CA1319591C

CA1319591C - Non-chrome cleaner/deoxidizer system

Info

Publication number: CA1319591C
Application number: CA000605932A
Authority: CA
Inventors: Mark W. Mcmillen
Original assignee: Henkel Corp
Current assignee: Henkel Corp
Priority date: 1988-07-19
Filing date: 1989-07-18
Publication date: 1993-06-29
Anticipated expiration: 2010-06-29
Also published as: AU616776B2; EP0351771B1; TR28132A; BR8903578A; DE68924012T2; JPH0277581A; MX170063B; DE68924012D1; EP0351771A1; ATE127167T1; AU3823089A

Abstract

ABSTRACT OF THE DISCLOSURE
The invention is a metal treating process which uses a chrome-free deoxidizing bath. The process is useful for cleaning and deoxidizing aluminum substrates.

Description

~3~9 ~ 27587-57 NON-C~QME CLEANER/DEOXIDIZER SYSTEM
Field of the Invention This invention relates to a novel process for cleaning and deoxidizing aluminum prior to conversion treatment. The process is based on an acid or alkaline cleaning system and a chromate-free deoxidizer system.
Backg~ound of the Invention Traditionally, chromated deoxidizers have been used to enable aluminum samples to pass designated corrosion tests, as for example, MIL-C-5541C. The aluminum is first cleaned in a relatively non-etching alkaline soak cleaner, deoxidized in an acidic chromate solution and subsequently chromated.
Alternatively, if etching was desired, an alkaline etch or alkaline chemical milling solution was used. This step was followed by a deoxidation step which usually employed a chromated deoxidizer, to remove "smut" produced by etching. The aluminum was then chromated. In the past, attempts to replace chromate in the deoxidizing step have generally involved the use of iron salts such as ferric sulfate. However, iron based deoxidizers have never provided results equal to the chromate containing deoxidizer systems.
U. S. Patent 4,451,304 to Batiuk provides a treatment for aluminum which employs an alkaline cleaning step and a deoxidizer step. The deoxidizer step employs a non-chromate deoxidizer which is an aqueous solution of sodium or potassium nitrite. This patent includes a detailed discussion of the prior art in this area.

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13~9~9~ 27587-57 Other than in the operating examples and claims, ox where otherwise indicated~ all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term "about".
DESCRIPTION OF THE INVENTION
The present inventicn is advantageous in that it eliminates the use of hexavalent chromium in the cleaning and deoxidizing step and further provides enhanced performance ~,.' .. . .

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over previously disclosed non-chromium processes for the cleaniny and deoxidlzing o$ aluminum prior ~o chemical conversion ~rea~ments.
According to one aspect, the invention provides a process for treating an aluminum ar~icle which comprises: a step of cleaning the aluminum article and a step of deoxidizing the ~ aluminum article by contact with an acidic deoxidizing solution selected from the group consisting of an acidic, stabilized hydrogen peroxida solution, an acidic heteropoly vandic acid solution or an acidic heteropoly vanadic acid salt solution.
According to another aspect, ~he inventlon proYides a process which comprises: contacting an aluminum article with a combined cleaning-etching deoxidlzing acid stabilized hydrogen peroxide solution at a temperature of from about 90F to abou~
175F for from ahout 2 to about 25 minutes, wherein the pH of ~he solution iæ below about 2.
In accordance with the present invention, aluminum is cleaned in an aqueous acidic or alkaline solution. The preferred acidulants are acids such as sulfuric acid, nitric acid, hydrofluoric acid, phosphoric acid, citric acid, oxalic acid, acetic acid, yluconic acid, hydroxyacetic acid and the like or mixtures of two or more such acids~ Preferably tha acidic solution is a dilute solution which provides low etching.
The alkaline cleaning solutions useful in the present invention generally contain alkali metal hydroxides or o~her water B

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soluble alkaline materlals such as ~risodium phosphate, alkali silicates r tetrasodium pyrophosphate and the like.
The etchants can also comprise acidic solution~ of fluoride compositions such as hydrogen fluoride and ~luoride salts, ~luoride complexes and the like, such as ammonium bifluoride, fluorosilicic acid, fluorophosphonic acid, its salts, and the like.
Following the cleaning step, the aluminum is then immersed in an aqueous acidic deoxidizer solution containing at least one of the following deoxidizer compositions hydrogen peroxide or heteropoly vanadic aclds or its salts. Optionally, the aluminum can be rinsed before contact with the deoxidizer solution. The use of a rinse in preferred.
In ano~her embodiment of the invention the aluminum article can be cleaned and deoxidi7ed in a single step by including a deoxidizer compound such as hydrogen peroxide in the acid cleaning solution.
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13~9~91 DETAILED DESCRIPTION OF THE II~VENTION
....
In the descrlptlon of the lnventlon, the term ~alumlnum~
used in connection with the substrate metal to be treated, lncludes aluminum metal per se and also those aluminum alloys which are generally sub~ected to a cleaning and deoxidizing treatment prior to chromatlng or other chemical or electrochemical conversion treatment.
Aluminum metal ~-r se invariably contains trace impurities of other metals. Exemplary of such impurity metals are coppor, manganese, nickel, zinc, titanium, vanadium, sodium and gallium.
Aluminum alloys generally con'ain larger amounts of other metals. Such alloying metals include silicon, chromium, lead, iron, copper, magneslum, manganese, zinc and the like.
Such metals in the form of ions as well as aluminum ions invariably are present in the deoxidizer solutions by virtue of the action of such solutions on the metal and smut. It is one aspect of the present invention that the deoxidizer solutions containing stabilizers can continue to function in the presence of such other metal ions, particularly iron~
copper and manganese. The multivalent metal ions tend to catalyze the decomposition of the hydrogen peroxide component.
This is especially true with copper and manganese.
In respect to the first step of this invention the aluminum substrate is subjected to cleaning and/or etchlng preferably with a dilute aqueous acidic solution at a pH of less than 2.
Preferably the pH ls below 2 and most preferably below 1.5. The cleaning solutions generally contaln from 0.005% to 5~ by volume or 10% by welgh~ of the aclds but can contaln up ~ 3~9~

to about 50% by weight, and preferably from about . 2 to abou~L
8% by weight and more preferably from about 0.4S to about 2.5%
by volume. It ls also preferred to employ a mlxture of aclds such as sulfuric acid and hydrofluoric acld.
While optional, sultable surfactants can be lncluded ln the cleaning solutions. They can be used in amounts of from o~ to 5~ by weight, and preferably up to about 2~ and most preferably up to about 0.5% by weight. Any suitable surfactants which are compatlble with the cleaning solutlon and do not leave an undesirable fiim on the aluminum's surface can be used. Such surfactants include the cationic, anionic, amphoteric and nonionic surfactants.
The cleaning and/or etching step can be done in an alkaline cleaner etchin9 solution. Xnown al~aline cleanlng solutions which contain alkali metal hydroxide, alkali metal carbonate, trialkali metal phosphate (such as trlsodlum phosphate) tetralkali metal pyrophosphate (tetrasodium pyrophosphate) alkali metal silicates and the llke, alone or in combination can also be used in the cleaning step of the present inventlon. Alkaline cleaning compositious such as Ridolin ~ 53, P3 Almec ~ 18 and Ridolin ~ 322 can be used in the cleaning step.
In an alternate embodyment of the invention, an acid cleaning-etching step can be combined with the deoxldi7er step by including hydrogen peroxide and a hydrogen pero~ide stabilizer with an acid cleaning solution. The combined cleaning and deoxidizlng steps can be carrled out at a temperature of from about ambient to about 170F and preferably from about 90F to about 150F. The pH of the 3~

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solutlor, ls preferably below about 3 and more preferably below about 1.5 and most preferably below about 0.5.
I~ wlll be appreciated that the cleaning-etchlng step can be conductsd in a short period of time with substantlally little etching or can be continued for a longer period of time if a deeply etched surface is desired.
It wlll also be appreciated that the cleanlng-etching step can be conducted at ambient temperatures but it ls preferred to conduct the cleaning step at elevated solution temperatures. Higher temperatures increase the rate of cleaning and/or etching action of the cleaner solution and a certain degree of care must be exercised to ensure that the desired de~ree of cleaning or etch is obtained. The temperature of the cleaning/etching solution is preferably lS from about 90F to about 175F and most preferably from about 100F to about 150F.
In respect to the deoxidizing step, it is preferred that the deoxidizer bath be acidic and preferably be below a pH of 4, and more preferably at or below 2. When the heteroploy ions are employed in the deoxidizer bath, they can be added to the bath as such or can be senerated in situ from their components.
~hen heteropoly vanadic acid or its salts are used, the deoxidizer comprises from 0.1 gram/liter to the solubility limit of the materlal and an acid to form a compositlon havlng a pH below 3. Generally, mineral acids are used and nitrlc acid is preferred.
When the deoxldizer ls hydrogen peroxide, it is preferred that the solutions contain from 0.03 to 30% by weight hydrogen peroxide and it is further preferred that one or more ~ 3 ~ ~ 3 9 ~ 27587-57 stabilizers for hydrogen peroxide also be employed in the solution. With respect to hydrogen peroxide deoxidizer solutions, it is also preferable to adjust the p~l to about 3 or less and preferably with nitric acid. The pH is preferably not greater than 1.5 and most preferably 0.5 or below. The deoxidizer solution is preferably maintained at a temperature from about ambient to about 150F depending on the time the aluminum article is in contact with the solution.
The aluminum article preferably is in contact with the deoxidizer solution from about l to about 25 minutes. The contact time is generally shorter at higher temperatures.
Stabilizers for peroxides are well known and are exemplified in U. S. Patent 4,509,678. Other suitable stabiliæers for hydrogen peroxide are well known in the art and any of these can be conveniently used provided they are compatible with acidic solutions.
After the deoxidation treatment, the treated aluminum substrate is then chromated by chromating treatments for aluminum, which are well known in the art. Chrornating with ch~omating compositions such as Alodine ~ 1200S or Alodine ~
600 product of ~arker + Amchem, a division of Henkel Corporation, are useful. The aluminum substrates are preferably rinsed before being treated with the chromating compositions. Rinsing is preferred to reduce contamination of the chromating composition with the components of the deoxidizing treatment composition.

~ 3 ~ 27587-57 ~he examples which follow are intended to illustrate this invention and are not to be considered limiting.

A cleaning solution was prepared as follows:
~. 70 mls of a solution prepared by diluting 323 mls of 96% sulfuric acid with water to one llter.
B. 70 mls of hydrofluoric acid concentra-te solution prepared by diluting 214 grams of 70% hydrofluoric acid to one liter. 70 mls A and 70 mls B were mixed and diluted to 7 liters with a mixture of 25% Ambler Borough ~PA.) tap water and 75%
deionized water. The mixture of tap water and deionized water had a conductance of 250 microohms.
A deoxidizer solution was prepared as follows:
A concentrate was first prepared by blending 3800 mls of 35% hydrogen peroxide and 200 mls of Dowfax ~ 241 (sodium dodecyl diphenyl oxide disulfonate).
1610 mls of the hydrogen peroxide concentrate as prepared above and 475 mls of 70% nitric acid were diluted to 18.9 liters.
Panels of aluminum alloy 2024-T3 were immersed in the cleaning solution at a temperature of 120F for a period of ten minutes. The panels were then removed, rinsed with deionized water and immersed in the deoxidizer solution at ambient temperature for fifteen minutes. The panels were rinsed and subsequently chromated. The chromated panels successfully passed MIL-C-5541C test for neutral salt spray specifications.

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~ _X~MPL~ 2 A cleaner solution concentrate was prepared by blendlng 100 mls of 96~ sulfurlc acld and 416 mls of 75~ phosphorlc acid and dllutlng to one llter.
5A cleaner solution was prepared by mixing 140 mls of cleaner solution and 70 mls of hydrfluoric acid solution concentrate as prepared in Example 1 and diluting to 7 liters.
The deoxidizer solution used in thls example was identical to that used in ~xample 1.
10Panels of aluminum alloy, 2024-T3, were immersed i~ the above cleaning solution at a tem?erature of 120F for a period of 10 minutes. Thereafter the panels were removed, rinsed with water and immersed in the deoxidizer solution at ambient temperatures for a period of 15 minutes. Thereafter, the 15panels were rinsed and chromated. These panels passed the MIL-C-5541C neutral salt spray s?ecifications.

A cleaner concentrate solution was prepared by blending 256 mls of 96~ sulfuric acid, 90 grams of Mirawet~ B
20~amphoteric surfactant), 90 grams of Surfoni ~ LF-17 ethoxylated alcohol) and diluting to one liter with water.
4 liter cleaning baths were prepared containing 50 mls of the cleaner concentrate to which varying amounts of hydrofluoric acld were added as shown in Tables I and II.
25The amount of hydrofluoric acid added in the baths set forth in Tables I and II and based on the hydrofluoric acld concentrate ac pr~pared in Example 1. In respect to the .17~
solutlons, 40 mllliliters of the hydrofluorlc concentrate were added. In respect to the .09% solutlons, 21 mllllliters of 30the hydrofluoric concentrate were added, and in respect to the ~319~9~

0.009%, 2 mllllllters of the hydrofluorlc acid concentrate were added.
A 4 liter deoxidlzer bath was prepared in a manner slmllar to that of ~xamples 1 above. The ingredients employed in the deoxidizer baths are set forth in Tables I and II below.
In respect to the baths exemplified in Table 1, it should be noted that reagent grade 70% nitric acid was used and the stabilizer of Table I was Dowfa ~ 2Al (sodium dodecyl diphenyl oxide disulfonate~. Further in respect to the baths of Table I, 10.2 milliliters of the stabili2er were added to obtain the .255% stabilizer concentration and 0.4 milliliters of the stabilizer were added to get the 0.01% stabilizer concen-tration.
In respect to the peroxide, 400 mllllliters of 3s%
hydrogen peroxide diluted to one liter with water, were used for the 10% concentrations and 240 milliliters were used for the 6~ concentrations.
In respect to the deoxidizer baths of Table II, commercial grade nitric acid at 67.5% was employed and the stabilizer was Monofa ~ 1214 (alkyi phosphate ester). In respect to the nitric acid, 400 milliliters of the nitric acid were used for the 10% solution, 240 milliliters ofr 6% solutions and 80 milllliters for the 2% solutions. Furthermore ~n respect to the peroxide, 400 mllliliters were used for the 10% solution, 240 milliliters for the 6~ solution and 80 milliliters for the 2% solutlon were employed.

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TABLE I
CLEANER DEO~IDIZER
96% pH
Sulfurlc 35~ Stabil- Ad~.
Acld 70% HF Surfactant Peroxide lzer w~HNO Time ~0.3% 0.17~ ~ 0.2% 6% 0.255% 0.510 ~in 0,3% 0.~9% 0.2% 6% 0.01% 1.05 Mln 0.3~ 0.09% 0.2% 6% 0.255% 0.515 Min 0.3% 0.09% 0.~ lC% 0.255% 0.510 Min TABLE II
CLEANER DEOXIDIZER

Sulfurlc 35% Stabil- 42Be Acid 70% HF Surfactant Peroxide izer XNO Tlme 0.3~ 0.17% 0.2% 6~ 0.19/1 6%15 Min 0.3% 0.09~ 0.2% 10% 2.55g/1 6% 15 Min 0.3% 0.0g~ 0.2% 10% 2.55g/1 6~ 15 Min 0.3% 0.09~ 0.2% 10% 2.559/1 6~ 5 Min 0.3% 0.09% 0.2% 6% 2.559/1 S~ 10 Mln 0.3~ 0.009% 0.2% 2~ 5g/1 6%10 Min 0.3% 0.17% 0.2~ 6% 2.55g/1 10%10 Min 0.3% 0.17~ 0.2% 6% 2.55g/1 2%10 Min Aluminum panels of alloy, 2024-T3, were cleaned in a specified cleaner bath set forth in Table I and Table II
above. The panels were then rinsed and immersed in the deoxidizer bath as indicated ln Tables I and II above, ea~h for a speclfied perlod of tim~ listed. After the deoxldizing step, the panels were removed, rlnsed and chromated. ~he chromated panels were then tested in neutral salt spray for 11 ' ~ 319~

336 hours (twlce as long as MIL-C-5541C requlres;. ~ panels showed no plttlng and no corroslon after testlng.
It has been found that preferred systems are those whereln the cleanlng solutlon contalns 0.3~ by volume sulfuric acld (96%), 0.17~ by volume hydrofluoric acid (70%), and up to 0.2%
by volume sodium 2-ethyl hexyl sulfate surfactant for a strong etch cleaner. Thls cleaner should be used for 5-10 minutes at temperatures of from about 110F to about 130F.
It ls preferred to then subject the aluminum panels to a deoxidiziang step for about 10-15 mi~utes by immersion ln a deoxidizing bath of preferrably 8% by volume hydrogen peroxide ~3s%), 3~ by volume (42oBe) nitric acid and up to 0.5% of a stabilizer for the peroxide (preferrably MIRATAIN ~ CBS
(cocoamidopropyl hydroxy sultaine).
When it ls desired to have an etchin~ cleaner with lower etching properties, it is preferred to employ a cleaning solution of 0.5% by volume sulfuric acid (96~), 1.~%
phosphoric acid by volume (75%), and up to 0.2% of a surfactant combination which is a mixture of Trito ~ N-100 ~nd Surfonic~ LF-17. This ls used at a temperature of from about 110F to about 140F for 5 to 10 minutes followed by the same deoxidizer step as established above for from about 5 to 15 minutes.
EX~MPLE 4 A cleaner-etchins-deoxidizer bath was prepared containing 8% H202, 2.5% HN03, 1.5~ phosphoric acid and 2 ml/liter of Trito ~ X-102 surfactant (octylphenoxy polyethoxy ethanol).
Alumlnum panels were lmmersed in the cleaning-etchlng deoxidlzer solutlon for 10 minutes at 120F. The panels were ~0 rlnsed and then chromated in an Alodln ~ 1200S chromatlng ` ` ~319591 solut~on accordlng to manufacturer's rec~mmendatlons. Th chromated panels were then teste~ in neutral salt spray for 336 hour~. There was no pltting or corrosion of the aluminum panels.

A cleaner-etching-deoxidizer bath was prepared containlng 8% H20~, 2.5% HN03, 1 ml/l~iter of 79% HBF~ and 2 ml/llter Trito~ X-102 surfactant. Aluminum panels were immersed ln the cleaner-etching-deoxidizer solution for 10 minutes at 120F. Th~ panels were rinsed and then chromated ln an Alodin ~ 1200S solution according to manufacturer's recommendations. The chromated panels were then tested in neutral salt spray for ~36 hours. There was no pitting or corrosion of the aluminum panels.
The combinlng of the acid cleaning-etch step wlth the deoxidizer step into one treating step is an advance ln the art. The combining of two steps into a single step reduces the equipment necessary to provide ~ commerical process and in additlon reduces the processiny tlme for each aluminum piece.

Claims

1. A process for treating an aluminum article which comprises: a step of cleaning the aluminum article and a step of deoxidizing the aluminum article by contact with an acidic deoxidizing solution selected from the group consisting of an acidic, stabilized hydrogen peroxide solution, an acidic heteropoly vandic acid solution or an acidic heteropoly vanadic acid salt solution.

2. A process of claim 1 wherein the pH of the acidic stabilized hydrogen peroxide solution is at a pH below about 3.

3. A process of claim 1 wherein the aluminum article is cleaned by contact with an alkaline cleaning solution, the aluminum article rinsed and then contacted with the acidic deoxidizing solution.

4. A process of claim 3 wherein the cleaning solution is at a temperature of from about 90°F to about 175°F.

5. A process of claim 3 wherein the deoxidizing solution is a stabilized hydrogen peroxide solution at a temperature of from about ambient to about 150°F and at a pH below about 3.

6. A process of claim 5 wherein the pH is below about 0.5.

7. A process of claim 1 wherein the aluminum article is cleaned by contact with an aqueous acidic solution at a pH below about 2.

8. A process of claim 7 wherein the aluminum article, after contact with the acidic cleaning solution, is contacted with a stabilized hydrogen peroxide solution at a pH below about 1.5.

9. A process of claim 8 wherein the pH of the stabilized hydrogen peroxide deoxidizing solution is below about 0.5.

10. A process of claim 7 which comprises:
a) contacting an aluminum article with an acidic solution at a temperature of from about 90°F to about 175°F, at a pH below about 2 for from about 1 to about 15 minutes to clean the aluminum article; and b) contacting the cleaned aluminum article with an acidic stabilized hydrogen peroxide solution at a temperature from about ambient to about 150°F
for from about 1 to about 25 minutes.

11. A process which comprises: contacting an aluminum article with a combined cleaning-etching deoxidizing acid stabilized hydrogen peroxide solution at a temperature of from about 90°F to about 175°F for from about 2 to about 25 minutes, wherein the pH of the solution is below about 2.

12. A process of claim 11 wherein the pH is below about 0.5

13. A process of claim 11 wherein the combined cleaning-etching-deoxidizing solution comprises:
a) a deoxidizing effective amount of hydrogen peroxide b) a stabilizing amount of a stabilizer for the hydrogen peroxide c) a pH adjusting amount of nitric acid d) an etching effective amount of a source of fluoride ion.

14. A process of claim 11 wherein the combined cleaning-etching and deoxidizing solution comprises:
a) a deoxidizing effective amount of hydrogen peroxide b) a stabilizing amount of a stabilizer for the hydrogen peroxide c) an etching effective amount of phosphoric acid d) a pH adjusting amount of nitric acid.

15. Process of claim 13 wherein the combined cleaning-etching-deoxidizing solution contains as the deoxidizing agent hydrogen peroxide in an amount from about 0.03% to about 30% by weight hydrogen peroxide.

16. A process of claim 1 wherein the aluminum is cleaned by contact with a cleaning solution comprising about 0.3% sulfuric acid (96%), about 0.17% hydrofluoric acid (70%), and about 0.2%
sodium 2-ethyl hexyl sulfate and wherein the aluminum substrate is cleaned in this solution for a period of about 5 to about 10 minutes at a temperature of from about 110°F to about 130°F.

17. A process of claim 1 wherein the deoxidizing solution comprises about 8% by volume hydrogen peroxide (35%), about 3% by volume 42°B? nitric acid and wherein the aluminum is immersed in the deoxidizing solution for a period of from about 10 to about 15 minutes at ambient temperatures.

18. A process of claim 1 wherein the aluminum is cleaned by contact with a cleaning solution which comprises about 0.5%
sulfuric acid (96%), about 1.7% phosphoric acid (75%), and up to about 0.2% of a surfactant and the aluminum is treated in this solution for a period of from about 5 to about 10 minutes at a temperature of about 110°F to about 140°F.

19. A combined cleaning-etching-deoxidizing solution of claim 13.

20. A combined cleaning-etching-deoxidizing solution of claim 14.

21. A deoxidizer solution of claim 1 wherein the deoxidizing agent is hydrogen peroxide in an amount of from about 0.03% to about 30% by weight wherein the solution contains a stabilizing amount of a stabilizing agent for hydrogen peroxide, aluminum and trace metal ions from the aluminum.

22. The deoxidizer solution of claim 1 wherein the deoxidizing agent is hydrogen peroxide in an amount of from about 0.03% to about 30% by weight wherein the solution contains a stabilizing amount of a stabilizing agent for hydrogen peroxide, an aluminum and alloy metal ions from an aluminum alloy.

23. The deoxidizer solution of claim 1 wherein the deoxidizing agent is hydrogen peroxide in an amount of from about 0.03% to about 30% by weight wherein the solution contains a stabilizing amount of a stabilizing agent for hydrogen peroxide, aluminum, copper and maganese.