KR101876283B1 - Method of high strength aluminum alloy component and connecting rod using the same - Google Patents

Abstract

The present invention relates to a method of manufacturing a high-strength Ti-6Al-4V titanium alloy part, which can be manufactured by a powder metallurgy method and has excellent mechanical properties by a uniform sintered structure at a low manufacturing cost.
To this end, the present invention relates to a powder mixing method for mixing a 60Al-40V powder and a titanium powder at a weight ratio of 1: 9; A preform forming step of putting the mixed powder mixed in the powder mixing step into a mold and then compressing to form a preform; A hot degreasing step of hot degreasing the preform formed in the preform forming step; A sintered body manufacturing step of producing a sintered body by sintering the preform in a molded body; And a final machining step of final machining the sintered body. The present invention also provides a method of manufacturing a high strength Ti-6Al-4V titanium alloy part.

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a high-strength Ti-6Al-4V titanium alloy component, and a connecting rod using the same,

The present invention relates to a method of manufacturing a high strength Ti-6Al-4V titanium alloy part, and more particularly, to a method of manufacturing a high strength Ti-6Al-4V titanium alloy part by a powder metallurgy method, a simple manufacturing process, High-strength Ti-6Al-4V titanium alloy parts.

The connecting rod includes a small end portion connected to the piston, a large end portion connected to the crank pin of the crankshaft, and a rod portion integrally connecting the small end portion and the large end portion to connect the piston and the crankshaft in a steam engine or an internal combustion engine, It converts the motion into rotational motion and transmits it to the crack axis.

Conventionally, the connecting rod is manufactured by a hot forging process using an alloy steel or a powder forging process using an iron-based powder. In particular, the sintering process is simpler than the hot forging process, and because the flash is not formed during the process, the amount of material lost during the manufacturing process is very small. Therefore, most of the connecting rods are manufactured by the sintering process .

More specifically, the method for producing a connecting rod by sintering forging comprises a mixing step (S110) of a metal powder of an iron type (Fe- (1.5 to 3.5) Cu- (0.45 to 0.9) C) The preform is preliminarily sintered at 930 to 950 ° C for 10 to 20 minutes (S 130), and the preform is heated to 1,230 ° C Sintering at about 1250 ° C for 20 minutes to form an alloy (S140); subjecting the sintered product to sintering at a temperature of about 900 ° C to 1000 ° C in a hot press die at a density of 7.8g / (S160); removing the burrs at the edges of the product produced during the high-temperature forging (S170); cooling the closed-forged sintered product by a shot blast or shot peening method A step of removing the oxide on the surface of the product (S180), and a step of performing the final machining (S190) It should.

Recently, automakers have adopted Gasoline Direct Injection (GDI) and Turbo Gasoline Direct Injection (TGDI), which directly inject fuel into cylinders to satisfy environmental regulations and improve fuel efficiency. have.

When the fuel is directly injected into the cylinder of the GDI / TGDI type engine, a higher combustion pressure is generated than in the conventional MPI (Multi Point Injection) method, and the combustion pressure generated at this time is transmitted to the piston, (Tensile strength, yield strength, and fatigue strength) are required because a larger tensile load and a compressive load are continuously and repeatedly received.

The requirements for the connecting rod used in the conventional MPI engine method are 800 MPa in tensile strength, but a tensile strength of 1000 MPa is required for application to GDI / TGDI engines. At present, the physical properties of the alloy steel powder forging are as follows: HS170 (Fe-3.25Cu-0.7C) has a yield strength of 810 MPa, tensile strength of 1100 MPa and fatigue strength of 410 MPa.

Titanium alloy has a density of 4.43g / ㎤, which is very promising as a connecting rod material because it has a high mechanical strength of only 60% of 7.8g / ㎤, which is the density of alloy steel used in conventional connecting rods.

Particularly, reducing the weight of the connecting rod can improve the fuel efficiency and reduce the noise, vibration and harshness (NVH) of the engine. Therefore, the connecting rod using the titanium alloy material is attracting much attention.

In general, a connecting rod using a titanium alloy is currently manufactured by a hot forging process, and the price of the titanium alloy material is high and it is difficult to process it, resulting in a high manufacturing cost.

In addition, the connecting rod using the titanium alloy manufactured by the hot forging process has a very hardness and a brittle surface oxidation structure which is formed by surface oxidation during hot forging, .

Accordingly, the connecting rod using the titanium alloy is limitedly used only in a race car or some expensive passenger cars.

Therefore, although a sintering forging process for reducing the manufacturing cost of the titanium alloy connecting rod has been developed, there is a problem that it is difficult to commercialize it.

Korean Registered Patent No. 10-1173054 (entitled "Powder Composition for Connecting Rods and Method for Producing Connecting Rod Using the Same")

A problem to be solved by the present invention is to provide a method of manufacturing a high strength Ti-6Al-4V titanium alloy part which can be manufactured by a simple powder metallurgy process, a low manufacturing cost and an excellent mechanical property by a uniform sintered structure .

In order to solve the above-mentioned problems, the present invention provides a method of manufacturing a powdery alloy, comprising: a powder mixing step of mixing 60Al-40V powder and titanium powder at a weight ratio of 1: 9; A preform forming step of putting the mixed powder mixed in the powder mixing step into a mold and then compressing to form a preform; A hot degreasing step of hot degreasing the preform formed in the preform forming step; A sintered body manufacturing step of producing a sintered body by sintering the preform in a molded body; And a final machining step of final machining the sintered body. The present invention also provides a method of manufacturing a high strength Ti-6Al-4V titanium alloy part.

The mixed powder may further include a lubricant for reducing the friction between the 60Al-40V powder and the titanium powder during molding of the preform, and for facilitating the extraction, and the lubricant may be removed in the hot degreasing step.

The removal of the lubricant in the hot degreasing step may be performed in an argon (Ar) atmosphere or a vacuum atmosphere at a temperature of 400 ° C to 500 ° C for 30 minutes to 240 minutes.

The relative density of the preform to be formed in the preform forming step may be 78% to 85%.

The forming pressure for molding the preform in the preform forming step may be 400 MPa to 700 MPa.

The production of the sintered body in the sintered body production step may be performed in an argon (Ar) atmosphere or a vacuum atmosphere at a temperature within a range of 1100 ° C to 1400 ° C for 30 minutes to 240 minutes.

In the step of manufacturing the sintered body, the density of the sintered body is 97% to 99.5%, and fine pores of 20 탆 or less can be uniformly distributed.

The method of manufacturing a high strength Ti-6Al-4V titanium alloy part and the connecting rod using the same according to the present invention have the following effects.

First, since a precise titanium alloy sintered body can be obtained by simply performing a die compression molding and a sintering process without an additional manufacturing process such as hot forging, there is an advantage that a final processing cost and material loss are lowered.

Second, since the final product can be manufactured only by processing the titanium alloy sintered body, there is an advantage that the final product can be manufactured with low manufacturing cost and simple manufacturing process.

Third, there is an advantage that the additional hot forging process capable of giving a change in texture of the titanium alloy sintered body is omitted, thereby preventing the formation of uneven tissue, and thus having uniform and excellent mechanical properties.

1 is a flowchart of a method for manufacturing a connecting rod by sintering forging according to the prior art.
2 is a flowchart of a method of manufacturing a high strength titanium alloy part according to the present invention.
3 is a graph showing the relationship between the molding pressure and the molding density of the mixed powder of titanium and 60Al-40V.
4 is a graph showing the relationship between the molding pressure of titanium and 60Al-40V mixed powder and the sintered density of Ti-6Al-4V sintered body.
5 shows the shape of the Ti-6Al-4V connecting rod sintered body of the embodiment according to the present invention.
6 shows the microstructure of the Ti-6Al-4V connecting rod sintered body of the embodiment according to the present invention.
7 shows the microstructure of the Ti-6Al-4V connecting rod sintered body of Comparative Example 1 according to the present invention.
8 shows the microstructure of the Ti-6Al-4V connecting rod sintered body of Comparative Example 2 according to the present invention.
9 shows the shape of the Ti-6Al-4V connecting rod forging body of Comparative Example 3 according to the present invention.
10 shows the microstructure of the Ti-6Al-4V connecting rod forging material of Comparative Example 3 according to the present invention.

Hereinafter, preferred embodiments of the present invention in which the above-mentioned problems to be solved can be specifically realized will be described with reference to the accompanying drawings. In describing the embodiments, the same names and the same symbols are used for the same configurations, and additional description thereof will be omitted in the following.

Referring to FIG. 2, a method of manufacturing a high strength Ti-6Al-4V titanium alloy part according to the present invention will be described below.

2, the high strength Ti-6Al-4V titanium alloy part manufacturing method according to the present invention includes a powder mixing step S210, a preform forming step S220, a hot degreasing step S230, a sintering step S240 ), And a final machining step (S250).

The mixed powder to be mixed in the powder mixing step (S210) includes 60Al-40V powder, titanium powder, and a lubricant.

In the powder mixing step (S210) of the present invention, 60Al-40V powder contained in the mixed powder includes 35 to 45% by weight of vanadium (V) and 55 to 67.5% by weight of aluminum (Al).

The 60Al-40V powder and the titanium powder are mixed in a weight ratio of 1: 9.

The lubricant is included in order to reduce friction with the metal mold during preforming of the mixed powder obtained by mixing the 60Al-40V powder and the titanium powder and to facilitate the extraction, and is removed at the hot end degreasing step (S230).

The amount to which the lubricant is added may be adjusted depending on the total weight of the 60Al-40V powder and the titanium powder.

In the preform forming step (S220), the mixed powder mixed in the powder mixing step (S210) is injected into a mold and compressed to form a preform.

FIG. 3 shows the relative density change of the preform formed according to the molding pressure when the 60Al-40V powder and the titanium powder are weighed at a weight ratio of 1: 9 and put into a mold and compression molded. As can be seen from FIG. 3, the higher the molding pressure, the higher the molding density can be obtained.

Generally, the molding pressure for forming the preform is as high as possible for increasing the molding density. However, when the molding pressure is high, the life of the mold is shortened, and due to the friction generated between the mold and the powder, .

Therefore, it is preferable that the pressure for forming the preform is as high as possible in order to increase the molding density. However, in the case of the molding metal used for powder metallurgy, the mold breakage easily occurs at a pressure of 800 MPa or more, It is usually molded at a pressure of 800 MPa or less.

As shown in FIG. 3, the increase of the molding density due to the increase of the pressure is low at a pressure of 600 MPa or higher, so that the mixed powder is heated to 400 MPa to 800 MPa (relative density) so that the preform has a molding density It is preferable to perform compression molding with a molding pressure in the range.

In the hot degreasing step (S230), the preform formed in the preform forming step (S220) is degreased by hot to remove the lubricant.

The hot degreasing step (S230) is performed in an argon (Ar) atmosphere or a vacuum atmosphere at a temperature within a range of 400 DEG C to 600 DEG C for 30 minutes to 240 minutes.

In the sintered body production step (S240), the sintered body is sintered by sintering the preform with the lubricant removed. The sintering temperature in the argon (Ar) atmosphere or vacuum atmosphere is in the range of 1100 to 1400 ° C. 30 minutes to 240 minutes. The sintering temperature and the sintering holding time in the sintering step (S240) may be changed according to the particle size of the titanium powder and the 60Al-40V powders to be used, and the sintered body is sintered so that the sintered density (relative density) is 97% to 99.5% .

The preforms formed by the molding pressures described above have a difference in sintering density as well as forming density as well as the size and number of residual pores to be formed depending on the molding pressure. FIG. 4 shows changes in the sintered density of the preform according to the molding pressure when sintering the mixed preform of 60Al-40V powder and titanium powder as shown in FIG. 3 at a sintering temperature of 1250 ° C for 2 hours. As shown in FIG. 4, when the molding pressure is high, a high sintered density can be obtained under the same sintering condition, and a sintered body having a high sintered density has relatively excellent mechanical properties.

In the final machining step (S250), the sintered body is finally machined to implement the sintered body having been subjected to the above-described process with the final required dimensions.

If the sintered body is densified to a sintered density of 4.30 g / cc or more (relative density of 97% or more) through the sintered body production step (S240) without additional hot forging, the hot forging process may be omitted because of its excellent mechanical properties. Therefore, it is possible to prevent the formation of the surface oxidation structure having high hardness and strong brittleness due to the alpha case generated in the hot forging, that is, the surface oxidation occurring in the hot forging, thereby facilitating the processing of the sintered body in the final processing step, The tool life can be improved and the machining cost can be greatly reduced.

In order for the sintered body to be densified to a sintered density of 4.30 g / cc or more (relative density of 97% or more) through the sintered body production step (S240) without the additional hot forging step, S220), it is preferable that the mixed powder is compression-molded at a pressure of 400 MPa or more so that the molding density of the preform becomes 3.46 g / cc or more (relative density is 78% or more).

As described above, the present invention can provide the connecting rod using the method of manufacturing the high strength Ti-6Al-4V titanium alloy part.

Hereinafter, preferred embodiments and comparative examples of the present invention will be described.

However, the following embodiments are intended to illustrate the present disclosure, and thus the scope of the present specification is not limited thereto.

<Examples>

A mixture powder of 60 Al-40 V powder having a particle size of 45 μm or less (-325 mesh) and titanium powder having a particle size of 150 μm or less (-100 mesh) at a ratio of 1: 9 was charged into a connecting rod- Then, preforms having the shape of a connecting rod are formed at a molding pressure of 600 MPa, and the preforms are subjected to a hot degassing process at a temperature of 500 ° C. for 1 hour in an argon (Ar) atmosphere. Next, the preform is subjected to a sintering step (S240) in which the preform is performed at a temperature of 1250 DEG C for 120 minutes in a vacuum atmosphere to produce a Ti-6Al-4V titanium alloy sintered body. Next, the sintered body is subjected to a final machining step (S250) to produce a high-strength Ti-6Al-4V titanium alloy connecting rod. FIG. 5 shows the shape of the Ti-6Al-4V titanium alloy connecting rod sintered body, and FIG. 6 shows the microstructure of the sintered body.

&Lt; Comparative Example 1 &

A Ti-6Al-4V titanium alloy connecting rod was prepared in the same manner as in the Example except that the forming pressure for forming the preform was 300 MPa. Fig. 7 shows the microstructure of the Ti-6Al-4V titanium alloy connecting rod sintered body.

&Lt; Comparative Example 2 &

A Ti-6Al-4V titanium alloy connecting rod was produced in the same manner as in Example except that the forming pressure for forming the preform was 400 MPa. 8 shows the microstructure of the Ti-6Al-4V titanium alloy connecting rod sintered body.

&Lt; Comparative Example 3 &

A Ti-6Al-4V titanium alloy connecting rod was prepared in the same manner as in Example except that the molding pressure for forming the preform was 400 MPa, and the sintered body was further hot-forged at a temperature of 960 ° C.

division Molding pressure (MPa) Hot forging Sintered density (g / cc)
(Relative density (%)) Tensile Strength (MPa) Yield strength (MPa) Elongation (%) Example 600 × 4.37 (98.5) 962 894 15 Comparative Example 1 300 × 4.26 (96.1) 884 796 12 Comparative Example 2 400 × 4.30 (97.0) 900 830 12 Comparative Example 3 400 ○ 4.42 (99.8) 1080 1030 12 ASTM B381
Forging material specification - - - > 895 > 828 > 10

As shown in Table 1, it can be confirmed that the mechanical properties of the high-strength Ti-6Al-4V titanium alloy part vary depending on the molding pressure for producing the sintered powder and the forging process.

As shown in Table 1, it can be seen that the mechanical properties of the high strength Ti-6Al-4V titanium alloy part are varied depending on the forming pressure and the addition of the hot forging step for producing the sintered powder of the mixed powder.

That is, as shown in Table 1, the conditions under which the forming pressure was 400 MPa and the hot forging process was added (Comparative Example 3) and the forming pressures were 600 MPa and 400 MPa, respectively, The tensile strength, yield strength and elongation of the Ti-6Al-4V titanium alloy component manufactured in Example 2 were found to conform to the Ti-6Al-4V titanium alloy forging material standard of ASTM B381. In addition, the tensile strength and yield strength of the titanium alloy parts manufactured under the conditions in which the forming pressure is 300 MPa and the hot forging step is omitted (Comparative Example 1) are somewhat inferior to the Ti-6Al-4V titanium alloy forgings of ASTM B381 Can be confirmed.

6 and FIGS. 7 and 8, the residual pores formed in the sintered body of the above Example were compared with those of Comparative Example 1 and Comparative Example 2 It is confirmed that the size is reduced as compared with the residual pores formed in the sintered body, and the number of the remaining pores is also reduced.

Therefore, the molding pressure for forming the preform affects not only the sintering density but also the number and size of the residual pores of the sintered body. It can be seen that as the molding pressure is increased, the size of the residual pores formed in the sintered body decreases and the number thereof decreases have.

As shown in FIG. 9, it can be seen that the oxide layer due to the high-temperature oxidation during the hot forging process is formed on the surface of the connecting rod forging body manufactured through Comparative Example 3.

10 is a microstructure of a comparative example subjected to a hot forging process, and it can be confirmed that residual pores are removed by hot forging.

As shown in Table 1, the high-strength Ti-6Al-4V titanium alloy part manufactured through the example, the comparative example 2 and the comparative example 3 has a mechanical strength corresponding to all of the Ti-6Al-4V titanium alloy forgings of ASTM B381 .

However, since the Ti-6Al-4V high-strength titanium alloy part of the embodiment is manufactured without adding a hot forging step, it can be seen that the above-mentioned high temperature oxidation layer is not observed on the surface of the sintered body, have. As a result, the additional process such as removing the oxidized surface of the forged product is omitted, and the manufacturing cost and the manufacturing time of the high-strength titanium alloy component are greatly reduced.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Modify or modify the Software.

Claims (7)

A powder mixing step of mixing 60Al-40V powder and titanium powder at a weight ratio of 1: 9;
A preform forming step of putting the mixed powder mixed in the powder mixing step into a mold and then compressing to form a preform;
A hot degreasing step of hot degreasing the preform formed in the preform forming step;
A sintered body manufacturing step of producing a sintered body by sintering the preform in a molded body; And
And a final machining step of final machining the sintered body,
The relative density of the preform to be formed in the preform forming step is 78% to 85%
Wherein the molding pressure for molding the preform in the preform forming step is 400 MPa to 700 MPa. The method according to claim 1,
Wherein the mixed powder further comprises a lubricant for reducing the friction between the 60Al-40V powder and the titanium powder during molding of the preform, and for facilitating the extraction, and the lubricant is removed in the hot degreasing step High strength Ti-6Al-4V titanium alloy parts manufacturing method. 3. The method of claim 2,
Wherein the removal of the lubricant in the hot degreasing step is performed in an argon (Ar) atmosphere or a vacuum atmosphere at a temperature of 400 ° C to 500 ° C for 30 minutes to 240 minutes. Way. delete delete The method according to claim 1,
The high-strength Ti-6Al-4V titanium alloy (1) is characterized in that the production of the sintered body in the sintered body production step is performed in an argon (Ar) atmosphere or a vacuum atmosphere at a temperature within a range of 1100 ° C to 1400 ° C for 30 minutes to 240 minutes Method of manufacturing parts. The method according to claim 6,
Wherein the sintered body has a density of 97% to 99.5% and fine pores of 20 μm or less are uniformly distributed in the sintered body manufacturing step.

Images