JP4189368B2 - Aluminum alloy foam - 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 at the time of a collision, such as an automobile structural member.

  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 has poor 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.

  Further, when a crush box as a foam aluminum simple substance is assumed, the plateau stress is insufficient in each foam aluminum of the related art as described above. For example, even in the case of foamed aluminum composed of a specific aluminum alloy composition, fine bubbles and specific relative density as in Patent Documents 6 and 7, the plateau stress in the compression test is only about 2 MPa as shown in the drawings. Absent.

  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.

  5. Up to 50% deformation of the crash box made of the above-mentioned 440 MPa class high strength steel plate. When the performance of the energy absorption amount of about 0 kJ / kg is seen as the compression stress (plateau stress) in the compression test, the plateau stress as the foamed aluminum simple substance needs to be 4 MPa or more.

  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 The relative density is 0.1 or more, the particle size is 0.5 nm or more, and the precipitate particles of 50 nm or less have a structure in which the volume fraction is 1.0% or more dispersed.

  The inventors have found that the plateau stress can be increased by dispersing fine precipitate particles in the structure of an aluminum alloy foam (hereinafter also referred to as foamed aluminum). Fine precipitate particles having a particle size of 0.5 nm or more and 50 nm or less as defined in the present invention have a significantly larger plateau stress improving effect than coarser precipitate particles.

  For this reason, as described above, the plateau stress of the aluminum alloy foam can be remarkably increased by dispersing or existing as many of these fine precipitate particles as possible in the structure. And the energy absorption amount of the crash box made of a single aluminum alloy foam can be increased.

  The reason why the plateau stress of the conventional aluminum alloy foam is low is also due to the fact that the fine precipitate particles are few. Incidentally, in the usual manufacturing method of foamed aluminum, since the cooling after foaming is allowed to cool to room temperature, these fine precipitate particles are hardly formed. For this reason, plateau stress becomes low compared with this invention aluminum alloy foam which produces | generates these fine precipitate particles.

  In order to increase the fine precipitate particles of foamed aluminum having a specific alloy composition as in the present invention, a special manufacturing method is required as described later.

  In the present invention, the relationship between the amount of the fine precipitates and the compression stress (plateau stress) in the compression test of foamed aluminum was quantitatively grasped. And in order to make the plateau stress of foam aluminum into 4 Mpa or more, it also recognized that the said fine precipitate particle | grains needed to disperse | distribute 1.0% or more by a volume fraction.

  Thus, according to the present invention, it is possible to provide an aluminum alloy foam that can achieve a high impact energy absorption that can be substituted for a structural member made of a high-tensile steel plate.

(Relative density of foam)
As a precondition for obtaining a plateau stress of 4 MPa or more of the aluminum alloy foam, the relative density of the foam (foam) is set to 0.1 or more. When the relative density of the foam is less than 0.1, even when the particle size is 0.5 nm or more and the precipitate particles of 50 nm or less are dispersed in a volume fraction of 1.0% or more, 4 MPa of the aluminum alloy foam The above plateau stress may not be obtained. The upper limit of the relative density of the foam is not particularly defined, but the higher the relative density, the larger the weight and the smaller the contribution to weight reduction of automobiles and the like. Depending on the application, a higher deformation stress may be required than the weight reduction effect, so 1.0 or less is preferable.

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 125 cm ³ = 125 g.

(Average foam diameter of foam)
In order to obtain the plateau stress of the aluminum alloy foam, the finer the foam diameter (foam or bubble particle diameter) of the aluminum alloy foam, the better. When the average foam diameter (foaming average particle diameter) is coarsened even when the structure has a structure in which the particle diameter is 0.5 nm or more and the precipitate particles of 50 nm or less are dispersed by 1.0% or more in terms of volume fraction, There is a possibility that a plateau stress of 4 MPa or more of the foam cannot be obtained. As a guideline, it is preferable that the average foam diameter 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 particular, in order to set the plateau stress of the aluminum alloy foam to 4 MPa or more, a structure in which precipitate particles having a particle size of 0.5 nm or more and 50 nm or less are dispersed in a volume fraction of 1.0% or more, To do. If the abundance of these fine precipitate particles is less than 1.0% in terms of volume fraction, it becomes difficult to set the plateau stress of the aluminum alloy foam to 4 MPa 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 Zn, which is an alloy element, a Zn-Mg compound derived from Mg, or Zn alone. 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 plateau stress improvement effect as described above. For this reason, even if such coarse precipitate particles increase, it becomes difficult to set the plateau stress of the aluminum alloy foam to 4 MPa 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 plateau stress 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 grain size is 0.5 nm or more and the precipitate particles of 50 nm or less are dispersed in a volume fraction of 1.0% or more, the required characteristics such as plateau stress of the aluminum alloy foam are obtained. In the range that does not impede, 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.

(Plateau stress)
In the present invention, the plateau stress (compressive stress in the compression test) of the aluminum alloy foam is preferably 4 MPa or more. If the plateau stress is less than 4 MPa, an energy absorption amount equal to or higher than that of a high-strength steel plate crash box cannot be secured on the assumption that the plateau has a volume equivalent to that of a high-strength steel plate crash box. Specifically, an energy absorption amount of about 8.0 kJ / kg cannot be secured until the crash box is deformed by 50%.

(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 plateau stress, Zn: 1.0 -20.0%, Ca: 0.1-5.0%, Ti: 0.1-5.0%, Mg: 0.1-5.0%, respectively, from the remaining aluminum and unavoidable impurities Shall be.

(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 1.0% 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 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, 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%.

  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, after the foamed particle diameter of the foamed aluminum having the specific alloy composition is made into fine bubbles as an average particle diameter, a structure in which precipitate particles of 50 nm or less are dispersed in a volume fraction of 1.0% or more and In order to do this, as described later, in particular, after removing the mold from the furnace (after completion of foaming), it is once cooled (cooled) to a range of about 100 to 150 ° C., and then at this temperature range for 3 hours or more and 100 hours. It is necessary to carry out a heat treatment that is held to a degree or less.

  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 in the atmospheric melting furnace in the temperature range for about 1 to 10 minutes to complete foaming.

  Conventionally, after this holding, the mold is taken out from the furnace and allowed to cool to room temperature. Therefore, the precipitate particles are inevitably hardly precipitated, and the fine precipitate particles can be dispersed in the required amount in the structure. Can not. In addition, the average hardness of the foamed cell walls must be low.

  On the other hand, as in the present invention, in order to disperse the necessary amount of the fine precipitate particles in the structure, it is not necessary to cool to room temperature as in the prior art upon cooling after completion of the foaming. However, after cooling to the range of about 100 to 150 ° C., it is necessary to perform a heat treatment in which the temperature is maintained for about 3 hours or more and about 100 hours or less in this temperature range.

  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. Moreover, the average hardness of the foamed cell wall can be improved as compared with the cooling to the room temperature.

  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. Cooling after foaming (cooling) shown in Table 2 Stopping temperature, holding time (heat treatment conditions), etc. were changed, and aluminum alloy foams having the respective chemical composition shown in Table 1 were produced. The relative density, cell wall hardness, volume fraction of precipitates, and compressive strength characteristics were evaluated.

  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 taken out of the furnace and allowed to cool to each cooling stop temperature shown in Table 2. And heat processing which hold | maintains for the predetermined time shown in Table 2 at each of these cooling stop temperature was performed. After such cooling, the foam was removed from the mold.

  A Φ3 mm thin film sample was cut out from a part of the foamed cells of these aluminum alloy foams, 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.

  Moreover, 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.

  Further, from the aluminum alloy foam, 50 mm high × 50 mm wide × 50 mm long were cut out by machining and the plateau stress when compressed in the longitudinal direction using a compression tester was determined. These results are also shown in Table 2.

  As is apparent from Tables 1 and 2, Invention Examples 1 to 5, which are aluminum alloys A to D within the composition of the present invention, are subjected to heat treatment that is held for a predetermined time at the cooling stop temperature shown in Table 2 after being allowed to cool. As a result, the volume fraction of the precipitate particles having a particle diameter of 0.5 nm or more and 50 nm or less is 1.0% or more. Further, the average foam diameter is 5 mm or less, the relative density of the foam is 0.1 or more, and the average hardness of the foamed cell wall is 60 Hv or more. As a result, in Invention Examples 1 to 5, the plateau stress of the aluminum alloy foam is 4 MPa or more. Incidentally, the plateau stress-displacement characteristic of Invention Example 1 is shown in FIG.

  On the other hand, Comparative Example 6 is an aluminum alloy A within the composition of the present invention, but, as in the prior art, the foam is allowed to cool to room temperature and is kept at a cooling stop temperature as in the inventive example for a predetermined time. Is not done. For this reason, the volume fraction of the precipitate particles having a particle size of 0.5 nm or more and 50 nm or less is less than 1.0%. Moreover, the average hardness of the foamed cell wall is less than 60 Hv, and the compressive stress is as low as less than 4 MPa.

  Comparative Examples 7, 8, 9, and 10 use the aluminum alloy A within the composition of the present invention. However, the holding time of Comparative Example 7 is too short, 2 hours. In Comparative Example 8, the holding time exceeds 100 hours and is too long. In Comparative Example 9, the holding temperature is too low at less than 100 ° C. In Comparative Example 10, the holding temperature exceeds 150 ° C. and is too high.

  For this reason, Comparative Examples 7, 8, 9, and 10 have a particle size of 0.5 nm or more and a volume fraction of precipitate particles of 50 nm or less being less than 1.0%. Moreover, the average hardness of the foamed cell wall is less than 60 Hv, and the compressive stress is as low as less than 4 MPa.

  Comparative Examples 11 to 18 use aluminum alloys E to L in Table 1 in which the contents of Zn, Ca, Ti, and Mg deviate from the lower limit or the upper limit of the composition of the present invention, respectively. For this reason, there is also an example in which the heat treatment is performed for a predetermined time at the cooling stop temperature as in the invention example, and the volume fraction of the precipitate particles having a particle diameter of 0.5 nm or more and 50 nm or less is 1.0% or more. However, generally, the compressive stress is as low as less than 4 MPa.

  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.

  Further, in comparison between Invention Examples 1 and 2 using the same aluminum alloy A, Invention Example 1 in which the cooling stop temperature shown in Table 2 is relatively high and the retention time is relatively long is more than that of Invention Example 2. The volume fraction of the precipitate particles having a particle size of 0.5 nm or more and 50 nm or less is high, and the plateau stress is also relatively high. When this is combined with the conditions and results of Comparative Examples 7, 8, 9, and 10, the heat treatment of the aluminum alloy foam including the cooling stop temperature and the holding time in the present invention, and the meaning of the conditions are also included. It is 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 stress-displacement characteristic of this invention aluminum alloy 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 An aluminum alloy foam characterized by having a structure in which precipitate particles of 50 nm or less are dispersed in a volume fraction of 1.0% or more.   The aluminum alloy foam according to claim 1, wherein the plateau stress of the aluminum alloy foam is 4 MPa or more. The aluminum alloy foam according to claim 1 or 2, wherein the aluminum alloy foam is used as an element for an energy absorbing member.

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