Abstract
The invention relates to a magnesium alloy. To obtain a magnesium alloy which exhibits both a high strength and also a high deformability, a magnesium alloy is provided according to the invention, comprising (in at %) 15.0% to 70.0% lithium, greater than 0.0% aluminum, and magnesium and production-related impurities as a remainder, wherein a ratio of aluminum to magnesium (in at %) is 1:6 to 4:6. The invention also relates to a method for producing the magnesium alloy.
Claims
1. A magnesium alloy, comprising (in at %), 15.0% to 70.0% lithium, greater than 0.0% aluminum, optionally also greater than 0.0 to 3.0 wt % calcium, optionally also greater than 0.0 to 3.0 wt % rare earth metals, in particular yttrium, optionally also 3.0 wt % to 10.0 wt % zinc, optionally also 2.0 wt % to 10.0 wt % silicon, magnesium and production-related impurities as a remainder, wherein a ratio of aluminum to magnesium (in at %) is 1.2:6 to 4:6.
2. The magnesium alloy according to claim 1, wherein the magnesium alloy comprises (in at %) 30.0% to 60.0%, in particular 40% to 50% lithium.
3. The magnesium alloy according to claim 1, wherein the ratio of aluminum to magnesium (in at %) is 2:6 to 3.5:6.
4.-5. (canceled)
6. The magnesium alloy according to claim 1, wherein the magnesium alloy contains calcium and rare earth metals, in particular yttrium, wherein a total amount of calcium and rare earth metals, in particular yttrium, is greater than 0.0 to 3.0 wt %.
7.-8. (canceled)
9. A method for producing a magnesium alloy according to claim 1, wherein a heat treatment of the magnesium alloy is carried out in order to optimize a strength and/or deformability of the magnesium alloy.
10. The method according to claim 9, wherein the heat treatment is carried out at a temperature greater than 200° C., in particular between 200° C. and 400° C., for more than 20 minutes, in particular more than 1 hour.
11. A feedstock, semi-finished product, or element having a magnesium alloy according to claim 1.
12. A feedstock, semi-finished product, or element obtainable using the method according to claim 9.
Description
[0032] FIG. 1 shows a schematic phase diagram illustration for Mg—Li—Al, in which composition ranges of the magnesium alloy according to the invention are indicated;
[0033] FIG. 2 shows a yield stress diagram of multiple magnesium alloy specimens from a magnesium alloy according to the invention;
[0034] FIG. 3 and FIG. 4 show scanning electron microscope images of a magnesium alloy specimen from a magnesium alloy according to the invention at different magnifications;
[0035] FIG. 5 shows a yield stress diagram of magnesium alloy specimens from a magnesium alloy according to the invention after completed heat treatments;
[0036] FIG. 6 shows a yield stress diagram of magnesium alloy specimens from a further magnesium alloy according to the invention after completed heat treatments;
[0037] FIG. 7 shows a hardness diagram of magnesium alloy specimens from a magnesium alloy according to the invention.
[0038] FIG. 1 shows a schematic phase diagram illustration (in at %) for magnesium-lithium-aluminum (Mg—Li—Al) according, to a typical ternary phase diagram design, wherein composition ranges or content ranges of alloy amounts of a magnesium alloy according to the invention are indicated. In the phase diagram illustration, an orientation composition of an Mg—Li—Al alloy with an aluminum-to-magnesium ratio (in at %) of approx. 3:6 is depicted as dash-dotted line A, since in accordance with a finding on which the invention is based, a particularly homogeneous, fine-scale, in particular fine lamellar, microstructure or morphology is found in a content range of 15.0 at % to 70.0 at % lithium at this ratio of aluminum to magnesium. In a range encompassing this ratio, indicated by an aluminum-to-magnesium ratio (in at %) of 1:6 to 4:6, this fine-scale or finely structured microstructure is furthermore found in a varyingly pronounced degree and explains an advantageously high strength, in particular compressive strength, and good deformability of the magnesium alloy in this range. A composition range (in at %) of 15.0% to 70.0% lithium and an aluminum-to-magnesium ratio (in at %) of 1:6 to 4:6 are illustrated clearly in FIG. 1 by a quadrangle depicted by a solid line, denoted by reference numeral 1. A pronounced strength and particularly pronounced deformability are found in particular in a composition range (in at %) of 30.0% to 60.0% lithium and an aluminum-to-magnesium ratio (in at %) of 1:6 to 4:6. This composition range is illustrated in FIG. 1 by a quadrangle depicted by a dashed line, denoted by reference numeral 2.
[0039] In the course of a development of the magnesium alloy according to the invention, series of tests were conducted with different alloy compositions of magnesium alloys, in particular of alloy compositions correspondingly defined according to the invention. Below, characteristics of magnesium alloy specimens fabricated from Mg-20% Li-15% Al-1% Ca-0.5% Y (in wt %) and Mg-20% Li-24% Al-1% Ca-0.5% Y (in wt %) are presented as being representative of the aforementioned composition ranges. The magnesium alloy specimens were produced by means of permanent mold casting, wherein in particular magnesium alloy specimens having a cylindrical shape, with a diameter of 5 mm and a length of 10 mm, were fabricated. The magnesium alloy specimens were subjected to compression tests at room temperature, approximately 20° C. and yield curves which depict a yield stress, in MPa, as a function of a degree of deformation, in %, were calculated as a result.
[0040] FIG. 2 shows a yield stress diagram with yield curves as a result of compression tests at room temperature using magnesium alloy specimens fabricated from Mg-20% Li-15% Al-1% Ca-0.5% Y (in wt %). Yield curves of magnesium alloy specimens immediately following a production of the magnesium alloy specimens (as cast) are illustrated, shown in FIG. 2 as solid lines, denoted by reference numeral 3. In addition, yield curves of magnesium alloy specimens after a completed heat treatment (aged) of the magnesium alloy specimens are illustrated, shown in FIG. 2 as dashed lines, denoted by reference numeral 4. For this purpose, magnesium alloy specimens were subjected to a heat treatment at 330° C. for 3 hours, and yield curves were then calculated by means of compression tests. A clear influence of the heat treatment on the compressive strength and deformability of the magnesium alloy specimens is evident, as a result of which there is the potential to set the compressive strength, and deformability in an optimized manner using heat treatment, in particular for an eventual intended application.
[0041] FIG. 3 and FIG. 4 show scanning electron microscope images of the magnesium alloy specimens fabricated from Mg-20% Li-15% Al-1% Ca-0.5% Y (in wt %) at different magnifications. Evident are, on the one hand, light grain boundary phases (in whitish-gray) that were identified as Al—Ca and, on the other hand, pronounced fine crystalline structures or morphologies in a region surrounded by the grain boundary phases, in particular in a center section of said region, or in the interior of the mixed crystal phase, clearly evident in FIG. 4 in particular. Also identifiable is a markedly different fine structure, in particular in the proximity of the grain boundary phases.
[0042] FIG. 5 shows a yield stress diagram with yield curves as a result of compression tests at room temperature using magnesium alloy specimens fabricated from Mg-20% Li-15% Al-1% Ca-0.5% Y (in wt %), wherein magnesium alloy specimens were examined after completed heat treatments at different heat treatment temperatures. Yield curves of magnesium alloy specimens which were subjected to a heat treatment at 270° C. for 4 hours are illustrated, depicted in FIG. 5 as dashed lines, denoted by reference numeral 5, and yield curves of magnesium alloy specimens which were subjected to a heat treatment at 330° C. for 4 hours, depicted in FIG. 5 as solid lines, denoted by reference numeral 6. Evident is a pronounced influence of heat treatment temperatures on the mechanical properties of the magnesium alloy specimens, wherein a heat treatment temperature of 330° C. compared to a lower heat treatment temperature of 270° C. leads to a pronounced improvement in the compressive strength, there also being a very good deformability of the magnesium alloy specimens at the same time.
[0043] FIG. 6 shows a yield stress diagram with yield curves as a result of compression tests at room temperature using magnesium alloy specimens fabricated from Mg-20% Li-15% Al-1% Ca-0.5% Y (in wt %), wherein magnesium alloy specimens were examined after completed heat treatments at different heat treatment temperatures. Yield curves of magnesium alloy specimens which were subjected to a heat treatment at 270° C. for 4 hours are illustrated, depicted in FIG. 6 as dashed lines, denoted by reference numeral 7, and yield curves of magnesium alloy specimens which were subjected to a heat treatment at 330° C. for 4 hours, depicted in FIG. 6 as solid lines, denoted by reference numeral 8. Here, analogously to the result illustrated in FIG. 5, a pronounced influence of heat treatment temperatures on the mechanical properties of the magnesium alloy specimens is once again found, wherein a heat treatment temperature of 330° C. compared to a lower heat treatment temperature of 270° C. leads to an improvement in the compressive strength, there also being a good deformability of the magnesium alloy specimens at the same time.
[0044] FIG. 7 shows a hardness diagram as a result of Vickers hardness tests at room temperature, approximately 20° C., using magnesium alloy specimens fabricated from Mg-20% Li-15% Al-1% Ca-0.5% Y (in wt %), wherein magnesium alloy specimens were examined after completed heat treatments with different heat treatment durations. 330° C. was used as a heat treatment temperature. In the hardness diagram, mean values of Vickers hardnesses (HV 0.1) from multiple measurements are respectively shown as a function of different heat treatment durations t, from 0 minutes (min) to 300 minutes, of the magnesium alloy specimens. Evident is a successive increase in the hardness with a heat treatment duration, wherein a high hardness can be achieved in particular at a heat treatment duration of more than 60 minutes. With regard to the image depictions shown in FIG. 3 and FIG. 4, these characteristics can potentially be explained by a diffusion of calcium into the inner region of the mixed crystal phase.
[0045] A magnesium alloy according to the invention thus advantageously exhibits both a high strength and also a good deformability, both of which can be optimized, or preferably increased, by means of heat treatment in particular. Specifically, there is also the possibility of optimizing, or setting in a defined manner, a hardness of the magnesium alloy. The magnesium alloy according to the invention, or an element having or being made from the magnesium alloy according to the invention, thus offers the potential to realize, preferably such that they suit a purpose, robust and resilient components, especially structural components, in particular in the automotive industry, aircraft industry, and/or space industry.
