JPH04131348A - High-strength aluminum alloy plate having excellent formability and production thereof - Google Patents

Abstract

PURPOSE:To produce the high-strength Al alloy plate for press forming having excellent press formability and strength after coating and baking by subjecting the slab of an Al alloy having a specific compsn. to a homogenization heat treatment, then working this slab to a plate material by hot rolling and cold rolling, and further heat treating the plate material under specific conditions. CONSTITUTION:The slab of the Al alloy contg., by weight %, 1.6 to 5.5% Mg, 0.03 to 0.29% Si, 0.42 to 2.5% Cu, 0.61 to 2.0% Zr, 0.005 to 0.15% Ti, 0.0002 to 0.05% B, and 0.03 to 0.4% Fe, and one or >=2 kinds among 0.01 to 0.20% Zr, 0.01 to 0.30% Cr, 0.02 to 0.18% Mn, and 0.01 to 0.30% V, is subjected to one stage or many stages of the homogenization heat treatments in a 480 to 560 deg.C temp. range. This slab is worked to the plate material having a prescribed thickness by the hot rolling and cold rolling and is then subjected to the heat treatment consisting in heating to 440 to 560 deg.C temp. range at >=3 deg.C/sec heating rate and holding for <=120 seconds at said time, then cooling at <=2 deg.C/sec cooling rate.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention has excellent press formability and high strength after paint baking even after heat treatment after rolling, and has excellent formability suitable for automobile bodies, etc. This invention relates to a high-strength aluminum alloy plate and its manufacturing method.

[Conventional technology] Surface-treated cold-rolled steel sheets have traditionally been widely used as plate materials for forming automobile body sheets, etc., but in recent years there has been an increasing demand for weight reduction in automobiles to improve fuel efficiency. In order to meet these requirements, aluminum alloy plates are beginning to be used in automobile body seats and the like.

As aluminum alloys for automobile body sheets, non-heat treated type 5182.5083 etc., heat treated type 2036 etc.
．． 6009.6010 etc. are used. Furthermore, as disclosed in JP-A-57-120648 and JP-A-53-103914, Cu
Aluminum alloys have been developed that are designed to be used after heat treatment and by adding trace amounts of Zn and Zn.

[Problems to be solved by the invention] However, these aluminum alloys have an elongation at break of 30% or more in a tensile test and a yield strength of 2.
0 kgf/■2 or more, which is both of the properties required for the above-mentioned use, but either press formability and Punto resistance, or both of these are insufficient. and,
This is an obstacle to using aluminum alloys instead of cold-rolled steel sheets for automobile body sheets.

This invention was made in view of such circumstances, and
To provide a high-strength aluminum alloy plate having an elongation at break of 30% or more in a tensile test and a yield strength after baking of a paint of 20 kgf'/am2 or more, excellent press formability and Punt resistance after painting, and a method for producing the same. The purpose is to

[Means and effects for solving the problem] As a result of various studies to achieve the above object, the inventors of the present application have conducted a tensile test by appropriately adjusting the chemical composition and optimizing the manufacturing conditions. The present invention was completed based on the discovery that it is possible to achieve the following conditions: an elongation at break of 30% or more and a yield strength after baking of the paint of 20 kgf/mtp2 or more. In particular, regarding the chemical composition, from the viewpoint of increasing the strength after baking the paint, Cu is actively added to the Al-Mg alloy, aiming at precipitation hardening of A, 172 Cu M g, and Zn is added as a complementary material. It was added to.

That is, the high-strength aluminum alloy plate for press forming according to the present invention contains 1.6 to 5.5% Mg and C in weight percent.
u 0.42 to 2.5%, Zn 0.61 to 2.0%,
Ti 0.005-0.15%, B 0.0002-0
．． 05%, Si 0.03-0.29%, Fe 0.0
Contains in the range of 3 to 0.4%, and 0.01 to 0.20
% Zr, 0.01-0.30% Cr.

M n of 0.02-0.18%, and C1,01-0
．． It is characterized in that it contains one or more of 30% glue, and the remainder consists of Afl and unavoidable impurities.

Further, the method for producing a high-strength aluminum alloy plate for press forming according to the present invention includes subjecting the aluminum alloy having the above composition to one or more stages of homogenization heat treatment at a temperature within the range of 480 to 560°C, and then The alloy is hot-rolled and cold-rolled to form a plate with a predetermined thickness, and then
Heat treatment is performed under the following conditions: heating to a temperature within the range of 440 to 560°C at a heating rate of 3°C/second or more, holding at that temperature for a time of 120 seconds or less, and cooling at a rate of 2°C/second or more. Features.

This invention will be explained in detail below. Note that in the following description, % indicates weight %.

First, the reasons for limiting the composition of the aluminum alloy according to the present invention will be explained.

Mg: Mg is an essential basic component in the alloy according to the present invention, and when alloyed in an appropriate amount, it greatly contributes to improving the strength and formability of the alloy. However, Mg is 1.6
If it is less than 5.5%, sufficient strength will not be obtained, and if it exceeds 5.5%, elongation will become small and moldability will deteriorate. Therefore, the Mg content is defined in the range of 1.6 to 5.5%.

Cu: Cu combines with Al-Mg, forming All2Cu
Mg has the effect of increasing strength through paint baking. However, if Cu is less than 0.42%, the effect will not be sufficient, and if it exceeds 2.5%, not only will the formability deteriorate, but the material properties will change significantly over time after solution heat treatment. Therefore, the content of Cu is defined in the range of 0.42 to 2.5%.

Zn: Zn combines with Mg to form M g Z n 2
Like Cu, it suppresses the decrease in strength due to paint baking. However, if the Zn content is less than 0.61%, the effect is not sufficient, and if it exceeds 2.0%, the moldability decreases. Therefore, the Zn content is defined in the range of 0.61 to 2.0%.

The above three elements are essential elements to ensure strength after baking the paint.

Ti, B: In the present invention, not only press formability but also
In addition to the above three elements, Ti1B is also added as an essential element for the purpose of controlling the structure of the ingot, which also affects cracks during hot rolling. Ti and B exist as TiB2 etc.
It has the effect of refining the crystal grains of the ingot, but if added in excess, it will produce coarse crystallized substances and conversely reduce formability, so the content of Ti and B should be adjusted to 0.005 to 0. ．．
15%, and within the range of 0.0002 to 0.05%.

Si, Fe: Si and Fe are usually impurity elements unavoidably contained in aluminum alloys, and from the viewpoint of suppressing the formation of coarse crystallized substances that adversely affect formability, the upper limits of these are set to 0.0. 29%, 014%. On the other hand, since adding a small amount of Si has the effect of improving moldability.

It is important that the Fe content is 0.03% or more in all cases. Therefore, the contents of Si and Fe are each 0.0
It is defined in the range of 3 to 0.29% and 0.03 to 0.29%.

Zr, Cr, MnNV: These elements suppress grain coarsening not only in the ingot but also after solution heat treatment, make the structure uniform, and contribute to increased strength and formability. Therefore, one or more of these elements are added in appropriate amounts in order to suppress coarsening of crystal grains after solution treatment, which causes surface roughness during press molding, and to further increase strength and improve moldability.

However, excessive addition of these elements produces coarse crystallized substances and reduces formability, so Zr.

The content of Cr and MnNV is 0.01 to 0, 20, respectively.
%, 0.01~0.30%, 0.02~0.18%
, 0.01% to 0.30%.

In addition to the above elements, unavoidable impurities are contained as in ordinary aluminum alloys, but the amount thereof is allowed within a range that does not impair the effects of the present invention. For example, Na≦0.0
If K≦0.001% and K≦0.001%, even if these elements are contained, there will be no problem in terms of properties.

Next, the manufacturing conditions for the alloy of this invention will be explained.

An aluminum alloy whose ingredients and composition are defined within the above range is melted and cast, and the ingot is subjected to one or more stages of homogenization heat treatment at a temperature within the range of 480 to 560°C. By performing such homogenization treatment, the diffusion solid solution of the eutectic compound crystallized during casting is promoted, and local micro-segregation is reduced. This treatment also suppresses grain coarsening in the final product and plays an important role in achieving uniformity.
r.

Compounds of Cr and MnNV can be precipitated uniformly and finely. However, when the temperature of this treatment is less than 480°C, the above-mentioned effects are insufficient;
Above 0°C, eutectic melting occurs. Therefore, the temperature of the homogenization treatment was set at 480 to 560°C. Note that the holding time within this temperature range is not particularly defined, but the preferred range is 1 to 1, in which the above-mentioned effects can be sufficiently obtained and economical efficiency is not impaired.
It is 72 hours.

Next, for the ingot that has been subjected to such homogenization treatment,
Hot rolling and cold rolling are performed in accordance with conventional methods to obtain a predetermined thickness. At this time, intermediate annealing for softening the material may be performed between hot rolling and cold rolling or between cold rolling.

This treatment does not impair the effects of the present invention in any way. Further, skin bath rolling of 5% or less may be performed for distortion correction and surface roughness adjustment.

Thereafter, such a rolled plate material is heated to a temperature within the range of 440 to 560°C at a heating rate of 3°C/second or more, held at that temperature for a time of 120 seconds or less, and cooled at a rate of 2°C/second or more. Heat treatment is carried out under the following conditions. This heat treatment is performed on Mg-5i compounds and Al-Mg-C, which have a large contribution to strength.
By making the Mg-Zn-based compound into a solution and adjusting the crystal grains, it is possible to improve press formability and strength. In this case, if the heating rate is less than 3° C./second, the heating temperature exceeds 560° C., or the holding time is longer than 120 seconds, the crystal grains will become coarse. Further, if the heating temperature is lower than 440° C., the above-mentioned solution effect cannot be sufficiently obtained. If the cooling rate is less than 2° C./sec, the above-mentioned compounds will coarsely precipitate during cooling, resulting in insufficient strength and press formability.

Note that the plate material subjected to such heat treatment may be subjected to stretching of 4% or less, leveling, or skin bath for the purpose of correcting distortion, if necessary.

The aluminum alloy plate thus obtained has an elongation at break of 30% or more and a yield strength of 20 kgf/sv after baking the paint.
2 or more, and has both excellent press formability and tent resistance. Another great advantage of this invention is that stretcher strain marks that adversely affect the appearance after pressing do not occur.

[Example] Examples of the present invention will be described below.

Example 1 An alloy having the components and composition shown in Table 1 was melted and continuously cast, and homogenized at 510°C for 12 hours.
Next, the slab was heated to 450°C and hot rolled to a thickness of 4I, subjected to intermediate annealing at 350°C for 2 hours, and then cold rolled to a thickness of IIIM. Note that the finishing temperature of hot rolling was 280°C. The plate material having a thickness of 1+ug thus formed was heated to 530° C., held for 60 seconds, and then cooled by forced air cooling at a cooling rate of 15 seconds° C./second.

After this heat treatment, natural aging was performed at 25° C. for 3 weeks, and a tensile test (JIS No. 5, same tensile force in rolling direction) and a conical cup test (JIS Z2249: test tool type 21) were performed. The conical cup test was conducted as a simulation of press forming, and the combined formability of overhang and deep drawing was evaluated using CCV (+m). The smaller the cccv, the better the formability.) To simulate, after adding 2% tensile strain strain 18
A heat treatment (corresponding to baking) was performed at 0° C. for 30 minutes, and a tensile test (same as the test after heat treatment) was performed. These results are also listed in Table 1. Furthermore, the presence or absence of stretcher strain marks was also noted.

In Table 1, alloy numbers 1 to 9 are examples within the composition range of the present invention, and alloy numbers 1O to 22 are comparative examples outside of that range. Moreover, alloy number 22 among the comparative examples corresponds to 5182 alloy, which has a proven track record for use in automobile body seats.

As is clear from Table 1, alloy numbers 1-
Alloy No. 9 showed excellent values such as elongation at break of 30% or more and yield strength after heat treatment simulating paint baking of 20 kgf'/112 or more, while comparative examples Alloy No. 10 to 2
In No. 2, either or both of elongation at break and proof stress after baking were smaller than these values. Furthermore, in terms of CCV, all of the Examples showed good values, whereas the Comparative Examples had poor or poor CCV values. Further, while no stretcher strain marks were observed in the Examples, stretcher strain marks were observed in some of the Comparative Examples. That is, it was confirmed that if the composition was within the range of the present invention, both press formability (evaluated by elongation and CCV) and strength after paint baking were excellent.

Example 2 Next, an alloy plate material was manufactured under the manufacturing conditions shown in Table 2 using an ingot having the composition of alloy number 1 among the alloys shown in Table 1. Note that for treatments not specifically listed in Table 2, the conditions of Example 1 were adopted (rolling and intermediate annealing conditions, etc.). Note that No. 2 A in Table 2 is an example within the range of the manufacturing method according to the present invention, and symbols BG are comparative examples outside the range.

The same evaluation test as in Example 1 was conducted on the plate material thus manufactured. The results are also listed in Table 2.

As is clear from Table 2, it was confirmed that the comparative examples that did not satisfy the conditions of the present invention were significantly inferior in formability and strength after baking. In particular, B, C, D, and F were particularly poor in moldability. This is because the crystal grains become coarse under these conditions. Also, E.

It was confirmed that G had low strength, especially extremely low yield strength after baking. These are Mg, Si, and Cu.

This is because uniform fine precipitation of the Zn compound cannot be obtained. In contrast, Example A has a breaking elongation of 30% or more and C
The CV is also good and the yield strength after baking is 20 kgf'/
It was confirmed that if the conditions were as high as si2 and within the scope of the present invention, a plate material excellent in both press formability and strength after paint baking could be obtained.

[Effect of the invention]

Claims (2)

[Claims] (1) In weight%, Mg is 1.6 to 5.5%, Cu is 0.
42-2.5%, Zn 0.61-2.0%, Ti 0
．． 005-0.15%, B 0.0002-0.05%
, Si 0.03-0.29%, Fe 0.03-0.
Contains Zr in the range of 4% and 0.01 to 0.20%
, 0.01-0.30% Cr, 0.02-0.18%
A high-strength aluminum alloy plate with excellent formability, characterized by containing one or more of Mn of . (2) In weight%, Mg is 1.6 to 5.5% and Cu is 0.
42-2.5%, Zn 0.61-2.0%, Ti 0
．． 005-0.15%, B 0.0002-0.05%
, Si 0.03-0.29%, Fe 0.03-0.
Contains Zr in the range of 4% and 0.01 to 0.20%
, 0.01-0.30% Cr, 0.02-0.18%
An aluminum alloy containing one or more of MnN and 0.01 to 0.30% of glue, with the remainder consisting of Al and unavoidable impurities, is subjected to one step at a temperature within the range of 480 to 560°C. Alternatively, the alloy is subjected to multi-stage homogenization heat treatment, then hot rolled and cold rolled to form a plate material having a predetermined thickness, and then heated to a temperature within the range of 440 to 560°C at a rate of 3°C/second or more. Heat at a speed of 1 at that temperature.
A method for producing a high-strength aluminum alloy plate with excellent formability, which comprises performing heat treatment under conditions of holding for a time of 20 seconds or less and cooling at a rate of 2° C./second or more.