JP2018111864A - Aluminum alloy forging material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy forging material excellent in strength and corrosion resistance.SOLUTION: There is provided an aluminum alloy forging material containing one or more kind selected from a group consisting of Mg:0.6-1.2 mass%, Si:0.7-1.5 mass%, Fe:0.01-0.5 mass%, Mn:0.05-0.8 mass%, Cr:0.01-0.5 mass% and Zr:0.01-to 0.2 mass% and the balance Al with inevitable impurities, and an aggregate structure thereof has area percentage of crystal particles with a <101> direction in 15° to a final forging direction of 65% or more, area percentage of crystal particles with a <001> direction in 15° to a final forging direction of 5% or less and an average crystal particle diameter of the crystal particles with a <101> direction in 15° to a final forging direction of 50 μm or less.SELECTED DRAWING: None

Description

  The present invention relates to an aluminum alloy forged material. More specifically, the present invention relates to a 6000 series aluminum alloy forged material suitable as an undercarriage part for a transportation device such as an automobile.

  In recent years, in response to global environmental problems caused by exhaust gas and the like, improvement in fuel efficiency has been pursued by reducing the weight of the body of a transport aircraft such as an automobile. In order to meet such demands, structural parts of transportation equipment such as automobiles, especially automobile underbody parts such as upper arms and lower arms, which are relatively excellent in strength and corrosion resistance, are 6000 series (Al-Mg) in the AA to JIS standards. -Si-based) aluminum alloy forgings are used.

  In order to further reduce the weight of an automobile, that is, to further reduce the thickness of the automobile underbody part, the automobile underbody part is required to have higher strength. Further, in view of reliability as a safety part, further improvement in corrosion resistance such as intergranular corrosion and stress corrosion cracking is required.

  In order to meet such demands, various methods for improving the composition and microstructure of 6000 series aluminum alloy forgings as materials for automobile undercarriage parts have been proposed.

  For example, in Patent Documents 1 and 2, as a metallurgical method for increasing the strength of an aluminum alloy material, after performing a solution treatment on a 6000 series aluminum alloy cast material, warm forging at about 150 to 250 ° C. It is disclosed that the strength is increased by repeatedly performing processing and then performing artificial aging treatment (artificial age hardening treatment).

JP 2014-218865 A JP 2008-196209 A

  However, in the methods disclosed in Patent Documents 1 and 2, when hot forging is performed at a high temperature of 500 ° C. or higher, the effect of increasing the strength is small, and the high strength and excellent strength required for the suspension parts are excellent. There was a possibility that sufficient corrosion resistance could not be obtained.

  The present invention has been made to meet such demands, and an object thereof is to provide an aluminum alloy forged material excellent in strength and corrosion resistance.

  Aspect 1 of the present invention includes Mg: 0.6 mass% to 1.2 mass%, Si: 0.7 mass% to 1.5 mass%, and Fe: 0.01 mass% to 0.5 mass%. And Mn: 0.05 mass% to 0.8 mass%, Cr: 0.01 mass% to 0.5 mass%, and Zr: 0.01 mass% to 0.2 mass%. 1 or 2 or more types, the balance being Al and unavoidable impurities, and the texture is such that the <101> orientation is within 15 ° with respect to the final forging direction and the area ratio of crystal grains is 65% The area ratio of the crystal grains whose <001> orientation is within 15 ° with respect to the final forging direction is 5% or less, and the crystal grains whose <101> orientation is within 15 ° with respect to the final forging direction Is an aluminum alloy forged material having an average crystal grain size of 50 μm or less.

  Aspect 2 of the present invention includes Cu: 0.05 mass% to 1.0 mass%, Ti: 0.01 mass% to 0.1 mass%, and Zn: 0.005 mass% to 0.2 mass%. The aluminum alloy forging according to aspect 1, further containing one or more selected from the group consisting of:

  ADVANTAGE OF THE INVENTION According to this invention, the aluminum alloy forging material excellent in intensity | strength and corrosion resistance can be provided.

Below, the aluminum alloy forging material which concerns on embodiment of this invention is demonstrated in detail.
The “forged material” in the embodiment of the present invention means an aluminum alloy forged material manufactured (plastically processed) by hot forging.

1. Structure As described below, the aluminum alloy forged material according to the embodiment of the present invention has excellent corrosion resistance by controlling the orientation distribution and crystal grain size of the texture in the final forging direction (that is, the warm working direction). High strength can be obtained while maintaining the above.

(The area ratio of crystal grains whose <101> orientation is within 15 ° with respect to the final forging direction is 65% or more, and the area ratio of crystal grains whose <001> orientation is within 15 ° with respect to the final forging direction is 5% or less)
The aluminum alloy forging according to the embodiment of the present invention may be referred to as crystal grains having a <101> orientation within 15 ° with respect to the final forging direction (hereinafter, simply referred to as “crystal grains having a <101> orientation”). ) Is 65% or more and the <001> orientation is within 15 ° with respect to the final forging direction (hereinafter, sometimes simply referred to as “<001> orientation crystal grain”). The area ratio is controlled to 5% or less. By controlling the area ratio of the <101> -oriented crystal grains and the <001> -oriented crystal grains in such a range, the <111> -oriented crystals included in the plane perpendicular to the final forging direction The grain ratio can be increased. In the aluminum alloy forging, the direction perpendicular to the final forging direction is the direction in which stress is most applied when used as an undercarriage part. Since the <111> orientation of the aluminum alloy is the highest strength orientation in all orientations, the proportion of <111> orientation crystal grains contained in the plane perpendicular to the final forging direction should be increased. Thus, it is possible to obtain a sufficiently excellent strength required as a suspension part.

The area ratio of the <101> oriented crystal grains is preferably 70% or more, and more preferably 75% or more.
The area ratio of the <001> oriented crystal grains is preferably 4% or less, more preferably 3% or less.

  On the other hand, when the area ratio of <101> oriented crystal grains is less than 65% or the area ratio of <001> oriented crystal grains is more than 5%, the in-plane direction perpendicular to the final forging direction Since the ratio of <111> -oriented crystal grains contained in is reduced, the strength is reduced.

(The average crystal grain size of crystal grains whose <101> orientation is within 15 ° with respect to the final forging direction is 50 μm or less)
In the aluminum alloy forged material according to the embodiment of the present invention, the average crystal grain size of the crystal grains whose <101> orientation is within 15 ° with respect to the final forging direction is 50 μm or less.
When manufacturing aluminum alloy forgings under general conditions, the grain structure after solution treatment is coarsened with <101> oriented grains, preventing the refinement of the structure and reducing the strength. To do.
As will be described later, the forged aluminum alloy according to the embodiment of the present invention reduces the average grain size of <101> -oriented grains by appropriately controlling the warm working process, and refines the entire structure. By doing, the intensity | strength of the aluminum alloy forging material obtained can be improved. The average crystal grain size of <101> oriented crystal grains is preferably 40 μm or less, and more preferably 30 μm or less.

  On the other hand, when the average crystal grain size of the <101> oriented crystal grains is more than 50 μm, the effect of improving the strength due to the refinement of the crystal grains cannot be obtained.

(Final forging direction)
In the embodiment of the present invention, the “final forging direction” means the pressing direction in the warm working process. The final forging direction can be specified from the aluminum alloy forging material as a product, for example, as follows.

  In the aluminum alloy forging material obtained by the forging process, a metal flow is formed according to the shape of the final product. Therefore, the final forging direction (that is, the warm working direction) can be specified based on the direction of the formed metal flow.

(Measuring method)
The area ratio of <101> -oriented crystal grains, the area ratio of <001> -oriented crystal grains, and the average crystal grain size of <101> -oriented crystal grains defined in the embodiment of the present invention are all determined by the EBSP method. Can be measured.

Specifically, an artificial aging treatment is applied to a forged material that has been subjected to solution treatment and quenching treatment, after being given strain by warm working. Then, from any position of the thickest part of the forged material after the artificial aging treatment and a longitudinal cross section of the maximum stress generation site where the maximum stress is generated during use, a measurement sample including the center of the wall thickness (for example, 3 pieces) ), And the sample is sliced parallel to the forged material surface, mechanically polished so that the center of thickness appears as the observation surface, and then electropolished after buffing to prepare a sample with a prepared surface To do. Then, using a scanning electron microscope (SEM) such as an FE-SEM (Field Emission Scanning Electron Microscope), crystal orientation measurement and crystal grain size measurement by EBSD may be performed. .
In addition, the area ratio of the crystal grain prescribed | regulated by embodiment of this invention can be considered equivalent to the volume ratio of the area | region measured by EBSD.

  Here, the thickness center portion is a plane parallel to the forged material surface at the thickness center (plate thickness center referred to as a plate) in a plan view of the forged material, and extends parallel to the forged material surface at the thickness center. It is an existing surface.

  As the EBSP measurement / analysis system, for example, EBSP: manufactured by TSL (OIM) or OXFORD (CHANNEL5) may be used. The measurement conditions by EBSD are, for example, 1.0 μm with respect to the measurement range of the rectangular region in which the length of the side of the forged material in the longitudinal direction is 1000 μm × the length of the side in the width direction is 320 μm. It is preferable to irradiate an electron beam with a pitch of. And it can determine by measuring the area ratio and average crystal grain diameter of each crystal grain per sample, and further averaging by the measured number of samples (three).

  The SEM / EBSP method is widely used as a texture measurement method, and is a crystal orientation analysis method in which an EBSP (Electron Back Scattering (Scattered) Pattern) system is mounted on an SEM such as an FE-SEM. . This measurement method has high measurement accuracy because of its high resolution as compared with other texture measurement methods. This method has an advantage that the average crystal grain size of the same measurement site of the forging can be simultaneously measured with high accuracy. The measurement itself of the texture and average crystal grain size of an aluminum alloy by the EBSP method has been conventionally known, for example, in publications such as JP2008-45192, JP4499369, JP2009-7617, In the present invention, this known method may be used.

  These disclosed EBSP methods project an EBSP onto a screen by irradiating an electron beam onto a sample made of an aluminum alloy set in the lens barrel of the SEM. This is taken with a high-sensitivity camera and captured as an image on a computer. In the computer, the orientation of the crystal is determined by analyzing this image and comparing it with a pattern obtained by simulation using a known crystal system. Each calculated orientation of the crystal is recorded as a three-dimensional Euler angle together with position coordinates (x, y) and the like. Since this process is automatically performed for all measurement points, tens of thousands to hundreds of thousands of crystal orientation data can be obtained at the end of measurement.

  Thus, the SEM / EBSP method has a wider field of view than the electron diffraction method using a transmission electron microscope, and has an average crystal grain size and an average crystal grain size of hundreds of crystal grains. There is an advantage that information on standard deviation or orientation analysis can be obtained within a few hours. In addition, since the measurement is performed by scanning a specified region at an arbitrary fixed interval instead of measurement for each crystal grain, there is also an advantage that each of the above-described information on the numerous measurement points covering the entire measurement region can be obtained. is there. Details of the crystal orientation analysis method in which the EBSP system is mounted on the SEM such as FE-SEM are described in detail in Kobe Steel Technical Report / Vol.52 No.2 (Sep.2002) P66-70.

  Here, in the case of a sample made of an aluminum alloy, a texture composed of many orientation factors (crystal grains having these orientations) shown below is usually formed, and there are crystal planes corresponding to them. These facts are described in, for example, “Cross Texture” (published by Maruzen Co., Ltd.) edited by Shinichi Nagashima, “Light Metal”, Vol. 43, 1993, P285-293, etc.

The formation of these textures differs depending on the processing and heat treatment methods even in the case of the same crystal system. In the case of the texture of the forged material by compression, it is expressed in the compression direction, and the crystal direction in the compression direction is expressed by a Miller index of <uvw> (uvw indicates an integer). Based on such expressions, typical crystal directions formed by compression of aluminum are as follows.
・ <001> orientation ・ <101> orientation ・ <111> orientation

  In the embodiment of the present invention, basically, those whose orientation deviation (inclination angle) is within ± 15 ° from these crystal directions belong to the same crystal direction (orientation factor). Further, the boundary between crystal grains in which the orientation difference (tilt angle) between adjacent crystal grains is 5 ° or more is defined as a crystal grain boundary.

  Then, using the crystal orientation analysis method in which the EBSP system is mounted on the SEM such as the above-described FE-SEM, the texture of the forged material is measured and included in the <101> orientation defined in the embodiment of the present invention. The area ratio of crystal grains, crystal grains included in the <001> orientation, and the like can be calculated.

  The average crystal grain size can also be measured and calculated at a grain boundary having an inclination angle of 5 ° or more. In other words, in the present invention, an orientation shift of less than ± 5 ° is defined as belonging to the same crystal grain, and a boundary between crystal grains having an orientation difference (tilt angle) of 5 ° or more between adjacent crystal grains is defined as a grain boundary. The average grain size can be calculated by the following formula. Average crystal grain size = (Σx) / n (where n is the number of crystal grains measured and x is the respective crystal grain size).

2. Chemical composition:
Next, the composition of the aluminum alloy forging material according to the embodiment of the present invention will be described. The aluminum alloy forging according to the embodiment of the present invention is made of a 6000 series aluminum alloy, and the component composition only needs to have a normal chemical composition as a 6000 series aluminum alloy.

(1) Si: 0.7 mass% to 1.5 mass%
Si, together with Mg, precipitates in the crystal grains mainly as an acicular β ′ phase (Mg ₂ Si) by artificial aging treatment, and contributes to high strength and high yield strength.
When there is too little content of Si, the precipitation amount at the time of an artificial aging treatment will decrease too much, and intensity | strength will fall. Further, due to the decrease in the amount of dissolved Si, recrystallization is likely to occur at a lower temperature during forging or solution treatment, and the texture formed during forging tends to disappear and the crystal grain structure becomes coarse. As a result, the area ratio of the <101> -oriented crystal grains decreases, the area ratio of the <001> -oriented crystal grains becomes excessive, the <101> -oriented crystal grains become coarse, and the strength decreases. Accordingly, the Si content is 0.7% by mass or more, and preferably 0.9% by mass or more.
On the other hand, if the Si content is too large, coarse single Si particles crystallize and precipitate during casting and during quenching after solution treatment, thereby reducing corrosion resistance and toughness. Moreover, excess Si increases and high corrosion resistance, high toughness, and high fatigue characteristics cannot be obtained. Furthermore, since elongation becomes low, hot forgeability and workability are reduced. Therefore, the Si content is 1.5% by mass or less, preferably 1.3% by mass or less.

(2) Mg: 0.6 mass% to 1.2 mass%
Mg also precipitates in the crystal grains mainly as an acicular β ′ phase together with Si by the artificial age hardening treatment, and contributes to high strength and high yield strength.
When there is too little content of Mg, the precipitation amount at the time of an artificial aging treatment will decrease too much, and intensity | strength will fall. In addition, the decrease in the amount of solid solution Mg makes it easier to recrystallize at a lower temperature during forging or solution treatment, and the texture formed during forging tends to disappear and the grain structure becomes coarse. As a result, the area ratio of <101> oriented crystal grains decreases, the area ratio of <001> oriented crystal grains becomes excessive, and the <101> oriented crystal grains become coarse, resulting in a decrease in strength. To do. Therefore, the Mg content is 0.6% by mass or more, preferably 0.7% by mass or more.
On the other hand, when there is too much Mg content, a coarse Mg containing compound will generate | occur | produce in the grain of a crystal | crystallization, and a grain boundary, and will reduce corrosion resistance and toughness. In addition, the strength (proof strength) at high temperatures becomes too high, and the hot forgeability and workability are lowered. Therefore, Mg content is 1.2 mass% or less, Preferably it is 1.1 mass% or less.

(3) Fe: 0.01% by mass to 0.5% by mass
Fe produces an intermetallic compound with Si to produce dispersed particles (dispersed phase), and hinders grain boundary movement after recrystallization, thereby suppressing recrystallization and preventing coarsening of crystal grains. In this way, there is an effect of refining crystal grains. Such an effect can be obtained if the Fe content is 0.01% by mass or more, and preferably 0.10% by mass or more.
On the other hand, if the content of Fe is too large, it becomes easy to form a coarse compound in the crystal grains and in the crystal grain boundaries, and the corrosion resistance and toughness are likely to be lowered. Moreover, since it is easy to contain Si in the intermetallic compound which Fe forms, the acicular (beta) 'phase produced | generated by the artificial aging treatment which requires Si will reduce, and intensity | strength will fall. Therefore, the Fe content is 0.5% by mass or less, preferably 0.40% by mass or less.

(4) Mn: selected from the group consisting of 0.05 mass% to 0.8 mass%, Cr: 0.01 mass% to 0.5 mass%, and Zr: 0.01 mass% to 0.2 mass% Mn, Cr and Zr, like Fe, form intermetallic compounds with Si to form dispersed particles (dispersed phase), prevent intergranular movement after recrystallization, and suppress recrystallization. In addition, by preventing the crystal grains from becoming coarse, there is an effect of making the crystal grains finer. In addition, due to this effect, recrystallization during forging or solution treatment is suppressed, and the texture formed during forging tends to remain and the grain structure becomes finer. Therefore, the area ratio of <101> oriented crystal grains can be increased, the area ratio of <001> oriented crystal grains can be reduced, and the <101> oriented crystal grains can be further miniaturized. When one or more of these elements are contained, if the Mn content is 0.05 mass% or more, the Cr content is 0.01 mass% or more, and the Zr content is 0.01 mass% or more, Such an effect can be obtained. Preferable contents of these elements are preferably Mn: 0.10% by mass or more, Cr: 0.10% by mass or more, and Zr: 0.05% by mass or more.
On the other hand, if the content of Mn, Cr and Zr is too large, it becomes easy to form a coarse compound in the crystal grains and in the crystal grain boundaries, and the corrosion resistance and toughness are liable to be lowered. Further, since Si is easily contained in the intermetallic compound formed by these elements, the acicular β ′ phase generated by the artificial aging treatment that requires Si is reduced, and the strength tends to be lowered. Therefore, when one or more of these elements are contained, the Mn content is 0.8% by mass or less, the Cr content is 0.5% by mass or less, and the Zr content is 0.2% by mass or less. And Preferably, Mn: 0.6 mass% or less, Cr: 0.3 mass% or less, Zr: 0.15 mass% or less.

(5) Balance In one preferred embodiment, the balance is Al and inevitable impurities. As unavoidable impurities, it is assumed that trace elements such as B, V, Na, Ca, In, Be, Sr, and Sc brought in depending on the conditions of raw materials, materials, manufacturing equipment, and the like are mixed.

  The aluminum alloy forging material according to the embodiment of the present invention is not limited to the above-described composition. As long as the characteristics of the aluminum alloy forging according to the embodiment of the present invention can be maintained, other elements may be further included as necessary. Other elements that can be selectively contained as described above are exemplified below.

(6) Selected from the group consisting of Cu: 0.05 mass% to 1.0 mass%, Ti: 0.01 mass% to 0.1 mass%, and Zn: 0.005 mass% to 0.2 mass% One or two or more kinds of Cu, Ti, and Zn are elements that improve the strength and toughness of the forged material, and may optionally be contained alone or in combination of two or more.

  Cu contributes to improving the strength and toughness of the forged material by solid solution strengthening, and also has an effect of significantly accelerating age hardening of the final product during the aging treatment. If the Cu content is too small, these strength improvement effects cannot be obtained. On the other hand, when there is too much content of Cu, the corrosion resistance and durability of an aluminum alloy forging material may be reduced. Therefore, if Cu is included, the Cu content is in the range of 0.05 to 1.0%.

  Ti has the effect of refining the crystal grains of the ingot and improving the strength and toughness by using the forged material structure as fine subcrystal grains. If the Ti content is too small, this effect cannot be exhibited. However, when there is too much content of Ti, a coarse crystallization thing will be formed and workability may be reduced. Therefore, when Ti is contained, the content of Ti is set to a range of 0.01 to 0.1%.

  In the artificial aging treatment, Zn precipitates and forms Zn-Mg precipitates with high density and improves strength and toughness. Further, the solid solution Zn has the effect of lowering the electric potential in the grains and reducing the corrosion form not from the grain boundaries but as the entire corrosion, resulting in reduction of the intergranular corrosion and stress corrosion cracking. On the other hand, when there is too much content of Zn, corrosion resistance may fall remarkably. Therefore, the Zn content when contained is in the range of 0.005 to 0.2%.

3. Manufacturing Method Next, a manufacturing method of the aluminum alloy forged material according to the embodiment of the present invention will be described.
The method for producing an aluminum alloy forged material according to an embodiment of the present invention is particularly characterized by a warm working process. Specifically, in the manufacturing method according to the embodiment of the present invention, the heating condition before warm working is maintained in a furnace heated to a temperature range of 150 to 250 ° C. for 20 to 120 minutes, and then the average strain rate is set. : Warm working under conditions of 0.1 / second or more and warm working rate: 5% or more. By controlling the conditions of warm working in this way, strain is easily introduced during warm working, strain is accumulated in crystal grains of <101> orientation, and a high strength effect due to dislocation strengthening is obtained. Furthermore, fine subcrystal grains are likely to be formed in the recovery process that occurs during the holding after the processing. As a result, crystal grains whose <101> orientation is within 15 ° with respect to the final forging direction can be refined, and the average crystal grain size can be reduced to 50 μm or less.
Also, by performing warm working under such conditions, the <101> orientation, which is a stable orientation during uniaxial compression or plane strain compression, can be developed. Thereby, the area ratio of the crystal grains whose <101> orientation is within 15 ° with respect to the final forging direction is set to 65% or more, and at the same time, the crystal grains whose <001> orientation is within 15 ° with respect to the final forging direction. The area ratio can be 5% or less. As a result, it is possible to increase the proportion of <111> oriented crystal grains included in the direction perpendicular to the final forging direction, which is the stress load direction when used as an undercarriage part. As a result, it is possible to obtain the strength of the aluminum alloy forged material having a sufficiently excellent strength as a suspension part.

(1) Casting process The casting process is a process of casting the molten metal adjusted to the above-described 6000 series aluminum alloy component composition into an ingot. Ordinary melt casting methods such as a continuous casting and rolling method, a semi-continuous casting method (DC casting method), and a hot top casting method may be appropriately selected for casting. The shape of the ingot is not particularly limited, and may be an ingot such as a round bar or a slab shape.

(2) Homogenizing heat treatment step The homogenizing heat treatment step is a step of subjecting the ingot to a homogenizing heat treatment. In the homogenization heat treatment step, it is preferable to hold at 450 to 580 ° C. for 2 hours or more.
If the holding temperature is less than 450 ° C., the temperature may be too low to homogenize the ingot. If the holding temperature exceeds 580 ° C., burning of the ingot surface may occur. In addition, after the homogenization heat treatment, an extrusion process prior to the hot forging process is unnecessary, but may be performed as necessary.

(3) Hot forging process The ingot after the homogenization heat treatment is reheated, the material temperature is in the range of 430 to 550 ° C, the mold temperature is in the range of 100 to 250 ° C, and the minimum thickness reduction rate is 25% or more. In addition, it is preferable to perform hot forging under the condition that the maximum thickness reduction rate is 90% or less.
Hot forging is forged into a final product shape (near net shape) of an automobile undercarriage part by a mechanical press or a hydraulic press. In the hot forging, hot forging is performed a plurality of times without reheating during forging or reheating as necessary, crushing, rough forging, finish forging, and so on.

  If the minimum thickness reduction rate is less than 25% as the hot forging rate, there is a possibility that the complicatedly shaped automobile undercarriage parts described above cannot be forged with high shape accuracy. On the other hand, when the maximum thickness reduction rate exceeds 90%, it is difficult to suppress recrystallization, and coarse recrystallized grains may be generated.

(4) Solution treatment and quenching treatment step After the hot forging step, solution treatment and quenching treatment are performed. The solution treatment is preferably held in a temperature range of 530 to 570 ° C. for 1 hour or more and 8 hours or less. If the solution treatment temperature is too low or the holding time is too short, the solution treatment is insufficient, the solid solution of the Mg-Si compound is insufficient, the amount of the precipitated compound in the subsequent artificial aging treatment is too small, and the strength is low. May decrease. The holding time may be long, but the effect is saturated after 8 hours.

  After the solution treatment, it is preferable to perform a quenching treatment from 500 ° C. to 100 ° C. at an average cooling rate of 25 ° C./second or more. Such an average cooling rate is preferably performed by water cooling, particularly water cooling (water bath immersion) in which cooling water is circulated while bubbling bubbles. With such a cooling method, the forged material can be uniformly cooled, so that distortion of the forged material can be prevented. If the cooling rate during this quenching process is low, Mg-Si compounds, Si, etc. are precipitated on the grain boundaries, and in the product after artificial aging, grain boundary fracture is likely to occur, and the toughness and fatigue characteristics may be reduced. There is. In addition, during the cooling, Mg—Si compound, Si, which is a stable phase, is also formed in the grains, and the precipitation amount of β phase and β ′ phase that are precipitated during artificial aging is reduced, and the strength may be lowered. is there.

  On the other hand, if the cooling rate at the time of quenching becomes too high, the amount of quenching distortion increases, and after quenching, a new straightening process becomes necessary, and the number of steps in the straightening process first causes a new problem. In addition, the residual stress increases, and a new problem arises that the dimensional and shape accuracy of the product is lowered. In this respect, in order to shorten the product manufacturing process and reduce the cost, hot water quenching at 30 to 85 ° C. in which quenching distortion is alleviated is preferable. Here, when the hot water quenching temperature is less than 30 ° C., the quenching strain increases, and when it exceeds 85 ° C., the cooling rate becomes too low, and the toughness, fatigue characteristics, and strength may be lowered.

(5) Warm working step The forged material thus obtained after solution treatment and quenching is warm-worked before artificial aging treatment.

  As warm working conditions, it is preferable to perform warm working within 48 hours after solution treatment and quenching treatment. Under such heating conditions, uniform and fine β ′ phase is first precipitated in the grains during heating and holding. Since warm processing is performed thereafter, non-uniform precipitation of β ′ phase due to dislocations introduced by warm processing is suppressed. In addition, the β ′ phase that has already precipitated pins the dislocation, suppresses the recovery of the dislocation during the artificial aging treatment, and secures the work hardening amount. In order to obtain such an effect, it is necessary to produce a large amount of β ′ phase during the heating and holding of the warm working, but the warm working was subjected to artificial aging over 48 hours after solution treatment and quenching treatment. In this case, because of the so-called negative effect, the formation of the β ′ phase is suppressed, and the above-described effect may not be obtained.

As heating before warm processing, it hold | maintains for 20 to 120 minutes in the furnace heated to the temperature range of 150-250 degreeC.
When the heating temperature before warm working is less than 150 ° C., dynamic recovery during working is difficult to proceed, and working texture other than <101> orientation is likely to develop by forging. The rate drops. As a result, the area ratio of <111> oriented crystal grains included in the direction perpendicular to the final forging direction is reduced, and the strength is reduced.
On the other hand, when the heating temperature before warm processing exceeds 250 ° C., the <001> orientation that is easy to develop in processing in a high temperature region develops, so that the area ratio of crystal grains of <001> orientation becomes excessive. In addition, the area ratio of the <111> oriented crystal grains included in the direction perpendicular to the final forging direction is reduced, and the strength is reduced. Further, in the processing in the high temperature region, the recovery of the introduced dislocation advances, and the sub-crystal grains tend to be coarsened, so that the <101> oriented crystal grains are coarsened and the strength is lowered.

Also, if the holding time in the furnace is less than 20 minutes, a sufficient heating effect cannot be obtained, and other than the <101> orientation develops, so that the area of the <101> orientation crystal grains decreases, and the strength increases. descend.
On the other hand, if the holding time in the furnace exceeds 120 minutes, precipitation proceeds and the amount of solid solution in the aluminum matrix decreases and the <001> orientation is easily developed. As a result, the area ratio becomes excessive. As a result, the area ratio of <111> -oriented crystal grains included in the direction perpendicular to the final forging direction decreases, and the strength decreases.

  As warming before warm working, warm working is performed without delay after being held in the furnace under the above conditions and taken out. In the manufacturing method according to the embodiment of the present invention, warm working is performed under conditions of an average strain rate of 0.1 / second or more and a warm working rate of 5% or more.

  By performing warm working with the strain rate and warm working rate in this range, strain is also accumulated in crystal grains with <101> orientation due to the introduction of strain during warm working, and the strength by dislocation strengthening In addition to obtaining an increase effect, fine subcrystal grains are likely to be formed in the recovery process that takes place during holding after processing. Therefore, crystal grains with <101> orientation can be refined, and the strength of the aluminum alloy forging can be improved. Also, by performing warm working under such conditions, it is possible to develop the <101> orientation by moderate dynamic recovery while suppressing recrystallization during forging to suppress the development of the <001> orientation. The area ratio of crystal grains with <101> orientation can be increased and the area ratio of crystal grains with <001> orientation can be decreased. As a result, it is possible to increase the ratio of <111> -oriented grains included in the direction perpendicular to the final forging direction, and to obtain an effect of improving the strength in the direction perpendicular to the forging direction of the undercarriage part. it can.

  When the average strain rate of warm working is less than 0.1 / sec, dynamic recovery during warm working becomes remarkable, the amount of accumulated strain decreases, and the effect of refining <101> oriented crystal grains is obtained. I can't. In addition, since the dynamic recovery during the warm working becomes remarkable, the <001> orientation is easily developed, so that the area ratio of the crystal grains of the <001> orientation is increased. Therefore, the strength of the finally obtained aluminum alloy forged material is lowered.

  If the warm working rate is less than 5%, the amount of strain introduced is small, and the effect of dislocation strengthening cannot be obtained. Furthermore, it becomes difficult to form fine subcrystal grains in the recovery process after processing, and the effect of miniaturizing crystal grains with <101> orientation cannot be obtained. Further, since the development of the <101> orientation does not proceed, the area ratio of the crystal grains with the <001> orientation becomes relatively large. Therefore, the strength of the finally obtained aluminum alloy forged material is lowered.

  The upper limit of the average strain rate and warm work rate of warm working is not particularly limited, but the upper limit of the average strain rate is 50 as an upper limit for industrially performing warm working in a temperature range of 150 to 250 ° C. / Second, the upper limit of the warm working rate is 60%.

  The mode of warm working is performed according to the shape of the forged material, and rolling and pressing with rolls can be applied if it is a simple shape such as a rod, plate, circle or cylinder, etc. If it is complicated shape, warm die forging, free forging, etc. may be used.

(6) Artificial aging treatment process Artificial aging treatment (artificial age hardening treatment) is performed after the above warm working. In order to prevent room temperature aging from proceeding, it is preferable to perform artificial aging treatment immediately after the warm working, for example, within one hour. This artificial aging treatment is preferably performed for 1 to 24 hours in a temperature range of 100 to 250 ° C.

However, even within this range of conditions, the optimum conditions should be selected according to the conditions of the previous process, such as composition, hot forging, solution treatment and quenching treatment, cold or warm processing, etc. If the artificial aging temperature is too low or too high, or the holding time is too short or too long, and the desired structure, high tensile strength and high yield strength, and high elongation are not met. You may not be able to get
In addition, an air furnace, an induction heating furnace, a nitrite furnace, etc. are used suitably for the above-mentioned homogenization heat treatment and solution treatment. Furthermore, an air furnace, an induction heating furnace, an oil bath, or the like is appropriately used for the artificial aging treatment.

  The forged material according to the present invention may be appropriately subjected to machining or surface treatment before and after the artificial aging treatment for automobile undercarriage parts.

  Those skilled in the art who have been in contact with the characteristics of the aluminum alloy forged material according to the embodiment of the present invention described above and the method for manufacturing the aluminum alloy forged material according to the present invention will perform a trial and error to manufacture the aluminum alloy forged according to the present invention using a manufacturing method different from the above-described manufacturing method. There is a possibility that a material can be obtained.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited by the following examples, and can be implemented with modifications within a range that can be adapted to the above-described gist, which are all included in the technical scope of the present invention. Is done.

1. Sample preparation Forged materials with the same aluminum alloy composition shown in Table 1 and the same manufacturing conditions until solution treatment and quenching treatment were subjected to warm working and artificial aging treatment under different conditions shown in Table 2 to produce automobile undercarriage parts The aluminum alloy forging material which becomes the raw material of was manufactured.

  Specifically, the ingot which consists of a chemical component of the aluminum alloy forging material shown in Table 1 was cast in common with each example. In addition, in each aluminum alloy example shown in Table 1, the hydrogen concentration in 100 g of Al was 0.10 to 0.15 ml in common. Here, in the display of the content of each element in Table 1, the display in which the numerical value column for each element is “−” indicates that the content is below the detection limit.

  The outer surface of each aluminum alloy ingot was chamfered 3 mm in thickness and cut into a round bar-like billet having a length of 120 mm × φ75 mm, followed by a homogenization heat treatment at 520 ° C. × 5 hours. Thereafter, the ingot was forcibly air-cooled using a fan at a cooling rate of 100 ° C./hour or more.

The hot forging of the ingot after homogenization heat treatment is common to each example, forging three times without reheating to the final wall thickness, the temperature at the start of forging is in the range of 500 to 520 ° C., mold temperature Was in the range of 170 to 200 ° C. and the thickness change rate of the forged material central part was 75% by a mechanical press using upper and lower molds.
In addition, in these hot forgings, in each example, in order to make the final forging material shape common in the warm processing described later, forging materials of each near net shape shape corresponding to each processing rate of warm processing. .

  These forged materials were cooled from 500 ° C. to 100 ° C. at an average cooling rate of 25 ° C./second or more after solution treatment at 550 ° C. for 5 hours using an air furnace in common with each example.

The forged material thus obtained after solution treatment and quenching treatment was subjected to warm working and artificial aging treatment under the conditions shown in Table 2.
Warm processing was performed under the heating conditions before warm processing shown in Table 2, and then warm processed by a mechanical press using upper and lower molds at the processing rate and average strain rate shown in Table 2 to obtain a final shape.

  The final shape of the manufactured forged material is the same as in each example, and has a generally triangular shape in plan view. The three ball joints that form the apexes of the triangle are narrow and thick (height) ) Is a peripheral part shape formed by a peripheral rib having a width of 60 mm and a thin central web having a wide wall thickness (height) of 31 mm and connected by an arm having a substantially H-shaped cross section.

2. Observation of structure For each alloy example, by the method described above, the area ratio of crystal grains whose <101> orientation is within 15 ° with respect to the final forging direction, and <001> orientation within 15 ° with respect to the final forging direction. The area ratio of a certain crystal grain and the average crystal grain size of the crystal grain whose <101> orientation was within 15 ° with respect to the final forging direction were measured. These results are shown in Table 3.

3. Mechanical properties Samples are taken from the thickness center portion of the thickest rib portion of the forged material and the maximum stress generation site, from this sample, including the thickness center at the center position in the thickness direction, Three tensile test pieces (L direction) were prepared so that the L direction extends in the longitudinal direction of the forged material, the outer diameter φ was 5 mm, the distance between the gauge points was 25 mm. And the mechanical property of 0.2% yield strength (MPa) and elongation (%) of this test piece was measured at room temperature, and the average value of these was obtained. The tensile speed was 5 mm / min up to 0.2% proof stress, and 20 mm / min after 0.2% proof stress.
Here, the acceptance criteria as a forging material for automobile underbody parts were 0.2% proof stress of 400 MPa or more and elongation of 10% or more. The results are shown in Table 3.

4). Corrosion resistance Corrosion resistance was evaluated in accordance with JIS H8711 according to the alternate dipping method. That is, stress of 300 MPa was applied to a test piece for stress corrosion cracking resistance evaluation (C-ring for SCC test), and the time (days) until the intergranular corrosion cracking occurred was measured regardless of the size of the crack. In the case of less than 30 days, it was evaluated as x, and in the case of 30 days or more and less than 60 days, it was evaluated as ○. The results are shown in Table 3.

4). Summary As shown in Tables 1 to 3, No. Examples 1 to 9 are examples that satisfy all the requirements (composition, production conditions, and structure) defined in the present invention. All of these inventive examples had a 0.2% proof stress of 400 MPa or more, an elongation of 10% or more, and excellent corrosion resistance.

  On the other hand, No. which is a comparative example. 10 to 19 had a 0.2% proof stress of less than 400 MPa, and the strength was poor.

  No. No. 10 is an example in which the warm working before artificial aging treatment was not performed, and the area ratio of <101> oriented grains and the area ratio of <001> oriented grains deviated from the definition of the present invention, and the strength was lowered.

  No. 11 is an example in which the heating temperature at the time of warm working is too low, and the area ratio of <101> oriented grains and the average grain size of <101> oriented grains deviated from the definition of the present invention, and the strength was lowered.

  No. No. 12 is an example in which the heating temperature at the time of warm working is too high. The area ratio of <001> oriented grains and the average grain size of <101> oriented grains deviated from the definition of the present invention, and the strength was lowered.

  No. 13 is an example in which the heating and holding time during the warm working is too short, and the average particle size of the <101> oriented grains deviated from the definition of the present invention, and the strength decreased.

  No. No. 14 is an example in which the heating and holding time at the time of warm working is too long, the area ratio of <001> oriented grains deviated from the definition of the present invention, and the strength was lowered.

  No. No. 15 is an example in which the working rate of warm working is too small, and the area ratio of <001> oriented grains and the average grain size of <101> oriented grains deviated from the definition of the present invention, and the strength decreased.

  No. No. 16 is an example in which the average strain rate of warm working is too small, and the area ratio of <001> oriented grains and the average grain size of <101> oriented grains deviated from the definition of the present invention, and the strength decreased.

  No. 17 is an example in which the content of Mg is too small. The area ratio of <101> oriented grains, the area ratio of <001> oriented grains, and the average grain size of <101> oriented grains are out of the definition of the present invention. Decreased.

  No. 18 is an example in which the content of Si is too small. The area ratio of <101> oriented grains and the area ratio of <001> oriented grains deviated from the definition of the present invention, and the strength was lowered.

  No. 19 is an example not containing any of Mn, Cr and Zn, and the area ratio of <101> oriented grains, the area ratio of <001> oriented grains, and the average grain size of <101> oriented grains are It was out of regulation and the strength decreased.

Claims (2)

Mg: 0.6% by mass to 1.2% by mass
Si: 0.7% by mass to 1.5% by mass;
Fe: 0.01% by mass to 0.5% by mass;
One selected from the group consisting of Mn: 0.05% by mass to 0.8% by mass, Cr: 0.01% by mass to 0.5% by mass and Zr: 0.01% by mass to 0.2% by mass or Containing two or more,
The balance is Al and inevitable impurities,
The organization is
The area ratio of the crystal grains whose <101> orientation is within 15 ° with respect to the final forging direction is 65% or more,
The area ratio of crystal grains whose <001> orientation is within 15 ° with respect to the final forging direction is 5% or less,
<101> orientation is within 15 ° with respect to the final forging direction, the average crystal grain size of the crystal grains is 50 μm or less,
Aluminum alloy forging. Cu: 0.05% by mass to 1.0% by mass,
Ti: 0.01% by mass to 0.1% by mass, and Zn: 0.005% by mass to 0.2% by mass
The aluminum alloy forging according to claim 1, further comprising one or more selected from the group consisting of: