JP2013220472A - Al-Cu BASED ALUMINUM ALLOY FORGED OBJECT - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Al-Cu based aluminum alloy forged material which prevents coarse crystal grains during solution treatment after free forging and has excellent heat resistance and strength.SOLUTION: An Al-Cu based aluminum alloy is manufactured by free forging. In the Al-Cu based aluminum alloy, when a series of hot free forging processes to be started after a material is heated at a temperature of 400°C or more includes a partial large-strain forging process wherein the material is forged while a compressed strain rate on at least a part of the whole forged object exceeds 50%, a series of hot free forging processes is terminated by performing partial large-strain forging while a part of the material to be applied with at least partial large-strain is maintained at a temperature of 400°C or more. Then, a microstructure of the forged object after a solution treatment process for heating and maintaining the forged object and a subsequent quenching treatment process for rapidly quenching the forged object is a hot processed structure including minute sub-grains of an average grain size of 30 μm or below.

Description

  The present invention relates to an Al—Cu-based aluminum alloy forged product excellent in strength and heat resistance.

  Al-Cu aluminum alloys used for aerospace equipment, transportation equipment such as automobiles and railways, or mechanical parts such as engine parts and compressors have a wide range of characteristics due to their light weight and high strength. It is used for In particular, in a rotating impeller or rotating rotor that rotates in a high temperature environment of 100 ° C. or higher, an Al—Cu aluminum alloy having excellent heat resistance is suitably used.

  In such applications, especially those used for ships and large machines are manufactured by machining a large Al—Cu aluminum alloy material having a diameter of 30 cm or more, for example. Such a large Al—Cu-based aluminum alloy material is manufactured by mainly forging a cast material by hot forging and then rapidly cooling (quenching) after holding at a high temperature called a solution treatment. There are many cases.

  In hot forging performed in the production of a large Al—Cu-based aluminum alloy material, a method called free forging suitable for forging a large material is often used. Free forging is a manufacturing technique as follows. First, an aluminum alloy material is inserted between a pair of steel flat plates called anvils that are driven up and down by a mechanism such as hydraulic pressure, and a predetermined amount of compressive deformation is applied between the anvils. Next, the aluminum alloy material is once taken out, the direction of the material is appropriately changed to a predetermined direction, inserted again between the anvils, and then subjected to compression deformation again. By repeating such a compressive deformation operation, casting defects such as voids originally existing in the ingot of the aluminum alloy are eliminated, and characteristics such as strength and ductility of the aluminum alloy material are improved.

  The purpose of free forging is to provide an aluminum alloy material in a form as close as possible to the final product shape, in addition to the purpose of improving the characteristics by forging the material as described above. That is, by making full use of the compression deformation by a pair of anvils, the desired various product shapes are finished by repeated compression deformation and material replacement in the anvil several times.

  In this way, after free forging is completed as close to the product shape as possible, the aluminum alloy material is subjected to a solution treatment that is heated and held at a high temperature and then subjected to a quenching treatment. Grain is generated. The generation of such coarse crystal grains impairs the appearance performance of the final product and causes a decrease in heat resistance and material strength. As a result, there arises a problem that the quality of the material is lowered.

  As a method for preventing the formation of such coarse crystal grains, for example, Patent Document 1 describes optimizing the addition amount of Cr, Zr, and Fe, which are transition elements added to an aluminum alloy. By optimizing the amount added, the distribution density of the dispersed particles mainly composed of these elements formed in the material is increased, and the grain boundary movement of the recrystallized grains generated during the solution treatment is controlled by these dispersed particles. By pinning with, the generation of coarse crystal grains is prevented.

JP-A-11-286757

  The present inventors have studied various methods for suppressing coarse crystal grains generated during solution treatment performed after forging of a free-forged Al—Cu-based aluminum alloy material. As a result, it has been found that in the free forging of an Al—Cu based aluminum alloy material, there is a problem that the method disclosed in Patent Document 1 cannot reliably prevent the formation of coarse crystal grains with sufficient reproducibility.

  It is an object of the present invention to prevent the formation of coarse crystal grains during solution treatment after free forging of an Al—Cu based aluminum alloy material, and to forge an Al—Cu based aluminum alloy having excellent heat resistance and strength. Is to provide materials.

  In order to solve the above-described problems, the inventors of the present application first clarified the relationship between the generation position of coarse crystal grains and the free forging process. On that basis, the generation mechanism of coarse crystal grains was clarified to prevent the formation of coarse grains, and it was found that an Al—Cu-based aluminum alloy forging material having a sound structure can be obtained.

  The present invention is the Al—Cu-based aluminum alloy manufactured by free forging according to claim 1, and is a forged product in a series of hot free forging processes started after heating the material to a temperature of 400 ° C. or higher. When including a partial large strain forging process in which the compressive strain rate in a portion of the entire portion is forged to exceed 50%, at least a portion of the material to which the partial large strain is applied is maintained at a temperature of 400 ° C. or more. A series of hot free forging processes were completed in such a way that partial large strain forging was performed, and then a solution treatment process for heating and holding the forged product, followed by a quenching process process for rapid cooling. Al-Cu-based aluminum excellent in strength and heat resistance, characterized in that the microstructure of the later forged product is a hot-worked structure containing fine subgrains having an average particle size of 30 μm or less It was a gold forgings.

  The present invention is the projecting region in which the region where the large strain is partially applied in the partial large strain forging process in the hot free forging step is located on the outer surface of the forged product. And the minimum value of the cross-sectional angle of the projecting region is 120 ° or less.

  In the third aspect of the present invention, in the first or second aspect of the invention, in the hot free forging step, forging is performed at a material temperature of 350 ° C. or lower before reaching the partial large strain forging process. Partial large strain forging was performed after reheating.

  According to the present invention, in claim 4, in the hot free forging process according to any one of claims 1 to 3, the anvil temperature used for forging is heated to 200 ° C. or higher before performing partial large strain forging. The contact time between the anvil and the material when performing partial large strain forging was set to within 5 seconds.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the Al-Cu-based aluminum alloy has Cu: 2.0-6.0 mass%, Si: 0.02-1.5 mass%. Contained, Mn: 0.05 to 1.2 mass%, Cr: 0.01 to 0.4 mass%, Zr: 0.01 to 0.3 mass%, Sc: 0.01 to 0.5 mass%, V: 0 .01 to 0.3 mass%, Ni: 0.02 to 1.2 mass%, and Fe: 0.02 to 1.2 mass%, or further containing one or more, and the balance consisting of Al and inevitable impurities It was.

  According to a sixth aspect of the present invention, in the sixth aspect, the Al-Cu-based aluminum alloy further contains at least one of Mg: 0.02-2.0 mass% and Ag: 0.01-2.0 mass%. It was.

  According to the present invention, the formation of coarse crystal grains can be prevented during the solution treatment after free forging of an Al—Cu-based aluminum alloy material, and an Al—Cu-based aluminum alloy forged material having excellent heat resistance and strength can be obtained.

It is explanatory drawing about the protruding area | region which is an area | region which becomes a partial large distortion. It is explanatory drawing which illustrates the process of training. It is a perspective view of the test sample for a hot free forging simulation test. It is a conceptual diagram of the testing apparatus used for a hot free forging simulation test. (A) is explanatory drawing which shows the position of the sample cut surface for macrostructure observation, (b) is explanatory drawing which shows the collection position of the sample piece for EBSD measurement, and the collection position of a tensile test piece and a creep test piece It is. It is a top view of a tensile test piece. It is a top view of a creep test piece.

Hereinafter, the embodiment of the present invention will be described in detail, and the significance of each component will be described.
1. Correlation between the generation position of coarse crystal grains and the free forging process First, the correlation between the generation position of coarse crystal grains and the free forging process was examined in detail. As a result, it has been clarified that coarse crystal grains are generated in a portion in which a particularly large strain is applied to a part of the aluminum alloy material in the free forging process. When examined in more detail, coarse crystal grains do not occur below a certain strain rate, but occur when a strain exceeding that is applied by a single compression deformation in a series of forging processes. Turned out to be. The constant strain rate (hereinafter referred to as “critical strain rate”) was also found to be a 50% value of the compressive strain rate defined by the following equation.
Compression strain rate (%) = {(L ₀ −L ₁ ) / L ₀ } × 100
Here, L ₀ in the formula indicates the length of the arbitrary part in the aluminum alloy material before deformation in the compression direction, and L ₁ indicates the length of L ₀ after deformation in the compression direction.

  Here, an important finding is that in the series of forging processes, when the critical strain rate is cumulatively reached by multiple compression deformations, coarse crystal grains are not generated, and the critical strain is generated by one compression deformation. Coarse crystal grains can be generated only by deformation exceeding the rate.

  More importantly, it has been found that the temperature of the aluminum alloy material during deformation greatly affects the existence of such a critical strain rate. That is, such a critical strain rate exists when the temperature of the aluminum alloy material at the time of deformation is less than 400 ° C., and such a critical strain rate does not exist when the temperature is 400 ° C. or higher. Therefore, even when the deformation of the critical strain rate or higher is imparted when the temperature of the aluminum alloy material during deformation is 400 ° C. or higher, coarse crystal grains are not generated.

Next, the correlation mechanism between the above-mentioned coarse crystal grain generation position and the free forging process will be described.
First, the reason for generating coarse crystal grains will be described. When deformation is applied to an Al—Cu-based aluminum alloy material by hot free forging, strain energy accumulates in the alloy material, and at the same time, recrystallization nuclei begin to form gradually as the strain rate increases. After that, when the alloy material is subjected to a solution treatment that is heated and held at a high temperature, the grain boundaries of a small number of recrystallization nuclei formed in the alloy material move using the accumulated strain energy as a driving force, and the crystal grains grow greatly. By doing so, it becomes coarse. This is the formation mechanism of coarse crystal grains.

2. Next, the reason why the critical strain rate exists regarding the generation of coarse crystal grains will be described. The hot free forging of the Al—Cu-based aluminum alloy material is performed at a temperature higher than room temperature, usually about 250 ° C. or higher. Here, even when the strain rate increases, the strain does not accumulate excessively due to the simultaneous recovery (release of strain energy due to the disappearance of dislocations) in the alloy material. As a result, when the strain rate is less than the critical strain rate, recrystallized grains are not formed in the subsequent solution treatment, and coarse crystal grains are not generated.

  However, when a large strain is imparted by compressive deformation in one direction, the shape of the originally existing crystal grains gradually becomes flat, and at the same time, subgrains are formed in the crystal grains. As a result, when the strain rate reaches the critical strain rate, the subgrains existing at the ends of the crystal grains are separated from the crystal grains, and the separated grains become recrystallization nuclei and cause the formation of coarse crystal grains. .

  The 50% value of the compressive strain rate defined by the above formula is the critical strain rate. The geometrical shape required for the crystal grains originally present to be flat and the grains to be divided at the ends. This is because a distortion rate of 50% or more is required as a typical shape. On the other hand, the reason why coarse crystal grains are not generated when the critical strain rate is cumulatively exceeded by a plurality of compression deformation processes is as follows. In other words, when a normal free forging is compressed and deformed in multiple steps, the alloy material is not always continuously compressed and deformed in the same direction, and the direction of the alloy material is changed for each forging. This is because they are compressed and deformed in different directions. For this reason, the crystal grains originally present in the material are not flattened in one direction as a result of repeated compression and deformation from various directions, so that the grains are not divided at the ends. In this way, since the grain is not divided, recrystallization nuclei are not formed and coarse crystal grains are not generated.

  Furthermore, when the temperature of the aluminum alloy material during deformation is 400 ° C. or higher, the cause of the disappearance of the critical strain rate that generates coarse crystal grains, that is, the compressive strain rate in the aluminum alloy material during the hot free forging process. In the case where a large strained part exceeding 50% is partially formed, by hot forging such a partially large strained part at a temperature of 400 ° C. or more, coarse crystal grains The cause for preventing the occurrence will be described. When the deformation is performed at 400 ° C. or higher, the grain boundary movement during the deformation of the originally existing crystal grains becomes active, and the grain boundary movement in the direction opposite to the macroscopic compression deformation direction occurs. The crystal grains do not have a flat shape, and no grain splitting occurs at the ends of the crystal grains, and no recrystallization nuclei are formed. For this reason, coarse crystal grains do not occur in the subsequent solution treatment.

3. Composition of Al—Cu-based aluminum alloy material The composition of the Al—Cu-based aluminum alloy material used in the present invention is Cu: 2.0 to 6.0 mass% (hereinafter, simply referred to as “%”), Si: 0.02 ˜1.5% is an essential additive element. Further, at least one of Mg: 0.02 to 2.0% and Ag: 0.01 to 2.0% is used as the first selective additive element. Furthermore, Mn: 0.05 to 1.2%, Cr: 0.01 to 0.4%, Zr: 0.01 to 0.3%, Sc: 0.01 to 0.5%, V: 0.0. One or more of 01 to 0.3%, Ni: 0.02 to 1.2%, and Fe: 0.02 to 1.2% are used as the second selective additive element. As described above, the Al—Cu-based aluminum alloy material used in the present invention is composed of the above essential elements, the first and second selective elements, and the balance of Al and inevitable impurities. Below, the role of these component elements and the reasons for the definition of their contents will be explained.

Cu:
Cu is an essential additive element in the Al—Cu-based aluminum alloy material used in the present invention. Cu is solid-dissolved in the matrix by solution treatment, and then rapidly cooled, and then solid-dissolves in the matrix in a supersaturated state. And by subsequent aging treatment, it precipitates in the matrix as fine precipitates to improve the material strength. Furthermore, Cu adheres to and interacts with dislocations generated in the material as a result of deformation during hot free forging, thereby inhibiting the disappearance of dislocations and promoting the formation of a subgrain structure. As described above, the formation of such a subgrain structure facilitates the formation of coarse crystal grains in the material. If the Cu content is less than 2.0%, sufficient strength cannot be improved by the aging treatment, and a high-strength forged product cannot be obtained. On the other hand, if the Cu content exceeds 6.0%, a large amount of crystallized particles containing Cu are produced during casting, and the ductility of the forged product is greatly impaired. Furthermore, a large amount of subgrain structure is formed, and the generation of coarse crystal grains increases. Therefore, the Cu content is in the range of 2.0 to 6.0%. In addition, preferable Cu content is 2.5 to 5.0% of range.

Si:
Si is also an essential additive element in the Al—Cu-based aluminum alloy material used in the present invention after Cu. Si, like Cu, is dissolved in the matrix by solution treatment, and then supersaturated in the matrix by rapid cooling treatment. And the fine precipitate containing Si is formed in a matrix by the aging process performed continuously, and it contributes to the strength improvement of material. When the Si content is less than 0.02%, the amount of precipitates containing Si is insufficient, and the effect of improving the strength cannot be obtained sufficiently. If the Si application content exceeds 1.5%, a large amount of crystallized particles containing Si are produced during casting, and the ductility of the forged product is greatly impaired. Therefore, the Si content is in the range of 0.02 to 1.5%. In addition, preferable Si content is 0.05 to 1.0% of range.

Mg:
Mg, after Cu and Si, is the first selective additive element that is fundamental in the Al—Cu-based aluminum alloy material used in the present invention. Similarly to Cu, Mg is also solid-dissolved in the matrix by solution treatment, and then is supersaturated in the matrix by rapid cooling treatment. Then, a very fine precipitate composed of Mg and Cu is formed in the matrix by the subsequent aging treatment, which contributes to the improvement of the strength of the material. Further, Mg, like Cu, sticks and interacts with moving dislocations generated in the material during deformation of the material during hot free forging, thereby inhibiting the disappearance of dislocations and promoting the formation of subgrains. As described above, the formation of such a subgrain structure facilitates the formation of coarse crystal grains in the material. When the Mg content is less than 0.02%, there are few precipitates composed of Mg and Cu, and a substantial effect of improving the material strength cannot be obtained. If the Mg content exceeds 2.0%, a large amount of crystallized particles containing Mg are produced during casting, and the ductility of the forged material is greatly reduced. Furthermore, a large amount of subgrain structure is formed, and the generation of coarse crystal grains increases. Therefore, the Mg content is preferably in the range of 0.02 to 2.0%. A more preferable Mg content is in the range of 0.05 to 1.5%.

Ag:
Ag is also the first selective additive element that is fundamental in the Al—Cu-based aluminum alloy material used in the present invention after Cu and Si. When Ag is added to the Al—Cu alloy, the structure of the precipitate containing Cu is changed, and the effect of making the precipitate distribution highly dense and fine is exhibited. As a result, the strength after the aging treatment is increased and the heat resistance is greatly improved. When the Ag content is less than 0.01%, the influence on the distribution density of the precipitates is slight and almost no improvement in strength is observed. If the Ag content exceeds 2.0%, a large amount of crystallized particles containing Ag is produced during casting, and the ductility of the forged product is greatly reduced. Therefore, the Ag content is preferably in the range of 0.01 to 2.0%. A more preferable Ag content is in the range of 0.05 to 1.5%.

Mn, Cr, Zr, Sc, V, Ni, Fe:
Mn, Cr, Zr, Sc, V, Ni, and Fe are the second selective additive elements after Mg and Ag. Each of these elements is uniformly deposited in the matrix as fine dispersed particles mainly composed of these elements during the homogenization treatment. These dispersed particles generally have the effect of stabilizing the crystal grains and making the structure fine by preventing the movement of grain boundaries during recrystallization. However, regarding the suppression of the generation of coarse crystal grains, which is the subject of the present invention, the generation mechanism is special unlike the general case. Therefore, the addition of these elements alone cannot sufficiently prevent the generation of coarse crystal grains. Further, the dispersed particles containing these elements as main components also have an effect of significantly increasing the heat resistance of the Al—Cu based aluminum alloy. For these reasons, it is preferable to add one or more of these predetermined amounts of elements to the Al—Cu based aluminum alloy.

  The Mn content is 0.05-1.2%, the Cr content is 0.01-0.4%, the Zr content is 0.01-0.3%, and the Sc content is 0.01%. -0.5%, V content is 0.01-0.3%, Ni content is 0.02-1.2%, Fe content is 0.02-1.2% Is preferred. For any element, if the amount is less than the respective prescribed amount, the formation of dispersed particles is insufficient, so that the effect of stabilizing the crystal grains cannot be sufficiently obtained. In addition, when any element exceeds the specified amount, a very coarse compound containing these elements as a main component is crystallized during casting (referred to as giant crystallized particles), and Al—Cu-based aluminum. The ductility and toughness of alloy forgings are greatly reduced.

In addition to the above essential additive elements and the first and second selective additive elements, they are basically composed of inevitable impurities and Al. However, in order to make the ingot structure fine, Ti: 0.01 to 0.15% may be contained alone or together with B: 0.0001 to 0.05%. When Ti is less than 0.01%, the effect of refining the ingot structure cannot be sufficiently obtained. Similarly, when B is less than 0.0001%, the effect of refining the ingot structure cannot be sufficiently obtained. On the other hand, if Ti exceeds 0.15%, a coarse compound of TiAl ₃ is crystallized during casting, and the ductility and toughness of the material are significantly reduced. On the other hand, when B exceeds 0.05%, a coarse compound of TiB ₂ is crystallized during casting, and the ductility and toughness of the material are significantly reduced. In addition to Ti alone or in addition to both Ti and B, a trace amount of Zn may be added as an element for enhancing corrosion resistance. In the present invention, 1.0% or less of Zn can be contained in the Al—Cu-based aluminum alloy material without impairing the desired effect.

4). Manufacturing method of Al-Cu-based aluminum alloy forged product The Al-Cu-based aluminum alloy forged product according to the present invention is a series of hot processes started after heating the Al-Cu-based aluminum alloy material to a temperature of 400 ° C or higher. A free forging step; a solution treatment step for heating and holding the Al-Cu aluminum alloy material after the series of hot free forging steps; and a baking for rapidly cooling the Al-Cu aluminum alloy material after the solution treatment step And an aging treatment step of aging treatment of the Al—Cu aluminum alloy material after the quenching treatment step. And in a hot free forging process, when the partial large strain forging process in which the compressive strain rate in a part of the entire forged product exceeds 50% is included, at least partial large strain is applied. A series of hot forging processes is completed by performing partial large strain forging while maintaining a part of the material at a temperature of 400 ° C. or higher.

4-1. Melting step, casting step, homogenizing treatment step and chamfering step The Al—Cu-based aluminum alloy material used in the present invention is obtained as an ingot by melting and casting an aluminum alloy according to a normal method. That is, an aluminum alloy adjusted to the above alloy composition is subjected to a melting step to prepare a molten metal. Next, this molten metal is subjected to a casting process by a normal method such as a semi-continuous casting method (DC casting method, hot top casting method) or a continuous rolling casting method to produce an ingot.

  Further, the ingot is subjected to homogenization treatment and chamfering according to a normal method. That is, the ingot is subjected to a homogenization treatment in which the ingot is heated and held for 1 hour or more in a temperature range of 450 to 550 ° C. The ingot that has been subjected to the homogenization treatment is cut after cooling to room temperature and subjected to a chamfering process in which the surface is chamfered. The chamfering process may be performed before the homogenization process.

4-2. Hot free forging process When subjected to the chamfering process after the homogenization process, a series of hot free forging processes are started after heating the chamfered aluminum alloy ingot to a temperature of 400 ° C or higher. Instead of this, when the homogenization process is performed after the chamfering process, a series of hot free forging processes are started at a temperature of 400 ° C. or higher continuously with the homogenization process.

  The hot free forging process eliminates the ingot structure containing many defects such as voids by repeatedly compressing and deforming Al-Cu aluminum alloy material from various directions, and improves various mechanical properties of the alloy material. It is roughly classified into a forging process to be performed and a process for machining into an optimum shape in order to be machined after forging and processed into a final product shape.

  In the forging process, there is no limitation on the temperature of the Al—Cu-based aluminum alloy material that is hot forged unless it includes a forging step in which a partially large strained portion is formed. In the present invention, the partial large strain portion refers to a portion to which a deformation having a partial strain rate exceeding 50% and a critical strain rate or more is given.

  As described above, the hot free forging temperature is not limited. However, if the forging temperature is less than 250 ° C., the load required for processing increases, so that a large amount of energy such as electric power is consumed, resulting in poor economic efficiency. In the present invention, forging is started from a temperature of 400 ° C. or higher, and the temperature of the alloy material gradually decreases during forging. Finally, forging is terminated at a temperature of 350 ° C. or lower, preferably 270 to 350 ° C. Is preferred. Thus, when the end temperature is 350 ° C. or less, preferably in the range of 270 to 350 ° C., a finer subgrain structure is formed in the aluminum alloy material, which contributes to the improvement of the heat resistance and strength of the final alloy material.

  In addition, although the forging process and the process to process into an optimum shape are consistently performed, forging can be performed even if forging is performed at a temperature of 400 ° C. or higher, the temperature range in this case is 400 to 480. It is preferable to carry out in the temperature range of ° C. When forging is performed at a temperature exceeding 480 ° C., the final subgrain size exceeds 30 μm and becomes coarse, and various properties are deteriorated. Similarly, when the temperature is set to 400 ° C. or higher for a process in which a partial large strain is applied, it is preferably performed in a temperature range of 400 to 480 ° C. Even when a process in which a partial large strain is applied at a temperature exceeding 480 ° C., the subgrain size exceeds 30 μm and becomes coarse, and various characteristics are deteriorated.

  In the case where a partial large strain portion is to be formed in such a training process, the temperature of the region that becomes at least the partial large strain portion is adjusted to a temperature of 400 ° C. or higher. Free forging is required. When the temperature in this region is less than 400 ° C., coarse crystal grains are formed during the subsequent solution treatment for the reasons described above, and the material characteristics are deteriorated.

  The process of processing into the optimum shape is basically the same as the forging process, but a partial large strain portion is often formed in the process of processing into the optimal shape. Specifically, the area of the protrusion located on the outer surface of the alloy material formed in the forging process is subjected to compression deformation by forging to flatten the area of the protrusion, or deformed into a more polygonal shape as a whole. When the shape is close to a circle, partial deformation concentrates on the protrusion. As a result, the protrusions where such partial deformations are concentrated become partial large strain portions. Therefore, at the stage before such a partial large strain portion is formed, at least a region that becomes the partial large strain portion is hot-forged at a temperature of 400 ° C. or higher, so that the critical strain in the partial large strain portion is obtained. The rate can be extinguished. In the present invention, the formation of coarse crystal grains can be effectively prevented by providing a forging step in which such a partial large strain portion is not formed during a series of hot free forging steps.

  Here, a description will be given of the form of the protrusion, which is a region that becomes a partial large strain portion. As shown in FIG. 1, the compression deformation direction of the protruding portion of the Al—Cu-based aluminum alloy material is defined as a protruding direction, and a line parallel to the protruding direction and passing through the tip of the protruding portion is defined as a protruding direction line. The degree of protrusion in the protrusion is defined by the cross-sectional angle that is the angle of the tip of the protrusion shown on the surface when the protrusion is cut by an arbitrary surface including the protruding direction line. The smaller the cross-sectional angle, the sharper the angle and the greater the strain due to compressive deformation.In the present invention, even if the minimum value of the cross-sectional angle is 120 ° or less, the formation of a partially large strain portion can be prevented, and the cross-sectional angle is limited. Even if the protrusion is close to 0 °, it is possible to prevent the formation of a partial large strain portion. In addition, when the tip of the projection has a certain curvature (that is, the tip is rounded) or when the tip of the projection is flat, the straight portion constituting the overall shape of the projection When the projection is cut by an arbitrary surface including the ridge direction line, assuming that the intersection point extending from is the tip, the cross-sectional angle is the angle of the virtual projection tip shown on the surface. In the case of such a rounded tip or a flat tip, since the effect on the distortion rate when this tip portion is compressively deformed by forging is negligible, the tip of the virtual projection as described above It is substantially appropriate to define the cross-sectional angle based on

  The temperature of the anvil used for forging is preferably 200 ° C. or higher. When the anvil temperature is less than 200 ° C., heat is extracted from the forged material when contacting the anvil even if the temperature of the forged material is within the specified range. As a result, the substantial material temperature at the time of compressive deformation becomes lower than specified, and coarse particles may be generated. The upper limit of the anvil temperature is not particularly specified, but if the anvil temperature exceeds 360 ° C., seizure of the lubricant used for forging to the anvil is likely to occur, so the anvil temperature is set to 360 ° C. or less. Is preferred.

  At the time of compressive deformation at the time of forging, it is preferable that the time for which the forged material comes into contact with the anvil is within 5 seconds. When the forged material and the anvil come into contact with each other for more than 5 seconds, the heat removal from the forged material to the anvil becomes remarkable, the substantial material temperature at the time of compressive deformation becomes lower than the specified value, and coarse grains may be generated. Further, the lower limit value of the contact time is not particularly specified, but due to the mechanism of the forging machine, it is difficult to compress and deform in a very short time contact, and usually a contact time of substantially 1 second or more is required.

4-3. Solution Treatment Process After a series of hot free forging processes is completed, a solution treatment of the aluminum alloy material is performed. Before performing the solution treatment, the aluminum alloy material may be cut to an appropriate size close to the final product size, or may be cut after performing the solution treatment in a hot free forged state. Good. In the solution treatment step, the aluminum alloy material is heated and held at a temperature of usually 450 ° C. or higher, so that Cu and Mg as the main additive components of the alloy are dissolved in the matrix. If the heating and holding temperature is less than 450 ° C., Cu and Mg are not sufficiently dissolved, and finally there is a case where sufficiently high strength cannot be obtained. The upper limit of the heating and holding temperature is not particularly specified, but if it exceeds 530 ° C., partial melting may occur depending on the amount of Cu added, and the material characteristics may deteriorate. The heating and holding time is preferably 1 hour or longer in order to sufficiently dissolve Cu and Mg. Even if the heating and holding time is 10 hours or more, the effect is saturated and uneconomical. Therefore, the heating and holding time is preferably 1 to 10 hours.

4-4. Quenching step The aluminum alloy material is subjected to a quenching step of quenching after the solution treatment step. By this quenching, Cu or Mg dissolved at high temperature can be brought into a supersaturated solid solution at room temperature, and the strength of the material can be increased by the subsequent aging treatment. Quenching by rapid cooling is usually performed by introducing an aluminum alloy material into water. However, a coolant other than water may be appropriately selected and used for rapid cooling. There is no particular limitation on the water temperature when it is poured into water, but it is preferable to select the temperature within the range of about room temperature (for example, about 20 ° C.) to 80 ° C. In order to reduce the residual stress after quenching with a large aluminum alloy material or the like, the water temperature is preferably 60 to 80 ° C.

4-5. Aging treatment After dissolving Cu and Mg in a supersaturated state by solution treatment and quenching, the aluminum alloy material is subjected to an aging treatment step. For the aging treatment, natural aging that is held at room temperature for a predetermined time or artificial aging that is heated to a predetermined temperature and held for a predetermined time is used. The strength of the aluminum alloy material can be increased by the aging treatment. In the present invention, the aging treatment conditions are not particularly specified. For example, natural aging is maintained at a room temperature of about 10 to 30 ° C. for 24 hours or more, and artificial aging is performed at a temperature range of 150 to 210 ° C. for 4 to 120 hours. Hold the degree.

  In addition, when processing aluminum alloy material with high dimensional accuracy, if there is residual stress in the aluminum alloy material, the processing accuracy is greatly hindered. For this reason, for the purpose of eliminating the residual stress, the aluminum alloy material may be cold-deformed and deformed between the solution treatment and quenching and before the aging treatment. In this case, the compression deformation rate is preferably in the range of 1 to 5%.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The technical scope of the present invention is not limited by these examples and comparative examples.

  An Al—Cu-based aluminum alloy adjusted to the alloy composition shown in Table 1 was melted and cast by a DC casting method to produce an ingot. These ingots were heated to 500 ° C. and subjected to a homogenization treatment step for 6 hours, and then the ingot surface was chamfered and cut into a size of 300 mm × 300 mm × 600 mm to obtain a sample for hot free forging. .

  After the hot free forging sample was heated to 450 ° C., hot free forging was started. The forging process performed to eliminate defects contained in the ingot structure was performed by the method shown in FIG. That is, in the first training, it was compressed and deformed in the main compression deformation direction. Subsequently, in the second training, compression deformation was performed in the left-right direction in the figure orthogonal to the main compression deformation direction. Furthermore, in the third training, it was again compressed and deformed in the main compression deformation direction.

  After finishing the training process, the process usually proceeds to a process of processing into an optimal shape in order to be processed into a subsequent part shape. However, for the purpose of investigating the correspondence between forging conditions and structural changes, water quenching was performed immediately after the forging process was completed, and the hot free forging structure at this point was once frozen. A required number of test samples having the shape shown in FIG. 3 were prepared using samples cooled to room temperature after the forging process.

  This test sample was subjected to a large strain process reproduction hot free forging simulation test described below. An outline of the test apparatus used in this test is shown in FIG. This test apparatus is equipped with a pair of upper and lower anvils for compressing a test sample, like a normal large-sized hot free forging machine, placing the test sample on the lower anvil, The test sample is compressed by driving the anvil downward at an arbitrary speed. In addition, the test apparatus is provided with an induction heating coil around the test sample. With this induction heating coil, a test sample can be rapidly heated to a desired test temperature at a heating rate of 20 ° C./second or more and maintained at that temperature, and the test sample temperature can be kept constant during compression deformation as well. Can be held. In addition, a heater is embedded in the upper and lower anvils, and the temperature of the anvil can be maintained at an arbitrary set temperature.

  The test sample shown in FIG. 3 was set in this hot free forging simulation test apparatus. A test sample was subjected to a compressive deformation test at an anvil driving speed of 1 mm / second immediately after the test sample was rapidly heated at a temperature increase rate of 20 ° C./second or more. Immediately after the deformation, the test sample was taken out from the apparatus and allowed to cool to room temperature in the atmosphere.

  Table 2 shows the start temperature of hot free forging (starting temperature of the forging process) and the end temperature of the forging process. Furthermore, the conditions of the hot free forging simulation test are the heating and deformation temperature of the sample sample for hot compressive deformation (= the sample sample temperature at the time of deformation), the minimum value of the cross section angle of the sample sample, the compressive strain rate, Table 2 also shows the upper and lower anvil temperature and the contact time between the sample sample and the anvil. The compressive strain rate in Table 2 is the maximum compressive deformation rate partially generated in the sample sample by giving a predetermined deformation amount (a numerical value obtained by numerically calculating the deformation rate in each part separately from the deformation amount). ).

  The sample solution after the compression deformation test produced as described above was subjected to a solution treatment for heating to a temperature of 500 ° C. and holding for 4 hours. Subsequently, this sample sample was immediately quenched by water quenching in 25 ° C. water. Furthermore, after subjecting the sample sample after quenching to artificial aging treatment at 190 ° C. for 10 hours, the characteristics of the forged product were evaluated by the following procedure.

  First, the test sample after the compression deformation test was cut at the position of the cut surface for observing the macrostructure shown in FIG. Next, after mechanically polishing the cut surface, macroetching was performed by immersing in aqua regia (32% hydrochloric acid 660 ml + 65% nitric acid 340 ml) for 30 seconds, washing with pure water, and drying. Thereafter, the presence or absence of coarse crystal grains in the forged product was observed by visually observing the macroetched surface. Furthermore, by performing image processing of image data obtained by photographing the macroetched surface, the area ratio occupied by the generation region of coarse crystal grains with respect to the entire observation surface was measured.

  Moreover, the test piece for EBSD measurement was extract | collected from the position shown in FIG.5 (b) of this cross section. After the surface of this test piece was mirror-polished, it was set in a scanning electron microscope (SEM) equipped with an electron beam backscatter diffraction analyzer, and EBSD measurement was performed. Specifically, EBSD measurement was performed under the measurement conditions of an SEM acceleration voltage of 200 kV, an SEM magnification of 500 times during measurement, a measurement area of 200 μm × 150 μm, and a measurement step interval of 0.4 μm. Image quality map of EBSD image obtained by this EBSD measurement (contrast between sub-grain boundaries and sub-crystal grains is clearly shown and sub-grains can be identified), originally present in the material The average grain size of the subgrain structure formed inside the crystal grains was determined. The average particle size was determined by drawing a total of four straight lines perpendicular to the vertical and horizontal directions and dividing the total length of the straight lines used for measurement by the number of crystal grains crossing the straight lines in the image quality map.

  Further, a tensile test piece (plate thickness: 1 mm) having the shape shown in FIG. 6 was taken from the position shown in FIG. Using this tensile test piece, a tensile test was performed at room temperature under a crosshead speed of 10 mm / min, and the strength of the forged product was evaluated by a proof stress value. Similarly, a creep test piece (plate thickness: 8 mm) having the shape shown in FIG. 7 was collected from the position shown in FIG. A creep test was performed in which a constant load was applied to the creep test piece at a high temperature to measure the creep life until the material broke. The creep test was performed by measuring the time from the start of loading to rupture (creep life) under a load condition of 10% of the proof stress evaluated in the tensile test at room temperature and at a temperature condition of 100 ° C.

  Hereinafter, the test results obtained under the conditions shown in Table 2 are shown in Table 3. Condition No. In 1, 2, 3, 4, and 6, hot free forging was performed within the scope of the present invention using the alloy A within the scope of the present invention. Condition No. In any one of 1, 2, 3, 4, and 6, coarse crystal grains were not generated in the macro structure observation, and had high proof stress and heat resistance (long creep life). In addition, Table 3 also shows the average grain size of sub-crystal grains (subgrains) by EBSP analysis.

  On the other hand, Condition No. No. 5, since the partial large strain forging process was performed in a temperature range exceeding 480 ° C., coarse grains were not generated, but the subgrain size exceeded 30 μm and became coarse, and the proof stress value and the creep life were reduced. .

  In addition, Condition No. In 7, a series of forging processes including a partial large strain forging process were performed at a temperature range above 480 ° C. As a result, coarse grains do not occur, but the subgrain size becomes coarse, and the proof stress value and the creep life are reduced.

  On the other hand, in the condition 8, the heating / deformation temperature of the sample sample in the hot free forging simulation test reproducing the large strain process was too low. For this reason, coarse crystal grains were generated in the region where the compressive strain rate was 50% or more defined in the present invention. In condition 8, compared to condition 1 in which only the heating and deformation temperature of the sample sample in the hot free forging simulation test is different, the proof stress value of the forged product is low, the creep life is shortened to about 50%, and the heat resistance is low. .

  In condition 9, the compressive strain rate in the hot free forging simulation test that reproduces the large strain process is smaller than the range defined in the present invention. Therefore, a partially large strain portion is not formed, and even if the heating and deformation temperature of the sample sample in the simulation test is 390 ° C. lower than the range specified in the present invention, coarse crystal grains are not generated in the forged product, It had high proof stress and heat resistance.

  In Condition 10, the shape of the test piece used for the simulation test was such that the minimum value of the cross-sectional angle of the protrusion was as large as 130 °. For this reason, the compressive strain rate in this portion is 40%, which is smaller than the range defined in the present invention. Therefore, even if the partially large strained portion is not formed and the heating and deformation temperature of the sample sample in the simulation test is 380 ° C. which is lower than the range of the present invention, coarse crystal grains are not generated in the forged product. It had high proof stress and heat resistance.

  In condition 11, the hot free forging start temperature was too lower than the temperature range defined in the present invention. For this reason, the hot working resistance at the beginning of hot free forging was large, a large load was applied to the sample sample, and forging cracks occurred starting from casting defects that existed in the early stage of hot free forging. For this reason, the forging process could not be completed, and the subsequent large strain process reproduction hot free forging simulation test could not be carried out.

  Under condition 12, the temperature of the anvil in the hot free forging simulation test reproducing the large strain process was too lower than the range of the present invention. For this reason, during the compression deformation of the sample sample by the anvil, a large amount of heat of the sample sample was taken away by the anvil. As a result, the sample sample temperature decreased during the deformation, and the heating / deformation temperature of the sample sample in the simulation test was lower than the range defined in the present invention. For this reason, coarse crystal grains were generated in the region where the compressive strain rate was 50% or more defined in the present invention. In condition 12, in the hot free forging simulation test, the proof stress value of the forged product is lower than that in condition 1 in which the heating / deformation temperature of the sample sample, the anvil temperature, and the contact time between the sample sample and the anvil are different, and creep. The service life was shortened and the heat resistance was low.

  Under condition 13, the contact time between the sample sample and the anvil during the compression deformation in the hot free forging simulation test reproducing the large strain process was too longer than the range defined in the present invention. For this reason, during the long contact time in which the sample sample was compressed and deformed by the anvil, a large amount of heat from the sample sample was taken away by the anvil. As a result, in the middle of deformation, the sample sample temperature was practically lower than the temperature range defined in the present invention. For this reason, coarse crystal grains were generated in the region where the compressive strain rate was 50% or more defined in the present invention. In condition 13, in the hot free forging simulation test, the proof stress value of the forged product is lower than that in condition 1 in which the heating / deformation temperature of the sample sample, the anvil temperature, and the contact time between the sample sample and the anvil differ. The service life was shortened and the heat resistance was low.

  Conditions 14 and 15 are test results for Alloy B within the scope of the present invention. Condition 14 was tested under the test conditions defined in the present invention. On the other hand, the condition 15 is a hot free forging simulation test in which the heating / deformation temperature is lower than the specified range of the present invention, and all other test conditions are the same as the condition 14. Under condition 14, coarse crystal grains were not generated, and under condition 15, coarse crystal grains were generated. Therefore, in condition 15, compared to condition 14, the proof stress value of the forged product was low, the creep life was shortened, and the heat resistance was low.

  Conditions 16 and 17 are the test results for Alloy C within the invention of the present invention. Condition 16 was tested under the test conditions defined in the present invention. On the other hand, in condition 17, the heating and deformation temperature in the hot free forging simulation test is lower than the specified range of the present invention, and all other test conditions are the same as condition 16. Under condition 16, coarse crystal grains were not generated, and under condition 17, coarse crystal grains were generated. Therefore, in condition 17, as compared with condition 16, the yield value of the forged product was low, the creep life was shortened, and the heat resistance was low.

  Conditions 18 to 23 were tested under the test conditions specified in the present invention using the alloys D to I in the invention of the present invention. Therefore, coarse crystal grains were not generated under these conditions, and had high proof stress and heat resistance (long creep life) according to the alloy components in each condition.

  According to the present invention, it is possible to prevent the formation of coarse crystal grains during solution treatment after free forging of an Al—Cu based aluminum alloy material, and to provide an Al—Cu based aluminum alloy forged material having excellent heat resistance and strength. Can be provided.

Claims (6)

  Compressive strain in a part of the whole forged product in a series of hot free forging processes, which is an Al—Cu-based aluminum alloy manufactured by free forging and started after heating the material to a temperature of 400 ° C. or higher. In the case of including a partial large strain forging process in which the rate is forged to exceed 50%, at least a part of the material to which the partial large strain is applied is maintained at a temperature of 400 ° C. or higher. After completing a series of hot forging processes, the microstructure of the forged product after performing the solution treatment process for heating and holding the forged product and the quenching process step for quenching subsequently is performed. An Al—Cu-based aluminum alloy forged product excellent in strength and heat resistance, characterized by comprising a hot-worked structure containing fine subgrains having an average particle size of 30 μm or less.   The region where large strain is partially applied in the partial large strain forging process in the hot free forging process is a projecting region located on the outer surface of the forged product, and the cross-sectional angle of the projecting region The Al—Cu-based aluminum alloy forged product excellent in strength and heat resistance according to claim 1, wherein the minimum value is 120 ° or less.   In the hot free forging process, before reaching the partial large strain forging process, the material temperature of the material is forged at a temperature of 350 ° C. or less, and this is reheated before performing partial large strain forging. Item 3. An Al—Cu-based aluminum alloy forged product having excellent strength and heat resistance according to item 1 or 2.   In the hot free forging step, before performing partial large strain forging, the anvil temperature used for forging is heated to 200 ° C. or more, and the contact time between the anvil and the material when performing partial large strain forging is 5 seconds. The Al-Cu-based aluminum alloy forged product having excellent strength and heat resistance according to any one of claims 1 to 3.   The Al-Cu-based aluminum alloy contains Cu: 2.0 to 6.0 mass%, Si: 0.02 to 1.5 mass%, Mn: 0.05 to 1.2 mass%, Cr: 0.01 -0.4 mass%, Zr: 0.01-0.3 mass%, Sc: 0.01-0.5 mass%, V: 0.01-0.3 mass%, Ni: 0.02-1.2 mass% and Fe: 0.02 to 1.2 mass%, or one or more of Fe, further comprising Al and inevitable impurities, excellent in strength and heat resistance according to any one of claims 1 to 4. Al-Cu based aluminum alloy forged product.   The said Al-Cu type aluminum alloy is excellent in the intensity | strength and heat resistance of Claim 5 which further contains at least one of Mg: 0.02-2.0mass% and Ag: 0.01-2.0mass%. Al-Cu based aluminum alloy forged product.

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