Methods of preparing 7xxx aluminum alloys for adhesive bonding, and products relating to the same
Methods of preparing 7xxx aluminum alloy products for adhesive bonding and products made therefrom are disclosed. Generally, the methods include preparing a 7xxx aluminum alloy product for anodizing, then anodizing the 7xxx aluminum alloy product, and then contacting the anodized 7xxx aluminum alloy product with an appropriate chemical to create a functionalized layer. The new 7xxx aluminum alloy products may realize improved shear bonding performance.
1. A method comprising:
(a) preparing a 7xxx aluminum alloy product for anodizing, wherein the 7xxx aluminum alloy product comprises an oxide layer on a base, and wherein the preparing step (a) comprises:
(i) cleaning surfaces of the 7xxx aluminum alloy product;
(ii) after the cleaning step (a)(i), exposing the 7xxx aluminum alloy product to a caustic;
(iii) after the exposing step (a)(ii), contacting the 7xxx aluminum alloy product with an acid; and
(iv) rinsing the 7xxx aluminum alloy product with water;
wherein, due to the preparing step at least some of the oxide layer is removed and a prepared oxide layer is produced on the base,
wherein, due to steps (a)(i)-(a)(iv), a prepared 7xxx aluminum alloy product is produced;
(b) anodizing the prepared 7xxx aluminum alloy product in an acidic electrolyte solution and for a time sufficient to produce an anodic oxide layer, thereby producing an anodized 7xxx aluminum alloy product;
(i) wherein a total thickness of the prepared oxide layer plus the anodic oxide layer is from 15 to 150 nanometers; and
(c) after the anodizing step (b), contacting the anodized 7xxx aluminum alloy product with a phosphorous-containing organic acid to create a functional layer on the anodic oxide layer of the anodized 7xxx aluminum alloy product,
wherein the contacting is selected from a group consisting of spraying, immersion, roll coating, and combinations thereof.
2. The method of claim 1 , wherein the base of the 7xxx aluminum alloy product comprises 2-12 wt. % Zn, 1-3 wt. % Mg, and 0-3 wt. % Cu.
3. The method of claim 2 comprising, after the contacting step (c), bonding at least a portion of the anodized 7xxx aluminum alloy product with a second material, thereby creating an as-bonded 7xxx aluminum alloy product.
4. The method of claim 1 , wherein, when the anodized 7xxx aluminum alloy product is bonded so as to form a single-lap-joint specimen having a joint overlap of 0.5 inches, the as-bonded 7 xxx aluminum alloy product achieves completion of 45 stress durability test (SDT) cycles according to ASTM D1002 ( 10 ).
5. The method of claim 4 , wherein a residual shear strength of the single-lap-joint specimen after completing the 45 SDT cycles is at least 80% of an initial shear strength of the single-lap-joint specimen.
6. The method of claim 4 , wherein a residual shear strength of the single-lap-joint specimen after completing the 45 SDT cycles is at least 85% of an initial shear strength of the single-lap-joint specimen.
7. The method of claim 4 , wherein a residual shear strength of the single-lap-joint specimen after completing the 45 SDT cycles is at least 90% of an initial shear strength of the single-lap-joint specimen.
8. The method of claim 1 , wherein the anodizing step (b) comprises applying a current to the acidic electrolyte solution at a current density sufficient and for a time sufficient to produce the anodic oxide layer, wherein a total thickness of the prepared oxide layer plus the anodic oxide layer is from 20 to 125 nanometers.
9. The method of claim 8 , wherein the duration of the applying step is not greater than 120 seconds.
10. The method of claim 8 , wherein the acidic electrolyte solution is selected from the group consisting of sulfuric acid, phosphoric acid, chromic acid, and oxalic acid.
11. The method of claim 10 , wherein the anodizing acidic electrolyte solution is a 10-20 wt. % sulfuric acid solution.
12. The method of claim 11 , wherein the current density is from 5 to 20 amperes per square foot (ASF).
13. The method of claim 10 , wherein the anodizing acidic electrolyte solution comprises 5-20 wt. % phosphoric acid.
14. The method of claim 1 , wherein the anodizing step (b) comprises applying a current to the acidic electrolyte solution at a current density sufficient and for a time sufficient to produce the anodic oxide layer, wherein a total thickness of the prepared oxide layer plus the anodic oxide layer is from 30 to 100 nanometers.
15. The method of claim 14 , wherein the duration of the applying step is from 10 to 60 seconds.
16. The method of claim 1 , wherein the anodic oxide layer consist essentially of aluminum oxide.
17. The method of claim 1 , wherein a surface of the anodic oxide layer comprises pits.
18. The method of claim 1 , wherein the preparing step (a) comprises removing at least some intermetallic particles from a surface of the 7xxx aluminum alloy product.
19. The method of claim 18 , wherein the intermetallic particles comprise copper-bearing intermetallic particles.
20. The method of claim 1 , wherein a total thickness of the prepared oxide layer plus the anodic oxide layer is not greater than 80 nanometers.