JPH05311204A - Production of alloy member - Google Patents

Abstract

PURPOSE:To prevent cracking at the time of normal forging and improve a working rate so as to enhance the production efficiency in the process for production of an aluminum alloy member through preforging and normal forging by a powder forging method. CONSTITUTION:A green compact is molded from aluminum alloy powder. After this green compact is heated, the green compact is subjected to closed forging to form a preform. Many bullets are struck against the surface of at least a part of the preform to impart work strains to the surface layer part; thereafter, the preform is reheated in a normal forging stage and is subjected to closed forging at hot. The similar effect is obtainable with an iron alloy as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an alloy member such as an aluminum alloy or an iron-based alloy using a powder forging method. By modifying the surface of an intermediate compact, cracks are generated during forging. The present invention relates to an improvement for preventing the above and improving the characteristics due to processing strain.

[0002]

2. Description of the Related Art For example, a molded body made of an aluminum alloy containing Fe, V, Zr, Cu, Mg, Si and the like has excellent strength, rigidity, toughness, heat resistance and corrosion resistance. Since the surface of the aluminum alloy powder to be covered is covered with a strong oxide film, it is impossible to manufacture it by ordinary sintering.

The applicant of the present invention has proposed the following manufacturing method in Japanese Unexamined Patent Publication No. 63-60265 as a manufacturing method of this type of aluminum alloy member. In this method, first, a green compact is formed from the aluminum alloy powder obtained by the rapid solidification method. Then, this green compact is heated and held in the air or an inert gas at 300 to 520 ° C for 15 minutes or more, and then a preliminary closed die forging is performed at a temperature in the same range to obtain a preliminary density ratio of 95 vol% or more. A molded body is molded. Furthermore, this preform is reheated to 350 to 500 ° C.,
As the main forging, hot die forging is performed once or plural times to obtain a compact.

[0004]

By the way, in the above manufacturing method, the surface layer of the compact is cooled by the contact with the forging die during the preliminary forging, and the compact which is in contact with the inner surface of the forging die is formed. It is unavoidable that dead metal is generated in the surface layer. In the cooling section and inside the dead metal, the powder particles do not deform or crush during forging, and the oxide film formed on the particle surface is not sufficiently broken.

For this reason, the degree of bonding between the particles cannot be sufficiently increased, resulting in insufficient mechanical properties and deformability of the material in the surface layer of the preform. Further, even if the mold temperature is raised to eliminate the cooling part, the generation of the insufficient deformation region cannot be avoided. Furthermore, the insufficient deformation region may remain after the main forging process.

Therefore, the above manufacturing method has a problem that a portion having insufficient mechanical properties may remain in the surface layer portion of the final product and that the following problems occur in the main forging step.

That is, in the main forging step, a large tensile strain may occur in the surface layer portion of the preform, and cracks are likely to occur in the surface layer portion where the degree of bonding between powder particles is insufficient due to the tensile strain. .. For this reason, when the shape of the final product is complicated and the workability required in the main forging step is large, the main forging step must be divided into a plurality of times to reduce the plastic deformation amount in each hot forging, There is a problem in that the number of steps increases and productivity decreases.

The present invention has been made in view of the above circumstances, and by increasing the deformability of the preform, particularly in the surface layer portion, cracks are generated in the preform even when the amount of plastic deformation in the main forging step is large. It is an object of the present invention to provide a manufacturing method capable of preventing the above, reducing the number of hot forgings in the main forging step, and leaving no deformation shortage region on the surface layer portion of the final product, and sufficiently improving the characteristics.

[0009]

The method for producing an alloy member according to the present invention will be specifically described below by taking the case of using an aluminum alloy as an example.

In this case, the aluminum alloy powder used as a raw material may be a powder obtained by any powder manufacturing method such as a gas atomizing method, a centrifugal method, a rotating cup method, a roll method, or the like. You may grind with a grinding means. As the element added to the powder, any element conventionally used in this kind of alloy can be used. For example, Si, Cu, Mg, Fe, Ni, Co,
Mn, Cr, Li, Ti, Zr, Ce, Mo, V, Zn etc. can be used,
Of course, plural kinds may be mixed.

Next, the above aluminum alloy powder is molded to obtain a green compact. The molding method may be any of the conventionally used methods, but generally 2 to
Applying a pressure of about 5 ton / cm ² , density ratio 70-80 vol%
A method of densifying to a certain degree is adopted. Through this forming step, a green compact having a shape that can be handled is formed.

Next, the molded green compact is subjected to a heating and holding treatment at 300 to 520 ° C. in the atmosphere or argon or nitrogen gas. This heat-holding treatment is for removing moisture and other volatile substances adsorbed on the powder, and if the temperature of the heat-holding treatment is less than 300 ° C or the heating rate is not appropriate, Water or the like cannot be sufficiently removed, or as a result of oxidation progressing, voids may occur in the final product, or the degree of interparticle bonding may decrease. On the other hand, if the heating temperature exceeds 520 ° C., the fine structure in the powder particles constituting the green compact is lost, the physical properties of the green compact may be deteriorated, and molding defects may occur.

The preliminary forging is a treatment for densifying the green compact so as to withstand the subsequent shot blasting and hot die forging as the main forging, and more specifically, 100 to 20.
For example, a method in which a powder compact heated to 300 to 520 ° C. is put into a forging die preheated to about 0 ° C. and a closed die forging is performed at a pressure of about 5 to 10 ton / cm ² is used. If the processing temperature of the closed die forging is less than 300 ° C., the deformation resistance of the green compact is large and it is difficult to make it compact. Further, when the temperature of the closed die forging exceeds 520 ° C., the fine structure in the particles is lost,
This leads to deterioration of the physical properties of the molded product.

Next, the obtained preforms are heated to 350-52.
Shot blasting is performed in a state of being heated to 0 ° C. to plastically deform the surface layer portion of the preformed body and impart working strain. Since the strength and deformability of the molded body improve with an increase in the amount of strain applied during hot forming, the amount of strain applied is small and the deformability is small, especially at the initial stage of deformation or the dead metal part. , The following deformations tend to cause cracks. By subjecting the molded body to shotgrass, a large amount of strain can be imparted by the accumulation of minute deformations,
Larger deformation is possible in the next step.

The shot blasting may be carried out uniformly over the entire surface of the preform, but depending on the shape of the preform, the surface layer portion of the portion where the insufficient deformation region occurs during hot die forging. You may give it intensively. In order to perform hot shot blasting, shot blasting is performed on the uncooled preformed body immediately after the hot die forging is completed, or the preformed body is heated again in a heating furnace or the like and then shot blasted. You can give it. The shot blasting device itself may be any conventionally used device. Further, in order to prevent cooling of the preformed body, it is effective to use a preheated bullet.

Since the amount of strain to be applied to a portion where dead metal is likely to occur varies depending on the shape of the preform and the hot die forging conditions, it is desirable to determine it by conducting an experiment.
The shot (bullet) of shot blasting is preferably spherical so that processing strain can be uniformly applied, but it is not limited to a perfect spherical shape as long as sufficient processing strain can be imparted. The material and particle size of the shot, the firing speed, and the total number of shots should be determined by experiments so that the above-mentioned processing strain amount can be obtained. In addition, the depth to which the processing strain should be applied should be determined based on experiments.

Specifically, in a molded body having a general shape, a depth of 0.5 mm, preferably a surface, from the surface of the pre-molded body at a place where dead metal is likely to occur or a place cooled by the contact of a jig. The equivalent strain of about 0.1 to 1.0, preferably about 0.5 to 1.0 is applied to the depth of 1.0 mm to 1.0 mm. However, this range is for a general molded product having a non-complicated shape, and should be adjusted for each special molded product.

Next, the pre-molded body after the shot blasting is reheated to 350 to 500 ° C., and then hot die forging is performed once or plural times as a main forging step to obtain a molded body. The hot die forging method is the same as in the case of the preliminary forging.

According to the manufacturing method having the above-described structure, the shot blasting step imparts a working strain to the surface layer portion of the preform to cause plastic deformation, thereby breaking the oxide film of the individual particles in the surface layer portion. It is possible to increase the degree of bonding of the, improve mechanical properties and deformability. Therefore, while stabilizing the mechanical properties of the final formed body, cracks are less likely to occur in the surface layer portion of the preformed body during the main forging process on the way, and the amount of plastic deformation in each hot forging of the main forging process is increased accordingly. It is possible to reduce the number of hot die forgings at the time of main forging, and it is possible to improve the production efficiency of the aluminum alloy member.

The present invention is not limited to aluminum alloys and can be applied to, for example, a powder forging method for iron-based alloys. The conditions may be similar to those of the above aluminum alloy.

[0021]

EXAMPLES Next, the effects of the present invention will be demonstrated with reference to examples. A powder having a composition of Al-10Fe-1.5V-1.0Zr and having a size of 100 mesh or less was mixed with 6 tons at room temperature.
/ Cm ³ was press-molded to obtain a plurality of rectangular parallelepiped compacts having a diameter of 20 mm and a length of 20 mm and a density ratio of 80 vol%. After heating these green compacts at 450 ° C for 15 minutes in the air,
Closed die forging was performed at 7 ton / cm ² to obtain a preform having a density ratio of 99 vol%.

Next, these preforms were divided into two groups, and only one of them was shot blasted by the following method. First, heat the preform once to 450 ° C,
They were shot blasted while they were not cold. As the bullet, a steel ball having an outer diameter of 10 mm was used, and the bullet was shot at a speed of 9 m / sec for 30 seconds on the preform. When a section of the preformed body was cut and the cross section was examined, the particles were deformed to an aspect ratio of 3 or more up to a depth of 1 mm from the treated surface, and a processing strain of about 1.0 was imparted. The surface strain was 0.7.

Next, the preforms of each group are heated to 450 ° C.
After heating to the above, hot closed die forging was carried out under various forging conditions shown in Table 1 to confirm the presence or absence of cracks.

[0024]

[Table 1]

As shown in the above table, in the examples subjected to shot blasting, the grain boundary strength is increased and the ductility is increased,
The occurrence of cracks due to subsequent processing could be reduced.

[0026]

As described above, in the method for manufacturing an alloy member according to the present invention, a work strain is applied to the surface layer portion of the preform by the blasting step, and the surface layer portion is intensively plastically deformed, It is possible to increase the bondability and deformability of the material by breaking the oxide film of the individual particles constituting the surface layer portion. By increasing the workability of the surface layer in this way, it becomes possible to process the inner part with insufficient workability without breaking due to the hydrostatic effect, and at the same time, the preform during hot die forging in the main forging process. It is possible to increase the amount of plastic deformation in the main forging, reduce the number of hot die forgings, and increase the manufacturing efficiency of the aluminum alloy member by increasing the amount of plastic deformation in the main forging.

Claims (3)

[Claims] 1. A manufacturing method in which an alloy powder is compacted at room temperature or hot to obtain a compact, and the compact is further plastic-processed to form an alloy member. A method for manufacturing an alloy member, characterized in that a blasting step is provided in the middle of the step of applying a large number of bullets to at least a part of the surface of the intermediate compact to impart strain to the surface layer portion of the surface. 2. The method for manufacturing an alloy member according to claim 1, wherein the alloy is an aluminum alloy. 3. The method for manufacturing an alloy member according to claim 1, wherein the alloy is an iron-based alloy.