A method for removing iron from Al-Si alloys by precise temperature control without introducing new impurities

Abstract

The invention discloses a method for removing iron without introducing new impurities by precise temperature control for Al-Si alloys. After the free Fe element in the Al-Si alloy melt is converted into a solid Fe-rich phase by adjusting the Si content, the Fe-rich phase is allowed to settle to the bottom of the melt based on a gravity sedimentation method, thereby reducing the iron content in the Al-Si alloy without introducing new impurity elements. The Fe content in the Al-Si alloy is 1.0-1.4wt.%, the condition for adjusting the Si content is that the Si content after adjustment is 7.9-13.3wt.%, the Fe-rich phase is β-AlFeSi, the holding temperature is 593-613°C, and the iron removal rate is 24.0-27.0%. The preparation method comprises the following steps: 1. preparation of the Al-Si alloy melt, 2. precise temperature control and iron removal operation of the Al-Si alloy. The invention has the following advantages: 1. The technical solution of the invention does not need to introduce new impurity elements, such as Mn and Sn, thereby reducing production costs; 2. The temperature range for precise temperature control is determined by thermodynamic calculations; 3. The invention has a simple operating process and relatively low requirements on equipment.

Description

Technical Field

[0001] The invention relates to the field of nonferrous metal materials and metallurgy, and in particular to a method for removing iron from Al-Si alloys by precisely controlling the temperature without introducing new impurities. Background Art

[0002] Al-Si alloy has the advantages of low density, low linear expansion coefficient, good dimensional stability and wear resistance. It is widely used in aerospace, automobile, electronic and electrical fields. Fe is the main impurity element in Al-Si alloy. Its source can be mainly divided into three aspects: (1) Aluminum ore itself contains a certain amount of iron; (2) During the processing of aluminum alloy, the iron element in the iron tool penetrates into the aluminum melt; (3) The continuous accumulation of iron in the recycling process of recycled aluminum. Fe usually exists in Al-Si alloy in the form of intermetallic compounds such as α-AlFeSi phase and β-AlFeSi phase. When the casting is subjected to stress, it cuts the matrix and becomes the crack source and expansion source of the crack, which significantly affects the mechanical properties of the alloy. If the iron content increases from 0.25wt.% to 1.00wt.%, the elongation of the aluminum alloy will be reduced by 40-75%.

[0003] At present, the ways to reduce the harm of Fe-rich phase can be divided into two categories:

[0004] The first type is to reduce the harmfulness of the iron content to the alloy by changing the morphology of the Fe-rich phase inside the aluminum alloy. Neutralizing elements, such as Mn, are usually added to replace the Fe in β-AlFeSi, so that the needle-shaped β-AlFeSi phase is transformed into a skeletal α-Al(Mn,Fe)Si phase. However, this method only changes the morphology of the Fe-rich phase and cannot reduce the iron content to a large extent. When the iron content increases to a certain value, it will restrict the recycling value of the recycled aluminum alloy. In addition, this method not only increases the production cost, but also introduces new elements. When the neutralizing element is added excessively, the mechanical properties of the alloy will also decrease.

[0005] The second type is to reduce the iron content inside the aluminum alloy. It is generally believed that when the iron content is less than the critical value (0.6wt.%), the Fe-rich phase will transform from the β-AlFeSi phase to the α-AlFeSi phase, which has less harm to the mechanical properties. This method essentially weakens the harmfulness of the Fe-rich phase, which is conducive to the development of high-performance Al-Si alloys and the recycling of recycled aluminum.

[0006] Common ways to reduce iron levels include:

[0007] 1. Centrifugal separation method: the technical problem of this method is that the operation is complicated and continuous processing is not possible;

[0008] 2. Electromagnetic separation method: the technical problem of this method is that it has too high requirements on equipment, resulting in high production costs;

[0009] 3. Filtration method: the technical problem of this method is that the iron removal effect is greatly affected by the size of the Fe-rich phase;

[0010] 4. Solvent method: the technical problem of this method is that it will introduce new impurity elements and affect the quality of alloy melt;

[0011] 5. Gravity sedimentation method: It achieves iron removal effect through physical sedimentation method, and the operation process is simple and the cost is low.

[0012] The basic principle of the gravity sedimentation method is that the density of the Fe-rich phase in the aluminum alloy melt is greater than that of the aluminum melt. When left stationary at a certain temperature, the Fe-rich phase settles downward under the action of its own gravity and overcomes the adhesion of the aluminum alloy melt, thereby reducing the iron content in the upper part of the melt.

[0013] For example, existing document 1 (Natural sedimentation iron removal process of aluminum-silicon-titanium alloy [J]. Journal of Luoyang Institute of Technology, 1999, (3): 5-7.) removes the iron content in high-iron Al-Si-Ti alloy by gravity sedimentation, and keeps the alloy melt at 720℃, 670℃, and 620℃ for 0.5h, 3h, 5h, and 7h respectively. However, the research results show that the amount of Fe-rich phase in the upper and lower samples of the alloy is almost unchanged. This technical solution shows that it is impossible to effectively reduce the iron content by gravity sedimentation alone without introducing new impurity elements. The reason for the above technical problems is that when the Fe-rich phase in the alloy melt precipitates simultaneously with other phases, the Fe-rich phase is difficult to settle to the bottom.

[0014] In order to achieve iron removal, a common solution in this field is to combine the solvent method and the gravity sedimentation method.

[0015] For example, the existing literature 2 (Effect of Mn / Fe ratio on Fe removal efficiency and tensile ductility of an Al-7.0Si-2.4Fe alloy[J].Journal of Materials Research, 2021, 36:1357-1366.) introduces Mn element to adjust the Mn / Fe mass ratio and promote the primary α-Al 15 (FeMn) 3 Si 2 The formation of Fe-rich phase is beneficial to the gravity sedimentation and removal of Fe-rich phase, thereby ultimately improving the iron removal efficiency of Al-7Si-2.4Fe alloy.

[0016] For example, the previous research results of the research group of the present invention, the existing document 3 (CN115233016B, a method for removing iron from aluminum melt based on Al-50Sn alloy) and the existing document 4 (CN115233004B, a method for removing iron from Al-Si alloy based on Al-50Sn alloy) introduce the Sn element to form a Sn phase attached to the Fe-rich phase, and it exists stably at high temperature without decomposition, thereby promoting the precipitation of the Fe-rich phase and gathering at the bottom, achieving the iron removal effect, and the iron removal rate reaches 29.0-43.0%.

[0017] Although the technical solutions of the above-mentioned existing documents 2, 3 and 4 can effectively reduce the iron content, they all have the problem of introducing new impurity elements.

[0018] Therefore, through the above analysis of the prior art, it can be seen that the technical problem to be solved is that the iron content cannot be reduced by simply using the gravity sedimentation method without introducing new impurity elements. Summary of the invention

[0019] The purpose of the present invention is to provide a method for removing iron from Al-Si alloy by precise temperature control without introducing new impurities. In view of the technical problems existing in the prior art, the following methods are adopted to solve the above problems:

[0020] 1. Si is easy to react with Fe to form Fe-rich phase. Increasing Si content can transform the free Fe element in the Al-Si alloy melt into a solid Fe-rich phase, and the solidified primary phase transforms from α-Al phase to Fe-rich phase. The isothermal cross-section diagrams and equilibrium solidification paths of Al-Si-Fe alloys with different Si contents at different temperatures are calculated through the Al-Si-Fe thermodynamic database, and then the type and content of the precipitated Fe-rich phase and the precipitation temperature range are obtained.

[0021] 2. Al-Si alloys with different compositions are obtained by increasing the Si content, and the temperature of the alloy melt is maintained at 800°C. Then, according to the thermodynamic calculation results and the DSC curve results measured by differential scanning calorimetry, the alloy melt is cooled from 800°C and kept at a certain temperature for a period of time. The Fe-rich phase is affected by its own gravity and overcomes the adhesion of the alloy melt to settle downward and accumulate at the bottom of the melt, thereby purifying the upper part of the alloy melt and making it lower than the iron content in the initial Al-Si alloy melt.

[0022] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme:

[0023] A method for removing iron from an Al-Si alloy by precise temperature control without introducing new impurities. The Al-Si alloy is an aluminum alloy with a high Fe content. The Si content is adjusted to convert the free Fe element in the Al-Si alloy melt into a solid Fe-rich phase. Based on a gravity sedimentation method, the alloy melt is controlled to stand at a certain temperature for a period of time to allow the Fe-rich phase to settle to the bottom of the melt, thereby reducing the iron content in the Al-Si alloy without introducing new impurity elements, and obtaining the Al-Si alloy after precise temperature control and iron removal.

[0024] In the Al-Si alloy, the Fe content is 1.0-1.4wt.%, and the condition for adjusting the Si content is that the Si content after adjustment is 7.9-13.3wt.%;

[0025] The Fe-rich phase is β-AlFeSi;

[0026] The insulation temperature is 593-613°C and the insulation time is 50-70min;

[0027] The iron removal rate is 24.0-27.0%.

[0028] A method for removing iron from Al-Si alloy by precise temperature control without introducing new impurities comprises the following steps:

[0029] Step 1, preparation of Al-Si alloy melt, first, adjusting the Si content after adjustment to meet a certain quality range, using Al-Si alloy with high Fe content as Al-Si alloy to be deironed, then taking Si as deironing agent, and then, under certain conditions, first heating and melting the Al-Si alloy, then adding Si and completely melting it, to obtain Al-Si alloy melt;

[0030] In the step 1, the adjusted Si content is in the range of 7.9-13.3wt.%, and the heating temperature for heating and melting is 800°C;

[0031] Step 2, precise temperature-controlled iron removal of the Al-Si alloy, under certain conditions, the Al-Si alloy melt obtained in step 1 is furnace-cooled to a temperature for precise temperature-controlled iron removal to perform precise temperature-controlled iron removal, after iron removal, it is cooled to room temperature in air to obtain the Al-Si alloy after the iron removal operation, and finally, the Al-Si alloy after the iron removal operation is cut from the bottom to complete the iron removal of the Al-Si alloy, and the remaining part after the cutting is the Al-Si alloy after the precise temperature-controlled iron removal;

[0032] In step 2, the conditions for precise temperature control for iron removal are: the temperature for precise temperature control for iron removal is 593-613° C., and the static holding time for precise temperature control for iron removal is 50-70 min;

[0033] The cutting condition is to cut off 1 / 6 of the distance from the bottom of the Al-Si alloy, and the remaining 5 / 6 after cutting is the Al-Si alloy after precise temperature control and iron removal.

[0034] The technical effects of the present invention have been tested experimentally, and the specific contents are as follows:

[0035] Thermodynamic calculations of the present invention show that the precipitation end temperature of the primary solidification phase β-AlFeSi of the Al-10Si-1.3Fe alloy is 594.1°C.

[0036] The present invention has been proved by DSC test that the precipitation end temperature of the solidified primary phase of the Al-10Si-1.3Fe alloy is 593.0°C, which proves that the thermodynamic calculation result is consistent with the experimental result.

[0037] The iron removal effect of the iron removal method of the present invention is known from ICP test. By increasing the Si content and controlling the insulation temperature of the alloy melt, that is, accurately controlling the temperature so that the Fe-rich phase settles to the bottom of the melt, the iron removal effect is achieved, and the iron removal rate is 24.0-27.0%.

[0038] The iron removal effect of the iron removal method of the present invention can be known from metallographic structure testing, which also proves that increasing the Si content and controlling the insulation temperature of the alloy melt, that is, accurately controlling the temperature so that the Fe-rich phase settles to the bottom of the melt, can achieve the iron removal effect.

[0039] The present invention uses Image Pro Plus software to count the proportion of the Fe-rich phase area in the metallographic organization diagram to the total image area, which also proves that increasing the Si content and controlling the insulation temperature of the alloy melt, that is, accurately controlling the temperature to make the Fe-rich phase settle to the bottom of the melt, can achieve the iron removal effect.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] 1. The technical solution of the present invention does not require the introduction of new impurity elements for iron removal.

[0042] 1.1. The basic principle is to increase the Si content to transform the free Fe element in the Al-Si alloy melt into a solid Fe-rich phase, and transform the solidified primary phase from the α-Al phase to the Fe-rich phase. Combined with the gravity sedimentation method, the Fe-rich phase is settled to the bottom of the melt, reducing the iron content in the upper part of the melt. Since no new impurity elements are introduced, the quality of the alloy melt is guaranteed;

[0043] 1.2. Since there is no need to introduce new impurity elements, such as Mn and Sn, the production cost is reduced;

[0044] 2. Through thermodynamic calculation, determine the temperature range for precise temperature control and achieve the precipitation of Fe-rich phase to obtain the iron removal effect. The specific principle is:

[0045] 2.1. Calculate the precipitation temperature range of the primary Fe-rich phase. Below this temperature range, the Fe-rich phase precipitates simultaneously with other phases.

[0046] 2.2. Above this temperature range, the alloy is in liquid phase and there is no Fe-rich phase.

[0047] Therefore, if the precise temperature control temperature exceeds the temperature of the present invention, the effect of the Fe-rich phase settling to the bottom of the alloy cannot be achieved.

[0048] 3. The operation process of the present invention is simple and has low requirements on equipment.

[0049] Therefore, compared with the prior art, the present invention has a simple operation process and has higher alloy melt quality after iron removal operation, reduces production costs, meets application requirements and production requirements, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The isothermal cross-section diagram of the Al-Si-Fe system at 600°C calculated by the present invention and the equilibrium solidification path of the alloy in Example 1 are shown in FIG. Figure 1 a is the isothermal cross section diagram, Figure 1 b is the equilibrium solidification path;

[0051] Figure 2 The isothermal cross-section diagram of the Al-Si-Fe system at 600°C calculated by the present invention and the equilibrium solidification path of the alloy of Comparative Example 1 are shown in FIG. Figure 2 a is the isothermal cross section diagram, Figure 2 b is the equilibrium solidification path;

[0052] Figure 3 The isothermal cross-section diagram of the Al-Si-Fe system at 595°C calculated by the present invention and the equilibrium solidification path of the alloy in Example 2 are shown in FIG. Figure 3 a is the isothermal cross section diagram, Figure 3 b is the equilibrium solidification path;

[0053] Figure 4 The isothermal cross-section diagram of the Al-Si-Fe system at 620°C calculated by the present invention and the equilibrium solidification path of the alloy of comparative example 2 are shown in FIG. Figure 4 a is the isothermal cross section diagram, Figure 4 b is the equilibrium solidification path;

[0054] Figure 5 The DSC curve of the alloy of Example 1 measured by differential scanning calorimetry of the present invention;

[0055] Figure 6 The curves of alloy iron content changing with height in Example 1, Comparative Example 1, Example 2 and Comparative Example 2 of the present invention are shown;

[0056] Figure 7This is the metallographic structure diagram of the alloy in Example 1 of the present invention. Figure 7 a is the metallographic structure at 4.5cm. Figure 7 b is the metallographic structure at 1.0 cm;

[0057] Figure 8 This is the metallographic structure diagram of the alloy of comparative example 1 of the present invention, Figure 8 a is the metallographic structure at 4.5cm. Figure 8 b is the metallographic structure at 1.0 cm;

[0058] Fig. 9 This is the metallographic structure diagram of the alloy in Example 2 of the present invention. Fig. 9 a is the metallographic structure at 4.5cm. Fig. 9 b is the metallographic structure at 1.0 cm;

[0059] Fig.10 This is the metallographic structure diagram of the alloy of comparative example 2 of the present invention, Fig.10 a is the metallographic structure at 4.5cm. Fig.10 b is the metallographic structure at 1.0 cm. DETAILED DESCRIPTION

[0060] The present invention is further described in detail through embodiments and in conjunction with the accompanying drawings, but the present invention is not limited thereto.

[0061] Note 1: In order to facilitate the evaluation of the iron removal rate, the Fe content of the Al-Si alloy involved in the present invention is unified to 1.3wt.%; at the same time, in order to meet the requirements of the control variables, Al-10Fe is additionally added in Example 1, but it is not necessary to add it in the actual iron removal process.

[0062] Note 2: According to the thermodynamic calculation results, when the Si content of the Al-Si alloy with an Fe content of 1.3wt.% increases to 7.9-13.3wt.%, the primary phase of the alloy solidification transforms from the α-Al phase to the Fe-rich phase.

[0063] In order to demonstrate the effect of increasing Si content on the primary phase transformation of Al-Si alloy during solidification, the initial Si content of the Al-Si alloy was 7wt.%, and the Si content of the Al-Si alloy after increasing Si content was 10wt.%.

[0064] In order to facilitate the distinction between various alloys and their basic information involved in various embodiments and comparative examples, Table 1 is provided.

[0065] Table 1 Alloy compositions and corresponding holding temperatures of the examples and comparative examples

[0066]

[0067] According to the Al-Si-Fe thermodynamic database, the isothermal cross-sectional phase diagrams of the corresponding alloys of Example 1, Comparative Example 1, Example 2 and Comparative Example 2 at their respective holding temperatures were obtained by thermodynamic calculation. The specific phase diagrams are shown in FIG. Figure 1 a. Figure 2 a. Figure 3 a and Figure 4 As shown in a, the phase region of Al-7Si-1.3Fe alloy at 600℃ is L 1 The three-phase region on the left side of the line (Liquid+α-Al+β-AlFeSi); after increasing the Si content, the phase region of the Al-10Si-1.3Fe alloy at 595℃ and 600℃ is L 1 The two-phase region on the right side of the line (Liquid + β-AlFeSi); the phase region where the Al-10Si-1.3Fe alloy is located at 620°C is a single-phase region (Liquid).

[0068] The equilibrium solidification path diagrams of the alloys corresponding to Example 1, Comparative Example 1, Example 2 and Comparative Example 2 were obtained by thermodynamic calculation. The specific path diagrams are as follows: Figure 1 b. Figure 2 b. Figure 3 b and Figure 4 As shown in (b), when the Al-7Si-1.3Fe alloy solidifies, the α-Al phase first precipitates at 609.9-613.2°C, and at 600°C, the α-Al phase and β-AlFeSi phase precipitate at the same time; after increasing the Si content, when the Al-10Si-1.3Fe alloy solidifies, the β-AlFeSi phase first precipitates at 594.1-612.8°C; at 595°C and 600°C, the β-AlFeSi phase precipitates alone, and at 620°C the alloy is a single liquid phase without any precipitated phase.

[0069] In order to prove the correctness of the thermodynamic calculation results, the alloy of Example 1 was tested by DSC using differential scanning calorimetry. The test results are as follows: Figure 5 As shown, the precipitation end temperature of the primary phase of the alloy in Example 1 is 593.0°C, which is consistent with the thermodynamic calculation results, that is, Figure 1 b is consistent with the precipitation completion temperature of the solidified primary phase (β-AlFeSi phase) of Example 1 alloy being 594.1°C.

[0070] In order to clarify the mass fraction of the β-AlFeSi phase of each embodiment and comparative alloy at each holding temperature, calculations were performed based on the isothermal cross-section diagram and the equilibrium solidification path, and the results are shown in Table 2.

[0071] Table 2 Mass fraction of β-AlFeSi phase in the embodiment and comparative alloys at respective holding temperatures

[0072]

[0073] Example 1

[0074] A method for removing iron from Al-Si alloy by precise temperature control at a holding temperature of 600°C without introducing new impurities, specifically comprising the following steps:

[0075] Step 1, preparation of Al-10Si-1.3Fe alloy melt, first, take 600g Al-7Si-1.3Fe alloy as Al-Si alloy to be deironed, then take 20.3g Si as deironing agent, at the same time, in order to meet the requirements of control variables, that is, the iron content in the raw material Al-7Si-1.3Fe alloy used in step 1 and the obtained alloy melt is maintained at 1.3wt.%, 3.0g Al-10Fe is additionally added, then, at a heating temperature of 800°C, the Al-7Si-1.3Fe alloy is first heated and melted, and then Si and Al-10Fe are added and completely melted to obtain Al-10Si-1.3Fe alloy melt;

[0076] Step 2, precise temperature-controlled iron removal operation of Al-Si alloy, the temperature of precise temperature-controlled iron removal is 600°C, the static holding time of precise temperature-controlled iron removal is 60 minutes, the Al-10Si-1.3Fe alloy melt obtained in step 1 is furnace-cooled to the temperature of precise temperature-controlled iron removal for precise temperature-controlled iron removal, and after iron removal, it is cooled to room temperature in air to obtain the Al-Si alloy after the iron removal operation, which is named as Example 1 alloy. Finally, the alloy of Example 1 is cut off at 1 / 6 of the bottom to complete the iron removal of the Al-Si alloy. The remaining 5 / 6 after cutting is the Al-Si alloy after precise temperature-controlled iron removal.

[0077] Note 3: The Al-Si alloys obtained after iron removal in all comparative examples and embodiments of the present invention are cylinders with a height of 6.5 cm and a diameter of 6.5 cm.

[0078] Note 4: For the purpose of subsequent testing, the Al-Si alloys after iron removal obtained in all comparative examples and embodiments of the present invention were sampled as follows: the Al-Si alloy after iron removal was cut at 1.0 cm, 2.5 cm and 4.5 cm from the bottom to obtain three cross sections, which were named 1.0 cm, 2.5 cm and 4.5 cm respectively.

[0079] In order to demonstrate the iron removal effect of the iron removal method of the present invention, ICP tests were performed on the alloy of Example 1 at 1.0 cm, 2.5 cm and 4.5 cm. The test results are shown in Tables 3 and Figure 6 As shown, the alloy of Example 1,

[0080] The iron content at 1.0 cm is 1.33 wt.%;

[0081] The iron content at 2.5 cm is 1.05 wt.%;

[0082] The iron content at 4.5 cm was 0.98 wt.%.

[0083] The test results show that the iron content of the Al-10Si-1.3Fe alloy at 4.5cm and 2.5cm decreased, while the iron content at 1.0cm increased. That is, increasing the Si content combined with the gravity sedimentation method achieved the effect of settling the Fe-rich phase to the bottom of the alloy, achieving the iron removal effect.

[0084] In order to quantify the iron removal effect, the change in iron content was calculated.

[0085] The iron content at 4.5cm dropped from 1.30wt.% to 0.98wt.%. After calculation, the iron removal rate can reach 24.6%.

[0086] Table 3 Iron content at different heights in the alloys of the examples and comparative examples

[0087]

[0088] In order to further demonstrate the iron removal effect of the iron removal method of the present invention, metallographic structure tests were performed on the 1.0 cm and 4.5 cm positions of the alloy in Example 1. The test results are as follows: Figure 7 As shown,

[0089] Figure 7 a is the metallographic structure of the alloy of Example 1 at 4.5 cm, with a small amount of Fe-rich phase;

[0090] Figure 7 b is the metallographic structure of the alloy of Example 1 at 1.0 cm, with a large number of Fe-rich phases and large size. According to the principle of metallographic stereology, the content of the phase in the two-dimensional image can be determined based on the percentage of the phase area to the total area of ​​the image. Therefore, the large size of the Fe-rich phase also proves that the content of the Fe-rich phase is high.

[0091] In order to further demonstrate the change of the Fe-rich phase in the metallographic structure diagram of the alloy of Example 1 at 4.5 cm and 1.0 cm by quantitative analysis, the proportion of the Fe-rich phase area in the metallographic structure diagram to the total image area was calculated using Image Pro Plus software. The statistical results were averaged from three images. The results are shown in Table 4.

[0092] The proportion of Fe-rich phase in the metallographic structure at 4.5 cm is 2.10%;

[0093] The proportion of Fe-rich phase in the metallographic structure at 1.0 cm is 4.26%;

[0094] Statistical results show that the proportion of Fe-rich phase at 1.0 cm in the Al-10Si-1.3Fe alloy is higher than that at 4.5 cm. That is, increasing the Si content combined with gravity sedimentation method can achieve the effect of settling the Fe-rich phase to the bottom of the alloy, thereby achieving the iron removal effect.

[0095] Table 4 Proportion of Fe-rich phase in metallographic structure diagrams of different heights of the alloys of the embodiment and the comparative example

[0096]

[0097] Therefore, the metallographic structure test results also support the above conclusions.

[0098] In order to demonstrate the iron removal effect of the iron removal method of the present invention, that is, the technical effect of increasing the Si content and combining the gravity sedimentation method, comparative example 1 is provided, which is an Al-7Si-1.3Fe alloy gravity sedimentation iron removal method without increasing the Si content.

[0099] Comparative Example 1

[0100] A method for treating an Al-7Si-1.3Fe alloy without increasing the Si content, wherein the steps not specifically described are the same as those of Example 1, except that: in Step 1, the weighing and addition of Si and Al-10Fe are not performed, so that an Al-7Si-1.3Fe alloy without increasing the Si content can be obtained, which is named Comparative Example 1 alloy.

[0101] In order to prove the effect of increasing Si content on iron removal, ICP tests were performed on the alloy of Comparative Example 1 at 1.0 cm, 2.5 cm and 4.5 cm. The test results are shown in Table 3 and Figure 6 As shown, the alloy of comparative example 1,

[0102] The iron content at 1.0 cm is 1.07 wt.%;

[0103] The iron content at 2.5 cm is 1.20 wt.%;

[0104] The iron content at 4.5 cm was 1.25 wt.%.

[0105] The test results show that the iron content of the Al-7Si-1.3Fe alloy at 4.5cm, 2.5cm and 1.0cm all decreases, and the decrease rate of the iron content increases with the decrease in height. This experimental phenomenon is different from the alloy in Example 1, which means that if the Si content is not increased, only step 2 cannot achieve the effect of the Fe-rich phase settling to the bottom of the alloy, and the iron removal effect cannot be obtained. The reason is that the primary phase of the Al-7Si-1.3Fe alloy solidification is α-Al phase. Figure 2From the equilibrium solidification path shown in b, it can be seen that when the Al-7Si-1.3Fe alloy melt is cooled from 800℃, the α-Al phase is first precipitated, and when it is cooled to 600℃ and kept warm, the α-Al phase and the β-AlFeSi phase are precipitated together, resulting in a low content of Fe-rich phase in the first solidified part and a high content of Fe-rich phase in the last solidified part. That is, the iron content is low in the part in contact with the bottom, side wall and air of the crucible, and the iron content is high in the center.

[0106] It can be seen from Example 1 and Comparative Example 1 that increasing the Si content can achieve the precipitation of the Fe-rich phase and obtain the iron removal effect.

[0107] In order to further demonstrate the iron removal effect of the iron removal method of the present invention, metallographic structure tests were performed on the alloy of comparative example 1 at 1.0 cm and 4.5 cm. The test results are as follows: Figure 8 As shown,

[0108] Figure 8 a is the metallographic structure of the alloy of comparative example 1 at 4.5 cm, with a large amount of Fe-rich phase;

[0109] Figure 8 b is the metallographic structure of the alloy of comparative example 1 at 1.0 cm, with a small amount of Fe-rich phase.

[0110] In order to further demonstrate the change of Fe-rich phase in the metallographic structure diagram of the alloy of comparative example 1 at 4.5 cm and 1.0 cm through quantitative analysis, the proportion of Fe-rich phase area in the metallographic structure diagram to the total image area was calculated using Image Pro Plus software, and the statistical results were averaged from 3 images. The results are shown in Table 4.

[0111] The proportion of Fe-rich phase in the metallographic structure at 4.5 cm is 4.13%;

[0112] The proportion of Fe-rich phase in the metallographic structure at 1.0 cm is 3.28%;

[0113] The statistical results show that the proportion of Fe-rich phase at 1.0 cm in the Al-7Si-1.3Fe alloy is lower than that at 4.5 cm, that is, without increasing the Si content, the effect of Fe-rich phase settling to the bottom of the alloy cannot be achieved by only using gravity sedimentation method.

[0114] Therefore, the metallographic structure test results also support the above conclusions.

[0115] In order to demonstrate the effect of the process parameters in the gravity sedimentation method, namely the holding temperature, on the iron removal effect, Example 2 and Comparative Example 2 are provided, which are iron removal methods with holding temperatures of 595° C. and 620° C., respectively.

[0116] Example 2

[0117] A method for removing iron from Al-Si alloy by precise temperature control at a holding temperature of 595°C without introducing new impurities, wherein the steps not specifically described are the same as those in Example 1, except that: in step 2, the standing holding temperature is 595°C, and an Al-10Si-1.3Fe alloy with a gravity sedimentation holding temperature of 595°C can be obtained, which is named as Example 2 alloy.

[0118] In order to demonstrate the effect of holding temperature on iron removal, ICP tests were performed on the alloy of Example 2 at 1.0 cm, 2.5 cm and 4.5 cm. The test results are shown in Table 3 and Figure 6 As shown, the alloy of Example 2,

[0119] The iron content at 1.0 cm is 1.35 wt.%;

[0120] The iron content at 2.5 cm is 1.04 wt.%;

[0121] The iron content at 4.5 cm was 0.96 wt.%.

[0122] The test results show that the iron content of the Al-10Si-1.3Fe alloy at 4.5cm and 2.5cm decreased, while the iron content at 1.0cm increased. This experimental phenomenon is the same as that of the alloy in Example 1, but the iron content of the alloy in Example 2 is lower at 4.5cm and higher at 1.0cm, that is, more Fe-rich phases in the alloy in Example 2 settle downward, and the iron removal effect is improved. The reason is that controlling the gravity sedimentation insulation temperature is conducive to allowing more Fe-rich phases to settle downward. Figure 3 From the equilibrium solidification path shown in b, it can be seen that the precipitation temperature range of the primary solidification phase of the Al-10Si-1.3Fe alloy, namely the β-AlFeSi phase, is 594.1-612.8℃, which is consistent with the calculated results. Figure 5 The DSC experimental results shown are consistent. In the precipitation temperature range of the β-AlFeSi phase, a lower holding temperature is conducive to the sedimentation of more Fe-rich phases, thereby improving the iron removal effect. As shown in Table 2, the mass fraction of the β-AlFeSi phase increases from 1.08wt.% in Example 1 to 1.44wt.% in Example 2.

[0123] In order to quantify the iron removal effect, the change in iron content was calculated.

[0124] The iron content at 4.5cm dropped from 1.30wt.% to 0.96wt.%. After calculation, the iron removal rate can reach 26.2%.

[0125] In order to further demonstrate the iron removal effect of the iron removal method of the present invention, metallographic structure tests were performed on the 1.0 cm and 4.5 cm positions of the alloy in Example 2. The test results are as follows: Fig. 9 As shown,

[0126] Fig. 9 a is the metallographic structure of the alloy of Example 2 at 4.5 cm, with a small amount of Fe-rich phase;

[0127] Fig. 9 b is the metallographic structure of the alloy of Example 2 at 1.0 cm, where the Fe-rich phase is large in number and size. This phenomenon also proves that the content of the Fe-rich phase has increased. In addition, the number and size of the Fe-rich phase at 1.0 cm in the alloy of Example 2 are greater than those at the same position in Example 1.

[0128] In order to further demonstrate the change of the Fe-rich phase in the metallographic structure diagram of the alloy of Example 2 at 4.5 cm and 1.0 cm by quantitative analysis, the proportion of the Fe-rich phase area in the metallographic structure diagram to the total image area was calculated using Image Pro Plus software. The statistical results were averaged over 3 images. The results are shown in Table 4.

[0129] The proportion of Fe-rich phase in the metallographic structure at 4.5 cm is 1.81%;

[0130] The proportion of Fe-rich phase in the metallographic structure at 1.0 cm is 4.94%;

[0131] The statistical results show that the proportion of the Fe-rich phase at 1.0 cm of the Al-10Si-1.3Fe alloy is higher than the proportion of the Fe-rich phase at 4.5 cm, that is, increasing the Si content combined with the gravity sedimentation method achieves the effect of settling the Fe-rich phase to the bottom of the alloy, and the iron removal effect is obtained. It can be seen from Examples 1 and 2 that the proportion of the Fe-rich phase at 4.5 cm of the alloy of Example 2 is lower than that at the same position of the alloy of Example 1, and the proportion of the Fe-rich phase at 1.0 cm of the alloy of Example 2 is higher than that at the same position of the alloy of Example 1, that is, controlling the gravity sedimentation insulation temperature is conducive to allowing more Fe-rich phases to settle downward, and the iron removal effect is improved.

[0132] Therefore, the metallographic structure test results also support the above conclusions.

[0133] Comparative Example 2

[0134] A method for treating an Al-10Si-1.3Fe alloy with a holding temperature of 620°C, wherein the steps not specifically described are the same as those in Example 1, except that: in step 2, the standing holding temperature is 620°C, and an Al-10Si-1.3Fe alloy with a gravity sedimentation holding temperature of 620°C can be obtained, which is named as Comparative Example 2 alloy.

[0135] In order to prove the effect of holding temperature on iron removal, ICP tests were performed on the alloy of comparative example 2 at 1.0 cm, 2.5 cm and 4.5 cm. The test results are shown in Table 3 and Figure 6 As shown, the alloy of comparative example 2,

[0136] The iron content at 1.0 cm is 1.34 wt.%;

[0137] The iron content at 2.5 cm is 1.27 wt.%;

[0138] The iron content at 4.5 cm was 1.20 wt.%.

[0139] The test results show that the iron content of the Al-10Si-1.3Fe alloy at 4.5cm and 2.5cm decreased, while the iron content at 1.0cm increased. This experimental phenomenon is the same as that of the alloy in Example 1, but the iron content of the alloy in Comparative Example 2 at 4.5cm and 2.5cm decreased slightly, that is, the Fe-rich phase of the alloy in Comparative Example 2 precipitated less downward, and the iron removal effect decreased. The reason is that the insulation temperature exceeds the precipitation temperature range of the solidified primary phase of the Al-10Si-1.3Fe alloy, that is, the β-AlFeSi phase, which is not conducive to the precipitation of the Fe-rich phase. Figure 4 From the equilibrium solidification path shown in b, it can be seen that the precipitation temperature range of the primary solidification phase of the Al-10Si-1.3Fe alloy, namely the β-AlFeSi phase, is 594.1-612.8℃, which is consistent with the calculated results. Figure 5 The DSC experimental results shown are consistent, exceeding the precipitation temperature range of the β-AlFeSi phase. As can be seen from Table 2, no β-AlFeSi phase is generated, which is not conducive to the precipitation of the Fe-rich phase and the iron removal effect is reduced.

[0140] In order to quantify the iron removal effect, the change in iron content was calculated.

[0141] The iron content at 4.5cm dropped from 1.30wt.% to 1.20wt.%. After calculation, the iron removal rate can reach 7.7%.

[0142] It can be seen from Example 1, Example 2 and Comparative Example 2 that controlling the gravity sedimentation holding temperature at 593-613°C is conducive to the sedimentation of the Fe-rich phase and the iron removal effect. Below this temperature range, due to the generation of α-Al phase, the effect of the Fe-rich phase settling to the bottom of the alloy cannot be achieved; above this temperature range, since the alloy is in liquid phase and there is no Fe-rich phase, the effect of the Fe-rich phase settling to the bottom of the alloy cannot be achieved.

[0143] In order to further demonstrate the iron removal effect of the iron removal method of the present invention, metallographic structure tests were performed on the 1.0 cm and 4.5 cm positions of the alloy of Comparative Example 2. The test results are shown in FIG. Fig.10 As shown,

[0144] Fig.10 a is the metallographic structure of alloy 4.5 cm in comparative example 2; Fig.10b is the metallographic structure of the alloy of comparative example 2 at 1.0 cm. Both alloys have more Fe-rich phases, and the number and size are similar. This phenomenon also proves that the content of Fe-rich phase does not change much.

[0145] In order to further demonstrate the change of Fe-rich phase in the metallographic structure diagram of the alloy of comparative example 2 at 4.5 cm and 1.0 cm through quantitative analysis, the proportion of Fe-rich phase area in the metallographic structure diagram to the total image area was calculated using Image Pro Plus software, and the statistical results were averaged from 3 images. The results are shown in Table 4.

[0146] The proportion of Fe-rich phase in the metallographic structure at 4.5 cm is 4.09%;

[0147] The proportion of Fe-rich phase in the metallographic structure at 1.0 cm is 4.47%;

[0148] The statistical results show that the proportion of Fe-rich phase at 1.0 cm of Al-10Si-1.3Fe alloy is higher than that at 4.5 cm, but the difference between the two is not large. It can be seen from Example 1, Example 2 and Comparative Example 2 that the proportion of Fe-rich phase at 4.5 cm of the alloy in Comparative Example 2 is higher than that at the same position of the alloys in Example 1 and Example 2, that is, controlling the gravity sedimentation insulation temperature at 593-613°C is conducive to the sedimentation of the Fe-rich phase and obtaining the iron removal effect. Beyond this temperature range, the iron removal effect decreases.

[0149] Therefore, the metallographic structure test results also support the above conclusions.

[0150] Based on the test results of Example 1, Comparative Example 1, Example 2 and Comparative Example 2, the following conclusions can be drawn:

[0151] 1. By increasing the Si content, the free Fe element in the Al-Si alloy melt can be transformed into a solid Fe-rich phase, and the primary solidification phase changes from the α-Al phase to the Fe-rich phase. At 600°C, the primary solidification phase of the Al-7Si-1.3Fe alloy is the α-Al phase, while the primary solidification phase of the Al-10Si-1.3Fe alloy is the β-AlFeSi phase. The change in the sequence of the primary solidification phases of the alloy is conducive to the downward sedimentation of more Fe-rich phases, thereby reducing the iron content in the upper part of the alloy and obtaining an iron removal effect.

[0152] 2. Controlling the gravity sedimentation temperature at 593-613℃ is conducive to the sedimentation of more Fe-rich phases, thereby purifying the upper part of the alloy melt and achieving iron removal. When the Al-10Si-1.3Fe alloy melt was kept at 595℃ for 1 hour, the iron content at 4.5cm dropped from 1.30wt.% to 0.96wt.%, and the iron removal rate was 26.2%.

Claims

1. A method for removing iron from Al-Si alloy by precise temperature control without introducing new impurities, characterized in that: The Al-Si alloy is an Al-Si alloy with a high Fe content. After the free Fe element in the Al-Si alloy melt is converted into a solid Fe-rich phase by adjusting the Si content, the alloy melt is controlled to stand at a certain temperature for a period of time based on a gravity sedimentation method so that the Fe-rich phase settles to the bottom of the melt, thereby reducing the iron content in the Al-Si alloy without introducing new impurity elements, and obtaining the Al-Si alloy after precise temperature control and iron removal; In the Al-Si alloy with high Fe content, the Fe content is 1.0-1.4wt.%, and the condition for adjusting the Si content is that the Si content after adjustment is 7.9-13.3wt.%; The iron removal method specifically comprises the following steps: Step 1, preparation of Al-Si alloy melt, firstly heating and melting Al-Si alloy with high Fe content, then adding Si and completely melting it, to obtain Al-Si alloy melt; Step 2, precise temperature-controlled iron removal of the Al-Si alloy, cooling the Al-Si alloy melt obtained in step 1 to a precise temperature-controlled iron removal temperature with the furnace to perform precise temperature-controlled iron removal, and after iron removal, cooling in air to room temperature to obtain the Al-Si alloy after the iron removal operation, and finally, cutting the Al-Si alloy after the iron removal operation from the bottom to complete the iron removal of the Al-Si alloy, and the remaining part after the cutting is the Al-Si alloy after the precise temperature-controlled iron removal; In step 2, the conditions for precise temperature control for iron removal are: the temperature for precise temperature control for iron removal is 593-613° C., and the static holding time for precise temperature control for iron removal is 50-70 min; The cutting condition is to cut off 1 / 6 of the distance from the bottom of the Al-Si alloy, and the remaining 5 / 6 after cutting is the Al-Si alloy after precise temperature control and iron removal.

2. The iron removal method according to claim 1, characterized in that: The Fe-rich phase is β-AlFeSi.

3. The iron removal method according to claim 1, characterized in that: The iron removal rate is 24.0-27.0%.

4. The iron removal method according to claim 1, characterized in that: In the step 1, the heating temperature for heating and melting is 800°C.

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