Powder Metallurgy Counterpart to Wrought Aluminum Alloy 6063

Abstract

A powder metal composition for a powder metal material to be compacted, sintered, and heat treated is comparable to wrought 6063 aluminum alloy. The powder metal composition consists essentially of an aluminum powder metal with no pre-alloyed alloying additions, an aluminum-silicon powder metal, an elemental magnesium powder metal, optionally an elemental tin powder metal, and optionally a ceramic addition (which is not included when calculating the weight percentages of the alloying elements). A weight percent of silicon is in a range of 0.2 to 0.6 wt % of the powder metal composition, of magnesium is in a range of 0.5 to 0.9 wt %, and of tin is in a range of 0.0 to 1.0 wt %. This powder metal is compactable to form a green compact which is further sinterable and heat treatable to provide a powder metal composition comparable to a wrought 6063 aluminum alloy and which offers exceptional thermal conductivity.

Claims

1. A powder metal composition providing a powder metal material to be compacted, sintered, and heat treated to be comparable to wrought 6063 aluminum alloy, the powder metal composition consisting essentially of: an aluminum powder metal with no pre-alloyed alloying additions apart from any inevitable non-effective trace amounts; an aluminum-silicon powder metal; an elemental magnesium powder metal; optionally an elemental tin powder metal; optionally a ceramic powder addition to provide a metal matrix composite upon sintering, which ceramic powder addition is not taken into account when calculating alloying percentages of the powder metal composition; and a lubricant wherein the weight percentages of the alloying elements are exclusive of the weight of the lubricant as the lubricant is configured to be burned off during sintering of the powder metal composition; wherein a weight percent of silicon in the powder metal composition is in a range of 0.2 to 0.6 wt % of the powder metal composition, a weight percent of magnesium in the powder metal composition is in a range of 0.5 to 0.9 wt % of the powder metal composition, and a weight percent of tin in the powder metal composition is in a range of 0.0 to 1.0 wt % of the powder metal composition.

2. The powder metal composition of claim 1, wherein: the weight percent of silicon in the powder metal composition is more narrowly in a range of 0.3 to 0.5 wt % of the powder metal composition; and the weight percent of magnesium in the powder metal composition is more narrowly in a range of 0.6 to 0.8 wt % of the powder metal composition.

3. The powder metal composition of claim 2, wherein: the weight percent of silicon in the powder metal composition is more narrowly in a range of 0.35 to 0.45 wt % of the powder metal composition; and the weight percent of magnesium in the powder metal composition is more narrowly in a range of 0.65 to 0.75 wt % of the powder metal composition.

4. The powder metal composition of claim 2, wherein: the weight percent of silicon in the powder metal composition is 0.4 wt % of the powder metal composition; and the weight percent of magnesium in the powder metal composition is 0.7 wt % of the powder metal composition.

5. The powder metal composition of claim 1, wherein the aluminum powder metal is at least 99.7% by weight aluminum.

6. The powder metal composition of claim 1, wherein the aluminum-silicon powder metal is an Al-12Si master alloy powder metal having 88 wt % aluminum and 12 wt % silicon.

7. The powder metal composition of claim 1, wherein the weight percent of tin in the powder metal composition is more narrowly in a range of 0.25 to 0.75 wt % of the powder metal composition.

8. The powder metal composition of claim 7, wherein the weight percent of tin in the powder metal composition is 0.5 wt % of the powder metal composition.

9. The powder metal composition of claim 1, wherein the ceramic powder addition is less than 15 volume percent of the powder metal.

10. The powder metal composition of claim 9 wherein the ceramic powder addition is an aluminum nitride.

11. The powder metal composition of claim 10, wherein the aluminum nitride 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 m and 1.4 m, D 50% of between 6 m and 10 m, and D 90% of between 17 m and 35 m.

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

13. The powder metal composition of claim 10, wherein the aluminum nitride (AlN) has a hexagonal crystal structure and is single phase.

14. The powder metal composition of claim 10, wherein the ceramic powder addition is silicon carbide (Sic).

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

16. A sintered powder metal component formed from the green compact of claim 15.

17. The sintered powder metal part of claim 16, wherein the powder metal part has a thermal conductivity of between 190 W/m*K and 205 W/m*K over a temperature range of 100 C. to 200 C.

18. The sintered powder metal part of claim 16, wherein the powder metal part has an ultimate tensile strength of between 100 and 140 MPa and a yield strength of between 90 and 105 MPa.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0021] FIG. 1A is a graph showing the percent of theoretical density of various samples of powder metal components compacted at 250 MPa and sintered at 20 minutes for various sintering temperatures from 610 C. to 640 C. in increments of 5 C. All sintered powder metal component samples are made from a powder metal composition of an aluminum alloy of 0.4 wt % silicon and 0.7 wt % magnesium with either 0.0 wt %, 0.25 wt %, 0.5 wt %, or 1.0 wt % tin (as indicated in the graph) with the remainder being aluminum and being made from a blend of an aluminum powder metal, an aluminum-silicon master alloy powder metal, an elemental magnesium powder metal, and an elemental tin powder metal, as well as lubricant.

[0022] FIG. 1B is a chart showing the average hardness of the various samples from FIG. 1A in the as-sintered state as a function of sintering temperature and tin content.

[0023] FIG. 1C is a graph showing the mass change percent of the various sintered samples from FIG. 1A as a function of sintering temperature and at various tin contents as indicated.

[0024] FIG. 1D is a graph showing the dimensional change percent of the various samples from FIG. 1A as a function of sintering temperature and at various tin contents as indicated.

[0025] FIG. 2A is a chart showing the effect of compaction pressure (150 MPa, 250 MPa, 350 MPa, 450 MPa, and 550 MPa) and tin content on green strength of compacts having a composition of Al-0.4Si-0.7Mg-xSn where x in xSn is one of 0.0 wt %, 0.25 wt, 0.5 wt, or 1.0 wt % tin. The horizontal line at 7500 kPa illustrates the target green strength.

[0026] FIG. 2B is graph showing the effect of compaction pressure on sintered density for samples sintered at 635 C. for 20 minutes at varied compaction pressures and tin contents.

[0027] FIG. 2C is a chart showing the effect of compaction pressure on the average hardness for a composition of Al-0.4Si-0.7Mg-xSn having various of tin weight percentages (where x in xSn is again one of 0.0 wt %, 0.25 wt %, 0.5 wt %, or 1.0 wt %).

[0028] FIG. 2D is a graph showing the effect of compaction pressure and tin content on mass change percent during sintering at 635 C. for 20 minutes.

[0029] FIG. 2E is a graph showing the effect of sintering temperature and tin content on mass change percent during sintering at 635 C. for 20 minutes.

[0030] FIG. 3A is a graph showing the effect of sintering time and tin content on density for aluminum alloy parts compacted at 350 MPa and sintered at 635 C. for the indicated durations having a composition of Al-0.4Si-0.7Mg-xSn where x in xSn is one of 0.0 wt %, 0.25 wt %, 0.5 wt %, or 1.0 wt % tin.

[0031] FIG. 3B is a chart demonstrating the effect of sintering time and tin content on average hardness for the sintered parts of FIG. 3A.

[0032] FIG. 3C is a graph showing the effect of sintering time and tin content on mass change for the sintered parts of FIG. 3A.

[0033] FIG. 3D is a graph showing the effect of sintering time and tin content on dimensional change for the sintered parts of FIG. 3A.

[0034] FIG. 4A is a graph illustrating the effect of sizing pressure on sizing reduction for aluminum alloy parts compacted at 350 MPa, sintered at 635 C. for 20 minutes, and having a composition of Al-0.4Si-0.7Mg-xSn where x in xSn is one of 0.25 wt % and 0.5 wt % tin.

[0035] FIG. 4B is a graph illustrating the effect of sizing pressure on theoretical density for the parts of FIG. 4A.

[0036] FIG. 4C is a chart illustrating the effect of sizing pressure on the average hardness for the parts of FIG. 4A.

[0037] FIG. 5A is a chart illustrating the effect of tin chemistry on Young's Modulus for aluminum alloy parts compacted at 350 MPa, sintered at 635 C. for 20 minutes, sized at 120 MPa in an unconstrained die, and having a composition of Al-0.4Si-0.7Mg-xSn where x in xSn is one of 0.0 wt %, 0.25 wt %, 0.5 wt %, and 1.0 wt % tin and further comparing these values to a wrought sample of unspecified temper.

[0038] FIG. 5B is a chart illustrating the effect of tin chemistry on ultimate tensile strength for the powder metal parts of FIG. 5A and comparing them to wrought T1 and T5 values of 6063 aluminum alloy from the literature.

[0039] FIG. 5C is a chart illustrating the effect of tin chemistry on yield strength for the powder metal parts of FIG. 5A and comparing them to wrought T1 and T5 values of 6063 aluminum alloy from the literature.

[0040] FIG. 5D is a chart illustrating the effect of tin chemistry on maximum elongation percentage for the powder metal parts of FIG. 5A and comparing them to wrought T1 and T5 values of 6063 aluminum alloy from the literature.

[0041] FIG. 6A is a chart comparing the effect of different tempers on the Young's modulus for samples of Al-0.4Si-0.7Mg-0.5Sn either sintered and sized or as subjected to a T8 heat treatment in which the parts were compacted at 350 MPa, sintered at 635 C. for 20 minutes, solutionized at 520 C. for 2 hours, sized at 120 MPa in an unconstrained die, and aged at 175 C. for 22 hours. These values are compared to wrought 6063 aluminum alloy parts subjected to a T8 heat treatment or subjected to an unspecified temper from the literature.

[0042] FIG. 6B is a chart comparing the effect of different tempers on the ultimate tensile strength for samples of FIG. 6A and again comparing them to wrought 6063 aluminum alloy parts subject to a T8, T1, or T5 treatment.

[0043] FIG. 6C is a chart comparing the effect of different tempers on the yield strength for the sintered powder metal samples of FIGS. 6A and 6B and comparing them to various wrought samples as in FIG. 6B.

[0044] FIG. 6D is a chart comparing the effect of different tempers on the maximum elongation percentage for the sintered powder metal samples of FIG. 6A and comparing them to various wrought samples of varying tempers.

[0045] FIG. 7A shows natural aging curves for Al-0.4Si-0.7Mg-xSn where x in xSn is one of 0.25 wt % or 0.5 wt % tin and in which the parts are compacted at 350 MPa and sintered at 635 C. for 20 minutes.

[0046] FIG. 7B shows a curve illustrating the T8 aging process for the 0.5 wt % tin sample of FIG. 7A in which the sample was solutionized at 520 C. for 2 hours, subject to a 3.5% sizing reduction, and artificially aged at 175 C.

[0047] FIG. 8A shows the thermal conductivity over a range of temperatures for Al-0.4Si-0.7Mg-xSn where x in xSn is one of 0.0 wt %, 0.25 wt %, 0.5 wt %, and 1.0 wt % tin and comparing these thermal conductivity values to a wrought sample of 6063 subjected to a T5 temper.

[0048] FIG. 8B illustrates thermal conductivity over a range of temperatures for Al-0.4Si-0.7Mg-0.5Sn comparing the effect of a T8 temper for this composition to just a sintered and sized component and further comparing these values to a wrought sample of 6063 subjected to a T5 or T8 temper.

[0049] FIGS. 9A and 9B provide images of as-sized surfaces (FIG. 9A) and as-ground surfaces (FIG. 9B), respectfully, of samples of Al-0.4Si-0.7Mg-0.5Sn (PM 6063, left columns) and of samples of Al-0.4Si-0.7Mg-0.5Sn plus 1 vol % AlN (PM 6063-AlN, right columns).

[0050] FIGS. 9C and 9D illustrate before and after anodized images of samples of Al-0.4Si-0.7Mg-0.5Sn (PM 6063) and of samples of Al-0.4Si-0.7Mg-0.5Sn plus 1 vol % AlN (PM 6063+1% AlN) in which the before samples are as-sized surfaces (FIG. 9C) and in which the before samples are surfaces ground with 240 grit SiC paper (FIG. 9D). Hard anodized surfaces appear blackened (two samples per material composition and surface type), while clear anodized surfaces maintained their grey appearance (one sample per material composition and surface type).

[0051] FIGS. 10A and 10B are images show the thickness and profile of the anodized layer in PM 6063 hard anodized as-sized samples and in PM 6063+1% AlN hard anodized as-sized samples, respectively.

[0052] FIGS. 10C and 10D are images show the thickness and profile of the hard anodized layer in PM 6063 ground samples and in PM 6063+1% AlN ground samples, respectively.

DETAILED DESCRIPTION

[0053] A powder metal composition is disclosed herein which offers mechanical and/or thermal properties intended to be comparable those of a wrought component fabricated from a 6063 aluminum alloy material. Below, exemplary powder metal compositions are disclosed and some variations thereto. Further various processing conditions are investigated as well as the effect of these processing conditions on mechanical and thermal properties of the resultant parts. While the alloying element additions are clearly different between the powder metal compositions and the wrought 6063 standard, certain mechanical properties and thermal properties compare favorably, which suggests that this powder metal formulation may provide a substitute for wrought 6063 in certain applications.

[0054] Powder metals were admixed in order to arrive at a base alloy chemistry of aluminum (bulk), magnesium in an amount of 0.7 wt % of the powder metal alloy composition, and of silicon in an amount of 0.4 wt % of the powder metal alloy composition. Tin was the only variable across the formulations studied and samples were prepared having no tin, 0.25 wt % tin, 0.5 wt % tin, and 1.0 wt % tin. In addition to the powder metals that were blended, a lubricant was added and, although data is not provided here, it is contemplated that ceramic powder additions might also be added to form a metal-matrix composite in some instances.

[0055] It should be appreciated that the alloying percentages described above are weight percentages of the total aluminum alloy powder metal composition including just the metal additions. To the extent that the powder metal composition includes other constituents, such as lubricant (wax and/or binder, such as for example Lico Wax C) or ceramic additions, these non-metallic constituents are not considered part of the alloying percentages. This is because, to the extent that any lubricant is present, that will be burned off during the sintering process. With respect to any ceramic powder additions, those are excluded from the weight percentage calculations insofar as those ceramic additions result in a metal-matrix composite (MMC) material and the alloying percentages of the metal characterize the metal matrix, not the total weight percent of the element in an MMC component.

[0056] To arrive at the Al-0.7Mg-0.4Si-xSn composition, the following constituents in Table I were admixed in proportions to arrive at the desired powder metal composition:

TABLE-US-00002 TABLE I Chemistry D50 Contribution Powder Used Maufacturer Method (m) Al Aluminum ECKA Granules Air 116.0 (99.7%) GmbH Atomized Si AlSi (88- ECKA Granules 32.8 12) GmbH Mg Elemental Mg Tangshen Weihao Air 31.0 Magnesium Powder Atomized Co. Sn Elemental Sn ECKA Granules Air 4.4 GmbH Atomized Lubricant LicoWax C Clariant Corporation
ECKA Granules GmbH is located in Velden, Germany; Tangshan Weihao Magnesium Powder Company Ltd. is located in Qianan City, Hebei Province, China; and Clariant Corporation is located in Louisville, Kentucky. While the exact powder amounts are not provided herein, given the powder metal ingredient list for each formulation or variant, it is trivial to work backwards to find the exact powder metal proportions combined in each case.

[0057] The lubricant addition is only a relatively small percent of the total weight of the composition powder metal composition. Conventionally, the lubricant is added in an amount of about 1.5 weight percent of the total weight of the powder metals mixed. The lubricant can be a wax such as Licowax C, 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 burned off during the sintering process in the preheating zone.

[0058] It is noted that, while magnesium and (optionally) tin are added as elemental powder metal additions, silicon is added as part of a master alloy powder having 88 wt % aluminum and 12 wt % silicon. This represents a composition reflective of the eutectoid composition of aluminum-silicon. Tin can help catalyze the densification response of powder metal alloys and investigated for this reason. So, to the avoidance of doubt in Table I, above the AlSi powder is an Al-12Si master alloy powder.

[0059] It is contemplated that the powder metal composition (or at least the metallic powder metal constituents) may include only these enumerated powder metals (Al, Al-12Si, Mg, and optionally Sn) and not include any other powder metals or alloying additions. In this respect, it is contemplated that the formulation can be a close-ended composition including exclusively these powder metals (as well as any lubricant and ceramic additions).

[0060] Furthermore, it should be appreciated that while specific powders are provided above, that some variation in sourcing may be made. Moreover, it is contemplated that in some instances the powder types could be slightly varied (for example, instead of one aluminum powder, two or more pure aluminum powder metals of varying powder size distributions could be blended).

[0061] While a target composition is provided of to arrive at the Al-0.7Mg-0.4Si-xSn in which x for Sn could be between 0.0 wt % and 1.0 wt % (and values of 0.0, 0.25, 0.5, and 1.0 for x are investigated in particular in the examples that follow), it is noted that the target compositions of one or both magnesium and silicon might also be expanded or varied to some extent. For example, the weight percent of silicon in the powder metal composition may be in a range of 0.2 to 0.6 wt % of the powder metal composition (or more narrowly in a range of 0.3 to 0.5 wt %, or more narrowly yet 0.35 to 0.45 wt %) and the weight percent of magnesium in the powder metal composition may be in a range of 0.5 to 0.9 wt % of the powder metal composition (or more narrowly in a range of 0.6 to 0.8 wt %, or more narrowly yet 0.65% to 0.75 wt %).

[0062] With respect to the aluminum powder metal, that powder metal is indicated as being 99.7 wt % aluminum in Table 1, and it is contemplated that this powder metal can be substantially only aluminum with only a minimal amount of non-effective trace elements.

[0063] Additionally, and as briefly mentioned above, it is contemplated that up to 15% by volume of ceramic powder additions can be provided to create a metal matrix composite which provides improvements in wear and strength to an as-sintered part. The ceramic additions are briefly characterized below with aluminum nitride (AlN) being primarily contemplated for addition to powder metal composition, although silicon carbide (SiC) and aluminum (Al.sub.2O.sub.3) are other ceramic additions that are contemplated as being viable additions.

[0064] 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.

[0065] 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 m.sup.2/g and 3.8 m.sup.2/g. The particle size distribution of the two different grades are illustrated in Table II below:

TABLE-US-00003 TABLE II 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

[0066] 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.

[0067] When ceramic powder additions are employed, the various powder metals, aluminum nitride or other ceramic additions, 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.

[0068] Turning now to the experimental data collected, four alloys were explored as powder metal counterparts to wrought 6063 aluminum alloy, all containing identical concentrations of magnesium and silicon and only varying in tin additions. All of the four variants were made from a blend of the powder metals in Table I above with enough Al-12Si powder metal to achieve 0.4 wt % Si in the total powder metal composition and enough elemental Mg powder metal to achieve 0.7 wt % Mg in the total powder metal composition. Approximately 1.5 wt % LicoWax C was also added. Again, the only variable in the composition was tin, and powder metal composition blends were made with no tin (0.0 wt % Sn), 0.25 wt % Sn, 0.5 wt % Sn, and 1.0 wt % Sn. For the sake of conciseness and accuracy, any experimental sample data provided in the figures and not indicated as wrought can be assumed to be aluminum with 0.4 wt % Si and 0.7 wt % Mg plus the indicated amount of tin, although the sample may be identified only by its respective tin content (optionally in combination with a varied processing condition or heat treatment).

[0069] The following method was used for alloy preparation and manufacture of powder metal samples investigated.

[0070] Initially, the starting powders were blended in the appropriate proportions using a Turbula shaker mixer. Alloying additions were added to the requisite base aluminum powder sequentially with blend times applied between each addition to ensure good blending.

[0071] Once the powder metal was prepared, transverse rupture strength (TRS) bars were die compacted as compacts (nominally 31.7 mm12.7 mm9.7 mm). Each sample was prepared from 10 g of the powder metal composition of interestagain, varied chemically only in tin contentand compressed at various compaction pressures from 150 MPa to 550 MPa.

[0072] The samples were subsequently and consistently sintered in a tube furnace in a controlled nitrogen atmosphere having multiple heating elements to allow for uniform heating fo the compacts.

[0073] Various data and studies were then performed to characterize the samples of the powder metal aluminum alloy composition as well as refine the potential processing parameters for this composition.

[0074] With reference being had to FIGS. 1A, 1B, 1C, and 1D, the effect of sintering temperature on density, hardness, mass change, and dimensional change are illustrated. In FIGS. 1A, 1B, 1C, and 1D, the samples or compacts are compacted at 250 MPa and were sintered for 20 minutes at temperatures between 610 C. and 640 C. at 5 C. increments for the various trials. As can be seen, the samples were also varied in chemistry with the samples having a composition of Al-0.7Mg-0.4Si-xSn in which x for Sn was 0.0, 0.25, 0.5, and 1.0. The findings from this comparative study of sintering temperature and tin chemistries are as follows.

[0075] First, from FIG. 1A, optimal densification begins to plateau at 630 C. for those chemistries that achieve reasonably high densities. That is to say, the three chemistries Al-0.7Mg-0.4Si-0.25Sn, Al-0.7Mg-0.4Si-0.5Sn, and Al-0.7Mg-0.4Si-1.0Sn all have densities that sinter to approximately 98% or more of theoretical densities at 630 C. or higher sintering temperatures. Only the Al-0.7Mg-0.4Si-0.0Sn (no tin added) struggled in densification, with the samples being just less than 96% of theoretical density at sintering at 640 C. for 20 minutes.

[0076] Second, from FIG. 1B, the average hardness of chemistries containing tin peak when sintered at 635 C. for 20 minutes when compared to sintering at either higher or lower temperatures for similar lengths of time.

[0077] Third, and from FIG. 1C, the mass change of the tin-containing compositions was approximately a 1.5% mass loss upon sintering at any of the temperatures between 610 C. and 640 C. This mass loss is as expected, given that lubricant is added in an amount of approximately 1.5% by weight of the total powder metal composition. The composition not containing tin did not experience this same level of lubricant burn off. While the mass change of the tin-less sample approached a 1.35% loss at the higher sintering temperatures (that is, around 640 C.), at the lower sintering temperatures (that is, around 610 C.) the mass loss was less than expected at only around a 1.15% loss.

[0078] Fourth, and with reference to FIG. 1D which shows the dimensional change, the shrinkage begins to level off or stabilize at around 630 C., which is also generally consistent with the leveling off with respect to density in FIG. 1A. It can again be seen that the tin-less composition struggles with sintering as reflected in this shrinkage data and only begins to show some amount of shrinkage at the highest temperature tested (640 C.) and even then, only shrinks about 0.7% as compared to the approximately 2.0% shrinkage of the tin-containing samples at those higher temperatures.

[0079] Across all the samples, it appears that the 0.25 wt % Sn and 0.5 wt % Sn samples provide the best results for the tested properties. While all the tin-containing samples sintered demonstrated good density and dimensional changes, there were differences in the observed average hardness. Most prominently at the higher end of the sintering temperatures investigated, the 0.25 wt % Sn and 0.5 wt % Sn samples exhibited greater average hardness than the 1.0 wt % Sn samples. So for those parts Al-0.7Mg-0.4Si-xSn that were the best sintered (that is, at 630 C. and above), some tin addition improved hardness when compared to those samples containing no tin but, based on the four chemistries tested, there was a drop off in average hardness as tin increased beyond 0.25 wt % with a modest decline between 0.25 and 0.5 wt % Sn and a continued decline from 0.5 to 1.0 wt % Sn.

[0080] Turning now to FIGS. 2A, 2B, 2C, 2D, and 2E, the effect of compaction pressure was investigated for Al-0.7Mg-0.4Si-xSn in which x for Sn was 0.0, 0.25, 0.5, and 1.0. Compaction pressures of 150 MPa, 250 MPa, 350 MPa, 450 MPa, and 550 MPa were all investigated for these powder chemistries. The findings from this investigation are as follows.

[0081] First, from FIG. 2A, it can be seen that green strength increases appreciably from 150 MPa to 250 MPa for all of the powder chemistries, and then to a lesser degree between 250 MPa and 350 MPa. Beyond that, the green strengths are all above 10,000 kPa (with the line of 7,500 kPa being the target strength).

[0082] FIG. 2B shows the effect of compaction pressure on sintered density for compacted parts that were compacted at the various compaction pressures and then subsequently sintered at 635 C. at 20 minutes. The three tin-containing samples all have consistent densities exceeding 98% of theoretical density at all pressures, and at compaction pressures above 250 MPa have densities which are above approximately 98.8% of theoretical density. The sample lacking tin (Al-0.7Mg-0.4Si-0.0Sn) or 0.0 Sn has comparably lower densities across the range of compaction pressures and only crosses 95% of theoretical density at the highest tested compaction pressure (550 MPa).

[0083] FIG. 2C shows the effect of compaction pressure on average hardness of the parts as sintered at 635 C. for 20 minutes. While the average hardness for the tin-less sample remains comparably low, the average hardness for the tin-containing compositions (the three rightmost bars in each cluster at each respective compaction pressure) are fairly consistent across the range of compaction pressures from 250 MPa to 550 MPa.

[0084] With reference to FIG. 2D, the mass change at varied compaction pressures during sintering (again, at 635 C. for 20 minutes) is generally consistent with the results from FIG. 1D. Namely, the mass change for all tin-containing samples exhibits approximately a 1.5% mass loss (consistent with the lubricant addition), while the tin-less sample exhibits a lesser mass loss closer to 1.3%, which drops slightly as compaction pressure increases.

[0085] Finally, and with reference to FIG. 2E, the dimensional shrinkage of the various sintered samples (again, at 635 C. for 20 minutes) is illustrated at varying compaction pressures. In this figure, it can be first observed that the tin-containing samples have appreciably greater shrinkage than the tin-less sample which is consistent with the findings in FIG. 1D. However, this chart further demonstrates that there is a sizable reduction in shrinkage as the compaction pressure is increased from 150 MPa to 250 MPa which then levels off or plateaus around-1.5% for the tin containing samples. This difference between 150 MPa and 250 MPa might be explained in that the samples pressed at the lower pressure are appreciably less dense to begin with in the green state and therefore have a larger dimension change when sintered.

[0086] Turning now to FIGS. 3A, 3B, 3C, and 3D, the effect of sintering time on density, average hardness, mass change, and dimensional change are further studied. For these four figures, the samples are each compacted at 350 MPa and sintered at 635 C. for one of 5, 10, 15, 20, 25, or 30 minutes. Again, and as with the other investigations described so far, the samples are also varied in tin chemistry (0.0, 0.25, 0.5, or 1.0 wt % Sn).

[0087] From FIG. 3A, the densification is shown as beginning to plateau at 20 minutes, with the tin-containing compositions outperforming the tin-less composition as has previously been the case in the other earlier-described studies. There is no appreciable difference in sintered density observed across the various amounts of tin in the tin-containing composition. That is to say, the densities for 0.25, 0.5, and 1.0 wt % Sn are all clustered together at between 98.5% and 99.0% theoretical density for sintering times between 20 minutes and 30 minutes.

[0088] With reference to FIG. 3B, the average hardness is illustrated with respect to the varied sintering times and chemistries. The average hardness for the 0.25 and 0.5 wt % Sn compositions are higher than the tin-less and 1.0 wt % Sn compositions and the data suggests a potential bimodal peak.

[0089] FIGS. 3C and 3D illustrate that mass change and dimensional change, respectively, are only minimally impacted by changes in sintering time. Again, and as in the previous examples, the tin-containing samples exhibit greater mass losses and dimensional changes than the tin-less composition; however, there is not much of a difference between those samples sintered for 5 minutes and those samples sintered for 30 minutes.

[0090] FIGS. 4A, 4B, and 4C show the effect of sizing pressures (100 MPa, 200 MPa, 300 MPa and 400 MPa) on dimensional change, density, and average hardness respectively for the parts made from the Al-0.7Mg-0.4Si-0.25Sn and Al-0.7Mg-0.4Si-0.5Sn powder metal compositions. These samples were compacted at 350 MPa, sintered at 635 C. for 20 minutes, and then sized.

[0091] FIG. 4A shows the effect of various sizing pressures on OAL change percentage. From this graph, beyond a sizing pressure of 200 MPa, there are diminishing returns on sizing reduction by increased pressure. This is believed to be primarily due to the relatively high density of the as-sintered parts. Likewise, FIG. 4B illustrates that there are some improvements to densification as the result of sizing pressure increases, but these are fairly marginal (note the scale of FIG. 4B is from 98.5% to 99.5% theoretical density). While the 0.5 wt % Sn samples see greater initial densification, further compaction provides only minimal improvements, while 0.25 wt % Sn samples see greater pore shrinkage and elimination with increasing pressure.

[0092] FIG. 4C shows the effect of sizing pressure on the average hardness. The data in this chart demonstrates that hardness did increase consistently with increased sizing pressure and at all stages of sizing pressure, the 0.25 wt % Sn samples maintained a slightly greater average hardness than the 0.5 wt % Sn samples.

[0093] Turning now to FIGS. 5A, 5B, 5C, and 5D, the effect of sizing and of chemistry (namely, varied tin content) on Young's Modulus, ultimate tensile strength (UTS), yield strength, and maximum elongation are illustrated and compared to wrought samples. These powder metal samples were compacted at 350 MPa, sintered at 635 C. for 20 minutes, and sized in an unconstrained die at 120 MPa.

[0094] From FIG. 5A, the 0.25 and 0.5 wt % Sn samples fabricated from powder metal each have a Young's Modulus that is comparable to that found in the literature (all literature comparative found in ASM Handbook, Volume 2: Properties and Selection, page 407). The tin-containing samples, and 0.25 and 0.5 wt % Sn in particular, perform quite well compared to wrought 6063 of an unspecified temper.

[0095] From FIG. 5B, the ultimate tensile strength of the powder metal sintered and sized components is less than the ultimate tensile strengths (UTS) of the wrought 6063 components with a T1 and T5 treatment (both are again taken from the ASM Handbook, Volume 2). While the UTS is less for the powder metal parts in all cases that the wrought components from the literature, the difference between the tin-containing powder metal sintered and sized components and the wrought 6063-T1 value from the literature is relatively small. That is, the UTS for the tin-containing powder metal components is approximately 130 MPa, while the wrought 6063-T1 data from the literature is approximately 150 MPa. However, the gap is much larger between the powder metal components and the wrought 6063-T5.

[0096] FIG. 5C illustrates that yield strength for the sintered and sized powder metal components actually exceeds the comparable wrought 6063-T1 yield strength from the literature with the tin-containing powder metal components generally exceeding 90 MPa, although they exhibit yield strengths much less than wrought 6063-T5, which has a yield strength of just over 140 MPa.

[0097] FIG. 5D illustrates the comparative maximum elongation. The wrought 6063-T1 from the literature has a maximum elongation of 20%, which exceeds the elongation of the powder metal components that have been sintered and sized. However, the powder metal components made from tin-containing compositions have maximum elongations in the 12 to 15% range, which is comparable with wrought 6063-15 from the literature. Comparatively, the components made from tin-less composition have very low maximum elongations (only around 2%).

[0098] FIGS. 6A, 6B, 6C, and 6D show further data comparative for the Young's Modulus, UTS, yield strength, and max elongation of Al-0.7Mg-0.4Si-0.5Sn (0.5 Sn samples) that have been sintered and sized or subjected to a T8 treatment. The powder metal samples were compacted at 350 MPa, sintered at 635 C. for 20 minutes. For those samples subject to the T8 heat treatment, they were solutionized at 520 C. for two hours, sized in an unconstrained die at 120 MPa, and aged at 175 C. for 22 hours.

[0099] FIG. 6A shows that the Young's modulus for the 0.5 wt % Sn samples, whether sintered and sized or subjected to the T8 heat treatment, exceeded those of the wrought 6063-T8 sample from the literature or the wrought 6063 sample from the literature of unspecified temper. The T8 powder metal components perform slightly better than the sintered and sized components, with the T8 samples having a Young's Modulus of over 80 GPa compared to around 75 GPa for the sintered and sized components.

[0100] FIG. 6B shows that the UTS for the 0.5 wt % Sn samples when subjected to a T8 treatment (240 MPa) was comparable to and slightly exceeded a comparative wrought 6063-T8 sample and exceeded the UTS values of wrought 6063-T1 and 6063-T5 from the literature. The 0.5 wt % Sn sample that was sintered and sized did not exhibit as impressive a UTS but was still roughly comparable with wrought 6063-T1. Similarly, FIG. 6C illustrates that the 0.5 wt % Sn samples when subjected to a T8 treatment had a yield strength of just above 200 MPa which greatly exceeded comparable wrought 6063-18 data and that from the literature. Again, the 0.5 wt % Sn sample that was sintered and sized did not perform quite as impressively, but still exceeded the yield strength for a wrought 6063-T1 sample from the literature.

[0101] FIG. 6D illustrates the performance tradeoff in the 0.5 wt % Sn samples when subjected to a T8 treatment instead of being just sintered and sized. In this figure, it is shown that the powder metal samples subjected to the T8 heat treatment only have a maximum elongation of 6%. In comparison wrought 6063-T8 has a maximum elongation of 15%. The 0.5 wt % Sn sintered and sized sample has maximum elongation of approximately 15%, which is comparable to wrought 6063-T8; however, from the description above, the sintered and sized component does not perform as well from the other measured mechanical metrics.

[0102] Turning now to FIGS. 7A and 7B, the aging response is illustrated for the sintered parts made from the Al-0.7Mg-0.4Si-0.25Sn and Al-0.7Mg-0.4Si-0.5Sn compositions. Both curves are based on parts compacted at 350 MPa and sintered at 635 C. for 20 minutes. FIG. 7A shows the natural aging curve (with time being presented on a log scale), while FIG. 7B shows the T8 aging process in which the components are further solutionized at 520 C. for two hours, sized to a 3.5% reduction MPa, and aged at 175 C.

[0103] From FIG. 7A, the Al-0.7Mg-0.4Si-0.25Sn sample exceeds 30 HRE after approximately 30 days and the Al-0.7Mg-0.4Si-0.5Sn sample is approximately 22 HRE after 30 days. For Al-0.7Mg-0.4Si-0.25Sn, hardening appears to initiate between 24 hours and 4 days and ends somewhere between 4 days and 9 days. For Al-0.7Mg-0.4Si-0.5Sn, hardening appears to initiate and end between 4 days and 9 days. In any event, the Al-0.7Mg-0.4Si-0.25Sn samples consistently have better hardness than Al-0.7Mg-0.4Si-0.5Sn samples at all post-sinter times.

[0104] When Al-0.7Mg-0.4Si-0.5Sn is artificially aged as illustrated in FIG. 7B, the hardness peaks at around 6 hours and maintains that plateau until approximately 24 hours. The peak hardness in this range is approximately 81 HRE.

[0105] Finally, and perhaps most important and impressive for practical application, the thermal properties of the powder metal formulations were assessed. This thermal data is meaningful as one potential use for the 6063 comparable powder metal formulation could be in fabrication of parts having thermal applications (for example, battery terminals or thermal management applications).

[0106] While the full set of data is not provided in this application, the equation for thermal conductivity is k=c.sub.P in which is thermal diffusivity, is density, and c.sub.P is specific heat capacity. Corrections are made for thermal expansion at a particular temperature.

[0107] An investigation was performed into how the components made from the powder metal compositions performed thermally compared to wrought and what the impact was of further T8 heat treatment on the thermal properties of the samples. A summary of the results is as follows. With respect to specific heat capacity, it was found that, while wrought 6063 showed improvement in specific heat capacity in the T8 state (compared to wrought 6063 that was not subjected to T8 treatment), the heat capacity of Al-0.7Mg-0.4Si-0.5Sn only saw negligible improvement between the as-sintered state and T8 state. In contrast, the powder metal components saw clear improvement in thermal diffusivity in the T8 state over the as-sintered state. However, that improvement in thermal diffusivity was not found to occur when the 6063 wrought component was subjected to a T8 treatment.

[0108] The resultant effect was that T8 treatment provided improved thermal conductivity for both the wrought 6063 and comparable powder metal compositions disclosed herein, albeit for different reasons as best understood. It is believed that, in the sintered powder metal components, the improvement in thermal conductivity is not attributable to improvements in specific heat capacity (as in wrought material), but rather to improvements in thermal diffusivity.

[0109] The resultant thermal conductivity data is found in FIGS. 8A and 8B. In FIG. 8A, the thermal conductivity at various temperatures is measured for each of the powder metal compositions Al-0.7Mg-0.4Si-0.0Sn, Al-0.7Mg-0.4Si-0.25Sn, Al-0.7Mg-0.4Si-0.5Sn, and Al-0.7Mg-0.4Si-1.0Sn and compared to wrought 6063-T5. From FIG. 8A, the thermal conductivity of the tin-containing powder metal samples (which have been sintered and sized) have very good thermal conductivity for a powder metal component, even if they remain below wrought 6063-T5. In particular, the parts having the Al-0.7Mg-0.4Si-0.5Sn composition have thermal conductivity that is surprisingly good and unexpected for powder metal, with thermal conductivity in the range of 190 W/m*K to 205 W/m*K over the temperature range of 100 C. to 200 C. Among all powder metal composition samples, there is an observed drop in thermal conductivity above approximately 200 C.; however, the Al-0.7Mg-0.4Si-0.5Sn, samples perform quite well up to that point and it is actually believed the drop in the data at 250 C. is attributable to a thermal event and thus this is not indicative of actual conductivity at that temperature.

[0110] FIG. 8B shows comparable data for parts fabricated from the Al-0.7Mg-0.4Si-0.5Sn composition in which a sized and sintered component is compared to a component subjected to the T8 heat treatment described above. It can be seen that the sample from Al-0.7Mg-0.4Si-0.5Sn subjected to the T8 heat treatment exhibits improved thermal conductivity between 200 C. and 250 C. demonstrates that this powder metal composition has great potential for use in thermal applications such as heat sinks and battery terminals.

[0111] To further show the effect of AlN additions on materials properties and provide additional data on samples subjected to T8 treatments, comparison data was also collected for parts fabricated from a PM6063 composition versus the PM 6063 with 1 vol % AlN added (PM6063-AlN). Table III below provides the particular powder formulation or blend for PM6063 that was used to provide the metal matrix for compared samples.

TABLE-US-00004 TABLE III Powder Amount Ecka Al (250/+60 micron) 943.3 g Ecka Al12Si (45 micron) 41.7 g Elemental Mg (China) 8.0 g Ecka Elemental Sn (20 5.0 g micron) Ecka Al50Cu Master Alloy 2.0 g Lico Wax C 15.2 g

[0112] Samples made from this powder composition will hereafter be referred to as PM6063 or PM6063-AlN in the examples below, with the AlN designation being used to indicate samples made from this composition but with 1 volume percent targeted aluminum nitride MMC additions. It will be appreciated that these compositions are not necessarily to the 6063 specification but rather are targeted to be comparably performing powder metal compositions to wrought 6063.

[0113] For each of PM6063 and PM6063-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 measured 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.

[0114] 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 PM6063 and PM6063-AlN. Those as-sintered dimensional change, mass change, average hardness, and sintered density results are found in Table IV below

TABLE-US-00005 TABLE IV Mass Sintered OAL Width Length Powder Change Density Change Change Change Composition (%) (g/cc) (%) (%) (%) PM6063 1.51 2.69 4.01 2.18 2.01 PM6063-AlN 1.46 2.70 3.79 2.60 2.24

[0115] 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 175 C. for 8 hours. The average hardness is provided for samples subjected to this T8 heat treatment and compared to those just subjected to the T1 heat treatment in Table V below:

TABLE-US-00006 TABLE V T1 T8 Powder Hardness Hardness Composition (HRE) (HRE) PM6063 47.6 93.7 PM6063-AlN 44.1 87.9

[0116] 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 PM6063 and PM6063-AlN, which can be found in Table VI below:

TABLE-US-00007 TABLE VI E Yield UTS Elongation Composition (GPa) (MPa) (MPa) (%) PM6063 66.3 271 295 1.9 PM6063-AlN 65.7 246 268 2.2
Again, and for the sake of clarity, these are mechanical properties of samples made from the powder composition and subjected to the T8 heat treatment.

[0117] Samples of each T8-processed composition were also subjected to a 3-point bending fatigue staircase, which are results are provided in Table VII, below:

TABLE-US-00008 TABLE VII Bending Fatigue Performance .sub.a, 10 .sub.a, 50 .sub.a, 90 Composition (MPa) (MPa) (MPa) PM6063 138.3 135.0 131.7 PM6063-AlN 142.8 135.8 128.8
For the sake of clarity the indication of .sub.a,x is the value at which there is a 50% change of confidence that x % of bars will pass 106 cycles where x % is 10, 50% or 90% in Table VII above.

[0118] 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 average thermal diffusivity results are found below in Table VIII:

TABLE-US-00009 TABLE VIII Thermal Diffusivity Composition (mm.sup.2/s) PM6063 81.0 PM6063-AlN 85.1

[0119] From Tables V, VI, VII, and VIII above, upon addition of 1 vol % AlN to the powder metal composition, most materials properties are comparable or may even slightly deteriorate from the comparative samples lacking AlN as an addition. A notable exception to this is that the addition of AlN increases thermal diffusivity from 81.0 mm.sup.2/s to 85.1 mm.sup.2/s.

[0120] Turning now to FIGS. 9A-9D, the results of anodizing are shown on PM6063 and PM6063-AlN. FIGS. 9A and 9B show PM 6063 samples and PM 6063-AlN samples in which PM 6063 here really corresponds to a powder metal comparable formulation to wrought 6063 and is actually Al-0.7Mg-0.4Si-0.5Sn (which, again, is not the compositional equivalent of wrought 6063). FIG. 9A shows the surfaces of the two sets of samples with the surfaces in the as-sized state, whereas FIG. 9B shows the two set of samples after grinding using 240 grit SiC paper. FIG. 9C then shows the before and after appearance change following anodizing separately showing the results of the powder metal composition and the powder metal composition plus 1 vol % AlN in the as-sized samples. FIG. 9D shows the before and after appearance change following anodizing separately showing the results of the powder metal composition and the powder metal composition plus 1 vol % AlN in the ground samples. Hard anodizing samples appeared blackened, while clear anodizing samples kept their grey appearance. In each of the after sets there are two samples that have been hard anodized (bottom two for PM 6063 in FIG. 9C, top two for PM 6063+1% AlN in FIG. 9C, bottom two for PM 6063 in FIG. 9D, and bottom two for PM 6063+1% AlN in FIG. 9D) and one sample that is clear anodized (top one for PM 6063 in FIG. 9C, bottom one for PM 6063+1% AlN in FIG. 9C, top one for PM 6063 in FIG. 9D, and top one for PM 6063+1% AlN in FIG. 9D)

[0121] FIGS. 10A-10D illustrate the anodized layer in samples that are hard anodized. FIGS. 10A and 10B show samples that were anodized as-sized, while FIGS. 10C and 10D show samples that were anodized as-ground. FIGS. 10A and 10C show the 6063-HA Sized and 6063-HA Ground which refers to the powder metal comparable version of 6063 described above after anodizing either as-sized or as-ground respectively, while FIGS. 10B and 10D show the 6063-AlN-HA Sized and 6063-AlN-HA Ground which refers to the powder metal comparable version of 6063 described above plus 1 volume percent AlN after anodizing either as-sized or as-ground respectively. From these comparative side views of the anodized layer, it can be seen that the anodized layer on the as-sized powder metal only sample (FIG. 10A) is comparably rough to the powder metal plus AlN sample (FIG. 10B) and that both of the ground samples (FIGS. 10C and 10D) are relatively smooth.

[0122] Surface finish data is provided below for these samples in Tables IX (for the 6063 comparable powder metal formulation) and Table X (for the 6063 comparable powder metal plus 1 volume percent AlN formulation.

TABLE-US-00010 TABLE IX Results for Material = A6063 Variable Surface N N* Mean SE Mean StDev Minimum Q1 Median Q3 Maximum RA (um) Ground 3 0 0.3267 0.0233 0.0404 0.2800 0.2800 0.3500 0.3500 0.3500 Sized 3 0 0.7600 0.0702 0.1217 0.6800 0.6800 0.7000 0.9000 0.9000 RZ (um) Ground 3 0 2.427 0.199 0.345 2.030 2.030 2.590 2.660 2.660 Sized 3 0 5.360 0.463 0.802 4.670 4.670 5.170 6.240 6.240

TABLE-US-00011 TABLE X Results for Material = 6063 + AIN Variable Surface N N* Mean SE Mean StDev Minimum Q1 Median Q3 RA (um) Ground 3 0 0.28000 0.00577 0.01000 0.27000 0.27000 0.28000 0.29000 Sized 3 0 0.7833 0.0633 0.1097 0.6600 0.6600 0.8200 0.8700 RZ (um) Ground 3 0 1.7100 0.0208 0.0361 1.6700 1.6700 1.7200 1.7400 Sized 3 0 5.213 0.224 0.388 4.780 4.780 5.330 5.530 Variable Surface Maximum RA (um) Ground 0.29000 Sized 0.8700 RZ (um) Ground 1.7400 Sized 5.530

[0123] The data in Tables IX and X demonstrate that the average surface roughness (Ra) was lower in the ground samples as compared to the sized samples. Similarly, the difference between the tallest peak and the deepest valley (Rz), was lower in the ground samples than the sized samples for each respective material. This is also generally consistent with the cross-section views and observations in regards to the layers.

[0124] 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.