JP5879181B2 - Aluminum alloy with excellent high temperature characteristics - Google Patents

Description

  The present invention relates to an aluminum alloy having excellent high-temperature characteristics for high-speed moving parts that rotate or slide at high speed.

  Aluminum has the characteristics of low density and high strength and easy processing. It has been known for a long time that it is used for transportation machines such as railway vehicles, automobiles, and ships, various machine parts, engine parts, etc. that require light weight, strength, and processing characteristics. Specifically, it is used for high-speed moving parts that rotate or slide at high speed, such as rotating rotors (small blades) such as generators and compressors, rotating impellers (large blades), and engine pistons.

High-speed moving parts used in these applications include high-temperature properties (heat resistance, high-temperature fatigue strength, creep resistance at high temperatures, Strength) is required.
As described in Patent Document 1 and Patent Document 2, a rotor that is one of the mechanical parts, which has been improved in these high-temperature characteristics, is known. This rotor is composed of an aluminum alloy (hereinafter, referred to as an Al alloy as appropriate) to which aluminum is basic and zirconium, manganese, iron or the like is added as a main component.

  The Al alloy according to the invention described in Patent Document 1 and Patent Document 2 contains 0.1 to 0.25% by mass of Zr as an alloy additive component, and has high static high-temperature strength and dynamic high-temperature strength and creep. It has characteristics. It is described that this Zr component contributes to Mn vacancies filling and thermal stability of the alloy.

Special table 2009-535550 gazette Special table 2009-5535551 gazette

However, in these conventional techniques, when the Zr content increases, the quenching sensitivity of the Al alloy becomes sharp, and there is a problem that the strength is lowered particularly in a large material when the cooling rate is low in the quenching process before the artificial age hardening treatment. Moreover, since the internal residual stress becomes large, the workability has also been a problem. As described above, the material characteristics including the high temperature characteristics of the Al alloy have not been sufficiently improved particularly in a large material.
Recently, rotating rotors and pistons have been used in situations such as higher speed rotation, sliding, and high temperature than before, and there has been a demand for improvement in metal fatigue strength of Al alloys.

  This invention is made | formed in view of the said problem, and makes it a subject to provide Al alloy excellent in the high temperature characteristic. More preferably, it is an object to provide an Al alloy having improved metal fatigue strength.

The Al alloy excellent in high temperature characteristics according to the present invention is Si: more than 0.1% by mass and 1.0% by mass or less, Cu: 3.0% by mass or more and 7.0% by mass or less, Mn: 0.05 1 mass% or more and 1.5 mass% or less, Mg: 0.01 mass% or more and 2.0 mass% or less, Ti: 0.01 mass% or more and 0.10 mass% or less, Ag: 0.05 mass% or more. 0 wt% or less, containing, and, Zr: restricted to less than 0.1 wt%, the remainder Ri is Do of Al and unavoidable impurities, the maximum equivalent circle diameter der Rukoto less 60μm intermetallic compound Features. The maximum equivalent circle diameter will be described later.

By adopting the above-described structure, the Al alloy can obtain normal temperature strength and high temperature strength, sufficient creep properties at high temperature, and normal temperature strength and high temperature strength. As a result, the performance required for the Al alloy for high-speed moving parts used at high temperatures, which is the object of the present invention, can be ensured.
By controlling the maximum equivalent circle diameter of the intermetallic compound as described above, the strength of the intermetallic compound and the matrix portion, the hardness, the difference in material properties such as Young's modulus, and the failure of the Al alloy material due to metal fatigue The possibility of becoming a starting point can be reduced. Thereby, the improvement of metal fatigue strength is achieved.

  Moreover, the Al alloy according to the present invention is the Al alloy, and preferably further contains V: 0.15% by mass or less.

  By further containing V in the above configuration, Al—V-based dispersed particles can be precipitated in the Al alloy. Since these dispersed particles have an effect of hindering grain boundary movement after recrystallization, coarsening of crystal grains is prevented. And normal temperature strength and high temperature strength, and especially high temperature metal fatigue strength can be improved.

  According to the present invention, an Al alloy having excellent high temperature characteristics can be obtained. Moreover, according to the present invention, an Al alloy having improved metal fatigue strength can be obtained.

Hereinafter, the Al alloy according to the present invention will be described in detail based on the embodiments of the present invention. By setting the element composition described below and the maximum equivalent circle diameter of the intermetallic compound, the Al alloy has high temperature characteristics. For this reason, high-speed moving parts such as rotors and pistons are manufactured using the Al alloy according to the present invention, and when these parts are incorporated in products such as generators, compressors and engines, the parts rotate at high speed. It can withstand frictional heat generated by contact between parts when sliding and contact with (compressed) air, use under high-temperature (compressed) air, and deformation stress applied to the parts. . Therefore, the Al alloy according to the present invention is optimal for high-speed moving parts that rotate or slide at high speed, such as rotating rotors (small blades) and rotating impellers (large blades) such as generators and compressors, or engine pistons. It is possible to use.
Note that the present invention is not limited to such an embodiment, and can be appropriately changed without departing from the technical idea of the present invention.

<Alloy components>
The Al alloy according to the present invention contains a predetermined amount of Si, Cu, Mn, Mg, Ti, and Ag, regulates Zr to be less than a predetermined amount, and the balance is made of Al and inevitable impurities.
Further, it contains V as a selective component in a predetermined amount or less.
Furthermore, the maximum equivalent circle diameter of the intermetallic compound is regulated to a predetermined value or less as an optional component.
Hereinafter, the reasons for limiting each component and the reasons for defining the maximum equivalent circle diameter of the intermetallic compound will be described.

(Si: more than 0.1% by mass and 1.0% by mass or less)
Si has the effect of increasing the strength of the Al alloy, and the addition of Si tends to increase the number of precipitates that are effective in improving the strength. Further, the addition of Si is effective in suppressing dislocation loops in the alloy. For this reason, the addition of Si is effective for the refinement of the precipitated phase and uniform precipitation.

The effect is small when the Si content is 0.1 mass% or less. On the other hand, if the Si content exceeds 1.0% by mass, a coarse intermetallic compound is produced, which causes poor molding of a high-speed moving part such as a rotating rotor, rotating impeller, and piston, and decreases or breaks the metal fatigue strength.
Therefore, the Si content is more than 0.1% by mass and 1.0% by mass or less. Preferably, it exceeds 0.1 mass% and is 0.7 mass% or less. More preferably, it is more than 0.1 mass% and 0.6 mass% or less.

(Cu: 3.0% by mass or more and 7.0% by mass or less)
Cu is a basic component of the Al alloy according to the present invention. The Al alloy of the present invention is an Al alloy used for machine parts such as a rotating rotor, a rotating impeller, and a piston. Cu is an indispensable component for ensuring the high temperature creep characteristics, room temperature proof stress, and high temperature proof strength, which are required for Al alloys mainly in the present invention due to the effects of both solid solution strengthening and precipitation strengthening. . Thus, Cu improves the strength of the Al alloy by the actions of both solid solution strengthening and precipitation strengthening. More specifically, Cu precipitates the θ ′ phase and Ω phase finely and densely on the (100) surface and (111) surface of the Al alloy during the high temperature artificial age hardening treatment, and after the artificial age hardening treatment. The strength of the Al alloy is improved.

This effect is exhibited when the Cu content is 3.0 mass% or more. If the Cu content is less than 3.0% by mass, the effect is small, and sufficient creep characteristics and high temperature proof stress of the Al alloy at high temperature cannot be obtained. On the other hand, if the Cu content exceeds 7.0% by mass, the strength becomes too high, and the forgeability of the Al alloy decreases. In addition, the intermetallic compound in the Al alloy structure tends to be coarse, and the metal fatigue strength of the Al alloy decreases.
Accordingly, the Cu content is set to 3.0% by mass or more and 7.0% by mass or less. Preferably, it is 4.0 mass% or more and 7.0 mass% or less. More preferably, it exceeds 4.5 mass% and is 7.0 mass% or less.

(Mn: 0.05 mass% or more and 1.5 mass% or less)
Mn fiber-structures the microstructure of the Al alloy and improves the normal temperature strength and the high temperature strength. Mn precipitates Al—Mn-based dispersed particles which are thermally stable compounds in the Al alloy matrix during the homogenization heat treatment. These dispersed particles include Al ₂₀ Cu ₂ Mn ₃ . Since these dispersed particles have an action of hindering grain boundary movement after recrystallization, they are effective in preventing the coarsening of crystal grains.

When the Mn content is less than 0.05% by mass, these effects are small. On the other hand, if the content of Mn exceeds 1.5% by mass, a coarse insoluble intermetallic compound is likely to be produced during melt casting, which causes defective molding and breakage of the Al alloy material.
Therefore, the Mn content is set to 0.05% by mass or more and 1.5% by mass or less. Preferably, it is 0.05 mass% or more and 1.0 mass% or less. More preferably, it is 0.05 mass% or more and 0.8 mass% or less.

(Mg: 0.01% to 2.0% by mass)
Mg, like Cu, ensures the creep characteristics at high temperatures and the normal temperature proof strength and the proof strength at high temperatures, which are mainly required for Al alloys in the present invention, by the action of both solid solution strengthening and precipitation strengthening. It is an essential ingredient to do. More specifically, Mg, like Cu, causes the θ ′ phase and Ω phase to be finely and densely deposited on the (100) surface and (111) surface of the Al alloy during the high-temperature artificial age hardening treatment. The strength of the Al alloy after the artificial age hardening treatment is improved.

The effect is exhibited when the Mg content is 0.01% by mass or more. When the Mg content is less than 0.01% by mass, the above-described effects are small, and sufficient characteristics of the Al alloy at high temperatures, and normal temperature resistance and high temperature resistance cannot be obtained. On the other hand, if the Mg content exceeds 2.0 mass%, the strength becomes too high, and the possibility of deterioration of workability such as forgeability increases.
Therefore, the Mg content is set to 0.01% by mass or more and 2.0% by mass or less. Preferably, it is 0.01 mass% or more and 1.5 mass% or less. More preferably, it is 0.01 mass% or more and 1.0 mass% or less.

(Ti: 0.01% by mass or more and 0.10% by mass or less)
Ti has the effect of refining crystal grains during casting.
This effect is small when the Ti content is less than 0.01% by mass. On the other hand, when the Ti content exceeds 0.10% by mass, a coarse intermetallic compound is formed. And since this intermetallic compound becomes a starting point of destruction of Al alloy material at the time of a shaping | molding process, if it adds exceeding 0.10 mass%, the moldability of Al alloy will fall.
Therefore, the Ti content is set to 0.01% by mass or more and 0.10% by mass or less.

(Ag: 0.05 mass% or more and 1.0 mass% or less)
Ag forms a fine and uniform Ω phase in an Al alloy, and at the same time, the room temperature strength and high temperature strength of the Al alloy are reduced by extremely narrowing the width of the region where no precipitated phase is present (PFZ; solution-depleted precipitate free zone). In addition, the high temperature creep property is improved.
If the content of Ag is less than 0.05% by mass, this effect is small. On the other hand, even if the content of Ag exceeds 1.0% by mass, the effect is saturated.
Therefore, the content of Ag is set to 0.05% by mass or more and 1.0% by mass or less. Preferably, it is 0.05 mass% or more and 0.7 mass% or less.

(Zr: less than 0.1% by mass (including 0% by mass))
Zr precipitates Al—Zr-based dispersed particles that are thermally stable compounds in the Al alloy structure during the homogenization heat treatment. The dispersed particles have an effect of forming the microstructure of the Al alloy into a fiber structure and improving the normal temperature strength and the high temperature strength.
However, in the quenching step after the solution treatment step, when the average cooling rate between 400 ° C. and 290 ° C. is slowed down to 500 ° C./second or less, when Zr is contained by 0.1 mass% or more, In the quenching treatment after the solution treatment, a stable phase such as AlCu ₂ is coarsely precipitated around the Al—Zr-based dispersed particles. As a result, even if the artificial aging treatment at a high temperature is performed next, the yield strength at a high temperature may be reduced.
Therefore, in order to lower the quenching sensitivity of the Al alloy, the Zr content is set to less than 0.1% by mass.

(V: 0.15 mass% or less)
V, which is an optional component, precipitates in the Al alloy structure as an Al—V compound, and can improve high-temperature metal fatigue strength. Further, V precipitates Al—V-based dispersed particles that are thermally stable compounds in the Al alloy structure even during the homogenization heat treatment. Since these dispersed particles have an action of hindering the grain boundary movement after recrystallization, there is an effect of preventing the coarsening of crystal grains.
Due to this effect, V causes the microstructure of the Al alloy to become a fiber structure, thereby improving the normal temperature strength and the high temperature strength, and particularly the high temperature metal fatigue strength. And since the effect | action which precipitates a stable phase coarsely is comparatively small compared with Zr, Cr, and Mn, it is more preferable in order to improve normal temperature strength, high temperature strength, and high temperature metal fatigue strength.

Therefore, in order to ensure the high temperature characteristics of the Al alloy more reliably, the V content is selected to be 0.15% by mass or less in order to refine the crystal grain size to 500 μm or less. It is preferable to make it contain. Moreover, the effect is small if content of V is less than 0.05 mass%. On the other hand, if the content of V exceeds 0.15% by mass, a coarse insoluble intermetallic compound is likely to be produced during melting and casting, which causes a molding failure and breakage of the Al alloy.
Therefore, the content of V is preferably 0.15% by mass or less, but may be 0% by mass. A preferred lower limit is 0.05% by mass.

(Balance: Al and inevitable impurities)
In addition to the above components, the Al alloy is composed of Al and inevitable impurities. Inevitable impurities such as Ni, Zn, B, etc., which are contained in bullion and intermediate alloys and are within the generally known range, inhibit the high temperature characteristics and other characteristics of the Al alloy according to the present invention. Inclusion in the range not allowed is allowed.

(Other elements)
Containing other elements within a range that does not impair the high temperature characteristics and other characteristics of the Al alloy according to the present invention is allowed.
Fe also has an effect of improving the high temperature characteristics of the Al alloy and may be mixed from scrap or the like. Therefore, its content is set to 0.15% by mass or less.

<Intermetallic compound: Maximum equivalent circle diameter of 60 μm or less>
The maximum equivalent circle diameter of the intermetallic compound is preferably 60 μm or less from the viewpoint of improving the metal fatigue strength. More preferably, it is 50 μm or less. More preferably, it is 40 μm or less. The maximum equivalent circle diameter indicates a diameter when the area of the maximum intermetallic compound is equivalent to a circle having the same area. A specific method for calculating the maximum equivalent circle diameter was estimated using extreme value statistics described later.

  When a large intermetallic compound is present in the Al alloy, the Al alloy material is destroyed starting from those due to differences in material properties such as strength, hardness, and Young's modulus with the matrix. As a result, the metal fatigue strength of the Al alloy material May decrease. In other words, if the size of the intermetallic compound is large, there is a high possibility that they will be the starting point of the destruction of the Al alloy material due to metal fatigue. Therefore, the maximum equivalent circle diameter (size) of the intermetallic compound contained in the Al alloy ) Is desirable.

  By controlling the maximum equivalent circle diameter (size) of the intermetallic compound to be smaller, the metal fatigue strength is further improved.

The size of these intermetallic compounds includes casting conditions (cooling rate, adjustment of casting diameter, etc.), homogenization heat treatment conditions (temperature, time, multi-stage temperature adjustment, etc.), forging conditions (forging ratio, forging temperature, etc.), It can be controlled by appropriately combining solution treatment conditions (temperature, time, etc.).
Here, for example, the cooling rate during casting is 0.05 ° C./second or more, the homogenization heat treatment is performed in a temperature range of 500 to 545 ° C., and the hot forging is performed in a temperature range of 280 to 430 ° C. The maximum equivalent circle diameter was controlled to 60 μm or less.

(Homogenization heat treatment)
Further, the homogenization heat treatment is preferably performed at a temperature as high as possible within the temperature range (500 to 545 ° C.) of the homogenization heat treatment and within a temperature range in which eutectic melting does not occur. Under such conditions, the dissolution and diffusion of the intermetallic compound in the base material are effectively performed. As a result, the size of the intermetallic compound can be reduced.
Depending on the type of intermetallic compound, a multi-stage homogenizing heat treatment in which the homogenizing heat treatment is divided into at least two stages is more effective as a method for reducing the intermetallic compound without eutectic melting.

This multistage homogenization heat treatment method is carried out by setting appropriate conditions (temperature increase rate, homogenization temperature, treatment time) according to the type of intermetallic compound.
For example, as an appropriate heat treatment for each intermetallic compound, the intermetallic compound is sufficiently dissolved and diffused by performing the heat treatment at a relatively low temperature within the temperature range (500 to 545 ° C.) of the homogenization heat treatment. Next, the intermetallic compound is reduced by performing heat treatment at a relatively high temperature within the temperature range of the homogenization heat treatment. Such a homogenizing heat treatment that adjusts the temperature in multiple stages is effective.

  Further, as a method capable of obtaining the same effect as this multi-stage homogenization heat treatment method, a method of increasing the temperature in a temperature range in which the intermetallic compound does not eutectic melt by making the speed to reach the homogenization heat treatment temperature relatively low There is. This method can also be performed in combination with the multistage homogenization heat treatment. This rate of temperature rise needs to be set appropriately depending on the type, size, amount, etc. of the intermetallic compound.

  These homogenization heat treatment methods make it possible to reduce the size of the intermetallic compound while preventing eutectic melting of the intermetallic compound. By reducing the intermetallic compound, fatigue fracture starting from the intermetallic compound is suppressed, and the fatigue strength is improved. In addition, since each element contained in the intermetallic compound is uniformly diffused into the base material by the homogenization heat treatment, the strength of the base material can be improved by solid solution strengthening and precipitation strengthening. At the same time, the elongation, impact value, and metal fatigue strength of the Al alloy can be further improved.

In addition, the effect of improving the metal fatigue strength by controlling the maximum equivalent circle diameter (size) of the intermetallic compound to be smaller not only in the range of the elemental composition according to the present invention but also in the range of other elemental compositions. The effect is recognized.
The value of the metal fatigue strength is not only the size of the intermetallic compound, but also the aspect ratio, shape, intermetallic compound hardness, Young's modulus, amount of the intermetallic compound, and the area ratio of the intermetallic compound in the metal structure. It may be related.

(Intermetallic compound measurement)
The size of the intermetallic compound (maximum equivalent circle diameter) is an extreme value described by Takanobu Murakami, “Effects of Metal Fatigue and Minor Defects and Inclusions” published by Yokendo (OD version 1st pages 233-250). It can be calculated by performing statistical estimation. The estimation by extreme value statistics is a method of estimating an extreme value after creating an extreme value estimation graph.

  The outline is that after the sample surface is polished, a predetermined inspection reference area is photographed with a microscope or the like so that the inspection portion does not overlap with a statistically sufficient portion. Thereafter, an intermetallic compound occupying the maximum area in each inspection reference area is selected, and the square root of the area of each maximum intermetallic compound is calculated. Next, a cumulative distribution function, a cumulative frequency distribution, and a normalization variable are calculated. Third, plot the square root of the area of the largest intermetallic compound on the horizontal axis and the cumulative distribution function or normalization variable on the vertical axis. Then, the square root of the area of the maximum intermetallic compound on the horizontal axis is replaced with the maximum equivalent circle diameter of the maximum intermetallic compound, and the maximum intermetallic compound distribution line is calculated.

Finally, using this maximum intermetallic compound distribution line, the maximum equivalent circle diameter of the maximum intermetallic compound in the area to be predicted is estimated. In this measurement, the maximum equivalent circle diameter of the maximum intermetallic compound was estimated with an inspection reference area of 0.37 mm ² , 40 inspection portions, and an area for prediction of 100 mm ² .

<Method for producing Al alloy>
Next, a method for producing an Al alloy according to the present invention will be described.
The Al alloy manufacturing process in the present invention is basically the same as the conventional Al alloy manufacturing process. That is, the Al alloy production process according to the present invention includes a casting process, a homogenization heat treatment process, a hot forging process, a solution treatment process, a quenching process, and an artificial age hardening process. A cold compression (processing) step may be included as necessary.
Further, T61 tempering and T6 tempering described later are performed in a solution treatment process, a quenching process, and an artificial age hardening process. Further, the T652 tempering is performed in a solution treatment process, a quenching process, a cold compression (processing) process, and an artificial age hardening process. In addition, these tempering is suitably selected according to the magnitude | size and use of the member to manufacture.

(Casting process)
The casting process is a process for producing an ingot by melting and casting the Al alloy having the above composition. The casting method is not particularly limited, and a conventionally known method may be used. For example, an ingot using an Al alloy melt adjusted to be dissolved within the component range of the present invention by a casting method appropriately selected from ordinary melting casting methods such as a continuous casting rolling method and a semi-continuous casting method (DC casting method). Can be cast.

(Homogenization heat treatment process)
By performing the homogenization heat treatment, the microsegregation generated by solidification is homogenized, the supersaturated solid solution element is precipitated, and the metastable phase is changed to the equilibrium phase. When the temperature of the homogenization heat treatment is less than 500 ° C., intermetallic compounds such as ingot crystallization are not dissolved, and the homogenization becomes insufficient. On the other hand, when the temperature of the homogenization heat treatment exceeds 545 ° C., the possibility of burning is increased.
Therefore, the temperature of the homogenization heat treatment is set to a range of 500 to 545 ° C.

  When performing multi-stage homogenization heat treatment, it is necessary to set heat treatment conditions according to the type of intermetallic compound as described above. Similarly, when performing a homogenization heat treatment that raises the temperature at a relatively low speed, it is necessary to set the heat treatment conditions according to the type of intermetallic compound.

(Hot forging process)
The temperature conditions for hot forging are important for producing the characteristics of the Al alloy with good reproducibility together with the forging ratio described later. That is, it is important to make the microstructure after the solution treatment step of the Al alloy into equiaxed crystal grains. When the hot forging temperature is less than 280 ° C., cracks are likely to occur in the Al alloy during hot forging, and forging itself is difficult. On the other hand, when it exceeds 430 ° C., coarse crystal grains are likely to be generated in the structure of the Al alloy. For this reason, the high temperature characteristic of Al alloy falls, and the Al alloy excellent in the high temperature characteristic cannot be manufactured with good reproducibility.
Therefore, the hot forging temperature is 280 ° C. or higher and 430 ° C. or lower.

(Discipline ratio)
The microstructure after the solution treatment of the Al alloy is greatly influenced by the forging ratio of hot forging. Therefore, in order to make the microstructure after solution treatment of the Al alloy into equiaxed grains, it is preferable that the forging ratio is 1.5 or more. When the forging ratio is less than 1.5, the Al alloy structure tends to be mixed grains. Moreover, it is preferable that the direction of training is not limited to one direction but at least two different directions, and the training ratio in each direction is 1.5 or more.

(Solution treatment process and quenching process)
Next, solution treatment and quenching treatment will be described. In this solution treatment and quenching treatment, JIS-H-4140, AMS-H-6088 and the like are specified in order to re-dissolve soluble intermetallic compounds and suppress reprecipitation during cooling as much as possible. It is preferable to carry out within the specified conditions. However, even if heat treatment is performed according to standards such as AMS-H-6088, if the solution treatment temperature is too high, burning occurs and the mechanical properties are significantly reduced. On the contrary, when the solution treatment temperature is lower than the lower limit temperature, the yield strength after the artificial age hardening treatment is not sufficient for the purpose of the present invention, and the solution treatment itself becomes difficult. Therefore, the upper limit of the solution treatment temperature is 545 ° C., and the lower limit is 510 ° C.

  As a furnace used for tempering (heat treatment) such as solution treatment and quenching, a batch furnace, a continuous annealing furnace, a molten salt bath furnace, an oil furnace, or the like can be used as appropriate. In addition, as a cooling means at the time of quenching, means such as water immersion, hot water immersion, boiling water immersion, polymer solution immersion, water injection, air injection can be appropriately selected. As a polymer used for the polymer solution immersion, for example, a U-Conchantant (trade name) manufactured by Union Carbide, Inc., such as polyoxyethylene / propylene / polyether, can be used.

(Cold compression (processing) process)
After quenching of the Al alloy, cold compression using a cold rolling mill, stretcher, cold forging, etc., for the purpose of straightening distortion during quenching and improving high-temperature properties such as yield strength and creep rupture strength of the final product. (Processing) may be performed.
If the amount of compression (processing) of cold compression (processing) is small, a sufficient residual stress reduction effect cannot be obtained. On the other hand, if the amount of cold compression (processing) is large, the amount of precipitation of the θ 'phase increases during artificial age hardening or during use of Al alloy products at high temperatures, so the yield strength decreases. It's easy to do. Therefore, it is preferable that the cold compression (processing) is performed at a compression (processing) rate of 1 to 5%.

(T6 tempering)
For products such as small parts up to about 100 mm in diameter and pistons, even if the residual stress is relatively large, for example, products that do not cause processing problems such as cutting are subjected to artificial age hardening treatment after solution treatment and quenching treatment, It is desirable to use a tempered T6 material. In this case, in order to obtain high strength characteristics and high temperature characteristics even if the residual stress becomes relatively large, it is desirable that the temperature of the quenching process is 50 ° C. or less.

(T61 tempering)
In a large product such as a rotor, the cooling rate between the product surface and the central part is greatly different during the quenching process, so that a high residual stress exceeding 10 kgf / mm ² is generated on the product surface. When such a high residual stress is generated, a large distortion occurs during the cutting of the product, and precise cutting becomes extremely difficult. In the worst case, the Al alloy material may be broken during the cutting process such as cracking due to residual stress. For example, even if no breakage such as cracking occurs during cutting, the product starts from an intermetallic compound such as a crystallized substance remaining in the material or from a slight surface flaw generated during product transportation. During long-term use, cracks tend to propagate and grow, which can lead to final failure.

Therefore, for products such as rotors where residual stress is a problem, the water quenching temperature after solution treatment should be a relatively high temperature of 90 ° C. or higher in order to remove or reduce the residual stress to preferably 3.0 kgf / mm ² or less. Then, it is preferable to perform an artificial age hardening treatment to obtain a tempered T61 material.

(T652 tempering)
Depending on the application, there is a product whose residual stress is strictly controlled regardless of the size of the product. For such products, in order to minimize the residual stress, cold compression (processing) is applied, the residual stress is preferably removed or reduced to 3 kgf / mm ² or less, and subjected to artificial age hardening treatment for tempering. T652 material is preferable.
In these products, it is preferable that the quenching temperature is 50 ° C. or less in order to remove or reduce the residual stress to 3 kgf / mm ² or less and obtain high temperature characteristics.

  If the amount of cold compression (processing) of the cold compression (processing) is small, a sufficient residual stress reduction effect cannot be obtained. On the other hand, if the amount of cold compression (processing) is large, the amount of precipitation of the θ ′ phase increases during the artificial age hardening treatment or during use at high temperatures, so the yield strength tends to decrease. Therefore, it is preferable that the cold compression (processing) is performed at a compression (processing) rate of 1 to 5%.

(Artificial age hardening process)
Artificial age hardening treatment in each tempering is performed in order to impart high temperature characteristics such as normal temperature resistance and high temperature resistance, and creep rupture strength of the Al alloy, and metal fatigue characteristics. By this artificial age hardening treatment, the Ω phase precipitated on the (111) face of the Al alloy and the θ ′ phase precipitated on the (100) face can be precipitated, and the above-described characteristics are exhibited. The method of artificial age hardening treatment is not particularly limited, and in the Al alloy of the present application, the precipitation state in which the Ω phase and the θ ′ phase satisfy the present application, high temperature characteristics such as normal temperature resistance and high temperature resistance, and creep rupture strength, and What is necessary is just to be able to obtain a metal fatigue characteristic.

As mentioned above, although the form for implementing this invention has been described, the Example which confirmed the effect of this invention is demonstrated concretely compared with the comparative example which does not satisfy | fill the requirements of this invention below. A room temperature proof stress of 400 MPa or higher, a high temperature proof stress of 300 MPa or higher, and a creep rupture strength at a high temperature of 150 MPa or higher were accepted, and the others were rejected.
The confirmation results of proof stress and creep rupture strength as a first example will be described below, and the confirmation results of metal fatigue strength as a second example will be described with reference to Examples 1 to 18 and Comparative Examples 1 to 7.
In addition, this invention is not limited to this Example.

<First embodiment>
(Sample material)
In order to grasp the influence of the composition of the Al alloy on the room temperature yield strength, the high temperature yield strength, and the high temperature creep rupture strength, the following test materials were prepared. First, an Al alloy ingot (diameter: 500 mm, length: 500 mm) having the composition shown in Table 1 was melted and subjected to a homogenization heat treatment at 510 ° C. for 20 hours to perform hot forging (280 to 360 ° C., forging ratio 1.). 5 mm or more), 150 mm square forged material and 80 mm square forged material were produced. Thereafter, each of the forged materials was subjected to a solution treatment at 528 ° C. for 6 hours using an air furnace. In Table 1, values that do not satisfy the scope of the present invention are underlined.

Next, for 150 mm square forgings, the residual stress is reduced to 3.0 kgf / mm ² or less by simulating a use in which residual stress is a problem and quenching with hot water at 70 to 100 ° C. after the solution treatment. did. Thereafter, the forged material was subjected to an artificial age hardening treatment at 175 ° C. for 18 hours to obtain a T61 tempered material. And the test material was produced from this tempered material (Examples 1-7, Examples 10-12, Comparative Examples 1-7).

In addition, some of the 150 mm square forged materials are simulated to be used in which residual stress is a problem, and after being subjected to water quenching at 30 to 60 ° C. after the solution treatment, 1.5% cold Cold compression (processing) was applied at a compression (processing) rate to reduce the residual stress to 3.0 kgf / mm ² or less. Thereafter, this forged material was subjected to an artificial age hardening treatment at 175 ° C. for 18 hours to obtain a T652 tempered material. And the test material was produced from this tempered material (Example 9).

  The 80 mm square forged material was subjected to a low-temperature water quenching treatment at 30 to 45 ° C. after the solution treatment, simulating the use where residual stress such as small parts and pistons may be relatively large. Thereafter, the forged material was subjected to an artificial age hardening treatment at 175 ° C. for 18 hours to obtain a T6 tempered material. And the test material was produced from this tempered material (Example 8).

(Room temperature characteristics and high temperature characteristics)
As a room temperature characteristic of the test material, 0.2% proof stress at room temperature and as a high temperature characteristic, 0.2% proof stress when the test material was held at 180 ° C. for 100 hours at high temperature were measured. The test pieces at room temperature had a parallel part diameter of 6.35 mm and a gauge distance of 25 mm, and the 180 ° C. test had a parallel part diameter of 6 mm and a gauge distance of 30 mm.
In the creep property test, the test piece was 6 mm in diameter at the parallel part and 30 mm in the gauge distance. Table 2 shows the measurement results of tensile properties and creep properties of these test materials.
Furthermore, the elongation of the specimen at room temperature was measured as the room temperature characteristic of the specimen. The measurement method was the same as the 0.2% proof stress measurement, and the test piece had a parallel part diameter of 6.35 mm and a gauge distance of 25 mm. The measurement result of elongation will be described later.

(Examples 1-12)
In comparison with Comparative Examples 1 to 7, Examples 1 to 12 were found to have excellent physical properties in all measurement items of room temperature yield strength, high temperature yield strength, and high temperature creep rupture strength. . These exhibit characteristics superior to those of the prior art when used in high-speed moving parts that rotate or slide at high speed, such as a rotary rotor, rotary impeller, or piston.

  Further, from the comparison of the yield strength values at room temperature in Example 6 and Example 7, it was found that the Cu addition amount can be reduced by increasing the Si addition amount of the Al alloy when the same yield strength value is obtained. Furthermore, the elongation at room temperature of Example 6 and Example 7 was 8.5% and 10.0%, respectively. From these facts, it is shown that intermetallic compounds related to Cu can be reduced at the same proof stress value. Further, as a result, it is shown that the elongation of the Al alloy can be improved and the metal fatigue strength can be improved. That is, by appropriately adjusting the amounts (ratio) of Si and Cu, it is possible to further improve the metal fatigue strength and the elongation of the Al alloy while keeping the proof stress value constant.

(Comparative Example 1, Comparative Example 5, Comparative Example 6)
Since Comparative Example 1, Comparative Example 5, and Comparative Example 6 have a small Si content of 0.06% by mass, the effects of refinement of precipitates and uniform precipitation are small.
Therefore, Comparative Example 1, Comparative Example 5, and Comparative Example 6 do not satisfy the values of room temperature yield strength of 400 MPa or higher, high temperature yield strength of 300 MPa or higher, and creep rupture strength at high temperature of 150 MPa or higher.

(Comparative Example 3, Comparative Example 4, Comparative Example 6, Comparative Example 7)
Since Comparative Example 3, Comparative Example 4, Comparative Example 6, and Comparative Example 7 have a high Zr content of 0.15% by mass, in the quenching treatment after the solution treatment, the stable phase such as AlCu ₂ is Precipitated roughly around the -Zr-based dispersed particles. For this reason, these comparative examples 3, 4, 4, and 7 do not satisfy any of the values of room temperature proof stress 400 MPa or higher, high temperature proof stress 300 MPa or higher, and high temperature creep rupture strength 150 MPa or higher.

(Reference example)
In addition, the following phenomenon was seen about the test piece exceeding the upper limit of the regulation value of the said alloy component.
The specimen having a Si content exceeding 1.0% by mass as a component of the comparative example produced a coarse intermetallic compound in the Al alloy, so that the metal fatigue strength decreased. Moreover, since the strength of the Al alloy was too high, the forgeability of the Al alloy was lowered in the specimen having a Cu content exceeding 7.0% by mass. Furthermore, in the specimen with the Mn content exceeding 1.5% by mass, an insoluble intermetallic compound was produced during melt casting, and the forgeability of the Al alloy was lowered. And the specimen whose Mg content exceeded 2.0 mass% increased the strength of the Al alloy, and decreased the forgeability of the Al alloy.

<Second embodiment>
In order to grasp the influence on the material properties of the Al alloy due to the difference in the size of the intermetallic compound, a test material was prepared by the method described later.

(Sample material)
When an Al alloy ingot having the composition shown in composition 1 in Table 1 was cast by sand casting, copper mold casting, continuous casting, etc., the casting speed was adjusted to melt the Al alloy ingot. Thereafter, the Al alloy ingot was subjected to a homogenizing heat treatment at 510 ° C. for 20 hours, and then a 150 mm square forged material was produced by hot forging (280 to 360 ° C., forging ratio of 1.5 or more).

  The 150 mm square forged material prepared above was subjected to a solution treatment for 6 hours at 528 ° C. using an air furnace, and then subjected to hot water quenching at 70 to 100 ° C. Further, an artificial age hardening treatment was performed at 175 ° C. for 18 hours to obtain a T61 tempered material.

(Size of intermetallic compound)
For the analysis of the size of the intermetallic compound, extreme value statistical analysis was used as described above. That is, the largest intermetallic compound within the inspection reference area of 0.37 mm ^{2 in} each photograph is extracted from 40 100 times optical microscope photographs, and the statistical processing is performed on the obtained 40 pieces of data. The maximum equivalent circle diameter of the intermetallic compound in the set predicted area was estimated for each material. In this measurement, the predicted area was set to 100 mm ² .

(Rotating bending fatigue strength test)
A test piece described later was prepared from the T61 tempered material, and the test piece was subjected to a metal fatigue strength test at a high temperature of 150 ° C. (maximum stress 130 MPa, stress ratio-1).
In this metal fatigue test, a round bar test piece having a parallel part diameter of 6 mm and a parallel part length of 13.55 mm and an emery paper finish of # 1000 was subjected to a rotating bending fatigue strength test.

  Table 3 shows the relationship between the maximum equivalent circle diameter and the number of repetitions of rupture, which is the measurement result of the rotating bending fatigue strength test. The number of repetitions of rupture refers to the number of repetitions until rupture in the rotational fatigue test. Note that the number of repetitions of breakage is shown as a relative value where the value when the maximum equivalent circle diameter is 90 μm is 1.

(Metal fatigue strength)
When a rotating bending fatigue strength test was performed on a material in which the maximum equivalent circle diameter of the intermetallic compound was adjusted, an alloy (test specimen) having the same composition (composition 7 in Table 1) had a maximum in the current predicted area (100 mm ² ). It has been found that when the equivalent circle diameter is 60 μm or less, the metal fatigue strength is improved. Further, the metal fatigue strength tended to improve as the maximum equivalent circle diameter decreased.

(Examples 13 to 18)
As shown in Table 3, by setting the maximum equivalent circle diameter to 60 μm or less in the test piece produced from the Al alloy ingot having the composition shown in Composition 7 of Table 1 (Examples 15 to 18), It was found that the maximum equivalent circle diameter was 4 times or more than 90 μm (Example 13).
Further, by setting the maximum equivalent circle diameter to 40 μm or less (Example 17), the number of repeated fractures is 9 times or more of the maximum equivalent circle diameter 90 μm (Example 13), and the metal fatigue strength of the Al alloy is further improved. It becomes possible. Then, by setting the maximum equivalent circle diameter to 25 μm or less (Example 18), the number of repeated fractures is 19 times or more of the maximum equivalent circle diameter 90 μm (Example 13), and the dramatic improvement in metal fatigue strength of the Al alloy is achieved. Is possible.

  Thus, it was found that the maximum equivalent circle diameter of 60 μm or less (Examples 15 to 18) of the intermetallic compound maximum circle equivalent diameter of 90 μm (Example 13) is more excellent in physical properties. These are superior to conventional ones when used in high-speed moving parts that are intermittently stressed, such as a rotating rotor, rotating impeller, or piston.

  The present invention is excellent in heat resistance, high temperature fatigue strength, high temperature creep resistance and high temperature strength, for rockets, aircraft and space equipment, railway vehicles, automobiles, ships and other transportation equipment, or engine parts, The present invention can be applied to Al alloy parts that are used in high-temperature usage environments exceeding 100 ° C., such as rotary rotors, rotary impellers, and pistons, such as for machine parts such as compressors.

Claims (2)

Si: more than 0.1% by mass and 1.0% by mass or less,
Cu: 3.0% by mass or more and 7.0% by mass or less,
Mn: 0.05 mass% or more and 1.5 mass% or less,
Mg: 0.01% by mass or more and 2.0% by mass or less,
Ti: 0.01% by mass or more and 0.10% by mass or less,
Ag: 0.05 mass% or more and 1.0 mass% or less, and
Zr: restricted to less than 0.1% by mass,
Remainder Ri is Do Al and inevitable impurities,
Excellent aluminum alloy to a high temperature properties up to the circle equivalent diameter of the intermetallic compound, characterized in der Rukoto below 60 [mu] m. The aluminum alloy according to claim 1,
V: An aluminum alloy excellent in high temperature characteristics, further comprising 0.15% by mass or less.