JPH04214834A - Aluminum alloy sheet excellent in corrosion resistance and press formability and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a high strength Al alloy sheet excellent in corrosion resistance and press formability by preparing an Al alloy having a specified compsn. in which each content of Ti, B and Zr is prescribed. CONSTITUTION:The ingot of an Al alloy contg., by weight, 3.0 to 10% Mg, 0.03 to 0.4% Si, 0.03 to 0.4% Fe, 0.005 to 0.15% Ti, 0.002 to 0.05% B and 0.001 to 0.09% Zr, furthermore contg. <=0.16% Cu, <=0.20% Zr, <0.10% Mn, <0.05% Cr and <0.05% V and the balance Al with inevitable impurities is subjected to single stage or multistage homogenizing treatment in the temp. range of 480 to 560 deg.C. Next, this ingot is subjected to hot rolling and cold rolling into a desired sheet thickness and is thereafter subjected to heat treatment in the temp. range of 320 to 560 deg.C. In this way, the Al alloy sheet excellent in corrosion resistance and press formability is obtd. and is suitable as material for an automobile body.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy plate suitable for automobile bodies, etc., which has excellent corrosion resistance and press formability, and a method for manufacturing the same.

0002

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

[0003] As an aluminum alloy for automobile body sheets, heat-treated 6009 for the purpose of bake hardening is used.
, 6010, 6011 (all Al-Mg-Si type)
and 2036 (Al-Cu type), but these do not necessarily have sufficient moldability. In addition, as a non-heat treatment type, 0
．． 5182 (Al
-Mg type) and 5182-SSF, which has suppressed the appearance of press distortion patterns by improving the manufacturing method, and these have slightly better formability than the heat-treated type, but do not have bake hardenability.

Furthermore, as disclosed in JP-A-57-120648 and JP-A-53-103914, Al
- Alloys containing Cu and Zn have been developed to impart some bake hardenability to Mg-based alloys. However, Cu-added materials have problems with corrosion resistance, and their formability is inferior to that of conventional surface-treated cold rolled steel sheets. At present, it cannot be used as a substitute for surface cold-rolled steel sheets.

[0005]

[Problems to be Solved by the Invention] The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an aluminum alloy plate having sufficient corrosion resistance and press formability as a material for automobile bodies, and a method for manufacturing the same. purpose.

[0006]

[Means and effects for solving the problem] In order to achieve the above object, the inventors of the present application have made various studies and found that by appropriately adjusting the chemical composition and adjusting the manufacturing conditions. They discovered that it is possible to achieve sufficient press formability and corrosion resistance, and have completed the present invention. In particular, regarding the chemical composition, instead of lowering the content of Mn and Cr, which are generally added as recrystallization suppressing elements in Al-Mg alloys, to a level lower than the intentional addition level, a trace amount of Zr was added. In addition to improving elongation, the content of Cu, which has a negative effect on corrosion resistance, was lower than the level of intentional addition, thereby improving corrosion resistance.

[0007] That is, the aluminum alloy plate having excellent corrosion resistance and press formability according to the present invention has M
g 3.0-10%, Si 0.03-0.4%, Fe
0.03-0.4%, Ti 0.005-0.15%
, B from 0.0002 to 0.05%, Zr from 0.001 to
Contains within the range of 0.09% and further contains C of 0.16% or less.
u, 0.20% or less Zn, less than 0.10% Mn, 0
．． It is characterized by containing less than 0.05% Cr, less than 0.05% V, and the remainder consisting of Al and inevitable impurities. In this case, it is preferable that the average grain size at the center of the plate thickness is 50 μm or more.

[0008] Furthermore, in the method for producing an aluminum alloy plate having excellent corrosion resistance and press formability according to the present invention, an aluminum alloy ingot having the above composition is subjected to one or multiple stages at a temperature within the range of 480 to 560°C. After homogenization treatment,
This ingot is hot-rolled and cold-rolled to a desired thickness, and then heat-treated at a temperature within the range of 320 to 560°C. In this case, intermediate annealing treatment at a temperature within the range of 320 to 560°C is performed once or twice between hot rolling and cold rolling, or between cold rolling and cold rolling, or both. It is preferable to carry out the process more than once. In the aluminum alloy according to the present invention, good corrosion resistance can be obtained, and elongation at break, which is closely related to press formability, can be 35% or more. 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 it is no exaggeration to say that it is the only strengthening element, and when alloyed in an appropriate amount, it greatly contributes to improving the strength and formability of the alloy. . However, Mg is 3.0
If it is less than 10%, sufficient strength and elongation cannot be obtained;
If it exceeds this, cracks will occur during hot rolling and hot workability will deteriorate. Therefore, the Mg content should be 3.0 to 1.
Specified in the range of 0%.

Si, Fe: Si and Fe are normally contained in aluminum alloys as inevitable impurities. If the content of these substances exceeds 0.4%, coarse crystallized substances that adversely affect moldability are likely to be generated, so from the viewpoint of suppressing the formation of such crystallized substances,
These upper limits are set at 0.4%. However, conversely, if their content is too small, moldability deteriorates, so the lower limit is set at 0.03%. That is, the content of both Si and Fe is in the range of 0.03 to 0.4%.

Ti, B: Ti and B exist as TiB2, etc., and have the effect of refining the crystal grains of the ingot and improving workability, etc., so it is extremely important to add them in combination. However, if they are added in excess, coarse crystallized substances will be generated and the formability will be deteriorated, so the contents of Ti and B should be adjusted to 0.005 to 0.15% and 0.00 to 0.15%, respectively.
It is defined in the range of 0002 to 0.05%.

Zr: Zr precipitates as Al3Zr, suppresses coarsening of crystal grains not only in the ingot but also during heat treatment, makes the structure uniform, and contributes to improving formability. Similarly, compared to Mn, Cr, and V, which have the effect of suppressing crystal grain coarsening, a sufficient effect can be obtained even with a small content, and in addition, Al3
Zr itself is finer than the compounds of Mn, Cr, and V. Therefore, compared to Mn, Cr, and V, it has extremely little adverse effect on moldability. However, if Zr is contained excessively, the formability will be deteriorated like Mn, Cr, and V, so the content is set in the range of 0.001 to 0.09%.

[0013]Cu: Conventionally, Cu was added to Al-Mg alloys to suppress softening due to baking, but in recent years, as baking temperatures have become lower than 170°C for reasons such as energy saving, It's almost ineffective. Moreover, Cu has the effect of greatly deteriorating corrosion resistance, and has an adverse effect, so it must be avoided to contain more than 0.16%. Therefore, the Cu content is specified to be 0.16% or less.

Zn: Like Cu, Zn is sometimes added to suppress softening due to baking, but as mentioned above, it has almost no effect when baked at low temperatures, and on the contrary has a large negative effect on formability. Addition of more than .20% must be avoided. Therefore, the Zn content is 0.2
Specify 0% or less.

Mn, Cr, V: These elements are Zr
Similarly, it has the effect of suppressing crystal grain coarsening, but Z
Unlike r, it greatly deteriorates moldability, so it is necessary to reduce their content. Therefore, Mn, Cr,
The content of V is less than 0.10%, less than 0.05%, and 0, respectively.
．． Specified as less than 0.05%.

[0016] 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,
Be≦0.001%, Na≦0.001%, K≦0.0
If the content of these elements is 0.01%, there will be no problem in terms of characteristics even if these elements are contained.

[0017] When an aluminum alloy having such a composition is used as an outer material rather than an inner material, a press strain pattern generated on the surface becomes a problem. This press strain pattern is more likely to occur when the crystal grain size is small. Therefore,
In order to eliminate such press distortion patterns, it is necessary to control the average crystal grain size to 50 μm or more. next,
The manufacturing conditions for the alloy of this invention will be explained.

[0018] An aluminum alloy whose ingredients and composition are specified in the above range is melted and cast, and the ingot is heated to 480~
A single or multi-stage homogenization heat treatment is carried out at a temperature in the range of 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. Furthermore, this treatment makes it possible to finely precipitate the Zr compound, which plays an important role in suppressing crystal grain coarsening and achieving uniformity in the final product. However, if the temperature of this treatment is less than 480°C, the above-mentioned effects are insufficient, while if it exceeds 560°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 a preferable range is 1 to 72 hours, in which the above-mentioned effects can be sufficiently obtained and economical efficiency is not impaired.

Next, the ingot subjected to such homogenization treatment is subjected to hot rolling and cold rolling according to a conventional method in order to obtain a predetermined thickness. Further, skin pass rolling of 5% or less may be performed for distortion correction and surface roughness adjustment.

[0020] After that, such a rolled plate material is
Heat treatment at a temperature within the range of 60°C. This makes the structure uniform, adjusts the crystal grains, and eliminates processing strain, resulting in improved press formability. At this time, if the heating temperature is lower than 440° C., the above-mentioned effects cannot be sufficiently obtained. On the other hand, if the temperature exceeds 560°C, grain coarsening and eutectic melting will occur, so a temperature exceeding 560°C must be avoided. Note that the heating and cooling rates are not particularly specified. Further, the holding time is preferably 10 hours or less from the economic point of view, but is not particularly limited in terms of characteristics. In addition,
When used as an outer panel material, the distortion pattern caused by pressing becomes a problem as described above, but in order to suppress this, it is desirable that the heating temperature is 450° C. or higher.

[0021] In addition to these steps, from the viewpoint of productivity improvement, one time between the above-mentioned hot rolling and cold rolling, or between cold rolling and cold rolling, or both. Alternatively, it is desirable to perform intermediate annealing two or more times. This intermediate annealing is
Prevents edge cracking during heavy reduction during cold rolling,
Furthermore, the Mg compound is precipitated to serve as recrystallized nuclei, which homogenizes the structure and thereby improves formability. These effects can improve productivity. The temperature at this time is 3
The effect is not sufficient below 20℃, and the temperature below 560℃
Since eutectic melting occurs when the temperature exceeds 320°C to 560°C, intermediate annealing is performed in the range of 320 to 560°C. Note that this intermediate annealing is not an essential process, and may be omitted from the viewpoint of process saving. Note that the plate material subjected to such heat treatment may be subjected to stretching of 4% or less, leveling, or skin pass for the purpose of correcting distortion, if necessary.

The aluminum alloy plate thus obtained has an elongation at break of 35% or more and also has excellent corrosion resistance. Therefore, such an aluminum alloy plate is suitable for use in automobile body seats.

[0023]

[Embodiments] Examples of the present invention will be described below. (Example 1)

[0024] An alloy having the components and compositions shown in Tables 1 and 2 was melted and continuously cast, homogenized at 510°C for 10 hours, and then the slab was heated to 450°C to reduce the plate thickness. Hot rolling was performed to a thickness of 5 mm, and intermediate annealing was performed at 350° C. for 2 hours. After that, the plate thickness was made 2 mm by cold rolling,
After performing intermediate annealing at 360°C for 1 hour again, the plate was finished by cold rolling to a thickness of 1 mm. Note that the finishing temperature of hot rolling was 280°C. Further, intermediate annealing was performed by gradual heating and cooling at a rate of 50° C./hour for both heating and cooling. This plate material having a thickness of 1 mm was heated to 510° C. at a rate of 10° C./second, held for 40 seconds, and then cooled by forced air cooling at a rate of 20° C./second.

[0025] The plate material thus produced was heated at 25°C for 3
After leaving it for a week, cut it into a specified shape, perform a tensile test (JIS No. 5, tensile direction: rolling direction) and a conical cup test (JIS No. 5, tensile direction: rolling direction).
SZ2249: Test tool type 21) was carried out. The conical cup test was conducted as a simulation of press forming, and the combined formability of overhang and deep drawing was evaluated by CCV (mm) (the smaller the CCV, the better the formability). In addition, in order to evaluate corrosion resistance, after applying a heat cycle at 170°C for 20 minutes as a paint baking heat cycle simulation, a salt spray test (JIS Z2371) was conducted.
The corrosion weight loss was measured after 96 hours. These results are also listed in Table 1. The presence or absence of a distorted pattern was also noted.

Alloy numbers 1 to 11 in Table 1 are examples within the composition range of the present invention, and alloy numbers 12 to 22 in Table 2
is a comparative example that falls outside the range. Further, alloy numbers 21 and 22 of the comparative examples correspond to 5182 alloy and 6111, respectively, which have been used for automobile body seats.

As is clear from Tables 1 and 2, alloys Nos. 1 to 11, which are examples, have a high elongation at break of 36% or more, and their corrosion loss is extremely small, 0.004 mg/cm2 or less, and is superior to the comparative examples. It was confirmed that the moldability and corrosion resistance were superior compared to the previous one. Also, alloy number 12~ which is a comparative example
Among No. 22 alloys, alloy numbers 16 and 22, which contain a large amount of Cu, are shown to be particularly susceptible to severe corrosion. Furthermore, alloy number 15, which contains a large amount of Zr, and alloy number 14, which contains a large amount of B and Ti, have been shown to have extremely low elongations at break. In addition, all of the examples showed good values for CCV, but in the comparative example, CCV
There were some items of inferior value. In particular, alloy numbers 14 and 15, which had low elongation at break, had low CCV values. Further, in alloy numbers 18 to 21, the average grain size was as small as 16 to 24 μm, and a strained pattern was observed. On the other hand, in alloy numbers 1 to 11 as examples and alloy numbers 12 to 17 as comparative examples, the average grain diameters were 54 to 68 μm and 53 to 72 μm, respectively, and no strain pattern was generated. In addition, in alloy number 22 corresponding to 6111, the average grain size was about 20 μm, but no strain pattern was observed. (Example 2)

Next, an alloy plate material was manufactured under the manufacturing conditions shown in Table 3 using an ingot having the composition of alloy number 10 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 conditions, etc.). Note that symbols A to D in Table 3 are examples within the scope of the manufacturing method according to the present invention, and symbols E to H are comparative examples outside the range. In addition, in Table 3, intermediate annealing 1 was performed between hot rolling and cold rolling, and the heating rate was 5.
The cooling rate was 0°C/hour and the cooling rate was 50°C/hour. In addition, intermediate annealing 2 was performed between cold rolling when changing the plate thickness from 4 mm to 2 mm and cold rolling when changing the plate thickness from 2 mm to 1 mm, with a heating rate of 50°C/hour and a cooling rate of 50°C/hour. 50℃/
It was time. The same evaluation test as in Example 1 was conducted on the plate material thus manufactured. The results are also listed in Table 3.

As is clear from Table 3, it was confirmed that the comparative examples that did not satisfy the conditions of the present invention were significantly inferior in elongation and moldability. Note that under manufacturing condition D, a distorted pattern appears during pressing, but no problem will occur if it is used for an inner panel.

[0030]

According to the present invention, there is provided an aluminum alloy plate suitable for use in automobile body sheets, which has much better corrosion resistance and press formability than conventional aluminum alloy plates, and a method for manufacturing the same. Therefore, it is of great value from the perspective of preventing global environmental pollution, such as by making it possible to promote weight reduction of automobile bodies.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

Claims (4)

[Claims] Claim 1: 3.0 to 10% Mg, S
i 0.03 to 0.4%, Fe 0.03 to 0.4%,
Ti 0.005-0.15%, B 0.0002-0
．． 05%, Zr in the range of 0.001 to 0.09%, further containing 0.16% or less Cu, 0.20% or less Z
n, less than 0.10% Mn, less than 0.05% Cr, 0
．． A high-strength aluminum alloy plate with excellent corrosion resistance and press formability, characterized by containing less than 0.5% V and the remainder consisting of Al and unavoidable impurities. 2. The high-strength aluminum alloy plate with excellent corrosion resistance and press formability according to claim 1, wherein the average grain size at the center of the plate thickness is 50 μm or more. Claim 3: 3.0 to 10% Mg, S
i 0.03 to 0.4%, Fe 0.03 to 0.4%,
Ti 0.005-0.15%, B 0.0002-0
．． 05%, Zr in the range of 0.001 to 0.09%, further containing 0.16% or less Cu, 0.20% or less Z
n, less than 0.10% Mn, less than 0.05% Cr, 0
．． 480-5 for aluminum alloy ingots containing less than 0.5% V and the remainder consisting of Al and unavoidable impurities.
After one-stage or multi-stage homogenization treatment at a temperature within the range of 60°C, the ingot is hot-rolled and cold-rolled to a desired thickness, and then homogenized at a temperature within the range of 320-560°C. A method for producing a high-strength aluminum alloy plate with excellent corrosion resistance and press formability, which is characterized by heat treatment at a high temperature. 4. 320 to 56 between hot rolling and cold rolling, or between cold rolling and cold rolling, or both.
Intermediate annealing treatment at a temperature within the range of 0°C once or twice
4. The method for producing a high-strength aluminum alloy sheet with excellent corrosion resistance and press formability according to claim 3, wherein the method is carried out at least once.