METHOD FOR DISSOLVABLE ALUMINUM ALLOYS

Abstract

The method for equal channel angular extrusion increases yield strength and ultimate tensile strength of a dissolvable aluminum alloy. A billet of a dissolvable aluminum alloy is wrapped with a sheet cover so as to form a wrapped billet. The wrapped billet is extruded through an equal channel angular extrusion die with an extrusion angle ranging 90-135 degrees so as to form an extruded billet. The step of extruding is at a temperature ranging 150-250 degrees C., an extrusion rate ranging 0.003-0.010 inches per second, and a back pressure ranging 200-10000 psi. The dissolvable aluminum alloy of the extruded billet has a yield strength and ultimate tensile strength 50% greater than the initial yield strength and initial ultimate tensile strength.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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THE NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

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STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINT INVENTOR

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method to process dissolvable aluminum alloy. More particularly, the present invention relates to a method for equal channel angular extrusion of the dissolvable aluminum alloy. Even more particularly, the present invention relates to a method to modify dissolvable aluminum alloy in order to be suitable for forming downhole components in the oil and gas industry.

2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.

Oil and gas production is commonly known to involve a borehole through a ground formation with downhole tools, such as plugs and sleeves positioned along and within the borehole. The plugs close and open portions of the borehole so that a zone of ground formation can be isolated. A sleeve opens and closes to make the fluid connection between the borehole and the ground formation. The downhole tools work to isolate and connect the zone for various operations to prepare and produce the hydrocarbons from the ground formation. When the operations are complete in the zone, components of the downhole tool or even the entire downhole tool may require removal. For example, a frac ball set in a plug to trigger a seal may be removed so that the seal is removed. Alternatively, the entire plug may be removed.

Dissolvable alloys were developed for the manufacture of downhole tool components in the oil and gas industry. There are mainly two types of dissolvable alloys: magnesium and aluminum based alloys. The dissolvable aluminum alloys typically have low ductility and low strength. The additives required for dissolvability negatively affect desirable physical properties needed for downhole tool components. The additives are low-melting-point elements, such as Ga, In and Sn, which reside at the grain boundaries or produce the secondary phase particles in order to create micro-scale galvanic corrosion with matrix materials. The low melting point alloys are dissolvable. However, there are difficulties forming more complex shapes of components with low ductility, and the components are not strong enough for downhole conditions of higher pressure and higher temperatures. The dissolvable aluminum alloys are typically brittle after casting due to the existence of embrittlement elements with low melting points such as Ga, In or Sn. Therefore, they are relatively difficult to be processed by traditional extrusion process.

There are prior art methods for post-processing casted dissolvable aluminum alloys. U.S. Pat. No. 8,211,248, issued on 3 Jul. 2012 to Marya, discloses heat treatment. Equal channel angular extrusion (ECAE) is another technique from the 1970′s known to increase the strength of metals and alloys.

Due to the intrinsic brittle nature of the dissolvable aluminum alloys, equal channel angular extrusion (ECAE) is not inherently compatible with dissolvable aluminum alloys. FIG. 2 shows that simply being a dissolvable can result in a critical failure. FIG. 2 shows a comparison that the regular aluminum alloy 6061 (a) can be easily processed by ECAE without issue, while using the same ECAE conditions, a dissolvable aluminum alloy (b) fails.

It is an object of the present invention to provide a method for processing dissolvable aluminum alloy.

It is an object of the present invention to provide a method to improve ductility and strength of a dissolvable aluminum alloy.

It is an object of the present invention to provide a method to modify a dissolvable aluminum alloy for suitability for downhole tool components.

It is another object of the present invention to provide a method for equal channel angular extrusion compatible with dissolvable aluminum alloys.

These and other objectives and advantages of the present invention will become apparent from a reading of the attached specification.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention include a method for equal channel angular extrusion. A billet of a dissolvable aluminum alloy is wrapped with a sheet cover so as to form a wrapped billet. The dissolvable aluminum alloy has an initial strength and an initial tensile elongation. The method includes extruding the wrapped billet through an equal channel angular extrusion die with an extrusion angle ranging 90-135 degrees so as to form an extruded billet. The step of extruding is at a temperature ranging 150-250 degrees C., an extrusion rate ranging 0.003-0.010 inches per second, and a back pressure ranging 200-10000 psi. The dissolvable aluminum alloy of the extruded billet has yield strength and ultimate tensile strength 50% greater than the initial yield strength and ultimate tensile strength.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic view of an equal channel angular extrusion method.

FIG. 2 are photos (a) and (b) of a regular aluminum alloy and a dissolvable aluminum alloy after an equal channel angular extrusion in the same conditions.

FIG. 3 are photos (a) and (b) of a dissolvable aluminum alloy after an equal channel angular extrusion in different temperature conditions.

FIG. 4 are photos (a) and (b) of a dissolvable aluminum alloy after an equal channel angular extrusion at different extrusion rates.

FIG. 5 are photos (a), (b), and (c) of a dissolvable aluminum alloy after an equal channel angular extrusion at different back pressures.

FIG. 6 are photos (a) and (b) of a dissolvable aluminum alloy after an equal channel angular extrusion with and without wrapping materials.

FIG. 7 are photos (AA), (AC), (AG), and (AH) of four dissolvable aluminum alloys after an equal channel angular extrusion within the critical range of conditions.

FIG. 8 are photos (a) and (b) of a dissolvable aluminum alloy before and after an equal channel angular extrusion within the critical range of conditions.

FIG. 9 is a graph illustration of tensile tests of dissolvable aluminum alloys before and after an equal channel angular extrusion within the critical range of conditions.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-9 show the embodiments of the present invention as a method for equal channel angular extrusion of a dissolvable aluminum alloy with improved yield strength and ultimate tensile strength. There is an incompatibility of dissolvable aluminum alloy with equal channel angular extrusion (ECAE) methods due to the very nature of the low melt elements used for the dissolvability. As a material composition for downhole tool components, the dissolvability cannot be eliminated. The dissolvability is the feature that is required of particular downhole tool components. FIG. 2 shows the critical limitation of the dissolvability. The regular aluminum alloy is easily processed without issue, while the dissolvable aluminum alloy is a complete failure. The dissolvable aluminum alloy can be rendered non-functional by the ECAE method in FIG. 2.

FIG. 1 shows the method for equal channel angular extrusion. A billet 10 is wrapped with a sheet cover 12 so as to form a wrapped billet. The billet 10 is comprised of a dissolvable aluminum alloy with an initial tensile yield strength, an initial tensile ultimate strength, and an initial tensile elongation. The sheet cover 12 can be comprised of brass or graphite. The method includes extruding the wrapped billet through an equal channel angular extrusion die 20 with an extrusion angle 22 ranging 90-135 degrees so as to form an extruded billet. The temperature of the method can be controlled. FIG. 1 shows a pressing plunger 30 to set an extrusion rate by pressure P and a back plunger 32 to set a back pressure PB. Temperature, extrusion rate, back pressure, and wrapping are ECAE conditions that can affect the extruded aluminum alloy in the ECAE method of the present invention

TABLE 1
results for temperature, extrusion rate, back pressure, and wrapping
			Back
	Temperature	Extrusion Rate	Pressure		Critical
FIG.	(degrees C.)	(inches/sec)	(psi)	Wrapping	Fail
2 (a), 4(a)	250	0.01	200	YES	YES
3 (a)	100	0.005	200	YES	YES
3 (b), 4	200	0.005	200	YES	NO
(b), 5 (a)
5 (b)	200	0.005	4000	YES	NO
5 (c)	200	0.005	8000	YES	NO
6 (a)	330	0.005	0	NO	YES
6 (b)	330	0.005	4000	YES	NO
7-AA	200	0.005	8000	YES	NO
7-AC	200	0.005	8000	YES	NO
7-AG	200	0.005	8000	YES	NO
7-AH	200	0.005	8000	YES	NO

There is a critical range of the temperature. FIG. 2-6 show that temperatures both above and below 250 degrees can avoid fracturing of the extruded dissolvable aluminum alloy by an ECAE method. There is no teaching either way that higher or lower temperatures are better for dissolvable aluminum alloys. Furthermore, FIG. 2 shows that a lower temperature can also be too low. Additionally, a higher temperature can also be too high. A trial at 330 degrees C. avoided fracturing, but the dissolvable aluminum alloy over 400 degrees C. is already known to be fracturing and non-functional based on known heat treatments at 400 degrees C. There are critical ranges for temperature above and below 250 degrees C., depending on other ECAE conditions.

There is a critical range of the extrusion rate. FIGS. 2-4 show that slower extrusion rates can avoid fracturing of the extruded dissolvable aluminum alloy by an ECAE method. Even at extrusion rates slower than 0.01 inches/sec, there can still be failure of the extruded dissolvable aluminum alloy. FIGS. 3 and 4 show that an extrusion rate lower than 0.01 inches/sec can avoid fracturing, depending on temperature. There is no teaching that increasing extrusion rate above 0.01 inches per second can avoid fracturing, but it is known that increasing extrusion rate is more likely to fail since the billet encounters less strain. When there is already failure at 0.01 inches/sec, the teaching is to go slower. However, the present invention shows that going slower than 0.01 inches/sec is not a guarantee to eventually avoid fracturing either. There is still a critical range for extrusion rate in FIGS. 2-4.

Back pressure can also be a critical ECAE condition. Table 1 shows failures between 0-200 psi, while FIG. 5 shows that the back pressure from 200-8000 psi can avoid fracturing. A minimal back pressure at 200 psi appears to be a critical pressure. Higher back pressures were also able to yield viable extruded dissolvable aluminum alloys after the ECAE process. The back pressure confines the material in the extrusion chamber in extrusion direction during the ECAP process, so that the material in the extrusion process will keep the integrity from all directions.

FIG. 6 shows the benefit of wrapping to improve the ECAE process. There can be failures with or without wrapping. Embodiments of the present invention include the sheet cover of the wrapping material as brass, graphite or pure aluminum, which can act as a solid lubrication for the billet 10 of dissolvable aluminum alloy. The results of Table 1 indicate that wrapping is a critical ECAE condition with the extruded dissolvable aluminum alloy only avoiding fractures when wrapped.

Table 1 identifies the critical ranges as now claimed. The temperature has a range of 150-250 degrees C. with an extrusion rate range of 0.003-0.010 inches per second and a back pressure range of 200-10000 psi. Additionally, these conditions require wrapping. The present invention indicates the critical ranges interacting to avoid fractures in the extruded dissolvable aluminum alloy.

Beyond achieving a functional extruded dissolvable aluminum alloy, the method of the present invention further includes unexpected performance. Simply avoiding complete structural failure is important for components of downhole tools, but there is a further benefit beyond forming an extruded dissolvable aluminum alloy.

TABLE 2
results of FIG. 7 for increased strengths and sometimes elongation.
			Tensile	Tensile
	Tensile	Tensile	Ultimate	Ultimate	Tensile	Tensile
	Yield Strength	Yield Strength	Strength	Strength	Elongation	Elongation
	BEFORE	AFTER	BEFORE	AFTER	BEFORE	AFTER
Sample	(MPa)	(MPa)	(MPa)	(MPa)	(%)	(%)
AA	137	275	190	325	3.3	8.7
AC	122	265	190	290	4.7	2.9
AG	153	273	187	320	1.4	2.1
AH	125	252	225	290	7.0	6.5

After identifying the ECAE conditions of the present invention, dissolvable aluminum materials were processed successfully, as shown in FIG. 7 and FIG. 8. The parts were processed without fractures that would render the extruded dissolvable aluminum alloy unuseable. FIG. 8 shows an example of microstructural evolution during the ECAE process with 8(a) showing a view before the ECAE process and 8(b) showing a view after the ECAE process. In the ECAE processed materials, there is less micro-porosity, and there is more even distribution of secondary phase particles. Micro-porosity and even distribution of secondary phase particles can contribute to the improvement of tensile mechanical properties. FIG. 9 shows the increased yield strength and ultimate tensile strength. Table 2 summarizes the improvement ranging 60-100% to support the unexpected 50% increase in yield strength and ultimate tensile strength of extruded dissolvable aluminum alloy.

In the present invention, just to achieve extruded dissolvable aluminum alloy that does not fracture is surpassed by the additional findings of Table 2. There are actual improvements to mechanical properties beyond just being able to form components of downhole tools without fractures.

The present invention provides a method for processing dissolvable aluminum alloy. After being cast, the dissolvable aluminum alloy must be formed into shapes that correspond to components of downhole tools. Being brittle makes the formation of parts difficult. Once formed, the component must have the necessary strength for downhole conditions, while remaining dissolvable. The present invention improves the strengths of a dissolvable aluminum alloy in a post processing treatment of dissolvable aluminum alloy. Previously unusable or at least time consuming and expensive processing for downhole tool components can be avoided. The method for an equal channel angular extrusion has been modified to be compatible with dissolvable aluminum alloys. Regular alloys do not require such modifications, and there are critical ranges to avoid fracturing and failure of the extruded material. The present invention identifies these critical ranges to avoid failure and further achieves an unexpected improvement in strengths.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated structures, construction and method can be made without departing from the true spirit of the invention.

Claims

1. A method for equal channel angular extrusion, comprising the steps of: wrapping a billet with a sheet cover so as to form a wrapped billet, said billet being comprised of a dissolvable aluminum alloy with an initial tensile yield strength; andextruding said wrapped billet through an equal channel angular extrusion die with an extrusion angle ranging 90-135 degrees so as to form an extruded billet,

2. The method of claim 1, wherein said temperature is 200 degrees C.

3. The method of claim 1, wherein said extrusion rate is 0.005 inches per second.

4. The method of claim 1, wherein said back pressure is 8000 psi.

5. The method of claim 1, wherein said sheet cover is comprised of one of a group consisting of brass and graphite.

6. A method for equal channel angular extrusion, comprising the steps of: wrapping a billet with a sheet cover so as to form a wrapped billet, said billet being comprised of a dissolvable aluminum alloy with an initial tensile ultimate strength; andextruding said wrapped billet through an equal channel angular extrusion die with an extrusion angle ranging 90-135 degrees so as to form an extruded billet,

7. The method of claim 6, wherein said temperature is 200 degrees C.

8. The method of claim 6, wherein said extrusion rate is 0.005 inches per second.

9. The method of claim 6, wherein said back pressure is 8000 psi.

10. The method of claim 6, wherein said sheet cover is comprised of one of a group consisting of brass and graphite.

11. A method for equal channel angular extrusion, comprising the steps of: wrapping a billet with a sheet cover so as to form a wrapped billet, said billet being comprised of a dissolvable aluminum alloy with an initial tensile elongation; andextruding said wrapped billet through an equal channel angular extrusion die with an extrusion angle ranging 90-135 degrees so as to form an extruded billet,

12. The method of claim 11, wherein said temperature is 200 degrees C.

13. The method of claim 11, wherein said extrusion rate is 0.005 inches per second.

14. The method of claim 11, wherein said back pressure is 8000 psi.

15. The method of claim 11, wherein said sheet cover is comprised of one of group consisting of brass and graphite.