Anodizing an article of aluminum or alloy thereof

Abstract

A method of anodizing an article of aluminum or aluminum alloy for forming a porous anodic oxide coating comprises an immersion step of immersing the article to be anodized in an electrolyte in a tank, wherein the electrolyte comprises an aqueous solution of 5-50 g/l sulphuric acid and 2-50 g/l phosphoric acid, and arranging the article as an anode with respect to one or more counter electrodes as arranged cathodes in the electrolyte, and an anodizing step of applying a positive anode voltage Va to the article, while the temperature of the electrolyte is in the range of 33-60° C.

Claims

1. A method of anodizing an article of aluminum or aluminum alloy for applying a porous anodic oxide coating in preparation of the subsequent application of an adhesive bonding layer and/or a primer layer, comprising: immersing the article in an electrolyte in a tank, wherein the electrolyte comprises an aqueous solution of sulphuric acid andphosphoric acid, and arranging the article as an anode with respect to one or more counter electrodes that are arranged as cathodes in the electrolyte; and anodizing by applying a positive anode voltage Va to the article switched as anode, wherein the concentration of sulphuric acid in the electrolyte is in the range of 10-40 g/l, the concentration of phosphoric acid in the electrolyte is in the range of 2-40 g/l, the temperature of the electrolyte is in the range of 33-60° C. during the anodizing, and the anodizing time is in the range of 15-35 minutes; wherein the electrolyte is maintained at an aluminum concentration of at most 4.8 g/l; and the voltage is varied to achieve a current density of 0.8±0.4 A/dm.sup.2, wherein the anodizing is followed by a rinsing step performed approximately 3 minutes after the anodizing.

2. The method of claim 1, wherein the rinsing step comprises rinsing the anodized article with a rinsing agent.

3. The method claim 1, wherein the phosphoric acid concentration is in the range of 4-16 g/l.

4. The method of claim 1, wherein the temperature of the electrolyte is in the range of 40-54° C.

5. The method of claim 1, wherein the anode voltage is in the range of 8-34 V.

6. The method of claim 1, wherein the electrolyte is free from additional corrosion inhibitors.

7. The method of claim 1, wherein the anodizing comprises: increasing the applied anode voltage at a gradient of 1-10 V/minute to a first valuein the range of 8-34 V, maintaining the applied anode voltage at said first value for a first anodizing time, raising the applied anode voltage to a second value in the range of 8-34 V, which second value is higher than the first value, and maintaining the applied anode voltage at said second value for a second anodizing time.

8. The method of claim 7, wherein the second anodizing time is less than the first anodizing time.

9. A method of manufacturing a painted anodized article, comprising: immersing the article in an electrolyte in a tank, wherein the electrolyte comprises an aqueous solution of sulphuric acid andphosphoric acid, and arranging the article as an anode with respect to one or more counter electrodes that are arranged as cathodes in the electrolyte; anodizing by applying a positive anode voltage Va to the article switched as anode, wherein the concentration of sulphuric acid in the electrolyte is in the range of 10-40 g/l, the concentration of phosphoric acid in the electrolyte is in the range of 2-40 g/l, the temperature of the electrolyte is in the range of 33-60° C. during the anodizing, and the anodizing time is in the range of 15-35 minutes; applying a paint primer to a surface to be painted of the anodized article; and painting the primed surface of the article; wherein the electrolyte is maintained at an aluminum concentration of at most 4.8 g/l; and the voltage is varied to achieve a current density of 0.8±0.4 A/dm.sup.2, wherein the anodizing is followed by a rinsing step performed approximately 3 minutes after the anodizing.

10. The method of claim 9, wherein a chromate (Cr(VI)) free bonding primer is applied to the anodized article prior to the application of the paint primer.

11. A method of manufacturing a metal bonded product comprising at least two metal articles of aluminum or aluminum alloy bonded to one another by means of an adhesive, comprising: providing the at least two metal articles that were anodized by immersing the respective articles in an electrolyte in a tank, wherein the electrolyte comprises an aqueous solution of sulphuric acid and phosphoric acid, and arranging the respective article as an anode with respect to one or more counter electrodes that are arranged as cathodes in the electrolyte; anodizing by applying a positive anode voltage Va to the respective article switched as anode, wherein the concentration of sulphuric acid in the electrolyte is in the range of 10-40 g/l, the concentration of phosphoric acid in the electrolyte is in the range of 2-40 g/l, the temperature of the electrolyte is in the range of 33-60° C. during the anodizing, and the anodizing time is in the range of 15-35 minutes; applying a layer of a bonding primer to surfaces of the metal articles to be bonded together; applying a layer of an adhesive to at least one of the surfaces to be bonded on top of the layer of bonding primer; stacking the at least two metal articles such that surfaces of the articles to which at least the layer of bonding primer is applied face each other; and bonding the stacked metal articles together under elevated pressure; wherein the electrolyte is maintained at an aluminum concentration of at most 4.8 g/l; and the voltage is varied to achieve a current density of 0.8±0.4 A/dm.sup.2, wherein the anodizing is followed by a rinsing step performed approximately 3 minutes after the anodizing.

12. The method of claim 11, wherein the at least two metal articles are metal sheets of aluminum or aluminum alloy, whereby the metal bonded product is a metal bonded laminate.

13. The method of claim 12, wherein the adhesive is a fiber-reinforced adhesive or the adhesive is impregnated into reinforcing fibers, so that the metal bonded product is a fiber metal laminate.

14. The method of claim 11, wherein the bonding primer is a chromate (Cr(VI)) free bonding primer.

15. A method of anodizing an article of aluminum or aluminum alloy for applying a porous anodic oxide coating in preparation of the subsequent application of an adhesive bonding layer and/or a primer layer, comprising: immersing the article in an electrolyte in a tank, wherein the electrolyte comprises an aqueous solution of sulphuric acid and phosphoric acid, and arranging the article as an anode with respect to one or more counter electrodes that are arranged as cathodes in the electrolyte; and anodizing by applying a positive anode voltage Va to the article switched as anode, wherein the concentration of sulphuric acid in the electrolyte is in the range of 10-40 g/l, the concentration of phosphoric acid in the electrolyte is in the range of 2-40 g/l, the temperature of the electrolyte is in the range of 33-60° C. during the anodizing, and the anodizing time is in the range of 15-35 minutes, wherein the anodizing comprises: increasing the applied anode voltage at a gradient of 1-10 V/minute to a first value in the range of 8-34 V; maintaining the applied anode voltage at said first value for a first anodizing time, the first anodizing time being 10-15 minutes; raising the applied anode voltage to a second value in the range of 8-34 V, which second value is higher than the first value; and maintaining the applied anode voltage at said second value for a second anodizing time, the second anodizing time being 2-5 minutes; wherein the electrolyte is maintained at an aluminum concentration of at most 4.8 g/l; and the first and second applied anode voltages are maintained at respective values to achieve a current density of 0.8±0.4 A/dm.sup.2, wherein the anodizing is followed by a rinsing step performed approximately 3 minutes after the anodizing.

16. The method of claim 1, wherein, after anodizing, the porous anodic oxide coating is capable of achieving 10% or less bondline corrosion in response to a neutral salt spray duration of 180 days.

17. The method of claim 1, further comprising drying the rinsed anodized article.

Description

SUMMARY OF THE DRAWINGS

(1) Examples are further illustrated by the attached drawing, wherein:

(2) FIG. 1 is a diagrammatical view of an example apparatus for carrying out the anodizing;

(3) FIG. 2 is a diagram showing the course of the anodic voltage as a function of time in an example of the anodizing method;

(4) FIG. 3 is a diagram showing the Bell peel strength versus rinse delay time of AA2024-T3 unclad, anodized at 28° C., with 120 g/l phosphoric acid and 80 g/1 sulphuric acid, and subsequently provided with phenol formaldehyde bonding primer Redux101 and bonded with 125° C. curing epoxy adhesive AF163-2K; and

(5) FIG. 4 is a diagram showing the Bell peel strength versus rinse delay time of AA2024-T3 unclad, anodized at 28° C., with 75 g/l phosphoric acid and 50 g/l sulphuric acid, and subsequently provided with phenol formaldehyde bonding primer Redux101 and bonded with 125° C. curing epoxy adhesive AF163-2K.

DESCRIPTION

(6) In FIG. 1 an example of an apparatus for anodizing an article of aluminum or aluminum alloy is represented diagrammatically. The apparatus in its entirety is indicated by reference numeral 10. The anodizing apparatus 10 comprises an immersion tank 12 having upstanding walls 14 and a bottom 16. Along one or more of the walls 14, in particular pair(s) of opposite walls counter-electrodes 18 are arranged, which are electrically connected as cathodes to a DC voltage source 20. A support 22 carries the article 24 to be anodized. The article 24 is electrically connected as an anode to the DC voltage source 20 by means of an anode connector 26. A heat exchanger 28 controlled by control unit 30 is provided as a temperature regulator enabling maintaining the anodizing temperature of a liquid electrolyte 32, that is contained in the tank 12, at a desired temperature value. The electrolyte 32 is an aqueous solution of sulphuric acid and phosphoric acid in a concentration of 5-50 g/1 and 2-50 g/l respectively. During operation the liquid electrolyte is typically replenished partially on a regular basis. The Al content is maintained at a level below 5 g/1. The tank 12 has an open top side so that the article 24 can be brought into the tank 12 from above and dipped into the electrolyte 32, and after anodizing can be lifted upwardly out of electrolyte 32 and the tank 12.

(7) FIG. 2 shows a preferred embodiment of the anodizing method as a plot of the anodic voltage Va (V) as a function of time (minutes), wherein initially the anodic voltage is raised at 1-10 V/min in a first substep A to a first anodic voltage Va1, such as 17 V. During a second substep B the anodic voltage Va1 is maintained for a first period of time t1 such as 10-20 minutes. At the end of this first period of time the anodic voltage is increased to a second anodic voltage Va2 in a third substep C and held at this voltage Va2 in a fourth substep D during an additional period of time t2, which is usually in the range up to 5 minutes.

(8) Experimental details and data about this embodiment for varying Va1, Va2, t1 and t2 are presented in Table 5, below.

Experiments

(9) Extensive and careful investigations of the standard PSA process have shown that the narrow temperature tolerance associated with this standard PSA process is defined and imposed by the porous oxide structure to be achieved for bonding. With increasing temperature such as at 29±2° C. (Tmax 29.5° C.) and 30±1° C. (Tmax 31.7° C.) (120 g/l phosphoric acid+80 g/1 sulphuric acid; Va=18 V) significant oxide dissolution occurs that affects the porous oxide structure, as has been evidenced by SEM pictures.

(10) Moreover, after anodizing the electrolyte needs to be removed such as by spray rinsing or immersion rinsing. On a lab scale the samples can be rinsed within seconds, such as 5 seconds. In commercial installations handling sheets of e.g. measuring 1 m×10 m, the time between anodizing and rinsing is in the order of minutes, typically 2±1 minutes. It has appeared that additional dissolution and thus deterioration of the porous oxide coating occurs during the delay between anodizing and removal of the electrolyte from the article by rinsing. In particular it has appeared that dissolution is most pronounced upon treating unclad aluminum alloy (e.g. AA2024-T3 bare) articles. The ultimate result of the deteriorated coating is a dramatic reduction of the adhesive bonding performance as evidenced by dry and wet Bell peel results (EN 2243-2) after testing according to EN 1967 using a non-chromate bonding primer (phenol formaldehyde bonding primer Redux 101, bonded with 125° C. curing epoxy adhesive AF163-2K), as shown in Table 1 and FIG. 3.

(11) In the context of this disclosure for both dry and wet Bell peel tests, if a sample has a bonding strength of 200 N/25 mm or more the sample is considered to fulfil the bonding requirements.

(12) TABLE-US-00001 TABLE 1 Bell peel strength values of 0.5 mm and 1.6 mm M2024-T3 unclad, anodized at 28 C. with 120 g/l phosphoric acid and 80 g/l sulphuric acid, subsequently provided with phenol formaldehyde bonding primer Redux101 and bonded with 125° C. curing epoxy adhesive AF163-2K with rinsing delay times varied. Time between Dry Bell peel on Wet Bell peel on anodizing 2024-T3 bare 2024-T3 bare Wet peel Anodizing and rinsing [N/25 mm] [N/25 mm] strength process (s) #1 #2 average #1 #2 average reduction (%) 120 g/l 5 285 277 281 223 240 232 =reference phosphoric 60 260 264 262 132 124 128 45 acid + 80 g/1 120 201 209 205 103 108 106 54 sulphuric 180 276 221 249 177 190 184 21 acid 300 230 236 233 103 119 111 52 at 18 V at 28 ± 1° C. for 23 min

(13) Further tests for solving the oxide dissolution problem were conducted at lower acid concentrations of 75 g/l phosphoric acid and 50 g/l sulphuric acid at essentially the same conditions regarding Va=18 V and T=28° C. In view of the lower acid concentrations the anodizing time was prolonged to 30 minutes (3 minutes ramp up and 27 minutes dwell time). Although these further tests showed that similar results regarding adhesive bonding and bondline corrosion resistance can be achieved, the delayed rinsing still had a pronounced negative effect on adhesive bonding performance as measured by Bell peel strength as shown in FIG. 4. FIG. 4 shows the Bell peel strength versus rinse delay time of AA2024-T3 unclad, anodized at 28° C. in an electrolyte comprising 75 g/l phosphoric acid and 50 g/l sulphuric acid, and subsequently provided with phenol formaldehyde bonding primer Redux101 and bonded with 125° C. curing epoxy adhesive AF163-2K.

(14) Solved herein are the problems associated with oxide dissolution and resulting peel strength reduction by a totally different approach, allowing elimination of all chromate ((Cr(VI) compounds in the metal bonded products.

(15) A sulphuric acid concentration of 10 g/l was selected for anodizing experiments and compared with previously tested sulphuric acid concentration of 50 g/l. Additionally the phosphoric acid concentration was varied with 0, 40 and 80 g/l to distinguish the role of the acids separately. Voltages have been varied to achieve a current density of 0.8±0.4 A/dm.sup.2. Tests were first started on AA2024-T3 bare, because of the observed oxide dissolution problems, and AA7075-T6 alclad, because this alloy is in general most susceptible to bondline corrosion.

(16) The extent of bondline corrosion is typically determined with samples of metal to metal bonded sheets that are machined to 25 mm wide strips, in the same way as peel specimens are made (e.g. according to EN 2243-2). These samples are exposed to a desired duration of neutral salt spray according to ISO 9227. The exposure to salt may, without mechanical loading, result in delamination, initiated by corrosion at the unprotected edges of the strips that were cut by machining. After the exposure the strips are peeled open to measure the extent of bondline corrosion, defined as the relative portion of the area of delamination initiated by corrosion, compared to the initial bond area. In the context of this disclosure (unless indicated otherwise) after a salt spray duration of 180 days, a bondline corrosion of 10% or less is considered “good”, and after a salt spray duration of 90 days, a bondline corrosion of 5% or less is considered “good”. In a 45 days lasting salt spray test 2% or less is “good”.

(17) Pretreated aluminum sheets have been provided with phenol formaldehyde bonding primer Redux 101 and bonded with 125° C. curing epoxy adhesive AF163-2K. Some typical results of bondline corrosion with AA7075-T6 alclad after 180 days salt spray exposure are given in Table 2. Table 3 offers wet Bell peel strength data for M 2024-T3. For both aluminum alloys in these Tables 2 and 3 respectively anodizing was performed at a constant voltage at the indicated current densities for 30 minutes, except #3 (20 min) in Table 3.

(18) TABLE-US-00002 TABLE 2 Bondline corrosion values after 180 days salt spray exposure of 0.8 mm and 1.6 mm AA7075-76 alclad, provided with phenol formaldehyde bondprimer Redux101 and bonded with 125° C. curing epoxy adhesive AF163-2K, with anodizing parameters varied. Sulphuric Phosphoric acid acid concen- concen- Anodizing Current Bondline tration tration temperature density corrosion (%) (g/l) (g/l) (° C.) (A/dm2) #1 #2 average 10 0 20 0.47 99 99 99 35 0.73 99 99 99 50 1.08 2 3 3 58 3 6 5 10 40 20 0.40 95 93 94 35 0.85 2 3 3 50 1.2 2 45 24 10 80 20 0.44 90 95 93 35 0.78 2 4 3 50 1.25 1 3 2 50 0 20 0.84 99 90 95 35 1.03 55 50 53 50 1.25 15 50 33 50 40 20 0.84 85 75 80 35 1.15 15 6 11 50 1.39 70 55 63 50 80 20 1.01 75 80 78 35 1.17 10 15 13 50 1.39 65 30 48 80 120 28 10 16 13

(19) Surprisingly the best bondline corrosion results had been obtained with the lowest sulphuric acid concentration of 10 g/l, at relatively high temperatures of 35° C. to 58° C. with higher anodizing temperature being required when no phosphoric acid is present in the electrolyte. The bondline corrosion values in Table 2 indicate that the optimum anodizing temperature varies between 35° C. and 50° C. and depends also on the composition of the electrolyte.

(20) TABLE-US-00003 TABLE 3 Wet Belll peel strength on AA2024-T3 unclad provided with phenol formaldehyde bondprimer Redux101 and bonded with 125° C. curing epoxy adhesive AF163 2K, with anodizing parameters varied. Sulphuric acid Phosphoric acid Anodizing Current concentration concentration temperature, density Wet Bell peel (N/25 mm) (g/1) (g/l (° C.) (A/dm2) #1 #2 #3 average 10 0 20 0.24 10 8 19 13 35 0.42 15 5 14 11 50 0.77 215 154 195 188 58 163 149 163 158 10 40 20 0.40 166 136 143 148 35 0.80 150 80 145 125 50 1.21 172 147 188 169 10 80 20 0.38 171 53 149 124 35 0.85 207 79 151 146 50 1.70 265 192 272 243 50 0 20 0.42 3 7 3 4 35 0.72 255 264 312 277 50 1.05 154 128 117 133 50 40 20 0.30 46 30 199 92 35 0.70 269 206 242 239 50 1.24 219 177 249 215 50 80 20 0.38 204 162 183 183 35 0.76 136 98 166 133 50 1.44 251 197 266 238 80 120 28 162 121 197 160

(21) From the above Tables 2 and 3 it appears that at a given set of process conditions no satisfying results are achieved regarding corrosion and bonding for these different alloys.

(22) Further tests with addition of various amounts of phosphoric acid were performed, because the phosphoric acid is believed to improve adhesion, moisture resistance, and thus durability of the bondline. Tests were conducted primarily with anodizing of AA2024-T3 bare, AA7075-T6 bare, and AA2024-T3 alclad. With sulfuric acid concentration of 10, 25, and 40 g/l, respectively, temperature has been varied with 33, 40, 47 and 53° C., and phosphoric acid concentration has been varied with 2, 5, 15 and 40 g/l. Additionally the time between anodizing and rinsing has been varied to validate that problems of oxide dissolution had been solved. Anodizing voltages of 8, 15 and 22V have been applied to obtain an appropriate current density.

(23) Wet Bell peel tests have been conducted on AA2024-T3 bare and AA7075-T6 bare according EN 1967 and a part of the results is given in Table 4 below.

(24) The data in Table 4 indicate that with the full range of combinations of sulphuric acid concentration from 5-50 g/l, in particular 10-40 g/l, phosphoric acid concentration from 2-40 g/l, and temperature from 33-54° C. good wet Bell peel results can be obtained. When phosphoric acid concentration is 2-50 g/l, the anodizing temperature can be 33° C. and increased temperature up to 54-60° C. generally improves adhesion. With respect to rinsing delay time the temperature can be at least increased up to 54° C. at 40 g/l phosphoric acid. Additionally it appears from the test data that with all the combinations the delay of rinsing after anodizing up to 3 minutes does not result into a reduction of Wet Bell peel strength.

(25) TABLE-US-00004 TABLE 4 Wet Bell peel strength values of bonded samples, made of 0.5 mm and 1.6 mm AA2024-T3 bare sheets and of 0.5 mm and 1.6 mm AA7075-T6 bare sheets, by anodizing the sheets at an anodizing voltage of 15 V during 28 minutes, and by subsequent application of phenol formaldehyde bondprimer Redux101 and bonding with 125° C. curing epoxy adhesive AF163-2K. The anodizing parameters regarding sulphuric acid concentration, phosphoric acid concentration, temperature and rinsing delay time were varied. Wet Bell peel on Wet Bell peel on 2024-T3 bare 7075-T6 bare [N/25 mm] [N/25 mm] Relative Relative Time to to Bondline corrosion on 2024- between direct, direct, T3 alclad (%) anodizing 5 s 5 s #1 #2 #3 #4 and delay delay 45 d 90 d 90 d 180 d H.sub.2SO.sub.4 H.sub.5PO.sub.4 Temp. rinsing ( rinsing rinsing salt salt salt salt (g/l) (g/l) (° C.) or min) #1 #2 (%) #1 #2 (%) spray spray spray spray 10 2 33 5 s.sup.  33 49 35 79 34 52 37 3.0 min 78 99 215 60 149 184 11 10 28 40 5 s.sup.  242 265 211 225 5 7 13 47 5 s.sup.  231 231 247 239 1 6 17 54 5 s.sup.  196 252 216 218 0 5 11 3.0 min 232 270 112 244 210 105 1 3 1 5 33 5 s.sup.  209 218 196 202 8 30 40 15 33 5 s.sup.  222 210 262 258 8 12 13 40 33 5 s.sup.  217 225 236 200 1 1 22 3.0 min 232 256 110 222 237 105 2 5 20 54 5 s.sup.  263 252 220 255 1 2 3 3.0 min 274 247 101 254 206 97 1 1 28 25 2 33 5 s.sup.  53 109 71 98 10 1 9 40 5 s.sup.  270 241 226 209 2 4 2 47 5 s.sup.  204 231 226 2 6 11 5 33 5 s.sup.  175 224 146 211 5 22 20 40 5 s.sup.  222 241 221 198 1 4 9 15 47 5 s.sup.  233 206 235 216 2 1 2 3.0 min 215 98 229 218 99 1 2 1 40 33 5 s.sup.  157 169 214 228 1 3 4 40 5 s.sup.  194 214 264 208 2 2 15 40 2 33 5 s.sup.  185 188 178 187 8 10 17 3.0 min 211 197 109 180 170 96 3 13 15 54 5 s.sup.  196 235 296 212 2 3 14 3.0 min 199 234 100 247 204 89 1 3 6 5 33 5 s.sup.  249 244 210 217 2 11 24 15 33 5 s.sup.  244 235 235 220 6 9 15 40 33 5 s.sup.  180 192 187 196 2 1 17 3.0 min 186 210 113 196 205 105 1 0 11 54 5 s.sup.  160 224 193 214 2 2 12 3.0 min 205 224 110 227 208 107 2 0 9 50 75 28 5 s.sup.  152 175 3.0 min 114 120 73 80 120 28 5 s.sup.  223 240 3.0 min 177 190 79

(26) TABLE-US-00005 TABLE 5 Bondline corrosion values after 90 days salt spray exposure of bonded samples, made of 0.5 mm and 1.6 mm AA7075-T6 alclad, by anodizing in an electrolyte comprising 25 g/l sulphuric acid and 10 g/l phosphoric acid at 45° C. (with further anodizing parameters varied), and by subsequent application of epoxy bondprimer Redux112 and bonding with 125° C. curing epoxy adhesive AF163-2K, with anodizing parameters varied. Anodizing substeps Anodic voltage Anodic voltage according FIG. 2 Bondline Va1 Va2 A B/t1 C D/t2 corrosion [V] [V] [min] [min] [min] (min] [%] 23 4.6 12 3 23 4.6 19 2 23 4.6 33 2 23 4.6 40 1 23 11.5 26 1 17 1.7 26 5 23 2.3 26 2 11 23 2.2 22 2.4 4 1 11 29 2.2 22 3.6 4 3 17 29 3.4 22 2.4 4 1 23 29 4.6 22 1.2 4 2 23 11 4.6 22 2.4 4 7

(27) TABLE-US-00006 TABLE 6 Dry and wet Bell peel values of various alloys and bondline corrosion values of AA2024-T3 alclad, by anodizing in an electrolyte comprising 14-33 g/l sulphuric acid and 10 g/l phosphoric acid at 46° C. and 15/19 V (with increasing metal concentration due to ageing, while sometimes sulphuric acid was added for replenishment). Sheets were provided with phenol formaldehyde bondprimer Redux101 and subsequently bonded with 125° C. curing epoxy adhesives AF163-2K or FM94 respectively. Run number 1 2 3 4 5 6 7 8 Concentrations of sulphuric acid aluminium and main alloying elements Sulphuric acid 15 21 30 25 17 22 33 21 (g/l) Phosphoric 10.2 10.6 10.5 10.2 10.2 10.0 9.9 10.3 acid [g/l] Aluminium 0.00 0.05 0.09 1.23 2.47 2.56 2.56 4.79 [g/l] Cupper (mg/l) 0 Zinc (mg/l) 0 Iron (mg/l) 0 Peel values of 0.5 mm and 1.6 mm AA2024-T3 alclad provided with Redux101 and bonded with AF163 (N/25 mm) AF163 #1 287 264 290 292 301 249 248 242 dry #2 252 270 256 260 246 249 238 245 AF163 #1 307 316 300 278 296 239 257 267 Wet #2 169 274 255 284 256 247 234 241 Peel values of 0.5 mm and 1.6 mm AA2024-T3 alclad provided with Redux101 and bonded with FM94 (N/25 mm) FM94 #1 199 201 215 161 dry #2 201 211 209 172 FM94 #1 216 219 216 189 Wet #2 188 216 220 173 Peel values of 0.5 mm and 1.6 mm AA2024-T3 bare, provided with Redux101 and bonded with AF163 (N/25 mm) AF163 #1 266 273 294 300 277 295 274 300 dry #2 249 244 261 302 241 262 240 253 AF163 #1 264 254 256 267 262 252 256 225 Wet #2 251 261 248 268 238 238 232 231 Peel values of 0.5 mm and 1.8 mm AA7075-T6 bare, provided with Redux101 and bonded with AF163 (N/25 mm) AF163 #1 252 273 285 294 258 271 260 288 dry #2 241 237 226 247 246 225 247 247 AF163 #1 271 277 282 285 253 275 259 238 Wet #2 250 232 228 236 246 215 221 229 Bondline corrosion values of 0.5 mm and 1.6 mm AA2024-T3 alclad, provided with Redux101 and bonded with AF163 (%)* AF163 #3 8.3 3.5 8.7 11 8.1 6.1 7.8 90 days Salt #4 2.0 9.1 7.0 1.6 3.7 9.1 2.4 6.5 spray Bondline corrosion values of 0.5 mm and 1.6 mm AA2024-T3 alclad, provided with Redux101 and bonded with FM94 (%)* FM94 #3 2.6 5.8 2.5 1.9 90 days Salt #4 0.9 3.2 4.3 2.2 spray FM94 #5 7.5 11 4.1 5.7 180 days Salt #6 3.5 8.8 8.3 7.3 spray Run number 9 10 11 12 13 14 15 Concentrations of sulphuric acid aluminium and main alloying elements Sulphuric acid 14 20 28 22 16 22 30 (g/l) Phosphoric 10.5 10.5 10.4 9.9 9.8 9.8 9.8 acid [g/l] Aluminium 5.95 6.03 6.10 7.39 8.66 8.55 8.50 [g/l] Cupper (mg/l) 254 222 194 192 101 96 291 Zinc (mg/l) 79 79 80 96 114 113 114 Iron (mg/l) 21 21 21 21 24 24 26 Peel values of 0.5 mm and 1.6 mm AA2024-T3 alclad provided with Redux101 and bonded with AF163 (N/25 mm) AF163 #1 289 277 252 247 260 274 265 dry #2 252 268 242 247 259 257 229 AF163 #1 238 266 259 214 226 260 242 Wet #2 227 241 227 242 239 287 227 Peel values of 0.5 mm and 1.6 mm AA2024-T3 alclad provided with Redux101 and bonded with FM94 (N/25 mm) FM94 #1 204 192 159 dry #2 204 173 174 FM94 #1 195 200 181 Wet #2 194 179 188 Peel values of 0.5 mm and 1.6 mm AA2024-T3 bare, provided with Redux101 and bonded with AF163 (N/25 mm) AF163 #1 290 277 279 294 317 301 309 dry #2 280 264 285 273 299 271 274 AF163 #1 239 260 227 245 245 234 298 Wet #2 251 271 260 254 252 254 267 Peel values of 0.5 mm and 1.8 mm AA7075-T6 bare, provided with Redux101 and bonded with AF163 (N/25 mm) AF163 #1 263 257 272 267 297 274 264 dry #2 248 233 237 246 244 238 235 AF163 #1 218 227 237 243 262 243 265 Wet #2 231 238 238 224 253 234 224 Bondline corrosion values of 0.5 mm and 1.6 mm AA2024-T3 alclad, provided with Redux101 and bonded with AF163 (%)* AF163 #3 15 3.8 8.8 15 13 19 18 90 days Salt #4 10 11 15 26 8.0 9.5 13 spray Bondline corrosion values of 0.5 mm and 1.6 mm AA2024-T3 alclad, provided with Redux101 and bonded with FM94 (%)* FM94 #3 2.9 2.6 1.3 90 days Salt #4 1.3 2.9 2.5 spray FM94 #5 6.0 9.1 7.6 180 days Salt #6 2.8 4.1 8.5 spray

(28) Table 6 shows that at aluminum concentrations below 5 g/l (Run no. 1-8) average bondline corrosion of AA2024-T3 alclad bonded with AF163-2K is less than 10%, which is considered acceptable in industry. At higher concentrations (Run no. 9-15) average bondline corrosion increases to an undesired level.