JPH05245609A - Production of high strength structural member with use of rapid solidified alloy powder - Google Patents

Abstract

PURPOSE:To obtain a high strength structural member excellent in mechanical property inherent in a rapid cooled and solidified Al alloy powder as well as a high degree of freedom for shape. CONSTITUTION:A high density solid material is manufactured by a rapid solidified Al alloy powder and successively by hot extruding. Then, the solid material is heated to be made to a partially solidified material, in which a solid and liquid phase coexist. This partially solidified material is charged into the charging hole 6 of the die 1, successively, the partially solidified material is filled into the cavity 4 through the gate 5 by the pressurizing plunger 9, subsequently, holding the plunger 9 at a stroke end to apply a pressurizing force on the partially solidified material filled in the cavity 4, and then a structural member is made with solidifying the partially solidified material under pressurizing.

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 a high strength structural member using a rapidly solidified alloy powder.

Since the alloy powder is manufactured under the application of the rapid solidification method, the alloy composition has a high degree of freedom in setting the alloy composition and a large amount of alloying elements can be added, so that it has high strength, particularly excellent high temperature strength. In addition, it has been put to practical use as a highly rigid material.

[0003]

2. Description of the Related Art A rapidly solidified alloy powder has the above-described excellent mechanical properties, but has the drawback of being difficult to process. To obtain the structural member, hot extrusion is mainly applied.

However, the hot extrusion process has a problem that the degree of freedom of the shape of the structural member is low, and therefore the structural member having the required shape cannot be obtained.

Therefore, as a method of manufacturing a structural member having a relatively high degree of freedom in shape, the method disclosed in Japanese Patent Laid-Open No. 2-268961 has been proposed.

In this method, the powder is put into a crucible to prepare a semi-molten material in which a solid phase and a liquid phase coexist under heating, and then the semi-molten material is transferred to a mold and pressurized. Means such as molding is adopted. The reason for using such a semi-molten material is to prevent the mechanical properties of the rapidly solidified alloy powder from being lost as much as possible.

[0007]

However, it has been found that the above method has the following problems due to the existence of innumerable voids in the powder aggregate.

That is, since the voids hinder the heat conduction between the powders during heating, the soaking degree of the semi-molten material is apt to deteriorate, and as a result, the flow of the semi-molten material is reduced during the molding process under pressure. If it is not performed uniformly over the whole and the shape of the member is complicated, defective molding such as chipping is likely to occur. Also, because the member is likely to have a nest due to the void,
In some cases, it may not be possible to achieve a sufficiently high strength.

In view of the above, it is an object of the present invention to provide the above-mentioned manufacturing method capable of solving the above problems by reducing the voids in the powder aggregate as much as possible.

[0010]

A method for producing a high-strength structural member using a rapidly solidified alloy powder according to the present invention is to prepare a high-density solid material by subjecting the rapidly solidified alloy powder to a forming and solidifying process, and then It is characterized in that the solid material is heated to prepare a semi-molten material in which a solid phase and a liquid phase coexist, and then the semi-molten material is used to perform molding under pressure.

[0011]

[Examples] In the preparation of a high-density solid material, as a forming and solidifying method using a rapidly solidified alloy powder, a compression forming method applied by an ordinary powder metallurgy method or the compression forming method followed by hot extrusion processing is used. The two-step processing method of performing is applied.

Further, in the preparation of the semi-molten material, a low frequency induction heating furnace is used for the purpose of shortening the heating time and soaking and heating.

As a molding method for the semi-molten material under pressure, a pressure casting method, a forging method and the like are applied.

FIG. 1 schematically shows a pressure casting apparatus used for carrying out the pressure casting method.

The mold 1 of the pressure casting apparatus is a fixed mold 2.
And the movable mold 3 facing it, both molds 2, 3
Is an alloy tool steel for hot molds (JIS SKD61 equivalent material)
It is composed of A molding cavity 4 having a circular cross section and a gate 5 communicating with one end of the molding cavity 4 are formed by both molds 2 and 3, and the gate 5 is a charging port 6 for the semi-molten material of the fixed mold 2.
Communicate with. The fixed mold 2 is provided with a sleeve 8 that communicates with the loading port 6, and a pressure plunger 9 that is inserted into and removed from the loading port 6 is slidably fitted into the sleeve 8. The cavity 4 has a relatively large capacity inlet side region 4a communicating with the gate 5, a relatively small capacity intermediate region 4b communicating with the region 4a, and a relatively large capacity deep region 4c communicating with the region 4b. Consists of.

In manufacturing the structural member, for example, the following steps are sequentially carried out. (A) A high-density cylindrical solid material is prepared by performing a two-step processing method using a rapidly solidified alloy powder. (B) A solid material is heated in a low frequency induction heating furnace to prepare a semi-molten material in which a solid phase and a liquid phase coexist. (C) The semi-molten material is charged into the charging port 6 of the pressure casting device. (D) The pressure plunger 9 is inserted into the charging port 6, and the semi-molten material is filled into the cavity 4 through the gate 5 by the pressure plunger 9. (E) While holding the pressure plunger 9 at the end of the stroke, a pressure is applied to the semi-molten material filled in the cavity 4, and the semi-molten material is solidified under the pressure to obtain a structural member.

As the rapidly solidified alloy powder, rapidly solidified Al alloy powder obtained by the atomizing method is used. The Al alloy powder is composed of the following chemical components and the balance Al.

17.0 wt% ≦ Si ≦ 18.0 wt% 4.0 wt% ≦ Fe ≦ 4.5 wt% 2.0 wt% ≦ Cu ≦ 2.5 wt% 1.8 wt% ≦ Mn ≦ 2.2 wt% 0.3 wt% ≤ Mg ≤ 0.5 wt% Cooling rate Cr during production of Al alloy powder is Cr ≥ 1
The temperature is set to 0 ² ° C / sec, whereby an Al alloy powder in which the maximum particle diameter D of the intermetallic compound is D = 15 µm is obtained.
However, when the cooling rate Cr is Cr <10 ² ° C./sec, an Al alloy powder having a fine metal structure unique to the rapid solidification method cannot be obtained, which makes it difficult to control the viscosity when preparing the semi-molten material. This can be said even when the maximum particle size D of the intermetallic compound is D> 15 μm.

In each chemical component of the Al alloy powder, Si
Has the effect of improving the wear resistance and Young's modulus of the structural member and reducing the coefficient of thermal expansion. However, if the Si content is Si <17.0% by weight, the above effect is small, while if Si> 18.0% by weight, the machinability deteriorates.

Fe has the effects of improving the high temperature strength and Young's modulus of the structural member and preventing seizure of the semi-molten material on the mold 1. This high temperature strength improvement mechanism is
This is due to the dispersion strengthening of the AlFeMn intermetallic compound. However,
If the Fe content is Fe <4.0% by weight, the above effect is small, while if Fe> 4.5% by weight, the elongation and toughness of the structural member decrease.

Cu has the effect of precipitating an Al ₂ Cu intermetallic compound by heat treatment and improving the strength of the structural member. However, when the Cu content is Cu <2.0 wt%, the strength improving effect is small, while when Cu> 2.5 wt%, the corrosion resistance of the structural member is reduced.

Mn has the effect of improving the high temperature strength of the structural member, and also has the function of agglomerating the AlFe intermetallic compound. However, if the Mn content is Mn <1.8% by weight, the above effect is small, while if Mn> 2.2% by weight, the elongation and toughness of the structural member decrease.

Mg has the effect of improving the strength of the structural member in cooperation with Si. However, if the content of Mg is Mg
If it is less than 0.3% by weight, the effect of improving the strength is small, while Mg
When it is> 0.5% by weight, the elongation and toughness of the structural member decrease.

The relative density d of the solid material is 70% ≦ d ≦ 10
It is set as high as 0%. When the relative density d of the solid material is increased as described above, the porosity of the solid material is zero or extremely low, so that the heat conduction in the solid material is performed efficiently and uniformly to improve the soaking degree of the semi-molten material. It is also possible to suppress the generation of cavities in the structural member as much as possible. However, when the relative density d of the solid material is d <70%, the soaking degree of the semi-molten material is deteriorated, and cavities are easily generated in the structural member.

When obtaining a semi-molten material from a solid material, the heating conditions are set as follows. The average heating rate Hr of the solid material is Hr ≧ 0.2 ° C./sec, the heating holding temperature T is the temperature between the solidus temperature T _S and the liquidus temperature T _L , that is, T _S <T <T _L It is desirable that the heating and holding time t be as short as possible, and depending on the size of the solid material, t ≦ 30.
The soaking degree ΔT of the semi-molten material is ΔT ≦ 4 ° C., and the viscosity μ of the semi-molten material is 0.1 Pa · sec ≦ μ ≦ 2000.
Pa · sec. By setting the heating conditions in this way, it is possible to efficiently prepare and handle the semi-molten material, improve the casting quality of the structural member, and improve its mechanical properties.

However, the average heating rate Hr of the solid material is H
When r <0.2 ° C./sec, it takes a long time to prepare the semi-molten material, which causes coarsening of the intermetallic compound, lowers moldability, and easily causes mold wear. The mechanical properties and the like of the structural member are impaired.

The optimum range of the average heating rate Hr is Hr ≧ 1.
It is 0 ° C./sec. The reason is that when the average heating rate Hr is Hr <1.0 ° C./sec, the productivity is likely to decrease, the metal structure is coarsened, and the surface oxidation is likely to occur.

The heating and holding temperature T is T≤T _S +0.5 (T
_L -T _S) is desirably ° C.. T> T _S +0.5
At (T _L −T _S ) ° C., coarsening of the intermetallic compound is caused and the same problem as described above occurs. Further, the heating holding time t is t
For> 30 minutes, coarsening of the intermetallic compound occurs as described above.

Further, the soaking degree ΔT in the semi-molten material is Δ
When T> 4 ° C., the viscosity μ is partially different in the semi-molten material, so that a melted-out portion is generated, and an unfilled portion in the cavity 4, that is, a chip in the structural member is generated. The optimum range of soaking degree is ΔT ≦ 3
℃. The reason is that the semi-molten material can be automatically handled in such a range, which can improve the productivity of the structural member.

The viscosity μ of the semi-molten material is set to be the same as that at the time of casting. Its viscosity μ is μ <0.1Pa
At sec, a melted-out portion is generated and the handling property of the semi-molten material is deteriorated, while the viscosity μ is μ> 2000 Pa.
At sec, the casting quality of the structural member deteriorates as described later.

The properties of the semi-molten material at the time of passing through the gate 5 during casting, that is, the viscosity μ of the semi-molten material, the Reynolds number Re and the velocity V are specified as follows.

The viscosity μ of the semi-molten material is 0.1 as described above.
Pa · sec ≦ μ ≦ 2000 Pa · sec is set. By setting the viscosity μ in this way, it is possible to prevent the gas from being entrained by the semi-molten material, and thus prevent the formation of pores in the structural member, and improve the casting quality.

However, the viscosity μ of the semi-molten material is μ <0.1
When the pressure becomes Pa · sec, the viscosity of the semi-molten material becomes low, and it becomes a turbulent state, so that the gas and the oxide are easily entrained. On the other hand, when the viscosity μ becomes μ> 2000 Pa · sec, the pressure loss due to the deformation resistance of the semi-molten material increases as the viscosity of the semi-molten material increases, so that it becomes difficult for the semi-molten material to pass through the gate and the unfilled portion in the cavity 4 Occurs.

The optimum range of the viscosity μ in the semi-molten material is 1
Pa · sec ≦ μ ≦ 1000 Pa · sec. The reason is that such a viscosity range can be easily realized by a pressure casting apparatus having a conventional mold temperature control mechanism. However, when the viscosity μ becomes low, such as μ <1 Pa · sec, the speed of the semi-molten material when passing through the gate 5 must be controlled at a low speed and precisely, and such control is performed by the conventional pressurization. Difficult with casting equipment. On the other hand, when the viscosity μ is high such that μ> 1000 Pa · sec, the semi-molten material is cooled by the mold 1 and the viscosity is rapidly increased. However, in order to prevent this, the temperature of the mold 1 is increased. It must be controlled to a high level, and such control is difficult with conventional pressure casting equipment.

The Reynolds number Re of the semi-molten material is Re ≦ 1
It is set to 500. By setting the Reynolds number Re in this way, it is possible to prevent the gas from entraining and the occurrence of a cold boundary in the semi-molten material. However, when the Reynolds number Re becomes Re> 1500, the semi-molten material becomes in a turbulent state, and it becomes easy to entrain gas or the like.

The optimum range of Reynolds number Re is Re ≦ 10.
It is 0. The reason is that the Reynolds number Re in such a semi-molten material can be easily realized by a conventional pressure casting apparatus. However, Reynolds number Re is Re
> 100, the shape of cavity 4 and gate 5
Depending on the shape of, the influence of the inertial force becomes large and the filling of the semi-molten material into the cavity 4 cannot be performed smoothly,
There is a risk of gas entrapment and hot water.

The velocity V of the semi-molten material is 0.2 m / sec ≦
V ≦ 30 m / sec is set. By setting the speed V in this way, the semi-molten material can be smoothly filled into the cavity 4 with an appropriate pressure. However, when the speed V is V <0.2 m / sec, the filling time of the semi-molten material into the cavity 4 becomes long, so that the productivity is reduced.
On the other hand, when the velocity V is V> 30 m / sec, when the viscosity μ of the semi-molten material is high, a large pressing force is required, which is not practical.

In order to improve the casting quality of the structural member, the Reynolds number Re of the semi-molten material and the cross-sectional area enlargement ratio Rs in the mold 1 become a problem. Here, the cross-sectional area enlargement ratio Rs is the cross-sectional area of the gate 5 and S ₀ 1, also when the cross-sectional area of the inlet-side region 4a in the cavity 4 was set to S _1, represented by Rs = S ₁ / S ₀ Be done.

The cross-sectional area enlargement ratio Rs is set to Rs ≦ 10. By setting the cross-sectional area enlargement ratio Rs in this way, it is possible to prevent the entrainment of gas by the semi-molten material and the occurrence of a molten metal boundary. However, the cross-sectional area expansion rate Rs is Rs> 10
Then, the semi-molten material becomes a jet flow from the gate 5 and is injected into the cavity 4, and the filling order is the inner region 4c,
Since it is next to the entrance side area 4a, a hot water boundary occurs.

The optimum range of the cross-sectional area enlargement ratio Rs is 1 ≦ Rs ≦
It is 5. The reason is that such a cross-sectional area enlargement ratio Rs can be easily realized by a conventional pressure casting device. However, when the cross-sectional area expansion ratio Rs becomes Rs> 5, the cross-sectional area of the gate 5 is substantially reduced, so that the solidification of the semi-molten material in the gate 5 precedes the final solidification of the semi-molten material in the cavity 4, As a result, the feeder effect cannot be obtained, and the inlet side region 4a and the inner region 4 are
There is a risk that shrinkage will occur in both thick-walled portions of the structural member corresponding to c. On the other hand, when the cross-sectional area enlargement ratio Rs becomes Rs <1, the cross-sectional area of the gate 5 becomes the entrance side region 4 a of the cavity 4.
Since the cross-sectional area is substantially equal to the cross-sectional area of, the yield of structural members decreases as the scrap portion corresponding to the gate 5 increases.
Causes operational problems.

Further, in order to improve the casting quality of the structural member, the pressure P applied to the semi-molten material filled in the cavity 4 is set to 10 MPa≤P≤120 MPa. However, when the applied pressure P is P <10 MPa, the high-viscosity semi-molten material cannot be sufficiently pressurized,
An unfilled portion occurs in the cavity 4. On the other hand, when the applied pressure P is P> 120 MPa, the apparatus becomes large in size, which is not practical.

Specific examples will be described below.

First, the relationship between the relative density d of the solid material and the soaking degree ΔT of the semi-molten material will be considered.

As the rapidly solidified Al alloy powder, one having the composition shown in Table 1 was selected.

[0045]

[Table 1] This Al alloy powder was obtained by the atomization method, and the cooling rate Cr during its production was Cr = 10 ²
2 × 10 ⁴ ° C / sec, maximum particle size D of intermetallic compound is D
= 7 μm, the solidus temperature T _S was T _S = 510 ° C., and the liquidus temperature T _L was T _L = 690 ° C.

A compact is formed by performing compression molding using an Al alloy powder, and then the compact is hot extruded under the conditions of an extrusion temperature of 420 ° C., a maximum pressing force of 2500 ton and an extrusion ratio of 12. After processing, the relative density d is d
= 100% solid material was obtained.

In the hot extrusion process, the relative density d is changed to d = 90%, 8 by changing the extrusion ratio.
Three solid materials of 0% and 70% were produced.

Then, the solid material was machined to produce a short cylindrical solid test piece having a diameter of 70 mm and a length of 100 mm.

Then, the solid test piece was set to an inner diameter of 70 mm,
Inserted in a 100 mm deep alumina crucible, installed the crucible in a low-frequency induction heating furnace, and heated the solid test piece to 570 ° C. with the output pattern of rapid soaking and heating. The temperature distribution of the test piece was measured. For each semi-molten test piece, the difference between the maximum value and the minimum value of the measured temperature was determined as the soaking degree ΔT.
Got the result.

In Table 2, in the comparative example, the Al alloy powder was filled in the crucible to obtain a solid test piece having the same size as the above, and the solid test piece was subjected to heat treatment under the same conditions as described above. This is the case where a semi-molten test piece was prepared.

[0051]

[Table 2] From Table 2, it can be seen that the semi-melted test piece of the example has an excellent soaking degree ΔT as compared with the semi-melted test piece of the comparative example. This is because the solid test piece having a high relative density d was used in the examples.

Next, a method of manufacturing a structural member using the Al alloy powder will be described.

First, a green compact is formed by performing compression molding using an Al alloy powder, and then the green compact is extruded at a temperature of 420 ° C. and a maximum pressure of 2500 tons.
A solid material was obtained by hot extrusion under an extrusion ratio of 12.

In this solid material, the Al alloy powders are sintered together and their relative density d is 100%.
And the maximum particle size D of the intermetallic compound was D = 7 μm.

In the die 1, the cross-sectional area S of the gate 5 is
_The cross-sectional area expansion ratio Rs (S ₁ / S ₀ ) established between ₀ and the cross-sectional area S ₁ of the inlet side region 4a of the cavity 4 is Rs = 4.
Set to.

Next, the solid material is placed in a low-frequency induction heating furnace and heated, with an average heating rate Hr = 1.3 ° C.
/ Sec, heat retention temperature T = 567 ° C., heat retention time t
= 1 minute, a semi-molten material having a soaking degree ΔT = 3 ° C. and a solid phase volume fraction Vf = 70% was prepared. This solid phase has the same metallic structure as the solid material. The semi-molten material was charged into the charging port 6 of the mold 1, and then the cavity 4 was filled with the semi-molten material through the gate 5 by the pressure plunger 9. In this case, the moving speed of the pressure plunger 9 is set to about 78 mm / sec, the speed V of the semi-molten material when passing through the gate 5 is V = 3.0 m / sec, the viscosity μ is μ = 300 Pa · sec, and the Reynolds number is Re is Re
Was 0.21.

Further, as shown in FIG. 1, the lower position G of the gate 5 in the mold 1, the upper position U1 and the lower position L1 of the inlet side region 4a of the cavity 4, and the inner region 4c.
When the filling behavior of the semi-molten material was examined by measuring the temperature rising start points of the upper position U2 and the lower position L2 of, the filling sequence was G → L1 → U1 → L2 and U2 at approximately the same time, It was confirmed to be ideal for avoiding the occurrence of casting defects.

While holding the pressure plunger 9 at the end of the stroke, a pressure was applied to the semi-molten material filled in the cavity 4, and the semi-molten material was solidified under the pressure to obtain a structural member. In this case, the pressure P on the semi-molten material is P = 30
It was confirmed that it was up to 90 MPa, and that the flash generated on the dividing surface 10 of the mold 1 was extremely small.

FIG. 2 is a photomicrograph (400 times) showing the metal structure of the structural member obtained by the pressure casting method, and FIG. 3 is a photomicrograph showing the metal structure of the solid material (400 times). ).

In FIGS. 2 and 3, the dark gray dot-like portions are intermetallic compounds. It can be seen from FIG. 2 that the maximum particle size D of the intermetallic compound is D = 15 μm, which is slightly larger than that of FIG. The reason why such a metallographic structure is obtained is that the maximum particle diameter D of the intermetallic compound in the solid phase of the semi-molten material is D = 7 μm, and that the intermetallic compound crystallized from the liquid phase has This is because the fineness is achieved because it is subjected to shearing force during passage and solidifies under pressure.

Further, as is clear from FIG. 2, this structural member does not have a boundary between the molten metal and pores due to the entrainment of gas, and has no chipping due to the non-filling of the semi-molten material into the cavity 4. It has also been found that this structural member has excellent casting quality.

To compare the mechanical properties, room temperature, 200
When the tensile strength σ _B and the 0.2% proof stress of the structural member (cast member) and the solid material (extruded member) at 0 ° C and 300 ° C were measured, the results shown in Table 3 were obtained.

[0063]

[Table 3] As is clear from Table 3, at room temperature, the solid material is slightly superior in strength to the structural member, but at high temperature, the two are substantially the same.

Therefore, according to the pressure casting method, it is possible to provide a structural member having excellent high-temperature strength and having a higher degree of freedom in shape as compared with the hot extrusion method.

For comparison, a crucible was filled with the Al alloy powder to prepare a solid material having a relative density d = 60%,
Then, the crucible was placed in a low-frequency induction heating furnace to prepare a semi-molten material having a soaking degree ΔT = 7 ° C. and a solid phase volume fraction Vf = 70% under the same heating conditions as described above. The semi-molten material was charged into the charging port 6 of the mold 1 to obtain a comparative structural member under the same casting conditions as described above.

FIG. 4 is a photomicrograph (100 times) showing the metal structure of the comparative structural member. From this figure, it can be seen that the comparative structural member has cavities (black portions). This nest is due to the fact that the relative density d of the solid material is low and that the material has numerous voids.

[0067]

According to the present invention, by using a high-density solid material composed of a rapidly solidified alloy powder, the rapidly solidified alloy powder has excellent mechanical properties and high strength with a high degree of freedom in shape. It is possible to obtain various structural members.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a pressure casting device.

FIG. 2 is a micrograph showing a metal structure of a structural member.

FIG. 3 is a micrograph showing a metal structure of a solid material.

FIG. 4 is a micrograph showing a metal structure of a comparative structural member.

[Explanation of symbols]

 1 Mold 4 Cavity 5 Gate 6 Loading Port 9 Pressurizing Plunger

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[Procedure amendment]

[Submission date] January 14, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

As the rapidly solidified alloy powder, for example, rapidly solidified Al alloy powder obtained by the atomizing method is used. The Al alloy powder has the following chemical components and the balance A
and l.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0064

[Correction method] Change

[Correction content]

Therefore, according to the pressure casting method, it is possible to obtain a structural member having excellent high-temperature strength and having a higher degree of freedom in shape as compared with the hot extrusion method.

Claims (1)

[Claims] 1. A rapidly solidified alloy powder is compacted and solidified to prepare a high-density solid material, and then the solid material is heated to prepare a semi-molten material in which a solid phase and a liquid phase coexist. A method for producing a high-strength structural member using a rapidly solidified alloy powder, characterized in that the semi-molten material is used for forming under pressure.