JP2613466B2 - Manufacturing method of aluminum alloy sheet excellent in bake hardenability - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an aluminum alloy sheet having excellent bake hardenability, and more particularly, to bake hardenability by heating during baking of a paint after forming. The present invention relates to a method for manufacturing an aluminum alloy sheet having excellent properties.

(Prior art) Conventionally, aluminum alloy plates used for automotive parts and other applications are subjected to forming processing such as pressing and bending, and in a coating process, in order to maintain strength of the coated coating film. After coating, heating (baking, baking) is performed, and at the same time, the strength of the aluminum alloy plate is improved using this heating.

In recent years, from the viewpoint of energy saving and cost reduction, there is a tendency that the baking temperature is low and the baking time is short, and there is a strong demand for an aluminum alloy plate whose strength is improved by baking at a low temperature for a short time.

Techniques that meet such demands include, for example,
There is a proposal by 62-89852. This is Mg: 0.4-1.5%
And Si: 0.3-1.5%, Cu 0.2-0.8%, and further, Ti
0.005 to 0.1%, B: 0.0005 to 0.03%, Mn: 0.8% or less, Cr:
0.4% or less, Fe: 0.5% or less, Zr: 0.2% or less and V: 0.1% or less selected from one or more, and
Contains inevitable impurities of 0.2% or less, with the balance being substantially Al
Al-Mg-Si-Cu-based alloy ingot consisting of, subjected to normal homogenization treatment at a temperature below the burning temperature, hot rolling and cold rolling to the desired plate thickness, heating as a tempering treatment Perform rapid heating to 480-580 ° C at a rate of 100 ° C / min or more, hold at this temperature for 3 seconds or more, then increase the cooling rate to 100 ° C by 3
This is a method in which a heat treatment of quenching at a temperature of 00 ° C./min or more is performed, and a final heat treatment is performed at a temperature of 40 to 120 ° C. for 8 to 36 hours within 72 hours. The aluminum alloy plate obtained by this method has the effect of improving the strength by heating (baking) at a high temperature and a long time at a high temperature of 200 ° C for 60 to 90 minutes, which has been conventionally performed. It is said that there is an effect that the strength is improved even by baking at a low temperature for a short time of holding for a minute.

(Problems to be solved by the invention) However, in the manufacturing method proposed above,
“480-580 ° C at a heating rate of 100 ° C / min or more as a tempering treatment
After heating rapidly for 3 seconds or more,
Perform a heat treatment in which the cooling rate to 0 ° C is quenched at 300 ° C / min or more, and then perform a final heat treatment at a temperature of 40 to 120 ° C for 8 to 36 hours within 72 hours. ” Although it is said that the final heat treatment is performed after cooling, the heat energy required for reheating (final heat treatment) is very large, and from the viewpoint of energy saving and cost reduction,
Further improvement was required.

The present invention has been made in response to such a demand, and a method capable of further improving the baking hardenability by low-temperature and short-time baking which can further save energy and reduce costs in the method according to the above-mentioned proposal. It is intended to provide.

(Means for Solving the Problems) In order to achieve the above object, the present inventor has proposed a method according to the above-mentioned proposal in which the reheating is performed after cooling to room temperature after the tempering treatment, Intensive research has been conducted on the effect of reheating on the bake hardenability due to short-time heating at low temperature.

As a result, it was found that the sheet material cooled to room temperature and reheated was inferior in bake hardenability. It is considered that the reason is that the nuclei of the aging precipitation formed at room temperature do not contribute to the improvement of the strength due to the growth of the precipitation phase during the subsequent baking coating.

The present invention has been completed based on such findings and further research on chemical components and production conditions in detail.

That is, the method for producing an aluminum alloy sheet having excellent bake hardenability according to the present invention is as follows: Mg: 0.4 to 1.5% and Si: 0.3 to
Contains 2.3%, Cu: 0.8% or less, Ti: 0.1% or less,
B: 0.06% or less, Mn: 0.8% or less, Cr: 0.4% or less, Be: 0.2%
Hereinafter, for alloy ingots containing one or more of Zr: 0.2% or less, V: 0.2% or less and Fe: 0.5% or less, with the balance being substantially Al, the temperature is below the burning temperature. After subjected to a homogenization treatment, hot rolling is performed, and then 300 to 580
After performing cold rolling at a cold rolling rate of 5% or more with or without rough annealing or intermediate annealing at a temperature of 100 ° C. to obtain a desired thickness, as a solution treatment, heating at 100 ° C./min or more 4 by speed
After rapidly heating to a temperature of 80 to 580 ° C and holding in this temperature range for 3 seconds or more, a heat treatment of quenching to a temperature of 50 to 130 ° C at a cooling rate of 300 ° C / min or more, and continuing as it is, 13
It is characterized in that the temperature is maintained at a temperature of 0 ° C. for 1 to 96 hours. In the above process, "the heat treatment of quenching to the temperature of ... is performed, and the temperature is continuously maintained at a temperature of 50 to 130 ° C for 1 to 96 hours" means that after quenching,
This means that the aluminum alloy plate at the quenching temperature is not cooled or heated from that temperature and then goes to the temperature holding step, but goes to the temperature holding step continuously at that temperature. In other words, after the quenching, the temperature holding step starts immediately from the quenching end temperature.

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

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

Mg: Mg is an element that strengthens in cooperation with Si,
%, The strength (hereinafter, “strength” refers to the strength of the material and after baking at 175 ° C.) is low, and micro-cracks tend to occur. If the content exceeds 1.5%, the moldability deteriorates.
Therefore, the Mg content is in the range of 0.4 to 1.5%.

Si: Si is an element that strengthens in cooperation with Mg, but 0.3%
%, The strength is low, and if it exceeds 2.3%, the moldability deteriorates and micro-cracks tend to occur. Therefore, the Si content is in the range of 0.3 to 2.3%.

The present invention, these Mg, Si as an essential component, further, the elements described below Cu, Ti, B, Mn, Cr, Be, Zr, V and
It contains one or more of Fe.

Cu: Cu is an element that imparts strength, but deteriorates corrosion resistance and formability exceeding 0.8%. Therefore, the Cu content is set to 0.8% or less.

Ti: Ti is an element that refines the crystal grains of the ingot and improves the formability. However, if it exceeds 0.1%, coarse crystals are formed and the formability is reduced. Therefore, the Ti content is set to 0.1% or less.

B: Like Ti, B is an element that refines the crystal grains of the ingot and improves the formability. However, if it is contained in excess of 0.06%, coarse crystals are formed and the formability is reduced. Therefore, the B content is set to 0.06% or less.

Mn, Cr, Zr, V, Fe: Mn, Cr, Zr, V are elements that have the effect of improving strength, but when the content increases, coarse crystals are generated,
Although the formability is reduced, and Fe has a small effect of improving the strength, the formability is reduced for the same reason. Therefore, Mn content is 0.8% or less, Cr content is 0.4% or less, Zr
Content is 0.2% or less, V content is 0.2% or less, Fe content is
0.5% or less.

Be: Be is an element that is effective in improving hot rolling properties and improving the formability of products, but its effect is saturated when it exceeds 0.2%. Therefore, the Be content is set to 0.2% or less.

In addition, other impurities may be contained in an amount of 0.2% or less without impairing bake hardenability and moldability.

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

The homogenization treatment of the aluminum alloy ingot having the above chemical components is preferably performed at a temperature equal to or lower than the burning temperature. Particularly, in the case of a composition having moldability and bake hardenability, the homogenization treatment is performed by heating to a target temperature. The speed may be 200 ° C./hr or less, or a multi-stage homogenization treatment of two or more stages may be performed.

Subsequently, hot rolling is performed. However, since this condition has little effect on bake hardenability, it is not necessary to particularly limit the condition.

Although cold rolling is performed after hot rolling, rough annealing may be performed after hot rolling, or intermediate annealing may be performed after cold rolling is started. When high formability is required depending on the processing state of the product, the formability is improved by performing such annealing. The annealing temperature is in the range of 300 to 580 ° C. 300 ℃
If it is less than 580 ° C., the effect of improving the moldability is small, and if it exceeds 580 ° C., burning occurs, and the moldability is undesirably reduced.

Cold rolling is effective in improving formability, and the improvement in formability increases as the cold rolling reduction increases. However, the effect is small when the rolling reduction is less than 5%. Therefore, cold rolling is performed at a rolling reduction of 5% or more.

After cold rolling, a solution treatment is performed. This solution treatment improves material strength, high formability, and post-bake strength by performing rapid heating, high-temperature, short-time heating, and then rapid cooling. Processing. That is, it is rapidly heated to a high temperature of 480 to 580 ° C. at a temperature of 100 ° C./min or more, and is maintained at this temperature for 3 seconds or more. At a temperature higher than this, burning occurs and the formability decreases. Also, the heating rate
If the temperature is less than 100 ° C./min or the holding time is less than 3 seconds, the above effects cannot be obtained.

Next, rapid cooling is performed. If the cooling rate is less than 300 ° C./min, the strength after baking is small, and the moldability is also reduced. Therefore, the cooling rate is 300 ° C./min or more.

In the present invention, quenching is performed at a temperature of 50 to 130 ° C. by the cooling rate, and the temperature is maintained at this temperature (quenching temperature) for 1 to 96 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 moldability is undesirably reduced. The temperature holding time is 1
If the time is less than the time, the effect of improving the strength is small, and if the time is more than 96 hours, the moldability deteriorates, which is not preferable. Therefore, the quenching temperature is in the range of 50 to 130 ° C, and
The temperature is maintained at a temperature of 1 to 96 hours.

In the case where the material is once cooled to room temperature and then reheated after quenching, the effect of improving the baking hardenability by heating at a low temperature for a short time as described above is smaller than in the above case.

In addition, baking is heating at a low temperature for a short time at about 175 ° C. for 30 minutes, and is distinguished from baking at a high temperature for a long time such as 200 ° C. for 60 minutes.

(Example) Next, an example of the present invention will be described.

Example 1 An aluminum alloy having the chemical components shown in Table 1 was melted and cast in a usual manner, and the obtained ingot was homogenized at a heating rate of 40 ° C./hr at 530 ° C. for 4 hours. Hot rolling and cold rolling (cold rolling rate 30%)
Was performed to obtain a plate having a thickness of 1.0 mm.

This plate is kept at a heating rate of 300 ° C / min at a temperature of 530 ° C for 20 seconds, quenched to a temperature of 60 ° C at a cooling rate of 800 ° C / min,
The temperature was kept at 60 ° C. for 48 hours.

Table 2 shows the properties of the obtained material and the bake hardenability (proof stress) after baking (175 ° C. × 30 minutes).

As is clear from Table 2, the present invention examples No. 1 to No. 12
It can be seen that is a well-balanced material with excellent strength and moldability as compared with Comparative Examples No. 13 to No. 23.

Example 2 An ingot obtained by melting and casting an aluminum alloy of No. 6 shown in Table 1 of Example 1 (the scope of the present invention) by a usual method was heated at a heating rate of 40 ° C./hr to 520 ° C. 6 for the temperature
After performing the homogenization treatment for holding for a time, hot rolling and cold rolling were performed to obtain a 1.0 mm thick plate.

Then, the plate is heated to a temperature of 450 to 590 ° C. at a heating rate of 400 ° C./min, held for 1 to 60 seconds, quenched to a temperature of 30 to 150 ° C. at a cooling rate of 600 ° C./min, and kept at a temperature of 30 to 150 ° C. It was kept at a temperature of ° C for 12-120 hours.

Table 3 shows the properties of the obtained material and the bake hardenability (proof stress) after baking (175 ° C. × 30 minutes).

As is clear from Table 3, the present invention examples No. 2 to No. 4, N
It can be seen that o.7 to No.8, No.10 to No.11, No.13 to No.14 are all well-balanced materials with excellent strength and moldability.

Example 3 An ingot obtained by melting and casting a No. 6 aluminum alloy (range 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 to 520 ° C. 6 for the temperature
After performing the homogenization process to hold for a time, perform hot rolling,
Subsequently, cold rolling was performed at a rolling reduction of 3 to 30% to obtain a 1.0 mm thick plate.

Next, heat to a temperature of 530 ° C at a heating rate of 50 to 300 ° C / min and hold for 20 seconds, quench to a temperature of 60 ° C at a cooling rate of 200 to 600 ° C / min, and keep at that temperature for 48 hours did.

Table 4 shows the properties of the obtained material and the bake hardenability (proof stress) after baking (175 ° C. × 30 minutes).

As is clear from Table 4, the present invention examples No. 2 to No. 3, N
It can be seen that o.5 and No.7 are both well-balanced materials with excellent strength and moldability.

Example 4 An ingot obtained by melting and casting an aluminum alloy of No. 6 shown in Table 1 of Example 1 (the scope of the present invention) by a usual method was heated at 520 ° C. at a heating rate of 40 ° C./hr. 4 for the temperature
After performing a homogenization treatment for holding for a long time, hot rolling and cold rolling (a cold rolling rate of 30%) were performed to obtain a plate having a thickness of 1.0 mm.

Then, the plate was heated to a temperature of 530 ° C. at a heating rate of 300 ° C./min, held for 20 seconds, quenched to a temperature of 60 ° C. at a cooling rate of 800 ° C./min, and kept at a temperature of 60 ° C. for 48 hours. .
For comparison, a part was left at room temperature for 0.5 to 24 hours after quenching, and then kept at a temperature of 60 ° C. for 48 hours.

Table 5 shows the properties of the obtained material and the bake hardenability (proof stress) after baking (175 ° C. × 30 minutes).

As is clear from Table 5, the present invention sample No. 1 is a type in which the temperature is maintained at the quenching temperature. .2N
Compared to o.4, the strength after baking is significantly improved.

(Effects of the Invention) As described above in detail, according to the present invention, it is possible to obtain an aluminum alloy plate having excellent moldability and excellent strength improvement even in low-temperature and short-time coating baking,
The effect of energy saving and cost reduction is great along with improvement in bake hardenability.

Claims (2)

(57) [Claims] (1) Mg: 0.4 to 1.5% by weight (hereinafter the same)
And Si: 0.3 to 2.3%, and further, Cu: 0.8% or less, Ti:
0.1% or less, B: 0.06% or less, Mn: 0.8% or less, Cr: 0.4% or less, Be: 0.2% or less, Zr: 0.2% or less, V: 0.2% or less, and Fe:
The alloy ingot containing one or more of 0.5% or less and the balance substantially consisting of Al is subjected to a homogenization treatment at a temperature equal to or lower than a burning temperature, and then hot-rolled, After performing cold rolling at a cold rolling rate of 5% or more to obtain a desired thickness, as a solution treatment, the material is rapidly heated to a temperature of 480 to 580 ° C. at a heating rate of 100 ° C./min or more. After holding for 3 seconds or more, the cooling rate should be 50-130 ° C at 300 ° C / min or more.
Heat treatment to a temperature of
A method for producing an aluminum alloy sheet having excellent bake hardenability, wherein the temperature is maintained at a temperature of 130 ° C. for 1 to 96 hours. 2. The method according to claim 1, wherein after the hot rolling, the cold rolling is performed by performing rough annealing or intermediate annealing at a temperature of 300 to 580 ° C.