A method for casting an aluminum alloy to remove fe elements

Abstract

The present application relates to a method for casting aluminum alloy to remove Fe elements, comprising the following steps: (1) obtaining a first melt at a first temperature; (2) sampling the first melt and analyzing the element content; (3) calculating the amount of Fe-rich phase precipitant; (4) adding the Fe-rich phase precipitant to the first melt and maintaining the temperature to obtain a second melt; (5) adding a refining agent to the second melt to obtain a third melt; (6) calculating the alpha-Al phase starting precipitation temperature; (7) cooling the third melt to produce Fe-rich phase particles and maintaining the temperature to obtain a fourth melt; (8) cooling the fourth melt to obtain an ingot blank; (9) sawing the ingot blank to obtain a purified ingot blank and a Fe-rich phase deposition layer. The method of the present application improves the Fe removal efficiency of the ingot blank, the Fe removal effect is remarkable; the final obtained purified ingot blank has large weight and high purity; and the production efficiency is taken into account, and the overall production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of metallurgy. Specifically, it relates to the field of waste aluminum purification and recycled aluminum production technology, and more particularly to a method for removing Fe element from cast aluminum alloys, especially a method for efficiently removing Fe element impurities from waste cast aluminum alloys. Background Technology

[0002] Recycled aluminum, as a green, environmentally friendly, energy-saving, and consumption-reducing product, can provide sufficient resource security for the sustainable development of my country's future aluminum alloy market. Therefore, the scientific development of the recycled aluminum industry is of great significance. However, due to the complex sources of waste aluminum and the difficulty of pretreatment, a large number of impurity elements are inevitably mixed in during the repeated recycling process to produce recycled aluminum. Among these, the harmful effects of the impurity Fe element are the most significant, seriously affecting the quality of recycled aluminum.

[0003] Current methods for reducing the harmful effects of Fe impurities mainly involve two steps. The first step is modification treatment, which involves adding chemical elements or using special processes to alter the morphology of the Fe-rich phase. Added elements include Mn, Cr, Be, Co, Mo, Ni, W, Sr, or rare earth elements such as Y, La, and Ce. The second step uses physical methods, utilizing the different physicochemical properties between the Fe-rich phase and the melt to remove the Fe-rich phase. These methods include gravity separation, centrifugal separation, gravity sedimentation, and flux refining. These methods have varying degrees of effectiveness in separating the Fe-rich phase, resulting in different qualities of purified aluminum recovered. However, these separation methods remain in the laboratory research stage and have not yet achieved large-scale industrial application.

[0004] Among these separation methods, gravity sedimentation utilizes the density difference between the Fe-rich phase and the molten aluminum alloy to cause the Fe-rich phase to deposit at the bottom of the melt, thereby reducing the Fe content in the melt. Relatively speaking, it is simple, feasible, and easy to industrialize. However, the current challenge lies in determining the appropriate temperature range, cooling rate, and holding time for effective precipitation of the Fe-rich phase, ensuring efficient and sufficient precipitation and sedimentation, thus minimizing the Fe content in the melt.

[0005] Existing patent CN111032890A discloses the initial Fe element content (greater than 0.20 wt.%) and Mn element content (not greater than 1.8 wt.%) of the alloy, as well as the temperature range for melt cooling (greater than 10°C). However, it does not disclose the melt cooling rate and requires additional Fe removal measures, as the melt viscosity increases after cooling, posing difficulties for industrial implementation. Existing patent CN111020255B discloses the alloy composition, the temperature range for Fe-rich phase precipitation (590–700°C), and the cooling rate (0.1–1°C / min), but it requires the addition of elements such as V and Cr. The Fe removal process introduces foreign impurities, increasing the difficulty of alloy recycling. Existing patent CN111254303B discloses the Mn / Fe mass ratio (0.6~1.2) and the temperature range for Fe-rich phase precipitation (630~680℃), but it requires heating the recycled aluminum alloy melt to 700~720℃ before adding element B. On the one hand, heating will cause the Fe-rich phase to remelt, and on the other hand, adding element B will increase the melt viscosity, reducing the efficiency of Fe-rich phase precipitation and removal. Summary of the Invention

[0006] Therefore, the purpose of this invention is to provide a method for efficiently removing Fe from waste cast aluminum alloys suitable for industrial applications, which can obtain purified low-Fe content recycled cast aluminum alloy raw materials after removing Fe from waste cast aluminum alloy melt.

[0007] To achieve the above objective, according to a first aspect of the present invention, the present invention provides a method for removing Fe element from cast aluminum alloys, comprising the following steps:

[0008] (1) The cast aluminum alloy is melted at a first temperature of 700-780°C to obtain a first melt.

[0009] (2) Sample and analyze the first melt obtained in step (1) to obtain the Fe, Si and Mn content of the cast aluminum alloy;

[0010] (3) Calculate the amount of Fe-rich phase precipitant based on the Si and Mn content obtained in step (2), wherein the Fe-rich phase precipitant is an Al-Mn master alloy.

[0011] (4) Add Fe-rich phase precipitant to the first melt obtained in step (1) and maintain it at the first temperature for a first time to obtain the second melt, wherein the first time is 10 to 30 min;

[0012] (5) Add a refining agent to the second melt obtained in step (4), and continue to pass inert gas at the first temperature for joint refining. Let it stand for a second time and remove the scum to obtain a third melt, wherein the second time is 10 to 30 minutes and the mass of the refining agent is 0.2 to 0.5% of the mass of the second melt.

[0013] (6) Calculate the precipitation temperature of the α-Al phase based on the element content obtained in step (2).

[0014] (7) Cool the third melt treated in step (5) to a second temperature at a first cooling rate to produce Fe-rich phase particles, and hold for a third time to obtain a fourth melt;

[0015] (8) Cool the fourth melt obtained in step (7) to a third temperature at a second cooling rate to obtain an ingot, wherein the third temperature is below 200°C and the second cooling rate is greater than or equal to 10°C / s;

[0016] (9) Starting from the bottom of the billet, the billet is sawn to a first length to obtain a first ingot as a purified billet and a second ingot as an Fe-rich phase deposition layer, wherein the first length is 1 to 20% of the total length of the billet; characterized in that:

[0017] The content of Fe-rich phase precipitant makes the mass ratio of Si:Mn in the second melt 3.0 to 9.0, the first cooling rate 0.02 to 10 °C / s, the second temperature within the range of ±50 °C of the α-Al phase precipitation start temperature calculated in step (6), and the third time 10 to 120 min.

[0018] Furthermore, the content of the Fe-rich phase precipitant makes the Si:Mn mass ratio in the second melt 3.0 to 4.0, preferably 3.16, 3.22, 3.54, 3.66 or 3.68; the first cooling rate is 0.02 to 10 °C / s, preferably 0.023 to 1.3 °C / s, more preferably 0.023 °C / s or 1.3 °C / s; the second temperature is within the range of ±45 °C of the Fe-rich phase precipitation temperature calculated in step (6), preferably 620 °C, 640 °C or 660 °C; and the third time is 10 to 60 min, preferably 10 to 30 min, more preferably 10 min, 30 min or 60 min.

[0019] Furthermore, the Mn content in the Al-Mn master alloy is 5–20 wt.%.

[0020] Furthermore, a degassing machine is used to degas and refine the product by introducing inert gas, with a blowing rate of 500–2000 ml / min.

[0021] Furthermore, step (7) is performed without stirring the melt, and the residual Mn content in the fourth melt is less than 0.6 wt.%.

[0022] Further, step (8) is carried out without stirring the melt, and the second cooling rate is 15-30°C / s, preferably 20°C / s or 10°C / s.

[0023] Further, the initial Fe content in the cast aluminum alloy is at least 0.5 wt.%; preferably, the Fe content of the cast aluminum alloy is 0.5–4.0 wt.%, the Si content is 7.0–15.0 wt.%, and the Mn content is 0–0.8 wt.%, with the remainder being Al; optionally, the Ni content of the cast aluminum alloy is 0–1.0%, the Sn content is 0–0.5 wt.%, the Mg content is 0–6.0 wt.%, the Cu content is 0–6.0 wt.%, the Zn content is 0–6.0 wt.%, the Ti content is 0–0.3 wt.%, and the remaining individual impurity elements are ≤0.05 wt.%, with the remainder being Al.

[0024] Furthermore, compared to cast aluminum alloy, the Fe content of the first ingot is reduced by 40-70%, and the weight of the first ingot is more than 80% of the weight of the cast aluminum alloy.

[0025] The present invention provides a method for removing Fe from cast aluminum alloys. By utilizing the initial Fe content in the cast aluminum alloy and adjusting the Si:Mn mass ratio, a sufficient number of primary Fe-rich phases are promoted to form in the melt. The solubility of the Fe-rich phase in the melt is controlled by controlling the melt temperature, thereby controlling the theoretical precipitation amount. The precipitation of the Fe-rich phase is accelerated by controlling the melt cooling rate. Furthermore, the size and sedimentation process of the Fe-rich phase are controlled by controlling the melt holding time. This method improves the Fe removal efficiency of the ingot, resulting in a significant Fe removal effect. The final purified ingot has a large weight and high purity. It also balances production efficiency and reduces overall production costs. Attached Figure Description

[0026] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0027] Figure 1 A flowchart of a method for removing Fe from cast aluminum alloys according to the present invention is shown.

[0028] Figure 2 The cooling curves of the melt at a first cooling rate of 0.023 °C / s are shown.

[0029] Figure 3 The cooling curves of the melt at a first cooling rate of 1.3 °C / s are shown.

[0030] Figure 4 The cooling curves of the melt at a first cooling rate of 3.2 °C / s are shown.

[0031] Figure 5 The cooling curves of the melt at a first cooling rate of 5.6 °C / s are shown.

[0032] Figure 6 The cooling curves of the melt at a first cooling rate of 30.8 °C / s are shown.

[0033] Figure 7 The image shows the microstructure of purified aluminum ingots produced when the melt was cooled from 760°C to 620°C at a cooling rate of 0.023°C / s and held for 60 min.

[0034] Figure 8 The image shows a microstructure of the Fe-rich phase deposited layer in the ingot after the melt was cooled from 760°C to 620°C at a cooling rate of 0.023°C / s and held for 60 min. Detailed Implementation

[0035] The following description is presented to enable those skilled in the art to obtain and use various embodiments. Descriptions of specific apparatuses, technologies, and applications are provided by way of example only. Various modifications to the embodiments described herein will be apparent to those skilled in the art, and the general principles defined herein can be applied to other instances and applications without departing from the scope of the various embodiments. Therefore, the various embodiments are not intended to be limited to the examples described and shown herein, but are consistent with the scope of the claims. It should be noted that, without conflict, the embodiments and features in the embodiments of this application can be combined with each other. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0036] As described in the background section, existing technologies have slow cooling rates, and sometimes require the addition of other elements, which introduces foreign impurities and increases the difficulty of alloy recycling. Furthermore, some methods require reheating the melt, leading to the remelting of the Fe-rich phase, which reduces production efficiency.

[0037] Due to the aforementioned problems, it is necessary to modify the traditional method for removing Fe from cast aluminum alloys in order to increase the weight of the final purified ingot, improve the Fe removal effect, and simultaneously improve production efficiency and reduce production costs.

[0038] The embodiments of the present invention provide a flowchart of a method for removing Fe elements from cast aluminum alloys.

[0039] Now refer to Figure 1 , Figure 1 A flowchart of a method for removing Fe from cast aluminum alloys according to the present invention is shown. Figure 1 In step (1), the cast aluminum alloy is melted at a first temperature to obtain a first melt. The first temperature can also be called the melting temperature, which depends on the composition of the cast aluminum alloy and is usually 700 to 780°C. In one embodiment, the first temperature (melting temperature) is 760°C.

[0040] In step (2) (not shown), the first melt obtained in step (1) is sampled and analyzed to obtain the Fe, Si, and Mn content of the cast aluminum alloy. In one embodiment, the Ni, Sn, Mg, Cu, Zn, Ti, and other possible impurity elements of the cast aluminum alloy are also obtained.

[0041] In step (3) (not shown), the amount of Fe-rich phase precipitant is calculated based on the Si and Mn content obtained in step (2), wherein the Fe-rich phase precipitant is an Al-Mn master alloy. The composition of the aluminum alloy determines whether a primary Fe-rich phase forms in the melt. In one embodiment, the cast aluminum alloy has an Fe content of 0.5–4.0 wt.%, a Si content of 6.0–15.0 wt.%, and a Mn content of 0–1.0 wt.%. In one embodiment, the cast aluminum alloy contains 0.5–4.0 wt.% Fe, 6.0–15.0 wt.% Si, 0–1.0 wt.% Mn, 0–1.0 wt.% Ni, 0–0.5 wt.% Sn, 0–6.0 wt.% Mg, 0–6.0 wt.% Cu, 0–6.0 wt.% Zn, 0–0.3 wt.% Ti, and ≤0.05 wt.% of other individual impurity elements; importantly, the initial Fe content in the cast aluminum alloy is at least 0.5 wt.%. Since the elemental content in the first melt may not meet the requirements of subsequent operations, it is necessary to limit the range of Si, Mn, and Fe elements that promote the precipitation of primary Fe-rich phases in order to form a sufficient quantity of primary Fe-rich phases in the melt. Sufficient quantity of primary Fe-rich phases in the melt is promoted by adding Fe-rich phase precipitants to adjust the Si:Mn mass ratio. Therefore, in one embodiment, the content of the Fe-rich phase precipitant results in a Si:Mn mass ratio of 3.0 to 9.0 in the second melt. In one embodiment, the content of the Fe-rich phase precipitant results in a Si:Mn mass ratio of 3.0 to 4.0 in the second melt. In one embodiment, the content of the Fe-rich phase precipitant results in a Si:Mn mass ratio of 3.16 in the second melt. In one embodiment, the content of the Fe-rich phase precipitant results in a Si:Mn mass ratio of 3.22 in the second melt. In one embodiment, the content of the Fe-rich phase precipitant results in a Si:Mn mass ratio of 3.54 in the second melt. In one embodiment, the content of the Fe-rich phase precipitant results in a Si:Mn mass ratio of 3.66 in the second melt. In one embodiment, the content of the Fe-rich phase precipitant results in a Si:Mn mass ratio of 3.68 in the second melt.

[0042] exist Figure 1In step (4), a Fe-rich phase precipitant is added to the first melt obtained in step (1), and the mixture is maintained at a first temperature for a first time to obtain a second melt. If subsequent operations are performed immediately after adding the Fe-rich phase precipitant, the precipitant will not melt sufficiently, affecting the precipitation of the initial Fe-rich phase. Maintaining the first melt at the first temperature (melting temperature) for a first time helps ensure the complete melting of the Fe-rich phase precipitant and the thorough mixing of all elements, which is beneficial for subsequent operations. In one embodiment, the first time is 10–30 min. In one embodiment, the first time is 20 min. In one embodiment, the first time is 15 min.

[0043] exist Figure 1 In step (5), a refining agent is added to the second melt obtained in step (4), and inert gas is continuously introduced at the first temperature for joint refining. The melt is allowed to stand for a second time, and scum is skimmed off to obtain the third melt. To obtain a melt with high cleanliness and low gas content, degassing refining can be performed by adding a refining agent. If subsequent operations are performed immediately after adding the refining agent, the refining agent will not melt sufficiently, affecting the removal of non-metallic inclusions and gases. Maintaining the second melt at the first temperature (melting temperature) for a second time will help ensure the complete melting of the refining agent, which will benefit subsequent operations. Therefore, in one embodiment, the second time is 10–30 min. In another embodiment, the second time is 10 min. In yet another embodiment, the second time is 15 min. The mass of the refining agent is 0.2–0.5% of the mass of the second melt; within this range, the removal of non-metallic inclusions and gases is beneficial.

[0044] In step (6) (not shown), the precipitation temperature of the α-Al phase is calculated based on the elemental contents obtained in step (2). The calculation can be performed using thermodynamic software commonly used in the field, such as Thermo-Calc or Pandat.

[0045] exist Figure 1In step (7), the third melt treated in step (5) is cooled to a second temperature at a first cooling rate to generate Fe-rich phase particles, and held for a third time to obtain a fourth melt. The cooling rate of the aluminum alloy melt is one of the important parameters of the Fe removal process. A faster cooling rate can bring a large degree of undercooling to the melt, making it easier to promote the nucleation of Fe-rich phases, thus increasing the number density of Fe-rich phases per unit volume of melt. Within a certain temperature range, an increase in the melt cooling rate means a reduction in cooling time, which is very beneficial for improving industrial production efficiency. However, if the melt cooling rate is too fast, although it can promote a large number of Fe-rich phase nucleations, their growth time is short and their size is relatively small, which is not conducive to sedimentation in the melt. Therefore, it is necessary to select a suitable melt cooling rate so that the number density of Fe-rich phases per unit volume of melt can be increased as much as possible without affecting the growth process of Fe-rich phases, and finally achieving sedimentation and enrichment in the melt. Therefore, in one embodiment, the first cooling rate is 0.02 to 10 °C / s. In another embodiment, the first cooling rate is 0.023 to 1.3 °C / s. In one embodiment, the first cooling rate is 0.023 °C / s. In another embodiment, the first cooling rate is 1.3 °C / s. The temperature of the melt determines the solubility of the Fe-rich phase in the melt. Theoretically, from the point where the Fe-rich phase begins to precipitate, the lower the temperature, the greater the amount of Fe-rich phase precipitated. However, the lower the melt temperature, the higher the melt viscosity, resulting in poorer melt flowability, which is less conducive to the sedimentation of the Fe-rich phase. Therefore, a suitable melt temperature range is needed to ensure that a sufficient amount of Fe-rich phase precipitates in the melt while also ensuring that the melt has a certain degree of flowability to not hinder the sedimentation of the Fe-rich phase. Therefore, in one embodiment, the second temperature is the α-Al precipitation start temperature ±50 °C. In another embodiment, the second temperature is the α-Al precipitation start temperature ±45 °C. In another embodiment, the second temperature is 620 °C, 640 °C, or 660 °C. The second temperature can be any value within the above-defined range and is lower than the Fe-rich phase precipitation start temperature. Holding the molten aluminum alloy at a certain temperature for a period of time promotes the growth and coarsening of the Fe-rich phase, increases its size, and facilitates its sedimentation within the melt. Furthermore, the Fe-rich phase precipitated in the molten aluminum alloy also requires time to settle; therefore, increasing the holding time promotes sedimentation and reduces the Fe content in the melt. It is important to understand that extending the holding time only approximates the theoretical precipitation amount of the Fe-rich phase. Moreover, the melt temperature determines the theoretical precipitation amount of the Fe-rich phase; therefore, the melt temperature must be considered when setting the holding time. However, excessively long holding times are detrimental to production efficiency. Therefore, considering both melt temperature and production efficiency, extending the holding time as much as possible promotes the precipitation, growth, and sedimentation of more Fe-rich phases. Thus, in one embodiment, the third time is 10–120 min. In another embodiment, the third time is 10–60 min.In one embodiment, the third time is 10–30 minutes. In one embodiment, the third time is 10 minutes. In one embodiment, the third time is 30 minutes. In one embodiment, the third time is 60 minutes. The third time can be any point value within the above-defined range.

[0046] exist Figure 1 In step (8), the fourth melt obtained in step (7) is cooled to a third temperature at a second cooling rate to obtain an ingot. Cooling is carried out in the original reaction system, for example, a crucible furnace cooling circulation system, causing the melt to solidify rapidly into an ingot. In one embodiment, the third temperature is below 200°C. The second cooling rate needs to be sufficiently high to allow the melt to solidify rapidly into an ingot. Therefore, in one embodiment, the second cooling rate is greater than or equal to 10°C / s. In one embodiment, the second cooling rate is 15-30°C / s. In one embodiment, the second cooling rate is 20°C / s. In one embodiment, the second cooling rate is 10°C / s.

[0047] exist Figure 1 In step (9), the billet is sawn from the bottom of the billet to a first length to obtain a first ingot as a purified billet and a second ingot as an Fe-rich phase deposition layer, wherein the first length is 1 to 20% of the total length of the billet. In one embodiment, the Fe content of the first ingot is reduced by 40 to 70% compared to the cast aluminum alloy, and the weight of the first ingot is more than 80% of the weight of the cast aluminum alloy. In one embodiment, the Fe content of the first ingot is reduced by 45% compared to the cast aluminum alloy, and the weight of the first ingot is 93% of the weight of the cast aluminum alloy. In one embodiment, the Fe content of the first ingot is reduced by 51% compared to the cast aluminum alloy, and the weight of the first ingot is 91% of the weight of the cast aluminum alloy. In one embodiment, the Fe content of the first ingot is reduced by 52% compared to the cast aluminum alloy, and the weight of the first ingot is 89% of the weight of the cast aluminum alloy. In one embodiment, the Fe content of the first ingot is reduced by 63% compared to the cast aluminum alloy, and the weight of the first ingot is 86% of the weight of the cast aluminum alloy. In one embodiment, the Fe content of the first ingot is reduced by 64% compared to the cast aluminum alloy, and the weight of the first ingot is 88% of the weight of the cast aluminum alloy. In one embodiment, the Fe content of the first ingot is reduced by 66% compared to the cast aluminum alloy, and the weight of the first ingot is 85% of the weight of the cast aluminum alloy. In one embodiment, the Fe content of the first ingot is reduced by 54% compared to the cast aluminum alloy, and the weight of the first ingot is 89% of the weight of the cast aluminum alloy.

[0048] Now refer to Figures 2 to 8 ,in, Figure 2 The cooling curve of the melt at a first cooling rate of 0.023 °C / s is shown; Figure 3 The cooling curves of the melt at a first cooling rate of 1.3 °C / s are shown. Figure 4 The cooling curves of the melt at a first cooling rate of 3.2 °C / s are shown. Figure 5 The cooling curves of the melt at a first cooling rate of 5.6 °C / s are shown. Figure 6 The cooling curve of the melt at a first cooling rate of 30.8 °C / s is shown; Figure 7 The image shows the microstructure of purified aluminum ingots produced when the melt was cooled from 760°C to 620°C at a cooling rate of 0.023°C / s and held for 60 min. Figure 8 The image shows a micrograph of the Fe-rich phase deposited in the ingot after the melt was cooled from 760°C to 620°C at a cooling rate of 0.023°C / s and held for 60 min. It can be seen that, considering the cooling rate (first cooling rate), melt temperature (second temperature), production efficiency, and the longest possible holding time (third time), more Fe-rich phase precipitation, growth, and sedimentation were promoted, achieving purification.

[0049] In some embodiments, the main components of the refining agent are MgCl2 and KCl. In some embodiments, the mass ratio of MgCl2 to KCl is 0.5–1.5, and the mass of the refining agent is 0.2–0.5% of the mass of the second melt. In some embodiments, the mass ratio of MgCl2 to KCl is 0.8, and the mass of the refining agent is 0.3% of the mass of the second melt. In some embodiments, a degassing refining process is performed using a degasser, introducing an inert gas, such as high-purity argon. In some embodiments, the blowing rate is 500–2000 ml / min.

[0050] In some embodiments, step (7) is performed without agitating the melt, as agitation at this point would interfere with particle size and thus affect its settling. Depending on the end use of the cast aluminum alloy, the residual Mn content in the fourth melt will typically be less than 0.6 wt.%.

[0051] In some implementations, step (8) is performed without stirring the melt, because stirring the melt at this time would interfere with the settling of particulate matter and affect the Fe removal effect of the final product.

[0052] The present invention will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention.

[0053] Example 1:

[0054] The recycled waste cast aluminum alloy was melted in a graphite crucible at a melting temperature of 760℃. Samples were taken for chemical composition analysis, revealing an Fe content of 0.96 wt.% and a Si content of 6.64 wt.%. The required mass of Al-Mn master alloy was calculated based on the Si content, and the α-Al precipitation temperature of this alloy was determined to be 617℃ using thermodynamic software. A certain amount of Al-10Mn master alloy was added to the melt to achieve a Si:Mn mass ratio of 3.16, with a measured Mn content of 2.10 wt.%. A refining agent with a MgCl2:KCl mass ratio of 0.8 was added at 0.3% of the melt mass. The melt was then refined for 15 minutes by passing high-purity argon gas through a degasser, allowed to stand for 10 minutes, and the slag was removed. The melt was then cooled at a first cooling rate of 0.023℃ / s (the cooling curve is shown in the figure). Figure 2 The melt was cooled from 760℃ to 660℃ and held for 10 minutes. Through the crucible furnace's cooling circulation system, the melt rapidly solidified into an ingot at a second cooling rate of 30℃ / s. Analysis of the chemical composition and low-magnification microstructure of the longitudinal section of this ingot revealed that the length of the Fe-rich phase deposition layer accounted for 5% of the total ingot length. Based on this length, the resulting purified aluminum alloy ingot contained 0.53 wt.% Fe, a 45% reduction compared to the original scrap aluminum. The weight of the purified ingot was 93% of the original scrap aluminum.

[0055] Example 2:

[0056] The recycled waste cast aluminum alloy was melted in a graphite crucible furnace at a melting temperature of 760℃. Samples were taken for chemical composition analysis, revealing an Fe content of 1.00 wt.% and a Si content of 7.00 wt.%. The required mass of Al-Mn master alloy was calculated based on the Si content, and the α-Al precipitation temperature of this alloy was determined to be 616℃ using thermodynamic software. A certain amount of Al-10Mn master alloy was added to the melt to achieve a Si:Mn mass ratio of 3.54, with a measured Mn content of 1.98 wt.%. A refining agent with a MgCl2:KCl mass ratio of 0.8 was added at a rate of 0.3% of the melt mass. The melt was then refined for 15 minutes by passing high-purity argon gas through a degasser, allowed to stand for 15 minutes, and the slag was removed. The melt was then cooled at a first cooling rate of 1.3℃ / s (the cooling rate curve is shown in the figure). Figure 3The melt was cooled from 760℃ to 660℃ and held for 10 minutes. Through the cooling circulation system of the melting furnace, the melt rapidly solidified into an ingot at a second cooling rate of 20℃ / s. Analysis of the chemical composition and low-magnification microstructure of the longitudinal section of this ingot revealed that the length of the Fe-rich phase deposition layer accounted for 6% of the total ingot length. Based on this length, the purified aluminum alloy ingot obtained had an Fe content of 0.49 wt.%, which is 51% lower than the Fe content in the original scrap aluminum. The weight of the obtained purified ingot was 91% of the original scrap aluminum weight.

[0057] Example 3:

[0058] The recycled waste cast aluminum alloy was melted in a graphite crucible at a melting temperature of 760℃. Samples were taken for chemical composition analysis, revealing an Fe content of 0.96 wt.% and a Si content of 6.64 wt.%. The required mass of Al-Mn master alloy was calculated based on the Si content, and the α-Al precipitation temperature of this alloy was determined to be 617℃ using thermodynamic software. A certain amount of Al-10Mn master alloy was added to the melt to achieve a Si:Mn mass ratio of 3.16, with a measured Mn content of 2.10 wt.%. A refining agent with a MgCl2:KCl mass ratio of 0.8 was added at 0.5% of the melt mass. The melt was then refined for 15 minutes by passing high-purity argon gas through a degasser, allowed to stand for 10 minutes, and the slag was removed. The melt was then cooled at a first cooling rate of 0.023℃ / s (the cooling curve is shown in the figure). Figure 2 The melt was cooled from 760℃ to 640℃ and held for 10 minutes. Through the crucible furnace's cooling circulation system, the melt rapidly solidified into an ingot at a second cooling rate of 10℃ / s. Analysis of the chemical composition and low-magnification microstructure of the longitudinal section of this ingot revealed that the length of the Fe-rich phase deposition layer accounted for 7% of the total ingot length. Based on this length, the resulting purified aluminum alloy ingot contained 0.46 wt.% Fe, a 52% reduction compared to the original scrap aluminum. The weight of the purified ingot was 89% of the original scrap aluminum.

[0059] Example 4:

[0060] The recycled waste cast aluminum alloy was melted in a graphite crucible at a melting temperature of 760℃. Samples were taken for chemical composition analysis, revealing an Fe content of 0.96 wt.% and a Si content of 6.64 wt.%. The required mass of Al-Mn master alloy was calculated based on the Si content, and the α-Al precipitation temperature of this alloy was determined to be 617℃ using thermodynamic software. A certain amount of Al-10Mn master alloy was added to the melt to achieve a Si:Mn mass ratio of 3.16, with a measured Mn content of 2.10 wt.%. A refining agent with a MgCl2:KCl mass ratio of 0.8 was added at 0.3% of the melt mass. The melt was then refined for 15 minutes by passing high-purity argon gas through a degasser, allowed to stand for 10 minutes, and the slag was removed. The melt was then cooled at a first cooling rate of 0.023℃ / s (the cooling curve is shown in the figure). Figure 2 The melt was cooled from 760℃ to 620℃ and held for 10 minutes. Through the cooling circulation system of the crucible furnace, the melt rapidly solidified into an ingot at a second cooling rate of 20℃ / s. Analysis of the chemical composition and low-magnification microstructure of the longitudinal section of the ingot revealed that the length of the Fe-rich phase deposition layer accounted for 10% of the total ingot length. Based on this length, the purified aluminum alloy ingot prepared thus had an Fe content of 0.36 wt.%, which is 63% lower than the Fe content in the original scrap aluminum. The weight of the obtained purified ingot was 86% of the original scrap aluminum weight.

[0061] Example 5:

[0062] The recycled waste cast aluminum alloy was melted in a graphite crucible at a melting temperature of 760℃. Samples were taken for chemical composition analysis, revealing an Fe content of 1.09 wt.% and a Si content of 7.02 wt.%. The required mass of Al-Mn master alloy was calculated based on the Si content, and the α-Al precipitation temperature of this alloy was determined to be 618℃ using thermodynamic software. A certain amount of Al-20Mn master alloy was added to the melt to achieve a Si:Mn mass ratio of 3.66, with a measured Mn content of 1.92 wt.%. A refining agent with a MgCl2:KCl mass ratio of 0.8 was added at 0.3% of the melt mass. The melt was then refined for 15 minutes by passing high-purity argon gas through a degasser, allowed to stand for 10 minutes, and the slag was removed. The melt was then cooled at a first cooling rate of 0.023℃ / s (the cooling curve is shown in the figure). Figure 2The melt was cooled from 760℃ to 620℃ and held for 30 minutes. Through the crucible furnace's cooling circulation system, the melt rapidly solidified into an ingot at a second cooling rate of 10℃ / s. Analysis of the chemical composition and low-magnification microstructure of the longitudinal section of this ingot revealed that the length of the Fe-rich phase deposition layer accounted for 9% of the total ingot length. Based on this length, the purified aluminum alloy ingot prepared thus had an Fe content of 0.39 wt.%, a 64% reduction compared to the original scrap aluminum. The weight of the obtained purified ingot was 88% of the original scrap aluminum weight.

[0063] Example 6:

[0064] The recycled waste cast aluminum alloy was melted in a graphite crucible at a melting temperature of 760℃. Samples were taken for chemical composition analysis, revealing an Fe content of 0.98 wt.% and a Si content of 7.00 wt.%. The required mass of Al-Mn master alloy was calculated based on the Si content, and the α-Al precipitation temperature of this alloy was determined to be 616℃ using thermodynamic software. A certain amount of Al-20Mn master alloy was added to the melt to achieve a Si:Mn mass ratio of 3.68, with a measured Mn content of 1.90 wt.%. A refining agent with a MgCl2:KCl mass ratio of 0.8 was added at 0.3% of the melt mass. The melt was then refined for 15 minutes by passing high-purity argon gas through a degasser, allowed to stand for 10 minutes, and the slag was removed. The melt was then cooled at a first cooling rate of 0.023℃ / s (the cooling curve is shown in the figure). Figure 2 The melt was cooled from 760℃ to 620℃ and held for 60 minutes. Through the crucible furnace's cooling circulation system, the melt rapidly solidified into an ingot at a second cooling rate of 10℃ / s. Analysis of the chemical composition and low-magnification microstructure of the longitudinal section of this ingot revealed that the length of the Fe-rich phase deposition layer accounted for 11% of the total ingot length. Based on this length, the purified aluminum alloy ingot obtained had an Fe content of 0.33 wt.%, a 66% reduction compared to the original scrap aluminum, and the weight of the purified ingot was 85% of the original scrap aluminum weight.

[0065] Example 7:

[0066] The recycled waste cast aluminum alloy was melted in a graphite crucible at a melting temperature of 760℃. Samples were taken for chemical composition analysis, revealing an Fe content of 1.05 wt.% and a Si content of 6.82 wt.%. The required mass of Al-Mn master alloy was calculated based on the Si content, and the α-Al precipitation temperature of this alloy was determined to be 619℃ using thermodynamic software. A certain amount of Al-10Mn master alloy was added to the melt to achieve a Si:Mn mass ratio of 3.22, with a measured Mn content of 2.12 wt.%. A refining agent with a MgCl2:KCl mass ratio of 0.8 was added at 0.3% of the melt mass. The melt was then refined for 15 minutes by passing high-purity argon gas through a degasser, allowed to stand for 10 minutes, and the slag was removed. The melt was then cooled at a first cooling rate of 0.023℃ / s (the cooling curve is shown in the figure). Figure 2 The melt was cooled from 760℃ to 660℃ and held for 60 minutes. Through the cooling circulation system of the crucible furnace, the melt rapidly solidified into an ingot at a second cooling rate of 10℃ / s. Analysis of the chemical composition and low-magnification microstructure of the longitudinal section of this ingot revealed that the length of the Fe-rich phase deposition layer accounted for 7% of the total ingot length. Based on this length, the purified aluminum alloy ingot prepared thus had an Fe content of 0.48 wt.%, which is 54% lower than the Fe content in the original scrap aluminum. The weight of the obtained purified ingot was 89% of the original scrap aluminum weight.

[0067] Example 8:

[0068] The recycled waste cast aluminum alloy was melted in a graphite crucible at a melting temperature of 760℃. Samples were taken for chemical composition analysis, revealing an Fe content of 1.07 wt.% and a Si content of 7.14 wt.%. The required mass of Al-Mn master alloy was calculated based on the Si content, and the α-Al precipitation temperature of this alloy was determined to be 618℃ using thermodynamic software. A certain amount of Al-10Mn master alloy was added to the melt to achieve a Si:Mn mass ratio of 3.64, with a measured Mn content of 1.96 wt.%. A refining agent with a MgCl2:KCl mass ratio of 0.8 was added at 0.3% of the melt mass. The melt was then refined for 15 minutes by passing high-purity argon gas through a degasser, allowed to stand for 10 minutes, and the slag was removed. The melt was then cooled at a first cooling rate of 3.2℃ / s (the cooling curve is shown in [reference needed]). Figure 4The melt was cooled from 760℃ to 660℃ and held for 10 minutes. Through the cooling circulation system of the crucible furnace, the melt rapidly solidified into an ingot at a second cooling rate of 10℃ / s. Analysis of the chemical composition and low-magnification microstructure of the longitudinal section of this ingot revealed that the length of the Fe-rich phase deposition layer accounted for 1.1% of the total ingot length. Based on this length, the purified aluminum alloy ingot prepared in this manner contained 0.89 wt.% Fe, a 17% reduction compared to the Fe content in the original scrap aluminum.

[0069] Example 9:

[0070] The recycled waste cast aluminum alloy was melted in a graphite crucible at a melting temperature of 760℃. Samples were taken for chemical composition analysis, revealing an Fe content of 1.07 wt.% and a Si content of 7.14 wt.%. The required mass of Al-Mn master alloy was calculated based on the Si content, and the α-Al precipitation temperature of this alloy was determined to be 618℃ using thermodynamic software. A certain amount of Al-10Mn master alloy was added to the melt to achieve a Si:Mn mass ratio of 3.64, with a measured Mn content of 1.96 wt.%. A refining agent with a MgCl2:KCl mass ratio of 0.8 was added at 0.3% of the melt mass. The melt was then refined for 15 minutes by passing high-purity argon gas through a degasser, allowed to stand for 10 minutes, and the slag was removed. The melt was then cooled at a first cooling rate of 5.6℃ / s (the cooling curve is shown in the figure). Figure 5 The molten aluminum was cooled from 760℃ to 660℃ and held at that temperature for 10 minutes. The cooling circulation system of the crucible furnace allowed the melt to rapidly solidify into an ingot at a second cooling rate of 10℃ / s. Analysis of the chemical composition and low-magnification microstructure of the longitudinal section of this ingot revealed that the length of the Fe-rich phase deposition layer accounted for 0.6% of the total ingot length. Based on this length, the purified aluminum alloy ingot prepared in this manner contained 0.98 wt.% Fe, which is 8% lower than the Fe content in the original scrap aluminum.

[0071] The parameters and results of Examples 1 to 9 are summarized in Table 1 below.

[0072] Table 1. Parameters and results of Examples 1 to 9

[0073]

[0074]

[0075] Comparative Example 1: Investigating the effects of the first cooling rate and the third time on the precipitation and deposition of Fe-rich phases.

[0076] The recycled waste cast aluminum alloy was melted in a graphite crucible furnace at a melting temperature of 760℃. Samples were taken for chemical composition analysis, revealing an Fe content of 1.05 wt.% and a Si content of 6.82 wt.%. A certain amount of Al-10Mn master alloy was added to the melt to achieve a Si:Mn mass ratio of 3.22, with a measured Mn content of 2.12 wt.%. A refining agent with a MgCl2:KCl mass ratio of 0.8 was added at 0.3% of the melt mass. The melt was then refined for 15 minutes by passing high-purity argon gas through a degasser, allowed to stand for 10 minutes, and the slag was removed. Thermodynamic calculations determined the α-Al precipitation temperature of this alloy to be 619℃. The melt was then cooled at a first cooling rate of 30.8℃ / s (the cooling rate curve is shown in [reference needed]). Figure 6 The melt was cooled from 760℃ to 660℃. Through the cooling circulation system of the melting furnace, the melt rapidly solidified into an ingot at a second cooling rate of 10℃ / s. Analysis of the chemical composition and low-magnification microstructure of the longitudinal section of this ingot revealed that the length of the Fe-rich phase deposition layer accounted for 0% of the total ingot length. The purified aluminum alloy ingot prepared in this manner contained 1.05 wt.% Fe, indicating that the Fe content in the cast ingot was too high and the waste cast aluminum alloy was not purified.

[0077] Compared to Example 2, Comparative Example 1 showed an increase in the first cooling rate from 1.3°C / s to 30.8°C / s and a decrease in the third time from 10 min to 0, resulting in rapid solidification of the melt. However, due to the excessively rapid cooling rate, the Fe-rich phase did not have enough time to precipitate or settle to the bottom, thus failing to achieve the desired Fe removal effect.

[0078] Comparative Example 2: Investigating the effect of the second temperature on the precipitation and deposition of Fe-rich phases

[0079] Compared with Example 5, the recycled waste cast aluminum alloy was melted in a graphite crucible at a melting temperature of 760°C. Samples were taken for chemical composition analysis, revealing an Fe content of 0.96 wt.% and a Si content of 6.64 wt.%. The required mass of Al-Mn master alloy was calculated based on the Si content, and the α-Al precipitation temperature of this alloy was determined to be 617°C using thermodynamic software. A certain amount of Al-10Mn master alloy was added to the melt to achieve a Si:Mn mass ratio of 3.16, with a measured Mn content of 2.10 wt.%. A refining agent with a MgCl2:KCl mass ratio of 0.8 was added at a rate of 0.3% of the melt mass. The melt was then refined for 15 minutes by passing high-purity argon gas through a degasser, allowed to stand for 10 minutes, and the slag was removed. The melt was then cooled at a first cooling rate of 0.023°C / s (the cooling curve is shown in [reference needed]). Figure 2The melt was cooled from 760℃ to 680℃ and held for 30 minutes. Through the crucible furnace's cooling circulation system, the melt rapidly solidified into an ingot at a second cooling rate of 20℃ / s. Analysis of the chemical composition and low-magnification microstructure of the longitudinal section of this ingot revealed that the length of the second ingot (Fe-rich phase deposition layer) accounted for 3% of the total ingot length. Based on this length, the purified aluminum alloy ingot obtained was sawn, and the Fe content was 0.74 wt.%, a 27% reduction compared to the original scrap aluminum. The high Fe content in the ingot indicated that the scrap cast aluminum alloy was not purified.

[0080] Thermodynamic calculations revealed the α-Al precipitation temperature, or Fe-rich phase precipitation temperature, of this alloy to be 617°C. Therefore, the second temperature should be within the range of 617 ± 50°C, i.e., 567–667°C. However, the second temperature in Comparative Example 2 is 680°C, which is not only higher than the second temperature of 620°C in Example 5, but also exceeds the upper limit of the second temperature. This increases the solubility of the Fe-rich phase in the melt, hindering precipitation and sedimentation, resulting in poor Fe removal efficiency.

[0081] Comparative Example 3: Examining the impact of the first cooling rate on production efficiency

[0082] The recycled waste cast aluminum alloy was melted in a graphite crucible furnace at a melting temperature of 760℃. Samples were taken for chemical composition analysis, revealing an Fe content of 1.03 wt.% and a Si content of 7.01 wt.%. The required mass of Al-Mn master alloy was calculated based on the Si content, and the α-Al precipitation temperature of this alloy was determined to be 617℃ using thermodynamic software. A certain amount of Al-10Mn master alloy was added to the melt to achieve a Si:Mn mass ratio of 3.44, with a measured Mn content of 2.04 wt.%. A refining agent with a MgCl2:KCl mass ratio of 0.8 was added at a rate of 0.3% of the melt mass. The melt was then refined for 15 minutes by passing high-purity argon gas through a degasser, allowed to stand for 15 minutes, and the slag was removed. The melt was then cooled at a first cooling rate of 0.023℃ / s (the cooling rate curve is shown in the figure). Figure 2 The melt was cooled from 760℃ to 660℃ and held for 30 minutes. Through the cooling circulation system of the melting furnace, the melt rapidly solidified into an ingot at a second cooling rate of 20℃ / s. Analysis of the chemical composition and low-magnification microstructure of the longitudinal section of this ingot revealed that the length of the Fe-rich phase deposition layer accounted for 6% of the total ingot length. Based on this length, the purified aluminum alloy ingot obtained had an Fe content of 0.50 wt.%, which is 51% lower than the Fe content in the original scrap aluminum. The weight of the obtained purified ingot was 91% of the original scrap aluminum weight.

[0083] Comparative Example 3 can reduce the Fe content in the alloy to the same level as in Example 2. However, the Fe removal process in Comparative Example 3 takes 102 minutes, which is 78 times longer than the Fe removal process in Example 2 (1.3 minutes), resulting in low production efficiency.

[0084] The parameters and results of Comparative Examples 1 to 3 are summarized in Table 2 below.

[0085] Table 2. Parameters and results of Comparative Examples 1 to 3

[0086]

[0087] The results of the above embodiments demonstrate that in the method of the present invention:

[0088] (1) By utilizing the initial Fe element content in the cast aluminum alloy and adjusting the Si:Mn mass ratio, a sufficient number of primary Fe-rich phases are formed in the melt.

[0089] (2) By controlling the melt temperature, the solubility of the Fe-rich phase in the melt is controlled, thereby controlling the theoretical amount of precipitation.

[0090] (3) Accelerate the precipitation of Fe-rich phase by controlling the melt cooling rate;

[0091] (4) The size and sedimentation process of the Fe-rich phase can be controlled by controlling the holding time of the melt.

[0092] Industrial applicability

[0093] As can be seen from the above description, this invention provides an effective method for removing Fe from cast aluminum alloys. The method of this invention significantly improves the Fe removal efficiency of ingots, resulting in a substantial Fe removal effect; the final purified ingot has a large weight and high purity; and it also balances production efficiency, thereby reducing overall production costs.

Claims

1. A method for removing Fe element from cast aluminum alloys, comprising the following steps: (1) The cast aluminum alloy is melted at a first temperature of 700~780℃ to obtain a first melt; (2) The first melt obtained in step (1) is sampled and analyzed to obtain the Fe, Si and Mn content of the cast aluminum alloy; (3) Based on the Si and Mn element content obtained in step (2), calculate the amount of Fe-rich phase precipitant according to the silicon-manganese ratio, wherein the Fe-rich phase precipitant is an Al-Mn master alloy. (4) Add the Fe-rich phase precipitant to the first melt obtained in step (1) and maintain it at the first temperature for a first time to obtain a second melt, wherein the first time is 10~30 min; (5) Add a refining agent to the second melt obtained in step (4), and continue to pass inert gas through the melt at the first temperature for joint refining. Let the melt stand for a second time and remove the scum to obtain a third melt, wherein the second time is 10 to 30 minutes and the mass of the refining agent is 0.2 to 0.5% of the mass of the second melt. (6) Calculate the precipitation temperature of the α-Al phase based on the content of each element obtained in step (2); (7) The third melt treated in step (5) is cooled to a second temperature at a first cooling rate to produce Fe-rich phase particles, and held for a third time to obtain a fourth melt; (8) The fourth melt obtained in step (7) is cooled to a third temperature at a second cooling rate to obtain an ingot, wherein the third temperature is below 200°C and the second cooling rate is greater than or equal to 10°C / s; (9) Starting from the bottom of the billet, the billet is sawn to a first length to obtain a first ingot as a purified billet and a second ingot as an Fe-rich phase deposition layer, wherein the first length is 1 to 20% of the total length of the billet; characterized in that: The amount of the Fe-rich phase precipitant used results in a Si:Mn mass ratio of 3.0 to 9.0 in the second melt; The first cooling rate is 0.02~10℃ / s; The second temperature is within ±50°C of the α-Al phase precipitation initiation temperature; and The third time is 10~120 minutes.

2. The method according to claim 1, characterized in that: The amount of the Fe-rich phase precipitant used results in a Si:Mn mass ratio of 3.0 to 4.0 in the second melt; The first cooling rate is 0.02~10℃ / s; The second temperature is within the range of ±45°C of the α-Al phase precipitation start temperature calculated in step (6); and The third time is 10~60 minutes.

3. The method according to claim 1, characterized in that: The amount of the Fe-rich phase precipitant used results in a Si:Mn mass ratio of 3.16, 3.22, 3.54, 3.66, or 3.68 in the second melt.

4. The method according to claim 1, characterized in that: The first cooling rate is 0.023~1.3℃ / s.

5. The method according to claim 1, characterized in that: The first cooling rate is 0.023℃ / s or 1.3℃ / s.

6. The method according to claim 1, characterized in that: The second temperature is 620°C, 640°C, or 660°C.

7. The method according to claim 1, characterized in that: The third time is 10~30 minutes.

8. The method according to claim 1, characterized in that: The third time is 10 minutes, 30 minutes, or 60 minutes.

9. The method according to claim 1, characterized in that: The Mn content of the Al-Mn master alloy is 5~20 wt.%.

10. The method according to claim 1, characterized in that; The main components of the refining agent are MgCl2 and KCl, wherein the mass ratio of MgCl2 to KCl is 0.5 to 1.

5.

11. The method according to claim 1, characterized in that: The combined refining process includes using a degasser to degas and refine the product by introducing inert gas, with a blowing rate of 500~2000 ml / min.

12. The method according to claim 1, characterized in that: Step (7) is performed without stirring the melt, and the residual Mn content in the fourth melt is less than 0.6 wt.%.

13. The method according to claim 1, characterized in that: Step (8) is performed without stirring the melt, and the second cooling rate is 15-30°C / s.

14. The method according to claim 1, characterized in that: Step (8) is performed without stirring the melt, and the second cooling rate is 20°C / s or 10°C / s.

15. The method according to any one of claims 1-14, characterized in that: The initial Fe content in the cast aluminum alloy is at least 0.5 wt.%.

16. The method according to claim 15, characterized in that: The cast aluminum alloy has an Fe content of 0.5~4.0 wt.%, a Si content of 7.0~15.0 wt.%, and a Mn content of 0~0.8 wt.%, with the remainder being Al.

17. The method according to claim 15, characterized in that: The cast aluminum alloy contains 0-1.0% Ni, 0-0.5 wt.% Sn, 0-6.0 wt.% Mg, 0-6.0 wt.% Cu, 0-6.0 wt.% Zn, 0-0.3 wt.% Ti, and other individual impurity elements ≤0.05 wt.%, with the remainder being Al.

18. The method according to any one of claims 1-14, characterized in that: Compared with the cast aluminum alloy, the Fe content of the first ingot is reduced by 40-70%, and the weight of the first ingot is more than 80% of the weight of the cast aluminum alloy.

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