KR100666771B1 - Method for reducing anisotropy of hemming of Al-Mg-Si alloy sheet - Google Patents

Abstract

The present invention relates to a method for inhibiting hemming anisotropy of an aluminum-magnesium-silicon alloy sheet, and after cold rolling of the AA6022 aluminum-magnesium-silicon alloy sheet, at a temperature of 180 ° C to 210 ° C for 3 minutes to 30 minutes before the T4 heat treatment step. By performing recovery heat treatment for the following time, the volume fraction of the cubic crystal orientation after the final T4 heat treatment is less than 50% compared to the existing method, and the cold rolled texture remains at a volume fraction of 8.8 or more, deteriorating the plastic anisotropy of the final production sheet It is intended to provide a method for inhibiting hemming anisotropy of an aluminum-magnesium-silicon alloy sheet which can be obtained, thereby enabling the effect of inhibiting hemming anisotropy during the hemming process.

Aluminum-Magnesium-Silicon Alloy, Hemming Anisotropy, Suppression Method

Description

Method for reducing anisotropy of hemming of Al-Mg-Si alloy sheet}             

1 is a {111} pole figure of an AA6022 sheet produced by the method for inhibiting hemming anisotropy of an aluminum-magnesium-silicon alloy sheet of the present invention,

Figure 2 is a micrograph showing the results of the T hemming molding (rolling direction / / hemming direction) test for AA6022 sheet specimens prepared by the method of inhibiting hemming anisotropy of the aluminum-magnesium-silicon alloy sheet of the present invention,

3 is a {111} pole figure of the AA6022 sheet produced by a conventional method,

Figure 4 is a micrograph showing the results of the T hemming molding (rolling / / hemming) test for the AA6022 sheet specimen prepared by a conventional method.

The present invention relates to a method for inhibiting hemming anisotropy of an aluminum-magnesium-silicon alloy sheet, and more particularly, a β-fiber aggregate structure developed during a cold rolling process by performing recovery heat treatment before T4 heat treatment after cold rolling, and then during T4 heat treatment. By restoring it from recrystallization (decreasing the recrystallization drive force), it is possible to prevent the cubic crystal texture from developing during T4 heat treatment to the maximum, thereby improving the hemming quality and yield while eliminating the planar anisotropy of the aluminum-magnesium-silicon alloy sheet. A method for inhibiting hemming anisotropy of an aluminum-magnesium-silicon alloy sheet.

One of the easiest ways to reduce the weight of the car is to reduce the weight of the body parts, and to reduce the weight from the part that does not significantly affect the driver's safety is less burdensome and effective for the designer or producer.

The material that is spotlighted to reduce the weight of the car body is AA6XXX aluminum-magnesium-silicon alloy plate, because the bake hardening property improves the strength after painting process to improve the strength by more than 20%. This is because it has an advantage in securing rigidity.

However, the AA6XXX aluminum-magnesium-silicon alloy sheet has a high planar anisotropy (plastic anisotropy) and a low average plastic deformation ratio, which is difficult to apply to automobiles due to the disadvantage of poor formability compared to the steel sheet.

This is because in the case of producing a face-centered cubic metal such as aluminum, the grains rotate in a specific orientation, whereby a strong texture is developed, resulting in plastic anisotropy.

The production process of aluminum body parts is divided into four processes: drawing, flanging, trimming, and hemming. Among them, the most frequent process of product defects is hemming> drawing> flanging> trimming.

In the drawing process, the material that is not deformed is molded. If the mold design and lubrication conditions are set well, the defect rate can be reduced to the maximum. However, in the hemming process, the sheet (accumulated plate) that accepts all the deformations of the previous stage is processed. Due to the nature of the process, a lot of defects in the hemming part are generated, and the overall defects increase.

The process that determines the failure of aluminum body parts is a hemming process, when hemming perpendicular to the rolling direction (rolling direction-hemming direction, L hemming), when hemming in parallel (rolling direction / / hemming direction, T hemming). A large number of defects may occur in the lateral direction of the general aluminum alloy because the plastic deformation ratio in the lateral direction is small, which means that grains having a large plastic strain ratio in the lateral direction should be developed during the manufacturing process.

Alternatively, it is necessary to control the texture of the aggregate so as to have a uniform plastic deformation ratio over the entire plate direction, because the plastic deformation ratio of the plate is directly related to the development of the texture.

In general, AA6022 plate is known to be suitable for automotive use because of its relatively good moldability and hardening ability.However, due to lack of elongation, surface quality in the form of leasing occurs during secondary molding such as hemming. have.

In addition, there is a disadvantage in that the quality of the T hemming decreases compared to the L hemming because there is a difference in the hemming performance according to the direction of the plate during the hemming process.

In the existing process, the design and mold manufacturing considering the plastic anisotropy of the plate were not made, and the heavier process was carried out by repeating the mold modification through trial and error, but in this case, the success rate was low and the manufacturing defect was many. There was a disadvantage that the manufacturing process is not stable.

In order to lower the defects in the hemming process, the mold surface development was sometimes changed in the previous drawing process, but the effect is not due to local draw shortage, which is a characteristic of aluminum. In order to overcome this problem, the design or design is often modified so that the deformation in the lateral direction does not occur, which may raise the problem of ineffective application of the aluminum sheet.

This is because the anisotropy, which is a characteristic of the aluminum sheet, is not taken into account.

Therefore, in the hemming molding of the AA 6022 sheet, a method for producing a sheet having no hemming anisotropy, that is, excellent in hemmability, has been continuously studied.

The present invention has been researched and developed in view of the above, and after cold rolling the AA6022 alloy plate, and subjected to a recovery heat treatment before T4 heat treatment, the β-fiber aggregate structure, which is a cold rolling texture, remains even after the heat treatment, It is an object of the present invention to provide a method for inhibiting hemming anisotropy of an aluminum-magnesium-silicon alloy sheet which suppresses the plastic anisotropy of the sheet by maximally suppressing the development of the cubic grain texture, which is a recrystallized texture of the aluminum alloy.

The present invention for achieving the above object is a method for producing an AA6022 aluminum-magnesium-silicon alloy sheet comprising a hot rolling, cold rolling, solution treatment (T4 heat treatment) and temper rolling process, the AA6022 alloy plate After the cold rolling step, before the T4 heat treatment step, a recovery heat treatment was performed for 3 minutes or more and less than 30 minutes in a section between 180 ° C. and 210 ° C. to recover the crystal grains of β fiber aggregates, which are cold rolling aggregates, without recrystallization. It features.
Here, the recovery refers to a state in which the grain orientation does not change even through heat treatment, that is, a continuous recrystallization state, and means that the ductility and electrical conductivity are restored before deformation without changing the orientation even through the heat treatment of the metal. .

That is, the present invention is to develop a cubic crystal texture of less than 50% compared to the existing cubic crystal texture to suppress the hemming anisotropy of the AA6022 alloy plate material and to be able to manufacture a plate with residual β-fiber aggregate structure It features.

Hereinafter, the present invention will be described in more detail.

In general, the AA6XXX aluminum-magnesium-silicon alloy, when cold rolled regardless of the amount of components, strongly develops the {112} <111> texture known as copper-like texture during rolling, and additionally, goth and other orientations are developed.

These orientations are recrystallized during the annealing process following the cold rolling so that the copper orientations develop into cubic orientations.

The cubic crystal structure is a bearing which rapidly develops when heat treatment including T4 heat treatment occurs when β fiber aggregate structure known as copper type texture is developed. It develops from aluminum alloy sheet which has undergone normal hot rolling and cold rolling. When is developed, the plastic deformation ratio in the rolling direction and the lateral direction (the transverse direction in the rolling direction) is high, and the characteristic is low in the 45 degree direction.

In order to improve the hemmability in the lateral direction, it is necessary to develop a bearing having a high plastic deformation ratio at 90 degrees in the rolling direction in view of the phenomenon in which plate breakage and cracking occur during T hemming of the manufactured sheet.

In order to have this characteristic, it is necessary to further develop a specific orientation, but considering that the cause of hemming anisotropy is plastic anisotropy, controlling the texture in the direction of reducing the anisotropy reduces the hemming anisotropy.

Therefore, according to the present invention, a method of retaining the cold-rolled texture known as β-fiber aggregate structure even after recrystallization is adopted.

In contrast to the cubic texture, the β fiber aggregate has high plastic strain ratio at 45 and low at 0 and 90 degrees with respect to the rolling direction. Thus, when β fiber aggregate and cubic texture coexist, plastic anisotropy occurs. Will be significantly reduced.

Accordingly, the present invention provides a method for producing an AA6022 aluminum-magnesium-silicon alloy sheet comprising a hot rolling, cold rolling, solution treatment (T4 heat treatment) and a temper rolling process, wherein the AA6022 alloy sheet is subjected to the cold rolling step. Hemming anisotropy of aluminum-magnesium-silicon alloy sheet to recover the grains of β-fiber aggregate structure, which is cold rolled texture, by recovering heat treatment for 3 minutes or more and less than 30 minutes in the section between 180 ° C and 210 ° C before the T4 heat treatment step. Provide a method of inhibition.

Hereinafter, the present invention will be described in more detail with reference to Examples. It will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples.

Example 1-6

Using a conventional DC casting method, an AA6022 alloy composed of 0.45 to 0.7% by weight of aluminum, 0.8 to 0.15% by weight of magnesium, 0.01 to 0.11% by weight of silicon, copper and other impurities was cast to a thickness of 150 mm, and then homogenized at 480 ° C. for 48 hours. The process was followed by hot rolling up to 5 mm. At this time, the hot rolling start temperature was 570 ℃ and the final winding temperature was 480 ℃, after which cold rolling was carried out to 1mm.

Subsequently, recovery heat treatment was performed before T4 heat treatment, and then flat hemming was performed after 10% tensile deformation using AA6022 plate subjected to T4 heat treatment.

In addition, the recovery heat treatment temperature of Example 1 was 180 ℃, the recovery heat treatment time was 3 minutes, the recovery heat treatment temperature of Example 2 was 200 ℃, the recovery heat treatment time was 3 minutes, the recovery heat treatment temperature of Example 3 was It was 210 degreeC, and the recovery heat processing time was 3 minutes.

Comparative Example 1-8

The AA6022 alloy was cast in the same content and method as in Example, then homogenized at 480 ° C. for 48 hours and then hot rolled to 5 mm. The hot rolling start temperature was 570 ° C. and the final winding temperature was 480 ° C. After that, cold rolling was performed up to 1 mm.

At this time, after cold rolling, Comparative Example 1 was immediately subjected to T4 heat treatment, Comparative Examples 2 to 8 were subjected to recovery heat treatment for 2 to 35 minutes at 170 ° C to 230 ° C, followed by T4 heat treatment, and then using AA6022 plate. Flat hemming was performed after 10% tensile strain.

Experimental Example 1

The fractions of β-fiber aggregated tissue and cubic crystal aggregated tissues according to the recovery heat treatment for the Examples and Comparative Examples were observed, and the results are shown in Table 1 below.

As shown in Table 1 above, it was found that the β-fiber aggregate structure (8.8-13.7%), which is a cold-rolled aggregate structure, remained after T4 heat treatment as the recovery heat treatment was performed according to the embodiment of the present invention. In other words, it was found that β-fiber aggregate tissue was not re-determined during T4 heat treatment.

In addition, according to the present invention, as the cubic orientation fraction is developed to 50% or less than the conventional method, β-fiber aggregate tissue remains after heat treatment, thereby reducing the planar anisotropy.

Experimental Example 2

After flattening after 10% tensile deformation using AA6022 sheet according to the Examples and Comparative Examples, cracks and leasing were observed using conventional equipment, and the results are shown in Table 2 below. same.

As shown in Table 2 above, due to the effect of reducing the planar anisotropy due to the β fiber assembly remains after heat treatment, Examples 1 to 3 according to the present invention show the same hemming result (see the photo of FIG. 2) according to the hemming direction. As the goth grain was not developed, it showed a side effect of suppressing the ridging phenomenon.

In the case of the plate produced according to Comparative Example 1 (conventional method), the cubic orientation fraction was 23% or more as shown in Table 1, and there was almost no residual cold rolled texture. As shown, cracks occurred in the T-direction hemming (see the photo of FIG. 4).

In Comparative Example 2, as the recovery heat treatment temperature was low, the cold rolled structure was not sufficiently recovered, and thus recrystallization occurred in the T4 heat treatment process.

In Comparative Examples 3 to 6, the recovery heat treatment was performed at a temperature range of 180 to 210 ° C, which is the temperature range of the present invention, but as the recovery heat treatment time was performed for 2 or 35 minutes outside the range of 3 to 30 minutes, It did not cause tissue remnants, which resulted in cracking during hemming.

In Comparative Examples 7 and 6, recrystallization occurred before recovery due to the high recovery heat treatment temperature, it was confirmed that the cubic texture is more developed than the basic method.

As described above, according to the present invention, by performing the recovery heat treatment before the T4 heat treatment step after the cold rolling, it is possible to recover the β fiber aggregate structure in the sheet and to minimize the development of the cubic texture structure. Anisotropy can be suppressed (suppressed).

 As described above, according to the method for inhibiting hemming anisotropy of the aluminum-magnesium-silicon alloy sheet according to the present invention, after cold rolling of the AA6022 aluminum-magnesium-silicon alloy sheet, the temperature of 180 ° C or higher and 210 ° C or lower before the T4 heat treatment step By performing recovery heat treatment for more than 3 minutes and less than 30 minutes at, the volume fraction of the cubic crystal orientation after the final T4 heat treatment is less than 50% compared to the existing method, and the cold rolling texture remains at a volume fraction of 8.8 or more, resulting in final production The plastic anisotropy of a board | plate material can be reduced, and the effect which suppresses hemming anisotropy at the time of a hemming process can be acquired.

In addition, the flat hemming degree of the AA6022 aluminum sheet is possible regardless of the direction, which increases design and design freedom, and significantly reduces product molding defects, and prevents bending of the hemming part, thus eliminating the polishing process, thereby reducing manufacturing costs. Can be planned.

Claims (1)

In the manufacturing method of the AA6022 aluminum-magnesium-silicon alloy plate material which consists of a hot rolling, cold rolling, solution treatment (T4 heat processing), and a temper rolling process, After the cold rolling step, the AA6022 alloy plate was subjected to a recovery heat treatment for 3 minutes or more and less than 30 minutes in a section between 180 ° C. and 210 ° C. before the T4 heat treatment step, thereby recovering crystal grains of β fiber aggregates, a cold rolling texture, without recrystallization. A method of inhibiting hemming anisotropy of an aluminum-magnesium-silicon alloy sheet material, which is caused to occur.

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