WO2023287981A1

WO2023287981A1 - Powder metal composition with aluminum nitride mmc

Info

Publication number: WO2023287981A1
Application number: PCT/US2022/037130
Authority: WO
Inventors: Donald Paul Bishop; Richard L. Hexemer, Jr.; Ian W. Donaldson
Original assignee: Gkn Sinter Metals, Llc
Priority date: 2021-07-15
Filing date: 2022-07-14
Publication date: 2023-01-19
Also published as: CA3224244A1; CN117651781A; DE112022003569T5

Abstract

A powder metal composition comprising an aluminum (Al) powder metal, an aluminum-copper (Al-Cu) powder metal, a magnesium (Mg) powder metal, a tin ( Sn) powder metal, an aluminum-silicon (Al-Si) powder metal, and aluminum nitride (AIN) as a metal-matrix composite additive. In at least some forms, the aluminum (Al) powder metal includes a portion which is fine aluminum powder metal. This powder metal composition is compressible to form a green powder metal compact which may be sintered to form a sintered part which has a composition and properties approximating that of a 6061 aluminum alloy product.

Description

POWDER METAL COMPOSITION WITH ALUMINUM NITRIDE MMC

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit of the filing date of United States Provisional Patent Application No. 63/222,240 entitled "Powder Metal Composition With Aluminum Nitride MMC" filed on July 15, 2021, which is hereby incorporated by reference for all purposes as if set forth in its entirety herein.

STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT [0002] Not applicable.

FIELD OF THE INVENTION

[0003] This disclosure relates to powder metallurgy formulations and sintered components made therefrom. In particular, this disclosure relates to an aluminum alloy powder composition including aluminum nitride (AIN) metal-matrix composite (MMC) additions.

BACKGROUND

[0004] The 6061 aluminum alloy is a precipitation-hardened aluminum alloy containing magnesium (Mg) and silicon (Si) as the main alloying elements. It exhibits good mechanical properties and weldability along with excellent corrosion resistance. Due to this combination of properties, it has become one of the most widely used aluminum alloys. Aluminum 6061 has a wide range of applications including in the automotive and marine sectors. As used herein, the 6061 aluminum alloy composition should be understood to mean, by mass percent, between 95.85% to 98.56% aluminum, 0.8% to 1.2% magnesium, 0.40% to 0.8% silicon, 0.0% to 0.7% iron, 0.15% to 0.40% copper, 0.04% to 0.35% chromium, 0.0% to 0.25% zinc, 0.0% to 0.25% titanium, and 0.0% to 0.15% manganese with the remainder being no more than 0.05% each in an amount of no more than 0.15% total.

[ 0005 ] There are a large number of ways of forming metal components and powder metal or "PM" processes represent one class of production techniques for forming metal components. Powder metallurgy generally involves producing or obtaining a powdery metal material, compacting this powder metal material in a tool and die set to form a green compact or preform having a geometry approximating the desired end product, and then sintering the green compact to cause the powder metal particles to diffuse into to one another and to density into a much more mechanically strong body. Powder metallurgy is well-suited for producing parts in large volumes and can offer the benefits of low scrap costs and the ability to produce components which may not require subsequent machining after being formed.

[ 0006 ] Although this is just general overview of the powder metal production processes, what can be appreciated from this description is that much of the powder metal processes can typically happen in the solid state or with only a limited amount of liquid being formed during the sintering process. However, this also highlights some of the challenges in using powder metal processes as, with sintering being a diffusion- dependent process, the resultant microstructure and porosity is a function of the powder formulation and processing conditions. Thus, attempting to convert a cast alloy to a powder metal formulation can present challenges in creating both a comparable microstructure and providing comparable mechanical properties. [ 0007 ] Returning now to the 6061 aluminum alloy, the powder metal alloy comparative equivalent to 6061 is available commercially, for example, as Alumix® 321 which can be obtained from ECKA Granules (Feurth, Germany). An example chemical composition of Alumix® 321 can have 1.31 wt% Mg, 0.5 wt% Si,

0.32 wt% Cu, 0.10 wt% Fe, 0.01 wt% Bi, 0.03 wt% Sn, and 0.01 wt% V with the balance being aluminum. While not truly within the 6061 specification, it can be seen that this powder formulation is roughly comparable. As with the 6061 aluminum alloy, the main alloying elements in this system are magnesium and silicon and these two elements are the basis of the heat treatment of this system. They form an intermetallic phase of MgSi which improves the mechanical properties. Copper is also responsible for improving mechanical properties. Iron exists as an impurity and forms different intermetallic phases which can affect corrosion and mechanical properties, while Sn, V, and Bi were added to improve the sintering response of the powder.

SUMMARY

[0008] Disclosed herein is an improved powder metal composition comparable to a 6061 aluminum alloy which further includes an aluminum nitride (AIN) MMC additive instead of MMC additions such as AIO or SiC, which are comparably more traditional. By altering the properties and morphology of the powder metal composition and including AIN as an MMC additive, a composition is provided which can have good corrosion resistance, moderate to high strength, high ductility, and good electrical and thermal properties. It can also offer improved wear resistance and further is believed to produce only minimal tool wear during compaction and sizing compared to other comparable compositions with MMC additives such as AI2O3 or SiC. [0009] According to one aspect, a powder metal includes an aluminum (Al) powder metal, an aluminum-copper (Al-Cu) powder metal, a magnesium (Mg) powder metal, a tin (Sn) powder metal, an aluminum-silicon (Al-Si) powder metal, and aluminum nitride (AIN) as a metal-matrix composite additive. [ 0010 ] In some forms, at least a portion of the aluminum (Al) powder metal may be a fine aluminum powder metal. For example, the portion of the aluminum (Al) powder metal that is the fine aluminum (Al) powder metal may be 10 wt% of the elemental aluminum (Al) powder metal in total. However, in other forms, it is contemplated that the amount of fine aluminum powder may be in a range of 5 wt% to 15 wt% of the total elemental aluminum (Al) powder metal or, more broadly 5 wt% to 30 wt% of the total elemental aluminum (Al) powder metal. In some forms, the majority of the aluminum (Al) powder metal may be an ECKA- Bahrain aluminum powder metal or comparable aluminum powder metal having +60 / -250 mesh and the fine aluminum powder metal may be an ECKA Al EF2 / fine EEG aluminum powder or comparable powder.

[ 0011 ] In some forms, a total aluminum content provided by the aluminum (Al) power metal, the aluminum-copper (Al-Cu) powder metal, and the aluminum-silicon (Al-Si) powder metal may be 95.2 wt% of the powder metal composition; the total copper content provided by the aluminum-copper (Al-Cu) powder metal may be 0.29 wt%; the total magnesium content provided by the magnesium (Mg) powder metal may be 1.07 wt%; the total tin content provided by the tin (Sn) powder metal may be 0.49 wt%; and the total silicon content provided by the aluminum-silicon (Al-Si) powder metal may be 0.49 wt%; the aluminum nitride (AIN) may be 0.98% wt%; the powder metal composition may further include a flow aid and the flow aid may be 0.02 wt%; and the powder metal composition may further includes a lubricant and the lubricant may be 1.46 wt%. All of these weight percentages are based on the total weight of the powder metal formulation including the various powder metals, the flow aid, and the lubricant. [0012] In some forms, the aluminum (Al) powder metal may be a majority of +60/-250 mesh powder and a portion of the aluminum (Al) powder metal may be fine aluminum powder metal, the aluminum-copper (Al-Cu) powder metal may be a -325 mesh, the magnesium (Mg) powder metal may be a -200 mesh, the tin (Sn) powder metal may be a -325 mesh, and the aluminum-silicon (Al- Si) powder metal may be -325 mesh.

[0013] In some forms, the aluminum-copper (Al-Cu) powder metal may be a 50Al-50Cu powder metal. The 50A1-50CU powder metal may be atomized and crushed.

[0014] In some forms, the aluminum-silicon (Al-Si) powder metal may be an 88Al-12Si powder metal.

[0015] In some forms, the powder metal composition may further include a lubricant, and, in some forms, the powder metal composition may further include a flow aid such as, for example, a fumed SiCp.

[0016] In some forms, the powder metal composition may have even distribution of the various powders which can include an even distribution of the fine aluminum powder. This even distribution may be achieved by mixing the powders in a high intensity mixer.

[0017] In some forms, the aluminum nitride may have a specific surface area of less than or equal to 2.0 m²/g and may have a particle size distribution of D 10% of between 0.4 and 1.4 pm, D 50% of between 6 and 10 pm, and D 90% of between 17 and 35 pm. This is similar to a grade AT aluminum nitride.

[0018] In some forms, the aluminum nitride may have a specific surface area of between 1.8 and 3.8 m²/g and may have a particle size distribution of D 10% of between 0.2 and 0.6 pm,

D 50% of between 1 and 3 pm, and D 90% of between 5 and 10 pm. This is similar to a grade BT aluminum nitride which is generally finer than a grade AT aluminum nitride. [0019] In some forms, the aluminum nitride may have a hexagonal crystal structure and may be single phase.

[0020] In some forms, the powder metal composition may have a flow rate of between 2.8 and 3.0 g/s.

[0021] In some forms, the powder metal composition may have an apparent density of 1.21 g/cc.

[0022] According to another aspect, a green compact may be formed from the powder metal composition (according to any of the forms described above or herein) by compaction of the powder metal composition such as in a tool and die set using uniaxial compaction. According to still another aspect, a sintered powder metal component formed from this green compact by sintering the green compact.

[0023] These and still other advantages of the invention will be apparent from the detailed description and drawings. What follows is merely a description of some preferred embodiments of the present invention. To assess the full scope of the invention the claims should be looked to as these preferred embodiments are not intended to be the only embodiments within the scope of the claims.

DETAILED DESCRIPTION

[0024] A powder metal composition is disclosed here which is comparable to those of a 6061 aluminum alloy. Below, a specific exemplary powder metal composition is disclosed and some variations to that powder metal will be discussed.

[0025] According to one specific composition formulation, the powder metal composition is as follows in Table I below: TABLE I

[0026] Table I illustrates the percentages of just the metallic component of that powder metal formulation, while Table II further includes the addition of non-metallic powder metal additions including aluminum nitride (AIN) as metal-matrix composite (MMC) additives, flow aid, and lubricant. The composition of Table I is more reflective of the alloy composition of the metallic composition, while Table II data is normalized to further take into account approximately 2.5 wt% that are further additions and very slightly impact the overall weight percentages of the actual powder metal composition blend.

TABLE II

[0027] Notably, rather than having a single type of aluminum powder, it can be seen that the aluminum composition has a composition which includes, by approximately 10% by weight of the elemental aluminum powder metal portion, fine aluminum powder metal. However, it is contemplated that this could be a different percentage of fines, for example, from between 5% to 15% by weight or 5% to 30% by weight of the aluminum powder metal. As yet another point of variance, it is contemplated that the percentage of the aluminum coming from the ECKA A1 EF2, Fine EEG A1 powder, could be instead provided by equally increasing the amount of ECKA-Bahrain, +60 / -250. For example, the ECKA-Bahrain, +60 / -250 could be 93.63 wt% (normalized, which is equal to 82.2% plus 9.13% from the separate powders). [0028] Moreover, that the total aluminum comes from a variety of sources. Beyond just the elemental aluminum powder metals, aluminum is provided as part of the 50A1-50CU powder metal and as part of the 88Al-12Si powder metal (collectively adding about another 4 wt% aluminum in this fashion) which also provides some of the alloying elements. The alloying and morphology in those instances, however, can be to obtain the final desired microstructure as well as to provide a chemistry which is conducive to sintering in the manner desired. That is to say, elemental copper and silicon have much higher melting and effective sintering temperatures than aluminum and, further by alloying these elements with aluminum, the starting powders have a different structure with some amount of copper and silicon already alloyed with the aluminum.

[0029] It should be appreciated that the particular mesh sizes and the powder morphology can impact the sinterability and the final microstructure and properties of the sintered part coming from this powder metal formulation. So, the mesh sizes and powder morphologies should be established to provide suitable resultant properties and densities. While the disclosed powders are workable, some variation to the powders may also be workable without deviating from the scope and spirit of the disclosed formulation.

[0030] For example, some of the alloying elements might be provided in slightly different forms than those found in the tables above. Likewise, the alloying composition might be somewhat different than that disclosed. For example, in the case of tin, tin at 0.5 wt% is believed optimal, but a range of 0.1 wt% to 1.0 wt% tin is believed to offer improved densification during sintering. It is also contemplated that some variation may be made to other elements from the exemplary composition above. For example, it is contemplated that the amount of silicon could be in a range of 0.40 to 0.8 percent by weight of the total metallic powder metal composition and the amount of magnesium could be in a range of 0.8 to 1.2 percent by weight of the total metallic powder metal composition as these are roughly comparable to the amounts of silicon and magnesium in a 6061 composition. Similarly, some amount range of copper (0.04 to 0.35 wt%) might also be workable in the powder composition and the 0.30 wt% copper of the exemplary composition falls within this range.

[0031] The lubricant can be a wax such as Licowax® (available from Clariant of Muttenz, Switzerland), which can help maintain the compacted green part together by keeping the powder particles together and can further help in the removal of the green part during ejection from the tool and die set after compaction. The lubricant is typically burnt off during the sintering process in the preheating zone.

[0032] The flow aid can be added to improve fill and particle packing. In the exemplary composition, the flow aid is a fumed silica (SiCk).

[0033] With respect to the aluminum nitride (AIN) MMC additions, it is contemplated those aluminum nitride additions might be, for example Grade AT aluminum nitride (an agglomerated powder with broader particle size distribution) or Grade BT aluminum nitride (which has a comparably fine particle size and is a deagglomerated powder). Both grades can be used in the disclosed powder metal formulation with the difference being in response to processing and properties.

[0034] Both grades AT and BT aluminum nitride have a hexagonal crystal structure and are single phase. For the sake of chemically characterizing these aluminum nitride additions, as mass fractions both Grade AT and BT have a minimum of 32.0%

N, a maximum of 0.15% C, and a maximum of 0.05% Fe. However, Grade AT has a maximum of 1.3% 0, while Grade BT has a maximum of 1.5% 0. The Grade AT has a specific surface area of less than or equal to 2.0 m²/g while the Grade BT has between 1.8 and 3.8 m²/g. The particle size distribution of the two different grades is illustrated in Table III below:

Table III

[0035] Aluminum nitride as the MMC additive can improve the wear, ductility and thermal conductivity properties of the powder metal formulation. In comparison to more traditional MMC additives such as AI₂O₃ or SiC, there is minimal tool wear.

[0036] The various powder metals, aluminum nitride, flow aid and lubricant are blended together during powder preparation, preferably in a high intensity mixer, in order to get an even distribution of the various particles, especially the fine particles, throughout the overall powder metal composition blend and to avoid segregation.

[0037] In terms of powder response prior to compaction, the flow rate of this powder was measured at 2.9 g/s on average and the apparent density was measured at 1.21 g/cc on average.

[0038] This powder metal composition was compacted into bars having a density of 2.50 g/cc. The green strength of the compacted green bars was 8,382 kPa on average. In terms of sintering response, over a set of three bars the average mass of the bars decreased 1.41% (which roughly corresponds to lubricant loss during sintering), the average sintered density was 2.69 g/cc, and, in terms of dimensional shrinkage resulting from densification, the average height dimensional change was a 3.93% decrease, the average width change was a 2.65% decrease, and the average length change was a 2.11% decrease. The average T1 hardness taken from 18 different readings was 58.1 HRE (with all data points falling between 55.4 HRE and 60.1 HRE) and the average laser flash analysis of thermal diffusivity was 72.3 (recorded at room temperature).

[ 0039 ] T1 tensile testing indicated across a group of five tests, an average Young's Modulus of 83.2 GPA, an average yield stress of 83 MPa, and average ultimate tensile strength (UTS) of 193 MPa, and an average elongation of 13.9%. Of this preliminary tensile data, it is worth noting that there was fairly high variation in the Young's Modulus results, with those results ranging from 54.2 GPa to 135 GPa, while the average yield stress was within about 5 MPa of the minimum and maximum measured amounts, the average UTS was within about 3 MPa of the minimum and maximum measured amounts, and the average elongation was within about 2% of the minimum and maximum measured amounts. [ 0040 ] In comparison wrought 6061 with a T1 treatment profile would have a UTS of 210 MPa, a yield stress of 110 MPa), and elongation of 16%. Thus, although sintered powder metal, this disclosed powder metal formulation has near-wrought properties. [ 0041 ] Further assessment of a powder metal having a similar composition was performed on samples subjected to a T8 heat treatment (further detailed below) and with and without further inclusion of 2 vol% AIN (targeted). This composition was made from powder metals having the chemistry of Table IV below. TABLE IV

[0042] Samples made from this powder composition will hereafter be referred to as "PM6061" or "PM6061-A1N" in the examples below, with the "-A1N" designation being used to indicate samples mad from this composition but with 2 volume percent targeted aluminum nitride MMC additions. It will be appreciated that these compositions are not necessarily to the 6061 specification, but rather are targeted to be comparably performing powder metal compositions to wrought 6061.

[0043] For each of PM6061 and PM6061-A1N, fifty transverse rupture strength (TRS) bars, five Charpys, and five Falex pucks (50mm OD x 12 mm OAL) were compacted from each blend targeting a green density of 2.50 g/cc and then sintered. Initially, fifteen TRS bars from each composition were sintered under different thermal profiles and the dimensional change, mass change, average hardness, and sintered density of all TRS bars to identify optimal conditions (as, furnace to furnace, optimal conditions could vary). All remaining TRS bars along with the Charpys, and Falex pucks were then sintered under conditions found to be optimal during the initial sintering runs and sample testing of the fifteen TRS bars.

[0044] For those samples prepared under optimal sintering conditions, those samples were then measured for their as- sintered dimensional change, mass change, average hardness, and sintered density of five of the TRS bars from each of PM6061 and PM6061-A1N .

[ 0045 ] Those as-sintered dimensional change, mass change, average hardness, and sintered density results are found in Tables V and VI below, along with comparative T8 hardness:

TABLE V

TABLE VI

[ 0046 ] All remaining samples were processed into the T8 heat treatment (target 2-3% RIH), in which the T8 heat treatment included solutionizing at 530°C (two hours at temperature), quenching, sizing 2% reduction in AOL, and aging at 160°C for 18 hours. For the T8 samples in Table VI above, the average hardness is provided for samples subjected to this T8 heat treatment.

[ 0047 ] Charpys were machined into threaded-end tensiles and then the Yield Strength, Ultimate Tensile Strength, Young's modulus, and total elongation to fracture were measured for five specimens for PM 6061 and PM6061-A1N, which can be found in Table VII below: TABLE VII

Again, these are mechanical properties of samples made from the powder composition and subjected to the T8 heat treatment.

[0048] Samples of each T8-process composition were also subjected to a 3-point bending fatigue staircase, which are results are provided in Table VIII, below:

TABLE VIII

[0049] Additionally, thermal diffusivity was measured at room temperature via laser flash analysis on each twice in which the specimens were machined from T8 TRS bars. These results are found below in table IX:

TABLE IX

[0050] It should be appreciated that various other modifications and variations to the preferred embodiments can be made within the spirit and scope of the invention. Therefore, the invention should not be limited to the described embodiments. To ascertain the full scope of the invention, the following claims should be referenced.

Claims

CLAIMS What is claimed is:

1. A powder metal composition comprising: aluminum (Al) powder metal; aluminum-copper (Al-Cu) powder metal; magnesium (Mg) powder metal; tin (Sn) powder metal; aluminum-silicon (Al-Si) powder metal; and aluminum nitride (AIN) as a metal-matrix composite additive.

2. The powder metal composition of claim 1, wherein at least a portion of the aluminum (Al) powder metal is a fine aluminum powder metal.

3. The powder metal composition of claim 2, wherein the portion of the aluminum (Al) powder metal that is the fine aluminum powder metal is 10 wt% of the aluminum (Al) powder metal.

4. The powder metal composition of claim 2, wherein the portion of the aluminum (Al) powder metal that is the fine aluminum powder metal is in a range of 5 to 30 wt% of the aluminum (Al) powder metal.

5. The powder metal composition of claim 1: wherein a total aluminum content provided by the aluminum (Al) power metal, the aluminum-copper (Al-Cu) powder metal, and the aluminum-silicon (Al-Si) powder metal is 95.2 wt% of the powder metal composition; wherein the total copper content provided by the aluminum- copper (Al-Cu) powder metal is 0.29 wt%; wherein the total magnesium content provided by the magnesium (Mg) powder metal is 1.07 wt%; wherein the total tin content provided by the tin (Sn) powder metal is 0.49 wt%; wherein the total silicon content provided by the aluminum- silicon (Al-Si) powder metal is 0.49 wt%; wherein the aluminum nitride (AIN) is 0.98% wt%; wherein the powder metal composition further includes a flow aid and the flow aid is 0.02 wt%; and wherein the powder metal composition further includes a lubricant and the lubricant is 1.46 wt%.

6. The powder metal composition of claim 1: wherein the aluminum (Al) powder metal is a majority of

+60/-250 mesh powder and a portion of the aluminum (Al) powder metal is fine aluminum powder metal; wherein the aluminum-copper (Al-Cu) powder metal is a -325 mesh; wherein the magnesium (Mg) powder metal is a -200 mesh; wherein the tin (Sn) powder metal is a -325 mesh; and wherein the aluminum-silicon (Al-Si) powder metal is -325 mesh.

7. The powder metal composition of claim 1, wherein the aluminum-copper (Al-Cu) powder metal is a 50A1-50CU powder metal.

8. The powder metal composition of claim 7, wherein the 50A1-50CU powder metal is atomized and crushed.

9. The powder metal composition of claim 1, wherein the aluminum-silicon (Al-Si) powder metal is an 88Al-12Si powder metal.

10. The powder metal composition of claim 1, wherein the powder metal composition further includes a lubricant.

11. The powder metal composition of claim 1, wherein the powder metal composition further includes a flow aid.

12. The powder metal composition of claim 11, wherein the flow aid is fumed SiCp.

13. The powder metal composition of claim 1, wherein the powder metal composition has even distribution of the various powders.

14. The powder metal composition of claim 1, wherein the aluminum nitride (AIN) has a specific surface area of less than or equal to 2.0 m²/g and has a particle size distribution of D 10% of between 0.4 and 1.4 pm, D 50% of between 6 and 10 pm, and D 90% of between 17 and 35 pm.

15. The powder metal composition of claim 1, wherein the aluminum nitride (AIN) has a specific surface area of between 1.8 and 3.8 m²/g and has a particle size distribution of D 10% of between 0.2 and 0.6 pm, D 50% of between 1 and 3 pm, and D 90% of between 5 and 10 pm.

16. The powder metal composition of claim 1, wherein the aluminum nitride (AIN) has a hexagonal crystal structure and is single phase.

17. The powder metal composition of claim 1, wherein the powder metal composition has a flow rate of between 2.8 and 3.0 g/s.

18. The powder metal composition of claim 1, wherein the powder metal composition has an apparent density of 1.21 g/cc.

19. A green compact formed from the powder metal composition of claim 1.

20. A sintered powder metal component formed from a green compact of claim 19.