JPH01230739A - Aluminum alloy cast containing composite material component - Google Patents

Abstract

PURPOSE:To prevent the generation of cracks in the title cast caused by thermal fatigue by enclosing a part of the surface of an Al alloy cast with a specific conjugate material in which an intermetallic compound between Al and other metal is finely dispersed into an Al matrix. CONSTITUTION:At least a part of the surface of Al alloy cast is enclosed by a conjugate material part in which an Al alloy is regulated to the one in which an intermetallic compound between Al and one or more kinds of metallic elements selected from Fe, Ni, Co, Cr, Cu, Mn, Mo, V, W, Ta, Nb, Ti and Zr is finely dispersed into the Al matrix. Viewed by the arbitrary section of the surface part in the conjugate material part, when the length and width are denoted by L and D, the areal rate of the intermetallic compound satisfying >3L/D is regulated to <=30% for the total. By this method, the thermal impact characteristics of the Al alloy cast is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an aluminum alloy casting, and more particularly to a composite material part having an aluminum alloy as a matrix and reinforcing materials as short fibers and whiskers. Strength,
It relates to an aluminum alloy casting having a composite material part with excellent friction and wear characteristics and adhesion resistance.

Conventional Technology It is known that it is effective to form intermetallic compounds in composite materials in order to improve the friction and wear characteristics of composite materials. A composite material is described in which an intermetallic compound is formed with a matrix on the surface layer of cast iron fibers.

Furthermore, in the specification of Japanese Patent Application No. 1983 filed on the same date as the present application by the same applicant as the present applicant, there is a patent application for improving the friction and wear characteristics, heat resistance, etc. of a composite material having an aluminum alloy as a matrix. , A in the matrix
A composite material in which an intermetallic compound of I and a specific metal element is finely dispersed is described, and according to the composite material proposed in the future, the conventional composite material that does not contain an intermetallic compound and the above-mentioned special It is possible to obtain a composite material that has better friction and wear characteristics, heat resistance, etc. than the composite material described in JP-A-61-132260.

Problems to be Solved by the Invention However, since intermetallic compounds are hard and brittle substances, embrittlement is unavoidable in composite materials containing intermetallic compounds, especially composite materials containing intermetallic compounds. Composite materials can crack due to thermal fatigue if they are subjected to severe cooling and heating cycles.

The inventors of the present application conducted various experimental studies to prevent cracks caused by thermal fatigue in composite materials containing intermetallic compounds. By limiting the form of the intermetallic compounds present in the composite material part of aluminum alloy castings in which a part of It has been found that cracks caused by fatigue can be avoided, and the strength etc. of composite material parts can be improved.

The present invention is based on the findings obtained as a result of experimental research carried out by the inventors of the present invention, and has a composite material part with an aluminum alloy as a matrix and short fibers or whiskers as a reinforcing material. We offer aluminum alloy castings that are partially delineated and do not crack due to thermal fatigue even when subjected to relatively severe cooling and heating cycles, and have excellent strength.
The purpose is to

Means for Solving the Problems According to the present invention, the above-mentioned object includes a composite material part in which an aluminum alloy is matrix-bound and short fibers or whisker particles are used as a reinforcing material. The matrix contains Al, FesNi, and Co.
5Cr, Cu, MnSMo, V, W, Ta5Nb, Ti
, an intermetallic compound with at least one metal element selected from the group consisting of Zr is finely dispersed, and the length and width of the intermetallic compound are Let L and D be respectively, then L/D>3
This is achieved by an aluminum alloy casting in which the area ratio of intermetallic compounds is 30% or less based on the total amount of intermetallic compounds.

Effects and Effects of the Invention According to the present invention, AI is contained in the matrix of the composite material part.
The intermetallic compounds between the reinforcing material and the specific metal elements are finely dispersed, and the intermetallic compounds strengthen, or consolidate, the matrix between the reinforcing materials, which allows the reinforcing materials to maintain their desired state even at high temperatures. Held, Ma!・Since direct contact of the repress with the mating material is avoided, it improves strength, wear resistance, and adhesion resistance at high temperatures compared to conventional composite materials that do not contain intermetallic compounds. In addition, when the length and width of the intermetallic compound are L and D, respectively, when viewed from an arbitrary cross section of the surface of the composite material part, L
/D>3, that is, the area ratio of acicular intermetallic compounds with directionality is 3 to the total amount of intermetallic compounds.
Since the temperature is set to 0% or less, cracks due to thermal fatigue occur in the composite material even when subjected to relatively severe cooling and heating cycles, as is clear from the results of experimental research later conducted by the inventors of the present application. It is possible to obtain aluminum alloy castings with excellent thermal shock properties.

According to the results of experimental research conducted by the inventors, L/
The area ratio of intermetallic compounds that is D>3 or the layer that is 30% or less of the total amount of intermetallic compounds or l from the surface of the composite material part
am, especially 1.5. It is possible to reliably avoid cracks caused by thermal fatigue in the surface layer of the composite material when the composite material is formed over a depth of mm or more. Therefore, according to one detailed feature of the invention, the layer in which the area ratio of intermetallic compounds with L/D>3 is 30% or less relative to the total amount of intermetallic compounds is I n+m from the surface of the composite material part, Especially 1.5
It is formed over one or more depths.

Also, according to the results of experimental research conducted by the inventors of the present application,
If the volume fraction of the reinforcing material is too low, it will not be possible to sufficiently improve the wear resistance and adhesion resistance of the composite material part, and conversely, if the volume fraction of the reinforcing material is too high, it will cause wear of the mating material. The amount increases. Furthermore, if the volume fraction of the metal open compound is too low, the adhesion resistance of the composite material part cannot be sufficiently improved.
On the other hand, if the volume fraction of the intermetallic compound is too high, the composite material portion becomes extremely brittle, making it difficult to ensure the strength of the composite material portion. According to another detailed feature of the invention, therefore, the volume fraction of the reinforcement is set between 3 and 50%, and the volume fraction of the intermetallic compound is set between 5 and 60%.

Also, according to the results of experimental research conducted by the inventors of the present application,
In order to improve the strength, wear resistance, and adhesion resistance of the composite material part, it is preferable that the ratio of acicular intermetallic compounds among the intermetallic compounds be higher than lower. According to yet another detailed feature of the invention, therefore, L/
A region in which the area ratio of the intermetallic compound with D>3 is 20% or more, preferably 40% or more of the total amount of the intermetallic compound is provided in the composite material part.

Also, according to the results of experimental research conducted by the inventors of the present application,
It is preferable that the intermetallic compounds are dispersed as uniformly as possible, and the average value of the shortest distance between the intermetallic compounds is 100
The average value of the shortest distance between intermetallic compounds is preferably 3 μm or more, particularly 5 μm or more in order to avoid embrittlement of the matrix. According to yet another detailed feature of the invention, therefore, the average value of the shortest distances between the intermetallic compounds is set between 3 and 100 μm, particularly between 5 and 50 μm.

Also, according to the results of experimental research conducted by the inventors of the present application,
The intermetallic compound may be an intermetallic compound of Al and any of the above-mentioned metal elements, but it is particularly preferable that the intermetallic compound has a Vickers hardness of 300 or more, and that it is lower than the hardness of the reinforcing material. preferable. Therefore, according to yet another detailed feature of the invention, the Vickers hardness of the intermetallic compound is set to a value of 300 or more and lower than the hardness of the reinforcing material.

Furthermore, according to the results of experimental research conducted by the inventors of the present application,
When the intermetallic compound is granular, its maximum particle size is 50
It is preferred that the intermetallic compound is acicular in length, preferably 30 μm or less, and the maximum length is 100 μm or less.
It is preferably 50 μm or less, particularly 50 μm or less.

Note that the reinforcing material in the casting of the present invention may be made of a pressure material that has been conventionally used in the production of composite materials, but the reinforcing material is excellent in the effect of improving wear resistance, high LA stability, etc. Preferably, it is made of ceramic.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will be explained in detail below by way of example embodiments with reference to the accompanying figures.

Example 1 Alumina short fibers (95% AI 203.5% 5I02, ICI
[Saphir RFJ and Nl powder (purity 99%) with a particle size of 3 to 7 μm were mixed into a colloidal silica aqueous solution at a weight ratio of 5.6:8.9, and this was thoroughly stirred. By performing suction molding, three molded bodies 10 as shown in FIG. 1 were formed. In this case, the molded body has an outer diameter of 9
It has a cylindrical shape with a diameter of 5+ cm, an inner diameter of 89 mm, and a height of 20 mm, and the volume ratio of alumina short fibers and N1 powder is 10 each.
%, 5%, and these were substantially uniformly mixed with each other.

Next, after preheating each molded body to 400°C in nitrogen gas, each molded body 10 is press-fitted into a mold cavity 16 of a mold 14 of a high-pressure casting device 12 at a temperature of 400°C, as shown in FIG. 750℃, 800℃, 850℃ aluminum alloy (JIS standard AC8A, 12%S1.1%Cu
s 196 M g s1%Nl, remainder substantially AI)
molten metal 18 is poured, and the molten metal is poured into 1
The pressure was increased to 000 kg/C-, and the pressurized state was maintained until the molten metal completely solidified.

Each casting thus formed is then removed from the mold,
By performing machining on these castings, as shown in FIG. 3) to 2
Formed one by one. A portion 22a made of a composite material reinforced with realumina short fibers was present in the radial outer circumferential surface of each test piece in a depth range of 2+m.

Next, we investigated the structure of the composite material part of one of the test specimens in each set, and found that it was formed by the N1 powder contained in the original compact reacting with Al in the matrix aluminum alloy during high-pressure casting. intermetallic compound N
I At ] was found to be finely dispersed in the aluminum alloy, and the volume fraction of the intermetallic compound formed in the composite material portion of each test piece was about 27%. When these intermetallic compounds were investigated in more detail, it was found that the morphology of the intermetallic compounds differed depending on the temperature of the molten aluminum alloy during high-pressure casting.

Figures 4 and 5 show the metallographic structure of the cross section of the composite material parts of test pieces No. 1 to 3, which were formed by setting the temperature of the molten aluminum alloy to 750°C, 800°C, and 850°C, respectively. It is an optical micrograph shown at 400 times magnification. In these figures, the white to gray island-like or granular parts are the N j-A I intermetallic compound parts, and the black rod-like or round parts are the alumina short fibers.

Comparison of these figures 4 to 6 shows that the form of the intermetallic compound formed depends on the fH degree of the matrix molten metal, and the higher the molten temperature, the more granular the form of the intermetallic compound. It can be seen that it changes to a needle shape. In addition to the above-mentioned temperature of the molten metal, it is recognized that factors that influence the form of the intermetallic compound include the temperature of 13 degrees of the mold and the preheating temperature of the compact.

Next, the other test piece N051 that was not subjected to the structure investigation
~3. Each specimen was heated with acetylene in Svarna for 40 minutes.
By heating to 0°C and then water quenching, a thermal shock test using a cold/heat cycle as shown in Fig. 7 is carried out for 500 degrees.
I went to the cycle.

The results are shown in FIG.

From Figure 8, no cracks have occurred in test specimens No. 1 and 2, while cracks have already occurred in test specimen No. 3 at the 50th cooling/heating cycle. It can be seen that the length of the crack increases as the heating and cooling cycle increases.

The results of this thermal shock test show that even when substantially the same amount of intermetallic compounds are dispersed in the matrix of a composite material, the thermal shock properties differ greatly depending on the form of the intermetallic compound, and It can be seen that the thermal shock resistance is high when the compound is granular, and the thermal shock resistance is low when the intermetallic compound is acicular.

Furthermore, the composite material shown in Fig. 5 contains granular intermetallic compounds and acicular intermetallic compounds, and test pieces No. 2 containing the metallographic structure shown in Fig. 5 showed no cracks. Judging from the fact that acicular intermetallic compounds are not generated, it can be seen that the presence of acicular intermetallic compounds is not completely unacceptable, and it is only necessary to suppress the ratio to a predetermined value.

Example 2 From the test results of Example 1 above, it was found that the ratio of acicular intermetallic compounds present in the matrix of the composite material is important. A test was conducted to examine the effect on the thermal shock characteristics of

First, the same molded body as in Example 1 was formed, and the temperature of the molten aluminum alloy (JIS standard AC8A) as a matrix during high-pressure casting was 8409C, 830C, 8C.
Example 1 above, except that the temperatures were set at 20°C and 810°C.
Castings were manufactured in the same manner and under the same conditions as in the case of Example 1, and thermal shock test pieces Nos. 4 to 7 were formed from each casting.

Next, test piece numbers 1 to 3 formed in Example 1 and test piece Nos. formed in this example.

Ten fields of view of the cross sections of the surface of composite material parts 4 to 7 were each observed with an optical microscope, and when the length of the intermetallic compound NiAl3 is L and the width is D, the intermetallic compound with L/D>3 was examined with a needle. As the acicular intermetallic compound, the area ratio of the acicular intermetallic compound to the total amount of intermetallic compound is 41 for each field of view.
1j was determined. The results are shown in Table 1 below.

Table 1 No. Molten metal temperature Area ratio of acicular intermetallic compound 1
850℃ 60% 4 840℃ 50% 5 830℃ 40% 6 820℃ 30% 7 810℃ 25% 2 800℃ 20% 3 750℃ 0% From Table 1, the lower the temperature of the molten aluminum alloy, the lower the temperature of the molten aluminum alloy. It can be seen that the proportion of acicular N l-A I intermetallic compounds formed in the matrix of the composite material decreases as the temperature increases.

Next, test piece No. formed in this example.

A thermal shock test was conducted on Samples 4 to 7 in the same manner and under the same conditions as in Example 1. The results are shown in FIG.

From Figure 8, if the area ratio of acicular intermetallic compounds with L/D > 3 exceeds 30%, the thermal shock characteristics of the composite material deteriorates, and therefore, in order to improve the thermal shock resistance of the composite material, It can be seen that the area ratio of the acicular intermetallic compound is preferably 30% or less.

Example 3 Instead of the N1 powder in Example 1 above, an average particle size of 10
Example 1 described above except that TI powder with an average particle size of 3 μm, Cr powder with an average particle size of 3 μm, FB powder with an average particle size of 3 μm, Cu powder with an average particle size of 1° μm, and Ta powder with an average particle size of 5 μm were used. A molded body is formed in the same manner and under the same conditions as in the case of
For each compact, castings were produced in the same manner as in Example 2 by setting the temperature of the molten aluminum alloy to various values, and two thermal shock test pieces were formed from each casting.

Next, one of the test pieces in each set was investigated for the type of intermetallic compound in the same manner as in Example 1, and it was found that TI was present in the aluminum alloy as a matrix.
At 3 , Cr At 7 , FeAl 3 , C
It was observed that u Al 2 and Ta Al 3 were finely dispersed. In addition, the area ratio of acicular intermetallic compounds with L/D > 3 was measured on the surface of the composite material part of each test piece, and the other of each pair of test pieces was further measured in Example 1.
A thermal shock test was conducted under the same procedure and conditions as in the case of .

The results of this test are shown in FIG. In FIG. 9, each element symbol indicates the element of the powder used to form the intermetallic compound.

From Figure 9, regardless of the type of intermetallic compound generated in the matrix of the composite material, the heat resistance of the composite material increases when the area ratio of acicular intermetallic compounds with L/D > 3 is 30% or less. It can be seen that impact resistance can be improved.

Example 4 A cylindrical molded body having an outer diameter of 95 mm, an inner diameter of 73 mm, and a height of 2 inffl was formed by the same suction molding method as in Example 1 described above. The alumina short fibers and N1 powder used were the same as those used in Example 1, and their volume fractions were the same as in Example 1.

Next, after preheating each molded body to 400°C in nitrogen gas, each molded body is placed in a mold of a high-pressure casting machine, and an aluminum alloy (JIS standard AC8
The molten metal A) was poured and high-pressure casting was performed in the same manner and under the same conditions as in Example 1. In this case, the temperature of the mold is 40
0℃, 350℃, 300℃, 250℃, 200℃, 15
The temperature was set at 0°C and 100°C, and castings were manufactured under each condition.

Next, the castings formed by setting the temperature of the mold at various values as described above were taken out from the mold, and the same as in Example 1 was carried out.
Thermal shock test piece No. of size and shape.

8 to 14 were formed by machining. The portion of each test piece within a depth of 10IIffl from the radial outer circumferential surface was made of a composite material reinforced with alumina short fibers.

Next, when the cross section of the composite material of each test piece was investigated, it was recognized that the form of the N i-A I intermetallic compound generated in the composite material differed depending on the temperature of the mold during manufacturing the casting. L/D generated in the surface matrix of the composite material part of each specimen thus formed
The area ratio of the acicular intermetallic compound with >' 3 is 30%.
Table 2 below shows the relationship between the width of the structure (hereinafter referred to as X structure) and the temperature of the mold.

Table 2 No. Mold temperature (°C) X Width of structure (++un
)9 B50 0.5 10 300 1,0 11 250 1,5 14 1,00 4 From Table 2, when the temperature of the mold is 400°C, the width of the It can be seen that when the temperature of is below 350°C, the width of the X structure gradually increases as the temperature of the mold decreases.

Next, a thermal shock test was conducted on each test piece No. 8 to 14 in the same manner and under the same conditions as in Example 1. The results are shown in FIG.

From Figure 10, in order to improve the thermal shock properties of the composite material part, the width of the X structure from the surface of the composite material part should be 1 mm.
5, it can be seen that it is particularly preferable that it is 1.5m+n or more.

Furthermore, from the results of Examples 2 and 3 mentioned above, it is known that the smaller the area ratio of the needle-like intermetallic compound, the better the thermal shock resistance of the composite material. It is clear that even in a composite material having a structure in which the area ratio of the intermetallic compound is less than 30%, good thermal shock resistance can be ensured as long as the width of the structure is within the above range.

Example 5 The procedure and conditions were the same as in Example 4, except that the types and weight ratios of fibers and powder in the molded body of Example 4 were changed as shown in Table 3 below. A thermal shock test was conducted on each casting in the same manner and under the same conditions as in Example 4. In all cases shown in Table 3, the volume fraction of fiber and powder in the compact is 1026.5%, the particle size of each powder is 10 μm or more, and the purity is 99% or more. there were. In addition, when the fibers were stainless steel staple fibers and cast iron staple fibers, the compacts were formed by compression molding.

Table 3 313 N4 short fiber” C.

Short carbon fiber 3 CrAl 20
3 Si 02 short fiber”M.

Glass fiber 5) Mn Mineral fiber 5mm V Stainless steel short fiber 7) TI Cast iron short fiber θ] Zr Note: 1) β-3i C, average fiber diameter 10μ12mm
β-313N4, fiber diameter 0.2-3) Bread type, fiber diameter 12 μm 1 average fiber 4) 47% Al2O3, 53% 5iO5 E glass, average fiber diameter 10 μ115) 40% CaO 110% Mg
O1 remaining 7. Average fiber diameter 20 μm, average fiber length B) Average fiber diameter 30 μm, average long fiber/powder weight ratio 1:1.2B 1:1.40 1:2 1:1.96 1:1. 54 1:1.27 1:0.29 1:0.45, fiber length 2-3 μm chopped fiber 0.5 μm, average fiber length 100 μm fiber length 3 opening 1 chopped fiber 2, fiber diameter 2-3 μm, fiber length 2 ~3 +nn+average fiber length 5mm5 chopped fiber portion SI02, average fiber diameter 5μm, average fiber length 2~
In the case of both 3ram3city and chopped fiber 3mtas chopped fiber test specimens, it is possible to ensure good thermal shock resistance in the cast composite material part when the width of the X structure is lllll11 or more, especially 1.5mff1 or more. It was recognized that it could be done.

Although not shown in this example, even when the powder contained in the compact is Nb powder, Ta powder, Cu powder, or W powder, the width of the X structure is 1 ram or more, especially 1.5 m11.
It was recognized that the above is preferable.

Although the present invention has been described above in detail with respect to several specific embodiments in connection with the experimental research conducted by the inventors of the present application, the present invention is not limited to these embodiments. Instead, it will be apparent to those skilled in the art that various other embodiments are possible within the scope of the invention. For example, the shape of the casting in each of the above-mentioned embodiments is a disk shape, but the shape of the casting according to the present invention may be any shape, and the shape of the casting according to the present invention may be any shape.
The surface layer in which the area ratio of the intermetallic compound of /D>3 is 30% or less may be any specific part of the casting or the entire outer periphery of the casting.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing a cylindrical molded body made of short alumina fibers and Ni powder, Fig. 2 is an injection port showing high-pressure casting performed using the molded body shown in Fig. 1; The figure is a partially cutaway perspective view of a thermal shock test piece formed from a casting obtained by high-pressure casting shown in Fig. 2, and Figs. 4 to 6 are each shown in Fig. 2. During high-pressure casting, the temperature of the molten aluminum alloy was set at 750°C and 800°C.
Optical micrograph showing the metallographic structure of a cross section of a cast composite material formed by setting the temperature to 50°C at 400x magnification;
Figure 7 is a graph showing the cooling and heating cycles in the thermal shock test, Figure 8 is a graph showing the results of the thermal shock test with the number of cooling and heating cycles on the horizontal axis, and Figure 9 is the graph showing the results of the thermal shock test at L/D.
A graph showing the area ratio of acicular intermetallic compounds with L/D>3 on the horizontal axis, and Figure 10 shows the results of the thermal shock test when L/D>3.
It is a graph showing the width of a structure in which the area ratio of acicular intermetallic compounds is 30% on the horizontal axis. 10... Molded body, 12... High pressure casting device, 14...
・Mold, 16...Mold cavity, 18...Aluminum alloy meltability, 20...Plunger, 22
...Thermal shock test piece, 22a... Part made of composite material Applicant: Toyota Motor Corporation representative
Patent Attorney Masaaki Akai Ratio ('/,) Fig. 1Q Width of X tissue (mml

Claims (1)

[Claims] The aluminum alloy casting has a composite material part having an aluminum alloy as a matrix and short fibers or whiskers as a reinforcing material, and at least a part of the surface is defined by the composite material part, and the matrix contains Al and Fe,
Ni, Co, Cr, Cu, Mn, Mo, V, W, Ta,
An intermetallic compound with at least one metal element selected from the group consisting of Nb, Ti, and Zr is finely dispersed, and the length of the intermetallic compound is Letting the length and width be L and D, respectively, L/
An aluminum alloy casting in which the area ratio of intermetallic compounds with D>3 is 30% or less based on the total amount of intermetallic compounds.