JPH05306440A - Manufacture of aluminum alloy sheet for forming excellent baking hardenability - Google Patents

Abstract

PURPOSE:To improve the formability and strength after the baking finishing treatment of an aluminum alloy sheet for forming suitable for an automotive outer sheet, a sheet for packaging, etc. CONSTITUTION:An Al alloy contg., by weight, 0.02 to 2.0% Cu, 0.5 to 2.5% Mg and 0.5 to 3.0% Si, and the balance Al with inevitable impurities and an Al alloy, in addition, contg. one or two kinds among 0.001 to 0.1% Cr and 0.001 to 0.2% Zr are melted and cast, and the ingot is subjected to homogenizing treatment at 400 to 600 deg.C for >=1hr, is thereafter subjected to a hot rolling treatment, is rapidly cooled to <=120 deg.C at >=3 deg.C/sec cooling rate immediately after the completion of the hot rolling, is subsequently subjected to a solution heating treatment at >=400 deg.C and is immediately subjected to rapid cooling treatment at >=3 deg.C/sec cooling rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for members which have excellent moldability and bake hardenability, are required to have strength, and are subjected to bake coating, such as automobile outer plates and packaging plate materials. The present invention relates to a method for manufacturing an aluminum alloy plate for forming.

[0002]

2. Description of the Related Art Conventionally, cold-rolled steel sheets have been mainly used for automobile outer panels. However, recently, the use of an aluminum alloy plate has been considered in order to reduce the weight of an automobile body. Materials for automobile outer panels are required to have excellent press formability and high strength. 5052 alloy, which is a material that satisfies such requirements
Al-Mg alloy (5000 series alloy) such as 5182 alloy, 6009
Al-Mg-Si alloys (6000 series alloys) such as alloys and 6061 alloys have been used.

[0003]

Since the above-mentioned 6000 series alloy can obtain high strength after baking and coating, it is applied to automobile outer plate materials and the like. The conventional baking temperature was 180 ° C for about 1 hour, but the baking temperature tends to be lower and shorter. Therefore, these alloys do not have sufficient strength after baking. Generally, 6000 series alloys
The press formability is inferior to that of the 5000 series alloy, and the press formability tends to be further deteriorated by increasing the amount of added alloy in order to increase the strength after baking coating. As a result of various studies in view of this, the present invention has developed a method for producing an aluminum alloy sheet for forming which is excellent in press formability and is excellent in bake hardenability at low temperatures.

[0004]

The present invention provides Cu 0.02 to 2.
0wt%, Mg 0.5-2.5wt%, Si 0.5-3.0wt%, balance A
1 and aluminum alloy consisting of unavoidable impurities are melt-cast, and the ingot is subjected to homogenizing treatment for 1 hour or more at a temperature of 400 ° C. or more and 600 ° C. or less, followed by hot rolling treatment,
Immediately after completion of hot rolling, 120 ℃ at a cooling rate of 3 ℃ / sec or more
It is rapidly cooled to the following, then cold-rolled, then solution-heated to 400 ° C or more and immediately cooled to 3 ° C.
The method for producing an aluminum alloy sheet for forming having excellent bake hardenability, which comprises performing rapid cooling treatment at a cooling rate of not less than / sec, is claim 1, and further comprises Cu0.02 to 2.0 wt% and Mg0.
5 to 2.5 wt%, Si 0.5 to 3.0 wt%, Cr 0.001
~ 0.1wt%, Zr0.001 ~ 0.2wt%, 1 or 2 kinds, aluminum alloy consisting of balance Al and unavoidable impurities is melt-cast, and the ingot is heated at a temperature of 400 ° C to 600 ° C After performing the homogenizing treatment for more than an hour, perform the hot rolling treatment, and immediately after finishing the hot rolling, rapidly cool to 120 ° C or less at a cooling rate of 3 ° C / sec or more, then perform the cold rolling treatment, and then perform the cold rolling treatment. Request a method for producing aluminum alloy sheet for forming with excellent bake hardenability, characterized by performing solution heat treatment at 400 ° C or higher after rolling treatment, and then performing rapid quenching at a cooling rate of 3 ° C / sec or higher. It is the item 2.

[0005]

In the present invention, the reason why the alloy composition is limited is as follows. Cu forms a solid solution in the matrix, and G. P. B. Zone, S'-Al Cu Mg
Etc. or promote precipitation of Mg ₂ Si to improve strength, especially proof stress. 0.02 to 2.0 wt%
The reason is that if less than 0.02 wt%, the effect is small,
This is because if it exceeds 2.0 wt%, the ductility at the time of molding is lowered due to solid solution hardening, and the corrosion resistance is deteriorated. Mg and G. P. Since the zone and Mg ₂ Si are deposited, the strength after baking coating is improved. The amount added is limited to 0.5 to 2.5 wt% because if it is less than 0.5 wt%, the effect is small, and if it exceeds 2.5 wt%, the elongation at the time of molding is lowered. Si is a G.I. P. Since the zone and Mg ₂ Si are deposited, the strength after baking coating is improved. 0.5 ~ 3.0wt%
The reason is that the effect is small when less than 0.5 wt%, 3.
This is because if it exceeds 0 wt%, it is precipitated as simple substance Si during the homogenization treatment to lower the press formability and deteriorate the corrosion resistance. Additions of Zr and Cr each have the effect of refining crystal grains, and are added for the purpose of improving the matrix strength. The addition amount of each is limited to 0.001 to 0.1 wt% and 0.001 to 0.2 wt% because the effect is small below the lower limit and the formability after solution treatment decreases below the upper limit. Further, since Fe, which is usually contained as an impurity in Al, easily forms Si and α-Al Fe Si, which are solid-solved in the matrix, reduces the amount of Si solid-solution and reduces the curability during baking coating. , Less than 0.5 wt% is desirable. In addition, in general, Ni, V added for refining the crystal grains and improving the matrix strength, and Ti, B, etc. added for refining the cast structure have a total amount of these elements.
If it is less than 1.0 wt%, the effect of the present invention is not particularly impaired.

Next, the heat treatment and rolling treatment of the alloy ingot obtained by the above alloy composition will be described. First, in the homogenization treatment, the crystallized substances generated during the cooling and solidification process during the production of alloy ingots are forcibly solid-solved by heating, the solid solubility of the ingot matrix is increased, and the segregation of additional elements is relaxed by diffusion. To do. Furthermore, residual stress generated in the cooling and solidifying process is eliminated, and cracking during hot rolling is prevented. The temperature was 400 ℃ or more and 600 ℃ or less.
This is because if the temperature is lower than 0 ° C, the diffusion of the additional element, especially the crystallized Si generated during the cooling and solidification process of the ingot is not sufficiently solid-solution diffused, and if it exceeds 600 ° C, partial melting due to the concentration segregation of the additional element occurs. is there. Further, the heat treatment time is set to 1 hour or more because if the heat treatment time is less than 1 hour, solid solution diffusion of the additional element is not sufficiently performed and the effect of the present invention is significantly impaired. The ingot that has been subjected to the homogenization treatment is subjected to a hot rolling treatment after being slightly cooled in order to prevent seizure with a rolling roll. This hot rolling temperature is not particularly limited to a temperature usually performed, but if the hot rolling start temperature is lower than 380 ° C, the workability during hot rolling is deteriorated, and the temperature is too low at the end of hot rolling. Precipitation of the element occurs, and even if a solution treatment is performed later, the additional element cannot be sufficiently solid-dissolved. Therefore, the hot rolling start temperature is 380
It is necessary to carry out at a temperature of not less than 0 ° C, and it is desirable to carry out at a temperature as high as possible in order to maintain the solid solution of the additional element.

Precipitates tend to coarsen in the rolled plate that has been gradually cooled after the completion of hot rolling, and the coarsened precipitates cannot be sufficiently solid-solved by the subsequent heat treatment. Therefore, in order to maintain the solid solution state of the high additive element obtained by the homogenization treatment of the ingot until the end of hot rolling, and to prevent precipitation and coarsening of the additional element, the rolled plate immediately after the hot rolling treatment is immediately finished. Rapidly cool to 120 ° C or less at a cooling rate of 3 ° C / sec or more. Limiting the cooling rate to 3 ° C / sec or more is 3
This is because, at a cooling rate of less than ° C / sec, additional elements are precipitated during cooling, which deteriorates press formability and curability during baking coating. Further, the temperature after cooling is limited to 120 ° C. or less, because when the cooling is finished at a temperature higher than 120 ° C., G.I. P. Zone, Mg ₂ S
This is because clusters such as i or Mg ₂ Si in the initial stage of precipitation occur, and the growth of the precipitation phase occurs in the subsequent manufacturing process, which lowers the solid solubility of the matrix of the rolled plate. Further, when the hot-rolled sheet is rapidly cooled, if the hot-rolled sheet thickness exceeds 10 mm, it is difficult to obtain a cooling rate of 3 ° C / sec or more during the rapid cooling after hot-rolling, and if the hot-rolled sheet has a thickness of less than 3 ° C / sec. At the cooling rate, precipitation of the additional element occurs during cooling, which deteriorates press formability and hardenability during baking coating. Therefore, it is desirable that the hot-rolled sheet thickness be less than 10 mm. The rolled sheet that has undergone quenching after hot rolling is subjected to solution treatment heating after the subsequent cold rolling treatment, and the precipitate is solid-solved in the matrix by immediate quenching, resulting in a supersaturated solid solution state. And The reason for limiting the solution treatment heating temperature to 400 ° C. is that if the heating temperature is less than 400 ° C., the precipitates do not form a solid solution sufficiently, and the strength improvement during baking coating is small. The holding time of the solution heat treatment is not particularly limited, but it is desirable that the temperature is 400 ° C. or higher and 5 seconds or longer. The cooling temperature after solution heat treatment was set to 3 ° C / sec or more because it was 3 ° C / sec.
This is because at a cooling rate of less than, during the cooling, precipitation of the additional element once solid-solubilized by the solution heat treatment occurs, and press formability and curability during baking coating are significantly reduced.

[0008]

EXAMPLES Examples of the present invention will be described below. Example 1 An Al alloy having the composition shown in Table 1 was melted by a conventional method, and an ingot was obtained by DC casting. This ingot is homogenized at 520 ° C for 1 hour, the thickness of the hot rolled sheet is increased to 7 mm, and immediately after the hot rolling, it is forcibly and rapidly cooled to 120 ° C at a cooling rate of 15 ° C / sec, and then cold-rolled. It was rolled into a plate with a thickness of 1 mm. This plate material was heated at 550 ° C. for 10 seconds and then subjected to solution treatment at a cooling rate of 15 ° C./sec. Tensile test, Erichsen bulge test, limit deep drawing (LDR)
The test was conducted. In addition, 150 ℃ × 20, 30, 60min, 170 ℃ × 20, 30, 60min, 200 which simulated baking coating processing
Tensile tests were also conducted after heating for × 20, 30, 60 minutes. Tensile test, JIS No. 5 tensile test piece, tensile strength,
The yield strength and elongation were measured. Erichsen overhang test is JIS Z
The overhang height was measured by the 2247 A method. Limit deep drawing (LD
In the R) test, a blank coated with lubricating oil was deep-drawn with a punch of φ33 mm, and the maximum blank diameter that did not break was divided by the punch diameter to obtain a value. The results are shown in Tables 2 and 3.

[0009]

[Table 1]

[0010]

[Table 2]

[0011]

[Table 3]

As is clear from Tables 2 and 3, it can be seen that Nos. 1 to 7 according to the present invention are all excellent in mechanical properties and moldability, and are excellent in strength after baking treatment. On the other hand, No. 8 out of the alloy composition targeted by the present invention
No. 9 has a large amount of Mg and a small amount of Si, and No. 9 has a large amount of Mg and a small amount of Si.
Since No. 11 has a large amount of Cr, one or more of the formability after the solution treatment and the strength after the baking coating treatment are inferior.

Example 2 Of the alloys of Table 1 in Example 1, two alloys Nos. 2 and 7 were subjected to hot rolling under the heat treatment conditions A to D shown in Table 4 and then hot rolled. The plate thickness was set to 7 mm, and then cold rolled to obtain a plate material having a thickness of 1 mm. This plate material was heated at 550 ° C. for 10 seconds and then solution-treated at a cooling rate of 15 ° C./sec. Tensile test, Erichsen bulge test, limit deep drawing (LDR)
The test was conducted. Also, simulated baking treatment
150 ° C x 20, 30, 60min, 170 ° C x 20, 30, 60min, 200 ° C
Tensile tests were also conducted after heating for × 20, 30, 60 minutes. The results are shown in Tables 5 and 6.

[0014]

[Table 4]

[0015]

[Table 5]

[0016]

[Table 6]

As can be seen from Tables 4 to 6, the conditions A and B of the method of the present invention are excellent in mechanical properties and moldability even in deviation, and are excellent in strength after baking coating. On the other hand, condition C, which deviates from the method of the present invention, has a slow cooling rate after hot rolling, and condition D has a low homogenization treatment temperature. Therefore, one of moldability after solution treatment and strength after baking coating treatment is required. One or more are inferior.

Example 3 No. 6 of the alloys shown in Table 1 in Example 1 was used as a plate material having a thickness of 1 mm as in Example 1. This plate material was subjected to solution treatment (holding time 10 sec) under the conditions shown in Table 7. A tensile test, an Erichsen bulge test, and a limit deep drawing (LDR) test were performed on the plate material manufactured through the above steps. Also,
Baking coating treatment simulated 150 ℃ × 20, 30min, 17
Tensile tests were also conducted after heating at 0 ° C. × 20, 30 min and 200 ° C. × 20, 30 min. The results are also shown in Table 7.

[0019]

[Table 7]

As is clear from Table 7, all of the products produced by the method of the present invention are excellent in mechanical properties and moldability, and are excellent in strength after baking treatment. On the other hand, in the comparative method deviating from the method of the present invention, the cooling rate of the solution heat treatment is slow, or the solution heat treatment temperature is low, so that the moldability after the solution heat treatment or the strength after the baking coating treatment is one of The above is inferior.

[002]

As described above, according to the present invention, it is possible to obtain an aluminum alloy sheet for forming which is excellent in formability after solution treatment and strength after baking, and particularly in the case of outer panels of automobile bodies. It has a baking coating process and is most suitable for molded products that require high moldability, high strength and high yield strength. further,
Since it exhibits excellent characteristics for molded products that have baking coating and manufacturing processes similar to it, it has a wide range of applications such as structural members for construction, plate materials for packaging, appliances, chassis of electrical equipment, etc., and has remarkable industrial effects Is.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsutoshi Sasaki 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Aluminum Co., Ltd. (72) Kunihiko Kishino 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Aluminum Co., Ltd.

Claims (2)

[Claims] 1. Cu0.02 to 2.0 wt%, Mg0.5 to 2.5 wt%,
An aluminum alloy containing 0.5 to 3.0 wt% of Si and the balance of Al and unavoidable impurities is melt-cast, and 40
After performing homogenizing treatment at a temperature of 0 ° C or more and 600 ° C or less for 1 hour or more, hot rolling treatment is performed, and immediately after hot rolling is finished.
Rapid cooling to 120 ° C or less at a cooling rate of 3 ° C / sec or more, then cold rolling treatment, solution heat treatment to 400 ° C or more after cold rolling treatment, and immediately cooling rate of 3 ° C / sec or more A method for producing an aluminum alloy sheet for forming, which is excellent in bake hardenability, characterized by performing a quenching treatment at. 2. Cu0.02 to 2.0 wt%, Mg0.5 to 2.5 wt%,
Si 0.5-3.0 wt%, Cr 0.001-0.1 wt%, Z
r 0.001 to 0.2 wt% of 1 or 2 types and balance Al
And aluminum alloy consisting of unavoidable impurities are melt-cast, and the ingot is homogenized at a temperature of 400 ° C or more and 600 ° C or less for 1 hour or more, then hot-rolled, and after hot-rolling is completed. Immediately, it is rapidly cooled to 120 ° C or less at a cooling rate of 3 ° C / sec or more, then cold-rolled, then solution-heated to 400 ° C or more after cold-rolling, and immediately 3 ° C / s.
A method for producing an aluminum alloy sheet for forming, which is excellent in bake hardenability, characterized by performing a quenching treatment at a cooling rate of ec or more.