JP3684313B2 - High-strength, high-toughness aluminum alloy forgings for automotive suspension parts - Google Patents

Description

【００５８】
【表２】

【００５９】
【表３】

【００６０】
【発明の効果】
本発明によれば、熱間鍛造の加工率が低くなる場合でも、より高強度で高靱性が要求される部品や部材に適用することが可能な高強度高靱性Al合金鍛造材を提供することができる。したがって、Al-Mg-Si系Al合金鍛造材の自動車用への用途の拡大を図ることができる点で、多大な工業的な価値を有するものである。
【図面の簡単な説明】
【図１】図1(a)は本発明、図1(b)は従来技術に各々係る、Al合金鍛造材のミクロ組織を示す説明図である。
【図２】自動車用のサスペンション部品用のAl合金鍛造材の一例を示す説明図である。
【符号の説明】
1:Al合金鍛造材、2:Mg₂Si 晶出物、3:Al-Fe-Si-(Mn、Cr、Zr) 系晶出物、[0001]
BACKGROUND OF THE INVENTION
  The present invention particularly relates to a suspension part of an automobile.To goodsThe present invention relates to a suitable Al-Mg-Si high-strength, high-toughness aluminum alloy forging (hereinafter, aluminum is simply referred to as Al).
[0002]
[Prior art]
As is well known, JIS 6000 series (Al-Mg), which has excellent formability and bake hardenability, for the purpose of weight reduction for structural materials of transportation equipment such as automobiles and vehicles or suspension parts such as knuckles, lower arms, and upper arms. Al alloy such as -Si type) is used. This JIS 6000 series Al alloy is excellent in other required characteristics such as mechanical properties such as elongation, corrosion resistance and stress corrosion cracking resistance, and also has a small amount of alloy such as Mg, and scrap is made into JIS 6000 series. It is also excellent in terms of recyclability that can be reused as an Al alloy melting raw material.
[0003]
Taking the automobile suspension part as an example, an Al alloy casting material or an Al alloy forging material is used from the viewpoint of reducing manufacturing costs and processing into a complex shape part. Among these, Al alloy forgings are used for parts that require higher strength and mechanical properties such as high toughness. And these Al alloy forging materials are manufactured by performing homogenization heat treatment of the Al alloy casting material, then performing hot forging such as mechanical forging and tempering treatment such as T6 and aging treatment.
[0004]
In recent years, there has been a demand for thinner and higher strength including these suspension parts for automobiles, and the need for higher strength and toughness of the Al alloy forged material has also arisen. However, the JIS 6000 series Al alloys currently used for these applications inevitably have insufficient strength.
[0005]
For this reason, improving the side of Al alloy material conventionally is performed. For example, in Japanese Patent Laid-Open No. 06-256880, JIS 6000 series (Al-Mg-Si series) casting materials such as Mg and Si are used as castings for Al alloy forgings used as parts such as automobile suspensions. In addition, the average particle size of the crystallized material is reduced to 8 μm or less, and the dendrite secondary arm spacing (DAS) is reduced to 40 μm or less to make Al alloy forgings stronger and tougher. It has been proposed.
[0006]
[Problems to be solved by the invention]
However, as shown in the examples of this Japanese Patent Laid-Open No. 06-256880, even if the dendrite secondary arm interval (DAS) of the Al alloy forging obtained by this prior art is small, it is about 30 μm at most. Yes, and the characteristics of Al alloy forgings are the processing rate [(original ingot height d₀-Height at which cracking occurred d_t) / d₀] Is 75%, the strength (σ_B) Is 39.2-39.3kgf / mm²(384 to 385N / mm²) Degree and toughness (I_C) 2.2 to 2.3kgf / mm² (Charpy impact value is about 22J / cm²) Degree.
[0007]
That is, in the upsetting forging test of the round bar as in this prior art, each part of the round bar is processed uniformly, so that the mechanical characteristics of each part of the round bar become uniform. However, as shown in Fig. 2 as an example of Al alloy forgings for automobile suspension parts, the actual Al alloy forgings have a low processing rate depending on the parts of the parts even by hot forging such as mechanical forging. The mechanical characteristics of each part of the forging material may not be uniform. For example, in the case of the shape shown in Fig. 2, T in Fig. 2₂The part is T₁Even if the processing rate of the part is 75%, the processing rate is only about 50%. And since the cast structure remains even if it is forged, the toughness of the part where the processing rate is low tends to be inevitably lower than other parts where the processing rate is high.
[0008]
Therefore, although the strength and toughness of the Al alloy forging obtained by this prior art is improved compared to Al alloys such as JIS 6061 and 6151, the toughness of this part is reduced due to the occurrence of a part with a low processing rate. The average toughness of the Al alloy forging material is particularly insufficient for the Al alloy forging material which is lowered. That is, in the prior art, at the site where the processing rate is less than 75% and further 50% or less, the toughness level is further lowered, and the high proof stress and high toughness value of the entire part required for the part are obtained. Can't get.
[0009]
As a result, parts that require higher strength and toughness as a whole, more specifically,_0.2 At 315N / mm²20 J / cm for higher strength and Charpy impact value²This method cannot be applied to parts and members that require the above toughness, and has hindered the expansion of the use of aluminum alloy forgings themselves to automobile suspension parts.
[0010]
The present invention has been made by paying attention to such circumstances, and its purpose is to provide excellent average mechanical properties as a whole forged material, even if there is a portion where the forging rate is low, and the forged material. As a whole, an object is to provide a high-strength, high-toughness Al alloy forging that can be applied to parts and members that require high strength and high toughness.
[0011]
[Means for Solving the Problems]
  To achieve this object, the present inventionFor automotive suspension partsThe summary of the Al alloy forging material is Mg: 0.6 to 1.6% (mass%, the same applies hereinafter), Si: 0.6 to 1.8%, Cu: 0.05 to 1.0%, Fe is restricted to 0.30% or less, Mn: Al alloy forging containing 0.15 to 0.6%, Cr: 0.1 to 0.2%, Zr: 0.05 to 0.2%, or more, and hydrogen: 0.25cc / 100g Al or less, the balance being Al and inevitable impurities An aluminum alloy ingot cast at a cooling rate of 10 ° C./sec or more is subjected to a homogenization heat treatment at a temperature of 530 to 600 ° C. and then hot forged into a forged material.Of the part where the forging rate is lowestMg in Al alloy structure₂The total area ratio of Si and Al-Fe-Si- (Mn, Cr, Zr), 800 When observed with a double scanning electron microscope,That is 1.5% or less per unit area.
[0012]
As a result of examining the relationship between the crystallized product crystallized by casting and the toughness of the forged Al alloy structure, the inventors have found that the area ratio of the specific crystallized product is the toughness of the forged Al alloy structure. I found out that I was deeply involved.
[0013]
That is, the inventors of the present invention are the origin of fracture of the forged Al alloy structure (the origin of dimples) of the crystallized product of the Al alloy ingot.₂Knowledge of Al and Fe-Si-Mn, Al-Fe-Si-Cr, Al-Fe-Si-Zr and other Al-Fe-Si- (Mn, Cr, Zr) did.
[0014]
And more importantly, it has been found that these crystallized substances present in the Al alloy structure are not in a large or long connected shape, but are dispersed at a distance from each other to contribute to the improvement of toughness. That is, these crystallized substances cannot be simply reduced or eliminated from the viewpoint of contributing to securing a necessary strength. However, it is necessary to control the form of these crystallized substances that are present or necessary, so that the necessary strength can be ensured and the forging rate is low or the forging rate is low. It has been found that high average toughness can be secured.
[0015]
For example, the crystal form control as described in the above-mentioned Japanese Patent Application Laid-Open No. 06-256880, that is, simply reducing the average grain size of the ingot crystallized material does not contribute much to the improvement of toughness. Contrary to the idea described in Japanese Patent Laid-Open No. 06-256880, the present inventors, even if the average particle size of the ingot crystallized material is large, it is dispersed at intervals (sparseness). It has been found that it contributes to the improvement of toughness. That is, even if the average particle size of the crystallized material is small, the toughness, particularly the fracture toughness, is deteriorated in a state where the distance between each other is small and dense. On the other hand, in the present invention, these Mg₂The amount of crystallized substances such as Si and Al-Fe-Si- (Mn, Cr, Zr) based crystallized substances itself is controlled or reduced except for the necessary strength.
[0016]
As an index that corresponds well to the control of the amount of crystallized substances and the situation where the crystallized substances are dispersed with a space between each other (the crystallized substances are not closely packed or connected). In the present invention, Mg per unit area₂The total area ratio of Si and Al-Fe-Si- (Mn, Cr, Zr) -based crystals is selected.
[0017]
The area ratio of these crystallized substances is determined by visual observation or image analysis observation of a 800-fold scanning electron microscope (SEM) of the structure of the cross section in the thickness direction of the Al alloy ingot or forging. The magnification of this scanning electron microscope does not change much even when measured at magnifications of 400 to 800, but at other magnifications, the number of crystallized substances to be measured is completely different. For this reason, when the magnification is different, the measured area ratio is greatly different, and the reproducibility of the area ratio regulation is lost. Therefore, the magnification of the scanning electron microscope, which is the standard for defining the area ratio of the crystallized product in the present invention, is set to 800 times. In addition, in order to have reproducibility of area ratio measurement, observe the number of visual fields (measurement points) of the target part for measuring the area ratio of the crystallized substance as 5 to 20 visual fields, and measure the crystallized substance in each visual field It is preferable to average the area ratio.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The definition of the crystallized product in the present invention will be described. Mg by visual observation or image analysis observation with 800X scanning electron microscope (SEM)₂By making the total area ratio of Si and Al-Fe-Si- (Mn, Cr, Zr) -based crystallized substances 1.5% or less per unit area, preferably 1.0% or less, suspension parts for automobiles, etc. Higher strength and toughness, preferably yield strength (σ_0.2) Average value is 350 N / mm²When having the above, average value 30J / cm²The above high toughness can be obtained.
[0019]
On the other hand, when the total area ratio of the crystallized substances exceeds 1.5% per unit area, the processing ratio is lowered even by hot forging (the processing ratio is less than 75%). It is impossible to obtain an average high toughness value for the entire part, including that the toughness of the part is significantly reduced.
[0020]
Fig. 1 shows the T for the Al alloy forging manufactured in the examples described later.₁FIG. 2 is a diagram showing a microstructure of a scanning electron microscope (SEM) at a magnification of 800 times in a cross section in the thickness direction of the region (a micrograph taken by SEM is made into a drawing). In the figure, 2 is Mg₂Si crystallized product, 3 is an Al-Fe-Si- (Mn, Cr, Zr) based crystallized product. Here, the Al—Fe—Si— (Mn, Cr, Zr) series crystallized materials 3 of the Al alloy forging according to the present invention shown in FIG. 1 (a) are finely dispersed at intervals. In contrast, the Al-Fe-Si- (Mn, Cr, Zr) -based crystallized material 3 in Fig. 1 (b), which is a forged Al alloy material according to the prior art, has a shape in which the crystallized materials are long connected. ing.
[0021]
And the Al alloy forging material in FIG._0.2 350N / mm²30J / cm with high strength²In contrast to the above high toughness, the Al alloy forging shown in Fig. 1 (b) is 20 J / cm.²The following toughnesses, both of which have a remarkable difference in toughness. Further, the size of each Al-Fe-Si- (Mn, Cr, Zr) -based crystallized product 3 in any of FIGS. 1 (a) and (b) is described in JP-A-06-256880. The average particle size is 8 μm or less. Therefore, simply reducing the average grain size of the ingot (cast material) does not contribute much to the improvement of toughness. In other words, sparsely exists, in other words, Mg₂If the total area ratio of Si and Al—Fe—Si— (Mn, Cr, Zr) based crystallized material is low, it is supported that a higher strength and toughness Al alloy forging can be obtained.
[0022]
Of course, the area ratio of other crystallized substances also affects the toughness. Typical examples of other crystallized substances are, for example, crystallized substances of Si alone, Al₇Cu₂Fe, Al₁₂(Fe, Mn)_ThreeCu₂, (Fe, Mn) Al₆Crystallized product of compound phase with Al of Cu, Mg, Al₂Cu₂Mg, Al₂Cu₂Etc. Among these, the crystallized substance of Si simple substance becomes the starting point of material destruction, and toughness falls remarkably. Therefore, it is necessary that the crystallized substance of Si simple substance does not exist substantially. More specifically, it is necessary that the crystallized substance of Si simple substance is not observed by a scanning electron microscope at a magnification of 800 times. However, in the case of the normal manufacturing method described later, Si crystallized substance is not substantially present in the structure of the Al alloy ingot or the Al alloy forged material.
[0023]
Also other Al₇Cu₂Fe, Al₁₂(Fe, Mn)_ThreeCu₂, (Fe, Mn) Al₆, Al₂Cu₂Mg, Al₂Cu₂For crystallization products such as Mg₂Similar to Si and Al-Fe-Si- (Mn, Cr, Zr) based crystals, it is necessary to reduce the area ratio in order to improve toughness. However, these crystals are₂The absolute amount is smaller than the amount of Si and Al-Fe-Si- (Mn, Cr, Zr) -based crystals, and the Mg₂As long as the total area ratio of Si and Al-Fe-Si- (Mn, Cr, Zr) crystallized substances is lowered, the area ratio is inevitably reduced. Therefore, in the present invention, the Mg₂There are no particular restrictions on crystallized substances other than Si and Al-Fe-Si- (Mn, Cr, Zr) based crystallized substances.
[0024]
And in order to satisfy the stipulation of the crystallized product of the Al alloy forging material in the present invention and to guarantee the high strength and high toughness of the Al alloy forged material, Mg at the stage of homogenization heat treatment₂It is important that the total area ratio of Si and Al-Fe-Si- (Mn, Cr, Zr) based crystallized substances is 1.5% or less per unit area. That is, the area ratio of the crystallized product is substantially impossible in the forging process, and the area ratio of the crystallized material of the forging material in the present invention is controlled by the homogenization heat treatment of the ingot and the ingot. Perform in stages.
[0025]
Note that the average value of proof stress and toughness in the present invention is the highest processing rate = T with the highest proof stress and toughness in the example of Fig. 2.₁Part (processing rate 75%) and the lowest processing rate = T with the lowest yield strength and toughness₂The average of the part (processing rate 50%). Of course, this does not only mean that the values of these two points are averaged, but depending on the shape of the member or member, it is also possible to average the values of a plurality of parts that require further guarantee of mechanical properties. good.
[0026]
 (Ingot) Further, the ingot for forging in the present invention has a dendrite secondary arm interval (DAS) of 30 μm or less in order to ensure high toughness of the Al alloy forging. As a result, the crystal grains of the Al alloy ingot and the Al alloy forged material are refined, and Mg₂The total area ratio of Si and Al-Fe-Si- (Mn, Cr, Zr) -based crystallized materials is lowered, and the toughness of Al alloy forgings is improved. When the dendrite secondary arm interval (DAS) of the ingot is increased beyond 30 μm, the dendrite secondary arm interval (DAS) of the Al alloy forging material of the Japanese Patent Application Laid-Open No. 06-256880 is about 30 μm. Thus, when the site | part with a low forge processing rate exists, the toughness of the whole Al alloy forging material cannot be improved.
[0027]
The forged material includes a case where the ingot is directly hot forged, and a case where the ingot is once extruded and hot forged. Therefore, the shape of the ingot includes an ingot such as a round bar, a slab shape, or a near net shape close to a product shape, and is not particularly limited.
[0028]
 (Chemical Component Composition of the Al Alloy of the Present Invention) Next, the chemical component composition in the Al alloy of the present invention will be described. The Al alloy of the present invention is mechanical properties such as strength, elongation, toughness, etc. for transport equipment, structural materials or parts such as automobiles and ships, corrosion resistance, stress corrosion cracking, recyclability with a small amount of alloy, etc. It is necessary to satisfy the characteristics of Of these, particularly for automobile suspension parts, preferably σ_0.2 350N / mm²More high strength and 30J / cm²It is necessary to obtain the above average high toughness.
[0029]
Therefore, in order to satisfy the above-mentioned characteristics, the chemical composition composition of the Al alloy of the present invention is the component standard of Al-Mg-Si JIS 6000 series Al alloys (JIS 6101, 6003, 6151, 6061, 6N01, 6063, etc. ) Basically includes Mg: 0.6 to 1.6%, Si: 0.6 to 1.8%, Cu: 0.05 to 1.0%, Fe is restricted to 0.30% or less, Mn: 0.15 to 0.6%, An Al alloy containing one or more of Cr: 0.1 to 0.2% and Zr: 0.05 to 0.2%, hydrogen: 0.25 cc / 100 g Al or less, and the balance Al and inevitable impurities. In addition, Zn: 0.005 to 1.0%, Ti: 0.001 to 0.1%, B: 1. to 300 ppm, and the like are selectively contained as necessary. However, even if it does not comply with each component standard of JIS 6000 series Al alloy, as long as it has the above basic characteristics, the composition of the ingredients can be changed as appropriate to further improve the characteristics and add other characteristics. Is acceptable. In this regard, it is allowed to appropriately include other elements such as Ni, V 2, Sc, and Ag according to changes in the component ranges of the above elements and more specific uses and required characteristics. Impurities that are inevitably mixed from the melted raw material scrap and the like are allowed within a range that does not impair the quality of the forged material of the present invention.
[0030]
   (Element amount of the Al alloy of the present invention) Next, the critical significance and preferred range of the content of each element of the Al alloy material of the present invention will be described.
[0031]
  Mg: 0.6-1.6%. Mg is Mg with Si due to artificial aging₂It is an essential element for precipitating as Si, and for forming a compound phase with Cu and Al in the Cu-containing composition to give high strength (yield strength) when the final product is used. When the Mg content is less than 0.6%, the work hardening amount decreases, and even artificial aging is σ._0.2At 315N / mm²The above high strength cannot be obtained. On the other hand, if the content exceeds 1.6%, the strength (yield strength) becomes too high and the forgeability is hindered.₂The total area ratio of the Si crystallized substances cannot be 1.5% or less, preferably 1.0% or less per unit area, and the toughness becomes low and high toughness cannot be obtained. Therefore, the Mg content is in the range of 0.6 to 1.6%.
[0032]
  Si: 0.6-1.8%. Si, together with Mg, can be treated with artificial aging₂It is an essential element for precipitating as Si and imparting high strength (yield strength) when the final product is used. If the Si content is less than 0.6%, sufficient strength cannot be obtained by artificial aging._0.2At 315N / mm²The above high strength cannot be obtained. On the other hand, when the content exceeds 1.8%, coarse single Si particles are precipitated during casting and quenching, and the toughness is lowered as described above. Mg₂The total area ratio of Si and Al-Fe-Si- (Mn, Cr, Zr) -based crystallized substances cannot be 1.5% or less per unit area, preferably 1.0% or less, and high toughness is obtained. I can't. Further, the moldability is also hindered, for example, the elongation is lowered. Therefore, the Si content is in the range of 0.6 to 1.8%.
[0033]
  Cu: 0.05-1.0%. Cu forms a compound phase with Mg and Al, and contributes to the improvement of matrix strength. In addition, during aging treatment, it causes nuclei to precipitate other alloy elements and finely disperses the precipitate. And has the effect of significantly accelerating age hardening of the final product. If the Cu content is less than 0.05%, these effects cannot be exhibited. On the other hand, if the Cu content exceeds 1.0%, these effects are saturated and the toughness or hot forgeability is decreased. Further, if the Cu content exceeds 0.3%, the corrosion resistance tends to decrease. Therefore, from the viewpoint of corrosion resistance, the Cu content is preferably set to 0.3% or less. Therefore, the Cu content is 0.05 to 1.0%, preferably 0.05 to 0.3%.
[0034]
  One or more of Mn: 0.15 to 0.6%, Cr: 0.1 to 0.2%, Zr: 0.05 to 0.2%. These elements are produced during homogenization heat treatment and subsequent hot forging.₂₀Cu₂Mn_Three, Al₁₂Mg₂Cr, Al_ThreeGenerate dispersed particles (dispersed phase) such as Zr. Since these dispersed particles have an effect of hindering the grain boundary movement after recrystallization, fine crystal grains can be obtained. Also, among these elements, Zr, when contained in combination with other Mn and Cr, is larger than Al-Mn and Al-Cr-based dispersed particles of tens to hundreds of angstroms in size. Finer Al—Zr-based dispersed particles are precipitated. For this reason, when Zr is contained together with Mn and Cr, it has a great effect of preventing the movement of crystal grain boundaries and sub-grain boundaries and suppressing the growth of crystal grains, and has the effect of improving fracture toughness and fatigue properties. large. On the other hand, excessive inclusion of these elements tends to generate coarse Al-Fe-Si- (Mn, Cr, Zr) -based intermetallic compounds and crystallized materials during melting and casting, which is the starting point of fracture and increases toughness. It causes a decrease. Therefore, the total area ratio of the Al-Fe-Si- (Mn, Cr, Zr) -based crystallized product cannot be 1.5% or less per unit area, preferably 1.0% or less, and high toughness is obtained. I can't. Therefore, the contents of these elements are set to Mn: 0.15 to 0.6%, Cr: 0.1 to 0.2%, and Zr: 0.05 to 0.2%, respectively.
[0035]
  Fe: 0.30% or less. Fe contained as an impurity in Al alloy is Al₇Cu₂Fe, Al₁₂(Fe, Mn)_ThreeCu₂ , (Fe, Mn) Al₆Alternatively, a coarse Al-Fe-Si- (Mn, Cr, Zr) -based crystallized product which is a problem in the present invention is generated. These crystallized materials deteriorate the fracture toughness and fatigue characteristics as described above. In particular, when the Fe content exceeds 0.3%, more strictly, 0.25%, the total area ratio of Al-Fe-Si- (Mn, Cr, Zr) based crystals is 1.5% or less per unit area. Preferably, it cannot be 1.0% or less, and the high strength and high toughness required for suspension parts for automobiles and the like cannot be obtained. Therefore, the Fe content is preferably 0.30% or less, more preferably 0.25% or less.
[0036]
Hydrogen: 0.25 cc / 100g Al or less. Hydrogen significantly reduces toughness and significantly degrades impact fracture resistance. Further, in automobile suspension parts and the like that have been made thinner and higher in strength, the impact damage resistance deterioration due to hydrogen is particularly significant. Therefore, the hydrogen content should be as low as possible below 0.25 cc / 100g Al.
[0037]
   (Zn, Ti, B, Be, V, etc.) Next, Zn, Ti, B, Be, V, etc. are elements that are selectively contained depending on the purpose.
   Zn: 0.005 to 1.0%. Zn is MgZn during artificial aging.₂Is deposited finely and densely to achieve high strength. However, if the Zn content is less than 0.005%, sufficient strength cannot be obtained by artificial aging. On the other hand, if it exceeds 1.0%, the corrosion resistance is remarkably lowered. Therefore, the Zn content is preferably in the range of 0.005 to 1.0%.
[0038]
  Ti: 0.001 to 0.1%. Ti is an element added to refine crystal grains of the ingot and improve press formability. However, when the Ti content is less than 0.001%, this effect cannot be obtained. On the other hand, when the Ti content exceeds 0.1%, a coarse crystallized product is formed and the formability is lowered. Therefore, the Ti content is preferably in the range of 0.001 to 0.1%.
[0039]
  B: 1 to 300 ppm. B, like Ti, is an element added to refine the ingot crystal grains and improve press formability. However, if the content of B is less than 1 ppm, this effect cannot be obtained. On the other hand, if the content exceeds 300 ppm, coarse crystals are formed and the moldability is lowered. Therefore, the B content is preferably in the range of 1 to 300 ppm.
[0040]
  Be: 0.1-100 ppm. Be is an element to be contained in order to prevent reoxidation of molten Al in the air. However, if the content is less than 0.1 ppm, this effect cannot be obtained. On the other hand, if the content exceeds 100 ppm, the material hardness increases and the moldability decreases. Therefore, the content of Be is preferably in the range of 0.1 to 100 ppm.
[0041]
  V: 0.15% or less. V, like Mn, Cr, Zr, etc., produces dispersed particles (dispersed phase) during the homogenization heat treatment and the subsequent hot forging. Since these dispersed particles have an effect of hindering the grain boundary movement after recrystallization, fine crystal grains can be obtained. However, excessive inclusion tends to generate coarse Al-Fe-Si-V intermetallic compounds and crystallized substances during melting and casting, which becomes a starting point of fracture and causes toughness to decrease. Therefore, when V is contained, the content is made 0.15% or less.
[0042]
Next, the preferable manufacturing method of the Al alloy forging material in this invention is described. In the present invention, the Al alloy forging material itself can be manufactured by a conventional method. For example, when casting an Al alloy melt that has been adjusted to be dissolved within the Al alloy component range, for example, a normal melt casting such as a continuous casting rolling method, a semi-continuous casting method (DC casting method), a hot top casting method, etc. The method is appropriately selected and cast.
[0043]
However, in order to improve the toughness of the Al alloy forging, the crystal grains of the Al alloy ingot are refined, and the Mg₂In order to reduce the total area ratio of Si and Al-Fe-Si- (Mn, Cr, Zr) -based crystallized products, cast an Al alloy melt at a cooling rate of 10 ° C / sec or more to form an ingot. It is necessary to. If the cooling rate of the ingot is less than 10 ° C / sec, the crystal grains become coarse, and the dendrite secondary arm interval (DAS) of the ingot cannot be made 30 µm or less. Mg₂The total area ratio of Si and Al-Fe-Si- (Mn, Cr, Zr) -based crystallized substances cannot be 1.5% or less per unit area, preferably 1.0% or less. Higher strength and higher toughness required for parts and the like cannot be obtained.
[0044]
Next, the homogenization heat treatment temperature of the Al alloy ingot (cast material) needs to be in the temperature range of 530 to 600 ° C. The normal homogenization heat treatment temperature of this kind of Al alloy cast material is about 470-480 ° C., but in the present invention, as described above, in order to improve toughness, one or more of Mn, Cr, and Zr are used. In the homogenization heat treatment, Al₂₀Cu₂Mn_Three, Al₁₂Mg₂Cr, Al_ThreeFine particles are obtained by producing dispersed particles (dispersed phase) such as Zr. In addition, in order to increase the yield strength and toughness of Al alloy forgings, at the stage of this homogenization heat treatment, Mg₂It is necessary to sufficiently dissolve the Si-based crystallized product.
[0045]
For this purpose, a homogenization heat treatment at a high temperature of 530 to 600 ° C. is necessary. When the homogenization heat treatment temperature is less than 530 ° C., the number of dispersed particles is insufficient and the crystal grains become large. Mg₂The amount of Si-based crystallized solid solution is also insufficient, and Mg₂The total area ratio of Si and Al-Fe-Si- (Mn, Cr, Zr) -based crystallized substances cannot be 1.5% or less per unit area, preferably 1.0% or less. Higher strength and toughness required for parts, more specifically, σ_0.2 At 315N / mm²Charpy impact value is 20 J / cm when having high strength above²The above high toughness cannot be obtained. On the other hand, even if the homogenization heat treatment temperature exceeds 600 ° C., the effect is not changed, but on the contrary, problems such as melting of the Al alloy ingot (cast material) occur.
[0046]
After homogenization heat treatment, it is hot forged by mechanical forging or hydraulic forging, etc., and formed into an Al alloy forging material of the final product shape (near net shape). Then, after forging, tempering heat treatment and aging treatment such as T6 treatment (quenching after solution treatment) for obtaining necessary strength and toughness are performed.
[0047]
In addition, in order to eliminate the cast structure remaining in the Al alloy forged material and to further improve the strength and toughness, the forging may be performed after the Al alloy ingot is subjected to homogenization heat treatment and extrusion.
[0048]
【Example】
Next, examples of the present invention will be described. The Al alloy ingots shown in Table 1 (Al alloy cast materials, both of which are φ68mm diameter x 580mm length round bars) are cast into the casting methods (DC casting method, hot top casting method) and cooling rate (Table 2). After melting by (° C / sec), homogenized heat treatment was performed for 8 hours at the temperatures shown in Table 2, and at the processing rates shown in Tables 2 and 3, the automotive suspension parts were hot forged by mechanical forging. An aluminum alloy forging material 1 having the shape shown in FIG. 1 was produced. Next, this aluminum alloy forging material 1 was subjected to a solution treatment at 560 ° C. for 1 hour using a glass furnace, followed by water cooling (water quenching), and then an aging treatment at 180 ° C. for 5 hours. The ingots of Invention Example No. 5 in Table 3 were hot forged after being subjected to the homogenization heat treatment, followed by extrusion at an extrusion ratio of 6.
[0049]
Then, specimens were taken from the Al alloy ingot and the Al alloy forged material 1, respectively, and the cross-sectional structure in the thickness direction of the ingot and the Al alloy forged material 1 was scanned by a scanning electron microscope (SEM) at a magnification of 800 times. To observe and analyze the image with the number of fields (measurement points) of the specimen as 10 fields of view.₂Total unit area of Si and Al-Fe-Si- (Mn, Cr, Zr) based crystals (0.0127mm²) Area ratio (average of each field of view). Also, the dendrite secondary arm spacing (DAS, μm) of Al alloy ingots is specified in `` Method of measuring aluminum dendrite arm spacing and cooling rate '' from the ingot microstructure photograph (1988.8, Japan Institute of Light Metals Research Committee) Obtained by the method of crossing. These results are shown in Tables 2 and 3.
[0050]
Furthermore, the tensile strength (σ_B, N / mm²), Yield strength (σ_0.2, N / mm²), Elongation (δ,%), toughness = Charpy impact value (J / cm²) And other mechanical properties were measured. At this time, in order to see the variation in the mechanical characteristics due to the difference in the forging rate at each site of the Al alloy forging material 1, the sampled site of the test piece is the T where the forging rate is the highest in Fig. 1.₁And T with the lowest forging rate₂It was. The forging rate was calculated as the reduction rate of the cross-sectional area. And the average of the mechanical characteristic of these parts was also calculated | required, and the average mechanical characteristic as the whole Al alloy forging material 1 was calculated | required. These results are also shown in Tables 2 and 3.
[0051]
As is clear from Table 2, the Al alloy No. 1 in Table 1 with a chemical composition within the scope of the present invention, such as keeping the Fe content below 0.30% and keeping the hydrogen content below 0.25 cc / 100gAl, Invention Examples No. 1 and 5 in which the casting cooling rate and the homogenization temperature satisfy the manufacturing method of the present invention are used, and the forging rate is the lowest at 50%.₂In addition, high strength and toughness are ensured, and the average mechanical properties of the forged Al alloy as a whole, especially the proof stress (σ_0.2) 350N / mm²Above, average toughness value is 30 J / cm² The above is secured. In the Al alloy forged material structure of these inventive examples, as shown in FIG. 1 (a), Al-Fe-Si- (Mn, Cr, Zr) -based crystallized materials 3 are finely dispersed at intervals. Had an organization.
[0052]
Among invention examples in Table 2, Invention Example No. 2 has a relatively low casting cooling rate and dendrite secondary arm spacing (DAS) is relatively large compared to Invention Examples Nos. 1 and 5. In addition, Invention Example No. 4 has a relatively low homogenization temperature, produces few dispersed particles such as Mn, Cr, and Zr, and has relatively coarse crystal grains. Further, Invention Example No. 3 uses the Al alloy of No. 2 in Table 1, which has a relatively high Si content, Fe content, and Mg content.₂The total area ratio of Si and Al-Fe-Si- (Mn, Cr, Zr) -based crystals is relatively high. As a result, these inventive examples show that the average mechanical properties of the Al alloy forging as a whole, especially the average proof stress (σ_0.2) Is 315N / mm²Above, average toughness value is 20 J / cm²Although the above is secured, the forging rate is the lowest at 50%.₂The strength and toughness of the steels were inferior to those of Invention Examples Nos.
[0053]
Further, in comparison between Invention Example No. 1 containing Zr together with Mn and Cr and Invention Example No. 6 (Table 3) having almost the same composition except that Zr is not included, the toughness value of Invention Example No. 1 Is expensive. From this result, the excellent toughness improving effect of Zr described above can be seen.
[0054]
On the other hand, as is apparent from Table 3, comparative example No. 7 using the No. 3 Al alloy in Table 1 in which the amount of Fe is outside the scope of the present invention is particularly₂The total area ratio of Si and Al-Fe-Si- (Mn, Cr, Zr) based crystallized substances is out of the scope of the present invention. Further, in comparative example No. 8 in which the casting cooling rate is lower than that of the production method of the present invention, the dendrite secondary arm interval (DAS) is out of the scope of the present invention. Furthermore, in Comparative Example No. 9, the homogenization temperature is lower than that of the production method of the present invention, the generation of dispersed particles such as Mn, Cr, and Zr is small, and the crystal grains are relatively coarse. Therefore, all of these comparative examples have the lowest forging rate, especially 50%.₂The strength and toughness of the Al alloy forgings1 as a whole are the average mechanical properties of the yield strength (σ_0.2) Is 315N / mm²The average toughness value is 20 J / cm²It is as follows. Further, Comparative Example No. 10 using the Al alloy of No. 5 in Table 1 where the amount of hydrogen deviated from the scope of the present invention was the same as the other comparative examples. Mechanical properties are yield strength (σ_0.2) Is 315N / mm²The average toughness value is 20 J / cm²Remarkably low as below.
[0055]
And, the Al-Fe-Si- (Mn, Cr, Zr) -based crystallized product of Comparative Example No. 7 had a shape in which the crystallized products were long connected as shown in FIG. 1 (b). .
[0056]
  From the above examples, according to the present invention, in particular, automaticCar naFor forgings of various shapes, such as for suspension parts such as knuckle, lower arm, upper arm, etc._0.2315N / mm²Above and 20J / cm²It turns out that the above high-strength, high-toughness aluminum alloy forging material can be obtained. Therefore, the present invention high strength high toughness aluminum alloy forgingEach in the materialThe critical significance of the requirements is supported.
[0057]
[Table 1]

[0058]
[Table 2]

[0059]
[Table 3]

[0060]
【The invention's effect】
  According to the present invention, when the hot forging rate is lowButIt is possible to provide a high-strength, high-toughness Al alloy forging that can be applied to parts and members that require high strength and high toughness. Therefore, automatic forging of Al-Mg-Si Al alloy forgingsFor carsIt has great industrial value in that it can be used for a wide range of applications.
[Brief description of the drawings]
FIG. 1 (a) is an explanatory view showing a microstructure of a forged Al alloy material according to the present invention and FIG. 1 (b) is a related art, respectively.
FIG. 2 is an explanatory view showing an example of an Al alloy forged material for automobile suspension parts.
[Explanation of symbols]
1: Al alloy forging material, 2: Mg₂Si crystallized product, 3: Al-Fe-Si- (Mn, Cr, Zr) crystallized product,

Claims (7)

Mg: 0.6 to 1.6% (mass%, the same applies hereinafter), Si: 0.6 to 1.8%, Cu: 0.05 to 1.0%, Fe is restricted to 0.30% or less, Mn: 0.15 to 0.6%, Cr: 0.1 Al alloy forging material containing one or more of ~ 0.2%, Zr: 0.05 ~ 0.2%, hydrogen: 0.25 cc / 100g Al or less, the balance being Al and unavoidable impurities, 10 ° C / The part where the forging rate in the forging material becomes the lowest after the Al alloy ingot cast at a cooling rate of sec or more is subjected to homogenization heat treatment at a temperature of 530 to 600 ° C and then hot forged into a forging material. of Mg ₂ Si in the Al alloy structure and Al-Fe-Si- (Mn, Cr, Zr) the crystallizate total area ratio of the system, when observed at 800 times of scanning electron microscope, unit area A high-strength, high-toughness aluminum alloy forging material for automobile suspension parts , characterized by not more than 1.5% per unit. The high-strength, high-toughness aluminum alloy forged material according to claim 1, wherein the area ratio of the Mg ₂ Si and Al-Fe-Si- (Mn, Cr, Zr) based crystallized material is 1.0% or less per unit area.   The high-strength, high-toughness aluminum alloy forged material according to claim 1 or 2, wherein the Fe is regulated to 0.25% or less.   The high-strength, high-toughness aluminum alloy forged material according to any one of claims 1 to 3, wherein a dendrite secondary arm interval (DAS) of the aluminum alloy ingot is 30 µm or less.   The high-strength, high-toughness aluminum alloy forging material according to any one of claims 1 to 4, wherein the aluminum alloy ingot is extruded after casting. 6. The high-strength, high-toughness aluminum alloy forging according to claim 1, wherein an average value of the proof stress (σ _0.2 ) is 350 N / mm ² or more and an average value of Charpy impact value is 30 J / cm ² or more. Wood.   The high-strength, high-toughness aluminum alloy forged material according to any one of claims 1 to 6, wherein the aluminum alloy forged material has a portion where the hot forging rate is less than 75%.

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