WO2004059035A1 - Method of obtaining chromate-free conversion coatings on aluminium alloys - Google Patents

Method of obtaining chromate-free conversion coatings on aluminium alloys Download PDF

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Publication number
WO2004059035A1
WO2004059035A1 PCT/ES2003/000665 ES0300665W WO2004059035A1 WO 2004059035 A1 WO2004059035 A1 WO 2004059035A1 ES 0300665 W ES0300665 W ES 0300665W WO 2004059035 A1 WO2004059035 A1 WO 2004059035A1
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Prior art keywords
conversion layers
chromate
aluminum alloys
free conversion
solutions
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PCT/ES2003/000665
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Spanish (es)
French (fr)
Inventor
Francisco Javier Botana Pedemonte
Manuel BETHENCOURT NÚÑEZ
Mariano MARCOS BÁRCENA
María José CANO IGLESIAS
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Universidad De Cádiz
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Priority to AU2003294994A priority Critical patent/AU2003294994A1/en
Publication of WO2004059035A1 publication Critical patent/WO2004059035A1/en

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
    • C23C22/56—Treatment of aluminium or alloys based thereon

Definitions

  • ALUMINUM SURFACE TREATMENT INDUSTRIES NAVAL, AEROSPACE, AUTOMOBILE, DECORATIVE, ARCHITECTURAL.
  • the present invention is related to the formulation of a bath for performing surface treatments of aluminum alloys, more particularly it is a bath in which a chemical conversion treatment free of Cr (VI) compounds is carried out.
  • US patent 5,362,335 describes a two-stage method, in the first one triethanolamine is used to cause the growth of an aluminum oxide layer on the alloy to be protected and in a second step a solution is used with a high concentration of CeCI 3 (8000 to 12000 ppm) to improve the protective properties of the layer.
  • WO 96/11290 it is proposed to use solutions with mixtures of different lanthanides to obtain conversion layers on different metal alloys, including aluminum alloys.
  • the baths in addition to containing at least one lanthanide salt in concentrations between 0.05 M and saturation, must incorporate significant concentrations of Al 3 * .
  • the main corrosion process that takes place on the surface of said alloy is localized alkaline corrosion (LAC) in the environment of the iron-rich precipitates, which act as permanent cathodes, without the rest of the precipitates are affected.
  • LAC localized alkaline corrosion
  • a second process takes place consisting of the formation of a protective oxide layer on the metal matrix, the thickness of which increases with exposure time.
  • the developed mixed layer decreases the activity of the system by a factor close to 25 and its resistance, in relation to the layer developed in NaCI, increases by a factor of the ord in of 42.
  • treatment times of 48 hours are necessary, which reduces the industrial viability of the invention.
  • the conversion layers will be developed by immersing samples of aluminum alloys in aqueous solutions at different temperatures using Ce (N0 3 ) 3 or CeCI 3 in a concentration range of 0.001 to 0.01 M.
  • the samples Before being immersed in the bath, the samples will be subjected to a treatment that ensures the absence of traces of oxides and grease on their surface. Subsequently, the samples will be introduced into previously prepared solutions in the mentioned concentration range, although the best results are obtained by using concentrations 0.001 to 0.01 M Ce (N0 3 ) 3 or 0.001 to 0.01 M CeCI 3 . Before immersing the samples in the corresponding solution, it must have been heated to the appropriate temperature.
  • the following table shows the thermal activation treatments depending on the treatment temperature, the cerium salt used and the duration of the treatment.
  • the following table shows the mixed thermal activation-chemical activation treatments, listing the treatments according to the temperature of the treatment, the concentration of H 2 0 2 in the bath and the duration of the treatment.
  • the system allows the development of mixed layers formed by cerium precipitates located on the cathodic intermetallic compounds and an alumina film that covers the metallic matrix.
  • the surface state of the samples will be homogenized by polishing.
  • Consistent thermal activation treatments can be carried out in a concentration range between 0.001 and 0.01 M, although the best results are obtained by using: 1) aqueous solutions of Ce (N0 3 ) 3 0.001 to 0.01 M 2) CeCI 3 aqueous solutions 0.001 to 0.01 M. These solutions are maintained throughout the treatment at a certain temperature, between 323 K and 363 K, and for time intervals between 0 and
  • Ce (N0 3 ) 3 0.001 to 0.01 M and CeCI 3 0.001 to 0.01 M The reagents used for its preparation are: CeCI 3 -7H 2 0 from Fluka, with a purity greater than 98.5%, and Ce (N0 3 ) 3 - Fluka 6H 2 0 or similar, with a purity greater than 99.0%. These are added to distilled quality water and the sample is homogenized by means of a magnetic stirrer.
  • the original solutions are prepared in the same way as solutions of Ce (N0 3 ) 3 0.001 to 0.01 M, but once they reach the desired temperature, H 2 0 2 is added in concentrations of 0.675, 1.25 and 2.5 mlJL.
  • the hydrogen peroxide used is 30% w / v of Panreac or the like.
  • salt spray chamber tests of 168 hours duration were carried out, in accordance with ASTM Standard B-117 of standard tests of resistance to corrosion by salt spray. These types of tests are the most widespread in the surface treatment industry. After this evaluation, the treated samples showed no signs of corrosion.
  • the resistance against corrosion of the treated samples was evaluated using the electrochemical techniques of Linear Polarization and Polarization Resistance in aerated solution of 3.5% NaCI. These measurements were carried out in a K235 flat cell from Pare EG&G, using a SI 1287 potentiostat from Solartron.
  • a Crison Ag / AgCI one was used as the reference electrode.
  • the samples thus evaluated presented a value of increase in resistance to polarization ⁇ R P of the order of up to 850, which implies an improvement of a factor close to 40 with respect to immersion treatments at room temperature, and in a time of up to 200 times less treatment.
  • the invention may be of interest in the aluminum surface treatment industry, in its naval, aerospace, automotive, decorative, architectural application, and ultimately, in all those specialties in which the use of aluminum requires anticorrosive protection.

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  • Chemical & Material Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Treatment Of Metals (AREA)

Abstract

The invention relates to a method of obtaining chromate-free conversion coatings on aluminium alloys. The inventive method involves the use of harmless cerium salts and the thermal and thermochemical activation of the system, thereby ensuring the accelerated growth of the film and a greater degree of coverage in relation to the mixed layer. In this way, increased protection against corrosion is obtained, treatment times are significantly shortened and, as a result, the costs associated with the process are reduced. Moreover, said method dispenses with the use of highly-contaminating chromium baths in favour of completely harmless lanthanide salts.

Description

OBTENCIÓN DE CAPAS DE CONVERSIÓN LIBRES DE CROMATOS SOBRE ALEACIONES DE ALUMINIO.OBTAINING CHROME-FREE CONVERSION LAYERS ON ALUMINUM ALLOYS.
Sector de la técnica.Technique sector.
INDUSTRIAS DE TRATAMIENTOS SUPERFICIALES DE ALUMINIO: NAVAL, AEROESPACIAL, AUTOMOVILÍSTICA, DECORATIVA, ARQUITECTÓNICA.ALUMINUM SURFACE TREATMENT INDUSTRIES: NAVAL, AEROSPACE, AUTOMOBILE, DECORATIVE, ARCHITECTURAL.
Estado de la técnica anterior a la fecha de presentación.State of the art prior to the filing date.
La presente invención está relacionada con la formulación de un baño para realizar tratamientos superficiales de aleaciones de aluminio, más particularmente se trata de una baño en el que se realiza un tratamiento de conversión química libre de compuestos de Cr(VI).The present invention is related to the formulation of a bath for performing surface treatments of aluminum alloys, more particularly it is a bath in which a chemical conversion treatment free of Cr (VI) compounds is carried out.
Una de los métodos más empleados para realizar el tratamiento superficial de estas aleaciones es llevar a cabo su inmersión en baños que contienen cromatos. Con estos tratamientos se consigue, por una parte, mejorar la resistencia a la corrosión de la aleación, y por otra, se facilita el anclaje posterior de otro tipo de películas protectoras, por ejemplo, pinturas. Los tratamientos basados en la utilización de cromatos se encuentran ampliamente extendidos ya que con ellos se obtienen excelentes resultados y su intervalo de aplicabilidad es muy amplio.One of the most widely used methods for surface treatment of these alloys is to immerse them in baths containing chromates. With these treatments it is possible, on the one hand, to improve the corrosion resistance of the alloy, and on the other hand, the subsequent anchoring of other types of protective films, for example paints, is facilitated. Treatments based on the use of chromates are widely used since excellent results are obtained with them and their range of applicability is very wide.
Sin embargo, estos compuestos presentan el inconveniente de poseer una alta toxicidad y un elevado poder contaminante. Esto ha provocado que algunos sectores industriales se hayan visto forzados a eliminar su empleo y otros tendrán que hacerlo en próximo futuro. Por esta razón, desde hace algunos años se han ido desarrollado diversas invenciones orientadas a la búsqueda de nuevos tratamientos no contaminantes libres de compuestos de Cr(VI).However, these compounds have the drawback of possessing high toxicity and high polluting power. This has caused some industrial sectors to be forced to cut their jobs and others will have to do so in the near future. For this reason, for several years, various inventions have been developed aimed at finding new non-polluting treatments free of Cr (VI) compounds.
Entre otras alternativas se encuentra aquellas basadas en el empleo de sales de elementos lantánidos en la formulación de baños. Así, es posible encontrar patentes en las que se utilizan compuestos lantánidos para la formulación de baños de decapado (WO 95/08008, EP 0 899 361 A2), GB 2 328 447 A); baños de enjuague (US 3,969,152). En lo que se refiere estrictamente a la formulación de baños para obtener capas de conversión cabe distinguir dos grupos. Por una parte, es posible encontrar patentes como la WO 88/06639, EP O 337 075 A2, US 2,512,493, US 5,356,492, US 5,221,371, que además de la sal del elemento lantánido incorporan en la formulación, algún compuesto oxidante como por ejemplo agua oxigenada o disoluciones de permanganato, u otro tipo de compuestos como sales de V, Zr, fosfatos, etc. Estos tratamientos por tanto se caracterizan por presentar formulaciones complejas en las que el elemento lantánidos es uno entre varios principios de la formulación. Por otra parte, en la patente US 5,362,335 se describe un método en dos etapas, en la primera de ellas se emplea trietanolamina para provocar el crecimiento de una capa de óxido de aluminio sobre la aleación a proteger y en un segundo paso se emplea un disolución con una elevada concentración de CeCI3 (8000 a 12000 ppm) para mejorar las propiedades protectoras de la capa. Por último, en la patente WO 96/11290 se propone utilizar disoluciones con mezclas de distintos lantánidos para obtener capas de conversión sobre distintas aleaciones metálicas, entre ellas aleaciones de aluminio. En el caso particular de estas aleaciones los baños, además de contener al menos una sal lantánida en concentraciones comprendidas entre 0.05 M y la saturación, debe incorporar concentraciones importantes de Al3*.Other alternatives include those based on the use of lanthanide element salts in the formulation of baths. Thus, it is possible to find patents in which lanthanide compounds are used for the formulation of pickling baths (WO 95/08008, EP 0 899 361 A2), GB 2 328 447 A); rinse baths (US 3,969,152). With regard strictly to the formulation of baths to obtain conversion layers, two groups can be distinguished. On the one hand, it is possible to find patents such as WO 88/06639, EP O 337 075 A2, US 2,512,493, US 5,356,492, US 5,221,371, which in addition to The salt of the lanthanide element incorporates in the formulation some oxidizing compound such as hydrogen peroxide or permanganate solutions, or other types of compounds such as salts of V, Zr, phosphates, etc. These treatments are therefore characterized by presenting complex formulations in which the lanthanide element is one of several principles of the formulation. On the other hand, US patent 5,362,335 describes a two-stage method, in the first one triethanolamine is used to cause the growth of an aluminum oxide layer on the alloy to be protected and in a second step a solution is used with a high concentration of CeCI 3 (8000 to 12000 ppm) to improve the protective properties of the layer. Finally, in WO 96/11290 it is proposed to use solutions with mixtures of different lanthanides to obtain conversion layers on different metal alloys, including aluminum alloys. In the particular case of these alloys, the baths, in addition to containing at least one lanthanide salt in concentrations between 0.05 M and saturation, must incorporate significant concentrations of Al 3 * .
En resumen, hasta la fecha no se encuentra descrito ningún tratamiento semejante al propuesto en la presente invención cuyas características más importantes son: utilizar disoluciones simples que solo incorporan como principio activo iones Ce3+ en un intervalo de concentración bajo (0.001 a 0.01 M) en un intervalo de temperaturas comprendidos entre 323 K y 363 K. El tipo de sal empleada, el intervalo de concentraciones y de temperaturas, y los tiempos de tratamiento empleados hacen que el tratamiento propuesto posean un enorme atractivo industrial.In summary, to date no treatment similar to that proposed in the present invention has been described whose most important characteristics are: using simple solutions that only incorporate Ce 3+ ions as active ingredient in a low concentration range (0.001 to 0.01 M) in a temperature range between 323 K and 363 K. The type of salt used, the range of concentrations and temperatures, and the treatment times used make the proposed treatment have enormous industrial appeal.
Explicación de la invenciónExplanation of the invention
En esta invención se propone el desarrollo de capas de conversión tomando como punto de partida el conocimiento previo de la microestructura de la aleación a proteger y de su comportamiento frente a la corrosión. Así, el análisis microestructural de las aleaciones de aluminio pone de manifiesto la existencia de diferentes tipos de compuestos intermetálicos dispersos en la matriz. El comportamiento frente a la corrosión de estas aleaciones en medios ricos en cloruros, como disoluciones aireadas de NaCI, viene condicionado por la presencia y distribución superficial de algunos de esos intermetálicos.In this invention the development of conversion layers is proposed taking as a starting point the prior knowledge of the microstructure of the alloy to be protected and of its behavior against corrosion. Thus, the microstructural analysis of aluminum alloys reveals the existence of different types of intermetallic compounds dispersed in the matrix. The behavior against corrosion of these alloys in media rich in chlorides, such as aerated NaCI solutions, is conditioned by the presence and surface distribution of some of these intermetallics.
Así, por ejemplo, cuando la aleación de aluminio-magnesio AA5083 se expone a una disolución aireada de NaCI al 3.5% el principal proceso de corrosión que tiene lugar en la superficie de dicha aleación es la corrosión alcalina localizada (LAC) en el entorno de los precipitados ricos en hierro, que actúan como cátodos permanentes, sin que el resto de los precipitados se vean afectados. Simultáneamente al proceso LAC, tiene lugar un segundo proceso consistente en la formación de una capa protectora de óxido sobre la matriz metálica cuyo espesor crece con el tiempo de exposición.Thus, for example, when the aluminum-magnesium alloy AA5083 is exposed to an aerated solution of 3.5% NaCI, the main corrosion process that takes place on the surface of said alloy is localized alkaline corrosion (LAC) in the environment of the iron-rich precipitates, which act as permanent cathodes, without the rest of the precipitates are affected. Simultaneously with the LAC process, a second process takes place consisting of the formation of a protective oxide layer on the metal matrix, the thickness of which increases with exposure time.
El diseño de un sistema de protección eficaz frente a la corrosión de las aleaciones de este tipo en disoluciones de NaCI debe orientarse hacia la minimización del proceso catódico desarrollado en los intermetálicos ricos en hierro. Una estrategia, de diseño podría basarse en el empleo de inhibidores catódicos. En este caso se han empleado sales lantánidas, habiéndose obtenido los mejores resultados al utilizar sales de cerio (III).The design of an effective corrosion protection system for alloys of this type in NaCI solutions should be oriented towards minimizing the cathodic process developed in iron-rich intermetallics. A design strategy could be based on the use of cathodic inhibitors. In this case, lanthanide salts have been used, having obtained the best results when using cerium (III) salts.
Cuando los cationes Ln3+ actúan como inhibidores se produce la formación de un compuesto lantánido altamente insoluble como consecuencia de la reacción del catión con los iones OH" generados en la reacción catódica que tiene lugar sobre los precipitados catódicos, bloqueando la reacción catódica de reducción de oxígeno y, consecuentemente, el proceso LAC. Durante el proceso de inmersión de la aleación en la sal lantánida se desarrolla una capa mixta formada por islas dispersas con alto contenido en cerio, localizadas sobre los intermetálicos catódicos, y una capa de óxido de aluminio que recubre el resto de la matriz. La capa mixta desarrollada en los tratamientos de inmersión es altamente protectora debido a que, tras estos tratamientos, toda la superficie del material queda cubierta. La capa mixta desarrollada disminuye la actividad del sistema en un factor próximo a 25 y su resistencia, en relación con la capa desarrollada en NaCI, aumenta en un factor del orden de 42. No obstante, para obtener los mejores resultados son necesarios tiempos de tratamiento de 48 horas de duración, lo que disminuye la viabilidad industrial de la invención.When Ln 3+ cations act as inhibitors the formation of a highly insoluble lanthanide compound resulting from the reaction of the cation with the OH "ions generated in the cathode reaction occurring on cathode precipitates, blocking occurs the cathodic reduction reaction oxygen and, consequently, the LAC process.During the immersion process of the alloy in the lanthanide salt, a mixed layer is developed, made up of dispersed islands with a high cerium content, located on cathode intermetallics, and a layer of aluminum oxide covering the rest of the matrix. The mixed layer developed in the immersion treatments is highly protective because, after these treatments, the entire surface of the material is covered. The developed mixed layer decreases the activity of the system by a factor close to 25 and its resistance, in relation to the layer developed in NaCI, increases by a factor of the ord in of 42. However, to obtain the best results, treatment times of 48 hours are necessary, which reduces the industrial viability of the invention.
Al objeto de acortar los tiempos de tratamiento, en la presente invención se propone utilizar un procedimiento de activación térmica, procedimiento que ha permitido obtener unos excelentes resultados de protección frente a la corrosión, disminuyendo apreciablemente los tiempos de tratamiento, y por lo tanto los costos del proceso.In order to shorten the treatment times, in the present invention it is proposed to use a thermal activation procedure, a procedure that has allowed obtaining excellent results of protection against corrosion, significantly reducing treatment times, and therefore costs of process.
Las capas de conversión se desarrollarán mediante inmersión de muestras de aleaciones de aluminio en disoluciones acuosas a diferentes temperaturas de utilizando Ce(N03)3 o CeCI3 en un intervalo de concentraciones de 0.001 a 0.01 M.The conversion layers will be developed by immersing samples of aluminum alloys in aqueous solutions at different temperatures using Ce (N0 3 ) 3 or CeCI 3 in a concentration range of 0.001 to 0.01 M.
Con anterioridad a su inmersión en el baño las muestras serán sometidas a un tratamiento que aseguren la ausencia de restos de óxidos y grasa sobre su superficie. Seguidamente, las muestras se introducirán en disoluciones preparadas previamente en el intervalo de concentraciones citado, si bien los mejores resultados se obtienen al utilizar concentraciones 0.001 a 0.01 M de Ce(N03)3 o 0.001 a 0.01 M de CeCI3. Antes de sumergir las muestras en la disolución correspondiente, esta se habrá calentado a la temperatura adecuada.Before being immersed in the bath, the samples will be subjected to a treatment that ensures the absence of traces of oxides and grease on their surface. Subsequently, the samples will be introduced into previously prepared solutions in the mentioned concentration range, although the best results are obtained by using concentrations 0.001 to 0.01 M Ce (N0 3 ) 3 or 0.001 to 0.01 M CeCI 3 . Before immersing the samples in the corresponding solution, it must have been heated to the appropriate temperature.
En la siguiente tabla se muestran los tratamientos de activación térmica en función de la temperatura del tratamiento, la sal de cerio empleada y el tiempo de duración del tratamiento.The following table shows the thermal activation treatments depending on the treatment temperature, the cerium salt used and the duration of the treatment.
Figure imgf000005_0001
Figure imgf000005_0001
En otra variante del proceso, diferentes cantidades de peróxido de hidrógeno se añadirán a disoluciones de Ce(N03)3 0.001 a 0.01 M una vez que estas hayan alcanzado la temperatura de trabajo.In another variant of the process, different amounts of hydrogen peroxide will be added to Ce (N0 3 ) 3 0.001 to 0.01 M solutions once they have reached the working temperature.
En la siguiente tabla se muestran los tratamientos mixtos de activación térmica- activación química, enumerándose los tratamientos en función de la temperatura del tratamiento, la concentración de H202 en el baño y del tiempo de duración del tratamiento.The following table shows the mixed thermal activation-chemical activation treatments, listing the treatments according to the temperature of the treatment, the concentration of H 2 0 2 in the bath and the duration of the treatment.
Temperatura (K) Tratamiento Concentración H2Q2 (mi/I) Tiempo (minutos)Temperature (K) Treatment Concentration H 2 Q 2 (mi / I) Time (minutes)
300-400 Ce(N03)3 0.5-30 0-30300-400 Ce (N0 3 ) 3 0.5-30 0-30
Las ventajas que se consiguen con la aplicación de este procedimiento son:The advantages obtained with the application of this procedure are:
1 ) El sistema propuesto evita el empleo de baños de cromo en los procesos de tratamientos superficiales de aleaciones de aluminio. Los cromatos son sustituidos por sales lantánidas totalmente inocuas.1) The proposed system avoids the use of chrome baths in the aluminum alloy surface treatment processes. The chromates are replaced by totally harmless lanthanide salts.
2) El sistema permite el desarrollo de capas mixtas formadas por precipitados de cerio ubicados sobre los compuestos intermetálicos de carácter catódico y una película de alúmina que cubre la matriz metálica.2) The system allows the development of mixed layers formed by cerium precipitates located on the cathodic intermetallic compounds and an alumina film that covers the metallic matrix.
3) Con este sistema se consigue la optimización del tiempo de tratamiento y por tanto el abaratamiento de los costes. Cuando estos tratamientos se efectúan a temperatura ambiente el tiempo óptimo de tratamiento se ve condicionado por la lentitud con la que se desarrolla la película de óxido sobre la matriz. La activación térmica de la disolución de Ce(lll) provoca un crecimiento más rápido de esta película y un mayor grado de cubrimiento de la capa mixta proporcionando un nivel de protección mayor que en los tratamientos efectuados a temperatura ambiente.3) With this system the optimization of the treatment time is achieved and therefore the cost reduction. When these treatments are carried out at room temperature, the optimal treatment time is determined by the slowness with which the oxide film develops on the matrix. Thermal activation of the Ce (lll) solution causes faster growth of this film and a higher degree of coverage of the mixed layer providing a higher level of protection than in treatments carried out at room temperature.
4) Cuando se desarrollan estos tratamientos en disoluciones de Ce(N03)3 y CeCI3 se consigue un descenso en la actividad del sistema en un factor próximo a 850 y un aumento en la resistencia de la capa mixta en un factor cercano a 1500. Estos resultados son notablemente superiores a los obtenidos a temperatura ambiente, habiéndose llegado a reducir el tiempo de tratamiento en un factor 200.4) When these treatments are developed in solutions of Ce (N0 3 ) 3 and CeCI 3 , a decrease in the activity of the system is achieved by a factor close to 850 and an increase in the resistance of the mixed layer by a factor close to 1500. These results are notably superior to those obtained at room temperature, having reduced the treatment time by a factor of 200.
5) Las muestras tratadas en estas condiciones superan los estándares impuestos, por ejemplo por la industria aeronáutica para este tipo de tratamientos (168 h en cámara de niebla salina), lo que, unido al corto tiempo de tratamiento, los hace viables y aconsejables desde el punto de vista industrial.5) The samples treated under these conditions exceed the standards imposed, for example by the aeronautical industry for this type of treatment (168 h in a salt spray chamber), which, together with the short treatment time, makes them viable and advisable from the industrial point of view.
Modo de realización de la invención.Embodiment of the invention.
El procedimiento descrito consta de las siguientes fases:The described procedure consists of the following phases:
1 Preparación de la muestra: Las muestras serán sometidas a los tratamientos de limpieza previos, habituales para la obtención de capas de conversión. Es por tanto posible, utilizar baño de desengrase y de decapado que se comercializan para tal efecto.1 Preparation of the sample: The samples will be submitted to the previous cleaning treatments, usual for obtaining conversion layers. It is therefore possible to use a degreasing and pickling bath that are marketed for this purpose.
Si la aplicación así lo requiere el estado superficial de las muestras se homogenizará mediante pulido.If the application requires it, the surface state of the samples will be homogenized by polishing.
Finalmente, se procederá a su limpieza cuidadosa con agua destilada, y serán secadas inmediatamente con aire comprimido.Finally, they will be carefully cleaned with distilled water, and they will be dried immediately with compressed air.
2. Desarrollo de la capa de conversión: Los tratamientos por activación térmica consistense pueden realizar en un intervalo de concentraciones comprendido entre 0.001 y 0.01 M, si bien los mejores resultados se obtienen al utilizar: 1 ) disoluciones acuosas de Ce(N03)30.001 a 0.01 M 2) disoluciones acuosas de CeCI30.001 a 0.01 M. Estas disoluciones se mantienen durante todo el tratamiento a una determinada temperatura, entre 323 K y 363 K, y durante intervalos de tiempo comprendidos entre 0 y2. Development of the conversion layer: Consistent thermal activation treatments can be carried out in a concentration range between 0.001 and 0.01 M, although the best results are obtained by using: 1) aqueous solutions of Ce (N0 3 ) 3 0.001 to 0.01 M 2) CeCI 3 aqueous solutions 0.001 to 0.01 M. These solutions are maintained throughout the treatment at a certain temperature, between 323 K and 363 K, and for time intervals between 0 and
120 minutos. A su vez, y a modo comparativo, se realizan tratamientos a 298 K en periodos de tiempo comprendidos entre 1 y 5 días. Las muestras no se sumergirán en las disoluciones hasta que estas no hayan alcanzado la temperatura de trabajo deseada.120 minutes. In turn, and by way of comparison, treatments are carried out at 298 K in periods of time between 1 and 5 days. The samples will not be immersed in the solutions until they have reached the desired working temperature.
En la variante que incluye activación química, se añadirán a las disoluciones de Ce(N03)3 0.001 a 0.01 M cantidades de H202 de 0.675, 1.25 y 2.5 mililitros por litro de disolución. Estas cantidades de no se añadirán hasta que la disolución inicial no haya alcanzado la temperatura de trabajo deseada.In the variant that includes chemical activation, amounts of H 2 0 2 of 0.675, 1.25 and 2.5 milliliters per liter of solution will be added to the Ce (N0 3 ) 3 0.001 to 0.01 M solutions. These amounts will not be added until the initial solution has reached the desired working temperature.
Para el desarrollo de las capas, se emplean disoluciones acuosas aireadas deFor the development of the layers, aerated aqueous solutions of
Ce(N03)3 0.001 a 0.01 M y CeCI3 0.001 a 0.01 M. Los reactivos empleados para su preparación son: CeCI3 -7H20 de Fluka, de pureza superior al 98.5%, y Ce(N03)3 -6H20 de Fluka o similar, de pureza superior al 99.0%. Estos se añaden a agua de calidad destilada y se homogeniza la muestra mediante un agitador magnético.Ce (N0 3 ) 3 0.001 to 0.01 M and CeCI 3 0.001 to 0.01 M. The reagents used for its preparation are: CeCI 3 -7H 2 0 from Fluka, with a purity greater than 98.5%, and Ce (N0 3 ) 3 - Fluka 6H 2 0 or similar, with a purity greater than 99.0%. These are added to distilled quality water and the sample is homogenized by means of a magnetic stirrer.
En la variante que incluye activación química las disoluciones originales se preparan de idéntica manera disoluciones de Ce(N03)3 0.001 a 0.01 M, pero una vez que alcancen la temperatura deseada, se le añade H202 en concentraciones de 0.675, 1.25 y 2.5 mlJL. El peróxido de hidrógeno empleado es al 30% p/v de Panreac o similar.In the variant that includes chemical activation, the original solutions are prepared in the same way as solutions of Ce (N0 3 ) 3 0.001 to 0.01 M, but once they reach the desired temperature, H 2 0 2 is added in concentrations of 0.675, 1.25 and 2.5 mlJL. The hydrogen peroxide used is 30% w / v of Panreac or the like.
3. Lavado y secado: Una vez preparadas las capas de conversión, las muestras se lavaran con agua destilada y se secaran al aire.3. Washing and drying: Once the conversion layers have been prepared, the samples will be washed with distilled water and air-dried.
Con objeto de estudiar del comportamiento frente a la corrosión de las muestras tratadas se efectuaron ensayos de cámara de niebla salina de 168 horas de duración, de acuerdo con la Norma ASTM B-117 de ensayos normalizados de resistencia a la corrosión por niebla salina. Este tipo de ensayos son los más extendidos en la industria de los tratamientos superficiales. Tras esta evaluación, las muestras tratadas no mostraban signos de corrosión.In order to study the behavior against corrosion of the treated samples, salt spray chamber tests of 168 hours duration were carried out, in accordance with ASTM Standard B-117 of standard tests of resistance to corrosion by salt spray. These types of tests are the most widespread in the surface treatment industry. After this evaluation, the treated samples showed no signs of corrosion.
La resistencia frente a la corrosión de las muestras tratadas fue evaluada haciendo uso de técnicas electroquímicas de Polarización Lineal y Resistencia de Polarización en disolución aireada de NaCI al 3,5%. La realización de estas medidas se llevó a cabo en una celda plana K235 de Pare EG&G, haciendo uso de un potenciostato SI 1287 de Solartron.The resistance against corrosion of the treated samples was evaluated using the electrochemical techniques of Linear Polarization and Polarization Resistance in aerated solution of 3.5% NaCI. These measurements were carried out in a K235 flat cell from Pare EG&G, using a SI 1287 potentiostat from Solartron.
Como electrodo de referencia se empleó uno de Ag/AgCI de Crison. Las muestras así evaluadas presentaron un valor de incremento a la resistencia a la polarización ΔRP del orden de hasta 850, lo que implica una mejora en un factor próximo a 40 con respecto a los tratamientos de inmersión a temperatura ambiente, y en un tiempos de tratamiento de hasta 200 veces menor.A Crison Ag / AgCI one was used as the reference electrode. The samples thus evaluated presented a value of increase in resistance to polarization ΔR P of the order of up to 850, which implies an improvement of a factor close to 40 with respect to immersion treatments at room temperature, and in a time of up to 200 times less treatment.
Los resultados obtenidos en estos trabajos permiten concluir que la capa desarrollada disminuye la actividad del sistema en un factor próximo a 850 y su resistencia, en relación con la capa desarrollada en NaCI, aumenta en un factor del orden de 42.The results obtained in these works allow us to conclude that the developed layer decreases the activity of the system by a factor close to 850 and its resistance, in relation to the layer developed in NaCI, increases by a factor of the order of 42.
Manera en que la invención es susceptible de aplicación industrial.Way in which the invention is susceptible of industrial application.
La invención puede resultar de interés en la industria de los tratamientos superficiales del aluminio, en su aplicación naval, aeroespacial, automovilística, decorativa, arquitectónica, y en definitiva, en todas aquellas especialidades en la que el empleo del aluminio requiera de protección anticorrosiva.The invention may be of interest in the aluminum surface treatment industry, in its naval, aerospace, automotive, decorative, architectural application, and ultimately, in all those specialties in which the use of aluminum requires anticorrosive protection.
Todo el material y reactivos químicos objeto de la invención se puede encontrar en el mercado con otras aplicaciones y ser posteriormente adaptados según la explicación. All the material and chemical reagents object of the invention can be found in the market with other applications and be subsequently adapted according to the explanation.

Claims

REIVINDICACIONES
1.- Procedimiento para la obtención de capas de conversión libres de cromatos sobre aleaciones de aluminio, caracterizado por el empleo de sales de cerio.1.- Procedure for obtaining chromate-free conversion layers on aluminum alloys, characterized by the use of cerium salts.
2.- Procedimiento para la obtención de capas de conversión libres de cromatos sobre aleaciones de aluminio, según reivindicación 1, caracterizado por comprender un tratamiento de inmersión en sales de cerio y un proceso de activación térmica que reduce el tiempo necesario de tratamiento.2. Procedure for obtaining chromate-free conversion layers on aluminum alloys, according to claim 1, characterized in that it comprises an immersion treatment in cerium salts and a thermal activation process that reduces the necessary treatment time.
3.- Procedimiento para la obtención de capas de conversión libres de cromatos sobre aleaciones de aluminio, según reivindicaciones 1 y 2 , caracterizado porque consta de las siguientes fases:3. Procedure for obtaining chromate-free conversion layers on aluminum alloys, according to claims 1 and 2, characterized in that it consists of the following phases:
- Preparación de las disoluciones. - Aplicación de tratamientos de inmersión a temperaturas y tiempos determinados.- Preparation of solutions. - Application of immersion treatments at certain temperatures and times.
- Limpieza con agua destilada y secado de las piezas.- Cleaning with distilled water and drying the pieces.
- Evaluación del resultado del tratamiento mediante ensayos en cámara de niebla salina o técnicas electroquímicas.- Evaluation of the treatment result by salt spray chamber tests or electrochemical techniques.
4.- Procedimiento para la obtención de capas de conversión libres de cromatos sobre aleaciones de aluminio, según reivindicaciones 1, 2 y 3, caracterizado porque las disoluciones a emplear se preparan con sales de cerio del tipo Ce(NOs)3 o CeCI3 a concentraciones entre 0.001 a 0.01 M, que evitan el empleo de baños de cromatos.4. Procedure for obtaining chromate-free conversion layers on aluminum alloys, according to claims 1, 2 and 3, characterized in that the solutions to be used are prepared with cerium salts of the type Ce (NOs) 3 or CeCI 3 a concentrations between 0.001 to 0.01 M, which avoid the use of chromate baths.
5.- Procedimiento para la obtención de capas de conversión libres de cromatos sobre aleaciones de aluminio, según reivindicaciones 1, 2, 3 y 4, caracterizado porque las muestras de aluminio se sumergen en disoluciones Ce(N03)3 entre 0.001 a 0.01 M o CeCb entre 0.001 a 0.01 M, durante intervalos de tiempo definidos y a temperaturas de trabajo determinadas.5. Procedure for obtaining chromate-free conversion layers on aluminum alloys, according to claims 1, 2, 3 and 4, characterized in that the aluminum samples are immersed in solutions Ce (N0 3 ) 3 between 0.001 to 0.01 M or CeCb between 0.001 to 0.01 M, during defined time intervals and at determined working temperatures.
6.- Sistema para la obtención de capas de conversión libres de cromatos sobre aleaciones de aluminio, según reivindicación 1, caracterizado por comprender un tratamiento de inmersión en sales de cerio y un proceso de activación térmico-química, mediante el empleo de disolusiones con peróxido de hidrógeno.6. System for obtaining chromate-free conversion layers on aluminum alloys, according to claim 1, characterized by comprising an immersion treatment in cerium salts and a thermal-chemical activation process, by means of the use of peroxide dissolutions. of hydrogen.
7.- Sistema para el desarrollo de capas de conversión sobre aleaciones de aluminio basadas en el empleo de sales de cerio, según reivindicaciones 1 y 6, caracterizado porque las muestras de aluminio se sumergen en disoluciones Ce(N03)3 entre 0.001 M a 0.01 M, con concentraciones determinadas de H202, durante intervalos de tiempo definidos. 7. System for the development of conversion layers on aluminum alloys based on the use of cerium salts, according to claims 1 and 6, characterized in that the aluminum samples are immersed in solutions Ce (N0 3 ) 3 between 0.001 M a 0.01 M, with determined concentrations of H 2 0 2 , during defined time intervals.
PCT/ES2003/000665 2002-12-27 2003-12-26 Method of obtaining chromate-free conversion coatings on aluminium alloys WO2004059035A1 (en)

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EP0534120A1 (en) * 1991-09-27 1993-03-31 Hughes Aircraft Company Chromium-free method and composition to protect aluminium
US5362335A (en) * 1993-03-25 1994-11-08 General Motors Corporation Rare earth coating process for aluminum alloys
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US5194138A (en) * 1990-07-20 1993-03-16 The University Of Southern California Method for creating a corrosion-resistant aluminum surface
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EP2915903A1 (en) 2014-03-05 2015-09-09 The Boeing Company Chromium-free conversion coating
US9290846B2 (en) 2014-03-05 2016-03-22 The Boeing Company Chromium-free conversion coating

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