EP1171331A1

EP1171331A1 - Deformation element comprised of a ductile metallic lightweight material and the use thereof

Info

Publication number: EP1171331A1
Application number: EP00925162A
Authority: EP
Inventors: Wolfgang Sebastian; Heinz Haferkamp; Peter Juchmann; Sönke SCHUMANN
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 1999-04-03
Filing date: 2000-04-03
Publication date: 2002-01-16
Also published as: WO2000059760A1; DE19915237A1

Abstract

The invention relates to deformation elements comprised of a metallic material having a density of no more than 2.5 g/cm<3> as well as a high degree of ductility and energy absorption. Said deformation elements are primarily comprised of a lightweight material whose work resulting from impact measured on non-nicked samples at room temperature is equal to at least 33 J. The invention also relates to deformation elements comprised of a metallic material having a high degree of ductility and energy absorption in which, during a measurement of energy absorption conducted in the quasi-static deformation trial and/or dynamic crash test at room temperature on cylindrical tubes having a 100 mm outer diameter and a 2 mm wall thickness, the material absorbs, along a deformation path of 200 mm, a specific level of work resulting from deformation of at least 5,000 Nm/kg and/or a level of work resulting from deformation of at least 3,000 Nm. The invention additionally relates to a deformation element comprised of a lithium alloy or of a magnesium alloy. Finally, the invention relates to an assembly consisting of supporting elements and deformation elements.

Description

Deformation element made of a ductile metallic light material and its use

The invention relates to deformation elements made of ductile metallic light materials, in particular magnesium alloys, and their use.

Deformation elements are used today in vehicles made of alloys based on aluminum or steel in vehicles, e.g. to as a shock absorber to mitigate the destructive forces of an impact or accident, reduce the destruction of the vehicle and protect the occupants. Such an impact damper is described in EP-A-0 486 058. Deformation elements can in principle also be used in railway technology and in devices and systems, in particular to protect them in areas that are particularly frequently or in the event of danger. In this case, the semi-finished product or component mainly experiences impact loads, less often the entire element, or tensile or compressive loads. The loads should be absorbed as far as possible by the deformation elements and transmitted as little as possible to adjacent elements. They can occur spontaneously, quickly or slowly, continuously, dynamically, repeatedly or once. The loads are usually multi-axis.

In the future, metallic lightweight materials will be used more and more for the lightweight construction of motor vehicles and airplanes in order to be able to compensate for the weight of additional elements due to increasing comfort and safety standards - especially in new low-emission automobiles. They are also of interest for transportable devices or systems that are particularly light-weight for other reasons. The lightweight construction enables the construction of energy-saving vehicles and planes, such as the 3-liter motor vehicle, to a particular extent. Because of their very low density, magnesium alloys are of great interest as metallic construction materials, especially for vehicles, in the range from 1.2 to 1.9 g / cm ³ , in some cases even down to about 0.9 g / cm ³ . and aircraft construction. In the future, manufacturing processes will include die casting and extrusion, pressing, forging and rolling is becoming increasingly important, since these processes can be used to produce lightweight components such as crash elements, impact absorbers, impact shields and impact carriers or corresponding components for aircraft.

The cold formability of the commercially available magnesium alloys is limited due to the hexagonal crystal structure and the associated low ductility. Polycrystalline magnesium and most magnesium alloys behave brittle at room temperature. In addition to good mechanical properties such as high tensile strength, ductile behavior is necessary for numerous applications or for certain manufacturing processes for semi-finished products made of magnesium alloys. An improved forming, energy absorption and deformation behavior requires a higher ductility and possibly also a higher strength and toughness. For this purpose, magnesium alloys with these properties have to be developed or their manufacturing processes have to be further developed, because many material variants have material properties that vary greatly with the manufacturing state.

Ductility is the ability of a material to undergo a permanent change in shape, which in the uniaxial state is ideally without any elastic component according to the stress-strain diagram. This property is limited by the occurrence of the break. In general, the permanent elongation achieved in the tensile test until fracture is considered ductility. Impact work and notch impact work, each with a slightly different statement, can also be regarded as a measure of ductility. These properties can be determined in accordance with EN 10 002, Part 1, or in accordance with DIN 50115 and 50116. The elongation at break A = A _p ι _as , characterizes the change in shape with its plastic part under a largely uniaxial load. In addition, according to the stress-strain diagram, the elastic part of the strain A _e ι _ast and the sum of the elastic and plastic part D = ∑A = A _e ia _st + Api _ast can be determined. A highly plastic material is called ductile.

The elasticity denotes the elastic part of the stress-strain diagram according to Hook's law, where under ideal linear-elastic conditions there is no permanent change in shape. Furthermore, the yield point ratio V can be specified as the ratio of the yield stress F = R _PO2 to the tensile stress Z = R _m . This results in two values for the largely uniaxial load that characterize the elasticity, two the plasticity and two their relationship to one another. The ratio of the elastic to the plastic part of the stretch gives the best approximation to reality.

One possibility of determining the energy consumption under multi-axis loading without separating the elastic and plastic components is a crash test e.g. on tubular profiles. The shape change e.g. a cylindrical tube, the formation of folds or cracks, the splitting of the loaded tube end into several chip-like deformations and the shortening or bending characterize the type and degree of energy consumption. The impact work and the notch impact work can give an indication of the energy absorption and deformability, the latter with multi-axis loading. A conclusion from uniaxial to multiaxial properties or relationships is only partially possible.

The impact work is above all a measure of the energy consumption of a semi-finished product and of plastic behavior, i.e. of the deformability and rate of deformation. A high impact work is therefore essential for the use of deformation elements such as Crash elements, impact absorbers, impact shields and impact carriers. The impact work - measured on notched specimens - is among other things due to higher absolute values for magnesium alloys more meaningful than the impact energy and concerns a largely uniaxial load. The impact energy, which is always determined on notched specimens, also characterizes the susceptibility of a material to failure under three-axis loading. Their significance is particularly low if the execution of the notch significantly influences the values of the impact energy. The impact work and the notch impact work are measured under dynamic load and can give an indication of the energy absorption and deformability. In comparison, tensile and compression tests are carried out under quasi-static loads. A conclusion from uniaxial to multiaxial properties or relationships is only partially possible.

The values listed below measured on samples in a certain manufacturing condition therefore reflect the current material properties. They provide an indication of the forming behavior that previously existed when forming had occurred. In this state, it is possible to draw a conclusion about the properties and behavior of a semi-finished product or even a component with this semi-finished product, which may be further refined, in later use. Furthermore, it is possible to draw a conclusion about the material properties of formed alloys, which are to be formed into further processed semi-finished products, for example by bending, pressing, pressure rolling, stretch drawing, deep drawing, hydroforming or roll profiling. Since the change in the material properties from the cast to the extruded state is similar to the change in the material properties from the cast to the forged, rolled or a similar formed state, it is therefore also possible to draw a conclusion about another formed state.

For the use of lightweight components, the elastic properties (rigidity) are usually used, unless this is the case, e.g. in an accident, the deformation properties and thus the energy consumption of the element and the plastic behavior are important. Therefore, regarding the multiple reshaping, in particular the plastic and, for use, the plastic and / or elastic properties play a role. For use, these properties are generally based on the respective ambient temperature, in extreme cases in the range from -40 ° C to +90 ° C, but at individual points in the vehicle or plane at the locally lower or higher temperatures. However, the load state is usually multi-axis. The conclusion from uniaxial to multiaxial load states is all the more possible the more isotropic the structure.

For the production of such automotive elements, the production by die casting or extrusion, forging and / or rolling is particularly suitable. A precondition for the use of semi-finished products made of magnesium alloys or of components or components made from them in automobiles may be the fulfillment of certain property profiles depending on the application, such as a tensile strength of the lightweight material of at least 100 MPa, preferably of at least 130 MPa, together with an elongation at break, for example for deformation elements measured at room temperature of at least 15%, preferably at least 18%. The higher the tensile strength, elongation at break and other properties that indicate high ductility and energy absorption, the more suitable these semi-finished products or components are generally for use. Furthermore, higher strength values and a higher ductility are also a relief and sometimes also a prerequisite for the forming of cast blanks or for the further forming of blanks that have already been formed or semi-finished products. The higher these properties are in the cast or powder-compacted state, the higher these are usually also in the formed state. A higher ductility can the forming or the renewed

Forming, especially extrusion, easier. Therefore, an elongation at break of at least 10% is also sufficient for the subsequent manufacturing steps to form elements

Magnesium alloys helpful. Therefore, a tensile strength of at least 150 MPa measured at room temperature, preferably at least 180 MPa, together with an elongation at break of at least 18%, preferably at least 20%, particularly preferably at least 25%, is recommended for several reasons. The elongation at break in commercially available magnesium alloys, measured at room temperature, is usually less than 12

%.

The density of the common aluminum alloys, in particular the wrought alloys, is between 2.64 and 3.44 g / cm ³ and is therefore not quite low for lightweight metallic materials. The density of the other common lightweight materials such as titanium alloys is even higher if magnesium alloys are not used.

Basically, there are various options for increasing the ductility and thus the elongation at break in magnesium alloys and related lightweight materials:

1. A very limited possibility of this increase results from optimization of the manufacturing process in connection with heat treatment processes and / or via optimized manufacturing parameters e.g. during extrusion. However, it is important when forming e.g. by extrusion that the dynamic recrystallization that may occur does not lead to coarse grain formation. Because the energy absorption and the mechanical properties of an alloy should generally be greater, the smaller the average grain size. The goal of alloy development can be a modification of the microstructure by forming temperature-stable precipitates or / and a stabilization of the microstructure by influencing the grain growth in order to produce the finest possible grain and the lowest possible porosity.

2. When the crystal structure of the Mg main phase changes from the hexagonally closest spherical packing to the body-centered cubic crystal structure, for example due to a higher addition of a doping element such as at least 10.8% by weight of Li a homogeneous ß-lithium-magnesium without additional doping elements

To produce mixed crystals, there is an improved elongation at break and better formability at room temperature due to an increased number of sliding systems. However, strength and corrosion resistance can deteriorate. 3. Because grain boundaries and other structural inhomogeneities or structural defects such as Inclusions, pores, coarse precipitates, oxide streaks and segregations when moving dislocations act as barriers, a refinement of the structure, a reduction in structural inhomogeneity errors or the avoidance of certain structural inhomogeneity errors can lead to an increase in strength, elongation at break and energy absorption. However, the relationships are very complex in individual cases. Grain refinement is an important tool to activate further deformation systems that allow grain boundary sliding and new flow processes at room temperature and thus improve ductility. This can be done by adding grain-refining additives or / and by heterogeneous nucleation when solidifying cast materials made of alloys with certain additives.

Even the commercially available Mg cast alloys or Mg wrought alloys have usually been relatively low in ductility and have a low energy absorption capacity in the cast and, if appropriate, subsequently formed, in particular extruded, pressed, rolled or / and forged and, if appropriate, subsequently heat-treated, condition. For the inexpensive manufacture of semi-finished products, in particular for vehicles and airplanes, there is a need for suitable alloys and simple processes for the production of magnesium alloys with somewhat increased strength and greatly increased ductility.

Since the interest in wrought magnesium alloys has only increased somewhat in recent years, so far only a limited number of alloys are available for large-scale use. These are alloys based on Mg-Al-Zn such as AZ31, AZ61 and AZ80, based on Mg-Zn-Zr such as ZK40 and ZK60 or based on Mg-Mn such as M1.

Haferkamp, Bach, Bohling & Juchmann (Proc. 3 "* Int. Magnesium Conf. Manchester April 10-12, 1996, The Institute of Materials, London 1997, ed .: GW Lorimer) and Haferkamp, Bach & Juchmann ("Status and development trends of density-reduced magnesium materials", lecture at the advanced training event "Magnesium - Properties, Applications, Potentials" of the German Society for Material Science Clausthal-Zellerfeld 1997) describe lithium-containing magnesium alloys based on MgLi with and without AI, AlZn, Ca, Si, SiCa, AICa, CaAlZn or SiAIZn. For the elongation at break or tensile strength, values for MgLi40at% Al6at%, for example of 19% or about 255 MPa, for Mgü40at% Si3at% 28% or about 160 MPa and for MgLi40at% 42% or about 129 MPa are given. Due to the small laboratory extrusion press used for those experiments, however, the forming speed and the degree of forming were low.

Furthermore, values of the elongation at break and tensile strength were presented by Haferkamp, Bach, Bohling & Juchmann at the Magnesium Conference in Garmisch-Partenkirchen 1992 (Magnesium Alloys and Their Applications, Eds .: BL Mordike & F. Hehmann, Oberursel 1992, 243-250) which led to values of up to 31% and 226 MPa and 25% and 240 MPa for MgüAI, possibly with Zn.

It was therefore the task to propose deformation elements made of a metallic light material or a composite with at least one deformation element by selecting the parameters which are most effective for these purposes, the deformation elements should have the highest possible ductility and energy absorption and the lowest possible density and moreover should also be manufactured as simply and inexpensively as possible. There was also the task of specifying lightweight metallic materials which are particularly suitable for the production of deformation elements on account of their very high ductility and energy absorption and very low density.

The object is achieved with a deformation element made of a metallic material with a density of not more than 2.5 g / cm ³ and with high ductility and energy absorption, in particular from a lithium or magnesium alloy, which is characterized in that it consists essentially of a light material consists whose impact energy measured at unnotched specimens at room temperature is at least 33 J, preferably at least 66 J, more preferably at least 90 J, most preferably not less than 105 J. preferably, the density is more than 2.3 g / cm ^3, particularly preferably not more than 2.1 g / cm ³ . The object is also achieved with a deformation element made of a metallic material of high ductility and energy absorption, in particular of a lithium or / and magnesium-containing alloy, which is characterized in that the material is measured in a quasi-static deformation test or / and when measuring the energy absorption dynamic crash test at room temperature on cylindrical tubes of 100 mm outer diameter and 2 mm wall thickness with a deformation path of 200 mm absorbs a specific deformation work of at least 5,000 Nm / kg, preferably of at least 10,000 Nm / kg, particularly preferably of at least 18,000 Nm / kg, quite particularly preferably of at least 19,000 Nm / kg, and / or a deformation work of at least 3,000 Nm, preferably of at least 5,000 Nm, particularly preferably of at least 5,000 Nm, very particularly preferably of at least 8,000 Nm. Furthermore, the object is achieved with a deformation element made of a lithium or magnesium alloy, which can essentially consist of this alloy.

The deformation element advantageously consists essentially of a material with a tensile strength of at least 100 MPa, particularly preferably of at least 130 MPa, very particularly preferably of 180 MPa, and an elongation at break measured on tensile samples of at least 15%. It also preferably consists essentially of a material of at least 18% regardless of its tensile strength, particularly preferably of at least 22%, very particularly preferably of at least 26%.

The deformation element preferably has a plastic portion of the stress determined in tensile tests according to the stress-strain diagram of at least 50 MPa.

It has been shown that the modification of grain sizes and phase distributions by alloying with accompanying elements such as lithium is helpful in producing significantly stronger and / or more ductile magnesium alloys. The addition of lithium in particular has proven to be beneficial for the further development of magnesium alloys for deformation elements. It is therefore recommended that the deformation element consists essentially of an alloy which is selected from the group of alloys based on AM, AZ or ZE, optionally with a lithium additive. The deformation element preferably consists essentially of a magnesium alloy with a Li content of at least 1% by weight, particularly preferably of at least 5% by weight, very particularly preferably of at least 11 and at most 30% by weight. It can essentially consist of a magnesium alloy based on 10 to 17% by weight of Li, in particular of one with 1 to 6% by weight of Al and in each case 0 to 4% by weight of Mn, Si, Zn or / and up to 1% by weight of at least one rare earth element including Y. In particular with a higher content of lithium, it is recommended that the magnesium alloy contains a proportion of at least 10% by volume of a body-centered, magnesium-rich phase, preferably more than 60% by volume .-%, particularly preferably more than 80 vol .-%, very particularly preferably more than 90 vol .-%.

The deformation element can essentially consist of an elongated, tubular or / and angled shaped body, in particular of a linear, angled or curved profile element. It preferably has a tubular - in particular circular or polygonal, T-shaped or U-shaped profile cross section. It can also be connected to a carrier, in particular to a longitudinal and / or transverse carrier.

When the deformation element is stressed, it is advantageous if it deforms during rapid or very rapid mechanical loading without sharp-edged breakage and / or without cracks. Furthermore, it is advantageous if it deforms to a bent or / and folded element during rapid or very rapid mechanical loading, the formation of one or more buckling bumps, as shown in FIG. 3, being preferred.

A composite of support elements and deformation elements, which contains at least one deformation element, can contribute to the fact that the deformation of the support elements and possibly other associated elements are stressed or destroyed significantly less, for example in the event of an accident. This is also evident in the energy consumption through the formation of wrinkles. The composite with at least one deformation element can be produced by at least one low-heat or heat-introducing joining method such as gluing, riveting, plugging, pressing, pressing, clinching, folding, shrinking or screwing and / or at least one heat-introducing joining method such as composite casting, composite forging, composite extrusion, Composite rolling, soldering or welding, in particular beam welding or fusion welding, in which the deformation element with is connected to at least one support element or another deformation element.

In principle, all methods of primary and / or forming are suitable as methods for producing deformation elements, preferably casting methods or extrusion, rolling and forging. The deformation element advantageously has a clearly recrystallized structure and, associated therewith, better material properties after a forming process such as the one just mentioned. The process steps, parameters, conditions and systems to be used here are basically known. The deformation element was preferably extruded, forged and / or rolled during manufacture and has a clearly recrystallized structure. A higher ductility can facilitate the forming, in particular the extrusion, pressing, forging and rolling. Therefore, an elongation at break of the starting alloys to be formed of at least 5%, preferably of at least 10%, is also helpful for the production of elements from light materials.

Process for the production of extruded profiles:

It is preferable to start from high-purity, commercially available alloys. Possibly. these alloys are alloyed with additives. The high-purity alloys can absorb small amounts of contaminants from the crucible during the melting process. The alloys can be melted, for example, in a nickel and chromium-free steel crucible under a protective gas atmosphere, for example of Ar and / or SF ₆ .

A prerequisite for the further processing of magnesium alloys by extrusion, pressing or / and forging is the production of suitable materials, for example in the form of blocks, bolts or slabs. A usually well-suited method is the production of the bolts or slabs by sand or permanent mold casting with a sufficiently large machining allowance. The cast bolts or slabs can first be homogenized by heat treatment at, for example, 350 ° C. for 12 h in order to eliminate segregations in the structure, to improve the partly heterogeneous structure and to increase the pressability. The homogenized bolts or slabs can then be machined to the required dimensions. The extrusion of the magnesium alloys can be carried out in the same extrusion plants that are used for the extrusion of aluminum alloys, both via direct and indirect extrusion. The deformation behavior must only be specifically taken into account when designing the tool (die). Sharp-edged inlets, such as those used with aluminum alloys, should be avoided with magnesium alloys, otherwise there is a risk of surface cracks. In many cases, an entry angle of approx. 50 ° is used for the die for magnesium alloys.

With the alloys according to the invention, solid and hollow profiles and other shaped bodies in simple or complicated cross-sections or shapes can be extruded without problems or shaped in some other way. The formed semi-finished products are then preferably subjected to a heat treatment, which can be, for example, in the range from 100 to 200 ° C., in particular over 0.5 to 24 hours. However, this heat treatment had less or almost no effect on the lithium-free magnesium alloys examined, while on the lithium-containing magnesium alloys, especially with a content of at least 0.5% by weight of aluminum, there was a significant improvement in the energy consumption can, since the extrusion often does not yet lead to sufficiently stable structural states and an even greater formation of finely divided precipitates is possible. Then the semi-finished products can be straightened, heat-treated, e.g. be further deformed and / or surface-treated by bending, pressing, pressure rolling, stretch drawing, deep drawing, hydroforming or roll profiling. The semi-finished products can be brought to the required dimensions, deburred and cleaned. For example, they can be provided with a protective layer or a coating.

The deformation element or the composite with at least one deformation element can be used as a crash absorber, crash tube, impact damper, impact shield, impact support, as an element of a device, system, vehicle or aircraft frame, as a frame-like two- or three-dimensional cell, in automotive and rail technology , in ships and quay systems, in apparatus and mechanical engineering, in portable devices and systems, as semi-finished products or components in automobiles or planes. For the purposes of this application, semi-finished products are to be understood as shaped bodies which have not yet been completed and are ready for use in their respective application. On the other hand, components are the shaped articles suitable for the intended purpose. However, both terms flow smoothly into one another, since the same molded body can be a semifinished product for one purpose, but can already be a component for the other. Furthermore, for reasons of linguistic simplification, the text does not make a strict distinction between semi-finished products and components, or both are mentioned at the same time, although both can be meant.

Characters:

Figure 1 shows a longitudinal section of the structure of the deformation system 1 of the Institute of Vehicle Technology at the University of Braunschweig schematically. On a longitudinal beam 2, a hydraulic press 3 with a measuring device 4 and 5 with a displacement sensor, four force measuring elements and a transverse force measuring element 6 and a displacement sensor for small deformations 7 is arranged on one side of the longitudinal beam 2. On the other side of the longitudinal beam 2, a support bracket 8 with a holder 9 for profiles and similar samples such as the crash tube 10 to be tested and with force measuring elements (not shown) and with a calibration unit 11 for the displacement transducer 7 is mounted.

Figures 2a / b show the measurement results in quasi-static deformation tests on the deformation system in the force-displacement diagram (f over s) and in the diagram of the specific deformation work over the displacement (d over s) for the materials tested. The figures show the results for the magnesium alloys MgAI3Zn1 (C) and Mgü15.5AI2.5Zn0.8 (D) as well as for comparison for steel St35 (A) and for the aluminum alloy AIMgSiO.5 (B). The regular dynamic curves in FIG. 2a obviously speak for the formation of a corresponding number of fold bumps.

Figure 3 shows the crash tubes made of the alloy Mgü15.5AI2.5Zn0.8 after dynamic tests in the drop mechanism depending on the heat treatment before the crash test. Left: Without heat treatment - without wrinkles. Second picture from left: With heat treatment at 100 ° C for 2 h. Third picture from left: With heat treatment at 150 ° C for 4 h with slightly asymmetrical load. Right: With heat treatment at 150 ° C for 4 h with symmetrical loading. FIG. 4 shows a crash tube made of the alloy MgLi15.5AI2.5Zn0.8 deformed in the dynamic crash test with buckling bulges.

Examples:

The following examples according to the invention represent selected embodiments without restricting the invention.

In the alloy designations used below, A AI, E denotes at least one rare earth element SE, with Y also being counted among the rare earth elements, M or MN Mn, S Si and Z Zn with contents in% by weight Zn - usually with contents in%. -%, unless otherwise noted. With commonly used alloy information such as AZ31 are indicated by the numbers, as usual for the respective alloy, only in the order of magnitude, which can vary to a relatively wide extent, as is customary in the industry.

The alloys were alloyed as high-purity commercially available alloys or usually from high-purity starting alloys such as, for example, AM, AZ or AS alloys by adding high-purity magnesium or high-purity lithium. The alloys were melted in a steel crucible under the protective gas atmosphere of an Ar-SF ₆ mixture. The blanks required for the subsequent extrusion were cast in a cylindrical steel mold with machining allowance. The element contents achieved were checked spectroscopically. With all alloys, care has been taken to ensure that the structure of the castings is as homogeneous as possible, since this can have a sensitive effect on ductility.

The bolts were then turned to 70 mm in diameter for the production of extruded profiles and brought to a length of 120 mm, or turned to 218 mm in diameter by extrusion for the production of crash tubes and brought to the required length. The bolts were then subjected to a homogenization treatment at, for example, 350 ° C. for 12 hours in order to eliminate segregations in the structure and to increase the pressability. Segregations can lead to uneven deformation and, under critical extrusion conditions, to cracks or local melting, which can lead to poor surface qualities. If the bolts are not homogenized well, an unnecessarily high compression pressure is required during extrusion. A) Extruded profiles in a technical center and examination of their mechanical properties:

Thereafter, the homogenized bolts were heated to the respective extrusion temperature, the "temperature of the bolt", heated and extruded in a 400 t horizontal press. The temperature of the billet is the temperature that the billet has when it enters the extrusion press. Several of the manufacturing parameters were systematically varied. The processes for producing extruded profiles from the alloys according to the invention are described in detail in a patent application filed on the same day by the same applicant with the German Patent and Trademark Office; that application is considered to be fully included in this application by name.

Depending on the sample, an extrusion temperature in the range from 150 to 300 ° C. and a heating time in the range from 50 to 110 min were set for the lithium-containing alloys and their lithium-free starting alloys. Depending on the sample, with a recipient diameter of 74 mm, a recipient temperature in the range from 180 to 259 ° C., a die diameter in the range from 15 to 18 mm, a compression ratio A / A ₀ in the range from 16.9 to 24.3, a degree of deformation φ = ln (A _o / A) in the range from 2.8 to 3.2, a punch speed in the range from 191 to 419 mm / min, an extrusion speed v in the range from 3.2 to 9.0 m / min Pressing pressure at the start of the extrusion in the range from 15.2 to 24.3 MPa and a pressing pressure at the end of the extrusion in the range from 10.0 to 14.8 MPa were selected.

The extruded profiles were processed by milling and turning into round specimens (d ₀ = 5 mm, l ₀ = 5 • d ₀ , small proportionality bar, according to DIN 50 125), pressure tests (d ₀ = 10 mm, l ₀ = 2 • d ₀ , according to DIN 50 106), impact bending tests (10 x 10 x 55 mm, according to DIN 50 116) and notched impact bending tests (according to DIN 50 115). 5 of these samples were produced and tested per alloy and test. For all samples, the longitudinal direction was chosen so that it coincided with the direction of extrusion. In the tensile test, tensile strength R _m , yield strength = yield strength R _P0 , ₂ and

Elongation at break A determined at a tensile speed of 0.5 mm / min. At the

Compression test values of compressive strength R _m> compression limit R _D o, 2 and

Compression A _{D obtained} at a printing speed of 0.5 mm / min. The beginning of the plastic deformation (expansion or compression limit) was determined graphically. The maximum applicable impact energy was 150 J. All measurements were found at

Room temperature instead.

In the tables, "casting" = material in the as-cast state and "extr." = Casting material which was subsequently formed by homogenization and extrusion (extrusion), "B" = example according to the invention and "VB" = comparative example according to the prior art.

Table 1a: Average values of the measurement results of the mechanical tests on lithium-containing magnesium alloys and their starting alloys

Table 1b: Average values that can be calculated from the stress-strain diagram

Tensile tests for lithium-containing magnesium alloys and their values

Starting alloys

The magnesium alloys based on AZ31 and ZE should be mentioned as examples:

In the case of the AZ31 material alloyed with lithium, significantly higher toughness values were determined on notched impact specimens and significantly higher elongation at break than on undoped specimens, the highest ductility occurring with the essentially two-phase alloy AZ31U15.5. In contrast, the tensile strength decreased with the lithium content. The compressive strength is proportional to the lithium content for samples in the as-cast state, but highest for extruded samples with medium lithium contents. With the ZE10 and ZE10U3.7 alloys, all mechanical properties of samples in the as-cast state with the lithium content increased dramatically. With the corresponding extruded samples, the mechanical properties, with the exception of tensile strength and yield strength, increased significantly with the lithium content. The ZE10U3.7 alloy showed very high values of the impact energy: Up to 140 J were measured on individual samples; other samples were taken through the abutment of the testing machine pulled without breaking completely: Then no measured value of the impact work could be determined.

The strength values determined on the cast and extruded samples were far higher than expected. Surprisingly, the deformability of these alloys was also very high. It was also surprising that the material properties of the modified alloys varied surprisingly little depending on the extrusion conditions, which is advantageous for production. It was also surprising that the impact energy of the ZE10 alloy was so high.

B) In an industrial plant, extruded tubes and crash tests on the crash tubes made from them:

Cylindrical hollow profiles were produced in a large-scale plant by casting in molds to a diameter of 230 mm, turning to a diameter of 218 mm, homogenizing at 150 ° C for 4 h, extrusion in the temperature range from 200 ° C to 350 ° C - and with lithium-containing alloys subsequent heat treatment - manufactured in the form of cylindrical tubes with an outer diameter of 100 mm, a wall thickness of 2 mm and a length of 500 mm or 200 mm. The alloys listed in Table 3 were used for this.

In addition to a steel and an aluminum alloy, magnesium alloys with different lithium contents were tested and the magnesium alloy AZ31 = MgAI3Zn1 was used as the reference alloy. With a lithium content of 12 at% or correspondingly measured at 3.6% by weight, the MgLi-rich phase was present in the hexagonal crystal structure, at a lithium content of 40 at% or correspondingly measured at 15.5% by weight. in the cubic crystal structure and with a lithium content of 21at% or measured accordingly of 6.8% by weight partly in the hexagonal and partly in the cubic crystal structure.

The crash tubes can also be called crash absorbers because they have absorbed all of the energy introduced in these tests. The crash tubes made of the different alloys were tested in one test series by quasi-static loading and in another test series by dynamic loading. The crash tubes were loaded in the longitudinal direction by linear loading against the front face of the crash tube. The hollow profiles in the form of these cylindrical tubes made of different alloys were tested in the deformation system of the Institute of Vehicle Technology at the University of Braunschweig in a quasi-static pressure test at room temperature. The hydraulic press was extended towards the crash tube at a speed of up to 2 mm / s, which then also corresponded to the rate of deformation. Their maximum compressive force could be 900 kN. The deformation work was converted to the specific deformation work taking into account the density. The originally 500 mm long crash tubes were compressed by up to about 400 mm, and then the tests were stopped so that a shortening to about 100 mm was achieved.

The dynamic testing of these hollow profiles was carried out in the drop mechanism of the Institute of Mechanics at the University of Hanover at room temperature. A falling weight of 120 kg was dropped vertically as a guided cuboid punch over a fall height of 4 m onto the crash tube standing on a base surface. The distance measurement was carried out with a laser triangulometer. The falling speed when the falling weight hit the end face of the crash tube was 8.7 m / s.

Table 2a: Results of the quasi-static deformation tests

depending on the heat treatment

Table 2b: Measurement results of the dynamic deformation tests

depending on the heat treatment

Some of the lithium-containing alloys showed an unexpectedly strong dependence of the material properties on the type of heat treatment when the lithium content was high. The alloy AZ31Li40at% = MgLi15.5AI2.5Zn0.8, on the one hand, was in a comparatively brittle state without heat treatment after extrusion, so that a crash tube of this kind, which had been tested in a crash test, tore open several times in the longitudinal direction of the tube in the vicinity of the end face subjected to the impact and was bent outwards in sections. However, if such a tube was converted into a highly plastic state during a heat treatment after extrusion at, for example, 150 ° C. for 4 h, the result was even greater compression and the formation of surprisingly regularly formed bumps under favorable conditions (FIGS. 3 and 4).

It was astonishing that a fairly even, strong fold bulge could be produced in the dynamic crash test with the alloy Mgü15.5AI2.5Zn0.8. Slightly hinted fold bumps were found in the dynamic crash test with the alloys MgLi6.8AI2.8ZnO.9 and

Win MgLi3.7Zn1.3SE1. It is advantageous to create bumps because this avoids tearing and sharp-edged corners and edges and significantly reduces the risk of injury. The deformation work or the specific deformation work differed only slightly depending on the heat treatment.

Furthermore, it is advantageous to introduce beads, small recesses, notches or other weakenings in the area of the loaded end face of the crash tubes or better just below, in order to achieve a weakening of the semi-finished product there and thus a defined start of deformation and a reduction in the initial maximum carrier force. It was particularly the aim to lower the initial peak of the load, which can be seen in the force-displacement diagram, so that the initial maximum and the later maxima of this curve come to be as high as possible, so that the envelope over these maxima approaches a rectangular curve. This results in e.g. for a combination of vehicle frame and deformation element (s), an average force that can be transmitted to the frame, which is not too high and which no longer puts as much strain on the occupants as in the case of a very high initial peak. It is therefore also good to achieve high degrees of compression, since the energy absorption is the integral of force and compression, at which the force transmitted to the frame and not due to the energy absorption must not be too high. The alloys AZ31 and MgLi15.5AI2.5Zn0.8 could be compressed to about 20% of the original length, the tests being stopped there. Some of the crash tubes used in these tests had 6 beads below the front face.

With some of the crash tubes according to the invention, a failure pattern could be achieved as with aluminum alloys and steels. With quasi-static as well as dynamic stresses, some or all of the magnesium alloys were able to produce the first or many well-developed wrinkles. Relatively brittle magnesium alloys such as AZ31 showed no Wrinkle bulges and only a relatively low energy consumption. Depending on the alloy and heat treatment, the precipitation structure of the alloy and thus the force-displacement characteristic as well as the specific deformation work could be influenced.

Claims

PATENT CLAIMS

1. Deformation element made of a metallic material with a density of not more than 2.5 g / cm ³ and of high ductility and energy absorption, in particular of a lithium or magnesium alloy, characterized in that it consists essentially of a light material, the impact work measured at least 33 J at room temperature on notched samples.

2. Deformation element made of a metallic material of high ductility and energy absorption, in particular of a lithium or / and magnesium-containing alloy, characterized in that the material when measuring the energy absorption in the quasi-static deformation test and / or dynamic crash test at room temperature on cylindrical tubes of 100 mm outside diameter and 2 mm wall thickness with a deformation path of 200 mm absorbs a specific deformation work of at least 5,000 Nm / kg and / or a deformation work of at least 3,000 Nm.

3. Deformation element made of a lithium or magnesium alloy.

4. Deformation element according to one of the preceding claims, characterized in that its material has an elongation at break measured on tensile specimens of at least 18%.

5. Deformation element according to one of the preceding claims, characterized in that it consists essentially of an alloy which is selected from the group of alloys based on AM, AZ or ZE, optionally with a lithium additive.

6. Deformation element according to one of the preceding claims, characterized in that its material has a tensile strength of at least 100 MPa and an elongation at break of at least 15%.

. Deformation element according to one of the preceding claims, characterized in that its material has a magnesium content of at least 60% by weight.

8. Deformation element according to one of the preceding claims, characterized in that its material is a magnesium alloy with a content of Li of at least 1 wt .-%, in particular one with 1 to 6 wt .-% Al and 0 to 4 wt. % Mn, Si, Zn or / and up to 1% by weight of at least one rare earth element SE including Y.

9. Deformation element according to one of the preceding claims, characterized in that its material is a magnesium alloy, which contains a proportion of at least 10 vol .-% of a body-centered cubic Mg-rich phase.

10. Deformation element according to one of the preceding claims, characterized in that it was extruded, forged or / and rolled during manufacture and has a clearly recrystallized structure.

11. Deformation element according to one of the preceding claims, characterized in that it consists essentially of an elongated, tubular or / and angled shaped body, in particular a linear, angled or curved profile element.

12. Deformation element according to claim 11, characterized in that it has a tubular - in particular circular or polygonal, T-shaped or U-shaped profile cross section.

13. Deformation element according to one of the preceding claims, characterized in that it is connected to a carrier, in particular with a longitudinal or / and cross member.

14. Deformation element according to one of the preceding claims, characterized in that it deforms at a fast or very fast mechanical load without sharp break or / and without cracks.

15. Deformation element according to one of the preceding claims, characterized in that it deforms at a rapid or very rapid mechanical load to a bent or / and folded element, preferably with one or more bumps.

16. Composite of support elements and deformation elements, characterized in that it contains at least one deformation element according to one of claims 1 to 15.

17. Composite according to claim 16, characterized in that at least one deformation element by at least one low-heat or heat-introducing joining process such as e.g. Gluing, riveting, inserting, pressing on, pressing in, clinching, folding, shrinking or screwing and / or at least one heat-generating joining process such as e.g. Composite casting, composite forging, composite extrusion, composite rolling, soldering or welding, in particular beam welding or fusion welding, has been connected to at least one support element or deformation element.

18. Use of a deformation element or a composite with at least one deformation element according to one of claims 1 to 17 as a crash absorber, crash tube, impact damper, impact shield, impact beam, as an element of a device, system, vehicle or aircraft frame, as a frame-like two- or three-dimensional cell , in automotive and rail technology, in ships or quay systems, in apparatus and mechanical engineering, in portable devices and systems, as semi-finished products or components in automobiles or planes.