A Method for Smelting and Removing Iron from Recycled Aluminum Alloys Using a Synergistic Ultrasonic-Electromagnetic Field

Abstract

This invention discloses a method for smelting and removing iron from recycled aluminum alloys using a synergistic ultrasonic-electromagnetic field. The method includes: melting scrap aluminum and pure aluminum ingots in a specific ratio and then skimming off the slag; adding a manganese-rich and chromium-rich master alloy for chemical neutralization and precise control of the Mn / Fe and Cr / Fe mass ratios in the melt; activating an electromagnetic stirring device at the furnace bottom for homogenization, utilizing Lorentz force to eliminate temperature and composition gradients; subsequently maintaining weak electromagnetic stirring and introducing high-energy ultrasound for synergistic purification, utilizing ultrasonic cavitation to break up the primary iron-rich phase and adsorb tiny bubbles to the surface; finally, casting after settling and two-stage ceramic filtration. This invention effectively transforms the coarse needle-like β-Fe phase in recycled aluminum into a fine, dispersed α-Fe phase through a dual approach of physical field synergistic chemical neutralization, significantly reducing the hydrogen content and micron-sized oxide inclusions in the melt. This greatly improves waste utilization while enabling the recycled aluminum alloy to achieve excellent elongation and surface quality.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy smelting and resource recycling technology, and particularly to a method for smelting and removing iron from recycled aluminum alloys using a synergistic ultrasonic-electromagnetic field. Background Technology

[0002] The recycling of scrap aluminum (i.e., recycled aluminum) has become an important development direction for the aluminum processing industry. In the recycling process of 6-series aluminum alloys (Al-Mg-Si series, such as 6063, 6061, etc.), due to the complex source of raw materials, including construction waste, cutting chips, etc., the melt usually contains a high content of impurity iron (Fe).

[0003] Under conventional smelting conditions, iron readily forms coarse, needle-like β-Fe during the solidification of molten aluminum. This needle-like phase is highly hard and brittle, acting like microscopic "blades" to cut through the aluminum matrix, causing severe stress concentration. This leads to quality problems in recycled aluminum materials during subsequent extrusion processing, such as cracks, low elongation at break, poor corrosion resistance, and surface pitting or black lines.

[0004] Currently, the main industrial methods for addressing the hazards of iron impurities in recycled aluminum include:

[0005] 1. Pre-treatment before melting: Use a strong magnet or magnetic separator to remove steel parts (such as screws and iron filings) mixed in with the waste aluminum. This is the most basic and economical method, but the solution does not have ultimate stability.

[0006] 2. Chemical element neutralization: Adding metallic manganese (Mn) or manganese-containing additives (such as Al-Mn master alloys) to molten aluminum can significantly improve the plasticity, toughness, and processing properties of the alloy, and is an essential standard process in the production of recycled aluminum, especially cast aluminum alloys. However, in traditional static furnaces, alloying relies on natural diffusion, and the distribution of the neutralizing agent metallic manganese (Mn) is often uneven, resulting in the continued presence of the β-Fe phase in local areas; at the same time, due to the lack of effective kinetic conditions, the primary α-Fe phase particles are often relatively coarse.

[0007] 3. Physical sedimentation and filtration: Ceramic foam filter plates are used for filtration. Before the melt is transferred or poured, it is passed through a filter box equipped with ceramic filter plates. Although this can remove some non-metallic inclusions, it is ineffective against dissolved iron elements, and the ceramic filter plates are prone to clogging.

[0008] Therefore, there is an urgent need for a composite process that can comprehensively utilize the advantages of chemical regulation and multiple physical fields to achieve precise control of iron-rich phase morphology, deep homogenization of composition, and efficient purification of melt. Summary of the Invention

[0009] (1) Technical problems to be solved

[0010] The purpose of this invention is to provide a method for smelting and removing iron from recycled aluminum alloys using a synergistic ultrasonic-electromagnetic field. This method overcomes the limitations of existing technologies that rely on manual screening, chemical neutralization, and physical sedimentation and filtration to effectively convert harmful iron impurities in recycled aluminum alloys. It reduces the content of needle-like β-Fe in recycled aluminum alloys, minimizing its damaging effects and reducing quality issues such as cracks, pitting, and black lines. This invention optimizes the needle-like β-Fe, transforming it into a more rounded, Chinese character-shaped α-Fe phase, thereby minimizing its harmful effects and improving the overall mechanical properties of the recycled aluminum alloy.

[0011] (2) Technical solution

[0012] To solve the above-mentioned technical problems, in a first aspect of the present invention, the following is provided:

[0013] A method for smelting and removing iron from recycled aluminum alloys using a synergistic ultrasonic-electromagnetic field, comprising the following steps:

[0014] 1) Batching and melting: 70-100% of scrap aluminum and 0-30% of pure aluminum ingots are loaded into the smelting furnace in proportion, heated and melted. When the melt temperature reaches 720-740℃, slag is removed.

[0015] 2) Chemical neutralization and regulation: The Fe content in the melt is detected, and manganese-rich master alloy and chromium-rich master alloy are added as iron phase neutralizers to adjust the Mn / Fe mass ratio and Cr / Fe mass ratio in the melt to promote the transformation of acicular β-Fe phase to α-Fe phase;

[0016] 3) Electromagnetic stirring homogenization: Turn on the electromagnetic stirring device at the bottom of the melting furnace, and use the Lorentz force to drive the melt to force convection, so that the added neutralizing agent can be quickly and evenly diffused to all parts of the melt.

[0017] 4) Ultrasonic-electromagnetic synergistic purification: Reduce the frequency of the electromagnetic stirring device to maintain the micro-flow of the melt, while inserting the ultrasonic amplitude transformer below the surface of the melt and turning on the ultrasonic generator for treatment; utilize the cavitation effect of ultrasound to break up the primary iron-rich phase and adsorb tiny bubbles to float to the surface.

[0018] 5) Settling and Filtration Casting: Turn off the electromagnetic stirring device and ultrasonic generator, let it settle, filter the melt through a double-stage ceramic filter plate, and finally carry out the casting operation.

[0019] Preferably, the scrap aluminum in step 1) is grade I or grade II scrap aluminum of the 6 series with an iron content of ≤0.5%.

[0020] Preferably, in step 2), the mass ratio of Mn / Fe in the melt needs to be controlled within the range of 0.5-0.7%, and the mass ratio of Cr / Fe needs to be controlled within the range of 0.1-0.2%.

[0021] Preferably, in step 3), the frequency of the electromagnetic stirring device is set to 2-5Hz, the current is set to 200-300A, and the stirring time is 5-8min.

[0022] Preferably, in step 4), the frequency of the electromagnetic stirring device is reduced to 1-2 Hz; the ultrasonic amplitude transformer is inserted into the melt to a depth of 50-100 mm; the power of the ultrasonic generator is 1.5-2.0 kW, the frequency is 19-21 kHz, and the processing time is 10-15 min.

[0023] Preferably, the dual-stage ceramic filter plate in step 5) includes a first-stage 30PPI ceramic filter plate and a second-stage 60PPI ceramic filter plate.

[0024] The second-stage 60PPI ceramic filter plate is coated with a fluoride adsorption layer, the main component of which is NaF.

[0025] Preferably, the casting method in step 5) is semi-continuous casting, and the casting temperature is controlled at 710-730℃.

[0026] Preferably, α-Fe is shaped like a rounded Chinese character.

[0027] (3) Beneficial effects

[0028] Compared with the prior art, the present invention has the following significant advantages:

[0029] 1. Complete improvement of iron phase morphology: Since iron impurities are difficult to completely remove under practical conditions, we can find a way to "transform" them, changing them from sharp "glass shards" to relatively mild and smooth "pebbles". Through the synergistic effect of "chemical neutralization + electromagnetic mass transfer + ultrasonic crushing", the harmful needle-like β-Fe is almost completely transformed into fine and dispersed α-Fe phase, eliminating stress concentration sources, thereby minimizing its harm and improving the comprehensive mechanical properties of aluminum alloys.

[0030] 2. High purification efficiency: Ultrasonic cavitation significantly reduces the hydrogen content and micron-sized oxide inclusions in the melt, solving the problem of "high pinholes" in recycled aluminum; the micro-flow of electromagnetic stirring in step 4) ensures that ultrasonic treatment can cover the entire melt area, avoiding processing dead zones.

[0031] 3. High waste utilization rate: This process allows the use of secondary waste aluminum with high iron content as raw material to produce high-quality aluminum alloy profiles, which greatly reduces raw material costs.

[0032] 4. Improved mechanical properties: Compared with traditional processes, recycled aluminum alloy bars produced using this method have an elongation rate that is more than 20% higher and a tensile strength that is more than 10% higher.

[0033] In summary, the method provided by this invention can be fully implemented from the laboratory to large-scale industrial applications, especially in the field of pursuing high value-added products. It is a forward-looking and advanced process solution that aims to solve industry pain points. Attached Figure Description To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a flowchart illustrating the steps of the ultrasonic-electromagnetic composite field synergistic method for regenerating aluminum alloys and removing iron. Detailed Implementation

[0034] The present invention will be described in detail below using different manufacturing processes. The examples listed will enable those skilled in the art to better understand the present invention, but will not limit the present invention in any way. For example, the present invention can be extended to the production of aluminum alloys of other strengths or other alloys with similar properties.

[0035] Example 1:

[0036] A method for producing 6063 recycled aluminum alloy:

[0037] 1) Batching and melting: The raw materials consist of 70% scrap aluminum profiles from buildings, with an Fe content of 0.35% and 30% primary aluminum materials. After melting, the temperature is controlled at 735℃, and slag is removed.

[0038] 2) Chemical neutralization and regulation: Add Al-20Mn and Al-10Cr master alloys to adjust the Mn / Fe mass ratio to 0.5% and the Cr / Fe mass ratio to 0.15%.

[0039] 3) Electromagnetic stirring for homogenization: Turn on the electromagnetic stirrer at the bottom of the furnace, set the frequency to 3Hz and the current to 250A, and run it for 6 minutes to ensure that the neutralizing agent is completely melted and evenly distributed.

[0040] 4) Ultrasonic-electromagnetic synergistic purification: Reduce the electromagnetic stirring frequency to 1Hz, insert a titanium alloy ultrasonic probe to a depth of 80mm, turn on the ultrasonic generator with a power of 1.8kW and a frequency of 20kHz, and process for 12 minutes.

[0041] 5) Settling and Filtration Casting: After settling for 15 minutes, the mixture is filtered through a dual-stage ceramic filter plate. After passing through a first-stage 30PPI ceramic filter plate and a second-stage 60PPI ceramic filter plate with a NaF adsorption layer, the mixture is semi-continuously cast at 720℃.

[0042] Example 2:

[0043] A method for producing 6061 recycled aluminum alloy:

[0044] 1) Batching and melting: The raw materials consist of 100% scrap aluminum profiles from buildings, with an Fe content of 0.45%. After melting, the temperature is controlled at 735℃, and slag is removed.

[0045] 2) Chemical neutralization and regulation: Al-20Mn and Al-10Cr master alloys were added to adjust the Mn / Fe mass ratio to 0.7% and the Cr / Fe mass ratio to 0.15%.

[0046] 3) Electromagnetic stirring for homogenization: Turn on the electromagnetic stirrer at the bottom of the furnace, set the frequency to 5Hz and the current to 250A, and run for 6 minutes to ensure that the neutralizing agent is completely melted and evenly distributed.

[0047] 4) Ultrasonic-electromagnetic synergistic purification: Reduce the electromagnetic stirring frequency to 1Hz, insert a titanium alloy ultrasonic probe to a depth of 50mm, turn on the ultrasonic generator with a power of 2.0kW and a frequency of 20Hz, and process for 15 minutes.

[0048] 5) Settling and Filtration Casting: After settling for 20 minutes, the mixture is filtered through a dual-stage ceramic filter plate. After passing through a first-stage 30PPI ceramic filter plate and a second-stage 60PPI ceramic filter plate with a NaF adsorption layer, the mixture is semi-continuously cast at 715℃.

[0049] Comparative Example 1

[0050] The only difference from Example 1 is that in step 5), a regular 60PPI ceramic filter plate is used without a fluoride adsorption layer.

[0051] Comparative Example 2

[0052] The traditional process is adopted, which differs from Example 1 in that electromagnetic stirring and ultrasonic waves are not turned on in steps 3) and 4), and only manual stirring and traditional nitrogen blowing refining are performed, with a refining time of 15 minutes.

[0053] Comparative Example 3

[0054] The method using a single ultrasonic field differs from Example 1 in that electromagnetic stirring is not activated in step 3), and ultrasonic treatment is performed directly. Due to the lack of forced convection and the large volume of the melt, the neutralizer is unevenly mixed due to natural diffusion.

[0055] The recycled aluminum alloys obtained by the methods in Example 1, Example 2 and the three comparative examples were subjected to performance tests, and the following experimental data were obtained, as detailed in Table 1.

[0056] Table 1. Detection results of mass percentage of different components

[0057] project Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Tensile strength / MPa 215 220 212 195 205 Yield strength / MPa 180 185 178 160 170 Elongation after fracture (%) 22.5 21.0 13.8 8.5 11.0 Hydrogen content (ml / 100g) 0.09 0.10 0.09 0.18 0.12

[0058] Based on the above data, the performance test and results were analyzed as follows:

[0059] 1. As can be seen from the comparison between Example 1 and Comparative Example 1, the filter plate with the adsorption layer has a slight improvement in performance, indicating that it helps to further intercept fine inclusions.

[0060] 2. As can be seen from the comparison between Example 1 and Comparative Example 2, the composite field synergistic process of the present invention increases the elongation at break from 8.5% to 14.5% and reduces the hydrogen content by about 50%. Metallographic observation shows that there are a large number of needle-like β-Fe phases that cut the matrix in Comparative Example 2, while the iron phase in Example 1 is transformed into harmless spherical or small Chinese character-shaped phases. This is the fundamental reason for the performance improvement.

[0061] 3. As can be seen from the comparison between Example 1 and Comparative Example 3, when electromagnetic stirring is absent, although ultrasound is used, the degassing and deterioration effects are reduced due to uneven composition and limited range of ultrasound. This shows that the synergistic effect of "electromagnetic + ultrasound" is necessary.

[0062] In summary, the recycled aluminum alloy profiles prepared by the method of this invention have the advantages of increased elongation at break and reduced hydrogen content, further improving the mechanical properties of the recycled aluminum alloy profiles. In addition, no cracks will appear after processing, the corrosion resistance is enhanced, and there will be no quality problems such as "pitting" or "black lines" on the surface, thus improving the quality of the product. Compared with recycled aluminum alloys made by traditional processes, it has more obvious advantages and better market prospects.

[0063] The above description is merely a preferred embodiment of the present invention. All equivalent variations and modifications made within the scope of the claims of this invention should fall within the scope of this invention. The scope of protection should be determined by the appended claims.

Claims

1. A method for smelting and removing iron from recycled aluminum alloys using a synergistic ultrasonic-electromagnetic field, characterized in that: Includes the following steps: 1) Batching and melting: 70-100% of scrap aluminum and 0-30% of pure aluminum ingots are loaded into the smelting furnace in proportion, heated and melted. When the melt temperature reaches 720-740℃, slag is removed. 2) Chemical neutralization and regulation: The Fe content in the melt is detected, and manganese-rich master alloy and chromium-rich master alloy are added as iron phase neutralizers to adjust the Mn / Fe mass ratio and Cr / Fe mass ratio in the melt to promote the transformation of acicular β-Fe phase to α-Fe phase; 3) Electromagnetic stirring homogenization: Turn on the electromagnetic stirring device at the bottom of the melting furnace, and use the Lorentz force to drive the melt to force convection, so that the added neutralizing agent can be quickly and evenly diffused to all parts of the melt. 4) Ultrasonic-electromagnetic synergistic purification: Reduce the frequency of the electromagnetic stirring device to maintain the micro-flow of the melt, while inserting the ultrasonic amplitude transformer below the surface of the melt and turning on the ultrasonic generator for treatment; utilize the cavitation effect of ultrasound to break up the primary iron-rich phase and adsorb tiny bubbles to float to the surface. 5) Settling and Filtration Casting: Turn off the electromagnetic stirring device and ultrasonic generator, let it settle, filter the melt through a double-stage ceramic filter plate, and finally carry out the casting operation.

2. The method for smelting and removing iron from recycled aluminum alloys using a synergistic ultrasonic-electromagnetic field as described in claim 1, characterized in that: The scrap aluminum in step 1) is grade I or grade II scrap aluminum of the 6 series with an iron content of ≤0.5%.

3. The method for smelting and removing iron from recycled aluminum alloys using a synergistic ultrasonic-electromagnetic field as described in claim 1, characterized in that: In step 2), the mass ratio of Mn / Fe in the melt needs to be controlled within the range of 0.5-0.7%, and the mass ratio of Cr / Fe needs to be controlled within the range of 0.1-0.2%.

4. The method for smelting and removing iron from recycled aluminum alloys using a synergistic ultrasonic-electromagnetic field as described in claim 1, characterized in that: In step 3), the frequency of the electromagnetic stirring device is set to 2-5Hz, the current is set to 200-300A, and the stirring time is 5-8min.

5. The method for smelting and removing iron from recycled aluminum alloys using a synergistic ultrasonic-electromagnetic field as described in claim 1, characterized in that: In step 4), the frequency of the electromagnetic stirring device is reduced to 1-2Hz; the ultrasonic amplitude transformer is inserted into the melt to a depth of 50-100mm; the power of the ultrasonic generator is 1.5-2.0kW, the frequency is 19-21kHz, and the processing time is 10-15min.

6. The method for smelting and removing iron from recycled aluminum alloys using a synergistic ultrasonic-electromagnetic field as described in claim 5, characterized in that: The dual-stage ceramic filter plate in step 5) includes a first-stage 30PPI ceramic filter plate and a second-stage 60PPI ceramic filter plate. The second-stage 60PPI ceramic filter plate is coated with a fluoride adsorption layer, the main component of which is NaF.

7. The method for smelting and removing iron from recycled aluminum alloys using a synergistic ultrasonic-electromagnetic field according to claim 1 or 6, characterized in that: The casting method in step 5) is semi-continuous casting, and the casting temperature is controlled at 710-730℃.

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