CORROSION RESISTANT ALUMINUM ELECTRODE ALLOY

Abstract

A method is disclosed, which includes the step of preparing an aluminum alloy body for solutionizing. The aluminum alloy body may include not greater than 0.06 wt. % Fe, where at least some Fe is present. The aluminum body may include not greater than 5.0 wt. % Mg. The balance of the aluminum alloy body may be aluminum and unavoidable impurities. The aluminum alloy body may include a first vol. % of Fe-bearing particles. The method may include solutionizing the as-prepared aluminum alloy body. The solutionizing step may include dissolving at least some of the Fe-bearing particles into solid solution, thereby decreasing the first vol. % of Fe-bearing particles to a second vol. % of Fe-bearing particles in the as-solutionized aluminum alloy body.

Claims

1. A method comprising: (a) preparing an aluminum alloy body for solutionizing, wherein the aluminum alloy body comprises: (i) not greater than 0.06 wt. % Fe, wherein at least some Fe is present; (ii) not greater than 5.0 wt. % Mg; (iii) the balance aluminum and unavoidable impurities; and (iv) a first vol. % of Fe-bearing particles; and (b) solutionizing the as-prepared aluminum alloy body, wherein the solutionizing step (b) comprises dissolving at least some of the Fe-bearing particles into solid solution, thereby decreasing the first vol. % of Fe-bearing particles to a second vol. % of Fe-bearing particles in the as-solutionized aluminum alloy body.

2. The method of claim 1, wherein the aluminum alloy body is suitable for use as an aluminum electrode alloy product.

3. The method of claim 1 comprising: determining, prior to the solutionizing step (b), conditions for the solutionizing step (b), wherein: (i) the conditions include a soak temperature range of from 515 C. to a Temperature2 ( C.); (ii) a value of Temperature2 is dependent on an actual wt. % Mg of the aluminum alloy body; and (iii) Temperature2=644.6 C.[15.73*(actual wt. % Mg)]; and completing the solutionizing step (b) according to the determining step.

4. The method of claim 3 comprising selecting a value for a target temperature ( C.) within the soak temperature range, wherein: (i) the conditions include a soak time range of from Time1 (hours) to Time2 (hours); (ii) Time1=1.214110.sup.8*e{circumflex over ()}(0.032516*target temperature); and (iii) Time2=1.446710.sup.10*e{circumflex over ()}(0.032828*target temperature).

5. The method of claim 1 comprising: determining, prior to the solutionizing step (b), conditions for the solutionizing step (b), wherein: (i) the conditions include a soak temperature within 50 C. and less than a solidus temperature of the as-prepared aluminum alloy body; and completing the solutionizing step (b) according to the determining step.

6. The method of claim 5, wherein the soak temperature is within 40 C. and less than the solidus temperature of the as-prepared aluminum alloy body.

7. The method of claim 6, wherein the soak temperature is within 30 C. and less than the solidus temperature of the as-prepared aluminum alloy body.

8. The method of claim 7, wherein the soak temperature is within 20 C. and less than the solidus temperature of the as-prepared aluminum alloy body.

9. The method of claim 8, wherein the soak temperature is within 10 C. and less than the solidus temperature of the as-prepared aluminum alloy body.

10. The method of claim 9, wherein the soak temperature is within 5 C. and less than the solidus temperature of the as-prepared aluminum alloy body.

11. The method of claim 1, wherein the second vol. % of Fe-bearing particles in the as-solutionized aluminum alloy body is at least 5% less than the first vol. % of Fe-bearing particles in the as-prepared aluminum alloy body.

12. The method of claim 11, wherein the second vol. % of Fe-bearing particles in the as-solutionized aluminum alloy body is at least 10% less than the first vol. % of Fe-bearing particles in the as-prepared aluminum alloy body.

13. The method of claim 12, wherein the second vol. % of Fe-bearing particles in the as-solutionized aluminum alloy body is at least 25% less than the first vol. % of Fe-bearing particles in the as-prepared aluminum alloy body.

14. The method of claim 13, wherein the second vol. % of Fe-bearing particles in the as-solutionized aluminum alloy body is at least 50% less than the first vol. % of Fe-bearing particles in the as-prepared aluminum alloy body.

15. The method of claim 14, wherein the second vol. % of Fe-bearing particles in the as-solutionized aluminum alloy body is at least 75% less than the first vol. % of Fe-bearing particles in the as-prepared aluminum alloy body.

16. The method of claim 15 wherein the second vol. % of Fe-bearing particles in the as-solutionized aluminum alloy body is at least 90% less than the first vol. % of Fe-bearing particles in the as-prepared aluminum alloy body.

17. The method of claim 1, wherein the aluminum alloy body comprises 20-400 ppm Fe.

18. The method of claim 1, wherein the aluminum alloy body comprises not greater than 3 wt. % Mg.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] FIG. 1 is a schematic view of an example of an electrochemical cell that is configured for use in evaluating the corrosion of electrodes in an electrolyte in accordance with the present disclosure.

[0070] FIG. 2 is a graph showing hydrogen gas generation and vol. % of Fe-bearing particles for solutionized and non-solutionized alloys for four different alloy compositions.

DETAILED DESCRIPTION

Examples

[0071] The following examples are intended to illustrate the invention and should not be construed as limiting the invention in any way.

Example 1Preparing Aluminum Electrode Alloy Product Samples

[0072] Aluminum alloys 1-4, having the compositions shown in Table 1, below, were cast as ingots and rolled to the desired thickness.

TABLE-US-00001 TABLE 1 Composition of Ex. 1 Alloys (in ppm) Alloy Mg Fe 1 24200 5 2 25800 71 3 25200 95 4 24500 182

[0073] Four disks having the desired thickness (4-10 mm) and diameter (9.35 cm) were machined from each of the four ingots. Each disk had a sufficient cross-sectional surface area (i.e., 68.7 cm.sup.2) to provide a viable testing surface for immersion into an electrochemical cell (schematically depicted in FIG. 1) for the evaluation and assessment of corrosion within the range of operating conditions of the cell (e.g. time, temperatures, current, etc.). For each of Alloys 1-4, two of the four disks were solutionized at a soak temperature of 590 C. and for a soak time of 48 hours. For each of Alloys 1-4, the remaining two disks were not subject to the solutionizing step (b) of the disclosed method. Non-solutionized disks were designated as reference aluminum electrode alloy products, and solutionized disks were designated as sample aluminum electrode alloy products.

Example 2Testing of the Aluminum Electrode Alloy Reference and Sample Products

[0074] The reference and sample disks were tested for corrosion resistance (hydrogen generation) via an electrochemical cell system (schematically depicted in FIG. 1). The electrochemical cell consists of a counter electrode and an aluminum electrode (the reference or sample) alloy product submerged in an aqueous electrolyte. The electrochemical cell is equipped with a mass-flow meter for measuring hydrogen gas (i.e., H.sub.2) evolved from the aluminum electrode alloy product. Current is applied on the aluminum electrode alloy product, and flows through the electrolyte and into the counter electrode.

[0075] The reference and sample disks 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.

[0076] The reference and sample disks were run under identical conditions including electrolyte temperature, applied current, and test duration. Results were generated based on hydrogen gas generation, by accumulating the overall amount of hydrogen measured by the mass flow meter. The hydrogen generation was normalized to the surface area of each electrode. Without being bound by a particular mechanism 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 aluminum electrode alloy product is that is being evaluated.

[0077] As shown in FIG. 2, sample disks (i.e. solutionized) from Alloys 2, 3 and 4 generated less hydrogen (11.3, 14.4, and 53.2 cc/cm.sup.2, respectively) than reference disks (i.e. non-solutionized) with the same composition (54.2, 75.5 and 115.1 cc/cm.sup.2, respectively). Both sample and reference disks from Alloy 1 produced the same amount of hydrogen.

[0078] In some embodiments, higher amounts of undissolved impurities, such as iron, in an aluminum electrode alloy may result in an increased hydrogen generation (when compared to an aluminum electrode alloy having a lower amount of undissolved impurities).

[0079] However, without wishing to be bound by theory, it is believed that, due at least in part to the solutionizing, disclosed herein, at least some of the iron may be dissolved into solid solution, which is believed to improve the corrosion resistance (e.g. generate a lower amount of hydrogen when evaluated in an electrochemical half-cell test as set out in Example 2).

[0080] Furthermore, without being bound by a particular mechanism or theory, it is believed that addition of Mg as a purposeful alloying element to Fe-containing aluminum alloy bodies may result in higher amounts of undissolved iron (e.g., due at least partly to formation of FeMg-bearing particles), and therefore a reduced corrosion resistance (increased hydrogen generation, increased corrosion of the aluminum electrode alloy products formed from such aluminum alloy bodies). Without being bound by a particular mechanism or theory, it is believed that the disclosed solutionizing of Fe-containing aluminum alloy bodies having Mg encourages dissolution of both Fe and Mg into solid solution, thereby suppressing formation of FeMg-bearing particles. In this regard, the aluminum electrode alloys of the present disclosure are configured with up to 5.0 wt. % Mg, as discussed above. Thus, lower hydrogen generation (i.e., reduced corrosion) is achievable with the disclosed Fe-containing aluminum electrode alloy products having up to 0.06 wt. % Fe and up to 5.0 wt. % Mg, as compared to the baseline (i.e., reference, non-solutionized) Fe-containing aluminum electrode alloy products. Furthermore, lower hydrogen generation (e.g. reduced corrosion) with these aluminum electrode alloy products, as compared to baseline (i.e., reference, non-solutionized) aluminum electrode alloy products may be achieved at Fe levels of 5-182 ppm and Mg levels of not greater than 2.6 wt. %.

Example 3Procedure for Calculating Volume Percent of Fe-Bearing Particles

[0081] The following is the procedure used for calculating the volume percentage of Fe-bearing particles in an Fe-containing aluminum alloy body:

[0082] Step 1. Preparation for Scanning Electron Microscope (SEM) Imaging

[0083] For each of the reference and sample disks that were not used for the electrochemical cell test of Example 2, sections were taken and then ground for about 30 seconds using progressively finer grit paper starting at 240 grit and followed by 320, 400, and 600 grit paper. After grinding, the samples were polished for about 2-3 minutes on cloths using a sequence of (a) 3 micron mol cloth and 3 micron diamond suspension, (b) 3 micron silk cloth and 3 micron diamond suspension, and (c) a 1 micron silk cloth and 1 micron diamond suspension. During polishing, an oil-based lubricant was used. Prior to SEM examination, a final polish was made using 0.05 micron colloidal silica for about 30 seconds, followed by a final rinse under water.

[0084] Step 2. SEM Image Collection

[0085] Using an FEI XL30 FEG SEM, or comparable FEG SEM, a minimum of 40 backscattered electron images were captured at both the center (T/2) and near the outer edge (sample surface) of the metallographically prepared (per step 1, above) sections, thus providing a minimum of 80 images total per section. The image size was 2048 pixels by 1600 pixels at a magnification of 1000. The pixel dimensions were x=0.059 m, y=0.059 m. The accelerating voltage was 7.5 kV at a working distance of 7.5 mm and spot size of 5. The contrast and brightness was set so that the average matrix grey level of the 8-bit digital image was approximately 128 and the darkest and brightest phases were 0 (black) and 255 (white), respectively.

[0086] Step 3. Discrimination of Secondary Phase Particles

[0087] The average matrix grey level and standard deviation were calculated for each SEM image. The average atomic number of the secondary phase particles of interest is higher than the matrix (the aluminum matrix), so the secondary phase particles appeared lighter in the image representations. The pixels that make up the particles were defined as any pixel that had a grey level higher than (>) the average matrix grey level plus 3.5 standard deviations. This critical grey level was defined as the threshold. A binary image was created by discriminating the grey level image to make all pixels higher than the threshold to be white (255) and all pixels at or lower than the threshold to be black (0).

[0088] Step 4. Removal of Small Particles

[0089] Any white particle that had 4 or fewer pixels was removed from the binary image by changing its color to the background color (black).

[0090] Step 5. Calculation of Volume Percent of Fe-Bearing Particles:

[0091] Once each image was converted into solely black and white pixels, the area fraction of particles was calculated as the total number of white pixels divided by the total number of pixels. This fraction was calculated for each image for a single location, and then averaged. The total area fraction (AF) for a given sample was then calculated as a weighted average of the area fraction at T/2 and near the surface, where the near surface number was weighted twice because it occurred twice in the sample. Area fraction was then converted into a percent by multiplying by 100. The volume percent of the Fe-bearing particles in the product was then determined based on Equation (I):

Fe-Bearing Particles (vol. %)=100*(AF.sub.T/2+2*AF.sub.S)/3

AF=# WhitePixels/# TotalPixels(I)

[0092] As shown in FIG. 2, sample disks from Alloys 1-4 all had a lower vol. % of Fe-particles (0.00014, 0.00003, 0.00000, and 0.01022 vol. %, respectively) as compared to reference disks of Alloys 1-4 (0.0046, 0.01115, 0.02335, and 0.04401 vol. %, respectively).

[0093] In some embodiments, higher amounts of undissolved iron in an aluminum alloy body may result in increased vol. % of Fe-bearing particles (when compared to an aluminum alloy body having a lower amount of undissolved iron). However, without wishing to be bound by theory, it is believed that, due at least in part to the solutionizing disclosed herein, at least some of the iron may be dissolved into solid solution, which is believed to reduce the vol. % of Fe-bearing particles and thereby improve the corrosion resistance, as described above in Example 2.

[0094] 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).