A high-strength aluminum alloy and a method for manufacturing the same

Abstract

The present application relates to a kind of high-strength aluminum alloy and its preparation method, the mass percentage of each alloying element in aluminum alloy is as follows:Si 0.75~0.83%, Mg 0.98~1.05%, Cu 0.44~0.55%, Mn 0.60~0.66%, Cr 0.04~0.25%, Fe≤0.165, Ti≤0.15%, Zn≤0.30%, V≤0.015%, Zr≤0.02%, the balance is Al and unavoidable impurities, the content of each impurity element is not more than 0.05%, and the total amount of impurities is not more than 0.15%.The preparation method includes alloy smelting, bar casting, homogenization heat treatment, extrusion forming, aging treatment steps.The obtained aluminum alloy has yield strength ≥350MPa, tensile strength ≥390MPa, elongation ≥10%, and is particularly suitable for automobile crash beam, and the lightweight weight reduction effect can reach more than 20%.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aluminum alloy and its manufacturing technology, in particular to a high-strength aluminum alloy suitable for the lightweighting technical requirements of automobile crash beams and a preparation method thereof. BACKGROUND

[0002] With the progress of society and the rapid development of technology, the use of aluminum alloys in production and life is becoming more and more extensive, and higher and higher requirements are put forward for the performance of aluminum alloys, which leads to the fact that existing aluminum alloys cannot meet the new demands.

[0003] Taking the automobile industry as an example, the automobile industry transformation and upgrading gradually develops in the direction of new energy, lightweight, intelligence and networking. In particular, in recent years, China's new energy vehicle has developed rapidly, and the production and sales have increased rapidly. Because aluminum alloy has many excellent properties, it has become a representative material for realizing lightweight of automobiles, especially new energy vehicles, and the application of lightweight aluminum alloy structural parts plays an increasingly important role in improving the performance and competitiveness of automobile products.

[0004] In recent years, with the gradual acceleration of automobile lightweighting process, the amount of aluminum used on domestic vehicle structural parts and cover parts has begun to increase. According to preliminary statistics, in 2019, the average amount of aluminum used per vehicle in China's passenger cars was 140 kilograms, which has increased year by year compared with some years ago; among them, the proportion of aluminum castings is about 85%, and the proportion of aluminum sheet, aluminum foil, aluminum extruded material and aluminum forgings and other processed materials is about 15%, especially in the aspect of automobile lightweighting, a few electric vehicles have made great progress, and the aluminum rate of the vehicle body has reached more than 92%.

[0005] However, after the vehicle body aluminum rate approaches or even reaches the limit, how to continue to realize automobile lightweighting has become a problem that needs to be solved. At the same time, in the past two years, the automobile industry has been under great price pressure, which requires reducing costs as much as possible under the premise of lightweighting, but the performance requirements of the vehicle on safety and other performances must be met. Therefore, how to develop new aluminum alloys to meet the design requirements of automobile lightweighting and market price pressure has become an important task of the aluminum alloy industry.

[0006] For example, the existing technology usually uses 6000 series aluminum alloy for the automobile anti-collision beam, but the yield strength is generally below 320 MPa, and the tensile strength is generally below 350 MPa. For example, a kind of aluminum alloy coil suitable for new energy vehicle chassis light weight technology and its preparation method (202011642400.4) claims that the new type of aluminum alloy prepared by the application has higher tensile strength and elongation than 6061 and 6082 aluminum alloy, the tensile strength of the aluminum alloy product reaches 320-360 MPa, the yield strength reaches 260-320 MPa, and the elongation at break is 10-19%. A kind of 6 series aluminum alloy plate and its manufacturing method (202111215879.8) claims that the 6 series aluminum alloy plate has very excellent strength, the yield strength is greater than or equal to 300 MPa, the tensile strength is greater than or equal to 330 MPa, and the elongation is greater than or equal to 12.5%. However, according to the data in the examples, the yield strength of the aluminum alloy described in the patent is below 320 MPa, and the tensile strength is below 350 MPa.

[0007] However, under the trend of lightweight in the automobile industry, the aluminum alloy with the above strength indicators still cannot meet the needs of the automobile industry. Therefore, how to develop a high-performance aluminum alloy that can meet the future lightweight requirements of the automobile industry while meeting the requirements of the 6000 series composition has become an urgent task. SUMMARY

[0008] The first technical problem to be solved by the present application is to provide a high-strength 6 series aluminum alloy to meet market demand in view of the current status of the prior art.

[0009] The second technical problem to be solved by the present application is to provide a preparation method of the above-mentioned aluminum alloy in view of the current status of the prior art.

[0010] The technical solution adopted by the present application to solve the above-mentioned first technical problem is: the high-strength aluminum alloy, characterized in that the mass percentage of each alloying element in the aluminum alloy is: Si 0.75-0.80%, Mg 0.98-1.05%, Cu 0.45-0.55%, Mn 0.60-0.65%, Cr 0.04-0.25%, Fe≤0.15, Ti≤0.15%, Zn≤0.30%, V≤0.015%, Zr≤0.02%, the balance being Al and unavoidable impurities, the content of each impurity element being not more than 0.05%, and the total amount of impurities being not more than 0.15%.

[0011] The percentage content ratio of Si and Mg in the aluminum alloy is in the range of 0.76-0.8.

[0012] The yield strength of the aluminum alloy is greater than or equal to 350 MPa, the tensile strength is greater than or equal to 390 MPa, and the elongation is greater than or equal to 10%.

[0013] The technical scheme adopted by the present application to solve the second technical problem is: the preparation method of the high-strength aluminum alloy, characterized in that it comprises the following steps:

[0014] Alloy smelting: the required elements or element alloys are batched into a smelting furnace for melting, and after complete melting, refining and degassing are performed to obtain an aluminum alloy melt;

[0015] Bar casting: the obtained aluminum alloy melt is used to prepare an aluminum alloy cast bar of the target composition by using a gas slide casting method, and the casting temperature is 710-730℃;

[0016] Homogenization heat treatment: the obtained aluminum alloy cast bar is subjected to homogenization heat treatment;

[0017] Extrusion forming: the obtained bar after homogenization treatment is subjected to extrusion processing, and the extrusion process temperature is 500-540℃;

[0018] Aging treatment: the extruded profile is subjected to aging treatment, the aging temperature is 170-180℃, and the aging time is 6.0-10.0h.

[0019] The homogenization heat treatment is preferably heating to 560-570℃ for 8-12h, and then air cooling.

[0020] The preferred conditions of the extrusion forming are: the extrusion ratio is 25-45, the rod speed is 2-3mm / s, water cooling or water mist cooling is used, and the quenching temperature is 20-30℃.

[0021] The aging treatment is preferably performed within 2 hours after the extrusion forming.

[0022] Based on cost considerations, the present inventors hope to develop an aluminum alloy with a yield strength ≥350MPa, a tensile strength ≥390MPa, and an elongation ≥10% based on the existing 6110 aluminum alloy during the research and development process. However, after optimizing various process parameters, the yield strength and elongation can basically meet the requirements, but the tensile strength can only reach about 370MPa, and the expected target aluminum alloy cannot be produced.

[0023] Based on this, the inventor team optimizes the alloy composition, and through a large number of experiments, the inventor team optimizes the production process of the aluminum alloy with the new designed alloy composition. Mainly by designing high components of Si and Mg, more strengthening phases Mg2Si and beta '' and the like are formed, the solid solubility of the alloy is improved in the quenching process of homogenization and extrusion, and more strengthening phases are formed in the process of natural aging and artificial aging, so that the tensile strength and yield strength of the alloy are improved; meanwhile, a certain amount of Cu element is added, which can combine with a certain amount of Mg to form Al2CuMg phase, further improving the strengthening effect of the profile; the addition of high content of Mn and Cr makes the alloy difficult to recrystallize in the extrusion process, further improving the strength and toughness of the material, and forming a fiber crystal organization with small size.

[0024] The first step is to produce the ingot by adopting gas slide casting in the casting process to ensure the quality of the ingot. The gas slide casting is the most advanced casting process in the aluminum processing industry at present, which adopts inert gas argon for one-time cooling to solve the one-time chilling organization ISZ of the hot top casting process in which the molten aluminum directly contacts with the crystallizer, and the grain size in the ingot is controlled at about 80 microns, so that the second phase is evenly distributed between the grains and the grain boundaries.

[0025] The second step is to adopt a high-temperature homogenization process in the homogenization heat treatment process. The conventional homogenization heat treatment is generally 550 DEG C for 6-8 hours, while the present application is increased to about 560 DEG C for 8-12 hours, and then strong air cooling is adopted to ensure that the second phase is evenly dissolved into the aluminum alloy matrix, and is dispersedly distributed and precipitated in the later extrusion process, which is more beneficial to strengthening effect.

[0026] The third step is to heat the extrusion process temperature to 500-540 DEG C, and then extrude to achieve better extrusion flow plasticity. A liquid nitrogen cooling device is arranged on the working belt of the die to protect the working belt area of the die and form coarse grains on the surface of the profile. The homogenization is carried out by using a gas heating furnace, and the homogenization is carried out by heating to about 565 DEG C for about 10 hours for air cooling to realize the effect of homogenization. After extrusion, the profile is quenched by water mist cooling or water cooling to ensure the cooling rate of the profile. At the same time, different aging temperature and aging time combinations are carried out.

[0027] Compared with the prior art, the aluminum alloy has the advantages that the yield strength is greater than or equal to 350 MPa, the tensile strength is greater than or equal to 390 MPa, the elongation is greater than or equal to 10%, and the bending angle can be kept above 60°. For the aluminum alloy with such strength, the bending angle is generally 30-35°, while the aluminum alloy can reach above 60°. Therefore, the aluminum alloy has better lightweight characteristics, stronger rigidity and toughness, can ensure that the whole vehicle collision, head-on collision and offset collision reach a better level, and can be applied to higher requirement SUV new energy vehicles as a crash beam, while keeping good lightweight effect, and the lightweight weight reduction effect can reach more than 20%. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a 6110-S1 cross-section coarse grain layer structure photo (500X);

[0029] Figure 2 is a 6110-S1 longitudinal cross-section coarse grain layer structure photo (500X);

[0030] Figure 3 is a 6110-S2 cross-section coarse grain layer structure photo (200X);

[0031] Figure 4 is a 6110-S2 longitudinal cross-section coarse grain layer structure photo (200X);

[0032] Figure 5 is a 6110-S2 cross-section coarse grain layer structure photo (500X);

[0033] Figure 6 is a 6110-S2 longitudinal cross-section coarse grain layer structure photo (500X);

[0034] Figure 7 is a 6110-S3 cross-section coarse grain layer structure photo (200X);

[0035] Figure 8 is a 6110-S3 longitudinal cross-section coarse grain layer structure photo (200X);

[0036] Figure 9 is a 6110-S3 cross-section coarse grain layer structure photo (500X);

[0037] Figure 10 is a 6110-S3 longitudinal cross-section coarse grain layer structure photo (500X);

[0038] Figure 11 is a 6110-S1 cross-section grain size measurement photo (500X);

[0039] Figure 12Figure 61 10-S1 cross section grain size measurement photo (500X);

[0040] Figure 13 Figure 61 10-S1 cross section grain size measurement photo (500X);

[0041] Figure 14 Figure 61 10-S1 longitudinal section grain size measurement photo (500X);

[0042] Figure 15 Figure 61 10-S1 longitudinal section grain size measurement photo (500X);

[0043] Figure 16 Figure 61 10-S1 longitudinal section grain size measurement photo (500X);

[0044] Figure 17 Figure 61 10-S2 cross section grain size measurement photo (200X);

[0045] Figure 18 Figure 61 10-S2 longitudinal section grain size measurement photo (200X);

[0046] Figure 19 Figure 61 10-S2 cross section grain size measurement photo (500X);

[0047] Figure 20 Figure 61 10-S2 longitudinal section grain size measurement photo (500X);

[0048] Figure 21 Figure 61 10-S3 cross section grain size measurement photo (200X);

[0049] Figure 22 Figure 61 10-S3 longitudinal section grain size measurement photo (200X);

[0050] Figure 23 Figure 61 10-S3 cross section grain size measurement photo (500X);

[0051] Figure 24 Figure 61 10-S3 longitudinal section grain size measurement photo (500X). DETAILED DESCRIPTION

[0052] The application will be further described with reference to the drawings, in which:

[0053] I. First Series of Trial Production Experiments

[0054] During the research and development of the present application, the inventors' team first carried out the following optimization research on the existing 6110 aluminum alloy in order to achieve the purpose of the alloy yield strength ≥ 350 MPa, tensile strength ≥ 390 MPa, and elongation ≥ 10%:

[0055] The composition of the experimental 6110-S1 aluminum alloy is: Si 0.912%, Mg 0.833%, Cu 0.157%, Mn 0.238%, Cr 0.159%, Fe 0.184%, Ti 0.0336%, Zn 0.0213%, V 0.0126%, Zr 0.002%, the balance being Al and unavoidable impurities, each impurity element content being not more than 0.05%, and the total amount of impurities being not more than 0.15%.

[0056] The manufacturing process parameters used, in addition to the aging process parameters in Table 1, are as follows:

[0057] Alloy melting: each required element or alloy of elements is batched into a melting furnace for melting, and after complete melting, refining and degassing are carried out to obtain an aluminum alloy melt;

[0058] Bar casting: the obtained aluminum alloy melt is used to prepare an aluminum alloy cast bar of the target composition by air slide casting method, and the casting temperature is 710-730℃;

[0059] Homogenization heat treatment: 565℃ for 8h, and then air cooling;

[0060] Extrusion forming: the obtained bar after homogenization treatment is subjected to extrusion processing, the extrusion process temperature is 500℃, the extrusion ratio is 26.65, the rod speed is 2.5-3.0mm / s, and water quenching is carried out, and the quenching temperature is 30℃.

[0061] Table 1, 6110 aluminum alloy aging process and the properties of the obtained aluminum alloy

[0062]

[0063] From the above table data, it can be seen that:

[0064] a: the experimental values in Table 1 ①-⑧ are average values.

[0065] b: the tensile strength of ①-⑧ schemes does not meet the requirement of ≥ 390, the bending angle is close to 60°, and individual products meet the requirement of ≥ 60°.

[0066] c: ⑤-⑧ are used to verify the effect of parking time on the mechanics and bending, and the average values have little effect.

[0067] d: the two production processes have no obvious effect on the mechanical properties and bending.

[0068] e: The mechanical properties of the alloy with aging system of 165℃*12h are slightly better than those of 175℃*8h, the bending difference is not large, the bending performance of 205℃ overaging is good, but the mechanical performance is poor.

[0069] Note: The test method of the bending angle in the application adopts standard VDA238-100-2017.

[0070] II. Second series of trial experiments:

[0071] After many experiments, it was found that the above component alloy could not realize yield strength ≥ 350 MPa, tensile strength ≥ 390 MPa, and elongation ≥ 10% even after adjusting the production process parameters, so the inventors adjusted the alloy components as follows:

[0072] The 6110-S2 aluminum alloy component is: Si 0.984%, Mg 0.825%, Cu 0.254%, Mn 0.327%, Cr 0.168%, Fe 0.153%, Ti 0.0314%, Zn 0.0081%, V 0.0139%, Zr 0.0012%, the balance is Al and unavoidable impurities, each impurity element content is not more than 0.05%, and the total amount of impurities is not more than 0.15%.

[0073] The trial process is the same as that of the first series of trial experiments, and the aging process is 175℃*8h and 165℃*12h respectively.

[0074] Test results Table 2

[0075] No. Aging Tensile strength MPa Yield strength MPa Elongation % Bending angle (°) 1 175℃*8h 387 361 12 45 2 165℃*12h 384 355 14.5 49

[0076] Test results show that:

[0077] a: The newly developed alloy, the experimental data shows that the tensile strength is improved compared to before, the tensile strength is close to 390 MPa, the yield strength is qualified, the bending is still unqualified, and the bending is lower than the first series.

[0078] b: Two aging systems 175℃*8h and 165℃*12h have little effect on performance.

[0079] c: The two aging processes have no obvious effect on the mechanical properties and bending.

[0080] III. Third series of trial experiments:

[0081] I) Component adjustment

[0082] The inventors adjusted the alloy components as follows:

[0083] The composition of the experimental 6110-S3 aluminum alloy is: Si 0.779%, Mg 1.01%, Cu 0.481%, Mn 0.637%, Cr 0.141%, Fe 0.134%, Ti 0.0319%, Zn 0.0068%, V 0.0133%, Zr 0.00069%, and the balance is Al and inevitable impurities, each impurity element content is not more than 0.05%, and the total amount of impurities is not more than 0.15%.

[0084] The manufacturing process parameters used are as follows, except for the aging process parameters in Table 3:

[0085] Alloy smelting: each required element or alloy of elements is batched into a smelting furnace for melting, and after complete melting, refining and degassing are performed to obtain an aluminum alloy melt;

[0086] Bar casting: the obtained aluminum alloy melt is used to prepare an aluminum alloy cast bar with the target composition by using a gas slide casting method, and the casting temperature is 710°C;

[0087] Homogenization heat treatment: 565°C for 8h, and then air cooling;

[0088] Extrusion forming: the obtained bar after homogenization treatment is subjected to extrusion processing, the extrusion process temperature is 500°C, the extrusion ratio is 26.65, the rod speed is 3.0mm / s, and water quenching is performed, and the quenching temperature is 30°C.

[0089] Aging treatment: the extruded profile is subjected to aging treatment, the aging temperature is 175°C, and the aging time is 4-16h.

[0090] Table 3, aging process of the aluminum alloy of the present application and properties of the obtained aluminum alloy

[0091]

[0092]

[0093] From the data in Table 2, it can be seen that the aluminum alloy using the composition and process of the present application has significantly improved comprehensive performance, and when the 175*8h aging process is used, the properties of the alloy fully meet the expected requirements.

[0094] II) Aging research

[0095] On the basis of the above results, the inventors' team has also made a large amount of experimental research on the optimization of alloy composition and other process parameters.

[0096] Using the above 6110-S3 alloy composition, a comparative study was made on aging immediately after extrusion forming (within 2 hours after extrusion forming) and aging after being placed for 5 days, and the results are shown in Table 4.

[0097] Table 4

[0098]

[0099] The above experiments show that:

[0100] 1. The natural aging time is very short, within 2h, the material does not obtain the energy to form GP zone, directly artificial rapid aging, forming Mg2Si and Al2CuMg phase, the bending angle basically meets the requirement of 60°, the yield strength at 175℃8H meets the requirement, and the yield strength at 165℃ is lower, indicating that the effect of aging temperature on yield strength is large, and higher aging temperature can obtain higher yield strength, which is consistent with the principle of 6000 aging precipitation; the bending angle of the data of the two processes is close, indicating that the alloy has high aging bending performance, and the effect of aging system is small;

[0101] 2. The mechanical property data of natural aging for 5 days decreases, and the bending angle increases, indicating that the effect of the intermediate natural aging storage time on 6110-S3 alloy is large.

[0102] III) Extrusion process research

[0103] Using the above 6110-S3 alloy composition, the extrusion temperature in the extrusion process is compared and studied, and the results are shown in Table 5.

[0104] The aging process is immediate aging, the temperature is 175℃, and the aging time is 8h. Other processes are as above "I) Composition adjustment"

[0105] Table 5

[0106]

[0107]

[0108] The bar temperature is increased to 520℃, the extruded product, the tensile strength and yield strength are qualified, and the bending angle is close to 60°, indicating that increasing the heating temperature of extrusion, combined with the aging process of 175℃8H, can obtain higher strength, indicating that increasing the solid solution saturation of Mg2Si and Al2CuMg phase is beneficial to improve the strength and bending performance of the material, and the elongation;

[0109] Mechanism: The coarse second phase is completely dissolved into the aluminum alloy matrix during the heating process and the extrusion quenching process, and during the later aging process, fine Mg2Si and Al2CuMg phases are formed, which can make the comprehensive performance of the material meet the requirements.

[0110] The extrusion temperature is increased to 535℃, and the mechanical properties are greatly improved, the performance index reaches 400Mpa-410Mpa, the average yield strength is above 370Mpa, and the average bending angle is above 65°.

[0111] IV) Comparative analysis of microstructure of the alloys

[0112] Based on the above tests, comparative analysis of the microstructure of the three alloys 6110-S1, 6110-S2 and 6110-S3 was made.

[0113] Referring to Figure 1 to Figure 14 , it was found that with the increase of Mn content from 0.236 of 6110-S1 to 0.637 of 6110-S3, the longitudinal section grain structure of the alloy mainly presented long strip fibrous crystal structure, and fine recrystallized mixed structure was formed at the grain boundary; this was beneficial to improve the elongation and bending performance of the material, which was basically consistent with the measured mechanical property data;

[0114] In the case of similar other trace elements, the increase of Si / Mg ratio was beneficial to refine the grain structure, and it was found that the grain size of 6110-S2 was about 15 um, while that of 6110-S1 was about 25 um; fine grain structure was beneficial to improve the strength and elongation of the material, which was basically consistent with the measured data;

[0115] The Si / Mg ratio of 6110-S2 alloy and 6110-S3 alloy was reduced from 1.2 to 0.77, but the Cu and Mn content was increased, and the grain structure showed that the two were basically similar; it was indicated that the effect of Mn content on grain structure refinement and inhibition of recrystallization was offset by the grain growth effect caused by the decrease of Si / Mg ratio.

[0116] III) Third series of trial production experiments

[0117] Alloy melting: the required elements or element alloys were batched into a melting furnace for melting, and after complete melting, refining and degassing were carried out to obtain an aluminum alloy melt;

[0118] Bar casting: the obtained aluminum alloy melt was used to prepare an aluminum alloy cast bar of the target composition by air slide casting method, and the casting temperature was 710-730℃;

[0119] Homogenization heat treatment: 565℃ for 8-12h, and then air cooling;

[0120] Extrusion forming: the obtained bar after homogenization treatment was subjected to extrusion processing, and the extrusion process temperature was 535℃, the extrusion ratio was 26.65, the rod speed was 2.5-3.0mm / s, and water quenching was carried out, and the quenching temperature was 20-30℃.

[0121] Table 6 of alloy composition

[0122]

[0123]

[0124] Table 7, Alloy performance parameters in Table 6

[0125] Example Tensile strength MPa Yield strength MPa Elongation % Bending angle (°) 1 412 378 14 67 2 404 371 13.5 64 3 413 373 14.5 63 4 412 378 14 67 5 410 377 13.5 70 6 404 367 15 64 7 407 372 14 62 8 406 368 13.5 67 9 406 364 14 61 10 413 378 14.5 62 Comparative Example 1 371 354 13 54 Comparative Example 2 387 361 12 45

Claims

1. A high strength aluminum alloy characterized by The mass percentage of each alloying element in the aluminum alloy is: Si 0.75-0.83%, Mg 0.98-1.05%, Cu 0.44-0.55%, Mn 0.628-0.66%, Cr 0.04-0.25%, Fe ≤0.165, Ti ≤0.15%, Zn ≤0.30%, V ≤0.015%, Zr ≤0.02%, the balance being Al and unavoidable impurities, the content of each impurity element being not more than 0.05%, and the total amount of impurities being not more than 0.15%. The yield strength of the aluminum alloy is ≥350 MPa, the tensile strength is ≥390 MPa, the elongation is ≥10%, and the bending angle is ≥60°.

2. The high strength aluminum alloy of claim 1, wherein The mass percentage ratio of Si to Mg in the aluminum alloy is in the range of 0.73-0.

83.

3. A method of producing the high-strength aluminum alloy according to claim 1, characterized by, The method comprises the following steps: Alloy smelting: each required element or alloy of elements is batched into a smelting furnace for melting, and after complete melting, refining and degassing are performed to obtain an aluminum alloy melt; Bar casting: the obtained aluminum alloy melt is used to prepare an aluminum alloy cast bar of the target composition by using a gas slide casting method, and the casting temperature is 710-730℃; Homogenization heat treatment: the obtained aluminum alloy cast bar is subjected to homogenization heat treatment; Extrusion forming: the obtained bar after homogenization treatment is subjected to extrusion processing, and the extrusion process temperature is 500-540℃; Aging treatment: the extruded profile is subjected to aging treatment, the aging temperature is 170-180℃, and the aging time is 6.0-10.0h.

4. The method of claim 3, wherein: The homogenization heat treatment is specifically heating to 560-570℃ for 8-12h, and then air cooling. The extrusion ratio of the extrusion forming is 25-45, the rod speed is 2-3mm / s, water cooling or water mist cooling is used, and the quenching temperature is 20-30℃.

5. The method of claim 4, wherein: The aging treatment is performed within 2 hours after the extrusion forming.

6. The method of claim 4, wherein: ​

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