JP4704720B2 - 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 excellent high-temperature toughness (heat resistance) and wear resistance as well as excellent high-temperature fatigue characteristics, such as engine parts (pistons, connecting rods) of automobiles and aircrafts. The present invention also 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 (high temperature 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, regarding the high temperature fatigue properties of Al-based alloys, it is known that the average grain size of Al crystal grains constituting the matrix is refined to improve the high temperature fatigue properties for engine parts such as automobiles and aircrafts described above. It has been. 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 in improving the high temperature 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 average of the maximum length of the pool of metal Al divided by is assumed to be 40 μm or less.

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

  In order to make the average of the maximum length of the pool of metal Al in the heat-resistant Al-based alloy excellent in high-temperature fatigue characteristics of the present invention to 40 μm or less, an Al-based alloy preform obtained by a spray forming method is used. It is preferably processed by any one of forging, extrusion and rolling while hot.

  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. On the other hand, the Al-based alloy according to the present invention increases the volume fraction of the intermetallic compound phase from 50 to 90%, in other words, after reducing the volume fraction of the metal Al, The high temperature fatigue characteristics are improved by refining the pool of Al metal (Al base phase) partitioned (enclosed) by the intermetallic compound phase.

  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. When such a soft metal Al matrix has a structure in which hard intermetallic compound phases are dispersed, the larger the size of the metal Al pool, the more the Al-based alloy is used as a heat-resistant machine component. Stress concentrates on the pool portion of the 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.

  Further, as the size of the metal Al pool increases, the dispersion state of the metal Al pool and the intermetallic compound phase in the Al-based alloy structure inevitably becomes non-uniform. In this way, when the hard intermetallic compound phase and the soft metal Al pool are dispersed non-uniformly, when a repeated stress of tension-compression is applied to the product Al-based alloy, such as high cycle fatigue, at a high temperature. The fatigue strength must be extremely low.

  In particular, 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 a spray forming method, the size of the metal Al pool tends to increase. On the other hand, when the Al-based alloy as obtained by the rapid solidification method is further solidified and molded by CIP (cold isostatic pressing) or HIP (hot isostatic pressing), the structure itself is densified. The However, the structure state in which the size of the metal Al pool is large is maintained as it is. This is why the high temperature fatigue strength of Patent Document 5 is low. Further, even if the average grain size of the Al crystal grains constituting the matrix of the Al-based alloy is miniaturized like these conventional heat-resistant Al-based alloys, the metal Al pool itself is not miniaturized.

  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. Therefore, compared with Patent Document 5, the size of the pool of metal Al advances in the direction of miniaturization, and the fatigue strength is high. However, 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 increases, and the size of the metal pool inevitably increases. 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, and the high temperature fatigue strength decreases. The hot extrusion process in Patent Document 6 merely refines an absolutely large metal pool relatively by comparison with this. In addition, when the amount of the intermetallic compound phase is small as described above, the intermetallic compounds are often present individually, which also contributes to the low high temperature fatigue strength.

  On the other hand, as in the case of the Al-based alloy of the present invention, first, when the amount of intermetallic compound is increased, a plurality of intermetallic compounds are adjacent to each other without interposing metal Al (matrix). Easy to form. As a result, the average of the maximum length of the metal Al pool partitioned by the intermetallic compound phase can be reduced.

  In other words, if an average of the maximum length of the pool of metal Al divided by the intermetallic compound phase in the present invention is 40 μm or less, the premise is that the Al-based alloy structure has a volume fraction of 50. It should have ~ 90% intermetallic phase.

  However, simply increasing the number of intermetallic compound phases in this way may ensure the average of the maximum length of the pool of metal Al exceeding 40 μm simply by ensuring the preconditions. Therefore, as in the present invention, in order to ensure that the average maximum length of the metal Al pool is 40 μm or less, it is preferable to further hot-work the Al-based alloy as will be described later.

(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.

The set formed of excellent heat resistance Al-based alloy to a high temperature fatigue characteristics of the present invention, as an element forming the intermetallic phase, Cr, Fe, Ti, Mn, V, an element selected from Si, these The total amount of elements is 15 to 50% by mass, and the balance is made of Al and inevitable 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 improves the high temperature fatigue characteristics selected from the elements forming these intermetallic compound phases, in particular, by mass%, Cr: 5-30%, Fe: 1-20%, A composition containing Ti: 1 to 15% is preferable. In such a composition, as will be described later, if a preform body is produced by a rapid solidification method such as a spray forming method, an intermetallic compound phase of 50 to 90% in volume fraction of the Al-based alloy structure is finally obtained. , Al-Cr-based, Al-Fe-based, and Al-Ti-based binary intermetallic compound phases can be used, and high-temperature fatigue characteristics can be further improved.

  In addition, these Cr, Fe, and Ti may be added to any of the intermetallic compound phases such as Al—Cr, Al—Fe, and Al—Ti by a rapid solidification method such as a spray forming method. Any element other than the constituent elements can be further dissolved to 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.

  The intermetallic compound phase in which either Cr, Fe, or Ti other than the elements constituting the intermetallic compound is dissolved, for example, when the Fe and Ti elements are not dissolved in the Al-Cr intermetallic compound phase. Compared to, the balance between heat resistance and wear resistance is excellent. 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. In the intermetallic compound phase (volume fraction) and each of these intermetallic compound phases, the solid solution amount of any element other than the elements constituting the intermetallic compound 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 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 constituting the intermetallic compound is dissolved in each intermetallic compound phase is obtained, the toughness is lowered and 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 such as a spray forming method, an intermetallic compound phase of 50 to 90% in the volume fraction of the Al-based alloy structure is finally obtained. , Al-Mn-Fe-Si system, or Al-Fe-V-Si system, etc. can be comprised from the intermetallic compound phase which makes a main phase a main phase, and a high temperature fatigue characteristic can be improved further.

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)
In addition, it is so preferable that the average size of each intermetallic compound (intermetallic compound particle | grains) which forms an intermetallic compound phase is small. When the average size of the intermetallic compound increases, the toughness of the Al-based alloy decreases. As a guide, the average size of the intermetallic compound is preferably 10 μm or less.

(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, the average of the maximum length of the metal Al pool partitioned by the intermetallic compound phase is set to 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. Thus, when stress is concentrated at a high temperature in a pool portion of low-strength metal Al, the high-temperature 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. Therefore, in the present invention, the average of the maximum length of the pool of metal Al divided by the intermetallic compound phase is set to 40 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 The Al-based alloy obtained by the above is processed by any one of forging, extrusion, and rolling while hot . 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.

  FIGS. 1 and 2 are photographs of the structure of each heat-resistant Al-based alloy by 500 times SEM. FIG. 1 is a heat-resistant Al-based alloy of the present invention (Invention Example 2 in Example Table 3 to be described later) in which the average maximum length of the metal Al pool is 40 μm or less. On the other hand, FIG. 2 shows a comparative heat-resistant Al-based alloy (Comparative Example 8 in Example Table 3 described later) in which the average maximum length of the metal Al pool exceeds 40 μm. 1 and 2, 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.

  1 and 2, 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. The maximum length of the metal Al pool portion that is a black streaky pattern in the visual field of FIG. 3 is small, and the maximum length of the metal Al pool portion that is a black streaky pattern in the visual field of FIG. You can see that it ’s big. 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. 1, in the Al-based alloy of the present invention, the intermetallic compound phase has a volume fraction of 50% or more, so a plurality of (individual) intermetallic compounds (particles) are aggregated adjacent to each other. It can be seen that a body (continuous body), that is, an intermetallic compound phase is formed. 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. Since the Al-based alloy of the present invention has a large amount of alloying elements, a preform body is produced by a rapid solidification method instead of a usual melt casting method in order to precipitate a large amount of intermetallic compound phases . 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 that each intermetallic compound phase can be precipitated in the structure in a large amount and finely. . Moreover, in the composition containing Cr, Fe, and Ti, any one of elements other than the elements constituting the intermetallic compound may be present in any of the intermetallic compound phases such as Al—Cr, Al—Fe, and Al—Ti. These elements can be forcibly dissolved to 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 once cooled, the spraying is started to crystallize the intermetallic compound to some extent, This is because there is an effect of finely crystallizing other intermetallic compounds during spray forming using the intermetallic compound as a nucleus. 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.

  When the cooling rate to the spray start temperature of the molten metal is less than 100 ° C./h, during the spray forming, the intermetallic compound is crystallized to some extent before the spray starts, and the crystallized intermetallic compound is used as a nucleus. In addition, it is highly possible that other intermetallic compounds cannot be crystallized finely and the intermetallic compounds 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, if the spray start temperature exceeds 1200 ° C., the cooling rate during the spray process becomes slow, and the intermetallic compound tends to be coarsened. In particular, the metal in the final Al-based alloy structure by hot working described later. The maximum length of the Al pool is likely to be coarse.

  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. Further, since the intermetallic compound particles are made fine, the frequency of contact with adjacent grains is reduced, and the outer dimensions of the intermetallic compound phase can be reduced.

  In the general spray forming method, the direction of densifying the preform is emphasized in order to improve the strength. For this reason, in order to form a loose solidified state that can form a dense preform, the cooling rate is reduced. As a result, in a general spray forming method, a fine intermetallic compound phase is hardly formed. For example, in the case where the porosity of the preform is 1% by mass or less as in Patent Document 4, the cooling rate is obviously too slow and inevitably the fine metal interstices as in the present invention. The compound phase is not obtained, and the intermetallic compound phase is coarse.

  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 finer intermetallic compound can be obtained. The maximum length of the metal Al pool in the Al-based alloy structure is finally obtained by hot working described later. The average thickness can be 40 μm or less. 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 average of the maximum length of the metal Al pool in the Al-based alloy structure is also obtained by hot working described later Is not likely to be 40 μm or less.

  The Al-based alloy obtained by such a spray forming method is either densified by performing HIP treatment in a state where the Al-based alloy preform is once sealed in a vacuum vessel, or the preform of the preform as it is. In the state, it is hot and processed by forging, extrusion, or rolling. Further, the powder obtained by the rapid powder metallurgy is also hot-worked with an Al-based alloy (preform body) once solidified with CIP or HIP.

  The conditions in the hot isostatic pressing (HIP treatment) are not particularly limited, but the preform is sealed in a vacuum vessel, for example, a temperature of 450 to 600 ° C., a pressure of 80 MPa (800 Atmospheric pressure) or more, treatment conditions for 1 to 10 hours are recommended. This is because pores tend to remain if the temperature and pressure are too low or the time is too short, and if the temperature is too high or the time is too long, the intermetallic compound phase tends to become coarse. A preferred temperature range is about 500 to 600 ° C, particularly about 550 to 600 ° C. A preferable pressure is 900 MPa or more, particularly 1000 MPa or more. The upper limit of the pressure is not particularly limited, but the effect is saturated even if the pressure is excessively applied, and is usually 2000 MPa or less. A preferable time is about 1 to 5 hr, particularly about 1 to 3 hr.

  As described above, the hot working (plastic working) of any one of forging, extruding, and rolling reduces the size of the metal Al pool in the Al-based alloy structure, and the metal Al pool and intermetallic compound phase. Are dispersed finely and uniformly. 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.

  If the CIP or HIP treatment is not performed, the densification is performed, but the maximum length of the metal Al pool in the Al-based alloy structure is not refined as defined in the present invention.

However, the processing temperature in hot working such as forging, extrusion, and rolling is preferably in the range of 420 to 500 ° C. and a relatively low alloy system in the present invention. Further, the processing rate in these hot workings is relatively high as 70% or more, and the strain rate is preferably in the range of 10 ⁻⁴ to 10 ⁻¹ (1 / s). When hot working is performed under such processing conditions, the above-described effects can be obtained with good reproducibility.

  In order to obtain the above-mentioned effects with good reproducibility during hot working, the holding time of the Al-based alloy preform (after CIP or HIP treatment) at the high temperature is the same as that during hot working. It is preferable to set it to 3 hours or more including the heat treatment time, hot working time, and cooling time after hot working. However, the holding time at this high temperature is 3 hours or more in the case of normal hot working.

  On the other hand, if the processing temperature is too low, the processing temperature is too low, the processing rate or the strain rate is too low, or the holding time at the high temperature is too short, the above-described effects due to hot processing are unlikely to be achieved. If the processing temperature and strain rate are too high, an intermetallic compound phase precipitates, making it impossible to secure the solid solution amount of the additive element that dissolves in the Al matrix, and the intermetallic compound itself becomes coarse. There is a high possibility of doing.

  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 the Al alloys having the component compositions A to G shown in Table 1 below are melted at the melting temperatures shown in Table 2, and the molten metal is 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 are Cr—Fe—Ti based compositions, F is a Mn—Fe—Si based composition, and G is a Fe—V—Si based composition.

  Each of the obtained preforms (Examples 1 to 7 and Examples 10 to 15 shown in Table 2) was hot-forged into a round bar under the heating temperature conditions, strain rate, and processing rate conditions shown in Table 2 after the HIP treatment. processed. In this case, the above-described high temperature holding time was 5 hours or more including the heating time. In Comparative Examples 8 and 9 shown in Table 2, the hot forging process was not performed and the HIP treatment was left as it was. In these series of hot forging processes, the holding time at a temperature of 400 ° C. or higher is about 5 hours.

  In the HIP treatment, each preform was loaded into a SUS can, depressurized to 13 kPa (100 Torr) or less, held at a temperature of 575 ° C. for 2 hours, degassed, and the can was sealed to form a capsule. The obtained capsule was subjected to HIP treatment [temperature: 550 ° C., pressure: 100 MPa (1000 atm), holding time: 2 hours]. In this series of HIP processes, the holding time at a temperature of 500 ° C. or higher is about 5 hours.

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

(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 metal Al phase and the intermetallic compound phase in the SEM photograph were distinguished by EDX (manufactured by Kevex, Sigma energy dispersive X-ray detector). Moreover, in order to observe the intermetallic compound phase clearly, it observed with the said reflected electron.

(Volume fraction of intermetallic compound phase)
The volume fraction of the intermetallic compound phase of the Al-based alloy structure is the same as the measurement method of the maximum length of the metal Al pool. After distinguishing between the metallic Al phase and the intermetallic compound phase by the EDX, the volume fraction of the intermetallic compound phase in the visual field 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.

(Average size of intermetallic compounds)
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, by further using EDX, the intermetallic compound phase and the metal Al phase can be easily distinguished.

(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 5 and Comparative Examples 8 to 12 in Table 2, the intermetallic compound phases are Al—Cr based, Al—Fe based, It was confirmed to be composed of an intermetallic compound having an Al—Ti binary system as a main phase and a metal Al matrix.

  Moreover, in the example using the Mn-Fe-Si-based Al alloy composition of Invention Example 6 in Table 2, the intermetallic compound phase is an intermetallic compound whose main phase is an Al-Mn-Fe-Si-based quaternary system. It consisted of a phase and a metallic Al matrix. Furthermore, in the example using the Fe—V—Si-based Al alloy composition of Invention Example 7 in Table 2, the intermetallic compound phase is an intermetallic compound whose main phase is a quaternary system such as an Al—Fe—V—Si system. It was composed of a compound phase and a metal Al matrix.

  Therefore, the volume fraction of the intermetallic compound phase shown in Table 3 is the binary system of Al—Cr, Al—Fe, and Al—Ti in the example using the Cr—Fe—Ti Al alloy composition. Represents the total volume fraction of each intermetallic compound. In the example using the Mn—Fe—Si-based Al alloy composition of Invention Example 6 in Table 2, 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 of Invention Example 7 in Table 2, the volume fraction of a quaternary intermetallic compound phase such as Al—Fe—V—Si based is represented.

(Amount of element dissolved in intermetallic compound phase)
Incidentally, in the examples using the Cr—Fe—Ti based Al alloy compositions of Invention Examples 1 to 5 and Comparative Examples 8 to 12 in Table 2, elements such as Fe and Ti dissolved in the Al—Cr based intermetallic phase. As a result of measuring the solid solution amount, it was confirmed that about 5 to 10% of Fe and Ti out of 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. A high temperature fatigue strength of 110 MPa or more was evaluated as a passing high temperature fatigue property.

  As is apparent from Table 3, Invention Examples 1 to 7 are composed of an Al-based alloy structure defined by the present invention in an intermetallic compound phase with a volume fraction of 50 to 90%, and the balance being a metal Al matrix. Has been. And the average size of the intermetallic compound (particle | grains) which comprises an intermetallic compound phase is 10 micrometers or less. Moreover, the average of the maximum length of the pool of metal Al partitioned by the intermetallic compound phase is 40 μm or less.

  As a result, as shown in Table 3, Invention Examples 1 to 7 are excellent in high temperature strength, wear resistance, and high temperature fatigue strength at a high temperature of 400 ° C.

  On the other hand, Comparative Examples 8 and 9 are densified by HIP treatment but not hot forged. For this reason, the average of the maximum length of the pool of metal Al exceeds 40 μm and is coarse. As a result, compared with Invention Examples 2 and 3 using the same alloy, high temperature strength and high temperature fatigue strength are particularly inferior among high temperature strength, wear resistance and high temperature fatigue strength.

  In Comparative Example 10, the processing temperature in the hot forging process is too low, and the processing rate is too low. For this reason, the average of the maximum length of the pool of metal Al delimited by the intermetallic compound phase exceeds 40 μm and is coarse. As a result, compared with Invention Example 2 using the same alloy, high temperature strength and high temperature fatigue strength are particularly inferior among high temperature strength, wear resistance, and high temperature fatigue strength.

  In Comparative Example 11, the processing temperature in the hot forging process is too high. For this reason, the average of the maximum length of the pool of metal Al delimited by the intermetallic compound phase exceeds 40 μm and is coarse. As a result, compared with Invention Example 2 using the same alloy, high temperature strength and high temperature fatigue strength are particularly inferior among high temperature strength, wear resistance, and high temperature fatigue strength.

  In Comparative Example 12, the strain rate in the hot forging process is too small. For this reason, the average of the maximum length of the pool of metal Al delimited by the intermetallic compound phase exceeds 40 μm and is coarse. As a result, compared with Invention Example 2 using the same alloy, high temperature strength and high temperature fatigue strength are particularly inferior among high temperature strength, wear resistance, and high temperature fatigue strength.

  In Comparative Example 13, the spray start temperature during spray forming is too low, and the intermetallic compound is relatively large. Moreover, the average of the maximum length of the pool of metal Al partitioned by the intermetallic compound phase exceeds 40 μm. As a result, compared with Invention Example 2 using the same alloy, high temperature strength and high temperature fatigue strength are particularly inferior among high temperature strength, wear resistance, and high temperature fatigue strength.

  In Comparative Example 14, the G / M ratio during spray forming is too low, the cooling rate is insufficient, and the intermetallic compound phase is relatively large. Moreover, the average of the maximum length of the pool of metal Al partitioned by the intermetallic compound phase exceeds 40 μm. As a result, compared with Invention Example 2 using the same alloy, high temperature strength and high temperature fatigue strength are particularly inferior among high temperature strength, wear resistance, and high temperature fatigue strength.

  In Comparative Example 15, the processing rate during hot forging is too low. For this reason, the average of the maximum length of the pool of metal Al separated by the intermetallic compound phase exceeds 40 μm. As a result, compared with Invention Example 2 using the same alloy, high temperature strength and high temperature fatigue strength are particularly inferior among high temperature strength, wear resistance, and high temperature fatigue strength.

  From the above results, the critical significance of each requirement of the present invention can be 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 drawing substitute photograph which shows the structure | tissue of a comparative example heat resistant Al group alloy.

Claims (2)

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 of the maximum length of the pool of metal Al divided by the intermetallic compound phase is 40 μm or less. A heat-resistant Al-based alloy with excellent high-temperature fatigue properties. 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, Al-Cr based, Al-Fe-based, Al-Ti-based high Yutaka疲 labor characteristics superior heat resistance Al-based alloy of claim 1 consisting of intermetallic phase.

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