JPH10204555A - Production of grain refiner for casting aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grain refiner functioning, without requiring holding time, as solidification nuclei immediately after addition to a molten to produce a grain refining effect, capable of easily preparing grains of fine grain size increased in a grain refining effect, and excellent in dispersibility into the molten metal. SOLUTION: The grain refiner has a composition containing heterogeneous solidification nuclei grains acting as solidification nuclei at the time of casting of a casting aluminum alloy and having the balance essentially aluminum. This grain refiner can be produced by solidifying a molten aluminum alloy, containing at least titanium in an amount of >10 to <40wt.% as a constituent of the heterogeneous solidification nuclei grains, by liquisol quenching into a solid solution, applying heat treatment to this solid solution, and forming at least titanium aluminide grains as the heterogeneous solidification nuclei grains by precipitation from a solid phase.

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 grain refiner for an aluminum casting alloy, and more particularly to a method for producing an aluminum casting alloy, which comprises foreign solidification nucleus particles which act as solidification nuclei during casting of an aluminum casting alloy, with the balance being substantially the same. The present invention relates to a method for producing a grain refiner comprising aluminum.

[0002]

2. Description of the Related Art In cast aluminum alloys, it is widely used to add a grain refiner to molten metal during casting in order to improve mechanical properties and castability. As a crystal grain refiner, an Al-Ti base alloy disclosed in Japanese Patent Application Laid-Open No. 2-504404 is known. This refining method using a refining agent involves adding an Al-Ti-based master alloy having a specific composition to a molten Al at the time of casting, and adding a specific amount of carbon or nitrogen to the molten aluminum. Titanium aluminide (Al ₃ Ti) or titanium carbonitride (TiC)
Heterogeneous solidification nucleus particles composed of an N) -based compound are precipitated from a liquid phase, and the nuclei are used as nuclei to crystallize fine crystals, thereby refining the crystal grains of the cast structure. A method using an Al-Ti-B-based master alloy as a crystal grain refiner is also known.

[0003] Such a master alloy type refining agent is prepared by casting Al ₃ Ti, TiCN, TiC, TiB in an Al melt at the time of casting.
It is necessary to precipitate heterogeneous coagulation nucleus particles such as ₂ from the liquid phase. Therefore, in order to exhibit a refining effect, a certain holding time (contact time) is required after the addition of the refining agent until solidified nucleus particles are generated in the molten metal to become stable particles. Generally, the holding time is optimally about 10 to 15 minutes. If the retention time exceeds this optimal time,
Due to the overreaction between the solidified nucleus particles and the molten metal, another product is formed on the surface of the particles, or the particles are aggregated, and the effect of reducing the size of the particles is lost as the retention time elapses.

[0004] In general, the finer the heterogeneous solidification nucleus particles, the higher the crystal grain refining effect. However, in the method using the conventional master alloy, it is necessary to control the precipitation reaction from the liquid phase in the molten metal. In practice, it is extremely difficult to control the particle size of the solidified nucleus particles. Further, from the viewpoint of minimizing the influence of the addition of the grain refiner on the original composition of the aluminum casting alloy, and from the viewpoint of facilitating uniform addition to the molten metal, the addition amount is desirably as small as possible. It is desirable that the refining agent contains the constituent components of the coagulation nucleus particles at a concentration as high as possible. However, in the conventional Al-Ti base alloy, the upper limit of the Ti content is about 15% by weight, and practically the upper limit is about 10% by weight due to restrictions of the melting temperature and gravity segregation.

[0005] As described above, there are various problems with the master alloy type grain refiner, and attempts have been made to directly add foreign solidified nucleus particles such as TiC particles as a powder to a molten metal. The dispersibility (stirring property) in the molten metal becomes worse, and the production and handling of the fine particle powder itself becomes difficult. Therefore, there is a limit to the improvement of the crystal grain refining effect.

[0006]

SUMMARY OF THE INVENTION The present invention provides a crystal grain refining effect by functioning as a solidification nucleus immediately without adding a holding time after addition to a molten metal, and has a high crystal grain refining effect. An object of the present invention is to provide a crystal grain refining agent which can easily produce heterogeneous solidification nucleus particles having a fine particle diameter and has excellent dispersibility in a molten metal.

[0007]

In order to achieve the above object, a method for producing a grain refining agent of the present invention comprises a method of manufacturing a cast aluminum alloy, comprising the steps of: Is a method for producing a grain refiner substantially consisting of aluminum, wherein an aluminum alloy melt containing at least titanium as a component of the heterogeneous solidification nucleus particles is solidified by a liquid quenching method to form a solid solution. It is characterized by producing at least titanium aluminide particles as the above-mentioned heterogeneous solidification nucleus particles by heat treatment and precipitation from a solid phase.

The grain refiner produced by the method of the present invention is an aluminum alloy in which heterogeneous solidification nucleus particles are dispersed in an aluminum matrix. Therefore, when it is added to a molten aluminum casting alloy, the aluminum in the matrix becomes molten. In addition to dissolving easily in the aluminum matrix, the heterogeneous solidified nucleus particles already existing as dispersed particles in the aluminum matrix are immediately dispersed in the molten metal and function as solidified nucleus particles. Unlike the agent, a holding time for forming solidified nucleus particles after addition in the melt is not required. Further, there is no problem that the dispersibility of the fine particles in the molten metal is reduced, which is inevitable when the powder is added as a conventional powder.
Furthermore, in the method of the present invention, the components of the heterogeneous solidification nucleus particles are forcibly dissolved in an aluminum matrix by rapid solidification by a liquid quenching method. Since the inevitable restrictions from the dissolution temperature and gravity segregation are greatly reduced, the solidification nucleus constituent component can be contained at a high concentration which could not be achieved conventionally. In addition, since the solid solution is heat-treated to generate heterogeneous coagulated nucleus particles by precipitation from the solid phase, the particle size of the precipitated particles can be easily controlled by simply setting the heat treatment conditions (basically temperature and time). Can be obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method of the present invention, a molten aluminum alloy containing constituents of foreign solidified nucleus particles is solidified by a liquid quenching method to form a solid solution. This solid solution is usually in the form of a thin strip or ribbon.
It is desirable that the molten aluminum alloy to be rapidly quenched contains 10 wt% or more of titanium as a constituent component of the foreign solidified nucleus particles. As described above, in the conventional master alloy type, the titanium content is 10% due to restrictions on the melting temperature and gravity segregation.
Since wt% was the upper limit for practical use, there was a limit in increasing the concentration. The present invention can reduce the amount of the refiner by adding titanium at a high concentration of more than 10% by weight, exceeding the conventional restriction, so that the influence on the original composition of the cast alloy can be extremely reduced. And uniform addition to the cast alloy melt is facilitated. On the other hand, as the content of the heterogeneous coagulation nucleus component increases, the refining effect increases, but at the same time, the viscosity in the molten state increases, and it becomes impossible to form a thin strip or ribbon stably by the liquid quenching method.
From this viewpoint, it is desirable that the titanium content of the aluminum alloy melt to be quenched by liquid is less than 40 wt%.

[0010] The aluminum alloy melt to be quenched by liquid is
In addition to titanium having the above-mentioned content, it is desirable to further contain at least one of 8 wt% or less of boron and 10 wt% or less of carbon as a constituent component of the foreign solidified nucleus particles. When the solid solution obtained by the liquid quenching method contains only titanium as a component of the heterogeneous solidification nucleus particles, titanium aluminide (Al ₃ Ti) is formed as the heterogeneous solidification nucleus particles by heat treatment.
Particles are generated, and the effect of refining the crystal grains of the aluminum casting alloy can be obtained. When boron (B) or carbon (C) is further contained in the above content range in addition to titanium, the crystal grain refinement effect is further improved. Although the reason has not been completely elucidated yet, if boron or carbon is present in addition to titanium, the heat treatment of the solid solution causes Al ₃ Ti
It is presumed that, in addition to the particles, particles of titanium boride (TiB ₂ ) or titanium carbide (TiC) are also generated, and both of them effectively act as heterogeneous coagulation nucleus particles.

The stability of TiB ₂ particles and TiC particles in a molten aluminum alloy is higher than that of Al ₃ Ti particles. For example, even if the TiC particles are kept in the molten metal for about one hour, they do not grow or disappear and remain. This means that the action as a coagulation nucleus is maintained extremely stably. The Al ₃ Ti particles decompose and disappear within a few minutes when held in the molten aluminum casting alloy. However, since the heterogeneous coagulation nucleus particles function immediately after the addition of the grain refiner of the present invention, a sufficient refining effect can be obtained by performing casting within several minutes after the addition. However, it is still more preferable in practical operation that there is sufficient time from addition to casting.

[0012] In view of the above, at least one of the aluminum alloy molten metal in addition to Ti B and C to the liquid quenching is contained at a content within the specified range, in addition to Al ₃ Ti particles by heat treatment of a solid solution Preferably, at least one of TiB ₂ particles and TiC particles is generated. Since the above-mentioned effects are observed even when B and C are considerably small, the lower limits of the contents thereof are not particularly defined. The higher the content of B and C, the greater the effect of improving the grain refinement. However, as in the case of Ti, if the content is too large, the viscosity in the molten state becomes high. The ribbon cannot be formed stably. From this point of view, B of the aluminum alloy
It is desirable that the content be 8 wt% or less and the C content be 10 wt% or less.

In the method of the present invention, the solid solution formed by quenching the liquid is made of Al ₃ T having a crystal grain refining action.
In order to precipitate particles such as i,
Heat treatment at a temperature in the range of 0 ° C. Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

[0014]

(Preparation of grain refiner)

(1) Preparation of ribbon by liquid quenching method An aluminum alloy having a composition indicated as a refining agent composition in Table 1 was melted by arc melting and cast to prepare an ingot.

As shown in Table 1, the composition of each ingot contains Ti in a content within a desirable range of the present invention in all of Examples 1 to 6, and in addition to Ti, Example 2 contains B in addition to Ti. , Examples 3 and 5 each contain C at a content within the desirable range of the present invention. The ingot of Comparative Example 2 had a Ti content higher than the desirable range of the present invention, and Comparative Example 3
The ingots have a Ti content less than the desired range of the present invention.

These ingots were subjected to a single-roll type liquid quenching apparatus shown in FIG. 1 to obtain a width of 1 to 2 mm and a thickness of 10 to 2 mm.
An aluminum alloy ribbon (ribbon) of 0 μm was obtained. However, Comparative Example 2 was 40 wt%, which was more than the desirable range of the present invention.
, The viscosity of the molten metal was increased, and the liquid quenching apparatus used in this example could not produce a good ribbon.

The obtained rapidly solidified ribbon is represented by X
As a result of X-ray diffraction (XRD), Al ₃ Ti (Example 1)
-6, Comparative Example 3), TiC (Examples 3, 5), TiB ₂
(Example 2) was found to be contained. On the other hand, observation of the structure with a transmission electron microscope shows that Al ₃ T
Only i particles were observed, and neither TiC particles nor TiB ₂ particles were observed. From this result, it is considered that Ti, C, and B exist as undissolved compound particles in the ribbon after the liquid quenching, but the amount is small and the particle size is extremely fine. Therefore, the ribbon in the rapidly solidified state may be considered to be substantially a solid solution, and is referred to as a solid solution in this specification.

(2) Precipitation heat treatment The ribbon obtained by the above-mentioned liquid quenching is subjected to A in an electric furnace.
The mixture was heated to 450 ° C. at a rate of 5 ° C./min in an r gas atmosphere to uniformly precipitate heterogeneous solidification nucleus particles such as Al ₃ Ti particles in an Al matrix. Differential scanning calorimetry (DSC)
As a result of the analysis, it was found that the exothermic reaction considered to correspond to the precipitation reaction started around 360 ° C. in the heating process and ended around 550 ° C. in any of the samples. Once 36
If the temperature is raised to 0 ° C., a precipitation reaction can be caused, so that the heat treatment temperature may be in the range of 350 ° C. to 550 ° C.

The structure of each sample after the heat treatment was observed by a transmission electron microscope (TEM). Examples of the observed tissue are shown in FIGS. FIG. 2 shows Al-20 wt% Ti
Table 1 shows the structure of the refiner of Example 1 in Table 1 and it can be seen that only Al ₃ Ti particles having a particle size of about 0.2 μm or less are uniformly dispersed in the Al matrix. FIG. 3 shows the structure of the refiner of Example 3 having a composition of Al-20 wt% Ti-6 wt% C, wherein the particle size is 1-2.
It can be seen that relatively large particles of about μm and much finer particles having a diameter of the order of 0.1 μm are uniformly dispersed. Although the composition of the particles could not be identified for each particle size, it is presumed that relatively large particles would be TiC particles and fine particles would be Al ₃ Ti particles.

(3) Casting Al-4.
An aluminum casting alloy having a composition of 5 wt% Cu was cast. As shown in FIG. 4, Al-4.5 wt% Cu
The alloy was heated and melted at 730 ° C. in a graphite crucible, a grain refiner was added, and the mixture was stirred for 3 minutes with a stirring pedal, and then placed in a stainless steel mold having an effective cavity shape shown in FIG. Cast into. The addition amount of each refining agent was set so that the Ti content in the alloy composition after casting was all unified to 0.15 wt%. The cast structure was observed with an optical microscope on a cross section (hatched surface in FIG. 5) passing through the center of the obtained cast material, and the crystal grain size was measured.

As shown in the rightmost column of Table 1, the crystal grain size was 1.50 mm when no refiner was added (Comparative Example 1).
In contrast, the addition of the grain refiner of the present invention significantly reduced the size to 0.05 to 0.11 mm. FIG. 6 shows a cast structure in the case where no refiner was added (Comparative Example 1), and FIG. 7 shows Al-20 wt% T according to the present invention.
The casting structure in the case of adding a refiner of i-6 wt% C (Example 3) is shown.

It can be seen that this refining effect tends to increase as the Ti concentration of the refining agent increases, and that the refining effect is further improved by the simultaneous addition of C or B. As described above, the Ti content of the cast material was unified to 0.15 wt%.
For example, when Example 1 and Example 4 are compared, the latter is higher as the Ti concentration of the refining agent, but in any of the examples, only the Al ₃ Ti particles exist as heterogeneous coagulation nucleus particles, The same amount of Al ₃ Ti particles
It is considered that it was added to the 4.5 wt% Cu alloy melt.
Nevertheless, the refining agent of Example 4 having a higher Ti concentration than Example 1 has a higher refining effect. This is because the refining agent of Example 1 having a low Ti concentration is T
In order to supply the same amount of Ti as in Example 4 having a high i-concentration to the molten metal, the addition amount as a refining agent increases, so that the original composition of the Al-4.5 wt% Cu alloy to which the refining agent is added is added. It is considered that the effect is larger and the dilutability and the stirring property in the molten metal are relatively reduced.

Al ₃ Ti particles, TiC particles and TiB
_{2 Although} the interaction with the particles is not clear, Examples 2 and 3, in which the refiner further contains C or B in addition to Ti as compared with Example 1 in which the refiner only contains Ti,
In No. 5, the miniaturization effect is clearly improved. If C or B exists in addition to Ti, TiC or TiB
_In addition to the possibility that ₂ directly acts as a foreign coagulation core particle,
It is also conceivable that TiC, TiB ₂ or C, B may promote nucleation of Al ₃ Ti.

As the Ti content of the refining agent increases, the effect of refining the crystal grains increases, but at the same time, the melting point of the alloy increases and the viscosity in the molten state increases. It becomes difficult to produce ribbons by the method.
In the range of the liquid quenching method performed in this example, the ribbon could not be formed in Comparative Example 2 in which the Ti concentration was 40 wt% Ti. Conversely, when the Ti concentration of the refining agent is reduced, the amount of the refining agent added increases in order to obtain a high refining effect. The properties and agitation properties are also reduced, and the miniaturization effect is reduced accordingly. Ti concentration of refining agent is 10
In Comparative Example 3 in which the content was wt%, the solubility in the molten cast alloy was poor, and a part thereof remained unmelted. For these reasons, in the grain refiner of the present invention, it is desirable that the Ti content be more than 10 wt% and less than 40 wt%.

As for C and B, the effect of increasing the crystal grain refining effect is recognized as described above by coexistence with Ti even in a small amount in the range where the present inventors have conducted experiments, and the lower limit is particularly set for the content. There is no reason. The upper limits of the contents of C and B were set for the same reason as the upper limit of the Ti content. In addition, a mother alloy type refining agent (for example, KB Alloy
As a result of casting an Al-4.5 wt% Cu casting alloy under the same conditions as in the above (3) using an Al-5Ti-1B refining agent manufactured by Co., Ltd., the average grain size of the cast structure was 0.12 mm. Met.
This is slightly inferior to the 0.11 mm of Example 6 having the lowest miniaturization effect among the examples shown in Table 1. According to the present invention, as shown by 0.05 to 0.08 mm in Examples 1 to 5, it can be seen that a high refining effect far exceeding the conventional commercial refining agent can be obtained.

The grain refiner of the present invention is also very effective as a dispersion enhancer. That is, the cast material cast by adding the refiner of the present invention is a dispersion-strengthened Al alloy in which heterogeneous solidification nucleus particles finely and uniformly dispersed in an Al alloy matrix function as reinforcing particles. The reinforcing particles are made of Al by the addition of a conventional master alloy type refiner or powder.
Since the particles can be made much finer than the particles that can be introduced into the alloy, the dispersion strengthening action can be greatly increased as compared with the conventional case.

[0027]

[Table 1]

[0028]

As described above, according to the present invention,
It functions as a solidification nucleus immediately without requiring a holding time after being added to the molten metal, expresses the effect of crystal grain refinement, and easily produces heterogeneous solidified nucleus particles having a fine grain size with a high crystal grain refinement effect. The present invention provides a crystal grain refining agent which is excellent in dispersibility in a molten metal.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a single-roll type liquid quenching device.

FIG. 2 is a micrograph (TEM photograph) showing the structure of a crystal grain refiner (Al-20 wt% Ti) produced by heat-treating a solid solution according to the present invention.

FIG. 3 is a grain refiner (Al-20 wt% Ti-6 wt% C) prepared by heat-treating a solid solution according to the present invention.
5 is a micrograph (TEM photograph) showing the structure of Example 1.

FIG. 4 is a sectional view showing an apparatus for adding a crystal grain refiner to a molten aluminum casting alloy and stirring the molten metal.

FIG. 5 is a perspective view (perspective view) showing the shape of a cast material of an aluminum casting alloy.

FIG. 6 shows Al-casted without adding a refining agent.
It is a microscope photograph (optical microscope photograph) which shows the cast structure of a 4.5Cu alloy.

FIG. 7 shows Al-20 wt% Ti-6 according to the present invention.
Al-4.5Cu cast with the addition of a wt% C refiner
It is a microscope photograph (optical microscope photograph) which shows the casting structure of an alloy.

Claims (4)

[Claims] 1. A method for producing a grain refiner comprising foreign solidified nucleus particles which act as solidification nuclei during the casting of an aluminum casting alloy and the balance substantially consisting of aluminum, comprising: An aluminum alloy melt containing at least titanium as a component is solidified by a liquid quenching method to form a solid solution, and this solid solution is heat-treated to form at least titanium aluminide particles as the above-mentioned heterogeneous solidification nucleus particles by precipitation from a solid phase. A method for producing a grain refiner for cast aluminum alloy. 2. The aluminum according to claim 1, wherein the molten aluminum alloy contains more than 10% by weight and less than 40% by weight of titanium as a component of the heterogeneous solidification nucleus particles, and the balance substantially consists of aluminum. A method for producing a grain refiner for a cast alloy. 3. The molten aluminum alloy further comprises at least one of 8 wt% or less of boron and 10 wt% or less of carbon as a component of the heterogeneous solidification nucleus particles in addition to the titanium. A method for producing a grain refiner for an aluminum casting alloy according to claim 2. 4. The method for producing a grain refiner for an aluminum casting alloy according to claim 1, wherein the heat treatment is performed at a temperature of 350 to 550 ° C.