JP4694439B2 - Method for producing porous metal - Google Patents

Description

  The present invention relates to a method for producing a porous metal.

  Porous metal has pores (pores) of several tens of nanometers on the surface and inside, and several millimeters on the large ones, and as the proportion of the pores (porosity) in the volume increases, The mass decreases. For example, the mass per volume with a porosity of 30% is 70% of the mass of the bulk metal without porosity.

  The pores in the porous metal are crushed by an external impact and absorb the impact energy. Therefore, this porous metal is expected to be applied to automobile bumpers and the like as a lightweight shock absorber.

  Moreover, when the porosity is increased, individually independent pores in the porous metal come into contact with each other and are connected. If the pores are connected to each other, fluid can flow from one of the porous metals to the other. When a catalyst is supported on the inner walls of the connected pores, a catalytic reaction occurs while a fluid flows in the pores, so that it can function as a so-called catalyst filter.

  In addition, application to soundproof and vibration-proof materials and heat insulating materials, and improvement in adhesion between materials utilizing the anchoring effect due to the unevenness of the porous metal surface are also expected.

  In order to create a porous metal that is desired to be widely used, in order to generate pores in the metal, for example, a metal powder that is a raw material of the porous metal and a binder resin that decomposes and disappears at a high temperature are mixed and mixed. There is a manufacturing method in which a body is formed and filled into a mold and sintered.

  In this manufacturing method, the contact portion between the metal powders is melted and bonded during sintering, and the binder resin filled between the metal powders decomposes and disappears to become pores. That is, since the ratio of the binder resin mixed first becomes the porosity as it is, the porosity can be adjusted by the mixing ratio of the metal powder and the binder resin. Moreover, if this metal powder and binder resin are mixed uniformly before sintering, the whole can be made into a porous metal having a uniform porosity.

  However, in this manufacturing method, there is a concern that the mixed binder resin does not completely decompose and disappear during sintering but remains in the porous metal, and the properties of the porous metal deteriorate. In addition, since the mixture of the metal powder and the binder resin is sintered in a heat treatment furnace, the maximum size of the compression molded body is limited by the size of the heat treatment furnace. It cannot be manufactured. For this reason, when this porous metal is used for a soundproof panel or the like, a large porous metal is required. Therefore, it is necessary to increase the size by joining the porous metal.

  In general, in order to join two members and increase the size, the surfaces of the members are brought into close contact with each other and joined by an adhesive or welding. However, since a large number of pores are exposed on the surface of the porous metal, even if the exposed surfaces of the pores face each other, the area where they are actually in close contact with each other is very small, and sufficient bonding strength can be obtained. Is difficult. Also, when porous metals are welded together, melting occurs near the weld interface due to the heat, and pores disappear at that portion, so the volume of the porous metal corresponding to the lost pore volume decreases, Dimensional accuracy may deteriorate.

Thus, in general, in order to join porous metals that are difficult to join or between a porous metal and a non-porous metal, pressure is applied so that the joint surfaces of the two are in close contact, and the joint surfaces A technique of supplying the same type of metal as the porous metal and joining them by laser welding has been proposed (see Patent Document 1, paragraph numbers 0019 to 0028).
In this technique, for example, when porous stainless steel and non-porous bulk stainless steel are joined, a pressure of 5 to 20 kPa is applied to these joining surfaces, and high manganese austenitic steel is supplied to the joining surfaces. In order to obtain good bonding strength.
JP 2001-276582 A

In addition, a technique in which a porous portion and a non-porous portion are separately formed in one member has been proposed (see Patent Document 2 FIG. 1).
This technology generates an arc discharge using an aluminum alloy as one electrode, supplies aluminum alloy powder containing hydrogen in advance during the arc discharge, deposits it on the surface of the aluminum alloy, and arcs the hydrogen in the aluminum alloy. Gasification occurs in the discharge, and the gas is taken into the aluminum alloy melted by the arc discharge to form pores, and a porous aluminum layer is partially formed only at the place where the arc discharge is performed.
JP 2004-114054 A

  In the technique shown in Patent Document 1, when a pressure is applied to the joining surfaces of two members in the joining process, a part of each member is sandwiched by a jig or the like and both are fixed. However, if the member is small or the shape of the sandwiched portion is complicated, the members may not be firmly sandwiched, or the member may be deformed or damaged by the pressure when sandwiched. For this reason, when such a fear becomes a problem, this technique cannot be applied.

  The technique shown in Patent Document 2 supplies aluminum alloy powder containing hydrogen in advance during arc discharge, which increases the cost of the aluminum alloy powder and stabilizes a predetermined amount of aluminum alloy powder during arc discharge. In order to obtain a uniform porous material, the direction of welding is also limited.

  In addition, the volume of the powder supplied by the porous portion rises, and the level difference between the porous portion and the non-porous portion is very large. Furthermore, although the aluminum porous body manufactured in this way is a composite of a porous body and a non-porous body, the control of the formation position of the porous body and the depth of the porous or non-porous portion is possible. It is very difficult and needs to be machined after being made porous.

  In view of such a current situation, the present invention can be easily made porous, can be made porous at a predetermined position to a predetermined depth, and can easily join porous members. Is an issue.

  In order to solve the above-described problems, the present invention forms a metal powder into a molded body having a predetermined shape, performs at least one heat treatment of arc discharge, laser irradiation, and plasma irradiation on a predetermined position of the molded body. It was decided to melt to a predetermined depth at a predetermined position on the body.

  As one of the molding methods of the molded body, a method of forming a molded body having a predetermined shape through a process of compressing or sintering metal powder can be applied.

  The compression process is, for example, compression molding. The metal powder is filled in a mold, and the metal powder is pressed and pressed to form a molded body or billet. The amount of pores remaining in the molded body or billet can be adjusted by changing the pressure level at the time of compaction, and the pressurizing force is increased when the porosity is lowered. In this compression molding, it is not always necessary to heat, but by heating, the pores in the metal powder easily come out of the mold, so that the molding can be completed in a shorter time. In addition, as a compression process, after heating metal powder to predetermined | prescribed temperature, this powder may be filled into the container of an extrusion apparatus, this may be pressurized, and may be extrusion-molded to the molded object of a predetermined shape and a dimension.

  In addition, the sintering step is, for example, sintering molding. The metal powder is filled in a mold, and the temperature is raised to a high temperature that does not reach the melting point of the metal, and generally heated for several hours. A compact or billet is used. At the time of this heating, the presence or absence of pressurization to the metal powder is appropriately selected depending on the desired porosity, and the pressurizing force is increased when the porosity is reduced, as in compression molding.

  In this sintering, unlike compression molding, a contact portion between adjacent metal powders is partially melted and solidified when cooled to room temperature, and adjacent metal powders are connected and integrated. Therefore, the mechanical strength of the molded body is increased as compared with the case of compression molding in which metal powder is simply pressed and compacted, and the molded body is less likely to be damaged by impact or the like.

  After the billet obtained by the compression molding or the sintering molding is heated to a predetermined temperature, the billet is filled in a container of an extrusion apparatus and extruded into a molded body having a predetermined shape and size. The molded body thus obtained has high strength, and its shape and dimensions can be freely changed by exchanging a mold used for extrusion molding.

  In the molded body thus obtained, fine pores remain at a high density, and are melted to a predetermined depth at a predetermined position of this molded body by the subsequent heat treatment. Agglomerates to reduce energy to form macroscopic pores, and the pores are efficiently made.

  According to this invention, heat treatment is performed directly by arc discharge or the like at a predetermined position of the molded body to a predetermined depth without newly supplying metal powder to the porous portion, and only that portion is made porous. The level difference between the porous portion that has been subjected to the heat treatment and the non-porous portion that has not been subjected to the heat treatment is small. Further, fine pores remain in the non-porous portion at a high density, but the surface of the molded body is hardly roughened (not roughened) by the pores.

  When the heat treatment is applied to a portion other than the peripheral portion of the molded body, a non-porous portion remains in the peripheral portion, and a flat surface state is maintained. When a plurality of the molded bodies are arranged and abutted at the end face of the peripheral edge, they can be joined by welding or a mechanical technique. When this joining is performed by welding, the joining portion is melted and made porous at the time of welding, so that the entire formed body after joining can be made porous.

  As an embodiment of the present invention, a metal powder is compressed or sintered to form a molded body having a predetermined shape, and the molded body is subjected to heat treatment and melted to a predetermined depth at the predetermined position. A configuration is adopted in which fine pores are aggregated to form macroscopic pores.

The heating means is preferably selected from arc discharge, laser irradiation, and plasma irradiation. Since these methods can irradiate the generated heat in a concentrated position at a desired position, it is possible to easily control the melting range, depth and solidification rate of the melted part of the molded body by adjusting the voltage, current, etc. Are better. The heating method is not limited to these methods as long as the melting range, depth, and solidification rate of the melted portion of the molded body can be easily controlled in the same manner as these methods.

  Magnesium, aluminum, and titanium can be adopted as the metal powder. Since these metals have high specific strength, it is possible to achieve both weight reduction and high strength. Also, alloys obtained by adding various metals to them can achieve both weight reduction and high strength. At that time, each element to be added is appropriately selected in consideration of improvement of various properties such as mechanical strength due to the addition.

  The magnesium alloy is composed of, for example, aluminum and zinc for improving mechanical strength, manganese for improving corrosion resistance, yttrium, calcium, strontium, silver, silicon and rare earth elements for improving heat resistance. It is assumed that zirconium is added for oxidization and beryllium and calcium are added for oxidation prevention. A plurality of these elements can be added in combination to improve the various characteristics.

  For example, copper, manganese, silicon, magnesium, zinc, and nickel are added to the aluminum alloy to improve mechanical strength. A plurality of these elements can also be added in combination.

  Titanium alloys include, for example, palladium for improving corrosion resistance, aluminum and tin for improving heat resistance, vanadium for improving ductility, and vanadium, chromium and tin for improving cold workability and mechanical strength. Each aluminum is added. Similarly, a plurality of these elements can be added in combination to improve the various characteristics.

  When the metal powder is made into a billet in the compression molding, it is desirable that the load pressure on the metal powder is 100 MPa or more so that the billet is not damaged when taken out from the mold.

  Further, when the metal powder is made into a billet in the above-described sintering molding, the sintering condition varies depending on the type of the alloy, the magnesium alloy is 400 to 500 ° C, the aluminum alloy is 500 to 650 ° C, and the titanium alloy is 900 to 1300 ° C. Each of these temperature ranges is heat treated for 0.1 to 1 hour. By this treatment, the contact portion of the adjacent metal powder is partially melted, and when it is cooled to room temperature, the molten portion is solidified and the adjacent metal powder is connected and integrated. Therefore, the strength of the molded body is improved, and there is little possibility that the sintered body is damaged in the heat treatment after the sintering treatment. When this sintering is performed under pressure, the porosity can be further reduced as compared with the case where the sintering is performed under atmospheric pressure.

In order to extrude the billet into a molded body, the billet is heated to 300 ° C. or higher and filled into a container of an extrusion apparatus, and a pressure of 100 kg / cm ² or more is applied to the billet, Extrude the billet.

  In order to prevent the billet from being damaged at the time of extrusion molding, it is preferable to produce the billet by compression molding or sintering molding. However, the metal powder is directly supplied continuously to the container of the extrusion device, and the metal It is also possible to subject the powder to pressure and heat treatment, directly form a billet in the extrusion apparatus, and then extrude the powder.

  When heat treatment such as arc discharge is performed on the molded body, the molded body is melted to a predetermined depth at a predetermined position of the molded body, and the pores remaining in the melted region are aggregated. These pores are very fine with a size equal to or smaller than that of metal powder. However, when a large number of these fine pores aggregate, they become macroscopic pores with a diameter of about several hundred μm at the maximum. Is taken into the molten layer and solidified to form a porous layer.

  When a hydroxide coating is formed on the surface of the metal powder, the compact made of the metal powder has the hydroxide uniformly dispersed throughout the entire area, and the compact is subjected to heat treatment such as arc discharge. The hydroxide uniformly dispersed in the molded body is decomposed by this heating to become hydrogen gas, and this hydrogen gas is taken into the molten layer on the surface to form pores.

  For this reason, since the pores resulting from the hydrogen gas and the pores in which the gaps are aggregated are simultaneously taken into this molten layer, if the heat treatment conditions such as arc discharge are the same, the surface of the metal powder When the hydroxide film is formed, the porosity is higher than when the hydroxide film is not formed.

  For example, when the amount of heat input during heating is increased, the pore size and porosity are melted from the surface of the molded body to a deeper region, and the gap in the melted region is taken into the pores. Increases porosity. If the cooling rate during cooling is low, pores are released from the melted region into the atmosphere while the surface layer of the molded body is melted, and the porosity in the melted surface layer is lowered.

  Large pores in particular have a high ascent rate from the melted region, so that small pores mainly remain in the melted region, and the average pore size decreases. The pore size and porosity are adjusted in consideration of such heating conditions and subsequent cooling conditions.

  The hydroxide film is formed by treatment in an atmosphere of 10 to 40 ° C. for 1 day to 2 weeks or in water vapor of 100 to 120 ° C. for 1 to 5 minutes. When the treatment is performed at a temperature higher than this temperature, an oxide film is formed on the surface, and this oxide film is not decomposed by the heat treatment and does not generate gas, so that it does not contribute to the formation of the porous layer. Moreover, even if it processes at the temperature below this, a hydroxide film is hard to be formed and its formation efficiency is low. Therefore, it is necessary to form the hydroxide film in this temperature range.

  According to the present invention, the surface of the porous metal subjected to the heat treatment is not formed with a large step and the flatness is maintained, but depending on the use of the porous metal, the porous portion is intentionally formed. It is assumed that a step may be provided. In that case, if a wire-like or rod-like filler is continuously fed into the arc discharge, etc. during the heat treatment for making the porous material, the filler melts to the surface of the porous portion. A step can be formed. Also, welding when there is a gap between two members and overlay welding for securing mechanical strength by partially thickening the members can be performed at the same time.

  The surface of the compact was directly heat-treated without supplying a porous material such as aluminum alloy powder containing hydrogen in advance as in the conventional example.

  FIG. 1 shows a cross-sectional photograph of the porous metal A in one embodiment of the present invention, and FIG. 2 shows an optical micrograph of the cross-section of the porous metal A. This compact is filled with a magnesium alloy (AZ31D: Mg-3 wt% Al-1 wt% Zn) powder having a particle size of 5 mm or less in a mold, and compression-molded under processing conditions of a temperature of 300 ° C. and a pressure of 400 MPa. After forming the billet, the billet was extruded at 400 ° C., and the surface of the molded body was irradiated with a semiconductor laser (output 4 kW) at a scanning speed of 4 m / min.

  The melting temperature of the magnesium alloy is about 600 ° C. In this laser irradiation, the region is heated to 600 ° C. or more from the surface of the molded body to a depth of several millimeters, and the region melts. The pores present in the melted region aggregate to form macroscopic pores, which are made porous. The size of the aggregated pores is about 0.1 to 0.5 mm, and these are exposed on the surface, so that the surface of the molded body is roughened. When the surface is roughened, an anchoring effect is exhibited when a resin layer or the like is formed on the surface of the molded body, so that the adhesion between the molded body and the resin layer or the like is improved.

  By adjusting the laser irradiation conditions, the porous layer can be made deeper and the total number of pores in the porous body can be increased. Since the pores are crushed when an impact is applied from the outside and the energy of the impact is efficiently absorbed, the porous body can be used as an impact absorbing material.

Cross-sectional photograph of one embodiment of the present invention Sectional photograph of an optical microscope in one embodiment of the present invention

Explanation of symbols

A Porous metal 1 Pore 2 Metal matrix

Claims (2)

A hydroxide film is formed on the surface of the metal powder, and the metal powder is formed into a billet by compression molding or sintering, and the billet is extruded to form a molded body having a predetermined shape. position arc discharge, laser irradiation, heating is concentrated at least one heating means of the plasma irradiation, and melted to Tokoro Teifuka is, the macroscopic pores by aggregated fine pores of the molten layer, before Symbol A method for producing a porous metal, wherein the predetermined position is cooled at a rate equal to or higher than a cooling rate at which the macroscopic pores can be taken into the molten layer and solidify. Only the peripheral part of the porous metal manufactured by the manufacturing method according to claim 1 is set as a non-porous region , the porous metals are butted together at the peripheral end faces, and the peripheral end faces are welded and connected, The manufacturing method of the porous metal which made the joining location of the said peripheral part porous.