JPH0558049B2 - - Google Patents

Description

[Detailed description of the invention]

A. Purpose of the invention (1) Industrial field of application The present invention is a high-strength aluminum alloy for mechanical structural members having excellent creep properties, in particular, a mixed powder consisting of rapidly solidified aluminum alloy powder and hard particles. This invention relates to a high-strength aluminum alloy manufactured by inter-plastic working. (2) Conventional technology Conventionally, large amounts of Si, Fe,
High-strength aluminum alloys containing elements such as Mn have been proposed. (3) Problems to be solved by the invention However, conventional high-strength aluminum alloys (hereinafter referred to as conventional alloys) have the following problems. (a) Conventional alloys have a fine metal structure, so they have excellent strength, but they have poor creep properties, so for example, they are subject to constant compressive stress at high temperatures.
Creep shrinkage increases in the bolted joints of the caps of internal combustion engine cooking rods over long periods of use, resulting in a decrease in the bolting force and, in extreme cases, the possibility of the bolted joints being destroyed. (b) Conventional alloys aim to reduce the coefficient of thermal expansion and improve Young's modulus by adding large amounts of Si, Fe, Mn, etc., but when considering productivity and toughness as an industrial material, the coefficient of thermal expansion is approximately 18 × 10 ^-6 /
℃, and Young's modulus is approximately 10,000 Kg/ ^mm2 . When mechanical structural members are constructed from aluminum alloy and used at high temperatures, it is unavoidable to use them in combination with mechanical structural members made of steel. Therefore, when determining clearances, press-fit allowances, etc., aluminum If the coefficient of thermal expansion of the alloy were close to that of steel, the degree of freedom in design would increase, but conventional alloys cannot meet these requirements. For example, when the connecting rod is constructed from a conventional alloy and the crankshaft is constructed from steel, the clearance between the connecting rod crank pin hole and the crankshaft crank pin increases significantly as the temperature increases. In addition, Young's modulus is an important factor that influences the displacement and strain in the elastic range of a member when subjected to a load.In order to miniaturize a member, it is necessary to make the Young's modulus sufficiently large. Alloys cannot meet these requirements. (c) Conventional alloys have primary Si and eutectic Si precipitated in them.
Because Si, intermetallic compounds, etc. are extremely fine,
The amount of sliding wear is relatively large, resulting in poor durability under high surface pressure and high speed sliding, which limits the field of use to a narrow range. An object of the present invention is to provide the above-mentioned high-strength aluminum alloy that can solve the above-mentioned problems. B. Structure of the Invention (1) Means for Solving the Problems The present invention is manufactured by hot plastic working using a mixed powder consisting of rapidly solidified aluminum alloy powder and hard particles, and has excellent creep properties. The rapidly solidified aluminum alloy powder is a high-strength aluminum alloy for mechanical structural members, and has the following properties: 12.0% by weight≦Si≦28.0% by weight, 0.8% by weight≦Cu≦5.0% by weight, 0.3% by weight≦Mg≦3.5% by weight, Al consisting of 2.0wt%≦Fe≦10.0wt%, 0.5wt%≦Mn≦2.9wt%, and the balance Al containing unavoidable impurities.
It is an aggregate of alloy particles and contains 45% by weight or more and 70% by weight or less of the Al alloy particles with a particle size of 325 mesh or less, and the hard particles include Al ₂ O ₃ particles,
At least one kind selected from SiC particles, Si ₃ N ₄ particles, and metal Si particles, and the content of the hard particles is set to 1.5% by weight or more and 15.0% by weight or less with respect to the rapidly solidified aluminum alloy powder. It is characterized by the presence of (2) Effect When the composition and hard particle content of the Al alloy particles and therefore the rapidly solidified aluminum alloy powder are specified as above, it has excellent high temperature strength, wear resistance and Young's modulus, and also has a low coefficient of thermal expansion. It is possible to provide a high-strength aluminum alloy with improved creep properties and stress corrosion cracking resistance at high temperatures. In addition, rapidly solidified aluminum alloys are generally difficult to process, but by characterizing the content of each chemical component as described above, hot plastic processing such as hot extrusion workability and hot forging workability can be achieved. It is possible to improve the productivity of aluminum alloys by improving the properties. The reason for adding each chemical component and hard particles, the reason for limiting the content, etc. are as follows. (a) About Si Si has the effect of improving the wear resistance, Young's modulus, and thermal conductivity of the matrix formed from rapidly solidified aluminum alloy powder (hereinafter simply referred to as the matrix), and lowering the coefficient of thermal expansion. . However, if it is less than 12.0% by weight, the above effects may not be obtained, while if it exceeds 28.0% by weight, formability in hot extrusion and hot forging will deteriorate and the aluminum alloy will be prone to cracking. (b) About Cu Cu has the effect of strengthening the matrix during heat treatment. However, if it is less than 0.8% by weight, the above effect cannot be obtained;
If it exceeds the weight%, hot forging workability decreases,
Moreover, the stress corrosion cracking resistance of the matrix deteriorates. (c) Regarding Mg Mg, like Cu, has the effect of strengthening the matrix during heat treatment. However, if it is less than 0.3% by weight, the above effect cannot be obtained,
On the other hand, if it exceeds 3.5% by weight, hot forging workability decreases and the stress corrosion resistance of the matrix deteriorates. (d) Regarding Fe Fe has the effect of improving the high temperature strength and Young's modulus of the matrix. However, 2.0
If it is less than 10.0% by weight, no improvement in the high temperature strength of the matrix can be expected, while if it exceeds 10.0% by weight, high-speed hot forging becomes virtually impossible. (e) About Mn Mn, especially in the range of Fe≧4% by weight,
It has the effect of improving hot forging workability and also improving the high temperature strength and stress corrosion cracking resistance of the matrix. However, if it is less than 0.5% by weight, the above effect cannot be obtained;
If it exceeds the weight percentage, adverse effects such as deterioration of hot forging workability will occur. (f) Constituting rapidly solidified aluminum alloy powder
The use of limiting the grain size and content of the Al alloy particles as described above is to improve the fatigue strength and creep properties of the matrix.
In this case, if the content of Al alloy particles with a grain size of 325 mesh or less is less than 45% by weight, the fatigue strength of the matrix will decrease, while if it exceeds 70% by weight, the creep characteristics of the matrix will deteriorate. (g) About hard particles The four types of hard particles characterized as described above are:
By dispersing it in a matrix, it has the effect of fixing dislocations in the crystal, improving the creep characteristics of aluminum alloys at high temperatures, lowering the coefficient of thermal expansion, and further improving Young's modulus and wear resistance. However, the content of hard particles in rapidly solidified aluminum alloy powder is 1.5
Below 15.0% by weight, the wear resistance of the aluminum alloy is not improved, and the degree of Young's modulus improvement and thermal expansion coefficient reduction is also low;
If it exceeds the weight%, hot forging workability decreases,
Furthermore, the fatigue strength and machinability of the aluminum alloy are significantly reduced, making it unapplicable as an industrial material. (3) Example The content of each chemical component in the rapidly solidified aluminum alloy powder is limited to the following in order to particularly improve stress corrosion cracking resistance and hot forging workability. 14.0% by weight≦Si≦18.0% by weight 2.0% by weight≦Cu≦5.0% by weight 0.3% by weight≦Mg≦1.5% by weight 3.0% by weight≦Fe≦6.0% by weight 0.5% by weight≦Mn≦2.5% by weight When constructing mechanical structural members for internal combustion engines that are subject to thermal effects from high-strength aluminum alloys, Young's modulus, coefficient of thermal expansion, creep properties, and machinability are issues for these members, so is limited to 9.0% by weight or more and 13.0% by weight or less. The reason for limiting the content in this way is that below 9.0% by weight,
This is because the effect of improving creep properties is small, and on the other hand, if it exceeds 13.0% by weight, machinability tends to decrease. Furthermore, when using the high-strength aluminum alloy according to the present invention to constitute a mechanical structural member in which sliding wear with steel is a problem, the content of the hard particles is 2.0.
It is limited to not less than 4.0% by weight and not more than 4.0% by weight. The reason why the content is limited in this way is that if it is less than 2.0% by weight, the amount of wear on the parts will increase and the practicality will decrease.
On the other hand, if it exceeds 4.0% by weight, the steel counterpart material will wear out and the practicality will similarly decrease. Further, the particle size of the hard particles is limited to 5 μm or more and 74 μm or less in order to improve wear resistance without impairing fatigue strength and to improve creep characteristics.
The reason for this limitation is that if the thickness is less than 5 μm, handling becomes difficult, whereas if it exceeds 74 μm, the fatigue strength will be significantly reduced. The high-strength aluminum alloy according to the present invention is applied to the cap of a stud type cooking rod, and in this case, the rod side is made of the aluminum alloy containing no hard particles, that is, 12.0% by weight≦Si≦
28.0, 0.8wt%≦Cu≦5.0wt%, 0.3wt%≦
Mg≦3.5wt%, 2.0wt%≦Fe≦10.0wt%,
It is formed using rapidly solidified aluminum alloy powder, which is an aggregate of Al alloy particles consisting of 0.5% by weight≦Mn≦2.9% by weight and the remainder being Al containing unavoidable impurities. The reason for this is that fatigue strength is prioritized on the rod side, so it is advantageous not to include hard particles.
On the other hand, the cap has less fatigue strength requirements than the rod side, but since the surface pressure of the bolted part is high and it is necessary to reduce creep shrinkage, it is advantageous for the cap to contain hard particles. The high-strength aluminum alloy according to the present invention can also be applied to shaft members other than the above-mentioned conrod caps, such as crank journal bearing caps. When producing the high-strength aluminum alloy according to the present invention, rapidly solidified aluminum alloy powder and hard particles are mixed to obtain a mixed powder, and then the mixed powder is subjected to cold isostatic pressing (CIP method), etc. A green compact is obtained by applying this process, and then the green compact is subjected to hot extrusion processing. Next, a method for producing a high-strength aluminum alloy according to the present invention (hereinafter referred to as the alloy of the present invention) and various test results regarding the alloy will be explained. As rapidly solidified aluminum alloy powder, Si
17.2% by weight, Cu 2.5% by weight, Mg 0.6% by weight, Fe
By applying an atomization method to an aggregate of Al alloy particles consisting of 4.3% by weight, 1.8% by weight of Mn, and the remainder Al containing unavoidable impurities, the cooling rate was 10 ³ - ^{10 4} °C/sec.
Manufactured under the following conditions. 50% by weight of Al alloy particles with a particle size of 325 mesh or less
Various hard particles are added to the rapidly solidified aluminum alloy powder in the amounts shown in the table, and the alloys of the present invention to XII are manufactured through the steps described below. That is, after rapidly solidifying aluminum alloy powder and each hard particle are mixed in a mold blender, a cold isostatic pressing method (CIP method) or a mold compression molding method is applied to each mixed powder to obtain a density ratio of 75. % green compact is obtained. In the cold isostatic press molding method, the mixed powder is placed in a rubber tube and molded under hydrostatic pressure of approximately 1.5 to 3.0 ton/cm ² .In the mold compression molding method, the mixed powder is placed in the mold. in the atmosphere at room temperature.
Molding is performed under pressure of approximately 1.5 to 3.0 ton/ ^cm2 . Each green compact was placed in a soaking furnace with an internal temperature of 400°C and held for 4 hours, and then hot extruded to form a round bar with a diameter of 18 mm and a length of 450 mm. Invention alloy ~XII is obtained. The extrusion method in this case may be either direct extrusion (forward extrusion) or indirect extrusion (backward extrusion), but the drop ratio needs to be 5 or more. If the extrusion ratio is less than 5, the variation in strength becomes large, which is not preferable.

[Table] For comparison, the comparative example alloys shown in the table were manufactured by the same method as above.

[Table] The comparative example alloy has the same composition as the matrix in the present invention alloys to XII, and the comparative example alloy corresponds to JIS AC8C, which is a cast material. The table shows the invention alloys to XII and comparative example alloys,
Thermal expansion coefficient (×10 ⁻⁶ , 20-200°C) and Young's modulus (200°C, Kg/mm ² ) are shown.

[Table] As is clear from the table, the present invention alloys to XII have a lower coefficient of thermal expansion and an improved Young _{'s modulus} than the comparative example alloys. This is due to the particles being dispersed. The table shows the results of stress corrosion cracking tests (JIS H8711) performed on the present invention alloys to XII and comparative example alloys. The stress corrosion cracking test was performed using a 80mm long, 10mm wide, 2mm thick
mm test piece, and the applied stress to it is σ _0.2 × 0.9 (however, σ _0.2 is 0.2% yield strength of each alloy)
28 in a NaCl aqueous solution with a temperature of 30℃ and a concentration of 3.5%.
The test piece is immersed for one day, and the stress corrosion cracking resistance is judged by the presence or absence of cracks in the test piece.

[Table] As is clear from the table, the present invention alloys to XII have better stress corrosion cracking resistance than the comparative example alloys, and this is mainly due to the inclusion of Mn. The table shows the results of a sliding wear test performed on the alloy of the present invention and the comparative example alloy. In the sliding wear test, a test piece measuring 10 mm long, 10 mm wide, and 5 mm thick was rotated at a speed of 2.5 m/sec.
A 135mm JIS S50C disc was pressed with a pressure of 200Kg/cm ² and lubricant was dripped at 5c.c./min over a sliding distance of 18Km, and the amount of wear was compared to that of a test piece. It is measured by determining the weight difference (g) before and after the test.

[Table] As is clear from the table, the alloy of the present invention,
has superior wear resistance compared to the comparative example alloy, which is due to the fact that the matrix contains Al ₂ O ₃ , SiC,
This is due to the fact that hard particles such as Si ₃ N ₄ are dispersed. The table shows the results of creep tests performed on the alloys of the present invention and comparative alloys. Creep test is 10mm in diameter and 40mm in parallel part length.
The test piece was subjected to a compressive force of 12 kg/ ^mm2 at 170℃ for 100 hours.
The amount of creep shrinkage is measured by determining the ratio (%) of the length of the test piece before and after the test.

[Table] As is clear from the table, the alloy of the present invention,
Compared to Comparative Example Alloy 1, the amount of creep shrinkage is reduced. This is because the creep characteristics of the matrix were improved by changing the grain size and content of the Al alloy particles as described above, and the inclusion of hard particles such as Al ₂ O ₃ , SiC, and Si ₃ N ₄ in the matrix This is due to the fact that dislocations in the matrix crystal are fixed due to the dispersion of the matrix. The creep shrinkage of the comparative alloy, which is a cast material, is 0.04%, and that of the alloy of the present invention is approximately comparable to that of the cast material. The table shows the relationship between temperature and the dimensional change of the crank pin hole (diameter 45 mm) in the stove.
The rod A of condensing rod A was made of the comparative mixture on the rod side, and the cap was made of the alloy of the present invention. Conrod B has its rod side and cap made of comparative alloy. In both cooking stoves A and B, the caps are fastened to the rod sides with bolts.

[Table] As is clear from the table, conrod A with a cap made of the alloy of the present invention has a smaller amount of change in diameter of the crank pin hole due to temperature rise than conrod B made of comparative example alloy. This makes it possible to suppress changes in the clearance between the crank pin and the crank pin hole during engine operation. This is 10% by weight in the matrix.
This is due to the fact that the thermal expansion rate of the cap is reduced by dispersing the Al ₂ O ₃ particles. C. Effects of the Invention According to the present invention, the rapidly solidified aluminum alloy powder and hard particles having the characteristics described above are used, and the application of hot plastic working is an essential requirement.
It not only has excellent creep properties at high temperatures, but also has excellent high-temperature strength, wear resistance, and Young's modulus, as well as a reduced coefficient of thermal expansion and improved stress corrosion cracking resistance. We can provide good high strength aluminum alloy.

Claims (1)

[Scope of Claims] 1. A high-strength aluminum alloy for mechanical structural members having excellent creep properties, manufactured by hot plastic working using a mixed powder consisting of rapidly solidified aluminum alloy powder and hard particles, The rapidly solidified aluminum alloy powder has the following properties: 12.0% by weight≦Si≦28.0% by weight, 0.8% by weight≦Cu≦5.0% by weight, 0.3% by weight≦Mg≦3.5% by weight, 2.0% by weight≦Fe≦10.0% by weight, 0.5% by weight %≦Mn≦2.9% by weight and Al consisting of the balance Al containing unavoidable impurities
It is an aggregate of alloy particles and contains 45% by weight or more and 70% by weight or less of the Al alloy particles with a particle size of 325 mesh or less, and the hard particles include Al ₂ O ₃ particles,
At least one kind selected from SiC particles, Si ₃ N ₄ particles, and metal Si particles, and the content of the hard particles is set to 1.5% by weight or more and 15.0% by weight or less with respect to the rapidly solidified aluminum alloy powder. A high-strength aluminum alloy for mechanical structural parts that has excellent creep properties. 2. The high-strength aluminum alloy for mechanical structural members having excellent creep properties according to claim 1, wherein the mechanical structural member is a bearing member.