JP2003034834A - Al-Mg-Si ALUMINUM ALLOY EXTRUSION MATERIAL SUPERIOR IN ENERGY IMPACT ABSORPTIVITY, AND MANUFACTURING METHOD THEREFOR - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Al-Mg-Si-based aluminum alloy extruded material superior in energy impact absorptivity. SOLUTION: This Al-Mg-Si aluminum alloy extrusion material has a composition containing, by mass%, 0.4-0.7% Si, 0.4-0.7% Mg, 0.02-0.2% Cu, 0.1-0.3% Fe, 0.002-0.2% Ti, and further containing at least one of 0.05-0.3% Mn, 0.05-0.2% Cr, and 0.05-0.4% Zr, so as to be 0.05-0.4% in total of Mn+Cr+Zr, has crystal grains controlled to 0.2 mm<2> or less in the cross section, and has width of a region free from precipitates in the vicinity of the crystal grains controlled to 3 μm or less. The manufacturing method for forming the above structure comprises holding an aluminum alloy billet having the above composition at 480-580 deg.C for 1-8 hours to homogenize it, cooling it at an average cooling rate of 300 deg.C/min or higher in a range of 450-520 deg.C, and then holding it at 160-230 deg.C for 1-15 hours.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy extruded material, which is particularly suitable for use in automobile space frames and bumpers.
The present invention relates to an l-Mg-Si-based aluminum alloy extruded material.

[0002]

2. Description of the Related Art In recent years, weight saving of automobiles has been demanded from the viewpoint of energy saving and environmental protection, and an aluminum alloy extruded material has been used as a structural material thereof. Aluminum alloys are lightweight and can be produced with extrusions of any cross-sectional shape, so they are about to be used for automobile space frames and bumpers. Considering this, an Al-Mg-Si-based aluminum alloy has been used.

[0003]

Recently, from the viewpoint of ensuring the safety of automobiles, the structural energy of automobiles is also required to have impact energy absorption. The present invention has been devised in order to solve such a problem.
It is an object of the present invention to provide an Al-Mg-Si-based aluminum alloy extruded material whose composition and structure are strictly adjusted to improve impact energy absorption performance.

[0004]

The Al-Mg-Si-based aluminum alloy extruded material of the present invention, which is excellent in impact energy absorption performance, has a composition of S and S in order to achieve its object.
i: 0.4 to 0.7 mass%, Mg: 0.4 to 0.7 mass%, Cu: 0.02 to 0.2 mass%, Fe: 0.1
0.3% by mass, Ti: 0.002 to 0.2% by mass, Mn: 0.05 to 0.3% by mass, Cr: 0.
05-0.2 mass%, Zr: 0.05-0.2 mass%, at least one or more of them are contained in a total amount of Mn + Cr + Zr of 0.05-0.4 mass%, and the cross-sectional area of the crystal grains is Of 0.2 mm ² or less, and a structure in which the width of a portion having no precipitate near the crystal grain boundaries is 0.3 μm or less is provided. If necessary, add B to 0.0
You may make it contain in the range of 005-0.01 mass%. Further, in order to obtain such a structure, the aluminum alloy billet having the above-mentioned components / compositions at 1 to 480 ° C.
After being kept for 8 hours and homogenized, it is manufactured by cooling at an average cooling rate of 450 to 520 ° C. at 300 ° C./min or more, and then holding at 160 to 230 ° C. for 1 to 15 hours after cooling. .

[0005]

When the aluminum alloy extruded material receives collision energy, it first absorbs the energy and is deformed, and is broken when the energy absorption capacity is exceeded. In order to sufficiently absorb the impact at the time of collision, it is important to increase the deformability of the aluminum alloy extruded material at the time of collision. Therefore, the present inventors first conducted earnest research on the mechanism of cracking. As a result, there is no precipitate near the grain boundaries, generally the Precipitate Free Zone (hereinafter "PFZ").
Called. It is found that there is a region called), and ductile fracture occurs in the PFZ when impact energy is applied, which causes cracking at the time of collision.

FIG. 1 shows the state of crack generation when an aluminum alloy extruded material is impacted in the extruding direction. Further, as can be seen from the enlarged observation state of the cracked portion shown in FIG. 2, the PFZ is softer than other portions because there are no precipitates, and stress is concentrated there when impact energy is applied, Ductile fracture has occurred. This situation is schematically shown in FIG.

Therefore, by narrowing the width of the PFZ formed in the vicinity of the grain boundary, it has been possible to prevent the stress from being concentrated on the PFZ and suppress the occurrence of cracks at the time of collision. By setting the width of the PFZ to 0.3 μm or less, breakage in the PFZ could be suppressed. FIG. 4 shows a schematic situation of crack generation when the PFZ width is narrowed. The PFZ can be formed on both sides of the crystal grain boundary with the grain boundary in between. Specifically, the precipitation area −
PFZ-grain boundary-PFZ-precipitation region, and the width of PFZ defined in the present invention means the distance from the grain boundary to the precipitation region in the crystal grain.

Further, in order to suppress the destruction at the grain boundary, it is necessary to make the crystal grain small. This is because the presence of the coarse recrystallized structure makes it easier for stress concentration to occur at the grain boundaries of the coarse recrystallized grains. By strictly adjusting the amount of alloying components such as Mn, Cr, and Zr having the effect of suppressing grain coarsening in the aluminum alloy and the heat treatment conditions, the crystal grains are made small, specifically, 0.
It should be ² mm ² or less.

Each element will be described in detail below. Si: 0.4-0.7 mass% By adding together with Mg, Mg-after the aging treatment
It forms Si-based precipitates and enhances strength. If it is less than 0.4%, sufficient strength cannot be obtained. On the contrary, if it exceeds 0.7%, extrusion defects such as tearing tend to occur and the extrudability deteriorates.

Mg: 0.4 to 0.7 mass% As described above, it is an element added to enhance strength.
If it is less than 0.4%, sufficient strength cannot be obtained after the aging treatment. If it is added in excess of 0.7%, the hot deformation resistance value increases and the extrudability decreases.

Cu: 0.02 to 0.2 mass% When added in the same manner as Si and Mg, the strength increases after the aging treatment. If it is less than 0.02%, the effect cannot be obtained. Also,
If added in excess of 0.2%, the corrosion resistance decreases.

Fe: 0.1 to 0.3 mass% An Al-Fe-Si-based crystallized product is formed during casting. Most of them remain even after the homogenization treatment, and they are divided by the extrusion process and distributed, which hinders the movement of grain boundaries. This action prevents coarsening of crystal grains. If it is less than 0.1%, the effect cannot be obtained. Further, if added in excess of 0.3%, a coarse Al-Fe-Si compound is generated, and the surface properties of the extruded material deteriorate.

Ti: 0.002 to 0.2 mass% The crystal grain structure during casting is refined to prevent casting cracks.
It also increases the corrosion resistance after aging treatment. If it is less than 0.002%, the effect cannot be obtained. If it is added in excess of 0.2%, a coarse Al-Ti compound is generated, and the surface quality of the extruded material is deteriorated. B: 0.0005 to 0.01% by mass In addition, 0.0005 to 0.01% of B can be added as necessary in order to refine the crystal grain structure during casting.

Mn: 0.05 to 0.3 mass%, Cr: 0.05 to 0.2 mass%, Zr: 0.05 to 0.2 mass%, Mn + Cr + Zr: 0.05 to 0.4 mass% Mn, Cr, and Zr are each Al-Mn after the homogeneous treatment.
-Type, Al-Cr-type, and Al-Zr-type precipitates are generated to prevent movement of grain boundaries, thereby preventing crystal grain coarsening of the extruded material (pinning effect). Further, Mn, Cr, and Zr also have an action of leaving subgrains (subcrystalline grains) that enhance the impact absorption performance during extrusion processing or heat treatment. If the subgrain is left, it has the same effect as making the crystal grains themselves fine. If their content is less than 0.05%, no effect can be obtained. On the contrary, Mn, Cr, and Zr are 0.3, respectively.
%, Cr, Zr added in excess of 0.2%, or Mn +
If added so that the total of Cr + Zr exceeds 0.4%, the hot deformation resistance increases and the extrudability decreases. Therefore, the amounts of Mn, Cr, and Zr added are as described above.

Homogenization conditions: 480 to 580 ° C. for 1 to 8 hours
The Mg, Si, Cu, etc. segregated and present in the ingot are sufficiently solutionized by the processing heat during extrusion (hereinafter, "press hardening").
Called. ) Homogenize as possible. Also, Al-M
By precipitating an n (or Cr, Zr) -based compound, movement of grain boundaries is prevented and coarsening of crystal grains is prevented. 480
If the temperature is lower than ° C, homogenization of segregated Mg, Si, Cu, etc. is insufficient. On the other hand, if the temperature exceeds 580 ° C., the Al—Mn (or Cr, Zr) -based precipitates become coarse, the effect of preventing the movement of grain boundaries decreases, and the crystal grains become coarse. Regarding the processing time, if the processing time is less than 1 hour, segregated Mg, Si, Cu
Is not sufficiently homogenized. Further, if it exceeds 8 hours, the Al-Mn (or Cr, Zr) -based precipitate tends to be coarsened, the effect of pinning the grain boundaries is reduced, and the crystal grains are likely to be coarsened.

Billet temperature condition before extrusion: 450 to 52
Mg, Si, and Cu are sufficiently solid-solved by press quenching at 0 ° C to obtain sufficient strength after aging treatment, and the temperature of the profile outlet is excessively increased (the profile die outlet temperature becomes too high. ) To prevent the crystal grains from coarsening. In order to obtain sufficient strength after aging treatment, the profile outlet temperature should be 51
It is necessary to make it 0 ° C or higher. If the billet temperature is lower than 450 ° C, the shape member outlet temperature of 510 ° C cannot be stably obtained. Also, if the profile outlet temperature exceeds 580 ° C, Al
-Fe-Si system crystallized product and Al-Mn (Cr, Zr)
The effect of pinning the grain boundaries of the system precipitates decreases, and the crystal grains tend to become coarse. When extruded at a billet temperature exceeding 520 ° C, the profile temperature may exceed 580 ° C. By strictly controlling the components / compositions of the aluminum alloy, particularly the Mn, Cr, and Zr contents, and by strictly controlling the homogenization conditions and the billet temperature conditions before extrusion, the cross-sectional area of the crystal grains of the extruded material is reduced to 0. It can be less than 0.2 mm ² .

PFZ width: 0.3 μm or less The PFZ width, which is the greatest feature of the present invention, will be described.
As described above, by narrowing the width of the PFZ generated near the grain boundaries, it was confirmed that stress could be prevented from concentrating on the PFZ and the occurrence of cracks during collision could be suppressed. The requirement of PFZ width ≦ 0.3 μm for obtaining this effect is set based on various experimental results described below.

Immediately after extrusion, cooling rate between 450 and 250 ° C .:
300 ° C./min or more In order to set the width of the PFZ to 0.3 μm or less as described above, this is also the result obtained from various experimental examples described below. 250
It is necessary to set the average cooling rate between ° C to 300 ° C / min or more. If this speed is not reached, the PFZ width will be 0.3μ.
If it exceeds m, grain boundary fracture will occur and the intended purpose will not be achieved. For reference, 6N01 material (S
i: 0.56%, Mg: 0.53%, Cu: 0.07
%, Mn: 0.15%, Fe: 0.18%, Ti: 0.
(01%, B: 0.001%) and then cooled at various cooling rates, the PFZ width is shown in FIGS. The cooling rate with water cooling is about 1000 ° C./sec. It can be seen that the PFZ width is 0.3 μm or less at the cooling rate of 300 ° C./min.

Aging treatment conditions: 160 to 230 ° C. × 1 to 1
For 5 hours , Mg, Si, and Cu solid-dissolved by press quenching as compounds are precipitated in an appropriate size and distribution state to increase strength and energy absorption performance. It takes a long time to process at less than 160 ° C. If the treatment time exceeds 15 hours, it is not economical. Also, the higher the aging temperature, the shorter the time required for the treatment, but the larger the precipitates and the lower the peak strength. If it exceeds 230 ° C, sufficient strength cannot be obtained. A holding time of 1 hour is required to stabilize the temperature in the heat treatment furnace.

Various experiments conducted for selecting an appropriate PFZ width will be described. Experimental Example Alloy No. shown in Table 1 After casting 1 to 4 in a 203φ ingot, the temperature was raised to 540 ° C. at 100 ° C./hour, held for 2 hours, and then cooled to room temperature at 250 ° C./hour (homogenization treatment). Then heat to 480 ° C., 50
Extruded into a square shape of mm × 50 mm × 2 mmt,
The shape during extrusion was cooled under the cooling conditions shown in Table 2. In addition,
The temperature of the extruded material immediately after coming out from the die (hereinafter, referred to as "outlet temperature") was 530 to 550 ° C.

[0021]

[0022]

After the obtained extruded material was aged at 180 ° C. for 6 hours. The PFZ width was measured, and a compression test in the axial direction was performed to measure the absorbed energy and determine the appearance after the test. The PFZ width was measured by scanning electron microscope observation. The absorbed energy is obtained by cutting the extruded material into a length of 25 cm, compressing and deforming the extruded material at a speed of 1 mm / sec in the extrusion direction, creating a load-displacement curve at that time, and measuring the portion formed by the curve and the horizontal axis. The area was defined as the amount of absorbed energy (absorbed energy = load x displacement). Table 3 shows the obtained PFZ width, absorbed energy amount and appearance after the test.
Shown in.

[0024]

The aluminum alloy extruded material of this type has a tensile strength of 245 MPa and a 0.2% proof stress of 20.
It is desirable to have a characteristic of 5 MPa and an absorbed energy of 2700 N · mm or more. From the results shown in Table 3, the average cooling rate of 300 ° C / min was measured between 450 and 250 ° C after extrusion.
Alloy No. Test Nos. 1 to 4 It can be seen that in the case of Nos. 1 to 3, the PFZ width is 0.3 μm or less, and the energy absorption amount is large. Observation of the extruded material that had been compressed and deformed revealed that no cracks had occurred and that it deformed into a bellows shape. Moreover, the above-mentioned required characteristics are sufficiently satisfied. Further, when the structure of these samples was observed, the cross-sectional area was 0.1 mm ² even though the crystal grains were large.
Below, subgrains were observed in many crystals.

On the other hand, after the extrusion, the test No. 1 was cooled between 450 ° C. and 250 ° C. at an average cooling rate of 150 ° C./min.
In the test piece of No. 4, although the tensile strength and the 0.2% proof stress were sufficient, the absorbed energy did not reach 2500 N · mm. During the axial compressive deformation, the extruded material did not undergo bellows deformation and was partially broken. The PFZ of this test piece is 0.3
This is due to the result of ductile fracture at the grain boundaries because the diameter exceeds μm.

In addition, the alloy No. In the test material that was cooled at 400 ° C./min after extrusion in No. 5, PF
Even if the width of Z was 0.3 μm or less, the extruded material did not undergo bellows deformation during compression deformation in the axial direction, and partly fractured. When the structure was observed, most of the structure was a fine recrystallized structure with a cross-sectional area of 0.1 mm ² or less, but sub-grains were hardly observed, and the coarse recrystallized partly had a cross-sectional area of more than 0.3 mm ^2. The texture was observed, and the texture was a mixture of fine and coarse grains as a whole. Alloy No. In 5, Mn + C
Since the amount of r + Zr is small, subgrains disappear,
In addition, when a coarse recrystallized structure is generated and compression deformation is performed,
It is presumed that stress was concentrated in the coarse recrystallized structure and grain boundary cracking occurred.

From the above, when the crystal grain size is small and the PFZ width of the grain boundary is 0.3 μm or less, when the extruded material is compressed and deformed, it deforms into a bellows shape and absorbs much energy. It can be seen that, while the destruction can be prevented, when the PFZ width exceeds 0.3 μm, it does not deform in a bellows shape during compression deformation and cracks, so that much energy cannot be absorbed.

[0029]

As described above, Al-Mg having improved impact energy absorption performance by reducing the PFZ width of the crystal grain boundary by strictly adjusting the components / compositions and controlling the production conditions. An -Si-based aluminum alloy extruded material can be obtained, and an extruded material suitably used for a space frame or bumper of an automobile can be provided.

[Brief description of drawings]

[Fig.1] Screen for observing crack locations during compression of extruded aluminum alloy

[Fig. 2] Observation screen for enlarged observation of cracks

FIG. 3 is a diagram schematically illustrating a crack generation state in a material having a large PFZ width.

FIG. 4 is a diagram schematically illustrating a crack generation state in a material having a small PFZ width.

FIG. 5: Cooling rate 50 ° C./mi after extruding 6N01 material
Screen for observing PFZ width of material cooled by n

FIG. 6 is a cooling rate of 300 ° C./m after extruding 6N01 material.
Screen for observing PFZ width of material cooled in in

FIG. 7: 6N01 material was extruded and then water-cooled (cooling rate 100
Screen showing the PFZ width of the material (0 ° C / sec)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI Theme Coat (reference) C22F 1/00 682 C22F 1/00 682 692 691 691B 691C 692 692A 692B (72) Inventor Shigeru Okaba Shizuoka Prefecture Anbara-gun 1-34-1, Kambara-cho, Kambara-cho F-term (reference) in the Group Technology Center of Nippon Light Metal Co., Ltd. 4E029 AA06

Claims (3)

[Claims] 1. Si: 0.4 to 0.7 mass%, Mg:
0.4-0.7 mass%, Cu: 0.02-0.2 mass%, Fe: 0.1-0.3 mass%, Ti: 0.002-
It contains 0.2% by mass and further Mn: 0.05 to 0.3.
% By mass, Cr: 0.05 to 0.2% by mass, Zr: 0.0
At least one of 5 to 0.2 mass% is Mn + C
The total content of r + Zr is 0.05 to 0.4% by mass, the balance is a component / composition substantially consisting of Al, the cross-sectional area of the crystal grains is 0.2 mm ² or less, and the vicinity of the crystal grain boundaries. An Al-Mg-Si based aluminum alloy extruded material having excellent impact energy absorption performance, characterized in that it has a structure in which the width of the precipitate-free portion is 0.3 μm or less. 2. The component / composition further has B: 0.0005.
The Al-Mg-Si based aluminum alloy extruded material excellent in impact energy absorption performance according to claim 1, which contains 0.01% by mass. 3. An aluminum alloy billet having the components and composition according to claim 1 or 2 is held at 480 to 580 ° C. for 1 to 8 hours and homogenized, and then 450 to 520.
Cooling at an average cooling rate of 300 ° C / min or more between ° C,
Al-M excellent in impact energy absorption performance characterized by holding at 160 to 230 ° C for 1 to 15 hours after cooling
A method for producing a g-Si based aluminum alloy extruded material.