Method for reducing anisotropy of aluminum alloy integrally-extruded wallboard

Abstract

The invention belongs to the technical field of heat treatment processes of high-performance aluminum alloy materials, and discloses a method for reducing anisotropy of an integrally extruded aluminum alloy wallboard, which comprises the following steps of: 1, extruding aluminum alloy on extrusion equipment; secondly, the extruded wall plate is cooled to the room temperature on line on extrusion equipment after being extruded; 3, the extruded wallboard cooled to the room temperature is subjected to two times of annealing treatment, and the first-time annealing temperature is higher than the second-time annealing temperature; and fourthly, the extruded wallboard obtained after heat treatment is unfolded and corrected, and the extruded wallboard is treated to be in the final state. According to the method, part of deformation energy storage is reserved through on-line rapid cooling of the extruded wallboard, then the annealing process combining high temperature and medium temperature is adopted, anisotropy caused by the extrusion effect is eliminated through a recrystallized structure, and therefore the aluminum alloy overall extruded wallboard with the low anisotropy is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment process of high-performance aluminum alloy materials, and in particular relates to a method for reducing the anisotropy of an aluminum alloy integral extruded wall panel. Background Art

[0002] With the rapid development of my country's aviation, aerospace and shipbuilding fields, higher requirements have been put forward for lightweight, high reliability and low manufacturing cost of the fuselage. Using aluminum alloy integral extruded wall panels to replace traditional thick plate machining, thin plate + profile riveting or welding has become an important measure to improve material utilization, increase structural reliability and reduce structural weight.

[0003] With the continuous commissioning of large-scale domestic extrusion equipment, the country has been able to prepare 5-series, 7-series and 2-series wide integral extruded wall panels, with the maximum width reaching 1800mm, and has formed corresponding technologies such as extrusion, annealing, flattening and heat treatment. Since the extrusion resistance of ribbed wall panels is relatively large, in order to avoid overburning caused by extrusion temperature rise, a slightly lower extrusion temperature is usually adopted during the extrusion of the integral wall panels, and then natural air cooling is adopted during the extrusion process. In order to facilitate subsequent expansion and correction, a medium-temperature single-stage annealing process is often adopted to eliminate work hardening behavior, reduce strength and increase plasticity. Medium-temperature single-stage annealing basically does not cause much change in the macrostructure of the extruded wall panels, and the "extrusion effect" during extrusion will be retained, which leads to more serious anisotropy in the prepared wall panels. The strength, elongation and fracture toughness in the extrusion direction are much higher than those in the vertical extrusion direction. In actual application, the performance of the extruded wall panels is restricted, and its weight reduction benefits and safety margins are greatly reduced. Summary of the invention

[0004] Purpose of the invention: In view of the problem of significant anisotropy of existing aluminum alloy integral extruded wall panels, a method for reducing the anisotropy of aluminum alloy integral extruded wall panels is invented. Part of the deformation energy storage is retained by online rapid cooling of the extruded wall panels, and then a high temperature + medium temperature combined annealing process is adopted to utilize the recrystallized structure to eliminate the anisotropy caused by the extrusion effect, thereby obtaining aluminum alloy integral extruded wall panels with low anisotropy.

[0005] Technical Solution

[0006] A method for reducing the anisotropy of an aluminum alloy integral extruded siding, comprising the following steps:

[0007] 1. Extruding the aluminum alloy on the extrusion equipment;

[0008] 2. Cooling the extruded siding to room temperature online on the extrusion equipment;

[0009] 3. After cooling to room temperature, the extruded wall panel is subjected to two annealing treatments, wherein the first annealing temperature is higher than the second annealing temperature;

[0010] Fourth, unfold and correct the heat-treated extruded wall panels to the final state.

[0011] Furthermore, in step 2, the extruded wallboard is sprayed with room temperature water online at the end of the cooling method, and passes through a cooling water tank with room temperature circulating water. The extruded wallboard is quickly cooled to room temperature by rapid cooling, avoiding air cooling after extrusion, which causes an "annealing" effect on the extruded wallboard due to the slow speed, thereby reducing the deformation energy storage caused by extrusion.

[0012] Furthermore, in step three, the first annealing process is to heat the metal to 475°C to 530°C and then put it into the furnace, and keep the temperature for 15 to 60 minutes after the metal reaches the temperature. Compared with the traditional annealing method of heating with the furnace, the high-temperature heating method specified in the present invention can avoid the "annealing" effect produced by the slow heating of the furnace to the greatest extent. This effect can eliminate the deformation energy storage during extrusion, inhibit the occurrence of recrystallization, and keep the structure still strong in orientation. After the high-temperature heating method of the present invention is adopted, the extruded wall panel can quickly reach the temperature at which recrystallization can occur, so that relatively sufficient recrystallization occurs within the specified time range. After a large number of experimental statistics, a holding time of 15 minutes to 60 minutes can not only ensure the occurrence of recrystallization of the extruded wall panel, but also avoid the high-temperature holding time being too long, which induces local grain growth.

[0013] Furthermore, in step three, after the first annealing, the furnace temperature is quickly reduced to 360℃~440℃, kept warm for 2~4h, slowly cooled to 150℃~200℃ with the furnace, and air-cooled to room temperature after being taken out of the furnace. The rapid cooling to 360℃~440℃ adopted in this step avoids the local grain growth caused by slow cooling. In addition, keeping warm at 360℃~440℃ for 2~4h can fully eliminate the work hardening supply of the extruded wall panel, and slow cooling with the furnace can make the precipitation phase in the aluminum alloy slowly precipitate and grow under equilibrium state, further reduce the strength of the extruded wall panel, and avoid the "quenching" effect caused by rapid cooling after being taken out of the furnace. According to a large number of experimental statistical results, when the furnace is cooled to the range of 150℃~200℃, the "quenching" effect of the aluminum alloy is already very weak and will not have much impact on the performance. Therefore, in order to improve production efficiency, it is air-cooled after being taken out of the furnace.

[0014] Furthermore, the method is applicable to 2 series, 5 series and 7 series aluminum alloys. The above three alloys are high-performance aluminum alloy materials with a wide range of applications, and integral wall panels are the main development trend of the above three alloys. Therefore, the present invention is mainly aimed at integral wall panels of the above three alloy systems.

[0015] Further, in step 1, for the 2-series aluminum alloy, the extrusion temperature range is 360° C. to 390° C. In view of the hot process plasticity characteristics of the 2-series aluminum alloy, the present invention has shown through a large number of experimental studies that the 2-series aluminum alloy has good hot process plasticity at a temperature of 360° C. to 390° C., and that the dislocation will not be completely restored during the extrusion process, retaining a certain amount of deformation energy storage, thereby providing a guarantee for the formation of a recrystallized structure during subsequent high temperature annealing.

[0016] Further, in step 1, for the 5-series aluminum alloy, the extrusion temperature range is 420° C. to 460° C. In view of the hot process plasticity characteristics of the 5-series aluminum alloy, the present invention has shown through a large number of experimental studies that the 2-series aluminum alloy has good hot process plasticity at a temperature of 420° C. to 460° C., and can also prevent dislocations from being completely restored during the extrusion process, retaining a certain amount of deformation energy storage, thereby providing a guarantee for the formation of a recrystallized structure during subsequent high-temperature annealing.

[0017] Further, in step 1, for the 7 series aluminum alloy, the extrusion temperature range is 320° C. to 350° C. In view of the hot process plasticity characteristics of the 7 series aluminum alloy, the present invention has shown through a large number of experimental studies that the 2 series aluminum alloy has good hot process plasticity at a temperature of 320° C. to 350° C., and that the dislocation will not be completely restored during the extrusion process, retaining a certain amount of deformation energy storage, thereby providing a guarantee for the formation of a recrystallized structure during subsequent high temperature annealing.

[0018] In summary, the beneficial effects of the present invention are as follows:

[0019] 1. Good results can be obtained by making appropriate adjustments to existing equipment and production process, which is convenient for industrial implementation;

[0020] 2. It can greatly improve the anisotropy of the aluminum alloy integral extruded siding. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The high-magnification microstructure images of the longitudinal and cross sections of 7A85 extruded sidings under different treatment processes;

[0022] (a) The longitudinal section of the wall panel is prepared by the present invention; (b) The cross section of the wall panel is prepared by the present invention; (c) The longitudinal section of the wall panel is prepared by the traditional process; (d) The cross section of the wall panel is prepared by the traditional process. DETAILED DESCRIPTION

[0023] A method for reducing the anisotropy of an integral extruded aluminum alloy siding, wherein a suitable temperature is adopted during the extrusion process and the extruded siding is rapidly cooled to retain reasonable deformation energy storage; a high temperature + low temperature combined graded annealing method is then adopted to promote rapid recrystallization in the extruded siding, thereby eliminating the strong deformation texture during extrusion and reducing the anisotropy of the siding. The specific steps are:

[0024] 1.1 Extruding 2 series, 5 series and 7 series aluminum alloy extruded panels on an extrusion device, wherein the extrusion temperature range of the 2 series aluminum alloy is 360°C to 390°C, the extrusion temperature range of the 5 series aluminum alloy is 420°C to 460°C, and the extrusion temperature range of the 7 series aluminum alloy is 320°C to 350°C;

[0025] 1.2 Cool the 2 series, 5 series and 7 series aluminum alloy extruded panels to room temperature on the extrusion equipment online, by spraying room temperature water online or passing the extruded panels through a water tank with room temperature circulating water for cooling;

[0026] 1.3 Put the extruded wall panel after the treatment in step 1.2 into an air circulation furnace or a salt bath furnace for annealing. The annealing process is to put the metal into the furnace at a temperature of 475℃~530℃, and then keep the temperature for 15~60min after the metal reaches the temperature. Then quickly reduce the furnace temperature to 360℃~440℃, keep the temperature for 2~4h, slowly cool it to 150℃~200℃ with the furnace, and then air cool it to room temperature after it comes out of the furnace.

[0027] 1.4 After the extruded wall panels processed in step 1.3 are unfolded and shaped, they are processed to the final required heat treatment state.

[0028] Embodiment 1

[0029] The method for reducing the anisotropy of the aluminum alloy integral extruded wall panel of the present invention is used to prepare the 7A85 aluminum alloy integral extruded wall panel, the integral wall panel substrate thickness is 5mm, the rib height is 60mm, and the rib spacing is 240mm. The integral wall panel is extruded on a 15,000-ton double-action extrusion equipment at an extrusion temperature of 330°C to 340°C, and a cooling water tank with circulating water is installed at the extrusion outlet. The cooling water temperature is 23°C to 33°C. The extruded integral wall panel is quickly cooled to room temperature after passing through the cooling water tank.

[0030] After cooling, the 7A85 integral wall panel is placed in an air circulation furnace for heating at a furnace gas temperature of 470°C. After keeping warm for 30 minutes, the furnace door is opened and the temperature is quickly lowered to 380°C. The furnace door is then closed and kept warm for 2 hours. The furnace is slowly cooled (cooling rate of 20°C / h) to 160°C and then air-cooled to room temperature.

[0031] The 7A85 siding treated by graded annealing was unfolded and flattened, and then solution quenched + pre-stretched + artificially aged to T74511 state. The tensile properties in different directions were measured and compared with the siding treated by air cooling + 380℃ single-stage annealing and treated to T74511 during extrusion. The results are shown in Table 1. The high-magnification microstructure morphology of the two sidings is shown in Table 1. Figure 1It can be found that the anisotropy of the 7A85-T74511 integral wallboard prepared by the present invention is significantly reduced, and the performance uniformity is greatly improved. The present invention forms a sufficient recrystallized structure and eliminates the extrusion effect.

[0032] Table 1 Performance test results of 7A85-T74511 integral wall panels prepared by different methods

[0033]

[0034]

[0035] Embodiment 2

[0036] The method for reducing the anisotropy of aluminum alloy integral extruded wall panels of the present invention is used to prepare 5 series aluminum alloy integral extruded wall panels, the alloy composition is Mg6.1%, Mn 0.85%, Zn 0.15%, Zr 0.1%, Ti 0.03%, Fe0.15%, Si 0.10, and the rest is Al.

[0037] The thickness of the integral wall panel is 6mm, the rib height is 100mm, and the rib spacing is 200mm. An automatic spray cooling device is installed at the extrusion outlet of the 15,000-ton double-action extrusion equipment, and the extruded integral wall panel is quickly cooled to room temperature through the spray device.

[0038] After cooling, the 5 series integral wall panels are placed in an air circulation furnace for heating at a furnace gas temperature of 520°C. After keeping warm for 40 minutes, the furnace door is opened and the temperature is quickly lowered to 360°C. The furnace door is then closed and kept warm for 1 hour. The furnace is slowly cooled (cooling rate of 50°C / h) to 200°C and then air-cooled to room temperature after being taken out of the furnace.

[0039] The 5 series siding treated by graded annealing was unfolded and flattened, and then pre-stretched by 5% deformation + stabilization treatment + 1% deformation pre-stretching was performed to the H116 state, and the tensile properties in different directions were measured, and compared with the siding treated by air cooling + 360°C single-stage annealing and treated to the H116 state during extrusion. The results are shown in Table 2. It can be found that the anisotropy of the 5 series H116 integral siding prepared by the present invention is significantly reduced, and the performance uniformity is greatly improved.

[0040] Table 2 Performance test results of H116 integral wall panels prepared by different methods

[0041]

[0042]

[0043] Four metallographic photographs respectively show the longitudinal section and cross-sectional high-magnification structure of the 7A85 extruded wall panel prepared by the method of the present invention (Figure a, Figure b) and the longitudinal section and cross-sectional high-magnification structure of the 7A85 extruded wall panel prepared by the traditional method (Figure c, Figure d). From the perspective of high-magnification structure, the high-magnification structure of the extruded wall panel prepared by the present invention is nearly equiaxed grains that have undergone full recrystallization in both longitudinal and cross-sectional directions, the aspect ratio of the grains is close to 1.5:1, and the grain morphology in the two directions is not much different, resulting in basically no anisotropy; the extruded wall panel prepared by the traditional process is a typical extruded fiber strip structure, the aspect ratio of the grains is close to 80:1 in the longitudinal section and close to 40:1 in the cross-sectional area, with a strong extrusion texture, resulting in large anisotropy.

Claims

1. A method for reducing the anisotropy of an aluminum alloy integral extruded wall panel, characterized in that: Here are the steps:

1. Extruding the aluminum alloy on the extrusion equipment; 2. Cooling the extruded wall panel to room temperature online on the extrusion equipment; 3. After cooling to room temperature, the extruded wall panel is subjected to two annealing treatments, wherein the first annealing temperature is higher than the second annealing temperature; Fourth, unfold and correct the heat-treated extruded wall panels to the final state.

2. The method according to claim 1, characterized in that: In step 2, the cooling method is to spray room temperature water online and pass the extruded wall panel through a cooling water tank with room temperature circulating water.

3. The method according to claim 1, characterized in that: In step three, the first annealing process is to heat the metal to 475°C to 530°C and then put it into the furnace. After the metal reaches the temperature, it is kept warm for 15 to 60 minutes.

4. The method according to claim 1, characterized in that: In step three, after the first annealing, the furnace temperature is quickly reduced to 360°C-440°C, kept at this temperature for 2-4 hours, slowly cooled to 150°C-200°C along with the furnace, and air-cooled to room temperature after being taken out of the furnace.

5. The method according to claim 1, characterized in that: The method is applicable to 2 series, 5 series and 7 series aluminum alloys.

6. The method according to claim 5, characterized in that: In step 1, for 2 series aluminum alloy, the extrusion temperature is 360°C to 390°C.

7. The method according to claim 5, characterized in that: In step 1, for 5 series aluminum alloy, the extrusion temperature ranges from 420°C to 460°C.

8. The method according to claim 5, characterized in that: In step 1, for 7 series aluminum alloy, the extrusion temperature range is 320°C to 350°C.

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