EP0298827B1 - Mixed phosphatation solution and process - Google Patents

Abstract

Mixed phosphatation acid solution suitable for resulting on a metal substrate in the simultaneous deposition of at least two metal ions, at least one of which is generally chosen from the group comprising zinc, manganese and iron, the said solution being characterised in that it includes - a polyphosphate of formula (XPO3)n in which n >/= 3 and X denotes an alkali or alkaline-earth metal or ammonium, and - a chelating agent.

Description

The subject of the invention is an acidic aqueous solution for mixed phosphating, this expression designating any phosphating capable of leading on a metal substrate to the concomitant deposition of at least two metal ions, at least one of which is generally chosen from the group including zinc, manganese and iron.

It also relates to a phosphating process using the above solution.

The metallic substrates suitable for being treated by implementing the above-mentioned solution and method are in particular those based on iron and alloys of this metal.

• de favoriser l'adhérence sur les substrats traités des revêtements organiques, notamment peintures et vernis, appliqués ultérieurement,
• d'accroître la résistance des substrats traités à la corrosion,
• dans le cas plus particulier des pièces métalliques destinées à être déformées à froid, de créer à la surface du métal une couche "anti-friction" qui permet d'améliorer les caractéristiques de surface du métal après déformation, d'éviter par ailleurs le contact direct avec l'outil et de réduire ainsi les frottements et d'augmenter la longévité de l'outil, et enfin, dans le cas de la lubrification des pièces mécaniques en mouvement, notamment durant la phase de rodage, d'éviter le contact métal-métal et, par conséquent, le phénomène de grippage.

It is recalled that the conventional phosphating treatments are intended, as the case may be

• to promote adhesion on treated substrates of organic coatings, in particular paints and varnishes, applied subsequently,
• increase the resistance of the treated substrates to corrosion,
• in the more particular case of metal parts intended to be deformed cold, to create on the surface of the metal an "anti-friction" layer which makes it possible to improve the surface characteristics of the metal after deformation, to avoid otherwise contact direct with the tool and thus reduce friction and increase the longevity of the tool, and finally, in the case of lubrication of moving mechanical parts, especially during the running-in phase, avoid metal contact -metal and, therefore, the seizing phenomenon.

• un polyphosphate, soluble dans l'eau et de formule (X PO₃)_n dans laquelle n ≧ 3 et dans laquelle X est un métal alcalin, alcalino-terreux ou l'ammonium,
• un agent chélatant organique et
• l'ion zinc.

In the case where it is a question of promoting the adhesion to the treated substrates of organic coatings, in particular paints and varnishes, applied subsequently, there are already known, from patent application EP-A-0 102 284, phosphating including:

• a polyphosphate, soluble in water and of formula (X PO₃) _n in which n ≧ 3 and in which X is an alkali, alkaline earth metal or ammonium,
• an organic chelating agent and
• the zinc ion.

When one seeks more particularly to obtain an "anti-friction layer", one generally has recourse to the processes of mixed phosphating, in particular to those of the zinc-manganese type, these processes then aiming in particular to increase the proportion of manganese in the deposits obtained.

In this regard, mention may be made of European patent application No. 81200442.2 (EP-A-4 2 631).

However, the qualities from the anti-friction point of view of the deposits obtained by implementing this process, although superior to those of the deposits obtained by the previous processes, remain insufficient taking into account the increasingly severe constraints imposed by the users. (metallurgical industries of transformation) to the manufacturers of phosphating solutions, said users demanding in addition an improvement in the anticorrosion properties of the treated substrates as well as an improvement in the adhesion of paints or other film-forming coatings on these substrates.

• d'une part, d'un polyphosphate soluble dans l'eau de formule (XPO₃)_n dans laquelle n ≧ 3 et X représente un métal alcalin, alcalino-terreux ou l'ammonium et
• d'autre part, un agent chélatant organique.

And it is to the credit of the Applicant Company that it has succeeded in decisively improving the properties mentioned above with regard to the deposits obtained and in particular in decisively increasing the proportion of manganese, when it is present in the layers obtained by mixed phosphating, by making the mixed phosphating solutions in question contain effective amounts

• on the one hand, of a water-soluble polyphosphate of formula (XPO₃) _n in which n ≧ 3 and X represents an alkali, alkaline-earth metal or ammonium and
• on the other hand, an organic chelating agent.

If the adhesion of the paints is Particularly sought after, the nickel ion will be introduced into the acid solution of mixed phosphating, in addition to or completely replacing manganese.

• au moins environ 2 g/l d'un polyphosphate de formule (XPO₃)_n dans laquelle n ≧ 3 et X représente un métal alcalin, alcalino-terreux ou l'ammonium,
• au moins environ 0,5 g/l d'un agent chélatant,
• au moins 0,3 g/l de fer et
• au moins l'une des deux combinaisons suivantes des ions d'un métal choisi dans le groupe comprenant le zinc, le manganèse et le nickel:
  • . l'ion zinc en une proportion d'au moins 0,5 g/l et l'ion manganèse en une proportion d'au moins 2 g/l, et
  • . l'ion zinc en une proportion d'au moins 0,5 g/l et l'ion nickel en une proportion d'au moins 0,5 g/l.

Consequently, the acid phosphating solution according to the invention which is based on polyphosphate and capable of leading on a metal substrate to the deposition of mixed phosphates based on zinc and at least one other metal chosen from manganese and nickel, includes

• at least about 2 g / l of a polyphosphate of formula (XPO₃) _n in which n ≧ 3 and X represents an alkali, alkaline-earth metal or ammonium,
• at least about 0.5 g / l of a chelating agent,
• at least 0.3 g / l of iron and
• at least one of the following two combinations of the ions of a metal chosen from the group comprising zinc, manganese and nickel:
  • . the zinc ion in a proportion of at least 0.5 g / l and the manganese ion in a proportion of at least 2 g / l, and
  • . the zinc ion in a proportion of at least 0.5 g / l and the nickel ion in a proportion of at least 0.5 g / l.

The invention also relates to a certain number of other arrangements implemented in isolation or in combination and which will be discussed.

Thus, the upper limits of the quantities of polyphosphate, of organic chelating agent, of Zn ions, of Mn ions and of Ni ions brought in the form of salts, possibly those of the chelating agent, entering into the composition of the solution according to the invention, are imposed, in theory, only by the solubility limits; in practice, care will be taken to choose an amount of polyphosphate compatible with a good yield from the process which is the subject of the invention, while preventing the sludge formed from being too large.

The above solution is also characterized in that it comprises at least one of the following combinations of metal ions from the group comprising zinc, manganese and nickel:
0.5 g / l n Zn ion ≦ 10 g / l
2 g / l M ion Mn ≦ 6 g / l
and
0.5 g / l n Zn ion ≦ 10 g / l
0.5 g / l Ni Ni ion ≦ 6 g / l.

• a) 0,5 g/l ≦ ion Zn ≦ 6 g/l
  2 g/l ≦ ion Mn ≦ 4 g/l
• b) 0,5 g/l ≦ ion Zn ≦ 6 g/l
  0,5 g/l ≦ ion Ni ≦ 3 g/l
• c) 0,5 g/l ≦ ion Zn ≦ 6 g/l
  2 g/l ≦ ion Mn ≦ 4 g/l
  0,5 g/l ≦ ion Ni ≦ 3 g/l.

Said acidic mixed phosphating solution is also characterized in that it comprises the following combinations of metal ions:

• a) 0.5 g / l Z Zn ion ≦ 6 g / l
  2 g / l ≦ ion Mn ≦ 4 g / l
• b) 0.5 g / l Z Zn ion ≦ 6 g / l
  0.5 g / l ≦ Ni ion ≦ 3 g / l
• c) 0.5 g / l Z Zn ion ≦ 6 g / l
  2 g / l ≦ ion Mn ≦ 4 g / l
  0.5 g / l Ni Ni ion ≦ 3 g / l.

According to an advantageous embodiment of the solution according to the invention, the polyphosphate is chosen from the group consisting of sodium trimeta-, tetrameta- and hexametaphosphate, sodium hexametaphosphate or HMPP being preferred.

• l'acide éthylène-diamine-tétracétique ou EDTA, l'acide nitrilo-triacétique ou NTA, l'acide diéthylène-triamine-pentacétique ou DTPA,
• les acides polycarboxyliques, notamment les acides citrique, oxalique, malique, glutamique, tartrique, aspartique et malonique ainsi que leurs sels.
• les acides polyhydroxycarboxyliques, notamment les acides gluconique et glucoheptonique (éventuellement apportés sous la forme lactone interne) ainsi que leurs sels.

According to another advantageous embodiment of the solution according to the invention, the chelating agent is chosen from the group consisting of:

• ethylene-diamine-tetracetic acid or EDTA, nitrilo-triacetic acid or NTA, diethylene-triamine-pentacetic acid or DTPA,
• polycarboxylic acids, in particular citric, oxalic, malic, glutamic, tartaric, aspartic and malonic acids as well as their salts.
• polyhydroxycarboxylic acids, in particular gluconic and glucoheptonic acids (possibly provided in the internal lactone form) as well as their salts.

According to another advantageous embodiment, the solution according to the invention comprises a mineral acid chosen from the group consisting of sulfuric, hydrochloric and nitric acids, nitric acid being preferred, in an amount sufficient to bring the pH to a initial value less than 2, preferably between 0.5 and 1.7.

The fact that nitric acid is preferred is linked to its oxidizing nature.

• de l'hexamétaphosphate de sodium,
• de l'acide gluconique sous la forme d'un de ses sels ou de sa lactone interne,
• l'ion zinc,
• l'ion manganèse,
• de l'acide nitrique.

According to another advantageous embodiment of the above solution, it comprises

• sodium hexametaphosphate,
• gluconic acid in the form of one of its salts or of its internal lactone,
• the zinc ion,
• manganese ion,
• nitric acid.

According to another advantageous embodiment of the solution according to the invention, the zinc ion and the manganese ion are introduced in the form of salts in particular chosen from the group consisting of oxides, sulfates, nitrates, carbonates and phosphates.

According to another advantageous embodiment of the solution according to the invention, the zinc ion and / or the manganese ion are introduced in combined form with the chelating agent, preferably in the form of citrate, tartrate, glucoheptonate and especially in the form of gluconate.

• de l'hexamétaphosphate de sodium,
• du gluconate de zinc,
• l'ion manganèse amené sous forme de sel ou sous forme de gluconate, et
• de l'acide nitrique.

According to another advantageous embodiment, the solution according to the invention comprises

• sodium hexametaphosphate,
• zinc gluconate,
• the manganese ion supplied in the form of a salt or in the form of a gluconate, and
• nitric acid.

According to another advantageous embodiment, the phosphating solution in accordance with the invention comprises from 8 g / l to 350 g / l, preferably from 14 to 300 g / l and, more preferably still, from 30 to 230 g / l of a composition consisting of polyphosphate, of the chelating agent and zinc and manganese ions in the form of their salts which may be those of the chelating agent.

• le rapport pondéral entre, d'une part, le mélange constitué par le zinc et par le manganèse (exprimés tous deux sous forme d'ion métallique) et, d'autre part, l'hexamétaphosphate de sodium, est compris entre environ 6/1 et 1/50, de préférence entre environ 3/1 et 1/20 et, plus préférentiellement encore, entre environ 1,5/1 et 1/5,
• le rapport pondéral entre le zinc et le manganèse est compris entre 0,01/1 et 50/1, de préférence entre 0,2/1 et 20/1 et, plus préférentiellement encore, entre 0,5/1 et 5/1, et
• le rapport pondéral entre l'ion gluconique et l'hexamétaphosphate de sodium est compris entre environ 50/1 et 1/30, de préférence entre environ 30/1 et 1/10 et, plus préférentiellement encore, entre environ 10/1 et 1/4.

According to another advantageous embodiment of the solution according to the invention,

• the weight ratio between, on the one hand, the mixture constituted by zinc and by manganese (both expressed in the form of metal ion) and, on the other hand, sodium hexametaphosphate, is between approximately 6 / 1 and 1/50, preferably between approximately 3/1 and 1/20 and, more preferably still, between approximately 1.5 / 1 and 1/5,
• the weight ratio between zinc and manganese is between 0.01 / 1 and 50/1, preferably between 0.2 / 1 and 20/1 and, more preferably still, between 0.5 / 1 and 5/1 , and
• the weight ratio between the gluconic ion and the sodium hexametaphosphate is between approximately 50/1 and 1/30, preferably between approximately 30/1 and 1/10 and, more preferably still, between approximately 10/1 and 1 / 4.

According to another advantageous embodiment of the solution according to the invention, the mixture constituted by the zinc ion and the manganese ion is used in an amount between 2.5 and 30 g / l and the amount of hexametaphosphate used is 2 to 30 g / l.

• une étape de dégraissage,
• une étape de rinçage,
• une étape acide de réactivation,
• une étape facultative de rinçage, notamment si le bain de réactivation est constitué par une solution d'acide nitrique,
• l'étape de phosphatation proprement dite,
• une étape de rinçage, puis une étape facultative de séchage en fonction des traitements à venir dans une phase ultérieure,

est caractérisé par le fait que, pour l'étape de phosphatation proprement dite, on a recours à la solution de phosphatation mixte au zinc conforme à l'invention qui est appliquée par immersion ou pulvérisation, l'étape de réactivation et l'étape facultative de rinçage ultérieur pouvant éventuellement être remplacées par une étape d'affinage comprenant par exemple des sels de Jernstedt à base de titane, étant entendu

• d'une part, que la température de la solution est comprise entre environ 40°C et 100°C, plus particulièrement supérieure à 70°C et, dans la pratique, voisine de 90-98°C,
• d'autre part, que le contact entre la solution de phosphatation et le substrat métallique est maintenu pendant un temps variant, dans la pratique, de 2 secondes à 30 minutes, de préférence de 5 à 20 minutes.

The zinc zinc phosphating process according to the invention and which successively comprises:

• a degreasing step,
• a rinsing step,
• an acid reactivation step,
• an optional rinsing step, in particular if the reactivation bath consists of a nitric acid solution,
• the actual phosphating step,
• a rinsing step, then an optional drying step depending on the treatments to come in a later phase,

is characterized in that, for the actual phosphating step, use is made of the mixed zinc phosphating solution according to the invention which is applied by immersion or spraying, the reactivation step and the optional step subsequent rinsing which can optionally be replaced by a refining step comprising, for example Jernstedt salts based on titanium, it being understood

• on the one hand, that the temperature of the solution is between approximately 40 ° C and 100 ° C, more particularly greater than 70 ° C and, in practice, close to 90-98 ° C,
• on the other hand, that the contact between the phosphating solution and the metal substrate is maintained for a time varying, in practice, from 2 seconds to 30 minutes, preferably from 5 to 20 minutes.

By comparing this process to the succession of steps of the processes of the prior art, one notes the simplification which it brings by in particular the elimination of the steps of passivation and "greasing" in the case where one seeks protection against corrosion.

Indeed, the objects treated by implementing the method according to the invention can be stored in the open air without any prior protective treatment, without the appearance of degradation of the layer phenomena.

According to a preferred embodiment, the pH of the phosphating solution is changed from the initial value between 0.5 and 1.7 to a value between 2.3 and 2.9 by adding a sufficient quantity of iron filings, between 0.3 and 5 g / l of solution and more preferably between 1 and 4 g / l.

After placement and curing, the phosphating solution is ready to use.

Iron plays a role of catalyst (or reducer) of conversion. In fact, in the absence of iron or in the presence of too small an amount of iron, less than 0.3 g / l, it can be seen that no phosphate deposit forms on the metal substrate. It is only when, due to the attack of the substrate by the solution, the concentration of the latter in iron has reached the minimum value necessary, that the conversion phenomenon takes place.

• des agents mouillants,
• des agents améliorant la conversion à la surface de corps creux tels que certaines pièces de carrosserie automobile, ces agents pouvant être des composés de titane comme TiCl₄,
• des accélérateurs de conversion tels que le nickel, le cuivre, et autres, amenés sous forme de nitrate, nitrite, fluorure, chlorate, molybdate ou leurs acides.

In addition to the constituents indicated above, the solution according to the invention can advantageously comprise:

• wetting agents,
• agents improving the conversion on the surface of hollow bodies such as certain automobile body parts, these agents possibly being titanium compounds such as TiCl₄,
• conversion accelerators such as nickel, copper, and the like, supplied in the form of nitrate, nitrite, fluoride, chlorate, molybdate or their acids.

The nickel content in the bath may be between 0.5 and 6 g / l and preferably between 0.5 and 3 g / l.

Thus, in the phosphating solution according to the invention, nitric acid is particularly preferred as an accelerating agent, and makes it possible to considerably improve the speed of formation of the deposit.

The preferred concentration of nitric acid is between 0.4 g / l and 60 g / l, more preferably between 2 and 50 g / l and, more preferably still, between 5 and 30 g / l.

The solution according to the invention leads to conversion layers having particularly advantageous characteristics. Thus, the analysis of deposits taken from the surface of the treated objects revealed that, surprisingly, the composition of these deposits was characterized by a manganese content significantly higher than that obtained with the phosphating solutions used in the prior art, this content may exceed 10%.

Due to the increase in the manganese content of the deposits, the properties thereof are improved, in particular from the point of view of applications aimed at the treatment of metal parts intended to undergo friction or else cold deformation.

These deposits, by their absorbent properties, retain lubricants more effectively on the surface of the part.

In addition, during the prowling phases, the surface condition makes it possible to reduce the frictional forces, to increase the forming rates and to reduce the wear of the material.

The thickness of the layers obtained is sufficient to ensure that the mechanical stresses are absorbed.

Finally, as a result of the acidity of the solution, the crystals constituting the deposits are perfectly anchored to the surface of the metal, which gives said deposits remarkable mechanical resistance.

In addition to the mechanical qualities mentioned above and due to both their structure and their manganese content, the deposits obtained thanks to the solution according to the invention have remarkable resistance to corrosion and constitute an excellent bonding base. for most organic coatings.

Other important advantages obtained thanks to the invention also reside, on the one hand, in the decisive reduction in the quantities of phosphate sludge formed during the phosphating treatments and, on the other hand, in the fact that the solution conform to the invention is essentially composed of biodegradable products.

The invention can be understood even better with the aid of the examples which follow and which relate to advantageous embodiments.

EXAMPLE 1

• 16,9 g/l d'acide phosphorique à 85 %,
• 19,7 g/l de ZnSO₄, H₂O, soit un équivalent en Zn de 7,2 g/l,
• 22,8 g/l de MnSO₄, H₂O, soit un équivalent en Mn de 7,4 g/l,
• 0,65 g/l de fer apporté sous forme de limaille,
• 4,2 g/l d'ion NO₃⁻.

Metallic steel specimens of dimensions equal to 9.5 x 6.5 cm having undergone chemical degreasing, followed by cold chemical pickling in 6N hydrochloric medium, are immersed in a phosphating solution according to the prior art comprising :

• 16.9 g / l of 85% phosphoric acid,
• 19.7 g / l of ZnSO₄, H₂O, i.e. a Zn equivalent of 7.2 g / l,
• 22.8 g / l of MnSO₄, H₂O, equivalent to an Mn of 7.4 g / l,
• 0.65 g / l of iron supplied in the form of filings,
• 4.2 g / l of NO₃⁻ ion.

During the treatment, which lasts 15 minutes, the bath temperature is maintained at 97 ° C. After treatment, the plates are rinsed with demineralized water and dried.

The crystalline deposit formed is collected by scraping.

• épaisseur : 20 µm,
• teneur en zinc : 26,2 %,
• teneur en manganèse : 4,41 %.

It has the following characteristics:

• thickness: 20 µm,
• zinc content: 26.2%,
• manganese content: 4.41%.

EXAMPLE 2

• 15 g/l d'hexamétaphosphate de sodium,
• 19,7 g/l de ZnSO₄, H₂O, soit un équivalent en Zn de 7,2 g/l,
• 22,8 g/l de MnSO₄, H₂O, soit un équivalent en Mn de 7,4 g/l,
• 1 g/l de fer apporté sous forme de limaille,
• 5,6 g/l d'ion NO₃⁻.

Metal steel samples similar to those used in Example 1 are subjected to chemical degreasing, followed by chemical pickling in 6N hydrochloric medium, then immersed in a phosphating solution comprising:

• 15 g / l of sodium hexametaphosphate,
• 19.7 g / l of ZnSO₄, H₂O, i.e. a Zn equivalent of 7.2 g / l,
• 22.8 g / l of MnSO₄, H₂O, equivalent to an Mn of 7.4 g / l,
• 1 g / l of iron brought in the form of filings,
• 5.6 g / l of NO₃⁻ ion.

As in Example 1, the duration of the treatment is 15 minutes, the temperature of the solution being adjusted to 97 ° C.

• épaisseur : 5 à 10 µm,
• teneur en zinc : 30,7 %,
• teneur en manganèse : 5,83 %.

The deposit obtained using this conversion solution has the following characteristics:

• thickness: 5 to 10 µm,
• zinc content: 30.7%,
• manganese content: 5.83%.

This example shows that the replacement of phosphoric acid by sodium hexametaphosphate leads to a deposit richer in manganese than that obtained by the solution described in Example 1.

However, this deposit has the disadvantage of a small, irregular thickness, comprising gaps in certain places on the treated plate; the irregularity of the deposit is incompatible with good protection against corrosion and effective lubrication of the metal part, in the event that it must undergo a cold deformation operation.

The use of a polyphosphate alone is therefore not sufficient.

EXAMPLE 3

• 16,9 g/l d'acide phosphorique à 85 %,
• 60 g/l de gluconate de zinc, soit un équivalent en zinc de 7,2 g/l,
• 60 g/l de gluconate de manganèse, soit un équivalent en Mn de 7,4 g/l,
• 1 g/l de fer apporté sous forme de limaille,
• 17,5 g/l d'ion NO₃⁻.

For this test, the test pieces and the experimental method used are identical to those described in Examples 1 and 2. The solution used is however different; she understands :

• 16.9 g / l of 85% phosphoric acid,
• 60 g / l of zinc gluconate, equivalent to a zinc equivalent of 7.2 g / l,
• 60 g / l of manganese gluconate, equivalent to an Mn of 7.4 g / l,
• 1 g / l of iron brought in the form of filings,
• 17.5 g / l of NO₃⁻ ion.

• épaisseur : 8 à 20 µm,
• teneur en zinc : 26,3 %,
• teneur en manganèse : 6,00 %.

The deposit obtained using this solution described above has the following characteristics:

• thickness: 8 to 20 µm,
• zinc content: 26.3%,
• manganese content: 6.00%.

It is noted that the addition of zinc and manganese in the form of gluconate makes it possible to substantially increase the manganese content in the deposit. The gluconic ion by its intervention on the chemical reaction equilibria favors the precipitation of manganese phosphate at the level of the steel plate and influences the size of the crystals: the crystalline deposit is finer and more homogeneous than that obtained with the solution conversion example 1.

On the other hand, the thickness of the coating is very irregular and all of the plates treated reveal phosphating defects.

The use of the chelating agent alone is also not sufficient.

EXAMPLE 4

• 15 g/l d'hexamétaphosphate de sodium,
• 60 g/l de gluconate de zinc, soit un équivalent en zinc de 7,2 g/l,
• 60 g/l de MnSO₄, H₂O, soit un équivalent en Mn de 7,4 g/l,
• 2 g/l de fer apporté sous forme de limaille,
• 17,5 g/l d'ion NO₃⁻.

In this example, the test pieces and the experimental method used are identical to those described in the previous examples. The phosphating solution used comprises:

• 15 g / l of sodium hexametaphosphate,
• 60 g / l of zinc gluconate, equivalent to a zinc equivalent of 7.2 g / l,
• 60 g / l of MnSO₄, H₂O, equivalent to an Mn of 7.4 g / l,
• 2 g / l of iron brought in the form of filings,
• 17.5 g / l of NO₃⁻ ion.

• épaisseur : 20 µm,
• teneur en zinc : 30,7 %,
• teneur en manganèse : 6,75 %.

The deposit obtained with this solution has the following characteristics:

• thickness: 20 µm,
• zinc content: 30.7%,
• manganese content: 6.75%.

This solution leads to the production of a deposit rich in manganese particularly suitable for use as a coating before cold deformation. In addition, this fine, dense and regular crystalline deposit ensures good protection against corrosion.

Consequently, the joint use of a polyphosphate and a chelating agent, as provided for by the invention, not only leads to a marked increase in the content of the manganese deposit, but also makes it possible to obtain a good quality deposit.

EXAMPLE 5

• 15 g/l d'hexamétaphosphate de sodium,
• 60 g/l de gluconate de zinc, soit un équivalent en zinc de 7,2 g/l,
• 60 g/l de gluconate de manganèse, soit un équivalent en Mn de 7,4 g/l,
• 1 g/l de fer apporté sous forme de limaille,
• 21 g/l d'ion NO₃⁻.

In this example, the test pieces and the method used are identical to those described in the previous examples. The phosphating solution used comprises:

• 15 g / l of sodium hexametaphosphate,
• 60 g / l of zinc gluconate, equivalent to a zinc equivalent of 7.2 g / l,
• 60 g / l of manganese gluconate, equivalent to an Mn of 7.4 g / l,
• 1 g / l of iron brought in the form of filings,
• 21 g / l of NO₃⁻ ion.

• épaisseur : 20 à 25 µm,
• teneur en zinc : 28,6 %,
• teneur en manganèse : 6,97 %.

The deposit obtained using this solution has the following characteristics:

• thickness: 20 to 25 µm,
• zinc content: 28.6%,
• manganese content: 6.97%.

This solution leads to a deposit, the manganese content of which is particularly high; this deposit is perfectly suited to cold deformation and also has a crystalline, fine, regular appearance, thus offering good protection against corrosion.

This example shows that very good results are obtained when the chelating agent is introduced under the form of its Zn and Mn salts.

EXAMPLE 6

• 15 g/l d'hexamétaphosphate de sodium,
• 19,7 g/l de ZnSO₄, H₂O, soit un équivalent en zinc de 7,2 g/l,
• 22,8 g/l de MnSO₄, H₂O, soit un équivalent en Mn de 7,4 g/l,
• 1 g/l de fer apporté sous forme de limaille,
• 17,5 g/l d'ion NO₃⁻,
• 114 g/l de gluconate de sodium.

In this example, the metal test pieces and the experimental method used are identical to those described in the previous examples. The phosphating solution used comprises:

• 15 g / l of sodium hexametaphosphate,
• 19.7 g / l of ZnSO₄, H₂O, i.e. a zinc equivalent of 7.2 g / l,
• 22.8 g / l of MnSO₄, H₂O, equivalent to an Mn of 7.4 g / l,
• 1 g / l of iron brought in the form of filings,
• 17.5 g / l of NO₃⁻ ion,
• 114 g / l sodium gluconate.

In this solution, the supply of gluconic ion takes place in the form of sodium gluconate, so that the quantity of gluconic ion present is identical to that encountered in the solutions in which zinc and manganese are provided in the form gluconate.

• épaisseur : 12 µm,
• teneur en zinc : 27,3 %,
• teneur en manganèse : 10,0 %.

The deposit obtained using this solution has the following characteristics:

• thickness: 12 µm,
• zinc content: 27.3%,
• manganese content: 10.0%.

This solution leads to the formation of an exceptionally rich manganese deposit. It is stable and regular in operation, and enables a fine, dense crystalline deposit of suitable thickness to be obtained, ensuring good protection against corrosion.

This example shows that the best results are obtained when, in the solution according to the invention, the chelating agent is introduced separately, that is to say not in the form of its Zn and / or Mn salt. .

Claims (18)

1. An acid phosphatization solution based on polyphosphate and suitable for producing on a metallic substrate a deposit of combined phosphates based on zinc and at least another metal selected from manganese and nickel, said solution comprising

   - at least about 2 g/l of polyphosphate of formula (XPO₃)_n wherein n ≧ 3 and X represents an alkaline, alkaline-earth metal or ammonium,

   - at least about 0.5 g/l of a chelating agent,

   - at least 0.3 g/l of iron and

   - at least one of the two following combinations of metal ions selected from the group comprising zinc, manganese and nickel:

   . zinc ion in a proportion of at least 0.5 g/l and manganese ion in a proportion of at least 2 g/l, and

   . zinc ion in a proportion of at least 0.5 g/l and nickel ion in a proportion of at least 0.5 g/l.
2. A combined acid phosphatization with zinc according to claim 1, characterized by the fact that it comprises at least one of the following combinations of metal ions of the group consisting of zinc, manganese and nickel:
      0.5 g/l ≦ ion Zn ≦ 10 g/l
      2 g/l ≦ ion Mn ≦ 6 g/l
   and
      0.5 g/l ≦ ion Zn ≦ 10 g/l
      0.5 g/l ≦ ion Ni ≦ 6 g/l.
3. A combined acid phosphatization solution according to claim 1, characterized by the fact that it comprises the following combination of metal ions:
      0.5 g/l ≦ Zn ion ≦ 6 g/l
      2 g/l ≦ Mn ion ≦ 4 g/l.
4. A combined acid phosphatization solution according to claim 1, characterized by the fact that it comprises the following combination of metal ions:
      0.5 g/l ≦ Zn ion ≦ 6 g/l
      0.5 g/l ≦ Ni ion ≦ 3 g/l.
5. A combined acid phosphatization solution according to claim 1, characterized by the fact that it comprises the following combination of metal ions:
      0.5 g/l ≦ Zn ion ≦ 6 g/l
      2 g/l ≦ Mn ion ≦ 4 g/l
      0.5 g/l ≦ Ni ion ≦ 3 g/l.
6. A combined acid phosphatization solution according to one of claims 1 to 5, characterized by the fact that polyphosphate is selected from the group consisting of sodium trimeta-, tetrameta- and hexametaphosphate.
7. A combined acid phosphatization solution according to one of claims 1 to 6, characterized by the fact that polyphosphate is sodium hexametaphosphate.
8. A combined acid phosphatization solution according to one of claims 1 to 7, characterized by the fact that the chelating agent is selected from the group consisting of:

   - ethylene-diamine-tetracetic acid or EDTA, nitrilotriacetic acid or NTA, diethylene-triamine-pentacetic acid or DTPA,

   - polycarboxylic acids,

   - polyhydroxycarboxylic acids.
9. A combined acid phosphatization solution according to claim 8, characterized by the fact that polycarboxylic acids are selected from citric, oxalic, malic, glutamic, tartric, aspartic and malonic acids, as well as the salts thereof.
10. A combined acid phosphatization solution according to claim 8, characterized by the fact that polyhydrocarboxylic acids are selected from gluconic and glucoheptonic acids, as well as the salts thereof.
11. A combined acid phosphatization solution according to one of claims 1 to 10, characterized by the fact that it comprises a mineral acid selected from the group consisting of sulfuric, hydrochloric and nitric acids, in a quantity sufficient to bring the pH to an initial value lower than 2.
12. A combined acid phosphatization solution according to one of claims 1 to 10, characterized by the fact that it comprises a mineral acid selected from the group consisting of sulfuric, hydrochloric and nitric acids, in a quantity sufficient to bring the pH to a value comprised between 0.5 and 1.7.
13. A combined acid phosphatization solution according to one of claims 1 to 12, characterized by the fact that it comprises

    - sodium hexametaphosphate,

    - gluconic acid under the form of one of its salts or of its internal lactone,

    - zinc ion,

    - manganese ion,

    - nitric acid.
14. A combined acid phosphatization solution according to one of claims 1 to 13, characterized by the fact that zinc ion and manganese ion are introduced under the form of salts selected from the group consisting of oxides, sulfates, nitrates, carbonates and phosphates.
15. A combined acid phosphatization solution according to one of claims 1 to 14, characterized by the fact that zinc ion and/or manganese ion are introduced under the form of citrate, tartrate, glucoheptonate and gluconate.
16. A combined acid phosphatization solution according to claims 1 to 15, characterized by the fact that it comprises

    - sodium hexametaphosphate,

    - zinc gluconate,

    - manganese ion introduced under the form of salt or under the form of gluconate, and

    - nitric acid.
17. A combined acid phosphatization solution according to one of claims 10 to 16, characterized by the fact that the concentration in nitric acid is comprised between 0.4 g/l and 60 g/l.
18. A combined phosphatization process comprising successively:

    - a degreasing step,

    - a rinsing step,

    - an acid step of reactivation,

    - an optional rinsing step, especially if the reactivating bath is constituted by a nitric acid solution,

    - a phosphatization step proper,

    - a rinsing step, then an optional drying step depending on future treatments posibly involved in a subsequent phase,

    characterize by the fact that, for the phosphatization step proper, one uses the combined phosphatization solution with zinc according to one of claims 1 to 17, this solution being applied by means of a dipping or spraying method, being understood that

    - on the one hand, the temperature of the solution is comprised between approximately 40°C and 100°C,

    - on the other hand, that the contact between the phosphatization solution and the metal substrate is maintained for a duration varying, in the practice, from 2 seconds to 30 minutes, preferably from 5 to 20 minutes.