CN112195376A - 6xxx series aluminum alloy plate for high-strength automobile body and preparation method thereof - Google Patents

Abstract

The invention discloses a 6xxx series aluminum alloy plate for a high-strength automobile body and a preparation method thereof, wherein the plate comprises the following components in percentage by mass: si: 0.4 wt.% to 1.2 wt.%; mg: 0.3 wt.% to 0.8 wt.%; zn: 0.3 wt.% or less; cu: 0.05 wt.% to 0.25 wt.%; mn: 0.05 wt.% to 0.2 wt.%; fe: 0.3 wt.% or less; ti: 0.01-0.03 wt.%, the balance being Al and impurities less than 0.05 wt.%. The aluminum alloy prepared by the invention has excellent mechanical property and surface quality, particularly high baking hardening property, and is particularly suitable for the outer plate of the automobile body covering part.

Description

6xxx series aluminum alloy plate for high-strength automobile body and preparation method thereof

Technical Field

The invention relates to the field of aluminum alloy materials, in particular to a 6xxx series aluminum alloy plate for a high-strength automobile body and a preparation method thereof.

Background

The light weight of the automobile is not only an economical effective means for realizing energy conservation and emission reduction, but also is beneficial to improving the safety performance and the driving performance. As a good lightweight material, aluminum alloy sheets are increasingly used in automobiles.

The 6xxx series aluminum alloy for the outer plate of the automobile body is required to have high baking hardening performance in addition to good surface quality (no paint brush line defect), flanging performance and mechanical property. This is because the high bake hardenability can ensure that the material rapidly rises from a low yield strength to a high yield strength as supplied during the paint bake process to ensure sufficient dent resistance. Meanwhile, one of the difficulties faced in the popularization and application of the aluminum alloy automobile plate at present is that the cost of parts prepared from the aluminum alloy plate is far higher than that of the traditional steel. Under the condition of ensuring the forming and rigidity requirements of parts, the improvement of the strength of the 6xxx series aluminum alloy can reduce the usage amount of aluminum materials and reduce the cost of the parts. However, while the bake hardenability of the sheet material is improved, it is necessary to ensure that the initial yield strength of the sheet material is not too high, and if it is too high, the press formability of the sheet material is affected.

In recent years, a lot of work has been done around 6xxx body panels in some domestic colleges and scientific institutions. For example, in terms of how to improve the bake hardenability of the alloy, patents CN201010199924.0, CN201410283404.6, CN201410064892.1, etc. achieve a high bake hardening effect by adding alloy elements of Cu, Zn, etc. to a conventional 6xxx series aluminum alloy; the patents CN200810194841.5, CN200710190078.4 and CN201711217322.1 improve the bake hardening performance of the plate by controlling the preheating treatment process after the plate is subjected to solution and water quenching, but the effect is not obvious; in the CN201480008337.5 patent, a method is proposed to increase the strength before baking varnish and the BH response synchronously by controlling the ratio of the total number of atoms of Mg and Si in the measured atomic cluster to the total number of solute atoms in the matrix to 10% -30%. The method comprises the steps of firstly carrying out first-stage reheating treatment at 100-250 ℃ for about 2 minutes after solution quenching, and then carrying out second-stage heating at 70-130 ℃ for several hours.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a high-strength 6xxx series aluminum alloy plate for an automobile body and a preparation method thereof.

The invention is realized by the following technical scheme.

A high-strength 6 xxx-series aluminum alloy sheet for an automobile body, wherein the sheet comprises the following components in percentage by mass: si: 0.4 wt.% to 1.2 wt.%; mg: 0.3 wt.% to 0.8 wt.%; zn: 0.3 wt.% or less; cu: 0.05 wt.% to 0.25 wt.%; mn: 0.05 wt.% to 0.2 wt.%; fe: 0.3 wt.% or less; ti: 0.01-0.03 wt.%, the balance being Al and impurities less than 0.05 wt.%.

The preparation method of the aluminum alloy plate is characterized by comprising the following steps: casting, homogenizing, hot rolling, cold rolling, intermediate annealing, solid solution, straightening, primary pre-aging and secondary pre-aging.

Further, the preparation method of the aluminum alloy plate comprises the following steps:

(1) mixing the components of the plate according to the proportion, melting and refining, and casting the mixture into a cast ingot by adopting semi-continuous casting equipment;

(2) homogenizing the cast ingot: controlling the heating temperature to be 540-570 ℃ and the heat preservation time to be 4-12 h;

(3) carrying out hot rolling on the ingot obtained in the step (2): controlling the initial rolling temperature to be 500-520 ℃, and carrying out hot rolling to be 5-8 mm, wherein the final rolling temperature is less than or equal to 270 ℃; then, multi-pass cold rolling is carried out, intermediate annealing is carried out, then, cold rolling is continuously carried out to 0.8 mm-2 mm, and the cold rolling reduction is ensured to be 40% -80%;

(4) carrying out solution treatment on the plate obtained in the step (3): the heat preservation temperature is 540-560 ℃, and the heat preservation time is 30-120 s; then cooling and straightening treatment with 0.1-2% of deformation;

(5) transferring the plate obtained in the step (4) to 100-250 ℃ for heat preservation for 5-120 s at the temperature of less than or equal to 30min for primary pre-aging; and then carrying out secondary pre-aging treatment at the temperature of 70-90 ℃ for 4-10 h to obtain a finished plate.

Further, the melting and refining process in the step (1) is carried out under the conditions of filtering by using a 50ppi filter plate, degassing and adopting an argon online degassing mode, and the hydrogen content is controlled to be lower than 0.14ml/100g of Al.

Further, after the three cold rolling steps in the step (3), intermediate annealing is carried out, wherein the heat preservation temperature of the intermediate annealing is 420-470 ℃, and the heat preservation time is 2-5 h.

Further, the cold rolling is continued after the intermediate annealing in the step (3), and the cold rolling reduction is ensured to be 50-70%.

Further, the plate obtained in the step (5) through the step (4) is transferred in less than 20 min.

Further, the temperature rise rate of the first-stage pre-aged plate in the step (5) is 10-80 ℃/s.

Further, the temperature rise rate of the first-stage pre-aged plate in the step (5) is 20-60 ℃/s.

Further, obtaining a finished plate: initial yield strength less than 110MPa, edge-covering factor r_minThe/t is less than 0.5, the surface painting line is better than the second level, and the yield strength is more than 230MPa after 2 percent of prestretching and 20min of heat preservation at 185 ℃.

The technical scheme provided by the invention is as follows:

(1) the temperature of the hot rolling and the finish rolling needs to be controlled below 270 ℃, so as to avoid the precipitation of coarse Mg in the cooling process after the hot rolling due to overhigh temperature₂Si particles, guaranteed Mg₂The Si is fully dissolved in the later solid solution treatment process, so that more effective clusters are precipitated in the pre-aging process, and finally the plate is subjected to later solid solution treatment

More strengthening beta' phase is formed in the baking treatment process, and the baking hardening performance of the plate is improved.

(2) After intermediate annealing, the cold rolling reduction rate is ensured to be 40% -80%, the plate is ensured to have excellent edge covering performance by cooperatively controlling the grain size and the texture distribution of the plate, and meanwhile, the painting and brushing on the surface of the plate are eliminated, so that the plate with high edge covering and high surface quality is obtained.

(3) The invention adopts the bipolar pre-aging to obviously improve the baking hardening performance of the plate, and the effect is far higher than that of the first-stage pre-aging.

(4) The transfer time from solid solution water quenching to primary pre-aging treatment is controlled to be less than 20min, so that the reduction of the baking hardening performance caused by the fact that the plate is not beneficial to forming reinforced beta-phase clusters through later-stage baking treatment due to precipitation in the natural aging process can be avoided.

(5) The temperature rise rate of the first-stage pre-aging is controlled to be more than 20 ℃/s, so that more clusters which can promote the later-stage baking treatment to form more strengthening beta phases can be precipitated in the first-stage pre-aging process, and the baking hardening performance of the plate is improved.

The invention has the beneficial technical effects that by adopting the alloy, the equilibrium state of the alloy can generate more nano precipitated phases than the conventional 6xxx series aluminum alloy, the alloy has higher baking hardening performance than the conventional 6xxx series aluminum alloy, the baking finish strength of the plate can be obviously improved on the premise of ensuring lower initial yield strength of the plate, and the edge covering performance and the surface quality of the plate can be ensured. The plate obtained by the method has excellent mechanical property and surface quality, particularly has high baking hardening performance, and is particularly suitable for high-strength automobile outer covering plate.

Detailed Description

The present invention will be described in detail with reference to the following embodiments.

In the development process of the 6xxx series aluminum alloy plate for the automobile body outer plate, the low initial yield strength and the high bake-hardening performance of the plate are realized by strictly controlling the alloy components and the preparation process, and the invention is better suitable for the high-strength automobile panel outer plate.

Firstly, melting pure aluminum and various intermediate alloys according to the mixture ratio (0.4-1.2 wt% of Si, 0.3-0.8 wt% of Mg, less than or equal to 0.3 wt% of Zn, 0.05-0.25 wt% of Cu, 0.05-0.2 wt% of Mn, less than or equal to 0.3 wt% of Fe, 0.01-0.03 wt% of Ti, and the balance of Al and normal impurities), and casting an ingot by utilizing semi-continuous casting equipment after refining the melt.

And (3) cutting the head and milling the surface of the cast ingot, putting the cast ingot into a heat treatment furnace for homogenization treatment, cooling the cast ingot after the homogenization treatment to the initial rolling temperature, preserving the temperature for a period of time, and then starting hot rolling. After hot rolling is finished, cold rolling and intermediate annealing are carried out on the obtained hot rolled plate, then the hot rolled plate is rolled to the thickness of a final finished plate, and bipolar pre-aging treatment is carried out on the obtained cold rolled plate after intermediate annealing, solid solution and water quenching treatment to obtain the finished plate.

Hereinafter, examples of the present invention and comparative examples are described in comparison, and the technical effects of the present invention can be further demonstrated by these examples and comparative examples. However, the illustrated examples are only preferred embodiments of the present invention, and it should not be understood that the scope of the above subject matter of the present invention is limited thereto, and any technical solutions formed based on the technical idea of the present invention fall within the protection scope of the present invention.

Example 1

The aluminum alloy comprises the following components in percentage by mass: si: 0.4 wt.%; mg: 0.6 wt.%; zn: 0.02 wt.%; cu: 0.15 wt.%; mn: 0.05 wt.%; fe: 0.22 wt.%; ti: 0.01 wt.%, the balance being Al and normal impurities.

Melting the alloy according to the proportion, refining the melt (filtering by using a filter with the aperture of 50ppi, degassing by using argon on line, and controlling the hydrogen content to be 0.13ml/100g Al), and then casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 570 ℃, and preserving heat for 4 hours; then cooling to 520 ℃, carrying out hot rolling and initial rolling until the thickness of the steel plate is 8mm, and carrying out final rolling at a temperature of 270 ℃; the method comprises the steps of three-pass cold rolling to 5mm, then intermediate annealing and cold rolling at 420 ℃ for 2h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to 80% of the plate with the final thickness, then carrying out solution treatment at 540 ℃ for 120s, then cooling, carrying out straightening treatment with the deformation of 0.1%, transferring the plate after solution treatment to 100 ℃ after 0.5min, carrying out heat preservation for 30s for primary pre-aging, wherein the temperature rise rate of the primary pre-aging is 10 ℃/s, then carrying out secondary pre-aging treatment at 80 ℃ for 10h, and finally obtaining a T4P state finished plate.

Example 2

The aluminum alloy comprises the following components in percentage by mass: si: 0.45 wt.%; mg: 0.8 wt.%; zn: 0.02 wt.%; cu: 0.05 wt.%; mn: 0.1 wt.%; fe: 0.18 wt.%; ti: 0.02 wt.%, balance Al and normal impurities.

Melting the alloy according to the proportion, refining the melt (filtering by using a filter with the aperture of 50ppi, degassing by using argon on line, and controlling the hydrogen content to be 0.12ml/100g Al), and then casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 560 ℃, and preserving heat for 6 hours; then cooling to 520 ℃ for hot rolling and initial rolling, and rolling to 5mm thickness, wherein the final rolling temperature is 260 ℃; cold rolling to 4mm, then performing intermediate annealing and cold rolling at 440 ℃ for 3h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the final thickness of the plate to be 75%, then performing solution treatment at the solution treatment temperature of 550 ℃ for 90s, then cooling, performing straightening treatment with the deformation of 0.3%, transferring the plate after solution treatment to the temperature of 180 ℃ for 10s after 5min for primary pre-aging, wherein the temperature rise rate of the primary pre-aging is 20 ℃/s, then performing secondary pre-aging treatment at the temperature of 85 ℃ for 8h, and finally obtaining a T4P state finished plate.

Example 3

The aluminum alloy comprises the following components in percentage by mass: si: 0.6 wt.%; mg: 0.4 wt.%; zn: 0.02 wt.%; cu: 0.25 wt.%; mn: 0.2 wt.%; fe: 0.22 wt.%; ti: 0.03 wt.%, balance Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 560 ℃, and preserving heat for 8 hours; then cooling to 510 ℃ for hot rolling and initial rolling, and rolling to 5mm thickness, wherein the final rolling temperature is 240 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 420 ℃ for 4h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the final thickness of the plate to be 70%, then performing solution treatment at the temperature of 550 ℃ for 45s, then cooling, performing straightening treatment with the deformation of 0.5%, transferring the plate after solution treatment to the temperature of 250 ℃ after 20min, performing primary pre-aging at the temperature rise rate of 60 ℃/s, then performing secondary pre-aging at the temperature of 85 ℃ for 8h, and finally obtaining a T4P state finished plate.

Example 4

The aluminum alloy comprises the following components in percentage by mass: si: 0.55 wt.%; mg: 0.6 wt.%; zn: 0.02 wt.%; cu: 0.1 wt.%; mn: 0.1 wt.%; fe: 0.22 wt.%; ti: 0.02 wt.%, balance Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 560 ℃, and preserving heat for 10 hours; then, cooling to 500 ℃, carrying out hot rolling and initial rolling until the thickness is 8mm, and carrying out final rolling at the temperature of 260 ℃; the method comprises the steps of three-pass cold rolling to 5mm, then intermediate annealing and cold rolling at 420 ℃ for 5h to obtain a cold-rolled plate with the thickness of 2mm, keeping the cold rolling reduction of the plate after annealing to the final thickness of the plate to be 60%, then carrying out solution treatment, wherein the solution treatment temperature is 560 ℃, the heat preservation time is 30s, then cooling, carrying out straightening treatment with the deformation amount of 1%, transferring the plate after solution treatment to the temperature of 150 ℃ after 30min, carrying out primary pre-aging treatment for 10s, wherein the temperature rise rate of the primary pre-aging treatment is 40 ℃/s, then carrying out secondary pre-aging treatment, the temperature is 90 ℃, the time is 4h, and finally obtaining a T4P state finished plate.

Example 5

The aluminum alloy comprises the following components in percentage by mass: si: 0.55 wt.%; mg: 0.6 wt.%; zn: 0.02 wt.%; cu: 0.2 wt.%; mn: 0.1 wt.%; fe: 0.22 wt.%; ti: 0.02 wt.%, balance Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 540 ℃, and preserving heat for 12 hours; then cooling to 520 ℃, carrying out hot rolling and initial rolling until the thickness is 8mm, and carrying out final rolling at the temperature of 265 ℃; cold rolling to 2.5mm, then performing intermediate annealing and cold rolling at 440 ℃ for 5h to obtain a cold-rolled plate with the thickness of 0.8mm, keeping the cold rolling reduction of the plate after annealing to 68% of the plate with the final thickness, then performing solution treatment at the temperature of 560 ℃, keeping the temperature for 90s, then cooling, performing straightening treatment with the deformation of 1.5%, transferring the plate after solution treatment to the temperature of 150 ℃ after 5min, performing primary pre-aging at the temperature of 10s, wherein the temperature rise rate of the primary pre-aging is 50 ℃/s, then performing secondary pre-aging at the temperature of 90 ℃ for 8h, and finally obtaining the finished plate with the T4P state.

Example 6

The aluminum alloy comprises the following components in percentage by mass: si: 0.5 wt.%; mg: 0.6 wt.%; zn: 0.02 wt.%; cu: 0.1 wt.%; mn: 0.1 wt.%; fe: 0.18 wt.%; ti: 0.02 wt.%, balance Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 8 hours; then cooling to 520 ℃, carrying out hot rolling and initial rolling until the thickness of the steel plate is 8mm, and carrying out final rolling at a temperature of 270 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 420 ℃ for 4h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to 70% of the plate with the final thickness, then performing solution treatment, wherein the solution treatment temperature is 560 ℃, the heat preservation time is 60s, then cooling, performing straightening treatment with the deformation amount of 2%, transferring the plate after solution treatment to the temperature of 150 ℃ after 5min, performing primary pre-aging at the temperature of 5s, wherein the temperature rise rate of the primary pre-aging is 50 ℃/s, then performing secondary pre-aging at the temperature of 85 ℃ for 8h, and finally obtaining a T4P state finished plate.

Example 7

The aluminum alloy comprises the following components in percentage by mass: si: 0.55 wt.%; mg: 0.5 wt.%; zn: 0.02 wt.%; cu: 0.1 wt.%; mn: 0.15 wt.%; fe: 0.22 wt.%; ti: 0.02 wt.%, balance Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then cooling to 520 ℃ for hot rolling and initial rolling until the thickness is 6mm, and finally rolling at the temperature of 260 ℃; cold rolling to 1.68mm, then performing intermediate annealing and cold rolling at 420 ℃ for 4h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the final thickness of the plate to be 40%, then performing solution treatment, wherein the solution treatment temperature is 560 ℃, the heat preservation time is 60s, then cooling, performing straightening treatment with the deformation amount of 0.5%, transferring the plate after solution treatment to the temperature of 180 ℃ after 5min, performing primary pre-aging at the temperature of 180 ℃ for 5s, performing secondary pre-aging at the temperature of 85 ℃ for 10h, and finally obtaining the T4P state finished plate.

Example 8

The aluminum alloy comprises the following components in percentage by mass: si: 1.02 wt.%; mg: 0.4 wt.%; zn: 0.01 wt.%; cu: 0.08 wt.%; mn: 0.12 wt.%; fe: 0.17 wt.%; ti: 0.015 wt.%, the balance being Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then cooling to 520 ℃ for hot rolling and initial rolling until the thickness is 6mm, and finally rolling at the temperature of 260 ℃; cold rolling to 5mm, then performing intermediate annealing and cold rolling at 470 ℃ for 2h to obtain a cold-rolled plate with the thickness of 2mm, keeping the cold rolling reduction of the plate after annealing to the final thickness of the plate to be 60%, then performing solution treatment at the solution treatment temperature of 550 ℃ for 2min, then cooling, performing straightening treatment with the deformation of 0.5%, transferring the plate after solution treatment to the temperature of 100 ℃ after 5min, performing primary pre-aging at the temperature of 30s, performing secondary pre-aging at the temperature of 75 ℃ for 8h, and finally obtaining a T4P state finished plate.

Example 9

The aluminum alloy comprises the following components in percentage by mass: si: 1.2 wt.%; mg: 0.4 wt.%; zn: 0.01 wt.%; cu: 0.08 wt.%; mn: 0.12 wt.%; fe: 0.17 wt.%; ti: 0.015 wt.%, the balance being Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then cooling to 520 ℃ for hot rolling and initial rolling until the thickness is 6mm, and finally rolling at the temperature of 260 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 470 ℃ for 3h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the final thickness of the plate to be 70%, then performing solution treatment at the temperature of 550 ℃ for 2min, then cooling, performing straightening treatment with the deformation of 0.5%, transferring the plate after solution treatment to the temperature of 180 ℃ after 5min, performing primary pre-aging at the temperature of 75 ℃ for 10s, performing secondary pre-aging at the temperature of 8h, and finally obtaining the T4P state finished plate.

Example 10

The aluminum alloy comprises the following components in percentage by mass: si: 1.02 wt.%; mg: 0.4 wt.%; zn: 0.01 wt.%; cu: 0.08 wt.%; mn: 0.12 wt.%; fe: 0.17 wt.%; ti: 0.015 wt.%, the balance being Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then cooling to 520 ℃ for hot rolling and initial rolling, and rolling to 5mm thickness, wherein the final rolling temperature is 260 ℃; cold rolling to 2mm, then performing intermediate annealing and cold rolling at 460 ℃ for 4h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the final thickness of the plate to be 50%, then performing solution treatment at the solution treatment temperature of 550 ℃ for 2min, then cooling, performing straightening treatment with the deformation of 0.5%, transferring the plate after solution treatment to the temperature of 250 ℃ after 5min, performing primary pre-aging at the temperature of 75 ℃ for 5s, performing secondary pre-aging at the temperature of 75 ℃ for 8h, and finally obtaining a T4P state finished plate.

Example 11

The aluminum alloy comprises the following components in percentage by mass: si: 1.02 wt.%; mg: 0.4 wt.%; zn: 0.01 wt.%; cu: 0.08 wt.%; mn: 0.12 wt.%; fe: 0.17 wt.%; ti: 0.015 wt.%, the balance being Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then cooling to 520 ℃, carrying out hot rolling and initial rolling until the thickness of the steel plate is 6mm, and carrying out final rolling at 240 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 450 ℃ for 5h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the final thickness of the plate to be 70%, then performing solution treatment at 550 ℃ for 2min, then cooling, performing straightening treatment with the deformation of 0.5%, transferring the plate after solution treatment to 180 ℃ after 5min, performing heat preservation for 10s for primary pre-aging, wherein the temperature rise rate of the primary pre-aging is 20 ℃/s, then performing secondary pre-aging treatment at 70 ℃ for 10h, and finally obtaining a T4P state finished plate.

Example 12

The aluminum alloy comprises the following components in percentage by mass: si: 1.02 wt.%; mg: 0.4 wt.%; zn: 0.01 wt.%; cu: 0.08 wt.%; mn: 0.12 wt.%; fe: 0.17 wt.%; ti: 0.015 wt.%, the balance being Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then cooling to 520 ℃, carrying out hot rolling and initial rolling until the thickness of the steel plate is 6mm, and carrying out final rolling at 240 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 450 ℃ for 2h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the final thickness of the plate to be 70%, then performing solution treatment at the temperature of 550 ℃, keeping the temperature for 2min, then cooling, performing straightening treatment with the deformation of 0.5%, performing primary pre-aging of the plate after solution treatment at the temperature of 180 ℃ for 10s, wherein the temperature rise rate of the primary pre-aging is 20 ℃/s, then performing secondary pre-aging treatment at the temperature of 85 ℃ for 6h, and finally obtaining the T4P state finished plate.

Example 13

The aluminum alloy comprises the following components in percentage by mass: si: 1.02 wt.%; mg: 0.4 wt.%; zn: 0.01 wt.%; cu: 0.08 wt.%; mn: 0.12 wt.%; fe: 0.17 wt.%; ti: 0.015 wt.%, the balance being Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then cooling to 520 ℃ for hot rolling and initial rolling, and rolling to 8mm thickness, wherein the final rolling temperature is 260 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 450 ℃ for 4h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the final thickness of the plate to be 70%, then performing solution treatment at the temperature of 550 ℃ for 2min, then cooling, performing straightening treatment with the deformation of 0.5%, performing primary pre-aging of the plate after solution treatment at the temperature of 180 ℃ for 10s, wherein the temperature rise rate of the primary pre-aging is 50 ℃/s, then performing secondary pre-aging at the temperature of 75 ℃ for 8h, and finally obtaining the T4P state finished plate.

Example 14

The aluminum alloy comprises the following components in percentage by mass: si: 1.02 wt.%; mg: 0.4 wt.%; zn: 0.01 wt.%; cu: 0.08 wt.%; mn: 0.12 wt.%; fe: 0.17 wt.%; ti: 0.015 wt.%, the balance being Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then, cooling to 500 ℃, carrying out hot rolling and initial rolling until the thickness of the steel plate is 6mm, and carrying out final rolling at a temperature of 260 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 470 ℃ for 4h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the final thickness of the plate to be 40%, then performing solution treatment at the temperature of 550 ℃, keeping the temperature for 2min, then cooling, performing straightening treatment with the deformation of 0.5%, performing primary pre-aging on the plate after solution treatment at the temperature of 180 ℃ for 10s, wherein the temperature rise rate of the primary pre-aging is 50 ℃/s, then performing secondary pre-aging treatment at the temperature of 70 ℃ for 10h, and finally obtaining the T4P state finished plate.

Comparative example 1

The aluminum alloy comprises the following components in percentage by mass: si: 0.55 wt.%; mg: 0.6 wt.%; zn: 0.02 wt.%; cu: 0.1 wt.%; mn: 0.1 wt.%; fe: 0.22 wt.%; ti: 0.02 wt.%, balance Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then hot rolling to 6mm thickness, the final rolling temperature is 330 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 450 ℃ for 2h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the plate with the final thickness of 70%, then performing solution treatment, wherein the temperature of the solution treatment is 550 ℃, the heat preservation time is 2min, transferring the plate after the solution treatment to the temperature of 150 ℃ after 5min, performing heat preservation for 10s, performing primary pre-aging, wherein the temperature rise rate of the primary pre-aging is 15 ℃/s, then performing secondary pre-aging treatment, the temperature is 85 ℃, and the time is 10h, and finally obtaining a T4P state finished plate.

Comparative example 2

The aluminum alloy comprises the following components in percentage by mass: si: 0.55 wt.%; mg: 0.6 wt.%; zn: 0.02 wt.%; cu: 0.1 wt.%; mn: 0.1 wt.%; fe: 0.22 wt.%; ti: 0.02 wt.%, balance Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then hot rolling to 8mm thickness, and finishing rolling temperature is 265 ℃; cold rolling to 6mm, then performing intermediate annealing and cold rolling at 450 ℃ for 2h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the final thickness of the plate to be 83%, then performing solid solution treatment at the temperature of 550 ℃ for 2min, transferring the plate after the solid solution treatment to the temperature of 150 ℃ for 10s after 5min, performing primary pre-aging at the temperature rise rate of 15 ℃/s, then performing secondary pre-aging at the temperature of 85 ℃ for 10h, and finally obtaining a T4P state finished plate.

Comparative example 3

The aluminum alloy comprises the following components in percentage by mass: si: 0.55 wt.%; mg: 0.6 wt.%; zn: 0.02 wt.%; cu: 0.1 wt.%; mn: 0.1 wt.%; fe: 0.22 wt.%; ti: 0.02 wt.%, balance Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then hot rolling to 6mm thickness, and finishing rolling temperature is 265 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 450 ℃ for 2h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the plate with the final thickness of 70%, then performing solution treatment, wherein the temperature of the solution treatment is 550 ℃, the heat preservation time is 2min, transferring the plate after the solution treatment to the temperature of 150 ℃ after 40min, performing heat preservation for 10s, performing primary pre-aging, wherein the temperature rise rate of the primary pre-aging is 15 ℃/s, then performing secondary pre-aging treatment, the temperature is 85 ℃, and the time is 10h, and finally obtaining a T4P state finished plate.

Comparative example 4

The aluminum alloy comprises the following components in percentage by mass: si: 0.55 wt.%; mg: 0.6 wt.%; zn: 0.02 wt.%; cu: 0.1 wt.%; mn: 0.1 wt.%; fe: 0.22 wt.%; ti: 0.02 wt.%, balance Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then hot rolling to 6mm thickness, and finishing rolling temperature is 265 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 450 ℃ for 2h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the plate with the final thickness of 70%, then performing solution treatment, wherein the temperature of the solution treatment is 550 ℃, the heat preservation time is 2min, transferring the plate after the solution treatment to the temperature of 150 ℃ after 5min, performing heat preservation for 10s, performing primary pre-aging, the temperature rise rate of the primary pre-aging is 3 ℃/s, then performing secondary pre-aging treatment, the temperature is 85 ℃, and the time is 10h, and finally obtaining a T4P state finished plate.

Comparative example 5

The aluminum alloy comprises the following components in percentage by mass: si: 1.02 wt.%; mg: 0.4 wt.%; zn: 0.01 wt.%; cu: 0.08 wt.%; mn: 0.12 wt.%; fe: 0.17 wt.%; ti: 0.015 wt.%, the balance being Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then hot rolling to 6mm thickness, and finishing rolling temperature is 265 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 450 ℃ for 2h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the final thickness of the plate to be 70%, then performing solution treatment, wherein the temperature of the solution treatment is 550 ℃, the heat preservation time is 2min, transferring the plate after the solution treatment to 80 ℃ after 5min, performing heat preservation for 10s, performing primary pre-aging, the temperature rise rate of the primary pre-aging is 15 ℃/s, then performing secondary pre-aging treatment, the temperature is 85 ℃, and the time is 10h, and finally obtaining a T4P state finished plate.

Comparative example 6

The aluminum alloy comprises the following components in percentage by mass: si: 1.02 wt.%; mg: 0.4 wt.%; zn: 0.01 wt.%; cu: 0.08 wt.%; mn: 0.12 wt.%; fe: 0.17 wt.%; ti: 0.015 wt.%, the balance being Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then hot rolling to 6mm thickness, and finishing rolling temperature is 265 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 450 ℃ for 2h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the plate with the final thickness of 70%, then performing solution treatment, wherein the temperature of the solution treatment is 550 ℃, the heat preservation time is 2min, transferring the plate after the solution treatment to the temperature of 280 ℃ after 5min, performing heat preservation for 10s for primary pre-aging, the temperature rise rate of the primary pre-aging is 15 ℃/s, then performing secondary pre-aging treatment, the temperature is 85 ℃, the time is 10h, and finally obtaining a T4P state finished plate.

Comparative example 7

The aluminum alloy comprises the following components in percentage by mass: si: 1.02 wt.%; mg: 0.4 wt.%; zn: 0.01 wt.%; cu: 0.08 wt.%; mn: 0.12 wt.%; fe: 0.17 wt.%; ti: 0.015 wt.%, the balance being Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then hot rolling to 6mm thickness, and finishing rolling temperature is 265 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 450 ℃ for 2h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the plate with the final thickness of 70%, then performing solution treatment, wherein the temperature of the solution treatment is 550 ℃, the heat preservation time is 2min, transferring the plate after the solution treatment to the temperature of 150 ℃ after 5min, performing heat preservation for 10s, performing primary pre-aging, wherein the temperature rise rate of the primary pre-aging is 15 ℃/s, then performing secondary pre-aging treatment, the temperature is 50 ℃, and the time is 10h, and finally obtaining a T4P state finished plate.

Comparative example 8

The aluminum alloy comprises the following components in percentage by mass: si: 1.02 wt.%; mg: 0.4 wt.%; zn: 0.01 wt.%; cu: 0.08 wt.%; mn: 0.12 wt.%; fe: 0.17 wt.%; ti: 0.015 wt.%, the balance being Al and normal impurities.

Melting the alloy according to the proportion, refining the melt, and casting a cast ingot by using semi-continuous casting equipment; carrying out homogenization treatment on the cast ingot after head cutting and surface milling, wherein the homogenization temperature is 550 ℃, and preserving heat for 10 hours; then hot rolling to 6mm thickness, and finishing rolling temperature is 265 ℃; cold rolling to 3.3mm, then performing intermediate annealing and cold rolling at 450 ℃ for 2h to obtain a cold-rolled plate with the thickness of 1mm, keeping the cold rolling reduction of the plate after annealing to the plate with the final thickness of 70%, then performing solution treatment, wherein the temperature of the solution treatment is 550 ℃, the heat preservation time is 2min, transferring the plate after the solution treatment to the temperature of 150 ℃ after 5min, performing heat preservation for 10s, performing primary pre-aging, wherein the temperature rise rate of the primary pre-aging is 15 ℃/s, then performing secondary pre-aging treatment, the temperature is 100 ℃, and the time is 10h, and finally obtaining a T4P state finished plate.

[ Performance test ]

1. And (3) testing mechanical properties:

testing the Yield Strength (YS), tensile strength (UTS) and Elongation (EL) of the obtained finished plate after the plate is parked for 1 month; the YS test was carried out after 2% pre-stretching and 185 ℃ x 20min simulated paint baking. All mechanical property test samples are sampled along the vertical rolling direction, and the sample size adopts the recommended A of GB/T228₅₀The test specimens were stretched and the test results are shown in Table 1.

2. Evaluation of curling Properties:

strip samples with the length of 250mm and the width of 30mm are cut from the finished plate and subjected to curling performance evaluation. The method comprises the steps of pre-stretching a sample by 10% in the length direction, cutting a rectangular sample with the thickness of 50mm multiplied by 30mm, and then performing a 180-degree bending test by using a pressure head (keeping r/t equal to 0.5, r as the radius of the pressure head, and t as the thickness of the plate), wherein in the test process, the interval between supporting rollers is ensured to be 2.9-3.0 mm. The external surface was subjected to metallographic photographing and rating evaluation after bending (level 1: smooth surface, no micro-cracks and continuous necking; level 2: slightly rough surface, no micro-cracks and continuous necking; level 3: micro-cracks or continuous necking; level 4: obvious cracks on the surface, of which levels 1 and 2 are acceptable to the automobile company and levels 3 and 4 are not acceptable), and the test results are shown in table 1.

3. Evaluation of paint line Strength:

and cutting a rectangular sample with the length of 250mm and the width of 35mm from the finished plate to evaluate the defects of surface painting and line brushing and orange peel, wherein the length direction of the sample is vertical to the rolling direction, and the width direction of the sample is along the rolling direction. The samples were pre-stretched 10% in the length direction, the surfaces of the panels were lightly sanded with 320# sand and then subjected to paint-brushing strength evaluation on the panel surfaces (grade 1: no white streaks on the surface; grade 2: discontinuous white streaks on the surface; grade 3: continuous white streaks on the surface, wherein grade 1 and grade 2 are acceptable by the automotive company and grade 3 is not acceptable), and the test results are listed in table 1.

Table 1: mechanical, baking varnish, hemming, paint brush line performance evaluation of examples

As can be seen from Table 1, the yield strength of the plates of examples 1 to 14 is kept between 100 MPa and 110MPa after the plates are parked for 7 days, the elongation is more than or equal to 26 percent, and the punching requirement of the plates is met; after 2% prestretching and 185 ℃ multiplied by 20min simulated baking finish, the yield strength of the plate is more than 230MPa, and the anti-sinking performance of the automobile outer covering part can be met. In the comparative examples, the following results were obtained in comparative examples 1 to 8, because the requirements of the present invention were not satisfied:

A. comparative example 1 coarse Mg was precipitated due to the excessively high finishing temperature₂Si, the solid solution is insufficient during the solid solution treatment, the hardening effect of the plate after baking is insufficient, and the yield strength is lower after baking finish;

B. in comparative example 2, due to excessive rolling reduction, the paint brush line of the plate is obvious, and the surface quality is unqualified;

C. in comparative example 3, due to too long transfer time after solid solution, clusters which are not beneficial to later-stage baking hardening are precipitated from the plate, so that the yield strength is lower after paint baking;

D. in comparative example 4, the heating rate of the primary pre-aging treatment is too slow, the initial yield strength of the plate is too high, and the bake-hardening performance is poor;

E. in comparative example 5, the short-time heating treatment temperature is too low, so that the hardening effect of the plate after baking is not obvious, and the yield strength of the plate after baking is lower;

F. in comparative example 6, the initial yield strength of the plate was too high due to the excessively high temperature of the short-time heat treatment;

G. in comparative example 7, the plate baking varnish strength is low due to the excessively low pre-aging temperature;

H. comparative example 8 resulted in an excessive initial yield strength due to an excessively high pre-aging temperature.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.

Claims (10)

1. A high-strength 6 xxx-series aluminum alloy sheet for an automobile body, wherein the sheet comprises the following components in percentage by mass: si: 0.4 wt.% to 1.2 wt.%; mg: 0.3 wt.% to 0.8 wt.%; zn: 0.3 wt.% or less; cu: 0.05 wt.% to 0.25 wt.%; mn: 0.05 wt.% to 0.2 wt.%; fe: 0.3 wt.% or less; ti: 0.01-0.03 wt.%, the balance being Al and impurities less than 0.05 wt.%.

2. A method of making the aluminum alloy sheet of claim 1, comprising: casting, homogenizing, hot rolling, cold rolling, intermediate annealing, solid solution, straightening, primary pre-aging and secondary pre-aging.

3. The method according to claim 2, wherein the aluminum alloy sheet is prepared by a method comprising the steps of:

(1) mixing the components of the plate according to the proportion, melting and refining, and casting the mixture into a cast ingot by adopting semi-continuous casting equipment;

(2) homogenizing the cast ingot: controlling the heating temperature to be 540-570 ℃ and the heat preservation time to be 4-12 h;

(3) carrying out hot rolling on the ingot obtained in the step (2): controlling the initial rolling temperature to be 500-520 ℃, and carrying out hot rolling to be 5-8 mm, wherein the final rolling temperature is less than or equal to 270 ℃; then, multi-pass cold rolling is carried out, intermediate annealing is carried out, then, cold rolling is continuously carried out to 0.8 mm-2 mm, and the cold rolling reduction is ensured to be 40% -80%;

(4) carrying out solution treatment on the plate obtained in the step (3): the heat preservation temperature is 540-560 ℃, and the heat preservation time is 30-120 s; then cooling and straightening treatment with 0.1-2% of deformation;

(5) transferring the plate obtained in the step (4) to 100-250 ℃ for heat preservation for 5-120 s at the temperature of less than or equal to 30min for primary pre-aging; and then carrying out secondary pre-aging treatment at the temperature of 70-90 ℃ for 4-10 h to obtain a finished plate.

4. The method as claimed in claim 3, wherein the process conditions of the step (1) of melt refining are that a 50ppi filter is used for filtering, degassing is carried out in an argon on-line degassing mode, and the hydrogen content is controlled to be lower than 0.14ml/100g Al.

5. The method according to claim 3, characterized in that the intermediate annealing is carried out after the three cold rolling passes in the step (3), the intermediate annealing temperature is 420-470 ℃, and the holding time is 2-5 h.

6. The method as claimed in claim 3, wherein the cold rolling is continued after the intermediate annealing in the step (3), and the cold rolling reduction is ensured to be 50-70%.

7. The method of claim 3, wherein the step (5) of transferring the sheet obtained in step (4) is performed in less than 20 minutes.

8. The method according to claim 3, wherein the temperature rise rate of the primary pre-aged plate in the step (5) is 10-80 ℃/s.

9. The method according to claim 8, wherein the temperature rise rate of the primary pre-aged plate in the step (5) is 20-60 ℃/s.

10. A method according to claim 3, characterized in that a finished board is obtained: initial yield strength less than 110MPa, edge-covering factor r_minThe/t is less than 0.5, the surface painting line is better than the second level, and the yield strength is more than 230MPa after 2 percent of prestretching and 20min of heat preservation at 185 ℃.