CA1118708A - Method for providing environmentally stable aluminum surfaces for adhesive bonding and product produced - Google Patents
Method for providing environmentally stable aluminum surfaces for adhesive bonding and product producedInfo
- Publication number
- CA1118708A CA1118708A CA000270187A CA270187A CA1118708A CA 1118708 A CA1118708 A CA 1118708A CA 000270187 A CA000270187 A CA 000270187A CA 270187 A CA270187 A CA 270187A CA 1118708 A CA1118708 A CA 1118708A
- Authority
- CA
- Canada
- Prior art keywords
- aluminum
- minutes
- adherend
- angstroms
- anodizing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/20—Layered products comprising a layer of metal comprising aluminium or copper
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/02—Anodisation
- C25D11/04—Anodisation of aluminium or alloys based thereon
- C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
- C25D11/08—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used containing inorganic acids
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- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Adhesives Or Adhesive Processes (AREA)
- Electrochemical Coating By Surface Reaction (AREA)
- Laminated Bodies (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Environmentally stable bond joints of aluminum metal and aluminum alloys in adhesively joined structures are formed by utilizing a prebonding anodization of the aluminum surfaces in a phosphoric acid electrolyte using an electrolyte bath temperature of 50° to 85°F. The anodized surface is then removed from the electrolyte bath and washed free of electrolyte within from one half to two and one half minutes from cessation of anodizing current, dried and coated with an adhesive resin.
The anodized aluminum metal surfaces are then juxtaposed with an adhesive resin and bonded together under pressure and heat to cure the adhesive resin. The resulting structure is resistant to failure of the bond joints on exposure to moist atmospheric conditions. The surface preparation provides a porous hydration resistant aluminum oxide surface which minimizes adhesive failure at the oxide-adhesive interface under aqueous exposure. Alloys containing copper and other alloying constituents may be successfully anodized and bonded by this process.
Environmentally stable bond joints of aluminum metal and aluminum alloys in adhesively joined structures are formed by utilizing a prebonding anodization of the aluminum surfaces in a phosphoric acid electrolyte using an electrolyte bath temperature of 50° to 85°F. The anodized surface is then removed from the electrolyte bath and washed free of electrolyte within from one half to two and one half minutes from cessation of anodizing current, dried and coated with an adhesive resin.
The anodized aluminum metal surfaces are then juxtaposed with an adhesive resin and bonded together under pressure and heat to cure the adhesive resin. The resulting structure is resistant to failure of the bond joints on exposure to moist atmospheric conditions. The surface preparation provides a porous hydration resistant aluminum oxide surface which minimizes adhesive failure at the oxide-adhesive interface under aqueous exposure. Alloys containing copper and other alloying constituents may be successfully anodized and bonded by this process.
Description
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This invention relates to methods of preparing environmental:Ly stable bonded aluminum structure and more particularly relates to methods of preparing bonded aluminum structures in which the aluminum surface is rendered especially well adapted to receive the adhesive resin and is resistant to subsequent delamination and failure of the adhesive bond at the adhesive resin-aluminum interface.
The structural bonding of metal to metal and composite .~ ~
`; ~
~ 8~7a8 1 ¦type assembly widely used in the aircraft industry and elsewhere
This invention relates to methods of preparing environmental:Ly stable bonded aluminum structure and more particularly relates to methods of preparing bonded aluminum structures in which the aluminum surface is rendered especially well adapted to receive the adhesive resin and is resistant to subsequent delamination and failure of the adhesive bond at the adhesive resin-aluminum interface.
The structural bonding of metal to metal and composite .~ ~
`; ~
~ 8~7a8 1 ¦type assembly widely used in the aircraft industry and elsewhere
2 ¦frequently require a resultant structure which is reasonably re-
3 ¦sistant to the extremes of atmospheric conditions found in use. For
4 ¦example, in aircraft construction the wing structure utilized in
5 ¦manufacture of large passenger, cargo, and military aircraft, utili-
6 ¦zes adhesively bonded structures which are subjected to extremes of
7 ¦temperature varying from substantially below zero Farenheit in
8 ¦ Arctic areas to temperatures in excess of 150F. in tropical areas ~ ¦ when the aircraft must be exposed to the tropical sun. Aircraft are 10 ¦ also exposed to marine environments and other highly corrosive at-11 ¦ mospheres. To avoid failures o~ the aircraft structures as well as 12 ¦ to meet the stringent requirements of the military aircraft 13 ¦ standards and the standards established by the aircraft industry for 1~ commercial passenger and cargo aircraft, bonded metal to metal and composite type assemblies must be able to withstand the environment-1~ al conditions to be encountered. Of particular importance is re-17 sistance to corrosion and delamination of composite structures 18 1 occasioned by hu~mid warm environments which attack prior art 19 ¦ materials. Heretofore, the adhesively bonded metal-to-metal and 20 ¦ composite type assemblies have performed less than satisfactorily 21 ¦ due to adhesive failure at the interface beteen the polymeric 22 ¦ adhesive and the aluminum surface, frequently necessitating field 23 ¦ repairs and occasionally removal of the aircraft from service so 24 j that extensive repairs may be undertaken.
25 1 It is welI known that aluminum or aluminum alloy surfaces 26 ¦ exhibit unpredictable and unreliable adherence to bonding media 27 ¦ particularly in moist and salt laden atmospheres. It has been pro-28 ¦ posed to increase adherence of surface coating such as electroplated 29 ¦ metal on aluminum base by means of an anodic treatment in an acid 30 ¦ bath and then dissolving a portion of the oxide film in an acid ~ 7~
1 ¦or alkaline bath prior to electroplating. See U.S. patent 2 ¦1,971,761. It has also been proposed to electroplate directly over 3 ¦an oxide film produced by anodizing aluminum or aluminum alloys in 4 ¦chromic acid or phosphoric acid solution without intermediate 5 ¦treatment of the oxide film such as is taught in U.S. patents 6 ¦1,947,981 2,036,962 and 2,095,519. In each of the above-noted 7 ¦patents the aluminum surface is being prepared for electroplating.
8 ¦ Similarly, it has been proposed in U.S. Patent 3,672,972
25 1 It is welI known that aluminum or aluminum alloy surfaces 26 ¦ exhibit unpredictable and unreliable adherence to bonding media 27 ¦ particularly in moist and salt laden atmospheres. It has been pro-28 ¦ posed to increase adherence of surface coating such as electroplated 29 ¦ metal on aluminum base by means of an anodic treatment in an acid 30 ¦ bath and then dissolving a portion of the oxide film in an acid ~ 7~
1 ¦or alkaline bath prior to electroplating. See U.S. patent 2 ¦1,971,761. It has also been proposed to electroplate directly over 3 ¦an oxide film produced by anodizing aluminum or aluminum alloys in 4 ¦chromic acid or phosphoric acid solution without intermediate 5 ¦treatment of the oxide film such as is taught in U.S. patents 6 ¦1,947,981 2,036,962 and 2,095,519. In each of the above-noted 7 ¦patents the aluminum surface is being prepared for electroplating.
8 ¦ Similarly, it has been proposed in U.S. Patent 3,672,972
9 ¦ to form anodic coatings having improved adhesive properties on alum-
10 ¦ inum surfaces by depositing coatings on the aluminum substrate by
11 ¦ subjecting the aluminum article to electrolytic treatment in an
12 ¦ aqueous solution of various acids such as phosphoric acid, oxalic
13 ¦ acid, sulphuric acid, malonic acid and the like at elevated tem-
14 ¦ peratures for a very short treatment period. Similarly, it is known
15 ¦ to treat oxides already formed on an aluminum surface by other means 1~ ¦ with a phosphate bath electrolysis to render the oxide surface hy-17 ¦ dration resistant. The elevated temperature phosphoric acid anod-18 1 ization process results in the deposition of an oxide surface 19 ¦ characterized as "pseudoboehmite," a highly active form of aluminum 20 ¦ oxide deposited in a very thin, nonporous and uniform layer on an 21 aluminum surface. The characteristics o~ this form of aluminum 22 ¦ oxide apparently permit failure within the oxide structure when high 23 ¦ stressed under humid conditions. In addition, lag time after ces-24 ¦ sation of anodizing current encountered in commercial processing of 2~ ¦ aluminum surfaces at the elevated temperatures t95-122F.) of this 26 ¦ patent cause dissolution of the aluminum surface by the phosphoric 27 ¦ acid electrolyte. Poor bonding results wherever the aluminum 28 ¦ surface is excessively dissolved.
7~
This invention is directe~d at preparing adhesively bonded aluminum or aluminum alloy structures wherein the adhesive-aluminum interface exhibits environmental stability in an aqueous environment.
This invention provides a method of forming adhesively bonded aluminum composite type structures in which adhesive failures at the aluminum-adhesive interface are minimized.
This invention provides an adhesively bonded aluminum structure wherein the aluminum surface is subjected to a low temper-ature anodic electrolysis in a dilute phosphoric acid bath under conditions which enhance the formation of an anodic porous coher-ent oxide while minimizing or controlling the dissolution of alu-minum oxide from the surface after termination of the anodization current.
Furthermore, this invention provides a process for phosphoric acid anodization of aluminum surfaces at low temper-atures and under conditions which form oxide coatings of 500 to : :
8,000 Angstroms in thickness and having a porous structure wherein the pores have a diameter in the range of 300 to 1,000 Angstroms and a depth of about 400 to 7,500 Angstroms extending into the film and wherein the aluminum film is not removed by dissolution in the phosphor:ic acid electrolyte during the necessary lag time before removal of the electrolyte by rinsing.
~:i One specific object of this invention is to provide an anodization process which may be used to prepare aluminum alloys containing copper for bonding into a structure which is environmentally stable.
The present invention contemplates the formation of an environ-mentally stable, porous oxide coating on the surface of an aluminum object which is well-suited to adhesion by known polymeric adhesives and resulting in an adhesively bonded structure which, UpOII exposure to severe environ-ments, resists hydration and thus maintains its structural integrity. When highly stressed under severe test conditions, the resultant structure pre-dominantly exhibits cohesive failure within the adhesive layer rather than adhesive failure within the oxide coating or at the adhesive-oxide interface.
The aluminum is prepared by a surface treatment to form a porous anodic oxide coating using a phosphoric acid electrolyte maintained at a temper-ature in the range of 50 to ~5F., and preferably from 65 to 80F., while imposing a potential of from about 1 to about 50 volts for a period of about lO to 30 minutes.
According to the present invention, there is provided a method of forming a porous columnar aluminum oxide coating on an aluminum alloy ar-ticle, said aluminum alloy article containing about 1.6 to about 4.5% by 20 weight copper, comprising anodizing said article in an aqueous solution com-prising phosphoric acid, the anodizing potential being from about 1.0 to about 50 volts, the phosphoric acid concentration being about 1.5 to about 50% by weight and the temperature of said solution being from about 50F.
to about 85F. and rinsing said article to remove said solution within a period of time no more than 2.5 minutes from cessation of anodizing current.
In another aspect, the invention provides a process for preparing a copper-containing aluminum alloy adherendfor adhesive bonding to another surface wherein said aclherend has a polymer receptive aluminum oxide sur-face thereon having a porous columnar structure with a thickness of from about 30 500 to about 8,000 Angstroms, having pores from about 300 to about 1,000 Angstroms in diameter cmd from about 400 to about 7,500 Angstroms in depth extending into said oxide surface, said surface prepared by the steps of:
,fA. i cleaning and deoxidizing said adherend;
anodizing said adherend in an aqueous phosphoric acid solution containing from about 1.5 to about 50% by weight H3P04 at a temperature of from about 50 to about ~5F~ for about 10 to about 30 minutes at a potential of about 1.0 to about 50 volts; and rinsing said adherend to remove said aqueous pllosphoric acid solution within a period of time no more than 2.5 minutes from cessation of anodizing current.
In yet another aspect, the inventin provides an aluminum alloy adherend containing from about 1.6 to about 4.5% by weight copper and having a polymer receptive aluminum oxide surface thereon having a porous columnar structure with a thickness of from about 500 to about 8,000 Angstroms, having pores from about 300 to about 1,000 Angstroms in diameter and from about 400 to about 7,500 Angstroms in depth extending into said oxide surface, said surface prepared by anodizing the surface of said adherend in an aqueous phosphoric acid solution containing from about 1.5 to about 50% by weight H3P04 at a temperature of from about 50Fto about S5F. for about 10 to about 30 minutes at a potential of from about 1.0 to about 50 volts and then rinsing said adherend to remove said solution with a period of time no more than 2.5 minutes from cessation of anodizing current.
The above-noted processing parameters for the anodizing step are suitable for anodization of both aluminum alloys and relatively pure alu-minum metal commonly employed in adhesive bonded structures. Various alloys and nearly pure aluminum have been processed at the same time using the following parameters for the process:
Temperature: 70 - 75F.
Anodization potential: 10 - 15 volts H3P04 concentration: 10 - 12 ~
Anodization time: 20 - 25 minutes Lag time before rinse: 1-1/2 to 2--1/2 minutes Part to solution potential: 4 - 12 volts _ 5a -7~
As is noted above, the processing parameters described herein produce an adherent porous aluminum oxide coating securely bonded to a barrier layer of aluminum oxide which in turn is tightly adhered to the aluminum metal surface. Attempts at producing aluminum oxide coatings suitable for bondings at temperatures below about 50F. resulted in small diameter pore structure or no observable pores at all in the surface of the aluminum oxide. As a consequence, poor bonding results were obtained by comparison to the adhesive bonds obtained upon aluminum oxide coated substrates prepared in H3P04 electrolytes maintained at temperatures of 50-85F.
Temperatures above about 85F. cause increasingly detrimental dissolution of the oxide coating by the phosphoric acid electrolyte, especially during the time period from cessation of the anodization current flow until the phosphoric acid is rinsed off the aluminum part with water.
In commercial processes, lag times of 1-1/2 to 2-1/2 minutes are usually unavoidable and, as a consequence, the electrolyte bath temperature must be kept at a level which minimizes dissolution of aluminum oxide, yet permits formation of the essential porous structure.
Anodizing under the conditions disclosed herein consistently produces a surface superior in performance to that produced by conventional industry standard methods, such as chromic acid anodizing or sulphuric acid-sodium dichromate etch. This superior performance is clearly demon-strated by the bond stability test shown in Figure 7 while exposing the speci~en to different water and salt environments. Conventionally processed 7075-T6 aluminum clad bondements prepared by chromic acid anodization fail at the oxide-primer interface within two to three days when exposed under stress to hot humid conditions. The same alloy, phosphoric acid anodized prior to bonding under the preferred anodization parameters set forth below ~,~
7~8 1 ¦ does not show any evidence of interfacial failure after exposure t 2 ¦ the same environmental conditions for more than 7 months. Typical 3 ¦ failure modes of specimens prepared with the production parameters 4 ¦ noted above are cohesive, i.e., the specimens fail in the adhesive 5 ¦ zone rather than at the adhesive-metal interface. Thus, interfacial 6 ¦ failure modes which typify service failures are eliminated or at 7 ¦ least minimized with this method of aluminum prebond phosphoric 8 1 acid anodization surface preparation.
9 ¦ Hydration resistance of oxides formed by anodization i 10 ¦ phosphoric acid appear to be a significant factor associated with th 1~ ¦ improvement in bond stability and their low reactivity to water. Th 12 ¦ applicants postulate that bonds of aluminum to adhesives which ar 13 ¦ exposed to water and then torn apart at the adhesive-metal interfac 14 ¦ are in reality cohesive failures within the oxide suggesting tha 15 ¦ most bond failures exhibiting adhesive failure after exposure to
7~
This invention is directe~d at preparing adhesively bonded aluminum or aluminum alloy structures wherein the adhesive-aluminum interface exhibits environmental stability in an aqueous environment.
This invention provides a method of forming adhesively bonded aluminum composite type structures in which adhesive failures at the aluminum-adhesive interface are minimized.
This invention provides an adhesively bonded aluminum structure wherein the aluminum surface is subjected to a low temper-ature anodic electrolysis in a dilute phosphoric acid bath under conditions which enhance the formation of an anodic porous coher-ent oxide while minimizing or controlling the dissolution of alu-minum oxide from the surface after termination of the anodization current.
Furthermore, this invention provides a process for phosphoric acid anodization of aluminum surfaces at low temper-atures and under conditions which form oxide coatings of 500 to : :
8,000 Angstroms in thickness and having a porous structure wherein the pores have a diameter in the range of 300 to 1,000 Angstroms and a depth of about 400 to 7,500 Angstroms extending into the film and wherein the aluminum film is not removed by dissolution in the phosphor:ic acid electrolyte during the necessary lag time before removal of the electrolyte by rinsing.
~:i One specific object of this invention is to provide an anodization process which may be used to prepare aluminum alloys containing copper for bonding into a structure which is environmentally stable.
The present invention contemplates the formation of an environ-mentally stable, porous oxide coating on the surface of an aluminum object which is well-suited to adhesion by known polymeric adhesives and resulting in an adhesively bonded structure which, UpOII exposure to severe environ-ments, resists hydration and thus maintains its structural integrity. When highly stressed under severe test conditions, the resultant structure pre-dominantly exhibits cohesive failure within the adhesive layer rather than adhesive failure within the oxide coating or at the adhesive-oxide interface.
The aluminum is prepared by a surface treatment to form a porous anodic oxide coating using a phosphoric acid electrolyte maintained at a temper-ature in the range of 50 to ~5F., and preferably from 65 to 80F., while imposing a potential of from about 1 to about 50 volts for a period of about lO to 30 minutes.
According to the present invention, there is provided a method of forming a porous columnar aluminum oxide coating on an aluminum alloy ar-ticle, said aluminum alloy article containing about 1.6 to about 4.5% by 20 weight copper, comprising anodizing said article in an aqueous solution com-prising phosphoric acid, the anodizing potential being from about 1.0 to about 50 volts, the phosphoric acid concentration being about 1.5 to about 50% by weight and the temperature of said solution being from about 50F.
to about 85F. and rinsing said article to remove said solution within a period of time no more than 2.5 minutes from cessation of anodizing current.
In another aspect, the invention provides a process for preparing a copper-containing aluminum alloy adherendfor adhesive bonding to another surface wherein said aclherend has a polymer receptive aluminum oxide sur-face thereon having a porous columnar structure with a thickness of from about 30 500 to about 8,000 Angstroms, having pores from about 300 to about 1,000 Angstroms in diameter cmd from about 400 to about 7,500 Angstroms in depth extending into said oxide surface, said surface prepared by the steps of:
,fA. i cleaning and deoxidizing said adherend;
anodizing said adherend in an aqueous phosphoric acid solution containing from about 1.5 to about 50% by weight H3P04 at a temperature of from about 50 to about ~5F~ for about 10 to about 30 minutes at a potential of about 1.0 to about 50 volts; and rinsing said adherend to remove said aqueous pllosphoric acid solution within a period of time no more than 2.5 minutes from cessation of anodizing current.
In yet another aspect, the inventin provides an aluminum alloy adherend containing from about 1.6 to about 4.5% by weight copper and having a polymer receptive aluminum oxide surface thereon having a porous columnar structure with a thickness of from about 500 to about 8,000 Angstroms, having pores from about 300 to about 1,000 Angstroms in diameter and from about 400 to about 7,500 Angstroms in depth extending into said oxide surface, said surface prepared by anodizing the surface of said adherend in an aqueous phosphoric acid solution containing from about 1.5 to about 50% by weight H3P04 at a temperature of from about 50Fto about S5F. for about 10 to about 30 minutes at a potential of from about 1.0 to about 50 volts and then rinsing said adherend to remove said solution with a period of time no more than 2.5 minutes from cessation of anodizing current.
The above-noted processing parameters for the anodizing step are suitable for anodization of both aluminum alloys and relatively pure alu-minum metal commonly employed in adhesive bonded structures. Various alloys and nearly pure aluminum have been processed at the same time using the following parameters for the process:
Temperature: 70 - 75F.
Anodization potential: 10 - 15 volts H3P04 concentration: 10 - 12 ~
Anodization time: 20 - 25 minutes Lag time before rinse: 1-1/2 to 2--1/2 minutes Part to solution potential: 4 - 12 volts _ 5a -7~
As is noted above, the processing parameters described herein produce an adherent porous aluminum oxide coating securely bonded to a barrier layer of aluminum oxide which in turn is tightly adhered to the aluminum metal surface. Attempts at producing aluminum oxide coatings suitable for bondings at temperatures below about 50F. resulted in small diameter pore structure or no observable pores at all in the surface of the aluminum oxide. As a consequence, poor bonding results were obtained by comparison to the adhesive bonds obtained upon aluminum oxide coated substrates prepared in H3P04 electrolytes maintained at temperatures of 50-85F.
Temperatures above about 85F. cause increasingly detrimental dissolution of the oxide coating by the phosphoric acid electrolyte, especially during the time period from cessation of the anodization current flow until the phosphoric acid is rinsed off the aluminum part with water.
In commercial processes, lag times of 1-1/2 to 2-1/2 minutes are usually unavoidable and, as a consequence, the electrolyte bath temperature must be kept at a level which minimizes dissolution of aluminum oxide, yet permits formation of the essential porous structure.
Anodizing under the conditions disclosed herein consistently produces a surface superior in performance to that produced by conventional industry standard methods, such as chromic acid anodizing or sulphuric acid-sodium dichromate etch. This superior performance is clearly demon-strated by the bond stability test shown in Figure 7 while exposing the speci~en to different water and salt environments. Conventionally processed 7075-T6 aluminum clad bondements prepared by chromic acid anodization fail at the oxide-primer interface within two to three days when exposed under stress to hot humid conditions. The same alloy, phosphoric acid anodized prior to bonding under the preferred anodization parameters set forth below ~,~
7~8 1 ¦ does not show any evidence of interfacial failure after exposure t 2 ¦ the same environmental conditions for more than 7 months. Typical 3 ¦ failure modes of specimens prepared with the production parameters 4 ¦ noted above are cohesive, i.e., the specimens fail in the adhesive 5 ¦ zone rather than at the adhesive-metal interface. Thus, interfacial 6 ¦ failure modes which typify service failures are eliminated or at 7 ¦ least minimized with this method of aluminum prebond phosphoric 8 1 acid anodization surface preparation.
9 ¦ Hydration resistance of oxides formed by anodization i 10 ¦ phosphoric acid appear to be a significant factor associated with th 1~ ¦ improvement in bond stability and their low reactivity to water. Th 12 ¦ applicants postulate that bonds of aluminum to adhesives which ar 13 ¦ exposed to water and then torn apart at the adhesive-metal interfac 14 ¦ are in reality cohesive failures within the oxide suggesting tha 15 ¦ most bond failures exhibiting adhesive failure after exposure to
16 ~ater are due to weakening in the oxide by hydration. The applicants
17 further postulate that the failure mechanism associated with adhesive
18 appearing failures of bonded structure are due to weakening of the
19 oxide by hydration resulting in delamination when the bond is
20 ¦ stressed. Once delamination occurs, corrosion can then take place in
21 ¦ the delaminated area causing additional damage to the bonded
22 ¦ structure. The applicants have found that phosphoric acid
23 ¦ anodization of the surface of aluminum metal and alloys using
24 ¦ relatively low temperatures and dilute phosphoric acid electrolytes
25 ¦ provides a hydration resistant oxide coating well adapted to prevent
26 ¦ delamination and subsequent corrosion.
27 ¦ The rnost significant aspects of low voltage, low tempera-
28 ¦ ture anodization in phosphoric acid of aluminum surfaces prior to
29 ¦ adhesive bonding are that the process provides positive control of
30 ¦ the oxide formation and therefore high reliability, thus producing a ~ 37a8 1 ¦porous oxide with desirable physical characteristics and which i 2 ¦more stable in the presence of water than are other anodically formec 3 lor deposited oxides including phosphoric anodized coatings producec 4 ¦at elevated temperatures. The process provides a range of anodizinc 5 ¦conditions in which both relatively pure aluminum metal and aluminun ¦alloys commonly used for bonding can be anodized, i.e., 2024-T3 7 ¦aluminum alloy and 7075-T6 aluminum alloy as well as those alloys of c 8 ¦ higher aluminum content. The process is also well suited to treat-9 ¦ ment of clad aluminum material.
lO ¦ Temperatures in excess of about 85F. in solutions of 11 ¦ phosphoric acid cause the dissolution rate of the oxide layer to 12 ¦ approach or exceed the rate at which it is formed so that the oxide 13 ¦ surface is removed, especially following termination of the 1~ 1 anodization current. In the commercial production of phosphoric 1~ ¦ anodized aluminum surfaces, it is necessary to have a process which 16 accommodates lag time of up to approximately 2 to 2-1/2 minutes from 17 the time the power supply is turned~ off until the parts can be IB removed from the phosphoric acid bath and rinsed to remove the phos-19 phoric acid. During this time, the dissolution of oxide surface at elevated temperatures becomes excessive and it is, therefore, neces-21 sary to maintain the temperature below 85F. and usually in the 22 range of 65 - 80F. in order to obtain the desired results.
23 Attempts to produced the anodized aluminum parts in phosphoric acid 24 at temperatures exceeding 85F. results in erratic oxide coating and frequent failure in the resultant adhesively bonded structure. Sub-26 stantial amounts of aluminum present in the phosphoric acid electro-27 lyte solution, may cause a deposition of aluminum oxide in another 28 form such as that designated "pseudoboehmite" in U.S. Patent No.
29 3,672,972 and U.S.Patent No. 3,714,001. The conditions under which this "pseudoboehmite" deposition occurs and under which the ~ ~
1 applicants' discovery of the environmentally stable oxide film 2 formed under the conditions taught herein varies with the tempera-3 ture, acid concentration and aluminum concentration. Generally, 4 phosphoric acid anodization at temperatures above about 95F. ac-~ cording to the teaching of U.S. Patents 3,672,972 and 3,71~,001 6 result in the deposition of "pseudoboehmite." Such temperatures 7 also result in undue amount of dissolution of porous aluminum oxide, 8 rendering such prior art processes unworkable for the applicants' 9 intended purpose. It is essential to hold the temperatures below lO ~about 85F. to obtain consistent and reproduceable aluminum oxide 11 ¦surfaces described herein, At lower temperatures substantial quan-12 ¦tities of aluminum may be present in the phosphoric acid electrolyte 13 ¦without causing deposition of "pseudoboehmite" and any aluminum 14 ¦oxide film is not in the form of "pseudoboehmite" but rather the 15 ¦porous, hydration resistant structure suitable for laminating alu-16 ¦minum articles together by adhesive bonding. Under the processing 17 ¦conditions set forth below a columnar-type closely adherent aluminum ~18 ¦ oxide film is formed by oxidation of the surface of the aluminum or 19 ¦aluminum alloy. This film has a thickness varying from 500 to 8rO00 2~ ¦ Angstroms with pores having a diameter in the range of 300 to 1,000 21 Angstroms and a depth of about ~00 to 7,500 Angstroms extending into 22 the film. These pores provide many additional locations for bonding 23 by providing more surface area and a mechanical interlock between 24 the adhesive and the aluminum oxide.
The above-noted objectives of this invention and the 26 features discussed briefly in the summary of this invention will 27 become more readily apparent from a detailed examination of the fol-28 lowing discussion of the preferred embodiments with reference to the 29 attached drawings and tabular data.
__ 11187~)~
¦ 1 ¦ BRIEF DESCRIPTION OF TllE DRAWI~GS
q ¦ FIGURE l is a schematic flow diagram of two widely used 3 ¦prior art processes for prepar.ing aluminum s~rfaces for adhesive 4 ¦ bonding;
5 ¦ FIGURE 2 is a schematic flow diagram of the process oE
6 ¦ this invention;
¦ FIGURE 3 is a graph showing sustained stress lap shear 8 ¦ test data for bonded structures prepared by one process of FIGURE l 9 ¦ as compared to bonded structures prepared by the process of 10 ¦ FIGURE 2;
11 ¦ FIGURE 4 is a graph similar to FIGURE 3 for tests 12 ¦ conducted at a lower temperature;
13 ¦ FIGURE 5 is a graph showing crack propagation data for 1~ ¦ various bonded structures treated by prior art processes and by the 15 ¦ process of this invention;
16 FIGURE 6 is a graphical representation oE test results of t7 varia~us bonded structures using prior art surface treatments and 18 variations in the ~rocess taught herein;
19 FIGURE 7 is a schematic representation of the crack pro-pagation test utilized in evaluating the laminates formed using the 21 process of this invention;
22 1 FIGURE 8 is a graphical representation of the sustained 23 ¦ stress lap shear test used in evaluating the bonded structures 24 ¦ formed according to this invention;
2~ ¦ FIGURE 9 is a graphical representation of test results ~6 ¦ comparing sustained stress lap shear test data for various methods 27 ¦ of pretreatment of the aluminum surface and the resultant effect on 28 ¦ adhesive versus cohesive failure;
I , ,_ 30 1 Re~erring specifically to FIGURE l, two of the well known ~ 8 1 prior art processes are set forth in a step-by-step ~ashion in which 2 aluminum material as received is first sub~ected to a degreasing and 3 cleaning process in preparation for the surface treatment. The al-4 kaline cleaner utilized is removed in a hot water rinse and the surface is then deoxidized by exposure to a suitable etchant such as 6 sodium dichromate-sulphuric acid deoxidizer. One widely used 7 deoxidizer or etchant for aluminum is sold by Amchem Products, Inc., ` 8 Ambler, Pennsylvania, under the trade name "Amchem No.6-16" to which 9 nitric acid is added. A suitable etchant for aluminum at room tem-10 ¦perature has the following composition: 4 to 9 percent by volume 11 ¦Amchem No. 6, 10 to 20 oz/gal nitric acid in an aqueous solution.
12 ¦ The aluminum is subjected to the above-noted solution at 13 165O to 90F. for a period of time sufficient to deoxidize the surface 14 ¦of the aluminum.
15 ¦ In the event that the aluminum as received is reasonably 1~ ¦elean and has a thin adherent oxide coating, the above-noted steps 17 ¦may be unnecessary prior to the anodization step.
18 ¦ After the surface has been deoxidized, if necessary, the 19 ¦surface is rinsed with cold water and then subjected to an acid 20 ¦anodization step utilizing chromic acid as the electrolyte. The 21 ¦ chromie acid is suitably of a concentration of about 5~ by weight 22 ¦ chromic acid in water.
~3 ¦ The aluminum surface is subjected to the anodization at 24 ¦ 95F. with an applied voltage in the range of 40 volts for a period 25 ¦ of time sufficient to form an oxide coating of about 20t000 to about 26 ¦ 30,000 Angstom thickness. The chromic acid is rinsed from the sur-27 ¦ face of the aluminum and the aluminum surface is dried in prepara-28 ¦ tion for the application of the adhesive materials.
29 1 __ 30 1 __ ~ J~ ~"h ~ 7~
1 Similarly, when the sulfuric acid-sodium dichromate etc~
2 process is elected, an aqueous solution containing about 4.1 tc 3 about 12 ounces of sodium dichromate dihydrate per gallon oE
4 solution and about 38.5 to 41.5 ounces H2SO~ per gallon is used. The etching process takes place at a temperature of about 140F. to 6 160F.
7 A suitable epoxy or other primer is used such as a cor-8 rosion inhibiting epoxy primer designated as BR127 manufactured and 9 sold by American Cyanamide Corporation. This epoxy primer is a 250F. cure epoxy resin suitable as a corrosion inhibiting primer 11 for bare metal surfaces.
12 ¦ An adhesive material such as a modified epoxy resin having 13 ¦ suitable curing characteristics is then applied to the primed alu-14 ¦ minum surface. Several modiEied epoxy resins are readily available and are suitable for use in this invention including a product de-16 signated at FM123-2 manufactured and sold by the Bloomingdale 17 Division of American Cyanamide; a product designated as AF126 mod-~1~ ified epoxy resin having a 250F. cure manufactured and sold by 19 Minnesota Mining and Manufacturing Corporation and the modified epoxy adhesive designated as Hysol 9628 manufacuted and sold by 21 Hysol Division of Dexter Corporation. Many other resins are work-22 able as adhesives for this invention. The primed and taped aluminum ~3 surfaces are then placed into engagement under pressure and cured at 24 an elevated temperature to effect the joint or bond between the surfaces.
26 FIGURE 2 shows a flow diagram of the process of this in-27 vention in which aluminum as received is subjected to similar clean-28 ing and deoxidizing steps as those outlined above for FIGURE 1 if 29 they are found to be necessary due to the condition of the aluminum surface. When the preliminary cleaning steps are completed, the ~,~,J. ~q r /; --12 -37~8 aluminum surface is subjected to a low temperature anodization process in a solution of phosphoric acid, removed from the H3P04 electrolyte and rinsed with water within one to two-and-one-half minutes of the time the power supply is turned off and dried. The following process par~meters have been found to give exemplary results in the performance of the resulting bonded laminate in use:
TABLE I
Power Supply Temperature Potential Time H3PO4 F (Volts~ (h~in.)Concentration Usable range 50-85 1-50 5-60 1.5-50%
Preferred range 65-80 3-25 10-30 3-20%
~lost preferred range 70-75 10-15 20-25 10-12%
Anodizing under the conditions set forth above consistently produces a surface superior in performance to that produced by conventional industry standard methods, i.e., chromic acid anodizing or sulfuric acid-sodium dichromate etch. This superior performance is clearly demonstrated by the bond stability test technique shown in Figures 7 and 8, and the resulting test data presented in Figures 3, 4, 5, 6 and 9.
EXAMPLE I
Comparative data for the aluminum surface preparation techniques shown in Figures 1 and 2 are presented in Figure 3 for various epoxy resin adhesives used in preparation of a composite structure. All samples were prepared by cleaning as follows prior to anodizing:
(1) The surface was vapor degreased by exposure to trichloroethylene for 3 minutes at 190F.
~,~
7~8 (2) The surfaces were then subjected to an alkaline cleaning agent such as Wyandotte Altrex*, manufactured by Wyandotte Chemicals Corporation, Wyandotte, Michigan; Pennsalt A31*, manufactured by Pennsalt Chemical Corporation of Philadelphia, Pennsylvania; or any of the other well-known equivalent aluminum cleaners available and known to the industry.
The aluminum surface is exposed to the alkaline cleaner for a period of about ~0 minutes.
(3) The aluminum surface is then rinsed with hot water for 5 minutes to remove the alkaline cleaning agent.
(4) A prebond etch in the sodium dichromate--sul-furic acid deoxidizer noted above for 10 minutes at 150F.
(5) The surface is then immersed in cold tap water rinse for 5 minutes to remove the prebond e-tchant material.
One-half of the samples were then dried and primed with BR 127*, an epoxy corrosion resistant primer, 250F. cure, manufactured by American Cyanamide. The remaining samples were subjected to an anodization in 3 percent phosphoric acid at 75F. for 10 minutes with an imposed voltage of 5 volts. The surfaces were then washed with a water rinse, dried and primed with BR 127* as noted above.
The 2 groups of samples were then divided into 3 sub-groups each and coated with the following adhesive materials:
TABLE II
Designation Material -FM123-2* Modified epoxy resin adhesive, 250F
cure, manufactured by American Cyanamide, Bloomingdale Division.
AF 126 * Modified epoxy resin adhesive, 250 F.
cure, manufactured by Minnesota Mining and Manufacturing.
*Trade Mark _ 14 -."~ ~
)8 Hysol 9628* Modified epoxy resin adhesive, 250F. cure, manufactured by Hysol Division, Dexter Corporation.
The samples were then assembled in a orm suitable for use in the test schematically shown in FIGURE 8 and subjected to endwise stress of 1,750 psi while immersed in 3.5 percent sodium chloride solution at 140F. In all cases the samples anodized in phosphoric acid presented substantially superior results to those prepared in the prior art process. Of par-ticular interest is the nature of the failure, those samples prepared with the prior art process having predominantly adhesive failure at the interface between the adhesive and the metal, while those manufactured utilizing the process of this invention had sukstantially less adhesive failure, with the failure being predominantly cohesive in the resin itself.
EXAMPLE II
Tests results for sustained stress lap shear tests at 2,750 psi while the sample was immersed in 3.5 percent sodium chloride at 75F. are presented in FIGURE 4 for samples prepared in a manner corresponding to those described above for FIGU~E 3.
Specimens prepared by prior art etching process failed within one day of the start of the tests. Those samples prepared using a phosphoric acid anodization in 3% H3PO4 at 70F. for 10 minutes at 5 volts demonstrated superior resistance to failure.
Four out of five specimens bonded with AF126* and all specimens bonded with Hysol 9628* survived 30 days test without failure.
EXAMPLE III
Table III shows the results of 120 F., 100 percent relative humidity test for a test specimen prepared as shown in FIGURE 7 and indicate the effect of solution temperature on bond stability for 8% and 12~ phosphoric acid solutions. Excellent ~ 7~
1 results were obtained indicating that less than 3/10 of an inch of 2 crack growth was encountered Eor both 8 and 12 percent solutions 3 after 60 days of exposure. Specimen F-l and F-5 showed a higher 4 degree of adhesive Eailure Eor anodization at 60F. suggesting that 60F. is a marginal temperature for the anodization process when the 6 substrate is pure or nearly pure aluminum or clad aluminum.
8 In order to determine the optimum process condition, 9 numerous samples of 7075-T6 aluminum clad panels, 6 inches square, having a thickness of 0.063 inches were prepared using a preanod-11 ization process in which the surfaces of the aluminum panels were 12 exposed to a solution of Amchem 7-17 (a proprietary solution 13 containing nitric acid sold by Amchem Products, Inc. Ambler, 14 Pennsylvania). This solution is a room temperature etchant for aluminum. After surface etching with the Amchem 7-17 solution, 4 16 panels per condition noted in Table IV were anodized and prepared 17 for bonding by spray rinsing the anodization solution from the sur-18 face and drying the surface at 140F. for 10 minutes. BR127 primer 19 was applied to the prepared surface and the panels were bonded with Hysol 9628. The epoxy was applied in a 10 mil thick layer. Ten 1-21 inch wide fracture specimens were saw cut from each pair of as-22 semblies. Six specimens from each assembly were exposed to boiling 23 water and the amount of crack growth was measured after 1, 4 and 24 24 hours for specimens prepared as shown in FIGURE 7. The remaining 4 specimens weré exposed to 5 percent salt spray at 90F. and the 26 amount of crack growth was measured. The test results are presented 27 in Table V for the water boil test and Table VI for the 5 percent 28 salt spray at 90F. test.
29 The average crack propagation rate and failure mode of the specimens subjected to boiling water indicated less than 8/10 inch ~ 37~i~
1 of crack growth after 24 hours exposure. Sorne specimens that were 2 anodized in 3 percent phosphoric acid at 65F. for 10 minutes (see 3 specimen Al and A2) showed adhesive failures. All other failures 4 were center-of-the-bond or cohesive.
The oxide coating weight varied from 15 mg/ft2 to 47 mg/ft2. No 6 ¦ correlation between the coating weight and the bond stability was 7 ¦ found.
8 ¦ The test results for the 5 percent salt spray at 95F. crack 9 ¦ growth data is shown in Table VI. Extended exposure to the salt lO ¦ environment induced failures of more anodized conditions than did 11 ¦ the water boil test. However, since the adherent was clad aluminum 12 ¦ alloy the cladding is sacrificial in a corrosive environment and it 13 I is uncertain if these adhesive failure modes were the result of 14 ¦galvanic corrosion, less than optimum surface preparation or a com-15 ¦ bination of both.
16 ¦ EXAMPLE V
17 ¦ Variations of the anodization process parameters were explored 18 ¦ and the results shown in Table VII. The initial room temperature lap 19 ¦ shear strength was S200 + 200 psi and the mode of failure 100 percent 20 ¦ cohesive for all specimens. Under sustained stress of 1750 psi, 21 ¦most of the specimens failed in 20 to 200 hours. The specimens 22 ¦ prepared in 17 percent H3PO4 at 100F. and 3 volts anodizing poten-23 ¦ tial (Test A6) showed poor bond stability and failed in less than 23 24 ¦ hours with 40 to 50 percent cohesive failure. The processing 25 ¦ conditions of this test would appear to cause excessive oxide dis-~6 ¦ solution during anodization and not permit the build-up of the 27 ¦desired type of oxide coating. The high temperature thus results in 28 la poor oxide film formation and resultant poor bond performance.
29 ¦ Corresponding specimens to Test A6 when tested in a sus-30 ¦tained stress/fracture test had complete separation of adhesive from ~ 3 7~8 1 the aluminum surface in less than 24 hours. ~he specimens of Test Al 2 failed after 2~ days exposure and all of the test specimens prepared 3 by processes A3, A4, and A7 showed excellent stability with less 4 than 2/10 inch of crack growth after 125 days of salt spray exposure.
These tests indicate that the process of this invention is capabl 6 of producing a stable bond surface using wide ranges of acid concen-7 trations, potential and temperature. An upper and lower temperature 8 range is shown at which decreasing bond performance results when 9 temperatures in excess of about 85F. are used and when temperatures below about 65F. are used. The optimum parameters appear to be the 11 following:
12 ¦ Orthophosphoric acid 10~ by weight 13 ¦ Potential 10 volts 14 ¦ Time 20 minutes 15 1 Temperature 75F.
16 Rinse lag time 1.0 - 2.5 minutes 18 Samples of 2024-T3 bare aluminum alloy plate (an alloy contain 19 ing about 4.5% copper, about 0.6% manganese and about 1.5~ magnesium) were prepared for bonding in a 10% phosphoric acid anodization, usin 21 10 volts potential for 20 minutes at 70F. The surfaces were prime~
22 with BR 127 and samples bonded together with AF126 epoxy resin.
23 Identical specimens were prepared using the H2S04-Na2Cr207-2H20 etc~
24 discussed above. Both sets of samples were exposed to 5~ salt spra~
at 95F. while the bond was placed under an initially high stress an 26 maintained under stressed conditions Eor an extended period of time.
27 At the end of 70 days the samples prepared with H2S04-Na2Cr207-2H
28 failed adhesively over the entire length of the stressed bond. The 29 samples prepared using H3P04 anodization exhibited no adhesive fail-ure at the end of 18 months exposure. A cohesive failure crack -extended about 1/2 inch along the bond, exclusively with the adhesive material.
EXAMPLE VII
In order to determine the relationship of higher temperature operation and lag time from cessation of power applied at the supply to the time of rinsing of the phosphoric acid from the surface of the anodized aluminum, several tests were run at 95F. and 100F. Marginal results were obtained in the idealized laboratory conditions utilized for this test with many of the tests exhibiting failure when rinse delay exceeded 30 seconds.
Data is presented in Table VIII.
EXAMPLE VIII
Tests were conducted in a production facility at a temperature of 85~., acid concentration 14%, at a power supply potential of 15 volts for 20 minutes. A lag time of 2-1/2 minutes from the time the power supply was turned off until the parts were rinsed to remove the H3PO4 electrolyte occurred. Parts subjected to the above processing parameters exhibited occasional failures and the process was adjudged to be inade~uate for commercial processing.
The failures were apparently due to excessive dissolution of the aluminum oxide from the surface before the phosphoric acid electrolyte could be removed by rinsing.
r"
3'7~8 EXAMPLE IX
Production runs of phosphoric acid anodization of aluminum surfaces for bonding were carried out at the following processing parameters:
Temperature 70-75F.
Phosphoric acid concentration 10-12%
Power supply potential 10-15 volts Part to solution potential ~-12 volts Time 20-25 minutes Lag time before rinse 2 to 2-1/2 minutes Excellent bonding characteristics are obtained on aluminum and aluminum alloys processed for bonding in the above anodi~ation procedure.
Various modifications and improvements can be made to the present invention without departing from the spirit thereof and from the scope of the claims set forth below.
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¦ TABLE IV
¦ANODIZE PROCESS OPTIMIZATION TEST MATI~IX
. ~ 2 r~ ~ I _ _ . ~ 9 4 ¦ Factor ll3PO~ Potential rll~mp. Time , i `~ 5 Studied Conc. F (~1in.1 -~,~ 6 I ~ase 71 Level10%10 volts 75F ?0 81 Unit 7~5 volts 10F 10 ' 1 91 . ~ ~ h . 1' ~ 10 I Level17~15 volts 85F 30 11 ¦ I,ow 13 ¦ Level3~5 volts 65F 10 , ~ 14¦ Test Al 3 5 65 10 . .. ~ A2 3 15 65 10 -r 1 . 16 A3 3 5 65 30 17 ~4 3 15 65 ' 30 \ `~ 18 ~5 ~3 5 85 10 t ~ -`' . 19 A6 3 15 85 10 " A73 5 85 30 , ~ ~ 21 A83 15 85 30 j 23 A10 17 15 85 10 ~ 24 All 17 5 ` 85 30 :~! 25 A12 17 15 85 30 r'- A13 17 5 65 10 . 2~ A14 17 15 65 10 .'' . ! 2 3 ~,i-..
~ 7~18 -2WEDGE TEST RESUI,TS, WATER r3OII.--7075-'1`6 CLI~D*, primecl with Epoxy resln prim~r (Epoxy resi~ ) AND coated 4with ~poxy adhesive (Epoxy resin C) .. _ _ Coating Initial Water Boil Test **
Test wei9ll2k Crack lElr. 411r. 241lr. I'ailure 6 No. mg/ft inch inch inch inch Mode 8 A1 16.8 .71 1.15 1.30 1.64 50%Adh.
9 A2 28.0 .78 1.15 1.34 1.59 50oAdh.
A3 21.2 .78 1.16 1.30 1.56 loooocoh.
11 A4 46.8 .78 1.17 1.32 1.55 100oCOIl. .
A5 15.6 .78 1.15 1.28 1.54 100~Col- .
13 A6 30.8 .78 1.20 1.35 1.52 100oCOh.
14 A7 16.0 .78 1.16 1.31 1.55 100%Coh.
I~8 33.2 .78 1.17 1.33 1.51 100%Coll.
16 A9 14.4 .78 1.17 1.34 1.51 100%Coh.
17 A10 35.2 .78 1.17 1.33 1.50 100%Coh .
18 A11 18.4e ' .78 1.131.33 1.52 100%Coh.
l9 A12 17.2 .78 1.16 1.31 1.56 100%Coh.
A13 21.6 .78 1.13 1.29 1.48 lOOsLoCOl-~
21 A14 38.8 .78 1.15 1.36 1.51 100%Coh.
2 A15 45.2 .78 1.14 1.29 1.54 100!'aCoh.
23 A16 29.2 .78 1.16 1.34 1.55 1û0%Coh.
* 0.063 inches thick 26 ** Average o~ 6 specimens ~ ~c ~ c ~
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lO ¦ Temperatures in excess of about 85F. in solutions of 11 ¦ phosphoric acid cause the dissolution rate of the oxide layer to 12 ¦ approach or exceed the rate at which it is formed so that the oxide 13 ¦ surface is removed, especially following termination of the 1~ 1 anodization current. In the commercial production of phosphoric 1~ ¦ anodized aluminum surfaces, it is necessary to have a process which 16 accommodates lag time of up to approximately 2 to 2-1/2 minutes from 17 the time the power supply is turned~ off until the parts can be IB removed from the phosphoric acid bath and rinsed to remove the phos-19 phoric acid. During this time, the dissolution of oxide surface at elevated temperatures becomes excessive and it is, therefore, neces-21 sary to maintain the temperature below 85F. and usually in the 22 range of 65 - 80F. in order to obtain the desired results.
23 Attempts to produced the anodized aluminum parts in phosphoric acid 24 at temperatures exceeding 85F. results in erratic oxide coating and frequent failure in the resultant adhesively bonded structure. Sub-26 stantial amounts of aluminum present in the phosphoric acid electro-27 lyte solution, may cause a deposition of aluminum oxide in another 28 form such as that designated "pseudoboehmite" in U.S. Patent No.
29 3,672,972 and U.S.Patent No. 3,714,001. The conditions under which this "pseudoboehmite" deposition occurs and under which the ~ ~
1 applicants' discovery of the environmentally stable oxide film 2 formed under the conditions taught herein varies with the tempera-3 ture, acid concentration and aluminum concentration. Generally, 4 phosphoric acid anodization at temperatures above about 95F. ac-~ cording to the teaching of U.S. Patents 3,672,972 and 3,71~,001 6 result in the deposition of "pseudoboehmite." Such temperatures 7 also result in undue amount of dissolution of porous aluminum oxide, 8 rendering such prior art processes unworkable for the applicants' 9 intended purpose. It is essential to hold the temperatures below lO ~about 85F. to obtain consistent and reproduceable aluminum oxide 11 ¦surfaces described herein, At lower temperatures substantial quan-12 ¦tities of aluminum may be present in the phosphoric acid electrolyte 13 ¦without causing deposition of "pseudoboehmite" and any aluminum 14 ¦oxide film is not in the form of "pseudoboehmite" but rather the 15 ¦porous, hydration resistant structure suitable for laminating alu-16 ¦minum articles together by adhesive bonding. Under the processing 17 ¦conditions set forth below a columnar-type closely adherent aluminum ~18 ¦ oxide film is formed by oxidation of the surface of the aluminum or 19 ¦aluminum alloy. This film has a thickness varying from 500 to 8rO00 2~ ¦ Angstroms with pores having a diameter in the range of 300 to 1,000 21 Angstroms and a depth of about ~00 to 7,500 Angstroms extending into 22 the film. These pores provide many additional locations for bonding 23 by providing more surface area and a mechanical interlock between 24 the adhesive and the aluminum oxide.
The above-noted objectives of this invention and the 26 features discussed briefly in the summary of this invention will 27 become more readily apparent from a detailed examination of the fol-28 lowing discussion of the preferred embodiments with reference to the 29 attached drawings and tabular data.
__ 11187~)~
¦ 1 ¦ BRIEF DESCRIPTION OF TllE DRAWI~GS
q ¦ FIGURE l is a schematic flow diagram of two widely used 3 ¦prior art processes for prepar.ing aluminum s~rfaces for adhesive 4 ¦ bonding;
5 ¦ FIGURE 2 is a schematic flow diagram of the process oE
6 ¦ this invention;
¦ FIGURE 3 is a graph showing sustained stress lap shear 8 ¦ test data for bonded structures prepared by one process of FIGURE l 9 ¦ as compared to bonded structures prepared by the process of 10 ¦ FIGURE 2;
11 ¦ FIGURE 4 is a graph similar to FIGURE 3 for tests 12 ¦ conducted at a lower temperature;
13 ¦ FIGURE 5 is a graph showing crack propagation data for 1~ ¦ various bonded structures treated by prior art processes and by the 15 ¦ process of this invention;
16 FIGURE 6 is a graphical representation oE test results of t7 varia~us bonded structures using prior art surface treatments and 18 variations in the ~rocess taught herein;
19 FIGURE 7 is a schematic representation of the crack pro-pagation test utilized in evaluating the laminates formed using the 21 process of this invention;
22 1 FIGURE 8 is a graphical representation of the sustained 23 ¦ stress lap shear test used in evaluating the bonded structures 24 ¦ formed according to this invention;
2~ ¦ FIGURE 9 is a graphical representation of test results ~6 ¦ comparing sustained stress lap shear test data for various methods 27 ¦ of pretreatment of the aluminum surface and the resultant effect on 28 ¦ adhesive versus cohesive failure;
I , ,_ 30 1 Re~erring specifically to FIGURE l, two of the well known ~ 8 1 prior art processes are set forth in a step-by-step ~ashion in which 2 aluminum material as received is first sub~ected to a degreasing and 3 cleaning process in preparation for the surface treatment. The al-4 kaline cleaner utilized is removed in a hot water rinse and the surface is then deoxidized by exposure to a suitable etchant such as 6 sodium dichromate-sulphuric acid deoxidizer. One widely used 7 deoxidizer or etchant for aluminum is sold by Amchem Products, Inc., ` 8 Ambler, Pennsylvania, under the trade name "Amchem No.6-16" to which 9 nitric acid is added. A suitable etchant for aluminum at room tem-10 ¦perature has the following composition: 4 to 9 percent by volume 11 ¦Amchem No. 6, 10 to 20 oz/gal nitric acid in an aqueous solution.
12 ¦ The aluminum is subjected to the above-noted solution at 13 165O to 90F. for a period of time sufficient to deoxidize the surface 14 ¦of the aluminum.
15 ¦ In the event that the aluminum as received is reasonably 1~ ¦elean and has a thin adherent oxide coating, the above-noted steps 17 ¦may be unnecessary prior to the anodization step.
18 ¦ After the surface has been deoxidized, if necessary, the 19 ¦surface is rinsed with cold water and then subjected to an acid 20 ¦anodization step utilizing chromic acid as the electrolyte. The 21 ¦ chromie acid is suitably of a concentration of about 5~ by weight 22 ¦ chromic acid in water.
~3 ¦ The aluminum surface is subjected to the anodization at 24 ¦ 95F. with an applied voltage in the range of 40 volts for a period 25 ¦ of time sufficient to form an oxide coating of about 20t000 to about 26 ¦ 30,000 Angstom thickness. The chromic acid is rinsed from the sur-27 ¦ face of the aluminum and the aluminum surface is dried in prepara-28 ¦ tion for the application of the adhesive materials.
29 1 __ 30 1 __ ~ J~ ~"h ~ 7~
1 Similarly, when the sulfuric acid-sodium dichromate etc~
2 process is elected, an aqueous solution containing about 4.1 tc 3 about 12 ounces of sodium dichromate dihydrate per gallon oE
4 solution and about 38.5 to 41.5 ounces H2SO~ per gallon is used. The etching process takes place at a temperature of about 140F. to 6 160F.
7 A suitable epoxy or other primer is used such as a cor-8 rosion inhibiting epoxy primer designated as BR127 manufactured and 9 sold by American Cyanamide Corporation. This epoxy primer is a 250F. cure epoxy resin suitable as a corrosion inhibiting primer 11 for bare metal surfaces.
12 ¦ An adhesive material such as a modified epoxy resin having 13 ¦ suitable curing characteristics is then applied to the primed alu-14 ¦ minum surface. Several modiEied epoxy resins are readily available and are suitable for use in this invention including a product de-16 signated at FM123-2 manufactured and sold by the Bloomingdale 17 Division of American Cyanamide; a product designated as AF126 mod-~1~ ified epoxy resin having a 250F. cure manufactured and sold by 19 Minnesota Mining and Manufacturing Corporation and the modified epoxy adhesive designated as Hysol 9628 manufacuted and sold by 21 Hysol Division of Dexter Corporation. Many other resins are work-22 able as adhesives for this invention. The primed and taped aluminum ~3 surfaces are then placed into engagement under pressure and cured at 24 an elevated temperature to effect the joint or bond between the surfaces.
26 FIGURE 2 shows a flow diagram of the process of this in-27 vention in which aluminum as received is subjected to similar clean-28 ing and deoxidizing steps as those outlined above for FIGURE 1 if 29 they are found to be necessary due to the condition of the aluminum surface. When the preliminary cleaning steps are completed, the ~,~,J. ~q r /; --12 -37~8 aluminum surface is subjected to a low temperature anodization process in a solution of phosphoric acid, removed from the H3P04 electrolyte and rinsed with water within one to two-and-one-half minutes of the time the power supply is turned off and dried. The following process par~meters have been found to give exemplary results in the performance of the resulting bonded laminate in use:
TABLE I
Power Supply Temperature Potential Time H3PO4 F (Volts~ (h~in.)Concentration Usable range 50-85 1-50 5-60 1.5-50%
Preferred range 65-80 3-25 10-30 3-20%
~lost preferred range 70-75 10-15 20-25 10-12%
Anodizing under the conditions set forth above consistently produces a surface superior in performance to that produced by conventional industry standard methods, i.e., chromic acid anodizing or sulfuric acid-sodium dichromate etch. This superior performance is clearly demonstrated by the bond stability test technique shown in Figures 7 and 8, and the resulting test data presented in Figures 3, 4, 5, 6 and 9.
EXAMPLE I
Comparative data for the aluminum surface preparation techniques shown in Figures 1 and 2 are presented in Figure 3 for various epoxy resin adhesives used in preparation of a composite structure. All samples were prepared by cleaning as follows prior to anodizing:
(1) The surface was vapor degreased by exposure to trichloroethylene for 3 minutes at 190F.
~,~
7~8 (2) The surfaces were then subjected to an alkaline cleaning agent such as Wyandotte Altrex*, manufactured by Wyandotte Chemicals Corporation, Wyandotte, Michigan; Pennsalt A31*, manufactured by Pennsalt Chemical Corporation of Philadelphia, Pennsylvania; or any of the other well-known equivalent aluminum cleaners available and known to the industry.
The aluminum surface is exposed to the alkaline cleaner for a period of about ~0 minutes.
(3) The aluminum surface is then rinsed with hot water for 5 minutes to remove the alkaline cleaning agent.
(4) A prebond etch in the sodium dichromate--sul-furic acid deoxidizer noted above for 10 minutes at 150F.
(5) The surface is then immersed in cold tap water rinse for 5 minutes to remove the prebond e-tchant material.
One-half of the samples were then dried and primed with BR 127*, an epoxy corrosion resistant primer, 250F. cure, manufactured by American Cyanamide. The remaining samples were subjected to an anodization in 3 percent phosphoric acid at 75F. for 10 minutes with an imposed voltage of 5 volts. The surfaces were then washed with a water rinse, dried and primed with BR 127* as noted above.
The 2 groups of samples were then divided into 3 sub-groups each and coated with the following adhesive materials:
TABLE II
Designation Material -FM123-2* Modified epoxy resin adhesive, 250F
cure, manufactured by American Cyanamide, Bloomingdale Division.
AF 126 * Modified epoxy resin adhesive, 250 F.
cure, manufactured by Minnesota Mining and Manufacturing.
*Trade Mark _ 14 -."~ ~
)8 Hysol 9628* Modified epoxy resin adhesive, 250F. cure, manufactured by Hysol Division, Dexter Corporation.
The samples were then assembled in a orm suitable for use in the test schematically shown in FIGURE 8 and subjected to endwise stress of 1,750 psi while immersed in 3.5 percent sodium chloride solution at 140F. In all cases the samples anodized in phosphoric acid presented substantially superior results to those prepared in the prior art process. Of par-ticular interest is the nature of the failure, those samples prepared with the prior art process having predominantly adhesive failure at the interface between the adhesive and the metal, while those manufactured utilizing the process of this invention had sukstantially less adhesive failure, with the failure being predominantly cohesive in the resin itself.
EXAMPLE II
Tests results for sustained stress lap shear tests at 2,750 psi while the sample was immersed in 3.5 percent sodium chloride at 75F. are presented in FIGURE 4 for samples prepared in a manner corresponding to those described above for FIGU~E 3.
Specimens prepared by prior art etching process failed within one day of the start of the tests. Those samples prepared using a phosphoric acid anodization in 3% H3PO4 at 70F. for 10 minutes at 5 volts demonstrated superior resistance to failure.
Four out of five specimens bonded with AF126* and all specimens bonded with Hysol 9628* survived 30 days test without failure.
EXAMPLE III
Table III shows the results of 120 F., 100 percent relative humidity test for a test specimen prepared as shown in FIGURE 7 and indicate the effect of solution temperature on bond stability for 8% and 12~ phosphoric acid solutions. Excellent ~ 7~
1 results were obtained indicating that less than 3/10 of an inch of 2 crack growth was encountered Eor both 8 and 12 percent solutions 3 after 60 days of exposure. Specimen F-l and F-5 showed a higher 4 degree of adhesive Eailure Eor anodization at 60F. suggesting that 60F. is a marginal temperature for the anodization process when the 6 substrate is pure or nearly pure aluminum or clad aluminum.
8 In order to determine the optimum process condition, 9 numerous samples of 7075-T6 aluminum clad panels, 6 inches square, having a thickness of 0.063 inches were prepared using a preanod-11 ization process in which the surfaces of the aluminum panels were 12 exposed to a solution of Amchem 7-17 (a proprietary solution 13 containing nitric acid sold by Amchem Products, Inc. Ambler, 14 Pennsylvania). This solution is a room temperature etchant for aluminum. After surface etching with the Amchem 7-17 solution, 4 16 panels per condition noted in Table IV were anodized and prepared 17 for bonding by spray rinsing the anodization solution from the sur-18 face and drying the surface at 140F. for 10 minutes. BR127 primer 19 was applied to the prepared surface and the panels were bonded with Hysol 9628. The epoxy was applied in a 10 mil thick layer. Ten 1-21 inch wide fracture specimens were saw cut from each pair of as-22 semblies. Six specimens from each assembly were exposed to boiling 23 water and the amount of crack growth was measured after 1, 4 and 24 24 hours for specimens prepared as shown in FIGURE 7. The remaining 4 specimens weré exposed to 5 percent salt spray at 90F. and the 26 amount of crack growth was measured. The test results are presented 27 in Table V for the water boil test and Table VI for the 5 percent 28 salt spray at 90F. test.
29 The average crack propagation rate and failure mode of the specimens subjected to boiling water indicated less than 8/10 inch ~ 37~i~
1 of crack growth after 24 hours exposure. Sorne specimens that were 2 anodized in 3 percent phosphoric acid at 65F. for 10 minutes (see 3 specimen Al and A2) showed adhesive failures. All other failures 4 were center-of-the-bond or cohesive.
The oxide coating weight varied from 15 mg/ft2 to 47 mg/ft2. No 6 ¦ correlation between the coating weight and the bond stability was 7 ¦ found.
8 ¦ The test results for the 5 percent salt spray at 95F. crack 9 ¦ growth data is shown in Table VI. Extended exposure to the salt lO ¦ environment induced failures of more anodized conditions than did 11 ¦ the water boil test. However, since the adherent was clad aluminum 12 ¦ alloy the cladding is sacrificial in a corrosive environment and it 13 I is uncertain if these adhesive failure modes were the result of 14 ¦galvanic corrosion, less than optimum surface preparation or a com-15 ¦ bination of both.
16 ¦ EXAMPLE V
17 ¦ Variations of the anodization process parameters were explored 18 ¦ and the results shown in Table VII. The initial room temperature lap 19 ¦ shear strength was S200 + 200 psi and the mode of failure 100 percent 20 ¦ cohesive for all specimens. Under sustained stress of 1750 psi, 21 ¦most of the specimens failed in 20 to 200 hours. The specimens 22 ¦ prepared in 17 percent H3PO4 at 100F. and 3 volts anodizing poten-23 ¦ tial (Test A6) showed poor bond stability and failed in less than 23 24 ¦ hours with 40 to 50 percent cohesive failure. The processing 25 ¦ conditions of this test would appear to cause excessive oxide dis-~6 ¦ solution during anodization and not permit the build-up of the 27 ¦desired type of oxide coating. The high temperature thus results in 28 la poor oxide film formation and resultant poor bond performance.
29 ¦ Corresponding specimens to Test A6 when tested in a sus-30 ¦tained stress/fracture test had complete separation of adhesive from ~ 3 7~8 1 the aluminum surface in less than 24 hours. ~he specimens of Test Al 2 failed after 2~ days exposure and all of the test specimens prepared 3 by processes A3, A4, and A7 showed excellent stability with less 4 than 2/10 inch of crack growth after 125 days of salt spray exposure.
These tests indicate that the process of this invention is capabl 6 of producing a stable bond surface using wide ranges of acid concen-7 trations, potential and temperature. An upper and lower temperature 8 range is shown at which decreasing bond performance results when 9 temperatures in excess of about 85F. are used and when temperatures below about 65F. are used. The optimum parameters appear to be the 11 following:
12 ¦ Orthophosphoric acid 10~ by weight 13 ¦ Potential 10 volts 14 ¦ Time 20 minutes 15 1 Temperature 75F.
16 Rinse lag time 1.0 - 2.5 minutes 18 Samples of 2024-T3 bare aluminum alloy plate (an alloy contain 19 ing about 4.5% copper, about 0.6% manganese and about 1.5~ magnesium) were prepared for bonding in a 10% phosphoric acid anodization, usin 21 10 volts potential for 20 minutes at 70F. The surfaces were prime~
22 with BR 127 and samples bonded together with AF126 epoxy resin.
23 Identical specimens were prepared using the H2S04-Na2Cr207-2H20 etc~
24 discussed above. Both sets of samples were exposed to 5~ salt spra~
at 95F. while the bond was placed under an initially high stress an 26 maintained under stressed conditions Eor an extended period of time.
27 At the end of 70 days the samples prepared with H2S04-Na2Cr207-2H
28 failed adhesively over the entire length of the stressed bond. The 29 samples prepared using H3P04 anodization exhibited no adhesive fail-ure at the end of 18 months exposure. A cohesive failure crack -extended about 1/2 inch along the bond, exclusively with the adhesive material.
EXAMPLE VII
In order to determine the relationship of higher temperature operation and lag time from cessation of power applied at the supply to the time of rinsing of the phosphoric acid from the surface of the anodized aluminum, several tests were run at 95F. and 100F. Marginal results were obtained in the idealized laboratory conditions utilized for this test with many of the tests exhibiting failure when rinse delay exceeded 30 seconds.
Data is presented in Table VIII.
EXAMPLE VIII
Tests were conducted in a production facility at a temperature of 85~., acid concentration 14%, at a power supply potential of 15 volts for 20 minutes. A lag time of 2-1/2 minutes from the time the power supply was turned off until the parts were rinsed to remove the H3PO4 electrolyte occurred. Parts subjected to the above processing parameters exhibited occasional failures and the process was adjudged to be inade~uate for commercial processing.
The failures were apparently due to excessive dissolution of the aluminum oxide from the surface before the phosphoric acid electrolyte could be removed by rinsing.
r"
3'7~8 EXAMPLE IX
Production runs of phosphoric acid anodization of aluminum surfaces for bonding were carried out at the following processing parameters:
Temperature 70-75F.
Phosphoric acid concentration 10-12%
Power supply potential 10-15 volts Part to solution potential ~-12 volts Time 20-25 minutes Lag time before rinse 2 to 2-1/2 minutes Excellent bonding characteristics are obtained on aluminum and aluminum alloys processed for bonding in the above anodi~ation procedure.
Various modifications and improvements can be made to the present invention without departing from the spirit thereof and from the scope of the claims set forth below.
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¦ TABLE IV
¦ANODIZE PROCESS OPTIMIZATION TEST MATI~IX
. ~ 2 r~ ~ I _ _ . ~ 9 4 ¦ Factor ll3PO~ Potential rll~mp. Time , i `~ 5 Studied Conc. F (~1in.1 -~,~ 6 I ~ase 71 Level10%10 volts 75F ?0 81 Unit 7~5 volts 10F 10 ' 1 91 . ~ ~ h . 1' ~ 10 I Level17~15 volts 85F 30 11 ¦ I,ow 13 ¦ Level3~5 volts 65F 10 , ~ 14¦ Test Al 3 5 65 10 . .. ~ A2 3 15 65 10 -r 1 . 16 A3 3 5 65 30 17 ~4 3 15 65 ' 30 \ `~ 18 ~5 ~3 5 85 10 t ~ -`' . 19 A6 3 15 85 10 " A73 5 85 30 , ~ ~ 21 A83 15 85 30 j 23 A10 17 15 85 10 ~ 24 All 17 5 ` 85 30 :~! 25 A12 17 15 85 30 r'- A13 17 5 65 10 . 2~ A14 17 15 65 10 .'' . ! 2 3 ~,i-..
~ 7~18 -2WEDGE TEST RESUI,TS, WATER r3OII.--7075-'1`6 CLI~D*, primecl with Epoxy resln prim~r (Epoxy resi~ ) AND coated 4with ~poxy adhesive (Epoxy resin C) .. _ _ Coating Initial Water Boil Test **
Test wei9ll2k Crack lElr. 411r. 241lr. I'ailure 6 No. mg/ft inch inch inch inch Mode 8 A1 16.8 .71 1.15 1.30 1.64 50%Adh.
9 A2 28.0 .78 1.15 1.34 1.59 50oAdh.
A3 21.2 .78 1.16 1.30 1.56 loooocoh.
11 A4 46.8 .78 1.17 1.32 1.55 100oCOIl. .
A5 15.6 .78 1.15 1.28 1.54 100~Col- .
13 A6 30.8 .78 1.20 1.35 1.52 100oCOh.
14 A7 16.0 .78 1.16 1.31 1.55 100%Coh.
I~8 33.2 .78 1.17 1.33 1.51 100%Coll.
16 A9 14.4 .78 1.17 1.34 1.51 100%Coh.
17 A10 35.2 .78 1.17 1.33 1.50 100%Coh .
18 A11 18.4e ' .78 1.131.33 1.52 100%Coh.
l9 A12 17.2 .78 1.16 1.31 1.56 100%Coh.
A13 21.6 .78 1.13 1.29 1.48 lOOsLoCOl-~
21 A14 38.8 .78 1.15 1.36 1.51 100%Coh.
2 A15 45.2 .78 1.14 1.29 1.54 100!'aCoh.
23 A16 29.2 .78 1.16 1.34 1.55 1û0%Coh.
* 0.063 inches thick 26 ** Average o~ 6 specimens ~ ~c ~ c ~
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.
Claims (20)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of forming a porous columnar aluminum oxide coating on an aluminum alloy article, said aluminum alloy article containing about 1.6 to about 4.5% by weight copper, comprising anodizing said article in an aqueous solution compris-ing phosphoric acid, the anodizing potential being from about 1.0 to about 50 volts, the phosphoric acid concentration being about 1.5 to about 50% by weight and the temperature of said solution being from about 50°F. to about 85°F. and rinsing said article to remove said solution within a period of time no more than 2.5 minutes from cessation of anodizing current.
2. The method of claim 1 wherein said electrolyte is rinsed from said coating within 0.5 to 2.5 minutes from cessation of anodization current.
3. The method of claim 1 wherein said aluminum alloy article consists of aluminum alloy 7075.
4. The method of claim 1 wherein said aluminum alloy article consists of aluminum alloy 2024.
5. The method of claim 1 wherein said temperature range is 75 ? 10°F.
6. A process for preparing a copper-containing aluminum alloy adherend for adhesive bonding to another surface wherein said adherend has a polymer receptive aluminum oxide surface thereon having a porous columnar structure with a thickness of from about 500 to about 8,000 Angstroms, having pores from about 300 to about 1,000 Angstroms in diameter and from about 400 to about 7,500 Angstroms in depth extending into said oxide surface, said surface having been prepared by the steps of:
cleaning and deoxidizing said adherend;
anodizing said adherend in an aqueous phosphoric acid solution containing from about 1.5 to about 50% by weight H3PO4 at a temperature of from about 50 to about 85°F. for about 10 to about 30 minutes at a potential of about 1.0 to about 50 volts;
and rinsing said adherend to remove said aqueous phosphoric acid solution within a period of time no more than 2.5 minutes from cessation of anodizing current.
cleaning and deoxidizing said adherend;
anodizing said adherend in an aqueous phosphoric acid solution containing from about 1.5 to about 50% by weight H3PO4 at a temperature of from about 50 to about 85°F. for about 10 to about 30 minutes at a potential of about 1.0 to about 50 volts;
and rinsing said adherend to remove said aqueous phosphoric acid solution within a period of time no more than 2.5 minutes from cessation of anodizing current.
7. The process of claim 6 wherein said electrolyte is rinsed from said coating within 0.5 to 2.5 minutes from cessation of anodization current.
8. The process of claim 6 wherein said adherend contains from about 1.6 to about 4.5% by weight copper.
9. The process of claim 6 wherein said adherend consists of aluminum alloy 2024.
10. The process of claim 6 wherein said adherend consists of aluminum alloy 7075.
11. The process of claim 6 wherein said temperature range is 75 ? 10°F.
12. The process of claim 6 wherein said temperature is about 70°F., said solution contains about 10% phosphoric acid, said potential is about 10 volts and said anodization time is about 20 minutes.
13. The process of claim 6 wherein said oxide surface is coated with an epoxy primer and adhered to another surface with an epoxy resin adhesive.
14. An aluminum alloy adherend containing from about 1.6 to about 4.5% by weight copper and having a polymer receptive aluminum oxide surface thereon having a porous columnar structure with a thickness of from about 500 to about 8,000 Angstroms, having pores from about 300 to about 1,000 Angstroms in diameter and from about 400 to about 7,500 Angstroms in depth extending into said oxide surface, said surface having been prepared by anodizing the surface of said adherend in an aqueous phosphoric acid solution containing from about 1.5 to about 50% by weight H3PO4 at a temperature of from about 50°F. to about 85°F. for about 10 to about 30 minutes at a potential of from about 1.0 to about 50 volts and then rinsing said adherend to remove said solution within a period of time no more than 2.5 minutes from cessation of anodizing current.
15. A method of forming a porous oxide coating on an aluminum surface, said oxide coating being a polymer receptive, substantially unhydrated alu-minum oxide having a porous columnar structure with a thickness of from about 500 to about 8,000 Angstroms, having pores from about 300 to about 1,000 Angstroms in diameter and from about 400 to about 7,500 Angstroms in depth extending into said oxide surface, comprising the steps of anodizing said article in an aqueous acidic solution, the acid component thereof consisting essentially of phosphoric acid, the anodizing potential being from about 1.0 to about 50 volts, the phosphoric acid concentration being about 1.5 to about 50% by weight and the temperature of said solution being from about 50°F. to about 85°F. and rinsing said article to remove said solution within a period of time no more than 2.5 minutes from cessation of anodizing current.
16. The method of claim 15 wherein said electrolyte is rinsed from said coating within 0.5 to 2.5 minutes from cessation of anodization current.
17. The method of claim 15 wherein said temperature range is 75 ? 10°F.
18. The method of claim 15 wherein said potential is 10 ? 2 volts.
19. The method of claim 15 wherein said anodization is conducted for from 10 to 30 minutes.
20. An aluminum adherend having a polymer receptive hydration-resistant, aluminum oxide surface therein, said oxide surface having a porous columnar structure with a thickness of from about 500 to about 8,000 Angstroms, having pores from about 300 to about 1,000 Angstroms in diameter and from about 400 to about 7,500 Angstroms in depth extending into said oxide surface, said surface having been prepared by anodizing the surface of said adherend in an aqueous acidic electrolyte, the acidic component of said electrolyte consist-ing essentially of H3PO4 present in an amount of from about 1.5 to about 50%
by weight of solution at a temperature of from about 60°F. to about 85°F.
for about 10 to about 30 minutes at a potential of from about 1 to about 50 volts and then rinsing said adherend to remove said solution within a period of time no more than 2.5 minutes from cessation of anodizing current.
by weight of solution at a temperature of from about 60°F. to about 85°F.
for about 10 to about 30 minutes at a potential of from about 1 to about 50 volts and then rinsing said adherend to remove said solution within a period of time no more than 2.5 minutes from cessation of anodizing current.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US73672676A | 1976-10-29 | 1976-10-29 | |
| US736,726 | 1976-10-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1118708A true CA1118708A (en) | 1982-02-23 |
Family
ID=24961060
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000270187A Expired CA1118708A (en) | 1976-10-29 | 1977-01-21 | Method for providing environmentally stable aluminum surfaces for adhesive bonding and product produced |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5355423A (en) |
| CA (1) | CA1118708A (en) |
| DE (1) | DE2705652A1 (en) |
| IT (1) | IT1077744B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2762773B2 (en) * | 1991-06-19 | 1998-06-04 | 住友金属工業株式会社 | Al or Al alloy plate and method for producing the same |
| GB9721650D0 (en) | 1997-10-13 | 1997-12-10 | Alcan Int Ltd | Coated aluminium workpiece |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1244723A (en) * | 1967-11-15 | 1971-09-02 | Howson Algraphy Ltd | Improvements in or relating to presensitised lithographic printing plates |
-
1977
- 1977-01-21 CA CA000270187A patent/CA1118708A/en not_active Expired
- 1977-02-10 DE DE19772705652 patent/DE2705652A1/en active Granted
- 1977-02-16 IT IT4806377A patent/IT1077744B/en active
- 1977-02-25 JP JP1937877A patent/JPS5355423A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5355423A (en) | 1978-05-19 |
| DE2705652C2 (en) | 1993-05-27 |
| IT1077744B (en) | 1985-05-04 |
| DE2705652A1 (en) | 1978-05-03 |
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