JP4523529B2 - Aluminum alloy foam and manufacturing method thereof - Google Patents

Description

  The present invention relates to an aluminum alloy foam used as an impact energy absorbing member that deforms and absorbs impact energy when subjected to a compressive impact load, such as a structural member of an automobile, and a method for manufacturing the same. is there. Hereinafter, the aluminum alloy foam is also referred to as foamed aluminum.

  As the impact energy absorbing member (crash box) as described above, a steel hollow member having a closed cross section is generally used as a structural member of an automobile. The steel hollow member is crushed and deformed to absorb the impact energy when it receives a compression impact input in the axial direction or the cross-sectional direction. At this time, in order to be able to absorb a larger amount of energy with a limited amount of deformation, it is effective to increase the size and thickness of the member. However, this leads to an increase in the volume and weight of the steel hollow member, which is not preferable because fuel consumption deteriorates and damage to the opponent vehicle at the time of collision between vehicles increases. Moreover, in place of a mild steel plate, a high-strength steel plate (HITEN) is used to suppress an increase in the volume and weight of the steel hollow member, but the high-strength steel plate is inferior in formability. Therefore, there are inconveniences such that the member shape is restricted and the molding process is increased.

  On the other hand, in recent years, foam metal such as foam aluminum having good recyclability has attracted attention as these impact energy absorbing members. This crash box is made of foamed aluminum in a prismatic shape. And this prismatic axis direction is arranged to coincide with the collision direction, and it absorbs the collision energy by receiving the compressive stress and collapsing at the time of collision, and reduces the impact on the occupant and the structure. is there.

  As an application example to such a crash box using aluminum foam, as a structural member such as a side member of an automobile body, foaming is performed in a hollow portion of a steel tube having a substantially circular or polygonal cross-sectional shape. What filled aluminum is known (refer patent documents 1, 2, 3, 4, 5).

  This utilizes the characteristic of foamed aluminum that compresses and deforms while exhibiting a constant reaction force. By controlling the compressive deformation of the tubular body, it is possible to increase the ability to absorb impact energy.

Furthermore, in order to increase the impact energy absorption capacity of the foamed aluminum itself, the aluminum composition is, by weight, Cu: 0.1-7%, Ca: 0.2-5%, Zn: 0.1-10%, An aluminum alloy containing one or more of the group consisting of Mg: 0.1 to 20% and Ti: 0.1 to 5%, with the balance being aluminum and inevitable impurities, has a relative density of 0.20 or less The average cell diameter is 3.7 mm or less (see Patent Documents 6 and 7).
JP-A-8-164869 (Claims, FIG. 1) Japanese Patent Laid-Open No. 11-59298 (Claims, FIG. 1) JP 2003-19977 A (Claims, FIG. 1) Japanese Patent Laying-Open No. 2003-28224 (Claims, FIG. 1) JP 2004-108541 A (Claims, FIG. 1) Japanese Patent Laid-Open No. 11-302765 (Claims, FIG. 1) JP 2000-328155 A (Claims, FIG. 1)

  However, the crush box of the type in which foamed aluminum is filled in the hollow portion of the steel pipe body or hollow member as described above has an initial instantaneous stress, that is, by the steel pipe body or hollow member as its skin material, that is, There is a problem that the maximum load in the load-displacement relationship (characteristic) becomes high and the stability of the plateau stress (compressive stress at the time of compressive deformation) is lacking. For this reason, as a practical problem, the impact energy absorption property of the foamed aluminum itself cannot be utilized.

  That is, the conventional foamed aluminum as described above cannot cope with the required energy absorption amount as an impact energy absorbing member, which has been increasing in recent years. For this reason, even if the structural member made of aluminum foam has the advantage of weight reduction, it cannot be replaced by a structural member made of high-tensile steel plate such as an automobile.

  For example, in recent years, automobile safety standards have been demanded for vehicle body front structures that can cope with medium-to-high-speed collisions such as 16km / h and 64km / h from conventional low-speed collisions of about 5mile / h. That is, even in such a medium-high speed collision, as in the case of a low-speed collision, it is necessary to design the structural members such as the left and right side members of the automobile body so as to absorb collision energy due to axial crushing deformation.

  On the other hand, a crush box made of a 440 MPa class high-tensile steel sheet that is currently used generally has an energy absorption amount of about 6.0 kJ / kg before the crush box is deformed by 50%. For this reason, in order for aluminum foam to be able to replace such a high tensile steel plate crash box, it is assumed that the aluminum foam crash box has the same volume as the high tensile steel plate crash box. An energy absorption amount equivalent to or higher than that of a high tensile steel plate crash box is required.

  In addition, if it does not have a volume equivalent to the high tensile steel plate crash box, the advantage of weight reduction that substitutes foam aluminum for the high tensile steel plate crash box does not occur.

  Increasing the density of the foamed aluminum inevitably improves the energy absorption. However, if the density of the foamed aluminum is increased, the weight increases, and the lightening effect, which is a great advantage of the foamed aluminum, is impaired.

  Therefore, there is a difficult problem of improving the amount of energy absorption without increasing the density (without impairing the weight reduction effect), and there is an aluminum alloy foam used as an energy absorbing member.

  The present invention has been made to solve such problems, and it is an object of the present invention to provide an aluminum alloy foam that can be substituted for an impact energy absorbing member made of a high-strength steel plate.

In order to achieve this object, the gist of the aluminum alloy foam of the present invention is an aluminum alloy foam used as an energy absorbing member, and is in mass%, Zn: 1.0 to 20.0%, Ca: 0.1% to 5.0%, Ti: 0.1% to 5.0%, Mg: 0.1% to 5.0%, respectively, and a foamed aluminum alloy composed of the balance aluminum and inevitable impurities A precipitate having a relative density of 0.1 or more, a particle size of 0.5 nm or more, and a particle size of 50 nm or less dispersed in a volume fraction of 1.0% or more , and having a cluster structure, and XAFS In the Zn absorption edge XANES spectrum of Zn by the analysis method, the photon energy of X-rays having the maximum normalized absorption is in the range of 9.660 keV to 9.680 keV, and 9.67. a tissue exhibiting Oite maximum value e V.

  In order to achieve this object, the gist of the method of the present invention for producing the above-described gist or a preferred embodiment of the aluminum alloy foam described below is that titanium hydride is added to the molten aluminum alloy and foamed. In mass%, Zn: 1.0 to 20.0%, Ca: 0.1 to 5.0%, Ti: 0.1 to 5.0%, Mg: 0.1 to 5.0%, respectively An aluminum alloy foam composed of the remaining aluminum and unavoidable impurities is obtained, the aluminum alloy foam is water-cooled after solution treatment at a temperature of 400 ° C. or higher, and then heat-treated at a temperature range of 100 to 150 ° C. is there.

  The inventors of the present invention previously described in Japanese Patent Application No. 2004-277531 (filed on Sep. 24, 2004) that an aluminum alloy foam having the same composition used as an energy absorbing member has a particle size of 0.5 nm. Thus, a patent application was filed characterized by having a structure in which precipitate particles of 50 nm or less were dispersed by 1.0% or more in volume fraction. This is because it has been found that the effect of improving the amount of energy absorption of fine precipitate particles having a particle size of 0.5 nm or more and 50 nm or less is much larger than coarse precipitate particles.

  Thus, the energy absorption amount of the aluminum alloy foam can be remarkably increased by dispersing or existing these fine precipitate particles as much as possible in the structure of the aluminum alloy foam. And the energy absorption amount of the crash box made of a single aluminum alloy foam can be increased.

  In contrast, in the present invention, in addition to the fine precipitate particle dispersion, the normalized absorption amount shows the maximum value in the K absorption edge XANES spectrum of Zn by the XAFS analysis method as described in the above summary. It has been found that the energy absorption amount can be improved without increasing the density of the aluminum alloy foam (without impairing the weight reduction effect) by setting the photon energy of the X-ray to the above specific range.

  The structure definition by the XAFS analysis method is a fine cluster (at the atomic structure level) composed of Al, Zn, Mg, which will be described later, composed of alloy elements such as Zn, Mg, and the like of the aluminum alloy foam. Of a group of atoms before crystallization).

  The presence of this fine cluster exhibits the effect of improving the energy absorption amount without increasing the density of the aluminum alloy foam due to a synergistic effect with the fine precipitate particles described above. In other words, the energy absorption amount is improved without increasing the density of the aluminum alloy foam by satisfying both the definition of the fine cluster by the XAFS analysis method and the fine precipitate particle specification. be able to.

  The low energy absorption of the conventional aluminum alloy foam described above is also due to the fact that the fine precipitate particles are few or the fine clusters do not exist. Incidentally, in the usual manufacturing method of foamed aluminum, since the cooling after foaming is allowed to cool to room temperature, the fine precipitate particles in the present invention are hardly generated. Moreover, in the usual manufacturing method of foamed aluminum, since the solution treatment and quenching treatment are not performed after foaming, the fine clusters in the present invention are hardly generated.

  For this reason, the conventional aluminum alloy foam can improve the energy absorption amount without increasing the density as compared with the aluminum alloy foam of the present invention, which is produced by combining these fine precipitate particles and clusters. Can not.

  As described above, in order to increase the fine precipitate particles and clusters of foamed aluminum having a specific alloy composition as in the present invention, a special manufacturing method is required as described later. And according to this invention, the aluminum alloy foam which can achieve the high impact energy absorption amount which can be substituted for the structural member made from a high-tensile steel plate can be provided.

(Relative density of foam)
In the present invention, the amount of energy absorption can be improved without increasing the density (without impairing the lightening effect). Nevertheless, in order to obtain the amount of energy absorption required for the aluminum alloy foam, it is assumed that the foam has a certain relative density.

  In this respect, as a guideline for obtaining an energy absorption amount up to 50% deformation of a general 440 MPa class high strength steel plate crash box described above, an energy absorption amount of 6.0 kJ / kg or more, The relative density is 0.1 or more. When the relative density of the foam is less than 0.1, the energy absorption amount of 6.0 kJ / kg or more of the aluminum alloy foam is obtained even in the structure having the fine precipitate particles and the cluster combined in the present invention. It may not be possible.

  Here, although the upper limit of the relative density of the foam is not particularly defined, the higher the relative density, the larger the weight, the weight reduction effect that is an advantage of the foam is impaired, and the contribution to weight reduction of automobiles and the like is reduced. However, depending on the application, a higher deformation stress than the weight reduction effect may be required. In this respect, the relative density is preferably 1.0 or less. Moreover, 0.6 or less is preferable especially for the use where the effect of weight reduction is required.

The relative density of the foam is controlled by adjusting the amount of foaming agent (TiH ₂ ) added according to the alloy composition, production conditions, equipment conditions, and the like. The relative density is obtained by cutting a 50 × 50 × 50 mm (125 cm ³ ) sample from the foam, measuring the weight of the sample, and dividing by a corresponding volume of water of 125 cm ³ = 125 g.

(Average foam diameter of foam)
In order to obtain the energy absorption amount of the aluminum alloy foam, the foam diameter (foam or bubble particle diameter) of the aluminum alloy foam is preferably as fine as possible. Even if the average foam diameter (average foam diameter) is coarsened, the energy of 6.0 kJ / kg or more of the aluminum alloy foam, when the average foam diameter (average foam diameter) is coarsened as a structure having the fine precipitate particles and clusters in the present invention. Absorption may not be obtained.

  As a guideline, it is preferable that the average foam diameter of the aluminum alloy foam is 5 mm or less. By setting the average foam diameter to a fine foam of 5 mm or less, the uniformity of the foamed particle diameter is ensured, and the compressive strength and impact absorption characteristics are improved. On the other hand, when the average foam diameter of the aluminum alloy foam exceeds 5 mm, the compressive strength and impact absorption characteristics are likely to deteriorate.

  The average foam diameter can be measured by an ordinary cross-section measurement method in which the cross-section of foamed aluminum is observed to measure the particle diameter of each foam.

(Precipitate particles)
In the present invention, in order to improve the energy absorption amount without increasing the density, first, the structure of the aluminum alloy foam is such that the precipitate particles having a particle diameter of 0.5 nm or more and 50 nm or less are 1 in volume fraction. A structure in which 0% or more is dispersed.

  If the amount of these fine precipitate particles is less than 1.0% in terms of volume fraction, it is difficult to make the energy absorption amount of the aluminum alloy foam 6.0 kJ / kg or more. The upper limit of the volume fraction of the precipitate particles is naturally determined by the alloy element content and manufacturing conditions, and is not particularly limited, but is about 10%.

The main body of the precipitate particles is a Zn—Mg compound or Zn simple substance derived from alloying elements such as Zn and Mg, mainly composed of MgZn ₂ and Mg ₂ Zn ₁₁ . In addition, the precipitate particles include Al, Ca, Ti compounds and the like. Accordingly, the precipitate particles in the present invention are mainly composed of a Zn-Mg compound and Al alone, to which Al, Ca, Ti compounds and the like are added. The elements of these precipitates can be identified and quantified by TEM observation described later.

  On the other hand, coarse precipitate particles having a particle size exceeding 50 nm have a small energy absorption improvement effect as described above. For this reason, even if the number of such coarse precipitate particles increases, it becomes difficult to set the energy absorption amount of the aluminum alloy foam to 6.0 kJ / kg or more. In addition, the precipitate particles having a particle size of less than 0.5 nm are difficult to detect and measure even with a transmission electron microscope described later. Compared with the precipitate particles having a particle size of 0.5 nm or more and 50 nm or less, After all, the energy absorption improvement effect is small.

These precipitate particles in the aluminum alloy foam structure are identified and quantified by observing the structure with a transmission electron microscope (TEM) of 100,000 to 300,000 times. In the present invention, the maximum diameter of each precipitate particle present in the structure in the TEM field of 1 μm × 1 μm (1 μm ² ) is measured as the particle diameter d of each precipitate particle. Then, the total area ratio of all the precipitate particles whose particle diameter d falls within the range of 0.5 to 50 nm is obtained, and this value is calculated as the volume fraction of the precipitate particles having a particle diameter of 0.5 nm or more and 50 nm or less. Rate. Of course, in order to achieve reproducibility and uniformity of the foam structure, the observation field of view may be made plural for each part of the foam. In this case, the area ratio and volume fraction are obtained by measuring the results of multiple fields of view. Further averaged.

  Therefore, in the present invention, precipitate particles having a particle diameter d (maximum diameter) of less than 0.5 nm or precipitate particles having a particle diameter d of more than 50 nm are not measured for the volume fraction.

  In other words, in the present invention, if the structure has a particle size of 0.5 nm or more and precipitate particles of 50 nm or less dispersed by 1.0% or more in volume fraction, a request for energy absorption amount of the aluminum alloy foam is required. The presence of coarse precipitate particles having a particle diameter d of more than 50 nm or precipitate particles having a particle diameter d of less than 0.5 nm is allowed within a range not impairing the characteristics.

(cluster)
In the present invention, in order to improve the energy absorption amount without increasing the density, in addition to the above fine precipitate regulation, the structure of the aluminum alloy foam is measured in the Zn K absorption edge XANES spectrum by the XAFS analysis method. In addition, it is assumed that the X-ray photon energy at which the normalized absorption amount has the maximum value is the above specific range.

  In the present invention, XAFS (X-ray Absorption Fine Structure, X-AFS) is a technique for grasping the microscopic (local) form and structure of Zn in the structure of an aluminum alloy foam at the atomic structure level of Zn. (Line absorption fine structure) analysis method was used.

As described above, the structure definition by this XAFS analysis method is such as Al _17-x Zn ₃ Mg _x , Al _19-x ZnMg _x , which is composed of the alloy elements of the aluminum alloy foam, such as Zn and Mg. It means the existence of fine clusters consisting of Al, Zn, Mg and below nano level.

  The presence of the fine clusters exhibits the effect of improving the energy absorption amount without increasing the density of the aluminum alloy foam together with the presence of the fine precipitate particles. In other words, the energy absorption amount can be improved without increasing the density of the aluminum alloy foam by causing both the fine clusters and the fine precipitate particles described above to exist in a specific amount.

Specifically, as a result of the XAFS analysis method, in the Zn K absorption edge XANES spectrum, the photon energy of the X-ray when the normalized absorption amount shows the maximum value is in the range of 9.660 keV or more and 9.680 keV or less. with some, to indicate Oite maximum value 9.67Ke V, the energy absorption amount increases.

Therefore, in the present invention, in the Zn K absorption edge XANES spectrum by the XAFS analysis method, the X-ray photon energy at which the normalized absorption amount shows the maximum value is in the range of 9.660 keV or more and 9.680 keV or less, a tissue exhibiting Oite maximum value 9.67ke V. This makes it possible to improve the energy absorption amount without increasing the density of the aluminum alloy foam together with the above-mentioned precipitate regulation.

(XAFS analysis method)
However, these fine clusters have a nanometer level or less, and their presence cannot be directly detected by ordinary tissue observation means including SEM, TEM and the like. On the other hand, in the present invention, the presence of an indirect presence due to the characteristics of the X-ray photon energy waveform in which the normalized absorption amount shows the maximum value in the K absorption edge XANES spectrum of Zn by the XAFS analysis method. Was detected.

  This is because the existence form and structure at the atomic structure level of Zn in the structure of the aluminum alloy foam containing Zn correlates with the energy absorption amount of the aluminum alloy foam. And as mentioned above, it is because it is difficult to grasp in detail at the atomic structure level of Zn even by microscopic analysis such as SEM and TEM used for normal structure analysis or X-ray diffraction test.

  As described above, in the microscopic analysis such as SEM and TEM used for the normal structure analysis, even when the magnification is increased, the Zn microscopic existence form and structure, the detailed grasp at the atomic structure level of Zn Is difficult. Moreover, information such as Zn clusters (a group of atoms before crystallization at the atomic structure level) cannot be obtained even in an X-ray diffraction test or the like.

  On the other hand, in the XAFS analysis method, information on the atomic structure or cluster can be obtained by analyzing the X-ray absorption spectrum of the measurement object. An example of using this XAFS analysis method to determine the arrangement of atoms (radial distribution around iron atoms) in a rust layer deeply related to the weather resistance of the steel surface is disclosed in Japanese Patent Laid-Open No. 2002-256463 ([0012]). ~ [0023]). An example of the structural analysis of Al-Nd around Nd in an Al-Nd alloy thin film for liquid crystal display panel wiring materials is the inspection technology 2000.1. "6th Analysis Technology for Local Structure of Electronic Materials" Page). A number of XAFS measuring devices themselves are also disclosed in JP 2002-318208 A, JP 2001-21507 A, JP 2001-33403 A, and the like.

(Principle of XAFS analysis method)
The principle of material structure analysis by the XAFS analysis method will be described below. When the absorptance of a material is measured while increasing the photon energy of X-rays, it decreases corresponding to the increase of photon energy of X-rays. However, there is an X-ray photon energy whose absorption rate increases rapidly at a certain X-ray photon energy (X-ray absorption edge) specific to the material. At this time, some of the photoelectrons generated by the X-ray absorption are reflected as structural information on the X-ray absorption amount by scattering and interference by a plurality of atoms. Therefore, if the amount of X-ray absorption of the material is monitored, information on the atomic structure of the material or clusters in the structure can be obtained.

  More specifically, when a substance is placed on the fluorescent X-ray beam line, the X-ray intensity irradiated to the substance (incident X-ray intensity: I0) and the X-ray intensity transmitted through the substance (fluorescent X-ray intensity) : I t), the amount of X-ray absorption (X-ray absorption coefficient μ) by the substance is calculated from μt = In (I 0 / I t) (where t: sample thickness).

  Here, the X-ray photon energy (wavelength) incident on the aluminum alloy foam containing Zn, which is the above substance, is changed, and the increase or decrease of the X-ray absorption coefficient μ is monitored (scanned). An X-ray absorption spectrum is measured. Then, a sharp rise (Zn atom absorption edge: Zn K absorption edge) at which the X-ray absorption coefficient is maximized is observed at a specific X-ray photon energy. This corresponds to the difference between the excitation energy of the incident X-ray and the binding energy of the core electron of Zn when the photon energy of the incident X-ray becomes comparable to the binding energy of the core electron of Zn as the target atom. This is because photoelectrons having kinetic energy are emitted.

  The energy position of the absorption edge is unique to each element, such as Zn. For this reason, if structural information can be extracted in the energy region near the absorption edge, this means that the information is unique to the element.

(ZAN XANES)
The X-ray absorption near edge structure (XANES) is a fine structure that appears in the photon energy at the absorption edge in XAFS, and the X-ray absorption spectrum of this fine structure is the XANES spectrum. Say. In the XAFS measurement by the fluorescent X-ray yield method, the XANES spectrum at the absorption edge of such Zn atoms can be selectively measured.

(Example by actual XAFS analysis method)
FIG. 1 shows the (absorption) spectrum of X-ray photon energy in the K absorption edge XANES spectrum of Zn by XAFS analysis of an aluminum alloy foam. In FIG. 1, A is an actually measured spectrum of X-ray photon energy of an invention example (invention example 1 in an example table 2 described later), and B is an actually measured X-ray photon energy spectrum of the invention example (invention example 2 in an example table 2 described later).

In FIG. 1, C is an Al _17-x Zn ₃ Mg _x , and D is an X-ray photon energy spectrum by simulation of an Al _19-x ZnMg _x cluster. Further, E is a photon energy spectrum of X-rays by simulation of MgZn ₂ precipitates and F is Mg ₂ Zn ₁₁ precipitates.

  In FIG. 1, the spectra are displayed with the zero point shifted so as not to overlap each other.

For reference, FIG. 2 schematically shows the atomic structures of the Al _17-x Zn ₃ Mg _x , Al _19-x ZnMg _x clusters, and the MgZn ₂ and Mg ₂ Zn ₁₁ precipitates.

In the spectra of Invention Examples A and B in FIG. 1, the photon energy of X-rays having the maximum normalized absorption is in the range of 9.660 keV or more and 9.680 keV or less. At the same time, has a spectrum shape illustrated a Oite maximum value 9.67ke V.

  On the other hand, in the spectra of Invention Examples A and B, the spectrum shape (waveform) in the above range where the normalized absorption amount shows the maximum value, especially the vibration period and amplitude on the high energy side after 9.67 keV are within the above range In FIG. 5, the spectrum shape (waveform) of the C, D Al, Zn, Mg cluster (estimated) is very similar.

  In the simulation spectrum shape of C, D Al, Zn, Mg clusters (estimated), the maximum value is shown on the high energy side from 9.67 keV to 9.68 keV. Note that C, D Al, Zn, and Mg clusters could not be observed by TEM, so they were assumed to be clusters.

  On the other hand, in the invention examples A and B of FIG. 1, the spectrum shape (waveform) from the rise of the absorption spectrum of 9.65 to 9.67 keV to the peak top (top, maximum value) is the MgZn precipitation of E and F The object exhibits a spectral shape very similar to the simulation spectrum in this range.

  In the simulation spectrum shape of the MgZn precipitates of E and F, the maximum value is shown on the low energy side from 9.66 keV to 9.67 keV. It was confirmed by TEM that the MgZn precipitates of E and F were actually precipitates.

That is, it can be seen that Invention Examples A and B in FIG. 1 have a spectrum shape (waveform) in which the waveforms of E and F MgZn precipitates in this range are synthesized. Maximum particularly definitive in 9.67Ke V of invention sample A (top) is, C, the high energy of the cluster of D - the waveform of the top in the side, E, the low-energy deposition of F - the top in the side It is composed by combining waveforms.

More specifically, in Invention Examples A and B, the X-ray photon energy is 9.660 keV or more and 9.680 keV or less when the normalized absorption amount shows the maximum value in the K absorption edge XANES spectrum of Zn. with the range, and has a spectral shape showing a Oite maximum value 9.67ke V.

  From FIG. 1, it can be seen that Invention Example A has a structure having both C and D clusters and E and F precipitates. In other words, Invention Example A in FIG. 1 has a structure that satisfies both the cluster definition of the present invention by the XAFS analysis method and the precipitate definition of the present invention.

On the other hand, like the structure of the aluminum alloy foam of the invention of the above-mentioned Japanese Patent Application No. 2004-277531 (filed on Sep. 24, 2004), the precipitates of E and F have the above-mentioned C and D. In the structure where no cluster exists, the maximum value is shown on the low energy side between 9.66 keV and 9.67 keV as in the simulation spectrum shape of the MgZn precipitates of E and F. In other words, the photon energy of X-rays normalized absorption indicates a maximum value, or 9.660KeV, although in the following range 9.680KeV, have a spectral shape showing a Oite maximum value 9.67Ke V Absent.

Further, in the structure of the aluminum alloy foam having the C and D clusters but not having the precipitates of E and F, as in the simulation spectrum shape of the C and D clusters, 9.67 keV and later, 9. The maximum value is shown on the high energy side up to 68 keV. In other words, the photon energy of X-rays normalized absorption indicates a maximum value, or 9.660KeV, although in the following range 9.680KeV, similarly, spectral shape indicating the Oite maximum value 9.67Ke V It is not.

(Experiment and analysis method of XAFS analysis)
Measurements were made by the transmission method using the XAFS experimental apparatus for the sun beam BL16B2, a dedicated industrial beamline construction and use consortium at the High Brightness Optical Science Research Center and SPring-8, a large synchrotron radiation experiment facility. A Si (111) crystal was adopted as the two-crystal spectrometer, and the K absorption edge measurement of Zn was performed at room temperature.

  The obtained data (spectrum) was analyzed by XAFS analysis software “WinXAS3.1” produced by Thorsten Ressler, University of California.

In addition, using the “FEFF8” XAFS spectrum simulation software by JJ Rehr published by the University of Washington FEFF Project, each cluster of Al _17-x Zn ₃ Mg _x of C and Al _19-x ZnMg _x of D in FIG. and MgZn _2, each deposit of F of Mg ₂ Zn ₁₁ of E, was performed XANES, RDF spectrum simulated (photon energy spectrum shape simulation of X-ray).

Theoretical analysis shows that an existing Al—Zn alloy (Al ₁₇ Zn ₃ , Al ₁₉ Zn) is filled with Mgx and two existing Mg—Zn alloys (MgZn ₂ , Mg _2). Zn ₁₁ ) is XANES spectrum simulation calculation by FEFF8.

  Each structural model is from "Pearson's Handbook of Crystallographic Data for Intermetallic Phases, Second Edition, 1996" (Al-Zn alloy: p1035, Mg-Zn alloy: pp4318-4319) published by "The Materials Information Society" Quoted.

(Aluminum alloy composition for foaming)
The aluminum alloy composition for foaming, which satisfies the characteristics of the aluminum alloy foam, such as required strength and energy absorbing ability as an energy absorbing member, and also relates to the uniformity of foaming, will be described below.

  In the present invention, the composition of the aluminum alloy for foaming is such that, in order to ensure the amount of fine precipitates and to satisfy the necessary properties as a foam, such as the amount of energy absorption, Zn: 1. 0 to 20.0%, Ca: 0.1 to 5.0%, Ti: 0.1 to 5.0%, Mg: 0.1 to 5.0%, respectively, the balance aluminum and inevitable impurities It shall consist of

(Zn)
Zn precipitates as a simple substance of Zn and coexists with Mg to form a Zn—Mg compound that is the main component of the precipitate particles. It is also an effective element for improving the strength by cluster formation. Further, it has an effect of coagulating and shrinking, and an effect of increasing the compressive deformability by forming a thin film portion on a part of the cell wall. In order to exert these actions, the content of 1.0% or more is necessary. However, if it is excessively contained exceeding 20.0%, a coarse Zn—Mg compound is formed, and on the contrary, the energy absorption amount is reduced. Moreover, stabilization of the bubble particle diameter of foaming aluminum will be inhibited, a bubble will become coarse, and compressive strength will be reduced. Therefore, the Zn content is in the range of 1.0 to 20.0%.

(Mg)
Mg coexists with Zn to form a Zn—Mg compound that is the main component of the precipitate particles. In addition, it is an element effective for improving the strength by cluster formation. Furthermore, in the production of foamed aluminum in cooperation with Zn, it acts to increase the viscosity of the molten metal and stabilize the bubbles to make the foam homogeneous. Have. In order to obtain the effect, it is necessary to contain at least 0.1% of Mg. On the other hand, when it contains excessively exceeding 5.0%, a coarse Zn-Mg compound will be formed and an energy absorption amount will be reduced on the contrary. Further, the viscosity of the molten metal is excessively increased, the fluidity of the molten metal is remarkably lowered, and the foaming agent is difficult to disperse. On the other hand, the fineness and uniformity of the foam are inhibited, and the compressive strength is lowered. Therefore, the Mg content is in the range of 0.1 to 5.0%.

(Ca)
Ca increases the viscosity of the molten aluminum alloy at the time of producing foamed aluminum and stabilizes the bubbles to make the foam homogeneous and to achieve foam refinement and uniformity. Have. In order to obtain the effect, the content of at least 0.1% is necessary. On the other hand, if the content exceeds 5.0% excessively, the viscosity of the molten metal is excessively increased, the fluidity of the molten metal is remarkably lowered, and it becomes difficult to disperse the foaming agent. And reduce the compressive strength. Therefore, the Ca content is in the range of 0.1 to 5.0%.

(Ti)
Ti is an element effective for improving the strength of foamed aluminum. In order to bring out the effect, it is necessary to contain at least 0.1% or more. On the other hand, when it contains excessively exceeding 5.0%, the fluidity | liquidity of a molten metal will be reduced and it will crystallize and it will make aluminum brittle. Therefore, the Ti content is in the range of 0.1 to 5.0%.

  In addition, Cu may inhibit the uniformity of the foamed particle diameter in the foaming process. For this reason, in the present invention, Cu is an impurity, and the Cu content is preferably as low as possible. Further, other elements are also impurities, and it is preferable that the content is as small as possible. However, there are also problems in the production of foamed aluminum, such as melting and refining to reduce the content of these other elements, and it does not degrade the characteristics of foamed aluminum. Inclusion is allowed.

(Production conditions)
Next, preferable production conditions for producing the foamed aluminum of the present invention will be described below. In the present invention, the manufacturing process itself of the foamed aluminum is the same as the conventional one.

  However, as described above, in order to make the foamed particle diameter of the foamed aluminum having a specific alloy composition into microbubbles as an average particle diameter and to make the structure defined in the present invention, as described later, an aluminum alloy foam is used as described later. After being obtained, this aluminum alloy foam needs to be subjected to a solution treatment at a temperature of 400 ° C. or higher, then water-cooled, and heat treatment (aging treatment) at a temperature of 100 ° C. or higher is required.

  First, in a melting furnace, alloy component elements such as Zn: 1.0 to 20.0% and Mg: 0.1 to 5.0% and calcium 0.1 to 5. 0% is added, and the molten metal is stirred in the atmosphere for about 5 minutes to increase the viscosity.

  And after pouring the molten metal after this thickening into the casting_mold | template in a 600-700 degreeC atmospheric melting furnace, a predetermined amount of titanium hydride is added. Then, for example, after stirring for 1 to 10 minutes, the stirrer is removed, and the mold is held for about 1 to 10 minutes in the atmospheric melting furnace in the temperature range to complete foaming.

  Conventionally, after this holding, the mold is taken out from the furnace and commercialized while being allowed to cool to room temperature. Therefore, the precipitate particles are inevitably hardly deposited, and the necessary amount of the fine precipitate particles is in the structure. Cannot be dispersed. In addition, the hardness of the foamed cell wall must be low.

  On the other hand, in the present invention, after the mold is taken out from the furnace and allowed to cool to room temperature (after obtaining the foam), this aluminum alloy foam is water-cooled after solution treatment at a temperature of 400 ° C. or higher, and 100 Heat treatment (aging treatment) is performed at a temperature of ℃ or higher.

(Solution treatment)
The solution treatment is performed at a temperature of 400 ° C. or higher. If this temperature is too low as less than 400 ° C., there will be no solution treatment effect, and it will be the same as when no solution treatment is performed, and fine clusters cannot be present in the aluminum alloy foam structure. For this reason, unless the heat treatment described later is performed, fine precipitate particles cannot be present, and the conventional aluminum alloy foam is obtained. Therefore, in the K absorption edge XANES spectrum of Zn by the XAFS analysis method, the photon energy of X-rays with the maximum normalized absorption amount is not in the range of 9.660 keV or more and 9.680 keV or less.

  Incidentally, when the solution treatment temperature is too low as less than 400 ° C. or when the solution treatment is not performed and the heat treatment described below is performed, the aluminum alloy foam structure has no fine clusters, 1 are present, and the K absorption edge XANES spectrum of Zn by the XAFS analysis method has a shape close to E or F in FIG.

After this solution treatment, it is rapidly cooled (forced cooling) by water cooling. When air cooling or standing cooling is performed after the solution treatment, the cooling rate is too low, and the Zn—Mg compound precipitate mainly composed of MgZn ₂ and Mg ₂ Zn ₁₁ is coarsened. For this reason, it is impossible to disperse precipitate particles having a particle size of 0.5 nm or more and 50 nm or less in the structure by 1.0% or more in terms of volume fraction. Further, the hardness of the foamed cell wall is also reduced.

(Heat treatment)
After solution treatment and water cooling, a heat treatment (aging treatment) is performed at a temperature of 100 ° C. or higher. The holding time is about 3 hours or more and about 100 hours or less in this temperature range. The upper limit of the heat treatment temperature is 150 ° C.

  This heat treatment may be reheated after the water cooling is performed to room temperature, or the water cooling may be stopped in a temperature range of 100 to 150 ° C. and then maintained in a temperature range of 100 to 150 ° C. good.

  By carrying out such a relatively low temperature and long-time heat treatment, precipitate particles having a particle size of 0.5 nm or more and 50 nm or less are dispersed in the structure by 1.0% or more by volume fraction. Can do. Further, the hardness of the foamed cell wall can be improved.

  Of course, depending on the component composition and other conditions, even if the holding temperature is too low or the holding time is too short, the effect of the heat treatment is lost. On the other hand, even if the holding temperature is too high or the holding time is too long, the precipitate particles are coarsened instead.

  After such cooling, the foam is taken out from the mold and machined to obtain a product aluminum alloy foam having a desired shape such as a prism or square.

  Examples of the present invention will be described below. By changing the heat treatment conditions after foaming shown in Table 2, aluminum alloy foams having respective chemical component compositions shown in Table 1 were produced. As the characteristics of these foams, X-rays exhibiting the maximum normalized absorption in the average foam diameter, relative density, cell wall hardness, volume fraction of precipitates, and the K absorption edge XANES spectrum of Zn by the XAFS analysis method. The photon energy of was investigated. Moreover, 50% energy absorption was evaluated as a performance of a foam.

  Specifically, first, alloy component elements such as Zn, Mg, and Ca were added to industrial pure aluminum in a melting furnace, and the molten metal was stirred in the atmosphere for about 5 minutes to increase the viscosity. And after pouring the molten metal after this thickening into the casting_mold | template in an about 700 degreeC air melting furnace, about 0.1 to 5.0% of titanium hydride was added as Ti. Then, after stirring for about 2 minutes, the stirrer was removed, and the mold was held in the atmospheric melting furnace at about 700 ° C. for about 4 minutes to complete foaming.

  After this holding, the mold was removed from the furnace and allowed to cool to room temperature. Each of these foams was heat-treated under the conditions shown in Table 2. Thereafter, samples were collected from each of these foams, and the structure, characteristics, and performance were investigated as follows.

(Average foam diameter, foam cell wall hardness)
The average foam diameter of the sample was measured by the above-described cross-sectional measurement method, and the relative density of these samples was also determined by the method described above. And the hardness of the foamed cell wall of these samples was also measured with a micro Vickers hardness tester by applying a load of 50 g at five locations, and the average values thereof were obtained.

(Precipitate)
As a pretreatment of the sample, a Φ3 mm thin film sample was cut out from a part of the foam cell of the above sample, and this sample was further thinned to 200 μm by chemical polishing with nitric acid and mechanical polishing, and further subjected to electrolytic polishing with nitric alcohol solution. Thinning was performed. This was measured by TEM observation using a bright field method, and the volume fraction of precipitate particles having a particle size of 0.5 nm or more and 50 nm or less was measured by the method described above. There were five measurement sites, and the volume fraction was the average. In addition, when the composition of these precipitate particles was confirmed by the method described above, the main components were a Zn—Mg compound and Zn alone.

(XAFS analysis method)
Using the above sample, the X-AFS experimental apparatus described above was used to measure Zn K absorption edge XANES spectrum by the transmission method, and the analysis was performed as described above. The photon energy of X-rays the normalized absorption indicates a maximum value, or 9.660KeV, as well as a range of 9.680KeV, ○ those that exhibit Oite maximum value 9.67Ke V, maximum Although the photon energy of X-rays showing the value is within the above range, those which do not exhibit Oite maximum value 9.67ke V △, as × those photon energy of X-rays showing the maximum value is outside the range evaluated.

(Energy absorption)
From the aluminum alloy foam, 50 mm in height, 50 mm in width, and 50 mm in length were cut out by machining, and when subjected to a static compression test in the longitudinal direction of the foam using an Instron universal compression tester 50% energy absorption was determined. These results are also shown in Table 2.

As apparent from Tables 1 and 2, Invention Examples 1 to 4, which are aluminum alloys A to D within the composition of the present invention, were subjected to solution treatment, cooling by water cooling, and subsequent heat treatment under appropriate conditions shown in Table 2. Yes. As a result, the grain size is 0.5 nm or more and 50 nm or less precipitate particles are dispersed in a volume fraction of 1.0% or more, and normalized in the Zn K absorption edge XANES spectrum by the XAFS analysis method. photon energy of X-rays absorption indicates the maximum value is more than 9.660KeV, as well as a range of 9.680KeV, it shows Oite maximum value 9.67ke V.

  For this reason, while the relative density is a relatively low density level of 0.24, the average hardness of the foamed cell wall is 60 Hv or more, and the energy absorption is 6.5 kJ / kg or more.

  On the other hand, although the comparative example 5 is the aluminum alloy A in this invention composition, the solution treatment of a foam and the subsequent heat processing are not performed like the past. For this reason, the volume fraction of the fine precipitate particles is less than 1.0%, and the K absorption edge XANES spectrum of Zn by the XAFS analysis method is also outside the scope of the invention. As a result, the average hardness of the foamed cell wall is less than 60 Hv, and the compressive stress and energy absorption are low.

  Comparative Example 6 is an aluminum alloy A within the composition of the present invention, in which the foam is heat-treated but not subjected to a solution treatment. Therefore, although the volume fraction of the fine precipitate particles is within the scope of the invention, the K absorption edge XANES spectrum of Zn by the XAFS analysis method is also outside the scope of the invention. As a result, the average hardness and energy absorption of the foamed cell walls are slightly lower than those of the inventive examples. Incidentally, this comparative example 6 corresponds to the above-mentioned Japanese Patent Application No. 2004-277531.

  FIG. 4 shows the structure of the foam of Invention Example 1 and FIG. 3 shows the structure of the foam of Comparative Example 6 as a 150,000-fold TEM (transmission electron microscope) photograph. 3 and 4, the white background is aluminum, and the black dots indicate precipitate particles. 3 and 4, it can be seen that Invention Example 1 has finer, more densely and uniformly dispersed precipitate particles.

  Comparative Example 7 is an aluminum alloy A within the composition of the present invention, and the solution treatment temperature is too low although the foam is heat-treated. For this reason, as in Comparative Example 6, although the volume fraction of the fine precipitate particles is within the range of the invention, the K absorption edge XANES spectrum of Zn by the XAFS analysis method is out of the range of the invention. For this reason, the relative density is 0.24, which is slightly higher than that of the invention example, and the average hardness and energy absorption amount of the foamed cell wall are slightly lower than those of the invention example.

  Comparative Example 8 is an aluminum alloy A within the composition of the present invention, which is subjected to solution treatment and subsequent heat treatment, but cooling after the solution treatment is air cooling, and the cooling rate is too small. For this reason, although the K absorption edge XANES spectrum of Zn by the XAFS analysis method is within the scope of the invention, the volume fraction of the fine precipitate particles is outside the scope of the invention. For this reason, the average hardness and energy absorption amount of the foamed cell wall are slightly lower than those of the inventive examples.

  Comparative Example 9 is an aluminum alloy A within the composition of the present invention, which is subjected to a solution treatment but is not subjected to a subsequent heat treatment. For this reason, although the K absorption edge XANES spectrum of Zn by the XAFS analysis method is within the scope of the invention, the volume fraction of the fine precipitate particles is outside the scope of the invention. For this reason, the average hardness and energy absorption amount of the foamed cell wall are slightly lower than those of the inventive examples.

  Comparative Examples 10 to 17 use aluminum alloys E to L in Table 1 in which the contents of Zn, Ca, Ti, and Mg are out of the lower limit or upper limit of the composition of the present invention, respectively. For this reason, heat treatment as in the invention example is performed, and although the K absorption edge XANES spectrum of Zn by the XAFS analysis method and the volume fraction of the fine precipitate particles are within the scope of the invention, the energy absorption amount is generally Low.

  From the above results, the significance of each requirement in the aluminum alloy foam of the present invention and the significance of preferred production conditions are supported.

  As described above, according to the present invention, it is possible to provide an aluminum alloy foam that can replace an impact energy absorbing member made of a high-tensile steel plate. As a result, the present invention can be applied to an impact energy absorbing member that deforms and absorbs impact energy when subjected to a compressive impact load at the time of collision, such as a structural member of an automobile.

It is explanatory drawing which shows the spectrum of the X-ray photon energy in the K absorption edge XANES spectrum of Zn by the XAFS analysis method of an aluminum alloy foam. _{Al 17-x Zn 3 Mg x} , it is a schematic diagram showing each an atomic structure of each deposit of Al _19-x each cluster ZnMg _x, and MgZn _2, Mg ₂ Zn _11. It is a drawing substitute photograph which shows the structure | tissue of invention example foam. It is a drawing substitute photograph which shows the structure | tissue of a comparative example foam.

Claims (3)

An aluminum alloy foam used as an energy absorbing member, and in mass%, Zn: 1.0-20.0%, Ca: 0.1-5.0%, Ti: 0.1-5.0% , Mg: 0.1 to 5.0% of each, foamed aluminum alloy consisting of the balance aluminum and inevitable impurities, the relative density is 0.1 or more, the particle size is 0.5 nm or more In addition, a precipitate particle of 50 nm or less is dispersed in a volume fraction of 1.0% or more , has a cluster structure, and has a maximum normalized absorption in the Zn K absorption edge XANES spectrum by the XAFS analysis method. the photon energy of the X-ray indicated, more 9.660KeV, as well as a range of 9.680KeV, characterized in that it is a tissue exhibiting Oite maximum value 9.67Ke V aluminum case Gold foam.   The aluminum alloy foam according to claim 1, wherein the aluminum alloy foam is used as a simple substance for an energy absorbing member.   A method for producing an aluminum alloy foam according to any one of claims 1 to 2, wherein titanium hydride is added to a molten aluminum alloy to cause foaming, and in mass%, Zn: 1.0 to 20 0.0%, Ca: 0.1 to 5.0%, Ti: 0.1 to 5.0%, Mg: 0.1 to 5.0%, respectively, and the balance aluminum and inevitable impurities A method for producing an aluminum alloy foam, characterized in that an alloy foam is obtained, the aluminum alloy foam is subjected to solution cooling at a temperature of 400 ° C or higher and then water-cooled, and then heat-treated at a temperature range of 100 to 150 ° C.

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