CN111057980B - Process control method for high-formability aluminum alloy heterogeneous structure for automobile - Google Patents

Abstract

The invention discloses a process control method for a high-formability aluminum alloy heterogeneous structure for an automobile, and belongs to the technical field of aluminum alloys. The method comprises the following steps: preparing high-formability Al-Mg-Si-Cu-Zn alloy for automobiles, smelting the alloy by using medium-frequency induction under non-vacuum condition, and casting the alloy in a water-cooling steel mould for cooling; carrying out short-time low-temperature structure stability treatment on the cast ingot; taking the short-time heating cast ingot out of the heating furnace, and directly carrying out hot rolling treatment; the two-stage heat treatment regulates and controls the distribution state of the original iron-rich phase and solute elements of the alloy; hot rolling, cold rolling, intermediate annealing and cold rolling are sequentially carried out; carrying out high-temperature short-time solution treatment, and then quenching and cooling the alloy sample subjected to solution treatment from the solution treatment temperature to room temperature; and transferring the quenched sample into an aging furnace for cooling and pre-aging treatment. The processing method can effectively control the sizes and the distribution of crystal grains and precipitated phases in the alloy and form an isomeric structure which has a remarkable promoting effect on the forming performance of the alloy.

Description

Process control method for high-formability aluminum alloy heterogeneous structure for automobile

Technical Field

The invention belongs to the technical field of aluminum alloy, and particularly provides a process control method for a high-formability aluminum alloy heterogeneous structure for an automobile, aiming at the current application situation that the forming performance, the flanging performance and the like of an aluminum alloy outer plate of an automobile body are still not high enough and the requirements of the automobile field on the performances are continuously improved.

Background

With the continuous improvement of the industrialization level of all countries in the world, a series of energy crisis and environmental problems become more serious, and energy conservation and emission reduction become the main melody of current social production and life. Under the theme, various countries adopt a plurality of measures to solve the problems of energy consumption and environment, and particularly, the method is more obvious in the field of automobiles: how to improve automobile engine efficiency, research new energy automobile, weight reduction car etc. become recent research focus, and each big car manufacturer adopts respectively can promote the lightweight scheme of self competitiveness. Overall, aluminum alloy has become a key material for light weight of automobiles due to its characteristics of light weight, corrosion resistance, high specific strength, easy processing, beautiful surface, abundant storage, recyclability, etc. In addition, according to statistics, the energy saved by adopting the aluminum alloy in the automobile is 6-12 times of the energy consumed by the original aluminum used for producing the part. Therefore, the development and application of advanced aluminum alloy sheets for automobile light weight have attracted extensive attention from automobile manufacturers and researchers all over the world, and the amount of aluminum for automobiles has increased year by year in recent years.

Compared with other series aluminum alloys, 6xxx (Al-Mg-Si-Cu) series aluminum alloys are more used in the manufacture of outer panels of vehicle bodies because of their excellent press formability, hemming performance, and bake hardening increment, etc. The aluminum alloys mainly used at present are AA6016, AA6111, AA6022 and the like, and the alloys have characteristics due to certain differences of components. However, compared with the conventional steel plate for an automobile, the 6xxx aluminum alloy still has the defects of higher cost, insufficient formability, bending performance, strength and the like, and a new alloy and a new process are urgently needed to be developed to better meet the requirements of practical application. Considering that the baking varnish hardening increment and the strength of the alloy plate can be effectively improved by two-phase or multi-phase synergistic precipitation and synergistic strengthening, a new high baking varnish hardening Al-Mg-Si-Cu-Zn alloy and a preparation method thereof are developed by the research team recently. In order to better meet the requirements of practical application, the key for further popularization and application of the series of alloys is how to greatly improve the stamping forming performance, the edge bending performance and the like of the series of alloys while ensuring the hardening characteristic of high baking finish. Particularly, if a short-process preparation method can be developed, the pre-aged alloy plate can be ensured to show excellent stamping forming performance, and the production cost of the alloy plate can be greatly reduced, so that the method has important significance for rapidly promoting the wide application of the novel aluminum alloy material.

Disclosure of Invention

The invention provides a process regulation and control method for a high-formability Al-Mg-Si-Cu-Zn alloy heterogeneous structure for an automobile, aiming at the defects that the traditional hot working process route of an Al-Mg-Si-Cu-Zn alloy plate is complex, the production cost is high, the improvement range of the stamping forming performance of the produced alloy plate is limited and the like, and aiming at better meeting the urgent demand of the light weight of the automobile on the high-performance aluminum alloy plate. The invention fully utilizes the texture characteristic that component segregation is inevitably generated during the traditional casting of the aluminum alloy, and regulates and controls the evolution and distribution of alloy textures and precipitation phases through a hot processing technical route without high-temperature long-time homogenization heat treatment, namely, firstly, the alloy ingot is subjected to short-time low-temperature texture stability treatment to eliminate low-melting-point precipitation phases, then, the alloy ingot is directly subjected to hot rolling deformation without high-temperature long-time homogenization treatment, then, the alloy ingot is subjected to short-time heat treatment to regulate and control the distribution condition of solute elements and other original phases in an alloy matrix, then, the alloy ingot is subjected to hot rolling or directly subjected to cold rolling, intermediate annealing and cold rolling, and finally, the cold-rolled alloy plate is subjected to solid solution and pre-aging treatment, the pre-aged alloy plate can present isomeric texture characteristics, such as the grain size presents bimodal distribution characteristics and multi-scale precipitation phase distribution characteristics, and the microstructure characteristics that soft areas and hard areas are alternately distributed in micro areas in the alloy matrix, and the like, so that the alloy plate can show better coordinated deformation performance among different crystal grains during stamping, and finally the stamping forming performance of the aluminum alloy plate can be greatly improved. Thereby realizing the purpose that the pre-aged Al-Mg-Si-Cu-Zn alloy plate has excellent stamping forming performance.

According to the first aspect of the invention, the process control method for the heterogeneous structure of the high-formability aluminum alloy for the automobile is provided, and the Al-Mg-Si-Cu alloy comprises the following chemical components in percentage by mass: 0.5 to 3.7wt% of Zn, 0.6 to 1.0wt% of Mg, 0.4 to 1.0wt% of Si, 0.1 to 0.4wt% of Cu, 0.1 to 0.7wt% of Fe, and Mn: 0.3-0.7 wt%, Cr <0.02wt%, Ti < 0.1wt%, B <0.01wt%, and the balance of Al; the method is characterized by adopting the following technical route:

(1) preparing Al-Mg-Si-Cu-Zn alloy by adopting recycled aluminum or common aluminum, then smelting the alloy by using medium-frequency induction under non-vacuum condition, casting the alloy in a water-cooling steel mold, and controlling the cooling rate to be more than 40 ℃/min so that the size of alloy crystal grains meets the subsequent regulation and control requirement;

(2) according to the ingot casting speed, carrying out short-time low-temperature structure stability treatment on the ingot, wherein the short-time low-temperature process is 420-500 ℃/0.5-5 h, and the heating rate is 10-45 ℃/h;

(3) taking the short-time heating cast ingot out of the heating furnace, and directly carrying out hot rolling (the initial rolling temperature is 410-478 ℃, the final rolling temperature is higher than 300 ℃, the pass reduction is 10-20%, and the rolling deformation is 60-99%);

(4) the distribution state of a primary iron-rich phase and solute elements of the alloy is regulated and controlled by double-stage heat treatment (the first stage is 440-490 ℃/1-12 h, the second stage is 520-575 ℃/3-15 h, the heating rate is 10-45 ℃/h, and the cooling rate is more than 30 ℃/h);

(5) hot rolling (deformation 0-80%, initial rolling temperature 410-560 ℃) + cold rolling (deformation 30-60%) + intermediate annealing (annealing temperature 380-;

(6) high-temperature short-time solution treatment (540-;

(7) transferring the quenched sample into an aging furnace within 1.5min for cooling and pre-aging treatment (the temperature is lower than 90 ℃, the time is longer than 10h, and the cooling rate is 3-6 ℃/h),

based on the integrated process regulation, the developed alloy plate can be ensured to have excellent stamping forming performance.

Preferably, the non-vacuum intermediate frequency induction melting process comprises the following steps: firstly, melting recycled aluminum or common aluminum, controlling the temperature to be 780-840 ℃, then respectively adding Al-Fe, Al-Mn, Al-Cr and Al-Ti intermediate alloys, respectively adding Al-Cu and Al-Si intermediate alloys after melting, then stirring the melt for 5min at high power, then controlling the temperature to be above 720 ℃, respectively adding pure Zn and pure Mg, respectively pressing the pure Zn and the pure Mg into the bottom of the melt by using a graphite bell jar during adding, taking out the bell jar after the pure Mg is completely melted, and regulating and controlling the power of a medium-frequency induction furnace to enable the temperature of the alloy melt to be stable above 720 ℃ again; then degassing and slagging off, casting the slag into a water-cooling steel die, and controlling the cooling rate to be more than 50 ℃/min.

Preferably, the hot rolling process comprises the following specific processes: the initial rolling temperature: 410-475 ℃; the final rolling temperature is more than 310 ℃, the pass reduction is 10-18%, the rolling deformation is 65-95%, and the deformation mode is as follows: and (4) unidirectional rolling.

Preferably, the specific process for regulating and controlling the distribution state of the primary iron-rich phase and solute elements of the alloy by the double-stage heat treatment comprises the following steps: the first stage is as follows: 470-490 ℃/1-10 h, the second level is: 530-565 ℃/7-15 h, the heating rate is 10-40 ℃/h, and the cooling rate is more than 50 ℃/h.

Preferably, the hot rolling (deformation amount of 0 to 77%, initial rolling temperature of 420 to 550 ℃) + cold rolling (deformation amount of 35 to 60%) + intermediate annealing (annealing temperature of 385 to 415 ℃/0.5 to 2.5h) + cold rolling (cold rolling deformation amount of 35 to 60%).

Preferably, the specific process of the high-temperature short-time solution treatment is as follows: 545-565 ℃/1-6 min, the heating rate is more than 100 ℃/s, and then the alloy sample after solution treatment is quenched and cooled to room temperature from the solution treatment temperature at the cooling rate of more than 200 ℃/s.

Preferably, the cooling pre-aging treatment process specifically comprises the following steps: transferring the quenched sample into an aging furnace within 1.5min for cooling and pre-aging treatment, wherein the treatment temperature is as follows: below 85 ℃, time: the cooling speed is 3-5 ℃/h when the temperature is more than 11 h.

According to a second aspect of the present invention, there is provided a high-formability aluminum alloy for automobiles, which is an Al-Mg-Si-Cu-Zn-based alloy that is produced and regulated by the process regulation method according to any one of the above,

the Al-Mg-Si-Cu alloy comprises the following chemical components in percentage by mass: 0.5 to 3.7wt% of Zn, 0.6 to 1.0wt% of Mg, 0.4 to 1.0wt% of Si, 0.1 to 0.4wt% of Cu, 0.1 to 0.7wt% of Fe, and Mn: 0.3-0.7 wt%, Cr <0.02wt%, Ti < 0.1wt%, B <0.01wt%, and the balance of Al.

According to a third aspect of the present invention, there is provided a use of the high formability aluminum alloy for automobiles as described in the above aspect in automobiles.

The invention has the beneficial effects that:

by adopting the technical scheme, the invention has the following advantages: the invention not only can enable the Al-Mg-Si-Cu-Zn alloy plate to show the isomeric structure characteristic after being regulated and controlled by the hot working process, namely the grain size is in a bimodal size distribution characteristic, the precipitation phase is in a multi-scale distribution characteristic, and simultaneously soft and hard alternating regions with lower concentration and higher concentration of the precipitation phase are also distributed in a micro region, so that the stamping forming performance of the final pre-aged alloy plate is greatly improved, but also the preparation method can effectively reduce the production cost of the alloy plate because the high-temperature long-time homogenization heat treatment process in the traditional hot working process is omitted, and has an important promotion effect on the further wide application of the aluminum alloy plate. The invention is very suitable for processing and producing aluminum alloy materials for automobiles, and is also suitable for other aluminum alloy material production enterprises which have special requirements on the organization characteristics, the stamping forming performance and the like of aluminum alloy plates, and is also suitable for other technical industries which have higher requirements on the organization and the comprehensive performance of other series of aluminum alloy materials.

Drawings

FIG. 1 shows a flow chart of a process control method for a high formability aluminum alloy heterogeneous structure for an automobile according to the present invention;

FIG. 2 shows the SEM microstructure of the pre-aged alloy of comparative example 1;

FIG. 3 shows the external surface morphology of the pre-aged alloy of comparative example 1 after crimping deformation in three directions, 0, 45 and 90;

FIG. 4 shows the SEM structure for the pre-aged alloy of example 1;

FIG. 5 shows the external surface topography of the pre-aged alloy of example 1 after it has been crimped and deformed in three directions, 0, 45 and 90;

FIG. 6 shows the SEM structure for the pre-aged alloy of example 2;

FIG. 7 shows the external surface topography after the pre-aged alloy of example 2 is crimped and deformed in three directions, 0, 45 and 90;

FIG. 8 shows the SEM structure for the pre-aged alloy of example 3;

FIG. 9 shows the external surface morphology of the pre-aged alloy of example 3 after it has been crimped and deformed in three directions, 0, 45 and 90.

Detailed Description

The invention will be further supplemented and explained below with reference to specific embodiments.

The invention provides a short-flow preparation method aiming at the current situations that the stamping forming performance of an Al-Mg-Si-Cu-Zn alloy plate for an automobile is still to be further improved and the production cost is urgently required to be greatly reduced, and the research and application are carried out. The method makes full use of the component segregation which inevitably occurs when the aluminum alloy is cast traditionally, firstly, the concentration of solute elements in the micro-area of the alloy matrix is enabled to have difference through comprehensive regulation and control of processing and heat treatment, then, the grain size in the micro-area of the alloy and the size, concentration and distribution of precipitation phases in the grains are further enabled to generate difference through regulation and control of heat processing, finally, not only grains in the pre-aged state alloy matrix have the size distribution characteristic of double-model grains with alternately matched thickness, but also the texture is obviously weakened, and the soft-hard alternate heterogeneous structure characteristic with the difference in the distribution of the precipitation concentrations in the micro-area also exists. Once the alloy plate prepared by the process has the structural characteristics, the coordinated deformation capability among different-size crystal grains and among different micro-regions in the stamping deformation process can be greatly improved, and the alloy can finally show excellent stamping forming performance, flanging performance and other excellent performances. The method is very suitable for manufacturing novel aluminum alloy for automobiles, and particularly suitable for manufacturing parts with complex shapes which have higher requirements on stamping performance, strength, surface quality, bending performance and the like.

According to the process control method of the automobile high-formability aluminum alloy isomeric structure, the raw materials respectively adopt intermediate alloys such as recycled aluminum or common aluminum, industrial pure Mg, industrial pure Zn, intermediate alloys Al-20wt% Si, Al-50wt% Cu, Al-20wt% Fe, Al-10wt% Mn, Al-10wt% Cr, Al-10wt% Ti and the like. As shown in fig. 1, the following technical route is adopted:

step 101: preparing Al-Mg-Si-Cu-Zn alloy by adopting recycled aluminum or common aluminum, then smelting the alloy by using medium-frequency induction under non-vacuum condition, casting the alloy in a water-cooling steel mold, and controlling the cooling rate to be more than 40 ℃/min so that the size of alloy crystal grains meets the subsequent regulation and control requirement;

step 102: according to the ingot casting speed, carrying out short-time low-temperature structure stability treatment on the ingot, wherein the short-time low-temperature process is 420-500 ℃/0.5-5 h, and the heating rate is 10-45 ℃/h;

step 103: taking the short-time heating cast ingot out of the heating furnace, and directly carrying out hot rolling (the initial rolling temperature is 410-478 ℃, the final rolling temperature is higher than 300 ℃, the pass reduction is 10-20%, and the rolling deformation is 60-99%);

step 104: the distribution state of a primary iron-rich phase and solute elements of the alloy is regulated and controlled by double-stage heat treatment (the first stage is 440-490 ℃/1-12 h, the second stage is 520-575 ℃/3-15 h, the heating rate is 10-45 ℃/h, and the cooling rate is more than 30 ℃/h);

step 105: hot rolling (deformation 0-80%, initial rolling temperature 410-560 ℃) + cold rolling (deformation 30-60%) + intermediate annealing (annealing temperature 380-;

step 106: high-temperature short-time solution treatment (540-;

step 107: transferring the quenched sample into an aging furnace within 1.5min for cooling and pre-aging treatment (the temperature is lower than 90 ℃, the time is longer than 10h, and the cooling rate is 3-6 ℃/h).

Specifically, the treatment process comprises the following steps: firstly, adding pure aluminum into a crucible and melting, controlling the temperature to be 780-880 ℃, then respectively adding intermediate alloys such as Al-20wt% Fe, Al-10wt% Mn, Al-10wt% Cr and Al-10wt% Ti, respectively adding intermediate alloys such as Al-50wt% Cu and Al-20wt% Si after melting, then stirring the melt for 5min at high power, then controlling the temperature to be above 720 ℃, respectively adding pure Zn and pure Mg, respectively pressing the melt into the bottom of the melt by using a graphite bell jar during adding, taking out the bell jar after the melt is completely melted, regulating and controlling the power of a medium-frequency induction furnace to enable the temperature of the alloy melt to be stabilized at 740 ℃, slagging off, and adding a refining agent for degassing and refining; then, when the temperature of the melt is reduced to 720 ℃, Al-5wt% Ti-1wt% B grain refiner is added and properly stirred, and finally, after the temperature is kept for 10min, the melt is cast into a steel die with water cooling at the periphery, and the cooling rate is controlled to be more than 50 ℃/min. The specific chemical compositions of the alloys of the invention are shown in table 1:

TABLE 1 alloy compositions (mass%; wt%) for carrying out the invention

Mg

Si

Cu

Fe

Mn

Zn

Cr

Ti

B

Al

1#

0.9

0.7

0.2

0.4

0.5

3.0

<0.02wt％

≤0.1wt％

<0.01

Balance of

Carrying out thermal processing treatment on the cast ingot, (1) carrying out short-time low-temperature tissue stability treatment on the cast ingot according to the casting speed of the cast ingot, wherein the short-time low-temperature treatment process is 420-500 ℃/0.5-5 h, and the heating rate is 10-45 ℃/h; (2) taking the short-time heating cast ingot out of the heating furnace, and directly carrying out hot rolling (the initial rolling temperature is 410-478 ℃, the final rolling temperature is higher than 300 ℃, the pass reduction is 10-20%, and the rolling deformation is 60-99%); (3) the distribution state of a primary iron-rich phase and solute elements of the alloy is regulated and controlled by double-stage heat treatment (the first stage is 440-490 ℃/1-12 h, the second stage is 520-575 ℃/3-15 h, the heating rate is 10-45 ℃/h, and the cooling rate is more than 30 ℃/h); (4) hot rolling (deformation 0-80%, initial rolling temperature 410-560 ℃) + cold rolling (deformation 30-60%) + intermediate annealing (annealing temperature 380-420 ℃/0.5-3 h) + cold rolling (cold rolling deformation 30-60%); (5) carrying out high-temperature short-time solution treatment (540-575 ℃/1-10min), and then quenching and cooling the alloy sample subjected to solution treatment to room temperature from the solution treatment temperature at a cooling rate of more than 200 ℃/s; (6) transferring the quenched sample into an aging furnace within 1.5min for cooling and pre-aging treatment (the temperature is lower than 90 ℃, the time is longer than 10h, and the cooling rate is 3-6 ℃/h). Based on the regulation and control of the hot working process, the developed pre-aged Al-Mg-Si-Cu-Zn alloy plate can be ensured to have excellent stamping forming performance. The specific implementation mode is as follows:

comparative example 1

The alloy 1# is implemented by adopting the following intermediate frequency induction melting and casting modes, firstly, pure aluminum is completely added into a crucible and melted, the temperature is controlled to be 780-880 ℃, then Al-20wt% of Fe, Al-10wt% of Mn, Al-10wt% of Cr and Al-10wt% of Ti intermediate alloy are respectively added, after the pure aluminum is melted, Al-50wt% of Cu and Al-20wt% of Si and other intermediate alloys are respectively added, then the melt is stirred for 5min at high power, then the temperature is controlled to be higher than 720 ℃, pure Zn and pure Mg are respectively added, during the adding, the pure aluminum is respectively pressed into the bottom of the melt by a graphite bell jar, after the pure aluminum is completely melted, the bell jar is taken out, the power of an intermediate frequency induction furnace is regulated to ensure that the temperature of the alloy melt is stabilized again at 740 ℃, then slag is removed, and a; then, when the temperature of the melt is reduced to about 720 ℃, adding Al-5wt% Ti-1wt% B grain refiner, properly stirring, finally, preserving the temperature for 10min, casting the melt into a steel die with water cooling at the periphery, and controlling the cooling rate to be more than 50 ℃/min; then carrying out two-stage homogenization treatment on the mixture, wherein the treatment process comprises the following steps: heating to 475 ℃ at the speed of 30 ℃/h, preserving heat for 3h, continuing heating to 555 ℃ at the speed of 30 ℃/h, preserving heat for 30h, and then cooling to 100 ℃ along with the furnace at the cooling speed of 30 ℃/h, and taking out a sample; after homogenization, cutting the head and milling the cast ingot, reheating to 490-560 ℃ for hot rolling (pass reduction is 4% -30%, total deformation of hot rolling is 70-96%, and final rolling temperature is lower than 300 ℃ to obtain a hot rolled plate, and performing unidirectional rolling); then carrying out cold rolling deformation on the steel plate (the deformation is 35-55%, and the pass reduction is 10-35%); then, carrying out intermediate annealing on the cold-rolled sheet, raising the temperature to 390-410 ℃ at a temperature-raising rate of 20-200 ℃/min, carrying out annealing treatment for 0.5-2 h, and then directly taking out for air cooling; then carrying out secondary cold rolling on the steel plate, wherein the deformation is 35-55%, and the pass reduction is 10-35%; then directly cutting a sample on the cold-rolled sheet, and putting the sample in a thermal treatment furnace at 545-565 ℃ for solid solution treatment for 1-6 min, wherein the temperature rise rate of the sample is more than 100 ℃/s; then cooling the alloy sample after the solution treatment from the solution treatment temperature to room temperature at a cooling rate of more than 200 ℃/s; and transferring the quenched sample into a heat treatment furnace within 1.5min for cooling and pre-aging treatment (the temperature is lower than 90 ℃, the time is longer than 10h, and the cooling rate is 3-6 ℃/h), and finally, measuring the mechanical properties of the pre-aged alloy plate and the bending properties along the rolling direction (r/t is 0.5). The mechanical properties of the pre-aged alloy are shown in Table 1, the SEM microstructure of the pre-aged alloy No. 1 is shown in FIG. 2, and the edge bending properties of the pre-aged alloy in three directions of 0 degrees, 45 degrees and 90 degrees are shown in FIG. 3.

Example 1

The alloy 1# is implemented by adopting the following intermediate frequency induction melting and casting modes, firstly, pure aluminum is completely added into a crucible and melted, the temperature is controlled to be 780-880 ℃, then Al-20wt% of Fe, Al-10wt% of Mn, Al-10wt% of Cr and Al-10wt% of Ti intermediate alloy are respectively added, after the pure aluminum is melted, Al-50wt% of Cu and Al-20wt% of Si and other intermediate alloys are respectively added, then the melt is stirred for 5min at high power, then the temperature is controlled to be higher than 720 ℃, pure Zn and pure Mg are respectively added, during the adding, the pure aluminum is respectively pressed into the bottom of the melt by a graphite bell jar, after the pure aluminum is completely melted, the bell jar is taken out, the power of an intermediate frequency induction furnace is regulated to ensure that the temperature of the alloy melt is stabilized again at 740 ℃, then slag is removed, and a; then, when the temperature of the melt is reduced to about 720 ℃, adding Al-5wt% Ti-1wt% B grain refiner, properly stirring, finally, preserving the temperature for 10min, casting the melt into a steel die with water cooling at the periphery, and controlling the cooling rate to be more than 50 ℃/min; the ingot was then subjected to the following thermal processing treatment: (1) according to the ingot casting speed, carrying out short-time low-temperature tissue stability treatment on the ingot, wherein the short-time low-temperature treatment process is 420-500 ℃/0.5-3 h, and the heating rate is 10-45 ℃/h; (2) taking the short-time heating cast ingot out of the heating furnace, and directly carrying out hot rolling (the initial rolling temperature is 410-475 ℃, the final rolling temperature is more than 310 ℃, the pass reduction is 10-18%, the rolling deformation is 65-95%, and the deformation mode is unidirectional rolling); (3) the distribution state of a primary iron-rich phase and solute elements of the alloy is regulated and controlled by double-stage heat treatment (the first stage is 470-490 ℃/1-10 h, the second stage is 530-565 ℃/7-15 h, the heating rate is 10-40 ℃/h, and the cooling rate is more than 30 ℃/h); (4) hot rolling (deformation 70%, initial rolling temperature: 420-550 ℃) + cold rolling (deformation: 35-60%) + intermediate annealing (annealing temperature: 385-415 ℃/0.5-2.5 h) + cold rolling (cold rolling deformation: 35-60%); (5) the specific process of the high-temperature short-time solid solution treatment comprises the following steps: 545-565 ℃/1-6 min, wherein the heating rate is more than 100 ℃/s, and then the alloy sample after solution treatment is quenched and cooled to room temperature from the solution treatment temperature at the cooling rate of more than 200 ℃/s; (6) transferring the quenched sample into an aging furnace within 1.5min for cooling and pre-aging treatment, wherein the treatment temperature is as follows: below 85 ℃, time: and (3) the temperature reduction rate is 3-5 ℃/h, and finally the bending performance (r/t is 0.5) and the tensile performance of the pre-aged alloy plate are measured along three directions of 0 degree, 45 degrees and 90 degrees. The SEM structure of the pre-aged alloy is shown in FIG. 4, the appearance of the outer surface after bending is shown in FIG. 5, and the tensile properties are shown in Table 1.

Example 2

The alloy 1# is implemented by adopting the following intermediate frequency induction melting and casting modes, firstly, pure aluminum is completely added into a crucible and melted, the temperature is controlled to be 780-880 ℃, then Al-20wt% of Fe, Al-10wt% of Mn, Al-10wt% of Cr and Al-10wt% of Ti intermediate alloy are respectively added, after the pure aluminum is melted, Al-50wt% of Cu and Al-20wt% of Si and other intermediate alloys are respectively added, then the melt is stirred for 5min at high power, then the temperature is controlled to be higher than 720 ℃, pure Zn and pure Mg are respectively added, during the adding, the pure aluminum is respectively pressed into the bottom of the melt by a graphite bell jar, after the pure aluminum is completely melted, the bell jar is taken out, the power of an intermediate frequency induction furnace is regulated to ensure that the temperature of the alloy melt is stabilized again at 740 ℃, then slag is removed, and a; then, when the temperature of the melt is reduced to about 720 ℃, adding Al-5wt% Ti-1wt% B grain refiner, properly stirring, finally, preserving the temperature for 10min, casting the melt into a steel die with water cooling at the periphery, and controlling the cooling rate to be more than 50 ℃/min; the ingot was then subjected to the following thermal processing treatment: (1) according to the ingot casting speed, carrying out short-time low-temperature tissue stability treatment on the ingot, wherein the short-time low-temperature treatment process is 420-500 ℃/0.5-3 h, and the heating rate is 10-45 ℃/h; (2) taking the short-time heating cast ingot out of the heating furnace, and directly carrying out hot rolling (the initial rolling temperature is 410-475 ℃, the final rolling temperature is more than 310 ℃, the pass reduction is 10-18%, the rolling deformation is 65-95%, and the deformation mode is unidirectional rolling); (3) the distribution state of a primary iron-rich phase and solute elements of the alloy is regulated and controlled by double-stage heat treatment (the first stage is 470-490 ℃/1-10 h, the second stage is 530-565 ℃/7-15 h, the heating rate is 10-40 ℃/h, and the cooling rate is more than 30 ℃/h); (4) hot rolling (deformation 0%, i.e., no hot rolling) + cold rolling (deformation: 35-60%) + intermediate annealing (annealing temperature: 385-415 ℃/0.5-2.5 h) + cold rolling (cold rolling deformation: 35-60%); (5) the specific process of the high-temperature short-time solid solution treatment comprises the following steps: 545-565 ℃/1-6 min, wherein the heating rate is more than 100 ℃/s, and then the alloy sample after solution treatment is quenched and cooled to room temperature from the solution treatment temperature at the cooling rate of more than 200 ℃/s; (6) transferring the quenched sample into an aging furnace within 1.5min for cooling and pre-aging treatment, wherein the treatment temperature is as follows: below 85 ℃, time: and (3) the temperature reduction rate is 3-5 ℃/h, and finally the bending performance (r/t is 0.5) and the tensile performance of the pre-aged alloy plate are measured along three directions of 0 degree, 45 degrees and 90 degrees. The SEM structure of the pre-aged alloy is shown in FIG. 6, the appearance of the outer surface after bending is shown in FIG. 7, and the tensile properties are shown in Table 1.

Example 3

The alloy 1# is implemented by adopting the following intermediate frequency induction melting and casting modes, firstly, pure aluminum is completely added into a crucible and melted, the temperature is controlled to be 780-880 ℃, then Al-20wt% of Fe, Al-10wt% of Mn, Al-10wt% of Cr and Al-10wt% of Ti intermediate alloy are respectively added, after the pure aluminum is melted, Al-50wt% of Cu and Al-20wt% of Si and other intermediate alloys are respectively added, then the melt is stirred for 5min at high power, then the temperature is controlled to be higher than 720 ℃, pure Zn and pure Mg are respectively added, during the adding, the pure aluminum is respectively pressed into the bottom of the melt by a graphite bell jar, after the pure aluminum is completely melted, the bell jar is taken out, the power of an intermediate frequency induction furnace is regulated to ensure that the temperature of the alloy melt is stabilized again at 740 ℃, then slag is removed, and a; then, when the temperature of the melt is reduced to about 720 ℃, adding Al-5wt% Ti-1wt% B grain refiner, properly stirring, finally, preserving the temperature for 10min, casting the melt into a steel die with water cooling at the periphery, and controlling the cooling rate to be more than 50 ℃/min; the ingot was then subjected to the following thermal processing treatment: (1) according to the ingot casting speed, carrying out short-time low-temperature tissue stability treatment on the ingot, wherein the short-time low-temperature treatment process is 420-500 ℃/0.5-3 h, and the heating rate is 10-45 ℃/h; (2) taking the short-time heating cast ingot out of the heating furnace, and directly carrying out hot rolling (the initial rolling temperature is 410-475 ℃, the final rolling temperature is more than 310 ℃, the pass reduction is 10-18%, the rolling deformation is 65-95%, and the deformation mode is unidirectional rolling); (3) the distribution state of a primary iron-rich phase and solute elements of the alloy is regulated and controlled through double-stage heat treatment (the first stage is 470-490 ℃/1-10 h, the second stage is 530-565 ℃/7-15 h, the heating rate is 10-40 ℃/h, and the cooling rate is more than 50 ℃/h); (4) hot rolling (deformation 70%, initial rolling temperature: 420-550 ℃) + cold rolling (deformation: 35-60%) + intermediate annealing (annealing temperature: 385-415 ℃/0.5-2.5 h) + cold rolling (cold rolling deformation: 35-60%); (5) the specific process of the high-temperature short-time solid solution treatment comprises the following steps: 545-565 ℃/1-6 min, wherein the heating rate is more than 100 ℃/s, and then the alloy sample after solution treatment is quenched and cooled to room temperature from the solution treatment temperature at the cooling rate of more than 200 ℃/s; (6) transferring the quenched sample into an aging furnace within 1.5min for cooling and pre-aging treatment, wherein the treatment temperature is as follows: below 85 ℃, time: and (3) the temperature reduction rate is 3-5 ℃/h, and finally the bending performance (r/t is 0.5) and the tensile performance of the pre-aged alloy plate are measured along three directions of 0 degree, 45 degrees and 90 degrees. The SEM structure of the pre-aged alloy is shown in FIG. 8, the appearance of the outer surface after bending is shown in FIG. 9, and the tensile properties are shown in Table 1.

TABLE 1 summary of tensile properties data for pre-aged alloy sheets treated by different hot working processes

In recent years, the process of automobile lightweight is gradually accelerated, the comprehensive performance of the aluminum alloy material for the automobile body outer plate is greatly improved, and particularly, after solute element Zn is further added on the basis of the traditional Al-Mg-Si-Cu alloy and is assisted with the regulation and control of a proper hot working process, the baking varnish hardening increment is greatly improved and can reach more than 160MPa at most. However, the stamping forming performance, the crimping performance and the like of the alloy are still required to be further improved for wide application, and the production cost of the alloy plate is also required to be greatly reduced. Therefore, there is an urgent need to develop a short-process preparation method suitable for the aluminum alloy sheet material and capable of ensuring that the stamping forming performance of the aluminum alloy sheet material is greatly improved. In order to further reduce the production cost of the series of alloys, it is necessary to melt and cast the series of alloys by fully utilizing recycled aluminum. However, the recovered aluminum generally contains Fe as an impurity element, and the Fe is easily present to generate dendritic, rod-like or coarse granular iron-rich phases in the cast alloy. Although these phases may be broken in the subsequent hot working process, coarse iron-rich phase particles which are not broken completely are inevitably distributed in the final alloy matrix, and micro cracks remain in the matrix, and the distribution is not uniform (as shown in fig. 2), which further affects the plasticity, formability, and burring performance of the alloy. Although the alloy plate prepared in comparative example 1 has less severe cracking after bending (as shown in fig. 3) and the average r value of 0.6122 and lower Δ r (as shown in table 1), the properties are mainly attributed to the refinement of the alloy grain structure, the weakening of the texture and the like. Therefore, if a new hot working process can be developed to further regulate the size, morphology, distribution and the like of the primary iron-rich phase and further improve the alloy structure, the stamping forming performance of the alloy can be certainly improved. The invention makes full use of the inevitable component segregation generated during the casting of aluminum alloy, and adopts a short-flow thermal processing route without long-time high-temperature homogenization heat treatment, namely, firstly, the alloy ingot is subjected to short-time low-temperature structure stability treatment to eliminate low-melting-point precipitated phases, then directly carrying out hot rolling deformation on the alloy without high-temperature long-time homogenization treatment, then carrying out short-time heat treatment on the alloy to regulate and control the distribution condition of solute elements and other original phases in an alloy matrix, then carrying out hot rolling or directly carrying out cold rolling, intermediate annealing and cold rolling, finally carrying out solid solution and pre-aging treatment on the cold-rolled alloy plate, wherein the pre-aged alloy plate can present the characteristics of an isomeric structure, such as the grain size with double model distribution characteristic, the multi-scale precipitation phase distribution characteristic, and the microstructure characteristic that the micro-area in the alloy matrix has soft area and hard area which are alternately distributed. Once the pre-aged alloy has an isomeric structure, the corresponding bending performance, stamping forming performance and the like of the pre-aged alloy can be greatly improved. From the alloy structure and properties obtained in example 1, it can be seen that the degree of homogeneity of the primary phase distribution in the pre-aged alloy matrix is greatly improved (as shown in fig. 4), the average plastic strain ratio r value characterizing the press-forming properties is also improved from 0.6122 in comparative example 1 to 0.670, and the anisotropy index Δ r is still low (as shown in table 1). In addition, the pre-aged alloy plate has smooth outer surface after bending deformation along three directions of 0 degree, 45 degrees and 90 degrees, and has no phenomena of cracks or wrinkles and the like (as shown in figure 5), and the bending performance of the alloy plate is greatly improved. On the basis of the above, by further improving the hot working process, particularly the hot rolling deformation amount after the short-term low-temperature structure stability treatment, it was found from the results of example 2 that the original phase distribution state in the pre-aged alloy matrix was further improved (as shown in FIG. 6). The cast ecological original phases can be broken to a greater extent mainly due to the increase of the hot rolling deformation, and then short-time heat treatment is carried out, so that the phases are easy to fuse to form spheres, coarsening and growth are not easy to occur in the heat treatment process, and finally the fact that the size of the original phases is proper and the distribution uniformity is improved is observed. In addition, it is more worth noting that the distribution condition of solute elements in the same region can be influenced by the change of the deformation, the increase of the hot rolling deformation is more beneficial to better regulating and controlling the isomeric characteristics of the solute elements in the micro-regions, and the isomeric distribution in the micro-regions of the solute elements can directly lead to the isomeric distribution characteristics of solute element clusters, GP regions and precipitation phases separated out from the pre-aged alloy, namely the isomeric structure characteristics of soft and hard alternation in the micro-regions of the alloy matrix. All these factors work together to make the alloy prepared in this example have more excellent stamping forming performance, the average r value can reach 0.714, and the pre-aged alloy sheet has very smooth outer surface after bending deformation along three directions of 0 degrees, 45 degrees and 90 degrees (as shown in figure 7). Therefore, the alloy can show excellent comprehensive performance after being regulated and controlled by a new hot working process, and the design and the utilization of the heterogeneous structure can really and greatly improve the stamping forming performance of the alloy.

On the basis, the Mg of a precipitation phase is considered to be precipitated during the hot working process₂Si, etc., which also adversely affect alloy structure and properties if not well regulated during hot working. In order to reduce the influence of these phases, in example 3, after the distribution of solute elements in the alloy matrix is regulated by short-time heat treatment after hot rolling deformation, the precipitation growth rate of the precipitation phase in the cooling process is reduced by increasing the cooling rate, so that the adverse effect is reduced. According to the structure and the performance of the alloy prepared in the embodiment 3, the comprehensive performance of the alloy plate prepared in the embodiment can be improved to a greater extent. As can be seen from fig. 8, the distribution of the primary phase is more uniform and the amount of the precipitated phase is significantly reduced. The average r value of the pre-aged alloy plate for representing the stamping forming performance is further improved to 0.720, and the delta r value is only 0.087 (shown in the table 1). Meanwhile, the alloy plate is very smooth in the outer surface after the bending deformation along the three directions of 0 degree, 45 degrees and 90 degrees (as shown in figure 9), and has excellent bending performance.

In summary, after the Al-Mg-Si-Cu-Zn alloy cast ingot is subjected to short-flow hot working process regulation and control, not only are the original phase size, shape and distribution in the alloy matrix remarkably improved, but also the segregation of solute elements during casting is fully utilized, the distribution state of the solute elements in micro areas is designed and regulated, firstly, the distribution in the micro areas is nonuniform, then, solute atom clusters, GP areas or precipitates with different concentrations are generated in aging micro areas, and the characteristics of the heterogeneous structure with soft and hard alternation in the micro areas are further realized, and finally, the stamping forming performance and the edge bending performance of the pre-aging alloy are greatly improved by utilizing the heterogeneous structure. In addition, the hot working process can improve the comprehensive performance of the alloy, greatly reduce the production cost of the alloy plate due to the omission of long-time high-temperature multi-stage homogenization treatment, and all the performance improvement and cost reduction have important promotion effect on the faster application of the alloy in the automobile light weight process. In addition, the method has certain guiding significance for the development, processing and application of the high-formability and high-strength aluminum alloy in other fields, and is worthy of paying attention to the method by automobile manufacturers and aluminum alloy processing enterprises, so that the method can be popularized and applied in the field as soon as possible.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (7)

1. A process control method for a high-formability aluminum alloy heterogeneous structure for an automobile is characterized in that the high-formability aluminum alloy for the automobile is an Al-Mg-Si-Cu-Zn alloy, and the method specifically comprises the following steps:

(1) preparing high-formability Al-Mg-Si-Cu-Zn alloy for automobiles, smelting the alloy by using medium-frequency induction under non-vacuum condition, casting the alloy in a water-cooled steel mold, and controlling the cooling rate to be more than 40 ℃/min so that the size of alloy crystal grains meets the subsequent regulation and control requirements, wherein the Al-Mg-Si-Cu alloy comprises the following chemical components in percentage by mass: 0.5 to 3.7wt% of Zn, 0.6 to 1.0wt% of Mg, 0.4 to 1.0wt% of Si, 0.1 to 0.4wt% of Cu, 0.1 to 0.7wt% of Fe, and Mn: 0.3-0.7 wt%, Cr <0.02wt%, Ti < 0.1wt%, B <0.01wt%, and the balance of Al;

(2) according to the casting speed of the cast ingot, carrying out short-time low-temperature structure stability treatment on the cast ingot;

(3) taking out the short-time heating cast ingot from the heating furnace, and directly carrying out hot rolling treatment, specifically: the initial rolling temperature: 410-478 ℃; the finishing temperature is as follows: the pass reduction is 10-20% above 300 ℃, and the rolling deformation is 60-99%;

(4) the two-stage heat treatment regulates and controls the distribution state of the primary iron-rich phase and solute elements of the alloy, and specifically comprises the following steps: the first stage is as follows: 440-490 ℃/1-12 h; the second stage is as follows: 520-575 ℃/3-15 h, the heating rate is 10-45 ℃/h, and the cooling rate is more than 30 ℃/h;

(5) hot rolling, cold rolling, intermediate annealing and cold rolling are sequentially carried out;

(6) carrying out high-temperature short-time solution treatment, and then quenching and cooling the alloy sample subjected to solution treatment from the solution treatment temperature to room temperature;

(7) transferring the quenched sample into an aging furnace within 1.5min for cooling and pre-aging treatment.

2. The process control method for the automobile high-formability aluminum alloy heterogeneous structure according to claim 1, wherein in the step (1), the alloy smelting process by medium-frequency induction under non-vacuum condition comprises the following steps: firstly, completely adding recycled aluminum or common aluminum into a crucible and melting, controlling the temperature to be 780-880 ℃, then respectively adding Al-20wt% of Fe, Al-10wt% of Mn, Al-10wt% of Cr and Al-10wt% of Ti intermediate alloy, respectively adding Al-50wt% of Cu and Al-20wt% of Si intermediate alloy after melting, then stirring the melt for 5min at high power, then controlling the temperature to be above 720 ℃, respectively adding pure Zn and pure Mg, respectively pressing the melt into the bottom of the melt by using a graphite bell jar during adding, taking out the bell jar after the melt is completely melted, regulating and controlling the power of a medium-frequency induction furnace to enable the temperature of the alloy melt to be stabilized at 740 ℃, slagging off, and adding a refining agent for degassing and refining; then, when the temperature of the melt is reduced to 720 ℃, Al-5wt% Ti-1wt% B grain refiner is added and properly stirred, and finally, after the temperature is kept at 720 ℃ for 10min, the melt is cast into a steel die with water cooling at the periphery, and the cooling rate is controlled to be more than 50 ℃/min.

3. The process control method for the automobile high-formability aluminum alloy isomeric structure is characterized in that in the step (2), the short-time low-temperature structure stabilizing process is 420-500 ℃/0.5-3 h, and the heating rate is 10-45 ℃/h.

4. The method for regulating and controlling the process of the automobile high-formability aluminum alloy heterogeneous structure according to claim 1, wherein the step (5) comprises the following specific steps of hot rolling, cold rolling, intermediate annealing and cold rolling: hot rolling treatment: the deformation is 0-80%, and the initial rolling temperature is 410-560 ℃; cold rolling treatment: the deformation is 30-60%; intermediate annealing: the annealing temperature is 380-; cold rolling treatment: the cold rolling deformation is 30-60%.

5. The process control method for the automobile high-formability aluminum alloy heterogeneous structure according to claim 1, wherein in the step (6), the high-temperature short-time solution treatment specifically comprises: 540-.

6. The process control method for the automobile high-formability aluminum alloy heterogeneous structure according to claim 1, wherein in the step (7), the cooling pre-aging treatment specifically comprises: the temperature is lower than 90 ℃, the time is longer than 10h, and the cooling rate is 3-6 ℃/h.

7. A highly formable aluminum alloy for automobiles, characterized in that the highly formable aluminum alloy for automobiles is an Al-Mg-Si-Cu-Zn system alloy, the Al-Mg-Si-Cu-Zn system alloy is production-regulated by the process regulating method according to any one of claims 1 to 6,

the Al-Mg-Si-Cu alloy comprises the following chemical components in percentage by mass: 0.5 to 3.7wt% of Zn, 0.6 to 1.0wt% of Mg, 0.4 to 1.0wt% of Si, 0.1 to 0.4wt% of Cu, 0.1 to 0.7wt% of Fe, and Mn: 0.3-0.7 wt%, Cr <0.02wt%, Ti < 0.1wt%, B <0.01wt%, and the balance of Al.

Images