METHODS OF RECYCLING ALUMINUM ALLOYS AND PURIFICATION THEREOF

Abstract

The present disclosure relates to methods of producing purified aluminum alloys from aluminum alloy scrap by producing a melt of the aluminum alloy scrap, adding one or more intermetallic former materials, producing iron-bearing intermetallic particles, removing the iron-bearing intermetallic particles, and solidifying the low-iron melt.

Claims

1. A method comprising: (a) melting aluminum alloy scrap, thereby producing a melt, wherein the aluminum alloy scrap comprises an initial iron content, wherein the initial iron content is at least 0.20 wt. % iron (Fe); (b) adding an excess of silicon (Si) to the melt, wherein the excess of silicon is an amount of silicon sufficient to produce both (i) iron-bearing intermetallic particles in the melt and (ii) a Si-based aluminum alloy from the melt; (c) forming iron-bearing intermetallic particles in the melt, wherein a first amount of silicon reacts with iron of the melt to form the iron-bearing intermetallic particles, and wherein a second amount of silicon remains in the melt in unreacted form, the second amount of silicon corresponding to an amount of the excess silicon employed in the adding step (b) required to create the Si-based aluminum alloy from the melt; (d) removing at least some of the iron-bearing intermetallic particles from the melt, thereby producing a low-iron melt with the second amount of silicon therein; (e) solidifying the low-iron melt, thereby producing the Si-based aluminum alloy having the second amount of silicon therein, wherein the Si-based aluminum alloy includes a purified iron content, wherein the purified iron content is less than the initial iron content and not greater than 0.5 wt. % Fe, and wherein the Si-based aluminum alloy includes silicon as the predominate alloying ingredient besides aluminum.

2. The method of claim 1, comprising, during the adding step (b), further adding manganese to the melt.

3. The method of claim 1, wherein the purified aluminum alloy is one of a 3xx aluminum casting alloy or a 4xxx wrought aluminum alloy.

4. The method of claim 1, wherein the purified aluminum alloy comprises not greater than 0.35 wt. % iron (Fe).

5. The method of claim 1, wherein the purified aluminum alloy comprises not greater than 0.20 wt. % iron (Fe).

6. The method of claim 1, wherein the purified aluminum alloy comprises not greater than 0.15 wt. % iron (Fe).

7. The method of claim 1, wherein the producing step (c) comprises: (i) cooling the melt from a first temperature to a second temperature, thereby producing the iron-bearing intermetallic particles.

8. The method of claim 7, comprising: at or below the second temperature, completing the removing step (d).

9. The method of claim 8, wherein the removing step (d) comprises at least one of filtration of the melt and sedimentation of the melt.

10. The method of claim 9, wherein the removing step (d) comprises filtration using a refractory filter material.

11. The method of claim 8, wherein the second temperature is at least 10 C. higher than a solidification temperature of fcc aluminum.

12. The method of claim 11, wherein the solidifying step (e) comprises: cooling the melt from the second temperature to below a solidus temperature of the low-iron melt.

13. The method of claim 12, wherein the first temperature is a liquidus temperature, and wherein the liquidus temperature is at least 10 C. higher than the second temperature.

14. The method of claim 1, comprising: after the removing step (d) and prior to the solidifying step (e), adding alloying additions to the low-iron melt, wherein the alloying additions are selected from the group consisting of chromium, nickel, zinc, titanium, tin, strontium, copper, magnesium, and combinations thereof; wherein, after the solidifying step (e), the Si-based aluminum alloy includes the alloying additions.

15. The method of claim 1, comprising, after the removing step (d) and prior to the solidifying step (e), adding alloying additions to the low-iron melt, wherein the alloying additions include at least one of copper (Cu), and magnesium (Mg); wherein, after the solidifying step (e), the Si-based aluminum alloy includes the alloying additions.

16. The method of claim 1, wherein the purified iron content is at least 10% less than the initial iron content.

17. The method of claim 1, wherein the purified iron content is at least 25% less than the initial iron content.

18. The method of claim 1, wherein the purified iron content is at least 60% less than the initial iron content.

19. The method of claim 1, wherein the Si-based aluminum alloy includes from 3.0 to 23.0 wt. % Si.

20. The method of claim 19, wherein the Si-based aluminum alloy includes at least 4.0 wt. % Si.

21. The method of claim 19, wherein the Si-based aluminum alloy includes at least 5.0 wt. % Si.

22. The method of claim 19, wherein the Si-based aluminum alloy includes at least 6.0 wt. % Si.

23. The method of claim 20, wherein the Si-based aluminum alloy includes at least 7.0 wt. % Si.

24. The method of claim 21, wherein the Si-based aluminum alloy includes not greater than 20.0 wt. % Si.

25. The method of claim 22, wherein the Si-based aluminum alloy includes not greater than 15.0 wt. % Si.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1a is an embodiment of producing a purified aluminum alloy.

[0028] FIG. 1b is an embodiment of producing a purified aluminum alloy using intermetallic former materials silicon (Si) and/or manganese (Mn).

[0029] FIG. 1c is an embodiment of producing a purified aluminum alloy having a pre-selected target composition.

[0030] FIG. 2a is a micrograph of as-cast MIC6 alloy, taken at 300 magnification.

[0031] FIG. 2b is a micrograph of as-cast MIC6 alloy, taken at 3000 magnification.

[0032] FIG. 3a is a solidification pathway diagram of MIC6 alloy of Example 1, generated by Pandat, for a solid fraction of from 0 to 1.

[0033] FIG. 3b is a solidification pathway diagram of MIC6 alloy of Example 1, generated by Pandat, for a solid fraction of from 0 to 0.2.

[0034] FIG. 4a is a solidification pathway diagram for MIC6, Alloy 1, and Alloy 2 of Example 1, generated by Pandat, for a solid fraction of from 0 to 1.

[0035] FIG. 4b is a solidification pathway diagram for MIC6, Alloy 1, and Alloy 2 of Example 1, generated by Pandat, for a solid fraction of from 0 to 0.2.

[0036] FIG. 5 is a plot of a solidification pathway diagram and the liquid aluminum Mn and Fe composition in the liquid aluminum, generated by Pandat, for a solid fraction of from 0 to 1.

[0037] FIG. 6a is a contour plot illustrating the effect of adding intermetallic former materials Si and Mn on the lowest possible iron content in a recycling simulation.

[0038] FIG. 6b is a contour plot illustrating the effect of adding intermetallic former materials Si and Mn on the purification temperature window in a recycling simulation.

[0039] FIG. 6c is a contour plot illustrating the effect of adding alloying additions Cu and Mg on the lowest possible iron content in a recycling simulation.

[0040] FIG. 6d is a contour plot illustrating the effect of adding alloying additions Cu and Mg on the purification temperature window in a recycling simulation.

[0041] FIG. 7 is a data table for the recycling simulation of Example 3 showing the solid phase fraction, the liquid aluminum composition, and the precipitation phases.

[0042] FIG. 8 is a data table for the recycling simulation of Example 4 showing the solid phase fraction, the liquid aluminum composition, and the precipitation phases.

[0043] FIG. 9 is a data table for the recycling simulation of Example 5 showing the solid phase fraction, the liquid aluminum composition, and the precipitation phases.

[0044] FIG. 10 is a data table for the recycling simulation of Example 6 showing the solid phase fraction, the liquid aluminum composition, and the precipitation phases.

[0045] FIG. 11 is a data table for the recycling simulation of Example 7 showing the solid phase fraction, the liquid aluminum composition, and the precipitation phases.

DETAILED DESCRIPTION

Example 1

[0046] A recyclable aluminum alloy of MIC6 was cast as ingot. Table 1a gives a typical composition of aluminum alloy MIC6.

TABLE-US-00001 TABLE 1a Composition of Aluminum Alloy MIC6 Element Composition (wt. %) Si 1.05 Fe 0.53 Cu 1.3 Mn 0.75 Mg 1.65 Zn 2.5 Cr 0.16 Al Balance

[0047] Micrographs were taken of the as-cast aluminum alloy. Micrographs taken at 300 and 3000 magnification are shown in FIGS. 2a and 2b, respectively. As shown, the as-cast microstructure of the aluminum alloy contains an intermetallic phase. The intermetallic phase exhibited a Chinese script-like structure, and was identified as Al.sub.15(Fe:Mn).sub.3Si.sub.2 using SEM-EDX analysis. The composition of the intermetallic phase was further confirmed by constructing a Pandat phase diagram using the composition given in Table 1, and analyzing the solidification pathway. The phase diagram constructed by Pandat, as shown in FIG. 3a-3b, illustrates the solidification pathway. As shown in FIG. 3b, a small purification temperature window of 2.5 C. exists where solid intermetallic Al.sub.15(Fe:Mn).sub.3Si.sub.2 forms absent of solid aluminum. In principle, intermetallic Al.sub.15(Fe:Mn).sub.3Si.sub.2 particles can be separated from the liquid phase (e.g., by filtration) in the 2.5 C. temperature window. However, in practice, the temperature window (2.5 C.) is too small to achieve a significant separation.

[0048] The addition of intermetallic formers silicon and manganese to the MIC6 alloy modifies the solidification pathway. As shown in Table 1b and FIGS. 4a-4b, adding manganese (Alloy 1) and a combination of silicon and manganese (Alloy 2) increases the purification temperature window (T) and the solid fraction of intermetallic Al.sub.15(Fe:Mn).sub.3Si.sub.2.

TABLE-US-00002 TABLE 1b Effect of Intermetallic Formers on Alloy MIC6 Al.sub.15(Fe:Mn).sub.3Si.sub.2 Solid Phase Composition, wt % T Fraction Alloy Si Mn Cu Fe Mg Zn Cr Al ( C.) (v/v %) MIC6 1.05 0.75 1.3 0.53 1.65 2.5 0.16 bal. 2.5 0.02 Alloy 1 1.05 2.00 1.3 0.53 1.65 2.5 0.16 bal. 43.5 3.77 Alloy 2 8.00 2.00 1.3 0.53 1.65 2.5 0.16 bal. 97.3 6.1

[0049] The solid fraction, iron and manganese compositions in the bulk aluminum, and phase change temperatures for Alloy 2 are shown in FIG. 5. As illustrated, intermetallic Al.sub.15(Fe:Mn).sub.3Si.sub.2 begins to form at approximately 690 C. At 592 C., solid aluminum (fcc) forms in equilibrium with the intermetallic and liquid phases. Thus, there is a temperature window of approximately 97 C., from 592 C. to 690 C., where intermetallic Al.sub.15(Fe:Mn).sub.3Si.sub.2 particles can be separated from the liquid aluminum phase absent of solid aluminum. This purification temperature window of approximately 97 C. is sufficient to separate the intermetallic particles from the bulk liquid aluminum. In one approach, the purification temperature window is at least 10 C. in order to separate the intermetallic particles from the bulk liquid aluminum.

[0050] As shown in FIG. 5, iron can be reduced in the bulk aluminum by adding intermetallic formers, and removing the intermetallic Al.sub.15(Fe:Mn).sub.3Si.sub.2 particles. As illustrated, the iron concentration in the aluminum is reduced from 0.53 wt. % to approximately 0.05 wt. % at the solidification point of fcc aluminum (592 C.). However, a separation that realizes 0.05 wt. % iron in the bulk aluminum without removing solid aluminum is likely not possible. Thus, in one approach intermetallic particles are removed (e.g., by filtration) above the aluminum solidification temperature (e.g., 10-20 C. above), thereby avoiding the removal of solid aluminum.

Example 2

[0051] Purifying aluminum alloys by adding intermetallic formers and removing the iron-bearing intermetallic particles may be performed on a variety of aluminum alloys. In this regard, recyclability process models were constructed for other common aluminum alloy compositions. Pandat, a thermodynamic simulation software, and an accompanying aluminum thermodynamic database, PanAluminum, were utilized to construct process models. As described in greater detail below, intermetallic formers were chosen for each aluminum alloy composition. The mixture of the intermetallic formers and aluminum alloy provides the process simulation with an overall composition. The overall composition was utilized by Pandat to determine the lowest iron concentration and the corresponding purification temperature window (T) of the mixture.

[0052] Intermetallic formers were chosen for each recycling process. The mass of intermetallic formers was chosen by a Java computer script that matches the amount of intermetallic formers with a composition in a simulation database that realizes a good separation result. In this approach, the mass of intermetallic formers was chosen based on maximizing T and minimizing the iron concentration. The database of simulations comprised 11,520 simulations carried out using each combination of the elements and compositions provided in Table 2, below.

TABLE-US-00003 TABLE 2 Elements and Compositions of Simulation Database Element Compositions (wt. %) Fe 0.5; 0.75, 1.0; 1.25, 1.5 Mn 0.1, 0.5; 1.0; 1.5; 2.0; 2.5 Si 1.0, 4.0, 7.0, 10.0, 13.0, 16.0, 19.0, 22.0 Mg 0.1; 0.4; 0.7 Cu 0.1, 0.25, 1.25, 2.25 Zn 0.1, 0.5; 1.5; 2.5

[0053] The 11,520 simulations were then used to construct contour plots. Contour plots illustrating the effect of Mn and Si, as intermetallic formers, on the iron concentration and the purification temperature window are shown in FIGS. 6a-6b for an aluminum alloy having 2.25 wt. % Cu, 0.7 wt. % Mg, 0.5 wt. % Zn. As illustrated, increasing the Si and Mn content decreases the iron concentration and increases the purification temperature window. For the shown Si and Mn content ranges and given composition, the iron concentration varies from 0.10 to about 0.70 wt. % and the purification temperature window varies from 20 C. to about 100 C. Contour plots illustrating the effect of Cu and Mg on the lowest possible iron concentration and purification temperature window are shown in FIGS. 6c-6d for an aluminum alloy having 2.0 wt. % Mn, 10.0 wt. % Si, and 0.5 wt. % Zn. As illustrated, increasing the Cu and Mg content decreases the iron concentration, and increases the purification temperature window. For the shown Cu and Mg content ranges and given composition, the iron concentration varies from 0.11 to about 0.14 wt. % and the purification temperature window varies from 94 C. to about 104 C.

Example 3

[0054] Using the simulation methodology of Example 2, a simulation was performed on an alloy (Alloy 3) having the composition shown in Table 3b, below. Intermetallic formers of manganese and silicon were added as (1) a manganese master alloy (85 wt. % Al and 15 wt. % Mn) and (2) as pure silicon. The simulation yielded a lowest possible iron composition of about 0.10 wt. % at a temperature of 600.2 C., providing a purification temperature window of about 77 C. The simulation shows that a final alloy composition having 0.13-0.17 wt. % iron will be realized by the removal of the intermetallic phases when the filtration is performed approximately 10-20 C. above the aluminum solidification temperature. The mass of Alloy 3 and intermetallic formers are provided below in Table 3a. The composition of Alloy 3, the melt composition (overall composition of Alloy 3 and intermetallic formers), and the final melt composition after purification are given in Table 3b. A complete set of data for the recycling simulation is shown in FIG. 7.

TABLE-US-00004 TABLE 3a Mass of Materials of Example 3 Material Mass (lbs) Alloy 3 1000 15% Al - 85% Mn Master Alloy 11.2 Pure Silicon 91.8

TABLE-US-00005 TABLE 3b Process Compositions of Example 3 Melt Composition Melt Composition Alloy 3 Composition Prior to Purification After Purification Element (wt. %) (wt. %) (wt. %) Si 0.75 9.00 8.94 Fe 0.57 0.52 0.13-0.17 Cu 0.20 0.18 0.19 Mn 1.03 1.80 0.63-0.74 Mg 0.50 0.45 0.47-0.48 Cr 0.09 0.08 0.08 Ni 0.05 0.05 0.05 Zn 0.12 0.11 0.12 Ti 0.05 0.04 0.04 Zr 0.02 0.01 0.01

Example 4

[0055] Using the methodology of Example 2, a simulation was performed on a mixture of two alloys (Alloy 4a and Alloy 4b), having the compositions shown in Table 4b, below. Alloy 4a is a typical 6061 aluminum alloy. Intermetallic formers of manganese, and silicon, were added as (1) a manganese master alloy (85 wt. % Al and 15 wt. % Mn), and (2) as pure silicon. Pure copper was also added to raise the copper level in the alloys to approximately 1.0 wt. %. The simulation yielded a lowest possible iron composition of about 0.08 wt. % at a temperature of about 594.9 C., providing a purification temperature window of about 105 C. The simulation shows a final alloy composition having 0.11-0.14 wt. % iron will be realized by the removal of the intermetallic phases when the filtration is performed at approximately 10-20 C. above the aluminum solidification temperature. The mass of Alloy 4a, Alloy 4b, Mn master alloy, pure Si, and pure copper are provided below in Table 4a. The compositions of Alloy 4a, Alloy 4b, the melt composition (overall composition of Alloy 4a, Alloy 4b, Mn master alloy, pure Si, and pure Copper), and the final melt composition after purification are given in Table 4b. A more complete set of data for the recycling simulation is given in FIG. 8.

TABLE-US-00006 TABLE 4a Mass of Materials of Example 4 Material Mass (lbs) Alloy 4a 400 Alloy 4b 600 15% Al - 85% Mn Master Alloy 10.7 Pure Silicon 96 Pure Copper 8

TABLE-US-00007 TABLE 4b Process Compositions of Example 4 Melt Melt Composition Composition Alloy 4a Alloy 4b Prior to After Composition Composition Purification (wt. Purification Element (wt. %) (wt. %) %) (wt. %) Si 0.6 0.82 9.27 9.25-9.26 Fe 0.7 0.23 0.37 0.11-0.14 Cu 0.275 0.42 1.03 1.07 Mn 0.15 0.99 1.40 0.58-0.69 Mg 1.00 0.42 0.58 0.4-0.6 Cr 0.20 0.045 0.10 0.10 Ni 0.00 0.05 0.03 0.03 Zn 0.25 0.05 0.12 0.12 Ti 0.15 0.134 0.13 0.04

Example 5

[0056] Using the methodology of Example 2, a simulation was performed on a mixture of two alloys (Alloy 5a and Alloy 5b), having the compositions shown in Table 5b, below. Intermetallic formers of manganese and silicon were added as (1) a manganese master alloy (85 wt. % Al and 15 wt. % Mn), and (2) as pure silicon. The simulation yielded a lowest possible iron composition of about 0.08 wt. % at a temperature of about 592.7 C., providing a purification temperature window of about 84 C. The simulation shows a final alloy composition having 0.10-0.13 wt. % iron will be realized by the removal of the intermetallic phases when the filtration is performed at approximately 10-20 C. above the aluminum solidification temperature. The mass of Alloy 5a, Alloy 5b, Mn master alloy, and pure Si are provided below in Table 5a. The compositions of Alloy 5a, Alloy 5b, the melt composition (overall composition of Alloy 5a, Alloy 5b, Mn master alloy, and pure Si), and the final melt composition after purification are given in Table 5b. A more complete set of data for the recycling simulation is given in FIG. 9.

TABLE-US-00008 TABLE 5a Mass of Materials of Example 5 Material Mass (lbs) Alloy 5a 400 Alloy 5b 600 15% Al - 85% Mn Master Alloy 15 Pure Silicon 110

TABLE-US-00009 TABLE 5b Process Compositions of Example 5 Melt Composition Alloy 5a Alloy 5b Prior to Melt Composition Composition Composition Purification After Purification Element (wt. %) (wt. %) (wt. %) (wt. %) Si 0.75 0.82 10.48 10.48 Fe 0.57 0.53 0.49 0.10-0.12 Cu 0.2 0.11 0.13 0.14 Mn 1.03 1.03 2.05 0.64-0.74 Mg 0.5 0.0488 0.20 0.21 Cr 0.085 0.05 0.06 0.06 Ni 0.05 0.05 0.04 0.04 Zn 0.12 0.087 0.09 0.10 Ti 0.049 0.05 0.04 0.03 Zr 0.015 0.046 0.03 0.03

Example 6

[0057] Using the methodology of Example 2, a simulation was performed on a mixture of two alloys (Alloy 6a and Alloy 6b), having the compositions shown in Table 6b, below. Intermetallic former silicon was added as pure silicon. The simulation yielded a lowest possible iron composition of about 0.10 wt. % at a temperature of about 597.9 C., providing a purification temperature window of about 67 C. The simulation shows a final alloy composition having 0.12-0.16 wt. % iron will be realized by the removal of the intermetallic phases when the filtration is performed at approximately 10-20 C. above the aluminum solidification temperature. The mass of Alloy 6a, Alloy 6b, and pure Si are provided below in Table 6a. The compositions of Alloy 6a, Alloy 6b, the melt composition (overall composition of Alloy 6a, Alloy 6b, and pure Si), and the final melt composition after purification are given in Table 6b. A more complete set of data for the recycling simulation is given in FIG. 10.

TABLE-US-00010 TABLE 6a Mass of Materials of Example 6 Material Mass (lbs) Alloy 6a 400 Alloy 6b 600 Pure Silicon 77.5

TABLE-US-00011 TABLE 6b Process Compositions of Example 6 Melt Alloy Composition 6a Alloy 6b Prior to Melt Composition Composition Composition Purification After Purification Element (wt. %) (wt. %) (wt. %) (wt. %) Si 1.5 2.35 9.06 9.05-9.06 Fe 0.22 0.25 0.22 0.12-0.16 Cu 0.53 0.45 0.45 0.46 Mn 0.92 1.05 0.93 0.63-0.74 Mg 0.35 0 0.13 0.13 Cr 0.06 0 0.02 0.02 Ni 0.05 0.03 0.04 0.04 Zn 0.75 0.8 0.72 0.73 Ti 0.07 0.1 0.08 0.04 Zr 0.007 0.01 0.01 0.01

Example 7

[0058] Using the methodology of Example 2, a simulation was performed on an alloy (Alloy 7) having the compositions shown in Table 7b, below. Intermetallic former silicon was added as pure silicon. Pure copper was also added to raise the copper level in the alloys to approximately 1.9 wt. %. The simulation yielded a lowest possible iron composition of about 0.09 wt. % at a temperature of about 595.1 C., providing a purification temperature window of about 100 C. The simulation shows a final alloy composition having 0.12-0.15 wt. % iron will be realized by the removal of the intermetallic phases when the filtration is performed at approximately 10-20 C. above the aluminum solidification temperature. The mass of Alloy 7, Mn master alloy, and pure Si are provided below in Table 7a. The compositions of Alloy 7, the melt composition (overall composition of Alloy 7, pure silicon, and pure copper), and the final melt composition after purification are given in Table 7b. A more complete set of data for the recycling simulation is given in FIG. 11.

TABLE-US-00012 TABLE 7a Mass of Materials of Example 7 Material Mass (lbs) Alloy 7 1000 Pure Silicon 92 Pure Copper 16

TABLE-US-00013 TABLE 7b Process Compositions of Example 7 Alloy 7 Melt Composition Composition Melt Composition Prior After Purification Element (wt. %) to Purification (wt. %) (wt. %) Si 0.82 9.04 9.04-9.05 Fe 0.23 0.21 0.12-0.15 Cu 0.42 1.82 1.84-1.85 Mn 0.99 0.89 0.89 Mg 0.042 0.04 0.04 Cr 0.045 0.04 0.04 Ni 0.05 0.05 0.05 Zn 0.05 0.05 0.05 Ti 0.134 0.12 0.12 Zr 0.055 0.05 0.05