Powder metal alloy composition for sintered powder metal inserts for aluminum castings

Abstract

A powder metal alloy composition is used to produce a sintered powder metal insert for casting into an aluminum casting. The powder metal alloy composition includes iron powder metal base, copper, and carbon such that the copper is 3.5 wt% or greater of the powder metal alloy composition, and the carbon content is 0.1 to 1.0 wt% of the powder metal alloy composition. After the powder metal alloy composition is compacted and sintered to form a sintered powder metal insert, the sintered powder metal insert has a copper gradient that provides a higher concentration of copper at the surface of the sintered powder metal insert than at the center of the sintered powder metal insert grains. The higher concentration of copper at the surface of the insert is capable of forming a strong metallurgical bond with the aluminum casting during casting.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 592,814, filed November 30, 2017, entitled “Powder Metal Alloy Composition for Sintered Powder Metal Inserts for Aluminum Castings,” which is incorporated herein by reference in its entirety for all purposes.

[0003] Statement of federally funded research or development

[0004] none. Invention Field

[0005] This disclosure relates to an improved iron-containing powder metal alloy composition for forming sintered powder metal inserts for casting into aluminum castings. Background Technology

[0006] In a piston engine, the camshaft controls valves, and the crankshaft is connected to the piston via connecting rods to convert linear motion into rotational motion that can then be effectively utilized (e.g., driving a vehicle). This shaft is held and supported by bearings that allow it to rotate during engine operation. During engine operation, these bearings and the shaft connected to them are subjected to considerable engine loads, thus requiring appropriate structural support.

[0007] While bearing supports are necessary to support the engine shaft, several engine design considerations (such as weight reduction for improved fuel economy and lower material costs) have led to many modern engine blocks being cast from aluminum or its alloys rather than iron or its alloys. While using aluminum helps reduce weight, using an aluminum-based engine block instead of an iron-based one typically requires additional support for the area housing the bearings.

[0008] For cast aluminum engine blocks, support inserts, often made of cast iron, are typically cast into the aluminum engine block. These inserts provide increased strength and rigidity in the bearing support area when the camshaft is engaged and applies engine loads. As a concrete example, for the main bearing insert (“MBI”), the insert may be formed of cast iron, and then an aluminum alloy (typically A380 aluminum alloy) is cast around the cast iron insert. During casting, the insert is mechanically locked in place, and the casting material solidifies around the geometrically shaped portions of the insert to hold it in place. Summary of the Invention

[0009] This paper discloses an improved powder metal composition for forming bearing inserts, which can be cast into aluminum or aluminum alloys in engine production. While conventional cast iron inserts rely on mechanical interlocking of the cast aluminum or aluminum alloy within the insert geometry, the disclosed iron-containing sintered powder metal bearing insert exhibits a higher copper content on its surface. This increased copper content on the surface of the sintered powder metal insert enables metallurgical bonding upon contact with the aluminum casting material. To achieve this copper increase at the insert surface for metallurgical bonding during casting, the powder metal formulation of the iron-containing insert can be carefully designed to create a copper gradient during powder metal insert manufacturing, which can be further utilized during casting.

[0010] According to one aspect, a powder metal alloy composition is disclosed for producing sintered powder metal inserts for casting into aluminum castings. The powder metal alloy composition comprises an iron powder metal substrate, copper added to the iron powder metal substrate, and carbon, such that copper accounts for 3.5% by weight or more of the powder metal alloy composition, and the carbon content accounts for 0.1 to 1.0% by weight of the powder metal alloy composition. It is contemplated that copper can be provided as pre-alloyed copper in the iron powder metal substrate and / or mixed copper-containing powder metals. After the powder metal alloy composition is compacted and sintered to form a sintered powder metal insert, the sintered powder metal insert has a copper gradient that provides a higher copper concentration on the surface of the sintered powder metal insert than at the grain center of the sintered powder metal insert.

[0011] In some forms of the composition, the mixed copper-containing powder metal can be elemental copper powder metal. This mixed copper-containing powder metal can also be non-ferrous (meaning it cannot be described as pre-alloyed in the case of an iron-containing composition).

[0012] In some forms of the composition, copper present in the powder metal alloy composition may be partially pre-alloyed in an iron powder metal substrate and may also be partially present in a mixed copper-containing powder metal mixed with the iron powder metal substrate. In this form, the amount of pre-alloyed copper in the iron powder metal substrate may be 3% by weight of the powder metal alloy composition, and the copper in the mixed copper-containing powder metal may exceed 0.5% by weight of the powder metal alloy composition. In other forms, it is generally expected that the amount of pre-alloyed copper in the iron powder metal substrate may be 1%, 2%, or 3% by weight of the powder metal alloy composition (and the remaining copper is provided by the mixed copper-containing powder).

[0013] In some forms of the composition, the copper present in the powdered metal alloy composition may comprise at least 3.5% by weight of copper supplied in the form of a mixed copper-containing powdered metal. It is possible that all copper added to the iron powdered metal substrate is derived from the mixed copper-containing powdered metal, and that no pre-alloyed copper is present in the iron powdered metal substrate.

[0014] In some forms of the composition, the iron powder metal substrate may contain, at least partially, carbon.

[0015] According to another aspect, a sintered powder metal insert for casting into aluminum castings is disclosed. The sintered powder metal insert comprises a sintered body containing any powder metal alloy composition as described herein, wherein a plurality of particles of the powder metal alloy composition are sintered together to form the sintered body. The sintered body has a copper gradient, resulting in a higher copper concentration at the surface of the sintered powder metal insert than at the grain centers of the sintered powder metal insert. When the sintered powder metal insert is cast into an aluminum casting material, this gradient and the increased copper content at the insert surface contribute to a metallurgical bond with the aluminum casting material of the aluminum casting.

[0016] In some forms of inserts, the sintered body may include: a pair of opposing ends on its lateral sides; a bearing receiving surface on a body side located between the pair of opposing ends, wherein the bearing receiving surface is adapted to receive a bearing therein; and a pair of bolt holes extending axially through the body in a direction perpendicular to the axis of the bearing receiving surface.

[0017] In some forms of inserts, the microstructure of the sintered body may include ferrite grains, pearlite grains, and discrete MnS grains.

[0018] In some forms of inserts, the microstructure of the sintered body contains free copper. In some forms, at least some of the free copper in the microstructure may be generated by adjacent iron grains reaching their copper solubility limit.

[0019] According to another aspect, a component is disclosed that includes a sintered powder metal insert as described herein and as stated above, wherein the sintered powder metal insert has been cast into an aluminum casting material, and a metallurgical bond is formed between the aluminum casting material and copper in the sintered powder metal insert.

[0020] In some forms of components, the microstructure of the metallurgical bonding region between copper and aluminum casting materials at the surface of the sintered powder metal insert may include Al-Cu α and θ phases.

[0021] In some forms of components, metallurgical bonding can be an interface layer containing aluminum and copper atoms that are mixed, diffused, or dispersed among each other.

[0022] According to another aspect, a method for forming sintered powder metal inserts and for forming castings using the inserts is disclosed. The powder metal alloy composition disclosed above and herein is compacted and sintered to form a sintered powder metal insert (wherein the powder metal alloy composition comprises an iron powder metal substrate, copper added to the iron powder metal substrate in the form of pre-alloyed copper in the iron powder metal substrate and / or a mixture of copper-containing powder metals), such that copper accounts for 3.5% by weight or more of the powder metal alloy composition, and carbon accounts for 0.1-1.0% by weight of the powder metal alloy composition. The sintered powder metal insert has a copper gradient that provides a higher copper concentration on the surface of the sintered powder metal insert than the copper concentration at the grain center of the sintered powder metal insert.

[0023] In some forms of the method, the method further includes casting a sintered powder metal insert into an aluminum casting material to form an aluminum casting having a cast sintered powder metal insert, wherein copper on the surface of the powder metal insert forms a metallurgical bond with the aluminum casting material.

[0024] These and other advantages of the invention will be understood from the following detailed description and accompanying drawings. The following description pertains only to some preferred embodiments of the invention. In order to assess the full scope of the invention, it should be understood from the claims that these preferred embodiments are not intended to be the only embodiments within the scope of the claims. Attached Figure Description

[0025] Figure 1 This is a side view of a casting component containing sintered powder metal inserts.

[0026] Figure 2A-2C It is a microstructure of 3% copper-ferrous microstructure, in which, Figure 2A , 2B The pre-alloying amounts of copper in 2C are 1 wt%, 2 wt%, and 3 wt%, respectively, and any remaining copper reaches 3 wt% in the form of mixed copper.

[0027] Figure 2D This shows a small amount of copper in a 2 wt% mixed sample containing 1 wt% pre-alloyed copper.

[0028] Figure 3A Here is an exemplary micrograph of the sample, showing the path along which the copper concentration was determined, where the path passes through multiple grains.

[0029] Figure 3B Displays a copper mapping line scan for 3% by weight of pre-alloyed copper.

[0030] Figure 3C Displays a copper mapping line scan for 3% by weight of mixed copper.

[0031] Figure 4 It is an aluminum-copper phase diagram. Detailed Explanation

[0032] This paper discloses an iron-containing powdered metal composition that provides metallurgical bonding when the powdered metal of the composition is compacted and sintered to provide an insert subsequently cast into aluminum or an aluminum alloy. By adding a sufficient amount of copper to the iron-containing powdered metal in a specific manner to create a microstructure with a high copper gradient (or even free copper) content on the powder surface of the compacted and sintered assembly, the resulting insert can be cast into and react with the aluminum-based material to form a metallurgical bond. Therefore, unlike conventional inserts that can rely solely on mechanical bonding (e.g., macroscopic geometric bonding where the cast material solidifies around the insert), this chemical change can form an even stronger metallurgical bond.

[0033] Figure 1 A side view of an exemplary component 100 is shown, which can be formed by casting an insert 102 into an aluminum material 104. As shown, the component 100 may be a half-bearing bracket for a bearing of a camshaft or crankshaft in an engine. It thus has a bearing receiving surface 106 in the form of a radially inwardly facing semi-cylindrical surface, which can mate with a component having another radially inwardly facing semi-cylindrical surface to capture the bearing therebetween, wherein the bearing may support a camshaft or crankshaft. The insert 102 also has a generally planar mating surface 108 positioned to contact other components and has two threaded holes 110 or bolt holes extending along a direction perpendicular to the central axis of the bearing receiving surface 106. When the component 100 and the mating surfaces of the mating components are placed together, these threaded holes 110 can be used to help secure the component to bolts or other fasteners.

[0034] It should also be noted that the insert 102 has an outer periphery 112, which has a geometry that helps to mechanically secure the insert 104 in the aluminum material when the aluminum material 104 is cast around it.

[0035] Inserts such as insert 102 can be formed from powder metal by compacting a powder metal composition (typically containing multiple individual particles and a certain amount of wax / lubricant) to form a preform with an insert-like rough geometry (typically in the case of uniaxial compression in a tool and die), followed by sintering the preform to fuse the individual particles together while reducing porosity. Compaction and sintering may occur separately and sequentially, or they may occur simultaneously (e.g., as part of a powder forging step). During sintering, as the preform is sintered to form insert 102, the component densifies during sintering, and as the process continues, the pore size decreases and closes. After the assembly is sintered, additional finishing or machining steps can be performed, such as drilling or opening holes in hole 110 or precision finishing of the dimensions of bearing receiving surface 106.

[0036] To form the component 100 shown, an insert 102 is placed in a specific configuration, and aluminum material, typically an aluminum alloy (e.g., A380, having 3% to 4% copper, 0.1% magnesium, a maximum of 1.3% iron, a maximum of 0.35% tin, a maximum of 0.5% nickel, 3% zinc, 0.5% manganese, 7.5% to 9.5% silicon, and other metals totaling no more than 0.5% by weight, with the balance being aluminum), is mentioned above because A380 is a well-known die-cast aluminum alloy. However, A380 is representative, not limiting, of aluminum casting materials that can be used.

[0037] In particular, in order to enable reactive metallurgical bonding between the sintered powder metal insert 102 and the aluminum material 104 during casting, the powder metal alloy composition used to form the insert 102 can be modified. It has been found that by adding an appropriate amount of copper to the ferrous powder metal composition used to manufacture the insert, a copper gradient can be formed, resulting in a copper-rich surface of the insert 102 (where the copper content in the ferrous grains is high, or where copper exists in the form of free copper). This can promote the reactive formation leading to a metallurgical bond between the insert 102 and the aluminum material 104, and this metallurgical bond has a stronger connection than the conventional mechanical bond that occurs during casting.

[0038] To promote metallurgical bonding between insert 102 and aluminum material 104, the copper content in the iron-containing powder metal is increased to an amount equal to or greater than 3.5% by weight. This 3.5% by weight of copper exceeds the solid solubility limit of copper in iron grains and results in a copper gradient, wherein a higher copper content is formed on the surface of the sintered powder metal particles, and even free copper may be present.

[0039] Therefore, the powder metal alloy composition used to produce sintered powder metal inserts for casting into aluminum castings can comprise multiple powder metal particles containing an iron powder metal substrate (i.e., grains of iron powder metal, which may include some or all of copper and / or carbon), copper at a content of 3.5% by weight or more of the composition (pre-alloyed and / or mixed with the substrate powder), and carbon at a content of 0.1% to 1.0% by weight of the composition to increase additional strength. Although it has now been found that carbon is not necessarily part of the iron powder metal substrate, it is foreseeable that, in most cases, carbon will be present in the iron powder metal substrate. When the powder metal alloy composition is compacted and sintered to form a sintered powder metal insert 102, the sintered powder metal insert 102 has a copper gradient that provides a higher copper concentration on the surface of the sintered powder metal insert 102 than at the grain center of the sintered powder metal insert.

[0040] Copper is expected to be added to the iron powder metal substrate in the form of pre-alloyed copper in the iron powder metal substrate and / or in the form of mixed copper-containing powder metal (which can simply be elemental copper powder metal mixed with the iron powder metal substrate). Thus, in some forms, copper present in the powder metal alloy composition can be partially pre-alloyed in the iron powder metal substrate and can also be partially present in the mixed copper-containing powder metal mixed with the iron powder metal substrate. In one form, 100% of the added copper up to the 3.5 wt% threshold may all come from the mixed copper-containing powder metal, and pre-alloyed copper is not present at all in the iron powder metal substrate. It is foreseeable that, unlike mixed copper, at least some amount of copper can advantageously form a copper-rich powder surface because mixed copper—unlike pre-alloyed copper—can lead to an increase in the copper gradient (from the following...) Figure 3B and 3C The structural results will be obvious.

[0041] For example, in some forms, the amount of pre-alloyed copper in the iron powder metal substrate may be 3% by weight of the powder metal alloy composition, and the amount of copper mixed in the copper-containing powder metal may exceed 0.5% by weight of the powder metal alloy composition. Similarly, it is anticipated that copper, accounting for 1%, 2%, or 3% by weight of the powder metal alloy composition, may be pre-alloyed in the iron powder metal substrate, and that an additional amount of mixed copper is present to reach a total threshold of 3.5% by weight (e.g., for 1% by weight of pre-alloyed copper, at least 2.5% by weight of mixed copper is present).

[0042] Now for reference Figure 2A-2CAfter production forging tests, the microstructures of 1 wt% pre-alloyed copper / 2 wt% mixed copper, 2 wt% pre-alloyed copper / 1 wt% mixed copper, and 3 wt% pre-alloyed copper were observed. Similarly, for clarity, the pre-alloyed copper was pre-alloyed in iron or iron-containing powdered metal. It can be seen that all 3% copper samples exhibited ferrite, pearlite, and discrete MnS phases.

[0043] refer to Figure 2D Free copper is also present in the microstructure.

[0044] Now go to Figures 3A-3C Copper mapping was performed on some of the prepared samples to show the copper gradient and copper distribution on the grains. Figure 3A An example path for the line scan is shown (performed using a JEOL JSM-6460LV SEM with EDX). The line scan was performed at a distance sufficient to traverse multiple preceding particles to demonstrate relative homogeneity. Sampling was performed in 7-micron increments.

[0045] Figure 3B The copper mapping results for a 3% by weight pre-alloyed sample are shown, while Figure 3C The copper mapping results for a 3 wt% mixed copper sample are shown. Relatively uniform copper distribution can be seen in the pre-alloyed sample, while distinct peaks and valleys can be seen in the mixed copper sample (representing the copper-rich surface of the grain and the copper-free region at the grain center, respectively).

[0046] It should be noted that incorporating copper into an iron powder metal substrate that already contains 3% by weight of pre-alloyed copper will result in a high-copper-bonded copper profile at the surface. This is because the solubility limit of copper in iron is approximately 4% by weight, and the incorporated copper will not diffuse significantly into the pre-alloyed iron grains.

[0047] Finally, turn Figure 4 The diagram shows the aluminum-copper phase diagram. During casting, when molten aluminum (or aluminum alloy) comes into contact with copper, some copper on the surface dissolves into the aluminum. Given the casting and cooling rates, it is expected that not all copper will dissolve into the molten aluminum. This will create some localized areas of molten aluminum with a low percentage of copper. As the liquid Al-Cu melt cools, an α phase will form, and depending on the kinetics and the composition of the dissolved copper, it is likely that some α phase plus a θ phase will form. This creates a localized region between the aluminum casting material and the copper, along which a metallurgical bond forms.

[0048] It should be understood that various other modifications and changes can be made to these preferred embodiments within the spirit and scope of the invention. Therefore, the invention should not be limited to the described embodiments. For determining the full scope of the invention, reference should be made to the appended claims.

Claims

1. A sintered powder metal insert for casting into an aluminum casting, the sintered powder metal insert comprising: A sintered body containing a powdered metal alloy composition, wherein a plurality of particles of the powdered metal alloy composition are sintered together to form the sintered body, wherein the powdered metal alloy composition comprises: Iron powder metal substrate; Copper is added to the iron powder metal substrate in the form of pre-alloyed copper in the iron powder metal substrate and mixed copper-containing powder metal, such that the copper accounts for 3.5% by weight or more of the powder metal alloy composition, wherein the copper present in the powder metal alloy composition is partially pre-alloyed in the iron powder metal substrate and partially pre-alloyed in the mixed copper-containing powder metal mixed with the iron powder metal substrate, and the pre-alloyed copper in the iron powder metal substrate accounts for 1 to 3% by weight of the powder metal alloy composition; and Carbon, in an amount ranging from 0.1% to 1.0% by weight of the powdered metal alloy composition. In this process, after the powder metal alloy composition is compacted and sintered to form a sintered powder metal insert, the sintered powder metal insert has a copper gradient that provides a higher copper concentration on the surface of the sintered powder metal insert than at the grain center of the sintered powder metal insert, in order to help form a metallurgical bond with the aluminum casting material when the sintered powder metal insert is cast into the aluminum casting material.

2. The sintered powder metal insert as described in claim 1, wherein, The sintered body includes: A pair of opposite ends on its lateral side; A bearing receiving surface located on one side of a sintered body between a pair of opposite ends, the bearing receiving surface being adapted to accommodate a bearing therein; and A pair of bolt holes extend axially through the sintered body, perpendicular to the axis of the bearing receiving surface.

3. The sintered powder metal insert as described in claim 1, wherein the microstructure of the sintered body comprises ferrite grains, pearlite grains, and discrete MnS.

4. The sintered powder metal insert as described in claim 1, wherein, The microstructure of the sintered body includes free copper.

5. The sintered powder metal insert as described in claim 4, wherein, At least some of the free copper in the microstructure is generated by adjacent iron grains reaching their copper solubility limit.

6. The sintered powder metal insert as described in claim 1, wherein, Mixed copper-containing powder metals are elemental copper powder metals.

7. The sintered powder metal insert as described in claim 1, wherein, The amount of pre-alloyed copper in the iron powder metal substrate accounts for 3% by weight of the powder metal alloy composition, and the amount of copper in the mixed copper powder metal exceeds 0.5% by weight of the powder metal alloy composition.

8. The sintered powder metal insert as described in claim 1, wherein, The copper present in the powdered metal alloy composition comprises at least 3.5% by weight of copper provided in the form of mixed copper-containing powdered metal.

9. The powder metal alloy composition according to claim 1, wherein, The iron powder metal substrate contains at least some carbon.

10. A component comprising the sintered powder metal insert as described in claim 1, wherein, The sintered powder metal insert has been cast into the aluminum casting material, and a metallurgical bond has been formed between the aluminum casting material and the copper in the sintered powder metal insert.

11. The component as claimed in claim 10, wherein, The microstructure of the metallurgical bonding region between copper and aluminum casting materials on the surface of the sintered powder metal insert includes Al-Cu α and θ phases.

12. The component as claimed in claim 10, wherein, Metallurgical bonding is an interfacial layer containing aluminum and copper atoms mixed together.

13. The component as claimed in claim 10, wherein, Aluminum castings are made of aluminum alloy.

14. A method comprising: Sintered powder metal inserts are formed by compacting and sintering powder metal alloy compositions.

15. The method of claim 14, further comprising the step of: casting a sintered powder metal insert into an aluminum casting material to form an aluminum casting having the sintered powder metal insert inside, wherein copper at the surface of the powder metal insert forms a metallurgical bond with the aluminum casting material.

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