High Strength Microalloyed Magnesium Alloy

Abstract

A magnesium composite material and method for manufacturing a magnesium composite alloy wherein the magnesium composite alloy has improved thermal and mechanical properties. The improved thermal and mechanical properties are at least in part obtained by the modification of grain boundary properties in the magnesium composite alloy by the addition of nanoscale fillers to the magnesium composite alloy.

Claims

1. A magnesium composite alloy that includes: at least 60 wt. % magnesium; more than 5 wt. % and less than 9 wt. % Rare Earth metal; at least 0.5 wt. % zinc; wherein said magnesium composite alloy has a thermal conductivity that is at least 170 W/m-K, and/or has a ductility exceeding 6% elongation to failure.

2. A magnesium alloy composite comprising: at least 60 wt. % magnesium; 2.5-16 wt. % Rare Earth metal, said Rare Earth metal includes yttrium and/or gadolinium; zinc, said zinc is less than 8 wt. %; less than 1 wt. % zirconium; up to 1 wt. % tin; up to 1 wt. % germanium; and, less than 10 wt. % aluminum; and wherein said magnesium alloy composite includes an LPSO phase.

3. A magnesium composite alloy that includes: at least 60 wt. % magnesium; more than 5 wt. % and less than 9 wt. % Rare Earth metal; at least 0.5 wt. % zinc; wherein said magnesium alloy contains at least 10% LPSO phase; and, wherein at least one additional precipitate in addition to the LPSO phase is present in an amount at least 1 vol. %; and, wherein said magnesium composite alloy has an ultimate tensile strength of at least 240 MPa and/or has a ductility exceeding 6% elongation to failure.

4. A magnesium alloy composite comprising: at least 60 wt. % magnesium; 2.5-16 wt. % Rare Earth metal, said Rare Earth metal includes yttrium and/or gadolinium; zinc, said zinc is less than 8 wt. %; and, wherein said magnesium alloy composite includes an LPSO phase.

5. The magnesium composite alloy as defined in claim 4, wherein said magnesium composite alloy includes 0.5-3 wt. % zinc.

6. The magnesium composite alloy as defined in claim 4, wherein said Rare Earth metal includes yttrium and non-yttrium rare earth metal, said non-yttrium includes gadolinium and/or neodymium, a weight ratio of non-yttrium rare earth metal to yttrium about 1:1 to 20:1.

7. The magnesium composite alloy as defined in claim 4, wherein said Rare Earth metal includes 0.5-2 wt. % cerium and one or more other of said Rare Earth metals selected from the group consisting of gadolinium, neodymium, and/or yttrium.

8. The magnesium composite alloy as defined in claim 4, wherein said Rare Earth metal includes up to 4 wt. % neodymium.

9. The magnesium composite alloy as defined in claim 4, wherein said Rare Earth metal further including one or more of lanthanum, cerium, europium, and ytterbium.

10. The magnesium composite alloy as defined in claim 4, wherein said Rare Earth metal includes more than 5 wt. % Rare Earth metal and less than 9 wt. % Rare Earth metal, said Rare Earth metal includes yttrium and non-yttrium rare earth metal, said Rare Earth metal includes 2-4 wt. % yttrium, at least 50% of said non-yttrium rare earth metal includes gadolinium, cerium, and/or neodymium, a weight ratio of non-yttrium to yttrium is 1:1 to 2.1.

11. The magnesium composite alloy as defined in claim 4, wherein said magnesium composite alloy further includes a precipitate forming additive selected from calcium, aluminum, tin, zirconium, strontium, and manganese.

12. The magnesium composite alloy as defined in claim 4, wherein said magnesium composite alloy further includes nickel and/or copper.

13. The magnesium composite alloy as defined in claim 4, wherein a weight ratio of Rare Earth metal to zinc is 1.2-6:1.

14. The magnesium composite alloy as defined in claim 4, wherein said magnesium composite alloy contains more than 0.5 wt. % zinc and less than 3 wt. % zinc.

15. The magnesium composite alloy as defined in claim 4, wherein a total of said LPSO phases in said magnesium composite alloy constitutes 2-60 vol. % of said magnesium composite alloy.

16. The magnesium composite alloy as defined in claim 4, wherein a total of said LPSO phases in said magnesium composite alloy constitutes 2-60 vol. % of said magnesium composite alloy, and said magnesium composite alloy includes at least 5 vol. % of one or more secondary phase precipitates.

17. The magnesium composite alloy as defined in claim 16, wherein a total of said secondary precipitate phases in said magnesium composite alloy constitutes 5-30 vol. % of said magnesium composite alloy.

18. The magnesium composite alloy as defined in claim 16, wherein said secondary precipitate phase includes magnesiumRare Earth metals and/or precipitate that is absent Rare Earth metals.

19. The magnesium composite alloy as defined in claim 16, wherein said LPSO phase and/or said secondary precipitate phase has a maximum dimension of less than 100 m.

20. The magnesium composite alloy as defined in claim 4, wherein said magnesium composite alloy has a tensile yield strength of greater than 280 MPa at 25 C., and/or an elongation to failure (Ef) of at least 6%.

21. The magnesium composite alloy as defined in claim 4, wherein said magnesium composite alloy has a) a UTS of at least 400 MPa, b) a YS of at least 300 MPa, and/or c) an Ef of at least 6%.

22. The magnesium composite alloy as defined in claim 4, wherein said magnesium composite alloy has a thermal conductivity greater than 175 W/m-K.

23. The magnesium composite alloy as defined in claim 4, further including carbon, carbide, or oxide nanoparticles in an amount of 0.5-3 wt %

24. A method for forming said magnesium composite alloy as defined in claim 4, wherein said magnesium composite alloy is direct chilled, sanded, and/or permanent mold cast, and then solutionized at 480-540 C. for at least 5 hours to partially or fully remove eutectic phases in said magnesium composite alloy.

25. A method for forming said magnesium composite alloy as defined in claim 4, wherein said magnesium composite alloy is subject to an annealing precipitation/aging heat treatment for 4-50 hours at a temperature of 200-350 C.

26. A method for forming said magnesium composite alloy as defined in claim 4, wherein said magnesium composite alloy is subject to a two-stage aging process wherein said LPSO phase is evolved continuously in said magnesium composite alloy at 300-400 C. for up to 24 hrs., and then heat treated at 200-300 C. for up to 48 hrs. to promote precipitation of said LPSO phase, a magnesiumRare Earth metals phase, and/or a secondary precipitate phase.

27. A method for forming said magnesium composite alloy as defined in claim 4, wherein said magnesium composite alloy is subject to a single stage heat treatment at 200-350 C. to co-precipitate said LPSO phase, and a magnesiumRare Earth metals phase and/or a secondary precipitate phase.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0127] Reference may now be made to the drawings, which illustrate various embodiments that the invention may take in physical form and in certain parts and arrangements of parts wherein:

[0128] FIG. 1 are the images of a magnesium-RE-zinc magnesium composite alloy in accordance with the present disclosure at a magnification of 350, 650, and 3500. At 350 and 650, only the LPSO phase can be seen. At 3500, both the LPSO phase and the secondary precipitate phase (i.e., intermetallic) can be seen. The average size of the each of the LPSO phases is illustrated to be about 10-20 m in length (or maximum dimension) and the average size of each of the secondary precipitate phases is illustrated to be less than 1 m in length (or maximum dimension).

[0129] FIGS. 2A-D illustrate the microstructure of a magnesium-RE-zinc-zirconium magnesium composite alloy in accordance with the present disclosure. Three phases were observed in the magnesium composite alloy: (1) interdendritic block LPSO phasesFIG. 2b, (2) thin plate LPSO phasesFIG. 2c, and (3) some locations of RE-rich phasesFIG. 2d.

[0130] FIGS. 3A-D illustrate Scheil and Equilibrium models for the min/max composition range of alloys 0010-1 and 0010-2.

[0131] FIG. 4 illustrates a phase diagram for a magnesium-zirconium system.

[0132] FIG. 5 illustrates a phase diagram for a magnesium-calcium system.

[0133] FIG. 6 illustrates a PANDAT calculated equilibrium phase diagram isopleths for a magnesium-5Gd-4Y-1Zn-xZr system.

[0134] FIG. 7 illustrates a PANDAT calculated equilibrium phase diagram isopleths for a magnesium-3 Gd-2Y-1Zn-xZr system.

[0135] FIG. 8 illustrates Scheil solidification models (PANDAT) in the magnesium-gadolinium-yttrium-zinc-zirconium system corresponding to the vertical lines in FIG. 6.

[0136] FIG. 9 illustrates Scheil solidification models (PANDAT) in the magnesium-gadolinium-yttrium-zinc-zirconium system corresponding to the vertical lines in FIG. 7.

[0137] FIG. 10 illustrates a PANDAT calculated equilibrium phase diagram isopleths for a magnesium-5Gd-4Y-1Zn-0.5Ca-xZr system.

[0138] FIG. 11 illustrates a PANDAT calculated equilibrium phase diagram isopleths for a magnesium-3Gd-2Y-1Zn-0.5Ca-xZr system.

[0139] FIG. 12 illustrates Scheil solidification models (PANDAT) in the magnesium-gadolinium-yttrium-zinc-calcium-zirconium system corresponding to the vertical lines in FIG. 10.

[0140] FIG. 13 illustrates Scheil solidification models (PANDAT) in the magnesium-gadolinium-yttrium-zinc-calcium-zirconium system corresponding to the vertical lines in FIG. 11.

[0141] FIGS. 14A-C illustrate PANDAT Scheil and equilibrium calculations of fraction phase (mol %) for each of the five compositions listed in Table 4, 0010-3 a), 0010-4 b), 0010-5 c).

[0142] FIGS. 15A-C illustrate PANDAT Scheil and equilibrium calculations of fraction phase (mol %) for each of the five compositions listed in Table 4, 0010-6 a), 0010-7 b), 0010-8 c).

[0143] FIGS. 16A-C illustrate PANDAT Scheil and equilibrium calculations of fraction phase (mol %) for each of the five compositions listed in Table 4, 0010-9 a), 0010-10 b), 0010-11 c).

[0144] FIGS. 17A-C illustrate Scheil and equilibrium models through PANDAT for alloys MC181207-1, MC181214-1, and MC181221-1.

[0145] FIGS. 18A-C illustrate Scheil and equilibrium models through ThermoCalc for alloys MC181207-1, MC181214-1, and MC181221-1.

[0146] FIGS. 19A-B is a chart that illustrates the comparison of phase fractions between Scheil and equilibrium models for PANDAT and ThermoCalc of the alloys illustrated in FIGS. 17 and 18.

[0147] FIGS. 20A-C illustrate ternary isothermal sections in the magnesium-gadolinium-yttrium-zinc system of increasing zinc content at 500 C.

[0148] FIG. 21A-D illustrate ternary isothermal sections in for the magnesium-gadolinium-yttrium-0.10 at. % zinc system at various temperatures (200 C., 300 C., 400 C., 500 C.)

DETAILED DESCRIPTION OF THE DISCLOSURE

[0149] A more complete understanding of the articles/devices, processes, and components disclosed herein can be obtained by reference to the accompanying drawings. These figures are merely schematic representations based on convenience and the ease of demonstrating the present disclosure, and are, therefore, not intended to indicate relative size and dimensions of the devices or components thereof and/or to define or limit the scope of the exemplary embodiments.

[0150] Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawings and are not intended to define or limit the scope of the disclosure. In the drawings and the following description below, it is to be understood that like numeric designations refer to components of like function.

[0151] The singular forms a, an, and the include plural referents unless the context clearly dictates otherwise.

[0152] As used in the specification and in the claims, the term comprising may include the embodiments consisting of and consisting essentially of. The terms comprise(s), include(s), having, has, can, contain(s), and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that require the presence of the named ingredients/steps and permit the presence of other ingredients/steps. However, such description should be construed as also describing compositions or processes as consisting of and consisting essentially of the enumerated ingredients/steps, which allows the presence of only the named ingredients/steps, along with any unavoidable impurities that might result therefrom, and excludes other ingredients/steps.

[0153] Numerical values in the specification and claims of this application should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.

[0154] All ranges disclosed herein are inclusive of the recited endpoint and independently combinable (for example, the range of from 2 grams to 10 grams is inclusive of the endpoints, 2 grams and 10 grams, and all the intermediate values).

[0155] The terms about and approximately can be used to include any numerical value that can vary without changing the basic function of that value. When used with a range, about and approximately also disclose the range defined by the absolute values of the two endpoints, e.g. about 2 to about 4 also discloses the range from 2 to 4. Generally, the terms about and approximately may refer to plus or minus 10% of the indicated number.

[0156] Percentages of elements should be assumed to be percent by weight of the stated element, unless expressly stated otherwise.

Example 1

[0157] Two magnesium composite alloys were created by casting the magnesium composite alloy in a gas fired furnace in a plain carbon steel crucible. The total charge weight of the metals used to form the magnesium composite alloy was 450 g. 99.9% pure gadolinium, yttrium, and zinc when added to the magnesium. A fluoride flux was applied as a cover material prior to the start of heating. The temperature of the carbon steel crucible was 850-900 C. to facilitate in rapid melting of the RE. The crucible was cooled to 750 C. and slagged, stirred, and cast into a warm 150 C. cylindrical 1 diameter molds. One magnesium composite alloy (0010-1) included 5 wt. % gadolinium, 4 wt. % yttrium, 1 wt. % zinc, and about 90 wt. % magnesium. The other magnesium composite alloy (0010-2) included 3 wt. % gadolinium, 2 wt. % yttrium, 1 wt. % zinc, and about 94 wt. % magnesium. FIG. 1 illustrates magnified regions of these two samples illustrating the formation of LPSO phases and secondary precipitate phases in both magnesium composite alloys.

Example 2

[0158] Magnesium composite alloys wherein one alloy included zirconium and the other two alloys included both calcium and zirconium were formed. When forming the magnesium-RE-zinc-zirconium alloy, magnesium was in the form of ingots, zirconium was added in the form of a master alloy of magnesium-30Zr wherein zirconium constituted 30 wt. % of the master alloy, gadolinium, and yttrium were shattered elemental pieces, and zinc was in the form of shot. When forming the magnesium-RE-zinc-calcium-zirconium alloy, calcium was added as shattered elemental pieces. When forming the magnesium composite alloys, the raw materials were charged into the plain carbon steel crucible at room temperature and approximately 50 mL of fluoride-containing flux was applied to the top surface of the raw materials. The temperature was raised using an electric band heater to 350 C. and allowed to settle for 30 min to allow moisture to evaporate from the surface of the raw materials. The temperature was then raised to 650 C. and allowed to sit for 30 min. The melt was raised slowly and allowed to sit idle at 780 C. for 45 min. The heater was turned off, the lid was removed at 780 C., and solid slag was removed from the surface of the melt. Approximately 5 g of C.sub.2Cl.sub.6 degasser was submerged with the porous ladle and stirred into the melt. Alloy 1 contained 93.48 wt. % magnesium, 2.96 wt. % gadolinium, 1.98 wt. % yttrium, 0.98 wt. % zinc, and 0.59 wt. % zirconium. Alloy 2 contained 92.23 wt. % magnesium, 3.08 wt. % gadolinium, 2.04 wt. % yttrium, 1 wt. % zinc, 0.6 wt. % zirconium, and 1.05 wt. % calcium. Alloy 3 container 88.5 wt. % magnesium, 2.94 wt. % gadolinium, 1.99 wt. % yttrium, 3.05 wt. % zinc, 0.53 wt. % zirconium, and 3 wt. % calcium. Table 2 illustrates the properties of several of the formed magnesium composite alloys.

TABLE-US-00004 TABLE 2 HV 0.2% YS UTS Alloy Processing (kg/mm.sup.2) (MPa) (MPa) E.sub.f % Mg-3Gd-2Y-1Zn-0.6Zr AC 75.1-79.5 Mg-3Gd-2Y-1Zn-0.6Zr AC + SOL-a 59.7-67.7 Mg-3Gd-2Y-1Zn-0.6Zr AC + SOL-b 59.6-63.1 7 Mg-3Gd-2Y-1Zn-0.6Zr AC + SOL-b + 64.6-75.6 112 208 13 AGE Mg-3Gd-2Y-1Zn-0.6Zr AC + EX-a 62.1-70.1 161-209 243-248 12-16 Mg-3Gd-2Y-1Zn-0.6Zr AC + SOL-a + 62.3-81.2 EX-a Mg-3Gd-2Y-1Zn-0.6Zr AC + SOL-a + 74.2-76.5 238-239 283-285 16-17 EX-b Mg-3Gd-2Y-1Zn-0.6Zr AC + SOL-a + 75.3-88.3 194 301 7 EX-b + HR Mg-3Gd-2Y-1Zn-0.6Zr-1Ca AC 65.3-71.5 Mg-3Gd-2Y-1Zn-0.6Zr-1Ca AC + SOL-a 65.3-73.4 Mg-3Gd-2Y-1Zn-0.6Zr-1Ca AC + EX-a 65.5-70.4 169-170 245-245 12-14 Mg-3Gd-2Y-1Zn-0.6Zr-1Ca AC + SOL-a + 81.3-86.4 176-180 250-255 15 EX-a Mg-3Gd-2Y-1Zn-0.6Zr-1Ca AC + SOL-a + 86.1-92.7 239-242 283-305 15-18 EX-b Mg-3Gd-2Y-1Zn-0.6Zr-1Ca AC + SOL-a + 84.8-96.3 200-223 270-305 2.5-4 EX-b + HR Mg-3Gd-2Y-1Zn-0.6Zr-1Ca AC + SOL-a + 96.9-111.7 163-179 296-310 6.5-8 EX-b + HR + AGE

[0159] ACAs cast.

[0160] SOL-aSolutionizing at 500 C. for 20 hrs. under argon.

[0161] SOL-bSolutionizing at 545 C. for 22 hrs. under argon.

[0162] AGEAging treatment (200 C. for 23 hrs.).

[0163] EX-aRound extrusion at 320 C., with an ER=10.3

[0164] EX-bFlat extrusion at 400 C., with an ER=16.6 and with post extrusion quench.

[0165] HRHot rolling at 350 C. with a 50% reduction in thickness.

[0166] FIGS. 2A-D illustrate the microstructure of a magnesium-RE-zinc-zirconium magnesium composite alloy in accordance with the present disclosure. Three phases were observed in the magnesium composite alloy: (1) interdendritic block LPSO phasesFIG. 2B, (2) thin plate LPSO phasesFIG. 2C, and (3) some locations of RE-rich phasesFIG. 2D. The interdendritic block LPSO phase regions show increased segregation of zinc and gadolinium with some calcium and much less zirconium or yttrium. The thin plate-like LPSO precipitates are also visible in the microstructure especially close to the interdendritic LPSO regions. These are too thin to resolve elemental compositions of individual plates but they also appear to be calcium, zinc, and gadolinium with lesser zirconium or yttrium. There does not appear to be much in the way of thin plate LPSO in the matrix of the alloy. Finally, RE-rich phase regions are specifically enriched in zirconium and yttrium. These RE-rich regions are rather non-uniformly distributed as patches in the microstructure of the as-cast alloy.

Example 3

[0167] Two magnesium composite alloys were created by casting the magnesium composite alloy in a gas fired furnace in a plain carbon steel crucible. The total charge weight of the metals used to form the magnesium composite alloy was 50 lbs. 99.9% pure gadolinium, yttrium, and zinc when added to the 99.9% pure magnesium. Pure magnesium was charged into the crucible and brought to 760 C. under inert (mixture SF.sub.6/CO2/air) atmosphere. Gadolinium and yttrium were added and stirred. After dissolution of the RE, approximately 15 minutes, the melt for each casting was degassed (C.sub.2Cl.sub.6 at a ratio of 1 g/1 lb. melt), slagged, and poured into an A36 steel permanent mold (774 block). The first magnesium composite alloy included 10.4 wt. % gadolinium, 3.6 wt. % yttrium, 2.9 wt. % zinc, and 83.1 wt. % magnesium. The second magnesium composite alloy included 10.2 wt. % gadolinium, 4.7 wt. % yttrium, 5.1 wt. % zinc, and 80 wt. % magnesium. Both magnesium composite alloys were homogenized at 500 C. for 17 hours and water quenched. The magnesium composite alloys were subsequently aged at 225 C. for 24 hrs. The Rockwell B hardness of the first magnesium composite alloy after aging was 22-30 and the Rockwell B hardness of the second magnesium composite alloy was 32-36. The UTS of the first magnesium composite alloy after aging was 230 MPa with an elongation to failure of 7%.

[0168] Compositions for CALPHAD models are found in TABLE 3. The compositions were converted to at % (atomic percent) and the values of Gd+Y and (Gd+Y)/Zn were computed for each of the four compositions. These values are used empirically to rate the magnitude of LPSO and intermetallic formation. Scheil (rapid) and Equilibrium (slow) cooling models were completed through PANDAT for each of the four compositions. The concentration of species (mol fraction) for the equilibrium cooling is also set forth in TABLE 3. For the two alloys under equilibrium conditions, there is a range of mol fraction 0.043-0.053 (or approximately 4-5%) for the LPSO content. According to the PANDAT predictions, the fraction of LPSO is relatively equal between 10-1 and 10-2. The SEM/EDX maps, however, much more closely match the Scheil solidification curves presented in FIG. 3 with 10-1 having a fraction LPSO of 4-5% and 10-2 of 2-3%. The RMg.sub.5 and R5Mg24 intermetallic phases are also predicted according to the Scheil model in very dilute concentrations. The RMg.sub.5 and R5Mg24 intermetallic phases may be gadolinium and/or yttrium-containing intermetallics.

TABLE-US-00005 TABLE 3 Comp. Mg Gd Y Zn Gd + Y (Gd + Y)/Zn LPSO RMg.sub.5 R.sub.5Mg.sub.24 10-1a wt. % 92.04 4.3 2.8 0.86 0.047 0.045 0.017 at. % 98.13 0.71 0.82 0.34 1.52 4.47 10-1b wt. % 90.49 4.8 3.8 0.91 0.051 0.051 0.034 at. % 97.71 0.8 1.12 0.37 1.92 5.26 10-2a wt. % 94.72 2.6 1.9 0.78 0.043 0.024 0.008 at. % 98.74 0.42 0.54 0.3 0.96 3.18 10-2b wt. % 93.74 3.2 2.1 0.96 0.053 0.03 0.007 at. % 98.50 0.52 0.6 0.38 1.12 2.99

[0169] The results set forth in TABLE 3 indicate the strong role thermal history plays in the development of a preferred microstructure as well as the power of thermodynamic modeling to predict said microstructures.

[0170] The 10-1 and 10-2 compositions were used as a baseline to examine the effect of microalloying zirconium and calcium content. Both equilibrium phase diagrams and Scheil solidification curves were modeled through PANDAT. Example phase diagrams for magnesium-zirconium and magnesium-calcium are shown below in FIGS. 4-5. Calcium was either present (0.5 wt. % in the compositions) or was absent. Zirconium content was varied in the equilibrium phase diagram from 0-1 wt. %. Scheil solidification curves were calculated assuming a zirconium concentration of 0.5 wt. %.

[0171] The equilibrium phase diagrams for zirconium content varied between 0-1 wt. % are presented in FIGS. 6-7 for two different magnesium composite alloys. As both alloys are dilute in RE and zinc, the diagrams are similar to the magnesium-zirconium binary diagram. The boundary for the formation of -Zr (HCP) is shifted to a lower weight percent (0.4 wt. % zirconium) than the magnesium-zirconium binary (0.565 wt. %). This indicates that less supersaturated zirconium is required in solution at elevated temperatures (750-800 C.) to facilitate in enhanced nucleation of -Mg (HCP) grains. The liquidus temperature of the alloy is depressed slightly from the magnesium-zirconium binary and the liquid+-Mg (HCP) phase field has opened. Both alloys are predicted to have the same phases -Mg (HCP), -Zr (HCP #2), R5Mg24, RMg5, and R8Mg70Zn6_14H (LPSO) present in equilibrium at room temperature. Both R5Mg24 and RMg5 are predicted to dissolve back into solution at lower temperatures for the lower RE content Mg-3Gd-2Y-1Zn-xZr than the higher RE content Mg-5Gd-4Y-1Zn-xZr. Likewise, the LPSO is stable to a higher temperature in the higher RE content alloy, indicating superior high temperature strength. Scheil models were also calculated for the compositions Mg-3Gd-2Y-1Zn-0.5Zr and Mg-5Gd-4Y-1Zn-0.5Zr as illustrated in FIGS. 8-9. Under rapid cooling conditions, the -Zr (HCP_#2) phase is not expected to form, despite the high concentration of zirconium in the alloys. It should also be noted that neither of these alloys is expected to have a single phase -Mg (HCP) condition at any temperature, indicating challenges to solutionizing the alloys during heat treatment. The RM3_W phase (a brittle intermetallic) is present at very high temperatures.

[0172] Scheil models were completed for the compositions with the addition of 0.5 wt % calcium as illustrated in FIGS. 10 and 11. The liquidus remains relatively the same, but the solidus is further depressed. There is a new phase Mg2Ca (C14) the laves phase from the magnesium-calcium binary diagram. This phase is stable to its eutectic temperature of 516 C. While the addition of the laves phase may prove beneficial to the strengthening of the alloy, it lowers the solidus temperature, thereby making elevated temperature processing such as extrusion more challenging. Again, the Scheil models indicate that the -Zr (HCP) phase does not form on rapid cooling. Although rapid cooling would assist in formation of a small, uniform grain size, the effect of zirconium nucleation of grains would not be present in the alloys.

[0173] An additional thermodynamic (ThermoCalc) assessment of the magnesium-gadolinium-yttrium-zinc quaternary system was performed with dilute as well as high concentrations of rare earth to evaluate the effect of varying the gadolinium/yttrium ratio on LPSO and intermetallic formation. The ratio of 5/2 was held constant as well as the magnitude of RE for this dilute model work. Both Scheil and Equilibrium models were completed for the alloys. From this work it was found that LPSO content depends both on the magnitude of the RE content as well as the above-mentioned ratio. Additionally, the intermetallic RMg5 is favored for high gadolinium content whereas R5Mg24 is favored for high yttrium content.

[0174] Further PANDAT models were evaluated with a high RE content (total Gd+Y of 4 at %, see TABLE 4. The ratio of (Gd+Y)/Zn was varied by increasing zinc content from 1 to 2 at %. As the zinc content increases (and the ratio of (Gd+Y)/Zn decreases) there is a significant increase in the predicted LPSO content. Similar to the dilute alloy calculations, as the ratio of gadolinium/yttrium changes, the relative concentration of RMg5 and R5Mg24 change as well.

TABLE-US-00006 TABLE 4 Comp. Mg Gd Y Zn Gd + Y (Gd + Y)/Zn LPSO RMg.sub.5 R.sub.5Mg.sub.24 10-3 wt. % 80.46 5.54 9.39 4.61 0.2803 0.0274 0.0512 at. % 94 1 3 2 4 2 10-4 wt. % 78.57 10.82 6.12 4.5 0.2802 0.0794 at. % 94 2 2 2 4 2 10-5 wt. % 76.77 15.85 2.99 4.39 0.2797 0.0799 at. % 94 3 1 2 4 2 10-6 wt. % 81.48 5.58 9.46 3.48 0.21 0.0389 0.0797 at. % 94.5 1 3 1.5 4 2.7 10-7 wt. % 79.55 10.89 6.16 3.4 0.2102 0.1155 0.0034 at. % 94.5 2 2 1.5 4 2.7 10-8 wt. % 77.71 15.96 3.01 3.32 0.21 0.12 at. % 94.5 3 1 1.5 4 2.7 10-9 wt. % 82.51 5.62 9.53 2.34 0.14.02 0.0503 0.1079 at. % 95 1 3 1 4 4 10-10 80.55 10.97 6.2 2.28 0.1399 0.1271 0.0318 95 2 2 1 4 4 10-11 78.67 16.07 3.03 2.23 0.1401 0.1594 95 3 1 1 4 4

[0175] At these high RE contents, the RM3_W phase is predicted almost always for rapid (Scheil) cooling conditions. Under equilibrium conditions, the R8Mg70Zn6_14H (LPSO) phase is stable very near the solidus and may even be stable with the liquid. This indicates that these alloys would be amenable to high temperature operation. Solutionizing to single phase -Mg would not be possible for these alloys. (See FIGS. 14-16).

[0176] Scheil and eqilbrium models were completed for three of the alloys (MC181207-1, MC181214-1 and MC181221-1) as illustrated in TABLE 5.

TABLE-US-00007 TABLE 5 Mg Gd Y Zn Sample (wt. %) (wt. %) (wt. %) (wt. %) MC181207-1 82.98 10.4 3.62 3.00 MC181214-1 81.73 10.57 5.25 2.45 MC181221-1 79.95 10.2 4.74 5.1

[0177] FIGS. 17A-C and FIGS. 18A-C illustrate PANDAT and ThermoCalc diagrams. The PANDAT predicts a phase called RM3_W in the Scheil condition for all three alloys that is defined as Mg0.25(Gd,Y)0.25(Mg,Zn)0.5. Thermo-Calc also predicts a similar phase called L12_RMGZN2, defined as Mg1(Gd,Y)1(Mg,Zn)2, for the MC21 alloy in the Scheil condition. A summary of the phase fractions for both sets of models is found in the chart illustrated in FIG. 19. The chart illustrates that there is significant (40% mol fraction as modeled through ThermoCalc and 30% mol fraction as modeled through PANDAT) LPSO expected to form in alloy MC181221-1.

[0178] A thermodynamic assessment was taken of dilute magnesium-gadolinium-yttrium-zinc alloys to identify likely composition space where a full solutionizing anneal (single phase -Mg) is feasible. A series of ternary isothermal sections in the magnesium-gadolinium-yttrium-zinc quaternary system were created through PANDAT for increasing zinc composition as illustrated in FIGS. 20-21. The ovals highlighted in the 0.05 at % zinc and 0.10 at % zinc isothermal sections indicate composition space likely to facilitate a full solutionizing treatment. The oval in the 0.05 at % zinc isothermal section has further been identified as 3-6 wt. % gadolinium, 0.2-0.7 wt. % yttrium, and 0.15 wt. % zinc. Further equilibrium isothermal sections have been completed for the magnesium-gadolinium-yttrium Y-0.10 at % zinc system. The region highlighted by the oval appears to facilitate solutionizing (avoiding the formation of the RM3 W phase completely and the LPSO 14H phase at 500 C.). Additionally, it experiences RMg5 precipitation at 200 C. An analysis such as this would prove powerful in development of an alloy system (possibly such as magnesium-gadolinium-neodymium or magnesium-gadolinium-yttrium) which can be solutionized and/or processed at high temperature with subsequent precipitation hardening sequence with a lower temperature aging treatment.

[0179] It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in the constructions set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. The invention has been described with reference to preferred and alternate embodiments. Modifications and alterations will become apparent to those skilled in the art upon reading and understanding the detailed discussion of the invention provided herein. This invention is intended to include all such modifications and alterations insofar as they come within the scope of the present invention. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention, which, as a matter of language, might be said to fall there between. The invention has been described with reference to the preferred embodiments. These and other modifications of the preferred embodiments as well as other embodiments of the invention will be obvious from the disclosure herein, whereby the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims.