JP2004255400A - Aluminum alloy difference thickness blank material manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a difference thickness blank material manufacturing method of high productivity for manufacturing an aluminum alloy difference thickness blank material to be used for manufacturing a car body. <P>SOLUTION: The differential thickness blank material (a tailored blank) is obtained by developing in the width direction an extruded material having an extruded sectional shape of a wall thickness changing part with the width of a wall thickness transition area having a wall thickness gradient from t<SB>1</SB>to t<SB>2</SB>being ≥ 1.5 × t<SB>1</SB>and extruded in a bent condition at a cross-section in the wall thickness changing part consisting of wall thickness of t<SB>1</SB>and t<SB>2</SB>(where t<SB>1</SB>< t<SB>2</SB>). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an aluminum alloy differential thickness blank used for manufacturing, for example, an automobile body, and more particularly to a method for manufacturing a differential thickness blank with high productivity.
[0002]
[Prior art]
There are many fields where material replacement from iron-based alloys to aluminum-based alloys is made for weight reduction, and automobile bodies are one of them.
Normally, an automobile body is manufactured by pressing a plate material with a uniform thickness and joining each part. However, as a technology that enables weight reduction and cost reduction, a difference thickness blank material (tailored blank) with different thickness depending on the part. There is a method of manufacturing a body that is processed into a specific member shape by press molding.
By using such a differential thickness blank material, the required strength and rigidity can be ensured by using a high-strength material or thick plate only for the parts where high strength is required, without using a reinforcing material separately. Is possible. Furthermore, since the thickness distribution can be easily optimized, the lightest member can be obtained while ensuring the necessary strength and rigidity.
As a manufacturing method of such a differential thickness blank material, a technique for manufacturing a single steel sheet by abutting end faces of a plurality of steel sheets and joining them by welding is disclosed. (For example, see Patent Document 1 and Patent Document 2)
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-180470 [Patent Document 2]
Japanese Patent Application Laid-Open No. 2001-122154 [Patent Document 3]
Japanese Patent Laid-Open No. 2002-224858
[Problems to be solved by the invention]
The manufacturing technology for automobile bodies using differential thickness blanks is already in practical use for iron-based materials, but active development studies have been made for aluminum-based materials, but they have not been applied. This is because the difference thickness blank material is generally manufactured by butt joining of a plurality of members having different plate thicknesses, but inferior weldability in an aluminum alloy compared to an iron-based alloy is a major obstacle.
That is, in melt welding such as laser welding and arc welding, there are problems inherent to materials or bonding methods, such as high temperature cracking and porosity are likely to occur, and softening in the heat affected zone is inevitable. In addition, for example, in the case of laser welding, there is a construction problem such that the gap tolerance of the butt surface is small and management is difficult. In these places, there are difficulties in obtaining stable joint strength and formability, and it can be said that aluminum alloys have not reached the practical level.
For example, if an undercut defect is created by fusion welding, for example, if a difference thickness blank material manufactured by butt joining is used, the blank material can be created, but during press processing, the formability is extremely reduced due to stress concentration at the same location, resulting in fracture. There is also a problem of reaching.
In order to solve the above-described difficulties in fusion welding, production of a differential thickness blank material by a friction stir welding method is also considered (for example, Patent Document 3). The friction stir welding method is a solid-phase joining where the maximum temperature of the base metal due to heating during joining is about 80% of the melting point, so there are no problems inherent to fusion welding such as high temperature cracking and porosity defects, and mechanical properties. Also excellent.
However, on the other hand, it is difficult to give a margin to the joint shape design as a problem inherent to the joining method. Also, in the friction stir welding method, metal discharge must be suppressed by pressing the shoulder against the joint surface, and ingenuity is required to finish the joint into a smooth shape. There is. Further, since the bonding method has a short history since it started to spread, there are still technically unclear points such as a so-called Kissing bond defect problem.
In addition, in the manufacturing method based on the butt joining of a plurality of members, whether it is fusion welding or solid phase joining, the number of joining steps increases with the increase in the number of members, and a reduction in productivity is inevitable.
The present invention has been made with the above circumstances as a background, and has been made for the purpose of providing an aluminum alloy differential thickness blank material having stable formability and strength and high productivity.
[0005]
[Means for Solving the Problems]
The present invention has been made with respect to the object, the thickness changing portion consisting of wall thickness _{t 1,} t _{2 (and t} 1 <t _2), the meat having a thickness gradient to t 1 ~t ₂ It has an extruded cross-sectional shape of a wall thickness changing portion with a width of a thickness transition region of 1.5 × t ₁ or more, and the extruded shape that has been extruded in a bent state in the cross-section is developed in the width direction. It is the manufacturing method of the aluminum alloy differential thickness blank material which is excellent in stability of formability and strength, and has high manufacturing productivity.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The aluminum alloy used in the present invention may be any aluminum alloy that can be extruded and developed. For example, when considering application to an automobile body, a 6000 series alloy is preferably used.
[0007]
-Extrusion cross-sectional shape of thickness change part:
The extrusion cross-sectional shape of the thickness change portion can be designed to an arbitrary shape within a range in which extrudability can be ensured, but it is important to have a smooth thickness gradient cross section that avoids an extreme change in thickness.
First, in the thickness changing portion consisting of thick _t 1 as shown in FIG. _1, t _{2 (and} t 1 _{<t 2),} the width of the thickness transition region having a thickness gradient to t 1 ~t ₂ The reason why the value is defined as 1.5 × t ₁ or more will be described.
Since this value to produce a local strain lead to stress concentration at t ₁ side toe thick transition region to t ₁ ~t ₂ during molding is less than 1.5 × t _1, the risk to fracture at the location There is. With 1.5 × t ₁ or contrast, no stress concentration on the thickness changing section when press-molding the resulting blank, good moldability is obtained. Furthermore, the design of the extruded cross-sectional shape of the wall thickness changing part is also important from the viewpoint of surface properties, and when extruding a shape having an extreme wall thickness deviation from the above range, the die line is noticeably seen and the surface It is also not preferable because the properties are deteriorated. It should be noted that there is almost no plate thickness change due to unfolding or the direction in which the wall thickness transition region extends, and if the width of the wall thickness transition region in the extruded cross-sectional shape is defined, the above condition is satisfied even after unfolding.
In addition, it is preferable that a bend R of (t ₂ −t ₁ ) or more is applied to the corner portion of the thickness change portion. By applying this bending R, it is possible to further reduce the stress concentration on the thickness change portion.
[0008]
-Bending shape of the cross section of the extruded profile:
There are many parts where a wide material of the order of several hundred mm is required, for example, when applied to an automobile body, but there is a limit to widening the conventional extrusion method due to various problems described below.
In other words, in widening by increasing the diameter of the billet,
1) A large capacity extrusion press is required.
2) Large dies have high production costs and short life.
3) Making thin materials difficult
With such problems. There is also a technology for increasing the billet diameter by means of a spreader die, but this also has a widening limit.
On the other hand, in the present invention, a method of developing the extruded shape member in the width direction after extruding in a bent state in the cross section, it is possible to easily obtain a long wide material. The obtained long and wide material may be used as it is or may be cut into a required size.
In addition, the bent shape of the cross section in the present invention can be designed to an arbitrary shape within a range in which the obtained extruded shape can be developed. For example, the spiral shape and the corner portion are arcuate and rounded. A bent shape such as a U shape, a V shape, or a polygonal shape can be suitably used.
[0009]
・ Deployment method:
As a method for developing the extruded shape obtained by extruding in a bent shape, a method of developing by pulling with vacuum suction or a holding jig, a method of developing by roll forming, or the like can be applied.
In addition, in the case of a differential thickness blank material in which local residual strain is generated in the vicinity of the bent part due to the unfolding process, it is troublesome to predict and manage the press forming behavior. Is preferred. For example, in the case of a 6000 series alloy, Mg ₂ Si is precipitated when left at room temperature after extrusion and the strength is improved. Therefore, it is desirable that the room temperature standing after extrusion is suppressed as much as possible, and the unfolding process is performed immediately after extrusion.
[0010]
【Example】
Examples of the present invention are introduced below.
JIS6063 alloy billet (200mmφ) cast, homogenized (510 ℃ -6h), die, container, etc. are preheated to 460 ℃ and extruded at a speed of 2.5m / min. The material was developed by roll forming to obtain a differential thickness blank. The cross-sectional shape of the extruded profile before and after the unfolding process is shown in FIGS.
Moreover, as a comparative example, the cross-sectional shape of the extruded profile before and after the development of the differential thickness blank material produced under the same conditions as in Example 1 is shown in FIGS.
The wall thickness is t ₁ = 2 mm and t ₂ = 3 mm in common with Example 1 and Comparative Example 1. In Example 1, the width of the wall thickness transition region from t ₁ to t ₂ is 4 mm (≧ 1. 5 × 2 mm (t ₁ )), and a corner portion has a bend R of 2 mm. On the other hand, in Comparative Example 1, the width of the thickness transition region is a stepped shape of 0 mm, and the corners are finished at right angles without bending R.
From the obtained differential thickness blank material, 8 points (0 m to 3.5 m) at a constant interval (0.5 m) in the longitudinal direction and JIS No. 5 tensile test pieces were cut in a direction perpendicular to the longitudinal direction, and a room temperature tensile test was conducted. The break position was checked. In addition, the tensile test piece was cut out so that the thickness change part was located at the center of the parallel part.
As a result of the test, in Example 1, all the breakage positions occurred at locations where the thickness was constant on the thin wall side, and no breakage was observed at the thickness change portion or at its end. On the other hand, in Comparative Example 1, all were broken at the stepped portion at the end of the thickness changing portion and the thin edge portion, and the elongation was about 2/3 that of Example 1.
Further, the obtained differential thickness blank was actually set in a mold and press-molded. As a result, in Example 1, it was possible to mold without breaking, whereas in Comparative Example 1, as with the result of the tensile test, fracture occurred at the thin edge portion of the thick step portion, and molding was not possible. It was.
From the above results, it was confirmed that the aluminum alloy differential thickness blank material manufactured according to the present invention has no stress concentration, high strength against breakage, and can withstand actual press forming.
[0011]
【The invention's effect】
As described above, according to the present invention, when the blank material obtained is press-molded by defining the width of the thickness transition region to 1.5 × t ₁ or more, the thickness changing portion, particularly its thin wall There is no stress concentration at the side toe, and therefore there is no risk of local strain occurring at the same location, leading to fracture, and a differential thickness blank with good formability can be obtained.
In addition, it is possible to easily produce wide and long materials by expanding the extruded shape that has been extruded in a cross-sectionally bent state in the width direction. It has become a method.
In particular, the present invention can be effective in the production of a differential thickness blank having a multi-stage thickness shape (that is, a large number of plate thickness differences when unfolded). That is, in the manufacturing method by butt joining of a plurality of members, the number of joining man-hours increases as the number of members increases, but according to the method of the present invention, it is possible to obtain a multi-stage wall thickness shape by one extrusion process. This can contribute to a significant improvement in productivity.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a cross-sectional shape of an extruded shape member before unfolding in Example 1. FIG.
FIG. 2 is a schematic diagram showing a cross-sectional shape of an extruded profile after development processing in Example 1;
FIG. 3 is a schematic diagram showing a cross-sectional shape of an extruded profile before development processing in Comparative Example 1;
4 is a schematic diagram showing a cross-sectional shape of an extruded profile after development processing in Comparative Example 1. FIG.
[Explanation of symbols]
t1 Thin plate thickness t2 Thick plate thickness

Claims (1)

In the thickness change portion composed of the thicknesses t ₁ and t ₂ (t ₁ <t ₂ ), the width of the thickness transition region having the thickness gradient from t ₁ to t ₂ is set to 1.5 × t ₁ or more. Excellent in formability and strength stability, characterized in that it has an extruded cross-sectional shape of the wall thickness changing part and is expanded in the width direction. A highly productive method for producing aluminum alloy differential thickness blanks.

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