ALUMINUM ALLOYS FOR USE IN ELECTROCHEMICAL CELLS AND METHODS OF MAKING AND USING THE SAME

Abstract

New aluminum electrode alloys and methods of making the same are disclosed. In one embodiment, a method comprises, casting an aluminum alloy into an as-cast product, wherein the aluminum alloy comprises from 0.005 wt. % to 0.06 wt. % Fe, and forming the as-cast product into an aluminum electrode alloy. The casting step may comprise solidifying at a solidification rate. The solidification rate may be at or above a threshold solidification rate. The threshold solidification rate is sufficient to achieve not greater than 0.04 vol. % of Fe particles.

Claims

1. A method comprising: (a) casting an aluminum alloy into an as-cast product, wherein the aluminum alloy comprises from 0.005 wt. % to 0.06 wt. % Fe; and (b) forming the as-cast product into an aluminum electrode alloy; wherein the casting comprises solidifying at a solidification rate; wherein the solidification rate is at or above a threshold solidification rate; wherein the threshold solidification rate is sufficient to achieve not greater than 0.04 vol. % of iron particles in the as-cast product.

2. The method of claim 1, wherein the threshold solidification rate is sufficient to achieve not greater than 0.03 vol. % of iron particles in the as-cast product.

3. The method of claim 1, wherein the aluminum alloy includes at least 0.02 wt. % Fe.

4. The method of claim 1, wherein the casting comprises continuous casting the aluminum alloy into a strip.

5. The method of claim 4, wherein the continuous casting comprises belt casting or roll casting.

6. The method of claim 1, wherein the casting comprises semi-continuous casting.

7. The method of claim 1, wherein the casting comprises additive manufacturing.

8. The method of claim 1, wherein the forming comprises working of the as-cast aluminum alloy.

9. The method of claim 8, wherein the working comprises rolling, forging, or extruding.

10. The method of claim 8, wherein the aluminum electrode alloy comprises a wrought structure.

11. The method of claim 1, wherein the threshold solidification rate is at least 10 K/s.

12. The method of claim 1, wherein the threshold solidification rate is at least 50K/s.

13. The method of claim 1, wherein the aluminum alloy comprises not greater than 5.0 wt. % Mg.

14. The method of claim 1, wherein the aluminum alloy comprises not greater than 4.0 wt. % Mg.

15. The method of claim 1, wherein the aluminum alloy comprises not greater than 3.0 wt. % Mg.

16. The method of claim 1, wherein the aluminum alloy comprises at least 0.5 wt. % Mg.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 provides a graphical representation of the relationship between iron in solid solution (in weight percent) vs. cooling rate (or, solidification rate) measured in K/sec, for four different aluminum alloys having different contents of Iron (e.g. 0.04 wt. % Fe, 0.1 wt. % Fe; 0.25 wt. % Fe; and 0.55 wt. % Fe.), available at: Miki, I et al (1975), J. Japan Inst Light Metals, Vol 25, 1-9.

[0029] FIG. 2 provides a schematic view of an example of an electrochemical cell that is configured for use in conjunction with Example 1 and Example 2, to evaluate the corrosion of electrodes in an electrolyte, in accordance with quantifying corrosion resistance with one or more of the present embodiments.

[0030] FIG. 3 provides experimental data on total hydrogen generated per kilogram aluminum and total volume fraction of Fe bearing particles when three different compositions (low iron, medium iron, and high iron), each produced at two different solidification rates, were analytically evaluated, in accordance with one or more embodiments of the present disclosure.

[0031] FIG. 4 is a flow chart illustrating one embodiment of the processing steps for producing an aluminum electrode alloy.

[0032] FIG. 5 is a flow chart illustrating another embodiment of the processing steps for producing an aluminum electrode alloy.

DETAILED DESCRIPTION

[0033] The various embodiments to the present disclosure will be further explained with reference to the attached drawings, wherein like structures are referred to by like numerals throughout the several views. The drawings shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention. Further, some features may be exaggerated to show details of particular components.

[0034] Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying figures. Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the invention that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention is intended to be illustrative, and not restrictive.

[0035] Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases in one embodiment and in some embodiments as used herein do not necessarily refer to the same embodiment(s), though it may. Furthermore, the phrases in another embodiment and in some other embodiments as used herein do not necessarily refer to a different embodiment, although it may. Thus, as described below, various embodiments of the invention may be readily combined, without departing from the scope or spirit of the invention.

[0036] In addition, as used herein, the term or is an inclusive or operator, and is equivalent to the term and/or, unless the context clearly dictates otherwise. The term based on is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise. In addition, throughout the specification, the meaning of a, an, and the include plural references. The meaning of in includes in and on.

[0037] The following examples are intended to illustrate the invention and should not be construed as limiting the invention in any way.

EXAMPLES

Example 1

[0038] The alloys of the comparative examples consist essentially of the Fe, and Mg weight percentages shown in Table 1, the balance being aluminum, incidental elements and impurities.

[0039] Aluminum alloys, having the compositions shown in Table 1, below, were cast as ingots (i.e. for slow solidification) or continuously cast using a belt caster (i.e. for fast solidification), rolled to the desired thickness, and machined into disks (samples) having the desired thickness and a diameter, with a sufficient cross-sectional surface area to provide a viable testing surface for immersion into an electrochemical cell, schematically depicted in FIG. 2, for the evaluation of corrosion within the range of operating conditions of the cell (e.g. time, temperatures, current, etc.).

TABLE-US-00001 TABLE 1 Sample Mg (wt. %) Fe (wt. %) Comparative Alloy - Low Iron 2.5 <0.006 wt. % (<60 ppm) Medium Iron 2.5 0.010 wt. % (100 ppm) High Iron 2.5 0.019 wt. % (190 ppm)

[0040] During casting, two different solidification rates were employed: a slow solidification rate and a fast solidification rate. The slow solidification rate was cast at a solidification rate of 0.4 K/s by pouring the molten aluminum alloy into a copper mold, while the fast solidification rate was cast using a belt caster at a solidification rate of at least 50 K/s to not greater than 200 K/s. In this embodiment, the threshold solidification rate was 50K/s.

[0041] As depicted in FIG. 1, preparing the aluminum alloy at a solidification rate (e.g. cooling rate K/s) above about 10 K/s allows more than 90% of the total iron to be retained in solid solution e.g. 92-99% of the total iron is in solid solution with a solidification rate above 10 K/sec.), for an aluminum alloy containing totally 0.04 wt. % Fe. Thus, in some embodiments, the threshold solidification rate may be at least 10K/s.

[0042] Next, disks of three different alloys at two different solidification rates were evaluated according an electrochemical cell test for hydrogen generation, the results of which are described in Example 2.

Example 2Testing Aluminum Electrode Alloys

[0043] The samples of Example 1 were evaluated for total hydrogen generation in liters per kilogram (e.g. corrosion) in an electrochemical cell. A schematic representation of the utilized electrochemical cell is depicted in FIG. 2. The results are illustrated in FIG. 3.

[0044] The electrochemical cell system is designed to simulate anode conditions in an electrochemical device. The electrochemical cell consists of a counter electrode and an aluminum electrode submerged in an aqueous electrolyte. The electrochemical cell is equipped with a mass-flow meter for measuring hydrogen gas evolved from the aluminum electrode as current is applied to the aluminum electrode.

[0045] The samples were tested according to the following procedure. A predefined temperature-and-current step control program was applied to the cell so that the hydrogen evolution rate was measured over a set range of operating temperatures, i.e. between room temperature and 100 C. and over a set of current densities, ranging from 0 to 300 mA/cm.sup.2.

[0046] The samples were run under identical conditions including electrolyte temperature, applied current, and test duration. Results are generated based on hydrogen generation, by accumulating the overall amount of hydrogen measured by the mass flow meter. Without being bound by a particular mechanism or theory, it is believed that the overall amount of hydrogen generated by the system corresponds to the corrosion reaction (undesired reaction). Thus, the less hydrogen produced, the more corrosion resistant the alloy is that is being evaluated.

[0047] Referring to the low iron samples containing <0.006 wt. % Fe (<60 ppm), it was observed that the total hydrogen generated with the fast solidification rate was 580 L/kg, performing better than the slow solidification rate which generated 700 L/kg. As a result, the difference between the fast and slow solidification rates was 120 L/kg.

[0048] Referring to the medium iron samples containing 0.010 wt. % (100 ppm), there is a significant difference between the fast solidification rate and the slow solidification rate in hydrogen generation. The fast solidification rate sample generated approximately 700 L/kg and the slow solidification rate generated approximately 1700 L/kg. Thus, the fast solidification rate sample containing 0.010 wt. % Fe (100 ppm) results in an aluminum electrode alloy that performs similarly to the low iron aluminum electrode alloy with slow solidification rates as typically found in DC casting.

[0049] Referring to the high iron samples containing 0.019 wt. % Fe (190 ppm), there is another significant difference between the fast solidification rate sample and the slow solidification rate sample in hydrogen generation. The fast solidification rate sample generated approximately 780 L/kg and the slow solidification rate sample generated approximately 2170 L/kg. Thus, the fast solidification rate sample containing 0.019 wt. % Fe (190 ppm) results in an aluminum electrode alloy that performs comparably to the low iron aluminum electrode alloy at slow solidification rates: 780 L/kg for samples containing 0.019 wt. % Fe (190 ppm) with fast solidification rate vs. 700 L/kg for samples containing <0.006 wt. % Fe (<60 ppm), with slow solidification rate.

[0050] Thus, without being bound by a particular mechanism or theory, it is believed that aluminum electrode alloy compositions having a higher content of iron can be utilized and will perform similarly and/or comparably to low iron content aluminum electrode alloys, provided that the high iron aluminum electrode alloys are processed/deposited with a process such that the solidification rate of the product is at least 50K/sec. Regarding the trends depicted in FIG. 3, it is believed that iron contents of up to around 0.06 wt. % Fe can be utilized with high solidification rates. The high solidification rates may maintain a high amount of iron in solid solution, meaning the iron is not within the grain structure, thereby reducing corrosion, (e.g. as quantified via hydrogen generation in an electrochemical cell).

[0051] Also referring to FIG. 3, for each of the 6 samples (at 3 different compositions), the vol. % of iron particles were detected via SEM analysis. For the low iron samples containing <0.006 wt. % Fe (<60 ppm) at either solidification rate, less than 0.001 vol. % of iron was visually observable in a representative SEM of the sample. For the medium iron samples containing 0.010 wt. % Fe (100 ppm): the fast solidification rate provided an anode containing approximately 0.01 vol. % of iron particles and the slow solidification rate provided approximately 0.02 vol. % of iron particles. For the high iron samples containing 0.019 wt. % Fe (190 ppm): the fast solidification rate provided approximately 0.02 vol. % of iron particles and the slow solidification rate provided approximately 0.04 vol. % of iron particles.

[0052] Thus, with these examples, it is observed that in one or more of the aluminum electrode alloys (e.g. anode alloys) prepared within the threshold solidification rate described allows for a comparable corrosion resistance as compared to a low iron content aluminum electrode alloy composition, when evaluated as an electrode in an electrochemical cell test.

[0053] In some embodiments, one or more of the aluminum electrode alloys (e.g. anodes) described allows for an improved corrosion resistance as compared to the same aluminum electrode alloy composition without processing within the solidification rate threshold, when evaluated as an electrode in an electrochemical cell test.

[0054] However, without wishing to be bound by theory, it is believed that, due at least in part to the processing of the aluminum electrode alloy in accordance with a threshold solidification rate, at least some of the iron may be dissolved into solid solution. This, in turn, is believed to improve the corrosion resistance (e.g. generate a lower amount of hydrogen when evaluated in an electrochemical cell test as set out in Example 2).

Example 3: Method for Determining Particles in the Microstructure

[0055] As one non-limiting example for quantifying the solidification rate, the following procedure can be used.

[0056] The alloy sample is prepared for SEM imaging wherein: Longitudinal (L-ST) samples of the alloy are ground (e.g. for about 30 seconds) using progressively finer grit paper starting at 240 grit and moving through 320, 400, and finally to 600 grit paper. After grinding, the samples are polished (e.g., for about 2-3 minutes) on cloths using a sequence of (a) 3 m Mol cloth and 3 m diamond suspension, (b) 3 m silk cloth and 3 m diamond suspension, and finally (c) a 1 m silk cloth and 1 m diamond suspension. During polishing, an appropriate oil-based lubricant may be used. A final polish prior to SEM examination is to be made using 0.05 m colloidal silica (e.g., for about 30 seconds), with a final rinse under water.

[0057] The SEM image is collected from the prepared sample, by obtaining 80 backscattered electron images at the center (T/2) and quarter thickness (T/4) of the metallographically prepared (per section 1, above) longitudinal (L-ST) sections using an FEI XL30 field emission gun scanning electron microscope (FEG-SEM), or comparable FEG-SEM. Using an image size of 2048 pixels by 1600 pixels at a magnification of 500, the pixel dimensions are x=0.059 m, y=0.059 m. The accelerating voltage is to be 5.0 kV at a working distance of 5.0 mm and SEM spot size of 5. The contrast and brightness are to be set such that the average matrix grey level of the 8-bit digital image is approximately 128 and the darkest and brightest phases are 0 (black) and 255 (white) respectively.

[0058] Next, the images are assessed and the second phase particles, i.e. the iron particles in this case are identified. The average matrix grey level and standard deviation are calculated for each image. The average atomic number of the second phase particles of interest is higher than the matrix (the aluminum matrix), so the second phase particles will appear bright in the image representations. The pixels that make up the particles are defined as any pixel that has a grey level more than (>) the average matrix grey level plus 3.5 standard deviations. This critical grey level is defined as the threshold. A binary image is created by discriminating the grey level image to make all pixels higher than the threshold to be white (255) and all pixels at or higher than the threshold to be black (0).

[0059] Finally, the small particles that are not secondary phases in the grain structure are removed/filtered from the image. More specifically, any bright particle that has 4 or fewer pixels is removed from the binary image by changing its color to the background color (white). The particle density is then calculated.

[0060] While a number of embodiments of the present invention have been described, it is understood that these embodiments are illustrative only, and not restrictive, and that many modifications may become apparent to those of ordinary skill in the art. Further still, the various steps may be carried out in any desired order (and any desired steps may be added and/or any desired steps may be eliminated).