JP2008002957A - Creep characteristics evaluation and formulation method of aluminum alloy material, estimation method for the creep characteristics of aluminum alloy, and manufacturing method of aluminum alloy casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method capable of simply calculating the creep characteristics of an aluminum alloy material, and a technique capable of quantifying the correlation properties of the creep characteristics, an alloy component and a texture state. <P>SOLUTION: Three test pieces 1, formed of the aluminum alloy material, are arranged at the apex positions of the regular triangle on a surface plate 2; a weight 3, capable of applying almost equal compression stress σ to three test pieces, is placed to be heated and held to a predetermined temperature T; the dimensional changes of three test pieces with the elapse of time are measured, and the relation between the average value ΔL of the dimensional change quantities of three test pieces and the elapse time (t) is approximated by Formula: ΔL=A×ln(t)+B (where A and B are constants determined for each alloy material, applied compression stress σ and heated and held temperature T) for formulating the creep characteristics of the alloy material. Furthermore, the cross-sectional texture observation and alloy component analysis of the test pieces are performed; the dimension and numerical values (α1, α2, etc.) of the principal crystallized substance and the actual measured values (β1, β2, etc.) of added element amounts are obtained and an estimate formula of A and B in the Formula is constructed by multivariate analysis for quantifying the correlation of the creep characteristics, alloy components and texture state of the aluminum alloy material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for evaluating and formulating creep characteristics of an aluminum alloy material, a method for predicting creep characteristics of an aluminum alloy, and a method for producing an aluminum alloy casting. This aluminum alloy casting manufacturing method adjusts the shape of the crystallized product formed by Si and Fe added to the aluminum alloy by adding P in order to improve the castability and the mechanical properties of the casting. It is intended to increase mechanical properties, particularly creep deformation resistance.

  The aluminum alloys currently used in various fields are often used as they are produced by casting, or by forging and rolling ingots (ingots, billets) produced by casting. The main elements added to the aluminum alloy as alloy additive elements are summarized as shown in Table 1 below.

  For aluminum alloys, various alloy designs have been made by utilizing crystallized dispersion strengthening / solid solution hardening / precipitation hardening by these additive elements, refinement of structure by forging / rolling, and directionality strengthening. It can be said that these strengthening mechanisms are manifested by preventing the movement of “dislocations” existing in the tissue at the atomic level.

The actual metal structure is an aggregate of “α crystal grains” having a structure close to a so-called single crystal structure, which has alignment consistency at the metal atom level, but the boundaries of each α crystal are at the atomic level. The crystal grain boundary is often inconsistent, and there are many crystallized products that are composed of elements different from various α crystals. (These can be visually confirmed with an optical microscope.)
Furthermore, when looking at the interior of each α crystal in more detail, an element different from the main element constituting the α crystal (solid solution element) is trapped in the atomic unit, or fine aging precipitates exist. I do. (These are not visible with an optical microscope.)

  Metal materials including aluminum alloys can be plastically deformed with smaller shear stress due to the presence of “dislocations” in the atomic arrangement, but foreign substances such as “solid solution elements” and “aging precipitates” are α If it exists between Al atoms, which are the main elements constituting the crystal, it can be said that the movement of dislocations at the atomic level is hindered and strengthened by this. From a macro perspective, even in the case of an interface between α-crystals at a grain boundary, dislocation movement is hindered due to misalignment at the atomic level. In addition, when crystallized materials such as Fe and Si are present at the grain boundaries, in addition to the incompatibility of atomic arrangement, the interstitial distance, which is the atomic spacing, will also differ, so that the dislocation movement is more strongly inhibited. Conceivable.

  In addition, dislocations proliferate due to external stress. Dislocation multiplication is performed as shown in FIG. The dislocation source A-B is called a flank lead source. When dislocations extend from the dislocation source A-B, the grown dislocations form a loop, and there are cases where dislocation loops are generated one after another. (In fact, this kind of dislocation growth occurs as a matter of course.) When stress is applied to the metal material from the outside, just moving one dislocation does not lead to a large deformation. In addition, it can be considered that the dislocations proliferate one after another from a plurality of dislocation sources, leading to a large deformation.

  As dislocations grow, many places where the grown dislocations are entangled with each other. When this entanglement becomes complicated, dislocations restrain each other's movements. This entangled structure is called a “cell structure”. It can be said that “work hardening”, which is a phenomenon of hardening when a metal material is plastically processed, is manifested mainly by this mechanism. Since the cell structure part is in an unstable state in terms of energy, when it receives heat energy from the outside, it releases the intertwining of its own dislocations, or forms new crystal grains (α crystals) using it as “nuclei”. There is a case. These are called “recovery” and “recrystallization”, respectively.

  In the case of an aluminum alloy, the recovery phenomenon is accelerated at about 100 to 200 ° C., and recrystallization occurs at 200 to 300 ° C. or higher. (It can be said that the entanglement of dislocation is reset to return to a state close to the initial state.) Aluminum alloys that are required to be used in the vicinity of 200 to 300 ° C, such as automotive (diesel) engine parts and tire molds. In, the “creep characteristics” associated with the ease of migration and proliferation of these dislocations becomes a problem. Creep is a phenomenon in which strain increases with the passage of time under a constant stress, and a phenomenon in which deformation gradually progresses under a constant stress. In the case of temperature, even when stress lower than the normal elastic limit is applied, it is often treated as a phenomenon in which deformation gradually progresses over a long period of time. However, at present, the creep characteristics have not been well established for quantification and design.

For example, Non-Patent Document 1, “Maglow Hill Book Co., Ltd.“ Material Strength Science ”, Ryoichi Koterazawa, P.146 and below” describes the following method as a general method. That is, a test piece as shown in FIG. 2 is held at a predetermined atmospheric temperature T with a (tension) load F applied, and the increase in the distance between the test pieces is measured to test the material. This is a method of obtaining a creep curve (FIG. 3) at temperature T and applied stress σ.
The creep curve thus obtained is formulated as Equation 1.

However, this method has the following weak points with respect to the evaluation of the creep characteristics of an aluminum alloy that undergoes creep deformation at a lower stress than steel.
1) A relatively large specimen is required. (Usually, the cross-sectional area S is about 50-100mm ² or more)
2) A large testing machine is required.
3) The obtained data (creep curve formula) is also complicated and difficult to handle.
For this reason, it was difficult to simply and appropriately evaluate the creep characteristics of the aluminum alloy.

The above-mentioned dislocation movement plays an important role in this creep property as well, but it is possible to optimize the creep property with an aluminum alloy by designing the alloy with any alloy composition and structure. However, there was no quantitative measure such as this, and there was no good method for adjusting the structure of the casting to the dispersion form of the crystallized product meeting this purpose.
McGraw-Hill Book Co., Ltd. “Material Strength Study” by Ryoichi Koterazawa P.146 and below

  The present invention has been made under such circumstances. The first object of the present invention is to provide an evaluation method for easily obtaining the creep characteristics of an aluminum alloy material. The second object of the present invention is the creep. The third objective is to provide a technology that can quantify the correlation between properties, alloy components, and microstructure, and the third objective is to improve the microstructure that can manifest the microstructure that can optimize the creep properties required from this. It is to provide a method.

In order to achieve the first object, the invention of claim 1 is characterized in that three rectangular parallelepiped or smooth cylindrical specimens made from the same aluminum alloy material are placed on the surface plate at the apex position of an equilateral triangle. These three test pieces are placed with a weight that can apply an almost uniform compressive stress σ, heated and held at a predetermined temperature T, and the dimensional changes of the test pieces over time are measured. The dimensions of the three test pieces The relationship between the average amount ΔL of change and the elapsed time t
ΔL ＝ A ・ ln (t) + B ・ ・ ・ (1)
(A and B are constants determined for each alloy material, applied compressive stress σ, and heating holding temperature T)
The creep characteristic of the corresponding alloy material is formulated by approximating the equation (1).

  The invention of claim 2 made to achieve the second object is the observation of the cross-sectional structure of the three test pieces used in the invention of claim 1 or a test piece separately manufactured from the same alloy material. Analyze the alloy components to obtain numerical values of the main crystallized dimensions and shapes (α1, α2, ...) and measured values of the amount of added elements (β1, β2 ...). Multivariate analysis using σ, T, (α1, α2,...), (Β1, β2,...) As explanatory variables, and ΔL = A · ln (t) + B in claim 1 By constructing the prediction formulas of A and B in the formula (1), the correlation between the creep characteristics of the corresponding aluminum alloy, the alloy composition, and the structure state is characterized.

  In order to achieve the third object, the invention according to claim 3 is characterized in that, when an aluminum alloy casting containing Si as a main component element is manufactured, P is added to the molten metal for casting, thereby obtaining a unit area. The sum of the longitudinal dimension of each Si crystal crystallizing the primary crystal and the eutectic crystal is reduced, and the creep deformation resistance of the corresponding casting is increased. When manufacturing an aluminum alloy casting containing Fe as a main component element, the length of each Fe crystal grain that produces primary and eutectic crystals per unit area by adding P to the molten metal for casting It is characterized by increasing the sum of dimensions and increasing the creep deformation resistance of the casting.

  According to the first aspect of the present invention, the creep characteristics of the aluminum alloy material can be easily obtained using a very small test piece. Further, according to the invention of claim 2, it becomes possible to quantitatively grasp the relationship between the creep characteristics of aluminum alloy, the structural state, and the alloy element amount, which has been difficult to grasp quantitatively in the past. Further, according to the third and fourth aspects of the present invention, it is possible to develop a structure state capable of optimizing the creep characteristics required by the first and second aspects in the casting.

<Claim 1>
As shown in FIG. 4, the invention of claim 1 prepares three match rod-like cubes as a test piece 1 on a surface plate 2 that is not deformed or damaged during a creep test. Is placed so that it is in the vicinity of the apex of an approximately equilateral triangle, and a weight 3 having a predetermined weight is placed so as to cover the three test pieces 1 at the same time, and a compressive stress σ is applied to the test piece 1 in this state Measure the dimensional change of the test piece 1 over time, and measure the relationship between the average value ΔL of the dimensional change amount of the three test pieces 1 and the elapsed time t, ΔL = A · ln (t) + B (A and B are constants determined for each alloy material, applied compressive stress σ, and heating holding temperature T) to approximate the creep characteristics of the corresponding alloy material. It is.

  Specifically, in FIG. 4 in which the test piece 1 having a rectangular parallelepiped shape or a smooth cylindrical shape is manufactured with three / one set, the diameter φD is a length L when the test piece 1 is a cylinder. These are placed on the surface plate 2 that will not be deformed / damaged during the creep test, so that they are close to the apex of the regular equilateral triangle, and a weight 3 of a predetermined weight is placed so that three test pieces 1 are covered simultaneously. A compressive stress σ is applied to each test piece 1. Then, the surface plate / test piece / weight assembly is put into the heating furnace 4 as shown in FIG. Preheating the surface plate 2 and the weight 3 to the temperature T in advance is more preferable because the temperature rise time lag of the test piece 1 can be minimized. The data of t−ΔL thus obtained is plotted with ΔL on the vertical axis and t on the horizontal axis as shown in FIG. 6, and the obtained curve is expressed by an approximate expression of ΔL = A · ln (t) + B. Recent (find coefficients A and B). The obtained approximate equations and A and B are the creep characteristics when the temperature T and compressive stress σ of the material are applied.

  So-called light alloys such as aluminum alloys having a low melting point have smaller creep deformation resistance and strength characteristics than various steel materials and nickel alloys (only about 10 to 50%). This tendency becomes more prominent as the temperature increases, and the applied load (weight of the weight) required for the creep test of the aluminum alloy is much smaller than that in the creep test of the steel / nickel alloy material. The present invention utilizes this characteristic.

For example, when the invention of claim 1 is used, if the specimen size is D = W = 4 mm (L dimension is arbitrarily set here), a compression load of 0.5 kgf / mm ² (4.9 MPa) is applied to the specimen. If you want to do that, the weight of the weight is 24kg. If this weight is made of steel, a single disk with a diameter of approximately 600 mm and a thickness of 11 mm is sufficient. The applied compressive stress required for the compression creep test of aluminum alloy is 20 kgf / mm ² (196 MPa) at most, and if there are 40 weights (960 kg), all tests are sufficient. If the size of the test piece is smaller, the required weight can be further reduced.

  The longer dimension L of the specimen is preferable from the viewpoint of ΔL detection accuracy during the creep test. However, if the specimen is too long, the specimen may buckle and the experimental data cannot be obtained. In the case of aluminum alloy, when D = W, it is preferable that L ≦ (5 to 10) D. Therefore, the size of one specimen when performing a creep test of various aluminum alloys using the invention of claim 1 is such that D (= W) = 2 to 4 mm and L = 10 to 20 mm. Become. This can be said to be 1/10 to 1/5 the size of a conventional creep test piece, which is extremely compact. Therefore, it is possible to perform a creep test by cutting out a test piece from an aluminum alloy material in which a large test piece is difficult to obtain or, in some cases, a product entity.

  Moreover, the approximate expression ΔL = A · ln (t) + B of the obtained creep curve is also simpler than the conventional approximate expression, making it easy to handle both in terms of data analysis and practical use. Yes. (It can be said that the smaller both A and B, the higher the creep deformation resistance.) The fact that the compression creep curves of various aluminum alloys can be approximated by the above approximate expression is shown in Example 1 described later. .

The material strength consideration about this approximate expression is added below.
As explained above, the creep deformation behavior is governed by the movement of dislocations in the crystal, but in “Material Strength Science 2nd Edition Iwanami Takeo Yokobori Takeo P.85”, The relationship between the dislocation speed v and the load shear stress τ
v = v ₁ · τ ^ (1 / n ^* kT) exp {−Q / kT}
n ^*: numeric value by the material, v _1, Q, k: constant, T: temperature (K)
It is expressed by the following formula.

From this equation, if the temperature T and the shear stress τ (numerically defined by the compressive stress in this test) are constant, the dislocation speed v is also constant, and the approximate expression “elapsed time t− The “L-direction deformation amount ΔL” should be “straight line”, but the actual experimental result is “logarithmic function”.
The difference is that the actual material (general material)
A) Solid solution hardening and precipitation hardening in α crystal (disturbance effect of dislocation transfer at atomic level)
B) Polycrystalline structure (disturbance effect of dislocation movement at grain boundaries)
C) Scattering of dissimilar metals (crystallized substances) at grain boundaries (disturbance effect of dislocation migration at macro level)
It is thought that it was caused by having the three strengthening mechanisms.

In order to obtain the dislocation speed v from the previous compression creep deformation behavior approximate equation, ΔL = A · ln (t) + B, the above equation may be differentiated with respect to the elapsed time t.
dL / dt = d {A · ln (t)} / dt + d (B) / dt
The equation v = A / t is obtained.
In other words, this test result shows that the dislocation speed v, which is theoretically constant in a single crystal under a constant (shear) stress and constant temperature atmosphere, decelerates over time in an actual material (polycrystalline reinforced material) (coefficient). A is inversely proportional). This is because the reasons A) to C) are described above.

The following is an explanation of these and the dislocation movement / proliferation mechanism.
The preceding approximate expression shows that the dislocation speed V _T1 in the corresponding metal material at the time when the constant compressive stress σ is received for a time t ₁ at a constant temperature T is V _T1 = A / t ₁ . . On the other hand, the theoretical formula of the movement of one dislocation in a single crystal shows that the dislocation speed is constant regardless of time and V = α. It is considered that the difference between the two shown in FIG. 7 is caused by the presence / absence of a failure to dislocation movement due to the difference in metal structure and the propagation behavior of dislocation. The actual aluminum alloy results (compression creep test results for polycrystalline materials including solid solution elements, aging precipitates, and crystallized materials) show that the dislocation rate is maximum immediately after the start of the creep test, and that It shows that decreases.

The reason why the dislocation speed decreases with time in the compression creep of an actual aluminum alloy is described in the order of phenomenon occurrence,
1) Dislocation movement is interfered by solid solution elements.
2) Dislocation movement is interfered by aging precipitates.
3) Dislocation growth is also delayed due to the effects of 1) and 2) above.
4) The presence of crystallized materials interferes with more macroscopic dislocation movements.
5) The effects of 1) to 4) make it difficult for dislocations to proliferate (the “cell structure”, which is the entanglement of dislocations), rapidly increases, and this cell structure becomes an obstacle to the movement of dislocations. ).
6) The longer the elapsed time, the slower the dislocation speed.
It is thought to be something like that.
The meaning of the constant B can be judged as an error function such as plastic deformation at the initial stage of the creep test of the contact surface (load application surface) between the test piece and the weight. (If the machined surface accuracy of the test piece is poor, B will increase.)

<Claim 2>
<Explanation of claim 2>
The approximate expressions A and B obtained in claim 1 are treated as representative values of the creep characteristics when the heating holding temperature T and compressive stress σ of the corresponding material are applied. Dimensional and shape characteristic values (α1, α2, ...) obtained from cross-sectional observation, and characteristic values of various alloy element amounts (β1, β2, ...) obtained from the component analysis results of the corresponding material In addition to this, multivariate analysis using the heated holding temperature T and the applied compressive stress σ as explanatory variables makes the objective variables A and B the explanatory variables (α1, α2,...), (Β1, β2 , ...), T, σ, quantifies the relationship between the creep characteristics of the aluminum alloy and each explanatory variable, and the composition design and structure design of the aluminum alloy with better creep characteristics Claim 2 is a technique that makes it useful quantitatively.

  The multivariate analysis (multiple regression analysis) used here is described, for example, in Japanese Standards Association, “New Edition, Statistical Method, Revised Edition”, Editor, Shigeru Moriguchi, Publisher, Masaaki Nishiya, P.215 to P.227. ing. Specific analysis examples and methods for utilizing the results will be described in detail in Example 2 described later.

<Claims 3 and 4>
According to the above-described methods of claims 1 and 2, the amount of alloying elements and the size and shape characteristic values of the main crystallized substance necessary for imparting high creep deformation resistance to the aluminum alloy can be quantified. The amount of alloying elements can be adjusted at the time of alloy preparation and is relatively easy to control, but the size and shape characteristic values of the main crystallized substances are controlled (for the purpose of increasing creep deformation resistance). Extremely difficult. Claims 3 and 4 were created to overcome this problem.

As shown in Example 2 to be described later, according to the invention of claim 2, from the results of multivariate analysis using explanatory variables of the structure parameter system such as the size and shape of various crystallized substances,
1) Set the α crystal state to a crystal grain shape with a short sum of longitudinal dimensions of α crystal per 1 mm ² .
2) longitudinal dimension sum of Fe crystal per 1 mm ² is long, to Fe-based crystallized matter state.
3) Si crystallized state with a short sum of longitudinal dimensions of Si crystals per 1 mm ² .
It can be seen that the compressive creep deformation resistance of the aluminum alloy increases.
Conventionally, however, there has been no good structure improvement method that can satisfy the above 1) to 3) particularly in an aluminum alloy member that is used in a cast form (casting).

  By adding P (about 10 ppm or more) to an aluminum alloy melt containing Si as a main component element or an aluminum alloy melt containing Fe as a main component element, the present inventor can obtain per unit area. For castings with a wide solidification cooling rate by reducing or increasing the sum of the longitudinal dimensions of each Si crystal or Fe crystal grain that eutectic crystal and eutectic crystal, and increasing the creep deformation resistance of the corresponding casting, It was discovered that organizational improvements that satisfy 2) and 3) above are possible. An experimental result confirming that the structure improvement of 2) and 3) above is achieved by adding P to the molten aluminum alloy is shown in Example 3 described later.

Various references exist for improving the structure of aluminum alloy castings. For example,
A “Aluminum Handbook” edited by Japan Light Metal Association
B “Nonferrous metals and alloys” published by Uchida Otsutsuru, authored by Jiro Matsuzumi P.120
C "Casting Engineering" Japan Foundry Engineering Society 2002January Vol.74 P.45-P.49 etc. <Summary>
☆ Refinement of eutectic Si by Na addition (improvement treatment): Described in A and B ・ Effective only for hypoeutectic Si alloys.
・ The improvement effect is low for castings with extremely slow melt solidification such as gypsum casting.
-No improvement effect on Fe crystals.
☆ Refinement of primary Si by adding P: Described in A and C ・ The effect of improving the structure only for primary Si in hypereutectic Si alloys is described.
-No improvement effect on Fe crystals is described. (The improvement effect of the present invention has not been found.)
As described above, the effect of improving the eutectic Si structure by adding P to the hypoeutectic Si alloy and the effect of improving the Fe crystal structure by adding P to the aluminum alloy containing Fe as a main element are as follows. It can be said that the contents were discovered for the first time.

For reference, “hypoeutectic Si alloy, hypereutectic Si alloy” and “primary crystal, eutectic” will be described with reference to FIG.
Hypoeutectic Si alloy: When the molten metal solidifies, first the aluminum (α phase) appears as a solid, and no Si solid is generated within the solid-liquid coexistence region temperature range. A type of aluminum alloy that generates Si solids (eutectic Si) at the moment when it falls below.
Hypereutectic Si alloy: When the molten metal solidifies, first, Si appears as a solid (primary Si) and does not generate any aluminum solid within the solid-liquid coexistence region temperature range. A type of aluminum alloy that generates Si solid (eutectic Si) and aluminum solid (α phase) at the moment when it falls below.
Primary crystal Si is “polygonal granular”. Eutectic Si is in the form of “fine grained”, “needle” or “thin flat plate”.
Examples of each invention are shown below.

Three test pieces of 4 x 4 x 12 mm are made from the same aluminum alloy material by wire electric discharge machining, and these are `` three-point jacks '', placing 1 to 10 weights of about 24 kg per piece, per weight The test jig was configured such that a compressive stress of 0.5 kgf / mm ² was applied to the test piece. (The compressive stress applied to the test piece was adjusted by the number of weights to be placed.) The test jig was placed in a heating furnace (hot air circulating furnace) and the change over time in the L dimension (12 mm) of the test piece was measured intermittently. In order to shorten the time when the test piece is attached to and detached from the jig (there is also the intention of preventing the temperature drop of the jig), and to prevent the occurrence of uneven load on the test piece, three metric trapezoidal screws are installed in the jig. This is a method of utilizing as a jack-up detaching device. Test specimens were taken from seven types of aluminum alloy castings shown in Table 2. In addition, all the above-mentioned test pieces were subjected to “overaging heat treatment” called air cooling after heating at 300 ° C. × 12 hr before the creep test.

  Changes with time in the deformation amount in the L direction are shown in FIGS. Tables 3 to 6 show data and approximate expressions of each figure.

  From these creep test results, it can be seen that the relationship ΔL = A · ln (t) + B holds between the deformation amount ΔL due to compression creep and the elapsed time t.

  A tissue photograph of the cross section of the test piece was taken, and a tissue analysis was also performed in the form of image analysis of the photograph data. In this structural analysis, the α crystal, Fe crystallized material, and Si based crystallized material are divided into three categories, and for each, the dimensional characteristics and aspect ratio (aspect ratio) when one crystal grain is regarded as a rectangle. Was calculated for each crystal grain, and the maximum value, minimum value, average value, and standard deviation were obtained.

Based on the results of such organization analysis, the following three were taken as explanatory variables as organization parameters.
1) Sum of α crystal longitudinal dimensions per 1 mm ²
(Calculated as α crystal longitudinal dimension average value × α crystal grains per 1 mm ² )
2) Total length of Fe crystallized crystals per mm ²
(Fe crystals longitudinal dimension average value × 1 mm calculated at Fe Akiratsubu per ²⁾
3) Total length of Si crystallized crystals per 1 mm ²
(Si crystals longitudinal dimension average value × 1 mm calculated by Si Akiratsubu per ²⁾
As the alloy element parameters, the contents of the four elements of Si, Mg, Cu, and Fe among the component analysis results in Table 2 were also taken as explanatory variables. Then, by taking A and B of the approximate expression of claim 1 as objective variables and performing multivariate analysis, A and B were regressed with the above explanatory variables and applied compressive stress. Because it is constant, the heat holding temperature is excluded from the explanatory variables).

  Table 7 shows the multivariate analysis results when only the structural parameter system explanatory variables are used, and Table 8 shows the multivariate analysis results when only the alloy element amount system explanatory variables are used.

As explained earlier, A of the objective variables is considered to be a variable that represents the true creep characteristics of the relevant material. Therefore, only the analysis results for objective variable A are summarized as follows. .
From the analysis results of explanatory variables of the tissue parameter system,
☆ Make α crystal state with short total length of α crystal per 1 mm ² .
☆ Fe crystallized state with long total length of Fe crystal per 1 mm ²
☆ Si crystallized product with a short total length of Si crystals per 1 mm ²
It can be seen that the compression creep deformation resistance increases.

From the analysis results by the explanatory variables of the alloy element system,
☆ For all of Si, Mg, Cu, and Fe, increasing the amount added increases the creep resistance.
☆ The order of increasing creep resistance increase is 1: Cu, 2: Mg, 3: Fe, 4: Si.
☆ When the additive effect of Si is 100, the effect of increasing the creep resistance of other additive elements is
Cu: 413, Mg: 339, Fe: 136. It can be seen that the solid solution element and the aging precipitate forming element are 3 to 4 times larger than the effect of increasing the creep resistance of the crystallized substance forming element.

As described above, when claim 2 is used, it becomes possible to quantitatively grasp the relationship between the creep characteristics of aluminum alloy, the structural state, and the amount of alloy elements, which has been difficult to grasp quantitatively in the past.
It ’s important to note that if you look only at the results of the previous multivariate analysis,
☆ Increase the number of solid solution elements, aging precipitates, and crystallized substances. ☆ The more the amount of added elements, the more likely it is to be mistaken for a good alloy, but this is not the case.
In order to maintain appropriate toughness (elongation) as a metal material, there is an upper limit for the number of aging precipitates and crystallized substances, and the added elements are affected by the bond between the added elements. Of course, there are cases where such improvement in creep characteristics cannot be obtained. (The alloy type used in this experiment is one with a composition that makes it difficult for “decrease in property improvement effect” to occur due to the bonding between the additive elements.) Use this analysis result after fully understanding this. Is essential.

(contents of the test)
1) Test casting alloy
AC4F (However, Fe0.7% added product)
AC7A modified (targeted for Mg3.5%, Si0.3%, Fe0.7%)
2) P addition amount The following 7 levels
0ppm, 20ppm, 40ppm, 80ppm, 160ppm, 320ppm, 1000ppm
At these levels, by casting into a gypsum mold and a hull mold (ingot case of about 30 × 45 × 200) shown in FIG. 13, the slow-cooled cast specimen and the quenched cast specimen shown in FIG. By observing the cross-sectional structure, the effect of improving the structure by adding P was confirmed. In addition, at the time of casting the test piece, all the solidification cooling curves of the molten metal in the vicinity of the structure observation site were collected. For the addition of P to the molten metal, an ALCUP agent manufactured by KBAlloys, Inc. was used. (Add to molten metal 15 minutes before casting)

  The component analysis results of each test piece are as shown in Table 9, and the melt solidification / cooling time measurement results of each test piece are as shown in Table 10. The elapsed time in Table 10 is as shown in FIG.

The cross-sectional observation photograph of each test piece was converted into image data, and the structural parameters such as crystallized matter were quantified by image analysis. Here, avoiding the definition of α crystal shape, which is difficult to recognize here, crystallized substances are A. community (Si crystal + Fe crystal entangled), B. Si crystal (one grain unit), C.Fe crystal (one grain) The unit was manually recognized and analyzed in three levels.
The histological image data used for community recognition in A. was as follows.
☆ Mold castings are 1280 pixels x 1000 pixels (0.8500mm x 0.6641mm field of view).
☆ Gypsum cast products are 1280 pixels x 1000 pixels (3.3980 mm x 2.6547 mm field of view) each.
The image data used for the recognition of the BC Si crystal and Fe crystal grain units is
☆ Mold castings are 1280 pixels x 1000 pixels (0.4250mm x 0.3320mm field of view) each.
☆ Gypsum cast products are 1280 pixels x 1000 pixels (0.8450 mm x 0.6602 mm field of view) each.
Each tissue photographic image data is a color photograph and will not be described as a patent drawing.

From this image analysis, as a qualitative trend of tissue improvement by P addition,
1) It can be seen from the structural photograph that the distribution of crystallized material (community formation state) becomes uniform with the addition of P in both die casting products, gypsum casting products, AC4F alloy and AC7A alloy products.
2) The structural change due to the addition of P in AC4F, which is an Al-Si alloy, is clear.
A characteristic of this structural change is that when P does not exist, the eutectic Si community is composed of innumerable fine Si crystals, whereas by adding P, the community becomes a relatively small number of relatively small communities. It changes to a form composed of large Si crystals.
This is shown in FIG. FIG. 17 shows a qualitative interpretation of the tissue analysis result.

  Qualitatively, if the Si content in the alloy is high (compared to the Fe content) due to the addition of P, the number of crystallization of Si crystals is reduced, and the area of each grain is increased. It is presumed that there is an effect of uniforming the community formation of objects, and in the opposite case, there is an effect of increasing the number of crystallization of Fe crystals and uniformly dispersing the Fe crystals. (It is presumed that P also has the effect of making the crystallization state of the “α crystal” uniform, which indirectly determines the distribution and size of the Si and Fe crystals.)

Next, quantitative analysis of the tissue improvement by addition of P was performed.
AC4F alloy (Si content> Fe content), AC7A modified alloy (Si content <Fe content)
<Objective variable>
・ Total length of Si crystal per 1 mm ² (mm)
・ Total length of Fe crystal per 1 mm ² (mm)
<Explanatory variable>
・ Mold material classification (mold: 0, plaster: 1)
・ P addition amount (ppm)
・ Total of molten metal solidification and cooling time T1 ～ TE (sec.)
・ Ca content (ppm) Introduced into explanatory variables only when analyzing AC4F alloy (* AC7A modified alloy has little variation in Ca content, and if introduced into explanatory variables, the solution will diverge during multivariate analysis. Multivariate analysis (multiple regression analysis) was performed by excluding Ca content from the explanatory variables), and an attempt was made to quantify the structure improvement characteristics by adding P to each alloy material.
<Analysis results>
Table 11 shows.

According to the above quantitative analysis, except for the results of multiple regression analysis with the total length (mm) of the Si crystal per 1 mm ^{2 of} AC7A modified alloy as the objective variable, the creep characteristics tend to be improved by adding P I understand that
The results of multiple regression analysis with the total length (mm) of Si crystal per 1 mm ^{2 of} AC7A modified alloy as the objective variable showed a low multiple regression coefficient (because the total Si content was low) and P Regardless of the presence or absence of addition, the sum of the longitudinal characteristics of the Si crystal can be considered to be almost constant, so adding P to the AC7A modified alloy tends to degrade the creep characteristics of the alloy. Therefore, it can be said that it does not contradict claims 3 and 4.
In this way, by adding P to the molten aluminum alloy, it becomes possible to improve the cast structure into a Si crystal or Fe crystal form in which creep deformation resistance can be increased.
In addition, this improvement effect is also unique to the present invention in that it is effective for slow cooling castings such as gypsum casting.

  In this way, if the present invention is used, creep property evaluation and formulation of an aluminum alloy, which has been difficult until now, can be easily performed, and creep property formulas (approximate formulas) formulated with various aluminum alloys. When the multivariate analysis is performed using the time coefficient term as an objective variable and the alloy element amount, structure parameter, etc. as explanatory variables, the optimum alloy element amount and structure parameter capable of enhancing the creep characteristics of the aluminum alloy can be quantified. Further, a specific method for improving the structure parameter for the above purpose can be easily provided by a method of adding P to the molten metal. Thus, it can be said that the significance of the present invention is extremely great for an aluminum alloy for high temperature use.

  Finally, specific improved alloy compositions are shown in Tables 12 and 13. These are examples in which various aluminum alloys for casting according to JIS standards are improved by the present invention, Table 12 is examples of improvements in various types of aluminum alloys for casting, and Table 13 is examples of improvements in various types of aluminum alloys for die casting. The reason why the amount of P added is 10 to 100 ppm is that when the amount is less than 10 ppm, there is little improvement in the structure, and when it exceeds 100 ppm, burnout consumption is severed during addition and the addition efficiency is poor.

It is a schematic diagram of the proliferation of dislocation. It is shape explanatory drawing of a creep test piece. It is a schematic diagram which shows a creep curve. It is explanatory drawing of embodiment of invention of Claim 1. It is explanatory drawing of embodiment of invention of Claim 1. It is a graph which shows a creep characteristic. It is a graph which shows a creep characteristic. It is an equilibrium diagram of an Al-Si binary alloy. It is a graph of a creep test result. It is a graph of a creep test result. It is a graph of a creep test result. It is a graph of a creep test result. 6 is a cross-sectional view of a mold used in Example 3. FIG. 6 is a cross-sectional view of a cast product used in Example 3. FIG. It is explanatory drawing of the elapsed time in Table 10. FIG. It is an organization chart which shows the qualitative tendency of organization improvement by P addition. It is explanatory drawing of the qualitative interpretation of a structure | tissue analysis result.

Explanation of symbols

1 Test piece 2 Surface plate 3 Weight 4 Heating furnace

Claims (4)

On the surface plate, three rectangular parallelepiped or smooth cylindrical specimens made from the same aluminum alloy material are equally distributed at the apex position of the equilateral triangle, and almost uniform compressive stress σ is applied to these three specimens. Place a weight that can be applied, heat and hold at a predetermined temperature T, measure the dimensional change of the test piece over time, the relationship between the average value ΔL of the dimensional change of the three test pieces and the elapsed time t,
ΔL ＝ A ・ ln (t) + B ・ ・ ・ (1)
(A and B are constants determined for each alloy material, applied compressive stress σ, and heating holding temperature T)
A creep property evaluation / formulation method for an aluminum alloy material, characterized in that the creep property of the alloy material is formulated by approximating the equation (1).   Observation of the cross-sectional structure of the three test pieces used in the invention of claim 1 or a test piece separately manufactured from the same alloy material and analysis of the alloy composition, and the size / shape numerical values (α1 , α2,...) and measured values of added elements (β1, β2...), A and B are used as objective variables, and σ, T, (α1, α2,. , (Β1, β2,...), And multivariate analysis is performed, and ΔL = A · ln (t) + B in claim 1 is constructed as a prediction formula for A and B in formula (1) A method for predicting the creep characteristics of an aluminum alloy, characterized by quantifying the correlation between the creep characteristics of the corresponding aluminum alloy and the alloy composition and structure state.   When manufacturing aluminum alloy castings containing Si as the main component element, the length of each Si crystal grain that produces primary and eutectic crystals per unit area by adding P to the casting melt A method for producing an aluminum alloy casting, characterized by reducing the sum of dimensions and increasing the creep deformation resistance of the casting.   When manufacturing an aluminum alloy casting containing Fe as a main component element, the length of each Fe crystal grain that produces primary and eutectic crystals per unit area by adding P to the molten metal for casting A method for producing an aluminum alloy casting, characterized by increasing a sum of dimensions and increasing a creep deformation resistance of the casting.

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