US3166415A

US3166415A - Magnesium-based alloys

Info

Publication number: US3166415A
Application number: US78849A
Authority: US
Inventors: Louis A Conant
Original assignee: Union Carbide Corp
Current assignee: Elkem Metals Co LP
Priority date: 1960-12-28
Filing date: 1960-12-28
Publication date: 1965-01-19
Anticipated expiration: 1982-01-19

Description

United tare are This invention relates to low density alloys having a high modulus of elasticity and, more particularly, to magnesium-base alloys and a method of producing said alloys.

'Magnesium alloys and other low density alloys have been the chief structural materials for applications requiring high strength-to-weight ratios in their construction materials. This has been especially the case in the aircraft and other transportation vehicles and additionally in many consumer items such as household goods, ofiice equipment, instruments and sporting goods.

. In the selection of structural materials, however, other factors than strength-to-weight ratios must be considered. For example, the resistance to elastic deformation of the structural material must be considered. The resistance of a material to elastic deformation is known as stiffness and represents the extent of the elastic deformations or defiections which take place under given stresses. The most desirable structural material should not only be capable of withstanding high stresses, but should also exhibit relatively little deformation under these stresses. This resistance to elastic deformations is measured by the value of the modulus of elasticity of the material and is a separate function of the yield point or ultimate strength of the material. The actual deformations or deflections produced in stressed members depend on the modulus of elasticity of the material and the geometry of the member. It is often necessary, especially in structures made of magnesium, to design the members on the basis of their stiffness rather than on their strength. Many members are designed with larger cross-sections than are required to carry the given stresses because the larger cross-section is needed to give the structure the required stiffness. Because manylo'w-density materials, such as magnesium and its alloys, have a comparatively low-modulus of elasticity, the savings in Weight that could be realized by the use of these materials is often offset by the need to design and use larger sections to provide the necessary stiffness.

. The modulus of elasticity of pure magnesium is about 65x10 pounds perv square inch while the modulus of elasticity of steel is about x10 pounds per square inch. It .is easily seen-how important a factor the lowmodulus of magnesium has. been in preventing the full employment of this metals valuable properties. Another factor to be considered in the selection of structural materials is the coefficient of expansion of the material. An excessively high rate of expansion can limit the usefulness of the material .and a low coefiicient of expansion is thereforedesirable. Unfortunately many lowdensity alloys have high coefficients of expansion.

It is the primary object. of this invention, therefore, to

' provide a magnesium-base alloy having a higher modulus of elasticityuthan pure magnesium and heretofore produced magnesium-base alloys.v 2

It is alsoyan object of this invention to provide a magnesium-base alloy having a high ratio of modulus, of

' elasticity to-density.

It is a further object of this invention to provide a magnesium-base alloy having a lower coefiicient of expansion than pure magnesium and many heretofore produced magnesium alloys. I

It is a further object of this invention to provide a 5 method for producing the'magnesium-base alloy described herein.

' Other aims and objects of this invention will be ap- 3,lh,4 l5 Patented Jan. 19, 19fi5 parent from the following description and appended claims.

In accordance with these objects a method for producing a high modulus magnesium-base alloy is provided which comprises dispersing finely divided particles of a refractory metal boride in a magnesium matrix. The process of the invention comprises preparing a mixture consisting essentially of from about 10 to about 50 volume percent of particles of borides of at least one metal selected from the group consisting of titanium, chromium, zirconium, tantalum, columbium, hafnium, vanadium and molybdenum, and the balance powdered magnesium material selected from the group consisting of magnesium and magnesium-base alloys, compacting the resulting mixture into a coherent slug, heating the resulting slug in the absence of air to a temperature at which the magnesium material melts without substantial vaporization and below the melting point of the metal borides, and allowing the slug to cool. In a preferred embodiment the slug is cooled to a temperature below the freezing point of the mag nesium material and worked into a desired shape.

In the practice of the process of this invention an alloy is produced consisting essentially of from about 10 to about 50 volume percent of particles of borides of at least one metal selected from the group consisting of titanium, chromium, zirconium, tantalum, columbium, hafnium, vanadium, and molybdenum, and the balance substantially all of a metal selected from the group consisting of mag nesium and magnesium alloys, said particles of metal borides being dispersed in a continuous matrix of the magnesium material.

Specifically an alloy is provided consisting essentially of from about 10 to 50 volume percent of titanium diboride dispersed in a continuous matrix 'of magnesium or a magnesium-base alloy. l Q

A particularly useful matrix material is a magnesiumaluminum alloy consisting of about 5 percent by Weight aluminum and the balance magnesium. This alloy was used as the matrix material in most of the examples fol- I lowing. In making the alloys of this invention the mag- I nesium-base alloy used as the matrix material is reported the matrix is defined in volume percents because the volume percent actually suggests the amount of dispersed phase in a cross-section of the matrix. Since the densities of the borides and the matrix of materials differ, it would I not be suggestive of the true amount of dispersed phase present if it were reported in wei ht percents;

Asummary of the properties of the alloy of this invention, as compared to the properties of a commercial magnesium alloy is presented in Table 1. As may be seen from the table, the specific modulus, or ratio of modulus of elasticity-to-density, of the alloy of the invention, containing as little as 10 percent by volume ofadispers'ed phase of titanium diboride in a magnesium-5 percent aluminum alloy is increased by more than 13 percent. The resulting modulus of elasticity of this alloy is greater than that of one of the best commercial magnesium alloys as listed in Table 1. When the amount of the dispersed titanium diboride phase'is increased to 40 percent by volume of the alloy, the increase in specific modulus over the best 0.5 percent zinc, 0.15 percent manganese and the balance magnesium.

The dispersed phase must be not 3 TABLE I 10 vol. 20 vol. 40 vol. percent; percent percent TiBz in T1132 in Til in Magne- Magne- Magne- Comsium-5 slum-5 slum-5 mereial weight weight Weight alloy percent percent percent aluminum aluminum aluminum alloy alloy alloy Tensile Strength:

Ultimate, 75 F- 47, 200 5-5, 000 44, 425 53, 000 Yield, 75 F 41, 000 40, 000 Ultimate, 750 3,090 3, 550 3, 600 Yield, 750 12. 2, 810 3, 000 Elongation, percent in 75 F 7. 5 5 7 F 11 12 3. 7 Reduction Area, percent:

y p.s.i.X10 75 F..-" 8.3 11 17.6 6. 5 Density, g/cc 2.02 2. 3 2.85 1. 8 Specific Modulus (Mod. of ElasJ Density) 4. 11 4. 7 6. 17 3. 6 Thermal Ooeflicient of Linear Expansion, C. 10 24-427 C. 28. 32 2l.o2 19. 59 29. 8 Condition containing as high as 50 volume percent titanium diboride show an increase in elastic modulus. It is to be noted that the modulus of elasticity of a volume percent titanium diboride magnesium alloy is almostdouble that of pure magnesium. It is also to be noted-that the strength of the 20 volume percent titanium diboride-aluminum alloy compares favorably with the commercial alloy; It has also been found that when titanium diboride or other metal borides are dispersed in high-strength commercial magneinsoluble in the matrix, but it must also be subject to an intimate bond with the matrix under the varying temperature and pressure conditions of the metalworking operation. These conditions are particularly well met by the combination of a titanium diboride phase dispersed in a magnesium or magnesium alloy'matrix. The magnesium material completely wets the titanium diboride and yet shows no tendency to react chemically with it. The unique character of the mixture is further illustrated by the fact that when an unsupported slug of the compacted powders, in which the low melting magnesium matrix occupies as much as 40 percent of the volume, is heated above the melting point of the magnesium, and maintained in that condition, the slug, although apparently molten, retains,

its original shape and does not slump into a formless pool of molten magnesium. This eitect, believed to be caused by a strong tendency of the magnesium to wet the diboride phase, is also believed to be responsible for the excellent degree of dispersion of the diboride particles in the magnesium matrix. Since heating is carried out in a vacuum or inert atmosphere, the fact that no gross melting occurs cannot be attributed to the presence of oxide or oxide coating acting as, a'skin to hold the shape of the article.

The most uniform dispersions of the titanium diboride phase in a magnesium matrix have been obtained by the use of a new technique combining compaction and con trolled melting.

In this process, .the'powders of the diboride and the 7 magnesium material are dry blended and cold compacted at a pressure of from about 30,000 to about 50,000 pounds per square inch into a slug of convenient dimensions. The

magnesium is the powder. produced by spraying molten magnesium and cooling it rapidly to form a powder. The

slug is heated, in a vacuum or in aninert atmosphere, to

about 800 .C. which is about 225 C. in excess of the meltingpoint of magnesium. Gross melting does not occur, probably as the result of capillarity dueto the wetting of'thetitanium diboride particles by the molten sium alloys such as that listed in Table La superior high- Y modulus alloy results.

Another featureof the alloy of this invention is its low coefiicient of linear expansion in'comparison with-comsion of pure magnesium.

TABLE II and only about tworthirds the normal coefiicient of expan- Ooelfieient of Expansion per Material degree 0.,

magnesium material. I, g

While ordinary powder metallurgical techniques, such as cold pressing and sintering, or hot pressing can be used to produce articles of this alloy they do not produce the same superioralloy product asthe compaction-controlled 10 vol. percent TlBziD. magnesium-5% Al alloy- 28. 32 20 vol. percent TiBg in magnesium-5% A1 alloy 21.32 40 vol. percent TiBg in magnesium-5% Al alloy. 19. 59 Commercial alloy 8 In orderto assure that the desired eiiect is permanent, it

is necessary that the constituentsbe mutually nonreactive and insoluble in each other. The diborides of tantalum, Zirconium, chromium, columbium, hafnium, vanadium and molybdenum are allrelatively insoluble an'd nonreac- V tive in magnesium materials. 4 only unreactive and melting technique described herein. Although to all out; ward appearancesthe constitution of the alloy is the same,

the two products have different properties; We're identical mixtures of titanium diboride and magnesium powders to be subjected to the same fabricating procedures, except .that hotpressingis-substituted for the compaction-controlled meltingtechnique, the modulus of elasticity-of the products would differ.. The 'sintered or hot pressed prod;

ilct would. have a modulus much less than that of the 7 product produced by the process of this invention.

Since a dense, strong material is produced after the .firinggoperation it is practical to lose the product in the as-fired condition, or to fabricate the as-fired composition by rolling, for'ging or swagingwithout the necessity of first extruding the product. Y V r When the firedproductis extruded, it canibe fabricated into useful shapes by conventional working techniques. V

ypracticeof the invention.

The-following example. is presented to illustrate the Y Example Thirty-nine percent by weight ('20 volume percent) of dry, finely divided titanium diboride was blended with 61 percentby weight volume percent) of a mixture containingS percent by weight of atomiged aluminum and the balance atomized magnesium and the mixture was .cold compacted at"40-,000 pJSjplntO l- /z' inch diam eter slug approximately 2, inches long. The slug was heated under vacuum conditions to 800 C. and held there for about minutes. Gross melting did not occur but rather the slug retained its shape while the molten magnesium-aluminum alloy flowed completely in and around each particle of titanium diboride producing thereby the desired dispersion. After this heat treatment, the slug was cooled below the point at which the magnesiumaluminum alloy solidified, and removed to an extrusion press where it was reduced from a 1 /2 inch ingot to a rod inch in diameter by the application of about 60,000 psi. The density of the rod is the as-extruded condition was about 2.3 g./ cc. and it exhibited a Youngs modulus of elasticity at 75 F. of about 11X 10 p.s.i. as determined sonic means. The coefiicient of linear expansion in the range of to 427 C. was found to be 2l.32 10 These and other properties are contained in Table 1. The other alloys noted in Table 1 were made in the same manner as above.

In another example 52.5 percent by weight titanium diboride volume percent) was mixed with 47.5 percent by weight powdered magnesium metal (70 volume percent). This mixture was cold compacted into a coherent slug. The slug was heated under vacuum conditions at about 770 C. There was no gross melting but rather the magnesium metal melted and flowed around the diboride particles to form the desired matrix. The fired slug was then extruded into a desired shape at around 480 C.

It is to be noted that while the description of the inven tion has been in terms of magnesium and magnesiumaluminum alloys as matrix materials, that other magnesium materials such as any of the many commercial magnesium-base alloys are included. It is only necessary that the magnesium-base alloy used be low melting, ductile and light weight and that it be mutually non-reactive and insoluble with the borides used in the dispersed phase and that the magnesium-base alloy have the property of flowing around and wetting the dispersed particles when the compacted slug of these materials are heated above the melting point of the magnesium-base alloy.

What is claimed is:

1. The method of preparing a magnesium-base alloy product characterided by an increased modulus of elasticity and a decreased coefiicient of thermal expansion which comprises preparing a mixture consisting essentially of from about 10 to about 50 volume percent of particles of borides of at least one metal selected from i the group consisting of titanium, chromium, zirconium,

tantalum, columbium, hafnium, vanadium and molybdenum, and the balance a powdered magnesium material selected from the group consisting of magnesium and magnesium-base alloys, compacting the resulting mixture into a coherent slug, heating the resulting slug in the absence of air at a temperature at which the magnesium material melts without substantial vaporization and below the melting temperature of the metal borides, cooling the slug to a temperature below the freezing tempera- :ture of the selected magnesium material, and forming the slug into a desired shape.

v 2. The method of preparing a magnesium-base alloy product characterized by an increased modulus .of elasticity and a decreased coefiicient of thermal expansion which comprises preparing a mixture consisting essentially of from about 10 to about 50 volume percent of particles of borides of at least one metal selected from the group consisting of titanium, chromium, zirconium, tantalum, columbium, hafnium, vanadium and molybdenum, and the balance a powdered magnesium material selected from the group consisting of magnesium and magnesiumbase alloys, compacting the resulting mixture into a coherent slug having a desired shape, heating the resulting slug in the absence of air at a temperature at which the magnesium material melts without substantial vaporization and below the melting temperature of the metal borides, and cooling the slug.

3. The method of preparing a magnesium-base alloy product characterized by an increased modulus of elasticity and a decreased coefficient of thermal expansion which comprises preparing a mixture consisting essentially of from about 10 to about 50 volume percent of particles of borides of at least one metal selected from the group consisting of titanium, chromium, zirconium, tantalum, columbium, hafnium, vanadium and molybdenum and the balance a powdered magnesium material selected from the group consisting of magnesium and magnesiumbase alloys, compacting the resulting mixture at a pressure of from about 30,000 to 50,000 pounds per square inch into a slug, heating the resulting slug in the absence of air at a temperature between the melting temperature of the selected magnesium material and about 800 C. cooling the slug to a temperature below the freezing temperature of the selected magnesium material, and forming the slug into a desired shape.

4. The method of preparing a magnesium-base alloy product characterized by an increased modulus of elasticity and a decreased coefiicient of thermal expansion which comprises preparing a mixture consisting essentially of from about 10 to about 50 volume percent of particles of titanium diboride, and the balance substantially all powdered magnesium, compacting the resulting mixture into a coherent slug, heating the resulting slug in the absence of air at a temperature at which the magnesium melts without substantial vaporization and below the melting temperature of the metal borides, cooling the slug to a temperature below the freezing temperature of the magnesium, and forming the slug intoa desired shape.

5. The method of preparing a magnesium-base alloy product characterized by an increased modulus of elasticity and a decreased coeflicien-t of thermal expansion which comprises preparing a mixture consisting essentially of from about 10 to about 50 volume percent of particles of titanium diboride, and the balance a powdered magnesium material containing 5 percent by weight aluminum and the balance substantially all magnesium, compacting the resulting mixture into a coherent slug having a desired shape, heating theresulting slug in the absence of air at a temperature at which the magnesium material melts without substantial vaporization and below the melting temperature of the metal boride for at least a time sufiicient for the magnesium material to melt, cooling the slug to a temperature below the freezing temperature of the magnesium material, and forming the slug into a desired shape.

References Cited in the file of this patent Edward Arnold Ltd, 1960, pp. 627-628. (Originally published in Iron Steel Inst. Special Report, No. 58, 1956, pp. 242-248, by MacDonald and Ransley.)

Progress in Powder Metallurgy, Capital City Press, volume 16, 1960, pp. 99-119.

Claims

1. THE METHOD OF PREPARING A MAGNESIUM-BASE ALLOY PRODUCT CHARACTERIZED BY AN INCREASED MODULUS OF ELASTICITY AND A DECREASED COEFFICIENT OF THERMAL EXPANSION WHICH COMPRISES PREPARING A MIXTURE CONSISTING ESSENTIALLY OF FROM ABOUT 10 TO ABOUT 50 VOLUME PERCENT OF PARTICLES OF BXXXXXX OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM, CHROMIUM, ZIRCONIUM, TANTALUM, COLUMBIUM, XXXNIUM, VANADIUM AND MOLYBDENUM, AND THE BALANCE A POWDERED MAGNESIUM MATERIAL SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM AND MAGNESIUM-BASE ALLOYS, COMPACTING THE RESULTING MIXTURE INTO A COHEREENT SLUG, HEATING THE RESULTING SLUG IN THE ABSENCE OF AIR AT A TEMPERATURE AT WHICH THE MAGNESIUM MATERIAL MELTS WITHOUT SUBSTANTIAL VAPORIZATION AND BELOW THE MELTING TEMPERATURE OF THE METAL BORIDES, COOLING THE SLUG TO A TEMPERATURE BELOW THE FREEZING TEMPERATURE OF THE SELECTED MAGNESIUM MATERIAL, AND FORMING THE SLUG INTO A DESIRED SHAPE.