JP4607731B2 - Metal foam filled composite member - Google Patents

Description

  The present invention relates to a metal foam-filled composite member used as a structural member such as a pillar constituting a vehicle body, and further relates to a metal foam-filled composite member in which electrolytic corrosion is suppressed.

  2. Description of the Related Art Conventionally, members having a closed cross-sectional structure have been frequently used as structural members such as pillars constituting a housing of a vehicle such as an automobile. The closed cross-sectional structure here means a structure in which the inside of the cross-section is hollow and cut off from the outside like a pipe.

  On the other hand, weight reduction of vehicles has been promoted for the purpose of improving fuel economy and preventing global warming, and the adoption of non-ferrous metal materials such as aluminum and magnesium and FRP instead of steel structural members is increasing. It is impossible to convert the structural member into a non-ferrous metal material or FRP from the viewpoint of cost and productivity.

  When a part of such a vehicle member is converted to a non-ferrous metal material, it is necessary to suppress and prevent electrolytic corrosion due to contact between different metals. Therefore, a method of forming a plating layer between different metals, or a method of interposing a Zn—Al—Mg alloy between a member made of an aluminum-based composite material and a member made of a steel material has been proposed (Patent Document 1). reference).

  The electric corrosion prevention structure according to the above-described conventional example in which a Zn—Al—Mg alloy is interposed between different metals will be described in detail below with reference to FIG. FIG. 4 is a cross-sectional view schematically showing a specific embodiment according to this conventional example as an embodiment of a disk rotor 11 and a hub 12 constituting a part of a disk brake of a vehicle.

  The structure for preventing electrolytic corrosion between dissimilar metals according to this conventional example includes a disk rotor 11 made of an aluminum-based composite material, a hub 12 made of carbon steel, a wheel 13 made of aluminum or an aluminum alloy, and a Zn-Al-Mg alloy. The plating layer 14, the bolt 15, and the nut 16 are provided. The plated layer 14 prevents electrolytic corrosion due to contact between different metals of the disk rotor 11 and the hub 12 and between different metals of the hub 12 and the wheel 13.

  Furthermore, a member in which a metal foam having a closed cross-sectional structure is filled with a foam metal body may be used as a structural member capable of obtaining high rigidity at the same time as reducing the weight of the vehicle. The reason why the metal foam is filled in the internal space of the metal member is that such a composite structure provides a lightweight member with high rigidity, and has the added value of improving vibration absorption and safety at the time of collision. This is because it can be granted.

  When filling such a foam metal body into a closed cross-section structural member, a method that does not generate a minute gap has also been proposed, and the above method prevents electrolytic corrosion in a foam metal body of a different type from the closed cross-section structure member. Has reached. A manufacturing method of the metal foam-filled composite member according to the conventional example will be described below with reference to FIG. 5 which is a manufacturing flow diagram showing a center pillar of an automobile as an example (see Patent Document 2).

  As shown in FIGS. 5A to 5G, the metal foam-filled composite member according to the conventional example is obtained by mixing a metal powder (aluminum powder) 21 with a foaming agent 22 and molding it into a flat plate shape. The obtained foaming agent molded body 24 is attached to one side of a metal flat plate (aluminum plate) 23, and the metal flat plate 23 is plastically deformed so as to wrap the foaming agent molded body 24, thereby obtaining an outer panel 30 of a center pillar.

And the closed cross-section structure 33 is obtained by covering the inner panel 31 and integrating by spot welding. The foaming agent molded body 24 encapsulated in the closed cross-section structure 33 is put into a heating furnace 34 and foamed by heating to a foaming temperature. As a result, the foaming agent molded body 24 foams and fills the closed cross-section structure 33, and a center pillar (closed cross-section structure) 38 filled with the foam 37 is obtained.
JP 2001-11665 A JP 2004-218035 A

  However, in the conventional methods for preventing galvanic corrosion between different kinds of metals as described above, it is inevitable that the steel material is subjected to a plating process, or a complicated and numerous process is required to obtain a structure that prevents contact between different kinds of metals. There is a concern that the manufacturing cost will increase.

  In addition, when filling the foamed metal into the closed cross-section structure without gaps, it is a production quality problem that gives a complicated shape, that is, when the foam metal is foamed inside the closed cross-section structure in particular, it is a dissimilar metal. Due to the heat removal effect during solidification, the metal foam is slightly shrunk and becomes smaller than a predetermined size, and there is a concern that desired performance may not be exhibited. The heat removal effect means that when different metals solidify, the shrinkage rate varies depending on the type of the metal, and therefore the size after shrinkage differs between metals.

  Accordingly, an object of the present invention is to provide a metal foam-filled composite that can be produced at a low cost by a simple manufacturing method as a structural member such as a pillar constituting a part of a vehicle casing, and that prevents electrolytic corrosion between different metals. It is to provide a member.

In order to achieve the above object, the metal foam-filled composite member according to claim 1 of the present invention employs a metal foam different from the metal member in the internal space of the metal member having a closed cross-sectional structure. A metal foam-filled composite member filled with a mold release agent for casting containing at least phosphorous graphite and alumina between the inner surface of the metal member having a closed cross-sectional structure and the metal foam different from the metal member the porous insulating film made of, which are produced and is characterized in.

  The metal foam-filled composite member according to claim 2 of the present invention employs the metal foam-filled composite member according to claim 1, wherein the porous insulating coating has at least 20% by weight of phosphorus. It contains graphite-like graphite and 20% by weight or more of alumina.

  Furthermore, the means employed by the metal foam-filled composite member according to claim 3 of the present invention is the metal foam-filled composite member according to claim 1 or 2, wherein the metal foam is 85% to 95%. It is an aluminum-based foam having a porosity in the range.

The metal foam filling portion according to claim 1 of the present invention is a casting containing at least phosphorous graphite and alumina between the inner surface of the metal member having a closed cross-sectional structure and the metal foam different from the metal member. since porous insulating film made use release agent is being generated, it is possible to obtain a metal foam filled composite member capable of preventing electrolytic corrosion between dissimilar metals easily at low cost.

  In the metal foam-filled composite member according to claim 2 of the present invention, since the porous insulating coating contains at least 20% by weight of phosphorus-like graphite and 20% by weight or more of alumina, it has excellent insulating properties. A metal foam-filled composite member that can reliably prevent electrolytic corrosion between dissimilar metals can be obtained.

  In the metal foam-filled composite member according to claim 3 of the present invention, since the metal foam is an aluminum-based foam having a porosity in the range of 85% to 95%, the weight of components such as vehicles can be reduced. In addition, the rigidity and vibration absorption can be improved.

  Next, a metal foam-filled composite member according to an embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a schematic cross-sectional view of a metal foam-filled composite member according to an embodiment of the present invention.

  In FIG. 1, a metal foam-filled composite member 1 according to an embodiment of the present invention includes a steel pipe 2 having a closed cross-sectional structure, and a metal different from the steel pipe filled in the steel pipe 2. And a porous insulating coating 4 interposed between the steel pipe 2 and the metal foam 3.

  In order to produce such a metal foam-filled composite member 1, first, a steel pipe 2 having a required diameter and length is prepared, and a casting mold release agent is added to the inner surface of the steel pipe 2 with water. A solution dissolved by stirring and dissolving is poured, and the casting release agent is applied. Thereafter, the steel pipe 2 is put into a drying furnace, heated to a predetermined temperature to dry the casting release agent solution, and a porous insulating coating 4 is formed on the inner surface of the steel pipe 2.

  And a foaming agent is added to the aluminum powder used as the raw material of the metal foam 3, and the molten metal which heat-melted this is directly cast in the said steel pipe 2, The metal foam filling composite member 1 is obtained. The metal foam 3 may be aluminum or magnesium powder, but is preferably an aluminum foam because mass production techniques are established, raw materials are easily available, and weight can be easily reduced.

The aluminum-based foam preferably has a porosity in the range of 85% to 95%. When the aluminum-based foam is used as a structural member of a vehicle or the like, if the porosity is less than 85%, weight reduction is insufficient, and if it exceeds 95%, rigidity as a steel member is insufficient. is there. On the other hand, titanium hydride (TiH ₂ ) or the like can be used as the foaming agent.

  The mold release agent used for producing the porous insulating coating 4 between the inner surface of the steel pipe 2 and the aluminum foam 3 is generally intended to facilitate the extraction of the cast product from the mold in the casting process. Commercially available products can be used, but those containing at least phosphorus-like graphite and alumina are preferred.

  And it is preferable to prepare and use this casting mold release agent aqueous solution so as to have a concentration of about 50% by weight with respect to water. This casting mold release agent can be expected to have high insulation and heat resistance by selecting one containing at least phosphorus-like graphite and alumina. However, at least 20% by weight or more of phosphorus is formed as the formed porous insulating film. It is preferable from the point of insulation that the graphite and 20% by weight or more of alumina are contained.

  Further, after the casting mold release agent aqueous solution is applied to the inner surface of the pipe 2, it is preferably dried at a temperature of about 600 ° C. for about 30 minutes. Thus, the porous insulating coating 4 produced | generated on the pipe 2 inner surface has thickness of about 300-800 micrometers normally.

  The casting mold release agent is added to water and stirred to form an aqueous solution, and this is applied to the inner surface of a metal member having a closed cross-section structure and dried by heating, so that even if it has a complicated shape, there is no gap. It is possible to coat the inner surface of the metal member. Finally, a brittle porous structure is formed on the inner surface of the metal member.

  Since the porous structure has a large surface area and a heat insulating effect compared to a dense material, it is possible to obtain a metal foam by directly casting a molten metal added with a foaming agent into the metal member having a closed cross-sectional structure. is there. By such direct casting operation, it is possible to obtain a metal foam-filled composite member with high dimensional accuracy and no gap, which is less likely to cause shrinkage spots between different metals due to the heat removal effect during solidification of the molten metal.

  When the metal foam is not directly cast into a metal member having a closed cross-sectional structure, but is manufactured separately and cut into a predetermined size for use, the porous structure inside the metal foam is exposed. A large number of gaps are formed between the inner surface of the metal member having the closed cross-sectional structure. On the other hand, in the metal foam manufactured by the direct casting operation described above, a skin is formed on the metal foam by the porous insulating coating interposed at the interface, so that a gap between the metal member inner surface is less likely to occur. .

When a minute gap is generated between the inner surface of the metal member and the porous insulating coating, or between the porous insulating coating and the dissimilar metal foam, an oxide such as rust is formed in these gaps by electrolytic corrosion. And hydrates may be formed. However, since the volume increases due to these generations, a minute gap space is closed, and the presence of the porous insulating coating makes it possible to suppress further progress of galvanic action between different metals. Become.
<Example>

In accordance with the above-described embodiment of the present invention, a metal foam-filled composite member was prototyped under the following trial conditions. In addition, it was 92% when the porosity of the metal foam after casting was measured. Further, the composition analysis of the produced porous insulating film was performed, and it was found that 30% by weight of phosphorus-like graphite and 40% by weight of alumina were contained.
[Trial conditions for metal foam filled composite material]

-Metal member having a closed cross-sectional structure: steel pipe (outer diameter: 51 mm, inner diameter: 47 mm)
・ Metal foam raw material: Industrial aluminum powder ・ Cast mold release agent: Top coat (manufactured by Keimei Shoji Co., Ltd.)
・ Concentration of casting mold release agent: 50% by weight
-Drying conditions: Drying at 600 ° C for 30 minutes

  The result of evaluating the prototype of this metal foam-filled composite member using a combined cycle corrosion test apparatus will be described below with reference to FIGS. 2 and 3. FIG. 2 is an explanatory diagram showing the combined cycle corrosion test conditions, and FIG. 3 is a diagram showing the weight change rate over time of the evaluation sample by the corrosion test.

  The combined cycle corrosion test is a standard defined in the Japan Society of Automotive Engineers standard JASO M609-91, and is a test that is continuously repeated with one cycle of 8 hours under the conditions shown in FIG. . The progress of corrosion was evaluated by the rate of change in weight.

  First, an evaluation sample is made from the prototype metal foam-filled composite member, and the sample is weighed, and then set in a composite cycle corrosion test apparatus. Test conditions are as shown in FIG. 2. First, in Step A, the evaluation sample is sprayed with 5% salt water at a temperature of 35 ° C. for 2 hours.

  Next, in Step B, the substrate is dried for 4 hours in an atmosphere at a temperature of 60 ° C. and a relative humidity of 30%. As described above, the test cycle of 8 hours in total is repeated successively.

  The combined cycle corrosion test was carried out for 14 days, and the weight of the sample was measured at the end of the 7th and 14th test cycles to determine the weight change rate. The result is shown by the solid line in FIG. That is, it can be seen that the sample weight increases with time. This is due to the fact that white rust (alumina hydrate) is generated due to the proximity of dissimilar metals, and red rust (iron oxide) is generated independently in a salt water or wet environment.

  A porous insulating film is formed in most of the minute gaps between the inner surface of the metal member having a closed cross-sectional structure and the metal foam, but there are minute gaps in which the porous insulating film is not formed. Since it exists somewhat, as shown by the solid line in FIG. 2, in the initial stage of the test, a moist environment is formed in the minute gap, and the above-described white rust and red rust are generated and the weight is increased.

  However, after that, it can be seen that the insulating property by the porous insulating coating is maintained, so that the steady state is obtained without increasing the weight, and the electrolytic corrosion effect is suppressed.

Therefore, when the metal foam-filled composite member according to the present invention is applied to a component such as an automobile, a minute gap exists between the inner surface of the metal member having a closed cross-sectional structure and the dissimilar metal foam. Even in this case, the formation of the porous insulating film suppresses the electrolytic corrosion action, and corrosion does not proceed.
<Comparative example>

  Next, a metal foam-filled composite member was manufactured under exactly the same conditions as in the above example except that the casting mold release agent was not applied to the inner surface of the steel pipe. And the test sample was produced as a comparative example from this metal foam filling composite member in which the porous insulating film is not formed. The test sample of the comparative example was set in a combined cycle corrosion test apparatus simultaneously with the test sample of the example, and a combined cycle corrosion test was performed.

The weight change rate with time of the comparative example test sample by this corrosion test is shown by a broken line in FIG.
In this case, it can be seen that the galvanic action actively proceeds between the dissimilar metals of the steel pipe and the pure aluminum which is the metal foam, and the weight is increased to nearly 15% with the elapsed time.

  In the embodiment of the present invention, an example of a metal foam-filled composite member that employs a steel pipe as a metal member having a closed cross-sectional structure has been described, but the present invention is not limited to a steel pipe. All metal members to which the gist can be applied are effective.

  As described above, in the metal foam filling portion according to the present invention, the mold release agent containing at least phosphorus-like graphite and alumina is applied to the inner surface of the metal member having a closed cross-sectional structure, and the minute portion between the metal foam and the metal foam is applied. Since the porous insulating film is formed in the gap, it is possible to obtain a metal foam-filled composite member that can easily prevent electrolytic corrosion between different metals at low cost.

  Further, the metal foam-filled composite member according to the present invention is excellent in insulation because the porous insulating coating contains at least 20% by weight of phosphorus-like graphite and 20% by weight or more of alumina. It is possible to reliably prevent electric corrosion.

  In the metal foam-filled composite member according to the present invention, since the metal foam is an aluminum-based foam having a porosity in the range of 85% to 95%, the rigidity and vibration absorption of components such as vehicles The weight can be reduced while improving the performance.

  As described above, according to the present invention, it is possible to provide a low-cost metal foam-filled composite member in which electrolytic corrosion between dissimilar metals is prevented. As a result, the metal foam-filled composite member according to the present invention is a high-rigidity lightweight member that constitutes a part of the vehicle casing, and further is expected to improve vibration absorption and safety at the time of collision. It can be applied to members.

It is typical sectional drawing of the metal foam filling composite member which concerns on embodiment of this invention. It is explanatory drawing which shows a combined cycle corrosion test condition. It is a figure which shows the weight change rate with time of the evaluation sample by a combined cycle corrosion test. It is sectional drawing which showed typically specific embodiment which concerns on a prior art example as embodiment of the disc rotor 11 and hub 12 which comprise some disk brakes of a vehicle. It is the manufacturing flowchart which showed the manufacturing method of the metal foam filling composite member which concerns on a prior art example for the center pillar of the motor vehicle.

Explanation of symbols

A: The evaluation sample is sprayed with 5% salt water at a temperature of 35 ° C. for 2 hours,
B: The evaluation sample is exposed to a dry atmosphere at a temperature of 60 ° C. and a relative humidity of 30% for 4 hours.
C: The evaluation sample is exposed to a humid atmosphere at a temperature of 50 ° C. and a relative humidity of 95% for 2 hours,
1 ... Metal foam filled composite member,
2 ... Steel pipe (metal member with closed cross-section structure),
3 ... Aluminum foam (metal foam),
4 ... Porous insulation coating

Claims (3)

In a metal foam-filled composite member in which an internal space of a metal member having a closed cross-sectional structure is filled with a metal foam different from the metal member, the inner surface of the metal member having a closed cross-sectional structure is different from the metal member. the metal during the foam, at least phosphorus-shaped graphite and metal foam filled composite member porous insulating coating of casting release agent characterized by comprising been generated containing alumina.   2. The metal foam-filled composite member according to claim 1, wherein the porous insulating film contains at least 20 wt% or more of phosphorus-like graphite and 20 wt% or more of alumina.   The metal foam-filled composite member according to claim 1 or 2, wherein the metal foam is an aluminum-based foam having a porosity in the range of 85% to 95%.

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