US20150283607A1

US20150283607A1 - Apparatus and method for manufacturing a turbocharger component

Info

Publication number: US20150283607A1
Application number: US14/744,118
Authority: US
Inventors: Nan Yang; Jeff Alan Jensen
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2013-02-13
Filing date: 2015-06-19
Publication date: 2015-10-08
Also published as: US20140224385A1

Abstract

A method of pressure casting a turbocharger component for an internal combustion engine may include heating an aluminum-scandium alloy to form a molten casting material including up to about 5 wt % scandium that is fully dissolved in the molten casting material, and introducing the molten casting material into a cavity of a mold from a bottom of the mold toward a top of the mold while applying a pressure to the molten casting material with a movable portion of a ram positioned in contact with the bottom of the mold. The method may also include solidifying the molten casting material by cooling the casting material as it comes into contact with a cooling member positioned on the top of the mold, wherein a coolant is pumped through coolant passages formed in the cooling member in order to cool the casting material at a cooling rate such that the solidifying preserves at least 70% of an original amount of the scandium in the aluminum-scandium alloy in solid solution in the casting material. The method may still further include removing the solidified casting material from the mold, and forming scandium precipitates within the casting material by aging the casting material at an aging temperature.

Description

This is a continuation of copending application Ser. No. 13/766,626, filed Feb. 13, 2013, which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to a turbocharger system, and more particularly to an apparatus and method for manufacturing a turbocharger component.

BACKGROUND

Internal combustion engines are supplied with a mixture of air and fuel for subsequent combustion within the engine that generates a mechanical power output. To increase the power generated by the combustion process, the engine may be equipped with a turbocharger system including one or more turbochargers. The turbocharger system can be arranged to use exhaust from the engine to compress air flowing into the engine, thereby forcing more air into a combustion chamber of the engine than could otherwise be draw in to the combustion chamber. The increased supply of air can allow for increased fueling, resulting in an increased power output.
An internal combustion engine having a turbocharger system may be composed of various components such as one or more turbine wheels, compressor wheels, and/or pistons. Turbocharger components have been constructed from materials capable of withstanding high temperatures and stresses that can be experienced during engine operation. For example, temperatures of compressed air can reach about 260-300° C. during engine operation. Such high operating stresses and temperatures may have an adverse effect on engine operation.
In an attempt to endure these high temperatures and stresses, turbocharger components, including compressor wheels, have been made of a titanium alloy. Titanium compressor wheels, however, may inhibit efficient engine operation due to their weight, and the costs associated with manufacturing titanium compressor wheels may be excessive. In lieu of using titanium, compressor wheels may be manufactured from aluminum. Aluminum, however, may not be able to withstand the high temperatures and stresses imparted on the compressor wheels during engine operation.
U.S. Pat. No. 8,118,556 (“the '556 patent”) describes a compressor wheel for a turbocharger system. In particular, the '556 patent discloses a compressor wheel formed of an aluminum alloy containing up to 5 weight percent (wt %) scandium. According to the manufacturing process described in the '556 patent, compressor wheels may be manufactured by a number of casting methods, such as vortex casting, vacuum casting, centrifugal casting, die casting, and pressure casting. In one example, molten material is pressure cast into a shell mold and solidifies to form a compressor wheel.
While an aluminum-scandium alloy like that disclosed in the '556 patent may be used to form a compressor wheel, depending on the manufacturing process, the compressor wheel may still not be able to sufficiently withstand high stresses and operating temperatures in the range of about 260-300° C. The present disclosure is directed to overcoming one or more of the these issues and/or other problems.

SUMMARY

In one aspect, a method of pressure casting a turbocharger component for an internal combustion engine is disclosed. The method may include heating an aluminum-scandium alloy to form a molten casting material including up to about 5 wt % scandium that is fully dissolved in the molten casting material, and introducing the molten casting material into a cavity of a mold from a bottom of the mold toward a top of the mold while applying a pressure to the molten casting material with a movable portion of a ram positioned in contact with the bottom of the mold. The method may also include solidifying the molten casting material by cooling the casting material as it comes into contact with a cooling member positioned on the top of the mold, wherein a coolant is pumped through coolant passages formed in the cooling member in order to cool the casting material at a cooling rate such that the solidifying preserves at least 70% of an original amount of the scandium in the aluminum-scandium alloy in solid solution in the casting material. The method may still further include removing the solidified casting material from the mold and forming scandium precipitates within the casting material by aging the casting material at an aging temperature.
In another aspect, a method of casting a turbocharger component for an internal combustion engine is disclosed. The method may include heating an aluminum-scandium alloy to form a molten casting material including up to about 5 wt % scandium that is fully dissolved in the molten casting material, introducing the molten casting material into a cavity of a mold from a bottom of the mold toward a top of the mold, and solidifying the molten casting material by cooling the casting material as it comes into contact with a cooling member positioned on the top of the mold. A coolant may be pumped through coolant passages formed in the cooling member in order to cool the casting material at a cooling rate such that the solidifying preserves at least 70% of an original amount of the scandium in the aluminum-scandium alloy in solid solution in the casting material before removing the solidified casting material from the mold.
In yet another aspect, a method of casting a component is disclosed. The method may include heating an aluminum alloy to form a molten casting material including up to about 5 wt % of an alloying element that is fully dissolved in the molten casting material, and introducing the molten casting material into a cavity of a mold from a bottom of the mold toward a top of the mold. The method may also include solidifying the molten casting material by cooling the casting material as it comes into contact with a cooling member positioned on the top of the mold, wherein a coolant is pumped through coolant passages formed in the cooling member in order to cool the casting material at a cooling rate such that the solidifying preserves at least 70% of an original amount of the alloying element in the aluminum alloy in solid solution in the casting material. The method may still further include removing the solidified casting material from the mold, and forming precipitates of the alloying element within the casting material by aging the casting material at an aging temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an internal combustion engine including a turbocharger system according to the present disclosure;

FIG. 2 is a schematic cross-sectional view of a casting apparatus for making a component of the turbocharger system of FIG. 1; and

FIG. 3 is a magnified schematic view of a portion of a compressor wheel of the turbocharger system of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary embodiment of an internal combustion engine 10. Although various internal combustion engines could be provided, for the purposes of illustration, the engine 10 shown in FIG. 1 is a four stroke, compression ignition engine. The engine 10 includes an engine block 12 defining a plurality of combustion chambers or cylinders 14. Although in the exemplary engine 10, six combustion chambers 14 are shown, the engine 10 may include any number of combustion chambers 14. The engine 10 also includes an intake manifold 16 in communication, for example, fluid communication, with the combustion chambers 14, such that the intake manifold 16 may be capable of providing air to the engine 10 via an intake conduit 18. An exhaust manifold 20 may also be in communication, for example, fluid communication, with the combustion chambers 14, such that the exhaust manifold 20 may be capable of expending exhaust gas from the engine block 12 via an exhaust gas conduit 22.
The engine 10 may also include a turbocharger system 24. The turbocharger system 24 may be a single stage turbocharger system or a multiple stage turbocharger system, as shown in FIG. 1. In one instance, the turbocharger system 24 may include a first turbocharger 26 and a second turbocharger 28. Although two turbochargers 26, 28 are shown in FIG. 1, in some instances an engine 10 may include one turbocharger or more than two turbochargers. The first turbocharger 26 may include a compressor 30 connected to a turbine 32 via a shaft 34. Similarly, the second turbocharger 28 may include a compressor 36 connected to a turbine 38 via a shaft 40.
During operation of the internal combustion engine 10, exhaust gas leaving the exhaust manifold 20 passes through the exhaust conduit 22 to turbine wheels 42, 44, causing the turbine wheels 42, 44 to rotate. The rotation of the turbine wheels 42, 44 turns the shafts 34, 40, which rotate compressor wheels 46, 48, respectively. Ambient air flows through the intake conduit 18, and the rotation of the compressor wheels 46, 48 compresses the ambient air. In some instances, a multiple stage turbocharger system may include compressor wheels operating in series, as shown in FIG. 1. In other instances, a multiple stage turbocharger system may include compressor wheels positioned and operating in parallel on a common shaft.
FIG. 2 is a schematic cross-sectional view of a casting apparatus 50, which may be referred to as a pressure casting apparatus 50, for making a component of a turbocharger. As described in detail in this disclosure, the casting apparatus 50 may be arranged to cast turbocharger components such as one or more of the turbine wheels 42, 44, the compressor wheels 46, 48, piston heads (not shown), cylinder heads (not shown), or a variety of other engine components.
As shown in FIG. 2, the casting apparatus 50 may include a mold 52. The mold 52 may include a cavity 62 defined by an interior mold wall 80 and configured to receive a casting material, also referred to as melt stock, during a casting process, as described in detail in this disclosure. In some instances, the mold may be referred to as a “retractable mold” made of multiple separable pieces. In other embodiments, the mold 52 may be constructed as a single piece. Whether the mold 52 is retractable or a single piece, the mold 52 may be either reusable or disposable. As described herein, the mold 52 shown in FIG. 2 is a schematic cross-sectional view of the mold 52, and therefore may not represent the actual shape of the mold 52 and/or mold cavity 62. For example, the mold cavity 62 may have a more complex shape into which the casting material can flow based on, e.g., the shape of compressor wheel blades.
The casting apparatus 50 may further include a ram 54, which, in some instances, may be a hydraulic ram. As shown in FIG. 2, the mold 52 may rest or be secured atop the ram 54. The ram 54 may include a piston 58, plunger, or similar device configured to introduce the casting material into the mold cavity 62, as described in this disclosure. The piston 58 may be linearly movable within an interior 74 of a cylinder 76 of the ram 54. The piston 58 may be movable up to or beyond an upper end 64 of the ram 54. The volume of casting material that can be contained within the cylinder 76 can be the same or substantially the same as the volume of the mold cavity 62. In other instances, the volume of casting material that can be contained within the cylinder 76 may be less than the volume of the mold cavity 62.
In some instances, the mold 52 and/or the ram 54 may be made from a metal, such as stainless steel. In other instances, the mold 52 and/or the ram 54 may be constructed of another metal. In yet other examples, the mold 52 and/or ram 54 may be made from a non-metallic material, such as sand, which may insulate the molten alloy until solidification via the cooling mold 56 occurs. If the mold 52 and/or the ram 54 are constructed of a non-metallic material, they may be encased by a supporting mechanism such as a metal housing or fixture. The mold 52 and the ram 54 may be either made of the same or different materials.
The casting apparatus 50 may also include a cooling mold 56 that may rest or be secured atop the mold 52. The cooling mold 56 may also be referred to as a chill mold, a cooling block, a cooling member, or the like. The cooling mold 56 may include a coolant passage 66 for receiving a coolant and allowing the coolant to flow within the cooling mold 56. In some instances, the coolant passage 66 may extend from a cooling mold inlet 68 to a pair of cooling mold outlets 70, 72. As shown in FIG. 2, the portion of the coolant passage 66 extending directly from the inlet 68 may be larger than the portion of the coolant passage 66 extending directly from either outlet 70, 72. In other embodiments, however, dimensions of the coolant passage 66 (e.g., internal width or diameter) may vary, or the coolant passage 66 may have a constant width or diameter throughout the cooling mold 56. Additionally, although FIG. 2 shows a single inlet 68 and two outlets 70, 72, any number of inlets or outlets may be constructed in the cooling mold 56. The inlet 68 can be configured to allow a fluid such as coolant to flow into the cooling mold 56, and each outlet 70, 72 can be configured to allow the fluid to flow out of the cooling mold 56. In some instances, the cooling mold 56 may be made of a metal or may be an alloy, such as a copper alloy or steel.
In some embodiments of the casting apparatus 50, a gasket 60 or similar device may be disposed between the cooling mold 56 and the mold 52. The gasket 60 may be also be referred to as an insulation gasket 60, and may be configured to seal and insulate the casting material within the mold cavity 62 during casting. Due to its position, the gasket 60 may insulate the cooling mold 56 from the mold 52, which, as described in more detail below, may be preheated prior to casting. The gasket 60 may be annular such that the underside 78 of the cooling mold 56 is exposed to the mold cavity 62. Thus, an annular gasket 60 may be disposed between the cooling mold 56 and the mold 52, but not between the cooling mold 56 and the mold cavity 62, such that casting material in the mold cavity 62 may be in contact with the underside 78 of the cooling mold 56. In some instances, the contact between the casting material within the mold cavity 62 and the cooling mold 56 may be direct physical contact and/or thermal contact, as described in more detail below.
FIG. 3 illustrates a magnified schematic view of a portion 82 of one of the compressor wheels 46, 48 of FIG. 1. The portion 82 may be a surface portion of one of the compressor wheels 46, 48 or a portion in a depth direction showing various depths of the material forming one of the compressor wheels 46, 48. The portion 82 includes a number of precipitates 84 formed by precipitation occurring after a cooling and solidification process, described in more detail below.
The process of precipitation may also be referred to as precipitation hardening. Precipitates 84 may be formed in the alloy casting material during an aging process. The precipitates 84 may be located within the cast component (e.g. the compressor wheel) and harden the component by preventing and/or obstructing the movement of irregularities (e.g. dislocations) within the crystal structure of the alloy.
The precipitates 84 may be referred to as nanometer-sized precipitates having a distance 300 representing a width or diameter of an individual precipitate 84. In some instances, the distance 300 may be between about 1 and 50 nm. The distance 300 may be substantially the same or vary slightly for each precipitate 84 of the compressor wheel. In some examples, the distance 300 may differ among the multiple precipitates 84 of the compressor wheel due to variations in shape among the precipitates 84. Although the precipitates 84 are shown in FIG. 3 as being circular, the precipitates 84 may actually have various, irregular shapes.
FIG. 3 also shows distances 400 and 500 between precipitates 84. Distance 400 may represent the distance between any one pair of precipitates, while distance 500 may represent the distance between any different pair of precipitates. The distances 400 and 500 may represent the distances between any precipitates in the portion 82, or in the any of the material forming one of the compressor wheels 46, 48. In some instances, the distances 400 and 500 between two pairs of precipitates may be substantially the same, having a value of between about 2 and 40 nm. In one exemplary embodiment, the distances 400, 500 may be about 25 nm. In other instances, the distances 400 and 500 may differ. When the distances 400, 500 are substantially the same throughout one of the compressor wheels 46, 48, the precipitates 84 may be referred to as being uniformly distributed throughout the compressor wheels 46, 48. When the distances, such as the distances 400, 500, between precipitates 84 vary throughout one of the compressor wheels 46, 48, the precipitates 84 may be referred to as being non-uniformly or randomly distributed throughout the compressor wheels 46, 48.
FIG. 3 shows only a portion 82 of one of the compressor wheels 46, 48, and additional precipitates 84 may be arranged in a similar fashion in other portions or throughout the material forming the entire structure of the compressor wheels 46, 48. Furthermore, the values for the distances 300, 400, 500 are exemplary only. Distances 300, 400, 500 may be greater than or less than the values described herein.
An exemplary method of manufacturing a compressor wheel using the casting apparatus 50 shown in FIG. 2 will now be described. The chemistry of the casting material, which may also be referred to as melt stock, an alloy, a molten alloy, an alloy material, an alloy casting material, or the like, may include one or more of the following: copper, magnesium, zinc, nickel, iron, scandium, zirconium, titanium, aluminum, manganese, chrome, lithium, and silicon. For example, the alloy may include about 1 to 4 wt % copper, 0 to 3 wt % magnesium, 0 to 7 wt % zinc, 0 to 2 wt % nickel, 0 to 2 wt % iron, at least one of the following: up to about 2 wt % scandium, 0 to 2 wt % zirconium, and 0 to 1 wt % titanium, with the balance of the alloy being aluminum. Other alloy materials may also be used. In some instances, various elements such as strontium and sodium may also be used in the casting material and may be referred to as modifying elements or microstructure modifiers. The scandium, zirconium, and titanium may each be referred to herein as an added alloying element, added alloying material, added material, or the like. In one instance, the alloy may be an aluminum-scandium alloy including up to about 5 wt % scandium. In another instance, an aluminum-scandium alloy may include up to about 2 wt % scandium. As used herein, “wt %” indicates a given element's percentage of the total weight of the alloy. The alloy may be melted and held at a temperature for a period of time. In one instance, the alloy may be held at about 750° C. for about thirty minutes, at which point the temperature may be lowered to about 730° C. before the alloy is ready to be introduced into the mold 52.
At a time either before or after the alloy is being melted, or during the melting of the alloy, one or more of the mold 52, the ram 54, and the cooling mold 56 can be prepared for casting. The mold 52 and/or the ram 54 may be preheated by one or more heating elements (not shown). Various types of heating elements may be used. For example, the heating element may be one or more internal passages formed within the mold 52 and/or the ram 54 through which a heated fluid (e.g. oil) may flow. The internal passages may have a variety of cross-sections (e.g. circular cross-sections) and may be arranged in any fashion within the mold 52 and/or ram 54. For instance, the internal passages may be a plurality of linear passages extending through the mold 52 and/or ram 54, or the internal passages may one or more curved or helical passages within the mold 52 and/or ram 54. In other examples, the heating element may be an induction coil or electrical resistive heating element disposed on the outside of the mold 52 and/or the ram 54. In one instance, the heating element may preheat the mold 52 and/or ram 54 to a temperature of about 200° C. prior to casting.
To prepare the cooling mold 56 for casting, a coolant can be introduced into the coolant passage 66 via the inlet 68 to flow in a direction 200 towards the outlets 70, 72. In some instances, the inlet 68 may serve as an outlet and the outlets 70, 72 may serve as inlets such that the coolant flow direction 200 can be reversed.
After the molds 52 and 56 are prepared, pressure casting may begin. Pressure casting may also be referred to as pressurized casting, and may encompass processes such as squeeze casting. To begin casting the compressor wheel, the piston 58 may advance within the cylinder 76 toward the mold cavity 62 in a direction 100 to pressurize the casting material, which, as described herein, may be an aluminum-scandium alloy. In some instances, the piston 58 may move in the direction 100 until the piston 58 reaches the upper end 64 of the ram 74. As the piston 58 moves in the direction 100, the alloy can be pressurized and introduced into the mold 52, specifically, into the mold cavity 62. The general flow of the alloy (i.e. the casting material) into the mold cavity 62 may be represented by arrow 51 in FIG. 2. As the piston 58 moves in the direction 100, the alloy fills the mold cavity 62, first from the a bottom portion of the mold (near the upper end 64 of the ram 54) then to the top of the mold (near the underside 78 of the cooling mold 56), as shown in FIG. 2. During casting, the pressure may be greater than about 1 MPa (about 0.145 ksi). In some instances, the pressure may be between about 10 and 100 MPa (about 1.45 and 14.5 ksi). The pressure may vary depending on, e.g., the geometry of the component being cast, which can determine the shape of the mold cavity 62.
After the mold cavity 62 is filled with the alloy, the pressure may no longer be applied. In some instances, the pressure may continue to be applied after the mold cavity 62 is filled with the alloy for a period of time until solidification of the alloy completes, which is described in more detail below, and/or until a temperature of the compressor wheel, also referred to as the casting temperature, reaches about 300° C. In some instances, the period of time after casting during which the pressure may continue to be applied can be between about 1 and 10 seconds, or between about 3 and 5 seconds.
After the mold cavity is substantially or entirely filled with the aluminum-scandium alloy casting material, solidification may take place to form a solid component, such as a compressor wheel, also referred to as a casting. Solidification may occur when the mold cavity 62 is filled such that the aluminum-scandium alloy contacts (e.g. directly, physically contacts) the underside 78 of the cooling mold 56. In one example, solidification may begin when the casting material first physically contacts the underside 78 of the cooling mold 56. In other instances, solidification may begin when the casting material is introduced into the mold cavity 62; however, most of the solidification may not take place until the casting material physically contacts the underside 78 of the cooling mold 56 having coolant flowing therethrough. Unless specified, “contact” may refer to direct or physical contact, or thermal contact. Once the mold cavity 62 is filled and the alloy contacts the underside 78 of the cooling mold 56, heat may be transferred directly from the alloy to the mold, causing the alloy to cool and solidify to form a solid solution aluminum-scandium alloy. Thus, the cooling mold 56 can draw out the heat from the casting material disposed within the mold cavity 62. The solid solution aluminum-scandium alloy may also be referred to herein as solid solution, a solid solution alloy, a solid solution casting, or the like. In the example of manufacturing a compressor wheel, cooling and solidification may occur with a back-disk of the compressor wheel being the portion of the alloy in physical contact with the underside 78 of the cooling mold 56. Solidification during the casting method described herein may preserve at least some of the amount of scandium within the molten alloy. In some examples, the disclosed solidification process may preserve all or substantially all of the scandium in solid solution within the casting material. For instance, where scandium makes up about 0.2 wt % of the casting material when the material is first introduced into the mold 52, scandium may still make up about 0.2 wt % of the casting material after solidification with about 0.2 wt % of the scandium in solid solution in the solidified casting.
When solidification is complete, the mold 52 may be opened and the compressor wheel can be removed from the mold cavity 62. If the mold 52 is a retractable mold composed of multiple pieces, one or more pieces of the mold 52 may be removed to allow for removal of the compressor wheel from the mold 52. If the mold 52 is a single piece, the mold 52 may be broken open to allow for removal of the compressor wheel.
After casting, once the compressor wheel is completely cooled, the compressor wheel may be aged at a temperature, which may be referred to as an aging temperature, for a period of time. In some instances, the aging temperature may be between about 200° C. and 400° C. (e.g. about 300° C.), and the aging time may be between about 1 and 24 hours (e.g., between about 2 and 8 hours). Prior to aging the compressor wheel, the compressor wheel may be pre-aged at a temperature for a period of time. The pre-aging temperature may be lower than the aging temperature, and the pre-aging time may be longer than the aging time. For example, the pre-aging temperature and time may be about 150° C. and about 20 hours, respectively.
During the aging process, the precipitates 84 may be formed within the casting. Specifically, Al₃Sc nanoscale or nanometer-sized precipitates may be formed. In some instances, the precipitates 84 may be non-uniformly or randomly distributed nanometer-sized precipitates 84, as shown in and discussed with respect to FIG. 3. In other instances, the precipitates 84 may be uniformly distributed in a portion, such as the portion 82, or throughout the entire compressor wheel 46, 48.
The precipitates 84 may be formed as a result of preserving the amount of scandium in solid solution during solidification. For example, the final amount of scandium in solid solution after solidification may be between about 50 and 100% (e.g., about 80 or 90%), of the initial amount of scandium in the casting material before solidification. In some instances, excess scandium can be initially provided in the casting material to achieve a desired final amount of scandium in solid solution during and after solidification. For example, to achieve 0.2 wt % scandium in solid solution after solidification, an initial amount of scandium greater than 0.2 wt % can be provided in the casting material. The amount of scandium initially provided in the casting material may be slightly greater than the desired final amount of scandium in solid solution, or the amount of scandium initially in the casting material may be substantially greater than the desired final amount of scandium. For instance, to achieve a greater amount of scandium in solid solution after solidification, e.g., between about 1 and 5 wt % scandium, the amount of scandium initially in the casting material may be substantially greater than between about 1 and 5 wt % scandium. On the other hand, to achieve a lesser amount of scandium in solid solution after solidification, e.g. about 0.2 wt % scandium, the amount of scandium initially in the casting material may be slightly greater than or substantially equal to about 0.2 wt % scandium. An initial amount of scandium may be considered “slightly greater” than the final amount if after solidification there is between about 0% and 30% less scandium in solid solution than in the initial casting material before solidification. An initial amount of scandium may be considered “substantially greater” than the final amount if after solidification there is between about 30% and 95% less scandium in solid solution than in the initial casting material before solidification. Furthermore, the amount of scandium initially in the casting material being slightly greater than or substantially equal to the amount of scandium in solid solution after solidification may be referred to herein as preserving a “substantial amount” of scandium, or another alloying element. In some instances, the amount of scandium preserved can be all or substantially all of the scandium initially in the casting material.
As described herein, during solidification the alloy may be rapidly cooled, or quenched, within the mold cavity 62 by the cooling mold 56 to preserve at least some of the amount of scandium initially in the casting material. The cooling rate applied to the alloy, which may be a predetermined cooling rate, may be sufficient to keep the scandium in solid solution in the casting material. For example, the cooling rate may be between about 5° and 200° C./second (between about 41° F. and 392° F./second). In one instance, the cooling rate may be about 100° C./second (about 212° F./second). In another instance, the cooling rate may be about 40° C./second (about 104° F./second). The cooling rate may also be referred to herein as the “solidification rate” because the cooling rate may determine the length of time required to solidify the molten alloy within the mold 52 to form the compressor wheel. Rapidly cooling the alloy may cause the alloy to solidify directly from a given temperature (e.g. a liquidus temperature), such that an amount of the scandium remains in solid solution in the casting material. For example, after solidification, scandium may make up about 0.2 wt % or more of the casting material by rapidly cooling the alloy as described herein. Because scandium is preserved in solid solution in the casting material, during the aging process precipitates, specifically Al₃Sc nanometer-sized precipitates, can be formed in the compressor wheel material. For example, aging a compressor wheel cast according to the method described herein at about 300° C. for about 2 hours can use the amount of scandium preserved in solid solution during solidification to produce a plurality of Al₃Sc nanometer-sized precipitates. In some instances, the amount of precipitates formed may be substantially the same as the amount of scandium in the casting material before and/or after solidification (e.g. about 0.2 wt %).

INDUSTRIAL APPLICABILITY

The above-described method and apparatus, while being described with respect to a compressor wheel of a turbocharger in an internal combustion engine, can be used generally in applications or industries (e.g. the automotive, gas turbine, or aerospace industries) involving components requiring high temperature and/or stress resistance. Additionally, the above-described method and apparatus can be used in applications or industries requiring lightweight components.
The method and apparatus of the present disclosure can provide a viable alternative to titanium engine components such as compressor wheels. In particular, the present disclosure can enable effective utilization of an alloying element such as scandium in the manufacture of aluminum-scandium alloy compressor wheels. As described herein, during manufacturing the alloy can be rapidly cooled by the cooling mold 56 configured to have a coolant flowing therethrough. This rapid cooling can cause solidification of the alloy to form the compressor wheel casting within the mold 52. The high cooling rate can preserve an amount of scandium in solid solution in the casting material, so that during the aging process, many nanometer-sized precipitates 84 (e.g. Al₃Sc precipitates) can be formed within the casting. For example, based on the disclosed method, scandium may make up about 0.2 wt % or more of the casting.
Due to the formation of many precipitates 84 within the casting, the compressor wheel can have high temperature and/or stress properties to enable the aluminum-scandium alloy compressor wheel to withstand high operating temperatures and stresses of an internal combustion engine. The formation of precipitates can prevent dislocation moving, and in doing so may increase the strength (e.g. the tensile strength and/or the yield strength) of the compressor wheel and decrease its malleability. In some instances, the aluminum-scandium alloy compressor wheel may withstand operating temperatures of about 260-300° C., and in some cases greater than about 300° C. Additionally, the formed compressor wheel may have a tensile strength of greater than or equal to about 250 MPa (about 36.25 ksi) to meet the high stress requirements.
Pressurized casting can facilitate rapid cooling, which may help to entrap alloying elements in solid solution, and thus allow for the formation of precipitates 84 within the compressor wheel during the subsequent aging process. During manufacturing, air gaps may exist between one or more sides of the mold 52 and/or the underside 78 of the cooling mold 56. The pressurized casting process can reduce the size of, or altogether eliminate, the air gaps. Reduction in size and/or elimination of the air gaps can improve heat transfer between the alloy casting material and the molds 52, 56, which can facilitate rapid cooling of the casting material and the eventual formation during the aging process of nanometer-sized precipitates 84 therein. For example, pressure casting may increase the heat transfer coefficient by causing direct physical contact between the compressor wheel being cast and the underside 78 of the cooling mold 56, thereby improving heat transfer from the compressor wheel to the cooling mold 56.
The pressure casting process described herein, which may include preheating the mold 52 and/or ram 54, may also help to avoid premature solidification of the alloy casting material within the mold 52. As described herein, the casting material may not contact the underside 78 of the cooling mold 56, and therefore may not be substantially cooled and solidified, until the mold cavity 62 is completely filled with the casting material. Moreover, the mold 52 and/or ram 54 may be preheated to help prevent early solidification of the casting material. In addition to the pressure casting process itself, the arrangement of the mold 52, the cooling mold 56, and the ram 54 may allow for the mold cavity 62 to be filled with casting material from the bottom portion (i.e. near the upper end 64 of the ram 54) to the top portion (i.e. near the underside 78 of the cooling mold 56). Thus, the arrangement can prohibit contact between the casting material and the underside 78 of the cooling mold 56 until the mold cavity 62 is filled, thereby helping to prevent premature solidification of the alloy casting material. In some instances, pressure casting may also reduce porosity of the casting material and thus eliminate other porosity reducing processes, such as hot isostatic processing, which may reduce the formation of nanometer sized precipitates (e.g. Al₃Sc) and lose some or all strengthening benefits from alloying elements. Additionally, forming the mold 56 of a thermally conductive alloy, such as copper or stainless steel, may further facilitate heat transfer from the casting material to the mold 56.
Using an aluminum-scandium alloy to form a turbocharger component such as a compressor wheel may also allow for cost savings when compared to another alloy, such as titanium. Additionally, an aluminum-scandium alloy compressor wheel formed by the process described herein may be lightweight, so as to reduce inertia of a turbocharger rotor, and thus increase the turbocharger response and performance. Compared to titanium, aluminum alloys may be about 40% lighter than typical titanium alloys. Therefore, providing an aluminum-scandium compressor wheel may increase engine transient response and reduce turbo-lag, while also improving fuel efficiency during engine operation.
When the manufacturing method described herein is used to cast a compressor wheel or other component potentially having a complex geometry, the mold 52 may be formed as a retractable, multiple-piece mold having a plurality of separable parts. These separable parts may be referred to as segments, modules, or the like. Providing a retractable mold 52 may allow for the component to be easily removed from the mold 52 after casting.
The compressor wheel of the present disclosure may be used in various turbocharger systems. Although FIG. 1 shows a multiple stage turbocharger system, the compressor wheel of the present disclosure may be used in a single stage turbocharger system. Furthermore, the compressor wheel of the present disclosure may be used in a first stage of a compressor and/or in one or more later stage compressors. Moreover, although the disclosed method and apparatus may refer to compressor wheels, the method and apparatus may be applicable to components other than compressor wheels. For example, the disclosed method and apparatus may be applicable to other turbocharger or internal combustion engine components such as turbine wheels, cylinder heads, piston heads, or the like. In addition, the method and apparatus may be applied to a variety of other internal combustion engine components, or to components used in various other industries and applications. Also, although the disclosed method and apparatus may refer to using scandium as an added material to form an aluminum-scandium alloy, the method and apparatus may be applicable to added materials other than scandium, such as zirconium and titanium. Furthermore, with regard to the mold 52, although the material forming the mold 52 may be stainless steel, other alloys (e.g. copper alloy) may be used depending on the geometry of the component being cast.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed apparatus and method for manufacturing a turbocharger component. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed apparatus and method. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.

Claims

What is claimed is:

1. A method of pressure casting a turbocharger component for an internal combustion engine, the method comprising:

heating an aluminum-scandium alloy to form a molten casting material including up to about 5 wt % scandium that is fully dissolved in the molten casting material;

introducing the molten casting material into a cavity of a mold from a bottom of the mold toward a top of the mold while applying a pressure to the molten casting material with a movable portion of a ram positioned in contact with the bottom of the mold;

solidifying the molten casting material by cooling the casting material as it comes into contact with a cooling member positioned on the top of the mold, wherein a coolant is pumped through coolant passages formed in the cooling member in order to cool the casting material at a cooling rate such that the solidifying preserves at least 70% of an original amount of the scandium in the aluminum-scandium alloy in solid solution in the casting material;

removing the solidified casting material from the mold; and

forming scandium precipitates within the casting material by aging the casting material at an aging temperature.

2. The method of claim 1, wherein the cooling rate is between about 5° C. per second and 200° C. per second.

3. The method of claim 1, wherein the aluminum-scandium alloy comprises:

1 to 4 wt % copper;

0 to 3 wt % magnesium;

0 to 7 wt % zinc;

0 to 2 wt % nickel;

0 to 2 wt % iron; and at least one of the following alloying elements:

up to about 2 wt % scandium;

0 to 2 wt % zirconium; and

0 to 1 wt % titanium, with the balance of the alloy being aluminum.

4. The method of claim 3, wherein the aluminum-scandium alloy includes about 0.2 wt % scandium as the at least one alloying element.

5. The method of claim 1, wherein the pressure is applied to the molten casting material during and after the molten casting material is introduced into the mold and until the material solidifies.

6. The method of claim 1, wherein the scandium precipitates are nanometer-sized precipitates randomly distributed throughout the turbocharger component.

7. The method of claim 1, wherein the scandium precipitates are nanometer-sized precipitates evenly distributed throughout the turbocharger component.

8. The method of claim 1, wherein a pressure of between 10 and 100 MPa is applied to the molten casting material by the movable portion of the ram.

9. The method of claim 1, wherein the aging temperature is between 200° C. and 400° C.

10. The method of claim 1, wherein the mold is pre-heated to 200° C. before introducing the molten casting material into the mold cavity.

11. The method of claim 1, wherein the scandium precipitates are formed by aging the casting material at 300° C. for about 2 hours.

12. The method of claim 1, wherein a coolant is pumped through coolant passages of the coolant member in directions both perpendicular to and parallel to the top of the mold.

13. The method of claim 1, wherein the turbocharger component is a compressor wheel.

14. A method of casting a turbocharger component for an internal combustion engine, the method comprising:

introducing the molten casting material into a cavity of a mold from a bottom of the mold toward a top of the mold;

solidifying the molten casting material by cooling the casting material as it comes into contact with a cooling member positioned on the top of the mold, wherein a coolant is pumped through coolant passages formed in the cooling member in order to cool the casting material at a cooling rate such that the solidifying preserves at least 70% of an original amount of the scandium in the aluminum-scandium alloy in solid solution in the casting material; and

removing the solidified casting material from the mold.

15. The method of claim 14, wherein the cooling rate is between about 5° C. per second and 200° C. per second.

16. The method of claim 14, wherein the aluminum-scandium alloy comprises:

1 to 4 wt % copper;

0 to 3 wt % magnesium;

0 to 7 wt % zinc;

0 to 2 wt % nickel;

0 to 2 wt % iron; and at least one of the following alloying elements:

up to about 2 wt % scandium;

0 to 2 wt % zirconium; and

0 to 1 wt % titanium, with the balance of the alloy being aluminum.

17. The method of claim 16, wherein the aluminum-scandium alloy includes about 0.2 wt % scandium as the at least one alloying element.

18. The method of claim 14, wherein the scandium precipitates are nanometer-sized precipitates randomly distributed throughout the turbocharger component.

19. A method of casting a component, the method comprising:

heating an aluminum alloy to form a molten casting material including up to about 5 wt % of an alloying element that is fully dissolved in the molten casting material;

solidifying the molten casting material by cooling the casting material as it comes into contact with a cooling member positioned on the top of the mold, wherein a coolant is pumped through coolant passages formed in the cooling member in order to cool the casting material at a cooling rate such that the solidifying preserves at least 70% of an original amount of the alloying element in the aluminum alloy in solid solution in the casting material;

removing the solidified casting material from the mold; and

forming precipitates of the alloying element within the casting material by aging the casting material at an aging temperature.

20. The method of claim 19, wherein the cooling rate is between about 5° C. per second and 200° C. per second.