EP1295957A2 - Method of producing a magnesium alloy by extrusion and use of the extruded semifinished products and components - Google Patents

Abstract

Production of a magnesium alloy of high ductility comprises extruding the alloy with a deforming degree of at least 1.5. The alloy contains traces of less than 1.8 wt.% Cd, up to 0.1 wt.% Cu, up to 0.005 wt.% Ni and 0.5-20 wt.% Li, and at least 0.1 wt.% of further chemical elements. After extruding, the alloy has a breaking elongation of at least 20%, a compression strength of at least 300 MPa and an energy absorbed in fracturing of at least 70 J.

Description

The invention relates to a method for producing a magnesium alloy high Ductility etc. through extrusion and the use of extruded semi-finished products or components.

Because of their very low density, magnesium alloys are approximately in the range from 1.2 to 1.9 g / cm ³ , occasionally, especially in the case of particularly lithium-rich magnesium alloys, down to approximately 0.9 g / cm ³ as metallic construction materials of particular interest for vehicle and aircraft construction. In the future, they 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. Among the manufacturing processes, die-casting and shaping, extrusion, forging, rolling and possibly subsequent forming such as stretching or deep-drawing will become increasingly important in the future, since lightweight construction components such as seats and windows can be produced using these processes - and door frames, elements of vehicle cells and vehicle outer skins, housings, floor elements, covers, tank elements, tank flaps, brackets, supports, brackets, angles, crash elements, impact absorbers, impact shields and impact carriers, small parts or corresponding components for aircraft, for which there is an increasing demand ,

The cold formability of the commercially available magnesium alloys is due to the hexagonal crystal structure and the associated low ductility limited. Polycrystalline magnesium and most magnesium alloys behave becomes brittle at room temperature. For a number of applications or for certain Manufacturing process of semi-finished products from magnesium alloys is in addition to good ones mechanical properties such as high tensile strength require ductile behavior. On improved forming, energy absorption and deformation behavior requires a higher one Ductility and possibly also higher strength and toughness. For this are To develop magnesium alloys with these properties or their To further develop manufacturing processes because many material variants match the manufacturing condition have widely varying material properties.

Ductility is the ability of a material to undergo a permanent change in shape, which, in the uniaxial state according to the stress-strain diagram, is ideally without any elastic component. This property is limited by the occurrence of the break. In general, the permanent elongation achieved in the tensile test up to fracture is considered ductility. The degree of ductility can also be seen as the constriction of fracture, impact work and notched impact work, each with a slightly different statement. 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 _plast 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 _elast and the sum of the elastic and plastic part D = ΣA = A _elast + A _plast can be determined. A highly plastic material is called ductile.

When specifying the elongation at break and the tensile strength to different Magnesium alloys make it clear that the elongation at break is often all the higher can take if only medium high tensile strength values are achieved and that conversely, only medium-high values of elongation at break with high values of tensile strength be achieved. Very high values of tensile strength can only be achieved by comparison reach low elongation at break values.

The elasticity denotes the elastic part of the stress-strain diagram according to Hook's law, where with ideal linear-elastic relationships no permanent change in shape occurs.

Furthermore, the yield point ratio V can be specified as the ratio of the yield stress F = R _P02 to the tensile stress Z = R _m . This results in two values that characterize the elasticity, two the plasticity and two their relationship to one another for the largely uniaxial load. The ratio of the elastic to the plastic part of the stretch gives the best approximation to reality.

The impact work is above all a measure of the energy consumption of a semi-finished product and for plastic behavior, i.e. for 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 are more meaningful than the impact energy and affects one largely uniaxial load. The impact work, which is always on notched samples is determined also indicates the susceptibility of a material to triaxial failure Burden. Their informative value is particularly low if the execution of the Notch significantly affects the values of the impact energy. The blow job and the Impact energy is measured under dynamic load and can be an indication give up on energy absorption and deformability. Tensile and compression tests are carried out in the Comparison to this under quasi-static loads. A conclusion from uniaxial on Multi-axis properties or relationships are only partially possible.

The values listed below measured on samples in a particular The state of manufacture therefore reflects the current material properties. she provide an indication of the forming behavior that previously occurred during the forming process was. In this state it is a conclusion about the characteristics and behavior of a person Semi-finished product or even a component with this semi-finished product, which may be further refined later use possible. Furthermore, there is a conclusion about the material properties formed alloys possible, e.g. by bending, pressing, pressure rolling, Stretch drawing, deep drawing, hydroforming or roll forming processed semi-finished products are to be shaped. Because the change in Material properties from cast to extruded condition similar to that Change in material properties from cast to forged, rolled or a similar reshaped state is therefore also an inference to one other forming condition possible.

For the use of lightweight components, the elastic is usually used Properties (rigidity) lifted, unless it is e.g. in the event of an accident Deformation properties and thus on the energy absorption of the element and on the plastic behavior arrives. Therefore, regarding the multiple forming especially the plastic ones and for the use the plastic ones and / or elastic ones Properties matter. These properties are typically for use on the respective ambient temperature, in extreme cases in the range from -40 ° C to +90 ° C individual points in the vehicle or plane, however, to the locally lower or higher Turn off temperatures. However, the load state is usually multi-axis. The Conclusion from uniaxial to multiaxial load conditions is all the more possible, ever more of an isotropic structure.

For the manufacture of such automotive elements, the manufacture is particularly suitable by die casting or extrusion, forging and / or rolling. requirement for the use of semi-finished products made of magnesium alloys or of or from them Components manufactured in automobiles can meet certain property profiles depending after application such as for deformation elements, seat and door frames one Tensile strength of the light material of at least 100 MPa, preferably at least 130 MPa, together with an elongation at break measured at room temperature of at least 10%, preferably at least 15%. The higher the tensile strength, Elongation at break and other properties due to high ductility and energy absorption point out, the more suitable these semi-finished products or components are generally for the Commitment. Furthermore, higher strength values and higher ductility are also one Relief and partly also a prerequisite for the forming of cast blanks or for the further forming of already formed blanks or semi-finished products. The higher these properties are in the cast state, the higher these are usually even in the deformed state. A higher ductility can the forming or the renewed Forming, especially extrusion, easier. Therefore an elongation at break of at least 10% also 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, or an elongation at break of at least 18%, preferably of at least 20%, particularly preferred of at least 25%, recommended. Usually this is Elongation at break in the commercially available magnesium alloys measured at Room temperature less than 12%.

With stronger substitution of other alloys by magnesium alloys to by Weight savings to save fuel or the installation of additional elements without Allowing weight gain is the advancement of the technology of the well-known Magnesium alloys and research into other magnesium alloys necessary especially regarding the combination of properties ductility - strength.

1. Eine recht begrenzte Möglichkeit dieser Steigerung ergibt sich durch Optimierung des Herstellungsprozesses in Verbindung mit Wärmebehandlungsverfahren oder/und über optimierte Herstellparameter z.B. beim Strangpressen. Wichtig ist jedoch beim Umformen z.B. durch Strangpressen, daß die auftretende dynamische Rekristallisation nicht zur Grobkornbildung führt. Denn die Energieaufnahme und die mechanischen Eigenschaften einer Legierung sollten in der Regel umso größer sein, je kleiner die mittlere Korngröße ist. Ziel einer Legierungsentwicklung kann dabei eine Modifikation des Gefügeaufbaus durch Einformen von temperaturstabilen Ausscheidungen oder/und eine Stabilisierung des Gefüges durch Beeinflussung des Kornwachstums sein, um möglichst feines Korn und eine möglichst geringe Porosität zu erzeugen.

2. Beim Übergang der Kristallstruktur der Mg-Hauptphase von der hexagonal dichtesten Kugelpackung auf die kubisch raumzentrierte Kristallstruktur z.B. aufgrund einer höheren Zugabe eines Dotierungselementes tritt eine verbesserte Bruchdehnung und eine bessere Umformbarkeit bei Raumtemperatur aufgrund einer erhöhten Anzahl von Gleitsystemen auf. Allerdings können sich dabei Festigkeit und Korrosionsbeständigkeit verschlechtern.

3. Da Korngrenzen und andere Gefügeinhomogenitäten bzw. Gefügefehler wie z.B. Einschlüsse, Poren, grobe Ausscheidungen, Oxidschlieren und Seigerungen bei der Bewegung von Versetzungen als Barrieren wirken, kann eine Verfeinerung des Gefüges, eine Verkleinerung von Gefügeinhomogenitäten/-fehlern bzw. eine Vermeidung bestimmter Gefügeinhomogenitäten/-fehler zu einer Steigerung der Festigkeit, der Bruchdehnung und der Energieaufnahme führen. Die Zusammenhänge sind jedoch im Einzelfall sehr komplex. Die Kornfeinung ist ein wichtiges Hilfsmittel, um weitere Verformungssysteme zu aktivieren, die ein Korngrenzengleiten und neue Fließprozesse bei Raumtemperatur erlauben und somit die Duktilität verbessern. Dies kann durch die Zugabe kornfeinender Zusätze oder/und durch heterogene Keimbildung beim Erstarren von Gußwerkstoffen aus Legierungen mit bestimmten Zusätzen erfolgen.

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, for example during extrusion. However, it is important when forming, for example by extrusion, that the dynamic recrystallization that occurs does not lead to the formation of coarse grains. Because the energy absorption and the mechanical properties of an alloy should generally be greater, the smaller the average grain size. The aim 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 cubic body-centered crystal structure, for example due to the higher addition of a doping element, an improved elongation at break and better formability at room temperature occur due to an increased number of sliding systems. However, strength and corrosion resistance can deteriorate.

3. Since grain boundaries and other structural inhomogeneities or structural defects such as inclusions, pores, coarse precipitates, oxide streaks and segregations act as barriers when moving dislocations, a refinement of the structure, a reduction in structural inhomogeneities / defects or a avoidance of certain structural homogeneities / errors lead to an increase in strength, elongation at break and energy consumption. However, the relationships are very complex in individual cases. Grain refinement is an important tool to activate further deformation systems that allow grain boundary gliding 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 from alloys with certain additives.

Even the commercially available Mg casting alloys or wrought Mg alloys are in the cast and, if necessary, subsequently formed, in particular extruded, pressed, rolled or / and forged and possibly thereafter heat-treated condition Usually previously relatively low ductility and low Energy absorption. For the inexpensive manufacture of semi-finished products, in particular for vehicles and airplanes, there is a need for suitable alloys and simple ones Process 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 to disposal. These are alloys based on Mg-Al-Zn such as AZ31, AZ61, AZ80 and AZ81, based on Mg-Zn-Zr such as ZK40 and ZK60 or on is the extrusion of Magnesium alloys hardly used.

Haferkamp, Bach, Bohling & Juchmann (Proc. 3 ^rd Int. Magnesium Conf. Manchester April 10-12, 1996, The Institute of Materials, London 1997, ed .: GW Lorimer) or Haferkamp, Bach & Juchmann ("Stand und Trends in the development of density-reduced magnesium materials ", lecture at the advanced training event" Magnesium - Properties, Applications, Potentials "of the German Society for Materials Science Clausthal-Zellerfeld 1997) describe lithium-containing magnesium alloys based on MgLi without and with Al, AlZn, Ca, Si, SiCa , AlCa, CaAlZn or SiAlZn. For the elongation at break or tensile strength, values for MgLi40at% Al6at%, for example of 19% or about 260 MPa, and for MgLi40at% 42% or about 134 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, Haferkamp, Bach, Bohling & Juchmann at the Magnesium Conference in Garmisch-Partenkirchen 1992 (Magnesium Alloys and Their Applications, Eds .: B. L. Mordike & F. Hehmann, Oberursel 1992, 243-250) values of elongation at break and Tensile strength carried forward, that of MgLiAl, possibly with Zn, up to 25% and 239 MPa led.

NASA report N67-22072, SP-5068, Properties and current applications of magnesiumlithium alloys, 1967, indicates possibilities for increasing the strength of lithium-containing ones Magnesium alloys and reports on singular values of high elongation at break or high tensile strength, but it can be assumed that the usual at that time Manufacturing process and available raw materials high Impurities occurred that greatly affected the result and that Corrosion resistance compared to the high-purity alloys that can be produced today significantly impaired.

Dow Chemical Company's "Magnesium Wrought Products" publication of August 1994 provides an overview of commercially available extruded magnesium alloys. The The greatest elongation at break is given here for AZ61 with typically 17%.

Neite describes in Materials Science and Technology, Vol. 8, ED .: K. H. Matucha, 199 ?, in Chapter 4.3.2 Manufacturing processes and mechanical properties of typical Magnesium alloys. For extruded magnesium alloys based on AZ in shape of bars - especially increasing with the aluminum content - tensile strengths of 204 up to 340 MPa and elongations at break of 9 to 17% indicated by an artificial Aging could be increased up to a tensile strength of 380 MPa, but the Elongation at break decreased to 6 to 8%. For AZ31 250 MPa and 14 to 15% are given. Alloy M1 typically had a tensile strength in the extruded state 225 MPa and an elongation at break of 12%.

GB 2,296,256 A gives values of elongation at break of 17.2 and 18% for alloys MgA10.5-1.1Mn0.10-0.12, which, however, had a rather low flexural strength.

Kamado et al. describe in Proc. 3 ^rd Int. Magnesium Conference April 10-12 1996, Manchester / UK, Ed .: GW Lorimer, for the alloy Al10Si1Ca0.5 values of about 170 MPa tensile strength and 2% elongation at break for the press-formed state.

By J. Becker, G. Fischer and K. Schemme, Light weight construction using extruded and forged semi-finished products made of magnesium alloys, lecture Wolfsburg 1998 for the magnesium alloy AZ31 in the extruded state values of 250 MPa Tensile strength and 14% elongation at break are communicated for the alloy M2 of 250 MPa for the Tensile strength, but only 4% for the elongation at break. The samples were therefore not up ductile material properties optimized.

In US 3,419,385 the tensile strength for individual extruded magnesium alloys with contents of Y, Zn and Zr with 248 to 352 MPa and the elongation at break with 14 to 26% each specified by composition. The chemically closest to the alloy ZE10Zr0.7 Coming alloy Zn2.1Y1.9Zr0.9 only showed an elongation at break when cast from 8% to. It can be assumed that with the then usual manufacturing processes and available raw materials, high levels of contamination occurred Result strongly influenced in this regard and the corrosion resistance compared to significantly impaired the high-purity alloys that can be produced today.

There was therefore the task of a method for extruding Magnesium alloys with increased ductility and, if possible, increased energy consumption, Compressive or tensile strength and toughness by selecting the for these purposes propose the most effective parameters that have the lowest possible density and can also be produced as simply and inexpensively as possible.

The object is achieved with a process in which the magnesium alloy contains a content of Zr in the range of 0.1 to 10% by weight and an elongation at break after extrusion of at least 18%, a compressive strength of at least 300 MPa and impact work measured at least 20 J on notched samples. The Zr content is in particular 0.15 to 6% by weight, preferably 0.2 to 3% by weight, particularly preferably 0.3 to 1.5% by weight.

The task is also solved with a corresponding method, in which the Magnesium alloy including at least one rare earth element SE La and Y in the range of 0.1 to 10% by weight in total, and one after extrusion Elongation at break of at least 18%, a compressive strength of at least 300 MPa and has an impact energy measured on notched specimens of at least 50 J. The total content of magnesium alloys without the addition of lithium is: Rare earth elements, in particular 0.15 to 8% by weight, preferably 0.2 to 6% by weight, particularly preferably 0.3 to 4% by weight, very particularly preferably 0.4 to 3% by weight.

It has been shown that the modification of grain sizes and phase distributions over the alloying of accompanying elements such as lithium, zirconium, rare earth elements SE such as e.g. Cerium, praseodymium, neodymium, samarium, gadolinium, ytterbium, yttrium and lanthanum or their mixtures or the alkaline earth metals - especially Ca, Sr, Ba - is helpful under Generation of significantly stronger and / or more ductile magnesium alloys. First of all Addition of lithium, calcium, strontium, zirconium or at least one Rare earth element including yttrium and lanthanum has proven to be beneficial for Further development of magnesium alloys proven.

That the alloy is dynamically recrystallized during extrusion, that it is additives or traces of Cd less than 1.8 wt% and traces of up to 0.1 wt% Cu, up to 0.05% by weight of Fe and up to 0.005% by weight of Ni may contain one Magnesium alloy based on AM, AS, EM, EZ, MA, ME, SA, ZA or ZE and that it is after extrusion, an elongation at break of at least 17.5%, a compressive strength of at least 300 MPa and impact work measured on unslotted samples of has at least 45 J.

The task is also solved with a corresponding method, in which the Magnesium alloy based on AZ with at least one addition of Ca, Sr, Li, SE or / and Zr is in each case at least 0.1% by weight and in which it is one after extrusion Elongation at break of at least 17.5%, a compressive strength of at least 350 MPa and has an impact energy measured on notched specimens of at least 50 J. The The proportion by weight of the respective additive can in particular be 0.15 to 6% by weight, preferably 0.2 to 4% by weight, particularly preferably 0.25 to 2% by weight. In addition, other additions can occur, preferably those that are dynamic Recrystallization behavior and fine grain influence.

The task is also solved with a corresponding method, in which the Magnesium alloy based on MN with at least 1% by weight Mn and with the addition of SE or / and Zr of at least 0.1 wt .-% and in which they after Extrusion has an elongation at break of at least 15%, a compressive strength of at least 300 MPa, and impact work measured on unslotted samples of has at least 20 J. The Mn content is preferably at least 1.3% by weight. The proportion by weight of the respective additive can in particular be 0.15 to 6% by weight, preferably 0.2 to 4% by weight, particularly preferably 0.25 to 2% by weight. In addition, other additions can occur, preferably those that are dynamic Influence recrystallization behavior.

The task is also solved with a corresponding method, in which the Magnesium alloy based on MZ or ZM, which is an addition of SE and / or Zr by each can contain at least 0.1 wt .-%, and in which they after extrusion an elongation at break of at least 15%, a compressive strength of at least 300 MPa and has an impact work of at least 40 J measured on notched specimens. After extrusion, the alloy preferably has a plastic component Stress determined in the tensile test according to the stress-strain diagram from the Difference of tensile stress and yield stress of at least 40 MPa.

The remaining contents of the chemical composition mentioned exist predominantly or essentially of magnesium. Levels of cadmium interfere with the Processing only because of their toxicity, but are otherwise particularly with regard to Formability is an advantage. Traces of copper, iron and nickel should be as possible be low since they affect the processing and / or the material properties impact.

It has been found that usually high ductile magnesium alloys Extrusion speeds can be achieved. There are still tests no effort has been made to achieve the highest extrusion speeds achieve, but rather there is a clear potential, even significantly higher To be able to reach speeds. The degree of deformation characterizes the degree of Reduction of cross-section during forming and is used as the natural logarithm of the Ratio of initial cross-section to cross-section specified after forming. He is therefore often correlated with the degree of dynamic recrystallization, where possible should not yet occur stronger growth of individual grains, but one if possible fine-grain structure is sought, which is high for some magnesium alloys Ductility conditional. The more stable the structure of a magnesium alloy, the more fine-grained the structure becomes or remains during forming. It has also been found that the degree of deformation is advantageously at least 1.5, preferably at least 2, particularly preferably at least 2.5. If the degree of deformation is less than 1.5, the dynamic Recrystallization when forming is quite low. It would also have a grade of 3.5 or more can be selected in the tests. The extrusion speed is advantageously at least 1.5 m / min, preferably at least 2.5 m / min, particularly preferably at least 5 m / min, very particularly preferably at least 7.5 m / min. It is above all due to the decreasing quality of the extruded profiles limited.

It is necessary that the magnesium alloy is selected from the group of Magnesium alloys due to dynamic recrystallization and fine grain get a higher ductility. The dynamic recrystallization and structural change from the original or compacted molded body to the finished semi-finished product, component or Compounding is often not only achieved through extrusion and the associated processes thermal or mechanical influences, but they are preferred performed essentially or even mainly in extrusion.

The task is finally solved with a semi-finished product made of a magnesium alloy or with a component made of it or with it or with a composite with a such semifinished product or component that was produced according to the invention.

The semifinished product or component according to the invention preferably consists essentially of a magnesium alloy selected from the group of alloys based AM, AS, AZ, EZ, MA, SA, ZA or ZE, EM, EZ, ME, MN, MZ, ZE and ZM with a salary on at least one rare earth element AM, AS, AZ, MA, MN, MZ, SA, ZA or EZ, MN or ZE with zirconium addition.

For the purposes of this application, semi-finished products are understood to be shaped articles which have not yet are completed and ready for use for their respective application. As components on the other hand, the molded articles are suitable for the intended purpose designated. However, both terms flow smoothly into one another, since it is the same shaped body for one purpose around a semi-finished product, but for the other can already be a component. Furthermore, for the sake of linguistic Simplification does not strictly differentiate between semi-finished products and components throughout the text or both mentioned at the same time or only spoken of magnesium alloy, although both can be meant.

The semifinished products made of magnesium alloys according to the invention or those thereof or therewith manufactured components or composites can be used as frame elements, Elements of the vehicle cell or vehicle outer skin, as a vehicle cell or Vehicle outer skin, cockpit support, cockpit skin, housing, floor element, floors, cover, Tank elements, tank flaps, brackets, supports, beams, angles, hollow profiles, pipes, Deformation elements, crash elements, crash absorbers, impact absorbers, impact shields, Impact beams, small parts, as a welded profile construction, for the vehicle body, for Seat, window or / and door frames, as semi-finished products, components or composites on or in Automobile or airplane.

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 Ar or / and SF ₆ . Instead of a casting process, the powder-metallurgical production of green compacts, possibly with subsequent annealing, can also be used. The process steps are known in principle, but require a different modification or optimization depending on the alloy.

Prerequisite for the further processing of magnesium alloys by extrusion, Rolling and / or forging is the production of suitable materials e.g. in the form of Blocks, bolts or slabs. There are for the production of bolts for extrusion two main options:

In the first method, a bolt with a very large diameter can be cast are then turned into round bolts using a high-performance extrusion press can be pressed with a diameter that corresponds to the recipient diameter. The segregation is reduced by the thermomechanical treatment.

A less complex process than this double extrusion is the production of the Bolts by sand, mold or continuous casting with a sufficiently large size Machining allowance. However, it is important to ensure that there are no severe segregations occur that are not or only insufficient due to long homogenization times be balanced. The consequences could otherwise be a bad compressibility and a greater dispersion of the mechanical properties, in particular the ductility.

The cast bolts can first be subjected to heat treatment depending on the Alloy composition in e.g. 350 ° C homogenized in the range from 6 h to 12 h to eliminate segregations in the structure, some of which heterogeneous structure too improve and increase the pressability. Then the homogenized bolts machined to the required dimensions.

Segregations can lead to uneven deformation and critical Extrusion conditions lead to cracks or local melting, which is bad Surface qualities can cause. With less well homogenized bolts is a unnecessarily high extrusion pressure required. The homogenized bolts are then prepared for extrusion.

The extrusion of the magnesium alloys can be carried out in the same extrusion plants take place, which are used for the extrusion of aluminum alloys, both via direct as well as indirect extrusion. Only with the Tool design (die), the deformation behavior must be specifically taken into account. There are sharp-edged inlets, such as those used in aluminum alloys Avoid magnesium alloys, otherwise there is a risk of surface cracks. In many cases e.g. for matrices of round profiles an entry angle of approx. 50 ° for Magnesium alloys used. A round profile was used in the tests.

The most important parameter besides the extrusion temperature is the extrusion speed, because they have the properties and surface quality of the Extruded profiles significantly influenced. A high pressure also means a high one Extrusion speed, which is aimed for economic reasons. A high Extrusion speed is usually with an even better surface quality connected. The extrusion speed is very different from the geometry of the strand dependent. The pressability of the magnesium alloys is comparable to that heavy-duty aluminum alloys. A high extrusion speed is true Desired from an economic point of view, but is not the case with magnesium alloys always feasible. It may also be used at particularly high extrusion speeds there are no cracks or burning of the magnesium alloy. In addition, the Degree of deformation of great importance. It goes along with the change in the structure. Of a high degree of forming is therefore an advantage. However, it is not allowed with high degrees of deformation local melting occurs. Despite certain knowledge of the extrusion of Magnesium alloys usually need the parameters for extrusion in detail be worked out because there is a huge potential for optimization.

The extrusion can advantageously be followed by a heat treatment. The Semi-finished products can be straightened if necessary, e.g. by bending, pressing, pressure rolling, stretch drawing, Deep drawing, hydroforming or roll forming further deformed, e.g. by Cutting, drilling, milling, grinding, lapping, polishing, machining, joining and / or e.g. by Etching, pickling, painting or other coating are surface treated. With the Alloys according to the invention can be solid and extruded profiles in simple or complicated cross sections can be extruded without problems. Here you can Semi-finished products are improved or components can be produced from them or, if necessary, from them.

When joining, the semi-finished product or the component made therefrom or with it can pass through at least one low-heat joining process such as Gluing, riveting, plugging, pressing, Pressing in, clinching, folding, shrinking or screwing and / or at least one heat-generating joining process such as Composite casting, composite forging, Composite extrusion, composite rolling, soldering or welding, in particular Beam welding or fusion welding, with a similar or different type Semi-finished product or component can be connected. The different semi-finished product or component can likewise essentially of a magnesium alloy or of another alloy or also consist of a non-metallic material. It can be the same or one have a different geometry than the semi-finished product or component according to the invention. The Joining methods can serve in particular to create a housing from several elements, to manufacture an apparatus, a system, a profile construction and / or a cladding.

Examples:

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

A Al, E indicates at least one of the alloy designations used Rare earth element SE, whereby Y is also counted among the rare earth elements, M or MN Mn, S Si and Z Zn - usually with content in% by weight, unless otherwise is noted. With commonly used alloy information such as AZ31 are made by the numbers as usual for the respective alloy only in the order of magnitude specified, which can vary to a relatively wide extent as is customary in the industry. In addition, at of the starting alloy used in the examples and of those produced therewith modified alloys based on AZ have a low manganese content. All Examples showed traces of less than 0.1 wt% Cd, less than 0.05 wt% Cu, less than 0.04 wt% Fe and less than 0.003 wt% Ni.

The alloys were made as high-purity, commercially available alloys or usually from high-purity starting alloys such as, for example, AM, AS or AZ alloys or by adding high-purity magnesium HP-Mg, a rare earth element-containing master alloy with a ratio of Nd to other rare earths, including yttrium of 0.92, a zirconium-containing master alloy and / or of calcium or strontium. The standard alloys contained an Mn content of up to about 0.2% by weight. 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 was taken to ensure that the structure of the cast body is as homogeneous and free of impurities as possible, as this can have a sensitive effect on ductility. All alloys could be melted, poured off and processed into bolts without any problems.

The bolts were then turned to a diameter of 70 mm and to a length of 120 mm brought. The bolts were then subjected to homogenization treatment in e.g. 350 ° C exposed for 4 h or 12 h to eliminate segregations in the structure and the Increase pressability. Segregations can lead to uneven deformation and critical extrusion conditions lead to cracks or local melting, which can cause poor surface qualities. With less well homogenized bolts an unnecessarily high pressing pressure is required during extrusion. The homogenized bolts were then well prepared for extrusion.

The homogenized bolts were then brought up to the respective extrusion temperature heated, warmed up and directly in a 400 t horizontal press Extrusion process extruded. The temperature of the bolt is the temperature which the bolt has when it enters the extrusion press.

The appropriate extrusion parameters were selected in systematic preliminary tests on the AZ31 reference alloy; The mechanical properties and the average grain sizes were determined on the extruded samples (Tables 1 and 2).
The results of the preliminary tests essentially determined the test parameters of the subsequent tests.

During the actual tests, several of the manufacturing parameters were systematically varied (Tables 4a to 4f). On the one hand, the die diameter was varied and were the die speed and extrusion temperature kept constant, on the other hand, the matrix geometry was kept constant and became the Die speed varied and finally the extrusion temperature varies depending on the alloy. The ram speed and the extrusion ratio gave the extrusion speed. With the help of such a parameter matrix it was possible to evaluate the influence of different forming conditions.

All alloys, both the starting alloys and those by additives modified alloys could easily be used in a wide temperature, Form extrusion speed and extrusion ratio range. Bolts showed good compressibility with a large scope in terms of pressing force and Compression speed. The extrusion speed was not yet in the tests maxed out to the highest possible speeds and therefore can still generally be significantly increased. The lower extrusion temperature is due to the insufficient plastic deformability below a temperature in the range of about 200 to 220 ° C. conditionally, the upper extrusion temperature is limited by the proximity to eutectic temperature and possibly through the initial formation of portions of a molten phase.

Depending on the extrusion conditions, the same result Alloy composition Differences in the structure of the samples. The occurred Extrusion pressures varied depending on the alloy used and the set one Strangpreßparametern. Generally a dynamic occurred during extrusion Recrystallization, depending on the extrusion parameters and the Alloy composition led to different average grain sizes. The The composition of the magnesium alloys varied only slightly or almost not at all from the composition of the melt to the composition before or after Extrusion to the composition of the semi-finished product made from it. The The semifinished product or component according to the invention preferably consists essentially of a Magnesium alloy, which is selected from the group of alloys based on AM, AS, AZ, EZ, MA, SA, ZA or ZE, EM, EZ, ME, MN, MZ, ZE and ZM containing with at least one rare earth element AM, AZ, MA, MN, MZ, ZA or EZ, MN or ZE Zirkoniumzusatz.

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

The extruded round profiles were processed by milling and turning into round specimens (d ₀ = 5 mm, I ₀ = 5 • d ₀ , small proportionality bar, according to DIN 50 125), pressure tests (d ₀ = 10 mm, I 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 or, in some cases, the constriction at break at the tensile test at a tensile speed of 0.5 mm / min were determined. Values of the compressive strength R _Dm , compression limit R _D0.2 and compression A _D at a printing speed of 0.5 mm / min were obtained in the compression test. The beginning of the plastic deformation (expansion or compression limit) was determined graphically. Brinell hardness measurements were also carried out in accordance with DIN 50351. All measurements took place at room temperature. The results of the mechanical determinations are summarized in Tables 4a-c and those of the structural examinations in Table 4d.

Grindings were made on selected samples, with respect to average grain size, Structural homogeneity as well as the type and distribution of the separated phases contained were assessed. This evaluation was used to further optimize the Manufacturing and processing parameters.

The variation of the extrusion parameters had a different influence on that Property profile of the extruded magnesium materials. Tendencies of Material properties of the different alloys depending on the manufacturing parameters can be seen from Tables 4e / f.

The measurement results of the Brinell hardness determinations did not allow any special ones Statement. The Brinell hardness of the extruded samples was found to be 7 to 22% greater than the cast samples. The hardness increased with the aluminum content.

Magnesium alloys containing SE and / or Zr:

Casting the stud: The melt was at a temperature in the range of 780 to 820 ° C, once also at 750 ° C, kept and cast. The shape showed depending on the experiment a diameter of 90 or 110 mm and a mold temperature in the range of 80 to 320 ° C. The element contents achieved were checked spectroscopically.

The castings were homogenized at 350 ° C. over 12 h. By turning bolts usually made 70 mm in diameter and 120 mm in length; with 6 samples of Alloy AZ31Ca0.3, however, was chosen to have a diameter of 74 mm. Depending on the sample was an extrusion temperature in the range of 200 to 450 ° C and a time to Heating and warming set in the range from 60 to 150 min.

Extrusion: Preliminary tests were carried out with the AZ31 alloy in a 400 t extrusion press direct extrusion carried out (Tables 1 and 2). With a The recipient diameter of 74 mm was successfully examined in a wide range of parameters become. The preliminary tests allowed the test parameters to be defined.

The specific extrusion tests were carried out in a 400 t extrusion press with direct extrusion. Extrusion temperature: 340 ° C, 365 ° C or 390 ° C each after 1 hour of heating and warming the stud. Press dies with a diameter of 15, 16 or 18 mm and a compression ratio of 1: 24.3, 1: 21.4 and 1: 16.9 were predominantly used. The pressing speed was 3.8 - 4.5, 5.0 - 5.5, 5.8 - 6.5 and 9.5 - 10 m / min. Only a small part of the extrusion tests are shown in Table 4f. Depending on the sample, a recipient temperature in the range from 250 to 380 ° C., a die diameter in the range from 14 to 18 mm, a compression ratio A / A ₀ in the range from 16.9 to 27.9, and a degree of deformation were obtained with a recipient diameter of 74 mm ϕ = In (A _o / A) in the range from 2.8 to 3.3, a punch speed in the range from 145 to 508 mm / min, an extrusion speed in the range from 3.2 to 10.8 m / min, a pressing pressure at the start of the extrusion in the range from 8.7 to 23.5 MPa and a pressure at the end of the extrusion in the range from 7.2 to 16.5 MPa and once from 23.3 MPa.

The parameter spectrum showed good compressibility with a large scope with regard to pressing force and pressing speed. The structure formation and the achieved Elongation at break correlated with the deformation parameters. There have been comparative high strength values achieved.

The extrusion pressures that occurred varied depending on the alloy used and set parameters in a wide range. The final pressures reached were for Alloys without the addition of SE or Zr in the range around 10 ± 2 MPa Extrusion temperatures greater than 300 ° C and for alloys containing SE or Zr up to 4 MPa higher. Cause for the higher extrusion pressures and thus for the increased resistance to deformation of magnesium alloys with SE or Zr addition is a higher proportion of stable excretions than magnesium alloys without this addition. For lower temperatures, generally higher ones were used Extrusion pressures determined.

The highest values of the tensile tests were with the extruded ME10 alloy the average tensile strength at values up to 336 MPa and the average yield strength at Values up to 327 MPa. The cast ME10 alloy showed a very high plastic part of the tension, while the ratio of the elastic to the plastic component during extrusion and reversed extreme values (Table 4b). Very small average grain sizes in the range from 3 to 5 µm occurred.

With the extruded alloy MN150Ca0.2 there was a very strong increase in most mechanical properties compared to the extruded alloy MN150 on. An addition of Zr0.7 to the extruded starting alloy MN150 only had an effect little out.

In the case of the extruded ZE10 alloy, there were fewer mechanical ones Properties determined, but these varied greatly with the temperature, so that still better mechanical properties can be achieved with an even higher temperature: The properties of the ZE10 alloy become essential from the rare earths influenced and can vary in the variation of rare earth elements including yttrium or their contents can be further optimized. Medium occurred with the ZE10 alloy Grain sizes in the range from 6.5 to 13 µm, which again with the extrusion temperature rather increased; however, this alloy warmed with increasing Extrusion speed relatively strong, which at higher extrusion speed also led to somewhat larger average grain sizes. With the extruded modified alloy ZE10Zr0.7 resulted very much due to the addition of zirconium higher strength than the ZE10 extruded base alloy. She pointed like that additionally extruded alloy containing Zr0.7 very high elongation at break values and the impact work. So when cooling aluminum-free zirconium-containing Melting use heterogeneous nucleation, which is due to a Grain boundary pinnings led to a particularly fine structure. The hammer work on however, the notched specimen was due to the inhomogeneous distribution of the zirconium-containing ones Phase slightly in comparison to the samples of the ZE10 alloy declined. The addition of zirconium stabilized the extruded ZE10Zr0.7 alloy the structure. Structures with medium grain sizes were created during extrusion Range from 2.2 to 4.5 µm. These small grain sizes were created over a wide range Strangpreßparameterbereich. With this alloy, the slight variation was Grain sizes depending on the extrusion parameters are striking.

Adding RE0.7 to the extruded ZM21 alloy had little effect on the mechanical properties.

It has been found that the trend of the Hall-Petch relationship is also valid for the magnesium alloys according to the invention, according to which the mechanical properties are improved with smaller grain sizes. In many cases, this applies above all to tensile and compressive strength, but also in principle to elongation at break and impact work. Results of the preliminary tests to determine the extrusion parameters with the AZ31 alloy at an extrusion temperature of 400 ° C, a die diameter of 16 mm, a recipient diameter of 74 mm and a compression ratio of 1:21 Compression speed Average grain diameter Tensile strength R _m Yield strength R _P0.2 Elongation at break A reduction of area m / min microns MPa MPa % % 4 8.8 277 134 12.5 29.2 5 9.3 281 141 12.7 29.3 8.4 9.0 282 137 15.6 35.2 Influence of the compression ratio on the average grain sizes and the mechanical properties from the tensile test at an extrusion temperature of 400 ° C in the preliminary tests to determine the extrusion parameters die diameter pressing ratio Compression speed medium grain diameter Tensile strength R _m Yield strength R _P0.2 Elongation at break A reduction of area mm m / min microns MPa MPa % % 16 1:21 4 8.8 277 134 12.5 29.2 12 1:38 5 9.3 281 141 12.7 29.3

In Table 4, "casting" means material in the as-cast state and "extr." = Casting material which was subsequently formed by homogenization and extrusion, "B" = example according to the invention and "VB" = comparative example according to the prior art. Average values of the measurement results of the mechanical tests on various samples of the SE and Zr-containing magnesium alloys and their starting alloys: sample alloy Tensile test Compression test Schlagvers. R _m MPa R _{P 0.2} MPa A
% R _Dm MPa R _upsetting MPa A _D
% C _G
J C _UG
J B 20a MN150Zr0.7 extr. 225 180 19.0 nb nb nb 4.4 22 VB 21 ZE10 Molding 88 22 11.0 172 20 11.0 7.8 13 B 21 ZE10 extr. 239 175 21.6 321 86 9.7 10.8 56 B 22 ZE10Zr0.7 extr. 281 250 22.7 382 170 11.6 13.2 55 B / VB 23 ZM21 extr. 258 192 13.3 318 78 8.7 8.8 43 B 24a ZM21SE0.7 extr. 264 206 20.4 nb nb nb 8.6 53 B 25 ZM21Zr0.7 extr. 252 188 15.4 nb nb nb 9.6 56 Average values of the values that can be determined from the stress-strain diagram of the tensile tests for modified lithium-free magnesium alloys and their starting alloys. F = R _P02 = yield stress = elastic part of the stress. V = yield strength ratio = F: Z. R _m = tensile stress Z = elastic + plastic part of the stress. No. alloy tensions strain Flow-F MPa Z - F MPa Zug-Z MPa V = F: Z A _plast = A
% B 20a MN150Zr0.7 extr. 180 45 225 0.81 19.0 VB 21 ZE10 Molding 22 66 88 0.25 11.0 B 21 ZE10 extr. 175 64 239 0.73 21.6 B 22 ZE10Zr0.7 extr. 250 31 281 0.89 22.7 B / VB 23 ZM21 extr. 192 66 258 0.74 13.3 B 24a ZM21SE0.7 extr. 206 58 264 0.78 20.4 B 25 ZM21Zr0.7 extr. 188 64 252 0.75 15.4 Highest mean values of the measurement results of the mechanical properties selected from various individual samples of the modified magnesium alloys: sample alloy Tensile test Compression test Schlagvers. R _m
MPa R _P0.2
MPa A
% R _Dm
MPa R _upsetting
MPa A _D
% C _G
J C _UG
J B 20a MN150Zr0.7 extr. 227 180 19.0 nb nb nb 4.7 22.3 B 21 ZE10 extr. 251 203 24.9 329 93 11.8 11.7 65.0 B 22 ZE10Zr0.7 extr. 309 288 25.5 405 213 14.8 14.3 75.7 B 23 ZM21 extr. 260 199 15.9 331 85 9.3 9.5 49.0 B 24 ZM21SE0.7 extr. 281 241 23.8 nb nb nb 10.7 64.7 B 25 ZM21Zr0.7 extr. 254 193 16.9 nb nb nb 10.7 62.0 Mainly occurring grain sizes in the as-cast state after homogenization at 350 ° C for 4 h or after extrusion with the modified lithium-free magnesium alloys and their starting alloys. sample alloy average grain sizes, µm B 20a MN150Zr0.7 extr. 6.4 - 6.5 VB 21 ZE10 Molding 85 B 21 ZE10 extr. 6.7 - 13.3 VB 22 ZE10Zr0,7 Molding 94 B 22 ZE10Zr0,7 extr. 2.3 - 4.6 B 24 ZM21SE0.7 extr. 6.8 - 10.3 B 25 ZM21Zr0.7 extr. 17.5-23.2 Process parameters for various samples of the modified lithium-free magnesium alloys and their starting alloys. sample alloy melting temperature Temperature of the bolt Degree of deformation ϕ = In (A _o / A) Anfangspreßdruck Compression speed number of samples ° C ° C MPa m / min B 20a MN150Zr0.7 extr. 780 300-340 3.0 - 3.1 12.0 - 12.2 4.0 - 4.4 2 VB 21 ZE10 Molding 780 340 1 B 21 ZE10 extr. 780-790 340-390 2.8 - 3.2 11.3 - 14.2 4.2-10.5 8th B 22 ZE10Zr0.7 extr. 780 - 820 250-400 2.8 - 3.1 15.5-21.6 3.3 - 8.2 9 B 23 ZM21 extr. 780-800 340-390 2.8 - 3.2 10.5 - 15.0 4.1-10.6 8th B 24 ZM21SE0.7 extr. 780 300 - 425 2.8 - 3.1 12.6 - 16.4 2.9 - 4.2 8th B 25 ZM21Zr0.7 extr. 780 400 - 425 2.8 - 3.1 10.3 - 11.2 3.6 - 4.5 3

Claims (16)

Method for producing a magnesium alloy of high ductility, inter alia by extrusion, characterized in that the alloy is extruded with a degree of deformation of at least 1.5, that it contains additives or traces of Cd less than 1.8% by weight and traces of up to 0 , 1% by weight of Cu, up to 0.05% by weight of Fe and up to 0.005% by weight of Ni can contain Zr in the range from 0.1 to 10% by weight or one Content of at least one rare earth element SE including La and Y in the range from a total of 0.1 to 10% by weight and, after extrusion, an elongation at break of at least 15%, a compressive strength of at least 300 MPa and an impact energy measured on non-notched samples of at least 20 J has. A method for producing a magnesium alloy according to claim 1, characterized in that after extrusion it has an elongation at break of at least 18% and an impact energy measured on notched samples of at least 50J. A method of producing a magnesium alloy according to claim 1 or 2, characterized in that the alloy is dynamically recrystallized during extrusion, that it is a magnesium alloy based on ZE (zinc / rare earths) and that after extrusion it has an impact energy measured on notched samples of has at least 45 J. Method for producing a magnesium alloy according to one of Claims 1 to 3, characterized in that the alloy is dynamically recrystallized during extrusion, in that it is a magnesium alloy based on MN (manganese) with at least 1% by weight Mn and with the addition of SE or / and Zr is in each case at least 0.1% by weight. Method for producing a magnesium alloy according to one of claims 1 to 4, characterized in that the alloy is dynamically recrystallized during extrusion, that it is a magnesium alloy based on MZ (manganese / zinc) or ZM (zinc / manganese), which is an additive in particular of SE or / and Zr each of at least 0.1% by weight, and that after extrusion it has an impact energy of at least 40 J measured on unskilled specimens. Method for producing a magnesium alloy according to at least one of the preceding claims, characterized in that it has a tensile strength of at least 200 MPa after the extrusion. Method for producing a magnesium alloy according to at least one of the preceding claims, characterized in that it has a plastic portion of the stress determined after the extrusion in the tensile test according to the stress-strain diagram from the difference between tensile stress and yield stress of at least 40 MPa. A process for producing a magnesium alloy according to at least one of the preceding claims, characterized in that the molded articles to be extruded, in particular bolts, are homogenized for 2 to 24 hours at temperatures in the range from 330 to 380 ° C. Method for producing a magnesium alloy according to at least one of the preceding claims, characterized in that it is extruded at a degree of deformation of at least 2. Process for producing a magnesium alloy according to at least one of the preceding claims, characterized in that it is extruded at an extrusion speed in the range from 0.5 to 20 m / min, preferably at 1 to 18 m / min, particularly preferably at 3 to 16 m / min, very particularly preferably at 5 to 15 m / min. Process for producing a magnesium alloy according to at least one of the preceding claims, characterized in that it is heat-treated or aged after extrusion at temperatures in the range from 80 to 250 ° C, preferably at 100 to 150 ° C. Method for producing a magnesium alloy according to at least one of the preceding claims, characterized in that it is subsequently shaped again or is subsequently shaped. Method for producing a magnesium alloy according to at least one of the preceding claims, characterized in that the semi-finished product or the component made from or with the semi-finished product is further shaped, processed, for example by bending, pressing, pressure rolling, stretch drawing, deep drawing, hydroforming or roll profiling , added and / or surface treated. Method for producing a magnesium alloy according to at least one of the preceding claims, characterized in that the semifinished product or the component produced therefrom or by means of at least one low-heat joining process such as gluing, riveting, inserting, pressing, pressing, clinching, folding, shrinking or screwing or / and at least one heat-introducing joining process such as composite casting, composite forging, composite extrusion, composite rolling, soldering or welding, in particular beam welding or fusion welding, is connected to a similar or different type of semi-finished product or component. Semifinished product made of a magnesium alloy or a component or composite produced therefrom or composite with such a semifinished product or component, characterized in that it was produced according to at least one of the preceding claims. Use of a magnesium alloy manufactured according to at least one of the Claims 1 to 15 as a frame element, element of the vehicle cell or Vehicle outer skin, vehicle cell or vehicle outer skin, cockpit support, Cockpit skin, housing, floor element, floor, cover, tank element, fuel filler flap, Bracket, support, bracket, angle, hollow profile, tube, deformation element, Crash element, crash absorber, impact damper, impact shield, impact carrier, small part, as welded profile construction, for the vehicle body, for seats, windows or / and Door frame, as a semi-finished product, component or composite on or in the automobile or plane.