Regulation and control method for circulating aluminum alloy and Fe-rich phase structure characteristics of circulating aluminum alloy

Abstract

The invention discloses a circulating aluminum alloy and a method for regulating and controlling the structure characteristics of a circulating aluminum alloy Fe-rich phase, and the method comprises the following steps: S1, taking an Al ingot and a recycled alloy as raw materials, and the raw materials comprise the following components in percentage by mass: 7% < = Si < = 10%, 0.5% < = Mg, 0.3% < = Cu, 0.1% < = Ti, 1% < = Fe, and the balance of Al and inevitable impurities; s2, the smelting temperature is kept at 760-800 DEG C, all the raw materials are added and then melted, and a grain refiner is added and stirred to be melted; s3, after the temperature is 720 DEG C, a modifier is added, and then argon is introduced for degassing refining; s4, the refined aluminum alloy is subjected to casting molding, and ultrasonic waves are applied; reducing the temperature to 680 DEG C, and stopping applying the ultrasonic waves; and S5, the cast ingot obtained after pouring is completed is naturally cooled to the room temperature. According to the method, a needle-sheet-shaped beta-Fe phase can be converted into a Chinese-character-shaped alpha-Fe phase in the growth stage, and the Chinese-character-shaped alpha-Fe phase is further refined, uniformly dispersed and distributed in the solidification stage, so that the mechanical property of the circulating aluminum alloy is equivalent to that of traditional primary aluminum.

Description

Technical Field

[0001] This invention belongs to the field of recycled aluminum alloy application technology, specifically relating to a recycled aluminum alloy and a method for controlling the Fe-rich phase microstructure characteristics of the recycled aluminum alloy. Background Technology

[0002] Cast aluminum alloys, due to their excellent casting fluidity, are widely used in the die-casting of new energy vehicle parts. Recycled aluminum alloys, on the other hand, are obtained by recycling and reusing waste aluminum. Compared to virgin aluminum alloys, the energy consumption required for their production is significantly reduced, making them important for energy conservation, environmental protection, and resource recycling.

[0003] Because Fe has extremely low solid solubility in Al, the continuous accumulation of Fe during the recycling of aluminum alloys leads to the formation of a Fe-rich phase in the alloy melt. In cast aluminum alloys with high Si content, the presence of Fe usually induces the formation of needle-like β-AlFeSi phases, which rupture the matrix and result in extremely low elongation of the aluminum alloy.

[0004] Traditional methods for eliminating the harmful effects of Fe-rich phases mainly involve adding transition elements such as Mn, Cr, and Ni. These elements utilize similar atomic characteristics to replace Fe atoms at their sites in the β-AlFeSi phase, thereby altering the preferred growth direction of the crystal structure. This transforms the Fe-rich phase into the less damaging α-Al(Fe,Mn,Cr,Ni)Si phase, reducing its cutting effect on the matrix and thus improving the elongation of recycled aluminum alloys.

[0005] However, due to the lack of clarity regarding the evolution mechanism of Fe-rich phase microstructure, the methods for precisely controlling the microstructure of the Fe phase are still unclear, leading to a weakening of the control effect on Fe-rich phase. Although the addition of rare earth elements such as La, Sc, or Er can also control the morphology of Fe-rich phase, their relatively high cost limits their use in industrial production.

[0006] Existing reports on the application of ultrasonic processing technology to the fragmentation and control of Fe-rich phases demonstrate how ultrasonic energy breaks down dendritic structures, resulting in finer, more uniformly distributed, regular microstructures. This regular microstructure can reduce stress concentration during service and improve the mechanical properties of alloy castings. However, the microstructure of Fe-rich phases in cast aluminum alloys is not that of traditional dendrites, but rather a lamellar β-AlFeSi phase with a significant preferred growth tendency. This lamellar structure lacks obvious weak points, and ultrasonic waves cannot achieve grain refinement like they can by breaking down the fragile necks between dendrites. Summary of the Invention

[0007] To address the problems of low energy utilization (approximately 35%), melt overheating, and cavitation effect attenuation in traditional continuous ultrasonic processing, this invention innovatively adopts a temperature-triggered intermittent ultrasonic strategy. By changing the frequency and loading time of the ultrasonic waves, the solute field during the nucleation and growth of the Fe-rich phase can be controlled. This provides a method for controlling the microstructure characteristics of the Fe-rich phase in cyclic aluminum alloys based on temperature gradient ultrasonic processing, which can effectively achieve grain refinement of the Fe-rich phase.

[0008] The present invention achieves the above objectives using the following technical solution: A recycled aluminum alloy, wherein the components in the aluminum alloy are in the following mass percentages: 7%≦Si≦10%, Mg≦0.5%, Cu≦0.3%, Ti≦0.1%, Fe≦1%, with the balance being Al and unavoidable impurities, wherein the total amount of unavoidable impurities is less than 0.05%.

[0009] This invention also provides a method for controlling the Fe-rich phase microstructure of recycled aluminum alloys, comprising the following steps: Step S1: Using Al ingots, recycled Al-Fe alloys, Al-Mg alloys, Al-Si alloys, and Al-Cu alloys as raw materials, the mass ratio of their composition is: 7%≦Si≦10%, Mg≦0.5%, Cu≦0.3%, Ti≦0.1%, Fe≦1%, with the balance being Al and unavoidable impurities, wherein the total amount of unavoidable impurities is less than 0.05%; Step S2: Maintaining the temperature of the melting furnace within the range of 760℃-800℃, adding the various alloys from Step S1 and melting them, and after all intermediate alloys have melted uniformly, adding an α-Al grain refiner and stirring to melt; Step S3: Add a slag remover to the melt at 730℃ to remove slag. The slag remover is 40% Na3AlF6 + 30% Na2CO3 + 20% CaF2 + 10% Na2B4O7, with an addition amount of 1.5-2.5 kg / ton of aluminum. Step S4: After slag removal, determine the total Fe content X in the melt (calculate the Mn content addition ratio based on a 1% mass ratio of Fe in the recycled aluminum alloy). Add a Fe-rich phase refiner containing Mn in two steps, with the total addition calculated as Mn / Fe = 1.2. The first addition is 70% of the total Mn content (i.e., 0.84X), added when the melt temperature is controlled at 730±5℃, and a second addition is made in subsequent steps. Step S5: After the furnace temperature is controlled at 720℃, add a eutectic Si modifier to modify the eutectic Si, and then introduce argon gas. Degassing and refining; Step S6: Cast the refined aluminum alloy into a mold, apply ultrasonic waves in the temperature range of 680-720℃, trigger an ultrasonic pulse for 1 minute every 5℃ decrease in temperature, and the parameters of each ultrasonic pulse are independently adjustable, for a total of 8 processing cycles; When the temperature of the melting furnace is controlled at 700±5℃, add 30% of the total Mn amount for the second time, i.e., 0.36X in step S43, and add the remaining 30% of the total amount of Fe-rich phase refining agent to maintain the dynamic balance of Mn / Fe ratio; When the melt temperature drops to 680℃, stop applying ultrasonic waves; Step S7: After casting, allow the aluminum alloy ingot to cool naturally to room temperature in the air.

[0010] Preferably, the α-Al grain refiner is Al-Ti-B, and the modifier of the eutectic Si is an Al-Sr master alloy.

[0011] Preferably, the amount of the added grain refiner Al-Ti-B and eutectic Si modifier Al-Sr does not exceed 0.2% of the aluminum melt by mass percentage.

[0012] Preferably, the argon gas is introduced for 30 minutes in step S3, and the alloy composition is tested after refining.

[0013] Preferably, the parameters of each ultrasonic pulse in step S6 are independently adjustable, with the initial high-temperature range of 700-720℃ using a low-frequency, high-energy pulse of 20Hz and 1.8W / cm. 3 For the low-temperature range of 680-700℃, a high-frequency fine-tuning of 30Hz and 1.2W / cm² is used. 3 .

[0014] Preferably, the parameters of each ultrasonic pulse in step S6 are independently adjustable, with the initial high-temperature range of 715-720℃ using a low-frequency, high-energy pulse of 20Hz at 1.8W / cm². 3 700-715℃ using low-frequency high-energy 25Hz, 1.5W / cm 3 685-700℃ using low-frequency high-energy 30Hz, 1.2W / cm² 3 In the low-temperature range of 680-685℃, a high-frequency fine-tuning of 40Hz and 0.8W / cm² is used. 3 .

[0015] Preferably, an additional 15-second ultrasonic micropulse at 40Hz and 0.8W / cm is added at 690℃. 3 This can further eliminate aggregates smaller than 3 μm.

[0016] Preferably, the probe for applying ultrasonic waves is coated with a tantalum alloy. When applying ultrasonic waves, it is inserted into the melt at a 20° angle to a depth of 1 / 3 of the molten pool height, forming a three-dimensional stereo sound field. The cavitation density gradient generated by each ultrasonic pulse is 10. 5 -10 7 The bubble density is 85-90% during the interval between adjacent pulses.

[0017] Preferably, when the melt volume is greater than 500 kg, dual probes with a 90° phase difference are used to work alternately.

[0018] Preferably, a static buffer zone of 4-5°C is set during the ultrasonic interval to allow the melt viscosity to increase naturally (from 0.89 mPa·s to 1.12 mPa·s), thereby enhancing the cavitation threshold of the next ultrasonic test; and an infrared temperature feedback system is used to control the cooling rate at 5±0.5°C / min to ensure that the temperature triggering accuracy reaches ±1.5°C.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The method of this invention, based on chemical modification of Mn, achieves multi-stage progressive refinement of the Fe-rich phase by precisely controlling intermittent ultrasonic treatment during the cooling process; by adding Mn, the Fe-rich phase type is transformed from β-AlFeSi phase to α-Al(Fe,Mn,Cr,Ni)Si phase; and by applying ultrasonic waves with different parameters based on temperature gradient changes to optimize the ultrasonic treatment process, the uniform nucleation and growth of the α-Al(Fe,Mn,Cr,Ni)Si phase is achieved.

[0020] 2. The control method of the present invention, by using the neutralizing element Mn and ultrasonic vibration at different stages of smelting, can transform the characteristics of the Fe-rich phase from needle-like β-Fe to Chinese character-shaped α-Fe. Furthermore, ultrasonic vibration can achieve a uniform distribution of α-Fe, reducing stress concentration during deformation and thus enabling aluminum alloy products to obtain high strength and elongation.

[0021] 3. The total energy consumption of intermittent ultrasonic treatment in this invention is 42% of that of continuous treatment, while the refining efficiency is improved by about 35% (the refining amount per unit energy consumption reaches 1.8 μm / kJ); when the melt temperature drops to 685℃, the final ultrasonic refining is performed, at which time the viscosity of the melt is measured to be 1.05 mPa·s, which can form a stable dispersion distribution without phase agglomeration.

[0022] 4. The method of the present invention is particularly suitable for castings with large differences in wall thickness (such as engine cylinder blocks), which can avoid the phenomenon of Fe-rich phase enrichment in thin-walled areas caused by traditional processes; at the same time, a multi-probe collaborative system has been developed, which can adopt a dual-probe alternating working mode with a phase difference of 90° when the melt volume is >500kg.

[0023] 5. The temperature gradient pulse ultrasound method of the present invention can also be extended to the regulation of other intermetallic compounds (such as Al2Cu, Mg2Si, etc.), and has successfully achieved the complete transformation of β-AlFe phase to α-Al(Fe,Mn) phase in Al-Cu-Mn alloys. Attached Figure Description

[0024] Figure 1 Schematic diagram of the evolution of Fe-rich phase microstructure in alloys under different treatment methods.

[0025] Figure 2 : A flowchart of a preferred embodiment of the control method of the present invention.

[0026] Figure 3 Scanning electron microscope image of the aluminum alloy product after ultrasonic treatment according to the preferred embodiment. Detailed Implementation

[0027] The control method of this invention mainly utilizes ultrasonic refinement, cavitation, and acoustic effects to optimize the solute and temperature fields during the solidification process of the Fe-rich phase, thereby realizing the intrinsic mechanism of Fe-rich phase morphology growth control. Based on Mn element chemical modification, intermittent ultrasonic treatment during the cooling process is precisely controlled to achieve multi-stage progressive refinement of the Fe-rich phase. Specifically, in the initial nucleation and growth stage, the needle-like β-Fe phase transforms into a Chinese character-shaped α-Fe phase. In the subsequent solidification stage, the Chinese character-shaped α-Fe phase is further refined and uniformly dispersed, transforming the harmful Fe-rich phase into a beneficial grain boundary second phase. This results in the mechanical properties of the recycled aluminum alloy being comparable to those of traditional primary aluminum.

[0028] like Figure 1 As shown in the figure, the morphological evolution of the Fe phase under different treatment methods is shown in the figure. (a) The iron phase obtained by modification without adding Mn is a needle-like beta-Fe phase; (b) The Fe-rich phase obtained by modification after adding Mn is an irregular Chinese character-shaped alpha-Fe phase; (c) The alpha-Fe phase obtained after modification with Mn and gradient ultrasonic treatment is a near-hexagonal and uniformly distributed alpha-Fe phase.

[0029] Figure 2 The diagram shown is a flowchart of a preferred embodiment of the control method of the present invention. The control method for the Fe-rich phase microstructure of recycled aluminum alloy provided in this embodiment involves the preliminary smelting of recycled pretreated waste aluminum in a resistance furnace, followed by slag removal and degassing, and then casting into shape using a mold after applying different ultrasonic treatments. The specific steps include: Step S1: Using Al ingots, recycled Al-Fe alloy, Al-Mg alloy, Al-Si alloy, and Al-Cu alloy as raw materials, the mass ratio of their composition is: Si=8%, Mg=0.5%, Cu=0.2%, Ti=0.1%, Fe=1%, with the balance being Al and unavoidable impurities, wherein the total amount of unavoidable impurities is less than 0.05%; Step S2: Maintain the temperature of the melting furnace within the range of 760℃-800℃, add the various alloys from step S1 and melt them. After all the intermediate alloys have melted evenly, add the Al-Ti-B grain refiner and stir to melt. Step S3: Add a slag remover to the melt at 730℃ to remove slag. The slag remover is 40% Na3AlF6 + 30% Na2CO3 + 20% CaF2 + 10% Na2B4O7, and the addition amount is 1.5-2.5 kg / ton of aluminum. The specific addition amount can be dynamically adjusted according to the Fe content.

[0030] Step S4: After slag removal, determine the total Fe content X in the melt (calculate the Mn content addition ratio based on a 1% mass ratio of Fe in the recycled aluminum alloy); add the Fe-rich phase refiner (Al-Mn master alloy) containing Mn in two batches. The amount of Mn added depends on the Fe content, and the total addition is calculated based on Mn / Fe=1.2. The first addition is 70% of the total Mn content (i.e., 0.84X), which will be added when the melt temperature is controlled at 730±5℃. A second addition will be made in subsequent steps. Step S5: After the temperature of the melting furnace is controlled at 720℃, Al-Sr master alloy is added to modify the eutectic Si. Then, argon gas is introduced for degassing and refining for 30 minutes. After refining, the alloy composition is tested.

[0031] The above-mentioned component testing process is generally carried out in the following way: after refining, the melt sample is taken, water-cooled to make a standard test block, and after grinding and polishing, it is placed in a spectrometer. The atomic emission spectrum is excited by high-voltage spark, the intensity of characteristic spectral lines (such as Fe 238.204nm, Si 288.16nm) is analyzed, and the content of each element is quantitatively calculated in combination with the standard curve.

[0032] Step S5: The refined aluminum alloy is cast into shape, and ultrasonic waves are applied within a temperature range of 680-720℃. An ultrasonic pulse is triggered for 1 minute every 5℃ decrease in temperature, and the parameters of each ultrasonic pulse are independently adjustable. A total of 8 processing cycles are performed. When the temperature of the melting furnace is controlled at 700±5℃, the remaining 30% of the total amount of the Fe-rich phase refining agent (Al-Mn master alloy), i.e., 0.36X from step S4, is added for the second time to maintain the dynamic balance of the Mn / Fe ratio. When the melt temperature drops to 680℃, the ultrasonic application is stopped. Step S6: After casting, the aluminum alloy ingot is allowed to cool naturally to room temperature in the air.

[0033] The added grain refiner Al-Ti-B and eutectic Si modifier Al-Sr are added at a mass percentage of 0.15% of the aluminum melt.

[0034] When the Fe content in the melt is greater than 1.0 wt%, the temperature range for applying ultrasound needs to be extended to 675-725℃. Within this temperature range, the ultrasound should be applied by triggering an ultrasonic pulse for 1 minute every 5℃ decrease in temperature.

[0035] As shown in Table 1, the parameters of each ultrasonic pulse applied in step S4 of this embodiment are set as follows: for the initial high-temperature range of 715-720℃, a low-frequency, high-energy pulse of 20Hz and 1.8W / cm² is used. 3 700-715℃ using low-frequency high-energy 25Hz, 1.5W / cm 3685-700℃ using low-frequency high-energy 30Hz, 1.2W / cm² 3 In the low-temperature range of 680-685℃, a high-frequency fine-tuning of 40Hz and 0.8W / cm² is used. 3 .

[0036] Table 1. Ultrasonic pulse parameter settings in the preferred embodiment

[0037] like Figure 2 As shown, this embodiment employs two ultrasonic probes in the temperature gradient-based ultrasonic processing, enabling the coupled addition of different frequencies, temperatures, times, and powers to the alloy melt. Both probes are coated with tantalum alloy, and the insertion depth during ultrasonic wave application is 1 / 3 of the molten pool height, forming a three-dimensional stereo sound field. Each ultrasonic pulse generates a cavitation density gradient of 10. 5 -10 7 The bubble density is 85-90% during the interval between adjacent pulses.

[0038] When the melt volume is greater than 500 kg, a dual-probe alternating working mode with a 90° phase difference can be used, as shown in the figure, where the included angle between the two ultrasonic probes is 90 degrees. This alternating ultrasonic application method can not only eliminate the dead zone of ultrasonic vibration, but also achieve the coupling addition of different frequencies / powers by alternately applying different ultrasonic power / time, thereby achieving more efficient refinement of the Fe-rich phase.

[0039] In addition, a 4-5°C settling buffer zone is set during the ultrasonic interval to allow the melt viscosity to increase naturally (from 0.89 mPa·s to 1.12 mPa·s), enhancing the cavitation threshold for the next ultrasonication. This embodiment also employs an infrared temperature feedback system to control the cooling rate at 5 ± 0.5°C / min, thereby ensuring a temperature triggering accuracy of ± 1.5°C.

[0040] In this embodiment, the average roundness of the Fe-rich phase in the AlSi7Mg alloy obtained after treatment increased from 0.21 to 0.63, and the coefficient of variation of the interphase spacing decreased from 38% to 12%. Meanwhile, metallographic analysis of the finished product showed that after eight pulse treatments, the Fe-rich phase size exhibited a bimodal distribution (main peak 8-12 μm, secondary peak 2-5 μm), which is more conducive to improving mechanical properties compared to the single-peak distribution (15-25 μm) observed with continuous ultrasonic treatment. Figure 3 As shown in the scanning electron microscope image of the aluminum alloy after processing in this embodiment, the dashed circle indicates the size and morphology of the Fe-rich phase, which can illustrate that the aluminum alloy after ultrasonic crushing has a regular morphology of the Fe-rich phase.

Claims

1. A recyclable aluminum alloy, characterized in that, The mass percentages of the components in this aluminum alloy are: 7%≦Si≦10%, Mg≦0.5%, Cu≦0.3%, Ti≦0.1%, Fe≦1%, with the balance being Al and unavoidable impurities, of which the total amount of unavoidable impurities is less than 0.05%.

2. A method for controlling the microstructure characteristics of Fe-rich phase in recycled aluminum alloys, characterized in that, Includes the following steps: Step S1: Using Al ingots, recycled Al-Fe alloy, Al-Mg alloy, Al-Si alloy, and Al-Cu alloy as raw materials, the mass percentage composition is: 7%≦Si≦10%, Mg≦0.5%, Cu≦0.3%, Ti≦0.1%, Fe≦1%, with the balance being Al and unavoidable impurities, wherein the total amount of unavoidable impurities is less than 0.05%. Step S2: Maintain the temperature of the melting furnace within the range of 760℃-800℃, add the various alloys from step S1 and melt them. After all the intermediate alloys have melted evenly, add the α-Al grain refiner and stir to melt. Step S3: Add a slag remover to the melt at 730℃ to remove slag. The slag remover is 40% Na3AlF6 + 30% Na2CO3 + 20% CaF2 + 10% Na2B4O7, and the addition amount is 1.5-2.5 kg / ton of aluminum. Step S4: After slag removal, determine the total Fe content X in the melt; add Fe-rich phase refiner containing Mn in two batches, with the total addition calculated as Mn / Fe=1.

2. The first addition is 70% of the total Mn content, i.e., 0.84X, and is added when the melt temperature is controlled at 730±5℃. The second addition will be made in subsequent steps. Step S5: After the temperature of the melting furnace is controlled at 720℃, a modifier for eutectic Si is added to modify the eutectic Si, and then argon gas is introduced for degassing and refining. Step S6: Cast the refined aluminum alloy into a mold, apply ultrasonic waves within a temperature range of 680-720℃, trigger an ultrasonic pulse for 1 minute every 5℃ decrease in temperature, and the parameters of each ultrasonic pulse are independently adjustable, for a total of 8 processing cycles; when the temperature of the melting furnace is controlled at 700±5℃, add 30% of the total Mn amount for the second time, i.e., 0.36X in step S4; when the melt temperature drops to 680℃, stop applying ultrasonic waves; Step S7: After casting, the aluminum alloy ingot is allowed to cool naturally to room temperature in the air.

3. The method according to claim 2, characterized in that, The α-Al grain refiner is Al-Ti-B, and the eutectic Si modifier is Al-Sr master alloy; the amount of the added grain refiner Al-Ti-B and the eutectic Si modifier Al-Sr master alloy added shall not exceed 0.2% of the aluminum melt by mass percentage.

4. The method according to claim 2, characterized in that, In step S3, argon gas is introduced for 30 minutes, and the alloy composition is tested after refining.

5. The method according to claim 2, characterized in that, Each ultrasonic pulse parameter in step S6 is independently adjustable. The initial high-temperature range of 715-720℃ uses a low-frequency, high-energy pulse at 20Hz and 1.8W / cm². 3 In the low-temperature range of 685-700℃, a high-frequency fine-tuning of 30Hz and 1.2W / cm² is used. 3 .

6. The method according to claim 2, characterized in that, Each ultrasonic pulse parameter in step S6 is independently adjustable. The initial high-temperature range of 715-720℃ uses a low-frequency, high-energy pulse at 20Hz and 1.8W / cm². 3 700-715℃ using low-frequency high-energy 25Hz, 1.5W / cm 3 685-700℃ using low-frequency high-energy 30Hz, 1.2W / cm² 3 In the low-temperature range of 680-685℃, a high-frequency fine-tuning of 40Hz and 0.8W / cm² is used. 3 .

7. The method according to claim 5 or 6, characterized in that, At 690℃, a 15-second ultrasonic micropulse at 40Hz and 0.8W / cm was added. 3 .

8. The method according to claim 5 or 6, characterized in that, The ultrasonic probe is coated with a tantalum alloy and is inserted into the melt at a 20° angle to a depth of one-third of the molten pool height. Each ultrasonic pulse generates a cavitation density gradient of 10. 5 -10 7 The bubble density is 85-90% during the interval between adjacent pulses.

9. The method according to claim 8, characterized in that, When the melt mass is greater than 500 kg, dual probes with a 90° phase difference are used to work alternately.

10. The method according to claim 8, characterized in that, During the ultrasonic interval, a static buffer zone of 4-5℃ is set up, and an infrared temperature feedback system is used to control the cooling rate to reach 5±0.5℃ / min.

Images