JPH0565568B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Technical field The present invention provides aluminum manufactured by powder metallurgy that is lightweight and has high strength, has higher heat resistance and wear resistance than conventional heat-resistant aluminum alloys and wear-resistant aluminum alloys, and has a low coefficient of thermal expansion. Concerning alloys and their manufacturing methods. (b) Background of the technology The manufacturing of Al alloy mechanical parts by powder metallurgy has already been industrialized, and in addition to the usual method consisting of mold forming, sintering, and sizing,
Also included is a type of sinter casting process that involves further sizing after sintering. Al by this conventional powder metallurgy method
However, alloy machine parts have not been able to surpass parts made by cutting, forging, or casting from melted materials in terms of mechanical properties, such as tensile strength, wear resistance, and heat resistance. On the other hand, Al alloys can be supersaturated with alloying elements by rapid cooling, and as a result, combined with the effects of rapid cooling to refine crystal grains and create a uniform structure without segregation, they can be compared to conventional melted materials. In recent years, it has become clear that incomparable high performance can be obtained. However, this rapidly solidified alloy can only be obtained by methods such as extrusion, which poses a problem in producing parts. This is because Al alloys generally have stable oxides on the powder surface.
Since it forms Al ₂ O ₃ , it is extremely difficult to perform solid phase sintering, making it impossible to manufacture parts. or
A method has been devised in which alloying elements that form a eutectic with Al, such as Cu, Mg, and Si, are added to generate a liquid phase and the Al ₂ O ₃ film is broken and sintered. In the case of powder, it cannot be used because it causes coarsening and segregation with precipitates. As described above, the production of high-performance mechanical parts using rapidly solidified alloy powder is often practically difficult due to many restrictive conditions. In particular, in the hot extrusion method, solidification of the rapidly solidified alloy powder is certainly achieved, and strength at high temperatures is guaranteed, as described in, for example, JP-A-60-125345.
This case is effective, for example, for long products with a constant cross-sectional shape as shown in FIG. However, when making products with irregular shapes or three-dimensionally complex shapes as shown in Figure 4, additional forging and reshaping or cutting operations are essential, resulting in a large amount of material loss and additional processing effort. There was a problem. Further, as mentioned above, although strength can be guaranteed up to a high temperature range if the material is selected, there is also a problem in that there is a difference in strength between the extrusion direction of the extruded body and the direction perpendicular to the extrusion direction. (C) Disclosure of the Invention The present invention aims to solve the problems caused by the conventional methods described above, and to facilitate direct shaping of products with three-dimensionally complex shapes. Aluminum alloy parts that exhibit excellent properties such as wear resistance and coefficient of thermal expansion are produced using powder hot forging method.
It provides an economical manufacturing method. The aluminum alloy powder used in the present invention is basically
Although it is an Al-Si-Fe alloy, Cu and Mg elements are added to the Al-Si-Fe alloy for the purpose of further increasing the strength of this alloy. The addition of Cu is intended to improve strength, but addition of 12% by weight or more of Cu does not significantly improve strength and increases density, so it is unnecessary. Mg also contributes to the improvement of strength, but since adding a large amount leads to deterioration of workability, it is limited to 3.0% or less. Si element is added to improve wear resistance, but the amount of addition is
If it is less than 10%, the wear resistance is not sufficient. If it exceeds 20%, the wear resistance will be improved, but the strength will be reduced. Fe element is added to improve heat resistance. The appropriate amount of addition is from 2 to 10% by weight; if it is less than this range, the improvement is poor, and if it is more than this, the problem is that the processability is poor. Addition of such Fe and SSi in an appropriate ratio significantly improves heat resistance and wear resistance, as well as improves strength, thermal expansion, etc. at room temperature. The Al alloys shown above cannot be manufactured by conventional forging methods because the large amounts of Si and Fe added cause primary crystal precipitates to become coarse during solidification, resulting in a decrease in strength. Therefore, the alloy must be manufactured by terminal metallurgy. At this time, in order to prevent the primary crystal particles of Si and Fe from becoming coarse, the alloy powder must be 40 mesh or less in the case of atomized powder, or the particle size of the primary crystal precipitates must be
Use powder with a diameter of 10 μm or less. These powders are made into products through the processes of molding, heating, and forging, but first a preform that can withstand forging and an accurate preform shape suitable for forging are required. In order to obtain a preform strong enough to prevent cracking during forging, it is essential to sufficiently increase the density and sinter the preform. In order to increase the density, good results are generally obtained by increasing the molding pressure, but isostatic pressing is more effective than mold molding for molding highly hard particles. This high-density compaction breaks the oxide film of the powder particles, significantly increases the contact area of the particles, and progresses sintering by solid phase diffusion during heating, resulting in a good sintered body for forging. The remaining pores are crushed during the forging process, and sintering proceeds by pressure bonding on a clean surface without an oxide film. In addition, the forging process must be hot rather than cold forging in order to achieve sufficient sintering, and to reduce the deformation resistance during forging and deform into a complex shape. If the density during molding is less than 95%, the pores will connect with the inside and create air permeability, which will cause oxidation to progress more easily.Therefore, the true density ratio must be at least 95%. Regarding the heating temperature, temperatures below 250°C are not suitable because the deformation resistance is large and sintering due to self-diffusion of Al does not proceed very well. On the other hand, temperatures above 550°C are not suitable because the fine structure and non-equilibrium phase of the rapidly solidified powder change and the characteristics of a rapidly solidified alloy are lost. Examples Example 1 4% Cu, 1% Mg, 12% Si, 5% with a particle size of 100 mesh or less obtained by gas atomization
An alloy powder having a composition of Fe and balance Al was molded by cold isostatic pressing at a pressure of 6 t/cm ² . The density of the molded product at this time was 2.73 g/cm ² and the true density ratio was 95.5%. In addition, similarly obtained by gas atomization,
12% Si with a particle size of 100 mesh or less, the remainder being 5% Fe
Alloy powder with Al composition is produced by cold isostatic pressing.
It was molded at a pressure of 6t/ ^cm2 . The density of this compact is
It was 2.67 g/cm ³ and the true density ratio was 96.0%.
The obtained high-density compact was heated to 470°C in the air and die-forged. Through forging, the height was reduced to about 1/2 and the diameter was aligned with the mold. The density of the forged body was 99.8% or more, and no cracks occurred.
After applying T6 heat treatment to this forged body, a test piece cut out was examined. Figure 1 shows the results of the strength measurement of the product of the present invention.
Al-Cu-Mg-Si-Fe material 1 and Al-Si-Fe material 2 have high temperature strength, and the tensile strength is 1 up to around 200℃.
is higher, but 2 is higher at high temperatures. Both are AC8A, which has traditionally been used as a piston material.
-It shows higher strength than T6 material 3. Next, Table 1 shows the wear resistance determined by the Okoshi type abrasion test. The product of the present invention has better wear resistance than the comparative AC8A-T6 material. Table 2 shows the measurement results of the coefficient of thermal expansion. The product of the present invention has a significantly smaller coefficient of thermal expansion than the comparative AC8A-T6 material, making it reasonable as a heat-resistant material.

【table】

[Table] As shown in the examples above, a preform with a high density ratio that can be forged is made in advance, and then hot forging is performed to create a lightweight and highly heat-resistant preform with a three-dimensionally complex shape. , it becomes possible to economically supply machine parts made of wear-resistant aluminum alloys. For this reason, high-performance automobile engine parts (pistons, conrods, liners, etc.) and home appliance parts,
It is expected to have wide application fields such as aircraft parts. Example 2 Two types of powder shown in Table 3 were heated to 200°C,
Mold molding was performed at a pressure of 4 ton/cm ² . The density of the compact at this time was the value shown in Table 3. This compact was heated to 470°C in an N ₂ atmosphere and die forged. The forging method is the same as in the previous example. The density of the obtained forged bodies is 99.8% for both No. 4 and No. 5.
This was the result, and no cracking occurred. After subjecting this forged body to T6 heat treatment, it was processed into a test piece and its tensile strength was evaluated. The results are shown in Figure 1, and the strength at room temperature for both No. 4 and No. 5 is
Although it was 2 to 3 kg/mm ² lower than No. 1, it showed almost the same strength as No. 1 at temperatures above 200°C.

[Table] Example 3 Powder used in Example 1 (4% Cu with a particle size of 100 mesh or less obtained by gas atomization, 1
%Mg, 12%Si, 5%Fe, balance Al) was solidified by both forging and extrusion, and the properties were compared. Forging was carried out under the same conditions as in Example 1. Extrusion was performed by isostatically pressing the powder, heating it to 450°C, and extruding at a ratio of 10:1. The obtained forged materials and extruded materials were subjected to T6 treatment (480℃
After solution heating for 2 hours, water quenching and aging treatment at 180°C for 8 hours) were performed. Samples were prepared in a direction parallel to the forging pressurization direction and the extrusion direction (L direction) and in a direction perpendicular to the forging direction (T direction), and a tensile test was conducted at each temperature. The results are shown in Figure 2. A forged material has a smaller difference in direction between the L direction and the T direction, that is, anisotropy, compared to an extruded material. In addition, the cast material has higher tensile strength in the T direction than in the L direction,
It is the opposite of extruded material. From the above, forged materials made from powder have the advantage of having smaller anisotropy and more uniform properties than extruded materials. Therefore, in the case of three-dimensional complex shapes, manufactured products are more preferable.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing changes in tensile strength at high temperatures of the product of the present invention and a conventional comparative product. FIG. 2 is a diagram showing changes in tensile strength at high temperatures of a hot forged material of the present invention and a comparative material produced by hot extrusion. Figure 3 shows an example of a hot extrusion product. Figure 4 shows an example of a hot forged product. (Explanation of numbers in the figure), 1...Al-Cu-Mg-Si
-Fe material (product of the present invention), 2...Al-Si-Fe material (product of the present invention), 3...AC8A-T6 material (comparative product), 4...
Al−12Si−5Fe−4Cu−1Mg material, 5……Al−20Si
−1Fe−3Cu−0.5Mg material.

Claims (1)

[Claims] 1 Substantial aluminum with 10 as an alloying element
Alloy powder containing ~20 wt% Si and 2-12 wt% Fe, or 10-20 wt% as alloying elements
Si, 2-12 wt% Fe, 1-12 wt% Cu, 0.1
An atomized aluminum alloy powder containing ~3% by weight of Mg with a particle size of 40 mesh or less, or an alloy powder with a primary crystal precipitate particle size of 10 μm or less, is formed by cold isostatic pressing or After producing a preform by compression molding to a true density ratio of 95% or more by molding, the preform is
A method for producing a highly heat-resistant and wear-resistant aluminum alloy, which is characterized by heating to 250°C to 550°C and casting in a mold.