Method For Reducing Or Eliminating Si, Fe, And Cu In Aluminum Alloys

Abstract

A method for reducing or eliminating Si contained in an aluminum alloy including: holding the aluminum alloy and Sn at a melt temperature at which the aluminum alloy and Sn are melted; lowering the melt temperature, and holding the aluminum alloy and Sn at a Si crystallization temperature at which solid Si is crystallized while maintaining a molten state of Sn and Al, and separating the solid Si; and further lowering the temperature and holding the aluminum alloy and Sn at an Al crystallization temperature at which Al is crystallized and Sn is in the molten state, to separate and recover solid Al.

Claims

1. A method for reducing or eliminating Si contained in an aluminum alloy comprising: holding the aluminum alloy and Sn at a melt temperature at which the aluminum alloy and Sn are dissolved; lowering the melt temperature, and holding the aluminum alloy and Sn at a Si crystallization temperature at which solid Si is crystallized while maintaining a molten state of Sn and Al, and separating the solid Si; and further lowering the temperature and holding the aluminum alloy and Sn at an Al crystallization temperature at which Al is crystallized and Sn is in the molten state, to separate and recover solid Al.

2. A method for reducing or eliminating Si and Fe contained in an aluminum alloy comprising: holding the aluminum alloy and Sn at a melt temperature at which the aluminum alloy and Sn are dissolved; lowering the melt temperature, and holding the aluminum alloy and Sn at a Si crystallization temperature at which solid Si and/or Al.sub.3Fe is crystallized while maintaining a molten state of Sn, Al, and Fe, and separating the solid Si and/or Al.sub.3Fe; and further lowering the temperature, and crystallizing and separating Al and/or Al.sub.3Fe while melting and holding Fe in molten Sn.

3. A method for reducing or eliminating Si and Cu contained in an aluminum alloy comprising: holding the aluminum alloy and Sn at a melt temperature at which the aluminum alloy and Sn are dissolved; lowering the melt temperature, and holding the aluminum alloy and Sn at a Si crystallization temperature at which solid Si and/or Al.sub.2Cu is crystallized while maintaining a molten state of Sn, Al, and Cu, and separating the solid Si and/or Al.sub.2Cu; and further lowering the temperature, and crystallizing and separating Al and/or Al.sub.2Cu while melting and holding Cu in molten Sn.

4. A method for reducing or eliminating Fe contained in an aluminum alloy comprising: holding the aluminum alloy and Sn at a melt temperature at which the aluminum alloy and Sn are dissolved; and lowering the melt temperature, and crystallizing and separating Al and/or Al.sub.3Fe while melting and holding Fe in molten Sn.

5. A method for reducing or eliminating Cu contained in an aluminum alloy comprising: holding the aluminum alloy and Sn at a melt temperature at which the aluminum alloy and Sn are dissolved; and lowering the melt temperature, and crystallizing and separating Al and/or Al.sub.2Cu while melting and holding Cu in molten Sn.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 illustrates solubility curves of Al and Si in molten Sn using an Al-Si system alloy.

[0018] FIG. 2 is an illustrative drawing of a Si elimination process in an aluminum alloy using molten Sn.

[0019] FIG. 3A illustrates an experimental furnace and FIG. 3 B illustrates experimental conditions, when using an Al-Si system alloy.

[0020] FIG. 4 illustrates a phase diagram of Sn, Al, and Si, and experimental values.

[0021] FIG. 5 illustrates a liquidus projection diagram for an Al-Si-Sn system.

[0022] FIG. 6 illustrates a partial enlargement of FIG. 5.

[0023] FIG. 7 is an illustrative drawing of a Fe elimination process.

[0024] FIG. 8A illustrates an experimental furnace and FIG. 8B illustrates experimental conditions, when using an Al-Fe system alloy.

[0025] FIG. 9 illustrates a graph plotting experimental values of the amount of Al dissolved and Fe concentration in Sn bath.

[0026] FIG. 10 is an illustrative drawing of a Cu elimination process.

DETAILED DESCRIPTION

[0027] The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. These are, of course, merely examples and are not intended to be limiting. In addition, the disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Further, when a first element is described as being connected or coupled to a second element, such description includes embodiments in which the first and second elements are directly connected or coupled to each other, and also includes embodiments in which the first and second elements are indirectly connected or coupled to each other with one or more other intervening elements in between.

[0028] An objective of the present disclosure is to provide a method for reducing or eliminating Si in aluminum alloys, and to be able to further reduce or eliminate Fe and Cu components.

[0029] Exemplary embodiments are described below. Note that the following exemplary embodiments do not in any way limit the scope of the content defined by the claims laid out herein. Note also that all of the elements described in the present embodiment should not necessarily be taken as essential elements.

[0030] The method for reducing or eliminating Si in an aluminum alloy according to the present disclosure includes: holding the aluminum alloy and Sn at a melt temperature at which the aluminum alloy and Sn are dissolved; lowering the melt temperature, and holding the aluminum alloy and Sn at a Si crystallization temperature at which solid Si is crystallized while maintaining a molten state of Sn and Al, and separating the solid Si; and further lowering the temperature and holding the aluminum alloy and Sn at an Al crystallization temperature at which Al is crystallized and Sn is in the molten state, to separate and recover solid Al.

[0031] Based on the phase diagram of Al and Sn disclosed in Non-Patent Document 2 and the phase diagram of Si and Sn disclosed in Non-Patent Document 3, the solubility curves of Al and Si in Sn are illustrated in FIG. 1.

[0032] Thus, in molten Sn at 873 K, about 50 mass % of Al is dissolved, but almost no Si is dissolved.

[0033] In addition, when the temperature of the molten Sn is lowered to 573 K, almost no Al is dissolved.

[0034] The present disclosure focuses on this point, and when an aluminum alloy and Sn are heated and held at 873 K or more, both Al and Si are dissolved, but when the melt temperature is lowered to about 873 K, Si crystallizes and can be separated as solid Si, and when the melt temperature is further lowered to about 573 K, Al crystallizes, and can be separated and recovered as solid Al for recycling.

[0035] In addition, Sn can be used repeatedly.

[0036] The present disclosure can also reduce Fe after eliminating Si in an aluminum alloy and includes: holding the aluminum alloy and Sn at a melt temperature at which the aluminum alloy and Sn are dissolved; lowering the melt temperature, and holding the aluminum alloy and Sn at a Si crystallization temperature at which solid Si and/or Al.sub.3Fe is crystallized while maintaining a molten state of Sn, Al and Fe, and separating the solid Si; and further lowering the temperature, and crystallizing and separating Al and/or Al.sub.3Fe while melting and holding Fe in molten Sn.

[0037] In addition, when the Si content in the aluminum alloy is low, the present disclosure is a method for reducing or eliminating Fe contained in the aluminum alloy, and includes holding the aluminum alloy and Sn at a melt temperature at which the aluminum alloy and Sn are dissolved, and lower the melt temperature, and crystallize and separate Al and/or Al.sub.3Fe while melting and holding Fe in molten Sn.

[0038] The present disclosure can also reduce Cu after removing Si in an aluminum alloy and includes: holding the aluminum alloy and Sn at a melt temperature at which the aluminum alloy and Sn are dissolved; lowering the melt temperature, and holding the aluminum alloy and Sn at a Si crystallization temperature at which solid Si and/or Al.sub.2Cu is crystallized while maintaining a molten state of Sn, Al, and Cu, and separating the solid Si; and further lowering the temperature, and crystallizing and separating Al and/or Al.sub.2Cu while melting and holding Cu in molten Sn.

[0039] In addition, when the Si content in the aluminum alloy is low, a method for reducing or eliminating Cu contained in an aluminum alloy comprising: [0040] holding the aluminum alloy and Sn at a melt temperature at which the aluminum alloy and Sn are dissolved; and [0041] lowering the melt temperature, and crystallizing and separating Al and/or Al.sub.2Cu while melting and holding Cu in molten Sn.

[0042] The present disclosure can utilize the difference in solubility between Si and Al in molten Sn to separate and recover solid Al after separating solid Si, and since Sn can be used repeatedly, Si can be reduced or eliminated from aluminum scrap materials, thereby improving recyclability.

[0043] Fe and Cu can also be reduced.

[0044] A process is described, in which Si is first eliminated and Al is recovered using a melt (molten) Sn according to the present disclosure.

[0045] A melt temperature that an aluminum alloy and Sn are dissolved is a temperature of more than 873 K, e.g., a heating temperature of about 1000 K. In addition, in the molten Sn illustrated in FIG. 1, at about 873 K, about 50 mass % of Al is dissolved, but almost no Si is dissolved, and the melt temperature can become a crystallization temperature of solid Si; and when the temperature is lowered to about 573 K, almost no Al is dissolved and Al crystallizes and separates, and it can become a crystallization temperature of Al. The present disclosure utilizes this phenomenon.

[0046] FIG. 2 is a schematic diagram of this process.

[0047] (1) Sn and an Al-Si system alloy (scrap material) are charged into a furnace which is heated to and held at a temperature of more than 873 K, e.g., about 1000 K, the whole mixture becoming in a molten state.

[0048] (2) When the above melt is gradually cooled to hold at 873 K, the solid Si is crystallized, separated and recovered.

[0049] (3) The remainder is a melt composed of Sn and Al, and when gradually cooled to 573 K, solid Al is crystallized, which is separated and recovered.

[0050] (4) The remaining Sn melt can be used repeatedly in the recycling process of aluminum scrap materials.

[0051] This process has been experimentally confirmed, and is described based on FIG. 3.

[0052] As illustrated in the schematic diagram of FIG. 3A, Sn and an Al-Si system alloy are charged into an Al.sub.2O.sub.3 furnace and heated.

[0053] A carbon holder was used for heat retention.

[0054] The Sn and the Al-Si system alloy were heated to a temperature of 10 to 200 K higher than 873 K, and stirred and dissolved with an Al.sub.2O.sub.3 rod.

[0055] Then, temperature was held at 873 K with stirring.

[0056] For the Al-Si system alloy, an alloy containing 12 mass % of Si was used, and the experiment was conducted in an Ar gas atmosphere as illustrated in FIG. 3B.

[0057] FIG. 4 illustrates a phase diagram of Sn, Al, and Si, and the experimental values of the amount of Al dissolved have been plotted on this diagram.

[0058] FIG. 5 illustrates a projection of the phase diagram for the Al-Si-Sn system, and FIG. 6 shows the range in which Si crystallizes and Al dissolves in molten Sn.

[0059] As a result, it can be seen that the range in which Al-12 mass % Si alloy dissolve in molten Sn is between 573 K or more and 1150 K or less.

[0060] Next, the phase diagrams for 800 C. and 1000 C. illustrated in Non-Patent Document 4 indicate that Al preferentially crystallizes when the alloy is cooled below the eutectic point of Al and Al.sub.3Fe (1.8 mass % Fe).

[0061] The process for reducing or eliminating Fe based on this is illustrated in FIG. 7.

[0062] After Si crystallizes at 873 K, when Fe is 1.8 mass % or less, Al and Fe dissolve in the molten Sn.

[0063] Next, when the alloy is cooled to 573 K, Fe remains in the molten Sn because the solubility of Fe in solid Al is very low.

[0064] If this process is repeated, the concentration of Fe in the molten Sn will increase, but it will crystallize as an Al.sub.3Fe compound.

[0065] This allows Fe to be eliminated.

[0066] In addition, scrap materials with a low Si content can be held directly at 573 K to eliminate Fe in Al.

[0067] This process has been experimentally confirmed, and is described based on FIG. 8.

[0068] As illustrated in the schematic diagram of FIG. 8A, Sn and Al-Fe system alloy are charged into an Al.sub.2O.sub.3 crucible and heated.

[0069] A carbon holder (crucible) was used for heat retention.

[0070] The Sn and the Al-Fe system alloy were heated to a temperature of 10 to 200 K higher than 1273 K, and stirred and dissolved with an Al.sub.2O.sub.3 rod.

[0071] Then, the temperature was held at 873 K with stirring.

[0072] For the Al-Fe system alloy, an alloy containing 10 mass % of Fe was used, and the experiment was conducted in an Ar gas atmosphere as illustrated in FIG. 8B.

[0073] In FIG. 9, the experimental values of the amount of Al dissolved and the Fe concentration in the Sn bath were plotted.

[0074] When the Al content becomes higher than the initial concentration of the case that Al-10 mass % Fe alloy illustrated by a broken line is charged into a Sn bath, and when the Fe concentration is more than or equal to the solubility, i.e., under the condition of the hatched area in FIG. 9, the Fe concentration can be reduced.

[0075] Next, the range where Cu remains in the molten Sn and Al crystallizes, can be seen from the phase diagram described in Non-Patent Document 5.

[0076] The process for eliminating Cu based on this is illustrated in FIG. 10.

[0077] When a temperature of the molten Sn is 573 K, Al crystallizes, but Cu dissolves in the molten Sn side.

[0078] When this process is repeated, and the Cu concentration in the molten Sn is 3.8 mass % or more, Cu crystallizes as a Al.sub.2Cu compound.

[0079] It can be seen that this allows Cu to be eliminated.

[0080] In addition, even in the case of Cu, when the Si content is low, the melt temperature is held at 573 K, and Cu in Al may be eliminated by leaving Cu on the Sn side.

INDUSTRIAL APPLICABILITY

[0081] The present disclosure can eliminate impurities such as Si, Fe, and Cu in aluminum alloys by using molten Sn, and can be used to recycle aluminum scrap containing impurities into aluminum products with low impurity tolerance.