CAST ALUMINUM ALLOYS FOR AUTOMOTIVE APPLICATIONS BY MICROSTRUCTURE REFINEMENT USING TSP TREATMENT

Abstract

A method of casting an aluminum alloy is provided. The method includes casting a master aluminum alloy having a trisilanol phenyl polyhedral oligomeric silsesquioxanes (TSP) modifier into an ingot and adding the master aluminum alloy ingot into a molten base aluminum alloy to form a modified aluminum alloy. The modified aluminum alloy is heated for a period of time and then cast into a cast component. A variation of the method includes mixing a powdered aluminum alloy with a powdered TSP and pressing the mixture of powdered TSP and powdered aluminum alloy into a compacted preform prior to casting the master aluminum alloy. The compacted preform is melted during the step of casting the master aluminum alloy.

Claims

1. A method of casting an aluminum alloy comprising: casting a master aluminum alloy having a trisilanol phenyl polyhedral oligomeric silsesquioxanes (TSP) modifier into an ingot; adding the master aluminum alloy ingot into a molten base aluminum alloy to form a modified aluminum alloy; heating the modified aluminum alloy for a period of time; and casting the modified aluminum alloy into a cast component.

2. The method according to claim 1 further comprising, prior to casting the master aluminum alloy: mixing a powdered aluminum alloy with a powdered TSP; and pressing the mixture of powdered TSP and powdered aluminum alloy into a compacted preform, wherein the compacted preform is melted during the step of casting the master aluminum alloy.

3. The method according to claim 2, wherein a plurality of compacted preforms are pressed and subsequently melted during the step of casting the master aluminum alloy.

4. The method according to claim 1, wherein the modified aluminum alloy is degassed prior to casting.

5. The method according to claim 1, wherein the master aluminum alloy is an aluminum-silicon (AlSi) based alloy.

6. The cast component according to the method of claim 5 comprising a microstructure having fibrous eutectic Si.

7. The method according to claim 1, wherein the modified aluminum alloy is cast into a clay-graphite crucible.

8. The method according to claim 1, wherein the modified aluminum alloy is continually heated for the period of time with a parts per million (ppm) loss of less than 10%.

9. The method according to claim 8, wherein the modified aluminum alloy is continually heated at or above 700 C. for the period of time.

10. The method according to claim 9, wherein the period of time is at least 1.5 hours.

11. The method according to claim 1, wherein the modified aluminum alloy is Al-7.5Si having an increase in ductility of at least 15% above an Al-7.5Si alloy without TSP.

12. The method according to claim 1, wherein the modified aluminum alloy is Al-7.5Si having an increase in ultimate tensile strength of at least 5% above an Al-7.5Si alloy without TSP.

13. The method according to claim 1, wherein the modified aluminum alloy is continually heated at or above 700 C. and the period of time is greater than 72 hours.

14. The method according to claim 13, wherein the modified aluminum alloy has a parts per million (ppm) loss of less than 10%.

15. A method of casting an aluminum alloy comprising: mixing a powdered aluminum alloy with a powdered TSP; pressing the mixture of powdered TSP and powdered aluminum alloy into a compacted preform; casting a master aluminum alloy from the compacted preform and into an ingot; adding the master aluminum alloy ingot throughout a molten base aluminum alloy to form a modified aluminum alloy; and casting the modified aluminum alloy into an ingot.

16. The method according to claim 15, wherein the modified aluminum alloy is degassed prior to casting.

17. The method according to claim 15, wherein the master aluminum alloy is an aluminum-silicon (AlSi) alloy and the modified aluminum alloy comprises a microstructure having fibrous eutectic Si.

18. The method according to claim 15, wherein the modified aluminum alloy has a parts per million (ppm) loss of less than 10% after being continually heated at or above 700 C. for a period of time greater than 1.5 hours.

19. A method of casting an aluminum alloy comprising: casting a master aluminum alloy having a trisilanol phenyl polyhedral oligomeric silsesquioxanes (TSP) modifier into an ingot; adding the master aluminum alloy ingot into a molten base aluminum alloy to form a modified aluminum alloy; heating the modified aluminum alloy for a period of time; and casting the modified aluminum alloy into an ingot, wherein the modified aluminum alloy has a parts per million (ppm) loss of less than 10% after being continually heated at or above 700 C. during the period of time, and the period of time is greater than 1.5 hours.

20. The method according to claim 19 further comprising, prior to casting the master aluminum alloy: mixing a powdered aluminum alloy with a powdered TSP; and pressing the mixture of powdered TSP and powdered aluminum alloy into a compacted preform, wherein the compacted preform is melted during the step of casting the master aluminum alloy.

Description

DRAWINGS

[0019] In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

[0020] FIG. 1 is a graph illustrating of Strontium fading as a function of time at temperature in Aluminum alloys, according to the teachings of the prior art;

[0021] FIG. 2 illustrates an initial method of incorporating trisilanol phenyl polyhedral oligomeric silsesquioxanes (TSPs) into Aluminum alloys, according to the teachings of the present disclosure;

[0022] FIG. 3 illustrates an intermediate low-volume foundry implementation of TSP integration into Aluminum alloys, according to the teachings of the present disclosure;

[0023] FIG. 4 illustrates another intermediate low-volume foundry implementation of TSP integration into Aluminum alloys, according to the teachings of the present disclosure;

[0024] FIG. 5 illustrates the formation of the Aluminum and TSP compacted preform, according to the teachings of the present disclosure;

[0025] FIG. 6 illustrates a low- to high-volume foundry implementation of the TSP compacted preform into Aluminum alloys, according to the teachings of the present disclosure;

[0026] FIG. 7 is a graph of Differential Scanning calorimetry (DSC) heating curves of the Al-7.5Si alloy without TSP and the Al-7.5Si alloy with TSP, according to the teachings of the present disclosure;

[0027] FIGS. 8A-8G are optical micrographs of an Al-7.5Si alloy without TSP and an Al-7.5Si alloy with TSP after various thermal treatments, according to the teachings of the present disclosure;

[0028] FIG. 9 is a graph of cooling curves of remelted Al-7.5Si alloys with and without TSP additions, according to the teachings of the present disclosure;

[0029] FIG. 10 is a flow diagram of a method of casting an aluminum alloy that includes casting a master aluminum alloy having a trisilanol phenyl polyhedral oligomeric silsesquioxanes (TSP) modifier into an ingot, according to the teachings of the present disclosure;

[0030] FIG. 11 is a flow diagram of a method of casting an aluminum alloy that includes mixing a powdered aluminum alloy with a powdered TSP, according to the teachings of the present disclosure; and

[0031] FIG. 12 is a flow diagram of a method of casting an aluminum alloy that includes casting a master aluminum alloy having a trisilanol phenyl polyhedral oligomeric silsesquioxanes (TSP) modifier into an ingot, according to the teachings of the present disclosure.

[0032] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

[0033] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0034] The inventors have discovered success by integrating reactive nano-structured silanols with light-weight aluminum alloys for structural applications. Their investigations found surprising success with laboratory-scale incorporation of reactive nano-structured chemicals based on polyhedral silsesquioxane. Polyhedral silsesquioxane has multiple silanol functionalities and was integrated into aluminum alloys in a small furnace by at least solid-phase mixing or an in-situ reaction forming structural silanol-metal compounds. The silanol-metal compounds form at low-temperatures into structured silanol-metal compounds. When the treated aluminum alloy is melted the embedded structured silanol-metal compounds, unexpectedly, enable refinement of the aluminum alloy microstructure. This refinement leads to significant mechanical property enhancement, including ductility, percent elongation, and reduction in area.

[0035] For example, by melting trisilanol phenyl polyhedral oligomeric silsesquioxanes (TSPs) treated A4047 powder (325 mesh) with a nearly eutectic AlSi composition a significant improvement in ductility (from 5% elongation for untreated control to 18% elongation for treated A4047) with modest improvements in yield strength and tensile strength in the as-cast condition with no additional heat treatment were observed.

[0036] Unexpectedly, the process also works with recycled aluminum alloys processed in a 100-pound casting furnace.

[0037] Analysis of the microstructure of aluminum alloys treated with structured silanol showed a dramatic refinement of the Si-cuboids in the AlSi eutectic micro-constituent along with refined Al grains. Both the refinement and the eutectic micro-constituent accounted for the observed improved tensile properties.

[0038] Now referring to FIG. 2, an unsuccessful method of incorporating TSP into aluminum based powders 10 is shown. In this method, powders of 44 m-A4047 (AlSi) and 50 m-A359 (Al-9Si-0.5Mg-0.2Ti) were combined to create a 150 g powder base alloy. In step 12, the powder base alloy was combined with a 10 g flux of (NH.sub.4Cl+stearic acid), 3 g of TSP in 100 ml of ethanol. This created a saturated solution of TSP in the ethanol, and the TSP was in a loose powder form. This mixture was heated to 180 C. for 10 minutes. In step 14, the TSP-coated powder base alloy was washed with hot water to remove any unused flux and dried in the air, creating a TSP-coated powder (TSP-coated A4047/A359 powder). In step 16, the TSP-coated powder was melted at 815 C. in a 3 kg-capacity graphite crucible. Powders desire higher melting temperatures than ingots and powders when heated to below 815 C. generally are not enabled to either melt and/or compact efficiently. In step 18, the melt was cast into a mold and air-cooled to form an as-cast sample 20 (25 mm50 mm12mm). Indicative of these prior art processes, the resultant as-cast sample 20 has an unmodified and unrefined microstructure 22.

[0039] Referring to FIGS. 2 and 3, for implementation on a foundry scale (low-volume, medium-volume, or high-volume production), aluminum alloy ingots 42 are desired as material precursors instead of alloy powders. Aluminum alloy ingots 42 have a lower melting temperature, are less volatile, are more commercially available, amongst other low-high volume commercialization benefits over aluminum powders.

[0040] During the development of foundry implementation 40 of the present disclosure, Aluminum alloy ingots were combined with TSP powders. In step 44, 27 kg of the Aluminum 356 ingots 42 were melted at 720 C. within a 35 kg-capacity clay-graphite crucible. In step 46, 3 kg of dried TSP-coated powder was added to the melt. The TSP-coated powder burned/ignited on the surface of the melt instead of integrating and mixing homogeneously into the molten Aluminum, indicative of an unsuccessful process. In step 48, the 30 kg melt contained 356AI (27 kg) and TSP-coated powder (3 kg) at 720 C., the 30 kg melt was degassed and stirred to homogeneously disperse the constituents throughout the melt. In step 50, the melt was transferred into molds and cooled into burned bars 52. The resultant microstructure 54 of the burned bars 52, was again unmodified and unrefined.

[0041] Now referring to FIG. 4, in another developmental foundry implementation 70 of the present disclosure, Aluminum alloy ingots were combined with TSP powders. In step 44, 27 kg of the Aluminum 356 ingots 42 were melted at 720 C. within a 35 kg-capacity clay-graphite crucible. In step 72, the A4047 powder (325 mesh) and TSP powder mixture was hot-pressed at 45 kN for 10 minutes at 180 C. into an A4047-6%TSP puck 74 (32 mm diameter19 mm). In step 76, the 30 kg melt contained 356AI (27 kg) and puck 74 (3 kg) at 720 C., the puck 74 burned on the surface of the melt indicative of an unsuccessful process. Where the 3 kg of pucks 74 is at least one puck 74. The 30 kg melt was degassed and stirred to homogeneously disperse the constituents throughout the melt. In step 50, the melt was transferred into molds and cooled into burned bars 78. The resultant microstructure 80 of the burned bars 78, was again unmodified and unrefined.

[0042] As used hereinafter, the puck 74 is referred to as a compacted preform 75. In one form, the compacted preform was hot pressed at 180 C. to aid in compaction without altering the powders as much as a sinter or melt would, and as such the compaction is not limited to hot-pressing, as such, other similar hot-pressing methods are also applicable (e.g. hot-isostatic-pressing). Further, it should be understood that the geometry of a puck is merely exemplary. Cylinders, ovoids, prisms, rectangular cubes, spheres, among other geometric shapes may be employed as compacted preforms, and thus the puck shape should not be construed as limiting the scope of the present disclosure.

[0043] Now referring to FIG. 5, the compacted preform implementation of the present disclosure is illustrated by reference numeral 100. In step 72, the A4047 powder and TSP powder mixture was hot-pressed at 45 kN for 10 minutes at 180 C. into a A4047-6% TSP compacted preform 75. In step 102, up to 3 kg of compacted preforms 75 were melted at 700 C. in a 3 kg capacity graphite crucible. In step 104, the melted compacted preforms 75 were cast into a graphite mold and air-cooled to form a TSP master aluminum alloy ingot 106 (25 mm50 mm12 mm).

[0044] Now referring to FIG. 6, the foundry implementation of the present disclosure is illustrated by reference numeral 120. In step 44, 27 kg of the Aluminum 356 ingots 42 were melted at 720 C. within a 35 kg-capacity clay-graphite crucible. In step 122, 3 kg of the TSP master aluminum alloy ingot 106 was added to the molten aluminum at 720 C., forming modified melt 124. In step 126, the modified melt 124 was degassed and stirred to homogeneously disperse the constituents throughout the melt. In step 50, the modified melt 124 was transferred into molds and cooled into modified bars 128. The resultant microstructure 130 of the modified bars 128, was unexpectedly modified and refined. The unrefined and unmodified microstructure 80 from FIG. 4 is shown in this figure for comparison purposes.

[0045] To improve the overall mechanical properties of aluminum-silicon based alloys, modifiers (e.g. additives, grain refiners, chemical modifiers) are added to the base alloy, which enhance the overall mechanical properties through microstructural refinement. For example, Titanium and Boron often react with aluminum to intermetallic compounds (IMCs), such as Al.sub.3Ti and TiB.sub.2. IMCs enable heterogeneous nucleation sites of primary Aluminum, refining the grain size.

[0046] Strontium additions to aluminum-silicon based alloys alter the growing ledge (i.e. the re-entrant corner) of eutectic Silicon modifying the morphology of the eutectic Silicon from a flaky morphology to a fibrous morphology. As the silicon content exceeds about 3 wt. % Si, the grain refinement effect of grain refiners (e.g. Aluminum, Titanium, and Boron) on the Aluminum grain size is significantly diminished. This is partially due to the formation of TiSi and TiSi.sub.2. Strontium additions reduce the arrest temperature of the AlSi eutectic by up to 10 C. and increase the amount of undercooling.

[0047] As shown in FIG. 7, Differential Scanning calorimetry (DSC) heating curves of the Al-7.55i alloy without TSP 140 and the Al-7.55i alloy with TSP 142 according to the teachings of the present disclosure in FIGS. 5-6 are shown. The onset melting temperature and the peak melting temperature of the AlSi eutectic are listed below in Table 2.

TABLE-US-00002 TABLE 2 Selected characteristic temperatures from FIG. 7 Al7.5Si Al7.5Si without TSP with TSP AlSi onset melting 577 577 temperature ( C.) AlSi peak melting 588 588 temperature ( C.) Al peak melting 616 611 temperature ( C.) Enthalpy (J/g) 386 402

[0048] The TSP additions nominally altered the onset and peak melting temperatures of the AlSi eutectic, however, there is a noticeable shoulder at around 578 C. observed from the Al-7.5Si alloy with TSP 142. The peak melting temperature of primary Al and the total enthalpy during the melting are also listed in Table 2 (FIG. 7 is the source for the data in Table 2). TSP additions reduced the peak melting temperature of primary Al by about 5 C., which is consistent with the cooling curves results. Surprisingly, TSP additions increased the total enthalpy from 386 to 402 J/g.

[0049] TSP modifications according to the teachings of the present disclosure refine the AlSi grains and microstructure, and with a nominal (improved) change in the undercooling of the AlSi eutectic during solidification. Unexpectedly, the TSP additions enhance or improve the eutectic reaction instead of arresting the eutectic reaction as experienced with Strontium additions. There is also a small shoulder observed in the DSC melting curve near the onset melting of the AlSi eutectic, suggesting that TSP enables nucleation sites on the AlSi eutectic resulting in the modified eutectic Si.

[0050] To better understand the microstructural stability of TSP additives within aluminum-silicon alloy melts, metallographic analyses and examinations were performed. Samples of the aluminum-silicon base alloy and the aluminum-silicon alloy with TSP additives were created from different stages of the time at temperature relationship, to eventually determine a TSP percentage as a function of time at temperature relationship analogous to FIG. 1, but for TSP instead of Sr. Concurrently, these samples into the microstructural stability of TSP additives within aluminum-silicon alloy melts produced metallographic samples displaying the microstructural impact of TSP additives on aluminum-silicon alloys.

[0051] Referring to FIGS. 8A-8G, metallographic samples of Al-7.5Si and Al-7.5Si with TSP additives were held at 720 C. for varying durations (all temperature holds for these samples were at 720 C.) and examined at 200 magnification. (The phases typically present in AlSi alloys are primary Aluminum and eutectic AlSi, where the eutectic AlSi appears as a dark phase in optical micrographs). [0052] FIG. 8A shows the microstructure of the eutectic Si in an Al-7.5Si base alloy and a lamellar and/or acicular silicon particle morphology without TSP additions; [0053] FIG. 8B shows the microstructure of the eutectic Si in an Al-7.5Si alloy with TSP additions and a fibrous morphology after a 1.5-hour hold; [0054] FIG. 8C shows the microstructure of the eutectic Si in an Al-7.5Si alloy with TSP additions and a fibrous morphology after a 4-hour hold; [0055] FIG. 8D shows the microstructure of the eutectic Si in an Al-7.5Si alloy with TSP additions and a fibrous morphology after a 4-hour-hold, followed by remelting, followed by an additional 24-hour hold; [0056] FIG. 8E shows the microstructure of the eutectic Si in an Al-7.5Si alloy with TSP additions and a fibrous morphology after a 4-hour-hold, followed by remelting, followed by an additional 48-hour hold; [0057] FIG. 8F shows the microstructure of the eutectic Si in an Al-7.5Si alloy with TSP additions and a fibrous morphology after a 4-hour-hold, followed by remelting, followed by an additional 72-hour hold; and [0058] FIG. 8G shows the microstructure of the eutectic Si in an Al-7.5Si alloy with TSP additions and a fibrous morphology after a 4-hour-hold, followed by remelting, followed by an additional 192-hour hold.

[0059] An unexpected and favorable aspect of TSP additions to aluminum-silicon alloys according to the teachings of the present disclosure is that the microstructural refinement (e.g. modification and solidification) of the Al-7.5Si alloys with TSP additions is still effective following remelting and additional temperature holds, as shown in FIGS. 8D-8G, up to at least 192 hours.

[0060] Referring to FIG. 9, DSC analyses and examinations also determined the effect of the TSP additives on the cooling morphologies of aluminum-silicon alloys as a function of holding time for the alloys from FIGS. 8A, and 8C-8G. As shown, the cooling curves of remelted Al-7.5Si alloys with and without TSP additions and held at temperature for different times, illustrating that remelting negligibly alters the temperature characteristics of both primary Al and AlSi eutectic (e.g. undercooling and arrest temperatures).

[0061] Interestingly, the secondary dendrite arm spacing (SDAS) of the Al-7.5Si alloy with TSP additions was slightly reduced when compare to the SDAS of the Al-7.5Si alloy without TSP additions. The SDAS of primary Al in the Al-7.5Si base alloy was 25 m while the average SDAS in Al-7.5Si with TSP was decreased to 18 m. The reduced SDAS in Al-7.5Si with TSP can be due to various factors including but not limited to the depressed nucleation and growth temperatures during the solidification of primary Al. After the TSP addition, the primary Al arrest exhibited much less undercooling than the base alloy, suggesting that TSP additions enable nucleation sites of primary Al by decreasing the interfacial energy of the aluminum melt.

[0062] Referring to FIG. 10, one form of the present disclosure, a method 160 for casting an aluminum alloy is provided. The method 160 comprises casting a master aluminum alloy having a trisilanol phenyl polyhedral oligomeric silsesquioxanes (TSP) modifier into an ingot 162 and adding the master aluminum alloy ingot into a molten base aluminum alloy to form a modified aluminum alloy 164. The modified aluminum alloy is then heated for a period of time 166, followed by casting the modified aluminum alloy into a cast component 168.

[0063] In another method of the present disclosure, prior to casting the master aluminum alloy, a powdered aluminum alloy is mixed with a powdered TSP, the mixture is pressed into a compacted preform, and the compacted preform is melted during the step of casting the master aluminum alloy. In some methods of the present disclosure, a plurality of compacted preforms are pressed and subsequently melted during the step of casting the master aluminum alloy.

[0064] In multiple methods of the present disclosure, the modified aluminum alloy is degassed prior to casting, the modified aluminum alloy is cast into a clay-graphite crucible, and the modified aluminum alloy is continually heated for the period of time with a parts per million (ppm) loss of less than 10%.

[0065] In other methods of the present disclosure, the master aluminum alloy is an aluminum-silicon (AlSi or AlSi) based alloy. In these methods of the present disclosure, the microstructure of the cast component includes fibrous eutectic Si.

[0066] In at least one method of the present disclosure, the modified aluminum alloy is continually heated at or above 700 C. for the period of time; the modified aluminum alloy is Al-7.5Si having an increase in ductility of at least 15% above an Al-7.5Si alloy without TSP; and the modified aluminum alloy is Al-7.5Si having an increase in ultimate tensile strength of at least 5% above an Al-7.5Si alloy without TSP.

[0067] In one method of the present disclosure, the period of time is at least 1.5 hours.

[0068] In numerous methods of the present disclosure, the modified aluminum alloy is continually heated at or above 700 C. and the period of time is greater than 72 hours; and the modified aluminum alloy has a parts per million (ppm) loss of less than 10%.

[0069] Now referring to FIG. 11, another form of the present disclosure, a method 180 of casting an aluminum alloy is provided. The method 180 comprises mixing a powdered aluminum alloy with a powdered TSP 182; pressing the mixture of powdered TSP and powdered aluminum alloy into a compacted preform 184; and casting a master aluminum alloy from the compacted preform and into an ingot 186. The method includes adding the master aluminum alloy ingot throughout a molten base aluminum alloy to form a modified aluminum alloy 188 and casting the modified aluminum alloy into an ingot 190.

[0070] In yet another method of the present disclosure, the modified aluminum alloy has a parts per million (ppm) loss of less than 10% after being continually heated at or above 700 C. for a period of time greater than 1.5 hours.

[0071] Now referring to FIG. 12, yet another form of the present disclosure, a method 200 of casting an aluminum alloy is provided. The method comprises casting a master aluminum alloy having a TSP modifier into an ingot 202 and adding the master aluminum alloy ingot into a molten base aluminum alloy to form a modified aluminum alloy 204. Subsequently, the modified aluminum alloy is heated for a period of time 206 and then the modified aluminum alloy is cast into an ingot 208. In this method, the modified aluminum alloy has a parts per million (ppm) loss of less than 10% after being continually heated at or above 700 C. during the period of time, and the period of time is greater than 1.5 hours.

[0072] The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.