JP2005273003A - Production method of aluminum-magnesium-silicon alloy sheet suitable for flat hemming - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method of an alloy sheet suitable for flat hemming, whereby cracks in a hem part can be prevented at manufacturing of a car body component and quality of product appearance can be ensured. <P>SOLUTION: The production method relates to a rolled sheet of an AA6000-series aluminum alloy comprising silicon and magnesium as essential alloying components. The rolled sheet is the aluminum alloy sheet which is capable of flat hemming, is excellent in moldability and has a volume percentage of cube system orientation being ≥35%. The alloy sheet is produced by the production method wherein an ingot is subjected to hot-rolling at a temperature of ≥300°C and ≤350°C to achieve a volume percentage of RW orientation being <10%, subsequently to cold-rolling and finally to T4 heat-treatment to obtain a property suitable for flat hemming. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing an AA6000-based aluminum-magnesium-silicon alloy plate material capable of flat hem, and more specifically, by improving formability and enabling flat hem, The present invention relates to a method for producing an AA6000 series aluminum-magnesium-silicon alloy sheet that can broaden the range of application.

  In general, automotive outer panels are required to have formability, shape freezing properties (highly dimensional accuracy due to little or no springback after press molding), dent resistance, corrosion resistance, and excellent surface quality. .

  Conventionally, AA5000 series aluminum-magnesium alloy sheet materials have been applied to automobile outer plates. However, since the effect of improving strength after molding cannot be expected and the surface quality is not good, AA6000 series aluminum-magnesium has recently been used. -The application of silicon alloy sheets tends to increase.

  This alloy is excellent in paint bake hardenability, and as a result, high strength can be obtained. Therefore, it has an advantage that it can be expected to be thinner and lighter, and various physical property improvements have been attempted (patents). Literature 1, Patent Literature 2).

Body parts such as a hood are formed by mechanical coupling of an outer plate and an inner plate.
A flange having an appropriate length is formed at the end of the outer plate of the vehicle body, the inner plate is fixed inside the outer plate, and then the flange of the outer plate is bent and mechanically joined to the inner plate. Come to do. Such a process is called hemming.

  In the hem process, flat hem (180 ° bending) in which the ratio (r / t) between the bending center radius (r) and the plate thickness (t) is small and the processing conditions are severe is performed, but AA6000 series aluminum-magnesium- Since the silicon alloy is inferior in bending workability compared to the AA5000 series alloy, the defective rate is remarkably increased when flat hem is performed in a portion where the degree of press work is large (a portion where a large deformation rate is added).

  In order to solve this problem, the curl hem (Curl hemming) is introduced in the design, and the flat hem part is replaced, but this impairs the product design and the appearance of the design, and the problem of the step between the car body parts. As a result, the merchantability is reduced.

JP-A-5-247610 JP-A-5-279822 A. A. Ridha and W.M. B. Hutchinson, Acta metal, Vol. 30, pp. 1929-1939, 1982

  The present invention has been devised in view of the above-described problems, and has a cubic effect that affects the flat heme property of an outer plate during the production of an AA6000 series aluminum-magnesium-silicon alloy plate for an automobile outer plate. In order to induce the development of the orientation, after performing the hot rolling method that suppresses the development of the RW orientation (cube orientation), by performing cold rolling and T4 heat treatment, cracks in the hem part are produced during the production of the body parts. It is an object to provide a method for producing an aluminum-magnesium-silicon alloy plate material capable of flat hem, which can suppress generation and ensure appearance quality.

  The purpose is to perform cold rolling at a temperature of 300 ° C. or higher and 350 ° C. or lower during hot rolling of an aluminum-magnesium-silicon alloy sheet to further suppress the development of the RW orientation to less than 10%. And the T4 heat treatment can be achieved by the method of the present invention.

  In order to achieve the above object, the present invention provides a method for producing an AA6000 series aluminum-magnesium-silicon alloy sheet, which is rolled at a temperature of 300 ° C. to 350 ° C. during hot rolling of the aluminum-magnesium-silicon alloy sheet. It is characterized by enabling flat hem during the hem process.

  The aluminum-magnesium-silicon alloy sheet is further subjected to cold rolling and T4 heat treatment after hot rolling under a temperature condition of 300 ° C. or higher and 350 ° C. or lower.

  According to the present invention, during the production of the AA6000 series aluminum-magnesium-silicon alloy sheet, rolling is performed at a temperature of 300 ° C. or higher and 350 ° C. or lower in the hot rolling stage, and the development of the RW orientation is suppressed to less than 10%. Then, by developing the volume fraction of the cubic orientation to 35% or more through cold rolling and T4 heat treatment, the formability is improved and flat hem becomes possible.

  As a result, it is possible to improve fuel efficiency and reduce exhaust gas through weight reduction by applying aluminum, and further improve the design and design freedom to solve the step problem between products and improve the merchantability.

  As a result of intensive research on the method for further improving the formability of the AA6000 series aluminum-magnesium-silicon alloy, particularly the bending workability, the present inventors have found that the bending workability of the AA6000 series aluminum alloy is the texture of the material ( It was found that the higher the degree of integration of the texture (cube orientation, {001} <100>), the higher the degree of integration.

  And in order to optimize the said characteristic, the RW direction (Rotated Cube orientation, {001} <110>) which optimizes the temperature which affects friction at the time of hot rolling, and inhibits the development of a cubic crystal orientation. I found out that it is important to suppress it.

  This invention is based on the above-mentioned content, The objective is to provide the manufacturing method of the AA6000 type | system | group aluminum-magnesium-silicon alloy board | plate material which has the outstanding moldability in which flat hem is possible.

In general, AA6000 series aluminum-magnesium-silicon alloy sheet is produced through hot rolling, cold rolling and T4 heat treatment process, and the texture of the final product is copper orientation, Goss orientation, P orientation and cubic. A crystallographic texture composed of crystal orientations develops.
These relative volume fractions affect the formability of the plate material.

  In the plate material produced by rolling, the crystal orientation is defined by the rolled plate surface and the rolling direction. That is, the texture can be shown by the crystal plane placed parallel to the rolling surface and the crystal orientation placed parallel to the rolling direction.

  A specific surface is represented by a Miller index {hkl}, and a specific direction is represented by <uvw>.

  Therefore, copper orientation: {112} <111>, Goss orientation: {011} <100>, brass orientation: {110} <112>, S orientation: {123} <634>, cubic orientation: { 001} <100>, RW orientation: {001} <110>, etc. are typical orientations.

  After cold rolling, the plate material is macroscopically composed of copper orientation + brass orientation + S orientation, and after T4 heat treatment, the texture changes to cubic orientation + S orientation + brass orientation.

  Also, a weak Goss orientation develops.

  Among these, the orientation that has the greatest influence on the formability of the plate material is the cubic orientation.

  In order to suppress the development of the cubic orientation, a special production process other than the current production process, such as shear rolling, must be introduced.

  In order to improve the flat heme workability, the cubic orientation should be developed. However, when the development of the cubic orientation is suppressed by the relative development of the S and P orientations, the flat heme workability is poor. Therefore, the development of the S direction and the P direction must be suppressed.

  The S orientation is an orientation that develops after cold rolling and cannot be suppressed, and the P orientation is an orientation generated by the addition of magnesium and silicon, which also suppresses development. It is not possible.

  However, when the development of the cubic orientation is promoted during the T4 heat treatment, the fraction of the crystal grains showing the S and P orientations due to the development and growth of the cubic orientation of the already developed S and P orientations. Can be reduced (development is suppressed).

In order to develop the cubic orientation, a copper-like texture may be developed in the cold rolling process.
This is because the copper-like texture grows in the cubic orientation during the heat treatment.
This can be confirmed by Non-Patent Document 1.

However, when a copper-like texture develops, the remaining of the S orientation after heat treatment cannot be prevented, and therefore the development of the cubic orientation becomes relatively weak.
This ultimately degrades the flat hem property.

  In the present invention, a copper-like texture is developed after cold rolling, a cubic orientation can be developed after the T4 heat treatment, the development of the S orientation is suppressed after the T4 heat treatment, and the development of the cubic orientation is 35% by volume. In order to be able to be more than%, a method for suppressing the development of the RW orientation during hot rolling is presented.

  The RW orientation is an orientation that develops when shear deformation is applied due to friction, such as hot rolling, and this orientation is the center of the copper-like orientation when the cold rolling process is performed thereafter. Since there is a feature that accelerates the development of the S orientation, and there is a feature that suppresses the development of the cubic orientation at the time of recrystallization heat treatment (at the time of T4 heat treatment), by controlling this development in advance, Can bring about development.

  The feature of the present invention is that, instead of the hot rolling method usually performed at a temperature of 350 to 400 ° C., the hot rolling is performed at a temperature of 300 ° C. or higher and 350 ° C. or lower to reduce the friction between the material and the rolling roll. As a result, the development of the RW orientation is suppressed, and the volume fraction of the cubic orientation is 35% or more in the AA6000 series aluminum-magnesium-silicon alloy sheet produced through the cold rolling and the T4 heat treatment process. The object is to provide a method for producing a material excellent in moldability capable of flat hem.

  Hereinafter, the present invention will be described in detail through examples.

  Using a general DC casting method, an aluminum-magnesium-silicon alloy was cast to a thickness of 120 mm, homogenized at 480 ° C. for 48 hours, and then hot-rolled to 5 mm.

  The hot rolling start temperature was 300 ° C. to 350 ° C., and the coiling temperature was fixed at 300 ° C. to limit the scope of the invention.

  This material was cold-rolled to 1.0 mm, and the subsequent heat treatment was in accordance with T4 heat treatment conditions for melting and quenching.

  The manufactured plate material was used, and after 10% tensile deformation, flat hem was performed to confirm the presence or absence of cracks in the hem cross section.

  In FIG. 1 and FIG. 2, the presence or absence of the crack generation | occurrence | production when performing flat hem using the test piece manufactured by this invention and the test piece manufactured by the conventional production method was displayed.

  FIG. 1 and FIG. 2 show the orientation distribution functions after hot rolling and T4 heat treatment, and compared the degree of development of the RW orientation and the cubic orientation.

  From FIG. 1 and FIG. 2, when manufactured by the method of the present invention (FIG. 1), the development of the RW orientation is suppressed compared to the conventional method (FIG. 2), and the cubic orientation has developed more than twice. Can be confirmed.

  The orientation distribution function can quantitatively analyze the degree of texture development, and the contour line indicates the degree of texture development. The higher the contour line, the higher the degree of development. As can be seen from FIG. 1, it can be seen that flat hems are possible when the cubic orientation develops.

  However, in the case of the sample of FIG. 2 manufactured by the usual method of the comparative example, it can be seen that cracks occurred during the flat hem.

  Table 1 shows the effects of the present invention through the present invention and the comparative method.

  In this invention, hot rolling is as having shown in Table 1, and the subsequent process passed through cold rolling and T4 heat processing which are the existing methods.

  The conventional method starts hot rolling at 450 ° C. and winds at 310 ° C.

  In order to eliminate the age hardening effect, T4 heat treatment was simultaneously performed on the present invention and the comparative method.

  As can be seen from Table 1, when hot rolling is performed in the temperature range of 300 ° C. or more and 350 ° C. or less provided by the present invention, the volume fraction of the RW orientation is 35% or more, and the occurrence of cracks after flat hem occurs. Is prevented.

  This is because, in the temperature section provided by the present invention, the adhesion friction between the plate material and the rolling roll is reduced, the shear deformation is reduced, and the development of the RW orientation is suppressed to 10 or less.

  However, when the conventional method is used, it can be seen that the development of the RW orientation is 28%, the development of the cubic orientation is weak thereafter, and cracks occur during flat hem.

  Moreover, in the case of Example 10, the plate breakage occurred in the temperature section, and the effect of the subsequent process could not be examined.

  In the case of Examples 7 to 9, which are sections outside the temperature range provided by the present invention, at the start of hot rolling, the development of the RW orientation is accelerated by the adhesion friction between the material and the rolling roll, thereby the final product. At the hem, cracks occurred.

  In the case of Example 11, there was no effect of adhesion friction during hot rolling, but because the operation temperature was low, the rolling pass increased from the existing 8 passes to 13 passes, leading to an increase in manufacturing costs, Nevertheless, the development of cubic orientation could not be induced.

  As described above, as can be seen from the examples, according to the present invention, a material capable of a flat hem process can be produced.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments. Those skilled in the art to which the present invention belongs from the embodiments of the present invention within the technical scope thereof. Could be changed more easily.

It is the texture after hot rolling of the AA6000 series aluminum-magnesium-silicon alloy sheet material manufactured by this invention, the texture of a final product, and a flat hem work photograph. It is the texture after hot rolling of the AA6000 series aluminum-magnesium-silicon alloy sheet material manufactured by the conventional method, the texture of the final product, and a flat hem work photograph.

Claims (2)

In the manufacturing method of AA6000 series aluminum-magnesium-silicon alloy sheet,
Aluminium-magnesium-silicon alloy sheet material that is capable of flat hem, characterized by being capable of flat hem during the hem process by rolling at a temperature of 300 ° C. to 350 ° C. during hot rolling of an aluminum-magnesium-silicon alloy sheet. -Manufacturing method of silicon alloy sheet.   2. The flat according to claim 1, further comprising a step of performing cold rolling and T4 heat treatment after hot rolling the aluminum-magnesium-silicon alloy sheet at a temperature of 300 ° C. to 350 ° C. 3. A method for producing an aluminum-magnesium-silicon alloy sheet capable of hemming.