JPH07252616A - Production of aluminum-magnesium-silicon alloy sheet - Google Patents

Abstract

PURPOSE:To increase strength and to provide superior press workability and curing performance for baking by using an alloy of specific composition, controlling cooling velocity at the time of continuous casting and after hot rolling by means of continuous casting and direct rolling, cold-rolling the alloy to prescribed sheet thickness, and then applying solution treatment and aging treatment to the resulting sheet. CONSTITUTION:This Al alloy has a composition which contains, by weight ratio, 0.3-1.0% Mg, 0.7-1.5% Si, 0.1-0.7% Mn, 0-1.0% Cu, 0-1.2% Fe, and 0.1-0.3% Cr and/or 0.1-0.3% Zr and in which the contents of Mg and Si satisfy the relaion in inequality I. A molten metal of this alloy is cast continuously at >=5 deg.C/sec cooling rate R at the time of solidification, under the condition satisfying inequality II. After casting, the resulting cast slab is held at a temp. not lower than hot rolling temp., followed by hot rolling. After rolling, the resulting plate is cooled at a rate of >=100 deg.C/min and further cold-rolled to prescribed sheet thickness. The sheet is subjected to solution treatment at 540-570 deg.C, to hardening, and then to aging treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an Al--Mg--Si alloy plate, and in particular, it uses an Al alloy molten metal having a specified content of alloying elements such as Mg, Mn, and Si, which is continuously processed. After casting, it is hot-rolled and then cold-rolled to form Al-
In forming an Mg-Si alloy plate, press forming property and baking are performed by defining cooling rates during continuous casting and after hot rolling, and devising heat treatment conditions after cold rolling performed thereafter. The present invention relates to a method for producing an Al-Mg-Si alloy plate having improved paint curability. And Al-Mg obtained by the present invention
The Si-based alloy plate can be widely used as an outer plate material for vehicles such as automobiles and home electric appliances, a building material, etc. by utilizing its excellent characteristics.

[0002]

2. Description of the Related Art For example, cold-rolled steel sheets have been used as a panel material for automobiles, but recently, as a measure to reduce the weight of a vehicle body for the purpose of reducing fuel consumption and exhaust gas, it is lightweight and has high specific strength. The tendency to use an Al alloy material which is also excellent in formability is rapidly increasing. Among them, as an Al-based alloy plate for automobiles, which is often used after being subjected to a coating treatment for improving the aesthetic appearance, an Al-Mg-Si-based alloy excellent in baking coating hardenability is drawing attention, and in some cases, Practical application is in progress.

By the way, what has been generally practiced as a conventional method for producing an Al alloy sheet is that an ingot produced by a semi-continuous casting method or the like is subjected to chamfering treatment or homogenization heat treatment,
It is a method of sequentially performing hot rolling, cold rolling, annealing, etc.,
The conventional Al alloy plate manufactured through such steps has good press formability and good baking coating hardenability, which satisfies the demands of consumers.

However, in recent years, the demands of consumers have become more severe, and there is a tendency for higher strength to be demanded in order to promote weight reduction, and further improvement in moldability and baking coating curing property is desired. Is covered,
Furthermore, demands for cost reduction due to improved productivity are also increasing.

As a relatively new Al alloy sheet manufacturing technique that meets such demands, a method of performing hot rolling and cold rolling by immediately sending to a rolling step after forming a moving strip by continuous casting (hereinafter referred to as continuous casting / direct sending A rolling method is sometimes used) and a method of omitting chamfering and homogenizing heat treatment is being studied (Japanese Patent Laid-Open No. 55-27497 and Japanese Patent Publication No. 62-54).
No. 182). According to this method, it is possible to reduce costs by omitting chamfering and homogenization heat treatment, and to prevent solid-solution elements that are solid-soluted in supersaturation during the casting process from precipitating during homogenization heat treatment. It is possible to obtain an advantage that the strength is enhanced.

The continuous casting method adopted at the time of performing such continuous casting and direct rolling is currently put into practical use is a water-cooled continuous casting method (formed from a fixed water-cooled continuous casting mold into a plate shape). The continuous cast piece that comes out is directly cooled and solidified with cooling water and continuously cast), a twin roll casting method developed by Hunter Engineering Co., Ltd. (the molten metal is supplied between a pair of rotating cooling rolls, Continuous casting method by cooling and solidifying between rolls), belt-type continuous casting method developed by Hatherley Co., Ltd. (supplying molten metal between two movable belt-shaped cooling members and cooling between the belts) Continuous solid plate casting while solidifying), Block type continuous casting method (movable type 2) developed by Swiss Aluminum Co.
A method of supplying a molten metal between two block-shaped cooling members and continuously casting in a plate shape while cooling and solidifying between the blocks).

[0007]

However, in the continuous casting / direct rolling method which has been put into practical use at present, in the cold rolling step performed after continuous casting and hot rolling, 350 to 500 is used in order to prevent work cracking or the like in the cold rolling step. Although intermediate annealing is performed at a relatively low temperature of about C, precipitation of supersaturated solid solution elements occurs in this intermediate annealing step, which causes a problem of hindering the strengthening of the final cold rolled product. Moreover, the obtained Al alloy sheet still has room for improvement in crack resistance during press forming and baking coating hardenability.

The present invention has been made by paying attention to the problems of the prior art as described above, and its purpose is to continuously cast an Al alloy melt, hot-roll it, and then cold-roll it. When producing an Al alloy sheet by performing the above, particularly, the precipitation of the supersaturated solid solution element in the series of steps of continuous casting, hot rolling, cold rolling and intermediate annealing is suppressed as much as possible, and the final cold rolled product is obtained. Therefore, it is intended to establish a method capable of increasing the strength of the coating composition and further improving the curing property by baking and the press moldability.

[0009]

[Means for Solving the Problems] The composition of the method for producing an Al--Mg--Si alloy plate according to the present invention, which was able to solve the above problems, is Mg: 0.3 to 1.0% Si: 0.7 .About.1.5% Mn: 0.1 to 0.7% Cu: 1.0% or less (including 0%) Fe: 1.2% or less (including 0%), and Cr: 0. 1-0.3% and / or Zr: 0.1
It contains 0.3% and the content of Mg and Si is the following (1).
Satisfying the relation of the formula, Si ≧ (4/7) Mg + 0.5 (1) A molten Al alloy containing the balance of Al and unavoidable impurities has a cooling rate during solidification of R ≧ 5 and R ≧ 6 ( [Fe] + [Si]) + 3 where R: cooling rate during solidification (° C./sec) [Fe], [Si]: continuous under the condition that the Fe and Si contents (%) in the Al alloy are satisfied After casting, the slab temperature is hot-rolled at a temperature equal to or higher than the hot-rolling temperature, and hot-rolled at 100 ° C. /
After cooling at a speed of not less than a minute, and further cold rolling to a predetermined plate thickness, solution treatment is performed at 540 to 570 ° C.
The essential point is that it is then quenched with warm water or water and then subjected to an aging treatment.

The present invention is based on the above-described basic concept, and the preferred embodiment or modified embodiment of the present invention will be described in more detail below. 1. As the continuous casting method, a water-cooled continuous casting method, a twin roll type continuous casting method, a belt type continuous casting method, a block type continuous casting method, etc. can be adopted, but the transition time from the continuous casting to the hot rolling step It is preferable to adjust the timing after the inside of the slab has fallen below the solidus temperature and has completely solidified. 2. The starting temperature of hot rolling performed after continuous casting is 35
The range of 0-550 degreeC is preferable. 3. In continuous casting, a plate-shaped slab with a wall thickness of about 4 to 30 mm is usually continuously produced, and 1 to 1 is obtained by hot rolling.
After rolling to about 5 mm, 0.1 to 1 by cold rolling
It is rolled into an Al alloy plate having a thickness of about mm. 4. The present invention is a so-called continuous casting / direct feed rolling method in which a moving strip obtained by continuous casting is immediately hot-rolled while being kept at a hot rolling temperature or higher, and subsequently or once wound and then sent to a cold rolling step. In addition to this, after continuous casting, the temperature is once maintained above the hot rolling temperature and sent to hot rolling before the slab temperature substantially drops, and hot rolling is performed, and further cold cooling is performed. It can also be applied to a method of performing hot rolling.

[0011]

As described above, in the present invention, the Al--Mg-- used
In addition to defining the component composition of the Si-based alloy, it defines the cooling rate during solidification during continuous casting, and immediately after that, or after holding once, hot rolling is performed while the slab temperature does not drop substantially. To a predetermined rate, and then cold-rolled and solution-treated under appropriate temperature conditions,
Then, quenching and aging treatment are performed, and by setting such conditions, together with the fact that the component composition of the Al-Mg-Si alloy is appropriately adjusted, the strength of the cold-rolled product is increased and , Al-M, which is more excellent in the yield strength after the baking and heat treatment that is carried out after that, and also in the crack resistance during press formability.
It has succeeded in obtaining a g-Si alloy plate. The composition of the Al—Mg—Si alloy defined in the present invention and the manufacturing conditions including the cooling conditions during continuous casting and after hot rolling will be described in detail below. First, the reason for defining the component composition of the Al-Mg-Si alloy used in the present invention will be described.

Mg: 0.3 to 1.0% or less Mg is an element that forms Mg ₂ Si and contributes to the increase in strength. In order to secure the strength required as the outer plate material as described above. It must be contained by 0.3% or more. However, if the content is too large, the formability deteriorates due to an increase in the amount of Mg that cannot be completely dissolved, so it must be suppressed to 1.0% or less. The more preferable lower limit value of Mg is 0.
6%, and a more preferable upper limit value is 0.9%.

Si: 0.7 to 1.5% It is an element that forms the above Mg and Mg ₂ Si and contributes to the strengthening.
% Must be contained. However, if the content is too large, the press-formability is adversely affected by the precipitation of Si single crystals, so the content must be suppressed to 1.5% or less. The more preferable lower limit value of Si is 0.9%, and the more preferable upper limit value thereof is 1.3%. Si ≧ (4/7) Mg + 0.5 (1) As described above, in the present invention, Mg and Si are added to G. It is an important element that forms an aggregate (cluster) of Mg ₂ Si composition called P zone or an intermediate layer and contributes to hardening by baking treatment. Mg ₂ Si is M
The g and Si contents are combined at a weight ratio of 7: 4, and if the Al alloy contains the theoretical amounts of Mg and Si, the Al alloy is considered to be hardened.

However, according to various researches conducted by the present inventors, even if the theoretical amounts of Mg and Si are contained, sufficient hardening does not necessarily occur, and sufficient hardening is achieved. It was found that, in order to generate the amount of Mg ₂ Si, 0.5% by weight or more of Si should be contained in excess with respect to the theoretical amount of Mg and Si, that is, Mg: Si = 7: 4. This is due to excess Si
Is G. P. Acts as the nucleus of the zone or intermediate layer and Mg
_It is considered that this is to promote the precipitation of ₂ Si, and if the amount of excess Si is less than 0.5% by weight, such an effect cannot be effectively exhibited. A more preferable excess amount of Si is 0.7% by weight or more in order to more surely achieve the above effect due to the formation of Mg ₂ Si.

Mn: 0.1 to 0.7% Mn is not only an element indispensable as a solid solution strengthening element and a crystal grain refining element, but also Al-Mn-based or Al-Fe-Mn-based crystallization. It also has a function of forming a product to enhance workability, and in order to effectively exhibit these functions, it must be contained at least 0.1% or more. However, if the amount becomes too large, the formability tends to deteriorate rather than increase due to the increase in the amount of Mn that cannot be completely dissolved. Therefore, it must be suppressed to 0.7% or less.

Cu: 1.0% or less Cu is not always essential, but Al--Mg
Since it has the effect of increasing the strength by the formation of the Cu-based crystallized substance, it is desirable to positively add it when the demand for the strength is high. However, if it is too large, the formability is adversely affected, so it must be suppressed to 1.0% or less. Considering the balance between strength and formability, the more preferable Cu content is in the range of 0.4 to 0.9%.

Fe: 1.2% or less Fe is not always essential, but since it has a function of enhancing strength like Cu, it should be positively contained when the demand for strength is high. Is desirable. However, if it is too large, the formability is adversely affected, so it must be suppressed to 1.2% or less. Considering the balance between strength and formability, the more preferable Fe content is 0.1.
Is in the range of 0.5%.

Cr: 0.1 to 0.3% and / or Z
r: 0.1 to 0.3% Cr and Zr each have an action as a grain refinement element, and one or both of them have a lower limit value in order to effectively exert their effects. The above must be contained. However, if their content exceeds the above upper limit, an insoluble metal compound is produced, and the formability is adversely affected.

The balance component of the Al alloy in the present invention is Al
Examples of the inevitable impurities include Ni, Zn, V, Ti, and Li. However, as long as the amounts of the inevitable impurities are inevitable impurities, they are exceptional in ensuring the performance intended in the present invention. Will not be an obstacle. next,
Each condition of continuous casting, hot rolling, cold rolling, etc. using the Al-Mg-Si alloy will be described.

In the present invention, an Al-Mg-Si alloy melt satisfying the above-mentioned compositional requirements is used, and the cooling rate during solidification is expressed by the following formulas (2) and (3) R ≧ 6 ([Fe] + [Si]) + 3 (2) R ≧ 5 (3) where R: cooling rate during solidification (° C./sec) [Fe], [Si]: Fe and Si content in Al alloy The moving strip that is continuously cast under the condition that (%) is simultaneously sent to the hot rolling process, or the continuously cast slab is adjusted to the hot rolling temperature or higher and sent to the hot rolling process. After hot rolling, cooling at a rate of 100 ° C./min or more after hot rolling, and further cold rolling to a predetermined plate thickness, 540 to 540
A characteristic of the manufacturing method is that the solution treatment is performed at 570 ° C., then the aging treatment is performed after quenching with warm water or water.

First, the inventors of the present invention have confirmed that the strength and drawability of the final rolled product are the cooling rate during solidification during continuous casting with the content ratio of Fe and Si contained in the Al alloy as a parameter. It was found that it is important to set the cooling rate at the time of solidification so as to satisfy the above equations (2) and (3) at the same time.

However, the above-mentioned characteristics of the final rolled product are affected by the continuous casting step and the subsequent rolling and solution treatment conditions. Particularly, Fe and Si in the Al alloy cause coarse crystallized substances during continuous casting. , Which adversely affect the above-mentioned properties of the final rolled product. However, the cooling rate at the time of solidification in continuous casting was
If it is set so as to satisfy the condition of the formula, the formation of coarse crystallized substances derived from Fe and Si is prevented, and this is combined with the setting of the cooling rate after the hot rolling and the solution treatment condition during the cold rolling. The properties of the final rolled product can be remarkably enhanced.

The recommended range represented by the conditional expressions (2) and (3) is [Fe] + [Si] as shown in FIG.
When the value of is 0.33% or less, it is defined by the formula (3), and when the value of [Fe] + [Si] is more than 0.33%, it is defined by the formula (2).

By the way, when the cooling rate during solidification in continuous casting is specified as described above, the amount of crystallized substances derived from Fe and Si in the continuously cast structure is decreased by the forced solid solution, and the crystallized substance size is The average size is reduced to about 2 μm or less, and the press moldability is remarkably enhanced. However, if the cooling rate during solidification during continuous casting becomes lower than the above rate condition, not only the amount of insoluble compound precipitated increases and the size also becomes coarse, but satisfactory press formability cannot be obtained. However, the solid solution strengthening effect provided by Fe, Si and Si becomes insufficient, and satisfactory strength cannot be achieved.

Further, in the hot rolling subsequently performed after the continuous casting, it is necessary to cool at a rate of 100 ° C./min or more. By adopting such rapid cooling, during the cooling after the hot rolling. The precipitation of the supersaturated solid solution component is suppressed and the supersaturated solid solution amount is maintained, and as a result, it is possible to achieve high strength by solid solution strengthening. By the way, when the cooling rate after hot rolling becomes a low rate of less than 100 ° C./minute, precipitation of a supersaturated solid solution component occurs and the purpose of strengthening by solid solution strengthening cannot be achieved.

After hot rolling, after cold rolling to a predetermined plate thickness, solution treatment is performed at 540 to 570 ° C., followed by quenching with warm water or water and then aging treatment. The solution treatment temperature at this time is determined as described above because the precipitation of the solid solution element during the solution treatment is suppressed to maintain a sufficient supersaturated solid solution amount, the strength is increased, and the solid solution element amount is increased. This is for improving the baking paint curing property. By the way, if the solution treatment temperature is less than 540 ° C,
Not only does precipitation occur during the solution heat treatment to cause a decrease in strength, but also the effect of improving the baking coating curability becomes insufficient,
On the other hand, when the temperature exceeds 570 ° C., the crystal grains become coarse and the eutectic melting causes burning, which deteriorates the press formability.

After the solution treatment, an aging treatment is performed after quenching with warm water or cold water to obtain an Al-Mg-Si system having high strength and excellent press moldability and baking coating curability. An alloy plate can be obtained. Quenching conditions and aging heat treatment conditions at this time are not particularly limited, but if shown as preferable conditions, water-quenching as quenching conditions, and preferable aging heat treatment conditions are 1
It is about 10 minutes to 8 hours at 50 to 200 ° C.

In the present invention, as described above, Al-Mg-Si is used.
In addition to specifying the component composition of the system alloy, the cooling rate during solidification and the cooling rate during subsequent hot rolling in continuous casting using the molten alloy, and further the solution treatment conditions after subsequent cold rolling are set. However, the other conditions are not particularly limited, but other preferable conditions and the like will be described below.

In the present invention, the continuously cast moving strip is immediately sent to the hot rolling step, or the continuously cast slab is adjusted to a temperature higher than the hot rolling temperature and then sent to the hot rolling step. A method of hot rolling and subsequently or temporarily winding and then sending to a cold rolling step is adopted, and hot rolling is performed by effectively utilizing the retained heat of a continuous cast piece.
Compared with the method of performing continuous casting, winding once, cooling and then hot rolling, there is less heat loss, and it is also effective in improving productivity. As the continuous casting method adopted here, a water-cooled continuous casting method, a twin roll continuous casting method, a belt continuous casting method, a block continuous casting method or the like as described above may be appropriately selected and used. You can

The starting temperature of hot rolling performed after continuous casting is 350 to 550 ° C., more preferably 400 to 500.
And the hot rolling finish temperature is 150 to 28
It is 0 ° C., and more preferably 210 to 260 ° C.
Further, in carrying out the present invention, a plate-shaped slab having a wall thickness of about 4 to 30 mm is usually continuously produced by continuous casting, and immediately hot-rolled to obtain a wall thickness of 1 to 5
mm to 0.1 to 1 m by cold rolling.
An Al alloy product plate having a wall thickness of about m is manufactured.

[0031]

EXAMPLES Next, examples of the present invention will be shown, but the present invention is not limited by the following examples, and may be carried out with appropriate modifications within a range compatible with the gist of the preceding and following description. Of course, it is possible, and all of them are included in the technical scope of the present invention.

Example After melting an Al alloy having the chemical composition shown in Table 1, continuous casting was performed to a plate thickness of 20 mm at a cooling rate of 18 ° C./sec at the time of solidification, and immediately thereafter, a rolling start temperature was 450 ° C. Direct-feed hot rolling was performed at a finishing temperature of 270 ° C. to prepare a hot-rolled sheet having a thickness of 5 mm. Incidentally, water mist spraying was adopted for cooling after hot rolling to secure a cooling rate of 200 ° C./min.
After that, cold-roll to 1 mm and 560 by rapid heating
After carrying out a solution heat treatment at 1 ° C. for 1 minute, water quenching was performed. In addition, in Table 1, No. 17, 18 are manufactured by the conventional method.

An Erichsen test was conducted on each of the obtained hardened materials. Immediately after the above water quenching, 170 ° C x 2
The aging treatment was performed for 0 minutes, and the obtained aging treated material was subjected to a tensile test to measure 0.2% proof stress. The results are shown in Table 2, and in Examples satisfying all the requirements of the present invention, high Erichsen value and 0.2% proof stress were obtained, and press moldability was good and It can be seen that the strength after aging heat treatment is also high, and that it has excellent quenching paint curability.

[0034]

[Table 1]

[0035]

[Table 2]

Next, after melting the Al alloy having the chemical composition shown in Table 3, continuous casting was performed to a plate thickness of 20 mm at the cooling rate at the time of solidification shown in the same table, and this was immediately rolled at a rolling start temperature of 50.
Direct hot rolling was performed with 0 ° C. and the end temperature set to 320 ° C., and cooled at a rate of 200 ° C./min to produce a hot-rolled sheet having a thickness of 5 mm. Then, it was cold-rolled to 1 mm, rapidly heated and subjected to a solution treatment at 560 ° C. for 1 minute, and then water-quenched, and an Erichsen test was conducted on the quenched material.

Immediately after water quenching, aging heat treatment was carried out at 170 ° C. for 20 minutes, and a tensile test was conducted on the aging heat treated material to measure 0.2% proof stress. The results are shown in Table 4, and the ones obtained in the examples have higher Erichsen values than the ones obtained in the comparative examples, are excellent in press formability, and have 0.2% proof stress after aging heat treatment. It can be seen that the composition has a high baking finish and is very excellent in curability.

[0038]

[Table 3]

[0039]

[Table 4]

Next, A having the same chemical composition as shown in Table 3 was used.
After melting the alloy, the cooling rate during solidification was 15 ° C / se
After continuous casting to a plate thickness of 20 mm in c, the hot rolling start temperature was immediately set to 500 ° C. and the end temperature was set to 320 ° C. to perform direct hot rolling, and immediately after hot rolling, the speeds shown in Table 5 were obtained. Then, a hot-rolled sheet having a thickness of 5 mm was produced. After that, it was cold-rolled to 1 mm, rapidly heated, solution-treated under the conditions shown in Table 5, water-quenched, and subjected to Erichsen test of the quenched material.

Immediately after water quenching, aging heat treatment was carried out at 170 ° C. for 20 minutes, and a tensile test was conducted on the aging heat treated material to measure 0.2% proof stress. The results are shown in Table 6, and those obtained in the examples have a higher Erichsen value and excellent press formability than those obtained in the comparative examples, and also have 0.2% proof stress after aging heat treatment. It can be seen that the composition has a high baking finish and is very excellent in curability.

[0042]

[Table 5]

[0043]

[Table 6]

[0044]

The present invention is configured as described above, and uses an Al-Mg-Si alloy having a specified composition.
Immediately send the continuously cast moving strip to the hot rolling process,
Alternatively, the continuously cast slab is adjusted to a hot rolling temperature or higher and then sent to the hot rolling step to be hot rolled, and further cold rolled to produce an Al alloy sheet, particularly during continuous casting. And specify the cooling rate after hot rolling,
Precipitation of supersaturated solid solution elements is suppressed as much as possible by applying solution heat treatment under the specified conditions in the cold rolling process to enhance the strength of the final cold rolled product and to improve the press workability and baking coating hardenability. It has become possible to manufacture an excellent Al-Mg-Si alloy plate.

[Brief description of drawings]

FIG. 1 is a graph showing preferable cooling rate conditions during continuous casting carried out in the present invention.

Claims (3)

[Claims] 1. Mg: 0.3 to 1.0% (meaning weight%; the same applies hereinafter) Si: 0.7 to 1.5% Mn: 0.1 to 0.7% Cu: 1.0 % Or less (including 0%) Fe: 1.2% or less (including 0%) and Cr: 0.1 to 0.3% and / or Zr: 0.1
It contains 0.3% and the content of Mg and Si is the following (1).
Satisfying the relation of the formula, Si ≧ (4/7) Mg + 0.5 (1) A molten Al alloy containing the balance of Al and unavoidable impurities has a cooling rate during solidification of R ≧ 5 and R ≧ 6 ( [Fe] + [Si]) + 3 where R: cooling rate during solidification (° C./sec) [Fe], [Si]: continuous under the condition that the Fe and Si contents (%) in the Al alloy are satisfied After casting, the slab temperature is hot-rolled at a temperature equal to or higher than the hot-rolling temperature, and hot-rolled at 100 ° C. /
After cooling at a speed of not less than a minute, and further cold rolling to a predetermined plate thickness, solution treatment is performed at 540 to 570 ° C.
Then, a method for producing an Al-Mg-Si alloy plate is characterized by quenching with warm water or water and then aging treatment. 2. The manufacturing method according to claim 1, wherein the continuously cast moving strip is immediately sent to the hot rolling step. 3. The manufacturing method according to claim 1, wherein the continuously cast slab is adjusted to a hot rolling temperature or higher and sent to a hot rolling step.