JPH05140687A - Aluminum plate for automobile parts and its manufacture - Google Patents

Abstract

PURPOSE:To provide an aluminum plate for automobile parts excellent in strength and formability. CONSTITUTION:This aluminum plate is a one contg., as essential components, 4 to 5% Mg and 0.1 to 0.5% Mn, furthermore contg. one or >= two kinds among 0.05 to 0.5% Cu, 0.1 to 0.3% Fe and 0.1 to 0.5% Zn and the balance Al with impurities and in which the existing ratio of subgrains is regulate to >=20%. At the time of subjecting an aluminum alloy ingot contg. the above chemical components to homogenizing heat treatment at 480 to 540 deg.C, hot rolling, cold rolling and finish annealing, the heat treatment is executed in the range of 230 to 280 deg.C at which recrystallization does not occur in the finish annealing to regulate the existing ratio of subgrains to >=20%. In this way, high local elongation can be obtd., and excellent formability can be brought about. This aluminum plate is suitable for automobile parts such as hoods, fenders and doors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semi-rigid aluminum plate material suitable for automobile parts such as hoods, fenders and doors, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years,
Fuel efficiency regulations, such as those found in the CAFE regulation bill, have been deliberated against the backdrop of global environmental problems, and in order to respond to these regulations, weight reduction of automobiles, in particular, use of aluminum has been actively promoted. In this aluminumization, compatibility with steel sheets is required, and strength and formability comparable to those of steel sheets are required.

From such demands, for example, in 5000 series aluminum alloys, development has been advanced based on 5182 (Al-4.5 Mg). In particular, a recent development trend is high ductility due to high Mg, and the conventional elongation rate of 30
% (Japanese Patent Application Laid-Open No. 53-103914) to 35-40%, approaching the elongation of steel sheet (Japanese Patent Publication No. 62-5485).
No. 5).

These aluminum sheet materials are manufactured by the usual homogenizing heat treatment, hot rolling, cold rolling (intermediate annealing as needed) and finish annealing, and rapid heating and cooling are used for finish annealing. CAL (continuous annealing) is adopted. However, although the obtained aluminum plate material surely exhibits high ductility, it has a drawback that it is inferior in formability to steel plates.

An object of the present invention is to solve the problems of the above technical techniques, to provide an aluminum alloy sheet material having excellent formability, and to provide a method for producing the same.

[0006]

The inventors of the present invention first compared the characteristics of a steel plate and an aluminum alloy plate in order to investigate the cause of the problems in the prior art. The result is
As shown in FIG. 1, it was revealed that the difference in formability was the local elongation. That is, the uniform (uniform) elongation does not differ greatly between the steel sheet and the aluminum alloy, but there is a difference in the local elongation from the highest load point, and this local elongation causes local deformation during forming, which results in local elongation. It has been found that an aluminum alloy having a small amount of aluminum causes a rapid constriction phenomenon, resulting in a decrease in formability.

Based on the results of the investigation of the cause, the present inventors have made extensive studies on the influence of alloying elements on the local elongation and the influence of the manufacturing process and conditions. As a result, they have found that the formation of sub-crystal grains is important for improving the local elongation, and that the finish annealing condition is particularly important for the formation thereof, and the present invention has been completed here.

That is, according to the present invention, Mg: 4-5% and M
n: 0.1-0.5% is contained as an essential component, and Cu:
0.05-0.5%, Fe: 0.1-0.3% and Zn: 0.1
~ 0.5% containing one or more, the balance Al
And an aluminum plate material containing impurities, wherein the abundance of sub-crystal grains is 20% or more.

Further, the manufacturing method is as follows: the aluminum alloy ingot having the above chemical composition is subjected to homogenizing heat treatment at 480 to 540 ° C., hot rolling, and then, if necessary, intermediate annealing, cold rolling and When performing finish annealing, heat treatment is performed in the range of 230 to 280 ° C. at which recrystallization does not occur in finish annealing, and the abundance ratio of sub-crystal grains is set to 20% or more.

The present invention will be described in more detail below.

[0011]

[Action]

First, the reasons for limiting the chemical components in the present invention will be shown.

Mg: Mg is an element that imparts strength. However, if it is less than 4%, the strength will be insufficient, and if it exceeds 5%, cracking will occur during casting and hot rolling.
The range is up to 5%.

Mn: Mn is also an element that imparts strength. However, if it is less than 0.1%, the strength is insufficient, and if it exceeds 0.5%, the compound becomes coarse and the moldability is deteriorated. Therefore, the amount of Mn is set in the range of 0.1 to 0.5%.

In the present invention, the above elements are used as essential components, but one or more of the following elements Cu, Fe and Zn are further contained in appropriate amounts.

Cu: Cu is an element that imparts strength and SCC resistance. Further, Cu has the effects of preventing softening due to baking after molding and suppressing diffusion of Mg to improve SCC resistance. However, if it is less than 0.05%, there is no effect, and if it exceeds 0.5%, the effect is saturated and the yarn rust resistance tends to decrease.
Therefore, the amount of Cu is set to the range of 0.05 to 0.5%.

Fe: Fe promotes the formation of precipitates in the homogenizing heat treatment, hot rolling step and finish annealing, and is effective in uniformly refining the crystal grains in the plate (improving the formability). But 0.
If it is less than 1%, its effect is small, and if it exceeds 0.3%, a relatively large compound is formed, resulting in deterioration of formability due to insufficient ductility. Therefore, the amount of Fe is set in the range of 0.1 to 0.3%.

Zn: Zn is effective in improving the moldability by uniformly dispersing the compound without affecting the strength. But,
If it is less than 0.1%, the effect is not obtained, and if it exceeds 0.5%, the effect is saturated, resulting in useless addition. Therefore, Z
The n content is in the range of 0.1 to 0.5%.

Others: As long as Si, Ti, Zr, and V are impurities, the effects of the present invention are not impaired. That is, it is acceptable if Si is 0.2% or less and Ti, Zr, and V are each 0.1% or less.

Next, the manufacturing method will be described.

The aluminum alloy having the above chemical composition is melted and cast by a conventional method. The homogenizing heat treatment after casting is performed in order to improve segregation during manufacturing and facilitate subsequent hot rolling. Since a high Mg content is contained in the present invention, it is necessary to regulate the homogenization conditions. That is, if the temperature is lower than 480 ° C., the effect of improving segregation cannot be obtained, the hot-rolling workability is poor, and ear cracks and the like are likely to occur. Further, the solid solubility of the additional element is small, and a predetermined performance is obtained. Absent. Further, if the temperature exceeds 540 ° C, the burning that the surface layer melts occurs and the surface defects are caused. Therefore, the homogenizing heat treatment temperature is restricted to the range of 480 to 540 ° C. The holding time is preferably 1 hour or more.

After the homogenizing heat treatment, hot rolling is performed. Hot rolling usually consists of rough rolling and finish rolling, and rough rolling is performed immediately after homogenizing heat treatment. For example, a large ingot (500 mm) is rolled to 50 mm or less by a rough rolling mill, and then continuously rolled into a hot rolled sheet of 10 mm or less by a finish rolling mill.
(Hot coil). At that time, the thinner the hot-rolled sheet thickness is, the more excellent the productivity is. However, this sheet thickness is determined by the relationship between the product thickness and the process, and is generally 2 to 8 mm. The hot-rolled sheet is then cold-rolled (if necessary, subjected to intermediate annealing before or during cold-rolling) and finish-annealed.

In the present invention, this finish annealing is important. Until now, materials for automobile parts have been subjected to complete annealing (recrystallization) for the purpose of improving the total elongation. There are two types of methods, batch type and CAL, both of which are complete annealing. On the other hand, in the present invention, sub-crystal grains are formed under a temperature condition where recrystallization is not performed, and local elongation is improved.

The sub-crystal grains are generated before the re-crystal grains, that is, the dislocations increased by work hardening cause rearrangement of the dislocations by the subsequent heating, and the crystal grains are formed in equiaxed fine grains. Is. The crystal grain size is about 1 μm
1 of normal recrystallized grains (grain size 20 to 50 μm)
/ 10 or less.

As shown in FIG. 2, the more the sub-crystal grains are present, the higher the local elongation is, and the more the formability is improved. Specifically, if it is less than 20%, the effect of cold rolling on the total elongation of the structure is large, and the formability is not improved. In addition, recrystallized grains lead to a decrease in local elongation. Therefore, the abundance of sub-crystal grains needs to be 20% or more.

In order to increase the abundance of the sub-crystal grains to 20% or more, finish annealing is performed at a temperature at which recrystallization does not occur.
Specifically, it is 280 ° C or lower. However, depending on the annealing time, if the temperature is lower than 230 ° C., it takes a long time and the productivity is poor. If the temperature exceeds 280 ° C., recrystallized grains can be formed for an extremely short time, but the safety is poor.
Therefore, the finish annealing needs to be performed in the temperature range of 230 to 280 ° C. The annealing time is preferably 30 seconds to 3 hours.

Next, examples of the present invention will be described.

[0028]

Example 1

[Table 1] The aluminum alloy ingot having the chemical composition shown in Figure 5 is subjected to homogenizing heat treatment at 510 ° C for 4 hours and hot rolled to a thickness of 3 mm.
After that, intermediate annealing was performed at 350 ° C. for 2 hours. Further, it was cold-rolled to a thickness of 1 mm and then subjected to finish annealing at 260 ° C. for 2 hours.

[Table 2] Shows the evaluation results of mechanical properties and moldability. For comparison, some of the test materials had a final annealing condition of 35
It was set to 0 ° C. × 2 hr.

The elongation is measured by a chart, and the local elongation is the elongation from the highest load point to the fracture. The square head drawability was evaluated by using an Erichsen tester at a limit draw height with a 40 mm square punch. The overhang property (overhang height) is
The Erichsen test B method was used. Further, the abundance of sub-crystal grains was obtained by polishing a sample, taking a 1000 to 2000-fold structure photograph with a TEM, and determining the amount per unit area.

As can be seen from Table 2, the materials No. 1 to No. 4 of the present invention have excellent local elongation (formability) as compared with the comparative materials No. 8 and No. 9 which have been subjected to conventional finish annealing. It can be seen that the product has high strength (especially yield strength) and excellent rigidity in the product. Particularly, the material No. 1 of the present invention is excellent in moldability. This is because sub-crystal grains are formed uniformly and finely and local elongation is high.

[0031]

Example 2 Using the material of Test No. 1 of Example 1 (before finish annealing),

[Table 3] As shown in, the finish annealing was performed by changing the finish annealing temperature in the range of up to 560 ° C. The homogenization temperature was also changed. Table 3 shows the evaluation results of mechanical properties and moldability.

From Table 3, the invention material No. 4 (annealing temperature 26
It can be seen that 0 ° C.) has a high local elongation and is excellent in moldability. On the other hand, the local elongation is low in the comparative material and the conventional material whose annealing temperature is lower than 230 ° C. Further, the comparative material having a low homogenization temperature also has a low local elongation. Burning occurs when the homogenization temperature is too high at 560 ° C.

[0033]

As described in detail above, according to the present invention,
Since a certain amount of sub-crystal grains are present together with the adjustment of the aluminum alloy composition, it is possible to provide an aluminum plate material with higher strength and higher formability than conventional aluminum alloy materials, which is sufficient for making aluminum parts for automobiles. I can respond. Therefore,
It contributes to the weight reduction of automobile parts and contributes to the improvement of environmental problems.

[Brief description of drawings]

FIG. 1 is a diagram showing a stress-strain curve.

FIG. 2 is a diagram showing a relationship between local elongation and abundance of sub-crystal grains.

Claims (2)

[Claims] 1. The composition contains Mg: 4 to 5% and Mn: 0.1 to 0.5% as essential components in weight% (hereinafter the same), and further contains C
u: 0.05-0.5%, Fe: 0.1-0.3% and Zn: 0.0.
An aluminum plate material containing 1 or 2 or more of 1 to 0.5%, and the balance being Al and impurities, wherein the abundance of sub-crystal grains is 20% or more. Plate material. 2. Mg: 4-5% and Mn: 0.1-0.5% are contained as essential components, and further Cu: 0.05-0.5%, F
e: 0.1-0.3% and Zn: 0.1-0.5%, containing 1 or 2 or more types, the balance being 480 to 540 ° C. in an aluminum alloy ingot containing Al and impurities When subjected to homogenizing heat treatment, hot rolling, cold rolling and finish annealing, recrystallization does not occur in finish annealing 230 to
Heat treatment is performed in the range of 280 ° C. to reduce the abundance of subgrains to 2
A method for manufacturing an aluminum plate material for automobile parts, which is characterized by being 0% or more.