Galvanically-Active In Situ Formed Particles for Controlled Rate Dissolving Tools

Abstract

A castable, moldable, and/or extrudable structure using a metallic primary alloy. One or more additives are added to the metallic primary alloy so that in situ galvanically-active reinforcement particles are formed in the melt or on cooling from the melt. The composite contain an optimal composition and morphology to achieve a specific galvanic corrosion rate in the entire composite. The in situ formed galvanically-active particles can be used to enhance mechanical properties of the composite, such as ductility and/or tensile strength. The final casting can also be enhanced by heat treatment, as well as deformation processing such as extrusion, forging, or rolling, to further improve the strength of the final composite over the as-cast material.

Claims

1-21. (canceled)

22. A magnesium composite that includes in situ precipitation of galvanically-active intermetallic phases to enable controlled dissolution of said magnesium composite comprising a magnesium or a magnesium alloy, an additive material having a greater melting point temperature than a solidus temperature of said magnesium or magnesium alloy, said additive material constituting about 0.05 wt. %-45 wt. % of said mixture, said additive material forming metal composite particles or precipitant in said magnesium composite that include said additive material and magnesium, said metal composite particles or precipitant forming said in situ precipitation of said galvanically-active intermetallic phases.

23. The magnesium composite as defined in claim 22, wherein said additive includes one or more metals selected from the group consisting of copper, silicon, nickel, titanium, iron, and cobalt.

24. The magnesium composite as defined in claim 22, wherein said magnesium alloy includes over 50 wt. % magnesium and one or more metals selected from the group consisting of aluminum, boron, bismuth, zinc, zirconium, and manganese.

25. The magnesium composite as defined in claim 22, wherein said magnesium alloy includes over 50 wt. % magnesium and one or more metals selected from the group consisting of aluminum in an amount of about 0.5-10 wt. %, zinc in amount of about 0.1-3 wt. %, zirconium in an amount of about 0.01-1 wt. %, manganese in an amount of about 0.15-2 wt. %, boron in amount of about 0.0002-0.04 wt. %, and bismuth in amount of about 0.4-0.7 wt. %.

26. The magnesium composite as defined in claim 22, wherein said additive metal includes about 0.05-35 wt. % nickel, said nickel forms intermetallic Mg.sub.xNi as a galvanically-active in situ precipitate in said magnesium composite.

27. The magnesium composite as defined in claim 22, wherein said additive includes about 0.05-35 wt. % copper, said copper forms intermetallic CuMg.sub.x as the galvanically-active in situ precipitate in said magnesium composite.

28. The magnesium composite as defined in claim 22, wherein said additive includes about 0.05-35 wt. % cobalt, said cobalt forms intermetallic CoMg.sub.x as the galvanically-active in situ precipitate in said magnesium composite.

29. The magnesium composite as defined in claim 22, where the use of a deformation processing such as forging or extrusion is used to reduce grain size of said magnesium composite, increase tensile yield strength of said magnesium composite, increase elongation of said magnesium composite, or combinations thereof.

30. The magnesium composite as defined in claim 22, wherein said magnesium composite is subjected to a surface treatment to improve a surface hardness of said magnesium composite, said surface treatment including peening, heat treatment, aluminizing, or combinations thereof.

31. The magnesium composite as defined in claim 22, wherein a dissolution rate of said magnesium composite is about 5-325 mg/cm2/hr in 3 wt. % KCl water mixture at 90° C.

32. The magnesium composite as defined in claim 22, wherein a dissolution rate of said magnesium composite is controlled by an amount and size of said in situ formed galvanically-active particles whereby smaller average sized particles of said in situ formed galvanically-active particles, a greater weight percent of said in situ formed galvanically-active particles in said magnesium composite, or combinations thereof increases said dissolution rate of said magnesium composite.

33. A magnesium composite that includes in situ precipitation of galvanically-active intermetallic phases to enable controlled dissolution of said magnesium composite comprising a magnesium or a magnesium alloy, an additive material having a greater melting point temperature than a solidus temperature of said magnesium or magnesium alloy, said composite including greater than 50 wt. % magnesium, said additive material constituting about 0.05-45 wt. % of said magnesium composite, said additive material having a melting point temperature that is greater than 100° C. than a melting temperature of said magnesium or magnesium alloy, an average particle diameter size of said additive material is at least 0.1 microns and up to about 500 microns, said additive including one or more metals selected from the group consisting of copper, nickel, cobalt, titanium, silicon, and iron, a portion of said additive material forming solid particles with said magnesium and a portion of said additive material remaining unalloyed additive material, said magnesium composite including in situ precipitation of galvanically-active intermetallic phases that includes said unalloyed additive material and said solid particles formed of magnesium additive material.

34. The magnesium composite as defined in claim 33, wherein said additive material is added to said magnesium or magnesium alloy while said magnesium or magnesium alloy is at a temperature that is above said solidus temperature of magnesium or magnesium alloy and a temperature that is less than a melting point of said additive material to form a mixture.

35. The magnesium composite as defined in claim 33, wherein said magnesium alloy includes over 50 wt. % magnesium and one or more metals selected from the group consisting of aluminum in an amount of about 0.5-10 wt %, zinc in amount of about 0.1-6 wt. %, zirconium in an amount of about 0.01-3 wt. %, manganese in an amount of about 0.15-2 wt. %; boron in amount of about 0.0002-0.04 wt. %, and bismuth in amount of about 0.4-0.7 wt. %.

36. The magnesium composite as defined in claim 34, wherein said magnesium alloy includes over 50 wt % magnesium and one or more metals selected from the group consisting of aluminum in an amount of about 0.5-10 wt. %, zinc in amount of about 0.1-3 wt. %, zirconium in an amount of about 0.01-1 wt. %, manganese in an amount of about 0.15-2 wt. %; boron in amount of about 0.0002-0.04 wt. %, and bismuth in amount of about 0.4-0.7 wt. %.

37. The magnesium composite as defined in claim 33, said additive metal includes about 0.05-35 wt. % nickel, said nickel forms intermetallic Mg.sub.xNi as a galvanically-active in situ precipitate in said magnesium composite.

38. The magnesium composite as defined in claim 36, wherein said additive metal includes about 0.05-35 wt. % nickel, said nickel forms intermetallic Mg.sub.xNi as a galvanically-active in situ precipitate in said magnesium composite.

39. The magnesium composite as defined in claim 37, wherein said additive metal includes about 3-7 wt. % nickel.

40. The magnesium composite as defined in claim 38, wherein said additive metal includes about 7-10 wt. % nickel.

41. The magnesium composite as defined in claim 37, wherein said additive metal includes about 3-7 wt. % nickel.

42. The magnesium composite as defined in claim 38, wherein said additive metal includes about 7-10 wt. % nickel.

43. The magnesium composite as defined in claim 33, wherein a dissolution rate of said magnesium composite is at least 45 mg/cm.sup.2/hr in 3 wt. % KCl water mixture at 90° C. and up to 325 mg/cm.sup.2/hr in 3 wt. % KCl water mixture at 90° C.

44. The magnesium composite as defined in claim 38, wherein a dissolution rate of said magnesium composite is at least 45 mg/cm.sup.2/hr in 3 wt. % KCl water mixture at 90° C. and up to 325 mg/cm.sup.2/hr in 3 wt. % KCl water mixture at 90° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] FIGS. 1-3 show a typical cast microstructure with galvanically-active in situ formed intermetallic phase wetted to the magnesium matrix; and,

[0061] FIG. 4 shows a typical phase diagram to create in situ formed particles of an intermetallic Mg.sub.x(M) where M is any element on the periodic table or any compound in a magnesium matrix and wherein M has a melting point that is greater than the melting point of Mg.

DETAILED DESCRIPTION OF THE INVENTION

[0062] The present invention is directed to a novel magnesium composite that can be used to form a castable, moldable, or extrudable component. The magnesium composite includes at least 50 wt. % magnesium. Generally, the magnesium composite includes over 50 wt. % magnesium and less than about 99.5 wt. % magnesium and all values and ranges therebetween. One or more additives are added to a magnesium or magnesium alloy to form the novel magnesium composite of the present invention. The one or more additives can be selected and used in quantities so that galvanically-active intermetallic or insoluble precipitates form in the magnesium or magnesium alloy while the magnesium or magnesium alloy is in a molten state and/or during the cooling of the melt; however, this is not required. The one or more additives are added to the molten magnesium or magnesium alloy at a temperature that is less than the melting point of the one or more additives. During the process of mixing the one or more additives in the molten magnesium or magnesium alloy, the one or more additives are not caused to fully melt in the molten magnesium or magnesium alloy. After the mixing process is completed, the molten magnesium or magnesium alloy and the one or more additives that are mixed in the molten magnesium or magnesium alloy are cooled to form a solid component. Such a formation in the melt is called in situ particle formation as illustrated in FIGS. 1-3. Such a process can be used to achieve a specific galvanic corrosion rate in the entire magnesium composite and/or along the grain boundaries of the magnesium composite. This feature results in the ability to control where the galvanically-active phases are located in the final casting, as well as the surface area ratio of the in situ phase to the matrix phase, which enables the use of lower cathode phase loadings as compared to a powder metallurgical or alloyed composite to achieve the same dissolution rates. The in situ formed galvanic additives can be used to enhance mechanical properties of the magnesium composite such as ductility, tensile strength, and/or shear strength. The final magnesium composite can also be enhanced by heat treatment as well as deformation processing (such as extrusion, forging, or rolling) to further improve the strength of the final composite over the as-cast material; however, this is not required. The deformation processing can be used to achieve strengthening of the magnesium composite by reducing the grain size of the magnesium composite. Further enhancements, such as traditional alloy heat treatments (such as solutionizing, aging and/or cold working) can be used to enable control of dissolution rates though precipitation of more or less galvanically-active phases within the alloy microstructure while improving mechanical properties; however, this is not required. Because galvanic corrosion is driven by both the electro potential between the anode and cathode phase, as well as the exposed surface area of the two phases, the rate of corrosion can also be controlled through adjustment of the in situ formed particles size, while not increasing or decreasing the volume or weight fraction of the addition, and/or by changing the volume/weight fraction without changing the particle size. Achievement of in situ particle size control can be achieved by mechanical agitation of the melt, ultrasonic processing of the melt, controlling cooling rates, and/or by performing heat treatments. In situ particle size can also or alternatively be modified by secondary processing such as rolling, forging, extrusion and/or other deformation techniques. A smaller particle size can be used to increase the dissolution rate of the magnesium composite. An increase in the weight percent of the in situ formed particles or phases in the magnesium composite can also or alternatively be used to increase the dissolution rate of the magnesium composite. A phase diagram for forming in situ formed particles or phases in the magnesium composite is illustrated in FIG. 4.

[0063] In accordance with the present invention, a novel magnesium composite is produced by casting a magnesium metal or magnesium alloy with at least one component to form a galvanically-active phase with another component in the chemistry that forms a discrete phase that is insoluble at the use temperature of the dissolvable component. The in situ formed particles and phases have a different galvanic potential from the remaining magnesium metal or magnesium alloy. The in situ formed particles or phases are uniformly dispersed through the matrix metal or metal alloy using techniques such as thixomolding, stir casting, mechanical agitation, chemical agitation, electrowetting, ultrasonic dispersion, and/or combinations of these methods. Due to the particles being formed in situ to the melt, such particles generally have excellent wetting to the matrix phase and can be found at grain boundaries or as continuous dendritic phases throughout the component depending on alloy composition and the phase diagram. Because the alloys form galvanic intermetallic particles where the intermetallic phase is insoluble to the matrix at use temperatures, once the material is below the solidus temperature, no further dispersing or size control is necessary in the component. This feature also allows for further grain refinement of the final alloy through traditional deformation processing to increase tensile strength, elongation to failure, and other properties in the alloy system that are not achievable without the use of insoluble particle additions. Because the ratio of in situ formed phases in the material is generally constant and the grain boundary to grain surface area is typically consistent even after deformation processing and heat treatment of the composite, the corrosion rate of such composites remains very similar after mechanical processing.

EXAMPLE I

[0064] An AZ91D magnesium alloy having 9 wt. % aluminum, 1 wt. % zinc and 90 wt. % magnesium was melted to above 800° C. and at least 200° C. below the melting point of nickel. About 7 wt. % of nickel was added to the melt and dispersed. The melt was cast into a steel mold. The cast material exhibited a tensile strength of about 14 ksi, an elongation of about 3%, and shear strength of 11 ksi. The cast material dissolved at a rate of about 75 mg/cm.sup.2-min in a 3% KCl solution at 90° C. The material dissolved at a rate of 1 mg/cm.sup.2-hr in a 3% KCl solution at 21° C. The material dissolved at a rate of 325 mg/cm.sup.2-hr. in a 3% KCl solution at 90° C.

EXAMPLE 2

[0065] The composite in Example 1 was subjected to extrusion with an 11:1 reduction area. The material exhibited a tensile yield strength of 45 ksi, an Ultimate tensile strength of 50 ksi and an elongation to failure of 8%. The material has a dissolve rate of 0.8 mg/cm.sup.2-min. in a 3% KCl solution at 20° C. The material dissolved at a rate of 100 mg/cm.sup.2-hr. in a 3% KCl solution at 90° C.

EXAMPLE 3

[0066] The alloy in Example 2 was subjected to an artificial T5 age treatment of 16 hours from 100° C.-200° C. The alloy exhibited a tensile strength of 48 ksi and elongation to failure of 5% and a shear strength of 25 ksi. The material dissolved at a rate of 110 mg/cm.sup.2-hr. in 3% KCl solution at 90° C. and 1 mg/cm.sup.2-hr. in 3% KCl solution at 20° C.

EXAMPLE 4

[0067] The alloy in Example 1 was subjected to a solutionizing treatment T4 of 18 hours from 400° C.-500° C. and then an artificial T6 aging treatment of 16 hours from 100° C.-200 C. The alloy exhibited a tensile strength of 34 ksi and elongation to failure of 11% and a shear strength of 18 Ksi. The material dissolved at a rate of 84 mg/cm.sup.2-hr. in 3% KCl solution at 90° C. and 0.8 mg/cm.sup.2-hr. in 3% KCl solution at 20° C.

EXAMPLE 5

[0068] An AZ91D magnesium alloy having 9 wt. % aluminum, 1 wt. % zinc and 90 wt. % magnesium was melted to above 800° C. and at least 200° C. below the melting point of copper. About 10 wt. % of copper alloyed to the melt and dispersed. The melt was cast into a steel mold. The cast material exhibited a tensile yield strength of about 14 ksi, an elongation of about 3%, and shear strength of 11 ksi. The cast material dissolved at a rate of about 50 mg/cm.sup.2-hr. in a 3% KCl solution at 90° C. The material dissolved at a rate of 0.6 mg/cm.sup.2-hr. in a 3% KCl solution at 21° C.

EXAMPLE 6

[0069] The alloy in Example 5 was subjected to an artificial T5 aging treatment of 16 hours from 100° C.-200° C. the alloy exhibited a tensile strength of 50 ksi and elongation to failure of 5% and a shear strength of 25 ksi. The material dissolved at a rate of 40 mg/cm.sup.2-hr. in 3% KCl solution at 90° C. and 0.5 mg/cm.sup.2-hr. in 3% KCl solution at 20° C.

[0070] 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.