A method for casting aluminum alloy upgrade recycling

Abstract

This invention relates to a method for upgrading and recycling cast aluminum alloys, comprising the following steps: (1) melting the cast aluminum alloy to obtain a first melt; (2) sampling the first melt and analyzing its elemental 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 and performing joint refining to obtain a third melt; (6) calculating the α-Al phase precipitation start temperature; (7) cooling the third melt to generate Fe-rich phase particles and maintaining the temperature for a time to obtain a fourth melt; (8) cooling the fourth melt to obtain an ingot; and (9) sawing the ingot to obtain an ingot and a Fe-rich phase deposition layer. Through the method of this invention, the Fe removal efficiency of the ingot is improved, and the Fe removal effect is significant; the final 4XXX forged aluminum alloy ingot has a large weight and high purity; and it also takes into account production efficiency, reducing overall production costs and achieving the goal of upgrading and converting into forged aluminum alloys with higher added value.

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] The recycled aluminum industry has the advantages of being low-carbon, environmentally friendly, energy-saving, and reducing consumption. It is an important way for my country's aluminum processing industry to achieve sustainable development. Especially under the circumstances of my country's scarcity of bauxite resources and the country's vigorous promotion of the "carbon peaking and carbon neutrality" strategy, the development of the recycled aluminum industry is of great significance.

[0003] However, compared to developed countries, my country's methods for recycling scrap aluminum are still relatively backward. For a long time, due to the complex composition of scrap aluminum raw materials, most of the recycled aluminum alloys produced in my country have high impurity content, making them only suitable for producing cast aluminum alloy products. Many high-quality wrought aluminum alloy scraps are downgraded, significantly reducing the recycling value of aluminum products and resulting in a huge waste of scrap aluminum resources. Statistics show that only about 20% of my country's recycled aluminum can be reused annually to produce corresponding grades of wrought aluminum alloys, achieving grade preservation and recycling. However, in developed countries, wrought aluminum alloys account for more than half of the recycled aluminum product structure. Therefore, how to effectively recycle or upgrade recycled aluminum is a pressing problem that the recycled aluminum industry needs to overcome.

[0004] Due to the complex sources and difficult pretreatment of scrap aluminum, a large number of impurity elements are inevitably introduced during the repeated recycling process to produce recycled aluminum. Effectively reducing the content of these impurity elements is a crucial prerequisite for ensuring the same or even upgraded recycling quality of the recycled aluminum. Among the many impurity elements, Fe (Fe) has the most significant harmful effect, severely impacting the quality of recycled aluminum. Currently, methods to reduce the harmful effects of Fe mainly include two approaches: the first is modification treatment, which involves adding chemical elements or using special processes to alter the morphology of the Fe-rich phase, such as adding elements like Mn, Cr, Be, Co, Ni, or rare earth elements; the second is physical methods, utilizing the different physicochemical properties between the Fe-rich phase and the melt to remove the Fe-rich phase, including 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.

[0005] 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, this method is simple, feasible, and easy to industrialize. However, the current challenge lies in finding a suitable additive element that can form primary Fe-rich phase particles with Fe, facilitating sedimentation and separation in the melt to reduce the Fe content in the waste aluminum alloy, while simultaneously not introducing new impurity elements. This would ensure that the purified waste aluminum alloy meets the alloy composition range for higher added value, achieving the same or upgraded recycling of waste aluminum.

[0006] Existing patent CN107619959B reduces the Fe content in recycled aluminum by jointly adding Al-Cr intermediates and K2TiF6 in a mass ratio of (1-1.34):(1.26-1.78) and using a ceramic foam filter to remove sediment from the bottom of the molten aluminum. This introduces Ti and requires additional Fe removal measures, and the increased viscosity of the melt after cooling poses challenges for industrial implementation. Existing patent CN111032890A discloses the initial Fe content (greater than 0.20 wt.%) and Mn content (not greater than 1.8 wt.%) of the alloy, as well as the cooling temperature range (greater than 10°C). Since this method uses Mn to reduce the Fe content, some Mn will inevitably remain in the alloy melt, making it unsuitable for alloys where Mn is controlled as an impurity element for reuse. Existing patent CN111020255B discloses the mass ratio of alloying elements (Mn / Fe = 1-5, Cr / Fe = 0.5-4, V / Fe = 0.2-4), the temperature range for Fe-rich phase precipitation (590-700℃), and the cooling rate (0.1-1℃ / min). However, it requires the addition of multiple foreign elements such as Mn and V, which increases the difficulty of recycling the alloy. Summary of the Invention

[0007] Therefore, the purpose of this invention is to provide a method for efficiently removing Fe from waste cast aluminum alloys suitable for industrial applications. This method can purify waste cast aluminum alloys and upgrade them for recycling as raw materials for wrought aluminum alloys, thereby further enhancing the value of waste aluminum.

[0008] 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:

[0009] (1) The cast aluminum alloy is melted at a first temperature to obtain a first melt, wherein the first temperature is 700-780°C;

[0010] (2) The first melt obtained in step (1) is sampled and analyzed to obtain the Fe, Si and Cr content of the cast aluminum alloy.

[0011] (3) Calculate the amount of Fe-rich phase precipitant based on the Si and Cr content obtained in step (2), wherein the Fe-rich phase precipitant is an Al-Cr master alloy.

[0012] (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 to 30 min;

[0013] (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 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.

[0014] (6) Calculate the temperature at which α-Al begins to precipitate based on the content of each element obtained in step (2);

[0015] (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;

[0016] (8) Cooling 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;

[0017] (9) Starting from the bottom of the billet, the billet is sawn to a first length to obtain a first ingot as a 4XXX forged aluminum alloy 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:

[0018] The content of the Fe-rich phase precipitant makes the Si:Cr mass ratio in the second melt 20-30; the first cooling rate is 0.01-1℃ / s; the second temperature is within the range of ±20℃ of the Fe-rich phase precipitation temperature calculated in step (6); the second cooling rate is greater than or equal to 20℃ / s; and the third time is 10-120min.

[0019] Further, the content of the Fe-rich phase precipitant is such that the mass ratio of Si:Cr in the second melt is 23 to 28, preferably 23.5, 25.2, 25.9, 27.0 or 27.6; the first cooling rate is 0.02 to 0.7 °C / s, preferably 0.023 °C / s; the second temperature is within the range of ±8 °C of the Fe-rich phase precipitation temperature calculated in step (6), preferably 580 °C, 576 °C or 575 °C; and the third time is 10 to 60 min, preferably 10 to 30 min, more preferably 10 min, 30 min or 60 min.

[0020] Furthermore, the Cr content in the Al-Cr master alloy is 5–20 wt.%.

[0021] Furthermore, 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.

[0022] 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.

[0023] Furthermore, step (7) is performed without stirring the melt, and the residual Cr content in the fourth melt is less than 0.1 wt.%.

[0024] Furthermore, step (8) is performed without stirring the melt, and the second cooling rate is 20°C / s.

[0025] 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 6.0-15.0 wt.%, and the Cr content is 0-0.1 wt.%, with the remainder being Al; optionally, the Ni content of the cast aluminum alloy is 0-1.0 wt.%, 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.

[0026] 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.

[0027] 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:Cr 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 significantly improves the Fe removal efficiency of the ingot, resulting in a substantial Fe removal effect. The final 4XXX forged aluminum alloy ingot has a large weight and high purity. It also balances production efficiency, reduces overall production costs, and achieves the goal of upgrading and transforming into forged aluminum alloys with higher added value. Attached Figure Description

[0028] 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:

[0029] Figure 1 A flowchart of a method for removing Fe from cast aluminum alloys according to the present invention is shown.

[0030] Figure 2 The cooling curves of the melt at a first cooling rate of 0.023 °C / s are shown.

[0031] Figure 3 The cooling curves of the melt at a first cooling rate of 1.3 °C / s are shown.

[0032] Figure 4 The image shows the microstructure of purified aluminum on the upper part of the ingot when the melt was cooled from 760°C to 580°C at a cooling rate of 0.023°C / s and held for 60 min.

[0033] Figure 5 The image shows a microstructure of the Fe-rich phase deposit at the bottom of the ingot, obtained by cooling the melt from 760°C to 580°C at a cooling rate of 0.023°C / s and holding it for 60 min. Detailed Implementation

[0034] The following description is presented to enable those skilled in the art to obtain and use various embodiments. Descriptions of specific apparatuses, techniques, 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.

[0035] 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.

[0036] Due to the aforementioned problems, it is necessary to modify the traditional method of removing Fe from cast aluminum alloys in order to increase the weight of the final 4XXX forged aluminum alloy ingot, improve the Fe removal effect, and simultaneously improve production efficiency and reduce production costs.

[0037] The embodiments of the present invention provide a flowchart of a method for removing Fe elements from cast aluminum alloys.

[0038] 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.

[0039] exist Figure 1 In step (2), the first melt obtained in step (1) is sampled and analyzed to obtain the Fe, Si, and Cr 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.

[0040] exist Figure 1In step (3), the amount of Fe-rich phase precipitant is calculated based on the Si and Cr content obtained in step (2), wherein the Fe-rich phase precipitant is an Al-Cr master alloy. The composition of the aluminum alloy determines whether a primary Fe-rich phase is formed 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 Cr content of 0–0.1 wt.%. In one embodiment, the cast aluminum alloy contains 0.5–4.0 wt.% Fe, 6.0–15.0 wt.% Si, 0–0.1 wt.% Cr, 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:Cr mass ratio. Therefore, in one embodiment, the content of the Fe-rich phase precipitant results in a Si:Cr mass ratio of 23 to 28 in the second melt. In one embodiment, the content of the Fe-rich phase precipitant results in a Si:Cr mass ratio of 23.5 in the second melt. In one embodiment, the content of the Fe-rich phase precipitant results in a Si:Cr mass ratio of 25.2 in the second melt. In one embodiment, the content of the Fe-rich phase precipitant results in a Si:Cr mass ratio of 25.9 in the second melt. In one embodiment, the content of the Fe-rich phase precipitant results in a Si:Cr mass ratio of 27.0 in the second melt. In one embodiment, the content of the Fe-rich phase precipitant results in a Si:Cr mass ratio of 27.6 in the second melt.

[0041] 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 minutes. In another embodiment, the first time is 10 minutes.

[0042] 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 carried out 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 first time will help the refining agent to melt fully, which will benefit subsequent operations. Therefore, in one embodiment, the second time is 10–30 min. In one embodiment, the second time is 10 min. In one 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.

[0043] exist Figure 1 In step (6), the temperature at which α-Al begins to precipitate 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.

[0044] 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 0.01 to 1 °C / s. In another embodiment, the first cooling rate is 0.02 to 0.7 °C / s. In one embodiment, the first cooling rate is 0.023℃ / 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 maintaining a certain level of melt flowability to facilitate the sedimentation of the Fe-rich phase. Therefore, in one embodiment, the second temperature is ±20℃ of the α-Al precipitation start temperature. In another embodiment, the second temperature is ±8℃ of the α-Al precipitation start temperature. In yet another embodiment, the second temperature is 580℃, 576℃, or 575℃. 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 aluminum alloy melt 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 in the melt. Furthermore, the Fe-rich phase precipitated in the aluminum alloy melt requires a certain amount of time to settle. Therefore, increasing the melt holding time is beneficial for the settling of the Fe-rich phase, thereby reducing the Fe content in the melt. It should be understood that extending the melt holding time can only approach 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 parameter must be considered when setting the melt 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 will promote the precipitation, growth, and settling of more Fe-rich phase. Therefore, in one embodiment, the third time is 10–120 min. In another embodiment, the third time is 10–60 min. In yet another embodiment, the third time is 10–30 min.In one embodiment, the third time is 10 minutes. In another embodiment, the third time is 30 minutes. In yet another embodiment, the third time is 60 minutes. The third time can be any point value within the aforementioned range.

[0045] 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 takes place within the original reaction system, for example, a crucible furnace cooling circulation system, causing the melt to rapidly solidify 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 rapidly solidify into an ingot. Therefore, in one embodiment, the second cooling rate is greater than or equal to 20°C / s. In one embodiment, the second cooling rate is 20°C / s.

[0046] exist Figure 1 In step (9), the billet is sawn from the bottom to a first length to obtain a first ingot as a 4XXX forged aluminum alloy 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, compared with the cast aluminum alloy, the Fe content of the first ingot is reduced by 40 to 70%, the weight of the first ingot is more than 80% of the weight of the cast aluminum alloy, and the Fe and Cr content in the prepared billet both meet the composition requirements of the 4XXX forged alloy. In one embodiment, compared with the cast aluminum alloy, the Fe content of the first ingot is reduced by 38%, and the Cr content is 0.084 wt.%, the content of each element is within the composition range of 4032 forged aluminum alloy, and the weight of the obtained 4032 forged aluminum alloy ingot is 92% of the original scrap aluminum weight. In one embodiment, compared to cast aluminum alloy, the first ingot has a 43% lower Fe content and a 0.091 wt.% Cr content, with all element contents within the composition range of 4032 forged aluminum alloy, and the weight of the obtained 4032 forged aluminum alloy ingot is 90% of the original scrap aluminum weight. In another embodiment, compared to cast aluminum alloy, the first ingot has a 51% lower Fe content and a 0.079 wt.% Cr content, with all element contents within the composition range of 4032 forged aluminum alloy, and the weight of the obtained 4032 forged aluminum alloy ingot is 86% of the original scrap aluminum weight. In another embodiment, compared to cast aluminum alloy, the first ingot has a 43% lower Fe content, and the weight of the first ingot is 90% of the weight of cast aluminum alloy. In yet another embodiment, compared to cast aluminum alloy, the first ingot has a 43% lower Fe content. In addition, the Cr content is 0.097 wt.%, and the content of each element is within the composition range of 4032 forged aluminum alloy. Furthermore, the weight of the obtained 4032 forged aluminum alloy ingot is 90% of the original scrap aluminum weight.

[0047] Now refer to Figures 2 to 5 ,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 image shows the microstructure of purified aluminum on the upper part of the ingot when the melt was cooled from 760°C to 580°C at a cooling rate of 0.023°C / s and held for 60 min. Figure 5 The image shows a micrograph of the Fe-rich phase deposit at the bottom of the ingot, obtained by cooling the melt from 760°C to 580°C at a cooling rate of 0.023°C / s and holding 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 are promoted, achieving purification.

[0048] 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.

[0049] 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 Cr content in the fourth melt will typically be less than 0.1 wt.%.

[0050] 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.

[0051] 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.

[0052] Example 1:

[0053] 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 1.06 wt.% and a Si content of 12.68 wt.%. A certain amount of Al-10Cr master alloy was added to the melt to achieve a Si:Cr mass ratio of 25.9, with a measured Cr content of 0.49 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 576℃. The melt was cooled at a rate of 0.023℃ / s (cooling curve shown in [reference needed]). Figure 1 The melt was cooled from 760℃ to 580℃ and held for 10 minutes. The cooling circulation system of the crucible furnace allowed the melt to rapidly solidify into an ingot at a 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 5.5% of the total ingot length. The purified aluminum alloy ingot obtained contained 0.66 wt.% Fe, a 38% reduction compared to the original scrap aluminum. Furthermore, the Cr content was 0.084 wt.%, and all element contents were within the composition range of 4032 forged aluminum alloy. The weight of the obtained 4032 forged aluminum alloy ingot was 92% of the original scrap aluminum weight.

[0054] Example 2:

[0055] 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 1.06 wt.% and a Si content of 12.68 wt.%. A certain amount of Al-10Cr master alloy was added to the melt to achieve a Si:Cr mass ratio of 25.9, with a measured Cr content of 0.49 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 576℃. The melt was cooled at a rate of 0.023℃ / s (cooling curve shown in [reference needed]). Figure 1The melt was cooled from 760℃ to 580℃ and held for 60 minutes. The cooling circulation system of the crucible furnace allowed the melt to rapidly solidify into an ingot at a cooling rate of 10℃ / s. The chemical composition and low-magnification microstructure of the ingot's longitudinal section were analyzed, revealing that the length of the Fe-rich phase deposition layer accounted for 7% of the total ingot length. The purified aluminum alloy ingot obtained contained 0.60 wt.% Fe, a 43% reduction compared to the original scrap aluminum. Furthermore, the Cr content was 0.091 wt.%, and all element contents were within the composition range of 4032 forged aluminum alloy. The weight of the obtained 4032 forged aluminum alloy ingot was 90% of the original scrap aluminum weight.

[0056] Example 3:

[0057] 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 12.43 wt.%. A certain amount of Al-10Cr master alloy was added to the melt to achieve a Si:Cr mass ratio of 27.6, with a measured Cr content of 0.45 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 575℃. The melt was cooled at a rate of 0.023℃ / s (cooling curve shown in [reference needed]). Figure 1 The melt was cooled from 760℃ to 575℃ and held for 60 minutes. The cooling circulation system of the crucible furnace allowed the melt to rapidly solidify into an ingot at a cooling rate of 20℃ / s. The chemical composition and low-magnification microstructure of the ingot's longitudinal section were analyzed, revealing that the length of the Fe-rich phase deposition layer accounted for 10% of the total ingot length. The purified aluminum alloy ingot obtained contained 0.47 wt.% Fe, a 51% reduction compared to the original scrap aluminum. Furthermore, the Cr content was 0.079 wt.%, and all element contents were within the composition range of 4032 forged aluminum alloy. The weight of the obtained 4032 forged aluminum alloy ingot was 86% of the original scrap aluminum weight.

[0058] Example 4:

[0059] 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 1.08 wt.% and a Si content of 12.21 wt.%. A certain amount of Al-10Cr master alloy was added to the melt to achieve a Si:Cr mass ratio of 23.5, with a measured Cr content of 0.52 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 574℃. The melt was cooled at a rate of 0.023℃ / s (cooling curve shown in [reference needed]). Figure 1 The melt was cooled from 760℃ to 580℃ and held for 60 minutes. The cooling circulation system of the crucible furnace allowed the melt to rapidly solidify into an ingot at a cooling rate of 30℃ / 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 7% of the total ingot length. The purified aluminum alloy ingot obtained contained 0.62 wt.% Fe, a 43% reduction compared to the original scrap aluminum. Furthermore, the Cr content was 0.097 wt.%, and all element contents were within the composition range of 4032 forged aluminum alloy. The weight of the obtained 4032 forged aluminum alloy ingot was 90% of the original scrap aluminum weight.

[0060] The parameters and results of Examples 1 to 4 are summarized in Table 1 below.

[0061] Table 1. Parameters and results of Examples 1 to 4

[0062]

[0063] Comparative Example 1: Investigating the effect of the second temperature on the precipitation and deposition of Fe-rich phases

[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 1.02 wt.% and a Si content of 12.44 wt.%. A certain amount of Al-10Cr master alloy was added to the melt to achieve a Si:Cr mass ratio of 27, with a measured Cr content of 0.46 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 576℃. The melt was cooled at a rate of 0.023℃ / s (cooling curve shown in [reference needed]). Figure 2The melt was cooled from 760℃ to 620℃ and held for 10 minutes. The cooling circulation system of the crucible furnace allowed the melt to rapidly solidify into an ingot at a cooling rate of 20℃ / s. Analysis of the chemical composition and low-magnification microstructure of the ingot's longitudinal section revealed that the length of the Fe-rich phase deposition layer accounted for 3% of the total ingot length. The purified aluminum alloy ingot obtained contained 0.82 wt.% Fe, a 20% reduction compared to the original scrap aluminum. However, the Cr content was only 0.24 wt.%, indicating that the Fe content was too high and the Cr content exceeded the standard, resulting in upgrade failure.

[0065] Compared with Example 1, Comparative Example 1 had a temperature 40°C higher, reaching 620°C, which exceeded the scope of the claims. The temperature was too high, causing Fe to be unable to be fully extracted.

[0066] Comparative Example 2: Investigating the effect of the first cooling rate on the precipitation and deposition of Fe-rich phases

[0067] Compared with Example 1, the recycled waste cast aluminum alloy was melted in a graphite crucible at a melting temperature of 760℃. A sample was taken for chemical composition analysis, revealing an Fe content of 1.03 wt.% and a Si content of 12.58 wt.%. A certain amount of Al-10Cr master alloy was added to the melt to achieve a Si:Cr mass ratio of 25.2, with a measured Cr content of 0.50 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 576℃. The melt was cooled at a rate of 1.3℃ / s (the cooling curve is shown in [reference needed]). Figure 1 The melt was cooled from 760℃ to 580℃ and held for 10 minutes. The cooling circulation system of the crucible furnace allowed the melt to rapidly solidify into an ingot at a cooling rate of 20℃ / s. Analysis of the chemical composition and low-magnification microstructure of the ingot's longitudinal section revealed that the length of the Fe-rich phase deposition layer accounted for 2% of the total ingot length. The purified aluminum alloy ingot obtained contained 0.90 wt.% Fe, a 13% reduction compared to the original scrap aluminum. Furthermore, the Cr content was 0.36 wt.%, indicating that the Fe content was too high and the Cr content exceeded the standard, resulting in upgrade failure.

[0068] In Comparative Example 2, compared to Example 1, the melt cooling rate was increased from 0.023°C / s to 1.3°C / s, which exceeds the maximum cooling rate claimed. The excessively high cooling rate prevented the dendritic Fe-containing phase from fully settling to the bottom of the furnace, resulting in poor Fe removal from the alloy.

[0069] The parameters and results of Comparative Examples 1 to 3 are summarized in Table 2 below.

[0070] Table 2. Parameters and results of Comparative Examples 1 to 2

[0071]

[0072] The results of the above embodiments demonstrate that in the method of the present invention:

[0073] (1) By utilizing the initial Fe element content in the cast aluminum alloy and adjusting the Si:Cr mass ratio, a sufficient number of primary Fe-rich phases are formed in the melt.

[0074] (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.

[0075] (3) Accelerate the precipitation of Fe-rich phase by controlling the melt cooling rate; and

[0076] (4) The size and sedimentation process of the Fe-rich phase can be controlled by controlling the holding time of the melt.

[0077] Industrial applicability

[0078] 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 4XXX forged aluminum alloy ingot has a large weight and high purity; and it also balances production efficiency, reducing overall production costs and achieving the goal of upgrading and transforming into forged aluminum alloys with higher added value.

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 Cr content of the cast aluminum alloy; (3) Based on the Si and Cr content obtained in step (2), calculate the amount of Fe-rich phase precipitant according to the silicon-chromium ratio, wherein the Fe-rich phase precipitant is an Al-Cr 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 (9) Starting from the bottom of the billet, the billet is sawn to a first length to obtain a first ingot as a 4XXX forged aluminum alloy 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 is such that the mass ratio of Si to Cr in the second melt is 20-30. The first cooling rate is 0.01~1℃ / s; The second temperature is within the range of ±20°C of the α-Al phase precipitation start temperature calculated in step (6); The second cooling rate is greater than or equal to 20°C / s; and The third time is 10~120 min.

2. The method according to claim 1, characterized in that: The amount of the Fe-rich phase precipitant used is such that the mass ratio of Si to Cr in the second melt is 23-28. The first cooling rate is 0.02~0.7℃ / s; The second temperature is within the range of ±8°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 2, characterized in that: The mass ratio of Si to Cr in the second melt is 23.5, 25.2, 25.9, 27.0, or 27.

6.

4. The method according to claim 2, characterized in that: The first cooling rate is 0.023℃ / s.

5. The method according to claim 2, characterized in that: The second temperature is 580℃, 576℃ or 575℃.

6. The method according to claim 2, characterized in that: The third time is 10~30 minutes.

7. The method according to claim 2, characterized in that: The third time is 10 minutes, 30 minutes, or 60 minutes.

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

9. 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.

10. The method according to claim 1, characterized in that: The degassing and refining process is carried out by introducing inert gas using a degasser, with a blowing rate of 500~2000 mL / min.

11. The method according to claim 1, characterized in that: Step (7) is performed without stirring the melt, and the residual Cr content in the fourth melt is less than 0.1 wt.%.

12. 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.

13. The method according to any one of claims 1-12, characterized in that: The initial Fe content in the cast aluminum alloy is at least 0.5 wt.%; optionally, the Ni content in the cast aluminum alloy is 0~1.0 wt.%, 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.

14. The method according to claim 13, characterized in that: 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 Cr content of 0~0.1 wt.%, with the remainder being Al.

15. The method according to any one of claims 1-12, 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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