JPH06272000A - Production of al alloy sheet excellent in formability and baking hardenability - Google Patents

Abstract

PURPOSE:To provide a method for producing an Al alloy sheet for forming used as body sheet of automobile, etc., excellent in formability, baking hardenability and having low secular change at room temp. CONSTITUTION:After the Al alloy ingot which contains 0.3-1.5% Mg and 0.5-2.5% Si as essential components, also containing a small amount of Cu, Zn, Mn, Zr, V, Fe, and Ti as required is subjected to homogenizing treatment, hot rolling and cold rolling, the ingot is subjected to solution treatment at >=480 deg.C, cooling to 150-300 deg.C by >=100 deg.C/min, holding treatment at the same temp. for 1-600sec and cooling to <=140 deg.C by 100 deg.C/min. Otherwise, after the same solution heat treatment, it is cooled to <=150 deg.C by 100 deg.C/min and, within 72hr, is reheated to 150-300 deg.C within 600sec, and then cooled to <=140 deg.C by >=100 deg.C/min, successively subjecting to the stabilizing heat treatment of 50-140 deg.C for 0.5-50hr within 72hr as the final heat treatment.

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 aluminum alloy sheet which is used as a raw material for automobile body sheets and parts, various machines and appliances, home electric appliances, etc. after being subjected to forming processing and paint baking. The present invention relates to a method for producing an aluminum alloy sheet for forming, which has particularly good formability, has high strength after coating baking, and has little change with time at room temperature.

[0002]

2. Description of the Related Art In the past, cold-rolled steel sheets were mainly used for automobile body sheets, but recently, from the viewpoint of weight reduction of vehicle bodies, use of rolled aluminum alloy sheets has been promoted. Since automobile body sheets are used after being pressed, it is required that they have excellent formability, that Luders marks do not occur during forming, and that they also have high strength. In particular, since coating baking is performed, it is required that high strength can be obtained after coating baking.

Conventionally, as an aluminum alloy for such an automobile body sheet, JIS having aging property is used.
The 6000 series alloy, that is, the Al-Mg-Si alloy is mainly used. This aging Al-Mg-Si
The type alloys have relatively low strength during forming before coating baking and have excellent formability, while they have the advantage of being aged by heating during coating baking and increasing strength after coating baking. It has the advantage that no dozen marks are generated.

By the way, as a method for producing an Al-Mg-Si alloy sheet, which is expected to age harden during baking, the ingot is homogenized and heat-treated, and then hot-rolled and cold-rolled to a predetermined sheet thickness. Further, if necessary, intermediate annealing is performed between hot rolling and cold rolling or in the middle of cold rolling, and it is usual to perform solution treatment after cold rolling and quench. However, it is difficult for such a conventional general manufacturing method to sufficiently satisfy the characteristics required for a recent automobile body sheet.

That is, in recent years, there has been a strong demand for further thinning in order to further reduce the cost, and therefore higher strength is required so that sufficient strength can be obtained even with thin thickness. However, in this respect, the Al-Mg-Si alloy plate obtained by the conventional general manufacturing method is insufficient.

Regarding coating baking, in order to save energy and improve productivity, and in combination with a material such as a resin which is not preferably exposed to a high temperature, the baking temperature is made lower than before, and There is an increasing tendency to shorten the baking time. Therefore, in the Al-Mg-Si alloy plate obtained by the conventional general manufacturing method, the curing at the time of baking the coating (baking hardening) is insufficient, and there is a problem that it becomes difficult to obtain sufficient high strength after baking the coating. .

Therefore, recently, with respect to Al-Mg-Si alloys, it has been attempted to solve the above-mentioned problems by studying a method of manufacturing a plate. There is a method proposed in JP-A-210456. This proposed method holds the material in the temperature range of 50 to 130 ° C. for 1 to 48 hours in the middle of the cooling process for quenching after the solution treatment, and then again 1
The low temperature heat treatment is performed for 3 to 10 minutes at a temperature in the range of 40 to 180 ° C.

[0008]

[Means for Solving the Problems] Japanese Patent Laid-Open No. 4-210 mentioned above.
According to the method proposed by No. 456, conventional general Al-
Compared with the Mg-Si alloy plate manufacturing method, it is considered to be effective to some extent in increasing the strength of the raw material and the strength after baking, but in reality, it has not reached a satisfactory level.

In addition, if age hardening is strengthened in order to achieve a large increase in strength during coating baking, if the plate is left for a long period of time after being manufactured and then subjected to molding and coating baking, it is left for a period before molding. There is a problem that natural aging (room temperature aging) progresses and the plate hardens and the formability deteriorates. In fact, the above-mentioned proposed method does not sufficiently consider this point.

Further, in the method proposed above, the final low-temperature heat treatment is carried out at 140 to 180 ° C. for 3 to 10 minutes. In this case, if a batch type annealing is applied, the holding time is too short, while the continuous type is used. On the contrary, if annealing is applied, the holding time is too long, and in either case, there is a problem that production is difficult.

The present invention has been made in view of the above circumstances, and it has good moldability and at the same time has excellent bake hardenability, resulting in a high increase in strength during coating baking, and at room temperature after plate production. Little change over time in
It is an object of the present invention to provide a method for producing an aluminum alloy plate for forming, in which there is little deterioration in formability due to hardening due to natural aging even when left for a long period of time.

[0012]

Means for Solving the Problems As a result of repeated experiments and studies by the present inventors in order to solve the above problems, Al-
It has been found that the above-mentioned problems can be solved by appropriately selecting the component composition of the Mg-Si alloy and at the same time performing an appropriate heat treatment after the solution treatment during the plate manufacturing process. I arrived.

Specifically, the method for producing an aluminum alloy sheet for forming according to the first aspect of the present invention provides Mg0.3 to 1.5.
%, Si 0.5 to 2.5%, and if necessary, Cu 0.03 to 1.2%, Zn 0.03 to 1.5%,
Mn 0.03-0.4%, Cr 0.03-0.4%, Z
r0.03-0.4%, V0.03-0.4%, Fe
0.03 to 0.5%, Ti 0.005 to 0.2%, and one or more selected from the rest, with the balance being Al.
And an alloy consisting of unavoidable impurities as a raw material, the ingot is homogenized, and then hot-rolled and cold-rolled to a rolled plate having a required thickness.
100 ℃ / after solution treatment at a temperature of 0 ℃ or higher
After cooling at a cooling rate of min or more to a temperature in the range of 150 to 300 ° C. and then performing a heat treatment of holding the temperature in the range of 150 to 300 ° C. for 1 to 600 seconds, 100
It is characterized by performing a stabilization treatment of cooling to a temperature of 140 ° C. or lower at a cooling rate of not less than C / min and holding the temperature within a range of 50 to 140 ° C. for 0.5 to 50 hours within 72 hours after that. To do.

The method of manufacturing an aluminum alloy sheet for forming according to the second aspect of the present invention uses the alloy having the same composition as that of the first aspect as a raw material, and performs the solution treatment at a temperature of 480 ° C. or higher. After the solution heat treatment, the solution is cooled to a temperature range of 150 ° C. or lower at a cooling rate of 100 ° C./min or higher, and then within 72 hours, 150 to 300 ° C.
After heating to a temperature within the range of no holding or a heat treatment of holding for 600 seconds or less, it is cooled to a temperature of 140 ° C or less at a cooling rate of 100 ° C / min or more, and then 72
The stabilization treatment similar to that of the invention of claim 1 is performed within the time.

[0015]

First, the reasons for limiting the component composition of the alloy used in the manufacturing method of the present invention will be described.

Mg: Mg is a basic alloying element in the alloy of the system of the present invention, and contributes to the strength improvement in cooperation with Si. When the amount of Mg is less than 0.3%, Mg ₂ Si contributes to the improvement of strength by precipitation hardening during coating baking.
Since the amount of Mg produced is small, sufficient strength cannot be obtained. On the other hand, if it exceeds 1.5%, the formability deteriorates. Therefore, the amount of Mg is set within the range of 0.3 to 1.5%.

Si: Si is also an alloying element which is a basic component of the alloy of the present invention, and contributes to the strength improvement together with Mg. Further, Si is generated as a crystallized product of metallic Si during casting, and the periphery of the metallic Si particles is deformed by processing to become a recrystallization nucleus generation site during solution treatment. Also contribute to. If Si is less than 0.5%, the above effect cannot be sufficiently obtained, while if it exceeds 2.5%, coarse Si is generated and the toughness of the alloy is deteriorated. Therefore, Si is set within the range of 0.5 to 2.5%.

Cu, Zn, Mn, Cr, Zr, V, T
i, Fe: These are not absolutely essential elements, but one or two, if necessary, for improving strength and refining crystal grains.
More than one seed is added. Of these, Cu is an element effective for improving strength, but if the Cu content is less than 0.03%, its effect is not sufficiently obtained, while if it exceeds 1.2%, the corrosion resistance decreases, so Cu is not added. Cu amount when added is 0.03
Within the range of 1.2%. Zn is an element that contributes to the strength improvement by improving the aging property of the alloy. If the content is less than 0.03%, the above effect is insufficient, while if it exceeds 1.5%, the formability and corrosion resistance are increased. , The Zn content in the case of adding Zn is 0.03 to 1.5%.
Within the range of. Further, Mn, Cr, Zr, and V are all elements effective in improving strength, refining crystal grains, and stabilizing the structure. If the content is less than 0.03%, the above effect is sufficiently obtained. Not available, while 0.4% each
If it exceeds, not only the above effect is saturated, but also a huge intermetallic compound may be generated to adversely affect the formability, so that Mn, Cr, Zr, and V are all 0.03 to 0.4. Within the range of%. Further, Ti is also an element effective for improving strength and refining the ingot structure, and if the content is less than 0.005%, a sufficient effect cannot be obtained, while if it exceeds 0.2%, the effect of Ti addition is Not only is it saturated, but giant crystallized substances may occur, so the Ti content was made 0.005 to 0.2%. And again Fe
Is an element effective for improving strength and refining crystal grains, and if its content is less than 0.03%, a sufficient effect cannot be obtained, while if it exceeds 0.5%, the formability may deteriorate. Therefore, Fe is set within the range of 0.03 to 0.5%. Fe of less than 0.03% is inevitably contained by using an ordinary aluminum base metal. These Cu, Zn, M
The ranges of n, Cr, Zr, V, Ti and Fe are shown for the case where these elements are included as positive additive elements, and all contain less than the lower limit value as impurities. There is no particular problem.

In addition to the above elements, basically Al and inevitable impurities may be used. However, in general, a small amount of Be may be added to the alloy containing Mg to prevent the oxidation of the molten metal. In the case of the alloy of the present invention, addition of Be of about 0.0001 to 0.01% is not recommended. Permissible. In general, B may be added at the same time as the above-mentioned Ti for grain refinement. In the case of the present invention as well, it is permissible to add B in an amount of 500 ppm or less together with Ti.

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

The process up to the solution treatment, that is, the process until a rolled plate having a required product plate thickness is carried out by the conventional J
It may be the same as the IS 6000 series Al-Mg-Si series alloy. That is, after casting by a DC casting method or the like, homogenization treatment (soaking treatment) is performed according to a conventional method, and then hot rolling and cold rolling are performed to obtain a required sheet thickness. Intermediate annealing may be performed as necessary during hot rolling or in the middle of cold rolling.

The solution treatment is a step necessary for solid solution of Mg ₂ Si or the like in the matrix, thereby imparting bake hardenability to improve the strength after baking for coating, and good recrystallization is also preferable. It is also a process for obtaining excellent moldability. If the solution treatment temperature is lower than 480 ° C., the solid solution amount of Mg ₂ Si is small and sufficient bake hardenability cannot be obtained. Although the upper limit of the solution treatment temperature is not particularly specified, it is usually desirable to set it to 580 ° C. or lower in consideration of the possibility of eutectic melting and coarsening of recrystallized grains. The solution treatment time is not particularly limited, but usually 120 minutes or less. After the solution treatment, at a cooling rate of 100 ° C./min or more, in the case of the method of the invention of claim 1, up to a temperature in the range of 150 to 300 ° C.,
In the case of the method of the second aspect of the invention, the material is cooled (quenched) to a temperature range of 150 ° C or lower. Here, if the cooling rate after the solution treatment is less than 100 ° C./min, a large amount of Mg ₂ Si precipitates during cooling, and the formability decreases, and at the same time, the bake hardenability decreases and the coating baking It is impossible to expect sufficient strength improvement.

The process from the solution treatment to the final stabilization treatment differs between the method of the invention of claim 1 and the method of the invention of claim 2.

That is, in the case of the method of the invention of claim 1,
As shown in FIG. 1, after solution treatment at a temperature of 480 ° C. or higher, 150 to 300 at a cooling rate of 100 ° C./min or higher.
Cooled to a temperature in the range of ℃, followed by 150-300
A heat treatment for holding at a temperature in the range of 0 ° C. for 1 to 600 seconds (hereinafter, this heat treatment is referred to as a holding treatment for convenience) is performed, and then cooled to a temperature of 140 ° C. or less at a cooling rate of 100 ° C./min or more.

On the other hand, in the case of the method according to the second aspect of the invention, FIG.
As shown in, after solution treatment at a temperature of 480 ° C. or higher, the solution is cooled to a temperature of 150 ° C. or lower at a cooling rate of 100 ° C./min or higher, and then reheated to 150 to 3 within 72 hours.
No holding or 60 by heating to a temperature in the range of 00 ℃
Heat treatment for holding within 0 seconds
A reheating treatment) is performed, and then cooling is performed to a temperature of 140 ° C. or less at a cooling rate of 100 ° C./min or more.

The holding treatment in the method of the invention of claim 1 or the reheating treatment in the method of the invention of claim 2 as described above, together with the subsequent stabilization treatment, reduces the change with time due to natural aging after plate production. At the same time, it is a process necessary for improving the bake hardenability. That is, stable clusters are likely to be formed by the holding treatment or the reheating treatment, so that the change over time at room temperature after the plate production is reduced and the G.D. P. The zones become finer and the bake hardenability improves.

Here, if the temperature of the holding treatment in the method of the invention of claim 1 or the reheating treatment in the method of the invention of claim 2 is lower than 150 ° C, the above effect cannot be obtained, while if it exceeds 300 ° C. The stability of the clusters deteriorates, and conversely, the temperature tends to change at room temperature after plate production, and the bake hardenability decreases. Further, if the holding treatment time in the method of the invention of claim 1 is less than 1 second, the above effect cannot be sufficiently obtained, while if it exceeds 600 seconds, the aging deteriorates the formability. On the other hand, in the reheating treatment in the method of the invention of claim 2, if the temperature in the range of 150 to 300 ° C. is reached, the above effect can be obtained by immediately cooling without holding, but if it exceeds 600 seconds, it is the same as above. The aging deteriorates the formability. Further, if the cooling rate to a temperature of 140 ° C. or less after the above holding treatment or reheating treatment is less than 100 ° C./min, the aging during the cooling reduces the formability.

In the method of the second aspect of the present invention, the time from the solution treatment to cooling to a temperature of 150 ° C. or lower to the reheating treatment must be 72 hours or less. If the (time) exceeds 72 hours, the strength of the material before the forming process becomes high due to natural aging, and the formability is deteriorated.

After carrying out the holding treatment or the reheating treatment as described above and cooling to 140 ° C. or less at a cooling rate of 100 ° C./min or more, the method of the invention of claim 1,
In each case of the method of the invention, the stabilization treatment is carried out within 72 hours. If the time until such stabilization treatment (leaving time) exceeds 72 hours, the strength of the material before the molding process will increase due to natural aging, and the moldability will decrease.

The stabilization treatment is necessary for finally improving the stability of the clusters, suppressing the aging after the plate production, ensuring good moldability and obtaining sufficient bake hardenability. It is a process, and this stabilization treatment is 50 to 1
It is necessary to keep the temperature within the range of 40 ° C. for 0.5 to 50 hours. If the stabilization treatment temperature is lower than 50 ° C, the above-mentioned effects cannot be sufficiently obtained, while if it exceeds 140 ° C, the material strength becomes high due to aging and the moldability is deteriorated. Further, when the holding time at a temperature within the range of 50 to 140 ° C. in the stabilization treatment is less than 0.5 hours, the change with time at room temperature thereafter becomes rapid and the moldability and the bake hardenability deteriorate, while 50 hours If it exceeds, the material strength will increase due to aging, the moldability will decrease, and the productivity will be impaired.

As described above, in the production method of the present invention, the composition of the alloy components is appropriately adjusted, and the alloy composition is specified during the cooling (quenching) process after the solution treatment at a temperature of 480 ° C. or higher during the production process. The holding treatment under the conditions (the method of the invention of claim 1) is performed, or the cooling after the solution treatment is performed, and then the reheating treatment under the specific conditions is performed again (the method of the invention of claim 2), and then 72 By subjecting the plate to stabilization treatment under specific conditions within a period of time, it becomes possible to prevent the change over time at room temperature after plate production, that is, the progress of natural aging at room temperature. Even if molding and coating baking are performed after that, it is possible to sufficiently secure good moldability and excellent bake hardenability.

[0032]

EXAMPLES A1 to A within the composition range of the components of the present invention shown in Table 1
The alloy No. 6 and the alloys B1 to B3 outside the composition range of the present invention were cast by the DC casting method according to the ordinary method, and the obtained ingot was subjected to a homogenizing treatment at 530 ° C. for 10 hours, and then the ordinary method. Then, hot rolling and cold rolling were performed according to the above procedure to obtain a rolled plate having a thickness of 1 mm. Then for each rolled plate,
After performing solution treatment at 540 ° C for 10 seconds, 10
Cooling is performed at a cooling rate of 0 ° C./min or more, and a holding treatment is performed during cooling according to the method of the invention of claim 1, or it is reheated after cooling to 150 ° C. or less according to the method of the invention of claim 2. The treatment was performed, and the stabilization treatment was further performed. Detailed conditions are shown in Table 2. In Table 2, the production numbers 1 to 3 and 10 are all examples in which the holding treatment is performed during cooling in accordance with the method of the invention of claim 1, and the production numbers 4 to 6 and 11, 12 are all claims. An example in which reheating treatment is performed according to the method of the invention will be described. On the other hand, manufacturing numbers 7 and 9 are comparative examples for the method of the invention of claim 1, and manufacturing numbers 8 are comparative examples for the method of the invention of claim 2. In addition, the cooling after the holding treatment or the reheating treatment was performed at room temperature at a cooling rate of 100 ° C./min or more, and the room temperature was set until the stabilization treatment.

The plate obtained by the final heat treatment as described above is further left to stand at room temperature for 1 day or 60 days, and each plate is subjected to coating baking treatment by heating at 175 ° C. for 30 minutes, and The mechanical properties and formability before baking and the mechanical properties after baking were examined. The results are shown in Table 3.
Shown in.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

Production Nos. 1 to 6 are those in which the composition of the alloy is within the range specified by the present invention and the manufacturing conditions also satisfy the conditions specified by the present invention. The elongation before coating baking and the Erichsen value are sufficiently high, the moldability is excellent, and the bake hardenability is high, and a large increase in strength occurs during baking, and even when left at room temperature for 60 days after plate production, The elongation and Erichsen value did not decrease so much that the moldability did not decrease, and sufficient bake hardenability was exhibited.

On the other hand, in Production Nos. 7 to 9, the alloy composition was within the range specified by the present invention, but the production conditions did not satisfy the conditions specified by the present invention.
In particular, the production number 7 (alloy symbol A2) had a final stabilization treatment time shorter than the time specified in the present invention, but in this case, an example of the present invention using the same alloy (A2) ( Bake hardenability is inferior to that of production number 2),
In particular, the moldability and bake hardenability after being left for 60 days were poor.
Manufacturing No. 8 (alloy symbol A3) is one in which the temperature in the solution treatment-reheating treatment after cooling is too high, and the standing time after the reheating treatment is too long. In this case, the same alloy is used. Compared with the example of the present invention (Production No. 3) using (A3), the material strength was too high and the moldability was poor, and the moldability was poor and the bake hardenability was not sufficient especially after standing for 60 days. Further, the production number 9 (alloy symbol A4) was one in which the holding temperature was too low and the holding time was too long in the holding treatment during the cooling after the solution treatment, and in this case, the same alloy (A4) was used. Sufficient bake hardenability was not obtained as compared with the inventive example (Production No. 4).

On the other hand, all of the production numbers 10 to 12 are alloys whose component compositions are out of the range specified by the present invention, and the processes under the conditions defined by the present invention are applied. In this case, Not only was the material strength low in all cases, but also the bake hardenability was low, and the strength after baking was not sufficiently obtained.

[0040]

EFFECTS OF THE INVENTION According to the method for producing an aluminum alloy sheet for forming of the present invention, not only excellent formability and high material strength, but also excellent bake hardenability, the strength after coating baking is extremely high. In addition, it is possible to obtain a stable aluminum alloy plate for forming, which has little change with time at room temperature and has little decrease in formability and little decrease in bake hardenability even after being left at room temperature for a long time after plate production. Therefore, it is optimal for the production of automobile body sheets, home electric appliances parts, various machine / equipment parts, and other aluminum alloy sheets for use in forming and baking.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a process after solution treatment in the method of the invention of claim 1;

FIG. 2 is a diagram for explaining the process after the solution treatment in the method of the invention of claim 2;

Claims (2)

[Claims] 1. A glass containing Mg 0.3 to 1.5% (weight%, the same hereinafter), Si 0.5 to 2.5%, and if necessary, Cu 0.03 to 1.2% and Zn 0.03. ~ 1.5
%, Mn 0.03 to 0.4%, Cr 0.03 to 0.4
%, Zr 0.03 to 0.4%, V 0.03 to 0.4%,
An alloy containing 1 or 2 or more selected from 0.03 to 0.5% of Fe and 0.005 to 0.2% of Ti, with the balance being Al and unavoidable impurities as a raw material After performing homogenization treatment, hot rolling and cold rolling are performed to obtain a rolled plate having a required plate thickness, and for the rolled plate,
100 after performing solution treatment at a temperature of 480 ° C or higher
After cooling to a temperature in the range of 150 to 300 ° C at a cooling rate of ℃ / min or more, and subsequently performing a heat treatment of holding the temperature in the range of 150 to 300 ° C for 1 to 600 seconds, 1
It is characterized by performing a stabilization treatment of cooling to a temperature of 140 ° C. or lower at a cooling rate of 00 ° C./min or more, and then maintaining the temperature within a range of 50 to 140 ° C. for 0.5 to 50 hours within 72 hours. A method for producing an aluminum alloy sheet, which has little change with time at room temperature and is excellent in formability and bake hardenability. 2. Mg 0.3-1.5%, Si 0.5-
2.5%, and if necessary, Cu0.03 ~
1.2%, Zn 0.03 to 1.5%, Mn 0.03 to
0.4%, Cr 0.03 to 0.4%, Zr 0.03 to
0.4%, V0.03 to 0.4%, Fe0.03 to 0.
1 selected from 5% and Ti 0.005 to 0.2%
, Or two or more, with the balance being Al and unavoidable impurities as the raw material, and subjecting the ingot to homogenization treatment, followed by hot rolling and cold rolling to achieve the required sheet thickness rolling. The plate is subjected to solution treatment at a temperature of 480 ° C. or higher, and then cooled to a temperature range of 150 ° C. or lower at a cooling rate of 100 ° C./min or higher, and subsequently, within 72 hours, 150 to After heating to a temperature in the range of 300 ° C. and performing heat treatment without holding or holding for 600 seconds or less, cool to a temperature of 140 ° C. or less at a cooling rate of 100 ° C./min or more, and then within 72 hours, 50-140
A method for producing an aluminum alloy sheet having a small change with time at room temperature and excellent in formability and bake hardenability, which is characterized by performing a stabilizing treatment in which the temperature is kept at a temperature in the range of 0 ° C for 0.5 to 50 hours.