Abstract
The invention relates to an alloy, in particular a light metal alloy, having an alloy composition with at least three components and a eutectic structure that is obtained by cooling the alloy from a liquid state to a solid state, under the condition that a composition of the alloy lies in a field around a pseudoeutectic point (pE) of a phase diagram of the alloy, so that at least 85 mol % eutectic structure is present in the alloy. The alloy also relates to a method for producing an alloy of this type.
Claims
1. An alloy, in particular a light metal alloy, having an alloy composition with at least three components and a eutectic structure that is obtained by cooling the alloy from a liquid state to a solid state, under the condition that a composition of the alloy lies in a field around a pseudoeutectic point (pE) of a phase diagram of the alloy, so that at least 85 mol % eutectic structure is present in the alloy.
2. The alloy according to claim 1, wherein the eutectic structure has an average spacing of the phase amounts thereof of less than 3 μm, preferably less than 1 μm.
3. The alloy according to claim 1, wherein the alloy comprises a residual solidification at an amount of maximally 5 mol %, preferably maximally 3 mol %.
4. The alloy according to claim 1, wherein the alloy comprises a primary solidification at an amount less than 10 mol %, in particular less than 5 mol %.
5. The alloy according to claim 4, wherein the primary solidification is formed having a mixed crystal phase.
6. The alloy according to claim 1, wherein the alloy has a density less than 8 g/cm.sup.3.
7. The alloy according to claim 1, wherein the alloy is a magnesium-based alloy, aluminum-based alloy, lithium-based alloy, or titanium-based alloy.
8. (canceled)
9. The alloy according to claim 1, wherein the alloy is an Al—Mg—Si alloy.
10. The alloy according to claim 9, wherein the Al—Mg—Si alloy comprises between 0.01 wt % and 5.0 wt %, in particular approximately 3.0 wt %, zinc.
11. A method for producing an alloy, in particular an alloy according to claim 1, having a eutectic structure, wherein the alloy has an alloy composition with at least three components and wherein the alloy is cooled, starting from a liquid state, to a solid state of the alloy in order to form the eutectic structure, under the condition that the alloy composition is provided such that it lies in a field around a pseudoeutectic point (pE) of a phase diagram of the alloy, so that the eutectic structure is embodied at an amount of at least 85 mol % during the cooling to the solid phase.
12. A feedstock, semi-finished product, or construction material having an alloy according to claim 1.
13. A feedstock, semi-finished product, or construction material obtainable using the method according to claim 11.
Description
[0034] Additional features, advantages, and effects follow from the exemplary embodiments described below. In the drawings which are thereby referenced:
[0035] FIG. 1 and FIG. 2 show phase diagram illustrations of an Al—Mg—Si system in which alloy compositions of exemplary alloys are indicated;
[0036] FIG. 3 through FIG. 12 show optical microscope images of exemplary alloys from FIG. 1 and FIG. 2;
[0037] FIG. 13 through FIG. 20 show yield stress diagrams of exemplary alloys from FIG. 1 through FIG. 12;
[0038] FIG. 21 shows a phase diagram illustration of an Al—Cu—Mg system with an alloy composition of an exemplary alloy being drawn;
[0039] FIG. 22 shows optical microscope images of the exemplary alloy from FIG. 21;
[0040] FIG. 23 shows a yield stress diagram of the exemplary alloy from FIG. 21 and FIG. 22;
[0041] FIG. 24 shows a phase diagram illustration of an Mg—Al—Li system in which alloy compositions of exemplary alloys are indicated;
[0042] FIG. 25 and FIG. 27 show optical microscope images of exemplary alloys from FIG. 24:
[0043] FIG. 28 and FIG. 29 show yield stress diagrams of exemplary alloys from FIG. 24 through FIG. 27;
[0044] FIG. 30 shows a phase diagram illustration of an Mg—Cu—Zn system with an alloy composition of an exemplary alloy being drawn;
[0045] FIG. 31 and FIG. 32 show optical microscope images of the exemplary alloy from FIG. 30;
[0046] FIG. 33 shows a yield stress diagram of the exemplary alloy from FIG. 30 through FIG. 32;
[0047] FIG. 34 shows electron microscope images of an exemplary alloy from an Al—Cu—Mg—Zn system;
[0048] FIG. 35 shows a yield stress diagram of the exemplary alloy from FIG. 34;
[0049] FIG. 36 shows a phase amount diagram of an exemplary alloy from an Al—Mg—Si—Zn system;
[0050] FIG. 37 shows a solid amount diagram of a Scheil-Gulliver calculation for the exemplary alloy from FIG. 36.
[0051] In the course of a development of the alloy according to the invention, series of tests were conducted with different alloy compositions of various alloy systems. In each case, alloys were thereby chosen with an alloy composition in the field of or around a pseudoeutectic point of a respectively related phase diagram, and a eutectic structure was formed by cooling the alloy from a liquid state to a solid state. The microstructure was then examined by means of microscopy. In addition, various dilatometric test series and compression tests were conducted at room temperature, approximately 20° C., as a standard, wherein yield curves which depict a yield stress, in MPa, as a function of a degree of deformation, illustrated as the amount of length change ΔL relative to a starting length L.sub.0, that is
[00001]
and correspondingly dimensionless, were calculated as a result.
[0052] Below, test results for exemplary alloys from the alloy systems Al—Mg—Si, Al—Cu—Mg, Mg—Li—Al, Mg—Cu—Zn, Al—Cu—Mg—Zn, and Al—Mg—Si—Zn are shown in a representative manner in order to illustrate the aforementioned concept on a broad basis.
[0053] Al—Mg—Si system:
[0054] FIG. 1 and FIG. 2 show illustrations of a ternary phase diagram of an Al—Mg—Si system, wherein FIG. 2 is a segment illustration from the phase diagram for the purpose of showing the relevant alloy composition range in detail. Ten exemplary alloys from the Al—Mg—Si system were produced and examined. The alloy compositions of the exemplary alloys from the Al—Mg—Si system are respectively indicated in percentage by weight and atomic percent as exemplary alloy 1 through exemplary alloy 10 in Table 1 and correspond to the reference numerals 1 through 10, which in particular denote the respective alloy composition in the phase diagram from FIG. 1 and FIG. 2.
TABLE-US-00001 TABLE 1 Ten exemplary alloys from the Al—Mg—Si alloy system. Al Mg Si Exemplary alloy 1 wt % 68.10 9.00 22.90 at % 68.04 9.98 21.98 Exemplary alloy 2 wt % 71.10 9.10 19.80 at % 70.94 10.08 18.98 Exemplary alloy 3 wt % 78.10 6.30 15.60 at % 78.04 6.99 14.97 Exemplary alloy 4 wt % 81.50 5.00 13.50 at % 81.48 5.55 12.97 Exemplary alloy 5 wt % 82.00 6.00 12.00 at % 81.85 6.65 11.51 Exemplary alloy 6 wt % 82.00 10.50 7.50 at % 81.30 11.56 7.14 Exemplary alloy 7 wt % 82.70 10.00 7.30 at % 82.03 11.01 6.96 Exemplary alloy 8 wt % 84.90 10.90 4.20 at % 84.03 11.98 3.99 Exemplary alloy 9 wt % 85.80 9.60 4.60 at % 85.05 10.56 4.38 Exemplary alloy 10 wt % 86.50 7.20 6.30 at % 86.03 7.95 6.02
[0055] As can be seen in the phase diagram from FIG. 1 and FIG. 2, the exemplary alloys 8 through 10 each have compositions which are arranged in a field around a pseudoeutectic point pE, wherein the exemplary alloys 8 and 9 are positioned very close to the pseudoeutectic point and the exemplary alloy 10 is positioned at a somewhat greater distance from the pseudoeutectic point pE. The alloy composition of the exemplary alloy 9 thereby virtually lies at the pseudoeutectic point pE. The pseudoeutectic point pE is illustrated in FIG. 2 by a drawn reference line, wherein the pseudoeutectic point pE is located at the intersection of the monovariant line in the direction of Al.sub.3Mg and the reference line. In FIG. 2, it can also be seen that the exemplary alloys 3 through 5 are arranged in a field around a eutectic point E of the phase diagram. Furthermore, the exemplary alloys 6 and 7 are provided as comparisons, the compositions of which are located at a large distance from the pseudoeutectic point pE, evident in FIG. 2, as well as the exemplary alloys 1 and 2 which, though positioned in direct proximity to a liquidus boundary line, are positioned at a greater distance from both the pseudoeutectic point pE and also the eutectic point E, evident in FIG. 1.
[0056] In FIG. 3 through FIG. 12, optical microscope images of the exemplary alloys 1 through 10 are shown in order to illustrate a respective microstructure. In FIG. 13 through FIG. 20, yield stress diagrams are illustrated as the results of dilatometric test series of the Al—Mg—Si exemplary alloys which were conducted at room temperature, approximately 20° C. Yield stress curves are shown, wherein a yield stress, in MPa, is illustrated as a function of the degree of deformation. Each of the yield stress diagrams shows multiple yield stress curves from alloy specimens with an alloy composition corresponding to the alloy composition of one of the exemplary alloys 1 through 10. Each yield stress diagram thus represents an alloy composition of one of the exemplary alloys 1 through 10.
[0057] As can be seen in FIG. 10 through FIG. 12, the microscope images of the exemplary alloys 8 through 10, which have alloy compositions in proximity to or in a field around the pseudoeutectic point pE, show a dominant finely structured or fine-scale eutectic structure. By comparison, microscope images of the exemplary alloys 4 and 5 can be viewed in FIG. 6 and FIG. 7, which alloys have an alloy composition in proximity to the eutectic point E. These show a pronounced degree of a eutectic structure which comprises a course structure compared to the microstructures of the exemplary alloys 8 and 9. If one compares these with the microscope images of the exemplary alloys 1 and 2 shown in FIG. 3 and FIG. 4, the alloy compositions of which are located at a large distance from, but in the region of, a liquidus boundary line, it is discernible that they exhibit an even courser eutectic microstructure. In FIG. 8 and FIG. 9, microscope images of the exemplary alloys 6 and 7 are also shown which have alloy compositions in a distant region of the pseudoeutectic point pE or at a great distance therefrom. It can be seen that a eutectic structure is already present, but with a relatively course structure and being notably less dominant and at a lower amount. In addition, high amounts of residual solidifications are also evident, identifiable in FIG. 8 and FIG. 9 in the form of light channels.
[0058] FIG. 13 and FIG. 14 show yield stress diagrams of the exemplary alloys 8 and 9, which have alloy compositions in proximity to or in a field around the pseudoeutectic point pE. It can be seen that both exemplary alloy 8 and also exemplary alloy 9 have high strength, in particular compressive strength, and pronounced deformability with yield stresses between 300 MPa and 400 MPa, wherein exemplary alloy 8 in particular, illustrated in FIG. 13, exhibits yield stresses of up to 400 MPa. By comparison, yield stress diagrams of the exemplary alloys 4 and 5 can be viewed in FIG. 15 and FIG. 16, which alloys have alloy compositions in proximity to the eutectic point E. The exemplary alloys 4 and 5 also exhibit high strength and, at least conditional on individual specimens, a high deformability, wherein yield stresses lie below those of the exemplary alloys 8 and 9 at approximately 300 MPa or, in relation to exemplary alloy 5, illustrated in FIG. 16, consistently below that. This result correlates with the finding that exemplary alloys with an alloy composition in the field of the pseudoeutectic point pE exhibit a particularly high fine structuring of the eutectic structure thereof, in particular also compared to the eutectic structure of exemplary alloys with alloy compositions in the field of a eutectic point E, which also explains the higher strength and pronounced elasticity of alloys in the field of the pseudoeutectic point.
[0059] In FIG. 20, a yield stress diagram of the exemplary alloy 10 is shown, the alloy composition of which is arranged at a somewhat greater distance from the pseudoeutectic point pE. Evident are slightly lower yield stress values and, in particular, a higher variance between the individual measurement results. In FIG. 17 and FIG. 18, it is furthermore shown that, by comparison, exemplary alloy 1 and exemplary alloy 2 with alloy compositions in the region of a liquidus boundary line, but at a distance from both the alloy composition of the pseudoeutectic point pE and also the eutectic point E, have notably poorer strength and deformability properties. In FIG. 19, a yield stress diagram corresponding to the alloy composition of the exemplary alloys 6 and 7 is additionally shown, the alloy composition of which is positioned at a relatively large distance from that of the pseudoeutectic point pE in the phase diagram. The corresponding yield stress curves show clearly reduced yield stresses compared to yield stresses of an alloy composition closer to the pseudoeutectic point pE, such as that of those shown in FIG. 13 for the exemplary alloy 8.
[0060] It is evident that an alloy composition in a field around a pseudoeutectic point pE corresponds to a finely structured eutectic microstructure and an accordingly high strength and pronounced deformability.
[0061] In a detailed view, it can be seen that, relative to the monovariant line or liquidus boundary line in the direction of Al.sub.3Mg.sub.2, the exemplary alloy 8 in the phase diagram from FIG. 2 lies above said line in the Mg.sub.2Si region, which is why a solidification begins with an undesirable formation of Mg.sub.2Si in particular, or a primary solidification is formed with an intermetallic Mg.sub.2Si phase, when the alloy is cooled from the liquid phase. It has been shown that a primary solidification formed with an intermetallic phase has negative effects for an embodiment of both high strength and also deformability. To achieve particularly advantageous strength and deformability, one therefore generally strives to keep a primary solidification having or being made of intermetallic phase as minor as possible, or to prevent it. However, the primary solidification for exemplary alloy 8 is so slightly pronounced that it entails virtually no restraint on mechanical properties. The microscope images of the exemplary alloy 8 in FIG. 10 show extensive regions with a fine eutectic structure, in this case formed with Al mixed crystal phase and Mg.sub.2Si. Advantageously, a residual solidification of Al mixed crystal phase is also only very slightly pronounced or hardly present. To keep from undermining the advantageous strength and deformability properties attainable with the eutectic structure, one strives to keep a residual solidification as small as possible or prevent it. In particular, the residual solidification is not bonded in a network-like manner, or is embodied in the form of units separated from one another, which likewise promotes an advantageous embodiment of high strength and pronounced deformability. The exemplary alloy 8 thus proves to be well suited, both with regard to low residual solidification and also low primary solidification, to controlling strength properties and deformability on the basis of the fine eutectic structure. This can be optimized even further if the alloy composition is chosen such that the primary solidification is formed having or being made of a mixed crystal phase and not with an intermetallic compound or phase, that is, if the primary solidification is located in the Al mixed crystal phase region in the case of the exemplary alloy 8.
[0062] This view of the exemplary alloy 8 and also the accompanying explanations apply analogously to the exemplary alloy 9. The exemplary alloy 9 has an alloy composition lying virtually at the pseudoeutectic point pE. The exemplary alloy 9, as can be seen in FIG. 11, also shows a fine eutectic structure with little residual solidification and little primary solidification. The somewhat lower strength in comparison with the exemplary alloy 8 is explained by the lower dissolved amount of Mg in the Al mixed crystal phase. A strength can be advantageously achieved by varying an amount of dissolved elements in the mixed crystal phase, with the primary solidification preferably lying, however, in the mixed crystal region and not in the region of an intermetallic phase, as stated above.
[0063] By comparison, the exemplary alloy 10, as can be seen in FIG. 12, also shows a fine eutectic structure, but with a greater amount of residual solidification, in the form of Al mixed crystal phase and Si, which residual solidification is also shaped in a network-like manner. Due to the low Mg content, most of the Mg is bonded in the form of Mg.sub.2Si so that a mixed crystal hardening of the Al mixed crystal phase is very slightly pronounced. This corresponds to lower yield stresses in the yield stress diagram from FIG. 20.
[0064] In a further detailed view of the exemplary alloys arranged at a distance from the pseudoeutectic point pE in relation to an alloy composition, it can be seen that the exemplary alloys 4 and 5, which lie in the field of the eutectic point E, illustrated in FIG. 6 and FIG. 7, comprise a low amount of primary solidification, around which a relatively course eutectic structure, formed with two phases, is arranged. A remaining predominant amount of eutectic structure is embodied as a ternary eutectic, formed with mixed crystal phase, Al.sub.2Si and Si. The mechanical properties, in particular strength and deformability, are negatively influenced by the course binary eutectic structure or phase in particular. A fine eutectic ternary structure is locally present to some extent, which structure transitions into markedly coarsened structures in some locations. The differences between the microstructures of exemplary alloys with alloy compositions at, or in the field of, the pseudoeutectic point pE compared to those at, or in the field of, the eutectic point E correlate with the finding of accordingly improved strength and deformability properties of alloy compositions at, or in the field around, the pseudoeutectic point pE.
[0065] It can furthermore be seen that the exemplary alloys 6 and 7 comprise course, polygon-shaped primary solidifications with the related microscope images shown in FIG. 8 and FIG. 9. This is explained by the positioning of the related alloy compositions in the Mg.sub.2Si region of the phase diagram, as a result of which a pronounced Mg.sub.2Si primary solidification forms. A course eutectic structure is identifiable therebetween, as well as a high amount of residual solidification, which is evident from the light regions or channels in FIG. 8 and FIG. 9. Due to this structural morphology, the exemplary alloys 6 and 7 exhibit markedly reduced strengths and yield stresses, which are associated in particular with crack initiation and brittle fracture.
[0066] In FIG. 2, a particularly advantageous region for the embodiment of an Al—Mg—Si alloy is drawn as a gray, planar region. This essentially designates or corresponds to an aforementioned alloy composition of the exemplary alloys 8 and 9, but with a variation of the alloy composition such that a mixed crystal phase is embodied as primary solidification and, in particular, no intermetallic phase is embodied. This enables an embodiment of particularly high strengths with pronounced deformability. A particularly advantageous implementation range for an Al—Mg—Si alloy of this type is thus ensured if the Al—Mg—Si alloy is arranged in a field around the pseudoeutectic point in the Al—Mg—Si phase diagram, wherein the alloy composition in the phase diagram is arranged starting from the aforementioned pseudoeutectic point of the phase diagram in FIG. 2 on a side of the corresponding monovariant line facing an increasing Al amount.
[0067] Al—Cu—Mg system:
[0068] FIG. 21 shows an illustration of a ternary phase diagram of an Al—Cu—Mg system. An exemplary alloy from the Al—Cu—Mg system was produced and examined. The related alloy composition is indicated in percentage by weight and atomic percent as exemplary alloy 13 in Table 2 and corresponds to reference numeral 13, which in particular denotes the alloy composition in the phase diagram from FIG. 21.
TABLE-US-00002 TABLE 2 Exemplary alloy from the Al—Cu—Mg alloy system. Al Cu Mg Exemplary alloy 13 wt % 66.00 24.00 10.00 at % 75.61 11.67 12.72
[0069] As can be seen in the phase diagram from FIG. 21, the exemplary alloy 13 has an alloy composition which is arranged in a field around a pseudoeutectic point pE. A related microstructure is illustrated in FIG. 22 with the aid of optical microscope images. Evident is a very fine-scale eutectic microstructure and a low amount of primary solidification formed with mixed crystal phase. In FIG. 23, a yield stress diagram is shown as the result of dilatometric test series of the Al—Cu—Mg exemplary alloy 13, wherein a yield stress, in MPa, is once again illustrated as a function of the degree of deformation. It is evident that very high strengths and yield stresses are achieved.
[0070] The elongation at break also lies in the technologically relevant range for this alloy system. The strength and deformability correspond to the fine eutectic microstructure and, in particular, to the low amount of primary solidification.
[0071] Mg—Al—Li system:
[0072] FIG. 24 shows an illustration of a ternary phase diagram of an Mg—Al—Li system. Three exemplary alloys from the Mg—Al—Li system were produced and examined. The alloy compositions of the exemplary alloys from the Mg—Al—Li system are respectively indicated in percentage by weight and atomic percent as exemplary alloy 14, 15, and 16 in Table 3 and correspond to the reference numerals 14, 15, and 16, which in particular denote the respective alloy composition in the phase diagram from FIG. 24.
TABLE-US-00003 TABLE 3 Three exemplary alloys from the Mg—Al—Li alloy system. Mg Al Li Exemplary alloy 14 wt % 55.00 29.00 16.00 at % 40.10 19.05 40.85 Exemplary alloy 15 wt % 56.00 24.00 20.00 at % 37.90 14.60 47.40 Exemplary alloy 16 wt % 65.00 15.00 20.00 at % 43.80 9.10 47.10
[0073] As can be seen in the phase diagram from FIG. 24, the exemplary alloys 14 through 16 respectively have an alloy composition which is arranged in a field around a pseudoeutectic point pE. The pseudoeutectic point pE is illustrated in FIG. 24 by a drawn reference line, wherein the pseudoeutectic point pE is located at the intersection of the monovariant line, or liquidus boundary line, and the reference line. With additions of CaY, in particular approximately 1 wt % Ca and approximately 0.5 wt % Y, oxidation properties of the exemplary alloys from the Mg—Al—Li system can feasibly be stabilized without negatively influencing how pronounced the structure is. In the phase diagram, the exemplary alloys 14 and 15 lie at a somewhat closer distance in a vicinity of the pseudoeutectic point and the exemplary alloy 16 somewhat farther away, wherein the alloy composition of the exemplary alloy 14 is positioned more or less at the pseudoeutectic point pE. According to currently available data, the exemplary alloys 14 through 16 are present in a mixed crystal region, in particular such that they form a body-centered cubic lattice, bec.
[0074] In FIG. 25 through FIG. 27, microstructures are respectively rendered visible with the aid of microscope images. The structural morphology from FIG. 25 and FIG. 26 indicates an embodiment of an extremely fine-scale structure which can no longer be resolved in the light microscope used. The grain boundaries which can thereby be recognized are attributable to oxidic impurities. The microstructure of exemplary alloy 16 was examined by means of scanning electron microscopy, illustrated in FIG. 27. Evident in FIG. 27 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 grain boundary phases, in particular in a center section of said region, or in the interior of the mixed crystal phase, clearly visible in particular in the right-hand image from FIG. 27. In the phase diagram from FIG. 24, the alloy composition of the exemplary alloy 16 appears to lie at a relatively far distance from the monovariant line and the pseudoeutectic point pE. In this case, however, it should be noted that, according to established technical knowledge, the slope in the region of the body-centered cubic lattice, bec,—in which the exemplary alloy 16 is also arranged—in the phase diagram is very flat, and that the three elements Mg, Al. and Li also exhibit a high solubility in one another. It its thus possible to explain why such an expansive field around the pseudoeutectic point results, in which field an advantageous fine-scale eutectic microstructure can be embodied in a high amount.
[0075] FIG. 28 and FIG. 29 show yield stress diagrams of the exemplary alloys 15 and 16 as the results of dilatometric test series, wherein a yield stress, in MPa, is once again illustrated as a function of the degree of deformation, with FIG. 28 showing yield stress curves relating to the exemplary alloy 15 and FIG. 29 showing yield stress curves relating to the exemplary alloy 16. It is evident that both exemplary alloys have high strengths and yield stresses, as well as pronounced deformabilities, corresponding to the fine eutectic microstructures identified. In FIG. 29, which relates to the exemplary alloy 16, a possibility of a further property optimization by means of heat treatment is also illustrated.
[0076] FIG. 29 shows yield curves of alloy specimens immediately after a production of the exemplary alloy 16 (as cast), depicted in FIG. 29 as solid lines, denoted by reference numeral 16-1, and additionally yield curves of exemplary alloy specimens after a conducted heat treatment (aged) of the exemplary alloy 16, depicted in FIG. 29 as dashed lines, denoted by reference numeral 16-2. For this purpose, specimens of the exemplary alloy 16 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 strength, in particular compressive strength, and deformability is evident, as a result of which there is the potential to set compressive strength and deformability in an optimized manner using heat treatment, in particular for an eventual intended application.
[0077] As previously explained above in the document, it has proven beneficial to the realization of an alloy with high application suitability if the alloy is a magnesium-based alloy comprising, in particular being made of, (in at %)
15% to 70.0% lithium,
greater than 0.0%, in particular greater than 0.01%, preferably greater than 0.05%, aluminum, magnesium and production-related impurities as a remainder,
wherein a ratio of aluminum to magnesium (in at %) is 1:6 to 4:6. The exemplary alloy 16 can be viewed as a representative example of this alloy definition, as is shown within the scope of European Patent Application Number 19184999.1 and also within the scope of International Application Number PCT. EP2020058280, both of which were filed in the European Patent Office. Here, reference is once again made in particular to FIG. 1 from each of these applications. In FIG. 24, a corresponding aluminum-to-magnesium ratio (in at %) of 1:6 is drawn as a dashed line. The aforementioned aluminum-to-magnesium ratio range (in at % or mol %) of 1:6 to 4:6 is thereby located to the left of this line in the phase diagram from FIG. 24 and, in particular, constitutes a specific embodiment in the field around the pseudoeutectic point pE.
[0078] A particularly advantageous implementation range for an Mg—Li—Al alloy that is usable as an application alloy, in particular for a structural part, is ensured if the Mg—Li—Al alloy is arranged in the Mg—Li—Al phase diagram in a region between the line indicating an aluminum-to-magnesium ratio (in at %) of 1:6 and the monovariant line or liquidus boundary line, in particular with an aforementioned Li content range. A range of this type is denoted in the phase diagram from FIG. 24 as a gray, planar region.
[0079] It becomes apparent, as was already the case previously within the scope of the exemplary alloys from the Al—Si—Mg system, that an alloy composition is preferably chosen such that the alloy composition lies in the field of the pseudoeutectic point pE and, moreover, preferably comprises a primary solidification having or being made of mixed crystal phase; that is, that the corresponding alloy composition is positioned in a mixed crystal region in the phase diagram.
[0080] Mg—Cu—Zn:
[0081] FIG. 30 shows an illustration of a ternary phase diagram of an Mg—Cu—Zn system. An exemplary alloy from the Mg—Cu—Zn system was produced and examined. The related alloy composition is indicated in percentage by weight and atomic percent as exemplary alloy 17 in Table 4 and corresponds to reference numeral 17, which in particular denotes the alloy composition in the phase diagram from FIG. 30.
TABLE-US-00004 TABLE 4 Exemplary alloy from the Mg—Cu—Zn alloy system. Al Cu Zn Exemplary alloy 17 wt % 58.00 16.5 25.5
[0082] As can be seen in the phase diagram from FIG. 30, the exemplary alloy 17 has an alloy composition which is arranged in a field around a pseudoeutectic point pE. A related microstructure is illustrated in FIG. 31 and FIG. 32 with the aid of optical microscope images. Evident is a very fine-scale eutectic microstructure that is at a limit of resolution of a light microscope. Here, a relatively large amount of primary solidification can be seen. It is therefore advantageous for a high strength and deformability if an alloy composition is selected even closer to the pseudoeutectic point pE or closer to the monovariant line or liquidus boundary line.
[0083] FIG. 33 shows a yield stress diagram as the results of dilatometric test series of the exemplary alloy 17, wherein a yield stress, in MPa, is once again illustrated as a function of the degree of deformation. It is evident that high strengths and yield stresses are achieved which, based on the pronounced amount of primary solidification apparent in the microscope images, can be further improved, however, by choosing an alloy composition even closer to the pseudoeutectic point pE.
[0084] In FIG. 33, yield curves of the exemplary alloy 17 immediately following a production of the exemplary alloy 17 (as cast) are thereby shown, denoted by reference numeral 17-1, and also yield curves of the exemplary alloy 17 after a conducted heat treatment, denoted by reference numeral 17-2. For this purpose, specimens of the exemplary alloy 17 were subjected to a heat treatment at 350° C. for 4 hours, and yield curves were then calculated by means of compression tests. A clear influence of the heat treatment on strength and deformability is evident, as a result of which there is the potential to further optimize strength and deformability by means of heat treatment.
[0085] Examinations of quaternary alloy systems and quaternary eutectics were then also carried out. The alloy systems Al—Cu—Mg—Zn and Al—Mg—Si—Zn in particular were considered for this purpose.
[0086] Al—Cu—Mg—Zn:
[0087] In regard to the alloy system Al—Cu—Mg—Zn, an exemplary alloy that lies in the field of a pseudoeutectic point pE was produced and examined. The alloy composition is indicated in percentage by weight and atomic percent as exemplary alloy 18 in Table 5 and corresponds to reference numeral 18.
TABLE-US-00005 TABLE 5 Exemplary alloy from the Al—Cu—Mg—Zn alloy system. Al Cu Mg Zn Exemplary alloy 18 wt % 6.20 75.40 5.40 13.00 at % 12.51 65.00 12.09 10.82
[0088] In order to examine the eutectic microstructure, electron microscope images of the exemplary alloy 18 were recorded, shown in FIG. 34. Evident is a finely structured eutectic structure, in particular with structural dimensions in the nanometer range, clearly visible in the right-hand image from FIG. 35 as an expansive grainy region in the center of the picture.
[0089] This is a binary eutectic structure in a system with four components or elements and thus an increase in the thermodynamic degree of freedom f, explained at the outset, from 1 to 3 (quaternary eutectic).
[0090] In FIG. 34, substructures are identifiable in the primary regions (in gray), wherein these are artifacts of an isostoichiometric structural transformation (bec to fec) in the solid state. In terms of a direct influence on strength and deformability, they are insignificant. Also visible is a relatively large amount of primary solidification in the form of a mixed crystal phase (in light gray to whitish), as well as an intermetallic secondary phase (in black), in particular in the form of a Laves phase.
[0091] FIG. 35 shows a yield stress diagram as the result of dilatometric test series with the exemplary alloy 18. Depicted are yield curves prior to a completed heat treatment, denoted by reference numeral 18-1, and yield curves following a completed heat treatment, denoted by reference numeral 18-2, wherein a yield stress, in MPa, is once again illustrated as a function of the degree of deformation. It is evident that the exemplary alloy 18 exhibits a very high strength with a simultaneously present elongation at break, wherein a deformability can be varied by means of heat treatment.
[0092] The pronounced primary solidification present as well as the secondary phase are to be regarded as brittleness-increasing factors, which is why it would be advantageous to further reduce these amounts in order to further improve strength and deformability, for example by reducing the distance of the alloy composition from or bringing it even closer to the pseudoeutectic point pE in the phase diagram.
[0093] Al—Mg—Si—Zn:
[0094] In regard to the alloy system Al—Mg—Si—Zn, an exemplary alloy that lies in the field of a pseudoeutectic point pE was examined by means of simulation. The alloy composition is indicated as exemplary alloy 19 in Table 6 and corresponds to reference numeral 19.
TABLE-US-00006 TABLE 6 Exemplary alloy from the Al—Mg—Si—Zn alloy system. Al Mg Si Zn Exemplary alloy 19 wt % 83.3 9.2 4.5 3.0
[0095] As a result of the simulation, phase amounts are illustrated in FIG. 36 as a function of the temperature of the exemplary alloy 19. Evident is a direct transition from the solid to the liquid phase, corresponding to an embodiment of a eutectic structure. In FIG. 35, corresponding thereto, an illustration of the solid amount as a function of the temperature is shown, determined by means of a Scheil-Gulliver solidification calculation. The equilibrium and Scheil-Gulliver solidification curves shown depict an alloy system which exhibits a binary eutectic solidification with four components or elements. Accordingly, there is therefore once again an increase in the thermodynamic degree of freedom from 1 to 3. In FIG. 37, the Scheil-Gulliver calculation shows a very small amount of primary solidification in the form of a mixed crystal phase at an amount of less than 3 mol % or at/o and in addition a virtually non-existent residual solidification.
[0096] It is thus analogously apparent that, in addition to a positioning of the alloy composition in the field of the pseudoeutectic point pE, an amount of primary solidification and/or residual solidification can advantageously also be minimized in order to further increase or improve strength properties and deformability properties.
[0097] An alloy according to the invention with more than three components having a eutectic structure created by a cooling from the liquid state to the solid state can thus advantageously be embodied with a finely structured eutectic structure, in particular with a fine structure in the nanometer range, which constitutes a dominant or principal phase amount or structure amount in the alloy if an alloy composition of the alloy is arranged in the field of or around a pseudoeutectic point in the phase diagram. The alloy can thus be embodied with advantageously high strength and pronounced deformability. This holds especially true if a primary solidification and/or residual solidification is embodied to be very small. Specifically, it is beneficial thereto if the primary solidification is formed having or being made of a mixed crystal phase, in particular not having or being made of an intermetallic phase, or if the alloy composition is chosen in a corresponding region in the phase diagram. An alloy formed in this manner thus offers the potential to realize, preferably depending on a specific purpose, robust and resilient components, especially structural components, in particular for an intended application in the automotive industry, aircraft industry, and/or space industry.
