JPS6310224B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention is a material with a low coefficient of linear expansion suitable for use in combination with a steel material or a cast iron material with a low coefficient of linear expansion.
Regarding Al alloy materials. (Prior art) In order to maintain good engine operation, an aluminum alloy cylinder liner is used on the piston sliding surface of a cast iron cylinder block in order to reduce the temperature of the cylinder block. Therefore, in an engine having such a cylinder structure,
It has been reported that the temperature of the cylinder block wall actually decreases by 20 to 30°C. (Problems to be Solved by the Invention) However, due to the difference in linear expansion coefficient of the materials of the cylinder liner and the cylinder block body,
A large tensile stress is generated in the cylinder block body during engine operation, and if the stress is significant, a gap may be formed at the boundary between the two, which will have a serious adverse effect on the operating performance of the engine. In this way, when an aluminum alloy material is used in combination with a steel material or a cast iron material as an element of a composite member that is subjected to a thermal load, due to the difference in linear expansion coefficient,
High thermal stress may occur at the interface, leading to voids and slippage, which may significantly impair the function of the composite member. By the way, the coefficient of linear expansion of cast iron is 10 from 0 to 100℃.
~11×10 ^-6 /℃, aluminum is 20~100
It is 23.9×10 ^-6 /℃ at 25 to 100℃, and 19.68×10 ^-6 /℃ at 25 to 100℃ for the 2218 heat-resistant Al alloy for casting specified in JIS-H4140, which is used as a cylinder member. 2.28 times that of cast iron, JIS2218
It has a coefficient of linear expansion of 1.87 times. The present invention was made in view of such problems,
The object of the present invention is to provide an aluminum alloy material that has strength comparable to conventional heat-resistant aluminum alloys for forging and has a low coefficient of linear expansion. (Means for Solving the Problems) The Al alloy material having a low coefficient of linear expansion of the present invention, which was taken to achieve the above object, is characterized by a chemical composition in weight% of Si: An extruded material or forged material of rapidly solidified Al alloy powder consisting of 15 to 25% Cr, 2 to 10% Cr, and the balance substantially Al, which is an Al solid solution in which Si and Cr are supersaturated as a solid solution in the Al base. The main reason for this is that fine-grained eutectic Si is uniformly dispersed. (Example) As a raw material for the Al alloy material of the present invention, a specific Al
The alloy obtained by rapidly solidifying the molten alloy by air atomization or water atomization is used, and its composition is, in weight percent, Si: 15 to 25%, Cr: 2 to 10%, and the remainder substantially Al. Become. First, the reason for the above composition limitation will be explained. Si is actively added to reduce the expansion coefficient of the alloy and to impart wear resistance. If it is less than 15%, this effect will be small, while if it exceeds 25%,
As described below, primary Si remains coarse and brittle even after rapid solidification.
crystallization cannot be suppressed, causing deterioration of toughness and local wear, which is undesirable. Cr is added to significantly solid solution harden the base, strengthen the base and prevent dislocations to lower the coefficient of linear expansion, suppress crystallization of primary Si, and increase heat resistance. If it is less than 2%, this effect will be too small, while if it exceeds 10%, it will be difficult to dissolve, which will cause problems in terms of production. When the molten metal with the above composition is rapidly solidified by air atomization, there is almost no crystallization of primary Si, which causes deterioration of toughness and strength, and no crystallization occurs in the Al matrix.
A fine eutectic structure is formed in an Al-Si-Cr solid solution containing supersaturated Si and Cr and solid solution hardened by Cr.
Si crystallizes, and an Al alloy powder with good mechanical properties and a low coefficient of linear expansion is obtained. In addition, in order to obtain the structure of the above powder alloy, 10 ²
It is necessary to rapidly solidify at a cooling rate of ℃/second or higher. At a speed lower than this, a large amount of primary Si crystallizes and
Formation of Al-Si-Cr intermetallic compounds occurs, leading to deterioration of mechanical properties. However, from an industrial production perspective, there is actually an upper limit, which is probably 10 ⁶ °C/sec. Such rapidly solidified Al alloy powder is subjected to extrusion processing in order to integrate a large amount of powder. That is,
The powder is subjected to strong shearing action during the extrusion process, which breaks up and destroys the inert and stable Al ₂ O ₃ film of several angstroms that is formed on the outer surface of the powder.
The eutectic Si in the base is further divided into fine particles, and these are uniformly dispersed in the high-strength Al solid solution.
This simultaneously promotes high strength and integrates the base by diffusion bonding. The extrusion processing method involves compressing the Al alloy powder isostatically using cold isostatic pressing (CIP), then degassing the compressed material in a sealed can, and then using long-term hot isostatic pressing (HIP). There are two methods: pressure sintering and extrusion of the sintered material, and a method of performing vacuum hot pressing or cold-axial compression on Al alloy powder and extruding the compressed material. During extrusion, Al ₂ O ₃ coating and
In order to sufficiently divide and disperse the eutectic Si in the Al solid solution, the extrusion ratio is preferably 5 to 20, and the extrusion temperature is 250 to 450°C to reduce the extrusion load and diffusion bond the matrix. It is better to The alloy material of the present invention can be subjected to forging in addition to extrusion to achieve the same effect as extrusion, and the desired alloy structure can be obtained. At this time, the forging temperature is preferably 260 to 510°C. The extruded material or forged material obtained as described above is processed into the desired product shape by forging, cutting, etc., as appropriate. The alloy material of the present invention is
It has excellent heat resistance, wear resistance, and strength, and has a small coefficient of thermal expansion, so it can be applied to high-precision parts that require these properties. For example, pistons, piston rings, cylinder liners, piston pins,
Suitable for applications such as cooking stoves, VTR cylinders, and oil pump bushes. Note that for products with a cylindrical shape, such as cylinder liners, the product may be extruded into a cylindrical shape in the extrusion step. Next, specific examples will be described. (1) By weight, Si17.8%, Cr5.2% balance substantially
An Al alloy of Al was melted and rapidly solidified powder was produced by air atomization at a cooling rate of 10 ³ to ^{10 4} °C/sec. (2) The obtained powder was classified, and those with a diameter of 44 μm or less were packed in a rubber container and pressurized at 3000 Kgf/cm ² for 1 minute to obtain a bar with a diameter of 140 mm. Add this to a thickness of 3 mm.
It was inserted into a can body made of JIS5052 material, thoroughly degassed under a pressure of 10 ^-2 to ^{10 -3} Torr, sealed by electron beam welding, and subjected to HIP treatment. The HIP treatment was performed at 350° C. and 1500 Kgf/cm ² for 1 hour. After sufficiently heating the obtained sintered material at 350℃ for about 30 minutes, it was heated to φ43mm at an extrusion ratio of 10.6 and an extrusion speed of 25mm/min.
It was pushed out. (3) A test piece of φ10×25 was taken along the extrusion direction from the extruded material and subjected to the following investigation.
For comparison, a similar investigation was also conducted on JIS2218 materials. JIS2218 material is Cr4.1%, Mg1.4
%, Ni2.1% balance has a composition of substantially Al,
T61 treatment (510℃ solution treatment, hot water quenching,
This was followed by aging treatment at 170°C for 10 hours. (4) Table 1 shows the results of examining mechanical properties.

[Table] From Table 1, compared to the 2218 material, the material of the present invention has
Although the elongation was slightly inferior, other properties were confirmed to be good, considering strength etc.
It was found that it can be a sufficient substitute for 2218 material. (5) Table 2 shows the results of examining the coefficient of linear expansion.

[Table] From Table 2, this is a particular problem in internal heat engines, etc.
It was confirmed that the coefficient of linear expansion was approximately 20% lower than that of 2218 material in the temperature range below 300°C. Furthermore, the coefficient of linear expansion decreases by more than 12% even at temperatures below 500°C. (6) The observation results of the metal structure are shown in Figs. 1 and 3. Figure 1 is a photograph of the metallographic structure of the material of the present invention (3000
Figure 3 shows the same photo of 2218 material (3000 times).
times). For reference, the following information regarding the present invention is provided.
Metal structure photograph of rapidly solidified Al alloy powder (3000x)
is shown in Figure 2. From FIG. 1, it is observed that in the material of the present invention, a large amount of fine grained eutectic Si is finely and uniformly dispersed in the matrix. Furthermore, no Cr precipitates were found, suggesting that Cr was completely dissolved in the matrix. Figure 2 shows the structure of the rapidly solidified powder before extrusion processing, and it is observed that network-like eutectic Si is crystallized over the entire surface, but primary crystal Si
No crystallization was observed. Also, on the surface of the powder
Although a film of Al ₂ O ₃ is formed, it is not visible because it is several Å thick. Similarly, in FIG. 1, no fragments of the Al ₂ O ₃ film were visible. On the other hand, from FIG. 3, it is observed that in the 2218 material, a white Nu-Cu intermetallic compound with an average size of about 3 μm and a black Mg-Si compound with an average size of about 5 μm are precipitated in the matrix. As is clear from FIG. 1, the material of the present invention has Si particles finely and uniformly dispersed in the matrix, and the reason why the material has excellent mechanical properties is also supported by the microstructure. (Effect of the invention) As explained above, the alloy material of the present invention contains 15% Si.
Since it contains ~25%, together with the addition of Cr, the coefficient of linear expansion is lower than that of conventional Al alloys for forging.
Decreases by more than 20% at temperatures below 300℃. In addition, a large amount of eutectic Si, which does not originally deteriorate mechanical properties, was added to Al.
Since it is uniformly dispersed in fine particles in a solid solution, it can impart good wear resistance without significantly deteriorating mechanical properties. In addition, since it contains 2 to 10% Cr, the matrix is solid solution hardened with supersaturated Cr, which contributes to improving the strength and reducing the coefficient of linear expansion by preventing dislocations. As described above, the alloy material of the present invention has excellent wear resistance without impairing mechanical properties, and furthermore, the coefficient of linear expansion can be kept low.
It has great utility as a material for parts that require all of these properties.

[Brief explanation of the drawing]

Figure 1 is a photograph of the metal structure of the Al alloy material of the present invention.
FIG. 2 is a photograph of the metallographic structure of the rapidly solidified Al alloy powder, which is the raw material for the alloy material of the present invention, and FIG. 3 is a photograph of the metallographic structure of the JIS2218 material.

Claims (1)

[Scope of Claims] 1. An extruded or forged material of rapidly solidified Al alloy powder having a chemical composition of 15 to 25% Si, 2 to 10% Cr, and the remainder substantially Al in weight percent, An Al alloy material with a low coefficient of linear expansion, characterized in that fine-grained eutectic Si is uniformly dispersed in an Al solid solution in which Si and Cr are supersaturated in an Al base.