CN114107747B - Preparation method of high-performance 6XXX aluminum alloy thin strip by jet casting - Google Patents

Abstract

A preparation method of a high-performance 6XXX aluminum alloy thin strip by injection casting and rolling, 1) smelting, smelting according to the following chemical components, the chemical components are: Si: 0.5-1.5%, Mg: 0.1-2.0%, Fe : 0.1-1.0%, Mn: 0.05-0.5%, Cu: 0.02-0.2%, the rest are Al and other inevitable impurities; and, the single impurity content ≤ 0.05%, the total impurity content ≤ 0.15%; 2) Nanoparticle reinforcement 3) spray deposition, continuous casting; 4) cooling; 5) first hot rolling; 6) second hot rolling; 7) coiling; 8) post-treatment. Compared with the existing 6XXX aluminum alloy, the preparation method of the invention uses the 6XXX aluminum alloy plate and strip cast and rolled by spray deposition combined with the twin-roll thin strip casting and rolling process. , easily achieve more than 50% lightweight.

Description

A kind of preparation method of high-performance 6XXX aluminum alloy thin strip by injection casting

technical field

The invention relates to the field of aluminum alloy preparation, in particular to a preparation method of spray casting and rolling high-performance 6XXX aluminum alloy thin strip.

Background technique

The thin strip continuous casting technology is a cutting-edge technology in the field of metallurgy today. The twin-roll thin strip continuous casting technology was first proposed by Henry Bessemer in 1865 (US Patent: 49053). Thin strip continuous casting integrates continuous casting, rolling, and even heat treatment processes, so that the thin strip produced can be formed into an industrial product at one time after a little subsequent rolling, which greatly simplifies the production process of aluminum alloy strips and shortens the time. The production cycle makes the aluminum alloy strip production process more compact, more continuous, more efficient and more environmentally friendly; at the same time, the production cost is significantly reduced, and the quality and performance of the thin strip produced are no less than or even better than the traditional process.

Vehicle lightweighting has become the focus of attention from countries all over the world. In recent years, technologies and innovations to achieve vehicle lightweighting have continued to emerge. The so-called lightweight is to reduce the net mass of the vehicle as much as possible on the premise of ensuring the strength and safety performance of the vehicle, thereby improving the dynamic performance of the vehicle and reducing the energy consumption during the driving process, so as to achieve the purpose of energy saving and emission reduction. The net weight of the whole vehicle is reduced by 10%, and the fuel efficiency can be improved by 6-8%; for every 100kg reduction in the vehicle weight, the fuel consumption per 100 kilometers can be reduced by 0.3-0.6L. Today, energy saving and emission reduction is a global task, and automobiles are an indispensable necessity in modern life, so the lightweight of automobiles has become the current development trend of automobiles in the world.

At present, the average energy consumption of Chinese cars is about 7.5L/100km, which still has a certain gap with developed countries. The national planning target is to reach 4.5L/km by 2020, which is equivalent to the European standard and surpasses the American standard. standard. To achieve this goal, it is necessary to accelerate the lightweighting of automobiles. European automakers are advancing "ultra-light vehicle engineering", and the United States has made leaps in automotive aluminum, with the goal of reducing the quality of vehicles by 30% on the basis of existing prices.

Aluminum is the earliest automobile manufacturing material to become a substitute for steel. In 1960, the average amount of aluminum used in passenger cars in the United States was 28.6 kg, which rose to 109 kg in 1999, and reached about 160 kg in 2015. The body frame and cover parts of the Audi A8 produced by the automobile company are all made of Alcoa's extruded aluminum materials and sheets, which is the first of its kind for an all-aluminum passenger car. The current data shows that replacing steel with aluminum in automobile manufacturing can reduce the quality of automobiles by 30-40%. If the second-generation aluminum alloy is used, the weight reduction effect is even more remarkable. Aluminum is second only to steel and cast iron materials in automobile manufacturing, and in all-aluminum passenger cars, the amount of aluminum has risen to second place. In addition, new energy vehicles are an emerging branch market in the development of the automobile industry. Different from traditional vehicles, new energy vehicles use batteries as power to drive the operation of the vehicle, which is restricted by the weight of the power battery and the cruising range of the power battery. In terms of material application, the need for lightweight car body is more urgent. No matter in terms of application technology, operation safety or recycling, etc., aluminum alloy materials with mature technology have great advantages and become the first choice of new energy vehicle companies.

At present, the automotive body sheet (abbreviation: ABS) is divided into two types, the inner panel and the outer panel. ABS has high performance requirements for outer plates and is difficult to produce. ABS must have good formability, strong surface flatness, good weldability and excellent bake hardening characteristics.

According to the performance of ABS aluminum alloy and its production process, it can be divided into two generations. The first generation is generally a conventional deformed aluminum alloy produced by the ingot-hot rolling method, and the final aluminum alloy sheet and strip products are obtained by subsequent cold rolling and heat treatment. The production cycle Longer, generally takes about 20 days, and now there are a total of 27 companies and workshops built around the world, all of which belong to the first generation.

The second generation of ABS is generally considered to be a deformed aluminum alloy sheet prepared by a new short-flow process with significantly improved performance. Typical new short-flow processes include Hazelett continuous casting and rolling process, twin-roll thin strip continuous casting and rolling process, etc. However, the traditional horizontal twin-roll thin strip continuous casting and rolling process can only produce aluminum foil rolled strip and relatively simple alloy series 1XXX and 3XXX series strip products, but cannot produce high-end 6XXX series aluminum alloy cover plate products for automobiles. . Moreover, the traditional horizontal twin roll caster is slow, usually only 1-3m/min, and the production efficiency is low.

In recent years, many famous aluminum alloy plate and strip twin roll casting machine equipment manufacturers in the world have done a lot of development work to increase the casting speed and increase the width of the strip, aiming to improve production efficiency and wider applications. The more famous companies are Fata Hunter in Italy and Pucky in France. The Speedcaster ^TM ultra-thin high-speed casting and rolling mill developed by Fatahhunter is characterized by: double-roller, double-drive, 15-degree inclination, casting roll diameter of 1118mm, The plate width is 2184mm, the rolling force is 3000t, the casting speed can reach up to 38m/min, and the thinnest thickness can reach 0.635mm. The characteristics of the Junbo3CM casting and rolling mill developed by Puji Company are: rolling force of 2900t, plate width of 2020mm, the thinnest casting thickness of 1mm, and the maximum casting speed of 15m/min. However, these equipments are still unable to produce high-end 6XXX series aluminum alloy panel strip products for automobiles.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a preparation method of spray casting and rolling high-performance 6XXX aluminum alloy thin strip, the aluminum alloy strip can realize the combined improvement of strength, elongation and formability by using the preparation method, and the prepared 6XXX aluminum alloy plate Compared with the existing 6XXX aluminum alloy, the belt has more than 25% higher strength and more than 35% higher formability; compared with the steel sheet for automobiles, it achieves more than 50% lighter weight; it can be widely used in automotive applications, especially in automotive engines The cover can also be used for parts such as fenders, doors, roofs and trunk lids, which provides a broad space for the automobile industry to reduce weight, reduce energy consumption and improve fuel economy; moreover, the aluminum alloy plate of the present invention The belt can be smoothly formed with a mold common to steel plates, and can be easily deformed into complex shapes without the need for additional mold design.

To achieve the above object, the technical scheme of the present invention is:

A method for preparing a high-performance 6XXX aluminum alloy thin strip by spray casting and rolling, comprising the following steps:

1) Smelting

Smelting according to the following chemical composition, the chemical composition is: Si: 0.5-1.5%, Mg: 0.1-2.0%, Fe: 0.1-1.0%, Mn: 0.05-0.5%, Cu: 0.02-0.2%, The rest are Al and other unavoidable impurities; and, the individual impurity content is less than or equal to 0.05%, and the total impurity content is less than or equal to 0.15%;

2) Nanoparticle enhancement

The smelted aluminum alloy liquid is introduced into the standing furnace to stand, and then transported to the front box through the launder, degassed and filtered, and then flows into the tundish. Hard particles with a higher melting point than aluminum, the added amount of the hard particles is 5-20 wt% of the aluminum alloy liquid; the temperature of the aluminum alloy liquid introduced into the static furnace is 780-850 ° C, and the temperature of the aluminum alloy liquid in the tundish is 780-850 ° C. 730～800℃;

3) Spray deposition

The aluminum alloy liquid flowing out from the tundish is atomized into fine droplets by inert gas, and the droplets are deposited on the surface of the twin rolls. The twin rolls are continuously cast with thin strips to obtain aluminum alloys with a thickness of 2-6mm and a width of 1000-2200mm Casting strip; the pressure of inert gas is 0.8～2.0MPa, the temperature of the aluminum alloy casting strip is 550～600℃, the diameter of the crystallizing roll is 400～800mm, the inside of the crystallizing roll is cooled by water, and the casting speed of the casting machine is 20～80m/min;

4) Cool down

After the aluminum alloy cast strip comes out of the casting machine, it is cooled to 410～510℃ by water quenching;

5) The first hot rolling

The cooled aluminum alloy cast strip is processed by pinch rolls and cut ends and then sent to the rolling mill for the first hot rolling; the first hot rolling temperature is 380 ~ 480 ℃, and the first hot rolling reduction rate is less than or equal to 50% ;

6) Cooling, second hot rolling

The aluminum alloy strip after the first hot rolling is air-cooled or water-cooled, followed by the second hot rolling;

The temperature of the second hot rolling is 280～420℃, the reduction ratio of the second hot rolling is ≤60%; the thickness of the aluminum alloy strip after the second hot rolling is 0.3～4mm, preferably 0.5～3mm;

7) Coil

The aluminum alloy strip after the second hot rolling is sent to the coiling machine through the pinch roller for coiling, and the coiling temperature is 200-370 °C;

8) Post-processing

After coiling, the aluminum alloy sheet and strip are sequentially solution heat treated and quenched.

Preferably, in step 2), the hard particles are one or more of TiC, TiN, WC, SiC, B ₄ C, Si ₃ N ₄ , and BN.

Preferably, in step 3), the inert gas is one or both of nitrogen and argon.

Preferably, in step 3), the molten drop is solid, semi-solid or liquid.

Further, after step 8) quenching, aging and paint baking processes are performed in sequence.

Preferably, the aging is artificial aging or natural aging or natural aging + artificial aging, wherein the artificial aging temperature is 90-200 ° C, the time is 25-120 min, and the natural aging time is 25-35 days.

Preferably, the paint baking temperature is 150-220° C., and the duration is 20-50 minutes.

In addition, after the paint baking, additional artificial aging is performed, and the temperature of the additional artificial aging is 90-200° C. and the time is 25-120 min.

Preferably, in step 8), the temperature of the solution heat treatment is 500-560° C., and the time is 8-50 min.

Preferably, in step 8), the temperature of the aluminum alloy strip after quenching is from room temperature to 120°C.

Preferably, one or more of off-line cold rolling, tension straightening, edge trimming, leveling, surface inspection, and shape inspection processes may be performed on the aluminum alloy strip before the post-treatment process in step 8).

Preferably, in step 3), the nozzle used for the spray deposition is a slit linear nozzle.

Preferably, in step 3), the continuous casting adopts a vertical casting machine or a horizontal casting machine.

Preferably, in the continuous casting process of step 3), the crystallizing roll is a copper roll, and the surface of the crystallizing roll has textures, grooves or embossing.

Preferably, the surface of the crystallizing roller is treated with chrome plating, and the thickness of the chrome plating layer is 0.05-0.10 mm.

The microstructure of the aluminum alloy strip of the present invention is a fine equiaxed crystal matrix structure + dispersed hard particles.

The aluminum alloy strip of the present invention can achieve a yield strength of 150-230 MPa, a tensile strength of 230-310 MPa, an elongation of 27-36%, and a forming limit test (in the specification of thickness 1.0 mm) under natural aging conditions, that is, T4 or T42 state. tested below) FLD ₀ ranged from 27-37%.

The aluminum alloy sheet and strip can achieve a yield strength of 170-250MPa, a tensile strength of 250-340MPa, an elongation of 25-34%, and a forming limit test (tested under the specification of thickness 1.0mm) under artificial aging conditions, that is, T6 state. FLD ₀ ranged from 24-34%.

The aluminum alloy plate and strip can achieve a yield strength of 250-290 MPa, a tensile strength of 330-370 MPa, and an elongation of 22-29% after being painted.

In the composition design of the 6XXX aluminum alloy strip of the present invention:

Si: It is the main component to improve the flow properties of aluminum alloys, which can greatly improve the casting properties of aluminum alloys. Adding a certain content of Si can improve the tensile strength, hardness and corrosion resistance of aluminum alloys; The presence of Si-containing hard particles in aluminum alloys leads to increased brittleness of the alloy and deterioration of cutting performance. Therefore, in the present invention, the Si content is controlled in the range of 0.5-1.5%.

Mg: It can improve the strength, hardness, heat resistance, corrosion resistance and machinability of aluminum alloys, but adding more Mg is prone to hot brittleness, making the alloy crack, and the formed Mg ₂ Si will make the alloy brittle. Therefore, in the present invention, the Mg content is controlled in the range of 0.1-2.0%.

Fe: FeAl ₃ , Fe ₂ Al or Al-Si-Fe flake or needle-like structure will be formed in the aluminum alloy, which will reduce the mechanical properties. This structure will also reduce the fluidity of the alloy and increase the hot cracking tendency. Therefore, the Fe content is controlled in the range of 0.1-1.0% in the present invention.

Mn: It can reduce the harmful effects of Fe in the aluminum alloy, and can make the flake or needle-like structure formed by Fe in the aluminum alloy into a fine crystal structure. Mn can organize the recrystallization process of the aluminum alloy and increase the recrystallization temperature. , and can significantly refine the recrystallized grains; too high Mn will cause segregation and reduce thermal conductivity. Therefore, in the present invention, the Mn content is controlled in the range of 0.05-0.5%.

Cu: The solid solution of Cu in the aluminum alloy can improve the strength, hardness, heat resistance and cutting performance, and can also improve the casting fluidity; but too high Cu content will affect the corrosion resistance and plasticity of the aluminum alloy, and make the Thermal cracking tendency increases. Therefore, the control range of the Cu content in the present invention is 0.02-0.2%.

In the present invention, the smelted aluminum alloy liquid is introduced into the static furnace for standing. One smelting furnace is generally used for 2-3 static furnaces. The temperature of the aluminum alloy liquid in the static furnace is 780-850°C. The aluminum alloy liquid is transported from the static furnace through the launder to the front box, and then flows into the tundish after degassing and filtering. Add hard particles with a size of 5 nanometers to 10 microns and a melting point higher than that of aluminum into the aluminum alloy liquid in the tundish, so that these high melting point hard particles are evenly dispersed in the aluminum alloy liquid, adding high melting point hard particles The amount of the hard particles is 5-20wt% of the aluminum alloy liquid.

The mechanism of the dispersion and distribution of the high melting point nano/micron hard particles into the aluminum alloy matrix is as follows:

During the solidification and crystallization process of aluminum alloy liquid, the nano/micron hard particles at the grain boundary can effectively limit the grain growth and refine the grains by pinning; at the same time, these nano/micron hard particles can also be used as effective isolating The quality nucleation point and excellent modifier can effectively increase the nucleation of aluminum alloy during solidification, optimize the microstructure, and the microstructure of the formed aluminum alloy strip is: fine equiaxed matrix structure + dispersed hard particles , significantly improve the mechanical properties of aluminum alloy strips.

During the spray deposition process, the aluminum alloy liquid flowing from the tundish flows into a slit linear nozzle, the slit of which is parallel to the centerline of the roll axis of the twin roll caster. Under the action of inert gas (such as N ₂ , Ar), The pressure of the inert gas is 0.8-2.0MPa, and the aluminum alloy liquid flowing into the slit linear nozzle is atomized into fine droplets and deposited on the surface of the twin rollers. During the flight of the droplets, thermal conduction or thermal radiation occurs with the outside world. The molten droplets can be solid, semi-solid or liquid; after that, they are continuously casted by a twin-roll thin strip caster to obtain an aluminum alloy cast strip with a thickness of 2-6mm and a width of 1000-2200mm.

The spray deposition combined with twin-roll thin strip casting and rolling process is a process that integrates aluminum alloy liquid atomization, spray deposition, and twin-roll casting and rolling into one process, which can economically and efficiently prepare aluminum alloy strips with uniform fine-grained structure and excellent comprehensive properties. , its main advantages are short process, low investment, low cost, low energy consumption, and can develop high-performance materials with low environmental load.

Compared with the traditional horizontal twin-roll casting and rolling, the spray deposition combined with the twin-roll thin strip casting and rolling process of the present invention has the following obvious advantages:

(1) The aluminum alloy strip produced has the characteristics of rapid solidification microstructure, almost no macrosegregation, almost no anisotropy, and the aluminum alloy strip has a fine equiaxed grain structure, and the mechanical properties are greatly improved after heat treatment;

(2) The density of the aluminum alloy strip produced is high, and the density of the aluminum alloy strip after spray deposition + twin-roll thin strip casting can easily reach 97% to 99%, and cracking in the subsequent rolling process is avoided. question;

(3) The production efficiency is high, and the casting speed can reach more than 3 times that of the traditional horizontal double-roll casting;

(4) The surface quality is excellent, which can avoid the uneven cooling of the upper and lower surfaces of the traditional horizontal twin-roll casting;

(5) The range of aluminum alloy varieties that can be produced is greatly expanded. The traditional horizontal twin-roll casting and rolling can produce very few aluminum alloy varieties. This process can form a uniform aluminum alloy liquid by spraying and depositing it on the surface of the crystallizing roll first. Fine-grained structure, so some alloys with a wide solidification temperature range can be produced, such as 2XXX, 6XXX, 7XXX and other aluminum alloys.

The aluminum alloy cast strip after water quenching and cooling is cut by the pinch rolls, and then enters the four-roll mill for the first hot rolling. In order to ensure that the aluminum alloy cast belt does not deviate from the deviation and ensure that the production runs smoothly, the pinch roller has the function of correcting deviation and centering.

The aluminum alloy cast strip is air-cooled or water-cooled after the first hot rolling, and then subjected to the second hot rolling, although the method of the present invention is described in the above scheme as a rolling step with two stands to achieve the target thickness, However, those skilled in the art can contemplate other embodiments, such as the use of any suitable number of hot rolling and subsequent cold rolling stands for the rolling steps to achieve the appropriate product target thickness.

The post-treatment process in step 8) includes steps such as solution heat treatment, quenching, aging, and paint baking.

After the coil is formed, the aluminum alloy strip can be subjected to solution heat treatment and quenching. The solution heat treatment temperature is 500-560 °C, and the time: 8-50min; the temperature range of the quenched aluminum alloy strip is from room temperature to 120 °C.

After solution heat treatment and quenching, artificial aging treatment can be carried out again, artificial aging temperature: 90-200 ℃, time: 25-120min. The condition of the artificially aged aluminum alloy product after solution treatment is called the T6 temper, which means that the final product has been solution heat treated, quenched and artificially aged.

The preparation method of the present invention can also choose other process treatments before the post-treatment in step 8), including offline cold rolling, tension straightening, trimming, leveling, surface inspection, plate shape inspection, etc., and then after reaching the final specification, Then solution heat treatment and quenching are carried out.

According to needs, after solution heat treatment and quenching, the aluminum alloy strip can be naturally aged. The natural aging time is generally 25 to 35 days. After solution treatment, the natural aging to a basically stable state is called T4 or T42 state. After natural aging, the coiled aluminum alloy products are shipped to customers for use.

After natural aging, the aluminum alloy strip can also be artificially aged to produce precipitation hardening as needed. Artificial aging temperature: 90-200℃, time: 25-120min. The artificial aging at this time is generally carried out after the aluminum alloy strip is made into automobile parts, and then can be baked (baking hardening), and the baking temperature range: 150-220 ℃, time: 20-50min. According to the need, the additional artificial aging after the paint can also be completed, the additional artificial aging temperature: 90-200 ℃, time: 25-120min.

The form of the twin-roll caster for continuous casting of the present invention may be vertical or horizontal. The crystallizing rolls used in the twin-roll thin strip continuous casting are copper rolls, and the surface of the crystallizing rolls is processed into textures, grooves or embossings, etc. The purpose is to improve the interface heat conduction efficiency, thereby increasing the thin strip continuous casting speed. After the surface morphology of the crystallizing roller is processed, it needs to be electroplated with chromium. The thickness of the chromium-plated layer is controlled at 0.05-0.10mm. The chromium-plated treatment can greatly improve the surface hardness and wear resistance of the crystallizing roller, and prolong the service life of the crystallizing roller.

The aluminum alloy sheet and strip are coiled in a double coiling form, or a Carrousel coiling form, to ensure continuous production of the aluminum alloy sheet and strip. The reel of the coiler has an automatic centering function to ensure a good coil shape when the aluminum alloy strip is coiled, and to ensure that the production runs smoothly.

Difference and improvement between the present invention and prior art:

There is no direct report on the preparation of 6XXX aluminum alloy thin strip by nanoparticle reinforcement, spray deposition and twin-roll strip continuous casting process as described in the present invention.

Chinese patent CN106164308A discloses "an aluminum alloy product and its preparation method", the aluminum alloy has at least 0.8wt% Mn, at least 0.6wt% Fe, and the near surface of the aluminum alloy strip contains small particles with an equivalent diameter <3μm Granules, with a volume fraction of at least 0.2%, the patent does not refer to the twin-roll strip casting process.

Chinese patent CN103119184B discloses "an improved 6xxx aluminum alloy and its production method", the aluminum alloy body can be produced by preparing an aluminum alloy body for post-solution cold working, cold working at least 25% and subsequent heat treatment, which can achieve improvement The strength and performance of the patent does not involve measures such as nanoparticle enhancement treatment.

Chinese patent CN104284745A discloses "an improved 6XXX aluminum alloy and its preparation method", the aluminum alloy body has a "sandwich" structure of two outer regions and an inner region, and the concentration of particles contained in the inner region is greater than that of the outer region , the patent does not involve spray deposition, nano-particle enhancement measures, and the microstructure of the obtained aluminum alloy is not uniform, while the microstructure of the aluminum alloy strip obtained by the present invention is uniform and non-layered.

Chinese patent CN200810098094 discloses "Continuous Casting Process of Aluminum Alloy Thin Strip Billet", and proposes that 5052 aluminum alloy can be produced by vertical twin-roll thin strip continuous casting process. This patent does not involve nano-particle enhancement measures, nor does it involve 6XXX Aluminum alloy.

Beneficial effects of the present invention:

1. In the present invention, hard particles with a size of 5 nm to 10 μm and a melting point higher than that of aluminum are added to the aluminum alloy liquid, so that these high melting point hard particles are evenly dispersed in the aluminum alloy liquid. Grain boundary nano/micro hard particles can effectively limit grain growth and refine grains through pinning; these hard particles can also be used as effective heterogeneous nucleation sites and excellent modifiers to effectively increase aluminum The nucleation during solidification of the alloy liquid optimizes the microstructure and forms a finer equiaxed matrix structure + dispersed hard particles, which play the role of dispersion strengthening and improving the comprehensive mechanical properties of the aluminum alloy.

2. The spray deposition combined with the twin-roll thin strip casting and rolling process is a process that integrates aluminum alloy liquid atomization, spray deposition, and twin-roll casting and rolling into one process, which can economically and efficiently prepare dense and uniform fine-grained structure and excellent comprehensive properties. Its main advantages are short process, low investment, low cost, low energy consumption, and can develop high-performance materials with low environmental load.

3. Compared with the traditional aluminum alloy production process, the present invention has the following advantages:

a) Short process, low investment, low cost and low energy consumption: using a twin-roll thin strip casting and rolling equipment can replace the traditional DC casting machine, heating furnace and hot rolling mill, and the equipment cost is greatly reduced; It is only 1/4 of the traditional process (casting + hot rolling workshop), and its energy consumption is only 50% of the traditional process;

b) The production efficiency is high, the processing time of semi-finished products is greatly shortened, and 5 processes are saved (1, ingot sawing head and tail; 2, homogenization annealing (this is a long process, which takes up to 50h); 3 , milling surface; 4. Heating before hot rolling; 5. Hot rolling), from the aluminum alloy liquid to the hot-rolled coil, the 20 days required by the traditional process can be shortened to 20 minutes;

c) The finished product rate is greatly improved: the consumption of cutting head and tail and milling surface is greatly reduced, so that the finished product rate is increased by more than 20%;

d) The production line is highly flexible: aluminum alloy sheet and strip products can be flexibly produced, and the continuous casting machine of the production line can change alloys at any time without having to stop, enabling seamless transitions between products in the automotive, industrial, home appliances and packaging markets.

4. Compared with the products generated by the traditional aluminum alloy production process, the present invention has obvious advantages in structure and performance:

a) High density and almost no macrosegregation: The microstructure of the produced aluminum alloy strip is small equiaxed grains with rapid solidification characteristics + dispersed hard particles, with high density, avoiding the subsequent rolling process. Cracking problem; almost no macrosegregation, almost no anisotropy, mechanical properties are greatly improved after heat treatment;

b) Good surface quality: Due to the use of spray deposition combined with the twin-roll thin strip casting and rolling process, the pulling speed can be greatly increased to 20-80 m/min compared to the traditional twin-roll casting (drawing speed of only 1-3m/min). , it can avoid the uneven cooling of the upper and lower surfaces of the traditional horizontal twin-roll casting, and the surface quality is greatly improved, which can meet the harsh requirements of the automotive industry;

c) Excellent performance and obvious advantages in light weight: the aluminum alloy sheet and strip produced has a formability of more than 35% and a strength of more than 25% higher than the existing 6XXX aluminum alloy; . The performance of the aluminum alloy strip is close to the performance of the steel plate, especially the formability is high, and it is not easy to crack during forming. The stamping forming can be smoothly formed with a common die for the steel plate, and it can be easily deformed into a complex shape without additionally designing a die.

5. Steel rolls are often used in the production of traditional double-roll cast-rolled aluminum alloys, and the cooling and heat transfer efficiency is low, resulting in a pulling speed of only 1-3m/min and low production efficiency.

The crystallizing roller used in the twin-roll thin strip continuous casting involved in the present invention adopts copper rollers, and the surface of the crystallizing roller is processed into shapes such as texture, groove or embossing, which can greatly improve the interface heat conduction efficiency, thereby increasing the thin strip continuous casting speed; At the same time, it can achieve a width of up to 2200mm, which truly achieves "wide width", which can completely cover the width range required by the car engine cover. After the surface morphology of the crystallizing roller is processed, electroplating chromium treatment can greatly improve the surface hardness and wear resistance of the crystallizing roller, and improve the service life of the crystallizing roller.

Description of drawings

FIG. 1 is a schematic diagram of the process of Embodiment 1 of the present invention (using vertical twin-roll thin strip continuous casting).

FIG. 2 is a schematic diagram of the process of the second embodiment of the present invention (using horizontal twin-roll thin strip continuous casting).

Detailed ways

The present invention will be further described below through examples and accompanying drawings, but this is not a limitation of the present invention. Those skilled in the art can make modifications or improvements according to the basic idea of the invention, but as long as they do not depart from the basic idea of the present invention, all within the scope of the present invention.

Referring to FIG. 1 , in the first embodiment of the present invention, a vertical casting machine is used to prepare high-performance 6XXX aluminum alloy strips.

The smelted aluminum alloy liquid conforming to the chemical composition design of the present invention is introduced from the smelting furnace 1 through the launder 2 into the standing furnace 3 for standing. The aluminum alloy liquid is transported from the static furnace 3 to the front box 4 through the launder 2, and flows into the tundish 7 after degassing 5 and filtration 6. The aluminum alloy liquid in the tundish 7 is added with a size of 5nm to 10μm and a melting point of 5 nm to 10 μm. The hard particles with a higher melting point than aluminum are uniformly dispersed in the aluminum alloy liquid, and the amount of the high melting point hard particles added is 5-20 wt % of the aluminum alloy liquid.

After the aluminum alloy liquid is reinforced with nanoparticles, it flows from the bottom of the tundish 7 through the immersion nozzle 8 into a slit linear nozzle 9. Under the action of the high-energy inert gas 11 (eg N ₂ ), it will flow into the slit linear nozzle. The aluminum alloy liquid of 9 is atomized into fine droplets D and deposited into a roll gap surrounded by two relatively rotating twin-roll thin strip continuous casting crystallizing rolls 10a, 10b and side sealing plates 12a, 12b. The droplets solidify on the rotating circumferential surfaces of the crystallization rolls 10a, 10b, and then form an aluminum alloy cast strip 15 with a thickness of 2-6mm and a width of 1000-2200mm at the smallest gap (nip point) between the two crystallization rolls 10a, 10b. The diameter of the crystallizing rolls 10a and 10b of the present invention is between 400-800 mm, and the inside is cooled by water. Depending on the thickness of the aluminum alloy casting strip 15, the casting speed of the casting machine ranges from 20 to 80 m/min.

The aluminum alloy casting strip 15 comes out of the twin-roll thin strip continuous casting machine and directly enters the closed chamber 14. The closed chamber 14 is connected with an inert gas to protect the aluminum alloy casting strip 15, so as to realize the anti-oxidation protection of the aluminum alloy casting strip 15, and prevent the aluminum alloy casting strip 15 from being oxidized. The atmosphere for oxidation protection can be N ₂ or Ar, or other non-oxidizing gases, such as CO ₂ gas obtained by sublimation of dry ice, etc. The oxygen concentration in the airtight chamber 14 is controlled at <5%, the airtight chamber 14 pairs The anti-oxidation protection of the aluminum alloy cast belt 15 reaches the entrance of the 1# pinch roll 17 . The aluminum alloy cast belt 15 is conveyed by the roller table 20 on the swinging guide plate 13. After being cooled by the water quenching and cooling device 16, it enters the 1# pinch roll 17, and after being cut by the flying shear 18, it enters the four-roller 1# hot rolling mill 19 For hot rolling, the flying shear 18 guides the cut tape head into the scrap hopper 26 through the guide plate 25. Another function of the flying shear 18 is the online slitting between coils, which can ensure continuous production. In order to ensure that the aluminum alloy cast belt 15 does not deviate and ensures that the production runs smoothly, the 1# pinch roller 17 has the function of correcting deviation and centering.

After the aluminum alloy cast strip 15 is hot rolled by the 1# hot rolling mill 19, the aluminum alloy strip running on the conveying roller table 20 enters the air cooling/water cooling device 21 for cooling, and then the aluminum alloy strip enters the four-roller 2# hot rolling The machine 22 is hot rolled again, and after hot rolling, a hot rolled aluminum alloy strip of 0.3-4 mm is formed. After rolling, the aluminum alloy strip enters the 2# pinch roll 23, and then directly enters the coiler 24 for coiling.

The coiler 24 adopts a double coiling form, or a Carrousel coiling form, to ensure continuous production of aluminum alloy strips. The 24 reels of the coiler have an automatic centering function to ensure a good coil shape when the aluminum alloy strip is coiled, and to ensure that the production runs smoothly.

Referring to FIG. 2 , in the second embodiment of the present invention, a horizontal casting machine is used to prepare high-performance 6XXX aluminum alloy strips.

The smelted aluminum alloy liquid conforming to the chemical composition design of the present invention is introduced from the smelting furnace 1 through the launder 2 into the standing furnace 3 for standing. The aluminum alloy liquid is transported from the static furnace 3 to the front box 4 through the launder 2, and flows into the tundish 7 after degassing 5 and filtration 6. The aluminum alloy liquid in the tundish 7 is added with a size of 5nm to 10μm and a melting point of 5 nm to 10 μm. The hard particles with a higher melting point than aluminum are uniformly dispersed in the aluminum alloy liquid, and the amount of the high melting point hard particles added is 5-20 wt % of the aluminum alloy liquid.

After the aluminum alloy liquid is reinforced with nanoparticles, it flows from the bottom of the tundish 7 through the immersion nozzle 8 into a slit linear nozzle 9. Under the action of the high-energy inert gas 11 (eg N ₂ ), it will flow into the slit linear nozzle. The aluminum alloy liquid of 9 is atomized into fine droplets D and deposited into a roll gap surrounded by two relatively rotating twin-roll thin strip continuous casting crystallizing rolls 10a, 10b and side sealing plates 12a, 12b. The droplets solidify on the rotating circumferential surfaces of the crystallization rolls 10a, 10b, and then form an aluminum alloy cast strip 15 with a thickness of 2-6mm and a width of 1000-2200mm at the smallest gap (nip point) between the two crystallization rolls 10a, 10b. The diameter of the crystallizing rolls 10a and 10b of the present invention is between 400-800 mm, and the inside is cooled by water. Depending on the thickness of the aluminum alloy casting strip 15, the casting speed of the casting machine ranges from 20 to 80 m/min.

The aluminum alloy casting strip 15 comes out of the twin-roll thin strip continuous casting machine and directly enters the closed chamber 14. The closed chamber 14 is connected with an inert gas to protect the aluminum alloy casting strip 15, so as to realize the anti-oxidation protection of the aluminum alloy casting strip 15, and prevent the aluminum alloy casting strip 15 from being oxidized. The atmosphere for oxidation protection can be N ₂ or Ar, or other non-oxidizing gases, such as CO ₂ gas obtained by sublimation of dry ice, etc. The oxygen concentration in the airtight chamber 14 is controlled at <5%, the airtight chamber 14 pairs The anti-oxidation protection of the aluminum alloy cast belt 15 reaches the entrance of the 1# pinch roll 17 . The aluminum alloy cast strip 15 directly exits the upper roller table 20 of the crystallization rollers 10a and 10b, after being cooled by the water quenching and cooling device 16, it enters the 1# pinch roller 17, and after being cut by the flying shear 18, it enters the four-roller 1# hot rolling The machine 19 performs hot rolling, and the flying shear 18 guides the cut tape head into the scrap hopper 26 through the guide plate 25. Another function of the flying shear 18 is the online slitting between coils, which can ensure continuous production. In order to ensure that the aluminum alloy cast belt 15 does not deviate and ensures that the production runs smoothly, the 1# pinch roller 17 has the function of correcting deviation and centering.

After the aluminum alloy cast strip 15 is hot rolled by the 1# hot rolling mill 19, the aluminum alloy strip running on the conveying roller table 20 enters the air cooling/water cooling device 21 for cooling, and then the aluminum alloy strip enters the four-roller 2# hot rolling The machine 22 is hot rolled again, and after hot rolling, a hot rolled aluminum alloy strip of 0.3-4 mm is formed. After rolling, the aluminum alloy strip enters the 2# pinch roll 23, and then directly enters the coiler 24 for coiling.

The coiler 24 adopts a double coiling form, or a Carrousel coiling form, to ensure continuous production of aluminum alloy strips. The 24 reels of the coiler have an automatic centering function to ensure a good coil shape when the aluminum alloy strip is coiled, and to ensure that the production runs smoothly.

After being rolled, the aluminum alloy strip can be subjected to a series of post-treatment processes, such as solution heat treatment, quenching, natural/artificial aging, and paint baking. Other process treatments, including offline cold rolling, tension straightening, edge trimming, levelling, surface inspection, plate shape inspection, etc., can be carried out before post-processing, and then a series of post-processing steps can be carried out after reaching the final specification.

The chemical composition of the aluminum alloy sheet and strip of the embodiment of the present invention is shown in Table 1, and the remainder of the composition is Al and other inevitable impurities. The process parameters of the preparation method of the embodiment of the present invention are shown in Table 2, the post-treatment process parameters are shown in Table 3, and the properties of the finally obtained aluminum alloy strip are shown in Table 4.

To sum up, the aluminum alloy sheet and strip manufactured according to the aluminum alloy composition design range and preparation method provided by the present invention can achieve a yield strength of 150-230 MPa and a tensile strength of 230-310 MPa under natural aging conditions (T4 or T42 state). , the elongation is 27-36%, and the forming limit test (tested under the specification of thickness 1.0mm) FLD ₀ is in the range of 27-37%.

The aluminum alloy plate and strip of the invention can achieve a yield strength of 170-250 MPa, a tensile strength of 250-340 MPa, an elongation of 25-34% under artificial aging conditions (T6 state), and a forming limit test (tested under the specification of thickness 1.0 mm). ) FLD ₀ ranged from 24-34%.

The aluminum alloy plate and strip of the present invention can achieve a yield strength of 250-290 MPa, a tensile strength of 330-370 MPa, and an elongation of 22-29% after being painted. Compared with the existing 6XXX aluminum alloy, the formability is more than 35% higher, and the strength is more than 25% higher; compared with the steel plate for automobiles, it can easily achieve more than 50% weight reduction.

The performance of the aluminum alloy strip produced by the method of the invention is close to the performance of the steel plate, especially the formability is high, and it is not easy to crack during forming. Additional design molds.

The aluminum alloy sheet and strip produced by the method of the invention can be widely used in automobile application fields, such as automobile engine covers, fenders, doors, vehicle roofs and trunk lids, etc. There is a lot of room for improving fuel economy.

Table 1 Unit: Weight Percent

Claims (16)

1. A preparation method of a spray casting and rolling high-performance 6XXX aluminum alloy thin strip is characterized by comprising the following steps:

1) smelting

Smelting according to the following chemical components in percentage by weight: si: 0.5-1.5%, Mg: 0.1-2.0%, Fe: 0.1-1.0%, Mn: 0.05-0.5%, Cu: 0.02-0.2%, and the balance of Al and other unavoidable impurities; moreover, the content of single impurity is less than or equal to 0.05 percent, and the content of total impurities is less than or equal to 0.15 percent;

2) nanoparticle reinforcement

Introducing the smelted aluminum alloy liquid into a standing furnace for standing, then conveying the aluminum alloy liquid to a front box through a runner, degassing, filtering, flowing into a tundish, and adding hard particles with the size of 5 nm-10 mu m and the melting point higher than the melting point of aluminum into the aluminum alloy liquid in the tundish, wherein the addition amount of the hard particles is 5-20 wt% of the aluminum alloy liquid; wherein the temperature of the aluminum alloy liquid introduced into the standing furnace is 780-850 ℃, and the temperature of the aluminum alloy liquid in the tundish is 730-800 ℃; the hard particles are TiC, TiN, WC, SiC and B ₄ C、Si ₃ N ₄ One or more of BN;

3) spray deposition, continuous casting

Atomizing the aluminum alloy liquid flowing out of the tundish into fine molten drops by adopting inert gas, depositing the molten drops on the surface of a double roller, and continuously casting a double-roller thin strip to obtain an aluminum alloy casting strip with the thickness of 2-6mm and the width of 1000-2200 mm; the pressure of inert gas is 0.8-2.0MPa, the temperature of the aluminum alloy cast strip is 550-600 ℃, the diameter of a crystallization roller is 400-800mm, water is introduced into the crystallization roller for cooling, and the casting speed of the casting machine is 20-80 m/min;

4) cooling down

The aluminum alloy casting strip is cooled to 410-510 ℃ through water quenching after coming out of the casting machine;

5) first hot rolling

Sending the cooled aluminum alloy cast strip to a rolling mill after pinch roll and crop treatment, and carrying out first hot rolling, wherein the temperature of the first hot rolling is 380-480 ℃, and the reduction rate of the first hot rolling is less than or equal to 50%;

6) cooling and second hot rolling

Air cooling or water cooling is carried out on the aluminum alloy plate strip subjected to the first hot rolling, then the second hot rolling is carried out, the temperature of the second hot rolling is 280-420 ℃, and the reduction rate of the second hot rolling is less than or equal to 60%; the thickness of the aluminum alloy plate strip after the second hot rolling is 0.3-4 mm;

7) coiling

Conveying the aluminum alloy plate strip subjected to the second hot rolling to a coiling machine through a pinch roll for coiling, wherein the coiling temperature is 200-370 ℃;

8) post-treatment

After the aluminum alloy plate strip is coiled, carrying out solid solution heat treatment and quenching in sequence; the microstructure of the obtained aluminum alloy plate strip is fine isometric crystal matrix structure and hard particles which are dispersed and distributed.

2. The method for producing a thin strip of high performance 6XXX aluminum alloy as claimed in claim 1, wherein in step 6), the thickness of the aluminum alloy strip after the second hot rolling is 0.5-3 mm.

3. The method of making thin strip of high performance 6XXX aluminum alloy as claimed in claim 1 wherein in step 3), the inert gas is one or both of nitrogen and argon.

4. The method of making thin strip of high performance 6XXX aluminum alloy as claimed in claim 1 wherein in step 3) the droplets are in a solid, semi-solid or liquid state.

5. The method of making a thin strip of high performance 6XXX aluminum alloy as specified in claim 1 wherein the quenching of step 8) is followed by aging and paint baking steps in that order.

6. The method for preparing the thin strip of the high-performance 6XXX aluminum alloy according to claim 5, wherein the aging is artificial aging or natural aging + artificial aging, wherein the artificial aging temperature is 90-200 ℃, the time is 25-120min, and the natural aging time is 25-35 days.

7. The method for producing the thin strip of high performance 6XXX aluminum alloy as claimed in claim 5, wherein the baking temperature is 150-220 ℃ and the baking time is 20-50 min.

8. The method of manufacturing the thin strip of high performance 6XXX aluminum alloy as claimed in claim 5 or 7, wherein the additional artificial aging is performed after the paint baking, and the additional artificial aging is performed at a temperature of 90-200 ℃ for 25-120 min.

9. The method of producing the strip of high performance 6XXX aluminum alloy as claimed in claim 1, wherein in step 8), the solution heat treatment is carried out at a temperature of 500 to 560 ℃ for a period of 8 to 50 min.

10. The method of making a thin strip of high performance 6XXX aluminum alloy as claimed in claim 1 wherein in step 8) the temperature of the quenched aluminum alloy strip is from room temperature to 120 ℃.

11. The method of making a jet cast-rolled high performance 6XXX aluminum alloy ribbon as claimed in claim 1, wherein prior to the post-treatment step of step 8), the aluminum alloy strip may be subjected to one or more of off-line cold rolling, tension straightening, edge trimming, flattening, surface inspection, and strip shape inspection.

12. The method of making thin strip of high performance 6XXX aluminum alloy as specified in claim 1 wherein in step 3) the spray deposition atomizing nozzle is a slot type linear nozzle.

13. The method of making thin strip of high performance 6XXX aluminum alloy as claimed in claim 1 wherein in step 3) the continuous casting is performed using a vertical caster or a horizontal caster.

14. The method of making a thin strip of high performance 6XXX aluminum alloy as specified in claim 1 wherein the crystallizing roller is a copper roller and the surface of the crystallizing roller is textured, grooved or embossed during step 3).

15. The method for preparing the high-performance 6XXX aluminum alloy thin strip by spray casting as claimed in claim 1 or 14, wherein the surface of the crystallization roller is electro-chromized, and the thickness of the electro-chromized layer is 0.05-0.10 mm.

16. The method for preparing the spray casting-rolling 6XXX aluminum alloy thin strip as claimed in claim 1, wherein the aluminum alloy strip can achieve 150-230MPa yield strength, 230-310MPa tensile strength and 27-36% elongation under natural aging condition, i.e. T4 or T42 state, the forming limit test is performed under the specification of 1.0mm thickness, FLD ₀ In the range of 27-37%;

the aluminum alloy plate strip can realize yield strength of 170-250MPa, tensile strength of 250-340MPa and elongation of 25-34% under the artificial aging condition, namely T6 state, and the forming limit test is carried out under the specification of thickness of 1.0mm, and FLD (flash deformation resistance) ₀ In the range of 24-34%;

after the aluminum alloy plate strip is subjected to paint baking, the yield strength is 250-290MPa, the tensile strength is 330-370MPa, and the elongation is 22-29%.

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