WO2013114928A1

WO2013114928A1 - Forged aluminum alloy material and method for producing same

Info

Publication number: WO2013114928A1
Application number: PCT/JP2013/050314
Authority: WO
Inventors: 稲垣　佳也; 雅是堀
Original assignee: 株式会社神戸製鋼所
Priority date: 2012-02-02
Filing date: 2013-01-10
Publication date: 2013-08-08
Also published as: EP2811042A4; CN103975085B; US20140367001A1; EP2811042B1; JP5863626B2; CN103975085A; EP2811042A1; JP2013177672A

Abstract

Provided is a forged aluminum alloy material which contains an excess of Si, which exhibits increased strength due to containing therein a large quantity of a strength-increasing element such as Cu or Mn, and by which high strength and high toughness can be stably obtained even if the forged aluminum alloy material is reduced in thickness, and also provided is a method for producing the same. A forged aluminum alloy material constituted from an aluminum alloy which contains prescribed quantities of Mg, Si, Cu, Fe, Ti and B and further contains prescribed quantities of one or more elements selected from among Mn, Cr and Zr, with the remainder comprising Al and unavoidable impurities, wherein the electrical conductivity at 20°C, as measured on the surface of the forged aluminum alloy material, is greater than 42.5% IACS but not more than 46.0% IACS, and the forged aluminum alloy material has a 0.2% proof stress of 360 MPa or higher and a Charpy impact value of 6 J/cm² or higher.

Description

Aluminum alloy forging and method for producing the same

The present invention relates to an aluminum alloy forged material suitably used for a strength member such as a transport aircraft, in particular, an automobile underbody member, and a manufacturing method thereof.

Conventionally, aluminum alloys such as 6000 series (Al-Mg-Si series) defined in JIS standard or AA standard have been used for structural materials of transportation equipment such as vehicles, ships, aircraft, motorcycles and automobiles. . This 6000 series aluminum alloy is relatively excellent in corrosion resistance, and is also excellent from the viewpoint of recyclability in which scrap can be reused as a 6000 series aluminum alloy melting raw material.

Also, aluminum alloy castings and aluminum alloy forgings are used as structural materials for transport aircraft from the viewpoint of reducing manufacturing costs and processing into complex shaped parts. Among these, aluminum alloy forgings are mainly used for strength members that require higher strength and mechanical properties such as high toughness, such as automobile underbody members such as upper arms and lower arms. These aluminum alloy forgings are subjected to homogenization heat treatment of the aluminum alloy cast material, followed by hot forging such as mechanical forging and hydraulic forging, and then solution hardening and artificial age hardening (hereinafter, simply referred to as aging treatment). It is manufactured after tempering treatment. For the forging, an extruded material obtained by extruding the cast material after homogenizing heat treatment may be used.

In recent years, in the strength members of these transport aircraft, the need for further weight reduction (thinning) has arisen due to increasing demands for low fuel consumption and low CO ₂ emissions. However, 6000 series aluminum alloy forgings such as 6061 and 6151 conventionally used for these applications inevitably have insufficient strength (0.2% yield strength) and toughness.

In order to solve such a problem, the present inventors, as described in Patent Document 1, Mg: 0.6 to 1.8% by mass, Si: 0.8 to 1.8% by mass Cu: 0.2-1.0% by mass, the mass ratio of Si / Mg is 1 or more, Mn: 0.1-0.6% by mass, Cr: 0.1-0.2% An aluminum alloy forging material comprising one or more of mass% and Zr: 0.1 to 0.2 mass%, consisting of the balance aluminum and unavoidable impurities, the thickness of the thinnest part being 30 mm or less, An aluminum alloy forging material was proposed in which the electrical conductivity measured on the surface of the aluminum alloy forging material after the artificial age hardening treatment was 41.0 to 42.5 IACS% and the 0.2% proof stress was 350 MPa or more.

Japanese Patent No. 3766357

However, the aluminum alloy forging described in Patent Document 1 has a high strength of 0.2% proof stress of 360 MPa or more when mass-producing an aluminum alloy forging having a thin portion with a thickness of 10 mm or less. However, there is a problem that a tough material with high toughness cannot be obtained stably.

Usually, in mass production of 6000 series aluminum alloy forgings, a certain range and variation of various conditions for homogenization heat treatment and various conditions for hot forging are allowed. However, in the case of an aluminum alloy forging material that contains Si excessively, increases the content of strengthening elements such as Cu and Mn, increases the 0.2% proof stress to 360 MPa or more, and is thinned. However, the width and variation of the manufacturing conditions that are normally allowed affect the 0.2% yield strength of the forging more sensitively. As a result, the 0.2% yield strength of the product forging material varies greatly within the manufacturing condition range, and a high strength and high toughness forging material cannot be obtained stably.

And, when the high strength and high toughness forging material cannot be stably obtained in this way, the reliability of the strength member application is impaired, and the yield of the product forging material is reduced and the manufacturing cost is also increased. Connected. In addition, reducing the allowable range such as the width of the manufacturing conditions to stabilize the 0.2% proof stress and toughness of the forged material also leads to an increase in manufacturing cost.

In view of such circumstances, the present invention is an aluminum alloy forging material which contains Si in excess, increases the content of elements for increasing the strength such as Cu and Mn, increases the strength, and reduces the thickness. The present invention also aims to provide an aluminum alloy forged material that can stably obtain high strength and high toughness, and a method for producing the same.

In order to solve the above problems, the forged aluminum alloy of the present invention has Mg: 0.60 to 1.80 mass%, Si: 0.80 to 1.80 mass%, Cu: 0.20 to 1.00 mass%. %, Fe: 0.05 to 0.40 mass%, Ti: 0.001 to 0.15 mass%, B: 1 to 500 ppm, Mn: 0.10 to 0.60 mass%, Cr: An aluminum alloy forging comprising one or more of 0.10 to 0.40 mass% and Zr: 0.10 to 0.20 mass%, the balance being made of an aluminum alloy consisting of Al and inevitable impurities The electrical conductivity at 20 ° C. measured on the surface of the aluminum alloy forging is more than 42.5 IACS% and not more than 46.0 IACS%, and the 0.2% proof stress of the aluminum alloy forging is 360 MPa or more, and , Shar Over impact value is equal to or is 6J / cm ² or more.

According to the above configuration, Mg, Si, Cu, Fe, Ti, B are included in a predetermined amount, a strengthening element such as Mn is included in a predetermined amount, and 0.2% proof stress and Charpy impact value are equal to or greater than a predetermined value. This improves the strength and toughness of the aluminum alloy forging. In addition, by setting the conductivity measured on the surface of the aluminum alloy forged material within a predetermined range, the proportion of the subgrain structure in the forged structure can be increased, and the strength and toughness can be maintained while maintaining the corrosion resistance of the aluminum alloy forged material. Can be improved.

Moreover, it is preferable that the mass ratio of Si / Mg of the said aluminum alloy is 1 or more in the aluminum alloy forging material of this invention.
According to the said structure, the 0.2% yield strength of an aluminum alloy forging material further improves.

The aluminum alloy forged material of the present invention preferably has a hydrogen gas concentration of 0.25 ml / 100 g Al or less.
According to the said structure, when the hydrogen gas concentration is below a predetermined value, forge defects, such as bubbles caused by hydrogen, are eliminated. As a result, since the starting point of fracture is reduced, the Charpy impact value of the aluminum alloy forged material is improved.

Moreover, the manufacturing method of the aluminum alloy forging according to the present invention includes a melting step of melting the aluminum alloy to form a molten metal, and a casting step of casting the molten metal at a cooling rate of 10 ° C./sec or more to form an ingot. The ingot is subjected to a homogenization heat treatment at a heating rate of 5 ° C./min or less and a holding temperature of 450 to 550 ° C., and the ingot subjected to the homogenization heat treatment is used as a forging material, and the forging material is started. A forging step for performing hot forging at a temperature of 460 to 540 ° C., a solution treatment for 520 to 570 ° C. after the forging step, and a tempering step for performing an artificial age hardening treatment for 4 to 9 hours at 170 to 200 ° C. , Including.

According to the above procedure, by performing each step under predetermined conditions, in particular, by performing the forging step at a start temperature of 460 to 540 ° C., the ratio of the subgrain structure in the forged structure increases, and the grain boundary of the forged structure is increased. Therefore, precipitation of Mg ₂ Si is promoted. As a result, the conductivity measured on the surface of the aluminum alloy forged material after the artificial age hardening treatment falls within a predetermined range.

That is, the present inventors have increased the content of Cu, Mn, and the like by excessively containing Si, increasing the 0.2% proof stress to 360 MPa or more, and reducing the thickness of the forging material for strength members. It was found that the conductivity measured on the surface of the aluminum alloy forging (hereinafter also referred to as surface conductivity) more closely correlates with the 0.2% proof stress of the forging.

Conventionally, even if it is not a 6000 series aluminum alloy forged material, the electrical conductivity of the aluminum alloy material surface represents the structural state of the aluminum alloy material, and the fact that it closely correlates with the 0.2% proof stress of the aluminum alloy material itself. It is known. However, in a normal 6000 series aluminum alloy forged material, the relationship between the electrical conductivity of the aluminum alloy forged material surface and the 0.2% proof stress is a gentle linear shape. And in such a correlation, unless the electrical conductivity of the aluminum alloy forging material surface changes so much, the influence of the electrical conductivity on the 0.2% proof stress of the aluminum alloy forging material is relatively small.

On the other hand, in the 6000 series aluminum alloy forged material containing excessive Si, increasing the content of Cu, Mn, etc. to increase the 0.2% proof stress to 360 MPa or more and reducing the thickness, When the electrical conductivity exceeds 42.5 IACS% and 46.0 IACS% or less, the 0.2% yield strength tends to maximize, and when the electrical conductivity is outside this range, the 0.2% yield strength of the aluminum alloy forged material rapidly increases. It shows a unique phenomenon that it decreases.

Therefore, in the 6000 series aluminum alloy forged material whose 0.2% proof stress is increased to 360 MPa or more and is thinned, the conductivity width on the surface of the aluminum alloy forged material due to the range or variation of the manufacturing conditions Variations more sensitively affect the 0.2% yield strength of the forging. As a result, as described above, the 0.2% proof stress of the product forging material varies widely within the range of normally acceptable manufacturing conditions and the range of variation, and the forging material having a 0.2% proof stress of 360 MPa or more is stable. It leads to not being obtained.

In the present invention, by utilizing the above phenomenon, the conductivity of the aluminum alloy forging material surface is set to 42.5 IACS% and 46.0 IACS% or less, thereby guaranteeing 0.2% proof stress of the Al alloy forging material of 360 MPa or more. And can be obtained stably. In other words, if the manufacturing conditions are such that the conductivity of the aluminum alloy forging surface exceeds 42.5 IACS% and 46.0 IAC% or less, a forging material having a 0.2% proof stress of 360 MPa or more can be stably produced. Obtainable.

According to the present invention, corrosion resistance is maintained even in the case of an aluminum alloy forging material that contains Si in excess, increases the strength of elements such as Cu and Mn, increases the strength, and reduces the thickness. However, it is possible to provide an aluminum alloy forged material that can stably obtain high strength and high toughness, and a method for producing the same. Therefore, it has a great industrial value in that the use of the aluminum alloy forging material for transportation equipment can be expanded.

It is a front view which shows the test piece used for the measurement of tensile strength, 0.2% yield strength, and elongation. The test piece used for the measurement of a Charpy impact value is shown, (a) is a side view, (b) is a front view, (c) is an enlarged view of the notch part of (b). The test piece used for a stress corrosion cracking test is shown, (a) is a side view and (b) is a front view.

First, the aluminum alloy forging material (hereinafter referred to as Al alloy forging material) of the present invention will be described. In the Al alloy forged material of the present invention, in order to guarantee a 0.2% proof stress of 360 MPa or more and to obtain stably, the electrical conductivity at 20 ° C. of the surface of the Al alloy forged material after the artificial age hardening treatment described later is 42 The range is more than 5IACS% and less than 46.0IACS%.

(Conductivity at 20 ° C .: more than 42.5 IACS% and 46.0 IACS% or less)
As in the present invention, in an Al alloy forging material containing an excessive amount of Si, increasing the content of Cu, Mn, etc. to increase the 0.2% proof stress to 360 MPa or more and thinning the Al alloy, If the electrical conductivity of the forged material surface at 20 ° C. is 42.5 IACS% or less, or exceeds 46.0 IACS%, a high strength of 360 MPa or more cannot be obtained with a 0.2% proof stress.

The conductivity of the Al alloy forged material shows the same tendency as the conductivity of the surface not only in the conductivity of the Al alloy forged material surface but also in the Al alloy forged material (including the center). In the present invention, the conductivity of the Al alloy forging material surface is selected because it is easy to measure the surface conductivity.

The Al alloy forged material whose electrical conductivity is to be measured is obtained by mechanically polishing the surface of the Al alloy forged material after the artificial age hardening treatment by about 0.05 to 0.1 mm, or after etching about several μm, and then adjusting the conductivity of the surface. For example, it is measured by an eddy current type conductivity measuring device (GE Inspection Technologies Japan Hocking AUTOSIGMA 3000DL). The device, probe, standard piece, and measurement object (Al alloy forging material) are left in the same inspection area so that the temperature is the same. Before the inspection, the temperature of the Al alloy forging material is the ambient temperature ± 1 ° C. Confirm that there is by measuring with a contact thermometer. In addition, as the electrical conductivity of the present invention, a measured value or a converted value when the temperature of the Al alloy forging is 20 ° C. is used. In the following, “conductivity at 20 ° C.” is referred to as “conductivity”.

The electrical conductivity of the Al alloy forging material surface represents the total amount of each alloy element of the Al alloy and the overall state of the structure such as the dispersed state and crystal grain size. Moreover, in addition to these material factors, the metallurgical state of the culmination that takes into account all the factors of the manufacturing conditions is shown.

Therefore, in the Al alloy forgings containing excessive Si, increasing the content of Cu, Mn, etc. to increase the 0.2% proof stress to 360 MPa or more and reducing the thickness, each of the individual Al alloys Even if the rough conditions such as the alloying element amount, the holding temperature of the homogenization heat treatment, and the hot forging start temperature coincide, the conductivity of the Al alloy forging material surface is not always the same.

In addition to the above temperature conditions, etc., the influencing factors on the electrical conductivity of the surface of the Al alloy forged material after artificial age hardening treatment include the cooling rate during casting and the increase during homogenization heat treatment of the ingot. Temperature rate, holding time and cooling rate, types of hot forging machines such as mechanical forging and hydraulic forging and the number of forgings, processing rate distribution and forging end temperature conditions at each forging, solution treatment, quenching, It is a finer level such as temperature and time conditions for artificial age hardening treatment.

For Al alloy forgings containing excessive Si, increasing the content of Cu, Mn, etc. to increase the 0.2% proof stress to 360 MPa or more and reducing the thickness, conditions at these fine levels The difference is due to the great influence on the conductivity of the Al alloy forging material surface.

Therefore, if the rough material conditions and manufacturing conditions coincide with each other, if the conductivity of the Al alloy forging material surface is the same, the technical problem of the present invention is 0. The problem of variation in 2% yield strength does not occur.

In the present invention, the 0.2% proof stress of the Al alloy forged material is 360 MPa or more, and the Charpy impact value is 6 J / cm ² or more.
(0.2% proof stress: 360 MPa or more and Charpy impact value: 6 J / cm ² )
By setting the 0.2% proof stress of the Al alloy forging material to 360 MPa or more and the Charpy impact value to 6 J / cm ² or more, the Al alloy forging material has high strength and high toughness. It can be used as a structural material or a part of a transport device such as an automobile or a ship.

The chemical component composition in the Al alloy forging material of the present invention will be described. The chemical component composition of the Al alloy forging of the present invention is made of an Al—Mg—Si (6000) Al alloy, and is used for structural materials or parts of transportation equipment such as automobiles and ships, and has high strength, high toughness and resistance. It is specified to guarantee high durability such as stress corrosion cracking. Moreover, the chemical component composition of the Al alloy forging material of the present invention is one of the major factors that define the electrical conductivity of the forging material surface.

Therefore, the chemical composition of the Al alloy forging of the present invention is Mg: 0.60 to 1.80 mass%, Si: 0.80 to 1.80 mass%, Cu: 0.20 to 1.00 mass %, Fe: 0.05 to 0.40 mass%, Ti: 0.001 to 0.15 mass%, B: 1 to 500 ppm, Mn: 0.10 to 0.60 mass%, Cr: One or two or more of 0.10 to 0.40 mass% and Zr: 0.10 to 0.20 mass% are included, and the balance is made of Al and inevitable impurities.

The chemical component composition of the Al alloy forged material of the present invention is not limited to the component standards such as JIS of 6000 series Al alloy, and further improvement of the characteristics is possible as long as the various characteristics of the present invention are not impaired. Changes in the component composition such as appropriately including other elements for adding other characteristics are allowed as appropriate. Further, inevitable impurities inevitably mixed from the melting raw material scrap or the like are allowed because they do not impair the quality of the forging material of the present invention.

Next, the critical significance and preferred range of the content of each element of the chemical component composition of the Al alloy forged material of the present invention will be described.

(Mg: 0.60 to 1.80 mass%)
Mg is an essential element for precipitating as Mg ₂ Si (β ′ phase) together with Si by artificial age hardening and imparting a high 0.2% proof stress to the Al alloy forging. When the Mg content is less than 0.60% by mass, the age-hardening amount decreases, and the Charpy impact value (hereinafter referred to as toughness) and corrosion resistance, which are important for the Al alloy forging material, are decreased. On the other hand, if the content exceeds 1.80% by mass, the 0.2% proof stress becomes too high, which hinders the forgeability of the ingot. Further, likely to precipitate a large amount of _Mg 2 Si during tempering after solution treatment insertion to be described later, and _Mg 2 Si present on the grain boundary, Al, Si, Mn, Cr , Zr, Fe is selectively bind The average grain size of the Al—Fe—Si— (Mn, Cr, Zr) based crystal precipitates does not decrease, and the average interval between these crystal precipitates cannot be increased. As a result, the corrosion resistance of the Al alloy forging is reduced. On the other hand, if the Mg content is too much above this range, it becomes difficult to adjust the electrical conductivity of the Al alloy forging material surface to more than 42.5 IACS% and not more than 46.0 IACS% by adjusting the production conditions. Therefore, the Mg content is in the range of 0.60 to 1.80 mass%.

(Si: 0.80 to 1.80 mass%)
Si, together with Mg, is an essential element for precipitating as Mg ₂ Si (β ′ phase) by artificial age hardening and imparting a high 0.2% proof stress to the Al alloy forging. When the Si content is less than 0.80% by mass, the age hardening amount decreases, the 0.2% proof stress of the Al alloy forging material decreases, and the corrosion resistance decreases. On the other hand, if the content exceeds 1.80% by mass, coarse single Si particles crystallize and precipitate during casting and during quenching after solution treatment. In addition, excessive Si is excessive, and the average particle diameter of Mg ₂ Si and Al—Fe—Si— (Mn, Cr, Zr) based crystal precipitates existing on the grain boundaries is not reduced. The average distance between each other cannot be increased. As a result, like the Mg, the corrosion resistance and toughness of the Al alloy forging are reduced. Furthermore, workability is also hindered, for example, the elongation of the aluminum alloy forging is reduced. Moreover, when there is too much Si content from this range, it will become difficult to make the electrical conductivity of the Al alloy forging material surface over 42.5 IACS% and 46.0 IACS% or less by adjustment of manufacturing conditions. Accordingly, the Si content is in the range of 0.80 to 1.80 mass%.

(Cu: 0.20 to 1.00% by mass)
Cu contributes to improvement of 0.2% proof stress by solid solution strengthening, and has the effect of remarkably accelerating the age hardening of the Al alloy forging during the artificial age hardening treatment. If the Cu content is less than 0.20% by mass, these effects cannot be expected, and the 0.2% yield strength decreases. In order to stably obtain these effects, the Cu content is preferably set to 0.30% by mass or more. On the other hand, when the Cu content exceeds 1.00% by mass, the susceptibility to stress corrosion cracking and intergranular corrosion of the structure of the Al alloy forging is remarkably increased, and the corrosion resistance of the Al alloy forging is lowered. Moreover, when there is too much Cu content from this range, it will become difficult to make the electrical conductivity of the Al alloy forging material surface over 42.5 IACS% and the range of 46.0 IACS% or less by adjustment of manufacturing conditions. Therefore, the Cu content is in the range of 0.20 to 1.00% by mass, preferably 0.30 to 1.00% by mass.

(Fe: 0.05-0.40 mass%)
Fe is an element added to improve the toughness of the Al alloy forging. However, Fe is Al ₇ Cu ₂ Fe, Al ₁₂ (Fe, Mn) ₃ Cu ₂ , (Fe, Mn) Al ₆ , or coarse Al—Fe—Si— (Mn, Cr, Zr) based crystal precipitates are formed. These crystal precipitates become a starting point of fracture, and deteriorate toughness and fatigue characteristics. In particular, when the Fe content exceeds 0.40 mass%, more strictly 0.35 mass%, the Al—Fe—Si— (Mn, Cr, Zr) -based crystal precipitates present on the grain boundaries The average particle size increases and the average interval between crystal precipitates decreases. As a result, toughness decreases. On the other hand, if the Fe content is less than 0.05% by mass, cracks during casting, abnormal structures, and the like occur. Therefore, the Fe content is 0.05 to 0.40 mass%. More preferably, it is 0.05 to 0.35% by mass.

(Ti: 0.001 to 0.15 mass%)
Ti is an element added to refine crystal grains of an ingot and improve workability during extrusion, rolling, and forging. However, when the Ti content is less than 0.001% by mass, the effect of improving workability cannot be obtained. On the other hand, if the Ti content exceeds 0.15% by mass, coarse crystal precipitates are formed and the workability is lowered. Therefore, when Ti is contained, the content of Ti is in the range of 0.001 to 0.15 mass%.

(B: 1 to 500 ppm)
B, like Ti, is an element added to refine crystal grains of the ingot and improve workability during extrusion, rolling, and forging. However, when B is less than 1 ppm, this effect cannot be obtained. On the other hand, when the content exceeds 500 ppm, coarse crystal precipitates are formed, and the workability is lowered. Therefore, when B is included, the B content is in the range of 1 to 500 ppm.

(Mn: 0.10 to 0.60% by mass, Cr: 0.10 to 0.40% by mass, and Zr: 0.10 to 0.20% by mass)
These elements are Al—Mn based, Al—Cr based, in which Fe, Mn, Cr, Zr, Si, Al, etc. are selectively bonded according to their contents during the homogenization heat treatment and the subsequent hot forging. This is an Al—Zr intermetallic compound, and produces dispersed particles (dispersed phase) collectively called (Fe, Mn, Cr, Zr) ₃ SiAl ₁₂ system.

Since these dispersed particles have an effect of hindering the grain boundary movement after recrystallization, the coarsening of the average crystal grain size in the ST direction of the parting line structure during the forging process is prevented and the Al alloy forging of the present invention is performed. Fine crystal grains and sub-crystal grains can be obtained over the entire material. Further, Mn, Cr and Zr can be expected to increase 0.2% proof stress due to solid solution.

The aluminum alloy of the present invention contains one or more of Mn, Cr, and Zr, and the content of elements when contained is within the above range. If the content of Mn, Cr and Zr is too small, the above effect cannot be expected. On the other hand, the excessive content of these elements is coarse Al—Fe—Si— (Mn, Cr, Zr) during melting and casting. It is easy to produce intermetallic compounds and crystal precipitates of the system, and serves as a starting point of fracture, causing a decrease in at least one of the electrical conductivity, 0.2% proof stress, toughness, and corrosion resistance of the Al alloy forged material. Therefore, each of these elements is one or two in the range of Mn: 0.10 to 0.60 mass%, Cr: 0.10 to 0.40 mass%, and Zr: 0.10 to 0.20 mass%. Add more than seeds.

(Inevitable impurities)
As the inevitable impurities, elements such as Zn, Be, and V can be assumed, but any of them is allowed to be contained at a level that does not impair the characteristics of the present invention. Specifically, the elements of these inevitable impurities are required to have a content of each element of 0.05% by mass or less and a total content of 0.15% by mass or less.

(Si / Mg mass ratio: 1 or more)
The aluminum alloy of the present invention preferably has a mass ratio of Si / Mg of 1 or more. On the premise of each content range, the 0.2% proof stress is further improved by setting the mass ratio of Si / Mg to 1 or more. When the mass ratio of Si / Mg is less than 1, a further improvement effect of 0.2% proof stress cannot be obtained.

Moreover, it is preferable that the Al alloy forging material of this invention prescribe | regulates the hydrogen gas concentration to the following ranges.
(Hydrogen: 0.25ml / 100gAl or less)
Hydrogen (H ₂ ) is prone to forging defects such as bubbles caused by hydrogen, particularly when the degree of processing of the Al alloy forging material is small, and is a starting point of fracture, so that toughness and fatigue characteristics are likely to deteriorate. And in the structural material etc. of the transport aircraft which strengthened, the influence by hydrogen is especially large. Therefore, it is preferable that the content of hydrogen is as low as possible with 0.25 ml / 100 g Al or less.

Next, a method for producing an Al alloy forged material according to the present invention will be described. The manufacturing method of the present invention includes a melting step, a casting step, a homogenizing heat treatment step, a forging step, and a tempering step. In the production of the Al alloy forged material in the present invention, the control of the electrical conductivity of the surface of the Al alloy forged material to a range of more than 42.5 IACS% and less than 46.0 IACS%, 0.2% proof stress and Except for control of toughness, it can be produced by conventional methods. Below, the conditions of each process which improves the characteristic of Al alloy forging material, such as making the said electric conductivity into the range, are demonstrated.

(Dissolution process)
The melting step is a step of melting the Al alloy having the chemical component composition to form a molten metal.

(Casting process)
The casting step is a step of casting the molten metal adjusted to the chemical component composition into an ingot. Then, a normal melt 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 selected for casting. The shape of the ingot includes ingots such as round bars and slab shapes, and is not particularly limited.

In addition, the crystal grains of the ingot are refined, and the average grain size of the Al—Fe—Si— (Mn, Cr, Zr) based crystal precipitates existing on the grain boundaries is reduced, so that the average of crystal precipitates is reduced. In order to increase the interval, the molten metal is cooled at a cooling rate of 10 ° C./sec or more to form an ingot. If the cooling rate is slow, the average particle size of the Al—Fe—Si— (Mn, Cr, Zr) -based crystal precipitates existing on the grain boundary cannot be reduced, and the average interval between the crystal precipitates is increased. Can not do it. As a result, the 0.2% yield strength of the Al alloy forged material after the artificial age hardening treatment is lowered. Here, let the cooling rate of a molten metal be an average cooling rate from liquidus temperature to solidus temperature.

(Homogenization heat treatment process)
The homogenization heat treatment step is a step of subjecting the ingot to a predetermined homogenization heat treatment. Then, the ingot is subjected to a homogenization heat treatment at a heating rate of 5 ° C./min or less and a holding temperature of 450 to 550 ° C.

If the holding temperature exceeds 550 ° C. and is too high, the (Fe, Mn, Cr, Zr) ₃ SiAl ₁₂ -based dispersed particles themselves become coarse and the number of dispersed particles themselves is insufficient. Further, a relatively large number of fine dispersed particles cannot be dispersed in the crystal grains, so that the crystal grains cannot be refined. As a result, the 0.2% yield strength of the Al alloy forged material after the artificial age hardening treatment is lowered.

On the other hand, even if the holding temperature is too low as less than 450 ° C., the number of (Fe, Mn, Cr, Zr) ₃ SiAl ₁₂ -based dispersed particles deposited decreases and the number of dispersed particles themselves is insufficient. Further, Al—Fe—Si— (Mn, Cr, Zr) -based crystal precipitates cannot be sufficiently dissolved, and exist on the grain boundaries of the structure of the Al alloy forged material after the tempering step described later. The average particle size of Mg ₂ Si or Al—Fe—Si— (Mn, Cr, Zr) based crystal precipitates cannot be reduced, and it is difficult to increase the average interval between these crystal precipitates. As a result, the electrical conductivity of the surface of the Al alloy forged material after the artificial age hardening treatment cannot be controlled to a range exceeding 42.5 IACS% and 46.0 IACS% (hereinafter referred to as the present invention range).

In addition, in order to maintain the 0.2% yield strength of the Al alloy forged material after the artificial age hardening treatment, the rate of temperature increase to the holding temperature is slowed to 5 ° C./min or less. Further, the holding time at the holding temperature is preferably 2 hours or more. Furthermore, an air furnace, an induction heating furnace, a glass stone furnace, or the like is appropriately used for the homogenization heat treatment. Here, the heating rate of the ingot is the average heating rate from room temperature to the holding temperature.

(Forging process)
The forging process is a process in which the ingot subjected to the homogenization heat treatment is used as a forging material and hot forging is performed on the ingot by mechanical forging, hydraulic forging, or the like. At this time, the starting temperature of hot forging of the forging material is set to 460 to 540 ° C. When the starting temperature is less than 460 ° C., the ratio of the subgrain structure in the forged structure is reduced, and the grain boundaries in the forged structure are reduced, so that the precipitation of Mg ₂ Si is suppressed. As a result, the electrical conductivity of the surface of the Al alloy forged material after the artificial age hardening treatment cannot be controlled within the range of the present invention, and the 0.2% yield strength decreases. On the other hand, when the starting temperature exceeds 540 ° C., part of the structure may melt due to processing heat generated during forging, and the conductivity cannot be controlled within the range of the present invention, and the 0.2% proof stress and corrosion resistance are reduced. To do.

The end temperature for hot forging of the forging material is preferably 350 to 540 ° C. from the viewpoint of bringing the conductivity into the range of the present invention. Furthermore, in order to eliminate the cast structure remaining in the Al alloy forging material and to further improve the 0.2% proof stress and toughness, as the forging material, the ingot is subjected to homogenization heat treatment, extruded or rolled. Also good.
And, in order to set the forging material hot forging end temperature to 350-540 ° C, it is necessary to devise such as reheating before hot forging or using a mold that can be kept at high temperature. is there.

In addition, in order to make the electrical conductivity of the Al alloy forged material surface after the artificial age hardening treatment easily fall within the scope of the present invention, the hot forging is preferably performed by the mechanical forging method, and the number of forgings is also performed within 3 times. Is preferred. Further, the shape of the Al alloy forged material includes a near net shape (near net shape) close to the final product shape, and is not particularly limited.

(Refining process)
The tempering step is a step of performing solution treatment and artificial age hardening treatment after the forging step in order to obtain the required 0.2% proof stress, toughness and corrosion resistance of the Al alloy forged material. Specifically, the tempering process includes T6 (artificial age hardening treatment for obtaining the maximum strength after solution treatment at 520 to 570 ° C.), T7 (artificial age hardening for obtaining the maximum strength after the solution treatment). Excessive aging treatment exceeding the treatment conditions), T8 (artificial age hardening treatment to obtain the maximum strength by performing cold working after the solution treatment) and the like.

The solution treatment is performed at a holding temperature of 520 to 570 ° C. If the holding temperature is too low, solutionization is insufficient, Mg ₂ Si is not sufficiently dissolved, the conductivity cannot be controlled within the range of the present invention, and the 0.2% yield strength is reduced. On the other hand, if the holding temperature is too high, local melting and coarsening of crystal grains occur, and the 0.2% proof stress decreases. In addition, it is preferable that the holding time and the heating rate in the solution treatment are a holding time of 20 minutes to 20 hours and a heating rate of 100 ° C./hr or more in order to guarantee 0.2% proof stress. Here, the rate of temperature rise of the Al alloy forging is the average rate of temperature rise from the temperature at the time of solution treatment to the arrival of the holding temperature.

In addition, you may perform a quenching process after solution treatment. The quenching treatment is preferably performed by cooling into water or hot water, and the cooling rate is preferably 40 ° C./sec or more in order to prevent deterioration of toughness and fatigue characteristics. In addition, an air furnace, an induction heating furnace, a glass stone furnace, or the like is appropriately used for the solution treatment.

The artificial age hardening treatment greatly affects the electrical conductivity of the surface of the Al alloy forged material after the artificial age hardening treatment. For this reason, in consideration of the manufacturing history so far, the conductivity is kept within the range of the present invention to obtain the required 0.2% proof stress, and other conditions for obtaining the required toughness and corrosion resistance are selected. There is a need. In this respect, it depends on the amount of alloying elements and the manufacturing history (conditions) up to the artificial age hardening treatment, and it is necessary to check in individual manufacturing processes and equipment, but the surface of the Al alloy forging after the artificial age hardening treatment In order to make the electrical conductivity within the range of the present invention, the artificial age hardening treatment is performed at 170 to 200 ° C. × 4 to 9 hours in consideration of the conditions (maximum strength) to be the temper treatment material of T6, T7, and T8. Select from a range. For the artificial age hardening treatment, an air furnace, an induction heating furnace, an oil bath, or the like is appropriately used.

Moreover, it is preferable that the manufacturing method of this invention includes a degassing process between a melt | dissolution process and a casting process.
(Degassing process)
In the degassing step, hydrogen gas is removed (degassing treatment) from the molten metal melted in the melting step, and the hydrogen gas concentration in 100 g of the aluminum alloy is controlled to 0.25 ml or less. The removal of hydrogen gas is performed in a holding furnace for component adjustment of molten metal and removal of inclusions, and is performed by fluxing, chlorine refining, or in-line refining. It is preferable to remove hydrogen gas by blowing an inert gas such as argon into the molten metal using SNIF (Spinning Nozzle Inert Floatation) or porous plug (see JP 2002-146447 A).

Here, the hydrogen gas concentration is confirmed by measuring the hydrogen gas concentration of the ingot manufactured in the casting process or the forged material manufactured in the forging process. The hydrogen gas concentration of the ingot is obtained, for example, by cutting a sample from the ingot before homogenization heat treatment and ultrasonically washing with alcohol and acetone. For example, an inert gas flow melting thermal conductivity method (LIS) A06-1993). The hydrogen gas concentration of the forging material is, for example, a sample cut out from the forging material, immersed in a NaOH solution, the surface oxide film is removed with nitric acid, and ultrasonically cleaned with alcohol and acetone. It can be determined by measuring by a vacuum heating extraction volume method (LIS A06-1993).

Moreover, the production method of the present invention can also be provided with a preforming process such as a forging roll before the forging process.

Next, examples of the present invention will be described. An Al alloy ingot (φ68 mm diameter × 580 mm length round bar) having the chemical composition shown in Table 1 was cast at a cooling rate of 20 ° C./sec by a hot top casting method. And this ingot was homogenized and heat-treated at 550 ° C. × 4 hr at a heating rate of 5 ° C./min.

Furthermore, at the forging start temperature and forging end temperature shown in Table 2, three times of hot forging is performed by mechanical forging using upper and lower molds so that the total forging rate becomes 75%, and the shape of the automobile underbody member A forged Al alloy was produced. This forged material had a thickness of the thinnest portion of 6 mm.

Next, the Al alloy forging was subjected to a solution treatment for 1 hr at 550 ° C. in an air furnace, followed by water cooling (water quenching), and then an artificial age hardening treatment at 190 ° C. for 5 hr in an air furnace.

And, three test pieces were collected from the Al alloy forging material, and as shown in Table 2, tensile properties such as surface conductivity, tensile strength, 0.2% proof stress, elongation, and the like, The Charpy impact value (mechanical property), which is an index of toughness, was investigated. Moreover, each value of Table 2 shows the average value of three collection test pieces, respectively. The tensile strength, 0.2% proof stress, and elongation were measured according to JISZ2241 by taking the specimen S1 shown in FIG. 1 from an Al alloy forged material. Further, the Charpy impact value was obtained in accordance with the provisions of JISZ2242 by collecting the specimen S2 shown in FIG. In addition, when the 0.2% proof stress was 360 MPa or more and the Charpy impact value was 6 J / cm ² or more, it was considered good.

Separately, a C-ring test piece S3 shown in FIG. 3 was sampled from an Al alloy forged material and subjected to a stress corrosion cracking test. The stress corrosion cracking test conditions were performed according to the provisions of the ASTMG47 alternate dipping method using the C-ring test piece S3. The test conditions were as follows: C-ring test piece S3 was subjected to stress immersion of 75% of the proof stress in the LT direction of test piece S3 and repeatedly immersed in salt water and pulled up for 90 days. The presence or absence was confirmed. Stress corrosion cracking resistance is x (defect) when stress corrosion cracking has occurred, stress corrosion cracking is the case when intergranular corrosion that is likely to lead to stress corrosion cracking is occurring, but not stress corrosion cracking Table 2 shows the results when the crack resistance is △ (slightly poor) and stress corrosion cracking or intergranular corrosion (including superficial overall corrosion) does not occur. Shown in

As shown in Tables 1 and 2, Al alloy forgings (Nos. 1 to 10, 10A to 10H: Examples) satisfying the claims of the present invention have 0.2% proof stress, Charpy impact value and Excellent resistance to stress corrosion cracking. On the other hand, Al alloy forgings (Nos. 11 to 34: Comparative Examples) that do not satisfy the claims of the present invention were inferior in any of 0.2% proof stress, Charpy impact value, and stress corrosion cracking resistance. .

Specifically, no. No. 11 was inferior in Charpy impact value and stress corrosion cracking resistance because the Mg content was less than the lower limit. No. No. 12, since the Mg content exceeded the upper limit, the conductivity was less than the lower limit, and the stress corrosion cracking resistance was poor. No. No. 13 was inferior in 0.2% yield strength and stress corrosion cracking resistance because the Si content was less than the lower limit. No. In No. 14, since the Si content exceeded the upper limit, the conductivity was less than the lower limit, and the Charpy impact value and the stress corrosion cracking resistance were inferior. No. No. 15 had an inferior 0.2% proof stress because the Cu content was less than the lower limit. No. In No. 16, since the Cu content exceeded the upper limit, the conductivity was less than the lower limit, and the stress corrosion cracking resistance was poor. No. In No. 17, since the contents of Mg, Si and Cu exceeded the upper limit, the conductivity was less than the lower limit, and the Charpy impact value and the stress corrosion crack resistance were inferior.

No. Since 18 contained no Mn, Cr and Zr, the 0.2% yield strength was inferior. No. In No. 19, since the Mn content exceeded the upper limit, the conductivity was less than the lower limit, and the 0.2% yield strength was inferior. No. No. 20 was inferior in 0.2% proof stress and stress corrosion cracking resistance because the Cr content exceeded the upper limit. No. No. 21 had inferior 0.2% yield strength and stress corrosion cracking resistance because the Zr content exceeded the upper limit. No. In No. 22, since the contents of Mn, Cr and Zr exceeded the upper limit, the conductivity was less than the lower limit and the 0.2% yield strength was inferior.

No. Although the chemical composition of No. 23 satisfied the scope of the claims, the cooling rate during casting was less than the lower limit value, so the 0.2% yield strength was inferior. No. No. 24, although the chemical component composition satisfies the scope of the claims, the rate of temperature rise during the homogenization heat treatment exceeds the upper limit value, so the 0.2% yield strength was inferior. No. No. 25, the chemical component composition satisfied the claims, but the holding temperature during the homogenization heat treatment exceeded the upper limit value, so the 0.2% yield strength was inferior. No. 26 is an Al alloy forging material of Patent Document 1, and the chemical component composition satisfies the claims, but because the forging start temperature is less than the lower limit value, the conductivity is less than the lower limit value, 0.2 % Proof stress was inferior. No. In No. 27, the chemical component composition satisfied the claims, but the forging start temperature exceeded the upper limit value, so the conductivity exceeded the upper limit value, and the 0.2% proof stress and stress corrosion cracking resistance were inferior. No. In No. 28, the chemical component composition satisfies the claims, but the solution treatment temperature is less than the lower limit value, so the conductivity exceeds the upper limit value and the 0.2% yield strength is inferior. No. In No. 29, the chemical component composition satisfied the claims, but the artificial age hardening temperature exceeded the upper limit, so the conductivity exceeded the upper limit and the 0.2% yield strength was inferior.

No. No. 30 had an inferior Charpy impact value because the Fe content exceeded the upper limit. No. In No. 31, since the Fe content was less than the lower limit, cracking occurred during casting, and forging was impossible. No. No. 32 had an inferior Charpy impact value because the Ti content exceeded the upper limit. No. No. 33 had an inferior Charpy impact value because the B content exceeded the upper limit. No. No. 34 contained no Ti and B, so the cast structure became coarse and cracks occurred during forging.

S1 ... Test piece S2 ... Test piece S3 ... Test piece

Claims

Mg: 0.60 to 1.80 mass%, Si: 0.80 to 1.80 mass%, Cu: 0.20 to 1.00 mass%, Fe: 0.05 to 0.40 mass%, Ti: 0.001 to 0.15 mass%, B: 1 to 500 ppm, Mn: 0.10 to 0.60 mass%, Cr: 0.10 to 0.40 mass%, and Zr: 0.10 to An aluminum alloy forging material comprising one or two or more of 0.20 mass%, the balance being made of an aluminum alloy consisting of Al and inevitable impurities,
The electrical conductivity at 20 ° C. measured on the surface of the aluminum alloy forged material is more than 42.5 IACS% and not more than 46.0 IACS%, the 0.2% proof stress of the aluminum alloy forged material is 360 MPa or more, and Charpy An aluminum alloy forged material having an impact value of 6 J / cm 2 or more.
The aluminum alloy forging according to claim 1, wherein the aluminum alloy has a Si / Mg mass ratio of 1 or more.
3. The aluminum alloy forging according to claim 1, wherein a hydrogen gas concentration of the aluminum alloy forging is 0.25 ml / 100 g Al or less.
It is a manufacturing method of the aluminum alloy forging material according to claim 1 or 2,
A melting step of melting the aluminum alloy to form a molten metal;
A casting process in which the molten metal is cast at a cooling rate of 10 ° C./sec or more to form an ingot;
A homogenization heat treatment step in which the ingot is subjected to a homogenization heat treatment at a heating rate of 5 ° C./min or less and a holding temperature of 450 to 550 ° C .;
A forging process in which the ingot subjected to homogenization heat treatment is used as a forging material, and hot forging at a starting temperature of 460 to 540 ° C. is performed on the forging material;
A method for producing an aluminum alloy forged material comprising: after the forging step, a solution treatment at 520 to 570 ° C. and a tempering step of performing an artificial age hardening treatment at 170 to 200 ° C. for 4 to 9 hours. .