FR2822852A1 - PROCESS FOR CARBOXYLATION TREATMENT OF METAL SURFACES - Google Patents

Abstract

The invention relates to a method for treating a metal surface by carboxylation before forming, said metal being selected from zinc, iron, aluminium, copper, lead and the alloys thereof as well as copper-coated, aluminium-coated, galvanised steels. Said method is carried out in oxidising conditions in relation to the metal by bringing said metal into contact with an aqueous, organic or hydro-organic bath comprising at least one organic acid in free form or in salt form. The inventive method is characterised in that: the organic acid is a saturated or unsaturated aliphatic monocarboxylic or dicarboxylic acid; the organic acid is in solution and/or emulsion in the bath at a concentration greater than 0.1 mole/litre; the pH of the bath is acid.

Description

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Method of treatment by carboxylation of metal surfaces
The invention relates to a method for the deposition of conversion layers on a metal surface selected from zinc, iron, aluminum, copper, lead, and their alloys as well as galvanized, aluminized, copper-coated steels to produce at high speed conversion layers formed of very small crystals.

 When applied prior to forming the sheet metal, these metal surface conversion treatments generally have at least one of the following effects: the improvement of friction properties under mechanical lubrication, for example for the stamping of sheets, - temporary protection against corrosion.

 For this first type of application, it is more particularly used so-called pre-phosphating treatments which result in the deposition of a metal phosphate layer whose weight is of the order of 1 to 1.5 g / m2.

 But, these conversion treatments can also be performed after shaping the sheet, to improve the adhesion of subsequently deposited organic coatings, such as paints. By way of example, mention may be made of the phosphating treatment which results in the deposition of a metal phosphate layer whose weight is greater than that of a pre-phosphatation treatment.

 These different conversion treatments generally consist of anodic dissolution of the metal elements of the surface, followed by precipitation on this surface of the compounds formed by the reaction of the dissolved metal elements with the species present in the conversion bath. Dissolution requires the creation of oxidizing conditions with respect to the metal of the surface and generally takes place in acidic medium. The precipitation of the metal compounds to form the conversion layer requires a sufficiently high concentration and is favored by a medium that is locally less acidic under the effect of the dissolution of the metal. It's nature and

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 the structure of the precipitated compounds on the treated surface which determine the degree of protection against corrosion, improvement of the tribological properties and / or adhesion, as well as the other properties of the layer.

 In order to ensure the superficial oxidation of the metal of the surface to be treated and to promote its dissolution, it is possible to proceed chemically or electrochemically: by means of a chemical agent for oxidizing the metal to be introduced into the treatment solution, and or by electric polarization of the surface while subjecting it to the action of the treatment solution.

 In addition to a possible oxidizing agent, the conversion baths essentially contain anions and cations capable of forming insoluble compounds with the dissolved metal of the surface. The main conversion treatments are thus chromating treatments on galvanized or aluminized steel, phosphating unalloyed bare steels or coated steels, or even oxalation on alloy steels such as stainless steels, for example.

 After being brought into contact with a conversion bath, the treated surface is generally rinsed to remove the components of the surface and / or the treatment solution that have not reacted, then this surface is dried in particular to harden the conversion layer. and / or to improve the properties thereof.

 The conditions of application, the nature and the concentration of the additives have an important influence on the structure, the morphology and the compactness of the conversion layer obtained, therefore on its properties.

 The conversion treatment may itself be preceded by a pretreatment, generally consisting of a preliminary degreasing and rinsing of the surface followed by a so-called refining operation using a pretreatment solution adapted to create and / or promote germination sites on the surface to be treated.

 For this purpose, commonly used on surfaces zinc plated colloidal sols or suspensions of titanium salts which allow the subsequent obtaining of a conversion layer having smaller crystals in a denser layer.

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 At the end of the conversion process, it is also possible to carry out a post-treatment to improve the properties of the conversion layer. Thus, a chromatin post-treatment can be carried out on a conversion layer obtained by phosphatation.

 The international patent application WO95 / 21277 describes an aqueous composition for treating zinc-coated surfaces comprising: a polyhydroxyaryl-carboxylic acid, for example gallic acid or protocatechuic acid, or a depside of this acid which may result from its reaction with glucose, such as tannic acid, and a silane adhesion promoter.

 With this treatment composition, conventional accelerating agents are used for galvanized surfaces, such as phosphates, nitrates, fluorides or organic acids.

 The treatment carried out using this composition provides both good protection against corrosion and good adhesion for paints.

 The patent application FR 2,465,008 describes a method for the deposition of conversion layers on galvanized surfaces, with the aid of a treatment solution that may contain a soluble oxalate, combined with activating agents which are carboxylic acids, especially short diacids.

 The oxalic acid concentration of the described treatment solutions is less than 7.5 g / l, ie 0.08 mol / l.

 EP 494 431 (KAWASAKI) teaches that the addition of a carboxylic acid to chromate treatment solutions containing colloidal silica makes it possible to improve the properties of the conversion layers obtained on galvanized surfaces and / or allows significantly lower the chromium content of these solutions.

The weight of layer, or grammage, resulting from these different treatments is very variable depending on the main objective pursued and can go less than
1 g / m2 up to 8 g / m2.

 The different treatments of the prior art, such as chromate treatment, phosphatation and oxalation, have a major disadvantage

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 which is the toxicity of these products vis-à-vis people and the environment in general. In addition, when spot welding plates carrying such conversion layers, it creates fumes toxic fumes.

 The object of the invention is therefore to provide a treatment for converting metal surfaces before they are shaped, using a bath that is free from compounds that are harmful to the environment but also makes it possible to deposit on these surfaces layers of conversion more effective to protect against corrosion and / or prelubrication than those obtained by the processes of the prior art.

 Another objective pursued by the invention is also to be able to apply an organic coating with good adhesion, in particular by cataphoresis, to a treated surface according to the invention, after it has been shaped and degreased, which supposes that the applied conversion layer is easily removed at the time of this degreasing.

 To this end, the subject of the invention is a process for treating a metal surface chosen from zinc, iron, aluminum, copper, lead, and their alloys as well as galvanized, aluminized, copper-coated steels. under oxidizing conditions with respect to the metal, by placing in contact with an aqueous, organic or hydro-organic bath comprising at least one organic acid in free form or in salt form, characterized in that: - said organic acid is a saturated or unsaturated aliphatic monocarboxylic or dicarboxylic acid, said organic acid is in solution and / or emulsified in the bath at a concentration greater than 0.1 mol / liter, the pH of the bath is acidic.

 The invention also relates to the use of said surface treatment method for the temporary protection against corrosion of said metal surface.

 The invention further relates to a method of manufacturing a shaped sheet having a metal surface selected from zinc, iron, aluminum, copper, lead, and their alloys and galvanized steels, aluminized, copper-coated, in which a surface treatment of said

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 sheet according to the invention, said oil is treated said sheet, and is shaped. It is more particularly preferred to apply this method according to the invention to a steel sheet coated with zinc or zinc alloy which is then shaped by stamping.

 The invention will be better understood on reading the description which follows, given by way of non-limiting example, and with reference to the appended figures in which: FIG. 1 illustrates the evaluation of the stamping behavior of sheets untreated according to the invention and oiled (symbol 0) and sheets treated according to the invention not oiled (symbol A) or oiled (symbol D); it represents the evolution of the maximum stamping force F max as a function of the blanking force Fs.

 FIG. 2 represents the evolution of the grammage P of the conversion layer obtained according to the invention, as a function of the dipping time Di in a carboxylate solution, using a chemical means of oxidation of zinc and the co solvents: ethanol (symbol +) n-propanol (symbol x), ') dimethyl sulfoxide (DMSO, symbol A),. N-methyl-2-pyrrolidone (NMP, symbol 0), diacetone alcohol (DAA, symbol o).

 FIG. 3 relates to the embodiment of the method according to the invention, in which an electrochemical zinc oxidation means is used and represents, for two different current densities (symbol # = 10 mA / cm 2 - symbol A = 25 mA / cM2) the evolution of the basis weight P of the conversion layer obtained as a function of the immersion time Dc in the carboxylate solution.

 FIG. 4 illustrates a potentiometric evaluation of the resistance to aqueous corrosion, in terms of the polarization resistance Rp as a function of the immersion time in the measurement electrolyte, for the following surfaces: untreated galvanized surface (bare) , represented by the symbols +,

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* surface zinguée traitée par carboxylatation selon l'invention sans posttraitement avec : - l'acide heptanoïque (symbole A), - l'acide décanoïque (symbole x), - un mélange d'acides heptanoïque et décanoïque (symbole surface zinguée traitée par carboxylatation avec l'acide heptanoïque, et avec post-traitement à l'aide d'une solution contenant des terres rares : symbole D pour Gd, symbole 0 pour Lu.

galvanized surface treated by carboxylation according to the invention without post-treatment with: heptanoic acid (symbol A), decanoic acid (symbol x), a mixture of heptanoic and decanoic acids (zinc-coated surface symbol treated by carboxylation) with heptanoic acid, and with post-treatment using a solution containing rare earths: symbol D for Gd, symbol 0 for Lu.

 According to the invention, conversion layers are deposited by carboxylation of metal surfaces by bringing the surface into contact with an organic or hydro-organic aqueous bath comprising at least one organic acid in solution or in emulsion under oxidizing conditions. metal screw.

 The present invention uses aliphatic monocarboxylic or dicarboxylic acids, optionally having one or more unsaturations.

 Since the acid constants of these acids are of the order of 4.8, the natural pH of the baths according to the invention will generally be lower than this value. If it is desired to lower the pH, it will be possible to acidify the treatment bath, for example using nitric acid. The pH of the bath can also be increased by adding sodium hydroxide, for example. The acid bath used in the treatment according to the invention must in all cases have a pH value of between 1 and 7, the upper limit making it possible to avoid the presence of a metal hydroxide in the conversion layer. As for the minimum value of the pH, it will be adapted according to the metal of the surface to ensure a satisfactory deposit of the conversion layer.

 The at least one organic acid used according to the invention is dissolved or emulsified in the bath at a concentration greater than 0.1 mol / liter.

 If the concentration of organic acid in the treatment bath is less than 0.1 mole / liter, the formation rate of the metal carboxylate conversion layer is no longer sufficient to obtain a conversion layer effective over time assigned to the treatment.

 In a preferred embodiment, the aliphatic organic acids

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 according to the present invention, are selected from saturated monocarboxylic acids having from 5 to 16 carbon atoms. Hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid and decanoic acid are more particularly preferred.

 In another preferred embodiment, the aliphatic organic acids according to the present invention are chosen from unsaturated monocarboxylic acids containing from 10 to 18 carbon atoms. Particularly preferred is undecenoic acid, oleic acid or linoleic acid.

 In another preferred embodiment, the aliphatic organic acids according to the present invention are chosen from saturated dicarboxylic acids containing from 4 to 12 carbon atoms. Sebacic acid or azelaic acid is more particularly preferred.

 In another preferred embodiment, the at least one aliphatic monocarboxylic acid retained is heptanoic acid.

 More preferably, the bath comprises, in addition to heptanoic acid, decanoic acid or undecenoic acid.

 Through the use of a mixture of organic acids, such as heptanoic acid and decanoic acid or undecenoic acid, a much denser and more efficient conversion layer is obtained to protect the metal surface against corrosion.

 The oxidizing conditions of the carboxylate bath are obtained by the following means: either by an addition in the bath of a metal oxidation chemical agent adapted to its nature, such as perborate tetrahydrate or hydrogen peroxide, or by circulating an electric current between the metal surface previously immersed in the bath and at least one counter-electrode also immersed.

 In the case where the oxidizing conditions with respect to zinc are obtained by addition, in the bath, of a chemical agent for oxidation of zinc, this oxidizing agent and / or accelerator is preferably chosen from the group

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 comprising sodium perborate, nitrites, hydrogen peroxide, hydroxylamine sulfate and nitro-guanidine.

 The conversion baths may optionally contain: pH regulating agents or buffering agents for regulating the conditions of formation of the conversion layer on the surface, additives facilitating the implementation of the treatment and the distribution of the bathing the surface to be treated, such as surfactants, - additives to increase the life of the bath such as, for example, chelating agents to delay the precipitation of other compounds than those desired obtain in the conversion layer, or bactericidal agents, and - accelerators treatment.

 The conversion treatment bath according to the invention may also comprise a co-solvent such as ethanol, propanol, butanol, DMSO, NMP, diacetone alcohol, glycol ethers, etc., or many other organic or mineral acids.

 A surprising result has been obtained when the carboxylation treatment bath comprises in solution rare earth ions such as gadolinium in the +3 oxidation state at a concentration greater than or equal to 1. 10-3 mol / l.

 The conversion layer obtained is then composed of two types of crystals of different composition and possibly of different shape and it proves an even greater efficiency for corrosion resistance.

 Preferably, the concentration of organic acids in the bath, the conditions of use of this bath and the oxidizing conditions with respect to the metal are adapted to obtain on the metal surface a carboxylation layer of grammage between 1 and 6 g / m2.

 Other advantages of the method of the invention will become apparent on reading the examples presented below without limitation of the present invention.

MATERIALS to obtain the conversion layers: 1) Characteristics of the substrates tested

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Sheet steel of ES quality (stamping steel) or HES (deep drawing steel), micro-alloyed or not, thickness between 0, 7 and 1.2 mm, bare or coated with a layer of zinc approximately 10 μm thick, applied by electroplating in a bath based on chlorides or sulphates, or by hot-dip galvanizing.

2) Components of the conversion treatment baths tested
2. a-Solvent and co-solvent (s)
The treatment solutions tested are generally based on water as the main solvent and ethanol as co-solvent; propanol, DMSO, NMP or 4-hydroxy-4-methyl-2-pentanone (diacetone alcohol) or other polar solvents at least partially miscible with water may also be used as co-solvents.

2. b-Organic acid
For the examples illustrating the invention, it is heptanoic acid (abbreviation: HC7, Aldrich product, reference 25,873-3) and / or decanoic acid (abbreviation: HC10, Rectapur product, reference 243.298, sulfuric ash 0.1% maximum).

2. c-Chemical agent of oxidation of the substrate
Unless otherwise indicated, zinc perborate tetrahydrate (NaB0 3, 4H 2 O) at 2 g / l is used as the chemical oxidation agent for zinc. Hydrogen peroxide (or hydrogen peroxide H2O2) can also be used.

2. d-pH
Unless otherwise indicated, the solutions are used at their natural acid pH; the possible increases in pH are obtained by adding sodium hydroxide.

2. e-Other components and additives
We can add metal cations: Cu2 +, Co2 +, Ni2 +, Fe2 +, Zen2 +,

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MnCr+, A!, Tr.

MnCr +, A !, Tr.

3) Standard procedure for treatment with conversion baths Table 1

<Tb>
<tb> Time <SEP> of
<tb> Ref. <SEP> Step <SEP> Composition <SEP> of the <SEP> bath <SEP> Temperature
<tb> stay
<tb> 1 <SEP> Degreasing <SEP> RidolineTM1,8% <SEP> + <SEP> RidosolTM0,18% <SEP> 55 C <SEP> 240 <SEP> s
<tb> 2 <SEP> Degreasing <SEP> RidolineTM0.4% <SEP> + <SEP> RidosolO, <SEP> 04% <SEP> 55 C <SEP> 240 <SEP> s
<tb> 3 <SEP> Rinse <SEP> Water <SEP> current <SEP> 25 C <SEP> 90 <SEP> s
<tb> Pretreatment <SEP> Fixodine <SEP> 50CF <SEP>: <SEP> 0.5 <SEP> g / l <SEP> 25C <SEP> 60s
<tb> 4 <SEP> ripening <SEP> in <SEP> water <SEP> permuted
<tb><SEP> Processing of <SEP> Variable <SEP> 25 C <SEP> Variable
<tb> 5 <SEP> conversion
<tb> 6 <SEP> Rinse <SEP> Water <SEP> current <SEP> 25 C <SEP> 60 <SEP> s
<tb> 7 <SEP> Drying <SEP> Air <SEP> Pulsed <SEP> 80 C <SEP> 300 <SEP> s
<Tb>

Ridotine is an aqueous degreasing solution containing alkali metal salts, surfactants and potassium hydroxide.

 RidosoP "is a wetting base for liquid degreaser comprising a mixture of surfactants.

 Fixodine 50CF is an activator (also referred to as a germinator) comprising compounds based on alkali metal salts such as titanium salts.

METHODS of evaluating conversion layers obtained:
1) Weight of deposited layer
In order to determine the grammage, the conversion layer formed is dissolved on a given surface with a complexing solution, the soaking time in this solution being adapted to obtain complete dissolution of the layer (of the order of one minute for one minute). layer made from HC7, at a rate of 0.3 mg / cm 2).

 The grammage, expressed in mg per cm2, is evaluated from the

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différence de poids entre l'échantillon revêtu et ce même échantillon ayant subi le traitement de dissolution.

difference in weight between the coated sample and the same sample having undergone dissolution treatment.

The composition of this solution of dissolution is as follows: disodium salt of ethylene di-amine tetraacetic acid: 0.1 M-MBT (mercaptobenzothiazole) or BZT (benzotriazol): 0.1 gll. These compounds limit the dissolution of the metal substrate
The pH of this solution is adjusted to a value close to 8 by addition of sodium hydroxide, in order to obtain an optimal complexation of the metal cation.

2) Resistance to aqueous corrosion
This test consists of a periodic potentiometric measurement of the polarization resistor Rp by a voltage sweep with an amplitude of +/- 10 mV around the corrosion potential Ecor.

 The device used for this evaluation comprises, in a conventional manner: - a polymethyl methacrylate tank, the bottom of which is pierced by a window, and which contains the standard aqueous electrolyte ASTM D1384-87. This electrolyte comprises 148 mg / l of sodium sulfate (Na 2 SO 4), 138 mg of sodium bicarbonate (NaHCO 3) and 165 mg of sodium chloride (NaCl) and has a pH in the region of 8; three electrodes immersed in the electrolyte: a working electrode consisting of the metal surface coated with the conversion layer to be evaluated obstructing the window of the bottom of the cell, a saturated calomel reference electrode (ESC), and a platinum as auxiliary counter-electrode; - A potientiostat type Princeton 273 or 263 connected to the three electrodes and driven by a software referenced m352 EG & G Princeton TM.

3) Resistance to atmospheric corrosion according to DIN 51160
The metal surface samples are first stored in a humid atmosphere in a controlled humidothermic enclosure according to

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successive cycles, each cycle having the following characteristics: - first part: duration: 8 hours-40 C; 100% relative humidity; - second part: duration: 16 hours-temperature and ambient humidity;
Unless otherwise indicated, the quotation then consists of counting the number of cycles at the end of which it is found that at least 10% of the treated surface is covered with white rust.

4) Friction behavior
This test consists of measuring the plane-plane friction coefficient by increasing the clamping pressure to 80 MPa.

 Before the test, the treated samples are covered with an oil referenced 6130 QUAKER Company, the amount of oil deposited is of the order of 1 to 2 g / m2 for example.

5) Behavior in stamping
This test consists of making complete stampings from sheet metal blank samples having undergone the conversion treatment. Thus, with an initial blank diameter of 64 mm, a bucket with a diameter of 32 mm and a depth of 25 mm is produced.

 On the same type of sheet blank whose surface treatment is desired to be tested, the maximum stamping force beyond which there is a rupture of the blank during stamping is evaluated for a clamping force of the clamps. predetermined blanks. This maximum value is identified for a series of clamping force values of the blanks, so as to plot, as illustrated in FIG. 1, curves representing the variation of the maximum drawing force Fmax as a function of the force of the clamping force. blank holder.

 6) Phosphatability after degreasing of the layer Firstly, the surface carrying a conversion layer is degreased according to the procedure specified in Table 1-steps 1 and 2 of 3) "standard procedure for treatment by baths conversion "/ Part" MATERIALS to obtain the conversion layers "-in order to eliminate the conversion layer, then performs a phosphating treatment

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 conventional on this degreased surface by applying an aqueous composition comprising: - 2% by volume Granodine 9580 M / CF (phosphating mixture containing 10 to 25% phosphoric acid and a small amount of hydrofluoric acid), 0, 7% by volume of Starter 958 / CF (aqueous solution containing zinc salts in the presence of a slight excess of nitric acid), - 0.04% by volume of Intensifier NO1 (aqueous solution of metal salts in presence of a small amount of phosphoric acid), - 0.5% by volume of M Primary (aqueous solution containing sodium hydroxide> 2%) to regulate the pH, - 0.05% by volume of Compensator M (aqueous solution based on sodium nitrite, accelerator for crystalline phosphating bath), * Operating conditions: - Demineralized water - Quenched treatment 2 min.

Les analyses doivent se situer dans les fourchettes suivantes :

- [Zn"] = 0, 9 à 1, 1 g/l - [Mn] = 0, 7 à 0, 9 g/l - [Ni2+] =0, 18à0, 25g/l - [F-] = 0, 25 à 0, 35 g/)

Dans un deuxième temps, on examine au microscope électronique la qualité de la couche de phosphatation obtenue. - Temperature = 55 C +/- 2OC Control of the bath by chemical analysis:

The analyzes should be in the following ranges:

- [Zn "] = 0.9 to 1.1 g / l - [Mn] = 0.7 to 0.9 g / l - [Ni2 +] = 0.18 to 0.25 g / l - [F-] = 0 , 25 to 0, 35 g /)

In a second step, the quality of the phosphatation layer obtained is examined using an electron microscope.

7) Ability to organic coating by cataphoresis after degreasing and phosphating
In a first step, the treated surface is degreased according to the procedure specified in Table 1-steps 1 and 2 of 3) "standard procedure for treatment with conversion baths" / Part "MATERIALS for

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- 8, 66 % en poids de pâte (dispersion de pigments) pour peinture par électrodéposition cationique, Avec :

- Extrait sec = 20-24% - pH = 5, 7à6, 1 (à25 C) - Conductivité du mélange = 1500-2000 mS (à 25OC) Conditions d'application : - Température du bain = 28 à 35 C - Temps d'application = 120 à 180 s - Rapport anode/cathode = 1/4 - Tension de travail = 200-320 V - Etuvage nominal (T palier) = 15 min à 175OC - Epaisseur visée = 18 à 24 um

Exemple 1 Cet exemple a pour but de déterminer des conditions de traitement de carboxylatation selon l'invention permettant d'obtenir, sur une surface de tôle zinguée, une couche de conversion à la fois compacte et finement cristallisée. The above conversion layers are obtained in order to eliminate the conversion layer and then, on this degreased surface, a phosphating treatment is carried out according to the procedure specified in 6) above. conventionally, an organic coating by cataphoresis on the phosphated surface according to the following conditions (example of the formulation PPG 752-965 1): Control bath formula: 43, 16% by weight of deionized water (10uS max), 48, 18% by weight of binder derived from polyamine-urethanes,

8, 66% by weight of paste (pigment dispersion) for cationic electrodeposition painting, With:

- Dry extract = 20-24% - pH = 5, 7 to 6, 1 (at 25 ° C) - Conductivity of the mixture = 1500-2000 mS (at 25 ° C.) Application conditions: - Bath temperature = 28 ° to 35 ° C. - Drying time application = 120 to 180 s - Anode / cathode ratio = 1/4 - Working voltage = 200-320 V - Steaming nominal (T bearing) = 15 min at 175OC - Target thickness = 18 to 24 μm

EXAMPLE 1 The purpose of this example is to determine carboxylation treatment conditions according to the invention making it possible to obtain, on a galvanized sheet surface, a conversion layer that is both compact and finely crystallized.

 The galvanized surfaces of steel sheets are treated according to the following steps: - preparation of the surface to be treated, - soaking of the prepared surface in the conversion bath, - drying and observation of the treatment layer obtained.

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 The initial preparation treatment is that mentioned in Table 1 in the successive references 1 to 4. The solvent of the conversion bath is a water-ethanol mixture whose ratio is adjusted in order to completely solubilize the added organic acid.

 In order to determine the optimal conditions of treatment, different parameters are varied.

1.1. pH
The pH is varied and it is found that the higher it is, the more the conversion layer appears poorly crystallized. In addition, too high a pH may result in parasitic precipitation of metal hydroxide. Therefore, in practice, it is limited to an acidic pH of between 1 and 7. The minimum pH value will be adapted according to the metal of the surface in order to ensure a satisfactory deposition of the conversion layer. Thus, in the case of zinc, the treatment will preferably be carried out at a pH of between 4 and 6.

1.2. Bath temperature
The temperature of the bath is varied between 20 and 80 ° C. and it is observed that the increase in temperature accelerates the deposition rate.

1.3. Concentration of the corresponding organic acid or salt
The concentration of the organic acid is varied and it is found that the concentration range must be between 0.1 and 1.5 M. As mentioned above, if the concentration is less than 0.1M, the formation rate of the metal carboxylate conversion layer is no longer sufficient to obtain a conversion layer effective in the time given to the treatment. A concentration greater than 1.5 M is not possible because of the solubility limit of the organic acid close to 1.4-1.5M.

 When the organic acid or acids are used in the form of salts, chlorides, nitrates or sulphates are preferably employed at a concentration of less than or equal to 3 g / l.

1.4. Length n of the carbon chain of organic acid
The length of the carbon chain is varied and it is found that the longer the carbon chain of the aliphatic acid (n high), the finer the crystals of the layer, and under equivalent conditions of treatment the

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 The weight of the conversion layer is high: about 1.5 times higher, for example, when n goes from the value 7 to the value 10.

 In addition, the compactness of the conversion layer also increases with the length of the aliphatic chain of the carboxylic acid used, as well as the resistance to corrosion provided by this layer.

1.5. Nature and concentration of oxidizing agents
Various oxidants are used, such as dissolved oxygen (02), nitrites (NO2-), hydrogen peroxide (H2O2) or perborates (BOg-). It is found that the presence of oxidizing agent or accelerating agent has a favorable effect on the compactness of the conversion layer.

- agent oxydant : perborate de sodium NaBO3, 4 H2O : 2 glu ; - pH4, 7. 1.6. Duration of immersion in the bath or duration of treatment
The galvanized surface to be treated is immersed for a few minutes in a bath having the following characteristics: water / alcohol ratio: 1; n = 7 (heptanoic acid), [HCy] = 50 g / I,

oxidizing agent: sodium perborate NaBO 3, 4H 2 O: 2 glu; pH4.7.

The duration of the treatment is varied and the grammage of the carboxylation layer obtained is observed: Table II

<Tb>
<tb><SEP> immersion time <SEP> (min. <SEP>) <SEP> 0.5 <SEP> 3 <SEP> 5 <SEP> 10
<tb> Weight <SEP> (g / m2) <SEP> 1 <SEP> 2.4 <SEP> 3.1 <SEP> 3.2
<Tb>

It is found that the increase in immersion time in the bath is favorable to the compactness of the layer.

Example 2-Comparison with the Prior Art
In parallel, the following treatments of blanks of the same galvanized sheet are carried out under the conditions indicated below.

1. Phosphate sheet having a layer whose weight is of the order of some 9 1 m2
The conventional surface phosphating treatment is carried out

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degreased according to the bath conditions specified in 6) (Phosphatability after degreasing of the layer), 2. Pre-phosphated sheet bearing a layer whose grammage is of the order of 1 9 1 m2
The pre-phosphatation treatment is carried out on a degreased surface under the following conditions: - conversion bath composed of phosphoric acid, Mn and Ni (Chemetall formulation VP 10118, for example) - drying at 200 ° C., - basis weight = 1, 1 to 1, 5 g / m2.

3. Oxalized sheet according to FR 2 465 008: the procedure described in Example 4 of this document is carried out using a treatment solution containing a complex fluoride and an oxalate.

4. Carboxylated sheet according to WO 95/21177: the procedure described in Example 1 of this document is carried out using a treatment solution containing gallic acid and 3-glycidoxypropyltrimethoxysilane. .

Nombre de Echantillon testé cycles Tôle zinguée sans traitement de conversion-huilé QUAKER 2130 10 Tôle pré-préphosphatée-non huilée 20 Tôle oxalatée selon FR 2 465 008 4 Tôle carboxylatée selon W095121277 7 Tôle traitée selon l'invention (avec Hic7) : 1 min-non huilée 23 Tôle traitée selon l'invention (avec HC7) : 2 min-non huilée 24 Tôle traitée selon l'invention (avec HC7) : 2 min + rinçage-non huilée 27 Tôle traitée selon l'invention (avec Hic7) : 5 min-non huilée 25 By carrying out the evaluations of the different types of conversion layers as defined above in points 3,4, 5,6 and 7 of the Methods section, the following results are obtained:
2.1. Resistance to atmospheric corrosion

Number of tested sample cycles Galvanized sheet without oil-conversion treatment QUAKER 2130 10 Pre-prephosphated sheet-not oiled 20 Oxalated sheet according to FR 2 465 008 4 Carboxylated sheet according to W095121277 7 Processed sheet according to the invention (with Hic7): 1 min -Oil oiled 23 Sheet treated according to the invention (with HC7): 2 min-non-oiled 24 Sheet treated according to the invention (with HC7): 2 min + rinse-not oiled 27 Sheet treated according to the invention (with Hic7) : 5 min-not oiled 25

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It can be seen that the treatment according to the invention provides better resistance to atmospheric corrosion than the treatments of the prior art. 2.2. Friction behavior

<Tb>
<tb> Type <SEP> of <SEP> Processing <SEP> Weight <SEP> Coefficient <SEP> of <SEP> Comments
<tb> before <SEP> oiling <SEP> (g / m2) <SEP> friction
<tb> max. <SEP> min. <SEP> medium
<tb> None <SEP> 0 <SEP> 0, <SEP> 13 <SEP> Strong <SEP> browsing <SEP> ascending
<tb> with <SEP> pressure <SEP> tightening
<tb> Prephosphatation <SEP> 1, <SEP> 5 <SEP> 0, <SEP> 19 <SEP> 0.17 <SEP> 0.11 <SEP> No <SEP> of <SEP> grazing
<tb> FR <SEP> 2 <SEP> 465 <SEP> 008 <SEP> 0, <SEP> 11 <SEP> Few <SEP> of <SEP> browsing
<tb> WO95 / 21277 <SEP> 0, <SEP> 12 <SEP> Average <SEP> grazing
<tb> Invention <SEP>: <SEP> HC7 <SEP> 1,2 <SEP> 0,09 <SEP> 0,05 <SEP> 0,07 <SEP> Very <SEP> few <SEP> of <SEP > grazing
<tb> Invention <SEP>: <SEP> HC7 <SEP> 5 <SEP> 0, <SEP> 09 <SEP> 0.04 <SEP> 0.05 <SEP> Not <SEP> of <SEP> browsing
<tb> Invention <SEP>: <SEP>HCo'50,<SEP> 09 <SEP> 0, <SEP> 04 <SEP> 0.05 <SEP> Not <SEP> of <SEP> grazing
<Tb>

The conversion treatments according to the invention carried out before oiling thus make it possible to eliminate grazing and a continuous decrease in the coefficient of friction is observed when the clamping pressure increases.

 It is also noted that the treatment according to the invention makes it possible to obtain substantially improved coefficients of friction with respect to the pre-phosphatation treatment.

 2.3. Behavior in stamping FIG. 1 illustrates the results obtained: on the one hand on the carboxylated sheets (duration: 5 min.) According to the invention: curve marked by the symbols L1 without additional oiling and by the symbols D with oiling complementary using the oil referenced 6130 of the QUAKER Company;

<Desc / Clms Page number 19>

- d'autre part sur les mêmes tôles non traitées : exemple comparatif représenté par la courbe repérée par les symboles 0.

on the other hand on the same untreated sheets: comparative example represented by the curve indicated by the symbols 0.

 In general, the more the curves obtained are low and little inclined, the better the stamping behavior is good.

 It can thus be seen that the invention very substantially improves the stamping behavior.

 It can be deduced from these three series of tests that the conversion treatment according to the invention can advantageously replace the conventional pre-phosphatation treatment, all the more so as it avoids the pollution problems posed by the use of phosphates.

Example 3-Ability to paint
The metal surfaces subjected to the conversion treatment according to the invention find their main use in the automotive field. It is therefore important to verify that these surfaces, once coated, are compatible with the methods usually used in industry for painting metal sheets, in particular galvanized sheets.

3.1. Suitability for degreasability
Embossing shaping generally requires that the metal surface be oiled, which requires, when it is desired to subsequently proceed with other operations such as painting or enameling, to remove any trace of oil from the surface. this surface and, at the same time, eliminate any conversion layer formed before shaping. This is done by a degreasing treatment, for which success it is important that the conversion layer is easily removed. It is therefore important to verify that the conversion layer according to the invention is easily degreasable.

 Firstly, alkaline degreasing of the metal surface carrying a conversion layer is carried out under the conditions specified in Table 1-steps 1 and 2 of 3) "standard procedure for treatment with conversion baths" / "Part) MATERIALS to obtain the conversion layers ".

<Desc / Clms Page number 20>

In a second step, we observe the surface of the samples treated then degreased to see if the conversion layer has disappeared.

 The complete disappearance of the carboxylation layer according to the invention is observed.

3.2. Phosphatability after degreasing
The following procedures are carried out according to the procedure defined in point 6) by treating the two faces of the sample according to the invention, namely the bare steel face and the galvanized face, and it is observed that the conversion layer obtained a covering aspect.

3.3. Ability to organic coating by cataphoresis after degreasing and phosphating
The observation of the samples treated according to the invention, degreased, phosphated and then coated, reveals no particular defect.

EXAMPLE 4 Incidence of Co-Solvent and Immersion Time on the Weight of the Conversion Coat
The procedure is as described in the Materials and Methods section, using heptanoic acid at a concentration of 0.38 mol.

 Before the application of the conversion treatment, a refining pretreatment is applied.

 As shown in FIG. 2, the grammage of the conversion layer obtained is evaluated as a function of the immersion time of the sheet blank to be treated in the solution according to the invention, for different solvent compositions (% by volume): Case 1: 62% water, 38% ethanol (+ symbol). Case 2: 61% water, 39% 1-propanol (symbol x),. Case 3: 43% water, 57% DMSO (symbol A),. Case 4: 56% water, 44% NMP (symbol 0),. Case 5: 60% water, 40% diacetone alcohol (symbol o).

<Desc / Clms Page number 21>

The above mixtures are optimized to solubilize as much as 95% heptanoic acid.

 From the curves obtained it can be deduced that: - the growth profiles of the conversion layer are similar in cases 1.4 and 5, - for immersion times of less than 180 s, the growth rate of the layer is more low in cases 2 and 3 than in cases 1.4 and 5.

 From observations using a scanning electron microscope, it is found that the morphologies of the crystals of the layers are identical: after 30 s of treatment in cases 1.4 and 5, after 300 s of treatment in cases 1.3 and 4.

 Other such solvents could be envisaged to implement the invention, including amide solvents such as N-methylformamide, N-N-dimethylformamide or sulfonic solvents such as tetramethylsulfone.

Example 5-Emulsion in the conversion treatment solution
To avoid the use of solvents which may pose safety problems, it is possible to obtain the highly concentrated organic acid treatment solutions according to the invention using suitable surfactants.

 With 1% by volume of product FORAFAC 1033 D from ATOFINA which is a 30% perfluorinated anionic surfactant in water, of the family of perfluoroalkylsulphonic acid, an emulsion containing 50 g of heptanoic acid and 2 g of sodium perborate tetrahydrate. The emulsion contains no other solvent than water and, thanks to the surfactant, all of the acid is in emulsion and / or solution in water.

 Two treatment solutions differing in pH are prepared: one at a natural pH ~ 4, the other at pH adjusted to about 4.7 by addition of sodium hydroxide.

 The procedures of the Methods section are followed by dipping the plate samples identical to those of Example 3 in either treatment solution for five minutes, then rinsing and drying the treated surface.

 From the observations made on the treated surfaces:

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 at pH ~ 4, a carboxylation deposit of 0.3 mg / cm 2 comparable to those obtained in Example 4 is obtained for the same immersion time; the deposit seems to contain traces of the surfactant, which shows that this agent is not passive with respect to the precipitation reaction; - At pH == 4, 7, the grammage obtained is a little. lower (-30% approximately) but the morphology of the deposit is comparable to those obtained in Example 4; the deposit no longer contains traces of surfactant.

Example 6 Carboxylation Under Electrochemical Oxidation of the Substrate
This is to produce the metal cations from the metal surface electrochemically. The substrate which is here a galvanized sheet is subjected to a potential and an anode current by immersion of the galvanized sheet in the treatment solution between two titanium plates electrically connected to the same potential.

 As a treatment solution, a 50% water / 50% ethano solution is used! containing 0.38 mole / liter of heptanoic acid and whose pH is between 3.2 and 4.7 depending on the amount of sodium hydroxide added.

 The procedure described in point 3) of the Equipment paragraph is applied; the conversion treatment according to the invention is applied by soaking the sheet sample in the treatment solution and passing an electric current between the submerged sheet and the titanium plates. The current densities are 10 and 25 mAJcm 2 for treatment times of 1.3, 5 and 10 seconds.

FIG. 3 represents the results obtained in terms of grammage, the symbol D representing the curve obtained with a current density of
10 mA / cm 2 and the symbol at representing the curve obtained with a current density of 25 mA / cm 2.

According to these results and according to the observations made on the treated surfaces, it is found that the conversion layers obtained after 1 to 10 seconds exhibit surface densities, morphologies and crystallizations comparable to those obtained by chemical oxidation after
60 to 300 seconds. This mode of application of the treatment according to the invention

<Desc / Clms Page number 23>

 improves the formation rate of the conversion layer by at least a factor of 10 or even 100 and is therefore particularly advantageous.

These findings are confirmed by the results of atmospheric corrosion tests of samples treated at a current density of 25 mA / cm and compiled in Table III:

<Tb>
<tb> Time <SEP> of <SEP> processing <SEP> in <SEP> s. <SEP> 1 <SEP> 3 <SEP> 5 <SEP> 10
<tb> Number <SEP> of <SEP> cycles <SEP> 2 <SEP> 5 <SEP> 30 <SEP> 30
<Tb>
Example 7-Mixture of Heptanoic Acid and Decanoic Acid
The procedure is as in Example 4, replacing the heptanoic acid at 0.38 mol / liter with a mixture 80/20 (case A) or 50/50 (case B) of heptanoic acid (abbreviation: HC7) and of decanoic acid (abbreviation: HC10), the immersion time being 5 minutes.

obtenus selon le test du paragraphe Méthodes. The atmospheric corrosion resistance of the samples is evaluated

obtained according to the test of the paragraph Methods.

Table IV

<Tb>
<tb> Composition <SEP> of the <SEP> mixture <SEP> Weight <SEP> Number <SEP> of
<tb> of acids <SEP> in <SEP>% <SEP> (mg / cm2) <SEP> cycles
<tb> HC7 <SEP> HCio
<tb> 100 <SEP> 0 <SEP> 0, <SEP> 30 <SEP> 25
<tb> 80 <SEP> 20 <SEP> 0, <SEP> 30 <SEP> 50
<tb> 50 <SEP> 50 <SEP> 0, <SEP> 32 <SEP> 50
<tb> 0 <SEP> 100 <SEP> 0.45 <SEP> 50 *
<Tb>
* to note the presence after 5 cycles of spots not attributable to the white rust.

 The resistance to aqueous corrosion is then evaluated by measurements of polarization resistances, the results of which are shown in FIG. 4, in which the untreated galvanized surface is represented by the symbols +, the galvanized surface treated according to the invention without post-treatment. with:

<Desc / Clms Page number 24>

- l'acide heptanoïque est représentée par les symboles A, - l'acide décanoïque est représentée par les symboles x, - un mélange d'acides heptanoïque et décanoïque dans un rapport HC7/HC10 égal à 80/20 en mole est représentée par les symboles *.

the heptanoic acid is represented by the symbols A, the decanoic acid is represented by the symbols x, a mixture of heptanoic and decanoic acids in an HC7 / HC10 ratio equal to 80/20 by mol is represented by the symbols *.

 The other curves of Figure 4 will be exploited later.

 It can be seen by comparing these three curves that the mixture of heptanoic and decanoic acids has improved resistance to aqueous corrosion compared to heptanoic or decanoic acids used alone.

 Observations made on the deposits obtained make it possible to see that the deposit corresponding to the solution of case B (50/50) has a morphology very different from that obtained with only one of the heptanoic or decanoic acids. The conversion layer obtained with this acid mixture seems much denser, which would explain the improvement of the resistance to aqueous corrosion. This effect is even more marked in case A (80/20).

RX diffractograms of the layer obtained in these two cases demonstrate not only the presence of zinc decanoate but also that of a mixed species.

Example 8-Post-treatments
It is common to perform a post-treatment to improve the properties of a conversion layer and the present inventors have therefore sought to determine the type of post-treatment most suitable for substrates carrying a conversion layer according to the invention. .

 A galvanized sheet is treated by soaking for five minutes in a 50/50 water / ethanol solution containing 0.38 mole / liter of heptanoic acid and 2 g / l of sodium perborate hydrate.

 The post-treatment is then carried out by soaking in a post-treatment solution, the characteristics of which are summarized in Table V for 60 seconds, before the final rinsing of the procedure described in point 3 of the Materials section.

<Desc / Clms Page number 25>

Tableau V-Solutions de post-traitement

Table V-Post-Processing Solutions

<Tb>
<tb> Test <SEP> Ref. <SEP> Company <SEP> Composition <SEP> Concentration <SEP> pH
<tb> If <SEP> (1) <SEP> 44, <SEP> 016-7 <SEP> ALDRICH <SEP> 3-glycodoxypropyl-5 <SEP> g / l <SEP> 4,7
<tb> trimethoxysilane
<tb> Ti <SEP> 30.838. <SEP> 2 <SEP> FLUKA <SEP> K2TiF6 <SEP> 37 <SEP> g / l <SEP> 3, <SEP> 4
<tb> Gdf "'19914-ACROS <SEP> Gd <SEP> (NO3) <SEP> 3, <SEP> 5 <SEP> H2O <SEP> 0, <SEP> 01 <SEP> M <SEP> 4, <SEP> 7
<tb> 0250
<tb> LuIII <SEP> Lu (NO3) 3 <SEP> 0.01 <SEP> M <SEP> 4.7
<Tb>
(1) solution comprising 10% methanol by weight
Once the post-treatment has been carried out, the treated surface of the samples is observed and / or analyzed and a potentiometric evaluation of the aqueous corrosion resistance according to item 2 of the Materials section is carried out.

 It is found that the post-treatment Ti has no impact but that the post-treatment Si slightly improves the corrosion resistance, apparently without morphological modification of the conversion layer.

 In the case of post-treatment solutions containing rare earths with oxidation state 3 (Gdlll, Lu '"), tested at the same concentration and at the same pH, a rare earth deposit is observed on the conversion layer, but the effect of this deposit on the polarization resistance Rp is different according to the nature of the lanthanide, as illustrated in FIG. 4: significant effect in the case of LU very important effect in the case of Gdlll.

 In conclusion, among the evaluated post-treatment solutions, it is the GdIII solution that seems to have the greatest impact on the morphology of the carboxylation layer and on the resistance to aqueous corrosion that it brings. It also makes it possible to increase the resistance to atmospheric corrosion because an improvement of approximately 10 cycles is observed during the tests carried out in the humidotherm.

Example 9-Addition of gadolinium ions in the treatment solution
In item 2 (e) of the Materials section, it is stated that other

<Desc / Clms Page number 26>

 components or additives may be introduced into the carboxylate solution according to the invention. In the previous example, the effect of certain compounds on a post-treatment operation has been evaluated and the effect of these same compounds on the treatment itself will now be evaluated using these compounds as an additive in the conversion solution.

 The treatment according to the invention is carried out by dipping for five minutes in a 50/50 water / ethanol solution containing 0.38 mol of heptanoic acid, 2 g / l of sodium perborate hydrate, and one of the additives cited above. in Table VI, the pH can be adjusted by addition of nitric acid.

 The procedure described in point 3 of the section Materials is applied without performing post-treatment.

Table VI-Processing Additives

<Tb>
<tb> Test <SEP> Ref. <SEP> Company <SEP> Composition <SEP> Concentration <SEP> pH
<tb> If <SEP> (1) <SEP> 44,016-7 <SEP> ALDRICH <SEP> 3-g <SEP>! <SEP> ycodoxypropy <SEP>! -5g / i4, <SEP> 8
<tb> trimethoxysilane
<tb> Ti <SEP> 30.838. <SEP> 2 <SEP> FLUKA <SEP> K2TiF6 <SEP> 3, <SEP> 7 <SEP> g / l <SEP> 4, <SEP> 5
<tb> Gc <SEP> 19914-0250 <SEP> ACROS <SEP> Gd <SEP> (NO3) <SEP> 3. <SEP> HH <SEP> 0, <SEP> 01 <SEP> M <SEP> 3 , <SEP> 5
<tb> GdIII <SEP> same <SEP> same <SEP> same <SEP> 0, <SEP> 01 <SEP> M <SEP> 4, <SEP> 7
<Tb>
(1) solution comprising 10% methanol by weight;
After observation and analysis of the treated surface of the samples, it is found that the case Ti has a negative effect on the carboxylation reaction, whereas the cases Si and Gdlll at pH = 4.7 do not allow to observe a difference with respect to to carboxylation without additives.

 On the other hand, the Gd "'case at pH = 3.5 gives a conversion layer composed of two types of composition crystals and probably of different shapes: the appearance of this structure for a pH greater than 4 is observed. polarization measurements according to point 2 of the Methods paragraph, Rp values are obtained approximately 5 times higher than those obtained on the standard sample obtained by carboxylation treatment without additive.

Claims (18)

 1. Process for treatment before shaping a metal surface selected from zinc, iron, aluminum, copper, lead, and their alloys as well as galvanized, aluminized, copper-coated steel under oxidizing conditions against the metal, by contact with an aqueous bath, organic or hydro-organic comprising at least one organic acid in free form or salt form, characterized in that: - said organic acid is an aliphatic monocarboxylic or dicarboxylic acid saturated or unsaturated, - said organic acid is in solution and / or emulsion in the bath at a concentration greater than 0.1 mol / liter, - the bath pH is acidic. 2. The method of claim 1 wherein said organic acid is selected from saturated monocarboxylic acids having from 5 to 16 carbon atoms. 3. The method of claim 1 wherein said organic acid is selected from unsaturated monocarboxylic acids having from 10 to 18 carbon atoms. 4. The method of claim 1 wherein said organic acid is selected from saturated dicarboxylic acids having from 4 to 12 carbon atoms. The process of claim 2 wherein said organic acid is selected from hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid and decanoic acid. The process of claim 3 wherein said unsaturated monocarboxylic organic acid is undecenoic acid, oleic acid or linoleic acid. The process of claim 4 wherein said saturated organic dicarboxylic acid is sebacic acid or azelaic acid. 8. Process according to claim 5, characterized in that said organic acid is heptanoic acid. <Desc / Clms Page number 28> 9. Process according to claim 8, characterized in that the bath comprises, besides heptanoic acid, decanoic acid or undecenoic acid. 10. Method according to any one of claims 1 to 9, characterized in that said bath further comprises multivalent cations in oxidation state + 3, selected from rare earths at a concentration greater than or equal to 1. 10-3 mol / liter, the pH of the bath being greater than 4. 11. The method of claim 10, characterized in that said multivalent cation is gadolinium. 12. Method according to any one of claims 1 to 11, characterized in that said oxidizing conditions are obtained by adding, in the bath, a chemical agent adapted to the metal to be treated. 13. Method according to any one of claims 1 to 11, characterized in that said oxidizing conditions are obtained by circulating an electric current between said surface previously immersed in the bath and at least one against-electrode also immersed. 14. Method according to any one of claims 1 to 13, characterized in that the concentration of organic acids in the bath, the conditions of use of said bath and the oxidizing conditions with respect to the metal to be treated are adapted to obtain on said metal surface a carboxylation layer of grammage between 1 and 6 g / m2. 15. Process according to any one of Claims 1 to 14, characterized in that the treatment of said surface is carried out after treatment with a bath containing multivalent cations. oxidation state + 3, selected from the rare earths at a concentration greater than or equal to 1. 10-3 mol / liter. 16. Use of the method according to any one of claims 1 to 15 for the temporary protection against corrosion of said metal surface. 17. A method of manufacturing a shaped sheet having a metal surface selected from zinc, iron, aluminum, copper, lead, and their alloys as well as galvanized, aluminized, copper-plated steels, wherein <Desc / Clms Page number 29>  a surface treatment of said sheet according to any one of claims 1 to 15 is carried out, said treated sheet is oiled and shaped. 18. The method of claim 17, characterized in that said sheet is steel coated with zinc or a zinc alloy and in that it is shaped by stamping.