JPH10219382A - Aluminum alloy sheet excellent in formability/ workability and coating/baking hardenability and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an Al alloy sheet excellent in formability and showing excellent coating/baking hardenability even in coating/baking treatment at a low temp. in a short time by forming a T4 material of an Al-Mg-Si series Al alloy sheet into the one free from an endothermic peak equivalent to Mg-Si cluster melting in a differential scanning thermal analysis curve. SOLUTION: In an Al-Mg-Si series Al alloy sheet, the differential scanning thermal analysis curve of the T4 material is formed into the one free from a peak equivalent to Mg-Si cluster melting. The compsn. of this Al alloy sheet is composed of the one contg., by mass, 0.4 to 1.1% Mg and 0.6 to 1.5% Si so as to satisfy -2.0>4Mg-7Si, furthermore contg., at need, 0.01 to 0.3% Sn, 0.1 to 1.0% Cu, one or more kinds among <=0.15% Ti, <=0.05% B, <=0.4% Mn, <=0.3% Fe and <=1.0% Zn, and the balance Al with inevitable impurities. At the time of its production, within 12hr after cold rolling and solution treatment, heat treatment is executed at 70 to 150 deg.C for 0.5 to 50hr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy sheet having excellent moldability and paint baking hardenability and suitable for an automobile body sheet and the like, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for weight reduction of a vehicle body for the purpose of improving fuel efficiency of an automobile. As one of means for reducing the weight, use of an aluminum alloy plate for an automobile body sheet or the like has been performed. Currently used aluminum alloys for automobile body sheets include non-heat-treated Al-M
g-based alloys and heat-treated Al-Mg-Si-based alloys. The non-heat-treated Al-Mg alloy is heat-treated A
Although the formability is slightly better than that of the l-Mg-Si alloy, the yield strength cannot be increased by the paint baking step.

[0003] The heat treatment type Al-
In the case of AA6009, AA6010, etc., which are Mg-Si based alloys, the deterioration in formability due to aging changes is large. In addition, these alloys hardly increase the yield strength in paint bake hardening at a temperature of 180 ° C. or less, which is currently the mainstream in Japan, for less than 30 minutes. Under such circumstances, the paint bake hardenability is determined by Al-Mg.
A method of increasing the yield strength by applying a heat treatment after solution-hardening and quenching a Si-based alloy by a low-temperature, short-time paint baking treatment is disclosed (Japanese Patent Publication No. 5-74).
No. 60 publication).

[0004]

However, in this method, since the yield strength before molding by heat treatment is greatly increased, the moldability is poor, and the paint bake hardening amount is also 50 N /.
mm ² about the not so large. Further, a method has been disclosed in which the quenching temperature after solution treatment is specified to be a high temperature equal to or higher than room temperature, and a heat treatment is subsequently performed to improve the amount of coating bake hardening (Japanese Patent Application Laid-Open No. Hei 4-210456). Quenching to a high temperature above room temperature not only increases the control factors, but is often difficult to manufacture, and it is hard to say that the coating bake hardening amount is sufficient.

[0005] As a material for an automobile body sheet, a low yield strength is required before molding from the viewpoint of molding workability, and a high yield strength is required after baking paint from the viewpoint of dent resistance. In other words, this property that the strength rise during solution storage at room temperature after standing is small and excellent formability immediately after quenching is maintained for a long time, and that a large strength rise can be achieved during paint baking, is sufficient for conventional aluminum alloy sheets. It is hard to say that it has a shape. In view of such circumstances, the present invention has a small increase in strength even when left at room temperature for a long time, has excellent moldability, and is currently one of the mainstream products in Japan.
Provided is an aluminum alloy plate having excellent paint bake hardenability even in a paint bake treatment at a temperature of 80 ° C. or less at a low temperature for a short time of less than 30 minutes and a method for producing the same.

[0006]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have developed a T4 aluminum alloy plate having excellent formability and high baking hardenability in an Al-Mg-Si alloy. Diligent research on wood. T
The four materials are JIS standard quality symbols, which mean those obtained by subjecting an aluminum alloy to a solution treatment and then naturally aging. As a result, in the measurement results of the T4 material by the differential scanning calorimetry, it was found that an Al-Mg-Si alloy plate having no endothermic peak corresponding to Mg-Si cluster dissolution was excellent in formability and paint baking hardenability. Was.

[0007] The Mg-Si clusters are formed during solution storage and left at room temperature, causing an increase in the strength of the alloy and lowering the formability. Further, in a heat treatment of about 180 ° C. for less than 30 minutes, which is a general baking condition, since the Mg-Si cluster exists stably, the supersaturated solid solution amount of solute atoms is reduced. P.
This hinders zone deposition. As a result, a large increase in strength cannot be obtained during the paint baking process. Therefore, in an Al-Mg-Si based alloy, Mg-Si clusters are hardly formed even when left at room temperature for a long period of time.
When there is no endothermic peak corresponding to i-cluster dissolution, moldability and paint bake hardenability are excellent.

[0008] The presence or absence of the formation of the Mg-Si cluster can be determined by the usual differential scanning calorimetry. If Mg-Si clusters exist, 5 to 3
When measured at a heating rate of 0 ° C./min, a peak corresponding to the dissolution is observed in the temperature range of 150 to 250 ° C. in the differential scanning calorimetry curve of FIG. In the measurement result of the T4 material by the differential scanning calorimetry, Al-Mg-S having no endothermic peak corresponding to Mg-Si cluster dissolution was found.
The preferred component system and manufacturing method for the i-based alloy sheet are as follows.

As the components, it is preferable that the component relationship between Mg and Si is made to be Si excess as compared with the balance composition, and to be a component system having excellent high-temperature aging characteristics. After the solution treatment, Mg-Si clusters are formed during standing at room temperature. However, in order to prevent the formation amount from becoming too large, a temperature of 70 to 150 ° C. within 12 hours after the solution treatment and quenching is applied. It is preferable to perform a heat treatment for 0.5 to 50 hours to suppress the formation of clusters during the subsequent standing at room temperature. The shorter the time from the solution treatment to the final heat treatment, the better. In addition, in order to obtain greater paint bake hardenability, in order to reduce the amount of Mg-Si clusters formed during standing at room temperature after solution treatment, it is combined with supersaturated frozen vacancies to prevent diffusion of solute atoms. It is effective to add an appropriate amount of Sn to be suppressed. It is also effective to add Cu, which has the effect of accelerating aging during baking.

The present invention has been made based on the above findings. First, the aluminum alloy plate excellent in formability and paint baking hardenability of the present invention is made of Al-Mg-Si.
The differential scanning calorimetry curve of the T4 material
It is characterized by having no peak corresponding to g-Si cluster dissolution. As a preferred method of manufacturing the above aluminum alloy plate, Mg: 0.4 to 1.1 mass
%, Si: 0.6 to 1.5 mass%, and -2.0>
4Mg-7Si, Sn: 0.01 if necessary
-0.3 mass%, Cu: 0.1-1.0 mass%
And 0.15 mass% or less of Ti, 0.1% by mass or less.
B of 05 mass% or less, M of 0.4 mass% or less
n, an alloy plate containing at least one of Fe of 0.3 mass% or less and Zn of 1.0 mass% or less, with the balance being Al and unavoidable impurities, after solution treatment and quenching,
It is characterized by being manufactured by performing a heat treatment at 70 to 150 ° C. for 0.5 to 50 hours within 12 hours.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. First, in the present invention, since the T4 material of the Al-Mg-Si-based aluminum alloy plate has formability and paint bake hardenability, the differential scanning calorimetry curve of the T4 material corresponds to the dissolution of Mg-Si clusters. There is no peak. The absence of this peak indicates that the M4
The absence of g-Si clusters is proved, and moldability and paint bake hardenability are ensured.

Next, a preferred method for producing the aluminum alloy sheet of the present invention will be described. The reason for limiting the preferred component composition range in the present invention will be described. Mg and Si: Mg
And Si are indispensable basic components of the present invention, and are contained in order to form fine precipitates and obtain high paint bake hardenability. As for the component ranges, Mg: 0.4 to 1.1 mass%, which is on the Si excess side with respect to the balance composition, Si:
It is preferable to be in the range of 0.6 to 1.5 mass%.
Even if the Si content is less than 0.6 mass%, sufficient paint baking curability cannot be obtained. On the other hand, if Mg is excessive and contained in excess of 1.1 mass%, the composition approaches the balance composition, and the paint baking hardenability decreases. If the content of Mg is less than 0.4 mass%, it is difficult to obtain sufficient paint baking curability.

Further, the component relation between Mg and Si is specified, and -2.0> 4Mg-7Si (Mg and Si are ma
ss%). If the content of Mg exceeds the above range in terms of the quantitative relationship between Mg and Si, the effect of Sn and the effect of heat treatment after solution treatment will not be sufficiently exerted, and the amount of clusters formed will increase. Will decrease.

In the preferred production method of the present invention, Sn and Cu may be contained as required. Sn: Sn has the effect of suppressing cluster formation at room temperature and maintaining excellent moldability immediately after quenching for a long time, and further improves the strength when subsequently aged at high temperatures. If the added amount of Sn is less than 0.01 mass%, the effect is small, and if it exceeds 0.3 mass%, not only the effect does not increase, but also hot brittleness is caused to significantly deteriorate hot workability. Therefore, when the Sn content is 0.01 to
It is preferable that the content be specified in the range of 0.3 mass%.

Cu: Cu improves the strength, moldability and chemical conversion treatment properties, and further improves paint bake hardenability.
It is preferable that the addition amount is in the range of 0.1 to 1.0 mass%. If the content is less than 0.1 mass%, the effect cannot be sufficiently obtained. If the content exceeds 1.0 mass%, precipitation is promoted, and the change with time during leaving at room temperature becomes large, so that the moldability is deteriorated and the corrosion resistance is reduced. Will also decrease. Therefore, a preferable content of Cu is 0.1 to 1.0 ma.
ss%.

In the present invention, if necessary,
One or more of Ti, B, Mn, Fe, and Zn may be contained. Ti and B: Since Ti and B have the effect of refining the crystal grains of the ingot and improving press formability by adding a small amount,
It is preferable that the content of Ti is specified in a range of 0.15 mass% or less and the content of B is specified in a range of 0.05 mass% or less. Each content is Ti0.15mass%, B
When the content exceeds 0.05 mass%, coarse crystals are formed,
Since the moldability deteriorates, each is 0.15 mass%,
The upper limit is preferably 0.05 mass%.

Mn: Mn is used to improve strength.
It is good to make it contain 0.4 mass% or less. If the content exceeds 0.4 mass%, coarse crystals are formed, and the moldability is reduced. Therefore, it is preferable to set the upper limit to 0.4 mass%. Fe: Fe has a small strength improving effect, and its content is 0.1%.
If it exceeds 3 mass%, coarse crystals are formed, and the moldability is reduced. Therefore, it is preferable to set the upper limit to 0.3 mass%.

Zn: Zn improves the strength.
It is good to make it contain 0 mass% or less. If the content exceeds 1.0 mass%, the moldability is reduced. Therefore, the upper limit is preferably 1.0 mass%. In addition to the above-mentioned elements, unavoidable impurities are contained as in the case of ordinary aluminum alloys, but the amount thereof is acceptable as long as the effects of the present invention are not impaired.

Next, preferred conditions for producing the aluminum alloy sheet of the present invention will be described. The aluminum alloy whose composition is specified as described above is subjected to casting, hot and cold rolling, and solution treatment according to a conventional method. In order to maintain excellent moldability for a long period of time and to obtain a further effect of improving the strength at the time of baking, 70 to 150 times within 12 hours after the solution heat treatment.
It is effective to carry out a heat treatment at a temperature of 0.5 to 50 hours. The reason for defining the range of the heat treatment is that the temperature is less than 70 ° C.
If the treatment is performed for less than 0.5 hour, the effect of suppressing the temporal change in strength during the standing at room temperature after the heat treatment cannot be sufficiently obtained.
This is because a treatment at a temperature exceeding 0 ° C. for more than 50 hours results in a large increase in strength during the heat treatment, which impairs the formability.

Further, 70 to 150 from the solution treatment / quenching treatment
The reason why the room temperature standing time until the start of the heat treatment at ° C is preferably within 12 hours is as follows. That is, since clusters considered to be composed of Mg and Si are formed during standing at room temperature, the amount of these clusters increases when the standing time exceeds 12 hours, and the strength increases due to precipitation during paint baking. G. P. This is because the deposition of the zone is hindered.

The thus obtained aluminum alloy sheet was found to have a Mg-
No endothermic peak corresponding to Si cluster dissolution is observed. And this aluminum alloy plate is 110 N / m
Since it has a low yield strength of not more than m ^2, it is excellent in molding workability, and at the time of paint baking, the yield strength is increased by 100 N / mm ² or more, and the paint bake hardenability is remarkably excellent. Therefore, such an aluminum alloy plate is suitable for an automobile body sheet.

[0022]

The present invention will be described below with reference to examples. (Example 1) An alloy having a component composition as shown in Table 1 was melted, cast and rolled by a usual method to form a plate having a thickness of 1 mm. The rolled plate was subjected to a solution treatment at 550 ° C. for 10 seconds and then air-cooled to room temperature. After 8 hours from the air cooling, heat treatment was performed at 100 ° C. for 8 hours. After leaving the aluminum alloy sheet thus manufactured at room temperature for 100 days, it is subjected to differential scanning calorimetry to examine the presence or absence of a cluster dissolution peak, and to hold at 175 ° C. for 30 minutes, which corresponds to mechanical properties and paint baking. Later yield strength was investigated. Table 2 shows the survey results.
Shown in

[0023]

[Table 1]

Table 2 shows that the aluminum alloy sheet N of the present invention
o1 to 9 have no endothermic peak corresponding to dissolution of the Mg-Si cluster and have excellent moldability because the yield strength can be suppressed to about 110 N / mm ² or less even after being left at room temperature for as long as 100 days. Further, it can be seen that the coating baking hardening amount is large at about 100 N / mm ² or more. Further, in alloy Nos. 10 to 14 of comparative examples having components outside the present invention, after leaving at room temperature for as long as 100 days, a cluster dissolution peak was observed, and the moldability and the amount of paint bake hardening were inferior to those of the present invention. I will. In other words, it is possible to produce a well-balanced material having both moldability and paint bake hardenability by having the component composition of the present invention and performing heat treatment within a specified time after solution heat treatment and air cooling. Becomes

[0025]

[Table 2]

(Example 2) Inventive alloy 4 shown in Table 1 was used in Example 1.
From the solution cooling to the air-cooling treatment, from the air-cooling to the heat treatment, left at room temperature for the time shown in Table 3, and then heat-treated under the heat treatment conditions in Table 3. After leaving the aluminum alloy plate thus manufactured at room temperature for 100 days,
Differential scanning calorimetry was performed to examine the presence or absence of a cluster dissolution peak, and to investigate mechanical properties and yield strength after a holding treatment at 175 ° C. for 30 minutes, which corresponds to a baking treatment. Table 4 shows the results of those investigations. As is clear from Table 4, when the treatment was performed under the production pattern conditions in the present invention, the production pattern of the comparative example had no cluster dissolution peak even after being left at room temperature for as long as 100 days, and the molding was not performed. It can be seen that the film has excellent properties and has a large baking hardening amount. In particular, the effect of the time from solution to heat treatment on the amount of paint bake hardening is great, and it can be seen that the shorter the time, the better the paint bake hardenability.

[0027]

[Table 3]

[0028]

[Table 4]

[0029]

According to the present invention, it is excellent in moldability and remarkably excellent in paint baking hardenability compared to conventional aluminum alloy sheets, and is used for automobile body sheets and the like which require dent resistance after baking. A suitable aluminum alloy plate can be provided. Therefore, for example, by applying the product of the present invention as an automobile body, the weight of the vehicle body can be reduced, which can contribute to improvement of fuel efficiency.

[Brief description of the drawings]

FIG. 1 is a differential scanning calorimetry curve (schematic diagram) of an Al—Mg—Si alloy.

[Explanation of symbols]

 Peak corresponding to the precipitation of K cluster L Peak corresponding to the dissolution of cluster PG. P. Peak corresponding to the precipitation of the zone TG. P. Peak corresponding to dissolution of zone Q Peak corresponding to precipitation of mesophase

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22F 1/00 691 C22F 1/00 691B 691C

Claims (5)

[Claims] 1. The differential scanning calorimetry curve of T4 material of an Al—Mg—Si based aluminum alloy sheet shows Mg—S
An aluminum alloy sheet excellent in formability and paint bake hardenability, characterized by having no endothermic peak corresponding to i-cluster dissolution. 2. The method for producing an aluminum alloy sheet according to claim 1, wherein: Mg: 0.4 to 1.1 mass%;
i: 0.6 to 1.5 mass%, and -2.0> 4Mg
After cold rolling an alloy filled with -7Si and the balance consisting of Al and unavoidable impurities, the alloy was subjected to a solution treatment and then 12%.
A method for producing an aluminum alloy sheet having excellent formability and paint bake hardenability, wherein the aluminum alloy sheet is produced by performing a heat treatment at 70 to 150 ° C. for 0.5 to 50 hours within a period of time. 3. The method according to claim 1, wherein the aluminum alloy further contains Sn: 0.
3. The method for producing an aluminum alloy sheet having excellent formability and paint bake hardenability according to claim 2, wherein the alloy contains 0.01 to 0.3 mass% of Sn. 4. An aluminum alloy further comprising 0.1 to
The method for producing an aluminum alloy sheet having excellent formability and paint bake hardenability according to claim 2 or 3, characterized by containing 1.0 mass% of Cu. 5. The method according to claim 5, further comprising adding 0.15
mass% or less Ti, 0.05 mass% or less B,
The moldability and paint bake hardening according to claim 2, 3, or 4, which contains at least one of Mn of 0.4 mass% or less, Fe of 0.3 mass% or less, and Zn of 1.0 mass% or less. Method of manufacturing aluminum alloy sheet with excellent heat resistance.