JP3001135B2 - Composite metal sheet with excellent BH properties and workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to provide a composite metal sheet which is lighter than the conventional use of thin steel sheets, and is used as a material for a structure requiring machining and welding. Suitable for curing, especially when placed at a temperature such as 170 ° C. for baking of paint after processing,
The present invention relates to a composite metal plate having further improved compatibility between workability and strength.

[0002]

2. Description of the Related Art Weight reduction as a structural material such as an outer panel of an automobile is a major problem, and various means have been proposed. As one of the means for reducing the weight, there is a method in which aluminum is used in a portion where a conventional steel plate is used. However, while weight reduction and strength by aluminum are theoretically possible, aluminum and aluminum alloys by themselves are significantly inferior in workability to steel plates. Furthermore, when both a steel material and an aluminum material are used for a structure, it is sometimes necessary to join them. However, both iron and aluminum have low joining strengths due to welding, so that sufficient joining strength cannot be expected. From the above, at present, aluminum can be used only for limited applications.

In order to solve these problems, a two-layer composite metal plate composed of an iron layer on one side and an aluminum layer on one side, and a thin plate in which the iron layer has bake hardenability after processing (hereinafter referred to as BH) is promising. it is conceivable that. For example, as disclosed in Japanese Patent Application Laid-Open No. 63-157774, an aluminum material is used in a plate material in which aluminum and iron are combined.
A method of heating to about 550 ° C. and hot-rolling and joining with an iron material; as disclosed in Japanese Patent Publication No. 56-52679, the surface of the iron material is previously plated with aluminum and heated to about 500 ° C. There is a method of hot rolling and joining with an aluminum material. However, there is a problem that the composite metal plate manufactured by these methods has insufficient workability and hardly hardens by baking after processing.

On the other hand, a single steel sheet having curability by baking has been studied so far, for example, Japanese Patent Application Laid-Open Nos. 2-197549 and 63-247338.
It has been found that this can be obtained by setting the amount of C, Ti or Nb in steel to a specific range and annealing under specific conditions, as disclosed in Japanese Unexamined Patent Publication (KOKAI) No. H11-163,086. However, since the steel sheets produced by these methods have a small total carbon content, the amount of bake hardening itself cannot be so high, and the steels disclosed in Japanese Patent Laid-Open No. 2-1975 / 1990 are not available.
At present, it is about 3 kgf / mm ² as disclosed in JP-A-49. Therefore, even if such a steel sheet can be combined with aluminum, a composite metal sheet having a high bake hardening amount cannot be expected. Thus, a composite metal plate of iron and aluminum having sufficient workability and bake hardenability has not been known so far.

[0005]

SUMMARY OF THE INVENTION In view of the above, the present invention has good workability, and furthermore, in order to reduce the weight by the amount of BH, a composite of iron and aluminum having a BH amount of 4 kgf / mm ² or more. It is intended to provide a metal plate.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have studied the composition and condition of the steel sheet and aluminum and found that a composite of iron and aluminum having good workability and bake hardenability is obtained. I found a metal plate.

That is, the present invention relates to a composite metal plate comprising two layers of iron on one side and aluminum on one side, wherein the iron layer has a chemical composition of 0.01 to 0.055% by weight in chemical ratio, Si:
0.1% or less, Mn: 0.04 to 0.5%, P: 0.1
%, SolAl: 0.002 to 0.1%, N: 0.
006% or less, solid solution C: 0.0004 to 0.0020
%, The balance being iron and unavoidable impurities, having a grain sized structure of not less than 10 μm and not more than 50 μm, and the aluminum layer being made of pure aluminum or aluminum alloy containing 99% or more by weight of Al as a chemical component. It is a bake-hardenable composite metal plate that is a feature. Further, the aluminum layer constituting the composite metal plate is characterized in that it is an aluminum alloy containing at least one of 6% or less of Mg and 2% or less of Mn instead of the above components. Further, in addition to the above components, one or more of 0.5% or less of Si, 0.5% or less of Cr, and 0.5% or less of Zn are further included.

[0008]

Hereinafter, the present invention will be described in detail. As the C content in the iron material increases, the average r value and the ductility deteriorate, the yield strength increases, and the workability decreases. Therefore, the smaller the amount of C, the better the press workability. Therefore, the content of C is preferably set to 0.055% or less. However, there is a problem that the cost of decarburization increases in order to make C lower than 0.010%. Therefore, the amount of C was limited to 0.055 to 0.010%.

Although there is no problem with a small amount of Si, the workability is reduced when the content is large. Therefore, it must be 0.1% or less.

Mn is a component necessary to prevent hot embrittlement due to S present as an unavoidable content in steel. However, if it is less than 0.04%, FeS is formed and the effect is not obtained. On the other hand, if it exceeds 0.5%, the workability deteriorates. Therefore, the amount of Mn was limited to 0.04 to 0.5%.

If P is contained in a large amount, it segregates at the grain boundaries and becomes brittle, causing a reduction in workability. Therefore, the P content was limited to 0.1% or less.

Al is an element necessary for controlling the amount of oxygen in the steel, and is added as a deoxidizer before adding Ti. If the acid-soluble Al content in the steel is less than 0.002%, deoxidation is not sufficiently performed, and the yield of Ti is significantly reduced. However, if it exceeds 0.1%, inclusions increase and the workability of the steel sheet decreases. Therefore, the amount of Al was limited to 0.002 to 0.1%.

When N forms a solid solution in steel, it significantly lowers workability, so that it must be fixed as TiN by Ti. Also, the amount of generated TiN is preferably as small as possible. Therefore, the N content is set to 0.0060% or less.

The reason why the amount of solid solution C is specified is to harden the composite metal plate by baking coating performed after processing, which is a feature of the present invention. As the amount of solid solution C increases, the baking hardening amount can be increased, but there is a problem that workability is reduced due to aging. FIG. 1 shows the amount of solid solution C in a steel plate portion when a composite metal plate composed of a steel plate and an aluminum plate having the chemical components shown in Table 1 and having one surface made of a steel plate and one surface made of an aluminum plate is manufactured by the equipment shown in FIG. FIG. 6 shows the effect of the amount of solute C on the amount of bake hardening and the amount of stretcher strain after 6 months from the production when various conditions were changed in the range of 0.2 to 30 ppm by changing the annealing conditions. . As is evident from FIG. 1, when the amount of solid solution C is in the range of 4 to 20 ppm, a stretcher strain due to aging does not occur and a multi-layer steel sheet having a high baking hardening amount of 4 kgf / mm ² or more is obtained. .

[0015]

[Table 1]

The components other than the above components are composed of Fe and unavoidable impurities.

The crystal grain size of the iron material of the above component must be 10 μm or more and 50 μm or less in order to have good workability. FIG. 2 shows that the annealing time of the steel plate portion is changed when manufacturing a composite metal plate composed of a steel plate and an aluminum plate having the chemical components shown in Table 1 and having one surface made of a steel plate and one surface made of an aluminum plate with the equipment shown in FIG. 5 shows the effect of the crystal grain size on the average r-value and elongation of the multilayer steel plate when the average crystal grain size of the steel plate portion of the multilayer steel plate is changed. As is clear from FIG. 2, it is found that a good average r value and elongation can be obtained when the average crystal grain size is 10 to 50 μm.

In the above investigation, it was found that good workability and bake hardenability were obtained even when the composition was changed within the range of the present invention. The method of manufacturing the steel sheet in the composite metal sheet is not particularly limited, and may be a method manufactured by hot rolling or a method manufactured through a cold rolling annealing step.

Next, conditions of the aluminum material will be described. The material of the aluminum material may be either pure aluminum or an aluminum alloy. Although the type of the aluminum alloy is not limited, an aluminum alloy containing at least one of Mg of 6% or less and Mn of 2% or less is particularly preferable. These alloy components increase the strength of aluminum in an annealed state, and do not significantly impair workability such as drawing. 6% of Mg
, Or when the amount of Mn exceeds 2%, the curing is remarkable,
Since the processability is impaired, the above ranges of these components are appropriate. Further, when 1 or 2 of 0.5% or less of Si, 0.5% or less of Cr, and 0.5% or less of Zn is added together with the above components, the strength is further increased while maintaining good workability. be able to. However, Si, Cr, Zn
If the amount exceeds the above range, the hardness becomes too high and the workability is impaired, so the above range is limited. The aluminum material of the above component may be either a cold-rolled material or an annealed material.

The energizing and heating equipment shown in FIG. 3 is provided with energizing rolls 11 and 12 on an iron layer 1 and an aluminum layer 2 of a material, respectively, and these two rolls 3 and 3 are used for both energization and pressurization. The two layers 1 and 2 are continuously fed between them, and they are pressure-bonded to produce the composite plate 4. As the power supply, either a low-frequency AC power supply or a DC power supply can be used. The current of the power supply 21 flows from the energizing roll 11 of the iron layer 1 to the energizing roll 12 through the iron layer 1 and the aluminum layer 2. In this case, the electric resistance of the iron layer is higher than that of the aluminum layer. Therefore, when the thickness of the iron layer is equal to or smaller than that of the aluminum layer, the iron layer generates more heat and becomes higher in temperature. If the heating temperature of the iron layer does not reach the target temperature, the auxiliary heating is performed by energizing the power supply roll 13 provided for the auxiliary heating from the auxiliary power supply 22. When joining the iron layer and the aluminum layer, the joining method is not particularly limited, and a method of applying an external force between two rolls as shown in FIG. 3 or a method of pressing may be used. The method of heating the joining material may be any method such as electric heating, induction heating, and heating by a heating furnace. By using a composite metal plate having an iron layer and an aluminum layer as described above, a composite metal plate excellent in bake hardenability and workability can be obtained.

[0021]

EXAMPLES Examples of the present invention will be described below together with comparative examples.
A steel plate and an aluminum plate having the compositions shown in Table 2 are superimposed so that one side has two layers of iron and one side has two layers of aluminum by the electric heating equipment shown in FIG. Then, an external force was applied to the iron layer and the aluminum layer to continuously join them. By changing the heating temperature and heating time of the steel plate portion, the crystal grain size and the amount of solute C in the steel plate portion were variously changed as shown in Table 2.

Sample Nos. (1) to (14) are all within the scope of the present invention in terms of composition, crystal grain size of the steel plate portion, and solid solution C. Samples (15) to (26) are any one of The above is out of the scope of the present invention.

After joining, the material of the obtained composite metal plate is shown in Table 3.
Shown in As can be seen from Table 3, composite metal sheets within the scope of the present invention exhibit excellent bake hardenability and workability.

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

As described above, the composite metal sheet comprising iron and aluminum according to the present invention has excellent bake hardenability and workability.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the amount of dissolved carbon in an iron layer on the amount of bake hardening of a composite plate and the amount of stretcher strain after aging.

FIG. 2 is a graph showing the influence of the crystal grain size of the iron layer on the r value and elongation of the composite plate.

FIG. 3 is a diagram showing an example of an apparatus used for manufacturing a composite plate.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 iron layer 2 aluminum layer 3 roll 4 composite plate 11, 12 energizing roll 13 auxiliary energizing roll 21 power supply 22 auxiliary power supply

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI C22C 21/06 C22C 21/06 38/00 301 38/00 301Z 38/04 38/04 (72) Inventor Hatsuhiko Oikawa Futtsu, Chiba 20-1 Ichi Shintomi Nippon Steel Corporation Technology Development Headquarters (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 30/00

Claims (3)

(57) [Claims] 1. A composite metal plate comprising two layers of iron on one side and aluminum on one side, wherein the iron layer has a chemical composition of C: 0.01-0.055% by weight and Si: 0.1% by weight. Hereinafter, M
n: 0.04 to 0.5%, P: 0.1% or less, solA
1: 0.002 to 0.1%, N: 0.006% or less, solid solution C: 0.0004 to 0.0020%, the balance being iron and unavoidable impurities. The aluminum layer has a chemical composition of 9% by weight.
A composite metal sheet excellent in bake hardenability and workability, characterized by being pure aluminum or an aluminum alloy containing 9% or more of Al. 2. An aluminum layer other than Al in a weight ratio,
The composite metal sheet according to claim 1, wherein the composite metal sheet is an aluminum alloy containing at least one of Mg of 6% or less and Mn of 2% or less. 3. The aluminum layer further comprises 1% of 0.5% or less of Si, 0.5% or less of Cr, and 0.5% or less of Zn.
3. The composite metal sheet according to claim 2 , wherein the composite metal sheet contains two or more.