JPH0788558B2 - Method for producing aluminum alloy sheet excellent in formability and bake hardenability - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an aluminum alloy sheet having excellent formability and bake hardenability, and more specifically, it is excellent in forming processability such as pressing and forming. The present invention relates to a method for producing an aluminum alloy sheet having excellent bake hardenability by heating during baking of a coating after processing.

(Prior Art) Conventionally, aluminum alloy plates used for automobile parts and other applications are subjected to forming processing such as pressing and bending,
In the coating process, a heating treatment (baking, baking) is performed in order to maintain the strength of the coated coating film, and at the same time, the strength of the aluminum alloy sheet is improved by utilizing this heating.

Recently, from the viewpoint of energy saving and cost reduction, the baking temperature tends to be low and the baking time tends to be short, and there has been a strong demand for an aluminum alloy sheet whose strength is improved by baking at this low temperature for a short time.

As a technique for responding to such a request, for example, Japanese Patent Laid-Open No.
-There is a proposal by No. 111851. This is Mg: 0.3-1.5%
And Si: Al-Mg-Si based aluminum alloy containing 0.2 to 2.0%, after solution treatment, cooled to 60 ~ 130 ℃ at a cooling rate of 100 ℃ / min or more, the range of 60 ~ 130 ℃ A method for producing an aluminum alloy having excellent bake hardenability and formability, which is characterized by holding at a temperature for 0.5 to 48 hours.

Aluminum alloy plate obtained by this method is 170 ℃
It is said that there is an effect that the strength is remarkably improved even in baking for a short time at a relatively low temperature.

(Problems to be Solved by the Invention) On the other hand, plate materials used for applications such as automobile parts include
Excellent moldability is required.

However, the Al-Mg-Si system (6000 system) according to the above proposal
Aluminum alloy sheets have a formability that, when the material strength is set above a certain level in order to have sufficient strength as a product, the formability is generally that of a steel sheet or a high formability structural aluminum alloy, Al-Mg series. It is said to be inferior to (5000 series).

Therefore, under the present circumstances, further improvement of the formability of the Al-Mg-Si alloy plate having excellent bake hardenability is required.

The present invention has been made in order to meet such a demand, and the molding processability can be further improved by the method according to the above proposal, but the bake hardenability by baking at low temperature for a short time can be improved. It is intended to provide a method.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present inventor has conducted earnest research to improve the method according to the above proposal.

As a result, it was found that Mg and Si, which are indispensable components, have proper contents that contribute to improvement of formability. That is, it was found that forming processability is improved by making the amount of Si excessive than the composition ratio of Mg ₂ Si. It is considered that the reason for this is that the excessive Si particles are dispersed to facilitate uniform deformation during processing and improve moldability.

The present invention has been completed based on such knowledge, and further detailed studies on other components and manufacturing conditions.

That is, the present invention, as an essential component, Mg: 0.2 ~ 0.6%
And Si: 0.9 to 1.6%, and the content ratio is S
i> 0.58 × Mg + 0.8, Cu: 0.3% or less, Ti: 0.1%
Below, B: 0.06% or less, Be: 0.2% or less, Mn: 0.3% or less, C
r: 0.4% or less, Fe: 0.5% or less, Zr: 0.2% or less and V: 0.2%
An aluminum alloy ingot containing one or more of the following and the balance substantially consisting of Al is subjected to homogenization treatment, hot rolling, and then cold rolling to obtain a desired result. After the plate thickness of the above, as a solution treatment, it is rapidly heated to a temperature of 480 to 560 ° C at a heating rate of 100 ° C / min or more, and kept in this temperature range for 3 seconds or more, and then a cooling rate is 300 ° C / min or more. In 5
Heat-treated at a temperature of 0 to 130 ℃
The gist of the present invention is to provide a method for producing an aluminum alloy sheet having excellent formability and bake hardenability, which is characterized by holding at a temperature of ~ 130 ° C for 1 to 48 hours.

The present invention will be described in more detail below.

(Operation) First, the reasons for limiting the chemical components in the present invention will be described.

Mg: Mg is an element that gives strength in cooperation with Si, but 0.2%
If it is less than the above, the strength (hereinafter, the strength means the material and the strength after baking at 175 ° C.) is low, and microcracks are likely to occur. Also
If the content exceeds 0.6%, the material strength becomes too high and the formability deteriorates. Therefore, the Mg content is 0.2-0.6%
The range is.

Si: Si is an element that gives strength together with Mg, and Mg ₂ S
If added in excess of the composition ratio of i, the Si particles are dispersed, and uniform deformation is likely to occur during the molding process, and the moldability is improved. However, if it is less than 0.9%, there is almost no effect of improving the formability, and if it exceeds 1.6%, the material strength becomes too high, the formability is lowered, and microcracks are likely to occur. Therefore, the Si content is in the range of 0.9 to 1.6%.

However, as described above, if Si is contained in excess of the composition ratio of Mg ₂ Si, the formability is improved.
The ratio of the contents of should satisfy the following formula.

Si> 0.58 × Mg + 0.8 In the present invention, these Mg and Si are essential components, and further, elements Cu, Ti, B, Be, Mn, Cr, Fe, and
It contains one or more of Zr and V.

Cu: Cu is an element that imparts strength improvement, but if it exceeds 0.3%, the corrosion resistance and formability deteriorate. Therefore, the Cu content is 0.3% or less.

Ti: Ti is an element that makes the crystal grains of the ingot finer and improves the formability, but if it is contained in excess of 0.1%, coarse crystallized substances are formed and the formability is reduced. Therefore, the Ti content is 0.1% or less.

B: B is an element which, like Ti, refines the crystal grains of the ingot and improves the formability, but when it is contained in excess of 0.06%, coarse crystallized substances are formed and the formability is lowered. Therefore,
The B content is 0.06% or less.

Be: Be is an element effective in improving the hot rolling property and the formability of the product, but the effect is saturated when the content exceeds 0.2%. Therefore, the Be content is 0.2% or less.

Mn, Cr, Zr, V, Fe: Mn, Cr, Zr, and V are elements that each have the effect of improving strength, but when the content increases, coarse crystallized substances are formed and formability deteriorates. Further, although Fe has a small effect of improving strength, it deteriorates formability for the same reason. Therefore, the Mn content is 0.3% or less, and the Cr content is 0.4%.
% Or less, Zr content is 0.2% or less, V content is 0.2% or less,
The Fe content is 0.5% or less.

Next, the manufacturing conditions of the present invention will be described.

First, the aluminum alloy ingot having the above chemical composition is subjected to homogenization treatment. The homogenization treatment should be carried out at a temperature below the burning temperature. Especially in the case of a composition having moldability and bake hardenability, should the heating rate up to the target temperature be 200 ° C / hr or less? Or, it is desirable to perform a multi-stage homogenization treatment of two or more stages.

Then, hot rolling is performed. However, this condition does not need to be particularly limited because the effect on bake hardenability is small.

Although cold rolling is performed after hot rolling, rough annealing may be performed after hot rolling, or intermediate annealing may be performed after starting cold rolling. When high formability is required depending on the processing condition of the product, the formability is improved by including such an annealing step. The annealing temperature is preferably in the range of 300 to 580 ° C. If it is less than 300 ° C, the effect of improving the moldability is small,
On the other hand, if the temperature exceeds 580 ° C, burning occurs and the moldability is deteriorated, which is not preferable.

After cold rolling, solution treatment is performed.
This is a treatment for improving material strength, high formability, and strength after baking by performing rapid heating at high temperature for a short time, followed by rapid cooling. For that purpose, first, it is rapidly heated to a high temperature of 480 to 560 ° C. at a heating rate of 100 ° C./minute or more and kept at this temperature for 3 seconds or more. Heating temperature is 48
If the temperature is lower than 0 ° C, the strength is not improved so much, and if the temperature is higher than 560 ° C, burning occurs and the moldability is deteriorated, which is not desirable. Further, if the heating rate is less than 100 ° C./minute or the holding time is less than 3 seconds, the above effect cannot be obtained.

Then, it is rapidly cooled, but if the cooling rate is less than 300 ° C./min, the strength after baking is not improved so much and the formability is also deteriorated.

In the present invention, by this cooling rate, quenching is performed at a temperature of 50 to 130 ° C., and the temperature is maintained at this temperature (quenching temperature) for 1 to 48 hours. If the quenching temperature and the temperature maintained after quenching are less than 50 ° C, the effect of improving the strength after baking is small, and if it exceeds 130 ° C, the effect of improving the strength is large, but the formability is deteriorated, which is not preferable. Also, the temperature holding time is
If it is less than 1 hour, the effect of improving the strength is small, and if it exceeds 48 hours, the moldability is lowered, which is not preferable. Therefore, the quenching temperature should be in the range of 50-130 ℃
The temperature is maintained at a temperature of ℃ for 1 to 48 hours.

(Example) Next, the Example of this invention is shown.

Example 1 An aluminum alloy having the chemical composition shown in Table 1 was melted and cast by a usual method, and the obtained ingot was homogenized by heating it at a temperature of 510 ° C. for 4 hours at a heating rate of 40 ° C./hr. Then, hot rolling and cold rolling (cold rolling rate 30%) were performed to obtain a plate having a thickness of 1.0 mm.

This plate was rapidly heated to a temperature of 530 ° C at a heating rate of 300 ° C / min and held for 30 seconds, quenched at a temperature of 60 ° C at a cooling rate of 700 ° C / min, and kept at the temperature of 60 ° C for 24 hours. .

Table 2 shows the characteristics of the obtained material and the bake hardenability (proof strength) after baking (175 ° C x 30 minutes).

As is apparent from Table 2, it is understood that the material is a material having excellent balance of strength and moldability as compared with the invention examples No. 1 to No. 13 and the comparative examples No. 14 to No. 26.

On the other hand, the comparative examples do not satisfy both strength and moldability at the same time.

Example 2 An ingot obtained by melting and casting No. 8 aluminum alloy (within the scope of the present invention) shown in Table 1 of Example 1 by a usual method was heated at a heating rate of 40 ° C./hr and 510 After carrying out a homogenizing treatment in which the temperature was kept at 6 ° C for 6 hours, hot rolling and cold rolling were performed to obtain a 1.0 mm thick plate.

The plate is then heated to a heating rate of 300 as shown in Table 3.
Rapidly heated to a temperature of 460-580 ° C at ℃ / min, held for 1-60 seconds, quenched at a temperature of 40-140 ° C at a cooling rate of 700 ° C / min, and kept at a temperature of 40-140 ° C for 0.5- Hold for 60 hours.

The characteristics of the obtained material and the bake hardenability (proof strength) after baking (175 ° C x 30 minutes) are also shown in Table 3.

As is clear from Table 3, the invention examples No. 2 to No. 4 and No. 7
It can be seen that each of No. 8, No. 10, No. 10, No. 11 and No. 14 is a well-balanced material having excellent strength and moldability.

On the other hand, the comparative examples do not satisfy both strength and moldability at the same time.

(Effect of the Invention) As described in detail above, according to the present invention, excellent moldability,
Further, it is possible to obtain an aluminum alloy plate having an excellent strength improving property even when coating baking is performed at a low temperature for a short time.

Claims (1)

[Claims] 1. In weight% (hereinafter the same), Mg: 0.2-0.6% and Si: 0.9-1.6% are contained as essential components, and the content ratio is Si> 0.58 × Mg + 0.8. Yes, further Cu: 0.3
% Or less, Ti: 0.1% or less, B: 0.06% or less, Be: 0.2% or less,
Mn: 0.3% or less, Cr: 0.4% or less, Fe: 0.5% or less, Zr: 0.2%
Aluminum alloy ingot containing one or more of the following and V: 0.2% or less, the balance being substantially Al, subjected to homogenization treatment, hot rolling, and then cooling. After performing hot rolling to a desired plate thickness, as solution treatment, it is rapidly heated to a temperature of 480 to 560 ° C at a heating rate of 100 ° C / min or more, and kept in this temperature range for 3 seconds or more, and then a cooling rate. To
Aluminum with excellent formability and bake hardenability, characterized by being heat-treated at a temperature of 50 to 130 ° C at a rate of 300 ° C / min or more and holding at a temperature of 50 to 130 ° C for 1 to 48 hours. Method for manufacturing alloy plate.