JPH06116689A - Production of al-mg-si alloy sheet excellent in formability and baking hardenability - Google Patents

Abstract

PURPOSE:To increase the strength of an alloy sheet by subjecting a cold rolled Al-Mg- Si alloy sheet having a specified compsn. to heat treatment under specified conditions and executing baking and coating. CONSTITUTION:An Al alloy contg., by weight, 0.3 to 1.0% Mg and 0.5 to 2.0% Si so as to regulate <=1 Mg/Si ratio and furthermore added, as the main adding element, with 0.05 to 1.0% Mn is subjected to homogenizing treatment at the burning temp. or below, is subjected to hot rolling, is, in the hot rolled stock, subjected to standard solution treatment and water hardening as grain refining treatment and is subjected to intermediate annealing at 300 to 450 deg.C for 4 to 8hr at >=40 deg.C/hr heating rate to form fine precipitates. It is subjected to cold rolling at >=50% draft to regulate its sheet thickness into a desired one, which is, as solution treatment, subjected to rapid heating to 500 to 580 deg.C at >=100 deg.C/min heating rate, is held for >=10sec, is thereafter immediately hardened at >=400 deg.C/min cooling rate and is furthermore held to 50 to 120 deg.C for 1 to 48hr to regulate its crystalline grains into <=30mum and to improve its formability, and baking and coating is executed to increase its strength. In this way, the Al-Mg-Si alloy sheet excellent in formability and baking hardenability can be produced.

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 based alloy sheet which is used for automobile parts, household electric equipment parts, machine parts and the like and which is excellent in formability and baking paintability. Is.

[0002]

2. Description of the Related Art Al alloys used for reducing the weight of automobile parts, household electric equipment parts, mechanical parts and the like include Al-Mg-Si based alloys and Al-Mg based alloys. Here, the heat treatment type Al-Mg-Si based alloys have been attracting attention for their curability at the time of baking coating in a coating line in the application as an automobile panel material. Regarding the conventional manufacturing process for this Al-Mg-Si based alloy, for example, "light metal" Vol. 30, No. 1
1, p.609 and Japanese Patent Application No. 62-267714.

However, in the conventional manufacturing process, a temperature of 140 to 170 ° C. is 10 to 3 as a baking coating process after quenching.
Even if a baking coating treatment of holding for 0 minutes is performed, no significant improvement in strength is observed, and a material having good moldability is not obtained.

[0004]

When Al alloy is used for automobile parts, household electric equipment parts, machine parts, etc., press working and bending work are required. Therefore,
It must have moldability (elongation, Erichsen value, etc.) that can sufficiently cope with those molding processes, and must also have sufficient strength as a product after processing.

However, in the conventional Al-Mg-Si alloys, the strength is insufficient when the formability is emphasized, and the formability is remarkably lowered when the strength is increased. The manufacturing method cannot be seen. Especially for automobile parts, the use of Al alloy and its thinning are being considered as the weight reduction of automobiles is promoted by the CAFE regulation. In order to meet these requirements, it is excellent in formability and baking paintability. It is necessary to establish a manufacturing process for Al-Mg-Si alloys.

In order to meet such demands, the present invention has an object to provide a method for producing an Al-Mg-Si alloy having excellent formability and baking coating property.

[0007]

As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that Al-Mg-Si
The inventors have found that this is possible by controlling the component composition and production conditions of the base alloy, and have completed the present invention.

That is, according to the present invention, Mg: 0.3 to 1.0.
%, Si: 0.5-2.0% at a Mg / Si ratio of 1 or less, and Mn: 0.05-1.0% as a main additive element, with respect to an Al alloy at a temperature not higher than the burning temperature. After homogenizing at temperature, hot rolling is performed, and then standard solution treatment and water quenching are performed on the hot-rolled material as grain refining treatment, and at a heating rate of 40 ° C / hr or more, 30
Intermediate annealing is performed at a temperature of 0 to 450 ° C. for 4 to 8 hours to generate fine precipitates, and then cold rolling at a reduction rate of 50% or more is performed to obtain a desired plate thickness, and finally, a liquid As a chemical treatment, it is rapidly heated to a temperature of 500 to 580 ° C. at a heating rate of 100 ° C./min or more, and held in this temperature range for 10 seconds or more, and then immediately quenched at a cooling rate of 400 ° C./min or more. By maintaining the temperature at 50 to 120 ° C. for 1 to 48 hours, the crystal grain is controlled to 30 μm or less to improve the formability, and further, the baking treatment is performed to enhance the strength. A with excellent bake hardenability
The gist is a method for producing an l-Mg-Si alloy plate.

The present invention will be described in more detail below.

[0010]

[Action]

The strengthening mechanism of the Al--Mg--Si alloy according to the present invention is based on the following age hardening mechanism.

SS (solid solution) → GP zone (T4 state)
→ β-Mg ₂ Si (after baking finish)

In the present invention, formability is emphasized in the Al-Mg-Si system alloy, and at the same time, appropriate strength is imparted by the above-mentioned strengthening mechanism. Therefore, since the strength improvement in the alloy of the present invention depends on the precipitation of β'-Mg ₂ Si, the addition amounts of Mg and Si are limited.

Further, in order to improve the formability, first, an additional element Mn for suppressing recrystallization of the alloy structure and refining the crystal grains is added. Further, by subjecting the hot-rolled material to a heat treatment, the precipitates in the alloy are finely and uniformly dispersed to control the crystal grains, thereby making the crystal grains finer.

In the manufacturing process of the present invention, in short, in the conventional manufacturing process, between the hot rolling and the cold rolling, the solution treatment and the step of performing intermediate annealing at 300 to 450 ° C. for 4 to 8 hours are interposed. The most characteristic point is the following manufacturing process.

Al alloy ingot → homogenizing heat treatment → hot rolling →
Liquefaction treatment → Intermediate annealing → Cold rolling → Solution treatment → Quenching
(Final heat treatment) → Baking coating treatment

First, the reasons for limiting the chemical composition of the Al alloy in the present invention will be explained.

Mg: Mg is an element which, together with Si, strengthens its own solid solution and gives strength in combination with Si. Aged precipitate β'-Mg ₂
Si is deposited and its precipitation hardening contributes to the improvement of strength. However, if it is less than 0.3%, sufficient strength (hereinafter, the strength means the material (T4) and the strength after baking treatment at 170 ° C.) cannot be obtained, and the strength is 1.0. %
If it is added over the range, the equilibrium phase Mg ₂ Si grows as a crystallized substance during casting, the elongation is lowered, and the formability is remarkably lowered. Therefore, the Mg content is set to the range of 0.3 to 1.0%.

Si: Si is an element which, together with Mg, contributes to the improvement of strength mainly by precipitation hardening due to the precipitation of the aging precipitate β'-Mg ₂ Si. However, if it is less than 0.5%, sufficient strength cannot be obtained, and if it exceeds 2.0%, the equilibrium phase Mg ₂
Si crystallizes out and the elongation decreases, so that the formability remarkably decreases. Therefore, the Si content is 0.5-2.0%
The range is.

Further, it is necessary to adjust the above components so that the ratio of the amount of Mg and the amount of Si (Mg / Si) is 1 or less. As a result, the strength after baking treatment can be efficiently improved, and the deterioration of the formability due to the change with time of the material can be suppressed.

Mn: Mn is an element that precipitates MnAl ₆ as a second phase precipitate, suppresses recrystallization of the alloy structure and makes the crystal grains finer, thereby contributing to the improvement of formability. However, if it is less than 0.05%, grain refinement is not observed,
Moreover, since the precipitation of the second-phase precipitate MnAl ₆ is not remarkable, the moldability is not improved. If it is added in an amount of more than 1.0%, coarse crystallized substances will be formed and the formability will be deteriorated. Therefore, the content of Mn is set to the range of 0.05 to 1.0%.

It is desirable that the amount of impurities is as small as possible. In particular, Fe has a small effect of improving the strength, but when the content thereof is large, the formation of crystallized substances remarkably deteriorates the formability, so that the content of Fe is suppressed to 0.5% or less. desirable.

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

The Al alloy ingot is homogenized at a temperature not higher than the burning temperature and immediately hot-rolled to process the ingot structure into a wrought material structure. Thereafter, standard solution treatment and water quenching are performed, and further intermediate annealing is performed at a heating rate of 40 ° C./h or more at a temperature of 300 to 450 ° C. for 4 to 8 hours.

Here, the standard solution treatment and water quenching are carried out by solid solution of Mg and Si to strengthen the solid solution of Mg, and at the same time, precipitates (Mg ₂ S
This is for sufficiently precipitating i). The conditions are not particularly limited.

When the intermediate annealing temperature is lower than 300 ° C. and the holding time is longer than 8 hours, the strength is increased, but the formability does not reach a desired level, and conversely, at a temperature higher than 450 ° C. When the holding time is less than 4 hours, a material having high moldability can be obtained, but the strength is insufficient. Therefore, the intermediate annealing condition is set to a temperature of 300 to 450 ° C. for 4 to 8 hours.

Precipitates are formed by this heat treatment, and during the subsequent cold rolling, high-density dislocations are generated around these precipitates to form fine crystal grains. In this cold rolling, if the rolling ratio is less than 50%, a sufficient dislocation density cannot be obtained, so that a desired fine crystal grain size cannot be obtained. Therefore, the cold rolling rate during finish rolling is 50% or more.

After this cold rolling, as a solution treatment, 1
It is rapidly heated to a temperature of 500 to 580 ° C. at a heating rate of 00 ° C./minute or more, held in this temperature range for 10 seconds or more, and immediately quenched at a rate of 400 ° C./minute or more, and further 50 to
Hold at a temperature of 120 ° C. for 1-48 hours.

Here, when the solution treatment condition is less than 500 ° C. or 500 to 580 ° C. and the holding time is less than 10 seconds, heat treatment (50 to 120 ° C. × 1 to 48 ° C.) is performed after quenching.
Hold for a time, and then baking coating (170 ° C x 20
However, sufficient strength cannot be obtained due to insufficient formation of precipitates. Further, the solution treatment temperature is 580
If it exceeds ℃, heat treatment (50-120
(Temperature C × 1 to 48 hours) and then baking coating treatment gives high strength, but the formability in the T4 state decreases. Further, even if the solution treatment of holding at 500 to 580 ° C. for longer than 10 seconds is performed, if the heat treatment condition after quenching is a temperature of less than 50 ° C. or a temperature of 50 to 120 ° C. and a holding time of less than 1 hour, a baking coating treatment is performed. Does not provide sufficient strength, and if the temperature is maintained at 50 to 120 ° C. for longer than 48 hours, the formability in the T4 state deteriorates. Therefore, the solution treatment condition after cold rolling is 50
The temperature is maintained at 0 to 580 ° C for 10 seconds or more, and the heat treatment condition after quenching is maintained at the temperature of 50 to 120 ° C for 1 to 48 hours. In this state (T4 material), the material of the present invention is excellent in formability, and is subjected to baking coating treatment to become a material having high strength.

Next, examples of the present invention will be described.

[0031]

[Example 1]

Mg: 0.8%, Si: 1.0%, Mn: 0.15
%, Fe: 0.13%, Al-Mg-Si based alloy having a chemical composition with the balance substantially consisting of Al is melted by a usual method,
After casting, the obtained ingot was subjected to a homogenizing treatment in which the heating rate was 40 ° C./h and the temperature was maintained at 540 ° C. for 4 hours, followed by hot rolling.

This plate is heated at a heating rate of 800 ° C./min or more to 53
Hold at 0 ° C for 30 minutes, perform water quenching at a cooling rate of 800 ° C / min, and then 250 to 5 at a heating rate of 40 ° C / h.
After holding at a temperature of 50 ° C. for 0.5 to 12 hours, cold rolling (reduction rate 88%) was performed.

Finally, at a heating rate of 800 ° C./min or more, 48
Hold at a temperature of 0-600 ° C for 1-40 seconds, 400-60
After forced air cooling at a cooling rate of 0 ° C./min, the temperature was maintained at 30 to 150 ° C. for 1 to 72 hours at a heating rate of 40 ° C./h.

Characteristics of the obtained material and baking coating treatment
The strength after (170 ° C. × 20 minutes) is shown in Table 1.

The tensile test was conducted using a JIS No. 5 test piece at a tensile speed of 5 mm / min. The Erichsen test was conducted according to JIS B method. Furthermore, the crystal grain size measurement is
After polishing with an emery paper having a cross section parallel to the rolling direction of the sample and buffing, the measurement was performed by the section method using a 100-fold polarized photograph of the surface subjected to electrolytic etching.

The strength and formability evaluation criteria in Table 1 are such that the strength is assumed to be work-hardened, and the increment of the yield strength from the T4 state of the sample subjected to 2% stretching and baking coating is 80N. / mm ² or more of the ○ (excellent) subjected, also formability is targeting high moldability, Erichsen value was denoted by ○ (excellent) to more than 9.9 mm.

As is clear from Table 1, the invention example No. 1
4 has a crystal grain size of 30 μ compared to Comparative Examples No. 5 to 15.
It can be seen that the material is controlled to m or less, has excellent moldability, has high strength, and has a suitable combination of moldability and strength.

Further, T of the invention sample No. 4 and the comparative sample No. 5
FIG. 1 shows a microstructure photograph of crystal grains in four states. Table 1 and FIG.
As is clearer, the crystal grain size of Inventive Example No. 4 is 16
.mu.m, which is considerably finer than the crystal grain size of 40 .mu.m of Comparative Example No. 5. It can be confirmed that the refinement of the crystal grains plays an important role in improving the formability in the examples of the present invention.

It can be seen that the Al--Mg--Si alloy thus obtained is excellent in formability, and that the material subjected to the baking coating treatment at 170 ° C. for 20 minutes can obtain the desired strength.

[0041]

[Table 1]

[0042]

Example 2

Al alloys having the chemical composition shown in Table 2
Table 2 shows the strength and formability of the material obtained by performing the manufacturing process based on the manufacturing conditions of Example No. 4 of the present invention of Example 1.
Are also shown. The tensile test and the Erichsen test were performed in the same manner as in Example 1.

As is clear from Table 2, the invention example No. 1
In Nos. 4 to 4, sufficient strength and moldability were obtained by performing the manufacturing process of the present invention. However, Comparative Example No. 5
In Nos. 10 to 10, sufficient strength and moldability cannot be obtained even if the production process of the present invention is performed. Therefore, in order to impart sufficient strength and moldability by applying the manufacturing process of the present invention, Mg: 0.3 to 1.0% and Si: 0.5 to 2.0% are required. It can be seen that the addition of Mn: 0.05 to 1.0% is effective for improving the properties.

[0045]

[Table 2]

[0046]

As described in detail above, according to the present invention,
Under the regulation of the composition of the Al-Mg-Si alloy, the solution heat treatment during the hot rolling and the cold rolling in the conventional manufacturing process,
By adding water quenching and intermediate annealing, it becomes possible to produce an Al-Mg-Si alloy having excellent formability and bake hardenability, and it is possible to expand the demand for Al alloys for automobile parts and the like. In addition, the use of Al alloy greatly contributes to the reduction of weight and the reduction of cost due to the reduction in thickness, and its practical effect is extremely large.

[Brief description of drawings]

FIG. 1 is an example No. 4 of the present invention and a comparative example N obtained in Example 1.
It is a microstructure photograph (metal structure) of the T4 state crystal grain of Al alloy of 0.5.

Claims (1)

[Claims] 1. In weight% (hereinafter the same), Mg: 0.3-
Burning of an Al alloy containing 1.0% and Si: 0.5 to 2.0% at a Mg / Si ratio of 1 or less, and Mn: 0.05 to 1.0% as a main additive element. After homogenizing at a temperature below the temperature, hot rolling is performed, and then standard solution treatment and water quenching are performed on the hot rolled material as grain refining treatment, and the heating rate is 40 ° C / hr. As described above, intermediate annealing is performed at a temperature of 300 to 450 ° C. for 4 to 8 hours to form fine precipitates, and then cold rolling at a reduction rate of 50% or more is performed to obtain a desired sheet thickness, and finally, As a liquefaction treatment, 500 to 58 at a heating rate of 100 ° C./min or more.
By rapidly heating it to a temperature of 0 ° C and holding it in this temperature range for 10 seconds or more, immediately quenching it at a cooling rate of 400 ° C / minute or more, and then holding it at a temperature of 50 to 120 ° C for 1 to 48 hours. , An Al-Mg-Si alloy plate excellent in formability and bake hardenability, characterized in that the crystallinity is controlled to 30 μm or less to improve the formability and further the baking treatment is performed to increase the strength. Manufacturing method.