Powder Metal Composition With Aluminum Nitride MMC

Abstract

A powder metal composition comprising an aluminum (Al) powder metal, an aluminum-copper (AlCu) powder metal, a magnesium (Mg) powder metal, a tin (Sn) powder metal, an aluminum-silicon (AlSi) powder metal, and aluminum nitride (AlN) 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.

Claims

1. A powder metal composition comprising: aluminum (Al) powder metal; aluminum-copper (AlCu) powder metal; magnesium (Mg) powder metal; tin (Sn) powder metal; aluminum-silicon (AlSi) powder metal; and aluminum nitride (AlN) 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 (AlCu) powder metal, and the aluminum-silicon (AlSi) powder metal is 95.2 wt % of the powder metal composition; wherein the total copper content provided by the aluminum-copper (AlCu) 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 (AlSi) powder metal is 0.49 wt %; wherein the aluminum nitride (AlN) 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 (AlCu) 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 (AlSi) powder metal is 325 mesh.

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

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

9. The powder metal composition of claim 1, wherein the aluminum-silicon (AlSi) 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 SiO.sub.2.

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 (AlN) has a specific surface area of less than or equal to 2.0 m.sup.2/g and has a particle size distribution of D 10% of between 0.4 and 1.4 m, D 50% of between 6 and 10 m, and D 90% of between 17 and 35 m.

15. The powder metal composition of claim 1, wherein the aluminum nitride (AlN) has a specific surface area of between 1.8 and 3.8 m.sup.2/g and has a particle size distribution of D 10% of between 0.2 and 0.6 m, D 50% of between 1 and 3 m, and D 90% of between 5 and 10 m.

16. The powder metal composition of claim 1, wherein the aluminum nitride (AlN) 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.

Description

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-US-00001 TABLE I Wt % Raw Material Element (nominal) Al (ECKA-Bahrain, +60/250 mesh) Al(90%) 84.27% Al (ECKA Al EF2, Fine EEG Al powder) Al(10%) 9.36% 50Al50Cu (ECKA-Velden, fine 325 mesh, Cu 0.30% atomized and crushed) Al 0.30% Mg (200 mesh, gas atomized) Mg 1.10% Sn (325 mesh) Sn 0.50% 88Al12Si (ECKA-Veldon, fine 325 mesh) Si 0.50% Al 3.67% Total (Powder Metal Only) 100%

[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 (AlN) 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-US-00002 TABLE II Wt % Raw Material Element (normalized) Al (ECKA-Bahrain, +60/250) Al(90%) 82.20% Al (ECKA Al EF2, Fine EEG Al powder) Al(10%) 9.13% 50Al50Cu (ECKA-Velden, fine 325 mesh, Cu 0.29% atomized and crushed) Al 0.29% Mg (200 mesh, gas atomized) Mg 1.07% Sn (325 mesh) Sn 0.49% 88Al12Si (ECKA-Veldon, fine 325 mesh) Si 0.49% Al 3.58% AlN Powder (BT Grade AlN 0.98% Flow Aid 0.02% Lubricant 1.46% Total (Powder Metal + MMC + Flow Aid + 100% Lubricant)

[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 Al EF2, Fine EEG Al 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 50Al-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 (SiO.sub.2).

[0033] With respect to the aluminum nitride (AlN) 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% O, while Grade BT has a maximum of 1.5% O. The Grade AT has a specific surface area of less than or equal to 2.0 m.sup.2/g while the Grade BT has between 1.8 and 3.8 m.sup.2/g. The particle size distribution of the two different grades is illustrated in Table III below:

TABLE-US-00003 TABLE III Particle Size Distribution Grade AT Grade BT D 10% 0.4-1.4 m 0.2-0.6 m D 50% 6-10 m 1-3 m D 90% 17-35 m 5-10 m

[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 Al.sub.2O.sub.3 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 % AlN (targeted). This composition was made from powder metals having the chemistry of Table IV below.

TABLE-US-00004 TABLE IV Powder Amount Ecka Al (250/+60 micron) 936.3 g Ecka Al12Si (45 micron) 41.7 g Elemental Mg (China) 11.0 g Ecka Elemental Sn (20 micron) 5.0 g Ecka Al50Cu Master Alloy 6.0 g Lico Wax C 15.2 g

[0042] Samples made from this powder composition will hereafter be referred to as PM6061 or PM6061-AlN in the examples below, with the -AlN 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-AlN, fifty transverse rupture strength (TRS) bars, five Charpys, and five Falex pucks (50 mm OD12 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-AlN.

[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-US-00005 TABLE V Mass Sintered OAL Width Length Powder Change Density Change Change Change Composition (%) (g/cc) (%) (%) (%) PM 6061 1.46 2.70 4.41 2.21 1.67 PM 6061-AlN 1.38 2.70 3.77 2.54 2.04

TABLE-US-00006 TABLE VI Powder Composition T1 Hardness (HRE) T8 Hardness (HRE) PM 6061 56.2 96.6 PM 6061-AlN 54.1 96.9

[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-AlN, which can be found in Table VII below:

TABLE-US-00007 TABLE VII Powder E Yield UTS Elongation Composition (GPa) (MPa) (MPa) (%) PM 6061 66.8 300 341 7.0 PM 6061-AlN 66.7 303 335 3.7
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-US-00008 TABLE VIII Powder Bending Fatigue Performance Composition a, 10 (MPa) a, 50 (MPa) a, 90 (MPa) PM 6061 147.7 141.7 135.7 PM 6061-AlN 151.3 140 128.7

[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-US-00009 TABLE IX Powder Composition Thermal Diffusivity (mm.sup.2/s) PM 6061 76.0 PM 6061-AlN 79.3

[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.