JP2013142168A - Aluminum alloy excellent in creep resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-resistant aluminum alloy which overcomes conventional technical problems and is excellent in creep resistance.SOLUTION: The aluminum alloy material for forging excellent in heat resistance is an aluminum alloy comprising 5.1-6.5% (mass%, this shall apply hereafter) Cu, 0.30-0.70% Mg, 0.10-1.0% Ag, 0.10-0.50% Mn, 0.07-0.11% Cr, and 0.06-0.30% Ti, with the balance comprising Al and unavoidable impurities, wherein the amount of Mn+Cr solid-dissolved is in the range of 0.05-0.50%, and the creep rapture life under conditions of 200°C and 160 MPa is 500 hr or longer.

Description

  INDUSTRIAL APPLICABILITY This invention is used for applications requiring high strength and creep resistance in a high temperature range exceeding 150 ° C. as parts of aircraft and space equipment, structural materials, parts of internal combustion engines such as automobiles and superchargers. The present invention relates to a heat resistant aluminum alloy.

  As a technique for increasing the strength of an aluminum alloy material, increasing the strength by age hardening has been widely used. However, in general, when such an aluminum alloy age hardened material is exposed to a high temperature range exceeding 100 ° C. for a long time, the softening is often caused by coarsening of precipitates. Therefore, in order to suppress such softening, JIS A2618 alloy and A2219 alloy, which are Al-Cu based alloys, are generally used as heat-resistant alloys by adding various elements and optimizing component compositions to improve high temperature strength. It is put into practical use as an aluminum alloy.

  In order to further improve the high-temperature strength of such an Al—Cu alloy, as shown in, for example, Patent Document 1 and Patent Document 2, a precipitate of θ ′ phase or Ω phase in an alloy in which Ag is added together with Mg. Attempts have been made to improve the high-temperature strength by dispersion strengthening of Al-V compounds by adding V and by adding V.

However, the use of higher temperature characteristics of these aluminum alloy members has been demanded from the point of increasing the usage environment of aluminum alloy members, and conventional alloys have insufficient creep resistance characteristics at high temperatures, and further improved creep resistance characteristics. There is a need to.
Japanese Patent No. 3999709 Japanese Patent No. 4088546 Japanese Patent No. 4058398

  An object of the present invention is to provide a heat-resistant aluminum alloy that eliminates the problems of the prior art as described above and has excellent creep resistance.

  In order to solve the above-mentioned problems, the present inventors have made various experiments and researches on an alloy in which Mg and Ag are added to an Al—Cu system, that is, an Al—Cu—Mg—Ag system alloy, and have an effect on creep resistance. As a result of detailed investigations on the effects of precipitation strengthening and solid solution strengthening of additive component elements, Mn and Cr, which have been used to improve strength by refining crystal grains or improve high temperature strength by dispersion strengthening, maintain a solid solution state. It was found that the creep characteristics were remarkably improved.

  Specifically, the heat-resistant aluminum alloy for extension work of the invention of claim 1 is Cu 5.1-6.5%, Mg 0.10-0.7%, Ag 0.10-1.0%, Mn 0.10. Creep rupture under conditions of 200 ° C. and 160 MPa in an aluminum alloy containing ˜0.50%, Cr 0.07 to 0.12%, Ti 0.06 to 0.30%, the balance being Al and inevitable impurities It is an aluminum alloy forged material excellent in heat resistance characterized by having a lifetime of 500 hours or more.

  Further, the invention of claim 2 is characterized in that in the heat resistant aluminum alloy for extension processing according to claim 1, the solid solution amount of Mn + Cr is in the range of 0.05 to 0.50%. It is an excellent aluminum alloy forging material.

  Further, the invention of claim 3 is characterized in that after the alloy ingot having the composition of claims 1 and 2 is subjected to homogenization treatment within 490 to 530 ° C. for 48 hours, the ingot ratio is determined from three directions orthogonal to each other. A method for producing an aluminum forged material excellent in heat resistance, characterized in that forging is performed at 2 or more and the total forging ratio in each direction is 7 or more, and the creep rupture life at 200 ° C. and 160 MPa is 500 hours or more. It is.

  The heat-resistant aluminum alloy of the present invention can improve the creep resistance in a temperature range of 200 ° C. or higher, which is difficult with conventional alloys, and is therefore suitable without deteriorating reliability even in a higher temperature and higher load environment. Can be used. That is, the aluminum alloy of the present invention can be used as a component or structural member that requires high strength and high toughness in a high temperature range of 200 ° C. or higher, and subjected to a stretching process such as rolling, forging, and extrusion. It can be suitably used for an outer wall of a high-speed moving body such as a rocket or an aircraft, an internal combustion engine or a supercharger member. Therefore, according to this invention, the outstanding effect that the use which can make use of the advantage of an aluminum alloy is expanded greatly can be produced.

  The heat-resistant aluminum alloy of the present invention is basically based on an Al-Cu-Mg-Ag alloy obtained by adding Mg and Ag to a so-called No. 2000 age-hardening heat-resistant alloy of Al-Cu type. Further, Mn and Cr are added in appropriate amounts at the same time.

  Here, in the Al—Cu—Mg—Ag based alloy that is the alloy of the present invention, an Al—Cu based so-called θ ′ phase or an Al—Cu—Mg—Ag based so-called Ω phase is precipitated by aging treatment. In this invention, high-temperature deformation characteristics and high-temperature creep characteristics are remarkably improved by further dissolving Mn and Cr in appropriate amounts. It becomes possible to improve.

  The component composition of the heat-resistant aluminum alloy for stretch processing according to the present invention is also determined from the viewpoint of sufficiently exhibiting these functions and obtaining high creep characteristics. Therefore, the reason for limiting the component composition in the heat-resistant aluminum alloy of the present invention will be described below.

Cu:
By adding Cu, the Al—Cu-based θ ′ phase or the Al—Cu—Mg—Ag-based Ω phase is precipitated by the aging treatment as described above, and contributes to curing. If the amount of Cu is less than 5.1%, the effect cannot be sufficiently obtained, and if it exceeds 6.5%, a stable phase θ that cannot be completely melted by the solution treatment is formed, resulting in a decrease in strength and ductility. . Therefore, the amount of Cu is set within the range of 5.1 to 6.5%. In addition, when higher intensity | strength is required, it is desirable that the amount of Cu shall be 5.3 to 6.5%.

Mg:
Mg also precipitates an Al—Cu—Mg—Ag Ω phase by aging treatment and contributes to hardening.
If the amount of Mg is less than 0.10%, the effect cannot be sufficiently obtained. On the other hand, addition of Mg exceeding 0.7% cannot be expected to further improve the strength, but also decreases ductility and toughness. It becomes remarkable. Therefore, the amount of Mg is set within the range of 0.10 to 0.7%. In particular, when high strength is required, the Mg content is desirably 0.2 to 0.7%.

Ag:
Ag also contributes to hardening by precipitating an Ω phase by aging treatment. If the amount of Ag is less than 0.10%, the effect cannot be sufficiently obtained. On the other hand, even if Ag exceeds 1.0%, further improvement in strength cannot be expected, and the amount of expensive Ag used increases. It only reduces the economy. Therefore, the Ag content is set in the range of 0.10 to 1.0%. In particular, when high strength is required, the Ag content is desirably 0.2 to 1.0%.

Mn:
Mn has a great effect on the suppression of creep deformation at high temperatures by forming a solid solution and fine precipitates. If the amount of Mn is less than 0.1%, the effect of improving the creep characteristics is not sufficient, and if it exceeds 0.5%, the effect is saturated and becomes a precipitation nucleation site when the cooling rate is slow, causing a decrease in strength.

Cr:
Cr is an important element that greatly improves the suppression of creep deformation at high temperatures by solid solution. When the Cr content is less than 0.07%, the effect of improving the creep characteristics is not sufficient, and when it exceeds 0.11%, the effect is saturated, and excessive addition of Cr forms a coarse Al—Cr crystallized product, When the cooling rate is slow, it becomes a heterogeneous precipitation nucleation site of the θ ′ phase or the Ω phase, causing a decrease in strength.

Ti:
Ti is added as a crystal grain refining material during casting. The effect is insufficient if it is less than 0.06%, and if it exceeds 0.30%, the effect is saturated and coarse intermetallic compounds are easily formed, and mechanical properties and fatigue properties are deteriorated.

  In addition, Ti considered as a refinement | miniaturization component in a general aluminum alloy is used in order to form a Ti-B type compound by adding B simultaneously, and to refine an ingot crystal grain. . For this reason, even if B is contained in a normal range, the effect of the present invention is not inhibited.

  In addition, Si contained as an inevitable impurity in the aluminum ingot easily forms a crystallized substance with other transition metals and the like, resulting in a decrease in material ductility and toughness. When the Si content exceeds 0.15%, a significant decrease in toughness occurs, which is not preferable. The allowable content of Si is largely related to the balance between the economic viewpoint based on the price of the raw metal and the required characteristics suitable for the application. On the other hand, Si has an effect of improving the strength of the aluminum alloy. Judging from the above, it is desirable that the Si content is in the range of 0.02 to 0.15%.

  Further, similarly to Si, Fe contained as an inevitable impurity in an aluminum ingot easily forms a crystallized substance together with other transition metals and the like, resulting in a decrease in material ductility and toughness. If the Fe content exceeds 0.20%, the toughness is clearly lowered, which is not preferable. The allowable content of Fe is also largely related to the balance between the economic viewpoint based on the price of the raw metal and the required properties suitable for the application. On the other hand, Fe has the effect of improving the high-temperature properties, and from these, Judging from the viewpoint, it is desirable that the Fe content is in the range of 0.05 to 0.20%.

  In addition to the elements described above, basically, Al and inevitable impurities may be used. However, other elements other than the above-described component elements may also be used for the high-temperature creep characteristics and mechanical properties of the heat-resistant aluminum alloy according to the present invention. Inclusion within the range that does not impair the physical characteristics and other characteristics is allowed.

Mn, Cr solid solution amount:
As described above, Mn and Cr have a function of remarkably improving the creep resistance in a solid solution state. The effect is insufficient if it is less than 0.05%. Although the upper limit is not particularly defined, Mn and Cr are precipitated as intermetallic compounds because of their low solubility in the aluminum alloy. As a result of various studies, 0.5% is the limit of the solid solution amount under industrial production conditions, and this is the upper limit in the present invention.

  In order to increase the high temperature strength and creep characteristics, it is extremely important to uniformly precipitate and disperse the aforementioned θ phase and Ω phase. In order to achieve this, it is essential to forge the ingot from three directions orthogonal to each other. In the forging from one or two directions, the structure simply extends in a certain direction, so that the precipitation phase is not sufficiently uniformized.

  The forging ratio is also important. The forging ratio in each direction is 2 or more, the total forging ratio in each direction is 7 or more, the ingot structure is destroyed, the solution effect is enhanced, and the θ phase and Ω phase during aging treatment are uniform. It is necessary to be precipitated and dispersed. If the forging ratio in each direction is 2 or less and the sum of the forging ratios in each direction is 7 or less, the ingot structure remains, so that the θ phase and the Ω phase cannot be uniformly precipitated.

  In addition, it becomes more effective for uniform precipitation by performing a heat treatment at 490 to 530 ° C. within 24 hours in the middle of forging in each direction or after completion of forging.

  Although the method for manufacturing the aluminum alloy for extending | stretching of this invention as mentioned above is not specifically limited, A preferable manufacturing method is demonstrated below.

First, an ingot is produced by casting an aluminum alloy melt adjusted to be within the component range of the present invention.
The cast ingot is then homogenized. In addition, when cutting an ingot before a homogenization process as needed, there is a possibility that the ingot may break due to residual stress. Therefore, even if the ingot is subjected to heat treatment at a temperature of 300 ° C. to 450 ° C. for less than 20 hours to relieve the residual stress of the ingot and then cut, it does not affect the achievement of the object of the invention.

  Here, the homogenization temperature is preferably 490 to 530 ° C. and less than 25 hours. If the homogenization temperature is less than 490 ° C., the homogenization of Cu, Mg, and Ag, which are the main alloy elements contributing to aging precipitation strengthening, is insufficient, and it is impossible to improve the strength. On the other hand, if the homogenization temperature exceeds 530 ° C., the possibility of burning increases. Moreover, if the homogenization treatment time is long, Mn and Cr that have been forcibly dissolved during the homogenization treatment start to precipitate as Al—Mn and Al—Cr compounds. The effect of Mn and Cr to refine precipitates such as the θ ′ phase and the Ω phase, and the effect of suppressing the coarsening of aging precipitates that occur during high-temperature exposure is that Mn and Cr are dissolved in the Al ground. Therefore, if an Al-Mn-based or Al-Cr-based compound precipitates more than necessary during the homogenization process, the intended effect of the present invention is hardly obtained. Therefore, the homogenization treatment time is preferably less than 25 hours, more preferably less than 15 hours.

  The ingot after the homogenization treatment is drawn into an aluminum wrought material having a desired shape depending on the application. More specifically, as the expansion process, a rolling process is performed on the plate material, a forging process is performed on the forging material, and an extrusion process is performed on the shape material. The Al—Cu—Mg—Ag alloy that is the subject of the present invention is likely to generate microporosity (a minute void-like defect remaining in the ingot) during casting, and this microporosity is the starting point of fracture. In order to damage the toughness, a process of crushing the microporosity is required.

  In general, a large number of crystallized substances exist in the ingot structure at the boundary of the solidification cell. In this case, even if the individual crystallized substances are fine, they are mechanically In order to deteriorate the fatigue characteristics, it is necessary to destroy the dense state of crystallized substances. Furthermore, in order to ensure ductility, it is also important to reduce the equivalent circle diameter of crystal grains in the final product, particularly in a cross section perpendicular to the rolling direction, to 500 μm or less. The crystal grains here include both equiaxed grains and flat grains, but the crystal grain size in the case of flat grains is defined as the length in the major axis direction. In order to improve the microstructure as described above, a drawing process such as rolling, extrusion, forging, or the like is essential. Although the microstructure is affected by the processing rate, in order to improve toughness, the rolling reduction is 50% or more in the case of rolling, the extrusion ratio is 2 or more in the case of extrusion, and the forging ratio is 2 in the case of forging. The above is preferable. Further, in the case of a forged product, it is more desirable that the forging direction is performed not only in one direction but in at least two different directions, and the forging ratio in each direction is 2 or more.

  The aluminum alloy material after such extension processing is further subjected to solution treatment and quenching treatment, and then subjected to high-temperature artificial aging treatment. In this solution treatment, the solution treatment is desirably performed in the range of 495 to 535 ° C. in order to make Cu, Mg, and Ag, which are alloy components contributing to age hardening, dissolve as much as possible. However, as in the case of the homogenization treatment described above, if the Mn and Cr that have been forcibly dissolved are precipitated as an Al—Mn-based and Al—Cr-based compound more than necessary during the solution treatment, the object of the present invention is achieved. It is difficult to obtain the effect. Accordingly, the solution treatment time is preferably less than 15 hours, more preferably less than 8 hours.

  In addition, in the quenching treatment, the quenching cooling rate in the temperature range of 280 to 480 ° C. is set to 10 ° C./min or more in order to suppress reprecipitation of Cu, Mg, and Ag as alloy components contributing to age hardening as much as possible. It is desirable to cool to a temperature of 60 ° C. or lower when high strength is required, and to a temperature of 75 ° C. or higher when residual stress becomes a problem.

  The artificial aging treatment is desirably performed at 160 to 200 ° C. for about 2 to 60 hours. If residual stress due to quenching is particularly problematic, it is desirable to perform cold working after quenching.

  Hereinafter, the present invention will be described in more detail based on examples. However, it goes without saying that the present invention is not limited to these examples.

  Each aluminum alloy having chemical components shown in Alloys A to T in Table 1 was melted and semi-continuously cast to obtain an ingot having a diameter of 160 mm and a length of 1000 mm. The ingot was subjected to homogenization treatment at 520 ° C. for 6 hours, and then a forging material having a diameter of 150 mm and a length of 250 mm was obtained by chamfering and cutting. In the hot working, the starting temperature was 400 ° C., the forging ratio was 4, and the plate thickness was 60 mm. The solution treatment was carried out at 520 ° C. for 4 hours, followed by warm water quenching at about 80 ° C. Thereafter, an aging treatment was performed at 200 ° C. for 5 hours to obtain a final product. In order to evaluate the mechanical properties and high-temperature creep properties of the test materials, a round bar specimen having a diameter of 10 mm was taken from the LT direction, and a tensile test at room temperature and a creep test at 200 ° C. were performed.

  In addition, A2618 alloy was also evaluated at the same time as a representative example of conventional heat-resistant alloys. Regarding the creep resistance, a stress of 160 MPa was applied at 200 ° C., and the rupture life was measured. As a result, those having a rupture life of 500 hours or more were judged to be excellent in creep resistance. The solid solution amount of Mn and Cr was analyzed by the phenol dissolution method. These results are also shown in Table 2.

  As is apparent from Table 2, the alloys P to W of comparative examples in which the alloy composition of Cu, Mg, Ag, Mn, Cr, and Ti is outside the scope of the present invention have good mechanical properties and creep resistance properties. Was not obtained. On the other hand, it was found that the alloys A to O of the examples of the present invention were good and excellent in both mechanical properties and creep resistance properties.

  Forging shown in Table 3 was performed on Alloy D in Table 1. After the solution treatment, it was manufactured and tested under the same conditions as described above. The results are shown in Table 4.

From these results, it was confirmed that the creep characteristics were further improved by forging a total of 7 or more at a forging ratio 2 or more in each direction.

Claims (3)

  Cu 5.1-6.5% (mass%, the same applies hereinafter), Mg 0.30-0.70%, Ag 0.10-1.0%, Mn 0.10-0.50%, Cr 0.07-0.11 %, Ti 0.06 to 0.30%, the balance being Al and inevitable impurities in an aluminum alloy, the creep rupture life at 200 ° C. and 160 MPa is 500 hours or more, excellent heat resistance Aluminum alloy forging.   Cu 5.1-6.5%, Mg 0.30-0.70%, Ag 0.10-1.0%, Mn 0.10-0.50%, Cr 0.07-0.11%, Ti 0.06-0 In an aluminum alloy containing 30% and the balance being Al and inevitable impurities, the amount of solid solution of Mn + Cr is in the range of 0.05 to 0.50%, and creep rupture at 200 ° C. and 160 MPa. An aluminum alloy forging material excellent in heat resistance, characterized by having a lifetime of 500 hours or more.   The alloy ingot having the composition of claims 1 and 2 is subjected to homogenization treatment at 490 to 530 ° C. within 48 hours, then forged at a forging ratio of 2 or more from three directions perpendicular to each other, and each A method for producing an aluminum forged material excellent in heat resistance, characterized in that a total forging ratio in a direction is 7 or more and a creep rupture life under conditions of 200 ° C. and 160 MPa is 500 hours or more.