JPH06190571A - Production of clad metal sheet excellent in bh property and ductility - Google Patents

Abstract

PURPOSE:To produce a clad metal sheet consisting of an iron and Al having good workability, light weight as compared to a steel sheet and the property to be hardened and strengthened through baking painting. CONSTITUTION:At producing a three layer clad metal sheet consisting of both faces of an iron and the center of Al, an iron layer consists of, by weight, 0.01-0.055% C, <=0.1% Si, 0.04-0.5% Mn, <=0.1% P, 0.002-0.1% sol Al, <=0.006% N and the balance Fe with inevitable impurities. An Al layer is of a pure Al containing >=99% Al or an Al alloy. The iron layer is heated to <=670 deg.C to >=1050 deg.C and the Al layer to <=550 deg.C, an external force is applied such that the reduction of area of the iron layer becomes <=5%, subsequently, it is cooled to 200-400 deg.C, holding at this temp. for 120-360sec and then is cooled to a normal temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a lightweight composite metal sheet, which is conventionally used for thin steel sheets, and is suitable for applications such as deep drawing. In particular, after press molding, for baking the paint, for example, 170
The present invention relates to a method for producing a composite metal plate which is hardened when placed at a temperature such as ℃ and further improved in compatibility between press workability and strength.

[0002]

2. Description of the Related Art Weight reduction as a structural material for automobile outer panels and the like has become a major issue, and various means have been proposed. One of the means for reducing the weight is to use aluminum in a portion where a steel plate has been used in the past. However, although the weight reduction and strength of aluminum are theoretically possible, aluminum must be considerably thicker than steel due to its low rigidity. For this reason, the weight reduction effect is reduced, which is also disadvantageous in terms of cost. Furthermore, aluminum and aluminum alloys are significantly inferior in workability to steel plates. For the above reasons, aluminum can only be used for a limited number of purposes at present.

In order to solve these problems, it is considered promising to have a three-layer composite plate composed of an iron layer on both sides and an aluminum layer at the center, and a thin plate having a bake hardenability (hereinafter referred to as BH) after the iron layer is processed. To be The production of a plate material that is a composite of aluminum and iron is technically difficult, so there are few practical examples. There is a practical example of a thick plate with an aluminum thickness of 5 mm and a steel plate thickness of 15 mm made by the explosion deposition method, but there is no practical example of a thin plate.

A method called lap rolling is known as a method for producing a thin plate in which aluminum and iron are compounded. For example, as disclosed in Japanese Patent Laid-Open No. 63-157774, an aluminum material is used in the range of 350-55.
As disclosed in Japanese Patent Publication No. 56-52679, the surface of an iron material is preliminarily plated with aluminum and heated to about 500 ° C. as described in Japanese Patent Publication No. 56-52679. There is a method of rolling and joining with an aluminum material in a warm state. However, the composite metal sheet produced by these methods has insufficient workability and has a problem that it is hardly cured by baking after press forming.

On the other hand, a single steel plate having a hardening property by baking coating has been studied so far, for example, JP-A-2-197549 and JP-A-63-247338.
It has been found that this can be obtained by annealing the steel in a specified range with the amount of C, Ti or Nb in the specified range, as disclosed in Japanese Patent Laid-Open Publication No. Hei. However, since the steel sheets manufactured by these methods have a small total carbon content, the baking hardening amount itself cannot be very high.
At present, it is about 3 kgf / mm ² as disclosed in Japanese Patent Publication No. 49.

Therefore, even if such a steel plate and aluminum can be composited, a composite metal plate having a high bake hardening amount cannot be expected. As described above, a method for producing a composite metal plate of iron and aluminum having sufficient workability and bake hardenability has not been known so far.

[0007]

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

[0008]

In order to solve the above problems, the present inventors have studied the composition, state, etc. of a steel plate and aluminum, and as a result, have found that a composite of iron and aluminum having good workability and bake hardenability. A method for manufacturing a metal plate has been found.

[0009] The gist of the invention is that when a three-layer composite metal plate having both surfaces of iron and a center of aluminum is manufactured, the iron layer has a chemical composition of C: 0.01 to 0.055% by weight,
Si: 0.1% or less, Mn: 0.04 to 0.5%, P:
0.1% or less, solAl: 0.002-0.1%,
N: 0.006% or less, the balance iron and unavoidable impurities, the aluminum layer is pure aluminum or aluminum alloy containing 99% or more by weight of Al in chemical composition, and the iron layer is 670 ° C or more and 900 ° C or less And the aluminum layer is heated to 550 ° C. or less, and when both layers are in these temperature ranges, they are superposed and immediately applied with an external force from both surfaces. At this time, the reduction rate of the iron layer due to the external force is 5%.
%, And then cooled to 200 to 400 ° C., held at this temperature range for 120 to 360 seconds, and then cooled to room temperature, which is excellent in bake hardenability and workability. Is the way. Further, the aluminum layer constituting this composite metal plate is also characterized by being an aluminum alloy containing at least one of 6% or less of Mg and 2% or less of Mn in place of the above components. Further, in addition to the above components, 0.5% or less of Si, 0.
It is also characterized by containing 1 or 2 or more of 5% or less of Cr and 0.5% or less of Zn.

[0010]

In the present invention, both the iron material and the aluminum material may be cold-rolled or annealed. The reason is that the iron material applied in the present invention is recrystallized by heating and becomes a steel sheet having sufficient workability even in cold rolling. Further, even an aluminum material after cold rolling is softened by the production method of the present invention and becomes an aluminum plate that can sufficiently withstand processing.

The present invention will be described in detail below. As the C content in the iron material increases, the average r value and ductility deteriorate,
Yield strength increases and workability decreases. Therefore, the smaller the amount of C, the better the press workability, so the C content is 0.055%.
The following is good. However, there is a problem that decarburization cost becomes high in order to make C lower than 0.010%. Therefore, the C content is limited to 0.010 to 0.055%.

Although a small amount of Si causes no problem, a large amount of Si deteriorates workability. Therefore, it must be 0.1% or less.

Mn is a component necessary to prevent hot embrittlement due to S existing as an unavoidable inclusion in steel, but if it is less than 0.04%, FeS is formed and its effect is not obtained. Further, if it exceeds 0.5%, the workability is deteriorated. Therefore, the amount of Mn was limited to 0.04 to 0.5%.

If a large amount of P is contained, it segregates at the grain boundaries and becomes embrittled, resulting in a decrease in workability. Therefore, the amount of P is limited to 0.1% or less.

Al is an element necessary for controlling the amount of oxygen in steel and is added as a deoxidizing agent before adding Ti. If the amount of acid-soluble Al 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 deteriorates. Therefore, the amount of Al is limited to 0.002 to 0.1%.

When N forms a solid solution in steel, the workability is significantly deteriorated, so N must be fixed as TiN by Ti. It is also preferable that the amount of TiN produced is as small as possible. Therefore, the N content is 0.0060% or less.

Other than the above components, Fe and inevitable impurities are contained. The iron material of the above components is normal hot rolling,
It may be manufactured by a cold rolling process. Further, either a cold rolled steel sheet or an annealed steel sheet may be used.

Next, the conditions for the aluminum material will be described. The aluminum material may be pure aluminum or aluminum alloy. The type of aluminum alloy is not limited, but 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 the annealed state, and do not impair workability such as drawing. The amount of Mg is 6%
Or the amount of Mn exceeds 2%, curing is remarkable,
Since the workability is impaired, the above ranges of these components are suitable.

Furthermore, 0.5% together with the above components
Si below, 0.5% below Cr, 0.5% below Zn
If 1 or 2 is contained, the strength can be further increased while maintaining good workability. However, Si, C
If the amount of r or Zn added exceeds the above range, the hardness becomes too high and the workability is impaired. The aluminum material of the above components may be either a cold rolled material or an annealed material.

Next, the heating temperature of the material will be described. The iron material as cold rolled is 670 to 90 which is the heating range of the present invention.
When heated to 0 ° C, it recrystallizes and becomes a plate with sufficient workability. At a temperature of less than 670 ° C., the recrystallization of the iron plate is not sufficiently performed and the deep drawability is not improved, and the diffusion of aluminum atoms and iron atoms is less likely to occur at the time of joining, which is not preferable. When heated to a temperature over 900 ° C., the structure of iron once becomes a γ phase, and the deep drawability deteriorates, which is not preferable. It should be noted that even an iron material that has already been annealed has a workability equal to or higher than that of the material before heating by heating within the scope of the present invention.

On the other hand, pure aluminum or aluminum alloy (hereinafter referred to as aluminum layer) must be soft to some extent in order to reduce the thickness reduction rate of the iron layer to 5% or less when it is joined to the iron layer by applying an external force. Therefore, if the material is hardened like an as-cold-rolled aluminum material, it is necessary to heat the material to 550 ° C. or lower to soften it before joining, if necessary. However, when the aluminum layer is heated to a temperature higher than 550 ° C., the brittle alloy layer is formed at the bonding interface with the iron layer because heat from the iron layer is applied during the bonding in addition to the temperature of the aluminum itself,
Bonding strength decreases. Therefore, the heating temperature of the aluminum layer is set to 550 ° C. or lower. The aluminum layer has already been softened sufficiently before joining, and the reduction rate of the iron plate thickness during joining is 5%.
It is not necessary to heat the aluminum layer if:

After heating the iron layer and the aluminum layer to the above temperature range, it is necessary to immediately apply an external force by superposing the respective metals when they are within this temperature range. Sufficient bonding strength cannot be obtained when the layers are stacked at a temperature outside the above temperature range.

Next, the reduction rate of the steel plate thickness required when joining the iron layer and the aluminum layer by an external force will be described. Since the iron layer is recrystallized by the above-mentioned heating before joining and has a good workability, if it is worked a lot during joining, the material is deteriorated due to work hardening, which is not preferable.

FIG. 1 shows an iron layer having the composition and plate thickness shown in Table 1,
Similarly, when joining both sides of the aluminum layer having the composition and plate thickness shown in Table 1, the iron layer was formed by the current heating and pressure welding equipment shown in FIG.
Heat to 50 ° C, while increasing the heating temperature of the aluminum layer to 5
After changing the hardness of aluminum by changing it within the range of 50 ° C or less, by applying an external force by two rolls contacting the iron layer, the reduction rate of the thickness of the iron layer is changed, and the mixture is left to cool. It shows the average r value of the obtained composite steel sheet and the reduction rate of the iron layer thickness that affects the elongation. As is clear from FIG. 1, when the reduction rate of the iron layer thickness exceeds 5%, the average r of the composite sheet
Value and elongation are greatly reduced. This tendency was confirmed by steel plates and aluminum plates having other compositions within the scope of the present invention. From the above, the thickness reduction rate of the iron layer must be 5% or less at the time of joining.

[0025]

[Table 1]

In the electric heating equipment shown in FIG. 3, electric current rolls 11, 12, and 13 are provided on the iron layers 1 and 3 and the aluminum layer 2 of the material, respectively.
The composite plate 5 is manufactured by continuously feeding it between the book rolls 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 source 21 passes from the energizing roll 11 of the iron layer 1 to the energizing roll 12 of the iron layer 1 and the aluminum layer 2. Similarly, the current of the power supply 22 flows through the series circuit of the aluminum layer 2 and the iron layer 3. If the phases of the two power supplies 21 and 22 are properly matched, the current in the aluminum layer 2 becomes the sum of the currents from the two power supplies. In this case, since the iron layer has a higher electric resistance than the aluminum layer, if the iron layer and the aluminum layer have the same thickness, the iron layer generates more heat and becomes hot. If the heating temperature of the iron layer does not reach the target temperature, the auxiliary heating power source 23,
Auxiliary heating is performed by supplying electricity from 24.

The joining of the plates is instantaneously performed under the above-mentioned conditions, but if they are held at a temperature of more than 400 ° C. after the joining, a brittle alloy layer is formed at the interface between iron and aluminum of the composite steel sheet, and the joining strength and workability are deteriorated. Therefore, the composite steel sheet must be cooled promptly. The cooling rate may be a rate that can be obtained by standing cooling, but forced cooling with gas or liquid may be used to further shorten the cooling time.

Improves the workability of the composite steel sheet, and further 4 kg
In order to have a high BH property of f / mm ² or more, it is necessary to cool the composite steel sheet after joining to a temperature of 400 ° C. or less and 200 ° C. or more. Further, the composite steel sheet cooled to this temperature range needs to be held in this temperature range for 120 seconds or more and 360 seconds or less. If held at a temperature lower than 200 ° C., the workability is deteriorated because the amount of residual solid solution C is large. If the composite steel sheet is held for more than 360 seconds in the above temperature range, a brittle alloy layer is formed at the interface between iron and aluminum of the composite steel sheet, the workability deteriorates, and the BH amount also decreases. In addition, if the retention time is shorter than 120 seconds, the residual amount of the solid solution C is large and the workability is deteriorated.

FIG. 2 shows an iron layer having the composition and plate thickness shown in Table 1,
Similarly, when joining both sides of the aluminum layer having the composition and plate thickness shown in Table 1, the iron layer was formed by the current heating and pressure welding equipment shown in FIG.
Heat to 50 ° C, while increasing the heating temperature of the aluminum layer to 5
After changing the hardness of aluminum by changing it within the range of 50 ° C or less, external force is applied by two rolls in contact with the iron layer and the thickness reduction rate of the iron layer is set to 2%. It shows the effect of holding temperature on the elongation after aging of the composite steel sheet when cooled at 100 ° C / s and held at that temperature for 150 seconds. As is clear from FIG. 2, good elongation can be obtained when the holding temperature of the composite steel sheet is in the range of 200 to 400 ° C.

FIG. 3 shows elongation and baking after aging of a composite steel sheet when the composite steel sheet joined under the same conditions as above was cooled to 350 ° C. at 100 ° C./s and held at that temperature for various times after being joined. It shows the effect of retention time on the amount of curing. As is clear from FIG. 3, it is understood that good elongation and bake hardening amount can be obtained when the holding time of the composite steel sheet is in the range of 120 to 360 seconds. This tendency is seen when the holding temperature is 200 to 400 ° C., and when held at a temperature outside this temperature range, elongation after aging,
Good values were not obtained for either or both of the baking and curing amounts.

When joining an iron layer and an aluminum layer,
The joining method is not particularly limited as long as the above conditions are satisfied, 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 for heating the joining material may be any method such as electric heating, induction heating, or heating with a heating furnace.

[0032]

EXAMPLES Examples of the present invention will be shown below together with comparative examples.
Using a steel plate with a plate thickness of 0.4 mm and an aluminum plate with a plate thickness of 0.6 mm as shown in Table 2, using the electric heating equipment shown in Fig. 3 so that both surfaces have iron and the center has three layers of aluminum. Simultaneously with the above, the external force was applied by two rolls contacting the iron layer as shown in FIG. 3 to continuously bond the iron layer and the aluminum layer. Heating temperature of steel plate part,
Table 3 shows the rolling ratio, the holding temperature after cooling the composite steel sheet, the holding time, and the like. Sample numbers (1) to (14) are within the scope of the present invention in terms of composition, heating of the steel sheet portion, rolling rate, holding temperature of the composite steel sheet, and time, and any of the samples (15) to (26). One or more are outside the scope of the present invention.
Table 4 shows the materials of the obtained composite metal plate after joining. Table 4
As can be seen, the composite plate produced within the scope of the present invention exhibits excellent bake hardenability and processability.

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

[Table 4]

[0036]

As described above, the composite plate of iron and aluminum produced by the method of the present invention has excellent bake hardenability and workability.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of the rolling ratio of an iron layer on the r-value and elongation of a composite steel sheet.

FIG. 2 is a diagram showing an influence of a cooling holding temperature after joining of iron and aluminum on elongation after aging of a composite steel sheet.

FIG. 3 is a diagram showing the influence of the holding time after cooling of the composite steel sheet on the bake hardening amount and elongation of the composite steel sheet.

FIG. 4 is a diagram showing an example of an apparatus used for manufacturing a composite plate.

[Explanation of symbols]

 1,3 Iron layer 2 Aluminum layer 4 Roll 5 Composite plate 11, 12, 13 Energizing roll 14, 15 Auxiliary energizing roll 21,22 Power supply 23, 24 Auxiliary heating power supply

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location C23C 30/00 B (72) Inventor Tadao Kiriyama 1 Fuji-cho, Hirohata-ku, Himeji-shi, Hyogo Made by Shin Nihon Hirohata Works, Ltd.

Claims (3)

[Claims] 1. When manufacturing a three-layer composite metal plate having both surfaces of iron and a center of aluminum, the iron layer has a chemical composition of C: 0.01 to 0.055% by weight and Si: 0.
1% or less, Mn: 0.04 to 0.5%, P: 0.1% or less, solAl: 0.002 to 0.1%, N: 0.00
6% or less, the balance iron and unavoidable impurities, the aluminum layer is pure aluminum or aluminum alloy containing 99% by weight or more of Al in chemical composition, and the iron layer is 6% or less.
The aluminum layer is heated to 70 ° C. or higher and 900 ° C. or lower and the aluminum layer is set to 550 ° C. or lower, and when both layers are in these temperature ranges, they are superposed and immediately applied with an external force from both surfaces. A composite excellent in bake hardenability and workability, characterized in that the reduction rate is 5% or less, then cooled to 200 to 400 ° C., held in this temperature range for 120 to 360 seconds and then cooled to room temperature. Manufacturing method of metal plate. 2. The aluminum layer has a weight ratio of 6 in addition to Al.
% Or less of Mg, and 2% or less of Mn, which is an aluminum alloy containing at least one.
A method for producing a composite metal sheet having excellent bake hardenability and workability as described above. 3. The aluminum layer further contains one or more of 0.5% or less of Si, 0.5% or less of Cr and 0.5% or less of Zn. A method for producing a composite metal plate having excellent bake hardenability and workability.