Machinable metal matrix composite and method for making the same

Abstract

A metal matrix composite comprises and/or consists of a uniform distribution of calcined ceramic particles having an average particle size of between 0.30 and 0.900 microns and a metal or alloy uniformly distributed with the ceramic particles and wherein the ceramic particles include oxides of two separate metals selected from the group consisting of Al, Li, Be, Pb, Fe, Ag, Au, Sn, Mg, Ti, Cu, and Zn, and in which said ceramic particles comprise at least 15 volume percent of the metal matrix sintered together and wherein said metal-matrix being machinable with a high speed steel (HSS) bit for greater than about one minute without excessive wear to the bit.

Claims

1. A metal-matrix composite comprising: a primary metal component consisting essentially of 6061 aluminum and alloys thereof and comprising 50-80 vol % of the metal-matrix composite; and a secondary ceramic component comprising calcined ceramic particles consisting essentially of alumina (Al.sub.2O.sub.3) and magnesium oxide (MgO), wherein the ceramic particles have an average particle size of between 0.35 and 0.90 microns; wherein the ceramic particles are prepared from a ceramic precursor mixture consisting essentially of TABLE-US-00003 Alumina (Al.sub.2O.sub.3) 41.37 wt % Magnesia (MgO) 0.02-7.00 wt % Carbon black 9.47 wt % Graphite 13.03 wt % Organic binders 2.15 wt % Deionized Water 33.96 wt % and further wherein the ceramic precursor mixture is subjected to a thermal treatment process to obtain a ceramic particle preform, wherein the ceramic particles are uniformly distributed throughout the primary metal component to form the metal-matrix composite, wherein the ceramic particles comprise 20-50 vol % of the metal-matrix composite, wherein the ceramic particles are chemically stable in the primary metal component at a temperature above a melting point of the primary metal component, wherein the metal-matrix composite has a first tensile modulus, the primary metal component has a second tensile modulus, the first tensile modulus and the second tensile modulus having a ratio of at least 1.3:1, and wherein the metal-matrix composite is machinable with a high speed steel (HSS).

2. The metal-matrix composite according to claim 1, wherein the ceramic particles have an aspect ratio of no greater than 3:1.

3. The metal-matrix composite according to claim 1, wherein the ceramic particles have an aspect ratio of no greater than 2:1.

4. The metal-matrix composite according to claim 1, wherein the metal-matrix composite has a first tensile strength, wherein the primary metal component has a second tensile strength, and wherein a ratio of the first tensile strength to the second tensile strength is least 2:1 to a temperature of at least 50% of the melting point of the primary metal component.

5. The metal-matrix composite according to claim 1, wherein the metal-matrix composite has a first ductility, wherein the primary metal component has a second ductility, and wherein a ratio of the first ductility and second ductility is at least 0.3:1.

6. The metal-matrix composite of claim 1, further comprising, in order, mixing the alumina, magnesia, and water to form a precursor slurry; milling the precursor slurry until the alumina exhibits an average particle size of not more than 0.5 micron; adding the carbon black and graphite to the precursor slurry; milling the precursor slurry for about 8 hours; adding the organic binders to the precursor slurry; milling the precursor slurry for about 12 hours to obtain a final precursor slurry; spray-drying the final precursor slurry to obtain the ceramic particles; cold-pressing the ceramic particles under an isostatic condition to obtain a ceramic particle preform; heating the ceramic particle preform according to the thermal treatment process to obtain a ceramic matrix preform; heating the primary metal component to a temperature above a melting point to obtain a molten mass of the primary metal component; and exposing the ceramic particle preform to the molten mass of the primary metal component under conditions resulting in the infiltration of the molten mass of the primary metal component throughout the ceramic matrix preform and obtain the metal-matrix composite.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graphical illustration of the heating steps for forming a metal matrix composition in accordance with a preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

(2) In the following embodiments of the invention, the preferred embodiment is illustrated by the second embodiment. Other embodiments are shown by Examples 1, 3 and 4. To be more specific, Example 1 where the first embodiment of the invention comprises a 65% by volume 6061 aluminum with a reinforcement by 35% by volume of alumina (Al.sub.2O.sub.3). The ceramic precursor material is typically batched according to the following recipe:

EXAMPLE 1

(3) TABLE-US-00001 Material Per Batch (lbs.) Almatis Calcined Alumina A-1000 100.0 SG Magchem 10 MgO 325 0.05 Carbon Black N990 22.9 Graphite M-450 31.5 Organic Binders 5.2 Water 82.1

(4) Alumina (Al.sub.2O.sub.3) and/or magnesium oxide (MgO) are dispersed in de-ionized water in a mixing tank while constantly mixing, the primary slurry is then milled until an alumina (Al.sub.2O.sub.3) particle size of about 0.5 micron is obtained, and then the carbon black is added followed by the graphite in the primary slurry and the entire mixture milled for about another 8 hours, additional binders are added to the secondary slurry which is milled for an additional 4 hours, and then spray dried. The dried powder is cold-pressed isostatically into a desired shape then fired in a kiln according to the steps in FIG. 1.

(5) The fired alumina preform, which is about 65% by volume inter-connected porosity and placed into a crucible along with 6061 aluminum, all of which is heated under vacuum to a temperature of about 750 C. in a pressure infiltration vessel and the resulting liquid aluminum is then squeezed into the preform by gradually applying inert gas pressure to about 2000 psi and subsequently cooled to room temperature.

(6) Example 2, or the preferred embodiment, comprises a composite matrix of 65% by volume aluminum 6061 and reinforcement of 30% by volume alumina (Al.sub.2O.sub.3) and about 5% by volume magnesium oxide (MgO). The batching recipe, is the same as in Example 1 except in Example 2 (preferred embodiment) there is 86 pounds of alumina and 13 pounds of magnesium oxide and the firing and infiltration processes are the same as in Example 1.

(7) In Example 3, the composite matrix contains 65% by volume AZ31B magnesium and the reinforcement is 30% by volume alumina (Al.sub.2O.sub.3) 5% by volume magnesium oxide (MgO) reinforcement and the batching recipe and the firing and infiltration processes are the same as in Example 2 (preferred embodiment).

(8) Example 4 has a composite matrix of 65% by volume AZ31B magnesium and the reinforcement is 35% by volume magnesium oxide (MgO) and the batching recipe and the firing and infiltration processes are the same as in Example 1 except alumina is 0 pounds and magnesium oxide is 91 pounds.

(9) Particularly attractive finished products are light weight, strong and stiff such as pistons, connecting rods and rocker arms for internal combustion engines and brake components made from the composite, for Example 1. Pistons and brake components made from composite, Example 3, additionally offer exceptionally low weight.

(10) It should also be recognized that the composites of the Examples have a tensile modulus which is at least 30 to 200% greater than the tensile modulus of the metal and wherein the metal ceramic composite has a ductility of at least about 30% of the ductility of the metal and wherein the composite has a tensile strength of at least twice that of the metal and retains the tensile strength ratio at temperatures up to about one-half the melting point of the metal and in which the metal matrix composite is machinable with a high-strength steel bit for greater than about one minute without serious damage to the bit.

(11) A metal-matrix composite comprising a uniform distribution of calcined ceramic particles having an average particle size of less than about one micron and a method or alloy substantially uniformly distributed with the ceramic particles.

(12) In a fifth embodiment of the invention at least about 80 percent of the ceramic particles are uniformly distributed on a scale of three (3) times the particle size.

(13) In a sixth embodiment of the invention at least 90 percent of the ceramic particles are uniformly distributed on a scale of two (2) times the particle size.

(14) In a seventh embodiment of the invention the ceramic particles have an aspect ratio of no greater than about three to one (3:1).

(15) Further, in an eighth embodiment of the invention the ceramic particles have an aspect ratio of no greater than about two to one (2:1).

(16) In a ninth embodiment of the invention the composite has a tensile modulus which is at least thirty (30) to two hundred (200) percent greater than the tensile modulus of said metal.

(17) In a tenth example of the metal-matrix composite has a tensile strength of at least twice of said metal and retains said tensile strength ratio at temperatures up to about one-half the melting point of said metal.

(18) An eleventh embodiment and/or example of the metal-matrix composite the metal-ceramic composite has a ductility of at least about 30 percent of the ductility of said metal and in which said metal-matrix composite comprises a uniform distribution of calcined ceramic particles having an average particle size of between 0.35 and 0.900 microns and a metal or alloy substantially uniformly distributed with said ceramic particles and in which said ceramic particles include oxides of two (2) separate metals selected from the group consisting of Al, Li, Be, Pb, Fe, Ag, Au, Sn, Mg, Ti, Cu, and Zn, and in which said ceramic particles comprise at least 15 volume percent of the metal matrix and wherein the metal-matrix composite being machinable with a high speed steel (HSS) bit for greater than about one (1) minute without excessive wear to said bit.

(19) In Example 12 the metal-matrix composite has a tensile strength of at least twice that of the metal and retains said tensile strength ratio at temperatures up to about one-half the melting point of said metal.

(20) In Example 13 the metal-matrix composite in which the metal matrix composite is machinable with a high-speed steel bit for greater than about one (1) minute without excessive wear to the bit.

(21) In Example 14 the metal-matrix composite wherein the composite has a tensile modulus which is at least about thirty (30) to two hundred (200) percent greater than the tensile modulus of the metal.

(22) Example 15 is a metal-matrix composite wherein a uniform distribution of calcined ceramic particles have an average particle size of no greater than about one (1) micron and a metal or alloy substantially uniform and distributed with the ceramic particles in which the ceramic particles comprise at least about 15 volume percent of the metal-matrix and in which the ceramic particles are thermally stable in the metal-matrix.

(23) In embodiment 16 the metal-matrix composite wherein the ceramic particles are chemically stable in the molten metal or alloy.

(24) In Example 17 the metal-matrix composite in which the ceramic particles comprise an oxide, boride, nitride, carbide, carbon or a combination thereof and a metal or alloy uniformly distributed with the ceramic particles, the metal or alloy comprising Al, Li, Be, Pb, Fe, Ag, Au, Sn, Mg, Ti, Cu, Zn, or a mixture thereof.

(25) In Example 18 the metal-matrix composite in which the metal is selected from the group consisting of aluminum, magnesium and mixtures thereof and the reinforcement is selected from the group consisting of alumina (Al.sub.2O.sub.3), magnesium oxide (MgO) and mixtures thereof and wherein the composite is 65% by volume 6061 aluminum and 35% by volume a mixture of alumina and magnesia (MgO), and wherein the ceramic precursor material is batched according to the following recipe:

(26) TABLE-US-00002 Material Per Batch (lbs.) Almatis Calcined Alumina A-1000 SG 100.0 Magchem 10 MgO 325 0.05 Carbon Black N990 22.9 Graphite M-450 31.5 Organic Binders 5.2 Water 82.1

(27) Alumina (Al.sub.2O.sub.3) and/or magnesium oxide (MgO) is dispersed in de-ionized water in a mixing tank while constantly mixing and the primary slurry is then milled until an alumina (Al.sub.2O.sub.3) particle size of about 0.5 micron is obtained, and the carbon black, followed by the graphite, is dispersed in a primary slurry and a resulting mixture milled for about 8 hours, additional binders are added which are milled for an additional 8 hours plus 4 hours, spray dried and cold-pressed isostatically into a desired shape and then fired in a kiln according to the steps in FIG. 1.

(28) The fired alumina preform, which is 65% by volume inter-connected porosity, is then placed into a crucible, along with the 6061 aluminum, all of which is heated under vacuum to a temperature of 750 degrees C. in a pressure infiltration vessel. The resulting liquid aluminum is then squeezed into the preform by gradually applying inert gas pressure to 2000 psi. The resulting billet is then cooled to room temperature.

(29) In Example 19 a metal-matrix composite comprising a uniform distribution of calcined ceramic particles having an average particle size of between 0.35 and 0.90 microns and a metal or alloy substantially uniformly distributed with the ceramic particles and in which the ceramic particles comprise at least 15 volume percent of the metal-matrix and the metal-matrix composites being machinable with a high-speed steel (HSS) for greater than about one (1) minute without excessive wear to the bit and in which the metal is selected from the group consisting of aluminum and magnesium and mixtures thereof; and wherein at least 80% of the ceramic particles are uniformly distributed on a scale of three times the particle size; and in which the ceramic particle have an aspect ratio of no greater than about three to one (3:1).

(30) While the invention has been described in connection with its preferred embodiments it should be recognized that changes and modifications may be made therein without departing from the scope of the appended claims.