JP2008106341A - Aluminum alloy foam for energy-absorbing member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy foam in which more deformation progresses in a state of a plateau stress being kept low and can provide excellent protection properties for pedestrians (leg). <P>SOLUTION: The aluminum alloy foam which is installed in front of a bumper beam and is suitable for an energy-absorbing member such as a protection member for pedestrians is produced by foaming an aluminum alloy comprising, by mass%, 0.5 to 20.0% Zn, 0.1 to 5.0% Ca, 0.1 to 5.0% Ti, 0.1 to 5.0% Mg, further at least one element of 0.1 to 5.0% Ag and 0.1 to 5.0% Zr, and the balance aluminum with unavoidable impurities. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an aluminum alloy foam used as an energy absorbing member in automobiles and the like. The energy absorbing member targeted by the present invention is deformed by receiving a compressive impact load in the event of a collision between an automobile and a pedestrian, such as a pedestrian protection member provided on the front side of an automobile bumper beam. It is an impact energy absorbing member (energy absorbing member) that absorbs. Hereinafter, the aluminum alloy foam is also referred to as foamed aluminum.

  As an impact energy absorbing member (crash box) for an automobile or the like, 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).

  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.

  For this reason, as a crash box made of aluminum foam alone, taking advantage of its light weight, it is possible to absorb collision energy even in medium-high speed collisions, as in the case of low-speed collisions. Various types of foamed aluminum, which can be substituted for, have been proposed.

  For example, the composition of the aluminum alloy foam is as follows: Zn: 1.0-20.0%, Ca: 0.1-5.0%, Ti: 0.1-5.0%, Mg: 0.1-5 0.04% each, consisting of the balance aluminum and unavoidable impurities, and further reducing the average particle size of the foam and making it an aluminum alloy with a higher relative density to make the foam particle size uniform. Has been proposed (Patent Document 8). In addition, it has been proposed to increase the average hardness of the cell wall of the foam of this aluminum alloy composition (Patent Document 9). Furthermore, it has also been proposed to form a structure in which a predetermined amount of precipitate particles of 50 nm or less of the foam of this aluminum alloy composition is dispersed (Patent Document 10).

  In addition, it has been proposed to increase the energy absorption by increasing the plateau stress of the foam or lengthening the plateau deformation region represented by the product of the stress and the deformation (Non-Patent Document 1, 2).

All of these proposals attempt to increase the plateau stress of the aluminum alloy foam to 4 MPa or more to meet the energy absorption performance of the currently used crush box made of 440 MPa class high-tensile steel plate. The aluminum alloy foam is being replaced with a high-tensile steel plate as a crash box.
JP-A-8-164869 JP-A-11-59298 Japanese Patent Laid-Open No. 2003-19977 JP 2003-28224 A JP 2004-108541 A JP-A-11-302765 JP 2000-328155 A JP 2006-77316 A JP 2006-77317 A JP 2006-89813 A Outline of the Spring Meeting of the Japan Institute of Metals (2004), p139 Porous Metals and Metal Foaming Technology (2005), p517

  As described above, the crash box made of foam aluminum alone disclosed so far only absorbs energy when it collides with other vehicles and other rigid bodies (guardrails, telephone poles, etc.). It is assumed. For this reason, as described above, an attempt is made to increase the plateau stress of the aluminum alloy foam in accordance with the energy absorption performance of the crash box made of a high-strength steel plate.

  On the other hand, in recent years, bumpers of automobiles and the like have been demanded to protect pedestrians, particularly their legs (lower limbs and knees), assuming that they collide with pedestrians. When protecting the leg part of such a pedestrian, the performance which protects a pedestrian's leg part by absorbing the collision energy which the bumper added by the pedestrian collision is calculated | required.

  In response to such a problem, an aluminum alloy foam is disposed on the front side of the bumper beam, and when the pedestrian collides with the automobile (front end or rear end), the impact load energy is applied to the disposed aluminum alloy foam. If the body is deformed and absorbed in the cross-section (width) direction or the axial (longitudinal) direction, it will lead to protection of pedestrians.

  Actual pedestrian protection is supported by providing a relatively thick absorber (cushion material, energy absorbing member) such as urethane foam or polystyrene on the front side of the bumper beam and the back side of the bumper cover. There are limits and restrictions on the performance and thickness of the absorber.

  On the other hand, since the aluminum alloy foam is lightweight and in some cases the absorber can be omitted or thinned, there is an advantage that the weight of the automobile body does not increase so much. Furthermore, there is a great advantage that the bumper beam strength and energy performance (collapse performance) on the premise of energy absorption at the time of collision with the above-mentioned “high-rigidity object” do not need to be lowered for pedestrian protection.

  However, as described above, when the plateau stress of the aluminum alloy foam is high, a pedestrian, particularly a pedestrian leg and a vehicle (front or rear), is loaded on the pedestrian leg when a collision occurs. Therefore, it cannot be used as a pedestrian protection member.

  In order to cope with pedestrian protection, the pedestrian protection member (energy absorption member, impact energy absorption member) provided on the front side of the bumper beam can preferably reduce the generated load, acceleration, and the like during a pedestrian collision. When protecting the legs of pedestrians in the event of a collision, the cross-section (width) direction and the axial (longitudinal) direction with a much smaller collision load than the collision between the vehicle bodies or between the vehicle body and other structures. Need to absorb the energy.

  In this respect, when applied to such an aluminum alloy foam as such a pedestrian protection member, unlike the above-described conventional aluminum alloy foam, more and more plateau stress can be maintained. It is required to have excellent characteristics for progressing deformation, that is, excellent protection characteristics for pedestrians (legs).

  The present invention has been made in order to solve such a problem, and has a characteristic that more deformation proceeds while keeping the plateau stress low, and is excellent in protection characteristics of a pedestrian (leg). It is to provide an aluminum alloy foam.

  In order to achieve this object, the gist of the aluminum alloy foam for an energy absorbing member of the present invention is mass%, Zn: 0.5-20.0%, Ca: 0.1-5.0%, Ti : 0.1 to 5.0%, Mg: 0.1 to 5.0%, respectively, and Ag: 0.1 to 5.0%, Zr: 0.1 to 5.0% Alternatively, the aluminum alloy containing two types and the balance aluminum and unavoidable impurities is foamed.

  As for the protective characteristics of pedestrians (legs), the plateau stress is kept low, and the aluminum alloy foam maintains a low plateau stress of 5 MPa or less in a deformation region of 85% or less. It is preferable to have the following characteristics.

  The use of the aluminum alloy foam of the present invention as an energy absorbing member is preferably for an automobile body that requires protection of pedestrians (legs). And it is preferable that an energy absorption member is a pedestrian protection member provided in the bumper beam front side.

  By making the aluminum alloy foam of the present invention have the above-described composition of the present invention, it is possible to improve the characteristics of more deformation while keeping the plateau stress of the aluminum alloy foam low. As a result, as a pedestrian protection member (energy absorbing member, impact energy absorbing member) provided on the front side of the bumper beam, it is possible to reduce the generated load, acceleration, and the like at the time of a pedestrian collision.

(Aluminum alloy composition for foaming)
Aluminum alloy composition for foaming that satisfies basic characteristics such as necessary strength of energy-absorbing member of aluminum alloy foam and pedestrian protection characteristics that allow more deformation to proceed while keeping plateau stress low Is described below.

  In the present invention, the composition as a premise of the aluminum alloy for foaming is Zn: 0.5 to 20 in mass% in order to satisfy basic properties (required properties) such as strength and compression deformability as a foam. 0.0%, Ca: 0.1 to 5.0%, Ti: 0.1 to 5.0%, and Mg: 0.1 to 5.0%, respectively. As a pedestrian protection member, Ag: 0.1 to 5.0%, Zr: 0.1 to 0.1 in order to satisfy pedestrian protection characteristics such that more deformation proceeds while keeping the plateau stress low. Contains one or two of 5.0%. Further, the balance composition (balance) is made of aluminum and inevitable impurities.

(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 when coexisting with Mg. 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 0.5% or more is necessary. However, when it exceeds 20.0% and it contains excessively, a coarse Zn-Mg compound will be formed and a plateau stress will be reduced on the contrary. 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 0.5 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, and further has the effect of increasing the viscosity of the molten metal and stabilizing the bubbles to make the foam homogeneous during the production of foamed aluminum in cooperation with Zn. 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 a plateau stress 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%.

(Ag, Zr)
In the present invention, as a pedestrian protection member provided on the front side of the bumper beam, one or two of Ag and Zr is used in order to satisfy a pedestrian protection characteristic in which more deformation proceeds while keeping the plateau stress low. It is characterized by containing. By containing Ag and Zr in the aluminum alloy foam, the aluminum alloy foam has a characteristic that a low plateau stress of 5 MPa or less is maintained in a deformation region of 85% or less.

  If the content of Ag and Zr is too small, this effect is not exhibited, and the plateau stress becomes higher than 5 MPa due to deformation of the aluminum alloy foam by 60 to 70%. As a result, more deformation cannot proceed while keeping the plateau stress low, and it cannot be applied as a protective member for pedestrians (legs).

  On the other hand, if the content of Ag and Zr is too large, the relative density increases because the specific gravity of Ag and Zr is large. On the other hand, the plateau stress increases, and the deformation region of 85% or less is 5 MPa or less. Therefore, the aluminum alloy foam cannot have the characteristic that the low plateau stress is maintained. Moreover, the cost required for the addition of Ag and Zr is also greatly increased. Therefore, the content of one or two of Ag and Zr is in the ranges of Ag: 0.1 to 5.0% and Zr: 0.1 to 5.0%, respectively.

(Other elements)
Other elements are basically impurities. As another element to be regulated, Cu that is likely to be mixed may hinder 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, it is preferable that the content of impurity elements other than Cu is as small as possible. However, in order to reduce the content of these impurity elements such as Cu, there is a problem that the cost for producing foamed aluminum such as melting and refining increases. Therefore, the inclusion in the impurity amount range and impurity level in normal foamed aluminum that does not deteriorate the properties of foamed aluminum is allowed. For example, the above-described Cu is allowed to contain up to 3% by mass at the upper limit.

(Relative density of foam)
As another foam requirement, the relative density of the aluminum alloy foam (foam) may be set to 0.1 or more in order to improve the energy absorption amount without increasing the density (without impairing the lightening effect). preferable. If the relative density of the foam is less than 0.1, the aluminum alloy foam may not be able to obtain a sufficient impact absorption capacity (energy absorption capacity).

  On the other hand, the higher the relative density of the aluminum alloy foam (foam), the greater the weight, and 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.

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.

(Plateau stress)
In the present invention, the plateau stress (compressive stress in the compression test) of the aluminum alloy foam is preferably 5 MPa or less. When the plateau stress exceeds 5 MPa, it is highly possible that the pedestrian (leg) protection characteristic cannot be obtained, as described above, while the plateau stress is kept low and more deformation proceeds. That is, there is a high possibility that the aluminum alloy foam does not have a characteristic that a low plateau stress of 5 MPa or less is maintained in a deformation region of 85% or less.

(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.

  First, in the melting furnace, the above Zn: 0.5-20.0%, Mg: 0.1-5.0%, further Ag: 0.1-5.0%, with respect to industrial pure aluminum Zr: 0.1 to 5.0% of one or two alloying element elements and calcium 0.1 to 5.0% are added, and the molten metal is stirred in the atmosphere for about 5 minutes to increase the viscosity. Let

  And after pouring the molten metal after this thickening into a mold in an atmospheric melting furnace at 600 to 700 ° C., a predetermined amount of titanium hydride (to 0.1 to 5.0% as Ti in the aluminum alloy) To). Then, for example, after stirring for 1 to 10 minutes, the stirrer is removed, and the mold is held in the atmospheric melting furnace in the temperature range for about 1 to 10 minutes to complete foaming.

  After this foaming is completed, it is allowed to cool in the furnace, and after cooling, the aluminum alloy foam is taken out from the mold, machined, and used as a pedestrian protection member (energy absorbing member) provided on the front side of the bumper beam, such as a prism or square. It is set as the product aluminum alloy foam of the desired shape.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

  Examples of the present invention will be described below. Aluminum alloy foams having respective chemical component compositions shown in Table 1 were produced. As the characteristics of these foams, a relative density and a plateau stress-deformation curve were measured and evaluated. Table 1 shows the relative density and plateau stress (MPa) at the time of deformation of 85%. FIG. 1 shows a plateau stress-deformation curve as an energy absorption characteristic.

  Specifically, first, in addition to Zn, Mg, Ca and the like, alloy component elements such as one or two of Ag and Zr are added to industrial pure aluminum in a melting furnace, and the molten metal is melted in the atmosphere. Was stirred for about 5 minutes to increase the viscosity. And after pouring the molten metal after this thickening into the casting_mold | template in a 700 degreeC air melting furnace, about 0.1 to 5.0% of titanium hydride was added as Ti. Then, after stirring for 2 minutes, the stirrer was removed, and the mold was held in an atmospheric melting furnace at 700 ° C. for about 4 minutes to complete foaming. After completion of the foaming, the product was allowed to cool in a furnace, and after cooling, the aluminum alloy foam was taken out of the mold and machined into a prismatic shape having a height of 50 mm, a width of 50 mm, and a length of 50 mm. The properties of this foam were investigated as described above.

(Relative density)
The relative density of the foam was determined by the method described above. That is, a 50 × 50 × 50 mm (125 cm ³ ) sample was cut out from the obtained foam, and the weight of this sample was measured, and divided by an equivalent volume of water of 125 cm ³ = 125 g.

(Plateau stress)
The machined aluminum alloy foam was subjected to a static compression test in the longitudinal direction using a universal compression tester manufactured by Instron, and a load stress-displacement curve and a plateau stress at the time of deformation of 85%. (MPa) was determined.

  As is apparent from Table 1, Invention Examples 1 to 6 are within the composition range of the aluminum alloy of the present invention containing Ag and Zr, which are characteristic in the present invention, and are manufactured under the above appropriate conditions. As a result, the relative density is a relatively low density level of 0.36 at the maximum, and the plateau stress at 85% deformation is 5 MPa or less. In addition, as shown in the stress-displacement curve of FIG. 1, Invention Examples 1 and 2 (Invention Example 1: a thick and thin solid line, Invention Example 2: a thick and thick solid line), which are representative of the invention examples, have a plateau stress as low as 5 MPa or less. While holding, more deformation proceeds, the energy absorption amount is high, and the protection characteristics of pedestrians (legs) are excellent.

  On the other hand, Comparative Examples 7 and 9 contain various amounts of Zn, Ca, Ti, and Mg, respectively, and are manufactured under the above-mentioned appropriate conditions, but the contents of Ag and Zr that are characteristic in the present invention are the lower limits. Less than and too little. Comparative Examples 11 and 12 are conventional examples that contain various amounts of Zn, Ca, Ti, and Mg, respectively, and are manufactured under the appropriate conditions, but do not contain Ag or Zr.

  For this reason, in Comparative Examples 7, 9, 11, and 12, although the relative density is a relatively low density level, the plateau stress at 85% deformation exceeds 5 MPa. In addition, as shown in the stress-displacement curve of FIG. 1, in Comparative Examples 9 and 11 (Comparative Example 9: thin dotted line, Comparative Example 11: thin thick solid line) shown as a comparative example, the plateau stress becomes 5 MPa as the deformation progresses. The protective properties of pedestrians (legs) are inferior.

  Further, Comparative Examples 8 and 10 contain various amounts of Zn, Ca, Ti, and Mg, respectively, and are manufactured under the above appropriate conditions, but the contents of Ag and Zr characteristic in the present invention exceed the upper limit. Too many. For this reason, Comparative Examples 8 and 10 have a relative density exceeding 0.5 and cannot be reduced in weight. Furthermore, the plateau stress at 85% deformation was so high that it could not be measured.

  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 aluminum alloy foam of the present invention, excellent protection characteristics for pedestrians (legs) can be obtained in which more deformation proceeds while the plateau stress is kept low. As a result, the aluminum alloy foam of the present invention is suitable for an energy absorbing member (impact energy absorbing member) such as a pedestrian protection member provided on the front side of the bumper beam.

It is explanatory drawing which shows each stress-displacement curve of an Example.

Claims (4)

  In mass%, Zn: 0.5-20.0%, Ca: 0.1-5.0%, Ti: 0.1-5.0%, Mg: 0.1-5.0%, respectively Further, it is made by foaming an aluminum alloy containing one or two of Ag: 0.1 to 5.0% and Zr: 0.1 to 5.0%, and the balance aluminum and unavoidable impurities. An aluminum alloy foam for an energy absorbing member.   The aluminum alloy foam according to claim 1, wherein the aluminum alloy foam has a characteristic that a plateau stress of 5 MPa or less is maintained in a deformation region of 85% or less.   The aluminum alloy foam according to claim 1, wherein the aluminum alloy foam is an automobile energy absorbing member.   The aluminum alloy foam according to any one of claims 1 to 3, wherein the aluminum alloy foam is a pedestrian protection member provided on the front side of an automobile bumper beam.

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