AU616776B2

AU616776B2 - Non-chrome cleaner/deoxidizer system

Info

Publication number: AU616776B2
Application number: AU38230/89A
Authority: AU
Inventors: Mark W. Mcmillen
Original assignee: Henkel Corp
Current assignee: Henkel Corp
Priority date: 1988-07-19
Filing date: 1989-07-19
Publication date: 1991-11-07
Anticipated expiration: 2009-07-19
Also published as: DE68924012T2; AU3823089A; EP0351771B1; CA1319591C; DE68924012D1; TR28132A; EP0351771A1; MX170063B; ATE127167T1; JPH0277581A; BR8903578A

Abstract

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

67 id Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952.69 COMPLETE SPECIFICATION

(ORIGINAL)

Class Application Number: Lodged: Int. Class 0.

Complete Specification Lodged: 0 Accepted: o Published: Prio;ity 0 Related Art: 0 0 4 Napie of Applicant: ,.ddress of Applicant 'ActualI nventor: Address for Service: HENKEL CORPORATION 300 Brookside Avenue, Ambler, Pennsylvania 19002, United States of America MARK W. McMILLEN -Watermark Patent Trademark Attorneys 50 QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.

Complete Specification for the invention entitled: NON-CHROME CLEANER/DEOXIDIZER SYSTEM The following statement is a full description of this invention, including the best method of performing it known to US 1.

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NON-CHROME 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.

01 0 0 0 0* 00 airr rr, a os c a 0 0 0 0 -1A- *Q T. P 1it? :e Background 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.

o0 0 However, iron based deoxidizers have never provided results equal to the chromate containing deoxidizer systems.

o 0O U.S. Patent 4,451,304 to Batiuk provides a treatment for S aluminum which employs an alkaline cleaning step and a deoxidizer step. The deoxidizer step employs a non-chromate deoxidizer which is an equeous solution of sodium or potassium nitrite. This patent, which is incorporated herein by reference, includes a detailed discussion of the prior art in this area.

o* Other than in the operating examples and claims, or where oo otherwise indicated, all numbers expressing quantities of 2 ingredients or reaction conditions used herein are to be understood as modified in all instances by the term "about".

o DESCRIPTION OF THE INVENTION 0 The present invention is advantageous in that it S eliminates the use of hexavalent chromium in the cleaning and deoxidizing r and further provides enhanced performance 2 1 over previously disclosed non-chromium processes for the cleaning and deoxidizing of aluminum prior to chemical conversion treatments.

In its broadest aspect the invention provides a process for treating an aluminium article which comprises: cleaning the aluminium article; and deoxidizing the cleaned aluminium article by contact with an acidic deoxidizing solution selected from the group consisting of an acidic, stabilized hydrogen peroxide containing solution; an acidic heteropoly vanadic acid containing solution, and an acidic heteropoly vanadic acid salt containing solution, and conversion coating the deoxidized aluminium article.

In accordance with the present invention, aluminium 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, gluconic acid, hydroxyacetic acid and the like or mixtures of two or more such acids.

Preferably the acidic solution i' a dilute solution which provides low etching.

p. r 2he alkaline cleaning solutions useful in the present invention generally contain alkali metal hydroxides or other water soluble alkaline materials such as trisodium phosphate, alkali silicates, tetrasodium pyrophosphate and the like.

o 0"0°00 The etchants can also comprise acidic solutions of fluoride compositions such as hydrogen fluoride and fluoride salts, fluoride complexes and the like, such as ammonium bifluoride, fluorosilicic acid, fluorophosphonic acid, its salts, and the like.

3 0 6 0 t 0 *i Following the cleaning step, the aluminum is then immersed in an aqueous acidic deoxidizing solution containing at least one of the following deoxidizing compositions hydrogen peroxide or heteropoly vanadic acids or its salts. Optionally, the aluminum can be rinsed before contact with the deoxidizing solution. The use of a rinse is preferred.

In another embodiment of the invention the aluminum article can be cleaned and deoxidized in a single step by including a deoxidizing agent such as hydrogen peroxide in the acid cleaning solution.

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IDETAILED DESCRIPTION OF THE INVENTION SIn the description of the invention, the term "aluminum" used in connection with the substrate metal to be treated, includes aluminum metal per se and also those aluminum alloys i 5 which are generally subjected to a cleaning and deoxidizing 'S treatment prior to chromating or other chemical or Selectrochemical conversion treatment.

SAluminum metal per se invariably contains trace impurities of other metals. Exemplary of such impurity metals are 4 10 copper, manganese, nickel, zinc, titanium, vanadium, sodium and gallium.

Aluminum alloys generally contain larger amounts of other metals. Such alloying metals include silicon, chromium, lead, S0o" o iron, copper, magnesium, 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 Booo 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.

o This is especially true with copper and manganese.

0 In respect to the first step of this invention the 04° aluminum substrate is subjected to cleaning and/or etching preferably with a dilute aqueous acidic solution at a pH of less than 2.

Preferably the pH is below 2 and most preferably below 0o0 1.5. The cleaning solutions generally contain from 0.005% to 5% by volume or 10% by weight of the acids but can contain up 4 to about 50% by weight, and preferably from about .2 to about 8% by weight and more preferably from about 0.4% to about by volume. It is also preferred to employ a mixture of acids such as sulfuric acid and hydrofluoric acid.

While optional, suitable surfactants can be included in the cleaning solutions. They can be used in ar'mnts of from 0% 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 compatible with the cleaning solution and do not leave an undesirable film on the aluminum's surface can be used. Such surfactants include the cationic, anionic, amphoteric and nonionic surfactants.

"to The cleaning and/or etching step can be done in an Salkaline cleaner etching solution. Known alkaline cleaning solutions which contain alkali metal hydroxide, alkali metal S carbonate, trialkali metal phosphate (such as trisodium o oo phosphate) tetralkali metal pyrophosphate (tetrasodium 0 o° pyrophosphate) alkali metal silicates and the like, alone or in combination can also be used in the cleaning step of the present invention. Alkaline cleaning compositious such as Ridolineg 53, P3 Almecd 18 and Ridoline 322 can be used in 4004 0 the cleaning step.

oo In an alternate embodyment of the invention, an acid cleaning-etching step can be combined with the deoxidizer step 250 ooo by including hydrogen peroxide and a hydrogen peroxide stabilizer with an acid cleaning solution. The combined cleaning and deoxidizing steps can be carried out at a o temperature of from about ambient to about 170 0 F and preferably from about 90°F to about 150 0 F. The pH of the 0 0

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I C I- l~ LI l( lll solution is preferably below about 3 and more preferably below about 1.5 and most preferably below about It will be appreciated that the cleaning-etching step can be conducted in a short period of time with substantially little etching or can be continued for a longer period of time if a deeply etched surface is desired.

It will also be appreciated that the cleaning-etching step can be conducted at ambient temperatures but it is preferred to conduct the cleaning step at elevated solution temperatures. Higher temperatures increase the rate of cleaning and/or etch.ng action of the cleaner solution and a certain degree of care must be exercised to ensure that the 0*.o desired degree of cleaning or etch is obtained. The oo ,0 temperature of the cleaning/etching solution is preferably 0 from about 900F to about 1750F and most preferably from about o 100°F to about 150 0

F.

o. In respect to the deoxidizing step, it is preferred that S° 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 generated in situ from their 0.0' components.

o o* When heteropoly vanadic acid or its salts are used, the deoxidizer comprises from 0.1 gram/liter to the solubility limit of the material and an acid to form a composition having a pH below 3. Generally, mineral acids are used and nitric acid is preferred.

0 When the deoxidizer is hydrogen peroxide, it is preferred *4ooo that the solutions contain from 0.03 to 30% by weight hydrogen peroxide and it is further preferred that one or more

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stabilizers for hydrogen peroxide also be employed in the solution. With respect to hydrogen peroxide deoxidizer solutions, it is also preferable to adjust the pH 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 150 0 F 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 1 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. This patent is incorporated herein by reference. Other suitable stabilizers for hydrogen peroxide are well known in the art and any of a 00 0 these can be conveniently used provided they are compatible with acidic solutions. A preferred group of stabilizers is Auvstrian Pcrfer A pplica-i- %S'2Z 's o disclosed inU.. tnt Appiction Scrial 5P. 07/221, 06 filed- o July 19, 190 in the name of Mark McMillen and entitled "Stabilization of Peroxide Solutions.

After the deoxidation treatment, the treated aluminum 00 substrate is then chromated by chromating treatments for 00 0 'o0 aluminum, which are well known in the art. Chromating with chromating compositions such Alodine® 1200S or Alodin& 600 2 °Oo product of Parker Amchem a division of Henkel Corporation are useful. The aluminum substrates are preferably rinsed before being treated with the chromating compositions.

o°S° Rinsing is preferred to reduce contaminatin of the chromating 0 composition with the components of the deoxidizing treatment composition.

7 0 P6 'i The examples which follow are intended to illustrate this invention and are not to be considered limiting.

EXAMPLE 1 A cleaning solution was prepared as follows: A. 70 mis of a solution prepared by diluting 323 mis of 96% sulfuric acid with water to one liter.

B: 70 mis of hydrofluoric acid concentrate solution prepared by diluting 214 grams of 70% hydrofluoric acid to one liter. 70 mis A and 70 mis B were mixed and diluted to 7 liters with a mixture of 25% Ambler Borough tap water and 75% deionized water. The mixture of tap water and deionized water had a conductance of 250 micromhos.

&000 S A deoxidizer solution was prepared as follows: 1o o A concentrate was first prepared by blending 3800 mis of 0 0 hydrogen peroxide and 200 mis of Dowfa> 241 (sodium dodecyl 0° 0 diphenyl oxide disulfonate).

1610 mis of the hydrogen peroxide concentrate as prepared above and 475 mis of 70% nitric acid were diluted to 18.9 liters.

Panels of aluminum alloy 2024-T3 were immersed in the S cleaning solution at a temperature of 120 0 F for a period of 4:i ten minutes. The panels were then removed, rinsed with deionized water and immersed in the deoxidizer solution at 2f ambient temperature for 15 minutes. The panels were rinsed and subsequently chromated. The chromated panels successfully passed MIL-C-5541C test for neutral salt spray specifications.

o° The MIL-C-5541C specification and test methods are incorprated herein by reference.

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-EXAMPLE 2 A cleaner solution concentrate was prepared by blending 100 mls of 96% sulfuric acid and 416 m1s of 75% phosphoric acid and diluting to one liter.

A cleaner solution was prepared by mixing 140 mis of cleaner solution and 70 mis of hydrfluoric acid solution concentrate as prepared in Example 1 and diluting to 7 liters.

The deoxidizer solution used in this example was identical to that used in Example 1.

Panels of aluminum alloy, 2024-T3, were immersed in the above cleaning solution at a temperature of 120 0 F 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 1o panels were rinsed and chromated. These panels passed the o 0 0 MIL-C-5541C neutral salt spray specifications.

EXAMPLE 3 00 S° o A cleaner concentrate solution was prepared by blending 256 mis of 96% sulfuric acid, 90 grams of Mirawet B (amphoteric surfactant), 90 grams of Surfonick LF-17 (ethoxylated alcohol) and diluting to one liter with water.

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0 4 liter cleaning baths were prepared containing 50 mis of S the cleaner concentrate to which varying amounts of hydrofluoric acid were added as shown in Tables I and II.

The amount of hydrofluoric acid added in the baths set forth in Tables I and II and based on the hydrofluoric acid concentrate as prepared in Example 1. In respect to the .17% 0" solutions, 40 milliliters of the hydrofluoric concentrate were o0o0* added. In respect to the .09% solutions, 21 milliliters of the hydrofluoric concentrate were added, and in respect to the 9 }i 0.009%, 2 milliliters of the hydrofluoric acid concentrate were added.

A 4 liter deoxidizer bath was prepared in a manner similar to that of Examples 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 Dowfax 2A1 (sodium dodecyl diphenyl oxide disulfonate). Further in respect to the baths of Table I, 10.2 milliliters of the stabilizer were added to obtain the .255% stabilizer concentration and 0.4 milliliters of the stabilizer were added to get the 0.01% stabilizer concentration.

0 In respect to the peroxide, 400 milliliters of 9 0 hydrogen peroxide diluted to one liter with water, were used for the 10% concentrations and 240 milliliters were used for 0 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 (alkyl phosphate ester). In respect to the o nitric acid, 400 milliliters of the nitric acid were used for the 10% solution, 240 milliliters ofr 6% solutions and milliliters for the 2% solutions. Furthermore in respect to the peroxide, 400 milliliters were used for the 10% solution, 240 milliliters for the 6% solution and 80 milliliters for the 2% solution were employed.

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TABLE I CLEANER DEOXIDIZER 96% Sulfuric Acid 0.3% 0.3% 0.3% 0.3% 70% HF 0.17% 0.09% 0.09% 0.09% Surfactant 0.2% 0.2% 0.2% 0.2% pH 35% Stabil- Adj.

Peroxide izer w/HNO Time 6% 0.255% 0.5 10 Min 6% 0.01% 1.0 5 Min 6% 0.255% 0.5 15 Min 10% 0.255% 0.5 10 Min TABLE II a a 0 0a El* f S4 4 ~14 4 0 a @4 a 2ao o a a a a a a 0*0 o a a Ia« 4 S 0

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96% Sulfuric Acid 0.3% 0.3% 0.3% 0.3% 0.3% 0. 3% 0.3% C. 3%

CLEANER

70% HF 0.17% 0 .09% 0.09% 0.09% 0.09% 0.009% 0.17% 0.17%

DEOXIDIZER

Surfactant 0 .2% 0.2% 0 .2% 0 .2% 0 .2% 0 .2% 0.2% 0 .2% 35% Stabil- 42°Be Peroxide izer HNO Time 6% 0.lg/l 6% 15 Min 10% 2.55g/l 6% 15 Min 10% 2.55g/l 6% 15 Min 10% 2.55g/l 6% 5 Min 6% 2.55g/l 6% 10 Min 2% 5g/l 6% 10 Min 6% 2.55g/l 10% 10 Min 6% 2.55g/l 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 in Tables I and II above, each o for a specified period of time listed. After the deoxidizing o, step, the panels were removed, rinsed and chromated. The chromated panels were then tested in neutral salt spray for

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336 hours (twice as long as MIL-C-5541C requires). All panels showed no pitting and no corrosion after testing.

It has been found that preferred systems are those wherein the cleaning solution contains 0.3% by volume sulfuric acid I5 0.17% by volume hydrofluoric acid and up to 0.2% by volume sodium 2-ethyl hexyl sulfate surfactant for a strong etch cleea?:r. This cleaner should be used for 5-10 minutes ii at temoe ':ures of from about 110 0 F to about 130 0

F.

I' preferred to then subject the aluminum panels to a deox." ang step for about 10-15 minutes by immersion in a :1 deoxidizing bath of preferrably 8% by volume hydrogen peroxide i 3% by volume (42Be) nitric acid and up to 0.5% of a stabilizer for the peroxide (preferrably MIRATAINE CBS (cocoamidopropyl hydroxy sultaine).

When it is desired to have an etching cleaner with lower etching properties, it is preferred to employ a cleaning I a solution of 0.5% by volume sulfuric acid 1.7% Sphosphoric acid by volume and up to 0.2% of a surfactant combination which is a mixture of Triton N-100 and Surfonic LF-17. This is used at a temperature of from about 110 0 F to about 1400F for 5 to 10 minutes followed by the same deoxidizer step as established above for from about 5 to S minutes.

EXAMPLE 4 5 .A cleaner-etching-deoxidizer bath was prepared containing 8% H 2 0 2.5% HNO 3 1.5% phosphoric acid and 2 ml/liter of Tritorn X-102 surfactant (octylphenoxy polyethoxy ethanol).

Aluminum panels were immersed in the cleaning-etching deoxidizer solution for 10 minutes at 120 0 F. The panels were 0 rinsed and then chromated in an Alodine 1200S chromating 12 1 t i! J i3 solution according to manufacturer's recommendations. The chromated panels were then tested in neutral salt spray for 4 I336 hours. There was no pitting or corrosion of the aluminum panels.

EXAMPLE A cleaner-etching-deoxidizer bath was prepared containing 8% H20, 2.5% HNO3, 1 ml/liter of 79% HBF 4 and 2 ml/liter Triton- X-102 surfactant. Aluminum panels were immersed in the cleaner-etching-deoxidizer solution for 10 minutes at 120OF. The panels were rinsed and then chromated in an AlodindE 1200S solution according to manufacturer's recommendations. The chromated panels were then tested in neutral salt spray for 336 hours. There was no pitting or corrosion of the aluminum panels.

e 0 The combining of the acid cleaning-etch step with the e o deoxidizer step into one treating step is an advance in the 0 art. The combining of two steps into a single step reduces S0* 0 the equipment necessary to provide a commerical process and in addition reduces the processing time for each aluminum piece.

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Claims

1. A process for treating an aluminum article which comprises: cleaning the aluminum article and deoxidizing the cleaned aluminum article by contact with an acidic deoxidizing solution selected from the group consisting of an acidic, stabilized hydrogen peroxide containing solution, an acidic heteropoly vanadic acid containing solution and an acidic heteropoly vanadic acid salt containing solution; and conversion coating the deoxidized aluminum article.

2. A process of Claim 1 wherein the pH of the acidic stabilized hydrogen peroxide solution is at a pH below 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 o contacted with the acidic deoxidizing solution. o 00 o o

4. A process of Claim 3 wherein the cleaning solution is at a temperature of from 90 0 F to 175 0 F.

5. A process of Claim 3 wherein the deoxidizing solution is a stabilized hydrogen peroxide solution 000 'at a temperature of from ambient to 150 0 F and at a o pH below 3. S6. A process of Claim 5 wherein the pH is below 14 "W :I I

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11. o o a 0 Q C O 0 0 0 0 0 90 0 00aJ0 9 o e :12. 6 e So a A process of Claim 1 wherein the aluminum article is cleaned by contact with an aqueous acidic solution at a pH below 2. 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 A process of Claim 8 wherein the pH of the stabilized hydrogen peroxide deoxidizing solution is below A process of Claim 7 which comprises: a. Contacting an aluminum article with an acidic solution at a temperature of from 90 0 F to 175 0 F, at a pH below 2 for from 1 to minutes to clean the aluminum article; and b. Contacting the cleaned aluminum article with an acidic stabilized hydrogen peroxide solution at a temperature from ambient to 150 0 F for from 1 to 25 minutes. A process of Claim 1 which comprises: Contacting an aluminum article with an acidic cleaning solution containing a deoxidising agent and an etching agent at a temperature of from 90 0 F to 175 0 F for from 2 to 25 minutes, wherein the pH of the solution is below 2. A process of Claim 11 wherein the pH is below

13. A process of Claim 11 wherein the acidic cleaning solution comprises: a. a deoxidizing effective amount of hydrogen peroxide b. a stabilizing amount of stabilizer for the hydrogen peroxide c. a pH adjusting amount of nitric acid d. an etching effective amount of a source of .1 fluoride ion.

14. A process of Claim 11 wherein the acidic cleaning solution comprises: a. a d-oxidizing 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 whereip the acidic cleaning solution 0 contains as the deoxidizing agent hydrogen peroxide in a o 0 S; S an amount from 0.03% to 30% by weight hydrogen peroxide.

16. A process of Claim 1 wherein the aluminum is cleaned by contacting with a cleaning solution comprising 0.3% sulfuric acid 0.17% hydrofluoric acid and 0.2% sodium 2-ethyl hexyl sulfate, and wherein the *aluminum substrate is cleaned in this solution for a period of 5 to 10 minutes at a temperature of from 110°F to 130 0 F. J S 16 I L 'A

17. A process of claim 13, wherein the acidic cleaning solution comprises 8% by volume hydrogen peroxide 3% by volume 42 0 Be nitric acid, and wherein the aluminum is immersed in the acidic cleaning solution for a period of from 10 to minutes at ambient temperatures.

18. A process of claim 1, wherein the aluminum is cleaned by contact with a cleaning solution which comprises 0.5% sulfuric acid 1.7% phosphoric acid and up to 0.2% of a surfactant, and the aluminum is treated in this solution for a period of from 5 to 10 minutes at a temperature of 110°F to 140 0 F. '19. An acidic cleaning solution as used in the process of claim 13.

20. An acidic cleaning solution as used in the process of claim 14. DATED this 14th day of August, 1991. ~HENKEL CORPORATION WATERMARK PATENT TRADEMARK ATTORNEYS a e THE ATRIUM a 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA it- 17- 0-i (M °J 07;