JP2003105474A - Al-Mg BASED ALUMINUM ALLOY HOLLOW EXTRUSION MATERIAL FOR BULGING - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Al-Mg based aluminum alloy hollow extrusion material for bulging which has excellent formability. SOLUTION: This Al-Mg based aluminum alloy hollow extrusion material contains, by mass, 1.5 to 5.0% Mg, and 0.005 to 0.2% Ti. If required, the aluminum alloy contains one or more metals selected from 0.05 to 1.0% Mn, 0.05 to 0.3% Cr, 0.05 to 0.2% Zr and 0.01 to 0.2% V. The mean axial ratio between the major axis and the minor axis of crystal grains in the center part of the sheet thickness is <=4.5, and the mean crystal grain diameter of recrystallized grains to 500 μm from the outer surface is <=500 μm. The extrusion material is suitable as an automobile suspension subframe having a complicated shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy hollow extruded material having an excellent bulge formability, which is suitable for forming a frame, a joint or the like of an automobile, a railway vehicle or a building member.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of environmental problems such as global warming and ozone layer destruction, weight reduction of automobiles and introduction of electric vehicles have been made in earnest in order to suppress an increase in carbon dioxide gas in the atmosphere. Is being considered. As part of this reduction in weight, replacement of materials, that is, use of aluminum alloy materials instead of steel plates that have been mainly used in the conventional structural materials for automobiles is increasing. Further, in an electric vehicle as well, there is a strong demand for reducing the weight of the vehicle body in order to compensate for an increase in weight for loading a battery. Furthermore, the use of aluminum alloy materials has attracted attention, as extruded materials that have a constant cross-sectional shape in the longitudinal direction can be obtained by increasing the degree of freedom in design and improving the formability by obtaining a cross-sectional shape close to the final shape. For example, Japanese Patent Application Laid-Open No. 2000-177621 describes that an aluminum alloy extruded material is used for manufacturing a suspension subframe.

On the other hand, bulge forming has attracted attention as a forming method of parts having a complicated shape such as a joint member used when joining frames to each other at the time of assembling a vehicle body and a suspension subframe. For example, an Al-Mg type aluminum alloy welded pipe is used. It is known to use a bulge-molded product as a suspension subframe. In addition, Japanese Patent Laid-Open No. 5-2
12464 discloses that a 5000 series (Al-Mg series) aluminum alloy plate is hydraulically formed.

[0004]

In the case of Al-Mg type aluminum alloy, an annealed material (O material), which is generally advantageous in terms of formability, has been used as a material for bulging. However, when the bulge height of the bulge molding was high, cracks were formed at the top of the bulge portion, and large bulge molding could not be performed. The present invention has been made in view of such problems with regard to bulge forming of an Al-Mg-based aluminum alloy, is excellent in bulge formability (particularly overhang height), and is a frame for automobiles, railway vehicles, or building members. And an Al-Mg-based aluminum alloy hollow extruded material suitable for molding a joining member and the like.

[0005]

[Means for Solving the Problems] In the process of conducting various experimental studies to develop an Al-Mg-based aluminum alloy hollow extruded material having excellent bulge formability, the inventors extruded the extruded material and then annealed it. In the O material, the surface layer portion is almost completely equiaxed, but dislocations introduced during cold working (drawing) disappear in the central portion, but in part, in equiaxed crystal. However, it was found that a structure stretched in the extrusion direction (a structure introduced at the time of extrusion or drawing) remained, and this hindered the bulge formability, and the present invention could be obtained based on this finding.

That is, Al for bulge forming according to the present invention
-Mg-based aluminum alloy hollow extruded material is Mg: 1.5
.About.5.0% and Ti: 0.005 to 0.2%, and is made of an Al--Mg-based aluminum alloy hollow extruded material, and the average axial ratio of the major axis and the minor axis of the crystal grains in the plate thickness central portion is 4 ．
It is characterized by being 5 or less. In the present invention, bulge molding is to bulge a part of a member using fluid pressure (sometimes called hydroform),
And that a part of the member is bulged by applying a negative pressure to the outside of the member.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the Al-Mg-based aluminum alloy hollow extruded material having the above composition, the average axial ratio (aspect ratio) between the major axis and the minor axis of the crystal grains at the center of the plate thickness is 4.5 or less. This is because excellent bulge formability can be obtained. The aspect ratio of 4.5 or less means that the crystal grains at the central portion of the plate thickness are equiaxed or near equiaxed. If the aspect ratio is 4.5 or less at the center of the plate thickness of the extruded material, 4.5 or less is similarly obtained in the surface layer portion. The aspect ratio is more preferably 3 or less. Further, in order to suppress the roughening of the surface portion after bulging, it is desirable that the average grain size of the recrystallized grains of at least the surface portion (portion from the outer surface to 500 μm) is 500 μm or less. It is preferably 300 μm or less, more preferably 100 μm or less.

The Al-Mg type aluminum alloy is M
As an additional element other than g and Ti, for example, M
One or more of n, Cr, Zr, and V may be contained, and Fe and other elements may be contained as unavoidable impurities. However, the total content of these additive elements and the like is preferably less than 6% (Al: 94% or more), which is the level of JIS 5000 series aluminum alloys. Hereinafter, the reason for adding each component to the aluminum alloy hollow extruded material according to the present invention will be described. Mg Mg forms a solid solution in the aluminum matrix and improves the alloy strength. Strength required for structural members such as automobile frames or joint members (proof strength value σ0.2 ≥ 50 MPa)
To obtain Mg, it is necessary to add 1.5% or more of Mg. However, if added in excess of 5.0%, the stress corrosion cracking resistance deteriorates, and the amount of solid solution becomes excessive and the elongation δ decreases, so that excellent bulge formability cannot be obtained. Therefore, Mg
The content is 1.5 to 5.0%. A more desirable range is 2.0 to 4.0%.

Ti Ti improves the alloy strength by refining the crystal grains during casting. To exert this effect, Ti
It is necessary that the addition amount be 0.005% or more. On the other hand, if it is less than 0.005%, the crystal grains are coarsened and the elongation is lowered, so that excellent bulge formability cannot be obtained. on the other hand,
When the amount of Ti added exceeds 0.2%, the above effect is saturated, and further, a coarse intermetallic compound crystallizes out, making it impossible to obtain a predetermined alloy strength and elongation. Therefore, the Ti content is 0.
005-0.2%, more preferably 0.01-0.
1%, and more preferably 0.01 to 0.05%.

Mn, Cr, Zr, V These elements control the structure in the manufacturing process, that is, crystallize and precipitate as intermetallic compounds to prevent coarsening of crystal grains and improve stress corrosion cracking resistance. If necessary, one kind or two or more kinds are added. 0.05 each
%, 0.05%, 0.05%, 0.01% or less has no effect, 1.0%, 0.3%, 0.2%, 0.2%
When it exceeds, the above effect is saturated and a coarse intermetallic compound precipitates to lower the elongation and deteriorate the bulge formability. When these elements are crystallized and precipitated as an intermetallic compound, recrystallization is suppressed and a structure (fibrous structure) stretched in the extrusion direction tends to remain in the extruded material, so that the aspect ratio is 4.5 or less. From the viewpoint of obtaining a structure, it is preferable that the addition amount of these elements is small. If added in excess of the above range, the stretched structure cannot be eliminated or other adverse effects (coarseening of recrystallized grains) will occur even if the manufacturing conditions described later are devised.

Inevitable Impurities Of the inevitable impurities, Fe is the most contained impurity in the aluminum base metal, and if more than 0.7% is present in the alloy, coarse intermetallic compounds crystallize during casting and the alloy mechanically acts. Spoil the nature. Therefore, the Fe content is regulated to 0.7% or less, preferably 0.5% or less. Further, when casting an aluminum alloy, impurities are mixed in through various routes such as a base metal, an intermediate alloy of additional elements, and a compound. Although various elements are mixed, Si is 0.5% or less, preferably 0.4% or less, and Cu is 0.3% among impurities other than Fe.
% Or less, preferably 0.2% or less, Zn is 0.3% or less, preferably 0.2% or less, and other impurities are 0.05% or less as a simple substance, and 0.15% or less in total amount is an alloy. Has almost no effect on the characteristics of. Therefore, these impurities should be below the above values. As for B among the impurities, 1/5 of the Ti content in the alloy is added as Ti is added.
It is mixed in a certain amount, but a more desirable range is 0.02%
Hereafter, 0.01% or less is desirable.

From the viewpoint of composition, it is effective to suppress the addition amount of transition elements such as Mn in order to make the structure at the center of the plate thickness of the extruded material 4.5 or less. In terms of manufacturing conditions, conditions under which the extruded material is likely to recrystallize are set. For example, the billet homogenization condition is high temperature long time side,
Alternatively, if the extrusion temperature is increased and the intermetallic compound grains of these elements are grown to reduce the pinning action, recrystallization easily occurs. Further, even if the extrusion ratio or the extrusion speed is increased to raise the temperature of the extruded material during extrusion, recrystallization easily occurs. Further, in the case of O material, it may be considered that after extruding the extruded material as it is extruded, it is annealed at a high temperature for a long time so that the recrystallization completely occurs up to the center portion of the plate thickness. On the other hand, if only the bulge formability is considered, it is sufficient to control the aspect ratio, but considering the rough surface of the surface after bulge formation, it is necessary to prevent coarsening of recrystallized grains on the surface at the same time. is there. To that end, when the addition amount of the transition element is so small that a fibrous structure is not formed, the coarsening of crystal grains is suppressed without increasing the extrusion temperature and the extrusion rate too much, and the addition amount of the transition element is higher than that. The homogenization treatment conditions are set to a high temperature for a long time, and the extrusion temperature and the extrusion rate are set relatively high to promote recrystallization. As described above, in order to keep the aspect ratio at 4.5 or less and the recrystallized grains from becoming too coarse, it is necessary to balance the composition aspect and the production condition aspect.

The Al-Mg-based aluminum alloy hollow extruded material according to the present invention can be manufactured by various extrusion methods. However, indirect extrusion rather than direct extrusion forms coarse recrystallized grains on the surface of the extruded material. Is desirable in the sense of preventing
Further, the mandrel method is more preferable than the porthole method in the sense that the uniformity of the structure in the cross section is ensured (there is no welded portion). INDUSTRIAL APPLICABILITY The Al-Mg-based aluminum alloy hollow extruded material according to the present invention is suitable for molding a frame or a joint portion of an automobile, a railroad vehicle, or a building member, and can be particularly suitably used for molding a suspension subframe of an automobile. The suspension subframe referred to in the present invention is simply a subframe, a suspension frame,
It is called a suspension member, engine mount, engine cradle, etc. In addition, the extruded material according to the present invention has good spreadability such as flange bending of the end portion and hemming workability.

[0014]

EXAMPLES Next, examples of the present invention will be described. First, an aluminum alloy ingot having the composition shown in Table 1 below was melted by a usual method, and No. The ingots of 1 to 4 and 8 to 10 were homogenized at 520 ° C. for 4 hours, and extruded under conditions of an extrusion temperature of 520 ° C. and an extrusion speed of 5 m / min. 570 ℃ × 4 for ingot 5
Homogenization treatment was performed for hr, and extrusion processing was performed under the conditions of an extrusion temperature of 520 ° C. and an extrusion speed of 10 m / min. 6
The ingot of No. 1 was subjected to homogenization treatment at 570 ° C. for 4 hours, and was extruded under conditions of an extrusion temperature of 520 ° C. and an extrusion speed of 5 m / min. 45 for 7 ingots
Homogenization treatment at 0 ° C x 8hr is applied and extrusion temperature is 470
Extruding under conditions of ℃, extrusion speed 3m / min,
In both cases, the material was air-cooled with a fan immediately after extrusion (cooling rate of about 10
After cooling at 0 ° C./min), a round pipe having an outer diameter of 38.5 mm and a wall thickness of 1.5 mm was obtained. No. The sample No. 7 was reheated at 550 ° C. for 4 hours and then allowed to cool. Using this as the test material (No. 1 to 10), the average axial ratio (aspect ratio) of the major axis and the minor axis of the crystal grains in the central part of the plate thickness and the average of the recrystallized grains of the surface part were measured as follows. Measure the particle size,
Tensile properties and bulge formability tests were conducted. Moreover, the rough surface of the surface after bulging was visually confirmed. The results are also shown in Table 1.

[0015]

[Table 1]

Aspect ratio: A test piece was taken from each test material, and a cross section perpendicular to the plate surface and parallel to the extrusion direction was observed. The major axis and the minor axis of 10 crystal grains located at the center of the plate thickness were observed. The length ratio was calculated and the average value was used as the aspect ratio. Average grain size of the surface portion: in a cross section perpendicular to the plate surface and parallel to the extrusion direction, the length in the direction parallel to the extrusion direction and the direction perpendicular to the direction of 10 recrystallized grains located in a portion up to 500 μm from the outer surface of the extruded material The length was determined and averaged to obtain the recrystallized grain size. Tensile test: A JIS No. 12A test piece was prepared from each test material, and a tensile test was carried out in accordance with JISZ2241 to determine tensile strength σB, proof stress σ0.2 and elongation.

Bulge forming test; length of each test material is 177 m
It cut | disconnected to m and the bulge forming test was done. FIG. 1 is a schematic diagram showing a bulge forming test method, in which each sample material (pipe) 5 is set in the lower mold 1, the mandrels 2 and 3 are inserted into the end faces of the pipes, and then the upper mold 4 is tightened. Water 6 was passed through the holes 2a and 3a inside 3 to apply pressure to the inside of the pipe, and at the same time, the mandrels 2 and 3 were moved to compress the pipe in the longitudinal direction to form a T-shape. Internal pressure (water pressure): 25.5 MPa, mandrel compression amount: 85 m
m (one side 42.5 mm), overhang height (see FIG. 2): 85
It was set to mm. For bulge formability, observe the presence or absence of cracks (cracks) that occur on the surface of the overhanging crown and the presence or absence of necking where the wall thickness becomes thin locally at the overhanging portion. If there was no cracking, but necking occurred, it was evaluated as △, and if there was cracking, it was evaluated as ×. Evaluation of skin roughness: The surface after bulge molding was visually observed, and those without skin roughness were rated as ⊚, those with large skin roughness were rated as ×, and the middle thereof was rated as ◯ and Δ, and evaluated in all four levels.

As shown in Table 1, No. 1 whose composition and aspect ratio satisfy the requirements of the present invention. All of 1 to 7 have good bulge formability, and the proof stress σ0.2 also satisfies the required strength as a structural member. N with a particularly small aspect ratio
o. Nos. 1 to 5 have excellent bulge formability. Looking at the evaluation of the rough skin, No. 1 having a small average crystal grain size on the surface portion was used. 1-4
No rough skin, No. In Nos. 5 to 7, as the average crystal grain size became larger, the rough skin gradually became larger. In addition, No. Immediately after extrusion, No. 7 had a fine fiber structure in the entire cross section (structure stretched in the extrusion direction). Since this was reheated and recrystallized, the crystal grains of the surface portion became coarse.

On the other hand, in No. 1 having a large amount of Mg. No. 8 is inferior in bulge formability and has a low Mg content. No. 9 has a low yield strength and a large aspect ratio. No. 10 is inferior in bulge formability.
Looking at the evaluation of rough skin, the crystal grain size of the surface part is small N
o. Nos. 8 to 9 have no rough skin and have a large crystal grain size. 1
0 is rough skin. In addition, No. In No. 10, coarse recrystallized grains grow only in the surface layer portion, and such a structure tends to be formed when the transition element is added in an excessive amount.

[0020]

As described above, Al-containing a predetermined composition
In the Mg-based aluminum alloy hollow extruded material, excellent bulge formability can be obtained by setting the average axial ratio (aspect ratio) of the major axis and the minor axis of the crystal grains in the central part of the plate thickness to 4.5 or less. In addition, the average grain size of the recrystallized grains in the surface layer is 5
By setting the thickness to 00 μm or less, it is possible to suppress skin roughness after bulge molding. This Al-Mg-Si-based aluminum alloy hollow extruded material is suitable as a material for bulge molding of frames and joint members of automobiles, railway vehicles, ships or construction members.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating a bulge forming test method according to an example.

FIG. 2 is an explanatory diagram of the overhang height by a bulge forming test of an example.

[Explanation of symbols]

1 Lower mold A few mandrels 4 Upper mold 5 Test material (pipe)

Claims (4)

[Claims] 1. Al-containing Mg: 1.5 to 5.0% (mass%, the same applies hereinafter) and Ti: 0.005 to 0.2%.
An Al-Mg-based aluminum alloy hollow extrusion for bulging, characterized by comprising a Mg-based aluminum alloy hollow-extruded material, and having an average axial ratio of the major axis and the minor axis of the crystal grains of 4.5 or less in the central portion of the plate thickness. Material. 2. Mg: 1.5 to 5.0%, Ti: 0.0
0.05 to 0.2%, and further Mn: 0.05 to 1.
0%, Cr: 0.05 to 0.3%, Zr: 0.05 to
0.2%, V: 0.01 to 0.2%, and at least one of Al-Mg-based aluminum alloy hollow extruded material containing the balance Al and impurities. An Al-Mg-based aluminum alloy hollow extruded material for bulging, characterized in that the average axial ratio of the major axis and the minor axis is 4.5 or less. 3. The bulge-forming Al-Mg-based aluminum alloy hollow extruded material according to claim 1, wherein the average crystal grain size of recrystallized grains from the outer surface to 500 μm is 500 μm or less. . 4. A suspension subframe using the Al-Mg-based aluminum alloy hollow extruded material for bulging according to claim 1.