JPH0941062A - Alum.-magnesium-silicon type alum. alloy sheet material for automotive body sheet small in secular change and excellent in baking hardenability and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an Al alloy sheet material small in a secular change and excellent in baking hardenability by preparing an Al alloy sheet material having a specified componental compsn. in which the contents of Si and Mg and electric conductivity rising by heating are prescribed. SOLUTION: An Al-Mg-Si Al alloy sheet material having a compsn. contg., by weight, 0.2 to 3.0% Si and 0.2 to 3.0% Mg, contg. one or >= two kinds among 0.01 to 0.5% Fe, 0.01 to 1.5% Cu, 0.01 to 0.5% Mn, 0.01 to 1.5% Cr, 0.01 to 0.5% Zr and 0.001 to 0.5% Ti, and the balance Al with inevitable impurities, and in which the raise of electric conductivity in the case of heating at 250 deg.C for 10sec is regulated to <=0.75% ACS is prepd. Thus, the Al alloy sheet material for an automotive body sheet small in a secular change and having excellent baking hardenability can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Al-Mg-Si-based aluminum alloy sheet material which has a small change with time and has an excellent bake hardenability and which is suitable for an automobile body sheet subjected to paint baking, and a method for producing the same. It is a thing.

[0002]

2. Description of the Related Art Conventionally, cold-rolled steel sheets have been mainly used for automobile body sheets. However, recently, the use of an aluminum alloy plate has been studied due to the demand for weight reduction of automobile bodies. Normally, materials for automobile body sheets are required to have excellent breath moldability, high strength, and excellent corrosion resistance.
Aluminum alloys such as JIS5052 alloy and JIS5182 alloy are aluminum alloy materials satisfying such requirements.
-Mg alloy (5000 series alloy) and Al-Mg-Si alloy (6000 series alloy) such as JIS6009 alloy and JIS6061 alloy have been used.

[0003]

The above-mentioned 6000 series alloys have relatively good press formability and can obtain high strength after coating baking and heating, and are therefore applied to automobile body sheet materials. By the way, the conventional baking temperature is 180 ℃
It took about 1 hour, but there is a tendency for the baking temperature to be lower and shorter, so high strength after baking for baking is required. However, by the conventional 6000 series alloys which left at room temperature after the solution treatment (natural aging) Then GP zone is precipitated, the mesophase of the called contributing beta 'improving the strength at the time of baking heat Mg ₂ Si Since the precipitation is hindered, the material which has been left for a long time after the solution treatment cannot obtain sufficient strength after coating baking.

[0004]

As a result of various studies in view of the above problems, the present invention suppresses the GP zone that precipitates during natural aging, rapidly precipitates β'during heating during baking of coating, has excellent formability, and changes with time. It is an object of the present invention to develop an Al-Mg-Si-based aluminum alloy sheet material for automobile body sheets having a small size and a high bake hardenability, and a manufacturing method thereof.

That is, Al for automobile body sheet of the present invention
-Mg-Si system Al alloy plate material, Si: 0.2 ~ 3.0 wt
%, Mg: 0.2-3.0 wt%, Fe: 0.01-0.5 wt%
%, Cu: 0.01 to 1.5 wt%, Mn: 0.01 to 0.5 wt%, C
r: 0.01 to 0.5 wt%, Zr: 0.01 to 0.5 wt%, Ti:
Including one or more of 0.001 to 0.5 wt%,
In an Al alloy plate material composed of the balance Al and unavoidable impurities, the increase in conductivity when heated at 250 ° C for 10 seconds
It is characterized in that it is 0.75% IACS or less.

Next, the aluminum for automobile body sheets of the present invention
One of the manufacturing methods of the —Mg—Si based Al alloy plate material is S
i: 0.2-3.0 wt%, Mg: 0.2-3.0 wt%, F
e: 0.01 to 0.5 wt%, Cu: 0.01 to 1.5 wt%, Mn: 0.
01-0.5 wt%, Cr: 0.01-0.5 wt%, Zr: 0.01-0.
5 wt%, Ti: 0.001 to 0.5 wt%, 1 or 2
Al containing at least one kind and consisting of balance Al and unavoidable impurities
After solution heat treatment of alloy plate material at 400 ℃ or more, cool it to 40 to 175 ℃ at a cooling rate of 2 ℃ / sec or more and wind it into a coil, then leave it at room temperature and / or within 36 hours in the furnace It is characterized by holding.

In the second manufacturing method of the present invention, the plate material having a holding temperature of 40 to 130 ° C. within 36 hours by the above manufacturing method is reheated to 180 to 320 ° C. and held for 25 minutes. It is characterized by.

The third manufacturing method of the present invention is the same as the second method described above.
The plate material treated by the method is cooled to 40 to 135 ° C at a cooling rate of 2 ° C / sec or more and held for 36 hours. At this time, as a holding method after reheating and cooling, 2
It is effective to wind the plate material cooled to 40 to 135 ° C at a cooling rate of ℃ / sec or more into a coil and then leave it at room temperature and / or hold it in a furnace for 36 hours or less.

Further, the fourth manufacturing method of the present invention is based on Si:
0.2-3.0 wt%, Mg: 0.2-3.0 wt%, Fe:
0.01-0.5 wt%, Cu: 0.01-1.5 wt%, Mn: 0.01-
0.5 wt%, Cr: 0.01 to 0.5 wt%, Zr: 0.01 to 0.5 wt%
%, Ti: 0.001 to 0.5 wt% Al alloy plate material containing one or more of 0.001 to 0.5 wt% and the balance Al and unavoidable impurities, and solution heat treated at 400 ° C or higher at a cooling rate of 2 ° C / sec or higher. After quenching and quenching, reheat to 180-320 ° C and hold for 25 minutes or less, cool to 40-135 ° C at a cooling rate of 2 ° C / sec or more and hold for 36 hours or less. As a holding method after reheating and cooling, a plate material cooled to 40 to 135 ° C at a cooling rate of 2 ° C / sec or more is wound into a coil and left at room temperature, and /
Or it is effective to keep it in the furnace for 36 hours.

First, the alloy composition of the Al alloy sheet material of the present invention is limited for the following reasons.

Si precipitates an intermediate phase of Mg ₂ Si called β ′ together with Mg during baking coating to improve the strength. The amount added was limited to 0.2-3.0 wt% because
If it is less than wt%, the effect is small, and if it exceeds 3.0 wt%, the formability after solution treatment is deteriorated.

[0012] Mg is a solid solution in the matrix after the solution treatment and contributes to the improvement of formability. Further, β ', Mg ₂ Si and the like are precipitated together with Si during baking coating to improve the strength. The amount added is limited to 0.2 to 3.0 wt% because if it is less than 0.2 wt%, its effect is small, and if it exceeds 3.0 wt%, the formability after solution treatment deteriorates.

As described above, Si and Mg are precipitated as β ', Mg ₂ Si, etc. during baking coating to improve the strength.
If the abundance ratio of these two elements is different, the bake hardenability is also different, and the weight ratio of Si and Mg is Si> 0.6 Mg (wt%) and M
If the amount of Si is excessive with respect to the amount of g ₂ Si, more excellent bake hardenability can be obtained. The effect of the present invention is not impaired even if Ag, Cd, etc. are added to control the aging behavior during baking coating.

Cu is applied in the GP zone, θ ', and
Precipitates S phase and improves the strength. Add 0.01
The reason for limiting the content to ˜1.5 wt% is that if it is less than 0.01 wt%, the strength improvement is small, and if it exceeds 1.5 wt%, the corrosion resistance decreases and the quenching sensitivity becomes too high.

Fe is usually contained as an impurity of Al. However, Fe easily forms a compound with Si,
If it is contained in excess of 0.5 wt%, it will hinder the improvement of strength during baking coating.

Mn, Cr, Zr and Ti are added to refine the crystal grains or improve the matrix strength. If it is less than the lower limit, the effect is small, and if it exceeds the upper limit, the formability after solution treatment is lowered. Further, even if the total amount of these elements exceeds 1.0 wt%, the formability after solution treatment is reduced.

The effect of the present invention is not particularly impaired if B or the like, which is usually added as a material for refining the cast structure, is 0.1 wt% or less.

Further, in the present invention, the alloy having the above composition is
0.75% IA increase in conductivity when heated at ℃ × 10 seconds
Although it is limited to CS or less, the reason will be described below.

When the 6000 series alloy is left at room temperature after solution treatment (natural aging), GP zones precipitate, so that Mg ₂ S called β'which contributes to the improvement of strength during baking is formed.
Since the precipitation of the intermediate phase of i is hindered, the material after a long time after the solution treatment cannot obtain sufficient strength after heating by baking for coating. By suppressing / reducing this GP zone, β'precipitates rapidly during coating baking heating and high bake hardenability can be obtained.

The present inventors have found a method for investigating a change in conductivity when heating at 250 ° C. for 10 seconds as a means for judging the magnitude of the amount of GP zone which has been precipitated. That is,
Due to the deposition of the GP zone, the conductivity after heating becomes high. Therefore, it is possible to judge the magnitude of the GP zone amount by comparing the conductivity before and after the treatment such that the GP zone is solid-dissolved and other precipitates are not formed.
Specifically, by heating at 250 ° C. for 10 seconds, the conductivity of the material in which the high-concentration GP zone is precipitated is greatly increased, and the increase of the conductivity is small in the material in which the GP zone precipitation amount is small. The reason for limiting the increase in conductivity to 0.75% IACS or less is that the increase in conductivity exceeding 0.75% IACS is
This is because the suppression / reduction of the GP zone is insufficient and the rapid precipitation of β ′ does not occur.

Next, the first to third manufacturing steps of the present invention using the Al--Mg--Si alloy having the above composition will be described. In the solution treatment, the additive elements such as Si and Mg are once solid-solved in the matrix, and fine compounds of β ′, Mg ₂ Si and the like are precipitated during the subsequent baking and heating to improve the strength. The solution treatment temperature is set to 400 ° C. or higher because if the temperature is lower than 400 ° C., the additive element cannot be sufficiently solid-dissolved and the strength improvement during baking and heating is small. The holding time is not specified, but
The time at which the temperature is 00 ° C. or higher is preferably 5 seconds or longer.

The cooling rate after the solution treatment is set to 2 ° C./sec or more because the coarse compound is precipitated at a cooling rate of less than 2 ° C./sec, so that the moldability is deteriorated and after the baking coating is heated. This is because the improvement in strength is reduced. However, when cooling to room temperature under the above cooling conditions, a large amount of quenching excess vacancies are introduced, and the precipitation in the GP zone is promoted. Therefore, in the material stored for a long period of time, the amount of precipitation in the GP zone increases, and the increase in conductivity when heated at 250 ° C. for 10 seconds exceeds 0.75% IACS.

Therefore, after the solution heat treatment, it is cooled to 40 to 175 ° C. at a cooling rate of 2 ° C./sec or more, and is kept at 40 to 175 ° C.
Hold for up to 36 hours. This is because if the cooling temperature is less than 40 ° C, there is no effect, and if the cooling temperature exceeds 175 ° C, β ', β, etc. precipitate and the strength of the base plate increases. This is also due to β ′, β, etc. precipitating out even after holding for more than 36 hours. Note that the term "holding" as used herein includes, in addition to holding at the same temperature, a treatment in which the starting temperature is 40 to 175 ° C and then leaving it to stand. (The same applies to the retention after solution treatment)

As means for achieving these, hot water,
There are quenching in oil, cooling by blowing hot air, etc. Furthermore, winding such a plate material into a coil,
By leaving it and / or holding it in the furnace,
A hold at 175 ° C within 36 hours is easily achieved. In addition, it is efficient in terms of manufacturing to perform the solution treatment and the cooling treatment in a continuous heating furnace.

Further, as a means for reducing the GP zone of the plate material after the above treatment, there is a method of further reheating to 180 to 320 ° C. and holding for 25 minutes or less. As a result, the GP zone deposited before the main treatment is re-dissolved.
However, if the main treatment temperature is 180 ° C or lower, the GP zone cannot be re-dissolved, and if the temperature exceeds 320 ° C, β ',
Since β and the like are deposited, the strength of the raw plate is increased. Furthermore, β ', β, etc. will precipitate even if the holding time exceeds 25 minutes. The subject of this treatment is one having a holding temperature of 40 to 130 ° C. within the above 36 hours. The reason for limiting in this way is that the precipitation in the GP zone is sufficiently suppressed when the temperature is kept at 130 ° C. or higher, and the reheating treatment is not necessary. Note that this treatment is more effective when applied to a material having a large amount of precipitation in the GP zone.

Also in the present treatment, depending on the cooling method after heating, excessive quenching holes may be introduced, and the GP zone precipitation may be promoted. Therefore, in this case, a method of reducing the excess vacancy concentration by quenching is carried out by cooling after heating to 40 to 135 ° C. at a cooling rate of 2 ° C./sec or more and holding for 36 hours or less. By reducing the quenching excess vacancy concentration in this way, the precipitation of the GP zone can be suppressed. However, the cooling temperature is 40
At temperatures below ℃, there is no effect, and at temperatures above 135 ° C, the difference from the heating temperature is small and the effect of reducing the excess vacancy concentration in quenching is small, and β ', β, etc. precipitate, and the strength of the base plate is high. This is because This is also due to β ′, β, etc. precipitating out even after holding for more than 36 hours.

As means for achieving these, hot water,
There are quenching in oil, cooling by blowing hot air, etc. Furthermore, winding such a plate material into a coil,
By leaving it and / or holding it in the furnace,
A hold at 135 ° C within 36 hours is easily achieved.

Next, a fourth manufacturing method of the present invention will be described. The target Al-Mg-Si-based Al alloy composition includes Si: 0.2 to 3.0 wt%, Mg: 0.2 to 3.0 wt%, Fe: 0.01 to 0.5 wt%, Cu: 0.01 to 1.5 wt%,
Mn: 0.01 to 0.5 wt%, Cr: 0.01 to 0.5 wt%, Zr:
0.01 to 0.5 wt% and Ti: 0.001 to 0.5 wt% One or more of them are contained, and the balance Al and unavoidable impurities are the same as the composition of the Al alloy sheet material of the present invention described above.

In this manufacturing method, the Al alloy plate material having the above composition is
First, solution treatment is performed at 400 ° C or higher, and cooling is performed at a cooling rate of 2 ° C / sec or higher. The solution treatment conditions and the cooling rate are as described above, but in this manufacturing method, after cooling, they are reheated to 180 to 320 ° C. and kept for 25 minutes. This reheating is to reduce the GP zone as described above. And then 40 ~ at a cooling rate of 2 ℃ / sec or more
It is cooled to 135 ° C. and held for 36 hours, but this treatment also reduces the quenching excess vacancy concentration in the same manner as described above and suppresses the precipitation of GP zones.

[0030]

【Example】

(Example 1) An Al alloy having the composition shown in Table 1 was melted by an ordinary method and DC ingot was obtained to obtain an ingot. After homogenizing this ingot, it was hot-rolled and cold-rolled to obtain a plate material having a thickness of 1 mm. This plate material is solution heated at 540 ° C for 2 seconds, cooled to room temperature at 15 ° C / sec, reheated at 200 ° C for 40 seconds, and cooled to 80 ° C at 15 ° C / sec. It was kept in warm water for 30 minutes. (No. 6 in Table 5)

The plate material thus produced was left at room temperature for 1, 5, 20, 60 days after completion of the treatment, and then subjected to a tensile test and an Erichsen bulge test, and a coating baking treatment was simulated at 180 ° C. Tensile tests were also conducted after heating for 60 minutes, and the results are compared and shown in Tables 2 and 3. 250 ℃
The change in conductivity before and after heating for 10 seconds was measured, and the results are shown in Table 4. In the tensile test, tensile strength (TS), proof stress (YS), and elongation (El) were measured using JIS No. 5 tensile test pieces. Erichsen overhang test is JIS Z 2247
The overhang height was measured by method A. The conductivity was measured by the double bridge method, and the increment of conductivity by heating at 250 ° C for 10 seconds was measured.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

[Table 4]

As is clear from Tables 2 to 4, the plate materials according to the comparative examples (Nos. 8 to 17), which deviate from the invention example, are solution-treated as compared with the plate materials according to the invention example (No. 1 to 7). Any one or more of the moldability after the treatment, the strength after the baking coating treatment, and the stability of these properties when left at room temperature (natural aging) are inferior.

Example 2 An ingot was obtained by melting Al alloys having compositions A to Q shown in Table 1 by a conventional method and performing DC casting. After homogenizing this ingot, it was hot-rolled and cold-rolled to obtain a plate material having a thickness of 1 mm. This plate material was subjected to solution treatment, cooling, holding, and reheating under the conditions of No. 1 to No. 21 shown in Table 5 in combination as shown in Table 6 to Table 8.

The plate material thus produced was left at room temperature for 1, 5, 20, and 60 days after completion of the treatment, and then subjected to a tensile test and an Erichsen bulge test, and a coating baking process was simulated. A tensile test was conducted even after heating at 60 ° C. for 60 minutes, and these results are also shown in Tables 6 to 8. After the treatment, the change in conductivity before and after heating at 250 ℃ for 10 seconds was measured and the results are shown in Table 9.
It was shown to. In the tensile test, tensile strength, proof stress, and elongation were measured using JIS No. 5 tensile test pieces. In the Erichsen overhang test, the overhang height was measured by the JIS Z 2247 A method. Conductivity is measured by the double bridge method, 250 ℃ ×
The conductivity increase with 10 seconds of heating was measured.

[0039]

[Table 5]

[0040]

[Table 6]

[0041]

[Table 7]

[0042]

[Table 8]

[0043]

[Table 9]

As is clear from Tables 6 to 9, the plate materials according to the comparative examples (No. 32 to 55) which are out of the range specified by the present invention are compared with the plate materials according to the present invention example (No. 21 to 31). Any one or more of the moldability after the solution treatment, the strength after the baking coating treatment, and the stability of these characteristics after being left at room temperature (natural aging) are inferior. Further, the plate materials of the present invention examples (Nos. 21 to 31) have a small change in conductivity due to heating at 250 ° C. for 10 seconds and a small change in characteristics due to being left at room temperature (natural aging). On the other hand, in the plate materials according to the comparative examples (Nos. 32 to 55) that deviate from the inventive example,
Some of them show a large change in conductivity due to heating at 250 ° C for 10 seconds, and their properties deteriorate when left at room temperature (natural aging), especially the increase in strength due to baking coating treatment.

[0045]

As described above, according to the present invention, the GP zone that precipitates during natural aging is suppressed, and β'precipitates rapidly during the baking and heating of a coating, which has excellent formability, has a small change over time, and has a high bake hardenability. An aluminum alloy sheet material for molding having is obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shigeru Kuramoto 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Yoichiro Toguji 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (7)

[Claims] 1. Si: 0.2-3.0 wt%, Mg: 0.2-3.
Including 0 wt%, Fe: 0.01 to 0.5 wt%, Cu: 0.01 to 1.
5 wt%, Mn: 0.01 to 0.5 wt%, Cr: 0.01 to 0.5 wt
%, Zr: 0.01 to 0.5 wt%, Ti: 0.001 to 0.5 wt%, and one or more of them, and the balance Al and unavoidable impurities are Al alloy sheet materials, and are heated at 250 ° C for 10 seconds. Al-Mg-Si system A for automobile body sheets, which has a small change with time and is excellent in bake hardenability, characterized in that the increase in the electrical conductivity is 0.75% IACS or less.
l Alloy plate material. 2. Si: 0.2-3.0 wt%, Mg: 0.2-3.
Including 0 wt%, Fe: 0.01 to 0.5 wt%, Cu: 0.01 to 1.
5 wt%, Mn: 0.01 to 0.5 wt%, Cr: 0.01 to 0.5 wt
%, Zr: 0.01 to 0.5 wt%, Ti: 0.001 to 0.5 wt%, and 1 or 2 or more of them, and after the solution treatment of the Al alloy sheet made of the balance Al and unavoidable impurities at 400 ° C. or higher, 2 Bake hardening with little change over time, characterized by cooling to 40 to 175 ℃ at a cooling rate of ℃ / sec or more, winding into a coil, then leaving it at room temperature and / or holding it in a furnace for 36 hours or less Aluminum for car body sheets with excellent properties
-A manufacturing method of a Mg-Si system Al alloy board. 3. The holding temperature within 36 hours according to claim 2
Al-M for automobile body sheet with excellent bake hardenability with little change over time, characterized by reheating plate material at 40 to 130 ° C to 180 to 320 ° C and holding it for 25 minutes or less.
A method for manufacturing a g-Si-based Al alloy plate material. 4. A plate material, which has been subjected to the treatment according to claim 3,
Al-Mg- for automobile body sheets, which has excellent bake hardenability with little change over time, characterized by cooling to 40 to 135 ° C at a cooling rate of 2 ° C / sec or more and holding for 36 hours.
A method for manufacturing a Si-based Al alloy plate material. 5. The method for holding after reheating and cooling is 2 ° C.
After coiling the plate material cooled to 40 to 135 ℃ at a cooling rate of / sec or more, leave it at room temperature and / or in a furnace.
The Al-Mg for an automobile body sheet according to claim 4, which is retained for 36 hours or less and is excellent in bake hardenability with little change with time.
-Method for manufacturing Si-based Al alloy sheet material. 6. Si: 0.2-3.0 wt%, Mg: 0.2-3.
Including 0 wt%, Fe: 0.01 to 0.5 wt%, Cu: 0.01 to 1.
5 wt%, Mn: 0.01 to 0.5 wt%, Cr: 0.01 to 0.5 wt
%, Zr: 0.01 to 0.5 wt%, Ti: 0.001 to 0.5 wt%, and 1 or 2 or more of them, and the solution treatment is performed at 400 ° C. or higher on the Al alloy plate material that comprises the balance Al and unavoidable impurities. After quenching at a cooling rate of ℃ / sec or more, reheat to 180 to 320 ℃, hold for 25 minutes or less, and cool to 40 to 135 ℃ at a cooling rate of 2 ℃ / sec or more.
Al for automobile body sheets with excellent bake hardenability, which is characterized by holding for 36 hours or less
-A manufacturing method of a Mg-Si system Al alloy board. 7. The holding method after reheating and cooling is 2 ° C./s
The plate material cooled to 40 to 135 ° C at a cooling rate of ec or more is wound into a coil and then left at room temperature and / or in a furnace.
7. Al-Mg- for an automobile body sheet, which is retained for less than an hour and is excellent in bake hardenability with little change over time.
A method for manufacturing a Si-based Al alloy plate material.