JP4704721B2 - Heat-resistant Al-based alloy with excellent high-temperature fatigue properties - Google Patents

Description

  The present invention is a heat-resistant Al-based alloy having high-temperature toughness (heat resistance) and wear resistance, as well as excellent fatigue characteristics, such as engine parts (pistons, connecting rods) of automobiles and aircrafts. The present invention relates to an Al-based alloy suitable for use in machine parts that require heat resistance and light weight.

  Engine parts such as automobiles and aircraft are required to have high-temperature toughness (heat resistance) and wear resistance up to about 300 to 400 ° C., and also fatigue characteristics in such a high-temperature region.

  First, regarding heat resistance, various conventional heat-cast alloys such as Al—Cu alloys (2000 series Al alloys such as 2618) have been developed, but the use temperature is higher than 150 ° C. Then, sufficient high-temperature strength could not be obtained. This is because Al—Cu-based alloys ensure strength with fine precipitates obtained by age hardening, and therefore, when the use temperature exceeds 150 ° C., the precipitate phase becomes coarse and the strength is significantly reduced.

  Thus, conventionally, Al-based alloys to which the rapid solidification method is applied have been developed. According to the rapid powder metallurgy method, which is one of the rapid solidification methods, the amount of addition of alloy elements such as Fe, Cr, Mn, Ni, Ti, Zr, etc. can be increased as compared with the melt cast Al alloy. Therefore, an Al alloy containing a large amount of these alloying elements can be pulverized by rapid solidification and solidified to obtain an Al-based alloy having excellent high-temperature strength even at high temperatures exceeding 150 ° C. Yes (see Patent Documents 1 and 2). This is because the alloy element disperses an intermetallic compound with Al that is stable even at high temperatures in the structure, thereby increasing the high-temperature strength.

  Furthermore, a technique for increasing the strength by increasing the fraction of the intermetallic compound by miniaturizing the intermetallic compound has been proposed (see Patent Document 3). In addition, alloying elements such as Fe, V, Mo, Zr, and Ti are added by spray forming, which is one of the rapid solidification methods, and the intermetallic compound between these alloying elements and Al is refined to reduce weight. A heat-resistant Al-based alloy has also been developed, and a high-strength Al-based alloy that also has wear resistance has been developed by adding excess Si and refining primary crystal Si (see Patent Document 4). ).

  Next, with respect to the fatigue characteristics of Al-based alloys, it is known that the average grain size of Al crystal grains constituting the matrix is refined to improve the fatigue characteristics for engine parts such as automobiles and aircrafts described above. Yes. For example, Si; 4 to 12 wt%, Cu; 0 to 7 wt%, Mg; 0 to 0.5 wt%, Ti; 0.15 to 0.5 wt%, Fe; 0 to 0.7 wt%, Mn: 0 to 0.7% by weight, balance Al and impurities, and having a hypoeutectic structure composed of a matrix phase and a crystallized product or hard particles having a higher elastic modulus than the matrix phase, An Al-based alloy having excellent fatigue resistance, characterized in that the crystal grain size is 24 times or less the unit cell size of the matrix phase surrounded by the crystallized product or hard particles (Patent Document) 5).

Further, it is an Al alloy containing Fe, Ti and Si as alloy elements and the balance being Al, and the contents of Fe, Ti and Si are 4 atomic% ≦ Fe ≦ 6.8 atomic%, 0.5%, respectively. Atomic% ≦ Ti ≦ 1.2 atomic%, 1.5 atomic% ≦ Si ≦ 2.5 atomic%, and the average grain size D1 of Al crystal grains (face-centered cubic structure) constituting the matrix is D1 ≦ 1 μm Furthermore, an Al-based alloy in which the average particle diameter D2 of the intermetallic compound is D2≤0.5 μm has been proposed (see Patent Document 6).
Japanese Patent No. 2911708 (Claims) Japanese Patent Publication No. 7-62189 (Claims) JP-A-5-195130 (Claims) JP-A-9-125180 (Claims) JP-A-11-199960 (Claims, Table 4) Japanese Patent No. 3151590 (Claims, Tables 4, 7, and 9)

  According to the quenching powder metallurgy method such as Patent Documents 1 and 2, the high temperature strength of the Al-based alloy can be increased by increasing the addition amount of the alloy element. However, if the addition amount of the alloy element is excessively increased, the intermetallic compound is coarsened, so that only a high temperature strength of about 300 MPa at 300 ° C. is obtained. The same applies to Patent Document 3 in which the fraction of intermetallic compounds is increased by miniaturization of intermetallic compounds. Further, even in an Al-based alloy by the spray forming method such as Patent Document 4 described above, only a similar high temperature strength is obtained.

Further, the fatigue characteristics of Patent Documents 5 and 6 described above must be low at high temperatures at about 300 to 400 ° C. For example, the thermal fatigue test in Patent Document 5 is only at a temperature of about 40 to 260 ° C., and the high cycle fatigue test (giving a constant tensile-compressive cyclic stress to the test piece) is also an evaluation at room temperature. The fatigue strength at a stress repetition rate of 10 ⁷ times is as low as about 80 MPa level.

Also in Patent Document 6, the fatigue strength at a stress cycle of 10 ⁷ times in a high cycle fatigue test at a relatively low temperature of about 200 ° C. is as low as about 180 MPa. Therefore, there is a limit to improve the fatigue characteristics by reducing the average grain size of Al crystal grains constituting the matrix of the Al-based alloy.

  The present invention has been made in view of such problems, and satisfies the required characteristics of engine parts such as automobiles and airplanes, and also has a high temperature toughness and wear resistance, and also has a high temperature fatigue property excellent in high temperature fatigue characteristics. The purpose is to provide.

In order to achieve this object, the gist of the heat-resistant Al-based alloy having excellent high-temperature fatigue characteristics according to the present invention is selected from Cr, Fe, Ti, Mn, V, and Si as elements forming the intermetallic compound phase. A preform body obtained by a rapid solidification method using a spray forming method, the composition comprising 15 to 50% by mass of the total of these three elements, the balance being composed of Al and inevitable impurities. An Al-based alloy obtained by processing, wherein the Al-based alloy structure is composed of an intermetallic compound phase having a volume fraction of 50 to 90% and the balance being a metal Al matrix, and the intermetallic compound phase The intermetallic compound area S and the perimeter L of the intermetallic compound among the intermetallic compounds having a particle size of 0.5 μm or more present in the visual field No seki That is, 40% or more of an intermetallic compound having a surface irregularity shape with an engagement L ² / S of 13 or more exists.

  In addition, as a combination for further improving the fatigue characteristics, selected from elements forming these intermetallic compound phases, in particular, by mass%, Cr: 5 to 30%, Fe: 1 to 20%, Ti : A composition containing 1 to 15% of each is preferable. In such a composition, the intermetallic compound phase with a volume fraction of 50 to 90% is composed of Al—Cr, Al—Fe, and Al—Ti binary intermetallic compounds, and high temperature fatigue This is preferable in that the characteristics can be further improved.

  Furthermore, in order to further improve the high-temperature fatigue characteristics, it is preferable that the average of the maximum length of the pool of metal Al divided by the intermetallic compound phase in the Al-based alloy structure is 40 μm or less.

In the heat-resistant Al-based alloy of the present invention, 50% or more of the intermetallic compound having a particle size of 0.5 μm or more has a surface irregularity shape with L ² / S of 13 or more. The preform of the Al-based alloy obtained by the spray forming method is within a temperature range of 400 to 550 ° C., and the holding time in this temperature range is within 30 minutes to 3 hours including heating before processing. It is preferable that a hot working selected from HIP, forging, extrusion, and rolling is performed.

  In the conventional heat-resistant Al-based alloy, the average grain size of Al crystal grains constituting the matrix of the Al-based alloy is refined in order to improve the high temperature fatigue characteristics. In contrast, the Al-based alloy according to the present invention increases the volume fraction of the intermetallic compound phase to 50 to 90% in order to improve the heat resistance at a higher temperature of 400 ° C. The surface shape of the intermetallic compound constituting the intermetallic compound phase is controlled to a shape having an effect of improving high temperature fatigue characteristics.

  In an Al-based alloy composed of a metallic Al matrix and an intermetallic compound phase, the metallic Al matrix is soft, the intermetallic compound phase is hard, and a structure in which the hard intermetallic compound phase is dispersed in the soft metallic Al matrix. ing. When stress is applied to such an Al-based alloy structure during use as a heat-resistant machine component, the hard intermetallic compound peels off from the soft metal Al matrix due to deformation of the Al-based alloy, and the hard intermetallic compound Tends to be the starting point of destruction. This tendency is particularly remarkable when a large amount of intermetallic compound phase is included for improving heat resistance. Thus, when a hard intermetallic compound tends to be a starting point of destruction, the high temperature fatigue characteristics naturally deteriorate.

  That is, when the amount of alloy element added is increased and the intermetallic compound phase is increased, the high temperature fatigue characteristics of the Al-based alloy are controlled by the strength of the interface between the Al matrix and the intermetallic compound phase. And when this interface strength is weak, the problem that it fractures | ruptures in an elastic deformation area and a high temperature fatigue characteristic falls arises newly.

  Therefore, in order to improve high temperature fatigue properties in Al-based alloys, it is necessary that the hard intermetallic compound has an interfacial strength that does not easily peel from the soft metallic Al matrix (interfacial strength of the intermetallic compound with the metallic Al matrix). It becomes.

  For this reason, in the present invention, in the Al-based alloy, the surface of the intermetallic compound constituting the intermetallic compound phase is controlled to have an uneven shape. As described later, the interfacial strength of the intermetallic compound increases as the surface of the intermetallic compound has an uneven shape (the surface of the intermetallic compound is uneven or jagged), and the surface of the intermetallic compound becomes smoother (metal The lower the surface of the intermetallic compound, the lower the surface.

  The intermetallic compound surface has an irregular shape, which increases the interfacial strength of the intermetallic compound with the metallic Al matrix, and even when stress is applied at high temperatures, the intermetallic compound is difficult to peel off from the metallic Al matrix and breaks. The high temperature fatigue characteristics of the Al-based alloy can be improved.

  In a dispersed state of a metal Al pool and an intermetallic compound phase in an Al-based alloy structure as obtained by a rapid solidification method such as spray forming, the surface of the intermetallic compound tends to be smooth. Also, when the Al-based alloy as obtained by the rapid solidification method is further solidified and molded by HIP (hot isostatic pressing), the surface of the intermetallic compound tends to be smooth. This is because, when the HIP treatment is performed by a conventional method, as described later, the high temperature holding time including the heating time becomes long and the structure itself is densified, but the surface of the intermetallic compound tends to be smooth. In addition, when the HIP treatment is performed, there is a problem that the size of the intermetallic compound is likely to become coarse due to the long high temperature holding time.

  When the surface of the intermetallic compound is smooth, the amount of the alloy element added increases, and the intermetallic compound phase increases, the above-described interface strength between the Al matrix and the intermetallic compound phase becomes weak. For this reason, a high temperature fatigue characteristic falls and possibility that it will fracture | rupture in an elastic deformation area becomes high. This is why the high temperature fatigue strength of Patent Document 5 is low. In addition, as with these conventional heat-resistant Al-based alloys, even if the average grain size of Al crystal grains constituting the matrix of the Al-based alloy is made fine, the surface of the intermetallic compound does not become uneven, and the surface is not The smooth state is maintained as it is.

  On the other hand, in patent document 6 mentioned above, the air atomized powder is shape | molded into billets by CIP, and this billet is hot-extruded. However, as will be described later, when hot extrusion is performed by a conventional method, the high temperature holding time including the heating time becomes long, and the surface of the intermetallic compound tends to be smooth. Moreover, in patent document 6, there is little content of Fe, Ti, and Si, and the said intermetallic compound phase does not become a big ratio exceeding 50% in a volume fraction. For this reason, the volume fraction of metal Al becomes large, and the size of the metal pool partitioned by the intermetallic compound inevitably increases. The less the intermetallic compound phase is and the larger the size of the metal Al pool is, the more stress is concentrated on the metal Al pool portion having a lower strength during the use of the Al-based alloy as the heat-resistant machine part. As described above, when stress concentrates at a high temperature on a pooled portion of metal Al having low strength, the fatigue characteristics naturally deteriorate.

(Al-based alloy composition)
First, a preferable chemical component composition (unit: mass%) of the Al-based alloy of the present invention will be described below including reasons for limiting each element.

In the present invention, in order to improve the heat resistance at a higher temperature of 400 ° C., it is necessary to provide a dispersed particle reinforced type in which the amount of alloy elements is large and the amount of intermetallic compounds is increased to 50 to 90% in volume fraction. There is. Such as the assembled configuration of excellent heat resistance Al-based alloy to a high temperature fatigue characteristics, as the element which forms the intermetallic phase, Cr, Fe, Ti, Mn, V, an element selected from Si, It comprises 15 to 50 wt% in total of these elements, the balance ing of Al and unavoidable impurities.

  When these elements selected from Cr, Fe, Ti, Mn, V, and Si are less than the lower limit of 15% by mass, the intermetallic compound phase (volume fraction) is insufficient. For this reason, the heat resistance and wear resistance of the Al-based alloy and the high temperature fatigue strength cannot be improved. On the other hand, when the sum of these elements exceeds the upper limit of 50% by mass, the toughness decreases and becomes brittle, and cannot be used for heat-resistant machine parts.

  And as a combination which selects from these elements which form an intermetallic compound phase and improves fatigue characteristics more, especially in mass%, Cr: 5-30%, Fe: 1-20%, Ti : A composition containing 1 to 15% of each is preferable. In such a composition, as will be described later, if a preform body is produced by a rapid solidification method using a spray forming method, an intermetallic compound phase of 50 to 90% in terms of the volume fraction of the preform body structure is Al. It is composed of an intermetallic compound whose main phase is a binary system of -Cr, Al-Fe, and Al-Ti, and can further improve high temperature fatigue characteristics.

  Further, these Cr, Fe, and Ti constitute the intermetallic compound in any of intermetallic compound phases such as Al-Cr, Al-Fe, and Al-Ti by a rapid solidification method using a spray forming method. Any element other than the element to be further dissolved can improve the heat resistance and wear resistance of the Al-based alloy.

  Any of Cr, Fe, Ti other than the elements constituting the intermetallic compound is dissolved in any of the binary intermetallic compound phases such as Al—Cr, Al—Fe, and Al—Ti. In this case, the strength, toughness and hardness (heat resistance strength and wear resistance) of the intermetallic compound and the Al-based alloy can be improved. As a more specific example, it means that either Fe or Ti or both are in solid solution in the Al—Cr intermetallic compound phase.

  These intermetallic compounds in which any one of Cr, Fe, and Ti other than the elements constituting the intermetallic compound are in solid solution are, for example, compared to the case where Fe and Ti elements are not dissolved in the Al-Cr intermetallic compound. In addition, it has an excellent balance between heat resistance and wear resistance. For this reason, the strength, toughness, and hardness of the Al-based alloy can be further improved.

  If the total content of Cr, Fe, Ti is less than the lower limit of the above, and the total content of Cr, Fe, Ti is less than the lower limit of 15% by mass, Al—Cr, Al—Fe, Al—Ti, etc. The intermetallic compound phase (volume fraction) and the respective intermetallic compounds are deficient in the solid solution amount of any element other than the elements constituting the intermetallic compound. For this reason, the heat resistance and wear resistance of the Al-based alloy and the high temperature fatigue strength cannot be improved.

  On the other hand, when the upper limit of each content of Cr, Fe, Ti is exceeded, and when the total content of Cr, Fe, Ti exceeds the upper limit of 50 mass%, the intermetallic compound phase and these Even if a structure in which any element other than the elements composing the intermetallic compound is obtained in each intermetallic compound is obtained, the toughness is lowered and the structure becomes brittle. For this reason, it cannot be used for heat-resistant machine parts.

  Therefore, in each of the compositions containing Cr, Fe, and Ti, the Cr content ranges from 5 to 30%, Fe from 1 to 20%, and Ti from 1 to 15%, and the total content of Cr, Fe, and Ti Is in the range of 15 to 50%.

  In addition, a composition containing Mn: 5 to 30%, Fe: 1 to 20%, Si: 1 to 10%, Fe: 1 to 20%, V: 0.5 to 5%, Si: 1 to 10 % Of each composition. In such a composition, as will be described later, if a preform body is produced by a rapid solidification method using a spray forming method, an intermetallic compound phase of 50 to 90% in terms of the volume fraction of the preform body structure is Al. It is composed of an intermetallic compound phase whose main phase is a quaternary system such as -Mn-Fe-Si system or Al-Fe-V-Si system, and can further improve high temperature fatigue characteristics.

When the total content of Mn, Fe, Si, and V is less than the lower limit and the total content of Mn, Fe, Si, and V is less than the lower limit of 15% by mass, a quaternary intermetallic compound phase ( Volume fraction) is insufficient. For this reason, the heat resistance and wear resistance of the Al-based alloy and the high temperature fatigue strength cannot be improved.
On the other hand, when the upper limit of each content of Mn, Fe, Si, V is exceeded, and when the total content of Mn, Fe, Si, V exceeds the upper limit of 50 mass%, the toughness decreases. And become brittle. For this reason, it cannot be used for heat-resistant machine parts.

(Intermetallic compound phase)
The Al-based alloy structure of the present invention is composed of the intermetallic compound phase having a volume fraction of 50 to 90% and the balance being a metal Al matrix. In the composition containing each of Cr, Fe, and Ti, the intermetallic compound phase mainly composed of an Al—Cr, Al—Fe, or Al—Ti binary is 50 to 90% in volume fraction. To occupy. Moreover, in the said composition containing Mn, Fe, and Si, the intermetallic compound phase which makes an Al-Mn-Fe-Si type | system | group quaternary system a main phase occupies 50 to 90% by a volume fraction. Further, in the composition containing Fe, V, and Si, the intermetallic compound phase having a quaternary system such as an Al—Fe—V—Si system as a main phase accounts for 50 to 90% in volume fraction. . In the Al-based alloy structure of the present invention, these main phases are allowed to contain intermetallic compound phases other than these main phases as long as the properties of the Al-based alloy are not impaired.

  In an Al-based alloy composed of a metal Al matrix and an intermetallic compound phase, the metal Al matrix is soft and the intermetallic compound phase is hard. The Al-based alloy has a structure in which hard intermetallic compound phases are dispersed in such a soft metal Al matrix. This hard intermetallic compound phase becomes the main phase that gives the Al-based alloy heat resistance, wear resistance, and high temperature fatigue strength. On the other hand, the soft metal Al matrix serves as a binder for these hard intermetallic compound phases, or serves as a foundation for these hard intermetallic compound phases and plays a role of exerting the functions of the intermetallic compound phases.

  When the amount of intermetallic compound is small, many intermetallic compounds exist alone, but when the volume fraction is 50% or more and the amount of intermetallic compound is increased as in the Al-based alloy of the present invention. A plurality of intermetallic compounds are adjacent to each other to easily form an aggregate (continuous body: intermetallic compound phase). For this reason, it becomes easy to exhibit the function as a main phase which gives Al base alloy heat resistance and abrasion resistance, and high temperature fatigue strength, and especially high temperature fatigue strength improves.

  Further, when the volume fraction is 50% or more and the amount of the intermetallic compound is increased to form the intermetallic compound phase, the average of the maximum length of the pool of the metal Al divided by the intermetallic compound phase Can be reduced.

  If the volume fraction of the intermetallic compound phase is less than 50%, the Al-based alloy lacks heat resistance and wear resistance, and the intermetallic compound phase that is the main phase for imparting high-temperature fatigue strength. Characteristics are degraded. Further, while the amount of the intermetallic compound phase is reduced, the volume fraction of the metal Al is increased, and the size of the metal pool divided by the intermetallic compound phase is necessarily increased. As a result, the average of the maximum length of the metal Al pool partitioned by the intermetallic compound phase inevitably increases beyond 40 μm. For this reason, heat resistance and wear resistance, and particularly high temperature fatigue strength are lowered.

  On the other hand, when the volume fraction of the intermetallic compound phase exceeds 90%, the amount of metal Al becomes too small, and the toughness of the Al-based alloy is lowered and becomes brittle. For this reason, it cannot be used as a heat-resistant Al-based alloy.

(Average size of intermetallic compounds)
Also in the Al-based alloy of the present invention, the smaller the average size of the individual intermetallic compounds (intermetallic compound particles) forming the intermetallic compound phase is preferable. As in the present invention, an Al-based alloy with a large amount of intermetallic compound is greatly improved in high-temperature strength and wear resistance compared to an Al-based alloy with a small amount of intermetallic compound, but the average of intermetallic compounds The effect of size on toughness is increased. In this respect, when the average size of the intermetallic compound is larger than 5 μm, the toughness of the Al-based alloy is significantly lowered. Therefore, in the present invention, the average size of the intermetallic compound (particles) forming the intermetallic compound phase is defined as 5 μm or less. In the present invention, an aggregate or continuum of these intermetallic compound particles is collectively referred to as an intermetallic compound phase, and the average size of these intermetallic compound particles is defined as described above. The average size of the intermetallic compound is measured by observing the Al-based alloy structure with a transmission electron microscope (TEM) of 5000 to 15000 times as described later.

(Surface shape of intermetallic compound)
In the present invention, in order to improve the high temperature fatigue characteristics, the surface of the intermetallic compound (particles) constituting the intermetallic compound phase is controlled to have an uneven shape. Specifically, depending on the size of the intermetallic compound, grains of 0.5 μm or more existing in the visual field when the Al-based alloy structure is observed with a transmission electron microscope (TEM) of 5000 to 15000 times Among each intermetallic compound having a diameter, the relationship between the intermetallic compound area S and the peripheral length L of the intermetallic compound is such that there is 40% or more of the intermetallic compound having a surface irregularity shape with a L ² / S of 13 or more. Control.

  In the Al-based alloy of the present invention, in order to form a large amount of intermetallic compound having a volume fraction of 50% or more, a large amount of alloying element is added to Al. For this reason, alloy elements that are supersaturated in the metal Al matrix have a strong tendency to form (deposit) intermetallic compounds to reach an equilibrium state. Even at the interface between the once formed intermetallic compound and the metallic Al matrix, the alloy element tends to precipitate (transfer) to the intermetallic compound from the metallic Al matrix and tends to be in an equilibrium state.

  When the alloy element moves from the metal Al matrix side to the intermetallic compound side and precipitates at the interface between the intermetallic compound and the metal Al matrix and reaches an equilibrium state, the intermetallic compound is the interface with the metal Al matrix. The surface becomes smooth (flat). This is why the surface of the above-mentioned ordinary Al-based alloy intermetallic compound is smooth. As described above, when the interface is in an equilibrium state, the interface strength between the Al matrix and the intermetallic compound phase is weakened, and it is easy to break in the elastic deformation region, and the high temperature fatigue characteristics are deteriorated.

  FIG. 3 shows a structure photograph of the intermetallic compound having a smooth surface when the Al-based alloy structure is observed with a 15000-fold TEM. In FIG. 3, the scattered spherical objects are intermetallic compounds. For example, it can be seen that the surface of the black intermetallic compound at the center of FIG.

  On the other hand, when the surface of the intermetallic compound has an uneven shape as in the present invention (the surface of the intermetallic compound is uneven or jagged), at the interface between the intermetallic compound and the metal Al matrix, The equilibrium state has not been reached and has stopped in the transitional phase of interface diffusion. That is, at this interface (surface of the intermetallic compound), the concentration of the alloy element that is going to migrate (precipitate) to the intermetallic compound continuously changes from the metallic Al matrix to the intermetallic compound. It is assumed that it is in an equilibrium state.

  Therefore, whether or not the surface of the intermetallic compound has a concavo-convex shape indicates not a concavo-convex shape effect such as a physical anchor effect but a metallurgical non-equilibrium state effect as described above. That is, it is presumed that the interfacial strength at which the hard intermetallic compound is difficult to peel from the soft metal Al matrix is maintained even by deformation at a high temperature due to the concentration gradient of the alloy element in the non-equilibrium state. Therefore, the interfacial compound interface strength increases as the surface of the intermetallic compound has a concavo-convex shape, resulting in a non-equilibrium state. On the other hand, the interface strength of the intermetallic compound becomes lower in an equilibrium state as the surface of the intermetallic compound is smoother.

  FIG. 1 shows a structure photograph of an intermetallic compound having an uneven surface on the surface when an Al-based alloy structure is observed with a 15000-fold TEM. In FIG. 1, as in FIG. 3, the large sphere in the center of the figure is an intermetallic compound, but the surface of these intermetallic compounds is not as smooth as the surface of the intermetallic compound in FIG. It can be seen that the surface has an uneven shape.

  However, there are various sizes of intermetallic compounds, and it is difficult to distinguish the shape of the surface if the size is extremely small in submicron units. In addition, these small ones are less likely to be peeled off and are less likely to be the starting point of destruction than large ones. Furthermore, if the surface of the intermetallic compound having a large size is controlled so as to have a concavo-convex shape, the surface of the intermetallic compound having a small size is also directed to have a concavo-convex shape, and is directed toward improving high temperature fatigue characteristics. Therefore, in the present invention, control is performed so that the surface of the intermetallic compound having a large size, which is likely to be a starting point of fracture and has a large influence due to high temperature fatigue characteristics, has a concavo-convex shape. For this reason, in this invention, the intermetallic compound which has a particle size of 0.5 micrometer or more is selected as a comparatively large intermetallic compound.

Then, the uneven shape on the surface of the intermetallic compound having a relatively large particle size of 0.5 μm or more is a shape in which the relationship L ² / S between the intermetallic compound area S and the peripheral length L of the intermetallic compound is 13 or more. It prescribes.

In FIG. 2, which schematically shows the intermetallic compound of FIG. 1, the perimeter L of each intermetallic compound forms an uneven shape on the surface of the intermetallic compound. Therefore, the perimeter L of the intermetallic compound represents the length of the unevenness on the surface of the intermetallic compound. For these intermetallic compound areas S, the longer the peripheral length L, the longer the unevenness and the larger the intermetallic compound surface unevenness. When the cross section of the intermetallic compound is a perfect circle, the ratio L ² / S between the square of the circumference L of the intermetallic compound represented by (2πr) ² and the area S represented by πr ² is (2πr) ² / πr ² = 4π (about 13). Therefore, the condition that the peripheral length L is long with respect to the intermetallic compound area S and the surface is uneven means that L ² / S is 4π = about 13 or more. When L ² / S related to the surface roughness of this intermetallic compound is less than 13, the length of the roughness becomes shorter (the roughness becomes smaller), the outer periphery of the intermetallic compound approaches a circle, and the conventional surface becomes No significant difference from smooth intermetallic compounds. For this reason, interface strength becomes low and high temperature fatigue characteristics cannot be improved.

In the present invention, in order to guarantee the number of intermetallic compounds having surface irregularities with L ² / S of 13 or more and to ensure high temperature fatigue characteristics improvement, 0.5 μm or more existing in the TEM visual field is ensured. Among these intermetallic compounds, it is specified that 40% or more of the intermetallic compound having a surface irregularity shape with L ² / S of 13 or more is present.

The larger the number of intermetallic compounds of 0.5 μm or more in which L ² / S is 13 or more, the more preferable, and all the intermetallic compounds of 0.5 μm or more present in the TEM visual field have L ² / S of 13 or more. I need it. However, there is a problem of manufacturing limit and manufacturing cost for controlling the intermetallic compound having a surface irregular shape, and the number of intermetallic compounds of 0.5 μm or more having L ² / S of 13 or more is high temperature fatigue property. It is sufficient if the amount is sufficient to improve the quality. In this respect, the ratio of the intermetallic compound having a surface irregularity shape with L ² / S of 13 or more is preferably 45% or more, more preferably 50% or more.

For example, in FIG. 1, if there are 20 intermetallic compounds of 0.5 μm or more present in the TEM field of view, preferably 9 or more, more preferably 10 or more of L ² / S is 13 That's it. On the other hand, if the intermetallic compound having an uneven surface shape with L ² / S of 13 or more is less than 40%, there are too many conventional intermetallic compounds having a low interfacial strength and a smooth surface (intermetallic compound serving as a starting point of fracture). , High temperature fatigue characteristics can not be guaranteed.

  In the present invention, by controlling the surface irregularity shape of the intermetallic compound in this way, the interfacial compound increases the interfacial strength of the intermetallic compound with the metallic Al matrix, and even when stress is applied at high temperatures, the intermetallic compound becomes metallic Al. It makes it difficult to peel off from the matrix, making it difficult for the intermetallic compound to become the starting point of destruction. As a result, the high temperature fatigue characteristics of the Al-based alloy can be enhanced.

  Thus, in order to control the surface irregularity shape of the intermetallic compound, as will be described later, an Al-based alloy preform obtained by the spray forming method is in a temperature range of 400 to 550 ° C., but before processing. In the hot working including heating, the holding in the temperature range is within 30 minutes to 3 hours, and hot working selected from HIP, forging, extrusion, and rolling is performed.

(Maximum length of metal Al pool)
In the heat-resistant Al-based alloy of the present invention, in particular, in order to improve high-temperature fatigue characteristics, it is preferable that the average of the maximum length of the metal Al pool partitioned by the intermetallic compound phase is 40 μm or less.

  In the case of an Al-based alloy having a structure in which an intermetallic compound phase is dispersed in a metallic Al matrix, as the size of the pool of metallic Al separated by the intermetallic compound phase increases, as described above, During the use of an Al-based alloy as a machine part, stress concentrates on a pool portion of low-strength metal Al. As described above, when stress concentrates at a high temperature on a pooled portion of metal Al having low strength, the fatigue characteristics naturally deteriorate.

  As the size of the metal Al pool increases, the dispersion state of the metal Al pool and intermetallic compound phase in the Al-based alloy structure inevitably becomes nonuniform. For this reason, in the Al-based alloy structure, there are many portions where the intermetallic compound phase is concentrated and portions where the intermetallic compound phase is absent or sparse. As described above, when the hard intermetallic compound phase and the soft metal Al pool are dispersed non-uniformly, high-cycle fatigue, etc., when tensile-compressive cyclic stress is applied to the product Al-based alloy at a high temperature. The fatigue strength must be extremely low. In addition, heat resistance and wear resistance must be lowered.

  This tendency becomes conspicuous when the size of the metal Al pool increases and the average maximum length of the metal Al pool exceeds 40 μm. For this reason, when the size of the metal Al pool is increased, there is a possibility that the effect of improving the high-temperature fatigue characteristics by controlling the surface unevenness of the intermetallic compound described above may be reduced. Therefore, in the present invention, the average of the maximum length of the pool of metal Al partitioned by the intermetallic compound phase is preferably 40 μm or less, more preferably 30 μm or less.

  When the volume fraction of the intermetallic compound phase is too small or the volume fraction of the metallic Al is too large, the size of the soft metal Al pool partitioned by the intermetallic compound phase is the maximum length. It tends to be larger than an average of 40 μm.

  Moreover, even if the volume fraction of the intermetallic compound phase is large, the Al-based alloy structure such as a preform body that has been obtained by a rapid solidification method such as a spray forming method has the largest metal Al pool size. It tends to be larger than the average length of 40 μm. This is the same even when an Al-based alloy such as a preform body obtained by the rapid solidification method is further solidified and molded by CIP or HIP.

  Therefore, in order to increase the volume fraction of the intermetallic compound phase and to make the average maximum length of the pool of metal Al partitioned by the intermetallic compound phase 40 μm or less, a rapid solidification method It is preferable to perform hot working selected from forging, extrusion, and rolling on the Al-based alloy obtained by the above. By these hot working (plastic working), the size of the metal Al pool in the Al-based alloy structure is refined, and the metal Al pool and the intermetallic compound phase are finely and uniformly dispersed. In the HIP or CIP, there is no such effect of refining the metal Al pool.

(Maximum length measurement of metal Al pool)
In the present invention, in order to reduce the measurement error and be reproducible, the maximum length is 20 μm or more with the maximum length of the pool of the metal Al partitioned by the intermetallic compound phase as a guide. If it is at the level, it will be described later with a 500 × scanning electron microscope (SEM). If the maximum length is at a level of 20 μm or less, it will be described later with a 1000 × scanning electron microscope (SEM). Measure as described in detail in the examples. The magnification of this SEM is determined according to the maximum length of the metal Al pool. If the magnification is too large, the size of the field of view will be smaller than the maximum length of the metal Al pool, and if the magnification is too small. The identification of the metal Al pool itself becomes unclear.

  FIG. 4 is a structural photograph of the heat-resistant Al-based alloy with a 1000 times SEM. FIG. 4 shows the heat-resistant Al-based alloy of the present invention (Invention Example 1 in Example Table 3 to be described later) in which the average maximum length of the pool of metal Al is 40 μm or less.

  In FIG. 4, a large number of white dots are intermetallic compounds (particles), and the black streak pattern is a pool portion (Al matrix portion) of metal Al. In the heat-resistant Al-based alloy of the present invention, the longest portion of each (each) metal Al pool portion, which is a black streak pattern in this field of view, is measured and averaged as described later.

  As shown in FIG. 4, in the Al-based alloy of the present invention, the intermetallic compound phase has a volume fraction of 50% or more, so that a plurality of intermetallic compounds are adjacent to each other (aggregate (intermetallic compound phase)). Can be seen. In other words, it can be seen that the pool portion of the metal Al is finely divided (partitioned) by the intermetallic compound phase. And, such an intermetallic compound phase is abundant and the microstructure state of the metal Al pool portion ensures the heat resistance and wear resistance of the Al-based alloy and the high temperature fatigue strength.

(Production method)
Below, the manufacturing method of this invention Al group alloy is demonstrated. The present invention Al-based alloy, since many amount alloy elements, in order to more precipitating an intermetallic compound phase, instead of the usual melting and casting method, the rapid solidification method, you produce a preform body. Also, of the rapid solidification, it is produced by the scan play forming method.

  The spray forming method has a much faster cooling and solidification rate than the usual melting and casting method (ingot making), so the crystallization nucleation frequency is high, each intermetallic compound phase is abundant and fine, It can be deposited in the structure. In addition, since the growth rate of each intermetallic compound particle is relatively small, the frequency of contact with adjacent grains is also reduced, and the size of the intermetallic compound continuum that is the intermetallic compound phase is also reduced.

  At this time, in the composition containing Cr, Fe, and Ti, any of the intermetallic compound phases such as Al—Cr, Al—Fe, and Al—Ti, other than the elements that constitute the intermetallic compound. Such elements can be forcibly solid-solved to further improve the heat resistance and wear resistance of the Al-based alloy.

  However, it is necessary to optimize the cooling and solidification rate even in the spray forming method. In a preferred embodiment by the spray forming method, the Al alloy having the composition of the present invention is melted at a melting temperature of 1100 to 1600 ° C., then spraying of the molten metal is started, and a preform is produced by the spray forming method.

  The reason why the melting temperature is set to 1100 ° C. or higher is to completely dissolve each intermetallic compound phase in the Al alloy having the composition of the present invention. Moreover, in order to dissolve each intermetallic compound phase completely as the content of each alloy element increases, the melting temperature is preferably higher than 1100 ° C., but the temperature exceeds 1600 ° C. There is no need.

  When the molten metal spray is started, the molten metal is preferably cooled to a spray start temperature at a cooling rate of 100 ° C./h or more, and then the molten metal spray is started at 900 to 1200 ° C. The reason for melting at the high temperature is to completely dissolve the intermetallic compound phase, but here, after the molten metal is cooled, the spraying is started after the intermetallic compound is crystallized to some extent. This is because there is an effect of finely crystallizing other intermetallic compounds during spray forming using the intermetallic compounds as nuclei. Moreover, when spraying is started from a low temperature, there is an effect that the spray cooling rate is increased and the intermetallic compound to be crystallized is further refined.

  As described above, when the molten metal is once cooled, if the cooling rate to the spray start temperature of the melt is less than 100 ° C./h, the above-described intermetallic compound is crystallized to some extent before the spray is started and crystallized. There is a high possibility that other intermetallic compounds cannot be crystallized finely during spray forming using the intermetallic compound as a nucleus, and the intermetallic compound to be crystallized cannot be miniaturized.

  The spray start temperature of the molten metal affects the cooling and crystallization speed in the spray process (spray forming process). That is, the lower the spray start temperature of the molten metal, the easier the cooling rate. However, if the spray start temperature is less than 900 ° C., the intermetallic compound is crystallized in the molten metal before the spray process, and the nozzle is likely to be blocked. On the other hand, when the spray start temperature exceeds 1200 ° C., the cooling rate during the spraying process is slow, and there is a high possibility that the intermetallic compound of the preform produced by the spray forming method cannot be miniaturized.

  In the spray process (spray forming process), it is important to sufficiently increase the cooling rate. When the cooling rate is sufficiently high, the frequency of crystallization nucleation of the intermetallic compound increases, so that coarsening of the intermetallic compound particles can be prevented and the intermetallic compound phase can be refined. In addition, since the intermetallic compound particles are miniaturized, the frequency of contact with adjacent grains is reduced, and the outer dimension of the intermetallic compound phase can be reduced.

  The cooling rate in spray forming (during the spray process) can be controlled by, for example, the gas / metal ratio (G / M ratio: the amount of gas sprayed on the molten metal per unit mass). In the present invention, the higher the G / M ratio, the faster the cooling rate, and the fine intermetallic compound phase as defined in the present invention can be obtained. The maximum length of the metal Al pool can be reduced. In addition, elements other than those constituting the intermetallic compound can be forcibly dissolved in the intermetallic compound phase.

The lower limit of the G / M ratio that satisfies these conditions is, for example, ³ Nm ³ / kg or more, preferably 5 Nm ³ / kg or more, more preferably 6 Nm ³ / kg or more. The upper limit of the G / M ratio is, for example, 20 Nm ³ / kg or less, preferably 15 Nm ³ / kg or less is recommended. If the G / M ratio is smaller than this (the cooling rate is slow), the intermetallic compound tends to be coarsened, and the maximum length of the metal Al pool in the Al-based alloy structure is reduced by hot working described later. There is a high possibility of not being able to.

  The Al-based alloy obtained by such a spray forming method is either subjected to CIP or HIP treatment in a state where the Al-based alloy preform body is once sealed in a vacuum vessel, or in the state of the preform body as it is. Processed by hot forging, extrusion or rolling. Moreover, it is preferable that the powder obtained by the rapid powder metallurgy is also hot-worked with an Al-based alloy (preform body) once solidified and formed by CIP or HIP. However, the HIP treatment exposes the Al-based alloy (preform body) for a long time of 3 hours or more to a high temperature, so that the intermetallic compound is likely to be coarsened and the average size is likely to exceed 5 μm. For this reason, in the present invention, it is preferable not to perform HIP processing.

  When performing hot working of any one of the forging, extrusion, and rolling, as described above, in order to control the surface of the intermetallic compound to have an uneven shape, the temperature range and holding time in hot working Need to control.

  That is, in order to control the surface irregularity shape of the intermetallic compound as in the present invention, the Al-based alloy preform obtained by the spray forming method or the like is hot-worked in a temperature range of 400 to 550 ° C. There is a need to. However, at this time, it is also necessary to perform hot working such as HIP, forging, extrusion, rolling, etc., with the holding in the temperature range in the hot working including heating before working within 30 minutes to 3 hours. Strictly speaking, these holding times are the total time for cooling to a temperature of less than 400 ° C. after hot working, including the hot working time, from the time when the heating temperature is reached in the heat treatment before hot working.

  If the hot working temperature of these forging, extrusion, and rolling is less than 400 ° C., hot working becomes difficult, and the effect of controlling the surface unevenness of the intermetallic compound by hot working cannot be obtained. Further, the effect of reducing the size of the metal Al pool and the effect of finely dispersing the metal Al pool and the intermetallic compound phase cannot be obtained.

  On the other hand, even when the hot working temperature exceeds 550 ° C., the effect of controlling the surface unevenness of the intermetallic compound by hot working cannot be obtained. In addition, the size of the metal Al pool becomes coarse. From the viewpoint of preventing the coarsening of the metal Al pool, the hot working temperature is preferably 450 ° C. or lower.

  In addition, the holding time of the Al-based alloy preform at the above-mentioned high temperature during hot working is important, and is stopped in a non-equilibrium state (transitional phase of interfacial diffusion) at the interface between the intermetallic compound and the metal Al matrix. In order to make the surface of the intermetallic compound into a concavo-convex shape as in the present invention, including the heat treatment time before hot working, as described above, holding in the temperature range of 400 to 550 ° C. for 30 minutes to It needs to be 3 hours. For this reason, it is preferable to shorten the heat treatment time and hot working time before hot working, and to rapidly cool after hot working.

  When the holding time at this high temperature exceeds 3 hours, as in the present invention, when the volume fraction of the intermetallic compound phase is large (when the amount of alloying elements is large), the intermetallic compound and the metal At the interface with the Al matrix, precipitation of the alloy element from the metal Al matrix to the intermetallic compound proceeds so much that the equilibrium state is reached. Incidentally, in hot processing such as normal HIP, forging, extrusion, and rolling, the holding time at a high temperature usually exceeds 3 hours including the heat treatment time before hot working. For this reason, precipitation of the alloy element from the metal Al matrix to the intermetallic compound proceeds excessively at the interface, reaching an equilibrium state, and the surface of the intermetallic compound that is the interface with the metal Al matrix is smooth (flat). ). As a result, the interfacial strength between the Al matrix and the intermetallic compound phase becomes weak, rate-limiting, and easily breaks in the elastic deformation region.

  On the other hand, if the holding in the temperature range is less than 30 minutes, uniform heating to the temperature range and hot working itself are difficult. As a result, the effect of controlling the surface unevenness of the intermetallic compound by hot working cannot be obtained substantially.

  In addition, by hot working such as forging, extrusion, rolling, etc. in these condition ranges excluding HIP, the size of the metal Al pool in the Al-based alloy structure is refined, and the metal Al pool and metal The intermetallic phase is finely and uniformly dispersed. Moreover, the solid solution amount of the additive element dissolved in the Al matrix is ensured, and the coarsening of the precipitated intermetallic compound particles can be prevented.

  The Al-based alloy thus hot-worked is used as it is or after appropriate processing such as machining to obtain a product Al-based alloy.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

The molten alloys of Al alloys having the component compositions A to J shown in Table 1 below were melted at the melting temperatures shown in Table 2, and the molten metal was cooled to the spray start temperature at a cooling rate of 100 ° C./h or more, and then Table 2 Spraying of the molten metal was started at the temperature shown in FIG. 2 and spray forming (gas used: N ₂ ) at the G / M ratio shown in Table 2 to prepare various preforms.
In Table 1, A to E, I, and J are Cr—Fe—Ti based compositions, F is a Mn—Fe—Si based composition, G is a Fe—V—Si based composition, and H is a Cr—Fe—Ti—Mn— composition. Si-V composition.

Each of the obtained preforms (Inventive Examples 1 to 9 and Comparative Examples 10 to 16 shown in Table 2) was subjected to the heating temperature and holding time (heating + hot working) conditions shown in Table 2, and the inventive examples were left as they were. Hot forging and the comparative example were HIP or hot forging. The holding time at a high temperature is a heating holding time at a temperature of 400 ° C. or higher before hot working, a hot working time, and a time for cooling to a temperature of less than 400 ° C. after hot working. Each retention time was adjusted. In each example, the strain rate of hot forging was the same as 10 ⁻⁴ / s and the reduction rate was 80%.

  In the HIP treatment shown in Table 2, each preform body is loaded in a SUS can, and depressurized to 13 kPa (100 Torr) or less, kept at a heating temperature of 575 ° C. for 2 hours, and sealed. To form a capsule. The obtained capsule was reheated to 550 ° C. and subjected to HIP treatment [pressure: 100 MPa (1000 atm), holding time: 2 hours] to obtain an Al-based alloy. In these series of HIP processes, the holding time at a temperature of 400 ° C. or higher is about 5 hours.

  The characteristics of the Al-based alloy after hot working and the test material after HIP treatment were evaluated as follows. These results are shown in Table 3, respectively.

(L ² / S evaluation analysis method of intermetallic compounds)
From the observation image of FE-TEM (manufactured by Hitachi, Ltd., HF-2000 Field Emission Transmission Electron Microscope) of 15000 times tissue, using Image-ProPlus made by MEDIACYBERNETICS as the image analysis software, the area and circumference of the intermetallic compound The length was determined by image analysis. That is, the area (S) and the perimeter (L) of each intermetallic compound particle image having a particle diameter of 0.5 μm or more existing in the visual field are image-analyzed, and L ² / S of the intermetallic compound phase is calculated. I asked for each. Then, among the intermetallic compounds (number) having a particle diameter of 0.5 μm or more existing in the visual field, the (number) of intermetallic compounds having a surface irregularity shape with L ² / S of 13 or more is obtained, The percentage (%) was determined. The average was obtained assuming that the number of fields of view was 5.

(Identification of intermetallic compound phase)
The crystal structure of each intermetallic compound phase in the field of view was analyzed from the X-ray diffraction and TEM electron diffraction patterns. As a result, in the examples using the Cr—Fe—Ti-based Al alloy compositions of Invention Examples 1 to 6 and Comparative Examples 10 to 12, 15, and 16 in Table 2, the intermetallic compound phase is Al—Cr based, Al— It was confirmed that it was composed of an intermetallic compound having a Fe-based and Al-Ti-based binary system as a main phase and a metal Al matrix.

  Moreover, in the example using the Mn-Fe-Si Al alloy composition of Invention Example 7 and Comparative Example 13 in Table 2, the intermetallic compound phase is an Al-Mn-Fe-Si quaternary system as the main phase. It consisted of an intermetallic compound phase and a metal Al matrix. Further, in the example using the Fe—V—Si based Al alloy composition of Invention Example 8 and Comparative Example 14 in Table 2, the intermetallic compound phase is a quaternary system such as Al—Fe—V—Si based. And an intermetallic compound phase and a metal Al matrix. Moreover, in the example using the Cr-Fe-Ti-Mn-Si-V-based Al alloy composition of Invention Example 9 in Table 2, the intermetallic compound phase is Al-Cr-Fe-Ti-Mn-Si-V-based. It was composed of an intermetallic compound phase having a multi-component system as a main phase and a metal Al matrix.

  Therefore, the volume fractions of the intermetallic compound phases shown in Table 3 represent the sum of the volume fractions of the main phases according to the Al alloy composition. For example, in the example using the Cr—Fe—Ti Al alloy composition, the sum of the volume fractions of each of the Al—Cr, Al—Fe, and Al—Ti binary intermetallic compounds is expressed. In the example using the Mn-Fe-Si-based Al alloy composition, the volume fraction of the Al-Mn-Fe-Si-based quaternary intermetallic compound phase is represented. Furthermore, in the example using the Fe—V—Si-based Al alloy composition, the volume fraction of a quaternary intermetallic compound phase such as Al—Fe—V—Si is represented. In the example using the Cr-Fe-Ti-Mn-Si-V-based Al alloy composition, the intermetallic compound phase is an intermetallic compound such as Al-Cr-Fe-Ti-Mn-Si-V. It represents the volume fraction of the compound phase.

(Volume fraction of intermetallic compound phase)
The volume fraction of the intermetallic compound phase of the Al-based alloy structure is approximately 500 μm × about 500 μm for each 10 fields by SEM of 500 times or 1000 times, similar to the method for measuring the maximum length of the metal Al pool. Of the structure of the Al-based alloy of the present invention and the distinction between the metallic Al phase and the intermetallic compound phase of the structure in the field of view subjected to the image processing were analyzed by EDX (Sigma energy dispersive X-ray detector: energy dispersive X-ray manufactured by Kevex). Then, the volume fraction of the intermetallic compound phase in the field of view was measured. Further, the metal Al pool having a maximum length of less than 1 μm was removed from the measurement target and cut off.

(Maximum length of metal Al pool)
The maximum length (μm) of the metal Al pool is measured by mirror-polishing the test material, and the structure of the polished surface is 500 times or 1000 times SEM (Hitachi, Ltd.) depending on the maximum length level as described above. Manufactured by S4500 type field emission scanning electron microscope FE-SEM: The structure of the Al-based alloy with about 10 fields of about 200 μm × about 150 μm was observed. By observing the reflected electron image, the metal Al pool (metal Al phase) is observed as a black image as shown in FIG.

  Then, these black image areas in the field of view are traced, and the maximum length of each metal Al pool (black image) (maximum center-of-gravity diameter) using Image-ProPlus made by MEDIACYBERNETICS as image analysis software Value) was determined by image analysis. The maximum length of the metal Al pool in the field of view to be measured is 1 μm or more, and the maximum lengths of all the metal Al pools of 1 μm or more are obtained and averaged as the maximum length of the metal Al pool in the field of view. Turned into. In addition, when the maximum length of the metal Al pool was less than 1 μm, it was difficult to measure. On the other hand, an error was generated. And this observation was performed in 10 visual fields and further averaged. In the structure observation, the distinction between the metal Al phase and the intermetallic compound phase in the SEM photograph was performed by EDX. Moreover, in order to observe the intermetallic compound phase clearly, it observed with the said reflected electron.

(Average size of intermetallic compound phase)
The average size of the intermetallic compound (intermetallic compound particles) was measured with a TEM (transmission electron microscope) of 5000 to 15000 times. That is, the intermetallic compound is traced from the observed tissue image in the TEM field of view, and the center-of-gravity diameter of each intermetallic compound is obtained and averaged using Image-ProPlus made by MEDIACYBERNETICS as image analysis software. Asked. The number of visual fields to be measured was 10, and the average size of each visual field was further averaged to obtain the average size of the intermetallic compound. However, if the observation magnification becomes too high, the difference in density of the intermetallic compound phase depending on the observation location is large, and the state of the entire sample is not represented. On the other hand, if the magnification is too low, the presence state of the intermetallic compound phase at the sub-μm level cannot be detected. For this reason, EDX is also used in combination to facilitate the distinction between the intermetallic compound phase and the metal Al phase.

(Amount of element dissolved in intermetallic compound phase)
Incidentally, in the example using the Cr—Fe—Ti Al alloy composition of Invention Examples 1 to 9 and Comparative Examples 10 to 16 in Table 2, elements such as Fe and Ti dissolved in the Al—Cr intermetallic compound phase. As a result of measuring the solid solution amount, about 5 to 10% of Fe and Ti out of the Fe and Ti contents were dissolved. The solid solution amount of the element was measured using the above-mentioned TEM and 45,000 times EDX (Kevex, Sigma energy dispersive X-ray spectrometer) attached to the TEM. -Cr-based intermetallic compound phases were measured at 10 points and averaged.

(High temperature strength)
The high temperature strength of these Al-based alloys was measured. Each Al-based alloy test piece having a parallel part Φ4 × 15 mmL was heated to 400 ° C. and held at this temperature for 15 minutes, and then the test piece was subjected to a high-temperature tensile test at this temperature. The tensile speed was 0.5 mm / min, and the strain speed was 5 × 10 ⁻⁴ (1 / s). The high temperature tensile strength or heat resistance of a material having a high temperature tensile strength of 250 MPa or more was evaluated as acceptable.

(Abrasion resistance)
The abrasion resistance test at high temperature was performed by a pin-on-disk abrasion test. Each test material was set on a pin material (Φ7 mm × 15 mm length, about 1 g), and the test disk material on the wear partner side was FC200 (cast iron). The test temperature was 400 ° C., the load was 10 kgf, the rotation radius of the pin was 0.02 m, and the test material was brought into contact with the rotating test disk material for 10 minutes without lubrication. The mass reduction rate due to wear of each test material at this time, (mass before test−mass after test) / mass before test of the test material was evaluated. A sample having a mass wear reduction rate of 0.2 g or less was evaluated as being acceptable for wear resistance at high temperatures.

(High temperature fatigue strength)
For high temperature fatigue characteristics, using an Ono-type rotary bending fatigue tester, test pieces of each Al-based alloy with a parallel part Φ8 × 30 mmL and a total length of 90 mmL were heated to 400 ° C. and held at this temperature for 15 minutes. Was subjected to a high-temperature rotational bending fatigue test at a rotational speed of 3000 rpm and a repetition rate of 10 ⁷ times to determine the fatigue strength. The high temperature fatigue strength of 135 MPa or more was evaluated as passing the high temperature fatigue characteristics.

As is apparent from Table 3, Invention Examples 1 to 9 are in the preferable ranges described above, and the Al-based alloy structure is 50% to 90% in volume fraction as defined in the present invention. The compound phase and the balance are composed of a metal Al matrix. Moreover, the average size of the intermetallic compound which comprises these intermetallic compound phases is 5 micrometers or less. Further, as apparent from Table 2, Invention Examples 1 to 9 have a holding time at a high temperature in hot forging within 3 hours. For this reason, as shown in Table 3, among the intermetallic compounds having a particle diameter of 0.5 μm or more, the ratio of the intermetallic compound having a surface irregularity shape with L ² / S of 13 or more is 40% or more. .

  As a result, as shown in Table 3, Invention Examples 1 to 9 are excellent in high temperature strength, wear resistance, and high temperature fatigue strength.

  However, in comparison between Invention Examples 1 and 2 using the same alloy A, the average of the maximum length of the pool of metal Al divided by the intermetallic compound phase is 40 μm or less in Invention Example 1. In contrast, Invention Example 2 exceeds 40 μm. For this reason, the high temperature fatigue strength is more excellent in Invention Example 1 in which the average of the maximum length of the pool of metal Al is smaller.

On the other hand, as is apparent from Table 2, Comparative Examples 10 and 12 to 15 have a holding time at a high temperature exceeding 3 hours, whether it is hot forging or HIP. For this reason, as is clear from Table 3, the ratio of the intermetallic compound having an uneven surface shape with L ² / S of 13 or more among the intermetallic compounds having a particle diameter of 0.5 μm or more is less than 40%. is there. As a result, the high-temperature strength, wear resistance, and particularly the high-temperature fatigue strength are significantly inferior to those of the inventive examples.

Among these comparative examples, Comparative Examples 10 to 12 using the same alloy example A have an Al-based alloy structure having an intermetallic compound phase of 50 to 90% in the volume fraction specified in the present invention. Of the intermetallic compounds having a particle size of 5 μm or more, the proportion of intermetallic compounds having a surface irregularity shape with L ² / S of 13 or more is less than 40%. As a result, the high-temperature strength, wear resistance, and particularly the high-temperature fatigue strength are significantly inferior to those of the inventive examples.

  Among these Comparative Examples 10 to 12, Comparative Examples 11 and 12 in which the average maximum length of the metal Al pool is 40 μm or less are compared with Comparative Example 10 in which the average maximum length of the metal Al pool exceeds 50 μm. In particular, the decrease in high temperature fatigue strength is relatively suppressed.

Further, Comparative Examples 10, 13, and 14 in which only the HIP treatment is performed without hot forging may cause the holding time at a high temperature to be too long, and the intermetallic compound has an uneven surface shape like a hot forged material. Does not have. Therefore, even when compared with other comparative examples, the ratio of L ² / S intermetallic compound having 13 or more surface irregularities significantly less.

  Comparative Example 15 uses Alloy Example I in which the alloy amount is too small outside the preferred range, and the volume fraction of the intermetallic compound phase is too small at less than 50%. For this reason, high-temperature strength and wear resistance, particularly high-temperature fatigue strength, are significantly inferior to those of the inventive examples.

  The comparative example 16 uses the alloy example J in which the alloy amount is out of the preferable range and is too much, and the volume fraction of the intermetallic compound phase is more than 90% and too high. For this reason, cracks are generated during hot forging, and the high temperature strength and high temperature fatigue strength are significantly inferior to those of the inventive examples.

From the above results, each requirement of the present invention, the volume fraction of the intermetallic compound phase, the average size of the intermetallic compound, the ratio of the intermetallic compound having a surface irregularity shape with L ² / S of 13 or more, the pool of metal Al The critical significance for improving the high-temperature fatigue strength, such as the maximum length of, is understood.

  As described above, the present invention can provide a heat-resistant Al-based alloy that is lightweight and has excellent high-temperature fatigue properties as well as high-temperature toughness and wear resistance. Therefore, it can be applied to various parts such as pistons and connecting rods that require heat resistance such as automobiles and airplanes.

It is a drawing substitute photograph which shows the structure | tissue of this invention heat resistant Al group alloy. It is a schematic diagram which shows the intermetallic compound of FIG. It is a drawing substitute photograph which shows the structure | tissue of the heat resistant Al group alloy of a comparative example. It is a drawing substitute photograph which shows the structure | tissue of the heat resistant Al group alloy of this invention.

Claims (3)

Three elements selected from Cr, Fe, Ti, Mn, V, and Si as elements forming the intermetallic compound phase, the total of these three elements being 15 to 50% by mass, the balance being Al and inevitable impurities An Al-based alloy obtained by hot working a preform body obtained by a rapid solidification method using a spray forming method, the Al-based alloy structure having a volume fraction of 50 to 90% of the intermetallic compound phase and the balance are composed of a metal Al matrix, and the average size of the intermetallic compound constituting the intermetallic compound phase is 5 μm or less, and 0.5 μm or more present in the visual field Among the intermetallic compounds having a particle size, the relationship between the intermetallic compound area S and the peripheral length L of the intermetallic compound is such that there is 40% or more of the intermetallic compound having a surface irregularity shape with a L ² / S of 13 or more. A heat-resistant Al-based alloy with excellent high-temperature fatigue characteristics. The element forming the intermetallic compound phase has a composition containing, by mass%, Cr: 5 to 30%, Fe: 1 to 20%, Ti: 1 to 15%, respectively, The heat-resistant Al-based alloy having excellent high-temperature fatigue characteristics according to claim 1 , comprising an Al-Cr-based, Al-Fe-based, or Al-Ti-based intermetallic compound . The heat-resistant Al with excellent high-temperature fatigue properties according to claim 1 or 2, wherein the Al-based alloy structure has an average maximum length of a pool of the metal Al divided by the intermetallic compound phase of 40 µm or less. Base alloy.

Images