FR2543580A1 - METHOD AND BATH FOR FIXING ALUMINUM AND ALUMINUM ALLOYS FOLLOWING ANODIZATION TREATMENT - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR FIXING ALUMINUM AND ITS ALLOYS FOLLOWING AN ANODIZATION TREATMENT. ACCORDING TO THE INVENTION, IT INCLUDES THE STEP OF IMMERSING THE MATERIAL TO BE TREATED FOR 5 TO 30 MINUTES IN A FIXATION BATH MAINTAINED AT 15-30C AND CONTAINING AN AQUEOUS SOLUTION OF AT LEAST ONE NICKEL SALT AT A CONCENTRATION BETWEEN 0.1 AND 50 GL, ADDED WITH A NON-IONIC SURFACE-ACTIVE AGENT EFFECTIVE TO LOWER THE SURFACE TENSION OF THE FIXATION BATH TO VALUES BETWEEN 30 AND 35 10 NCM, THE SURFACE-ACTIVE AGENT BEING ADDED TO THE BATH A CONCENTRATIONS BETWEEN 25 AND 200PPM. THE INVENTION APPLIES IN PARTICULAR TO THE SURFACE TREATMENT OF METALS.

Description

The present invention relates to a method and a bath for the

  fixing aluminum and aluminum alloys

  as a result of anodizing treatment.

  The most widely used industrial treatments of anodized aluminum directed at fixing the porous layer of anodic oxide by plugging the pores can be subdivided into a preliminary attempt, into two separate classes: a) high temperature treatments where the fixation is carried out either by immersion in deionized water just before boiling or by immersion in a hot solution of nickel salts; b) low temperature treatments where the anodized aluminum is immersed in an aqueous solution containing organic solvents and

  metal salts, such as nickel fluoride.

  The methods mentioned in a) above are very disadvantageous in that they require a high energy consumption to heat the bath and that they can not give, at the end of the treatment, surfaces which do not have

  dust, the removal of which requires a post-

  treatment of parts with oils and paraffins, the method in b), as disclosed in Japanese Patent Publication No. 5415856, while providing a reasonably good solution to the problems inherent in the consumption of energy to heat the bathing, involves the use of considerable amounts of organic solvents, some of which are possible sources of pollution and are sometimes difficult and dangerous

  to handle because they are flammable or corrosive.

  Alternatively, the Italian patent application No. 41546 A / 81 proposes the use of nickel salts dissolved in a simple aqueous solution, but the experimental results confirmed that such a fixing bath could not give satisfactory results in the treatment. anodized aluminum. In the light of the above technical problems, the present invention has the task of eliminating the disadvantages described above by providing a fixing method and a bath for the low temperature fixing of aluminum.

  and aluminum alloys following the anodizing treatment.

  to improve the resistance of the aluminum oxide surface layer resulting from the anodic oxidation while being subjected to attack by

  chemical substances and / or weathering agents.

  The present invention has the task of improving the quality of the binding compared to that obtained with fixing treatments currently applied at low temperature. Another object of the present invention is to avoid the formation of the cited "surface dust", thereby reducing the consumption of the fixing product and thereby eliminating or reducing

  post-treatment with oils or paraffins.

  Another object of the present invention is to lower the degree of danger of the fixing bath compared to low temperature processes using solvents.

  flammable or polluting organic substances.

  These tasks or these objects are obtained by a process for fixing aluminum and alloys, characterized in that it comprises the step of imbibing the material to be treated, for a period of 5 to 30 minutes, in a bath of fixation maintained at 15-300 ° C. and containing an aqueous solution of at least one nickel salt at a concentration of between 0.1 and 50 g / l, said solution being supplemented with an effective nonionic surfactant for lowering the surface tension of said fixing bath at values between 30 and 35 × 10 N / cm, said surfactant being added to said bath at concentrations comprised

between 25 and 200 ppm.

  According to another aspect of the invention, the objectives are achieved by a fixing bath for anodized aluminum or anodized aluminum alloys having the

composition above specified.

  The present invention is based on the use, in the fixing treatment of anodized aluminum, of an aqueous bath comprising a nickel salt and a particular surfactant which can lower the surface tension of the bath to the critical value of 35 x 10-5 N / cm quoted above, or

below.

  The preferred surfactant for use with the invention is a fluorocarbon ester such as a product sold under the name FC 430 Fluorad by 3M ITALY, or under the name AG 650 by Tessilchimica, ITALY As an alternative, a silicone surfactant can be used, a dimethylpolysiloxane characterized by a viscosity of about

350 centistokes being preferred.

  The surfactant is used in the fixing bath at a concentration between a minimum value of 25 ppm and a maximum value of 200 ppm. The preferred types of fluorocarbon surfactant mentioned above already give the performance of fixation according to the invention at very low concentrations of 25-50 ppm, to considerably reduce the surface tension of the

aqueous bath.

  Suitable nickel salts for use with the invention preferably comprise nickel fluoride, alone or in admixture with one or more additional nickel salts, such as nickel acetate, formate, sulfate and sulfamate. Total concentration of the nickel salt (s) in the fixing bath is included

between 0.1 and 50 g / l.

  Advantageously, the fixing bath is adjusted for a pH between 5.5 and 6.5 by appropriately proportioning the various component nickel salts and / or the agent.

respective surfactant.

  The process according to the invention is carried out by operating with the bath at temperatures of 15-30.degree.

  immersion time which can vary from 5 to 30 minutes.

  Optionally, the fixation process may be completed, in accordance with conventional techniques, with "aging" for a few hours following removal of the fixing bath, for a period of from 0 to 24 hours. Other features and advantages of the invention

  will become clearer after reading the description

  The following is a detailed description of two exemplary embodiments of the process and examples of the formula of the S attachment bath.

EXAMPLE 1

  A sample of UNI 3569 aluminum alloy was used, which was oxidized by anodizing in a solution of sulfuric acid at a concentration of 180 g / l, at 15 volts and at a temperature of 18 C until the we get

  an oxide thickness of about 15 microns.

  Following the rinsing, it is immersed for fixation, an aqueous solution having the following composition: Nickel fluoride trihydrate 6 g / 1 Nickel acetate 1.5 g / 1 Nickel formmiate 1.0 g / 1 Sulfate of nickel heptahydrate 3.0 g / 1 Fluorocarbon ester surfactant (FC 430 Fluorad 3 M) 25 ppm The fixing bath is maintained at a temperature of 22 C, p H = 6, for 15 minutes The fixation quality test is carried out according to ISO 3210 by measuring the weight loss after immersion of the anodized aluminum sample

  in a phosphochromic solution for 15 minutes.

  Weight loss measured one hour after removal from

  solution was 18.1 mg per dm 2 fixed area.

  Other samples prepared in a similar manner showed respectively: after 2 hours, loss = 13.4 mg / dm 2 after 6 hours, loss = 9.2 mg / dm 2 after 24 hours, loss = 6.8 mg / dm 2

EXAMPLE 2

  An aluminum alloy sample, also according to UNI 3569, was oxidized in a solution of sulfuric acid at 180 g / l, 15 volts direct current at a temperature of 18 C until a thickness of about

  microns has been reached for the oxide layer.

  After rinsing, the sample is electro-

  staining in an aqueous solution of Sn SO 4 (15 g / l) with H 2 SO 4 (18 g / l), at 13 volts alternating current for minutes to obtain a dark bronze color After rinsing, the sample is immersed in a fixing solution having the following composition: Nickel fluoride trihydrate 6 g / l Nickel acetate 1.5 g / l Nickel formate 1.0 g / l Nickel sulphate heptahydrate 3.0 g / l surfactant active fluorocarbon ester (AG 650 Tessilchimica) 25 ppm The fixing is carried out at a temperature of 22 C

for 15 minutes at p H = 6.

  The quality of the fixation is again tested by determining the weight loss following immersion in

  a phosphochromic solution, according to the ISO 3210 standard.

  Weight loss after 1 hour was measured

at 19.9 mg per dm 2.

  Samples prepared as above gave, by extending the test over longer periods of time, the following values of weight loss: after 3 hours, loss = 16.37 mg / dm 2 after 6 hours. hours, loss = 9.4 mg / dm 2 after 24 hours, loss = 8.22 mg / dm 2 For comparison, the following will be given in detail in the values obtained with a conventional fixing bath comprising a salt nickel (which is formed in situ) and an organic solvent, but without the surfactant according to the invention. In this case also, the sample of the material to be treated is represented by a UNI 3569 aluminum alloy,

  which has been oxidized under the same conditions as those

  described above to a thickness dimension of the layer

  anodic oxide of about 18 microns.

  After rinsing, the sample is immersed in a solution having the following composition: Nickel acetate 6.5 g / l sodium luoride 2.0 g / l Isobutanol 50.0 g / l for 10 minutes at 350 ° C. fixing quality is again tested according to

the ISO 3210 standard.

  After two hours, a loss of

weight equal to 34 mg per dm 2.

  Referring to the above examples, the treatment of Example 1 demonstrated, in addition to a decrease

  weight loss, two special features.

  First, a reduction of surface dust has been observed, which imparts to treated surfaces in a

  conventional fixing bath a milky white appearance.

  Secondly, it was observed that the dramatic reduction in surface tension, produced by the presence of the surfactant in the fixing bath, allowed for lower adsorption of nickel on the outer surface

of the anodic oxide layer.

  Excessive adsorption would be particularly harmful by the fact that it hinders a complete filling

  pores in the anodic oxide layer.

  In particular, when using FC 430 Fluorad in water, the surface tension drop is approximately 20 x 105 N / cm

from the concentration of 25-50 ppm.

  To illustrate the above decreased adsorption of nickel due to the presence of the surfactant, we will relate

  hereinafter an experiment undertaken by the plaintiff.

  Two samples of aluminum alloy were treated, respectively, in a fixing bath such as that produced in Example 1 and a similar fixing bath

  but removing the surfactant fluorocarbon.

  Then, the oxide present on the surfaces of the sample as a result of the anodic oxidation treatment was dissolved in a phospho-chromic mixture at a temperature of

850 C.

  The nickel amounts obtained in the two etching solutions, one for each sample, were determined by atomic absorption in the etching solution of the first sample, i.e., that treated with the surfactant, at room temperature. 51 mg Ni which corresponds to 7.14 mg Ni + / dm 2; the etching solution of the second sample showed 66 mg Ni, which corresponds to 7.84 mg / dm 2 Ni The two treated samples had a surface of 200 cm The increase of the nickel adsorption by the surface of the sample fixed in an agentless bath

  surfactant is accordingly apparent.

  The advantages to be derived from the application of the fixing method and the bath according to the invention will also be apparent: in particular, an increase in the resistance of the oxidized surface layer to the attack by the chemical substances and to the weather is obtained, which is reflected in a better quality

  fixing relative to the conventional product.

  The use of F-type anions, which accelerate the absorption of nickel by the aluminum oxide layer, as well as the use of acetate and formate ions, which are

  effective in maintaining both the solution of

  bath and in the pores present in the oxidized aluminum layer, a p H-which tends to become

  alkaline, allow the formation of salts of type A 1203.

  Ni O n H 20 or the like, to accelerate which form the materials by which the pores are filled during the process

of fixation.

  In particular, residence times in the bath of 5 to 30 minutes, depending on the thickness of the oxide layer formed in the anodizing process of the material to be treated, are particularly advantageous for the quality of the fixing.

to obtain.

  As can be appreciated from the examples given, the.

  process achieves accomplishment in a few hours following removal of the room from its 1-5 fixation bath (O to 24 hours at most if a correct process has been followed), and successive changes can be observed

  resulting from the aging of the room.

R E V E N D I C AT IO N S

  1.A process for fixing aluminum and aluminum alloys following anodization treatment, characterized in that it comprises the step of immersing the material to be treated for 5 to 30 minutes in a bath fixing agent maintained at 15-30 C and containing an aqueous solution of at least one nickel salt at a concentration of between 0.1 and 50 g / l supplemented with a nonionic surfactant effective to lower the tension of surface of said fixing bath at values of between 30 and 35 × 10 -5 N / cm, said surfactant being added to said bath

  at concentrations between 25 and 200 ppm.

  2 Process according to Claim 1, characterized in that the aforementioned nickel salt is chosen from fluoride, acetate, formate, sulphate and

  nickel sulfamate, either alone or mixed.

  Process according to any one of the claims

  1 or 2 characterized in that the aforementioned fixing bath

  is maintained at a pH between 5.5 and 6.5.

  Process according to any one of the claims

  characterized in that the surfactant

  aforementioned nonionic is selected from surfactants

  active ingredients comprising fluorocarbon esters and compounds

of silicone.

  Process according to Claim 4, characterized in that the abovementioned surfactant is chosen from products such as FC 430 Fluorad (product 3 M), AG 650

  (Tessilchimica product) and dimethylpolysiloxanes.

  6 Bain for fixing aluminum and its alloys following anodization treatment, characterized in that it comprises an aqueous solution of at least one such nickel at a concentration of between 0, 1 and 50 g / l supplemented with a nonionic surfactant effective to lower the surface tension of said fixing bath to values between 30 and 35 x 10-5 N / cm, said surfactant being added to said bath in concentrations

between 25 and 200 ppm.

  Bath according to Claim 6, characterized in that the abovementioned nickel salt is chosen from nickel fluoride, acetate, formate, sulphate and sulphamate,

either alone or in mixture.

  Bath according to claim 6 or

  7, characterized in that the aforementioned nonionic surfactant is selected from surfactants comprising fluorocarbon esters and silicone compounds. Bath according to claim 8, characterized in that the surfactant mentioned above is MC 430 Fluorad produced from 3 M. Bain according to claim 8, characterized in that the aforementioned nonionic surfactant is AG 650,

Tessilchimica product.

  Bath according to claim 8, characterized in that

  the above-mentioned surfactant is a dirmethylpolysilon

Xane.

  Bath according to any one of claims 6

  at 11 characterized in that it has a p H between 5.5 and

6.5.

  13 Fixing method according to any one of

  characterized in that the

  material to be treated is subjected to aging as a result of immersion in the abovementioned bath during an aging time of 0 to 24 hours