Method Of Refinement Of Microstructure Of Metallic Materials

Abstract

The present invention provides a method for refining microstructure of metallic materials and the present invention relates to a method in which cavitation (cavities) is formed in molten metal by the application of high-energy vibrating force to a metal in the process of solidification, and the newly formed solid crystal particles are crushed by the impact pressure generated during the collapse of the cavities to refine the microstructure of the material, and high-energy electromagnetic vibrating force is applied to a solidifying metal sample 10 by the simultaneous imposition of an electric current and a magnetic field in an apparatus comprising an electromagnet 12 for applying a stationary magnetic field and an electrode 11 for passing an alternating current through the metal sample, so that the solid crystal particles are crushed into small pieces, yielding a fine microstructure thereof.

Description

DESCRIPTION OF THE INVENTION

[0001] This invention relates to a method for refining a microstructure of metallic materials. More particularly, the present invention relates to a method of refinement of microstructure of metallic materials characterized in that allows microstructure of metallic materials to be refined irrespective of the type of metal or refining agent, wherein high-energy vibration force such as electromagnetic vibrating force, ultrasonic vibrating force, or the like is applied directly to molten metallic materials. The present invention also relates to a method for refining solid metal particles by the above-described method to move them to a prescribed location.

BACKGROUND OF THE INVENTION

[0002] Methods for refining microstructure of metallic materials are broadly classified into two types such that methods in which refining agents are added to molten metallic materials to refine the microstructure of the metallic materials solidified, and methods in which the solid metallic materials are subjected to forming processes and heat treatments to refine the microstructure thereof.

[0003] Specifically, in the first group of the methods, refining agents act as nuclei for the solid metal crystal particles to be formed during solidification, yielding a refined microstructure that corresponds to the dispersion state of the refining agents, whereas in the second group of the methods, microstructures refined are obtained by recrystallization of the metals generated by heat treatments that follow forming processes such as rolling, extrusion, or the like.

[0004] In the methods of the first group, however, a close crystallographic relationship achieved between the refining agent and the solid-crystal particles is required in order to allow the refining agent to be effective, and it is impossible to obtain adequate refining agents for some types of metals.

[0005] In addition, the refined structure smaller than the particle size of the refining agent cannot be made.

[0006] In the methods of the second group, it is difficult to yield adequate refining because forming processes such as rolling, extrusion and the like are limited in their effects, and exceeding these limits causes fracture of the metal, and there is a tendency to cause metals recrystallized as well as metal particles enlarged as a result of the heat treatment that follows forming.

[0007] An urgent need therefore existed for developing a novel method for refining microstructure of metallic materials that would be able to solve the above-described problems of the conventional methods.

[0008] An objective of the present invention is to overcome these subjects.

ABSTRACT OF THE INVENTION

[0009] The present invention provides a method for refining microstructure of metallic materials.

[0010] The present invention relates to a method which comprises forming cavitation (cavities) in molten metal by the application of high-energy vibrating force to a metal in the process of solidification, and crushing the newly formed solid crystal particles by the impact pressure generated during the collapse of the cavities to refine the microstructure of the material. High-energy electromagnetic vibrating force is applied to a solidifying metal sample 10 by the simultaneous imposition of an electric current and a magnetic-field in an apparatus comprising an electromagnet 12 for applying a stationary magnetic field and an electrode 11 for passing an alternating current through the metal sample, so that the solid crystal particles are crushed into small pieces, yielding a fine microstructure thereof.

DETAILED DESCRIPTION OF THE INVENTION

[0011] Specifically, an objective of the present invention is to provide a novel method for refining microstructure of metallic materials that capable of refining the microstructure thereof irrespective of the type or composition of the metallic materials.

[0012] Another objective of the present invention is to provide a method for refining microstructure of metallic materials that facilitates refining even for metals that have been difficult to refine in the past.

[0013] Still another objective of the present invention is to provide a method for refining microstructure of metallic materials to move it to a prescribed location.

[0014] The following technological means are employed in the present invention, which is aimed at overcoming the aforementioned subjects.

[0015] (1) A method for refining microstructure of metallic materials, characterized in that comprises forming cavitation (cavities) in molten metal by the direct application of high-energy vibrating force such as electromagnetic vibrating force, ultrasonic vibrating force to the molten metal, crushing the resulting solid metal crystal particles into small pieces by the impact pressure generated during the collapse of the cavities, and yielding a refined microstructure thereof.

[0016] (2) The method for refining microstructure of metallic materials according to (1) above, wherein the high-energy vibrating force is applied during the solidification of said metal.

[0017] (3) The method for refining microstructure of metallic materials according to (1) or (2) above, wherein the high-energy vibrating force is applied to a metal in the process of solidification by the simultaneous imposition of an electric current and a magnetic field to said molten metal or solidifying metal.

[0018] (4) A method for refining microstructure of metallic materials, characterized in that comprises forming cavitation (cavities) in molten metal by the direct application of high-energy vibrating force such as electromagnetic vibrating force, ultrasonic vibrating force to the molten metal, crushing solid particles of other metals, intermetallic compounds, or the like dispersed in the molten metal as well as the solid metal formed during solidification into small pieces by the impact pressure generated during the collapse of the cavities, and yielding refined microstructure thereof.

[0019] (5) A method for refining microstructure of metallic materials, characterized in that comprises forming cavitation (cavities) in molten metal by the direct application of high-energy vibrating force such as electromagnetic vibrating force, ultrasonic vibrating force to the molten metal, crushing the solid particulate ceramics or other nonmetals dispersed in the molten metal as well as the solid metal formed during solidification into small pieces by the impact pressure generated during the collapse of the cavities, and yielding refined microstructure thereof.

[0020] (6) A method for refining solid metal particles formed during solidification to move them to a prescribed location by the simultaneous imposition of an electric current and a magnetic field on the molten metal in the process of final solidification.

[0021] (7) The method according to (6) above, wherein the solid metal particles formed during solidification are refined to shift them to a periphery of a tube by the simultaneous imposition of an electric current and a magnetic field on the molten metal in the process of final solidification.

[0022] (8) The method according to (6) above, wherein the solid particles of other metals, intermetallic compounds, or the like dispersed in molten metal as well as solid metal particles formed during solidification are refined to shift them to a periphery of a tube by the simultaneous imposition of an electric current and a magnetic field on the molten metal in the process of final solidification.

[0023] (9) The method according to (6) above, wherein the solid particulate ceramics or other nonmetals dispersed in molten metal as well as solid metal particles formed during solidification are refined to shift them to a periphery of a tube by the simultaneous imposition of an electric current and a magnetic field on the molten metal in the process of final solidification.

[0024] (10) The method according to (6) above, wherein the solid particles dispersed in molten metal are refined to move them to a location separated from the location of the initial dispersed state by the simultaneous imposition of an electric current and a magnetic field.

[0025] The present invention will now be described in detail.

[0026] The invention of this application is characterized in that the microstructure of metallic materials is refined by the direct application of high-energy vibrating force to them. In this case, it is important that electric current and magnetic field be simultaneously applied as the high-energy vibrating force, whereas applying the electric current or magnetic field alone has no significant effect on the fine microstructure of metallic materials. The reason is that the electromagnetic vibrating force is a Lorentz force that can only be generated when an electric current and a magnetic field are applied simultaneously.

[0027] Electromagnetic vibrating force and ultrasonic vibrating force are exemplified as specific examples of high-energy vibrating force, but these examples are not all-encompassing and include all other types of force capable of exerting high-energy vibrating force on molten metal in the same manner.

[0028] The high-energy vibrating force is applied to molten metal, in which case it is preferable for the high-energy vibrating force to be applied to solidifying metal.

[0029] As used herein, the term "molten metal" refers to a metal that is completely liquefied which kept at a temperature above its melting point. In addition, the term "solidifying metal" refers to a liquid metal containing solid metal crystals that form at a temperature below the melting point.

[0030] The present invention can be adequately applied, for example, to aluminum alloys such as Al--Si alloys or magnesium alloys, but a distinctive feature of the present invention is that it allows any refining agent or metal to be used, and that, in particular, there is no dependence on the type or composition of metal.

[0031] When high-energy vibrating force is applied to a solidifying metal in accordance with the above-described method, the microstructure thereof is refined by forming cavitation (cavities) in the molten metal and allowing the impact pressure generated during the collapse of the cavities to crush the resulting solid metal crystal particles into small pieces.

[0032] Because cavitation is induced while some of the metal is still in the molten state, not only the newly formed solid metal crystals but also the already existing solid metal particles are crushed by the application of high-energy vibrating force until the molten metal has completely solidified, making it possible to obtain a refined microstructure thereof.

[0033] A solidified microstructure of metallic materials can therefore be refined as well.

[0034] The high-energy vibrating force should be applied during (in the process of) solidification. It is difficult to form cavitation (cavities) when high-energy vibrating force is applied to metallic materials after solidification thereof, and therefore there is a possibility that the solid metal crystal particles will not be crushed.

[0035] In addition, in this invention, even metals that are difficult to refine by conventional methods can be readily refined because the refining effect of this invention by the high-energy vibrating force does not depend on the type or composition of the metal.

[0036] Silicon crystals as initially crystallized particles in a hypereutectic aluminum-silicon alloy, can, for example, be refined to a crystal particle diameter of 0.5-3.0 .mu.m by the method for refining microstructure of metallic materials through application of high-energy vibrating force in accordance with the present invention.

[0037] The present invention also allows solid particles of other metals, intermetallic compounds, or the like, as well as solid particulate ceramics or other nonmetals dispersed in molten metal to be crushed in the same manner as the solid metal formed during solidification

[0038] The method of the present invention allows, for example, 20- to 30-.mu.m silicon carbide particles dispersed in an aluminum alloy to be refined to a size of 0.1-2.0 .mu.m.

[0039] Another feature of the present invention is that the solid metal particles formed during solidification can be refined to move them to a prescribed location by the simultaneous application of electric current and magnetic field to the molten metal in the process of final solidification thereof. Specifically, the solid metal formed during solidification can be refined to shift it to the periphery of a cylindrical tube or container disposed such that the axial direction of the cylinder is orthogonal to the magnetic field; solid particles of other metals, intermetallic compounds, or the like, as well as solid particulate ceramics or other nonmetals dispersed in molten metal can be shifted in the same manner as the solid metal formed during solidification to the periphery of a cylindrical tube or container disposed in the same manner as the solid metal; and the aforementioned solid particles can be refined to move them to a separate location the inside tube or container from the location of the initial dispersed state. Another specific feature is that the shifting locations can be concentrated in the end portion of a sample by moving the sample within the magnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG. 1 is a schematic view illustrating an example of an apparatus suitable for implementing the present invention.

DESCRIPTION OF MARKS

[0041] 10 metal sample [0042] 11 electrode [0043] 12 electromagnetic coil

EXAMPLES

[0044] The present invention will now be described in detail through examples thereof, but the present invention is not limited by these examples.

[0045] FIG. 1 shows an example of the apparatus for implementing the present invention. In the drawing, 10 is a metal sample, 11 is an electrode disposed in contact therewith, and 12 is an electromagnetic coil disposed such that it envelops the metal sample.

[0046] When an alternating current of about 80 A is passed through the metal sample via the electrode, the metal sample is melted by Joule heat generated, and the temperature of the metal sample reaches a prescribed temperature. The temperature of the molten metal sample is then lowered and solidification of the metal sample is started by reducing the electric current. An electromagnetic vibrating force based on the alternating current and a stationary magnetic field is created by the application of a stationary magnetic field of 1.4 T (Tesla) through the intermediary of the electromagnet 12, and at this time the molten metal sample is vibrated by the vibrations. As a result, cavities are formed in the metal sample, and the solidified metal crystals are crushed by the cavitation phenomenon.

[0047] The above-described apparatus was used to impose electromagnetic vibrating force upon a solidifying alloy in the form of a hypereutectic Al-17% Si alloy. The results are shown in Table 1. As shown in Table 1, it was found that the silicon particles initially crystallized were crushed into small pieces. TABLE-US-00001 TABLE 1 Crystal grain diameter (.mu.m) Example of present Introduction of high 0.5-3 invention vibrational energy Conventional example Use of refining agents 30-50

Examples of the Inventions Defined in Claims 4-5

[0048] The above-described apparatus was used to apply electromagnetic vibrating force to a solidifying aluminum alloy and to solidifying zinc in order to refine silicon carbide particles dispersed in the aluminum alloy and to refine Fe.sub.3P compound particles dispersed in the zinc. The results are shown in Table 2. It was found that the dispersed silicon carbide particles and Fe.sub.3P compound particles were crushed into small pieces. TABLE-US-00002 TABLE 2 Diameter of Fe.sub.3P Diameter of SiC particles particles in zinc (.mu.m) in aluminum alloy (.mu.m) Example of present 10-1 2-0.1 invention Conventional 50-100 20-30 dispersant

Examples of the Inventions Defined in Claims 6-10

[0049] Electromagnetic vibrating force was applied to an Al-17% Si alloy in the process of final solidification in order to refine the alloy. As a result, the refined silicon particles as initially crystallized in a uniformly dispersed sample could be moved to the surface of the surrounding walls of a cylindrical tube.

[0050] In addition, an alloy obtained by dispersing Fe.sub.3P particles in zinc, and an alloy obtained by dispersing SiC particles in an aluminum alloy could also be moved to the surface of the surrounding walls of the cylindrical tube in the same manner as in the case of the Al-17% Si alloy.

[0051] Examples of the present invention have been described in detail above, but these examples merely serve as an illustration, and the same effect can be achieved for other metals, alloys, intermetallic compounds, semimetals, nonmetals, and the like. The present invention allows embodiments incorporating various changes based on the knowledge possessed by those skilled in the art to be implemented as long as these changes remain within the scope of the present invention.

[0052] The present invention relates to a method for refining microstructure of metallic materials characterized in that comprises forming cavitation (cavities) in molten metal by the direct application of high-energy vibrating force such as electromagnetic vibrating force, ultrasonic vibrating force to the molten metal, and crushing the resulting solid metal crystal particles into small pieces by the impact pressure generated during the collapse of the cavities, and yielding a refined microstructure of the metal. The present invention allows microstructure of metallic materials to be readily refined to the level of fine particles without the use of refining agents and without any relation to the type or composition of the metal. It is also possible to refine solid particles of other metals, intermetallic compounds, or the like dispersed in the molten metal. It is further possible to shift solid metal particles and solid particles dispersed in molten metal toward the periphery of a tube or container.

Claims

1-14. (canceled)

15. A method for shifting a refined microstructure of a metallic material, comprising: solidifying a molten metallic material at temperatures lower than a liquidus of the molten metallic material; and vibrating the solidifying molten metallic material by applying an alternating electric current and a magnetic field simultaneously at a current value and a Tesla value configured to crush solid crystal particles of the solidifying metallic material into small pieces; and shifting the small pieces to a periphery of a cylindrical tube or container with said alternating current and said magnetic field set at a current value and a Tesla value configured to concentrate said refined microstructure of the metallic material in the periphery of the cylindrical tube or container.

16-17. (canceled)

18. The method of claim 15, wherein the applying further comprises applying the electric current and the magnetic field during last stages of solidifying of the solidifying metallic material.

19. (canceled)

20. The method of claim 15, wherein the magnetic field is generated with an electromagnetic coil enveloping the metallic material.

21. The method of claim 15, wherein said current value and said Tesla value configured to crush solid crystal particles comprises: a current value less than a current value used to melt said metallic material.

22. The method of claim 15, wherein said current value and said Tesla value configured to concentrate said refined microstructure comprises: a Tesla value of 1.4 Tesla.

23. The method of claim 15, wherein said metallic material is Al--Si alloy and said small pieces have a crystal grain diameter between 0.5 and 3 .mu.m.

24. The method of claim 15, wherein said metallic material is Al--Si alloy with silicon carbide particles dispersed therein and said small pieces comprise small silicon carbide particles having a crystal grain diameter between 0.1 and 2 .mu.m.

25. The method of claim 15, further comprising: concentrating said metallic material in an end portion of said metallic material by moving the metallic material within the magnetic field.