SEM-EDS testing confirmed that the Mg content in the master alloy was essentially consistent with the actual addition amount, demonstrating that the semi-solid-state method eliminates the issue of burnout of the low-melting-point Mg element during the preparation process.

[0035] Metallographic examination revealed that the cast Al-Si-Mg alloy prepared using the Al-42Si-1.8Mg ternary master alloy contained both α-Al and eutectic Si phases, exhibited a uniform microstructure with no significant segregation. No residual primary Si particles were observed in the cast Al-Si-Mg alloys subjected to different holding times. Metallographic results demonstrate that the Al-Si-Mg ternary master alloy can be rapidly prepared for casting at a melting temperature of 800°C.

[0036] Direct reading spectroscopy (DES) analysis revealed that the Si and Mg elements in the cast Al-Si-Mg alloy prepared using the Al-42Si-1.8Mg ternary master alloy as raw material were within the target composition range. The composition remained stable with increasing holding time, and there was no significant burnout of Mg during the holding process. DES test results demonstrate that the cast Al-Si-Mg alloy prepared using the Al-Si-Mg ternary master alloy can achieve a uniform alloy structure and accurate alloy composition in a short period of time.

[0037] The present invention has the following beneficial effects:

[0038] 1. The production process of casting Al-Si-Mg alloy is simplified in terms of raw material types and preparation procedures, reducing the amount of master alloy, shortening the smelting time and reducing energy consumption;

[0039] 2. The low-melting-point Mg element is introduced through the semi-solid method, which eliminates the direct addition of low-melting-point elements in the preparation process of cast Al-Si-Mg alloy, solves the burning problem during the Mg addition process, and improves the composition accuracy of cast Al-Si-Mg alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is the liquid phase projection surface diagram of Al-Si-Mg ternary system;

[0041] Figure 2 The solidification paths and semi-solid interval diagrams of Example 1, Example 2 and Comparative Example 1;

[0042] Figure 3 1 is the metallographic organization diagram of Example 1 and Example 2;

[0043] Figure 4 The SEM-EDS composition distribution diagrams of Example 1 and Example 2;

[0044] Figure 5 This is the metallographic structure diagram of the cast Al-Si-Mg alloy prepared from the master alloy of Example 1. Specific implementation methods

[0045] Example 1

[0046] A method for screening an Al-Si-Mg ternary master alloy based on a semi-solid process, specifically comprising the following steps:

[0047] Step 1: Set up phase diagram calculation and solidification simulation parameters. Phase diagram calculation includes selecting the phase diagram type and setting the alloying element types. Solidification simulation includes selecting the calculation model and setting the alloying element types and compositions.

[0048] The phase diagram type is selected as follows: the calculated phase diagram is the liquid phase projection surface and liquidus temperature contour line of the ternary system, and the calculation is performed using Pandat software and Phase Projection in the PanPhaseDiagram phase diagram module;

[0049] The calculation step size of the liquidus temperature contour line is 100°C;

[0050] The alloy element types calculated in the phase diagram are set as follows: the alloy element types include Al, Si and Mg;

[0051] The calculation model of the solidification simulation is selected by using Pandat software and selecting the Scheil-Gulliver model in the PanPhaseDiagram phase diagram module for solidification simulation;

[0052] The composition setting in the solidification simulation is Si: 7d, Mg: 0.3d, and the balance is Al, where d ≥ 4;

[0053] Step 2: Based on the phase diagram calculation results and the solidification simulation results, set the intermediate alloy composition screening conditions. The screening conditions include the composition range and the temperature range. The screening conditions must meet the three screening conditions at the same time, specifically,

[0054] The master alloy composition screening condition 1 is that the master alloy composition is Mg: (0.25-0.45) d wt.%, Si: (6.5-7.5) d wt.%, wherein the parameter d ≥ 4, and the balance is Al;

[0055] The intermediate alloy composition screening condition 2 is: f(Si)>30wt.%;

[0056] The intermediate alloy composition screening condition 3 is that the semi-solid temperature range ΔT during the solidification process is ≥ 50°C;

[0057] Step 3, confirm the composition of the intermediate alloy that meets the screening requirements. In the Al-Si-Mg alloy thermodynamic phase diagram, select the liquid phase projection surface and the phase composition area that meets the screening requirements in step 2. The phase composition area that meets the screening requirements is named area 1. The specific area is as follows: Figure 1 shown.

[0058] To demonstrate the effectiveness of the master alloy screening method, Al-35Si-1.5Mg was selected to prepare a master alloy in region 1. The types and molar fractions of the phases obtained by the screening method in Example 1 are shown in Table 1.

[0059] Table 1 Thermodynamic phase diagram theoretical calculation of the phases and the amount of substance in the Al-Si-Mg master alloy and the measured value of Si phase

[0060]

[0061] A method for preparing an Al-Si-Mg ternary master alloy based on a semi-solid process specifically comprises the following steps:

[0062] First, prepare the raw materials to meet the conditions of Al-42Si-1.8Mg alloy by mass ratio. Specifically, the addition amount of pure Al is 464g, the addition amount of pure Si is 400g, the addition amount of Al-50Mg master alloy is 36g, and the addition amount of Al-20Si master alloy is 100g. Put pure aluminum, pure Si and Al-20Si master alloy into the crucible, then preheat the crucible and master alloy at a preheating temperature of 400℃ to remove the water vapor in the crucible and the alloy, and then melt at a melting temperature of 1000℃ until pure Al is added. After pure Si and Al-20Si master alloy are melted, surface slag and oxide scale are removed to obtain an aluminum alloy melt. Then, the Al-50Mg master alloy is wrapped with aluminum foil and preheated at 150°C. The temperature of the aluminum alloy melt is lowered to a semi-solid temperature range, specifically 750°C. The preheated Al-50Mg master alloy is pressed into the semi-solid aluminum alloy melt. Finally, the alloy is cast at a casting temperature of 900°C and solidified and cooled to obtain an Al-Si-Mg ternary master alloy prepared by a semi-solid method, referred to as a master alloy.

[0063] The casting mold is made of cast iron, and the casting time is less than 30 seconds;

[0064] The semi-solid interval is as follows Figure 2 As shown, the solid phase in the semi-solid melt accounts for 20-80 mol.%;

[0065] In order to prove the phase composition of the master alloy, the test results are as follows: Figure 3 As shown, by statistically analyzing the area ratio of the primary Si phase and calculating the amount of matter according to the area ratio of the phase, the statistical results are shown in Table 1;

[0066] α-Al phase is the base phase;

[0067] The primary Si phase is a supersaturated Si crystal in the melt, which has the characteristic of preferential nucleation and growth during the solidification process, that is, it is the first precipitated phase; at the same time, the primary Si phase often presents a relatively coarse block or plate-like structure in the aluminum alloy matrix. Therefore, in the target alloy composition, the primary Si phase plays a role in significantly improving the hardness of the alloy and its wear resistance. At the same time, the dispersed primary Si phase increases the contact area between Si and the melt during the preparation of the cast Al-Si alloy, thereby accelerating the diffusion of Si in the melt and promoting the homogenization of the cast Al-Si alloy.

[0068] The eutectic Si phase is the Si phase formed during the eutectic reaction of aluminum alloys. It has the characteristic of crystallizing and precipitating at the same time as the α-Al phase at a specific temperature and is a key component of the eutectic structure. The eutectic Si phase generally presents a fine needle-like, fibrous or lamellar structure in the aluminum alloy matrix. Therefore, in the design of cast Al-Si alloys, the eutectic Si phase plays a role in refining the alloy structure and improving the comprehensive performance of the alloy's strength and toughness, thereby greatly optimizing the mechanical performance of the alloy under complex stress environments. At the same time, the eutectic Si phase further improves the dispersion of Si in the melt, enabling the Si element to fully diffuse in the Al-Si alloy, thereby shortening the preparation time of cast Al-Si alloys.

[0069] Mg2Si phase is an intermetallic compound with a nanoparticle structure in microstructure. It has a high melting temperature (1358K), a low thermal expansion coefficient (7.5×10 -6 K -1 ) and high Young's modulus (120GPa), and is distributed in a fine and dispersed state in the aluminum matrix. Therefore, the Mg2Si phase can act as a reinforcement, which helps to improve the strength and rigidity of the alloy. At the same time, the presence of the Mg2Si phase promotes the uniform diffusion of the Mg element in the cast Al-Si alloy, reduces the loss of the Mg element, and ensures the accuracy of the composition.

[0070] In order to prove the element content of the master alloy, the master alloy was subjected to SEM-EDS surface composition analysis under the conditions of 100 times magnification and 3 statistical positions. The test results are as follows: Figure 4 As shown, the test results are statistically analyzed, and the statistical results are shown in Table 2;

[0071] Table 2 SEM-EDS results of master alloy composition

[0072]

[0073] The test results show that the measured results of the phase composition and element content in the master alloy of Example 1 are consistent with the theoretical addition amount;

[0074] In order to demonstrate the role of the master alloy, that is, the feasibility of preparing a cast Al-Si alloy based on the master alloy, the master alloy was used to prepare a cast Al-Si-Mg alloy.

[0075] A method for preparing a cast Al-Si-Mg alloy using a ternary master alloy as a raw material, comprising: first, weighing pure aluminum and a master alloy to satisfy a mass ratio of 5:1, specifically, adding 200 g of the master alloy and 800 g of pure Al; placing the pure Al into a crucible; then preheating the crucible at a preheating temperature of 400°C to remove moisture in the crucible and the alloy; then, melting the pure Al at a melting temperature of 800°C, removing surface slag and oxide scale after the pure Al is melted; then, wrapping the master alloy with aluminum foil and preheating it at 150°C; pressing the preheated master alloy into the pure Al melt; fully stirring it for 30 seconds; then standing it at 800°C for 1 hour, fully stirring it every 20 minutes during the standing period; then, adjusting the casting temperature to 720°C; casting the melt into a permanent mold preheated at 250°C, and solidifying and cooling it to obtain a cast Al-Si-Mg alloy;

[0076] In order to prove the uniformity of the structure of the cast Al-Si-Mg alloy and the dissolution of the primary Si phase, the metallographic structure characterization test of the cast Al-Si-Mg alloy at different holding times was carried out at a magnification of 50 times. The test results are shown in Figure 2. Figure 5 As shown in Figure 2, the primary Si phase in the master alloy is rapidly dissolved during the preparation process of the cast Al-Si-Mg alloy, and a cast Al-Si-Mg alloy with uniform structure is obtained;

[0077] In order to prove the element content of the obtained cast Al-Si-Mg alloy, component analysis was carried out by direct reading spectroscopy test. Three test positions were tested for each sample. The test results are shown in Table 3. The measured results of the elemental composition of the intermediate alloy obtained by the preparation method of the present invention are consistent with the target addition amount, that is, the intermediate alloy prepared by the present invention can be used for casting Al-Si-Mg alloy.

[0078] Table 3 Direct reading spectrometry results of Al-Si alloys prepared using master alloys

[0079]

[0080] Metallographic structure tests and direct reading spectroscopy tests show that the intermediate alloy prepared by the semi-solid method can promote the rapid dissolution of eutectic Si. At the same time, combined with the semi-solid method, the problem of burnout of low-melting-point Mg elements during the smelting process is solved, so that the composition of the obtained cast Al-Si-Mg alloy is consistent with the design value, and ultimately the preparation process of the cast Al-Si-Mg alloy is simplified.

[0081] In order to demonstrate the effectiveness of the screening method of the present invention, Example 2 and Comparative Example 1 are provided, wherein:

[0082] The alloy composition of Example 2 belongs to composition region 1, that is, the alloy composition that meets the screening conditions, and also meets the temperature range and semi-solid temperature range of the screening conditions. The alloy composition of Example 2 is Al-49Si-2.1Mg;

[0083] The alloy composition of Comparative Example 1 belongs to composition region 2, that is, the composition interval that meets the screening conditions, but does not meet the phase content requirements and the semi-solid temperature range of the screening conditions. Specifically, the alloy composition of Comparative Example 1 is Al-28Si-1.2Mg;

[0084] Example 2

[0085] A method for screening an Al-Si-Mg ternary master alloy based on a semi-solid process, wherein the steps not otherwise specified are the same as those of Example 1, except that: to satisfy composition region 1, the alloy mass ratio satisfies the conditions of Al-49Si-2.1Mg, and the specific types and molar fractions of each phase are shown in Table 1;

[0086] Furthermore, the preparation method of the Al-Si-Mg ternary master alloy based on the semi-solid method is the same as that in Example 1 unless otherwise specified, except that: the amount of pure Al added is 388 g, the amount of pure Si added is 470 g, the amount of Al-50Mg master alloy added is 42 g, and the amount of Al-20Si master alloy added is 100 g. In addition, since the change in alloy composition leads to a change in the melting point of the alloy, the melting temperature and the casting temperature are adjusted accordingly. Specifically, the melting temperature is 1100°C and the casting temperature is 1000°C. In particular, in Example 2, the semi-solid temperature range is still maintained at 750°C.

[0087] The area ratio of the primary Si phase in Example 2 was statistically analyzed, and the amount fraction of the substance was calculated based on the area ratio of the phase. The statistical results are shown in Table 1. The test results show that the measured results of the phase composition and the amount fraction of the substance of each phase are consistent with the theoretical calculation results, that is, the screening method of the present invention is effective and accurate;

[0088] The master alloy of Example 2 was subjected to surface composition analysis using SEM-EDS, and the test results were statistically analyzed. The statistical results are shown in Table 2. The test results show that the measured results of the phase composition and element content in the master alloy of Example 2 are consistent with the theoretical addition amount;

[0089] The test results of Examples 1 and 2 show that the Al-Si-Mg alloy in composition region 1, that is, the master alloy composition satisfies the following conditions: Mg: (0.25-0.45) d wt.%, Si: (6.5-7.5) d wt.%, where the parameter d ≥ 4, the balance is Al, the phase content satisfies f(Si) > 30 wt.%, and the semi-solid temperature range ΔT ≥ 50°C, all have the following conclusions:

[0090] 1. The screening method of the present invention can accurately predict the content of primary Si phase and eutectic Si phase in the master alloy;

[0091] 2. The components obtained by the screening method of the present invention and the master alloy obtained by the preparation method of the present invention can obtain uniformly dispersed primary Si phase and Mg2Si phase in the alloy, reduce the segregation and burning loss of the Mg element, and accurately obtain a multi-element master alloy containing both high-melting-point Si element and low-melting-point Mg element.

[0092] Comparative Example 1

[0093] A method for screening an Al-Si-Mg ternary master alloy based on a semi-solid process, wherein the steps not otherwise specified are the same as those of Example 1, except that: in order to meet composition region 2, that is, to meet the master alloy composition of Mg: (0.25-0.45) d wt.%, Si: (6.5-7.5) d wt.%, where the parameter d ≥ 4, the phase content requirements and the semi-solid temperature range requirements are not met, that is, the phase content f(Si) is less than 30 wt.%, and the semi-solid temperature range ΔT is less than 50°C. The specific types and amount fractions of each phase are shown in Table 1;

[0094] Furthermore, the preparation method of the Al-Si-Mg ternary master alloy based on the semi-solid method is the same as that in Example 1 unless otherwise specified, except that: the amount of pure Al added is 616 g, the amount of pure Si added is 280 g, the amount of Al-50Mg master alloy added is 24 g, and the amount of Al-20Si master alloy added is 100 g. It is particularly noted that in Comparative Example 1, the change in alloy composition leads to a change in the melting point of the alloy, and has no substantial effect on the melting temperature, casting temperature, and semi-solid temperature range, that is, no adjustment is required.

[0095] The area ratio of the primary Si phase in Comparative Example 1 was statistically analyzed, and the amount fraction of the substance was calculated based on the area ratio of the phase. The statistical results are shown in Table 1. The test results show that the measured results of the phase composition and the amount fraction of each phase are consistent with the theoretical calculation results, that is, the screening method of the present invention is effective and accurate;

[0096] In order to verify the element content of the master alloy, the master alloy was subjected to SEM-EDS surface composition analysis at a magnification of 100 times and three statistical positions, and the test results were statistically analyzed. The statistical results are shown in Table 2. The test results show that the measured Mg content in the master alloy of Comparative Example 1 is inconsistent with the theoretical addition amount;

[0097] A comprehensive comparison of Example 1 and Comparative Example 1 shows that the composition region and semi-solid range have a significant impact on the preparation of the master alloy, that is, when the alloy composition Mg: (0.25-0.45) d wt.%, Si: (6.5-7.5) d wt.%, where the parameter d ≥ 4, and the phase content f(Si) < 30 wt.%, the Si phase content in the alloy is too low, and the preparation process of the cast Al-Si alloy cannot be effectively simplified. When the semi-solid range ΔT of the alloy is < 50°C, due to the small semi-solid range, it is difficult to control the solid phase rate in the melt during the preparation process, resulting in a higher Mg element burnout, and the Mg content in the master alloy cannot be accurately controlled.

Claims

1. A method for screening Al-Si-Mg ternary master alloy based on a semi-solid process, characterized in that The following steps are involved: Step 1: Set up phase diagram calculation and solidification simulation parameters. Phase diagram calculation includes selecting the phase diagram type and setting the alloying element types. Solidification simulation includes selecting the calculation model and setting the alloying element types and compositions. Step 2: Based on the phase diagram calculation results and the solidification simulation results, set the master alloy composition screening conditions, which include the composition range and the temperature range. The screening conditions must meet all three screening conditions at the same time. Step 3: Confirm the composition of the intermediate alloy that meets the screening requirements. In the Al-Si-Mg alloy thermodynamic phase diagram, select the liquid phase projection surface and the phase composition area that meets the screening requirements in step 2 to confirm the phase composition area that meets the screening requirements.

2. The alloy screening method according to claim 1, characterized in that: In step 1, the phase diagram type is selected as follows: the calculated phase diagram is the liquid phase projection surface and liquidus temperature contour line of the ternary system, and the calculation is performed using Pandat software and Phase Projection in the PanPhaseDiagram phase diagram module; The calculation step size of the liquidus temperature contour line is 100°C; The alloy element types calculated in the phase diagram are set as follows: the alloy element types include Al, Si and Mg; The calculation model of the solidification simulation is selected by using Pandat software and selecting the Scheil-Gulliver model in the PanPhaseDiagram phase diagram module for solidification simulation; The composition setting in the solidification simulation is Si: 7d, Mg: 0.3d, and the balance is Al, where d≥4.

3. The method for screening the master alloy according to claim 1, characterized in that: In step 2, the screening conditions for the intermediate alloy composition simultaneously meet the following three screening conditions: The master alloy composition screening condition 1 is that the master alloy composition is Mg: (0.25-0.45) d wt.%, Si: (6.5-7.5) d wt.%, wherein the parameter d ≥ 4, and the balance is Al; The intermediate alloy composition screening condition 2 is: f(Si)>30wt.%; The intermediate alloy composition screening condition 3 is that the semi-solid temperature range ΔT during the solidification process is ≥ 50°C.

4. The method for screening the master alloy according to claim 3, characterized in that: In the screening condition 3, the semi-solid period of the solidification process of the master alloy must meet the solid phase ratio: f(s)=0.2-0.

8.

5. A method for preparing an Al-Si-Mg ternary master alloy based on a semi-solid process, characterized in that: First, raw materials are prepared to meet the mass ratio, and pure Al, pure Si and Al-20Si master alloy are placed in a crucible. Then, the crucible and the master alloy are preheated at a preheating temperature to remove water vapor in the crucible and the alloy. Thereafter, they are heated at a melting temperature. After the pure Al, pure Si and Al-20Si master alloys are melted, surface slag and oxide scale are removed to obtain an aluminum alloy melt. Next, the Al-50Mg master alloy is wrapped with aluminum foil and preheated at a preheating temperature, and the temperature of the aluminum alloy melt is lowered to a semi-solid temperature range. Subsequently, the preheated Al-50Mg master alloy is pressed into the semi-solid aluminum alloy melt. Finally, it is cast at a casting temperature and solidified and cooled to obtain an Al-Si-Mg ternary master alloy prepared by a semi-solid method.

6. The preparation method according to claim 5, characterized in that: The preheating temperature of the crucible and the master alloy is 200-400°C; The melting temperature of the master alloy is 900-1200°C; The casting temperature of the master alloy is 800-1000°C.

7. A method for preparing a cast Al-Si-Mg alloy using a ternary master alloy as raw material, characterized in that The method comprises the following steps: firstly, weighing pure Al and an intermediate alloy so as to meet a mass ratio condition, placing the pure Al into a crucible, then preheating the crucible at a preheating temperature to remove moisture in the crucible and the alloy, then heating at a melting temperature, removing surface slag and oxide scale after the pure Al is melted, then wrapping the intermediate alloy with aluminum foil and preheating it at a preheating temperature, pressing the preheated intermediate alloy into the pure Al melt, fully stirring it for a stirring time, then standing it at the melting temperature for 1 hour, fully stirring it every 20 minutes during the standing process, then adjusting the casting temperature, casting the melt into a permanent mold preheated at the preheating temperature, solidifying and cooling it, thereby obtaining a cast Al-Si-Mg alloy.

8. The preparation method according to claim 7, characterized in that: The preheating temperature of the crucible and raw materials is 200-400°C; The melting temperature of the cast Al-Si-Mg alloy is 750-850°C; The casting temperature of the Al-Si-Mg alloy is 700-750°C.

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