6-series aluminum alloy for automotive exterior members and method for producing the same

Abstract

This invention relates to the field of aluminum alloy recycling technology, specifically to a 6-series aluminum alloy for automotive body panels and its preparation method, comprising the following steps: waste pretreatment, second melting, casting, homogenization, hot rolling, cold rolling, solution heat treatment, and pre-aging; the waste pretreatment conditions include: first melting of aluminum waste at a melt temperature of 640-660℃ for 2-3 hours, and casting the molten aluminum waste into a composite ingot. This 6-series aluminum alloy has a high scrap ratio, neutralizes Fe elements, and exhibits excellent performance.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy recycling technology, specifically to a 6-series aluminum alloy for automotive body panels and its preparation method. Background Technology

[0002] With the continuous advancement of lightweighting and green manufacturing in the automotive industry, 6-series aluminum alloys (especially 6016 and 6014) are widely used in the automotive outer panel sector due to their excellent formability, paint hardening properties, and surface quality. At the same time, the automotive industry generates a large amount of scrap aluminum annually, making high-proportion recycling a key approach to reducing carbon emissions and raw material costs.

[0003] However, the application of traditional recycled 6000 aluminum alloy in the automotive outer panel field still faces the following technical bottlenecks: high Fe content causes microstructure embrittlement; insufficient synergistic regulation of microstructure and properties.

[0004] Chinese patent CN202110512415.7 discloses a method of refining grains by adding a quaternary grain refiner Al-Si-VB, but without removing Fe, thus failing to address the Fe element issue at its root. Chinese patent CN202110980049.8 discloses ball milling of composite salts into small balls of varying diameters in a vacuum ball mill, requiring the addition of a mixed powder of MgO, Al2O3, and C2Cl6. While this method can remove Fe, it incurs higher production costs and involves complex processes. Chinese patent CN202210804692.X discloses a method of purifying the melt by low-temperature pretreatment for degreasing waste and two refining processes during smelting. This method can only remove impurities from the melt but cannot effectively remove Fe.

[0005] Existing patents have failed to achieve Fe neutralization and gradient microstructure control under high scrap ratio conditions. They have not considered the chain effect of Fe on microstructure and performance under high scrap ratio scenarios, nor have they designed corresponding microstructure control processes. They cannot solve problems such as poor microstructure uniformity and insufficient formability caused by high Fe. Recycled aluminum alloys can only be used in low-performance requirement fields and cannot enter high-end application scenarios such as automotive outer panels.

[0006] In summary, there is an urgent need for a 6-series aluminum alloy with a high scrap ratio, neutralized Fe element, and excellent performance that can be used in automotive body panels. Summary of the Invention

[0007] The present invention aims to solve the technical problem of how to provide a 6-series aluminum alloy with a high scrap ratio, neutralized Fe element, and excellent performance that can be applied to automotive body panels.

[0008] To achieve the above objectives, the first aspect of the present invention provides a method for preparing 6-series aluminum alloy for automotive body panels, comprising the following steps:

[0009] Scrap pretreatment, secondary smelting, casting, homogenization, hot rolling, cold rolling, solution heat treatment, pre-aging;

[0010] The conditions for waste pretreatment include: first melting the aluminum waste at a temperature of 640-660 ℃ for 2-3 h, and casting the molten aluminum waste into composite ingots.

[0011] The waste ratio is 85-95%;

[0012] The components and their weight percentages in the 6-series aluminum alloy used for automotive body panels are as follows:

[0013] The Si content is 0.60-1.00%;

[0014] The Mg content is 0.40-0.80%;

[0015] The Cu content is 0.15-0.35%;

[0016] The Mn content is 0.30-0.40%;

[0017] Fe content ≤ 0.80%;

[0018] The Ni content is 0.10-0.20%;

[0019] The Zr content is 0.05-0.20%;

[0020] The Ti content is 0.02-0.10%;

[0021] The content of B is 0.005-0.05%;

[0022] The weight ratio of (Mn+Ni) to Fe is 0.70-0.78;

[0023] The content of a single impurity is ≤0.05%;

[0024] The total content of other impurity elements is ≤0.15%;

[0025] The balance is Al.

[0026] A second aspect of the present invention provides a 6-series aluminum alloy obtained by the above-mentioned method for preparing 6-series aluminum alloys for automotive body panels, wherein the scrap ratio of the 6-series aluminum alloy is ≥85%;

[0027] The bake hardening value BH2 of the 6-series aluminum alloy is greater than 60 MPa.

[0028] The beneficial effects of this invention are as follows:

[0029] (1) This invention uses multi-dimensional synergistic regulation technology of physical purification, microstructure control and heat treatment path optimization to achieve efficient regulation of Fe element and construct a "hard shell and tough core" gradient structure, thereby achieving integrated improvement of anti-dentation and formability, so that the 6-series recycled aluminum alloy with high waste ratio (85%-95%) meets the stringent requirements of automobile outer panels, and breaks through the bottleneck of high-end application of recycled aluminum.

[0030] (2) The present invention achieves high waste ratio utilization: the waste ratio can reach 95%, the aluminum liquid is highly purified, the material recovery rate is increased to over 98%, ultrasonic physical refining replaces chemical refining agents, reduces harmful emissions, and achieves green manufacturing.

[0031] (3) The pinhole and stripe defect rate of the 6-series aluminum alloy provided by the present invention is reduced to less than 0.5%, which fully meets the automotive outer panel standard and significantly improves the surface quality. Detailed Implementation

[0032] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0033] In existing technologies, the recycling of 6-series aluminum alloys with high scrap ratios cannot effectively control the Fe element, easily forming harmful Fe phases that cause embrittlement, and there are no suitable means to synergistically control the microstructure and properties. The process is complex and costly, and the recycled materials cannot meet the stringent requirements for formability and surface quality in high-end fields such as automotive outer panels.

[0034] This invention proposes a multi-dimensional synergistic control process to solve the technical problems of high Fe tolerance, microstructure refinement, programmable performance, and green and low-carbon manufacturing, and to achieve the adaptation of high-waste ratio 6-series aluminum alloy recycling to high-end applications.

[0035] Therefore, the first aspect of the present invention provides a method for preparing 6-series aluminum alloy for automotive body panels, comprising the following steps:

[0036] Scrap pretreatment, secondary smelting, casting, homogenization, hot rolling, cold rolling, solution heat treatment, pre-aging;

[0037] The conditions for waste pretreatment include: first melting the aluminum waste at a temperature of 640-660 ℃ for 2-3 h, and casting the molten aluminum waste into composite ingots.

[0038] The waste ratio is 85-95%;

[0039] The components and their weight percentages in the 6-series aluminum alloy used for automotive body panels are as follows:

[0040] The Si content is 0.60-1.00%;

[0041] The Mg content is 0.40-0.80%;

[0042] The Cu content is 0.15-0.35%;

[0043] The Mn content is 0.30-0.40%;

[0044] Fe content ≤ 0.80%;

[0045] The Ni content is 0.10-0.20%;

[0046] The Zr content is 0.05-0.20%;

[0047] The Ti content is 0.02-0.10%;

[0048] The content of B is 0.005-0.05%;

[0049] The weight ratio of (Mn+Ni) to Fe is 0.70-0.78;

[0050] The content of a single impurity is ≤0.05%;

[0051] The total content of other impurity elements is ≤0.15%;

[0052] The balance is Al.

[0053] The waste ratio is defined as the ratio of the mass of waste to the mass of raw materials input.

[0054] In this invention, the temperature of the first smelting in the waste pretreatment is lower than the conventional smelting temperature of 720-760℃. This temperature is close to the solid-liquid two-phase region of aluminum alloy. The solubility of iron in aluminum melt is extremely low. The iron-rich impurity phase brought in by the waste will precipitate, aggregate and enter the slag in advance, thus achieving the initial removal of impurities.

[0055] According to the present invention, the conditions for the second smelting include: the temperature of the second smelting is 700-730℃, Ti-B-Zr composite refining agent is added, stirring is carried out for 10-15 min, then Mn-Ni composite agent is added, the temperature is raised to 740-760℃, the temperature is held for 20-30 min, ultrasonic refining is carried out, 20kHz ultrasound is applied for 5-10 min, and the hydrogen content is ≤0.13ml / 100gAl;

[0056] In the Ti-B-Zr composite refining agent, the mass ratio of Ti, B and Zr is 2.7-3.1:1-1.2:1.8-2.2;

[0057] In the Mn-Ni composite agent, the mass ratio of Mn to Ni is 2.8-3.2:0.8-1.2.

[0058] In this invention, under high waste ratio conditions, there is a greater amount of iron-rich phase. Traditional fine wire Al-5Ti-1B is easily poisoned by Fe, while the Zr element in the Ti-B-Zr composite fine wire has a stronger binding ability with Fe, and can preferentially form high-melting-point, diffusely distributed intermetallic compounds such as Al-Zr-Fe, thus avoiding the fine wire being poisoned by Fe.

[0059] Subsequently, a Mn-Ni composite agent is added to the melt to transform the harmful needle-like β-AlFeSi phase into a dense, low-hazard α(FeMnNi)Si phase, significantly improving the alloy's plasticity. Addressing the issues of localized aggregation and size segregation of the α-(FeMnNi)Si phase under high scrap aluminum addition conditions, as well as severe gas absorption, high hydrogen content in the melt, and numerous oxide inclusions during scrap aluminum remelting, ultrasonic refining is introduced after Mn-Ni composite modification and heat preservation. This achieves triple enhancement through composition homogenization, phase refinement, and gas and impurity removal. The second smelting process of this invention controls the hydrogen content to within 0.13 ml / 100 g Al. Conventional argon-chlorine mixed gas refining cannot guarantee the hydrogen content control requirements under high scrap ratios.

[0060] Ultrasonic refining technology has been used in the treatment of aluminum alloy melts, but its application is limited in the recycling system of 6-series aluminum alloys with high scrap ratios. Under high scrap ratio conditions, the Fe-enriched phase and oxide inclusions in the melt increase significantly, and traditional argon-chlorine refining cannot achieve efficient degassing and inclusion removal at the same time.

[0061] This invention synergistically utilizes ultrasonic refining with Mn-Ni composite regulation and a Ti-B-Zr grain refinement system. Through cavitation and acoustic flow, it promotes the aggregation and flotation of Fe-rich impurity phases and oxide inclusions, and fosters a uniform distribution of nucleation cores, thereby significantly improving the purity and microstructure uniformity of high scrap ratio aluminum alloy melts. Specific ultrasonic refining parameter ranges stably generate cavitation effects and ensure melt processing uniformity. The microjets generated by the collapse of cavitation bubbles promote the aggregation and flotation of oxide inclusions and Fe-rich impurity phases, while simultaneously breaking dendrites and increasing the number of nucleation cores. This achieves a synergistic effect of melt purification and grain refinement. Compared to traditional argon-chlorine refining, this method eliminates the need for chemical refining agents to achieve degassing and inclusion removal, and improves the microstructure uniformity and formability of high scrap ratio recycled aluminum alloys. Traditional recycled aluminum refining mainly relies on argon-chlorine refining or chemical refining agents; this invention uses ultrasonic physical refining to replace chemical refining agents, reducing chloride emissions and improving melt purity.

[0062] According to the present invention, the casting conditions include: casting at 700-710°C, casting rate of 60-80 mm / min, cooling water pressure of 0.2-0.3 MPa, to obtain an ingot.

[0063] According to the present invention, the homogenization conditions include: employing a two-stage homogenization process, first holding the ingot at 480-500℃ for 4-6 h, then raising the temperature to 530-550℃ and holding it for 6-12 h.

[0064] According to the present invention, the hot rolling includes roughing and finishing:

[0065] The conditions for rough rolling include: 13 passes, a reduction of 35-50 mm per pass, an intermediate billet temperature of 380-420℃, and an intermediate billet thickness of 40-45 mm.

[0066] The conditions for the finishing mill include: using a four-roll continuous rolling mode; and the cooling method for the finishing mill is: a fan-shaped nozzle is installed at the inlet of the finishing mill, with a pressure of 0.8-1.2 MPa and a flow rate of 1000-2000 m³ / h. 3 A flat nozzle is installed at the finishing mill outlet, with a pressure of 0.3-0.5 MPa and a flow rate of 500-1000 m³ / h. 3 / h, using a laminar flow cooling water curtain, water is sprayed onto the upper and lower surfaces of the finished rolled plate for cooling. The final rolling cooling results in a surface temperature of 260-263℃, a temperature of 265-273℃ at 1 / 4 of the surface, and a core temperature of 277-279℃, with a temperature difference ΔT of 5-20℃.

[0067] The coiling temperature is 260-280 ℃, and the final rolled thickness is 3.9-4.1 mm.

[0068] In this invention, "1 / 4 of the distance from the surface" refers to the temperature of the surface of the high scrap ratio 6-series aluminum alloy used for automotive body panels at a distance of 1 / 4 of the thickness in the thickness direction.

[0069] In this invention, the cooling system design of the finishing mill adopts an emulsion control system that combines upper and lower dual-spray, zoned differential cooling and laminar flow cooling. The finishing mill inlet is equipped with high-pressure fan-shaped nozzles to form a dense cooling zone; the finishing mill outlet uses low-pressure flat nozzles to compensate for the core temperature drop by utilizing the heat of rolling deformation; the finishing mill outlet is equipped with a laminar flow cooling water curtain system with symmetrical water spraying from the top and bottom, and asymmetric enhanced cooling is implemented in the final rolling section, so that the surface cools down faster than the core, forming a "cold surface, hot core" structure from the surface to the core. The cooling design provided by this invention enables the formation of ultrafine grains on the surface and fine grains in the core after subsequent annealing.

[0070] In conventional hot finishing rolling processes, the mill emulsion cooling system typically employs a symmetrical and uniform spray pattern, with the inlet and outlet spray volumes usually controlled at approximately 800-1200 m³. 3The spray pressure is approximately 1.0 MPa, and laminar cooling also employs a uniform cooling method, ensuring a relatively consistent temperature distribution along the thickness of the sheet, with a temperature difference generally less than 5 °C. This invention utilizes high-pressure fan-shaped nozzles at the finishing mill inlet to form a dense cooling zone, increasing the surface cooling rate of the sheet. At the finishing mill outlet, low-pressure flat nozzles are used, combined with a laminar cooling water curtain, to achieve a zoned differential cooling method where the surface cools faster than the core, thus creating a certain temperature gradient along the thickness. By controlling the thickness temperature difference ΔT, a "cold surface, hot core" temperature distribution is achieved, resulting in a difference in the energy storage state between the surface and core after rolling. This provides conditions for microstructure control during subsequent annealing, thereby facilitating the acquisition of a fine-grained microstructure in the surface and a relatively fine-grained microstructure in the core, improving the dent resistance and formability of the automotive outer sheet.

[0071] According to the present invention, the cold rolling conditions include: four consecutive cold rolling passes, with thicknesses of 3.2 mm, 2.6 mm, 1.3 mm, and 1.0 mm after each pass, and a rolling thickness of 1.0 mm.

[0072] In this invention, the high scrap ratio 6-series aluminum alloy has a high Fe phase content. If intermediate annealing is used, Fe phase segregation is easily accompanied during recrystallization, inducing {001} <100> The formation of harmful cubic textures leads to anisotropy during sheet metal stamping, resulting in defects such as orange peel and streaks on the surface. The intermediate annealing process of this invention suppresses the static recrystallization process through continuous cold rolling deformation, fundamentally avoiding the harmful texture induced by Fe phase segregation. The continuous accumulated strain causes the internal texture of the sheet metal to evolve from "preferred orientation" to "random uniform orientation", making the internal texture orientation of the sheet metal more uniform. At the same time, the gradient structure of hot rolling and low-temperature final rolling makes the cold rolling deformation uniform, avoiding localized preferential textures. The accumulated strain of continuous cold rolling makes the texture orientation uniform. The two work together to achieve "texture homogenization without annealing and recrystallization", which not only meets the requirements of automotive outer panels for favorable textures, but also avoids the risk of harmful textures under high Fe content.

[0073] Traditional processes, such as high-temperature final rolling followed by cold rolling with intermediate annealing, follow the theory of "annealing recrystallization dominating texture control" and are suitable for low scrap ratio scenarios with low Fe content and no risk of harmful texture induction. They achieve plasticity recovery and texture optimization through annealing. The present invention, with its low-temperature final rolling temperature gradient followed by cold rolling and intermediate annealing, is suitable for high scrap ratio scenarios with high Fe content and a high risk of inducing harmful textures. By constructing the gradient structure in low-temperature final rolling and suppressing recrystallization in intermediate annealing, it fundamentally solves the texture defect problem under high scrap ratios and achieves the triple goals of high scrap utilization, performance improvement, and surface quality optimization.

[0074] According to the present invention, the conditions for the solution heat treatment include: a solution heat treatment temperature of 540-550 °C, a holding time of 30-40 s, and an elongation of 0.2-0.5%.

[0075] According to the present invention, the surface layer of the plate after solution heat treatment has 15-25 μm ultrafine crystals, and the core has 25-40 μm fine crystals.

[0076] According to the present invention, the pre-aging conditions include: heating at 100-120 ℃, holding at that temperature for 20-30 s, then cooling to 60-70 ℃ and holding at that temperature for 55-65 s.

[0077] In this invention, the nucleation and growth of the GP region are controlled by two-stage pre-aging to form a high-density fine GP region, so that the baking hardening value BH2 > 60MPa, realizing "programmable heat treatment" and meeting the performance requirements of different automotive outer panels.

[0078] A second aspect of the present invention provides a 6-series aluminum alloy obtained by the above-mentioned method for preparing 6-series aluminum alloys for automotive body panels, wherein the scrap ratio of the 6-series aluminum alloy is ≥85%;

[0079] The bake hardening value BH2 of the 6-series aluminum alloy is greater than 60 MPa.

[0080] Test methods

[0081] The tensile strength Rm was measured according to GB / T 228.1.

[0082] The yield strength Rp0.2 was measured according to GB / T 228.1.

[0083] The elongation A80 was measured according to GB / T 228.1.

[0084] The elongation Ag was measured according to GB / T 228.1.

[0085] The strain hardening index n value was measured according to GB / T 5028.

[0086] The plastic strain ratio r was measured according to GB / T 5027.

[0087] Baking hardening increment ΔRp 0.2 According to GB / T 228.1, the Rp value in state T64 is... 0.2 - T4 state Rp 0.2 .

[0088] The technical solution of the present invention will be further described in detail below with reference to the embodiments. Obviously, the embodiments described herein are only some embodiments of the present invention and are not intended to limit the present invention. All other embodiments implemented by those skilled in the art based on the embodiments of the present invention without creative improvements are within the protection scope of the present invention.

[0089] Example 1

[0090] Calculate the amount of each aluminum alloy raw material and prepare the aluminum alloy raw materials according to the following ratio: Si: 0.781%, Mg: 0.544%, Cu: 0.227%, Mn: 0.328%, Fe: 0.615%, Ni: 0.146%, Zr: 0.119%, Ti: 0.027%, B: 0.008%, other individual impurities ≤0.05%, total other impurities ≤0.15%, balance is Al. The weight ratio of (Mn+Ni) to Fe is 0.77.

[0091] Waste pretreatment: The recycled aluminum waste is smelted in a double-chamber furnace at a smelting temperature of 650℃ and held for 2.5 hours. After slag removal, the molten aluminum is poured into a mold and cooled into composite ingots.

[0092] Melting and casting: The calculated weights of primary aluminum ingots, 90% composite scrap, master alloy, and alloying additives are loaded into a melting furnace. After melting at 720℃, 0.12% Ti-B-Zr master alloy is added, with a Ti:B:Zr mass ratio of 2.8:1.1:2.1, and the mixture is stirred for 12 minutes. Then, 0.10% Mn-Ni composite agent is added to the melt, with a Mn:Ni mass ratio of 3.0:0.9. The temperature is raised to 750℃ and held for 25 minutes. Electromagnetic stirring is used at 220 rpm for 20 minutes, followed by standing for 40 minutes. Ultrasonic refining is then performed by applying 20 kHz ultrasound for 8 minutes, achieving a hydrogen content ≤0.13 ml / 100gAl. Casting is then carried out at 705℃ with a casting speed of 75 mm / min and a cooling water pressure of 0.22 MPa to obtain the ingot.

[0093] Saw and milling: saw belt speed 2210m / min, saw belt feed speed 450mm / min, milling feed speed 4.2m / min, waste cut at the ingot drawing end 387mm, large surface milling amount 12mm, small surface milling amount 6mm, milling thickness 585mm.

[0094] Irradiation: The ingot is first held at 490℃ for 4.5 hours, and then heated to 540℃ and held for 8 hours.

[0095] Hot rolling: The roughing process uses 13 passes, with a reduction of 35-50 mm per pass. The intermediate billet temperature is 413℃, and the intermediate billet thickness is 40 mm. The finishing process involves four consecutive finishing mills. A fan-shaped nozzle is installed at the finishing mill inlet, and the emulsion spray rate is 1200 m³ / h. 3 / h, pressure 1.15MPa, flat nozzles are installed at the finish mill exit, and the outlet emulsion spray rate is 585m³ / h. 3The rolling mill operates at a rate of 0.38 MPa per hour, with a laminar flow cooling water curtain system at the outlet. The coiling temperature is 268°C, and the final rolling thickness is 3.998 mm. The surface, 1 / 4 depth from the surface, and core temperatures of the sheet are 262°C, 268°C, and 277°C, respectively.

[0096] Cold rolling: a total of 4 passes, with thicknesses of 3.2mm, 2.6mm, 1.3mm, and 1.0mm after each pass.

[0097] Continuous annealing: solution temperature is 547℃, holding time is 35s, elongation is 0.3%, pre-aging temperature is 105℃, heating time is 25s, then the temperature is reduced to 65℃ and held for 60s.

[0098] After solution heat treatment, the surface of the plate forms ultrafine crystals of 15-25μm, and the core forms fine crystals of 25-40μm.

[0099] Aluminum alloy A1 was obtained. The scrap ratio was 90%.

[0100] Example 2

[0101] Calculate the amount of each aluminum alloy raw material and prepare the aluminum alloy raw materials according to the following ratio: Si: 0.60%, Mg: 0.40%, Cu: 0.15%, Mn: 0.30%, Fe: 0.56%, Ni: 0.10%, Zr: 0.05%, Ti: 0.02%, B: 0.005%, other individual impurities ≤0.05%, total other impurities ≤0.15%, balance is Al. The weight ratio of (Mn+Ni) to Fe is 0.71.

[0102] Waste pretreatment: The recycled aluminum waste is smelted in a double-chamber furnace at a smelting temperature of 640℃ and held for 2 hours. After slag removal, the molten aluminum is poured into a mold and cooled to form composite ingots.

[0103] Melting and casting: The calculated weights of primary aluminum ingots, 85% composite waste, master alloy, and alloying additives are loaded into a melting furnace and melted at 700℃. Then, 0.12% Ti-B-Zr master alloy is added, with a Ti:B:Zr mass ratio of 2.7:1:1.8, and the mixture is stirred for 10 minutes. Next, 0.10% Mn-Ni composite agent is added to the melt, with a Mn:Ni mass ratio of 2.8:0.8. The temperature is raised to 740℃ and held for 20 minutes. Electromagnetic stirring is used at 220 rpm for 20 minutes, followed by standing for 40 minutes. Ultrasonic refining is then performed by applying 20 kHz ultrasound for 5 minutes, resulting in a hydrogen content ≤0.13 ml / 100gAl. Casting is then carried out at 700℃ with a casting speed of 60 mm / min and a cooling water pressure of 0.2 MPa to obtain the ingot.

[0104] Saw and milling: saw belt speed 2210m / min, saw belt feed speed 450mm / min, milling feed speed 4.2m / min, waste cut at the ingot drawing end 387mm, large surface milling amount 12mm, small surface milling amount 6mm, milling thickness 585mm.

[0105] Irradiation: The ingot is first held at 480℃ for 4 hours, and then heated to 530℃ and held for 6 hours.

[0106] Hot rolling: The roughing process uses 13 passes, with a reduction of 35-50 mm per pass. The intermediate billet temperature is 380℃, and the intermediate billet thickness is 40 mm. The finishing process involves four consecutive finishing mills. A fan-shaped nozzle is installed at the finishing mill inlet, and the emulsion spray rate is 1000 m³ / h. 3 / h, pressure 0.8 MPa, flat nozzles are installed at the finish mill exit, and the outlet emulsion spray rate is 500 m³ / h. 3 The rolling mill operates at a speed of 0.3 MPa and a pressure of 0.3 MPa. It is equipped with a laminar flow cooling water curtain system at the outlet, with a coiling temperature of 260°C and a final rolling thickness of 3.9 mm. The surface, 1 / 4 depth, and core temperatures of the sheet are 261°C, 270°C, and 277°C, respectively.

[0107] Cold rolling: a total of 4 passes, with thicknesses of 3.2mm, 2.6mm, 1.3mm, and 1.0mm after each pass.

[0108] Continuous annealing: solution temperature is 540℃, holding time is 30 s, elongation is 0.2%, pre-aging temperature is 100℃, heating time is 20 s, then the temperature is reduced to 60℃ and held for 55 s.

[0109] After solution heat treatment, the surface of the plate forms ultrafine crystals of 15-25μm, and the core forms fine crystals of 25-40μm.

[0110] Aluminum alloy A2 was obtained. The scrap ratio was 85%.

[0111] Example 3

[0112] Calculate the amount of each aluminum alloy raw material and prepare the aluminum alloy raw materials according to the following ratio: Si: 1.00%, Mg: 0.80%, Cu: 0.35%, Mn: 0.40%, Fe: 0.80%, Ni: 0.20%, Zr: 0.20%, Ti: 0.10%, B: 0.03%, other individual impurities ≤0.05%, total other impurities ≤0.15%, balance is Al. The weight ratio of (Mn+Ni) to Fe is 0.75.

[0113] Waste pretreatment: The recycled aluminum waste is smelted in a double-chamber furnace at a smelting temperature of 660℃ and held for 3 hours. After slag removal, the molten aluminum is poured into a mold and cooled into composite ingots.

[0114] Melting and casting: The calculated weights of primary aluminum ingots, 95% composite waste, master alloy, and alloying additives are loaded into a melting furnace and melted at 700℃. Then, 0.12% Al-Ti-B-Zr master alloy is added, with a Ti:B:Zr mass ratio of 3.1:1.2:2.2, and the mixture is stirred for 15 min. Next, 0.10% Mn-Ni composite agent is added to the melt, with a Mn:Ni mass ratio of 2.8:0.8. The temperature is raised to 760℃ and held for 30 min. Electromagnetic stirring is used at 220 rpm for 20 min, followed by standing for 40 min. Ultrasonic refining is then performed by applying 20 kHz ultrasound for 10 min, achieving a hydrogen content ≤0.13 ml / 100gAl. Casting is then carried out at 710℃ with a casting speed of 80 mm / min and a cooling water pressure of 0.3 MPa to obtain the ingot.

[0115] Saw and milling: saw belt speed 2210m / min, saw belt feed speed 450mm / min, milling feed speed 4.2m / min, waste cut at the ingot drawing end 387mm, large surface milling amount 12mm, small surface milling amount 6mm, milling thickness 585mm.

[0116] Irradiation: The ingot is first held at 500℃ for 6 hours, and then heated to 550℃ and held for 12 hours.

[0117] Hot rolling: The roughing process uses 13 passes, with a reduction of 35-50 mm per pass. The intermediate billet temperature is 420℃, and the intermediate billet thickness is 40 mm. The finishing process involves four consecutive finishing mills. A fan-shaped nozzle is installed at the finishing mill inlet, and the emulsion spray rate is 2000 m³ / h. 3 / h, pressure 1.2 MPa, flat nozzles installed at the finish mill exit, emulsion spray rate at the exit is 1000 m³ / h. 3 The rolling mill operates at a speed of 0.5 MPa and a pressure of 0.5 MPa. A laminar flow cooling water curtain system is installed at the outlet. The coiling temperature is 280℃, and the final rolling thickness is 4.1 mm. The surface, 1 / 4 depth from the surface, and core temperatures are 262℃, 269℃, and 278℃, respectively.

[0118] Cold rolling: a total of 4 passes, with thicknesses of 3.2mm, 2.6mm, 1.3mm, and 1.0mm after each pass.

[0119] Continuous annealing: solution temperature is 550℃, holding time is 40 s, elongation is 0.5%, pre-aging temperature is 120℃, heating time is 30 s, then the temperature is reduced to 70℃ and held for 65 s.

[0120] After solution heat treatment, the surface of the plate forms ultrafine crystals of 15-25μm, and the core forms fine crystals of 25-40μm.

[0121] Aluminum alloy A3 was obtained. The scrap ratio was 95%.

[0122] Comparative Example 1

[0123] Aluminum alloy material was prepared according to the processing method of Example 1, except that the Mn+Ni / Fe content was below the lower limit, with Si: 0.890%, Mg: 0.664%, Cu: 0.219%, Mn: 0.306%, Fe: 0.656%, Ni: 0.133%, Zr: 0.122%, Ti: 0.024%, B: 0.009%, and Mn+Ni / Fe: 0.669%. Aluminum alloy material DA1 was obtained.

[0124] Comparative Example 2

[0125] Aluminum alloy material was prepared according to the processing method of Example 1, except that the Mn+Ni / Fe content was higher than the upper limit. The composition was: Si: 0.889%, Mg: 0.690%, Cu: 0.220%, Mn: 0.328%, Fe: 0.553%, Ni: 0.149%, Zr: 0.155%, Ti: 0.023%, B: 0.014%, and Mn+Ni / Fe: 0.86%. The resulting aluminum alloy material was DA2.

[0126] Comparative Example 3

[0127] Aluminum alloy material was prepared according to the processing method of Example 1, except that the furnace exit temperature during waste pretreatment was 720°C. Aluminum alloy material DA3 was obtained.

[0128] Comparative Example 4

[0129] Aluminum alloy materials were prepared according to the processing method of Example 1, except that only a Ti-B-Zr composite agent was added. Aluminum alloy material DA4 was obtained.

[0130] Comparative Example 5

[0131] Aluminum alloy materials were prepared according to the processing method of Example 1, except that only Mn-Ni composite agent was added. Aluminum alloy material DA5 was obtained.

[0132] Comparative Example 6

[0133] Aluminum alloy materials were prepared according to the processing method of Example 1, except that a traditional refining method was used, with an argon-chlorine mixture and an argon flow rate of 14.5 m³ / s. 3 / h, chlorine flow rate 6.5m 3 The refining time is 50 minutes per hour. Aluminum alloy material DA6 is obtained.

[0134] Comparative Example 7

[0135] Aluminum alloy materials were prepared according to the processing method of Example 1, except that the spray volume of the emulsion at the inlet and outlet of the hot finishing section was 1200 m³. 3 Aluminum alloy material DA7 was produced by using a high-pressure fan-shaped nozzle at a pressure of 1.15 MPa per hour.

[0136] Comparative Example 8

[0137] Aluminum alloy material was prepared according to the processing method of Example 1, except that the cold rolling adopted an intermediate annealing process, the cold rolling passes were 6mm, 3.5mm, and the box annealing was carried out at a temperature of 360℃ for 3 hours, with a thickness of 2.6mm, 1.3mm, and 1.0mm, to obtain aluminum alloy material DA8.

[0138] Comparative Example 9

[0139] Aluminum alloy material was prepared according to the processing method of Example 1, except that the continuous annealing was replaced with isothermal single-stage pre-aging: the solution temperature was 547℃, the holding time was 35s, the elongation was 0.3%, the pre-aging temperature was 110℃, and the heating time was 26s. Aluminum alloy material DA9 was obtained.

[0140] Comparative Example 10

[0141] Aluminum alloy material was prepared according to the processing method of Example 1, except that the non-isothermal multi-stage pre-aging was below the lower limit of the range: the solution temperature was 549℃, the holding time was 35s, the elongation was 0.3%, and the pre-aging regime was 80℃ / 10s + 55℃ / 30s. Aluminum alloy material DA10 was obtained.

[0142] Comparative Example 11

[0143] Aluminum alloy material was prepared according to the processing method of Example 1, except that the non-isothermal multi-stage pre-aging was higher than the upper limit of the range: the solution temperature was 546℃, the holding time was 36s, the elongation was 0.3%, and the pre-aging regime was 150℃ / 50s + 100℃ / 70s. Aluminum alloy material DA11 was obtained.

[0144] Comparative Example 12

[0145] Traditional outer panel manufacturing process with low waste addition.

[0146] Calculate the amount of each aluminum alloy raw material and prepare the aluminum alloy raw materials according to the following ratio: Si: 0.69%, Mg: 0.556%, Cu: 0.208%, Mn: 0.107%, Fe: 0.190%, Ni: 0.039%, Zr: 0.026%, Ti: 0.022%, other individual ≤0.05%, other total ≤0.15%, and the balance is Al.

[0147] Waste pretreatment: The recycled aluminum waste is smelted in a double-chamber furnace at a smelting temperature of 710℃ and held for 2.5 hours. After slag removal, the molten aluminum is poured into a mold and cooled to form composite ingots.

[0148] Melting and casting: The calculated weight of primary aluminum ingots, 40% composite waste, intermediate alloy, and alloying additives are loaded into a melting furnace and melted at 740℃. Electromagnetic stirring is used at a speed of 220 rpm for 20 minutes, followed by a settling period of 40 minutes. Refining is then performed using an argon + chlorine mixture with an argon flow rate of 18 m³ / s. 3 / h, chlorine flow rate 6.7m 3 Casting was carried out at 710℃, with a casting speed of 75 mm / min and a cooling water pressure of 0.21 MPa, to obtain ingots.

[0149] Saw and milling: saw belt speed 2210m / min, saw belt feed speed 450mm / min, milling feed speed 4.2m / min, waste cut at the ingot drawing end 387mm, large surface milling amount 12mm, small surface milling amount 6mm, milling thickness 585mm.

[0150] Immersion heating: The ingot is heated at 535℃ for 6 hours.

[0151] Hot rolling: The roughing process uses 21 passes, with an intermediate billet temperature of 420℃ and a thickness of 40mm. The finishing process involves four consecutive hot finishing mills. Emulsion parameters are controlled in the hot finishing section, with the inlet and outlet emulsion spray rates for F1-F4 both being 1200m³. 3 / h, pressure 1.15MPa, high-pressure fan-shaped nozzle, final rolling temperature 318℃, final rolling thickness 6.018mm.

[0152] Cold rolling: Employing a multi-pass process with intermediate annealing, the number of cold rolling passes is 6-3.5 (box annealing: temperature 360℃, holding time 3 hours) -- 2.6 -- 1.3 -- 1.0

[0153] Continuous annealing: solution temperature 545℃, holding time 35s, elongation 0.3%, pre-aging temperature 110℃, heating time 25s. Aluminum alloy DA12 was obtained.

[0154] Table 1

[0155]

[0156] In Table 1, T4 represents the room temperature tensile properties of the material after solution treatment and special aging treatment, and T64 represents the tensile properties of the material after 2% pre-deformation and then simulated baking at 185°C for 20 minutes.

[0157] By comparing the examples and comparative examples, it can be seen that the 6-series aluminum alloy provided by the present invention, through composition adjustment, composite modification, refining optimization and hot rolling, cold rolling and pre-aging process control, can achieve better performance than traditional processes when using high proportion of scrap. The elongation, n, r value and strength after baking paint are significantly optimized, and the grain size is significantly refined, reaching below 30μm.

[0158] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing 6-series aluminum alloy for automotive body panels, characterized in that, Includes the following steps: Scrap pretreatment, secondary smelting, casting, homogenization, hot rolling, cold rolling, solution heat treatment, pre-aging; The conditions for waste pretreatment include: first melting the aluminum waste at a temperature of 640-660 ℃ for 2-3 h, and casting the molten aluminum waste into composite ingots. The waste ratio is 85-95%; The components and their weight percentages in the high scrap ratio 6-series aluminum alloy used for automotive body panels are as follows: The Si content is 0.60-1.00%; The Mg content is 0.40-0.80%; The Cu content is 0.15-0.35%; The Mn content is 0.30-0.40%; Fe content ≤ 0.80%; The Ni content is 0.10-0.20%; The Zr content is 0.05-0.20%; The Ti content is 0.02-0.10%; The content of B is 0.005-0.05%; The weight ratio of (Mn+Ni) to Fe is 0.70-0.78; The content of a single impurity is ≤0.05%; The total content of other impurity elements is ≤0.15%; The balance is Al.

2. The method for preparing 6-series aluminum alloy for automotive body panels according to claim 1, characterized in that, The conditions for the second smelting include: the temperature of the second smelting is 700-730℃, Ti-B-Zr composite refining agent is added, stirred for 10-15 min, then Mn-Ni composite agent is added, the temperature is raised to 740-760℃, held for 20-30 min, ultrasonic refining is performed, 20kHz ultrasound is applied for 5-10 min, and the hydrogen content is ≤0.13ml / 100gAl; In the Ti-B-Zr composite refining agent, the mass ratio of Ti, B and Zr is 2.7-3.1:1-1.2:1.8-2.2; In the Mn-Ni composite agent, the mass ratio of Mn to Ni is 2.8-3.2:0.8-1.

2.

3. The method for preparing 6-series aluminum alloy for automotive body panels according to claim 1, characterized in that, The casting conditions include: casting at 700-710℃, casting rate of 60-80 mm / min, cooling water pressure of 0.2-0.3 MPa, to obtain an ingot.

4. The method for preparing 6-series aluminum alloy for automotive body panels according to claim 1, characterized in that, The homogenization conditions include: a two-stage homogenization process, in which the ingot is first held at 480-500 ℃ for 4-6 h, and then heated to 530-550 ℃ and held for 6-12 h.

5. The method for preparing 6-series aluminum alloy for automotive body panels according to claim 1, characterized in that, The hot rolling includes roughing and finishing: The conditions for rough rolling include: 13 passes, a reduction of 35-50 mm per pass, an intermediate billet temperature of 380-420℃, and an intermediate billet thickness of 40-45 mm. The conditions for the finishing mill include: using a four-roll continuous rolling mode; and the cooling method for the finishing mill is: a fan-shaped nozzle is installed at the inlet of the finishing mill, with a pressure of 0.8-1.2 MPa and a flow rate of 1000-2000 m³ / h. 3 A flat nozzle is installed at the finishing mill outlet, with a pressure of 0.3-0.5 MPa and a flow rate of 500-1000 m³ / h. 3 / h, using a laminar flow cooling water curtain, water is sprayed onto the upper and lower surfaces of the finished rolled plate for cooling. The final rolling cooling results in a surface temperature of 260-263℃, a temperature of 265-273℃ at 1 / 4 of the surface, and a core temperature of 277-279℃, with a temperature difference ΔT of 5-20℃. The coiling temperature is 260-280 ℃, and the final rolled thickness is 3.9-4.1 mm.

6. The method for preparing 6-series aluminum alloy for automotive body panels according to claim 1, characterized in that, The cold rolling conditions include: four consecutive cold rolling passes, with thicknesses of 3.2 mm, 2.6 mm, 1.3 mm, and 1.0 mm after each pass, and a total rolling thickness of 1.0 mm.

7. The method for preparing 6-series aluminum alloy for automotive body panels according to claim 1, characterized in that, The conditions for the solution heat treatment include: a solution heat treatment temperature of 540-550 ℃, a holding time of 30-40 s, and an elongation of 0.2-0.5%.

8. The method for preparing 6-series aluminum alloy for automotive body panels according to claim 1, characterized in that, The surface of the plate after solution heat treatment has 15-25μm ultrafine crystals, and the core has 25-40μm fine crystals.

9. The method for preparing 6-series aluminum alloy for automotive body panels according to claim 1, characterized in that, The pre-aging conditions include: heating at 100-120 ℃, holding at that temperature for 20-30 s, then cooling down to 60-70 ℃ and holding at that temperature for 55-65 s.

10. The 6-series aluminum alloy obtained by the method for preparing 6-series aluminum alloy for automotive body panels according to any one of claims 1-9, characterized in that, The scrap ratio of the 6-series aluminum alloy is ≥85%; The bake hardening value BH2 of the 6-series aluminum alloy is greater than 60 MPa.

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