JPH1147946A - Production of tailored blank made of steel plate and aluminum alloy plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of the tailored blank material, in which a steel plate and an aluminum alloy plate are joined by mush-seam welding, and which is excellent in joint performance and has a small step difference. SOLUTION: A production method of the tailored blank material is that the ends of a steel plate 3 and of an aluminum alloy plate 2 are overlapped and the overlapped part is subjected to mush-seam welding in a range of a welding force and a welding current in a formula of 0.2L+0.2T+0.1L.T+1<= welding force (KN)<=0.6+0.2T 0.2L.T+4 and a formula of 2L+6<= welding current (A)<=5L+4. Here, L is an initial overlap margin (mm), T is a plate thickness (mm) of the aluminum alloy plate. Further, mush-seam welding is conducted under the welding conditions that the initial overlap margin is >=1.5 times of the plate thickness of a thinner one out of the steel plate and the aluminum alloy plate, a reduction rate of a weld zone to the aluminum alloy plate is 20-50% and a thickness of a fused part of the weld zone of the aluminum alloy plate is <=50% of a thickness of the aluminum alloy plate of the weld zone after welding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an automobile, a railway vehicle,
The present invention relates to a method for manufacturing a material for integrated molding (hereinafter, referred to as a “tailored blank”) in which a steel plate and an aluminum alloy plate are welded and used in a structure such as a ship.

[0002]

2. Description of the Related Art In recent years, there has been a tendency for automobile bodies to have higher and higher safety for protecting occupants in the event of a collision.
However, as the collision safety measures progress, the vehicle body becomes sturdier, but on the other hand, the vehicle body weight increases, fuel efficiency deteriorates, and the load on the global environment increases. So we also ensure safety,
In addition, in order to realize a lighter vehicle body, there is an increasing tendency to apply an aluminum alloy to a vehicle body. However, the fact that the joining of steel and aluminum alloy is not as easy as joining steel is a major bottleneck in expanding the application of aluminum alloy to vehicle bodies, and aluminum alloy is currently used only in a small part. .

[0003] In the recent field of automobile body manufacturing, the use of tailored blank materials, in which various steel plates are manufactured by laser welding or mash seam welding to produce tailored blanks and then press-formed, has become widespread. Therefore,
When a method for producing a tailored blank material that combines a steel sheet and an aluminum alloy sheet is developed, it is expected that the application site of the aluminum alloy will be greatly expanded. Therefore, it is expected to establish a welding technique for a steel sheet and an aluminum alloy sheet. For smooth molding, butt welding of the steel plate and the aluminum alloy plate or a lap welding method that does not cause a large difference in the welded portion is required. Until now, butt welding of the steel plate and the aluminum alloy plate has been required. The law is unknown.

[0004] The reason why welding of steel and aluminum alloy is difficult is due to the following phenomena.

[0005] (a) When a steel and an aluminum alloy react at a high temperature, a very brittle intermetallic compound is formed. Therefore, in fusion welding by an arc or the like, an intermetallic compound is formed in a welded portion, and welding strength cannot be secured.

(B) A strong oxide film exists on the surface of the aluminum alloy, which impairs the bondability.

As a joining method for overcoming such a cause, a lap welding method of a steel sheet and an aluminum alloy sheet has been proposed.
The following methods have been proposed.

[0008] The clad material of steel and aluminum (multi-layer steel plate) produced by the rolling method is used as an insert metal, and the aluminum surface of the clad is aligned with the aluminum alloy plate and the steel plate of the clad is aligned with the steel plate. A method of pinching and resistance spot welding (for example, JP-A-6-63762).

Using a direct current, the anode is placed on the aluminum side,
Spot welding method in which the cathode is arranged on the steel plate side
No. 111776).

A mechanical joining method using a rivet or the like.

A bonding method by adhesion.

Further, as a joining method for producing a clad of an aluminum plate and a steel plate, the following rolling joining method is known.

A joining method by rolling having characteristics such as pretreatment and rolling temperature (Japanese Patent Laid-Open No. 3-8587).

However, the above-mentioned methods (1) to (6) have the following major problems.

In the method (1), it takes time and effort to insert an insert material before welding, and the insert material increases the cost. Therefore, this method is not suitable for mass-produced parts such as automobile bodies.

In the method (1), formation of an intermetallic compound at the joint interface is unavoidable, the strength of the welded portion is insufficient, and there is a problem in application to the production of an automobile body requiring a high degree of safety.

In the mechanical joining method, the swelling of the rivet head portion is not suitable for integral molding, and the appearance quality is deteriorated. It is also a costly method.

[0018] The bonding method has a lower strength reliability than the welding method, and is susceptible to deterioration over time, and cannot be used for a strength member.

The roll joining method is a joining method for joining sheet materials, and cannot be applied to the production of a joint between a steel sheet and an aluminum alloy sheet as in the present invention.

Therefore, any of the above joining methods cannot be adopted as a method for producing a tailored blank made of an aluminum alloy plate and a steel plate at a production site where high-efficiency production is required.

[0021]

SUMMARY OF THE INVENTION The present invention provides a method of manufacturing a tailored blank material having excellent joint performance and a small step for joining end faces of a steel plate and an aluminum alloy plate by applying a mash seam welding method. The purpose is to: More specifically, an object of the present invention is to provide the following method for producing a tailored blank material.

A composite material in which a steel plate and an aluminum plate or an aluminum alloy plate are joined.

The composite material has a joint having a small step so as not to hinder the integral molding by pressing or the like. The step is set to 0.8 mm or less. Here, the step is the difference between the thickness of the welded portion and the thickness of the thicker aluminum alloy plate or steel plate.

Breakage of base metal in tensile test of joint.

[0025]

Means for Solving the Problems The inventors of the present invention conducted a test of a method of manufacturing a tailored blank material usable for an automobile body, including welding methods other than the mash seam welding method, and confirmed the following. Was completed.

(A) A tailored blank made of a steel plate and an aluminum alloy plate having a weld portion having high strength and having a small step can be obtained only by a mash seam welding method in which a certain range of pressing force and current are applied. Obtainable.

(B) In order to further stably obtain a welded joint that does not cause a weld fracture in a tensile test of a weld,
(B-1) minimizing the melting of the bonding interface to minimize the formation of brittle intermetallic compounds, and (b-2) eliminating the oxide film on the surface of the aluminum alloy plate.
The point is important.

The present invention has been completed on the basis of the above items through trial production tests on an actual production line, and the gist of the invention lies in the following method for producing a tailored blank material.

(1) Manufacture of a tailored blank material consisting of a steel plate and an aluminum alloy plate in which the ends of a steel plate and an aluminum alloy plate are overlapped, and the overlapped portion is subjected to mash seam welding according to the following formula and the range of the pressing force and current. Method (referred to as [Invention 1]).

[0030] Here, L and T represent the initial overlap margin (mm) and the thickness (mm) of the aluminum alloy plate, respectively.

(2) The initial overlap allowance of the steel plate and the aluminum alloy plate is 1.5 times or more the thinner of the steel plate and the aluminum alloy plate, and the rolling reduction of the welded part to the aluminum alloy plate is 20 to Tailored blank material consisting of a steel plate and an aluminum alloy plate to be mash seam-welded under welding conditions in which the fusion zone thickness of the aluminum alloy plate of the weld zone is 50% or less of the thickness of the aluminum alloy plate of the weld zone after welding (Hereinafter referred to as [Invention 2]).

In the above [Invention 1] and [Invention 2], the steel plate refers to a metal plate whose main component is iron, and a stainless steel plate is also included in the category. The aluminum alloy plate in the present invention may be any aluminum alloy plate as long as the main component is aluminum. The present invention does not depend on the fluctuation of the chemical composition of the steel sheet or the aluminum alloy sheet.

[0033]

Next, the reason why the scope of the present invention is limited as described above will be described.

1. Mash seam welding FIG. 1 is a diagram showing an outline of a mash seam welding method. Mash seam welding is a type of resistance welding, but as shown in FIG. 1, the ends of the plates are overlapped, and the portion is pressed down in the plate thickness direction by a pair of upper and lower electrode wheels 1 while being crushed and energized and heated. It is characterized by continuous welding. Since the welded portion is crushed, after welding, it has the appearance of a butt weld. At this time, since a strong deformation is applied to the bonding interface by the pressure, the oxide film on the aluminum alloy surface is broken, and the clean surface of the aluminum alloy and the steel surface can be brought into contact with each other and adhered to each other. Furthermore, since it is continuous welding, the reliability of the entire welded portion is higher than that of spot welding such as spot welding. Mash seam welding is a heating welding method using resistance heat generation of a material, so that heating can be minimized to a minimum and generation of fragile intermetallic compounds can be suppressed.

[Invention 1] In the above-mentioned mash seam welding, the pressing force is performed in the range of the formula and the current is performed in the range of the formula. The formulas and the upper and lower limits of the formulas are formulas set based on the test results performed so far. Pressing force is 0.2 ・ L + 0.2 ・ T + 0.1 ・ L ・ T + 1 (k
If it is less than N), the welded portion is not sufficiently crushed, the step cannot be reduced to 0.8 mm or less, and the damage to the mold during the integral molding is accelerated. On the other hand, the pressure is 0.6L + 0.2T +
If it exceeds 0.2 · L · T + 4 (kN), the thickness of the aluminum alloy at the welded portion becomes excessively thin, and the strength of the welded portion cannot be secured.

The current value of the mash seam welding is 2.
If it is less than L + 6 (kA), the joint between the steel plate and the aluminum alloy plate is not sufficiently heated, so that the broken oxide film is not sufficiently melted and discharged, and the strength of the joint interface cannot be obtained. On the other hand, when the current value exceeds 5 · L + 10 (kA), heating near the bonding interface becomes excessive, and a fragile intermetallic compound is generated near the bonding interface.

An ordinary tailored blank made of a steel plate and an aluminum alloy plate can be manufactured by the method of the above [Invention 1].

In order to stably secure a higher bonding strength, a mash seam welding method according to [Invention 2] described below, which imposes conditions such as an initial overlap margin and a reduction ratio, is used.

2. FIG. 2 is a longitudinal sectional view of a mash seam welded portion between an aluminum alloy plate and a steel plate, wherein (a) shows before welding and (b) shows after welding.

In [Invention 2], the initial overlap margin 4 shown in FIG. 2A is 1.5 times or more the thinner of the steel plate 3 and the aluminum alloy plate 2. If the initial overlap margin 4 is long, the length of the joining interface in the longitudinal section after welding is also large. Therefore, it is desirable that the joining interface length be long from the viewpoint of joint strength. The initial overlapping allowance is 1.5 of the above thinner plate thickness
If it is less than twice, the length of the bonding interface becomes smaller, and the load applied to the bonding interface per unit length increases,
Separation easily occurs at the bonding interface. In order to obtain a more stable joint strength, the initial overlap margin is desirably at least twice the thinner of the steel plate and the aluminum alloy plate.

The upper limit of the initial overlapping margin is not particularly set. However, if the overlapping margin is too large, a portion that cannot be crushed due to the reduction of the electrode wheel 1 by one joining occurs, and is integrally formed as a tailored blank material. Unsuitable for In order to avoid such a situation, it is preferable to set the initial overlap margin to about 10 mm or less.

3. Reduction rate of aluminum alloy plate at welded part In the mash seam welding method, most deformation occurs in the aluminum alloy plate because the aluminum alloy plate is softer than the steel plate. As the rolling reduction of the aluminum alloy plate increases, the plastic deformation at the welded portion of the aluminum alloy plate increases, so the oxide film on the surface of the aluminum alloy plate is destroyed, and the area where the clean surface of the aluminum alloy is exposed on the bonding interface increases. It is preferable. In [Invention 2], the rolling reduction of the aluminum alloy plate at the welded portion is 2
0% to 50%. If the rolling reduction is less than 20%, the discharge of the oxide film becomes insufficient, so that good bonding strength cannot be obtained. Further, in order to thoroughly discharge the oxide film and obtain higher bonding strength, the rolling reduction is preferably set to 25% or more.

Here, the rolling reduction Rr of the aluminum alloy plate at the welded portion is expressed by the following equation.

Rr (%) = {(T−Tw) / T} × 100 (%) Rr: Reduction ratio (%) of aluminum alloy plate Tw: Thickness of aluminum alloy plate at welded portion T: Aluminum Thickness of alloy plate base material (thickness measured on the aluminum alloy base material side of the welded part) If the rolling reduction of the welded part of the aluminum alloy plate exceeds 50% and becomes too large, the welded part on the aluminum alloy plate side The cross-sectional area becomes too small and breaks occur at the welded portion, lowering the reliability of the welded portion.

FIG. 3 is a longitudinal sectional view showing a case where the rolling reduction to the aluminum alloy plate is too large. In the case of FIG. 3, a break occurs at the toe of the welded portion on the aluminum alloy plate side. Therefore, the rolling reduction of the aluminum alloy plate at the welded portion is 50
% Or less.

4. The thickness Tm of the molten portion 5 of the aluminum alloy plate of the aluminum alloy plate shown in FIG. 2B has a correlation with welding heat input, and the higher the heat input, the thicker the molten portion. When the thickness of the fusion zone is large, the intermetallic compound layer generated on the bonding interface is also thick, and the reliability of the strength of the welded joint is low. The ratio of the thickness Tm of the fusion zone to the thickness Tw of the aluminum alloy plate at the weld zone, (Tm / Tw) × 100%, is referred to as the fusion ratio Rm (%). In Table 2 in Examples described later, the melted portion thickness is indicated by the melt ratio.

In [Invention 2], the thickness of the molten portion is 50% or less of the thickness of the aluminum alloy plate in the welded portion after welding;
Preferably, the melting ratio Rm is controlled to 50% or less, preferably 40% or less. This is a range limitation for suppressing the formation of the intermetallic compound. On the other hand, the lower limit of the fusion zone thickness may be 0 mm. That is, even if no welded portion is formed in the welded portion, a sufficient bonding strength is often exhibited. However, in order to ensure the strength of the welded portion, it is desirable that the thickness of the fused portion be about 10% of the thickness of the aluminum alloy plate at the welded portion.

[0048]

EXAMPLES Next, the effects of the present invention will be described with reference to examples.

Embodiment 1 First, Embodiment 1 in which the effect of [Invention 1] was tested will be described.

Mash seam welding was performed using cold rolled steel sheets (SPCC) having a thickness of 1.0 mm and 1.6 mm and aluminum alloy plates (A5052) having a thickness of 1.0 mm and 2.0 mm as test metal plates. The welding condition is 4cm welding speed.
/ Min, and the overlap margin, electrode pressing force and welding current were changed.

Table 1 shows the test numbers P1 to P1 in Example 1.
It is a list of welding conditions of P7. Table 2 shows the upper and lower limits of the pressing force expressed by the equation when welding under these welding conditions, and the upper and lower limits of the current in the equation.

[0052]

[Table 1]

[0053]

[Table 2]

After welding, a cross section was observed, a step was measured, and a tensile test in a direction perpendicular to the welding line was performed to evaluate the performance of the welded portion. The determination of the weldability was made at the fracture position after the tensile test. That is, the base material fractured was judged to be acceptable, and the one fractured at the joint interface and in the welded portion or at the weld toe was judged as unacceptable.

Table 1 shows the test results.

Test Nos. P1 and P5, which are comparative examples, resulted in a large step at the welded portion because the pressing force was small. Test No. P1 also broke at the joint interface because the current was small. In Test Nos. P3 and P7, since the pressing force was excessive, the thickness of the aluminum alloy plate in the welded portion was too thin, and the welded portion was broken at the toe portion on the aluminum side. Test number P
No. 4 broke at the joint interface due to excessive current.

On the other hand, the test number P of the present invention example
2 and P6 each had a sound joining strength, and the base material was broken.

[Embodiment 2] The following embodiment is directed to [Invention 2].
This is an example performed to explain the effect of (1). As test steel sheets, cold-rolled steel sheets having a thickness of 1.0 mm and 1.6 mm (S
Mash seam welding was performed using PCC) and aluminum alloy plates (A5052) having a plate thickness of 1.0 mm and 2.0 mm. The welding conditions were such that the welding speed was constant at 4 m / min, the overlap margin, the electrode pressing force, and the welding current were changed to change the rolling reduction and the thickness of the molten portion of the aluminum alloy plate. In order to measure the rolling reduction and the thickness of the fusion zone, a cross section was observed after welding. A tensile test perpendicular to the weld line was performed to evaluate the performance of the weld. The determination of the weldability was made at the fracture position after the tensile test. That is, the base material fractured was judged to be acceptable, and the joint interface, the welded part and the weld toe fractured were judged to be rejected.

Table 3 shows the test results.

[0060]

[Table 3]

Test Nos. 1, 2, 15, and 17 as Comparative Examples
All fractured at the joint interface because the overlap margin was small. Test numbers 4, 5, 12, and 13 which are also comparative examples
Also, the fracture occurred at the joint interface because the rolling reduction of the aluminum alloy plate at the weld was small. Test Nos. 4 and 13 sometimes broke at the base material and showed relatively high bonding strength. Test numbers 8 and 11 were obtained by welding under the condition that the rolling reduction to the aluminum alloy plate was too large. Among them, test No. 11 broke on the aluminum alloy plate side of the welded portion. On the other hand, Test No. 8 is an example in which the thickness of the melted portion was also excessively large at the same time.
Breakage occurred at the joint interface. In addition, Test Nos. 7, 9, and 19 of the comparative examples were broken at the joint interface because the thickness of the molten portion was large. Among them, Test No. 9 showed a relatively high strength in some cases where the base material was broken.

On the other hand, Test Nos. 3, 6, 10, 14, 16, 18, and 20, which are examples of the present invention, all have sound bonding strength, and the result of base material fracture was obtained.

[0063]

According to the present invention, a tailored blank material in which a steel plate and an aluminum alloy plate are welded with high efficiency and at low cost can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a mash seam welding method.

FIG. 2 is a diagram showing a vertical section of a mash seam weld. (A) shows before welding and (b) shows after welding.

FIG. 3 is a view exemplifying a vertical section when the rolling reduction of an aluminum alloy plate is too large.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrode wheel 2 ... Aluminum plate 3 ... Steel plate 4 ... Initial lap allowance 5 ... Molten part T ... Thickness of aluminum plate Tw ... Thickness of aluminum plate of welded part Tm ... Thickness of aluminum melted part

Claims (2)

[Claims] 1. A tailored steel plate and an aluminum alloy plate, wherein the ends of the steel plate and the aluminum alloy plate are overlapped, and the overlapped portion is subjected to mash seam welding according to the following formula and the range of the pressing force and current. Manufacturing method of blank material. Here, L and T represent the initial overlap margin (mm) and the thickness (mm) of the aluminum alloy plate, respectively. 2. The initial overlap allowance of the steel sheet and the aluminum alloy sheet is 1.5 times or more the thickness of the thinner of the steel sheet and the aluminum alloy sheet, and the rolling reduction of the welded part to the aluminum alloy sheet is 20 to 50. %, The mash seam welding under welding conditions in which the thickness of the welded aluminum alloy sheet is 50% or less of the thickness of the welded aluminum alloy sheet after welding. Manufacturing method of tailored blanks.