JP2017155288A - Aluminum alloy member and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method providing a high strength aluminum alloy member consisting of a casting by a heat treatment in short time.SOLUTION: There is provided a manufacturing method of an aluminum alloy member consisting of a hypoeutectic aluminum alloy (called "hypoeutectic Al alloy") having temperature difference between phases (ΔT=Tl-Ts), which is temperature difference between a solidus line temperature (Ts) and a liquidus line temperature (Tl), of 20°C or more including conducting a solution process for heating casting which becomes the hypoeutectic Al alloy to a solution temperature of Ts or more and less than Tl in a compression atmosphere. The compression atmosphere is preferably gas atmosphere to which hydrostatic pressure of 0.5 to 15 MPa is applied for example. The solution temperature is preferably at (Ts+3°C) to (Ts+25°C). Time of the solution process for holding the solution temperature is enough with short time of 60 minutes or less.SELECTED DRAWING: Figure 1B

Description

  The present invention relates to a high-strength aluminum alloy member made of a cast material and a method for producing the same.

  In order to reduce the weight of automobiles and the like, aluminum alloy members have been used for structural members that require high strength. In order to further expand the application, not only forged materials but also aluminum alloy members made of cast materials (castings) are required to have excellent mechanical properties (particularly strength).

  In order to improve the mechanical properties of the casting, not only the alloy composition but also heat treatment (solution treatment, cooling (quenching), aging, etc.) is very important. As the heat treatment of the aluminum alloy, T4 to T7, etc., which are compliant with JIS standards are generally performed. Any of the heat treatments is common in that a solution treatment is performed in which the casting is heated to a high temperature to make the solid solution uniform. Most generally, since the solution treatment takes a long time, it has been a factor in increasing the manufacturing cost of the aluminum alloy member. Therefore, a method for shortening the processing time has been proposed. For example, there is a description related to the following patent document.

JP 60-208460 A Japanese Patent Laid-Open No. 9-272942 JP 11-293430 A Japanese Patent Laid-Open No. 11-246925 JP 2001-262295 A JP 2004-52087 A

  Patent Documents 1 to 4 propose that a solution treatment of a casting made of an aluminum alloy is performed in a short time by heating at a high temperature near the solidus temperature. However, when the casting is simply heated at a high temperature, melting (burning) occurs in a part of the casting, and voids (pores) occur in the cast structure after the solution treatment. On the contrary, the mechanical properties of the casting may be deteriorated. In addition, since casting has a complicated shape and often has a different thickness depending on a part, it is difficult to suppress melting during solution treatment only by temperature control.

  Patent Documents 5 and 6 reduce the porosity or casting defects and reduce the solution treatment time by performing at least part of the solution treatment using hot isostatic pressing (HIP treatment). Propose to plan. For example, in Patent Document 5, the solution treatment time is 4 to 5 hours by performing HIP treatment in which a casting is held for 20 to 40 seconds in a molten salt bath at 470 to 540 ° C. × 700 to 1200 bar (70 to 120 MPa). ([0011] to [0013]). Moreover, in patent document 6, the compaction process and the solution treatment are simultaneously performed in about 2-3 hours by hold | maintaining a casting in the gas of 500-530 degreeC x 50-200 MPa ([0035]-[0037). ]).

  However, even with such a method, the solution treatment for at least several hours is still required, and it cannot be said that the time required for the heat treatment (particularly the solution treatment) can be sufficiently shortened. In addition, since the HIP process is performed under a very high pressure, a large and special device is required and the mass productivity is poor. For this reason, it is difficult to reduce the manufacturing cost of a high-strength aluminum alloy member made of a cast material by the method using the HIP process. All HIP treatments are intended to crush pores and defects, such as cast holes contained in the casting, by applying a very high hydrostatic pressure to the casting that is in a completely solid state. doing.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a high-strength aluminum alloy member made of a cast material and a manufacturing method thereof.

  As a result of diligent research to solve this problem, the present inventor has applied a hydrostatic pressure to the casting in a temperature range in which a liquid phase can be slightly generated in a solution treatment of a casting made of a hypoeutectic Al alloy. Inspired to do. And it confirmed that the aluminum alloy member excellent in the mechanical characteristic was obtained by actually performing the heat processing including this solution treatment. By developing this result, the present invention described below has been completed.

<< Method for Manufacturing Aluminum Alloy Member >>
(1) The method for producing an aluminum alloy member of the present invention (also simply referred to as “Al alloy member”) includes an interphase temperature difference (ΔT) which is a temperature difference between a solidus temperature (Ts) and a liquidus temperature (Tl). = Tl−Ts) is a method for producing an aluminum alloy member made of a hypoeutectic aluminum alloy (referred to as “hypereutectic Al alloy”) having a temperature of 20 ° C. or more, and is Ts or more and less than Tl in a pressurized atmosphere. A heat treatment including a solution treatment step of heating the casting made of the hypoeutectic Al alloy is performed at a certain solution treatment temperature.

(2) According to the production method of the present invention, it is possible to obtain an aluminum alloy member that has almost no defects such as pores, has a good cast structure in which crystal grains are granulated, and can exhibit excellent mechanical properties. The reason is considered as follows.

  By applying a solution treatment (solution process) to a casting made of a hypoeutectic Al alloy, the alloy elements (Mg, Si, Cu, etc.) are homogeneously dissolved in the aluminum matrix (referred to as “Al matrix”). Can be made. If the hypoeutectic Al alloy contains Si that enhances castability, the eutectic phase of Al and Si can also be spheroidized by solution treatment.

  By performing such a solution treatment at a high temperature near the solidus temperature of the casting, it is possible to improve the solid solution limit of the alloy element in the Al matrix and the diffusion rate of the alloy element. In particular, since the solution treatment step according to the present invention is performed by causing a liquid phase to appear in the casting, the solid solution and homogenization of the alloy elements are remarkably promoted, and the heat treatment time is greatly shortened, and the dendritic shape is reduced. Granulation of primary crystal aluminum (referred to as “primary crystal Al”), spheroidization of eutectic phase (eg, Al—Si), and the like are promoted, and a good cast structure is easily generated.

  However, when a solution treatment is performed in a high temperature region that generates a liquid phase, local melting occurs at the segregation site of the alloy element (solute element) generated during solidification of the casting, and voids are formed at that site, and the strength is reduced. May be incurred. However, since the solution treatment step according to the present invention is performed in a pressurized atmosphere, the liquid phase generated in the casting during the solution treatment described above is also in a pressurized state, and voids (pores) are also formed by local melting or the like. It is suppressed. In addition, the inside of the casting is pressurized through the liquid phase during the solution treatment, so that hydrogen diffuses easily into the Al base, and the casting cavity (gas cavity) generated due to hydrogen gas is reduced. And suppression of the occurrence thereof.

  Furthermore, when a liquid phase appears in the casting, sweating may occur on the casting surface due to its volume expansion. However, since the casting surface is pressurized during the solution treatment according to the present invention, the sweating is also suppressed. Can be done.

  Thus, according to the production method of the present invention, it is considered that an Al alloy member having a good cast structure and capable of exhibiting high properties comparable to a forged material can be obtained. Moreover, since the solution treatment step according to the present invention is performed via a liquid phase at a higher temperature than in the past, the diffusion of alloy elements in the casting and the grain size of each crystal grain (crystallization phase) are very short. Is made. Therefore, according to the manufacturing method of the present invention, an Al alloy member made of a cast material having excellent mechanical characteristics can be obtained in a short time, and the manufacturing cost can be greatly reduced.

《Al alloy member》
The present invention can be grasped not only as the manufacturing method described above, but also as an Al alloy member made of a casting excellent in mechanical characteristics. That is, the present invention is an aluminum alloy member having a cast structure made of a hypoeutectic Al alloy having an interphase temperature difference of 20 ° C. or more, which is a temperature difference between a solidus temperature and a liquidus temperature, Aluminum having a porosity of 0.5% or less, a crystal grain size of 50 μm or more, and a crystal grain made of dendritic primary Al having a circularity of 0.6 or more and containing 30% or more It can also be grasped as an alloy member.

<< Al alloy member manufacturing equipment >>
Further, the present invention can be grasped not only as the above-described manufacturing method but also as a manufacturing apparatus capable of implementing it. That is, the present invention is a production apparatus for obtaining an aluminum alloy member by subjecting a hypoeutectic Al alloy casting having a temperature difference between the solidus and liquidus temperatures of 20 ° C. or more to heat treatment. A treatment furnace capable of accommodating the casting in an airtight state, a heating means capable of raising the temperature in the treatment furnace to a heating temperature (for example, 700 ° C.) equal to or higher than a solution temperature at which a liquid phase can be generated in the casting, and the treatment A pressurizing unit capable of pressurizing the inside of the furnace to a desired gas pressure (for example, 0.5 to 15 MPa), a heating unit and a control unit (temperature control unit and pressure control unit) for controlling the pressurizing unit are provided. It can also be grasped as an aluminum alloy member manufacturing apparatus characterized by this.

<Others>
(1) The solution temperature in the present invention is an intermediate temperature between the solidus temperature (Ts) and the liquidus temperature (Tl), and is a temperature at which a liquid phase can be generated in a casting made of a hypoeutectic Al alloy. is there. If the solution temperature is excessive, the outline shape of the casting becomes difficult to be maintained. For this reason, the solution temperature is preferably a temperature close to the solidus temperature within a range in which solution treatment can be promoted, crystal grains can be granulated, and the like.

  In this specification, for convenience, the solidus temperature or the liquidus temperature is referred to, but the composition of the hypoeutectic Al alloy according to the present invention is not limited to the binary system. Strictly speaking, even if it should be referred to as solid phase temperature or liquidus temperature, in this specification, it is referred to as solidus temperature or liquidus temperature for convenience.

(2) Unless otherwise specified, “x to y” in this specification includes a lower limit value x and an upper limit value y. A range such as “a to b” can be newly established with any numerical value included in various numerical values or numerical ranges described in the present specification as a new lower limit value or upper limit value.

3 is a photomicrograph showing a cast structure before heat treatment according to Sample 23. It is a microscope picture which shows the cast structure after the heat processing. It is a microscope picture which shows the cast structure before the heat processing which concerns on the sample C21. It is a microscope picture which shows the cast structure after the heat processing. It is a microscope picture which shows the casting structure | tissue before the heat processing which concerns on sample C32. It is a microscope picture which shows the cast structure after the heat processing.

  One or two or more components arbitrarily selected from the present specification may be added to the above-described components of the present invention. The contents described in the present specification appropriately correspond not only to the aluminum alloy member of the present invention but also to the production method thereof. Constituent elements related to the manufacturing method are fixed (when it is impossible or impractical (impossible / unpractical circumstances), etc.) to directly identify the “product” by structure or characteristics It can also be a component related to “thing” as a product-by-process. Which embodiment is the best depends on the target, required performance, and the like.

Hypoeutectic Al alloy
The hypoeutectic Al alloy (also simply referred to as “Al alloy”) has an interphase temperature difference (ΔT = Tl−Ts), which is a temperature difference between the solidus temperature (Ts) and the liquidus temperature (Tl), of 20 ° C. As described above, it has an alloy composition of 30 ° C. or higher, further 40 ° C. or higher. The liquidus temperature (Tl) here is a temperature at which a solid phase starts to appear from an alloy in a liquid phase state. The solidus temperature (Ts) is a temperature at which a state including a liquid phase is completely changed to a single solid phase. Solidification in the casting process does not proceed in an equilibrium state shown in a general phase diagram, but usually proceeds in a non-equilibrium state, and as a result, a casting is obtained. Therefore, the liquidus temperature (Tl) or the solidus temperature (Ts) of the Al alloy can be determined by, for example, measuring the melting temperature based on the DSC curve by differential scanning calorimetry (DSC) or measuring the alloy in the molten state. It may be specified as a solidification temperature obtained from a solidification curve obtained by cooling with the above. It is preferable that the solution treatment temperature of various Al alloys is determined based on these temperatures. If the alloy composition is known, a thermodynamic calculation system that performs thermodynamic equilibrium calculation and phase diagram calculation (for example, Scheil solidification simulation using “Thermo-calc”, liquidus temperature (Tl), solid It is also possible to estimate the phase line temperature (Ts).

  Various such alloy compositions are conceivable. For example, an alloy composition as shown below is preferable. In addition, the alloy composition demonstrated below is a mass ratio of each element when the hypoeutectic Al alloy whole is 100 mass% (it is only called "%").

(1) Si
The Al alloy preferably contains 3 to 11%, 3.5 to 10%, 4.5 to 9%, or even 5.5 to 8% of Si. If the amount of Si is too small, castability deteriorates, and casting defects such as cracks and pipe-shaped shrinkage cavities tend to occur. When Si is excessive, the amount of crystallization of fragile Si particles increases, and mechanical properties (particularly, elongation and strength) tend to decrease. Incidentally, the eutectic point of the Al-Si alloy is Si: 12.6%.

(2) Mg, Cu, Cr
The Al alloy preferably contains 0.15 to 1.5%, 0.3 to 1.2%, 0.4 to 0.9%, or even 0.5 to 0.65% of Mg. Mg can be dissolved in the Al base to strengthen the Al base. In addition, when Mg coexists, Mg can be precipitated as Mg ₂ Si by heat treatment to improve the mechanical strength (tensile strength, yield strength, etc.) of the Al alloy. If Mg is too small, such an effect becomes poor. If Mg is excessive, the ductility and toughness of the Al alloy can be lowered.

The Al alloy preferably contains 0.3 to 6%, 0.4 to 5%, 0.5 to 4.5%, or even 0.6 to 4% of Cu. Cu can be precipitated as CuAl ₂ by heat treatment, or as an MgCu-based compound when Mg coexists. Thereby, Cu can improve the mechanical strength (tensile strength, yield strength, etc.) of the Al alloy. Also, Cu can be dissolved in the Al base to strengthen the Al base. If Cu is too small, such an effect becomes poor. If Cu is excessive, the ductility and toughness of the Al alloy may be reduced.

  The Al alloy preferably contains Cr in an amount of 0.01 to 0.3%, 0.05 to 0.25%, and further 0.1 to 0.2%. Cr can be dissolved in the Al base to strengthen the Al base, or can be precipitated as a Cr-based compound by heat treatment to improve the mechanical strength (tensile strength, yield strength, etc.) of the Al alloy. If Cr is too small, such an effect becomes poor. When Cr is excessive, coarse Cr-based compounds are crystallized, and the ductility and toughness of the Al alloy can be reduced.

(3) Ti, Zr, etc. The Al alloy preferably contains 0.05 to 0.5%, more preferably 0.07 to 0.3% of Ti. Further, it is preferable that Zr is contained in an amount of 0.05 to 0.5%, further 0.07 to 0.3%. Within this range, both Ti and Zr may be included. Ti or Zr refines the crystal grains and strengthens the Al base by solid solution strengthening or precipitation strengthening. Further, when the crystal grains are sufficiently refined by Ti or Zr, it becomes easy to obtain a cast structure in which crystallized substances are isotropically distributed (small segregation). If Ti or Zr is too small, such an effect is poor. In particular, when directivity from the mold is strong, columnar crystals tend to develop, and the pressurizing effect (solution suppression, etc.) during the solution treatment can be reduced. When Ti or Zr is excessive, coarse Ti compound or Zr compound is crystallized in the cast structure, and the mechanical properties of the Al alloy may be lowered.

  In addition to Ti and Zr, it preferably contains at least one of Sr: 0.005 to 0.05%, Na 0.001 to 0.03%, and Sb: 0.05 to 0.15%. Sr, Na or Sb can refine eutectic Si and contribute to the improvement of the mechanical strength of the Al alloy. The Al alloy may contain other modifying elements and may naturally contain inevitable impurities.

<Casting structure>
The Al alloy member (cast after heat treatment) of the present invention is preferably excellent in mechanical properties if it has the following cast structure. First, the porosity is preferably 0.5% or less, 0.3% or less, 0.1% or less, and more preferably 0.05% or less. If the porosity is excessive, the mechanical properties (particularly strength) of the Al alloy member cannot be improved.

  Next, the crystal grains of dendritic primary crystal aluminum (referred to as “primary crystal Al”) having a crystal grain size of 50 μm or more and a circularity of 0.6 or more are 30% or more, 40% or more, and even 50%. % Or more is preferable. The more the primary crystal Al (α-Al) granulated, the better the Al alloy member with excellent mechanical properties.

The porosity can be determined by density measurement by Archimedes method. That is, the density (actual density: ρ) is calculated by dividing the casting weight measured in the atmosphere by the volume of the solid obtained from the buoyancy in the liquid according to Archimedes' principle. Further, the density (true density: ρ ₀ ) of the casting containing no pores is similarly calculated by the Archimedes method. From these two densities, the porosity (100 × (ρ ₀ −ρ) / ρ ₀ ) of the casting containing the pores is calculated. The true density can be obtained as the density of a sound part of a casting that is rapidly cooled in a mold of a directionally solidified method after melting an Al alloy having the same composition and removing the gas from the molten metal. In addition, the density of an Al alloy without pores prepared by sufficiently compressing (upsetting or the like) an Al alloy member to be measured and crushing residual pores such as a cast hole may be set as a true density.

The crystal grain size, circularity, and crystal grain presence ratio (referred to as “content”) are all observed with a microscope for a sample of an Al alloy member that has been subjected to a predetermined treatment, and the resulting metal structure image is analyzed software. It is specified by processing. “Crystal grain size” is the maximum length of crystal grains obtained by the image processing. “Circularity” is a value calculated by 4π · S / L ² as an area occupied by crystal grains: S and a circumference of crystal grains: L. Note that the circularity of a perfect circle is 1, and the distorted crystal grain has a smaller circularity. The content rate of crystal grains is the ratio of the number of crystal grains satisfying a specific condition with respect to the total number of crystal grains in the measurement visual field.

"Production method"
(1) Solution treatment step The solution treatment step according to the present invention is performed to sufficiently and uniformly dissolve the alloy elements in the Al matrix, but a treatment temperature and treatment atmosphere different from those of a normal solution treatment. Made in

  First, the solution treatment step is performed at a solution temperature that is equal to or higher than the solidus temperature (Ts) and lower than the liquidus temperature (Tl). On the other hand, the conventional solution treatment is performed at a temperature higher than the solid solution limit (solubility line) temperature and lower than the solidus temperature (Ts) (particularly, about 20 ° C. lower than Ts). There were many. Therefore, the solution temperature according to the present invention is considerably higher than the conventional processing temperature. However, if the solution temperature is excessive, the amount of liquid phase generated in the casting increases and it is difficult to maintain its shape. Therefore, the solution temperature is preferably near Ts.

  Specifically, the solution temperature is (Ts + 3 ° C.) or more, (Ts + 5 ° C.) or more, (Ts + 7 ° C.) or more, (Ts + 25 ° C.) or less, (Ts + 20 ° C.) or less, Ts + 15 ° C.) or less. Note that the interphase temperature difference (ΔT = Tl−Ts), which is the temperature difference between Ts and Tl, can vary depending on the type and amount of the alloy element. Therefore, the solution temperature may be defined as (Ts + 0.5ΔT) or less, (Ts + 0.3ΔT) or less, and further (Ts + 0.2ΔT) or less. As described above, the lower limit of the solution temperature may be a temperature in the vicinity of Ts. However, it may be defined as (Ts + 0.05ΔT) or more and further (Ts + 0.1ΔT) or more.

Next, the solution treatment step is performed in a pressurized atmosphere, unlike the conventional solution treatment. Although various pressurization methods are conceivable, it is preferable to apply a hydrostatic pressure so that each part of the casting having a complicated shape is evenly pressurized. Specifically, it is preferable to pressurize a casting using a fluid (gas or liquid) as a pressurizing medium. In the case of using a gas, a gas such as Ar, N ₂ , and air that does not dissolve (solid solution) in Al (alloy) (does not have solubility) is preferable. In the case of using a liquid, a molten salt or the like which is in a liquid phase in a processing temperature range in which the solution treatment step is performed and does not react with Al (alloy) is preferable.

  The pressure when the fluid is used as a pressurized medium (simply referred to as “hydrostatic pressure”) is preferably 0.5 to 15 MPa, 0.7 to 10 MPa, and more preferably 0.9 to 8 MPa. If the hydrostatic pressure is too low, it is difficult to transmit the pressure to the casting. If the hydrostatic pressure is excessive, it is difficult to maintain the shape of the casting in which the liquid phase appears. In addition, application of high pressure is not preferable because a large-scale facility is required or time is required for pressure removal and the solution treatment process is prolonged. The hydrostatic pressure according to the present invention is orders of magnitude smaller than the pressure used in HIP processing, hot pressing, and the like.

  Since the solution treatment step is performed at a higher temperature than the conventional solution treatment and through the liquid phase, the treatment time can be greatly shortened. The specific treatment time is appropriately selected according to the Al alloy composition, treatment temperature, casting form (wall thickness, etc.), etc., but the solution temperature retention time is 90 minutes or less, 60 minutes or less, and 45 minutes or less. You can also Incidentally, in order to sufficiently advance the diffusion of alloy elements and the granulation of crystals during the solution treatment step, it is preferable that the holding time is 5 minutes or more, further 15 minutes or more.

(2) Rapid cooling step and aging step The casting after the solution treatment step is usually rapidly cooled (so-called quenching) to form a cast structure in which the alloy elements are in a solid solution in a supersaturated state. Considering the Al alloy composition, casting form (thickness, etc.), etc., by appropriately selecting a cooling medium (water, hot water, oil, etc.) and cooling method (spraying, dipping, etc.), the solution at an appropriate cooling rate The casting after the conversion step can be rapidly cooled. It is preferable that the casting after the solution treatment step is immersed in warm water or oil and rapidly cooled to prevent cracking of the casting.

  The casting after the rapid cooling step becomes a high-strength Al alloy member by precipitation of fine compounds due to aging. Although the aging treatment also has natural aging, stable quality Al alloy members can be obtained in a short time by performing artificial aging. The artificial aging is preferably performed by holding the casting after the rapid cooling step at 150 to 220 ° C. for 0.5 to 5 hours, for example.

《Al alloy member》
The Al alloy member of the present invention is made of a cast material (casting) and can be obtained by various casting methods. Such casting methods include gravity casting, low pressure casting or die casting, sand casting or die casting. However, the Al alloy member of the present invention is a heat-treated casting, and a casting that is not heat-treated is out of scope. Accordingly, die casts that are not generally heat-treated are not subject to the Al alloy member of the present invention.

  The form and use of the Al alloy member of the present invention are not limited. For example, various structural members for automobiles, specifically suspension members such as suspensions, wheel members, chassis members, subframe members, joint members, actuator members, brake members, engine members, etc. are suitable. is there.

  Various samples were produced by solution treatment of Al alloy castings. For each sample, the cast structure was observed or the mechanical properties and density were measured, and the effects of the alloy composition and solution treatment conditions were evaluated. The present invention will be described in more detail below with specific examples.

[Example 1]
<Production of sample>
(1) Casting The raw material mix | blended with each alloy composition shown in Table 1 was melt | dissolved, and various molten metal was prepared. These molten metal was poured into a boat-shaped mold (JIS No. 7) and allowed to cool naturally in the atmosphere and solidified (casting process).
(2) Heat treatment T6 heat treatment (JIS) was performed on each casting thus obtained. Specifically, as shown in Table 1, the following heat treatment was performed. First, each casting was held at 560 ° C. for 60 minutes in an Ar gas atmosphere adjusted to about 7 MPa (solution treatment step). This heating temperature is equal to or higher than each solidus temperature (Ts), but is sufficiently lower than the liquidus temperature (Tl), and is a temperature at which the liquid phase appears slightly.

  Each casting in a heated state was immersed in hot water at 50 ° C. and quenched (quenching process). Further, the cast product after quenching was kept in the atmosphere at 185 ° C. for 45 minutes and subjected to an aging treatment (aging process). Various specimens made of Al alloy castings thus heat-treated were obtained.

(3) As a comparative sample, a sample subjected to a solution treatment in which the atmosphere (the presence or absence of pressure), the heating temperature, or the heating time was changed with respect to the above-described solution treatment step was also manufactured. The details are also shown in Table 1. The quenching and aging treatment after the solution treatment was performed in the same manner as the sample described above.

<Measurement / Observation>
(1) Tensile test A tensile test was performed using a round bar tensile test piece having a balanced portion of 5 mm taken from the thickness center of each specimen after heat treatment. The tensile test was performed by an autograph (manufactured by Shimadzu Corporation) at a crosshead speed of 0.5 mm / min. The 0.2% proof stress was obtained from a stress-strain curve calculated based on the displacement and load obtained by a video extensometer. Each test was performed in a room temperature atmosphere. Table 1 shows the tensile strength, 0.2% proof stress and elongation obtained for each sample.

(2) Casting structure The casting structure which concerns on each sample was observed as follows, and the form was specified. First, the observation piece cut out from each specimen is polished to a mirror surface. Electrolytic etching was further performed on the observation piece finished to a mirror surface. In addition, the electrolytic etching was performed by using a Bakker solution as an electrolytic solution, connecting a stainless steel plate to the cathode, and a test material to the anode, and setting the DC power supply: 20 V and the energization time: 60 to 120 seconds.

The metal structure of each observation piece after electrolytic etching was observed with a polarizing microscope. Thus, each tissue image (data) photographed at a magnification of 50 to 100 was obtained. These tissue images were analyzed using an image processing apparatus (LUZEX manufactured by Nireco Corporation). Specifically, the outline of each crystal grain was traced, and the crystal grain size and its circularity were determined by image analysis. The crystal grain size was the maximum length of each crystal grain. The degree of circularity was calculated as 4π · (area of crystal grains) / (peripheral length of crystal grains) ² . Table 1 also shows the arithmetic value of the circularity and the crystal grain size obtained for the primary crystal Al of each sample.

The porosity is calculated by the above-described method using the density of the casting after the heat treatment (actual density: ρ) and the density of the casting not including the cast hole (true density: ρ ₀ ): 2.681 g / cm ^3. did. The porosity thus obtained is also shown in Table 1.

<Evaluation>
The cast structures according to Samples 1 to 5 have a porosity of 0.3 or less (less than), and most (at least 30% or more) primary Al crystal grains have a crystal grain size of 50 μm or more and a circularity of 0.00. It was 6 or more.

  Samples 1 to 5 all exhibited sufficient elongation and high strength (tensile strength or 0.2% yield strength) and were excellent in mechanical properties.

  On the other hand, as is clear from the sample C1, it is understood that high strength cannot be achieved by simply performing a conventional solution treatment at a low temperature without applying pressure in the same manner as in the samples 1 to 5. As can be seen from sample C3, it takes a long time to increase the strength by the solution treatment. Further, as apparent from Sample C2, even when a high-temperature solution treatment was performed in a pressurized atmosphere, the casting with a small amount of Si caused concentrated shrinkage inside, and did not even lead to strength measurement. Further, as apparent from the sample C4, even in a high temperature region where a liquid phase appears, when a solution treatment is performed in a non-pressurized atmosphere, voids associated with the appearance of the melted portion (burning) are formed inside the casting, It turned out that elongation falls.

[Example 2]
<Production of sample>
A plurality of castings having the same composition as Sample 2 shown in Table 1 were produced in the same manner as in Example 1. Each casting was subjected to the same heat treatment as in Example 1. However, solution treatment conditions (heating temperature and heating time) were variously changed as shown in Table 2. The pressurized atmosphere was an Ar gas atmosphere. Thus, various samples shown in Table 2 were obtained.

<Measurement>
The density of each sample was measured by the Archimedes method. The density was measured in advance not only after the heat treatment but also before the heat treatment. The density before and after heat treatment relating to each sample thus obtained is also shown in Table 2. The porosity (100 × (ρ ₀ −ρ) / ρ ₀ ) calculated by the method described above is also shown in Table 2. Also in this case, the true density: ρ ₀ was 2.681 g / cm ³ .

<Evaluation>
In all samples 21 to 23, which were subjected to solution treatment in a temperature range where a liquid phase appeared in a pressurized atmosphere, the density increased after the heat treatment, and the porosity was 0.3% or less. On the other hand, even in the same pressurized atmosphere, the sample C21 subjected to the solution treatment in the solid phase temperature range (below the solidus temperature) had almost no change in density before and after the heat treatment, and the cast hole remained. .

[Example 3]
<Production and measurement of sample>
A plurality of castings were produced in the same manner as in Example 2. Each casting was subjected to the same heat treatment as in Example 1, but the pressure atmosphere of the solution treatment was variously changed as shown in Table 3. The density of each sample thus obtained before and after heat treatment was measured by the Archimedes method, and the amount of change and the porosity were also shown in Table 3.

<Evaluation>
When solution treatment is performed in the temperature range where the liquid phase appears (above the solidus temperature), the density hardly changes before and after the heat treatment if the pressure is too low in the pressurized atmosphere as well as in the non-pressurized atmosphere. The rate also exceeded 0.5%, and the cast hole could not be crushed sufficiently.

[Casting structure]
With respect to Sample 23, Sample C21, and Sample C32, photographs of the cast structure before and after heat treatment observed with the polarization microscope described above are shown in FIGS. 1A to 3B, respectively. As is clear from comparison of these, by performing the solution treatment at a temperature higher than the solidus temperature and in a pressurized atmosphere as in the present invention, a desired dense cast structure that cannot be obtained in other cases can be obtained for the first time. You can see that In each structure photograph, black portions are pores (pores), light gray portions are primary crystal Al, and agricultural gray portions are compound phases.

Claims (10)

A hypoeutectic aluminum alloy (“hypereutectic Al alloy”) having an interphase temperature difference (ΔT = Tl−Ts), which is a temperature difference between the solidus temperature (Ts) and the liquidus temperature (Tl), of 20 ° C. or more. A method for producing an aluminum alloy member comprising:
The manufacturing method of the aluminum alloy member characterized by performing the heat processing including the solution treatment process which heats the casting which consists of said hypoeutectic Al alloy in the pressurization atmosphere to the solution temperature which is more than Ts and less than Tl.   The method for producing an aluminum alloy member according to claim 1, wherein the pressurized atmosphere is an atmosphere to which a hydrostatic pressure of 0.5 MPa to 15 MPa is applied.   3. The method for producing an aluminum alloy member according to claim 1, wherein the solution temperature is (Ts + 25 ° C.) or less.   The method for producing an aluminum alloy member according to claim 1, wherein the solution temperature is (Ts + 0.5ΔT) or less.   The method for producing an aluminum alloy member according to claim 1, wherein the solution temperature is (Ts + 3 ° C.) or higher.   The method for producing an aluminum alloy member according to any one of claims 1 to 5, wherein a retention time of the solution temperature is 90 minutes or less. An aluminum alloy member having a cast structure made of a hypoeutectic Al alloy having an interphase temperature difference of 20 ° C. or more, which is a temperature difference between a solidus temperature and a liquidus temperature,
The cast structure is
The porosity is 0.5% or less,
Aluminum alloy member comprising 30% or more of crystal grains made of dendritic primary crystal aluminum (referred to as “primary crystal Al”) having a crystal grain size of 50 μm or more and a circularity of 0.6 or more .   The aluminum alloy member according to claim 7, wherein the hypoeutectic Al alloy contains Si: 3 to 11% as a whole by 100 mass% (simply referred to as “%”).   The aluminum alloy member according to claim 8, wherein the hypoeutectic Al alloy further contains at least one of Mg: 0.15 to 1.5% or Cu: 0.3 to 6%.   The aluminum alloy member according to claim 8 or 9, wherein the hypoeutectic Al alloy further contains at least one of Ti: 0.05 to 0.5% or Zr: 0.05 to 0.5%.