JPH06212338A - Al-zn-mg alloy hollow shape excellent in strength and formability and its production - Google Patents

Abstract

PURPOSE:To obtain an Al-Zn-Mg alloy hollow shape excellent in strength, bendability, SCC resistance, and corrosion resistance by forming the whole metallic structure into a structure in a state of fibers parallel to the direction of extrusion. CONSTITUTION:An ingot of an Al-Zn-Mg alloy, which has a composition consisting of, by weight, 5.0-6.0% Zn, 1.2-1.8% Mg, 0.20-0.50% Cu, 0.10-0.50% Zr, Fe and Si by the amounts in the ranges where (Fe+Si) and (Fe/Si) are regulated to 0.10-0.60wt.% and >=1.5, respectively, further 0.01-0.10% Mn and/or 0.01-0.10% Cr, and the balance essentially Al, is subjected to homogenizing treatment at 420-520 deg.C for 2-24hr, extruded at 430-520 deg.C, cooled down to room temp., and then subjected, as artificial ageing treatment, to first-stage heat treatment at 90-110 deg.C for 2-12hr and to second-stage heat treatment at 120-170 deg.C for 5-24hr.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to A which is excellent in strength and moldability.
The present invention relates to an l-Zn-Mg-based alloy hollow shape member and a method for manufacturing the same, and more specifically, it is suitable for automobile bumper reinforcements and the like and can be extruded and has strength, formability, stress corrosion cracking resistance, The present invention relates to a hollow shape member required to have corrosion resistance and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for weight reduction of various parts of automobiles from the viewpoint of consideration for the global environment and energy saving. A typical example is a body sheet material, which is a plate material, and is partially made of aluminum. on the other hand,
If the weight of the bumper line hosement, door beam, etc. is made aluminum to reduce the weight, the weight reduction effect will be great. However, there is a strong demand for aluminum because the steering stability is improved and the material of the door beam is made of aluminum because the material itself is lightweight, which makes it possible to design the shape according to the vehicle type.

[0003]

By the way, automotive parts such as bumper reinforcements and door beams have strength, formability such as bending workability, stress corrosion cracking resistance (hereinafter
It is required to have excellent SCC resistance) and corrosion resistance. Further, automobile members such as bumper reinforcements and door beams are hollow members having a complicated shape, and it is necessary to make them thin in order to further reduce the weight. Therefore, the materials used for these members are required to be capable of extruding not only large-sized profiles, but also small-sized thin hollow profiles with a large extrusion ratio. Conventionally, JIS 6000 series alloys have been used for small-sized, thin-walled hollow members having a large extrusion ratio, but their strength was insufficient for automobile members such as bumper reinforcements and door beams. Also,
JIS 7N0 is used for extruded profiles that require strength and corrosion resistance.
1 alloy and JIS 7003 alloy are used.
IS 7N01 alloy is inferior in formability and SCC resistance.
S7003 alloy does not have sufficient strength.

As described above, since no aluminum alloy has hitherto been available which satisfies the properties required for automobile members such as bumper reinforcements and door beams in a well-balanced manner, the aluminization of these members has not progressed, and high-tensile steel plates and the like have not been developed. Is used. Therefore, the present invention is suitable for a thin hollow member having a complicated shape that requires strength, formability, SCC resistance, and corrosion resistance, and is excellent in strength and formability.
An object is to provide a hollow Mg-based alloy material and a method for producing the same.

[0005]

The present inventor has found that the above object can be achieved if the metal structure after aging treatment is a fibrous structure along the extrusion direction.
The composition of the —Zn—Mg-based alloy is limited, and the conditions for homogenization treatment, extrusion processing, and artificial aging treatment are limited as a manufacturing method thereof.

That is, according to the present invention, Zn 5.0 to 6.0 wt%,
Mg 1.2-1.8 wt%, Cu 0.20-0.50 wt%, Zr0.10-
0.50wt%, Fe + Si 0.10-0.60wt% and Fe / Si
Content of 1.5 or more, and Mn of 0.01 to 0.10
wt%, Cr 0.01-0.10 wt% containing one or two,
Other impurities are 0.05 wt% or less, respectively, and 0 in total.
Al-Zn- with 15 wt% or less, balance aluminum
Al-Zn-M excellent in strength and formability, characterized in that it is a hollow section of an Mg-based alloy, and the metal structure of the hollow section is a fibrous structure along the extrusion direction.
The g-based alloy hollow shape and its manufacturing method are
-Zn-Mg alloy ingot is homogenized at 420 to 520 ° C for 2 to 24 hours, then extruded at 430 to 520 ° C, cooled to room temperature, and then the first step as artificial aging treatment.
90 ~ 110 ℃ 2 ~ 12 hours, the second stage 120 ~ 170 ℃ 5 ~
It is intended to provide a method for producing an Al—Zn—Mg-based alloy hollow profile excellent in strength and formability, which is characterized by performing heat treatment under a condition of 24 hours.

[0007]

In the present invention, recrystallization is prevented, and the metal structure has a fibrous structure along the fine extrusion direction, so that the strength is high and the formability such as bending is excellent. It can prevent the orange peel and improve the corrosion resistance. Here, Al-Zn-Mg in the present invention
The reason for adding the additional element of the alloy and the reason for limiting the addition amount will be described. Zn has the effect of improving mechanical properties. If the addition amount is less than 5.0 wt%, the effect is small, while 6.0
If added in excess of wt%, SCC resistance, corrosion resistance and moldability deteriorate. Therefore, in the present invention, the amount of Zn added is
Limited to 5.0-6.0wt%.

Mg is also an element for improving mechanical properties, but if its addition amount is less than 1.2 wt%, its effect is small,
On the other hand, if added in excess of 1.8 wt%, SCC resistance, moldability and extrusion processability deteriorate, and productivity also decreases. Therefore, in the present invention, the addition amount of Mg is limited to 1.2 to 1.8 wt%.

Cu has the effect of improving the SCC resistance as well as improving the mechanical properties. The amount added is 0.20 wt%
If it is less than 0.50% by weight, it is not effective. If it is added in excess of 0.50% by weight, the corrosion resistance is adversely affected. Therefore, in the present invention, the amount of Cu added is limited to 0.20 to 0.50 wt%.

Zr has the effects of suppressing the coarsening of recrystallized grains in the alloy, stabilizing the structure by using the crystal grains as a fibrous structure, and improving the formability such as bending. If the addition amount is less than 0.10 wt%, the effect is small, while if it is added over 0.50 wt%, a coarse Al—Zr intermetallic compound is formed and the toughness and the like are deteriorated. Therefore, in the present invention, the added amount of Zr is limited to 0.10 to 0.50 wt%.

Mn and Cr, in the coexisting state, are finely dispersed in the aluminum matrix to prevent recrystallization of the fibrous structure and stabilize the structure, and orange is formed on the surface of the extruded material after forming such as bending. It is effective in preventing peel-like rough skin. If the addition amount is less than 0.01 wt% each, the effect is small. Conversely, if the addition amount exceeds 0.10 wt%, the effect is saturated, while coarse intermetallic compounds are generated and quenching sensitivity increases. In addition, it adversely affects strength and extrudability. Therefore, in the present invention, the addition amounts of Mn and Cr are each 0.01
Limited to ~ 0.10wt%.

Fe and Si have the effect of improving the toughness and mechanical properties, but the addition amount of Fe + Si is 0.10 wt%.
If it is less than 0.6%, the effect is not exerted. On the contrary, if the content exceeds 0.60% by weight, a coarse intermetallic compound is formed. Therefore, in the present invention, the content of Fe + Si is limited to 0.10 to 0.06% by weight. If Fe / Si is less than 1.5, ingot cracking after casting and coarsening of crystal grains cannot be prevented.
Set to 1.5 or more.

Impurities such as Ti, Ni and Bi may be contained if they are 0.05 wt% or less and 0.15 wt% or less in total, since they do not adversely affect the effects of the present invention.

By the way, the profile of the Al--Zn--Mg alloy is generally manufactured by a method in which a homogenized ingot is hot extruded, press-hardened, and then artificially aged. The present invention achieves the object by using the above alloy and limiting the temperature conditions and the treatment time conditions at each stage of the production. Next, the manufacturing conditions will be described.

First, the ingot of the alloy is homogenized.
The homogenization treatment is performed at a relatively high temperature in order to finely and uniformly disperse compounds such as Zr, Mn, and Cr. However, if the temperature is higher than 520 ° C or if the treatment is performed for more than 24 hours, the precipitates are coarsened and the properties such as extrudability and quenching sensitivity are deteriorated. On the other hand, homogenization is inadequate in treatments at less than 420 ° C or less than 2 hours. Therefore, in the present invention, the homogenization treatment is 420 to 5
Perform at 20 ℃ x 2-24 hours.

Next, the ingot is heated to the extrusion temperature for hot extrusion, and immediately after that, press quenching is performed by air cooling or water cooling. Regarding the extrusion temperature, it is possible to process thin hollow sections with a large extrusion ratio, which are difficult to extrude.
Perform at a high temperature above ℃. When a conventional alloy is extruded at such a high temperature, recrystallization progresses and coarse recrystallized grains are generated, so that the SCC resistance is remarkably lowered, and a coarse intermetallic compound is formed, and thus extrudability is improved. , Moldability, corrosion resistance, etc. deteriorate. However, in the alloy of the composition according to the present invention, the addition of Zr results in a fibrous structure without recrystallized grains, and Mn and Cr are finely dispersed to suppress the progress of recrystallization. By limiting the content, the formation of coarse intermetallic compounds is suppressed, and further Cu
Addition significantly improves SCC resistance, enabling extrusion at high temperatures. In addition, since extrusion hardening is performed at a high temperature, press quenching is sufficiently performed, so that the artificial aging treatment significantly increases the strength. However, 520
If the extrusion process is performed at a temperature higher than 0 ° C, recrystallization and formation of coarse intermetallic compounds proceed, and each property deteriorates. Therefore, in the present invention, the extrusion temperature is limited to the temperature range of 430 to 520 ° C.

After press hardening, the extruded material cooled to room temperature is subjected to artificial aging treatment. The artificial aging treatment is a two-step aging, in which the fine precipitates of MgZn ₂ are uniformly dispersed in the first step, and the high-temperature aging in the second step grows into a coarse GP zone or an intermediate phase. The first stage aging treatment is performed at 90 to 110 ° C for 2 to 12 hours in order to disperse fine precipitates sufficiently uniformly while preventing coarsening of the precipitates. The second-stage aging treatment is performed at a higher temperature than the first-stage treatment, but if the treatment is performed at a temperature higher than 170 ° C, MgZn ₂ will be coarsely precipitated, resulting in deterioration of formability and corrosion resistance, and variation in specific heat. . On the other hand, if the treatment is carried out at a temperature lower than 120 ° C., the growth in the GP zone or the intermediate phase becomes insufficient and the strength becomes insufficient. Further, in consideration of productivity, in the present invention, the second aging treatment is performed at 120 to 170 ° C. for 5 to 24 hours.

The metallic structure of the Al-Zn-Mg-based alloy hollow profile produced by the manufacturing method of the present invention as described above has a fibrous structure along the extrusion direction. When a forming process such as bending under particularly severe conditions is required, the artificial aging treatment may be performed after press hardening (T4 treatment) and after forming process such as bending. Also in this case, the artificial aging treatment may be performed under the above treatment conditions.

[0019]

EXAMPLES Next, the present invention will be explained based on examples. Inventive examples (No. 1 to 4) and conventional examples (No. 5 to 5) having the compositions shown in Table 1
8), the alloys of Comparative Examples (No. 9 and 10) were φ 3 by DC casting.
It was cast into a 45 mm ingot for extrusion, and homogenized, respectively.
It carried out on the conditions shown in. After that, each was reheated to the extrusion temperature shown in Table 1 and extruded with a model die having a hollow square tube shape and a wall thickness of 2 mm. At that time, press hardening was performed by air-cooling the shape member with a fan. Then, two-step aging treatment was performed under the conditions shown in Table 1, respectively.

[0020]

[Table 1]

Mechanical properties, toughness, extrudability, moldability, corrosion resistance and metallographic structure of the profile processed in the above steps were examined. The mechanical properties were evaluated by taking a JIS No. 5 tensile test piece from the longitudinal direction of extrusion and performing a tensile test to determine tensile strength, proof stress, and elongation. The toughness is determined by the JIS No. 3 test piece U-notch Charpy test and UPE tear test (hereinafter referred to as UPE
Was evaluated by calculating the absorbed energy with an Instron tester using JIS standard test pieces.
For the extrudability, the maximum extrusion pressure was measured while converting the extrusion speed from the limiting ram speed (ipm). Formability is evaluated comprehensively by bending a bumper basic type hollow square tube (50 mm × 40 mm, wall thickness 2 mm) with a draw bender to a radius of curvature of 200 mm, its deformability, wrinkles after processing, and the state of cracking. , ◎ good bending, ○ wrinkle occurrence, △ wrinkle / deformation large,
× was not bendable. The SCC resistance was tested by U-bending under a load stress of 95% with a chromic acid accelerator, and ○ was evaluated as unchanged, Δ as peeling corrosion state, and × as cracking. The corrosion resistance was evaluated in the salt spray test by the weight loss due to corrosion after 500 hours. Regarding the metallographic structure, a recrystallized structure is not shown and the entire surface is a fibrous structure, ○, a recrystallized surface layer is △, and a coarse recrystallized structure is ×.
Expressed as Table 2 shows the test results for each of these characteristics.

[0022]

[Table 2]

As is clear from Table 2, the invention examples No. 1 to 4
Has better mechanical properties, toughness, formability, and corrosion resistance than the conventional JIS 7N01 alloy, and has significantly improved mechanical properties than the JIS 7003 alloy. Furthermore, it has the same or better extrudability as conventional alloys. On the other hand, JIS 7N01 alloy has a problem particularly in formability and cannot be applied to applications such as bumper reinforcements where bending is performed after extrusion. Further, although JIS 7003 alloy has excellent toughness, extrudability, formability, and corrosion resistance, it has poor mechanical properties and cannot be applied to automobile parts such as bumper reinforcements and door beams.

[0024]

As described above, the alloy of the present invention is excellent in a well-balanced manner in various properties required for hollow members for automobiles such as bumper reinforcements and door beams.
It is possible to make these members aluminum, that is, to reduce the weight.
Further, it is possible to extrude a thin hollow material, and the condition management can be surely and easily performed according to the regulation of the manufacturing condition, so that the productivity is enhanced and the industrially significant effect is exhibited.

Claims (2)

[Claims] 1. Zn 5.0-6.0 wt%, Mg 1.2-1.8 wt
%, Cu 0.20 to 0.50 wt%, Zr 0.10 to 0.50 wt%, Fe +
Si is contained in an amount of 0.10 to 0.60 wt% and Fe / Si is 1.5 or more, and further, Mn 0.01 to 0.10 wt% and Cr 0.01 to
A hollow profile of an Al-Zn-Mg-based alloy containing 0.10 wt% of one or two kinds, other impurities of 0.05 wt% or less and a total of 0.15 wt% or less, and the balance being aluminum. , Characterized in that the metal structure of the hollow profile is a fibrous structure along the extrusion direction,
A hollow Al-Zn-Mg alloy material with excellent strength and formability. 2. Zn 5.0-6.0 wt%, Mg 1.2-1.8 wt%
%, Cu 0.20 to 0.50 wt%, Zr 0.10 to 0.50 wt%, Fe +
Si is contained in an amount of 0.10 to 0.60 wt% and Fe / Si is 1.5 or more, and further, Mn 0.01 to 0.10 wt% and Cr 0.01 to
An Al-Zn-Mg-based alloy ingot containing 0.10 wt% of one or two kinds, other impurities of 0.05 wt% or less, and a total of 0.15 wt% or less, and the balance of aluminum, 420 to 520 Homogenize at 2 ℃ for 2-24 hours,
After that, extrude at 430 to 520 ° C, cool to room temperature, and then heat-treat as artificial aging treatment at 90 to 110 ° C for 2 to 12 hours for the first step and 120 to 170 ° C for 5 to 24 hours for the second step. Which is excellent in strength and formability.
A method for producing a hollow Zn-Mg alloy material.