Method Of Reprocessing Secondary Aluminum, And Reprocessed Secondary Aluminum Alloy

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject application claims priority to and all the benefits of U.S. Provisional Patent Application No. 63/650,735, filed May 22, 2024, the disclosure of which is incorporated by reference in its entirety herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to a method of reprocessing secondary aluminum, and to a reprocessed secondary aluminum alloy.

2. Description of the Related Art

Primary aluminum commonly refers to aluminum that has been mined and processed, but has yet to be formed into a product. In a typical process to form primary aluminum, the Bayer process, a sedimentary rock referred to as bauxite is mined and treated with a sodium hydroxide solution at elevated temperatures to generate an aluminum oxide(s). The aluminum oxide(s) are dissolved in a synthetic cryolite and then subjected to electrolysis in the Hall-Héroult process to reduce the aluminum oxide(s) and form the primary aluminum. Electrolysis is an energy-intensive process which consumes copious amounts of electricity which is typically generated through combustion of hydrocarbons. As such, electrolysis in the Hall-Héroult process typically results in high levels of carbon dioxide emitted into the atmosphere, contributing to air pollution and climate change. Moreover, although synthetic cryolite is necessary to reduce the melting point of the aluminum oxide(s) for easier electrolysis, it contains fluorine. The synthetic cryolite to some degree reacts during electrolysis, generating fluorocarbon compounds as byproducts which may further contribute to air pollution and climate change.

Secondary aluminum, also referred to as recycled aluminum, commonly refers to aluminum which has already been formed into a product and which is ready to be reprocessed and reformed into another product. However, secondary aluminum tends to contain measurably higher amounts of iron as compared to primary aluminum. More specifically, aluminum (whether primary or secondary) is typically cast in tools comprised of iron to form products. Each time aluminum is cast, the aluminum tends to leech iron from the tool which both increases the iron content of the aluminum and which tends to damage the tool itself. Increased iron contents in secondary aluminum are disadvantageous because iron tends to form particular intermetallic phases within the secondary aluminum, such as β-Al₅FeSi. These intermetallic phases reduce the strength of the secondary aluminum and prevent the secondary aluminum from being used to form structural components.

As such, there remains a need for an improved method of reprocessing secondary aluminum and for an improved reprocessed secondary aluminum alloy.

SUMMARY OF THE INVENTION AND ADVANTAGES

A method of reprocessing secondary aluminum is provided. The method includes obtaining a measurement of an iron content in a secondary aluminum to be reprocessed. The measurement of the iron content in the secondary aluminum is expressible as a percent by weight of iron in the secondary aluminum to be reprocessed. The method also includes obtaining a measurement of a manganese content in the secondary aluminum to be reprocessed. The measurement of the manganese content in the secondary aluminum is expressible as a percent by weight of manganese in the secondary aluminum to be reprocessed. The method further includes adding to the secondary aluminum to be reprocessed at least one chosen from iron and manganese to form a reprocessed secondary aluminum alloy such that a sum of the measured iron content, the measured manganese content, any added iron content, and any added manganese content is between about 0.7 to about 1.2 percent by weight of the reprocessed secondary aluminum alloy.

Accordingly, a ratio of the manganese content and the iron content in the reprocessed secondary aluminum alloy permits the reprocessed secondary aluminum alloy to be used to form structural components not otherwise possible with secondary aluminum. Moreover, because structural components may be formed with the reprocessed secondary aluminum alloy, primary aluminum need not be used. As such, the method results in immense energy savings which would otherwise have to be expended to form primary aluminum. Further, because hydrocarbons need not be burned to generate energy used to form primary aluminum, the method lowers the amount of carbon dioxide emitted into the atmosphere, reducing air pollution and climate change. And, because synthetic cryolite is not necessary to reprocess secondary aluminum as it is necessary to produce primary aluminum, fluorocarbon compounds are not created as byproducts of the method which may further contribute to air pollution and climate change.

DETAILED DESCRIPTION OF THE INVENTION

A method of reprocessing secondary aluminum includes obtaining a measurement of an iron content in a secondary aluminum to be reprocessed. The measurement of the iron content in the secondary aluminum is expressible as a percent by weight of iron in the secondary aluminum to be reprocessed. The method also includes obtaining a measurement of a manganese content in the secondary aluminum to be reprocessed. The measurement of the manganese content in the secondary aluminum is expressible as a percent by weight of manganese in the secondary aluminum to be reprocessed. The method further includes adding to the secondary aluminum to be reprocessed at least one chosen from iron and manganese to form a reprocessed secondary aluminum alloy such that a sum of the measured iron content, the measured manganese content, any added iron content, and any added manganese content is between about 0.7 to about 1.2 percent by weight of the reprocessed secondary aluminum alloy.

Accordingly, a ratio of the manganese content and the iron content in the reprocessed secondary aluminum alloy permits the reprocessed secondary aluminum alloy to be used to form structural components not otherwise possible with secondary aluminum. Moreover, because structural components may be formed with the reprocessed secondary aluminum alloy, primary aluminum need not be used. As such, the method results in immense energy savings which would otherwise have to be expended to form primary aluminum. It is estimated that reprocessing secondary aluminum requires only approximately 5% of the energy which would be needed to form primary aluminum. Further, because hydrocarbons need not be burned to generate energy used to form primary aluminum, the method lowers the amount of carbon dioxide emitted into the atmosphere, reducing air pollution and climate change. Thus, the method is capable of reducing the carbon footprint of forming structural components by approximately 95%. And, because synthetic cryolite is not necessary to reprocess secondary aluminum as it is necessary to produce primary aluminum, fluorocarbon compounds are not created as byproducts of the method which may further contribute to air pollution and climate change.

Beyond these advantages, it is to be appreciated that the method permits the use of secondary aluminum scrap, which is much less expensive than primary aluminum. As such, the method may realize significant cost savings, particularly when producing structural components. The reprocessed secondary aluminum alloy may be capable of producing structural components because the reprocessed secondary aluminum alloy may have high mechanical properties, good weldability, and the ability to be riveted without cracking. The reprocessed secondary aluminum alloy may also have good corrosion properties. It is to be appreciated that the reprocessed secondary aluminum alloy may have mechanical properties, weldability, and/or corrosion properties similar to, including as good as, primary aluminum.

Secondary aluminum to be reprocessed is to be understood as aluminum which has first been formed as primary aluminum, formed (such as by casting) into a first product, recycled and reprocessed to form a secondary aluminum, formed (such as by casting) into a second product, and then recycled to form the secondary aluminum to be reprocessed. As such, it is to be appreciated that the secondary aluminum to be reprocessed has already formed a first product and a second product. The secondary aluminum to be reprocessed may even have already formed a third product, a fourth product, or more than four products. However, aluminum has a natural affinity for iron. As such, each instance of the aluminum being formed into a product, such as by casting, results in the aluminum leeching iron from a tool (e.g. a die) used to create the product. This phenomenon is typically referred to as die soldering. It is therefore to be appreciated that the secondary aluminum to be reprocessed includes much higher iron contents as compared to both primary aluminum and recycled primary aluminum. The method may utilize only secondary aluminum to be reprocessed and may be free of any primary aluminum whatsoever. In other words, the method may reprocess only scrap from products already formed from secondary aluminum.

Moreover, over a series of shots exhibiting die soldering, a significant amount of aluminum becomes stuck to the tool itself. Aluminum sticking to the tool can damage the tool. Further, the resulting product formed under die soldering conditions can begin to miss critical tolerances or to lose integrity. To avoid missing critical tolerances or integrity requirements, after repeated castings (e.g. shots), the tool must be shut down and cleaned, adding both manufacturing time and increased cost. As such, die soldering is not only damaging to both the tool and the products, but also results in increased manufacturing time and increased costs. It is estimated that between about 1 percent and 1.5 percent of variable overhead is directly attributed to die soldering in casting plants.

Of the elements present in the secondary aluminum to be reprocessed, iron has the greatest effect on die soldering. Higher iron contents in the secondary aluminum to be reprocessed are associated with lower die soldering because the chemical potential gradient between the aluminum in the secondary aluminum to be reprocessed and the iron in the tool is lessened as compared to that between primary aluminum and the iron in the tool. However, even with relatively high iron content, the secondary aluminum to be reprocessed may still exhibit some degree of die soldering. It is understood that alloys with aluminum alloys with iron content under about 1 percent will exhibit die soldering under certain conditions. However, manganese also serves to minimize die soldering.

The reprocessed secondary aluminum alloy includes both relatively high iron content and relatively high manganese content. As such, the amount of iron leeched from the tool when forming a product from the reprocessed secondary aluminum alloy is negligible. In other words, die soldering is minimized because the reprocessed secondary aluminum alloy includes both relatively high iron content and relatively high manganese content. The tool, therefore, is not damaged when forming the product with the reprocessed secondary aluminum alloy, increasing the lifespan of the tool itself. Additionally, the products formed (e.g. cast) from the reprocessed secondary aluminum alloy do not begin to miss critical tolerances or lost integrity, which products formed from primary aluminum exhibit as subsequent, repeated castings tend to do.

Although not required, the step of adding to the secondary aluminum to be reprocessed may be conducted such that the sum of the measured iron content, the measured manganese content, any added iron content, and any added manganese content is between about 0.7 to about 0.9 percent by weight of the reprocessed secondary aluminum alloy. More specifically, the step of adding to the secondary aluminum to be reprocessed may be conducted such that the sum of the measured iron content, the measured manganese content, any added iron content, and any added manganese content is about 0.8 percent by weight of the reprocessed secondary aluminum alloy. Thus, the sum of the measured iron content, the measured manganese content, any added iron content, and any added manganese content may be referred to herein as a solder-properties factor. The solder-properties factor is indicative of the degree of die soldering the reprocessed secondary aluminum alloy will exhibit. A solder-properties factor of between about 0.7 and about 1.2, or more particularly between about 0.7 and about 0.9, or about 0.8, has been discovered to be ideal for the manufacture of structural components.

As described above, the method includes the step of adding to the secondary aluminum to be reprocessed at least one chosen from iron and manganese to form the reprocessed secondary aluminum alloy. Said differently, the method may include adding iron to form the reprocessed secondary aluminum alloy, may include adding manganese to form the reprocessed secondary aluminum alloy, or may include adding both iron and manganese to form the reprocessed secondary aluminum alloy. It is to be appreciated that the method may be used to reprocess secondary aluminum from a variety of sources, and which therefore may have a range of different measured iron contents and measured manganese contents. For example, secondary aluminum from cast aluminum scrap from automobile component manufacture typically is different compositionally from secondary aluminum from aluminum cans used to hold beverages. The method is therefore flexible to account for these varied measured iron contents and measured manganese contents.

With the varied measured iron contents and measured manganese contents resultant from the various sources of secondary aluminum in mind, it is occasionally necessary to add to the secondary aluminum to be reprocessed only iron or only manganese. In a non-limiting example, if the measured iron content were to be low and the measured manganese content were to be high, the method may include adding only iron to the secondary aluminum to be reprocessed to form the reprocessed secondary aluminum alloy. Conversely, in another non-limiting example, if the measured iron content were to be high and the measured manganese content were to be low, the method may include adding only manganese to the secondary aluminum to be reprocessed to form the reprocessed secondary aluminum alloy.

As such, the step of adding to the secondary aluminum to be reprocessed may be further defined as adding manganese to the secondary aluminum to be reprocessed. As discussed herein, although not required, the step of adding manganese to the secondary aluminum to be reprocessed may be conducted such that no iron is added to the secondary aluminum to be reprocessed. The step of adding manganese to the secondary aluminum to be reprocessed may be conducted such that the sum of the measured manganese content and the added manganese content in the reprocessed secondary aluminum alloy is within about 0.1 percent by weight of the measured iron content in the secondary aluminum to be reprocessed. In the embodiments where no iron is added to the secondary aluminum to be reprocessed, it is to be appreciated that the step of adding manganese to the secondary aluminum to be reprocessed may be conducted such that the sum of the measured manganese content and the added manganese content in the reprocessed secondary aluminum alloy is within about 0.1 percent by weight of the iron content in the reprocessed secondary aluminum alloy.

Further still, the step of adding manganese to the secondary aluminum to be reprocessed may be conducted such that the sum of the measured manganese content and the added manganese content in the reprocessed secondary aluminum alloy approximately balances the measured iron content in the secondary aluminum to be reprocessed. In the embodiments where no iron is added to the secondary aluminum to be reprocessed, it is to be appreciated that the step of adding manganese to the secondary aluminum to be reprocessed may be conducted such that the sum of the measured manganese content and the added manganese content in the reprocessed secondary aluminum alloy approximately balances the measured iron content in the reprocessed secondary aluminum alloy.

Moreover, the step of adding manganese to the secondary aluminum to be reprocessed may be conducted such that the manganese content of the reprocessed secondary aluminum alloy is between about 0.1 and about 0.5 weight percent higher than the measured manganese content of the secondary aluminum to be reprocessed. In other words, the step of adding manganese to the secondary aluminum to be reprocessed may raise the manganese content by about 0.1 and about 0.5 weight percent. The step of adding manganese to the secondary aluminum to be reprocessed may also be conducted such that the manganese content of the reprocessed secondary aluminum alloy is between about 0.1 and about 0.4 weight percent higher than the measured manganese content of the secondary aluminum to be reprocessed, between about 0.1 and about 0.3 weight percent higher than the measured manganese content of the secondary aluminum to be reprocessed, between about 0.1 and about 0.2 weight percent higher than the measured manganese content of the secondary aluminum to be reprocessed, between about 0.2 and about 0.5 weight percent higher than the measured manganese content of the secondary aluminum to be reprocessed, between about 0.2 and about 0.4 weight percent higher than the measured manganese content of the secondary aluminum to be reprocessed, between about 0.2 and about 0.3 weight percent higher than the measured manganese content of the secondary aluminum to be reprocessed, between about 0.3 and about 0.5 weight percent higher than the measured manganese content of the secondary aluminum to be reprocessed, between about 0.3 and about 0.4 weight percent higher than the measured manganese content of the secondary aluminum to be reprocessed, or between about 0.4 and about 0.5 weight percent higher than the measured manganese content of the secondary aluminum to be reprocessed. It is to be appreciated that the step of adding manganese to the secondary aluminum to be reprocessed may be conducted such that the manganese content of the reprocessed secondary aluminum alloy is even more than about 0.5 weight percent higher than the measured manganese content of the secondary aluminum to be reprocessed because the distribution coefficient of manganese is about 0.8. The solubility of manganese in a solid is very similar to the solubility of manganese in a liquid. As such, although benefits from the manganese content of the reprocessed secondary aluminum alloy being even more than about 0.5 weight percent higher than the measured manganese content of the secondary aluminum to be reprocessed are minimal, the properties of the reprocessed secondary aluminum alloy will not suffer.

Beyond the ability of manganese to neutralize the iron content in the secondary aluminum to be reprocessed, chromium may also be used to neutralize the iron content in the secondary aluminum to be reprocessed. As such, the method may further include adding chromium to the secondary aluminum to be reprocessed. The method may further include obtaining a measurement of a chromium content in the secondary aluminum to be reprocessed. The measurement of the chromium content in the secondary aluminum is expressible as a percent by weight of chromium in the secondary aluminum to be reprocessed. The step of adding chromium to the secondary aluminum to be reprocessed may be conducted such that a sum of the measured iron content, the measured manganese content, the measured chromium content, any added iron content, any added manganese content, and any added chromium content is between about 0.7 to about 1.2 percent by weight of the reprocessed secondary aluminum alloy.

As detailed herein, the measured iron content may vary according to the source of the secondary aluminum. In a non-limiting example, the measured iron content may be between about 0.3 and about 0.45 percent by weight of the secondary aluminum to be reprocessed. More specifically, the measured iron content may be between about 0.35 and about 0.45 percent by weight of the secondary aluminum to be reprocessed. More specifically still, the measured iron content may be between about 0.4 and about 0.45 percent by weight of the secondary aluminum to be reprocessed. These measured iron contents are indicative of commercially available sources of secondary aluminum scrap. It is to be appreciated that these measured iron contents are higher than the iron contents found in both primary aluminum before forming a product and primary aluminum after forming a product.

As also detailed herein, the measured manganese content may vary according to the source of the secondary aluminum. The measured manganese content may be between about 0.2 and about 0.4 percent by weight of the secondary aluminum to be reprocessed. More specifically, the measured manganese content may be between about 0.3 and 0.4 percent by weight of the secondary aluminum to be reprocessed. More specifically still, the measured manganese content may be between about 0.3 and about 0.35 percent by weight of the secondary aluminum to be reprocessed. These measured manganese contents are indicative of commercially available sources of secondary aluminum scrap.

The method may be applicable for reprocessing secondary aluminum to form any reprocessed secondary aluminum alloy having significant precipitation hardening with meaningful benefit from “solution” heat treating. Where solution heating has proven to be useful, solution heat treating is typically a requisite in the casting finishing process to achieve proper hardening. The reprocessed secondary aluminum alloys are termed “heat-treatable” alloys to distinguish them from those alloys for which the solution heating gives no significant strengthening or hardening.

The reprocessed secondary aluminum alloy may include aluminum, silicon, and magnesium. In other words, the reprocessed secondary aluminum alloy may be an alloy of aluminum, silicon, and magnesium. In one embodiment, the reprocessed secondary aluminum alloy is Al—Si₁₀—Mg. More specifically, the reprocessed secondary aluminum alloy may be Al—Si₁₀—Mg 0.3. In another embodiment, the reprocessed secondary aluminum alloy is Al—Si₇—Mg.

The method may further include high pressure die casting (HPDC) the reprocessed secondary aluminum alloy to form a structural component. High pressure die casting may be used to create thin walls. Thus, because the reprocessed secondary aluminum alloy may have similar mechanical properties as primary aluminum alloys, the reprocessed secondary aluminum alloy may be high pressure die cast to create a structural component with relatively thin walls without fear of the thin walls cracking. It is also to be appreciated that the structural component may be used in the transport industry. The structural component may also include an intermetallic phase of α-Al₁₅(Fe, Mn)₃Si₂.

The intermetallic phase of α-Al₁₅(Fe, Mn)₃Si₂ is a script type which has a compact morphology, forms a dendritic structure, and which does not initiate cracks in the structural component resultant from high pressure die casting the reprocessed secondary aluminum alloy. It is to be appreciated that the intermetallic phase of α-Al₁₅(Fe, Mn)₃Si₂ exhibits some variation in composition and morphology depending upon, inter alia, the cooling conditions of the molten aluminum and kinetic factors which may influence both nucleation and growth of the intermetallic phase as the intermetallic phase precipitates.

The structural component including the intermetallic phase of α-Al₁₅(Fe, Mn)₃Si₂ minimizes formation of the intermetallic phase of β-Al₅FeSi. The intermetallic phase of β-Al₅FeSi has a plate-like morphology and forms needle-like extensions up to several millimeters which are visible on micrographs. The intermetallic phase of β-Al₅FeSi is brittle, decreases the strength and ductility of cast products, and is problematic while soldering. Importantly, the intermetallic phase of β-Al₅FeSi is susceptible to cracking, making aluminum alloys including the intermetallic phase of β-Al₅FeSi incompatible with forming structural components. It is noted that high cooling rates can also suppress formation of the intermetallic phase of β-Al₅FeSi but tend to result in the intermetallic phase of α-Al₅Fe₂Si.

At manganese contents in the reprocessed secondary aluminum alloy at about 0.3 percent by weight or higher, it has been found that the intermetallic phase of α-Al₁₅(Fe, Mn)₃Si₂ begins to be selected for instead of the intermetallic phase of β-Al₅FeSi. Thus, it is to be appreciated that because the method may result in the reprocessed secondary aluminum alloy having a manganese content higher than about 0.3 percent by weight, the reprocessed secondary aluminum alloy may primarily form the intermetallic phase of α-Al₁₅(Fe, Mn)₃Si₂ and thus be particularly suited for structural components.

Although not intended to be limiting, a reprocessed secondary aluminum alloy may include silicon from about 6 percent by weight to about 11 percent by weight of the total weight of the reprocessed secondary aluminum alloy. More specifically, the reprocessed secondary aluminum alloy may include silicon from about 9 percent by weight to about 11 percent by weight of the total weight of the reprocessed secondary aluminum alloy. The reprocessed secondary aluminum alloy may also include magnesium from about 0.25 percent by weight to about 1.5 percent by weight of the total weight the reprocessed secondary aluminum alloy. More specifically, reprocessed secondary aluminum alloy may also include magnesium from about 0.25 percent by weight to about 0.45 percent by weight of the total weight the reprocessed secondary aluminum alloy. The reprocessed secondary aluminum alloy may further include iron from about 0.3 percent by weight to about 0.6 percent by weight of the total weight of the reprocessed secondary aluminum alloy. More specifically, the reprocessed secondary aluminum alloy may further include iron from about 0.3 percent by weight to about 0.45 percent by weight of the total weight of the reprocessed secondary aluminum alloy. More specifically still, the reprocessed secondary aluminum alloy may further include iron from about 0.3 percent by weight to about 0.4 percent by weight of the total weight of the reprocessed secondary aluminum alloy. The reprocessed secondary aluminum alloy may further still include manganese from about 0.3 percent by weight to about 0.6 percent by weight of the total weight of the reprocessed secondary aluminum alloy. More specifically, the reprocessed secondary aluminum alloy may further still include manganese from about 0.3 percent by weight to about 0.45 percent by weight of the total weight of the reprocessed secondary aluminum alloy. The reprocessed secondary aluminum alloy may further include a balance of aluminum. It is also to be appreciate that the reprocessed secondary aluminum alloy may even include other elements, which is discussed further hereinafter.

The limits for the iron and the manganese may be constrained such that the amount of the iron and the amount of the manganese present in the reprocessed secondary aluminum alloy are between about 0.7 to about 1.2 percent by weight of the total weight of the reprocessed secondary aluminum alloy. As one non-limiting example, the iron may be between about 0.3 percent by weight to about 0.45 percent by weight of the total weight of the reprocessed secondary aluminum alloy, the manganese may be between about 0.4 percent by weight to about 0.5 percent by weight of the total weight of the reprocessed secondary aluminum alloy, and the limits for the iron and the manganese may be constrained such that the amount of the iron and the amount of the manganese present in the reprocessed secondary aluminum alloy are between about 0.7 and about 0.9 percent by weight of the total weight of the reprocessed secondary aluminum alloy.

As described herein, a structural component resultant from high pressure die casting the reprocessed secondary aluminum alloy may include an intermetallic phase of α-Al₁₅(Fe, Mn)₃Si₂. The reprocessed secondary aluminum alloy, therefore, has good strength and fracture resistance, making the reprocessed secondary aluminum alloy appropriate for structural components, including structural components which are used for safety purposes.

The reprocessed secondary aluminum alloy may optionally include other elements in addition to aluminum, magnesium, silicon, iron, and manganese described herein. In non-limiting examples, the reprocessed secondary aluminum alloy may include vanadium, zirconium, calcium, phosphorus, copper, nickel, titanium, lead, tin, boron, strontium, and/or zinc. The reprocessed secondary aluminum alloy may include between 0.1 and 0.2 percent by weight vanadium, and more specifically may include about 0.15 percent by weight vanadium. The reprocessed secondary aluminum alloy may also include up to 0.1 percent by weight zirconium. The reprocessed secondary aluminum alloy may further include about 5 parts per million calcium, and about 10-20 parts per million phosphorus, preferably about 13 parts per million phosphorus. The reprocessed secondary aluminum alloy may include between about 0.03 and about 0.15 percent by weight copper. The reprocessed secondary aluminum alloy may include between about 0.01 and about 0.1 percent by weight nickel, or about 0.05 percent by weight nickel. The reprocessed secondary aluminum alloy may include between about 0.01 and about 0.2 percent by weight titanium, or about 0.15 percent by weight titanium. The reprocessed secondary aluminum alloy may include between about 0.01 and about 0.1 percent by weight lead, or about 0.05 percent by weight lead. The reprocessed secondary aluminum alloy may include between about 0.01 and about 0.1 percent by weight tin, or about 0.05 percent by weight tin. The reprocessed secondary aluminum alloy may include between about 0.01 and about 0.02 percent by weight strontium. The reprocessed secondary aluminum alloy may include between about 0.01 and about 0.1 percent by weight zinc, or about 0.1 percent by weight zinc. The balance of aluminum, therefore, may take into account other elements which may be present in the reprocessed secondary aluminum alloy.

Of the optional elements above, strontium particularly has the potential to help alleviate die soldering in addition to its typical use as a eutectic modifier. Even a relatively low amount of strontium, for example between about 0.01 and 0.02 percent by weight, has been shown to reduce die soldering by more than 20 percent. Strontium has an effect on the viscosity and surface tension of the reprocessed secondary aluminum alloy, reducing the ability of the reprocessed secondary aluminum alloy wet the surface of the tool and reduce a contact area for reaction therebetween.

The step of adding to the secondary aluminum to be reprocessed at least one chosen from iron and manganese to form a reprocessed secondary aluminum alloy may be further defined as melting the secondary aluminum to be reprocessed, any added iron, any added manganese, and/or any added chromium. Molten aluminum is reactive, particularly with any moisture present. Reactions between molten aluminum and moisture decompose the moisture into hydrogen gas, which is released into the molten aluminum and which has a determinantal effect on the mechanical properties of any cast products. To remove hydrogen gas, the method may further include the step of degassing the melted secondary aluminum to be reprocessed, any melted iron, any melted manganese, and/or any melted chromium. Degassing may include injecting an inert gas into the melted secondary aluminum to be reprocessed, any melted iron, any melted manganese, and/or any melted chromium to remove the hydrogen gas. Although not required, the step of degassing may be undertaken for at least 6 minutes. A degassing time of at least 6 minutes is relatively long compared to known processes, but better aids the reprocessed secondary aluminum alloy in being acceptable for structural components.

The method may also include the step of fluxing the molten aluminum. Fluxing the molten aluminum removes non-metallic inclusions (e.g. slag) from the molten aluminum which may prevent the reprocessed secondary aluminum alloy from being acceptable for structural components, and also prevents excessive oxide formation. The method may further include the step of increasing the refinement of the grains of the reprocessed secondary aluminum alloy. Grain refinement may be accomplished in several ways. In a non-limiting example, thermal grain refinement involves controlling the cooling rate of the molten aluminum. In another non-limiting example, grain refinement involves mechanically agitating the molten aluminum while cooling. In yet another non-limiting example, grain refinement includes adding a grain refiner to the molten aluminum. The method may further include the step of silicone modification.

The following examples are intended to illustrate the present disclosure and are not to be read in any way as limiting to the scope of the present disclosure.

Examples 1-4 and Comparative Examples 1 and 2

Examples 1-4 are of reprocessed secondary aluminum alloys that are in accordance with the subject disclosure and which can be found in Tables 1 and 2. Comparative Examples 1 and 2 are of primary aluminum which were not formed in accordance with the subject disclosure and are included to highlight advantages of the reprocessed secondary aluminum alloys described herein. Comparative Example 1 can be found in Table 1 and Comparative Example 2 can be found in Table 2.

Example 1 is shown in Table 1 and identified as Reprocessed Secondary Aluminum Alloy #1 at HT-T5 Conditions. Example 1 is of a reprocessed secondary aluminum alloy having a ratio of iron to manganese of about 1:2. Example 2 is shown in Table 1 and identified as Reprocessed Secondary Aluminum Alloy #2 at HT-T5 Conditions. Example 2 is of a reprocessed secondary aluminum alloy having a ratio of iron to manganese of about 1:1. Comparative Example 1 is shown in Table 1 and identified as Primary Aluminum at HT-T5 Conditions. More specifically, Primary Aluminum at HT-T5 Conditions is Silafont 36. Example 3 is shown in Table 2 and identified as Reprocessed Secondary Aluminum Alloy #1 at HT-T7 Conditions.

Referring now to Table 1, each of Examples 1 and 2 and Comparative Example 1 are reprocessed at HT-T5 conditions. HT-T5 conditions refers to a step of heat treatment which is used to increase the strength of the reprocessed secondary aluminum alloy. HT-T5 conditions are used to age the reprocessed secondary aluminum, for example, at an elevated temperature of between about 150 and 230 degrees centigrade. HT-T5 conditions are understood in the art and are representative of heat treatment appropriate for aluminum alloys used for structural components.

Example 3 is the same compositionally as Example 1, but has undergone a different heat-treatment. In other words, Example 3 is of a reprocessed secondary aluminum alloy having a ratio of iron to manganese of about 1:2. Example 4 is shown in Table 2 and identified as Reprocessed Secondary Aluminum Alloy #2 at HT-T7 Conditions. Example 4 is the same compositionally as Example 2, but has undergone a different heat treatment. In other words, Example 4 is of a reprocessed secondary aluminum alloy having a ratio of iron to manganese of about 1:1. Comparative Example 2 is shown in Table 2 and identified as Primary Aluminum at HT-T7 Conditions. More specifically, Primary Aluminum at HT-T5 Conditions is Silafont 36.

Referring now to Table 2, each of Examples 3 and 4 and Comparative Example 2 are reprocessed at HT-T7 conditions. HT-T7 conditions refers to a step of heat treatment which is used to increase the strength of the reprocessed secondary aluminum alloy. HT-T7 conditions consist of two stages, one stage requiring dissolution and tempering and another stage requiring over-aging of the reprocessed secondary aluminum alloy. HT-T7 conditions are understood in the art and are representative of heat treatment appropriate for aluminum alloys used for structural components.

Structural components were formed from the reprocessed secondary aluminum alloys in each of Examples 1-4. The ultimate tensile strength, yield tensile strength, elongation, and bending angle were measured for each of these structural components, and the range of measurements observed are reported in Tables 1 and 2.

As shown in Table 1, the ultimate tensile strength of the reprocessed secondary aluminum alloys in Examples 1 and 2 are as high, or higher, than that of the primary aluminum in Comparative Example 1. Moreover, the yield tensile strength of the reprocessed secondary aluminum alloys in Examples 1 and 2 are also as high, or higher, than that of the primary aluminum in Comparative Example 1. The elongation and bending angle of the reprocessed secondary aluminum alloys of Examples 1 and 2 are also comparable to the primary aluminum alloy of Comparative Example 1.

As shown in Table 2, the ultimate tensile strength of the reprocessed secondary aluminum alloy of Examples 3 and 4 are comparable to the primary aluminum alloy of Comparative Example 2. Moreover, the yield tensile strength of the reprocessed secondary aluminum alloy of Example 3 is comparable to the primary aluminum alloy of Comparative Example 2, and the yield tensile strength of the reprocessed secondary aluminum alloy of Example 4 is as high, or higher, than that of the primary aluminum in Comparative Example 2. The elongation and bending angle of the reprocessed secondary aluminum alloys of Examples 3 and 4 are also comparable to the primary aluminum alloy of Comparative Example 2.

The ultimate tensile strengths, yield tensile strengths, elongations, and bending angles of the reprocessed secondary aluminum alloys of Examples 1-4 which were formed in accordance with the subject disclosure are comparable to (or higher than) those of the primary aluminums of Comparable Examples 1 and 2. Thus, it is to be appreciated that the reprocessed secondary aluminum alloys formed in accordance with the subject disclosure are appropriate to use to form structural components. Each of Examples 1-4 also underwent riveting testing and successfully were able to be riveted without forming cracks, further exemplifying the utility of the reprocessed secondary aluminum alloys formed in accordance with the subject disclosure.

The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings, and the invention may be practiced otherwise than as specifically described.