JP5723192B2 - Aluminum alloy forging and method for producing the same - Google Patents

Description

The present invention relates to an Al—Mg—Si-based (6000-based) aluminum alloy forged material and a method for producing the same. Hereinafter, aluminum is also simply referred to as Al.

In recent years, with respect 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. For this reason, 6000 series (Al-Mg-Si series) Al alloy forgings, which are referred to in the AA to JIS standards, especially as structural parts or structural parts of transport equipment such as automobiles, especially undercarriage parts such as upper arms and lower arms. Is used. The 6000 series Al alloy forging has high strength and high toughness, and is relatively excellent in corrosion resistance. 6000 series A
The l-alloy itself is also excellent in recyclability in that the amount of alloying elements is small and scrap can be easily reused as a 6000-based Al alloy melting raw material.

Suspension parts such as suspensions are required to have high strength, high toughness, and high corrosion resistance. In this respect, the aluminum alloy forged material is an undercarriage forged part, which is superior in strength and high in reliability as compared with an aluminum alloy cast material or the like.

In recent years, these transport aircraft structural materials are also required to have higher strength and higher toughness after being made thinner in order to further reduce the weight of automobiles. For this reason, Al alloy castings and A
Various attempts have been made to improve the microstructure of l-alloy forgings.

For example, the average grain size of the crystallized 6000 series Al alloy cast material is reduced to 8 μm or less, and the dendrite secondary arm interval (DAS) is reduced to 40 μm or less, so that the Al alloy forging material has higher strength. It has been proposed to increase the toughness (see Patent Documents 1 and 2).

It has also been proposed to increase the strength and toughness of Al alloy forgings by controlling the average grain size and average spacing of crystallized materials in the crystal grains and grain boundaries of 6000 series Al alloy forgings. ing.
These controls can increase the corrosion resistance against intergranular corrosion and stress corrosion cracking. In accordance with the control of these crystallized substances, transition elements having a crystal grain refining effect such as Mn, Zr, Cr, etc. are added to refine the crystal grains or sub-crystal grains, thereby toughness and fatigue. Improvement of characteristics is also described in these proposals (see Patent Documents 3, 4, and 5).

However, these 6000 series Al alloy forgings tend to generate coarse crystal grains due to recrystallization of the processed structure in the forging and solution treatment steps. When these coarse crystal grains are generated, even if the microstructure is controlled, the strength and toughness cannot be increased, and the corrosion resistance also decreases. Moreover, in each of these patent documents, the processing temperature in forging is relatively low at less than 450 ° C., and in such low temperature hot forging, it is difficult to make the target crystal grains fine or sub-grains. Become.

On the other hand, in order to suppress the generation of coarse crystal grains recrystallized from the processed structure, Mn, Zr, C
It is known to start hot forging at a relatively high temperature of 450 to 570 ° C. after adding a transition element having a crystal grain refining effect such as r (Patent Documents 6 to 7, 8 to 8). 10).

These 6000 series Al alloy forgings usually use an Al alloy ingot (casting material) as a forging material, and after the ingot is homogenized and heat treated, it performs hot forging (die forging) such as mechanical forging and hydraulic forging. Thereafter, a so-called T6 tempering treatment including solution treatment and quenching treatment and artificial age hardening treatment is performed. On the other hand, in order to obtain a high strength of 350 MPa or more in proof stress and a high toughness of Charpy impact value of 20 J / cm ² or more, an extruded material once hot-extruded from the cast material is used as a forging material. Has been proposed (see Patent Documents 11, 12, and 13). In these techniques, in addition to the usually used cast material, the structure in the center of the thickness of the forged material cross section is made as a fine subcrystalline structure with an average crystal grain size of 10 μm or less, more excellent strength and toughness, or It has corrosion resistance.

Japanese Patent Laid-Open No. 07-145440 Japanese Patent Laid-Open No. 06-256880 Japanese Patent No. 3684313 JP 2001-107168 A JP 2002-294382 A JP 05247574 A JP 2002-348630 A JP 2004-43907 A JP 2004-292937 A JP 2004-292892 A JP 2004-68076 A JP 2007-169699 A JP 2007-177308 A

However, Patent Documents 11, 12, and 13 using an extruded material obtained by once hot-extruding a cast material as a forging material have a great limitation. That is, when hot forging is performed at a high processing rate with a minimum thickness reduction rate of more than 25% among the thickness reduction rates that differ depending on the forging parts by hot forging, the forging cross section Even in the thick central portion of the steel, recrystallization is likely to occur, and coarse recrystallized grains are generated, which makes it difficult to avoid a decrease in strength and toughness.

Therefore, in the technique using an extruded material obtained by once extruding a cast material as a conventional forging material (hereinafter referred to as an extrusion forging technique), a high strength of 350 MPa or more in proof stress and a Charpy impact value of 20 J / cm ² or more. In order to obtain such high toughness, hot forging must be performed at a small processing rate with a minimum thickness reduction rate of 25% or less. Actually, for example, in the example of Patent Document 12, an extruded billet (round bar) having a diameter of 20 mm is hot forged into a square bar shape with corners R each having a length of 15 mm, and the thickness is reduced. The rate is only about 25%.

Therefore, in these conventional extrusion forging techniques, the shape that can be hot forged at a small processing rate is largely limited and constrained to a simple forged product shape such as the aforementioned bar shape. However, undercarriage forged parts such as upper arm and lower arm that are widely used,
It has a complicated shape such that it has a substantially Y-shaped arm portion in plan view and ball joint portions (three places) at each of the three end portions of the arm portion. Therefore, inevitably, the minimum thickness reduction rate is a large processing rate exceeding 25%.

Further, these undercarriage parts such as suspension arms, in order to further reduce the weight, have a cross section consisting of a narrow and thick peripheral rib and a wide and thin central web.
Has the shape of a mold. And in recent years, in order to make such automobile underbody parts thinner and lighter, the web is made thinner or wider, and the ribs are made narrower.
It has a thickened shape (hereinafter also referred to as a lightweight shape). For this reason, for example, automobile undercarriage parts in which the thickness of the web is reduced to 10 mm or less have begun to be adopted.

Such a forged part of an automobile undercarriage having a light weight shape or a complicated shape inevitably has a large processing rate with a minimum thickness reduction rate exceeding 25%. For this reason, when hot forging is performed, as described above, it becomes easy to recrystallize even in the thickness center part of the cross-section of the forged material, and coarse recrystallized grains are generated, resulting in strength and toughness. The decline is inevitable. For this reason, with the conventional extrusion forging technology, it is impossible to manufacture such a light weight shaped automobile underbody part with high strength.

The present invention has been made paying attention to such circumstances, and its purpose is to improve the above-mentioned extrusion forging technology, and is a forging material obtained by hot forging an aluminum alloy extruded material, which has high strength. An object of the present invention is to provide a lightweight forged material with high corrosion resistance.

In order to achieve this object, the gist of the aluminum alloy forging material of the present invention is a forging material obtained by hot forging an aluminum alloy extruded material, in mass%, Si: 0.8 to 1.3%, Mg: 0.70 to 1.3%, Cu: 0.01 to 0.5%, Zn: 0.005 to 0.2%, Fe: 0.01 to 0.45%, Mn: 0.30% And 0.8% or less, Cr: 0.01 to 0.25%, Zr: 0.01 to 0.25%, Ti: 0.01 to 0.1%, respectively, and the Si and Mg Content of [Si%]-[Mg%] / 1.73> 0.25, and the composition of the balance Al and unavoidable impurities. A low-angle grain boundary having an inclination angle of 2 ° or more and less than 15 ° identified by measurement by the SEM-EBSP method in the entire cross-section excluding the surface layer portion Including an unrecrystallized region including a large-angle grain boundary having an inclination angle of 15 ° or more, and an average particle size of a region surrounded by a boundary having an inclination angle of 2 ° or more in the non-recrystallized region is 10 μm or less. The average area ratio of the non-recrystallized region to the entire cross-section excluding the surface layer portion of the forged material is 75% or more, and the average density of dispersed particles having a maximum length of 10 nm to 800 nm in the non-recrystallized structure region Is 10 pieces / μm ³ or more, and the average area ratio of crystallized substances having a maximum length of 0.5 μm or more is 2.5% or less.

Moreover, in order to achieve the said objective, the summary of the manufacturing method of this invention aluminum alloy forging material is the mass%, Si: 0.8 to 1.3%, Mg: 0.70 to 1.3%, Cu : 0.01-0
. 5%, Zn: 0.005 to 0.2%, Fe: 0.01 to 0.45%, Mn: more than 0.30%, 0.8% or less, Cr: 0.01 to 0.25% , Zr: 0.01 to 0.25%, T
i: each containing 0.01 to 0.1%, and the contents of Si and Mg are [Si%]-[Mg
%] / 1.73> 0.25, an aluminum alloy ingot having a composition consisting of the balance Al and inevitable impurities is subjected to a homogenization heat treatment in a temperature range of 450 to 580 ° C.
A hot extrusion process with an extrusion ratio of 2.4 or more and less than 3.7 is performed at a temperature of 400 to 580 ° C., and the extruded material is subjected to a material temperature in the range of 430 to 550 ° C. and a mold temperature of 100 to 250. ℃ range,
The forging material is subjected to hot forging under the condition that the minimum thickness reduction rate exceeds 25% and the maximum thickness reduction rate is less than 90%, and further subjected to solution treatment and quenching treatment and artificial aging treatment SEM- in the entire cross section excluding the surface layer portion of any three or more parts of this forging
An unrecrystallized region including a low-angle grain boundary with an inclination angle of 2 ° or more and less than 15 ° and a large-angle grain boundary with an inclination angle of 15 ° or more, identified by measurement by the EBSP method, is provided. The average grain size of the region surrounded by the boundary having an inclination angle of 2 ° or more in the region is set to 10 μm or less, the average area ratio of the non-recrystallized region to the entire cross section excluding the surface layer portion of the forged material is set to 75% or more, and In this non-recrystallized structure region, the average density of dispersed particles having a maximum length of 10 nm or more and 800 nm or less is 10 particles / μm ³ or more, and the average area ratio of crystallized substances having a maximum length of 0.5 μm or more is 2.5% It is as follows.

In the present invention, in the extrusion forging technique, the weight-reduced automobile undercarriage forged part (=
For example, the minimum thickness reduction rate is 25 out of the thickness reduction rates that differ depending on the forging material site.
Even if hot forging is performed at a large processing rate exceeding%, coarse recrystallized grains due to recrystallization do not occur in the entire cross section excluding the surface layer portion of the forged material, and a fine crystal grain structure is provided. . Therefore, in the present invention, in the extrusion forging technique, fine dispersed particles that suppress recrystallization and hinder grain boundary movement after recrystallization are formed at a higher density, and crystallization that becomes the nucleus of recrystallization is achieved. Suppresses the material and suppresses recrystallization and coarse grain growth in hot forging. As a result, the crystal grain structure in the entire cross section excluding the surface layer portion of the forged material is refined. In addition, the said surface layer part is a thin surface layer part with which the crystal grain is coarse and can distinguish with an internal structure | tissue with an optical microscope.

However, this refinement of the grain structure is also measured or defined as a low-angle grain boundary having an inclination angle of 2 ° or more and less than 15 ° by high-density formation of the fine dispersed particles and suppression of crystallized substances. Not only the crystal grains but also the entire non-recrystallized region including the crystal grains of the large tilt grain boundary having an inclination angle of 15 ° or more can be made more thorough. Therefore, the average grain size of the entire non-recrystallized region is 1
It is possible to reduce the size to 0 μm or less, and it is possible to increase the average area ratio of such an unrecrystallized region (unrecrystallized grain structure) to 75% or more of the entire cross-section of the forged material.

In addition, in the entire cross section excluding the surface layer portion of the forged material, coarse recrystallized grains due to recrystallization do not occur, and in order to have a fine crystal grain structure, the extruded material before hot forging In this structure, it is important that the fine dispersed particles defined in the present invention are formed with high density and crystallized substances are suppressed. However, it is difficult to measure these dispersed particles and crystallized materials with extruded materials that are intermediate materials during production, and even forged materials after forging or after tempering treatment. Even if it is a material, the size, density, or area ratio of the dispersed particles and the crystallized material in the extruded material does not change greatly. Therefore, the structure of the dispersed particles and the crystallized product in the present invention is determined by a forged material after forging or a forged material that has undergone a tempering treatment.

The present invention defines the structure of the entire area of the cross section at a plurality of locations of the forged material as described above, not the structure of only the local or partial region such as the central thickness of the forged material as in the prior art. As a result, in the present invention, the weight-reduced automobile undercarriage forged part can be made to have higher strength and higher corrosion resistance, and these characteristics can be guaranteed over the entire portion of the forged material. it can.

  Hereinafter, embodiments of the present invention will be described in detail.

(Chemical composition)
In the Al alloy forging material in the present invention, the Al alloy extruded material that is the material for this forging process, the Al alloy cast material that is the material for this extrusion process, the Al alloy molten material that is the material for this casting,
The chemical component composition of the Al alloy will be described below.

The chemical composition of the 6000 series Al alloy in the present invention needs to ensure high corrosion resistance and durability such as high strength and stress corrosion cracking resistance as the above-mentioned undercarriage forged parts. For this reason, the Al alloy composition in the present invention in the 6000 series Al alloy composition range is mass%.
Si: 0.8 to 1.3%, Mg: 0.70 to 1.3%, Cu: 0.01 to 0.5%,
Zn: 0.005 to 0.2%, Fe: 0.01 to 0.45%, Mn: more than 0.30%, 0.8% or less, Cr: 0.01 to 0.25%, Zr: 0.01 to 0.25%, Ti: 0.
The content of Si and Mg is [Si%]-[Mg%] / 1.
. 73> 0.25 is satisfied, and the balance is Al and inevitable impurities. In addition,
All percentages in the amounts of each element mean mass%.

Impurity elements that are inevitably mixed from melting raw material scrap and the like are allowed to contain a normal amount based on the upper limit of the JIS standard and the like within a range that does not impair the characteristics of the present invention. Next, the critical significance and preferable range of the content of each element will be described.

Mg: 0.70 to 1.3%
Mg is an essential element for precipitating in the crystal grains mainly as an acicular β ′ phase together with Si by artificial age hardening (aging treatment) and imparting high strength (proof strength) of automobile undercarriage parts. When there is too little content of Mg, the age hardening amount at the time of artificial aging treatment will fall. On the other hand, if the content of Mg is too large, the strength (yield strength) becomes too high and the forgeability is impaired. Further, a large amount of Mg—Si compound or simple substance Si is likely to precipitate during the quenching after the solution treatment, and on the contrary, the strength, toughness, elongation, corrosion resistance, etc. are lowered. Therefore, the Mg content is in the range of 0.70 to 1.3%.

Si: 0.8 to 1.3%
Si, together with Mg, is an essential element for precipitating mainly as an acicular β ′ phase by artificial aging treatment and imparting high strength (yield strength) when using automobile undercarriage parts. If the Si content is too small, sufficient strength cannot be obtained by artificial aging treatment. 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. In addition, excess Si increases, high corrosion resistance and high toughness,
High fatigue properties cannot be obtained. Furthermore, workability is also hindered, for example, elongation becomes low. Therefore, the Si content is in the range of 0.8 to 1.3%.

Relationship between Si content and Mg content Si and Mg satisfy the above-mentioned respective contents, and in order to increase the strength,
As a relational expression between [Si%] which is the content and [Mg%] which is the Mg content, [Si%] −
[Mg%] / 1.73> 0.25 is also satisfied. That is, as an excessive Si-type 6000 series alloy having an excessive Si content relative to the Mg content, the age-hardening property of the forged material after solution treatment and quenching treatment is enhanced, and the strength is increased by aging treatment.

Cu: 0.01 to 0.5%
Cu contributes to improvement of strength by solid solution strengthening, and also has an effect of significantly accelerating age hardening of the final product during aging treatment. When there is too little content of Cu, there will be no these strength improvement effects. On the other hand, if the Cu content is too large, the sensitivity of stress corrosion cracking and intergranular corrosion of the structure of the Al alloy forging is remarkably increased, and the corrosion resistance and durability of the Al alloy forging are lowered. Therefore,
The Cu content is in the range of 0.01 to 0.5%.

Zn: 0.005 to 0.2%
In the artificial aging treatment, Zn precipitates and forms Zn-Mg precipitates in a fine and high density to realize high strength. 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. However, when there is too much content of Zn, corrosion resistance will fall remarkably. Therefore, Zn
The content of is in the range of 0.005 to 0.2%.

Fe: 0.01 to 0.45%
Fe, together with Mn and Cr, produces fine dispersed particles (dispersed phase) composed of Al-Fe intermetallic compounds, hinders grain boundary movement after recrystallization, prevents crystal grains from becoming coarse, There is an effect to refine the grain. That is, fine dispersed particles are formed at a higher density to suppress recrystallization and grain growth in the forging material. As a result, the crystal grain structure in the entire cross section excluding the surface layer portion of the forged material is refined as defined in the present invention. If the Fe content is too small, these effects are not obtained. On the other hand, when there is too much content of Fe, coarse crystallization products, such as an Al-Fe-Si crystallization product, will be generated. These crystallized substances deteriorate fracture toughness and fatigue characteristics. Therefore, the Fe content is in the range of 0.01 to 0.45%.

Mn: More than 0.30% and 0.8% or less Mn generates dispersed particles (dispersed phase) composed of Al-Mn intermetallic compounds during the homogenization heat treatment and the subsequent hot forging, and is recrystallized. This has the effect of hindering the subsequent grain boundary movement, preventing the crystal grains from becoming coarse, and making the crystal grains finer. That is, fine dispersed particles are formed at a higher density to suppress recrystallization and grain growth in the forging material. As a result, the crystal grain structure at the center of the wall thickness of the cross-section of the forged material is refined as defined in the present invention. Mn is also expected to increase in strength and Young's modulus due to solid solution in the matrix. If the Mn content is too small, the dispersed particles are insufficient, and these effects cannot be expected. Recrystallization proceeds during hot forging, the crystal grains become coarse, and the strength and toughness decrease. On the other hand, when Mn is excessively contained, coarse intermetallic compounds and crystallized substances are likely to be formed during melting and casting, which becomes a starting point of fracture and causes toughness and fatigue characteristics to be lowered. For this reason, Mn is contained together with Cr and Zr, and more than 0.30% and 0.8% or less.

Here, the Al—Mn intermetallic compound and the Al—Fe intermetallic compound, which are dispersed particles, are represented by Al— (Fe, Mn, Cr) —Si, Fe, Mn, Cr, Si, Al and the like are known compounds that are selectively bonded according to their contents.

Cr: 0.01 to 0.25%
Cr, like Mn, generates dispersed particles (dispersed phase) during homogenization heat treatment and subsequent hot forging, preventing grain boundary migration after recrystallization, preventing coarsening of crystal grains, There is an effect of refining crystal grains. That is, fine dispersed particles are formed at a higher density to suppress recrystallization and grain growth in the forging material. If the Cr content is too small, these effects cannot be expected, recrystallization proceeds during hot forging, the crystal grains become coarse, and the strength and toughness decrease. On the other hand, excessive inclusion of these elements tends to generate coarse intermetallic compounds and crystallized substances during melting and casting, which becomes a starting point of fracture and causes toughness and fatigue characteristics to be lowered. Therefore, Cr is Mn
And Zr, and the content thereof is set to a range of 0.01 to 0.25%.

Zr: 0.01 to 0.25%,
Zr is also dispersed particles during homogenization heat treatment and subsequent hot forging, as with Mn and Cr.
(Dispersed phase) is generated, movement of the grain boundary after recrystallization is prevented, and coarsening of the crystal grains is prevented,
There is an effect of refining crystal grains. That is, finely dispersed particles are formed at a higher density,
Suppresses recrystallization and grain growth in the forging. If the Zr content is too small, these effects cannot be expected, recrystallization proceeds during hot forging, the crystal grains become coarse, and the strength and toughness decrease. On the other hand, excessive inclusion of these elements tends to generate coarse intermetallic compounds and crystallized substances during melting and casting, which becomes a starting point of fracture and causes toughness and fatigue characteristics to be lowered. For this reason, Zr
Is contained together with Mn and Cr, and the content thereof is in the range of 0.01 to 0.25%.

Ti: 0.01 to 0.1%
Ti has the effect of refining the crystal grains of the ingot to make the forged material structure fine subcrystal grains. T
If the content of i 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 the said workability will be reduced. Therefore, the Ti content is 0.0
The range is 1 to 0.1%.

In addition, the elements described below are impurities, and the contents described below are allowed. Hydrogen is easily mixed as an impurity, especially when the forging material has a low degree of processing.
Bubbles caused by hydrogen do not press-bond in forging or other processing, blisters are generated, and become the starting point of fracture, so that the toughness and fatigue characteristics are significantly reduced. In particular, in the undercarriage parts with increased strength, the influence of hydrogen is large. Therefore, it is preferable that the hydrogen concentration per 100 g of Al is 0.25 ml or less and the content is as small as possible. V and Hf are also likely to be mixed as impurities and hinder the characteristics of the undercarriage parts, so the total of these is made less than 0.3%. Further, although B is an impurity, like Ti, it has the effect of refining the crystal grains of the ingot and improving the workability during extrusion and forging. However, when the content exceeds 300 ppm, coarse crystallized matter is formed, and the workability is lowered. Therefore, B 2 is allowed to contain up to 300 ppm.

(Organization)
On the premise of the above alloy composition, the present invention performs hot forging at a large processing rate with a minimum thickness reduction rate of more than 25% for the weight-reduced automobile undercarriage forged part (= forged material). Even if the process is performed, a coarse recrystallized grain structure due to recrystallization does not occur in the entire cross section except for the surface layer part of the forged material, and a fine uncrystallized grain structure is provided. As a result, in the present invention, the weight-reduced automobile undercarriage forged part can be made to have higher strength and higher corrosion resistance, and these characteristics can be guaranteed over the entire portion of the forged material. it can.

  For this reason, in the present invention, the small inclination angle of 2 ° or more and less than 15 °, which is identified by the measurement by the SEM-EBSP method, in the entire cross section excluding the surface layer portion of any three or more portions of the forging. An unrecrystallized region including a grain boundary and a large-angle grain boundary having an inclination angle of 15 ° or more is provided, and an average particle size of a region surrounded by a boundary having an inclination angle of 2 ° or more in the non-recrystallized region is 10 μm or less. At the same time, the average area ratio of the non-recrystallized region to the entire cross-section of the forged material is 75% or more. This fine uncrystallized grain structure includes not only sub-grains measured or defined as small-angle grain boundaries with an inclination angle of 2 ° or more and less than 15 °, but also large-grain grain boundaries with an inclination angle of 15 ° or more. It is an unrecrystallized region including. In the present invention, the average crystal grains in the entire non-recrystallized region are refined to 10 μm or less. And the average area ratio with respect to the forging material cross section which such an unrecrystallized area | region (non-recrystallized grain structure) occupies for the cross-sectional center part of a forging material is increased with 75% or more.

In order to obtain such a fine crystal grain structure, the crystal grain structure of the crystal grain structure (actually the structure corresponding to the crystal grain structure of the extruded material before forging, which is measured by this extrusion A crystal having a maximum length of 10 nm / μm ³ or more and an average density of 10 particles / μm ³ or more and a maximum length of 0.5 μm or more). The average area ratio of items is 2.5% The following.

As will be described later in the examples, these measurements are performed by collecting the entire cross-sectional area of the forged material from three or more arbitrary portions of the forged material, and using them as measurement samples. Therefore, for example, if the size of the sample collection site of the forged material is 4 mm wide × 4 mm high, the entire area of 4 mm × 4 mm becomes the size of the sample = area, and the size of the sample depends on the cross-sectional area of the measurement site of the forged material Determined. After polishing this sample cross section (the entire cross section of the forged material), chemical etching, and using a 400 times optical microscope, the surface layer region (generally from the sample surface layer to the surface layer) where the recrystallized crystal grains occupy the sample cross section Near) and exclude it from the measurement target. Then, cut out 5 parts including the boundary between the recrystallized structure area and the non-recrystallized structure area measured with an optical microscope (particularly, it is difficult to determine the position of the boundary with an optical microscope) for observation. After sample preparation, the region including the boundary was analyzed using SEM-EBSP (1 field of view: 4 mm × 2 mm), the position of the boundary was clarified, and then the area ratio of the non-recrystallized structure region in the entire cross section ( %) Is calculated and averaged according to the measurement results of all the measurement sites (three or more locations). On the other hand, the crystallized product and dispersed particles were obtained by cutting out a sample from any three sites in the non-recrystallized texture region of the cross section and observing each structure by means described later, and by averaging the three sites. The average area ratio (%) and the average density (particles / μm ³ ) of the dispersed particles are calculated. Incidentally, since these crystallized substances and dispersed particles are greatly involved in the formation of the unrecrystallized structure in the entire cross-section of the forged material, of course, in order to investigate the influence and correlation, Measure these existence states.

In these structure rules, the average value when three or more arbitrary sites such as the ribs or webs of the forged material are measured satisfies the specified structure. The forging material differs greatly in the hot forging rate, that is, the thickness reduction rate, depending on the part. In this respect, the structure is also greatly different. However, even for such a forging, in the present invention, such a prescribed structure is satisfied as an average value of a plurality of locations when three or more arbitrary locations are measured. Further, the present invention is not partially or partially like the thickness center portion of the cross-section of the forged material, and does not generate a coarse recrystallized grain structure due to recrystallization in the entire cross-section excluding the surface layer portion, A fine crystal grain structure is provided. For this reason, high strength and high corrosion resistance can be guaranteed over almost the entire portion of the automobile undercarriage forged part (forged material) having the lightened shape. Incidentally, it is important that the dispersed particles and the crystallized product in the present invention are as defined in the structure of the extruded material before hot forging. However, as described above, the size, density, and area ratio of the dispersed particles and the crystallized material in the extruded material are greatly changed even for a forged material after forging or a forged material subjected to a tempering treatment. Therefore, the structure of the dispersed particles and the crystallized product in the present invention is determined by a forged material after forging or a forged material that has been subjected to a tempering treatment.

(Measurement of non-recrystallized region)
Subgrains measured or defined as small-angle grain boundaries with an inclination angle of 2 ° or more and less than 15 °;
Identification of the non-recrystallized region including a crystal grain of a large tilt grain boundary having an inclination angle of 15 ° or more is identified by measurement by the SEM-EBSP method in the entire cross section excluding the surface layer portion of the forged material. SEM
-The EBSP method is a field emission scanning electron microscope (Field Emission Scanning Electron Microscope).
scope: FESEM) and backscattered electron diffraction image [EBSP: ElectronBack Scattering (Scattered) Pa
ttern] Crystal orientation analysis method equipped with the system. By observing the entire cross section of the forged material except the surface layer portion with the optical microscope, the surface layer region where the recrystallized crystal grains are coarse is determined, and the boundary between the recrystallized structure region and the non-recrystallized structure region is determined. And, in particular, in the optical microscope, cut out five parts including the part that preferentially determines the position of the boundary,
After adjusting the sample for observation, using SEM-EBSP, an unrecrystallized structure including a low-angle grain boundary with an inclination angle of 2 ° or more and less than 15 ° and a large-angle grain boundary with an inclination angle of 15 ° or more. The boundary region of the region is accurately analyzed (1 field of view: 4 mm × 2 mm). Then, together with the observation result of the optical microscope, the non-recrystallized structure region is clarified, and the area ratio (%) of the non-recrystallized structure region in the entire cross section is calculated.

More specifically, in the preparation of the observation sample of SEM-EBSP, the observation sample (cross-sectional structure) of the optical microscope is further mechanically polished and electrolytically etched to make a mirror surface. And FESEM
The surface of the sample that was set in the lens barrel was irradiated with an electron beam on the screen.
Project SP. 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. The calculated crystal orientation 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 in the cross section of the forged material are obtained at the end of the measurement.

From such crystal orientation data in the forged material cross section, the unrecrystallized region and the recrystallized region are clearly distinguished and identified. The non-recrystallized region is a region of sub-crystal grains defined as small-angle grains of less than 15 °, a region composed of large-angle particles of 15 ° or more, and a complex structure region having small-angle particles in large-angle particles. The average size of the region (grain) surrounded by the boundary of 2 ° or more is 10 μm or less. In addition, the region composed of grains with a large inclination of 15 ° or more is not newly generated fine recrystallized grains, but during the extrusion process or the hot forging, the small inclination grains generated during the processing are rotated during the processing, This is presumed to be caused by an increase in the orientation difference between the boundaries. On the other hand, the recrystallized structure region is
It consists of large-angle grains exceeding an average size of 10 μm, and some recrystallized grains with a size of several mm are also generated, such as the surface layer portion of the forged material that is excluded from the structure measurement target. From this result, the area ratio of the non-recrystallized region in the entire cross-section of the forged material can be obtained.

On the other hand, the average crystal grain size of the non-recrystallized region is the SE on the mirrored surface of the sample.
In the non-recrystallized region identified by the M-EBSP method, polarized microscopic observation is performed with an optical microscope of 400 times, followed by the crystal grains in the non-recrystallized region, and the particle size is measured by image analysis. The average crystal grain size is calculated.

Incidentally, the fine subgrain structure with an average crystal grain size of 10 μm or less in Patent Documents 11 to 13 is a subcrystal grain usually defined as a low-angle grain boundary with an inclination angle of less than 15 °, and an inclination angle However, it is only an unrecrystallized grain structure excluding a large tilt grain boundary of 15 ° or more. That is, the non-recrystallized grain structure as used in the present invention is a sub-crystal grain measured or defined as a low-angle grain boundary with an inclination angle of 2 ° or more and less than 15 °, and a large-angle grain boundary with an inclination angle of 15 ° or more. This is a region including crystal grains. Therefore, in Patent Documents 11 to 13 in which only the subgrain structure is defined without including a large-angle grain boundary having an inclination angle of 15 ° or more, an unrecrystallized grain structure is not specified, and the inclination angle is 15 ° or more. Depending on the size of the crystal grain and the area ratio of the large tilt grain boundary, it inevitably deviates from the definition of the present invention.

In addition, the measurement of the average crystal grain size and area ratio of the sub-grain structure of Patent Documents 11 to 13 is also possible.
With only an optical microscope of about 0 times, the color of the recrystallized grains with large size is easy to reflect the light color and the color density of the crystal grains including other subcrystals with small size They are identified by the difference in shading or the difference in size. For this reason, the measurement must be inaccurate as compared with the identification of the grain structure by the SEM-EBSP method of the present invention, including the removal of the large-angle grain boundary having an inclination angle of 15 ° or more. .

(Dispersed particles and crystals)
In the present invention, in order to guarantee the above structure even if the minimum thickness reduction rate in the hot forging process of the underweight forged product of the lightweight shape exceeds 25%, in the present invention, In addition to suppressing recrystallization and preventing grain boundary migration after recrystallization, fine dispersed particles are formed at a higher density, and crystallized substances that are the core of recrystallization are suppressed, so that Suppresses crystal and coarse grain growth.

(Dispersed particles)
In the present invention, the average density of dispersed particles having a maximum length of 10 nm or more and 800 nm or less is set to 10 as an average value when three arbitrary portions of the non-recrystallized structure region in the SEM-EBSP observation sample are measured. Pieces / μm ³ or more. The maximum length of the irregularly dispersed particles is the longest axis or the longest side.

In order to improve strength and toughness, it is important to suppress recrystallization of the entire cross-section of the forged material, which is easy to recrystallize when the minimum thickness reduction rate exceeds 25%. Therefore, in the present invention, dispersed particles that suppress recrystallization at the most recrystallized portion are defined to suppress recrystallization and to suppress coarsening of crystal grains due to recrystallization. This suppresses grain boundary breakage due to recrystallization and coarsening of crystal grains, and improves the strength and toughness of automobile undercarriage forged parts.

The dispersed particles referred to in the present invention are Al—Mn, Al—Cr, and Al—Zr intermetallic compounds. If these dispersed particles are finely and densely dispersed, they have the effect of hindering the grain boundary movement after recrystallization, so that the effect of making the crystal grains finer is prevented while preventing recrystallization and coarsening of the crystal grains. Is expensive. However, in the normal manufacturing process, if the temperature rise rate or cooling rate is too small in the heat history such as casting, homogenizing heat treatment, hot forging, solution treatment and quenching treatment, depending on the production conditions, it tends to be coarse. . For this reason, the effect of suppressing recrystallization (grain refinement) is lost, and on the contrary, the fracture toughness and fatigue characteristics of automobile undercarriage parts may be deteriorated.

Therefore, in the present invention, the maximum length and the number (density) are defined as the size of the dispersed particles so that the dispersed particles in the tissue are finely and densely dispersed and not coarsened.

(Measurement of dispersed particles)
Here, the maximum length and the average density of the dispersed particles are one cross section of TEM (transmission electron microscope) at a magnification of 20000 times at any three sites in the non-recrystallized structure region in the SEM-EBSP observation sample. Observe 9 fields of view. This is subjected to image analysis, and the maximum length of each dispersed particle and the average density (10 particles / μm ³ ) of dispersed particles having a maximum length of 10 nm to 800 nm are measured. At this time, the sample thickness of the TEM observation part is almost constant at 200 nm.

(Crystal)
Next, in the present invention, the average value of crystallized substances having a maximum length of 0.5 μm or more as an average value when measuring three arbitrary sites in the non-recrystallized structure region in the above-described SEM-EBSP observation sample. 2.5% area ratio It regulates as follows. The maximum length of an amorphous crystallized product is the longest axis or the longest side.

In order to suppress recrystallization of the entire cross-section of the forged material, which is easy to recrystallize when the minimum thickness reduction rate exceeds 25%, a crystallized substance that becomes the core of recrystallization during forging of that portion Suppression is important in improving strength and toughness. Incidentally, the crystallized product as referred to in the present invention is a complex intermetallic compound typically composed of Si, Fe, Mn, Cr, Zr and the like. In the present invention,
Since these contents are relatively large, it is easy to form coarse crystallized materials that are the starting point of fracture and deteriorate the characteristics of the forged product. There is.

(Measurement of crystallized matter)
Here, the maximum length and the average area ratio of the crystallized materials are the SEM (scanning electron microscope) with a magnification of 200 times at any three sites in the non-recrystallized texture region in the SEM-EBSP observation sample.
Then, 25 visual fields per cross section (75 visual fields or more with one forging material) are observed and photographed, and the obtained image is calculated by digital processing.

(Production method)
Next, a method for producing an Al alloy forged material in the present invention will be described. Al in the present invention
The alloy forging manufacturing process itself can be manufactured by a conventional method. However, in order to increase the strength, toughness, and corrosion resistance of an aluminum alloy ingot having the above-described composition even if it is a forged automotive underbody forged part having a structure described above, After performing a homogenization heat treatment in a temperature range of ˜580 ° C., a hot extrusion process with an extrusion ratio of 2.4 or more and less than 3.7 is performed at a temperature of 400 to 580 ° C. Is in the range of 430-550 ° C, mold temperature is in the range of 100-250 ° C, the minimum thickness reduction rate is over 25%, and the maximum thickness reduction rate is less than 90%. Preferably, the forged material is subjected to solution treatment and quenching treatment and artificial aging treatment. The extrusion ratio is defined as ln (A / B) using the cross-sectional area A before extrusion and the cross-sectional area B after extrusion. The thickness reduction rate is defined as {(AB) / A} × 100% using the diameter A of the extruded material and the thickness B after forging. A is the diameter when the cross section of the extruded material is circular, and A is the maximum length within the cross section in other shapes.

(casting)
When casting a molten Al alloy melt adjusted within the specific Al alloy component range, a normal melting casting method such as a continuous casting rolling method, a semi-continuous casting method (DC casting method), or a hot top casting method is appropriately used. Select and cast.

However, when casting an aluminum alloy melt having the specific Al alloy component range, an average cooling rate of 100 ° C / ° C is used in order to refine the crystallized material and the dendrite secondary arm spacing (DAS). It is preferable to set it as s or more.

(Homogenization heat treatment)
The homogenized heat treatment of the cast ingot is carried out by keeping it in a temperature range of 450 to 580 ° C. for 2 hours or more. If the homogenization heat treatment temperature is less than 450 ° C., the temperature is too low to homogenize the ingot, and if the homogenization heat treatment temperature exceeds 580 ° C., burning of the ingot surface occurs.

(Hot extrusion)
After this homogenization heat treatment, the temperature is adjusted as it is, or it is once cooled to room temperature and reheated, and at a temperature of 400 to 580 ° C., under an extrusion ratio of 2.4 or more and less than 3.7. Then, hot extrusion of the ingot is performed to process the extruded material. When the hot extrusion temperature exceeds 580 ° C., burning of the surface of the extruded material occurs and the possibility of generating coarse recrystallized grains increases. When the hot extrusion temperature is less than 400 ° C., the load during extrusion increases, and the surface of the extruded material is easily damaged. If the extrusion ratio is too high, there is a high possibility that coarse recrystallized grains will be generated, and it will be difficult to refine the crystal grain structure even in the entire region of the forged material cross section or even in the thickness center.
On the other hand, if the extrusion ratio is too small, the content of the crystallized product-forming element is relatively large, the crystallized product cannot be refined, and there is a risk that elongation, toughness, fatigue properties, and the like are lowered.

(Hot forging)
The extruded material is reheated, the material temperature is in the range of 430 to 550 ° C., and the mold temperature is 100 to 25.
Hot forging is performed in the range of 0 ° C., with the minimum thickness reduction rate exceeding 25% and the maximum thickness reduction rate being less than 90%. Hot forging is forged into the final product shape (near net shape) of automobile undercarriage parts using mechanical press forging or hydraulic press.
This shape is the above-described weight reduction shape, for example, a relatively narrow and thick peripheral rib,
It is processed into an automobile undercarriage part having an arm portion having a substantially H-shaped cross section composed of a thin web having a thickness of 10 mm or less and a relatively wide central web.

Automotive undercarriage parts can be reheated without reheating during forging or as needed,
Rough forging, intermediate forging, finish forging, and hot forging are performed multiple times. If the material temperature after each forging and after the final forging is less than 430 ° C., in the forging and solution treatment process, the processed structure may be recrystallized to generate coarse crystal grains. When these coarse crystal grains are generated, even if the microstructure is controlled, the strength and toughness cannot be increased, and the corrosion resistance also decreases.
Moreover, in hot forging at low temperature, it is difficult to refine crystal grains that target the entire region of the cross-section of the forged material. On the other hand, when the material temperature exceeds 550 ° C., burning of the forged material surface occurs and the possibility of generating coarse recrystallized grains increases.

If the mold temperature is less than 100 ° C., the material temperature becomes too low, and in the forging and solution treatment process, the processed structure may be recrystallized to generate coarse crystal grains. Mold temperature is 25
When the temperature exceeds 0 ° C., the material temperature becomes too high, and the forging material surface is burned and seized, and the possibility of generating coarse recrystallized grains increases.

If the minimum thickness reduction rate is 25% or less as the processing rate of hot forging that differs depending on the part, the above-described lightweight (complex) shaped automobile underbody part cannot be forged. On the other hand, when the maximum thickness reduction rate is 90% or more, there is a high possibility that coarse recrystallized grains are generated.

(Refining treatment)
After this hot forging, tempering treatment of T6, T7, T8, etc. for obtaining the necessary strength, toughness and corrosion resistance as an automobile undercarriage part is appropriately performed. T6 is an artificial age hardening treatment that obtains the maximum strength after solution treatment and quenching treatment. T7 is an excessive age hardening treatment that exceeds the artificial age hardening treatment conditions for obtaining the maximum strength after solution treatment and quenching treatment. T8 is an artificial age hardening treatment for obtaining the maximum strength by performing cold working after solution treatment and quenching treatment.

The solution treatment is held in a temperature range of 530 to 570 ° C. for 20 minutes to 8 hours. If the solution treatment temperature is too low or the time is too short, the solution treatment is insufficient, the solid solution of the MgSi compound becomes insufficient, and the strength decreases.

After this solution treatment, it is preferable to perform a quenching treatment from 500 ° C. to 40 ° C. at an average cooling rate of 25 ° C./s or more. In order to secure this average cooling rate, it is preferable that the cooling during the quenching process is performed by water cooling. When the cooling rate during the quenching process is lowered, MgSi compounds, Si, and the like are precipitated on the grain boundaries, and in the product after artificial aging, grain boundary fracture is likely to occur, and toughness and fatigue characteristics are lowered. In addition, during the cooling, the stable phase M
Since the gSi compound and Si are formed and the amount of β phase and β ^′ phase precipitated during artificial aging is reduced, the strength is lowered.

However, on the other hand, when the cooling rate is increased, the amount of quenching distortion increases, and a new correction process is required after quenching, and there is a new problem that the number of steps in the correction process increases. 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 50 to 85 ° C. in which quenching distortion is alleviated is preferable.
Here, when the hot water quenching temperature is less than 50 ° C., the quenching strain increases, and when it exceeds 85 ° C., the cooling rate becomes too low, and the toughness, fatigue characteristics, and strength decrease.

The artificial age hardening treatment after solution treatment and quenching treatment is performed within the temperature range of 160 to 210 ° C. and the holding time of 20 minutes to 8 hours within one hour in order to prevent room temperature aging after quenching treatment. Select the tempering conditions such as T6, T7, T8.

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. Further, an air furnace, an induction heating furnace, an oil bath, or the like is appropriately used for the artificial age hardening treatment.

The automobile underbody parts of the present invention may be appropriately subjected to machining, surface treatment, and the like necessary as automobile undercarriage parts before and after the tempering treatment.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

Next, examples of the present invention will be described. The ingot of aluminum alloy composition shown in Table 1 (which is also the final forged product composition) is subjected to homogenization heat treatment, hot extrusion, and hot forging under the conditions shown in Table 2. The forged material was manufactured by solution treatment, quenching treatment and artificial aging treatment. And the structure, mechanical characteristics, and corrosion resistance of this forged material were measured and evaluated as shown in Table 3.

More specifically, the ingot of the aluminum alloy composition shown in Table 1 (also the final forged product composition)
Was cast by semi-continuous casting method. In addition, in each aluminum alloy alloy example shown in Table 1, the hydrogen concentration in 100 g of Al was all 0.10 to 0.15 ml.

The outer surface of each of these Al alloy ingots was chamfered to a thickness of 3 mm, cut to a length of 500 mm, and then subjected to a homogenization heat treatment under each condition shown in Table 2. After the homogenization heat treatment, forcible air cooling was commonly performed using a fan at a cooling rate of 100 ° C / hr or more. The hot extrusion was performed by ordinary direct extrusion under the conditions shown in Table 2, and after extrusion, forced air cooling was performed using a fan. Hot forging is performed by a mechanical press using upper and lower molds with the mold temperature adjusted to a range of 100 to 250 ° C. under the conditions shown in Table 2, and the final meat is formed with a clearance of 1.5 to 3 mm in the flash land. Forged to thickness 3 times without reheating. This forged material was subjected to solution treatment using an air furnace and water quenching under each condition shown in Table 2, and then subjected to artificial aging treatment under each condition shown in Table 2, respectively. did.

The manufactured forged material has a ball joint part (one place) and a rubber bush part (two places) at the apex part of each triangle as an automobile undercarriage part having the light weight shape, and these are substantially triangular overall shapes. It was made into the shape which connected by the arm part which consists of each. The arm portion is composed of a thin web portion and a thick rib portion having a thickness of 10 mm or less extending in the longitudinal direction of the arm portion at the center in the width direction. In such an automobile undercarriage part, each measurement sample was collected from three portions of the thick rib portion where the maximum stress is likely to occur and close to the one ball joint portion. This rib part is a part that should have strength and toughness. If the rib part is prone to coarsening of crystal grains, it is lightweight while maintaining the strength of the arm part and thus the entire automobile undercarriage component. It becomes difficult to make it easier.

  Each cross section of the measurement sample collected from the three locations was polished and then chemically etched, and the recrystallized surface layer region occupying the sample cross section was determined using a 400 × optical microscope and excluded from the measurement target. After that, five parts including the boundary between the recrystallized structure region and the non-recrystallized structure region, which are difficult to determine the position of the boundary with an optical microscope, are cut out preferentially, and after adjusting the sample for observation, SEM -The region including the boundary was analyzed using EBSP (1 visual field: 4 mm x 2 mm), the position of the boundary was clarified, and then the area ratio (%) of the non-recrystallized structure region in the cross section was calculated. Then, the average crystal grain size of the non-recrystallized region was measured and calculated through image analysis by performing polarization micro observation with the optical microscope. As a result, in the example having the non-recrystallized region in the cross section of the forged material, including the invention example and the comparative example, the average particle size of the region surrounded by the boundary of the tilt angle of 2 ° or more in this non-recrystallized region is all 10 μm or less. Met.

On the other hand, for the crystallized product and dispersed particles, a sample was cut out from any three sites from the non-recrystallized texture region of the cross section, and each structure was observed and the average value was calculated as the average area ratio of crystallized product (%, Table 3). The average area ratio is indicated), and the average density of dispersed particles (number / μm ³ , indicated as the average number in Table 3) was calculated.
And even if these organization rules prescribed in the present invention are satisfied as an average value, for each one of the three locations, each of these locations is individually defined in the present invention. X which does not satisfy, x which satisfies the organizational rules of the present invention individually even in one place
Those satisfying the organizational rules of the present invention were evaluated as “◎” individually at two or more locations (two or all three locations).

(Mechanical properties)
Tensile test specimens (L direction) are prepared from the measurement samples taken from three locations of the ribs, and mechanical properties such as tensile strength (MPa), 0.2% proof stress (MPa), and elongation (%) are measured. And each average value of these three places (three test pieces) was calculated | required.

(Intergranular corrosion sensitivity)
In order to evaluate corrosion resistance, an intergranular corrosion susceptibility test in accordance with the provisions of the former JIS-W1103 was performed on measurement samples (three test pieces) collected from three portions of the rib portion. The test condition was that the sample was pulled up after 6 hours of immersion in the test solution, and then the cross section of the test piece was cut and polished, and the corrosion depth from the sample surface was measured using an optical microscope. The magnification is x100 and the corrosion depth is
Less than 200 μm was evaluated as “◯” as minor corrosion. Moreover, the case where it exceeded 200 μm was evaluated as “×” as large corrosion.

As is apparent from Table 3, the composition and production conditions of each invention example are within the preferred ranges. As a result, the inventive examples satisfy these organizational rules defined in the present invention individually with at least one place together with the average value. As a result, the inventive examples have a minimum tensile strength of 394 MPa or more, and are excellent in intergranular corrosion sensitivity.

On the other hand, Comparative Examples 16 to 25 manufactured out of the optimum manufacturing conditions have compositions within the scope of the present invention, but do not satisfy the present invention organization regulations or have not been manufactured into forged materials. Therefore,
Even if it can be manufactured, either the strength or corrosion resistance of the comparative example is significantly inferior to that of the inventive example.

In Comparative Example 16, the soaking temperature was too high, and local melting (burning) occurred. In Comparative Example 17, the soaking temperature was too low, the homogenization heat treatment was insufficient, the area ratio of the crystallized substance was increased, and the elongation was lowered. In Comparative Example 18, the extrusion temperature was too high, and burning occurred on the sample surface layer. In Comparative Example 19, the extrusion temperature was too low, the extrusion load was high, and the surface layer was frequently scratched. In Comparative Example 20, the extrusion ratio was too high, and the recrystallized area became large, and the strength and elongation decreased. In Comparative Example 21, the extrusion ratio was too low, the area ratio of the crystallized product increased, and the elongation decreased. In Comparative Example 22, the forging temperature was too high, and the burning and seizure occurred. In Comparative Example 23, the forging temperature was too low, the recrystallized region was large, and the strength was particularly reduced. In Comparative Example 24, the forging rate was too high, and the recrystallized region became large, and the strength and elongation decreased. In Comparative Example 25, the solution temperature was too high, and the burning occurred. In the comparative examples in which the burning and scratches occurred, the measurement and investigation of the structure and characteristics as in the invention examples were omitted.

Further, although Comparative Examples 1 to 15 which are Al alloys having compositions outside the scope of the present invention are manufactured within the optimum manufacturing conditions, either strength or corrosion resistance is remarkably inferior to that of the inventive examples.

In Comparative Example 1, Zr is too small. In Comparative Example 2, Cr is insufficient. In Comparative Example 3, Mn is insufficient. For this reason, as shown in Table 3, the recrystallized region becomes large and the strength, elongation, and corrosion resistance are reduced. Comparative Example 4 is excessive in Zr. Comparative Example 5 is excessive in Cr. In Comparative Example 6, Mn is excessive. For this reason, as shown in Table 3, the area ratio of the crystallized substance increases and the decrease in elongation is particularly remarkable. In Comparative Example 7, the amount of Si is excessive, and as shown in Table 3, the area ratio of the crystallized product is increased and the elongation is decreased. In Comparative Example 8, the Si content is low, and as shown in Table 3, the strength is low. In Comparative Example 9, Fe is excessive, and as shown in Table 3, the area ratio of the crystallized product is increased and the elongation is remarkably reduced. In Comparative Example 10, Fe is insufficient, and as shown in Table 3, the recrystallized region is large and the strength is low. Comparative Example 11 is excessive Cu, and as shown in Table 3, the corrosion resistance is significantly reduced. In Comparative Example 12, Cu is too small and the strength is low as shown in Table 3. In Comparative Example 13, the Zn content is excessive, and as shown in Table 3, the corrosion resistance is significantly reduced. In Comparative Example 14, Ti is excessive, and as shown in Table 3, a coarse intermetallic compound is produced, and surface defects frequently occur from the intermetallic compound as a starting point during extrusion. Comparative Example 15 is a Ti too small, as shown in Table 3, the ingot of recrystallized grains coarse, arising cracking during extrusion.

From the above results, the critical significance of improving the strength and corrosion resistance of a forged material obtained by hot forging an aluminum alloy extruded material according to the present invention composition, structure definition or optimum production conditions can be understood.

According to the present invention, a forged material obtained by hot forging an aluminum alloy extruded material with high strength and high corrosion resistance, a forged material that guarantees these characteristics over the entire portion of the forged material, and a method for producing the same Can be provided. Therefore, the Al—Mg—Si based aluminum alloy forging material has a great industrial value in that it can be used for transportation equipment such as automobile undercarriage parts.

Claims (2)

It is a forging material formed by hot forging an aluminum alloy extruded material, and is expressed by mass%, Si: 0.8
To 1.3%, Mg: 0.70 to 1.3%, Cu: 0.01 to 0.5%, Zn: 0.005
-0.2%, Fe: 0.01-0.45%, Mn: more than 0.30%, 0.8% or less, C
r: 0.01 to 0.25%, Zr: 0.01 to 0.25%, Ti: 0.01 to 0.1%, respectively, and the Si and Mg contents are [Si%] − [Mg%] / 1.73> 0.25
The inclination is identified by the measurement by the SEM-EBSP method in the entire cross section excluding the surface layer portion of any three or more parts of the forging material having a composition composed of the balance Al and inevitable impurities. An unrecrystallized region including a low-angle grain boundary of 2 ° or more and less than 15 ° and a large-angle grain boundary of 15 ° or more is provided, and the unrecrystallized region is surrounded by a boundary having an inclination angle of 2 ° or more. The average grain size of the region is 10 μm or less, the average area ratio of the non-recrystallized region to the entire cross section excluding the surface layer portion of the forged material is 75% or more, and the maximum in the non-recrystallized structure region wherein the length is 10nm or more, with an average density of less dispersed particles 800nm is 10 pieces / [mu] m ³ or more, the maximum length of the average area ratio of 0.5μm or more crystallizate is less than 2.5% Aluminum Gold forged material. In mass%, Si: 0.8 to 1.3%, Mg: 0.70 to 1.3%, Cu: 0.01 to 0
. 5%, Zn: 0.005 to 0.2%, Fe: 0.01 to 0.45%, Mn: more than 0.30%, 0.8% or less, Cr: 0.01 to 0.25% , Zr: 0.01 to 0.25%, T
i: each containing 0.01 to 0.1%, and the contents of Si and Mg are [Si%]-[Mg
%] / 1.73> 0.25, an aluminum alloy ingot having a composition consisting of the balance Al and inevitable impurities is subjected to a homogenization heat treatment in a temperature range of 450 to 580 ° C.
A hot extrusion process with an extrusion ratio of 2.4 or more and less than 3.7 is performed at a temperature of 400 to 580 ° C., and the extruded material is subjected to a material temperature in the range of 430 to 550 ° C. and a mold temperature of 100 to 250. ℃ range,
The forging material is subjected to hot forging under the condition that the minimum thickness reduction rate exceeds 25% and the maximum thickness reduction rate is less than 90%, and further subjected to solution treatment and quenching treatment and artificial aging treatment SEM- in the entire cross section excluding the surface layer portion of any three or more parts of this forging
An unrecrystallized region including a low-angle grain boundary with an inclination angle of 2 ° or more and less than 15 ° and a large-angle grain boundary with an inclination angle of 15 ° or more, identified by measurement by the EBSP method, is provided. The average grain size of the region surrounded by the boundary having an inclination angle of 2 ° or more in the region is set to 10 μm or less, the average area ratio of the non-recrystallized region to the entire cross section excluding the surface layer portion of the forged material is set to 75% or more, and In this non-recrystallized structure region, the average density of dispersed particles having a maximum length of 10 nm or more and 800 nm or less is 10 particles / μm ³ or more, and the average area ratio of crystallized substances having a maximum length of 0.5 μm or more is 2.5% The manufacturing method of the aluminum alloy forging material characterized by the following.