JP2006102807A - Method for reforming metallic structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for reforming a metallic structure by which the whole of the metallic structure can be refined without relying on complicated and large-sized equipment, and further, not only there is no limitation on an applying range but also mold releasing is not made difficult even when it is applied to casting. <P>SOLUTION: A horn 2 integrated with an ultrasonic vibrator 3 is arranged at the upper part of a mold 1 in such a manner that the same is separated from the surface of a molten metal M in the mold 1 by a prescribed distance L, the molten metal M is poured into the mold 1, thereafter, ultrasonic waves are emitted from the horn 2 to the molten metal M in the mold 1 in a suitable timing, and ultrasonic vibration is applied thereto. By the application of the ultrasonic vibration, fine nuclei for solidification are generated in the molten metal and are dispersed, further, dendrite as primary crystals is destroyed and is made into fine grains so as to be dispersed. Thus, the solidification progresses with these nuclei and grains as the centers, and the solidified structure is refined. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a metal structure modification method for making a solidified metal structure fine.

  It has heretofore been known that applying ultrasonic vibration to molten metal in the solidification process is effective in reducing the solidification structure. In order to apply ultrasonic vibration to the molten metal, an indirect excitation method (for example, Patent Document 1) in which an ultrasonic vibrator is generally attached to the side wall of the mold and ultrasonic vibration is applied to the molten metal through the side wall. And a direct vibration method (for example, refer to Patent Document 2) in which a horn is immersed in the molten metal in the holding container and ultrasonic vibration is directly applied to the molten metal. However, in the indirect vibration method, miniaturization proceeds near the side wall of the mold, but the effect of miniaturization does not reach the inside. On the other hand, in the direct vibration method, miniaturization proceeds in the vicinity of the immersed horn, but the container ( The effect of miniaturization does not reach to the vicinity of the side wall of the mold), and any method has a problem that it is difficult to miniaturize the whole. Furthermore, the problem that the melted metal adheres to a container etc. also arises by the improvement of the wettability in the vicinity of the vibration part.

By the way, Patent Document 3 describes that cavitation is generated in molten metal by using ultrasonic vibration and electromagnetic vibration in combination, and miniaturization is achieved by impact pressure generated at the time of disappearance. Therefore, according to this method, it is expected that the effect of miniaturization will reach the whole.
JP-A-3-165506 JP-A-4-158852 JP-A-11-90615

  However, according to the miniaturization method described in Patent Document 3, since ultrasonic vibration and electromagnetic vibration excitation are used in combination, there is a problem that the equipment is complicated and the size is increased and the cost burden is increased. Moreover, since there is a restriction on the installation of the excitation source, there is a problem that the application range such as the shape of the product to be manufactured and the processing field to be applied is greatly limited. In addition, since the excitation force is strong and the solid-liquid interface is vigorously activated, the oxide film is destroyed, and the cast product adheres to the wall of the mold (seizures), making it difficult to release the mold. When applied to casting of an alloy, there is a problem that the degree of adhesion becomes intense and it becomes almost impossible to release the cast product from the mold.

  The present invention has been made in view of the above-described conventional problems, and the problem is that the whole can be miniaturized without relying on complicated and large-sized equipment, and the scope of application is not limited. Another object of the present invention is to provide a metallographic modification method that does not become difficult to release even when applied to casting.

In order to solve the above-described problems, the present invention provides an ultrasonic vibration to the metal by directly irradiating ultrasonic waves from a separated position toward the molten metal surface in the cooling process of cooling the molten metal. It is characterized by that.
In the present invention, the “molten metal” means a metal in a completely liquid state before the start of solidification and a metal in a semi-solid state after the start of solidification. Further, the “cooling process” includes one or both of a process before the start of solidification and a process after the start of solidification. Therefore, “applying ultrasonic vibration to the molten metal in the cooling process” means applying ultrasonic vibration to the metal in the completely liquid state before the start of solidification, and applying ultrasonic vibration to the metal in the semi-solid state after the start of solidification. It includes applying vibration and applying ultrasonic vibration to the metal from a completely liquid state to a semi-solid state.

  In the metal structure refinement method performed as described above, ultrasonic vibration is efficiently applied to the entire molten metal by irradiating the molten metal in the cooling process with ultrasonic waves from a position appropriately spaced from the molten metal surface. Is granted. Then, by applying this ultrasonic vibration, solidified fine nuclei are generated and dispersed in the molten metal in the cooling process, and the primary dendrites are destroyed and dispersed as fine particles. Solidification progresses around the core and particles, and the solidified structure becomes finer. In addition, since the ultrasonic vibration is applied independently, and the ultrasonic vibration is applied in a non-contact manner with a container such as a molten metal or a mold for holding the molten metal, the apparatus is not complicated and does not increase in size. Not only are there any restrictions on the shape of the product to be manufactured, but there are also almost no restrictions on the applied processing field. Furthermore, by irradiating ultrasonic waves from a position appropriately spaced from the molten metal surface, the excitation force of ultrasonic vibration applied to the molten metal becomes an appropriate magnitude and the solid-liquid interface is not vigorously activated. Thus, the cast product does not adhere to the mold at the time of casting, especially when applied to casting of an aluminum alloy.

  The processing field to which the present invention is applied is arbitrary, and can be applied to various fields such as welding, thermal spraying, and soldering as well as casting including a semi-solid casting process (thixocasting) for forming in a semi-solid state. Therefore, the cooling process is a casting process, a welding process, a thermal spraying process, or a solder metal soldering process according to these application fields.

  According to the metal structure refinement method according to the present invention, the entire structure can be refined without depending on complicated and large-sized facilities, so that the cost burden on the facilities is reduced. In addition, there are almost no restrictions on the shape of the product to be manufactured, and there are almost no restrictions on the applied processing field, so that the application range is remarkably expanded. Furthermore, when it is applied to casting, the cast product does not adhere to the mold, so that the mold release is easy, and it is particularly suitable for casting of an aluminum alloy.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows one embodiment of a metallographic modification method according to the present invention. The present embodiment is applied to casting. Ultrasonic irradiation is performed above the mold 1 into which a molten metal (molten metal) M is poured and separated by a predetermined distance L from the surface of the molten metal M in the mold 1. A horn 2 is arranged. The horn 2 is attached to an ultrasonic transducer 3, and ultrasonic waves are applied to the ultrasonic transducer 3 from an ultrasonic oscillator 4 provided separately. In carrying out this method, after injecting the molten metal M into the mold 1, the ultrasonic oscillator 3 is operated at an appropriate timing by the ultrasonic oscillator 4, and ultrasonic waves are applied from the horn 2 to the molten metal M in the mold 1. Irradiate and apply ultrasonic vibration.

  The timing of applying ultrasonic vibration to the molten metal M in the mold 1 (ultrasonic vibration) is the cooling process before the start of solidification or the cooling process (solidification process) after the start of solidification. Alternatively, the range may include a cooling process before the start of solidification and a cooling process after the start of solidification. Before the start of solidification, the molten metal M is in a completely liquid state. When the molten metal M in the completely liquid state is subjected to ultrasonic vibration, fine nuclei of solidification in the molten metal M according to cooling. Is generated and dispersed, and solidification progresses around the core to refine the cast structure. On the other hand, after the start of solidification, the molten metal M is in a semi-solid state. However, when this semi-solid state molten metal M is subjected to ultrasonic vibration, the primary crystal dendrite is destroyed and fine particles and Then, the particles are dispersed and solidification progresses around the fine particles, and the cast structure is similarly refined. In addition, when the molten metal M is subjected to ultrasonic vibration within a range including the cooling process before the start of solidification and the cooling process after the start of solidification, the fine nuclei generated by the solidification and the destruction of the primary dendrite described above are generated. The cast structure is refined by a synergistic effect with the generation of particles. Therefore, in order to maximize the effect of miniaturization, it is desirable to perform ultrasonic vibration before and after the solidification start point. In this case, since the solidification start point varies depending on the type of the molten metal M, the size (injection amount) of the mold 1, and the like, the solidification start point is grasped by obtaining a cooling curve in advance.

  FIG. 2 shows a cooling curve when a molten aluminum alloy for casting (ADC12) is poured into a mold 1 of a laboratory scale (upper inner diameter 48 mm, lower inner diameter 26 mm, depth 53 mm), and a solidification start point P1. Is approximately 570 ° C., the time from the injection point to the coagulation start point P1 is about 70 seconds (sec), and the time from the coagulation start point P1 to the coagulation end point P2 is about 190 seconds (about 260 seconds from the injection point). It has become. Therefore, in this case, it is desirable to perform ultrasonic vibration for a predetermined time continuously around about 70 seconds after injection.

  FIG. 3 shows a macrostructure of an ingot (the material of the present invention) obtained by ultrasonically oscillating from about 600 ° C. for about 120 seconds after pouring a melt of ADC12 into the laboratory scale mold 1. This is shown in comparison with an ingot (comparative material) obtained without any vibration. The solidified structure of the present invention material is clearly made finer than the comparative material. A characteristic point grasped from FIG. 3 is that a large shrinkage nest is recognized in the comparative material, whereas such a large shrinkage nest is not recognized in the material of the present invention. This difference is related to the size of the riser to be set, and in the method of the present invention in which an ingot with a small shrinkage cavity is obtained, the riser can be set small, and the yield is improved by that amount, which is advantageous in terms of cost. It becomes.

  Here, since the present invention irradiates ultrasonic waves from a position apart from the molten metal M as described above, it can be applied to various processing fields such as welding, thermal spraying, and soldering in addition to the above-described casting. . FIG. 4 shows one embodiment when the present invention is applied to the butt welding of two steel plates 5A and 5B, and is separated from the upper surface of the steel plates 5A and 5B by a predetermined distance L above the welded portion. Then, the horn 2 for ultrasonic irradiation and the ultrasonic vibrator 3 are arranged, and the horn 2 and the ultrasonic vibrator 3 are moved in the welding direction (here, on the paper surface) according to the progress of the welding by the welding rod 6. Move vertically). By performing welding in this manner, ultrasonic vibration is applied to the welded portion (molten metal) 7 between the two steel plates 5A and 5B, and the solidified structure is refined as in the above casting.

  As shown in FIG. 5, a boat-shaped mold 10 is prepared, and the horn 2 and the ultrasonic vibrator 3 are arranged above the mold 10 so as to be spaced 6 mm from the surface of the molten metal M injected into the mold 10. did. The mold 10 has an average inner width of 35 mm, an average length of 20 mm, and a depth of 39 mm. Then, the mold 10 is preheated to 300 ° C., and a melt (molten metal) M of ADC12 which is an aluminum alloy for casting is poured into the mold 10 at 710 ° C., and the melt M is fed from the horn 2 for 60 seconds immediately after the pouring. Then, an ultrasonic wave having an amplitude of 40 μm was irradiated toward the surface, and after solidification, the tensile test piece 11 was taken out from the lower part of the ingot as shown in the figure, and a tensile test was performed. The tensile test piece 11 has a parallel portion 11a having a diameter of 12.3 mm and a parallel portion 11a having a length of 71 mm. For comparison, the same casting was performed without irradiating ultrasonic waves, and tensile test pieces were similarly collected from the resulting ingots and subjected to a tensile test.

FIG. 6 shows the results of the tensile test performed as described above. From the results shown in the figure, the average of the tensile strength is about 185 N / mm ² with the ultrasonic vibration, whereas the average tensile strength is about the one without the ultrasonic vibration. It was about 166 N / mm ^2, and it was revealed that application of ultrasonic vibration greatly contributes to improvement in strength.

  The molten metal of ADC12 was poured into the mold 1 at 710 ° C. shown in FIG. 1 at 710 ° C., and then an ultrasonic oscillation horn placed 14 mm away from the molten metal surface with an amplitude of 42 μm toward the molten metal surface. Ultrasonic waves were emitted at various timings (excitation conditions) as described below.

1) Excitation from 620 ° C. for 120 seconds (completely molten state to initial stage of solidification process)
2) Vibration from 620 ° C. for 30 seconds (completely melted state)
3) Excitation at 570 ° C for 30 seconds (initial stage of solidification process)
4) 30 seconds of vibration after 90 seconds from 570 ° C (the middle stage of the solidification process)
5) 30 seconds after 180 seconds from 570 ° C (the final stage of the solidification process)

  And about the ingot obtained on the above-mentioned various vibration conditions, the macro test and the micro test were done and the metal structure was observed. As a result, miniaturization was observed under each excitation condition, but it was found that miniaturization was most advanced under the excitation conditions 1) and 3) including the initial stage of solidification.

  As the two steel plates 5A and 5B shown in FIG. 4, SS400 having a plate thickness of 6 mm × plate width of 40 mm is selected, and LB-26 (low hydrogen welding rod) manufactured by Kobe Steel is selected as the welding rod 6. The butted portions of the two steel plates 5A and 5B are welded by the welding rod 6, and during this time, an ultrasonic wave having an amplitude of 42 μm is directed from the horn 2 arranged 30 mm away from the upper surface of the steel plates 5A and 5B toward the weld portion 7. After irradiation and welding, the macrostructure of the weld was observed. For comparison, the same welding was performed without irradiating ultrasonic waves, and the macrostructure of the welded portion was similarly observed. As a result, those with ultrasonic irradiation (application of ultrasonic vibration) have a fine granular structure, while those without ultrasonic irradiation have a relatively coarse needle-like structure. Also in welding, it was confirmed that the application of ultrasonic vibration greatly contributed to the refinement of the structure.

It is a schematic diagram which shows embodiment at the time of applying the metal structure refinement | miniaturization method which concerns on this invention to casting. It is a graph which shows an example of the cooling curve used as the basis of the timing setting of the ultrasonic vibration with respect to the molten metal of a cooling process. It is the photograph which shows by contrast the case where ultrasonic vibration is performed and the case where ultrasonic vibration is not performed about the macro structure of the ingot obtained on the laboratory scale. It is a schematic diagram which shows embodiment at the time of applying the metal structure refinement | miniaturization method which concerns on this invention to welding. It is a schematic diagram which shows the Example of this invention performed in order to extract | collect a tensile test piece. It is a graph which compares and shows the tensile test result obtained in the Example of this invention with what performed ultrasonic vibration, and what did not perform ultrasonic vibration.

Explanation of symbols

1 Mold 2 Horn 3 Ultrasonic Vibrator 4 Ultrasonic Oscillator M Molten Metal

Claims (5)

  In the cooling process of cooling the molten metal, a method of modifying a metal structure is characterized by directly irradiating ultrasonic waves from a spaced position toward the molten metal surface to impart ultrasonic vibrations to the metal.   The method of modifying a metal structure according to claim 1, wherein the cooling process is a casting process.   The method for modifying a metallographic structure according to claim 1, wherein the cooling process is a welding process.   The method for modifying a metallographic structure according to claim 1, wherein the cooling process is a thermal spraying process. The metal structure modification method according to claim 1, wherein the metal is solder, and the cooling process is a soldering process.

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