A melting and casting method for controlling surface black spot defects of 5-series aluminum alloy slab

Abstract

The application discloses a kind of control 5 series aluminum alloy flat ingot casting mouth surface black spot defect melting and casting method, belong to aluminum alloy melting and casting technical field, to solve the existing 5 series aluminum alloy flat ingot production process, casting mouth black spot defect is serious, internal ultrasonic flaw detection qualified rate is low, magnesium element burn loss is serious, finished product rate is not high, and lack of systematized complete production process technical problem.Method includes raw material and equipment;Smelting and magnesium addition;Cover and transfer injection;Refining;Filtering;Casting.The application method constructs a set of source inhibition, process purification, three-stage collaborative control magnesium oxide inclusion end protection whole-process melting and casting method, the 5 series aluminum alloy flat ingot black spot defect significantly reduced using the application method is melted and cast, ultrasonic flaw detection qualified rate and product finished product rate are improved, magnesium element burn loss is effectively inhibited, production stability is enhanced, realizes production cost reduction.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy casting technology, specifically relating to a casting method for controlling black spot defects on the surface of the casting port of 5-series aluminum alloy flat ingots. Background Technology

[0002] 5-series (Al-Mg series) aluminum alloys are widely used in shipbuilding, transportation, building decoration, high-end electronic product casings, and cosmetic packaging due to their excellent corrosion resistance, good weldability, and moderate strength. Currently, the industrial industry commonly uses deep-well semi-continuous direct water-cooled (DC) casting technology to produce large-size 5xxx series aluminum alloy flat ingots using electrolytic aluminum liquid as raw material.

[0003] In actual production, it has been found that large-scale, irregular "black spots" or continuous black oxide films frequently appear at the casting gate (i.e., the casting end) of flat ingots. In severe cases, slag pits of more than 5mm can even form on the surface of the ingot. Figure 1 As shown.

[0004] This defect is almost never seen in 1xxx series (such as 1050D, 1100D) and 3xxx series (such as 3003D) alloys produced using the same process. This defect not only seriously affects the appearance quality of the ingot, but also leads to failure in internal flaw detection, and causes problems such as sand holes, peeling, and cracks in subsequent rolling processes, which greatly restricts the product yield and the ability to supply to the high-end market.

[0005] Initially, technicians generally believed that the "black spots" were caused by carbon impurities (such as carbon powder from graphite rotor wear or carbon particles mixed in with molten aluminum). They implemented strict controls by investigating carbon sources in the electrolysis and smelting processes, but the problem persisted. Some technicians also suggested it might be related to excessive levels of alkali metals (K, Na, Ca, Li, etc.), but targeted adjustments yielded no significant improvement. Finally, the researchers used precise phase analysis (XRD, SEM-EDS), such as... Figure 2 and Figure 3 As shown, this study confirms for the first time that the "black spots" are essentially aggregates of micron-sized magnesium oxide (MgO) particles, rather than carbon impurities.

[0006] A comprehensive analysis of the nature of the black spots and product defects revealed the following: Existing technologies have failed to establish a complete control scheme for the high oxidation activity of Mg in 5-series alloys from the perspective of the entire casting process. Most of them are scattered, empirical, and temporary adjustment methods, which cannot reliably eliminate black spot defects, resulting in unstable product quality. In particular, the ultrasonic flaw detection pass rate of flat ingots is only about 75%-80%, the magnesium element burn-off rate is as high as 8%-10%, the overall yield is only about 80%-82%, and the occurrence rate of black spot defects at the gate is as high as about 70%, which seriously affects production efficiency and economic benefits and cannot meet the strict requirements of the high-end market for the surface quality and internal purity of materials.

[0007] Based on the problems mentioned above, researchers have proposed a casting method to control black spot defects on the surface of the casting port of 5-series aluminum alloy flat ingots. Summary of the Invention

[0008] The purpose of this invention is to provide a casting method for controlling black spot defects on the surface of the casting port of 5-series aluminum alloy flat ingots, so as to solve the problems of severe black spots on the casting port of 5-series aluminum alloy flat ingots, low pass rate of internal flaw detection, severe magnesium loss, low yield, and lack of systematic production methods in the prior art.

[0009] To solve the above problems, the technical solution of the present invention is as follows: A casting method for controlling black spot defects on the surface of the casting gate of 5-series aluminum alloy flat ingots, comprising the following steps: S1. Raw materials and equipment; S1.1 Raw material preparation; Electrolytic aluminum liquid (Al content ≥ 99.7%), pure magnesium ingots (Mg content ≥ 99.9%), Al-10%Mn master alloy, Al-5%Cr master alloy and other additive alloys, No. 2 sodium-free covering agent (KCl content 45%, MgCl2 content 50%, other 5%), granular refining agent (sodium-free type); the quality is prepared according to the calculated value of the target composition of the alloy.

[0010] Two points to note in this step: One approach is to optimize the batching scheme and control the amount of melt added in each batch to ensure that the melt can be cast completely in each batch, thus avoiding the continuous oxidation of the melt due to prolonged high-temperature stay in the holding furnace (for several hours).

[0011] Secondly, the covering agent must be selected as No. 2 flux based on KCl and MgCl2 to avoid the "sodium embrittlement" caused by Na-containing flux to high Mg alloys.

[0012] S1.2 Main equipment commissioning and preparation; Gas-fired smelting furnace, gas-fired holding furnace, automatic refining system for the side wall of holding furnace, online degassing device, double-layer ceramic filter plate (40ppi+40-60ppi), bipolar deep bed filter (filter media particle size, first stage: 5-10mm; second stage: 3-6mm), DC casting machine.

[0013] S2. Smelting and magnesium addition; Add molten aluminum to the smelting furnace. Once the temperature of the molten aluminum in the furnace reaches 710-730℃, use a basket to quickly press solid magnesium ingots into the bottom of the molten aluminum. Move the basket back and forth in the molten aluminum 3-5 times to accelerate dissolution. The basket is immersed to a depth of 500-600mm throughout the process, and the operation time is 25-30 seconds. This prevents the magnesium ingots from being exposed to air, cuts off the direct contact channel between Mg and O2, and allows the magnesium to melt and dissolve inside the molten aluminum. This avoids the violent oxidation and combustion caused by adding magnesium ingots directly to the high-temperature liquid surface.

[0014] The theoretical magnesium requirement is calculated as the mass of electrolytic aluminum liquid × (2.43% - 4.35%); The actual amount of magnesium added is taken as an integer multiple of the magnesium ingot mass that is closest to the theoretical required amount of magnesium.

[0015] S3. Coverage and Transfer; A sodium-free covering agent is evenly spread on the surface of the molten aluminum, with a dosage of 1.5-2 kg / t-Al (1.5 kg of sodium-free covering agent per ton of aluminum). The covering layer is about 2-4 cm thick, forming a physical isolation barrier to prevent the molten metal from contacting the furnace gas / air.

[0016] When transferring the melt to the holding furnace, the depth of the flow channel is 150-180mm, the flow rate is controlled at 0.4-0.8m / s, the flow channel is covered throughout, and the inner wall of the cover plate is equipped with heating elements. A small amount of argon gas can be introduced for protection to maintain the temperature of the melt in the flow channel at 705-715℃, and the positive and negative temperature difference is controlled within 5℃, so as to ensure the casting temperature while avoiding local overheating.

[0017] The S1-S3 covering stage, as a source control phase, aims to minimize MgO formation. From selecting sodium-free covering agents and refining agents, to oxygen isolation and magnesium addition in the basket, and further to air isolation with covering agents, these are all measures to inhibit MgO formation at its source. The amount of oxides generated in these stages can be reduced by more than 90%. S4. Refining; S4.1 Level 1 Refinement: After smelting is completed in the smelting furnace, high-purity argon gas is introduced through the refining pipeline, with the gas flow rate controlled between 20-30 L / min; refining agent is added simultaneously, with the dosage controlled between 1.2-1.8 kg / t-Al, and the refining time is 10-15 minutes to remove large inclusions, hydrogen and alkali metals. S4.2 Level 2 Refinement: Inside the holding furnace, an automatic refining system is used on the side wall. High-purity argon or a mixture of argon and chlorine is introduced for refining. The gas flow rate is controlled at 15-20 L / min. Refining agent is added simultaneously, with the dosage controlled at 1-1.5 kg / t-Al. The refining time is 20-30 minutes. The covering agent is kept intact during the refining process.

[0018] This step preferably uses an automatic refining system on the side wall of the insulated furnace to avoid opening the furnace door and exposing the furnace to air.

[0019] Note that the refining gas can be an inert gas Ar, or a mixture of Ar and Cl2 (Cl2 volume fraction 5%-10%), which utilizes the strong oxidizing properties of Cl2 to remove alkali metals. A tail gas treatment device must be installed simultaneously. However, the use of N2 is prohibited to prevent N2 from reacting with Mg to form a dark brown Mg3N2 inclusion.

[0020] S5. Filtration; The melt is filtered using a three- or four-stage filtration system, as follows: Online degassing device (rotor speed 400-500 rpm, argon flow rate 10-15 L / min, degassing chamber temperature 705℃); Double-layer ceramic filter plate (first layer 40ppi, second layer 40-60ppi, filtration temperature 695-705℃). Deep bed filter 1 (filter media particle size 5-10mm, bed thickness 300mm); Deep bed filter 2 (filter media particle size 3-6mm, bed thickness 300-400mm); The deep bed filter 1 is optional.

[0021] S4 and S5 are the main process purification stages, tasked with removing the generated MgO. The combined filtration scheme of online refining, double-layer ceramic filter plate, and bipolar deep bed filter utilizes the physical interception of the ceramic filter plate and the adsorption of the deep bed filter to effectively capture and remove micron-sized fine MgO particles in the melt; the removal efficiency for inclusions larger than 5 microns can reach over 98%.

[0022] S6. Casting; Thirty minutes before casting, windproof the area around the crystallizer and seal any gaps.

[0023] Casting parameters: Casting temperature 695-700℃ (temperature measured at the end of the runner), casting speed 45-55mm / min, cooling water flow rate 160-200m³ / min. 3 / h, water temperature 25±2℃.

[0024] The transfer process in S3 and the final protection stages in S6 isolate the oxidation source during the casting process. During the transfer process, a heated runner cover plate covers the entire runner and upper part of the distribution plate from the furnace outlet, preventing the high-temperature melt from being directly exposed to air during flow. Increasing the runner depth reduces the free surface area of ​​the melt, decreasing the probability of contact between the melt and air, and reducing the formation and entrapment of oxide films. The casting process also shields the area around the crystallizer to prevent water vapor generated by the evaporation of cooling water from entering the crystallizer and surrounding runner area, thus avoiding a humid environment that could exacerbate the oxidation reaction of Mg.

[0025] The beneficial effects of this invention are as follows: (1) The casting method of the present invention constructs a three-stage synergistic control method for magnesium oxide in the whole process of source suppression, process purification and end protection. By adding magnesium in the basket, the melting process of magnesium is transferred from the liquid surface to below the liquid surface, thus suppressing the formation of MgO from the source. By physically isolating the covering agent and the flow channel cover plate, the diffusion path of oxygen to the surface of the melt is blocked, thus delaying the oxidation kinetics of Mg. By precisely controlling the temperature, the reaction temperature is reduced, the rate constant of the Mg oxidation reaction is reduced, and the evaporation loss of Mg at high temperature is reduced. In the multi-stage argon refining, the air flotation and stirring effect of Ar gas is used to carry the fine MgO particles that have been generated to the surface of the melt. Ar is used instead of N2 to avoid the generation of secondary inclusions. In the combined filtration, the micron-sized MgO particles that are still suspended in the melt after refining are effectively removed through multi-stage physical interception, thus achieving deep purification of the melt. In the casting, the generated cooling water vapor is prevented from contacting the melt by shielding, thus avoiding the humid environment (H2O) from becoming an additional source of oxidation.

[0026] (2) The 5-series aluminum alloy flat ingots cast using the method of the present invention have the following performance advantages: ① Significantly reduces dark spot defects; After adopting the method of this invention, more than 50 batches of 5-series alloy flat ingots (including grades such as 5052, 5083, and 5L52) were produced continuously. The "black spot" area on the surface of the casting port completely disappeared or was greatly reduced, and the surface quality met the strict requirements of aluminum sheet and strip for high-end electronic product shells and cosmetic bottle caps.

[0027] ② Significantly improve internal quality; The ultrasonic flaw detection pass rate of ingots has steadily increased from approximately 75%-80% to over 92%-98%, effectively solving the problem of internal defects caused by oxide inclusions. Based on a production line with an annual output of 90,000 tons, this reduces scrap and rework materials by approximately 7,200-9,000 tons annually.

[0028] ③ Significantly improve yield; The overall yield rate increased by an average of 8-10 percentage points, significantly reducing energy and labor waste caused by scrap. In a typical furnace (furnace number 182501058), before the improvement, problems such as slag pits and cracking led to the scrapping of ingots No. 2 and No. 5; after the improvement, the yield rate of the same furnace increased from 78% to 91%.

[0029] ④ Reduce magnesium loss during burning, saving costs; By using a suspended basket to add magnesium and controlling the temperature, the magnesium oxidation loss rate was reduced from 8%-10% to 5%-6%. Taking the production of 5052 alloy in a 60-ton furnace as an example, the average amount of magnesium saved per furnace is about 63 kg. Based on 120 furnaces per month and a magnesium price of 15,000 yuan / ton, the monthly savings are about 113,400 yuan.

[0030] ⑤ Improved production stability; Before the improvement, the average time for production interruptions and auxiliary tasks such as cleaning the flow channel caused by defects such as black spots, slag pits, and cracks was about 1.5 hours per furnace. After the improvement, it was reduced to less than 0.5 hours, and the production efficiency was increased by about 20%.

[0031] ⑥ The comparative experimental data showed excellent performance; In a comparative test of producing 5052 aluminum alloy flat ingots in a 60-ton furnace (15 heats each), the flaw detection pass rate increased from the statistical average of 80.4% for the traditional casting method to 96.2% for the casting method of this invention; the magnesium recovery rate increased from the statistical average of 90.8% for the traditional casting method to 94.4% for the casting method of this invention, an increase of 3.6 percentage points; and the occurrence rate of black spots at the gate decreased from approximately 70% for the traditional casting method to 3.3% for the casting method of this invention. Attached Figure Description

[0032] Figure 1 Macroscopic photographs of black spot defects on the surface of the gating gate of 5-series aluminum alloy flat ingots produced by conventional casting methods; (a) shows the blackening of the surface at the gating gate of 5052 flat ingot; (b) shows the blackening of the surface at the gating gate of 5L52 flat ingot; (c) shows the blackening of the surface at the gating gate of 5083 flat ingot; (d) shows the blackening of the surface at the gating gate of 3003D flat ingot (normal control); (e) shows the blackening of the surface at the gating gate of 1050D flat ingot (normal control); (f) shows the blackening of the surface at the gating gate of 1100D flat ingot (normal control). Figure 2 X-ray diffraction (XRD) patterns of samples with black spot defects are shown; (a) shows the sample morphology and detection location; (b) shows the XRD pattern, which indicates the presence of diffraction peaks for only Al and MgO, and the absence of characteristic peaks for carbon-containing phases such as C and Al4C3. Figure 3The images show scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) analysis results of the black spot defect sample; (a) SEM image, showing that the blackened material is a micron-sized fine particle aggregate; (b), (c), and (d) EDS spectra at points A, B, and C, showing that it mainly contains Mg, O, and Al elements. Figure 4 A schematic diagram of the equipment and process for producing aluminum alloy flat ingots from molten aluminum; Figure 5 A bar chart comparing the ultrasonic flaw detection pass rates of ingot samples produced by traditional methods and the method of this invention. Figure 6 The images show a comparison of the gate conditions of the conventional method and the method of the present invention; (a) is the gate of the product produced by the conventional method, which is severely blackened and has slag pits; (b) is the gate of the product produced by the method of the present invention, which has a bright gate surface and no black spots. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Therefore, the following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0035] Example 1

[0036] Taking our Liancheng branch's 60-ton flat ingot production line as an example, such as Figure 4 As shown, the production grade is 5052 aluminum alloy flat ingot (specifications 630mm×1130mm×6100mm).

[0037] The target chemical composition (mass fraction) of the 5052 aluminum alloy is as follows: Mg 2.38%-2.48%, Mn≤0.10%, Cr 0.16%-0.22%, Si≤0.20%, Fe 0.15%-0.25%, the remainder being Al.

[0038] The casting method for controlling the black spot defect on the surface of the casting gate of the above-mentioned 5-series aluminum alloy flat ingots consists of the following steps: S1. Raw materials and equipment; S1.1 Raw material preparation; The additives used for electrolytic aluminum liquid (Al content ≥ 99.7%), pure magnesium ingots (Mg content ≥ 99.9%), Al-10%Mn master alloy, Al-5%Cr master alloy, etc., and melt covering agents are Wenxi County Kailida Trading Co., Ltd.'s customized No. 2 sodium-free granular covering agent (main components: KCl 45%, anhydrous MgCl2 50%, balance 5% CaCl2 and trace MgF2) and Wenxi Kailida KLDM-J103 sodium-free granular refining agent.

[0039] S1.2 Main equipment commissioning and preparation; 60-ton gas-fired smelting furnace, 60-ton gas-fired holding furnace, automatic refining system for the side wall of the holding furnace, online degassing device, double-layer ceramic filter plate (30ppi+50ppi), bipolar deep bed filter (filter media particle size, first stage: 5-10mm; second stage: 3-6mm), DC casting machine.

[0040] S2. Smelting and magnesium addition; 60 tons of molten aluminum were added to the smelting furnace and heated to 710℃. During the heating process, K-type thermocouples were used for continuous temperature measurement with an accuracy of ±3℃.

[0041] The theoretical magnesium requirement is calculated as 60 tons × 2.43% = 1458 kg. Taking 73 magnesium ingots weighing 20 kg each, totaling 1460 kg, and considering the mass error of the magnesium ingots, the actual amount of magnesium added is close to the calculated magnesium requirement.

[0042] Solid magnesium ingots are quickly pressed into the bottom of molten aluminum using a basket. The basket moves back and forth in the molten aluminum 3-5 times to accelerate dissolution. The entire process involves immersion depth of the basket ≥500mm and operation time ≤30 seconds to prevent magnesium ingots from being exposed to air.

[0043] S3. Coverage and Transfer; Spread No. 2 sodium-free covering agent evenly on the surface of the molten aluminum, at a dosage of 1.5 kg / t-Al (1.5 kg of sodium-free covering agent per ton of aluminum), with a covering layer thickness of about 2-3 cm.

[0044] When transferring the melt to the holding furnace, the depth of the flow channel is 150mm, the flow rate is controlled at 0.5-0.8m / s, the flow channel is covered throughout, and the inner wall of the cover plate is equipped with silicon carbide heating elements to maintain the temperature of the melt in the flow channel at 705±5℃.

[0045] S4. Refining; S4.1 Level 1 Refinement; Inside the smelting furnace, high-purity argon gas (flow rate 20L / min) and granular refining agent (dosage 1.2kg / t-Al) are introduced through the refining pipe, and the refining time is 10 minutes.

[0046] S4.2 Level 2 Refining; Inside the holding furnace, an automatic sidewall refining system is used, with high-purity argon gas (flow rate 15L / min) and granular refining agent (dosage 1kg / t-Al) introduced. The refining time is 20 minutes, and the covering agent is kept intact during the refining process.

[0047] S5. Filtration; The melt passes through the following three-stage filtration system in sequence: Online degassing device (rotor speed 400 rpm, argon flow rate 10 L / min, degassing chamber temperature 705℃); Double-layer ceramic filter plate (first layer 40ppi, second layer 60ppi, filtration temperature 695-705℃); Deep bed filter 2 (filter media particle size 3-6mm, bed thickness 400mm).

[0048] S6. Casting; Thirty minutes before casting, wind protection was provided around the crystallizer, and gaps were sealed with aluminum silicate fiber blankets.

[0049] Casting parameters: Casting temperature 695℃ (temperature measured at the end of the runner), casting speed 45mm / min, cooling water flow rate 160m³ / min. 3 / h, water temperature 25±2℃, casting length 6100mm.

[0050] S7. Product Evaluation; The following tests and evaluations were performed on the finished products cast in S6: S7.1 Flaw Detection: The USMGo ultrasonic flaw detector was used, with a 5MHz straight probe, a scanning speed of 150mm / s, and a sensitivity equivalent to a Φ1.2mm flat-bottom hole.

[0051] S7.2 Chemical Composition Detection: An ARL4460 direct-reading spectrometer was used, and the procedure was performed in accordance with GB / T7999-2015 standard.

[0052] S7.3 Surface Quality Evaluation: Visually inspect the percentage of black spots within 200mm of the casting gate.

[0053] S7.4 Average Magnesium Recovery Calculation: The average magnesium recovery rate is calculated as (theoretical magnesium requirement ÷ actual magnesium addition) × 100%.

[0054] S7.5 Evaluation Results: In this embodiment, 15 batches of continuous production were carried out, and the product evaluation results are summarized as follows: The flaw detection pass rate was 96.5%, the average magnesium recovery rate was 93.8%, the overall finished product rate was 90.5%, the black spot occurrence rate at the gate was 5% (black spot area was 8%), and the auxiliary time per furnace was 0.6 hours.

[0055] Example 2

[0056] The difference from Example 1 is that: Produces aluminum alloy flat ingots with grade 5083 (specifications: 630mm×1130mm×6100mm).

[0057] The target chemical composition (mass fraction) of the 5083 alloy is as follows: Mg 4.20%-4.50%, Mn 0.45%-0.65%, Cr 0.06%-0.12%, Si≤0.30%, Fe 0.15%-0.35%, the remainder being Al.

[0058] In S1.1, the amount of Al-10%Mn master alloy is increased.

[0059] The melting temperature in S2 is 730℃.

[0060] The theoretical magnesium requirement is calculated as 60 tons × 4.35% = 2610 kg. 130 magnesium ingots weighing 20 kg each and 1 magnesium ingot weighing 10 kg each are used, totaling 2610 kg. The actual amount of magnesium added matches the calculated requirement.

[0061] Using magnesium-added basket technology, the basket is immersed to a depth of ≥600mm and the operation time is ≤25 seconds.

[0062] The amount of covering agent used in S3 is 2.0 kg / t-Al, and the thickness of the covering layer is 3-4 cm.

[0063] The flow channel is 180mm deep, the flow rate is controlled at 0.4-0.6m / s, the flow channel is covered and a small amount of argon gas is introduced for protection (flow rate 5L / min), and the flow channel is kept at a temperature of 715±5℃.

[0064] In S4.1, the argon flow rate is 30 L / min, the refining agent dosage is 1.8 kg / t-Al, and the refining time is 15 minutes.

[0065] In S4.2, a mixture of Ar and Cl2 gas is used for refining (Cl2 volume fraction 5%), the mixed gas flow rate is 20 L / min, the refining agent dosage is 1.5 kg / t-Al, the refining time is 30 minutes, and a tail gas absorption device (NaOH solution spray absorption) is provided.

[0066] In S5, the melt passes through the following four-stage filtration system in sequence: The online degassing device operates at a speed of 500 rpm and an argon flow rate of 15 L / min. Double-layer ceramic filter plate (first layer 40ppi, second layer 60ppi); Deep bed filter 1 (filter media particle size 5-10mm, bed thickness 300mm); Deep bed filter 2 (filter media particle size 3-6mm, bed thickness 400mm).

[0067] In S6, the casting temperature is 700℃, the casting speed is 55mm / min, and the cooling water flow rate is 200m³ / min. 3 / h.

[0068] The product evaluation results for 15 consecutive batches of S7.5 production are as follows: The flaw detection pass rate was 98.2%, the average magnesium recovery rate was 94.5%, the overall finished product rate was 92.0%, the black spot occurrence rate at the gate was 2% (black spot area was 4%), and the auxiliary time per furnace was 0.4 hours.

[0069] Example 3

[0070] The difference from Example 1 is that: Produces aluminum alloy flat ingots with grade 5L52 (specifications: 630mm×1130mm×6100mm).

[0071] The target chemical composition (mass fraction) of the 5L52 alloy is as follows: Mg 2.38%-2.48%, Mn≤0.10%, Cr≤0.20%, Si≤0.08%, Fe≤0.10%, the remainder is Al.

[0072] The melting temperature in S2 is 720℃.

[0073] The theoretical magnesium requirement is calculated as 60 tons × 2.43% = 1458 kg. This is equivalent to 73 magnesium ingots, each weighing 20 kg, totaling 1460 kg.

[0074] Using magnesium-added basket technology, the basket immersion depth is ≥550mm and the operation time is ≤28 seconds.

[0075] The amount of covering agent used in S3 is 1.8 kg / t-Al, and the thickness of the covering layer is 2.5-3 cm.

[0076] The flow channel is 165mm deep, and the flow rate is controlled at 0.5-0.7m / s. The entire flow channel is covered and insulated, with a flow channel temperature of 710±5℃.

[0077] In S4.1, the argon flow rate is 25 L / min, the refining agent dosage is 1.5 kg / t-Al, and the refining time is 13 minutes.

[0078] S4.2 is a pure argon refining process with a flow rate of 18 L / min, a refining agent dosage of 1.2 kg / t-Al, and a refining time of 25 minutes. An automatic refining system using the side wall of the holding furnace is employed.

[0079] In S5, the melt passes through the following four-stage filtration system in sequence: The online degassing device operates at 450 rpm and has an argon flow rate of 13 L / min. Double-layer ceramic filter plate (first layer 40ppi, second layer 40ppi); Deep bed filter 1 (filter media particle size 5-10mm, bed thickness 300mm); Deep bed filter 2 (filter media particle size 3-6mm, bed thickness 300mm).

[0080] In S6, the casting temperature is 698℃, the casting speed is 50mm / min, and the cooling water flow rate is 175m³ / min. 3 / h.

[0081] The product evaluation results for 15 consecutive batches of S7.5 production are as follows: The flaw detection pass rate was 97.8%, the average magnesium recovery rate was 94.4%, the overall finished product rate was 91.5%, the black spot occurrence rate at the gate was 3% (black spot area was 5%), and the auxiliary time per furnace was 0.5 hours.

[0082] Comparative Example 1 On the same production line, namely the 60-ton flat ingot production line of our Liancheng branch, 5052 aluminum alloy flat ingots are produced using the traditional melting and casting method. The difference from the example is: S2. In the smelting and magnesium addition process, magnesium ingots are directly thrown onto the surface of the molten metal in the smelting furnace. A clear flame and thick smoke are visible. The operation takes about 2 to 3 minutes.

[0083] S3. During the covering and transfer process, the flow channel is open without a cover plate or argon protection, and the melt is exposed. The crystallizer is unobstructed, and cooling water vapor directly contacts the melt.

[0084] S4. In the refining process, only one batch of argon gas (flow rate 25L / min) and refining agent (dosage 1kg / t-Al) is used manually in the holding furnace for 15 minutes.

[0085] S5. The filtration process uses only a single-layer 40ppi ceramic filter plate and a single-stage deep bed (filter media particle size 5-10mm, bed thickness 300mm).

[0086] S6. The casting temperature during the casting process is 715℃.

[0087] S7.5 Evaluation Results: After 15 consecutive production runs, the statistical results are as follows: flaw detection pass rate 80.2% (lowest furnace 65%), average magnesium recovery rate 90.8%, overall finished product rate 82.0%, gate black spot occurrence rate 73.3%, and auxiliary time per furnace 1.6 hours.

[0088] The product evaluation results of Examples 1-3 and Comparative Example 1 are summarized in Table 1: Table 1: Summary of Evaluation Results of Examples 1-3 and Comparative Example 1

[0089] It is evident that the method of this invention significantly improves various quality indicators of the product compared to the traditional casting method.

[0090] The following is a statistical table of magnesium recovery data before and after the improvement of the smelting and casting method for 5052 alloy flat ingots produced by the production line of the example embodiment, as shown in Table 2. Table 2: Statistical table of magnesium recovery data before and after improvement in the production of 5052 alloy flat ingots by the 60-ton furnace in the example.

[0091] As shown in Table 2, the distribution of magnesium burn-off rate in 15 heats before and after using the casting method of the present invention is as follows: the data of the traditional method is distributed in the range of 8%-10%, with a median of about 9%; the data of the method of the present invention is distributed in the range of 5%-6%, with a median of about 5.5%.

[0092] Continue to statistically analyze the ultrasonic flaw detection pass rate of 5-series alloy flat ingots produced on the production line before and after the improvement of the casting method, and draw a comparative bar chart, such as... Figure 5 As shown, the ultrasonic flaw detection pass rate of the products produced by the method of the present invention is significantly improved.

[0093] Continue to observe the gate condition of the products produced in the examples and comparative examples, and randomly select two ingots for comparison. (Photos are shown below.) Figure 6 As shown, (a) is the product gate of the traditional method, with a severely blackened surface and slag pits; (b) is the product gate of the method of the present invention, with a bright gate surface and no black spots.

Claims

1. A casting method for controlling black spot defects on the surface of the casting gate of 5-series aluminum alloy flat ingots, comprising the following steps: S1. Raw materials and equipment; Prepare raw materials and debug equipment; S2. Smelting and magnesium addition; Add the electrolytic aluminum liquid to the smelting furnace, and after the temperature of the aluminum liquid in the smelting furnace rises to 710-730℃, add magnesium ingots. S3. Coverage and Transfer; A covering agent is evenly spread on the surface of the molten aluminum and then transferred to a holding furnace. S4. Refining; S4.1 Level 1 Refinement: After melting is completed in the melting furnace, high-purity argon gas is introduced through the refining pipeline; refining agent is added simultaneously, and the refining time is 10-15 minutes. S4.2 Level 2 Refinement: In the heat-insulating furnace, high-purity argon or a mixture of argon and chlorine is introduced for refining, and refining agent is added simultaneously. The refining time is 20-30 minutes, and the covering agent is kept intact during the refining process. S5. Filtration; The melt is filtered using a three- or four-stage filtration system, as follows: Online degassing device (rotor speed 400-500 rpm, argon flow rate 10-15 L / min, degassing chamber temperature 705℃); Double-layer ceramic filter plate (first layer 40ppi, second layer 40-60ppi, filtration temperature 695-705℃). Deep bed filter 1 (filter media particle size 5-10mm, bed thickness 300mm); Deep bed filter 2 (filter media particle size 3-6mm, bed thickness 300-400mm); S6. Casting; Casting parameters: Casting temperature 695-700℃ (temperature measured at the end of the runner), casting speed 45-55mm / min, cooling water flow rate 160-200m³ / min. 3 / h, water temperature 25±2℃.

2. The casting method for controlling black spot defects on the surface of the casting gate of 5-series aluminum alloy flat ingots as described in claim 1, characterized in that: In S2, the theoretical magnesium requirement is calculated as the mass of electrolytic aluminum liquid × (2.43%-4.35%); the actual amount of magnesium added is the nearest integer multiple of the magnesium ingot mass to the theoretical magnesium requirement.

3. The casting method for controlling black spot defects on the surface of the casting gate of 5-series aluminum alloy flat ingots as described in claim 1 or 2, characterized in that: In S2, a basket is used to quickly press solid magnesium ingots into the bottom of the molten aluminum. The basket moves back and forth in the molten aluminum 3-5 times to accelerate dissolution. The entire process involves immersing the basket to a depth of 500-600mm and taking 25-30 seconds.

4. The casting method for controlling black spot defects on the surface of the casting gate of 5-series aluminum alloy flat ingots as described in claim 3, characterized in that: In S3, the amount of sodium-free covering agent used is 1.5-2 kg / t-Al, and the thickness of the covering layer is 2-4 cm.

5. The casting method for controlling black spot defects on the surface of the casting gate of 5-series aluminum alloy flat ingots as described in claim 4, characterized in that: When transferring the S3 melt to the holding furnace, the depth of the flow channel is 150-180mm, the flow rate is controlled at 0.4-0.8m / s, the flow channel is covered throughout, and the inner wall of the cover plate is equipped with heating elements. A small amount of argon gas can be introduced for protection to maintain the temperature of the melt in the flow channel at 705-715℃, with the positive and negative temperature difference controlled within 5℃.

6. The casting method for controlling black spot defects on the surface of the casting gate of 5-series aluminum alloy flat ingots as described in claim 5, characterized in that: In S4.1, the flow rate of high-purity argon is controlled between 20-30 L / min; the amount of refining agent is controlled between 1.2-1.8 kg / t-Al. In S4.2, a sidewall automatic refining system is preferred, with the gas flow rate controlled at 15-20 L / min and the refining agent dosage controlled at 1-1.5 kg / t-Al.

7. The casting method for controlling black spot defects on the surface of the casting gate of 5-series aluminum alloy flat ingots as described in claim 6, characterized in that: The deep bed filter 1 of the S5 is optional.

8. The casting method for controlling black spot defects on the surface of the casting gate of 5-series aluminum alloy flat ingots as described in claim 7, characterized in that: In S6, wind protection and sealing of the area around the crystallizer are carried out 30 minutes before casting.

9. The casting method for controlling black spot defects on the surface of the casting gate of 5-series aluminum alloy flat ingots as described in claim 1, characterized in that: S1 is divided into raw material preparation and main equipment debugging and preparation stages; S1.1 Raw material preparation; Prepare electrolytic aluminum liquid with an Al content ≥ 99.7%; pure magnesium ingots with a Mg content ≥ 99.9%; Al-10%Mn master alloy; Al-5%Cr master alloy or similar additive alloys, sodium-free covering agent, granular refining agent (sodium-free type); prepare the quality according to the calculated value of the target alloy composition.

10. The casting method for controlling black spot defects on the surface of the casting gate of 5-series aluminum alloy flat ingots as described in claim 9, characterized in that: wherein, S1.2 Main equipment commissioning and preparation; Prepare a gas-fired smelting furnace, a gas-fired holding furnace, an automatic refining system for the side wall of the holding furnace, an online degassing device, a double-layer ceramic filter plate, a bipolar deep bed filter, and a DC casting machine, and complete the commissioning of the above equipment.

Images