Methods of preparing 7XXX aluminum alloys for adhesive bonding, and products relating to the same

Abstract

Methods of preparing 7xxx aluminum alloy products for adhesive bonding are disclosed. Generally, the methods include chemical and/or mechanically preparing a 7xxx aluminum alloy product to reduce the amount of magnesium oxides while maintaining any copper-containing intermetallic particles located proximal the surface of the 7xxx aluminum alloy product. After preparation, a functionalized layer may be produced thereon for adhesive bonding.

Claims

1. A method comprising: (a) receiving a 7xxx aluminum alloy sheet, wherein the 7xxx aluminum alloy sheet comprises a surface oxide layer; (i) wherein the surface oxide layer comprises an as-received thickness; (ii) wherein the surface oxide layer comprises magnesium oxides and aluminum oxides; (iii) wherein the 7xxx aluminum alloy sheet comprises copper-bearing intermetallic particles at least proximal the surface oxide layer; (b) reducing the as-received thickness of the surface oxide layer to a preparation thickness, wherein the reducing comprises maintaining a volume fraction of the copper-bearing intermetallic particles proximal the surface oxide layer; (c) after the reducing step (b), creating a functional layer bonded to the 7xxx aluminum alloy sheet.

2. The method of claim 1, wherein the copper-bearing intermetallic particles comprise Al.sub.7Cu.sub.2Fe particles.

3. The method of claim 1, wherein the reducing step (b) comprises: contacting the surface oxide layer with a preparation solution for a time sufficient to reduce the as-received thickness to the preparation thickness while maintaining the volume fraction of the copper-bearing intermetallic particles proximal the surface oxide layer.

4. The method of claim 3, wherein the preparation solution is alkaline.

5. The method of claim 4, wherein the preparation solution comprises a pH of not greater than 10.

6. The method of claim 4, wherein the contacting step occurs for at least 20 seconds.

7. The method of claim 4, wherein the contacting step occurs for at least 60 seconds.

8. The method of claim 4, wherein the contacting step occurs for at least 90 seconds.

9. The method of claim 4, wherein the preparation solution comprises a preparation temperature during the contacting step, wherein the preparation temperature is from 100-150° F.

10. The method of claim 3, wherein the preparation solution is acidic.

11. The method of claim 10, wherein the preparation solution comprises a pH of not greater than 3.

12. The method of claim 10, wherein the preparation solution is nitric acid.

13. The method of claim 10, wherein the preparation solution comprises a preparation temperature during the contacting step, wherein the preparation temperature is from 70-90° F.

14. The method of claim 3, wherein the reducing step (b comprises contacting the surface oxide layer with a preparation solution for a time sufficient to reduce the as-received thickness to the preparation thickness and in the absence of substantial de-alloying of the copper-bearing intermetallic particles proximal the surface oxide layer.

15. The method of claim 1, wherein the reducing step comprises mechanical preparation.

16. The method of claim 15, wherein the mechanical preparation comprises media blasting.

17. The method of claim 15, wherein the mechanical preparation comprises at least one of grit blasting, machining and sanding.

18. The method of claim 1, wherein, after the reducing step, the preparation thickness of the surface oxide layer is not greater than 20 nm.

19. The method of claim 1, wherein, due to the reducing step (b), the surface oxide layer comprises not greater than 10 at. % magnesium oxides.

20. The method of claim 1, wherein the 7xxx aluminum alloy product comprises 2-12 wt. % Zn, 1-3 wt. % Mg, and 1-3 wt. % Cu.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional schematic view of an as-received 7xxx aluminum alloy product having surface oxides thereon (not to scale; for illustration purposes only).

(2) FIG. 2 is a flow chart illustrating one embodiment of a method for producing 7xxx aluminum alloy products in accordance with the present disclosure.

(3) FIG. 3 illustrates various aspects of the reducing step (200) of the FIG. 2.

(4) FIGS. 4a-4b, 5a-5b, and 6a-6b are XPS graphs from Example 1 illustrating various concentrations and thicknesses of various 7xxx aluminum alloy products, the figures being as-received (FIG. 4a-4b), prepared (FIG. 5a-5b), and functionalized (FIG. 6a-6b).

(5) FIGS. 7a-7b are XPS graphs from Example 4 illustrating various concentrations and thicknesses of various 7xxx aluminum alloy products after mechanical abrasion.

(6) FIG. 8 is an SEM micrograph showing typical microstructural features of an as-received oxide of 7075-T6.

(7) FIG. 9 is an SEM micrograph showing pure elemental copper particles in the 7075-T6 product due to de-alloying of copper-bearing intermetallic particles.

DETAILED DESCRIPTION

Example 1—Preparation with Alkaline Solution

(8) A 7xxx aluminum alloy sheet (7075-T6) was received and cut into various samples. FIG. 8 shows a typical as-received oxide. The as-received oxide thickness and compositions were measured via XPS (X-ray photoelectron spectroscopy), the results of which are show in FIG. 4a-4b, below. The surfaces of these 7075-T6 samples were then prepared by wiping via a solvent (e.g., hexane or acetone) to remove organic contaminants and dirt, followed by contacting with a dilute BONDERITE 4215 NC solution at 140° F. for 2 minutes. Due to this preparation, the oxide thickness of the samples were reduced. For one sample, the oxide thickness was reduced to less than 11 nm, as shown in FIG. 5a-5b, with a substantial reduction of the magnesium oxide content (to less than 10 at. % Mg). The samples were then rinsed in city water for 2 minutes and were found to be water-break free, indicating sufficient removal of organic contaminants and dirt. The samples were then treated with an organic phosphoric-containing acid at 150° F. for 8 seconds to produce a functionalized layer thereon. FIG. 6a-6b illustrates the XPS measurement of one sample with a functionalized layer thereon. As illustrated, the composition and the thickness of oxide remain unchanged, with the net effect being the intended penetration of the acid into the oxide layer, which is indicated by the presence of phosphorus (P) to a depth of 8 nm. The removed magnesium oxides facilitates this penetration.

(9) The samples were then sequentially bonded and then subjected to an industry standard cyclical corrosion exposure test, similar to ASTM D1002, which continuously exposes the samples to 1080 psi lap shear stresses to test bond durability. Surprisingly, all samples (four in this case) completed the required 45 cycles. The samples were found to have 6102, 6274, 6438, and 6101 psi retained shear strength after the testing, well above the nominal value of 5000 psi generally obtained in 5xxx alloys, and comparable to those observed in 6xxx alloys. These results indicate that no substantial de-alloying of the copper-containing intermetallic particles occurred during the BONDERITE preparation, resulting in appropriate production of a functionalized layer thereon.

Example 2—Preparation with Alkaline Solution Followed by Acidic Solution

(10) For example 2, the same 7075-T6 sheet and procedure was used as per example 1, except after the BONDERITE preparation and rinse, a conventional acid preparation was used (6.5 vol. % Deoxidizer LFN by CLARIANT, BU Masterbatches, Rothausstrasse 61, CH-4132 Muttenz, Switzerland), followed by another rinse, and then application of the organic phosphoric-containing acid. The samples from this example 2 were then subjected to the same lap shear stress testing as per example 1. All samples failed after no more than 7 cycles, indicating substantial de-alloying of the copper-bearing intermetallic particles occurred during the preparation, resulting in elemental copper being present and interfering with production of the functional layer. FIG. 9 shows such elemental copper particles.

Example 3—Preparation with Acidic Solution

(11) For example 3, the same 7075-T6 sheet and procedure was used as per example 1, except an 8 wt. % nitric acid solution was used in lieu of the BONDERITE preparation. The nitric acid temperature was 80° F. and the treatment time was 60 seconds. The samples from this example 3 were then subjected to the same lap shear stress testing as per example 1. Surprisingly, all samples completed the required 45 cycles. The samples were found to have an average retained shear strength of 5600 psi after testing, indicating sufficient bonding occurred.

Example 4—Media Blasting

(12) For example 4, the same 7075-T6 sheet was used, but, instead of a chemical preparation, media blasting was used to reduce the as-received oxide thickness. As shown in FIGS. 7a-7b, the blasting removed the magnesium oxide layer (within the accuracy of the XPS) and without any chemical attack. The blasting also beneficially created a roughened surface for the subsequent functionalization layer creation.

(13) Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be madepc without departing from the invention as defined in the appending claims.