ITMI20082275A1 - ELECTROLYTIC PROCEDURE FOR OBTAINING DARK OR BLACK COVERINGS ON NON-FERROUS METAL MATERIALS - Google Patents

Description

OBJECT OF THE INVENTION

The present invention relates to a process for the electrolytic treatment of non-ferrous metal materials such as for example magnesium, aluminum, titanium, vanadium, tantalum and hafnium and their alloys, in particular a process for the production of a surface coating which has both function aesthetic than protective. This coating is characterized by the fact that it has a dark or black color produced at the same time as its formation. Also object of the present invention are the products made of non-ferrous metal material, provided with a surface coating obtained according to the aforesaid process.

STATE OF THE TECHNIQUE

In recent years there has been a notable development in the use of metals such as magnesium, titanium, their alloys, while it has been kept alive and indeed, the use of aluminum or its alloys, for example alloys with a high silicon content, has increasingly increased. . Furthermore, also metals such as tantalum and hafnium have found increasing application, also from an industrial point of view. The increase in demand in the use of these materials is not matched by an adequate development of surface treatment technologies, necessary for subsequent metal processing and for the uses for which they are intended.

Increasing interest is currently aimed at the possibility of creating products composed of several metals, to be able, for example, to combine and therefore exploit the lightness of magnesium with the rigidity or mechanical characteristics of titanium. Again by way of example, among the metals mentioned above, aluminum, magnesium and titanium have always been treated separately and, often with regard to the last two, inadequate to the technical needs of the market.

Aluminum, in its extrusion and rolling alloys, provides for well-defined treatments such as, for example, the anodic oxidation or anodization treatment and painting.

As for the anodic oxidation treatment, this is conventionally carried out in sulfuric acid solutions (160 - 220 g / 1). The anodic layer thus formed can be further treated, for example it can be colored either by absorption, i.e. by immersing the aluminum pieces in solutions of organic or inorganic dyes, or by electrolytically treating the pieces under current in suitable solutions based on salts of tin or nickel. After a pore-closing treatment of the oxide that formed during the anodizing phase and which is conventionally called "fixing", the aluminum products thus produced show excellent resistance to corrosion and, if colored, the colors imparted have a suitable light fastness.

Similarly to other metals, aluminum can also be painted. In this case it is necessary to proceed to a preliminary phase, which involves a "chemical conversion" treatment, at the end of which it is possible to apply a paint that can be of the "powder" or "liquid" type. Once painted, the product must be subjected to a "firing" treatment which generally consists of a hot polymerization of the paint. The material thus obtained shows good light fastness and good resistance to corrosion.

Aluminum finishes have been defined for years now, but among others, the problem of how to treat alloys with a high silicon content, such as some alloys for diecasting, remains unsolved. When the silicon percentage of the aluminum alloy exceeds 5%, both the anodic oxidation and the painting process become difficult, and the quality of the manufactured article is often poor. As for magnesium, on the other hand, it is necessary to take into account that until about ten years ago it was considered a metal for particular applications, in case it was necessary to make the most of its mechanical characteristics and lightness. In recent years, however, due to the sharp price reduction due to the high market offer, its use has become more extensive and competitive, for example with respect to aluminum, also due to its better characteristics of lightness and malleability. In practice, a magnesium alloy weighs about 35% less than a similar aluminum alloy with similar mechanical characteristics and can also be "cast" in much finer thicknesses and without the formation of "bubbles". Magnesium is also frequently used instead of plastic for refined applications such as the shells for laptops, cameras or CD players and is also partially replacing aluminum in mechanical die-castings.

The corrosion resistance of magnesium and its alloys is very poor and, in the absence of surface treatments, it is inadequate for most applications. Until a few years ago all the magnesium material was destined to be painted after chemical conversion treatment, but in any case, even with regard to magnesium, the best treatments, both as such and preliminary to painting, remain those of anodizing.

The operational complexity, the toxicity of the aforementioned processes and / or the not exceptional resistance to corrosion and abrasion of the materials thus treated, over time, have led to the formulation of new technologies.

A typical scheme for the anodizing treatment, common to all the treatments usually used, is the following:

a) Alkaline degreasing

b) Washing in running water

c) Acid pickling (activation)

d) Washing in running water

e) Anodizing in direct or alternating current

f) Washing in running water

g) Washing in deionized water

h) Washing in hot deionized water

i) Fixing (chemical or by means of resins).

Broadly speaking, we can say that the most recently developed treatments, chromium-free and with low toxicity, have the following characteristics:

1) produce colorless coatings,

2) use medium or high alkalinity treatment solutions,

3) guarantee a substrate with excellent adhesion for paints,

4) guarantee the substrate medium or high resistance to corrosion (depending on the type of treatment),

5) guarantee medium or high abrasion resistance to the substrate (depending on the type of treatment),

6) allow the use of direct or alternating current, characterized by high voltage (150 - 600 V) and in some cases also high current density (3 - 30 A / dm <2>).

It should be borne in mind that, in some processes, there is an intense "brightness" that surrounds the piece under treatment, due to a dense series of discharges that reach it and contribute to the formation of the protective layer.

As for titanium, the most common treatment, also in this case, is that of anodic oxidation, produced, similarly to what happens for aluminum, both in an acidic and alkaline environment. Anodizing in an acidic environment (indifferently produced by sulfuric or phosphoric acid) produces colored coatings (due to interference effect), whose hue depends on the applied voltage (15-100 Volts) and the purity of the alloys. The oxide layer thus formed contributes to the aesthetic appearance of the pieces and finds a particular application in the dental technology sector and in prostheses more generally, because the color imparted serves to identify the mechanical characteristics of the piece itself. There is no procedure described for the treatment of pieces formed by coupling parts of different metals selected for example from aluminum, magnesium, titanium or their alloys.

The oxide layer formed by discharge (for example both in the case of magnesium and aluminum materials) is mainly formed by two components: a more compact one with a thickness of 10-20 microns depending on the duration of the process and a much more rough one than thickness of 2-3 microns. This happens because the discharges that reach the surface of the metal compress the underlying layers, increasing their compactness and hardness and, obviously, the outermost parts are made rough by the discharges themselves. In common industrial practice it is customary to mechanically eliminate the first 2-3 microns of the layer produced in order to fully exploit the hardness properties of the remaining part of the layer.

In summary, the processes according to the known art have the following drawbacks.

- All processes that involve the discharge effect (micro ares or plasma) are very expensive.

- The solutions of the anodizing baths that contain silicates and / or aluminum are not very stable and tend to form precipitates which must be eliminated for a better functioning of the solution itself. It is also difficult to keep the composition of the solution constantly monitored.

- The compositions containing salts of fluorine, boron and animins are toxic, and difficult to manage and maintain.

- Often the compositions contain mixtures of anions and / or cations whose control and balancing during the management phase of an industrial tank for the anodization treatment are difficult.

- All the processes according to the known art (regardless of the metal considered), provide for one or more preliminary cleaning, pickling and / or activation steps of the surface to be treated. The degreasing products to be used often contain borates, while the "activation" products contain mainly fluorinated compounds in an acid environment (hydrofluoric acid, its compounds or derivatives).

- None of the claimed processes envisages being able to treat coupled or mixed materials or materials made by alloying or otherwise combining different metals.

- Furthermore, the anodizing baths according to the known art do not allow to treat several different metals at the same time, but require a different bath for each type of metal to be subjected to the anodizing process and therefore additional costs for replacing the bath each time need to treat a different type of metal.

A further problem that can be highlighted, directly correlated to the processes according to the known art described above, relates to the need to obtain the surface of the metal thus treated with a shade of dark and / or black color, especially as regards magnesium and aluminum. In fact, a very dark / black color finds some very interesting specialized applications, such as for example that relating to the use of panels as solar collectors (which are generally made of both aluminum and magnesium) or that relating to the wheels of motorcycles or go-karts that for weight reasons, they are currently preferably made of magnesium.

Conventional methods are known, for example, for coloring previously anodized aluminum in sulfuric acid solutions black. One system is based on the coloring of the metal piece by absorption by immersion in suitable organic dyes very similar to those used for fabrics. Alternatively, the dark coloring is carried out by electrolytically depositing metal particles of suitable metals such as tin, nickel, cobalt and copper on the surface of the metal to be colored. However, these methods require the presence of an aluminum oxide layer and, as a final result, reduce the thermal conduction of the metal once the coloring treatment is completed.

Another system for obtaining a dark / black color on non-ferrous metal materials and their alloys treated as previously described, is that which involves the deposition of black nickel, but also in this case technical and environmental problems of great importance arise.

In the case of the dark or black coloring of magnesium, it is also advisable to highlight other aspects. In fact, some processes involving magnesium-based materials, involve the coloring of the metal, including dark and / or black coloring, by "color absorption" in the layer formed by anodic method on the metal substrate. The results obtained with this technique, they are very poor from an aesthetic point of view and strongly depend on the characteristics of the starting material. It must in fact be considered that certain metal products have a significant market only if they are aesthetically attractive. For example, it is unthinkable to market a ZK60 magnesium alloy wheel which, colored black by immersion, has areas of different shades. In this case, the poor result is achieved as the coloring by absorption highlights the macro crystals generated during the forging phase, and consequently takes on different shades depending on the distribution of the aforementioned crystals on the piece to be colored.

AIMS OF THE INVENTION

The purpose of the present invention is to provide a process for the surface treatment of non-ferrous metal materials which is economical, which does not involve the use of toxic or potentially harmful substances and which is capable of generating a dark or black color on the surface of the treated material.

It is also an object of the present invention to provide a process for the surface treatment of non-ferrous metallic materials which provides for the use of stable solutions, with a constant composition, which does not require frequent replacement of the solutions used and which is capable of generating a dark or black color on the surface of the treated material.

Another object of the present invention is to provide a process for the surface treatment of non-ferrous metal materials which does not provide for distinct preliminary cleaning, and / or degreasing and / or activation phases of the metal surfaces which must be subjected to treatment and which therefore allows to carry out the surface treatment of the metallic material in a single main stage, obtaining a dark or black color.

Another object of the present invention is to provide a process for the surface treatment of non-ferrous metal materials which allows the simultaneous treatment of different metals and / or products made in different parts with different metals and / or non-ferrous metal alloys. ferrous, within the same bathroom.

Another object of the invention is to provide a method for the surface treatment of non-ferrous metal materials which allows the simultaneous surface treatment of coupled, mixed materials or materials made by combining alloys or other materials of different metals, with consequent advantages also from the economic point of view.

A further object of the present invention is to provide non-ferrous metals, materials and products made using said metals and / or their alloys, provided with a surface coating obtained by the process object of the present invention and which is therefore dark or black in color. .

DESCRIPTION

These and other objects and related advantages, which will be better highlighted by the following description, are achieved by an electrolytic process for the treatment of non-ferrous metal materials which comprises at least one main treatment phase or anodic phase carried out in a tank or cell, said phase being made by using an alkaline solution which comprises at least one metal ion selected from iron, cobalt or nickel in a concentration greater than or equal to 0.1 g / i.

In particular, according to the present invention, said metal ions, which can also be used in a mixture with each other, are present in a concentration between 1 and 2 g / 1.

This process, thanks to its innovative characteristics, allows to obtain a dark or black, uniform, compact and aesthetically pleasing color on the treated material, which cannot be reached with the coloring procedures according to the known technique.

The process according to the invention has as a further advantage the possibility of carrying out the simultaneous treatment of metallic materials, even different from each other, and / or materials made by alloy association and / or coupling and / or other kind of association of different metals.

In particular, said alkaline solution comprises phosphoric acid, ammonia and / or alkaline hydroxides, and has a pH value between 7 and 10. In particular, said ammonia and / or said alkaline hydroxides are selected from lithium hydroxide, sodium hydroxide , potassium hydroxide, where said alkaline hydroxides are present in a concentration between 3 and 150 g / I, preferably in a concentration between 45 and 60 g / 1, said phosphoric acid is present in a concentration between 1 and 50 g / 1, preferably at a concentration between 15 and 20 g / 1, while said metal ion chosen from iron, cobalt or nickel is present in quantities from 0.1 g / 1 up to maximum solubility, with the only condition that these ions are stable in the solution base indicated above.

In some cases, it may be convenient to provide for the addition, as an adjuvant of stability, of some organic oxyacids (or their preferably ammoniacal salts) such as for example oxalic, citric and tartaric acids. Their quantity, if present, can vary until reaching a concentration at which maximum solubility is obtained under operating conditions. In some cases, the addition of hydrogen peroxide (hydrogen peroxide) has proved to be advantageous to bring said metal ions to the maximum stable chemical value under the operating conditions of the base solution indicated above. The concentration of hydrogen peroxide can, for example, be between 0 and 50 It is not necessary that there be a rigid stoichiometric ratio between the various components of the solution.

Said non-ferrous metals to be treated are advantageously selected from aluminum, titanium, magnesium, vanadium, tantalum and hafnium.

The process according to the present invention, therefore, allows to obtain a dark or black coloring of the surface of the non-ferrous metal to be subjected to treatment, by means of a single passage in a single solution, with extremely satisfactory results, contrary to what happens instead if one use the techniques according to known part.

The process according to the present invention also offers numerous other advantages, and in particular allows to eliminate the pre-treatment steps, normally provided for in the processes according to known Part. In practice, with the process object of the invention, the distinct preliminary phases of cleaning, and / or degreasing and / or activation of the metal surfaces to be treated, for example to achieve a surface anodic oxidation, are completely eliminated, and it is possible to use a single tank or bath for the main treatment phase, without having to resort to a succession of different tanks, containing different solutions, to carry out, respectively, for example, the cleaning phase, then the degreasing phase, and finally that of activating the surface of the material to be treated. In this way, it is possible to carry out the main anodizing treatment as a single phase, and it is thus possible to create a system that does not include a series of successive tanks, but a single main tank, with consequent considerable advantages, both in relation to the dimensions of the plant, which also benefits of an economic nature.

Again with the process object of the invention, it is possible to carry out the main anodizing treatment, and the simultaneous dark or black coloring of the surface, of non-ferrous metallic materials, even different from each other, or even on products made up of different non-ferrous metals combined with each other. inside of the same material or on materials made at least partially, in non-ferrous metal alloys. Such combinations of metals lead in any case to the formation of a surface layer of dark or black color which is homogeneous, uniform and aesthetically valuable, with the achievement of the purposes indicated above in detail.

The foregoing represents a significant technical progress with respect to the anodizing processes according to the known technique, on the basis of which it was always necessary to provide separate and distinct tanks from the main one, to carry out the so-called pre-treatments (cleaning, and / or degreasing and / or activation). In fact, the pre-treatments according to the known art are carried out through the use of different solutions, at different concentrations and, in some cases even only through the use of water. For this reason, it is necessary to carry out each single step in a different tub or bathroom, in order to use the most suitable solution for the type of treatment to be carried out in view of the main anodizing treatment. According to the present invention, moreover, the use of the basic solution as described above, allows to treat at the same time and in the same anodizing tank or bath, non-ferrous metals, even different from each other, or even products made from different metals coupled or associated with each other. or even products made of non-ferrous metal alloys. With the procedures according to the known art, however, it was necessary to carry out a specific anodizing treatment for each type of metal and it was not possible to treat different metals simultaneously and in the same bath.

As regards the realization of the dark or black coloring on the surface of non-ferrous metals according to the present invention, the advantages achieved with respect to what can be obtained using the coloring techniques according to the known art, are for example the following.

For example, in the case of aluminum, if you want to achieve a dark or black color on the surface of the piece using the techniques of the known art, it is essential to previously form an anodic oxide layer to be subjected to absorption coloring, to be made using a suitable solution of organic dyes very similar to those used for dyeing fabrics. The fundamental drawbacks of this technique are represented by the high commercial cost of the dyes to be used and by the high difficulty of eliminating waste water and exhausted or in any case no longer functioning solutions.

According to the known art, aluminum can be colored dark or black also by electrolytic coloring in solutions of metal salts. Even in this case, however, a special tank connected to a power supply is required, with consequent increased costs, linked to the consumption of electricity and the use of chemicals necessary for coloring.

Furthermore, in some specific sectors such as that of solar collectors, these techniques, even if they give black colors, do not allow an optimal yield of the energy managed by the panels object of the invention.

As far as magnesium is concerned, the coloring procedures according to the known art do not guarantee the quality and reproducibility of the colors obtained and if these colors are carried out by color absorption, the procedures used require either intermediate treatments between the anodizing and coloring stages ( for example to be able to use the same dyes as aluminum) or the formulation of ad hoc dyes, with a consequent increase in the costs and times necessary for the development of the process. To be able to color anodized magnesium materials by immersion, it is necessary that the dyes used are stable in an alkaline environment or that in any case do not react with the alkalinity released by the anodized layer when immersed in the coloring solution. Unfortunately, however, dyes suitable for aluminum are used in medium acid solutions which become unstable if brought into contact with any alkalinity, such as that released by osmotic effect from a piece of anodized magnesium immersed in it.

Therefore, one of the main purposes of the present invention is to simplify the existing technology by reducing its operational complexity and the relative costs and to allow to treat in the same solution, for example, magnesium, aluminum and titanium materials (and their alloys) even simultaneously or in pieces. in which they can be coupled in any form, obtaining a uniform, homogeneous and aesthetically valid dark or black color.

For example, in the case of magnesium, for many years the latter has found a specific and highly appreciated use in advanced mechanics, especially for military or aerospace use, where even high finishing costs were easily absorbed by the high added value of the final product. Since, however, the cost of magnesium metal has become comparable, if not lower than that of aluminum, its use has expanded enormously to consumer products, with the consequence that the cost of the finish must be proportionate to the real value. of the produced item.

To contain costs and make the product competitive even with respect to consumer materials, it is therefore necessary to simplify both the chemical and electrical parts (power consumed) of the anodizing process. The process according to the invention allows to achieve the objectives set out above, boasting the characteristics set out below.

With the process object of the invention, it is possible to provide for the elimination of any preliminary cleaning, degreasing and, above all, activation treatment. These treatments, indispensable if the anodization process is carried out according to the known technique, involve the treatment of metallic materials with solutions based, for example, of fluorinated acids or fluorine salts, which constitute both a considerable operational complexity and an environmental problem and health of the workers involved in the process.

The process of the present invention also constitutes a considerable simplification as regards the solution with which the main treatment is carried out, the composition of which is not binding but chosen on the basis of low cost and its operational practicality. The solution must be suitable for treating, even simultaneously, magnesium, aluminum, titanium vanadium, tantalum and afhium. For example, according to the invention, a small quantity of phosphoric acid (for example 15 g / 1) and a variable quantity of ammonia or alkaline hydroxides (lithium, sodium or potassium) in sufficient quantity is essential to bring the pH of the solution to values between pH 7 and 10. An indispensable component for the formation of a dark or black layer is the presence of at least one metal ion chosen from iron, cobalt or nickel in low concentration (for example 2g / l as ion).

The presence of small quantities (for example 10 g / 1) of organic oxyacids such as oxalic, citric and / or tartaric acid, taken individually or in a mixture with each other (or their ammonia salts or alkali metal salts) has proved to be advantageous. hydrogen peroxide (hydrogen peroxide) in similar quantities.

The preferred temperature for carrying out the process object of the invention is between 15-25 ° C, without the need for particularly accurate control. This solution is easy to manage because a filter pump can keep it accurately clear by eliminating all traces of dirt and precipitates.

The electrolytic treatment of the anodizing step is preferably carried out using a known power supply, as described for example in EP 0619643. This power supply is well suited to the purposes indicated, as it is equipped with an automatic adjustment system of the parameters of the deliverable current. . In the electrolytic cell, that is to say in the treatment tank, an electrolyte of the type indicated above is introduced, on the long walls of the same tank two plates, preferably of stainless steel, will be placed, which will essentially perform the function of cathode, while parallel to these, in the part median of the cell or tank, one or more pieces to be treated will be immersed.

The following table shows some examples of treatment, carried out with the process according to the invention, with the obtaining of different thicknesses of the surface layer of oxide that is formed on the metal and the contextual obtaining of the desired dark or black colors. The steps performed by the power supply managed by a suitable computer are indicated. As can be seen, it is preferred to operate at constant current in order to minimize the effect of any variations in the composition or temperature of the solution. If we were to operate at constant voltage we would not have the certainty of the thickness formed (and relative color) because this depends only on the current actually passed (on the basis of Faraday's law).

Table 1 - Example of a treatment program

Phase

Description Waiting Cleaning / activation Waiting Anodizing None Negative current None Positive current current (cathode phase) current (anodic phase) Duration 30 sec. Ramp 30 seconds Duration 5 sec. Ramp 1-5 minutes Current 2.0 A / dm <2> Current 2.0 - 10 Duration 2 minutes A / dm <3>

Duration 1-20 minutes Function Allow to Remove dirt, and Allow the Layer the pieces to be greasy from the surfaces, depolarizing whose color and adequately activating them and and of the pieces and thickness will be wetted by making them reactive elimination function of time solution to the next of the gases produced. of treatment.

anodizing

Notes to the table.

The color generated is a function of the thickness and of the metal ion, considered an essential component and chosen from iron, cobalt or nickel, (also in mixture) present in solution. Usually very dark or black colors are produced with oxide thicknesses of 15-20 microns, which are usually obtained in the times indicated above.

Working with constant current, the voltage increases as the treatment time increases; its final value obviously depends on the applied current density but it remains on average below 350 volts.

It should be borne in mind that it is however difficult to accurately measure the thickness of the layer obtained, with the induced current method (the same used for anodized aluminum in an acidic environment), as on some alloys the final surface is rough. It should also be kept in mind that there are many factors that influence the maximum tension reached at the end of the process, for example the type of alloy, the temperature of the solution used and the type of material used for the coupling of the materials to be treated.

Still according to the invention, it is possible to carry out treatments subsequent to the main one of anodizing and contemporary coloring as described above. These subsequent treatments, also defined post-treatments, must be commensurate with the final application, for which various options will be indicated below. For example, always taking magnesium as the chosen material, after a thorough washing in water, the magnesium material is sent either to drying, if it is intended for a transparent varnish, or if you want to keep the black / dark satin appearance obtained with the anodic oxidation process, the material is destined for a fixing treatment with one of the methods of current use.

The electrolytic solution by means of which the main anodizing treatment object of the process according to the invention is carried out, has proved to be polyvalent (or multi-use), since it can be advantageously used both for metals such as magnesium, and for titanium, vanadium, tantalum, hafnium or aluminum, even when alloyed with each other, when coupled together or hooked onto the same charge of pieces to be treated.

The present invention therefore relates to an electrolytic process for the production of both an aesthetic and protective coating of dark or black color on non-ferrous materials such as magnesium, titanium, vanadium, tantalum, hafnium and aluminum (and their alloys), even when these metals are coupled together in various ways to form a single product, the process is carried out by providing the pieces to be treated, duly immersed in an electrolytic solution contained in a cell with adequate characteristics and equipped with "counter-electrodes", a preferably continuous current , but with particular characteristics.

The electrolytic solution is alkaline in nature and has been specially formulated free from toxic ions such as hexavalent and trivalent chromium, fluorides, borates or amino derivatives in any form.

Said process is characterized by the fact that it does not foresee any preliminary degreasing or activation treatment, so that the treatment is carried out in a single tank or cell, allowing a considerable simplification of the plant, as well as a considerable saving from the economic point of view. The dark or black color is generated by the presence of particular metal ions added to the solution itself. Metal ions such as iron, cobalt and nickel, which, remaining incorporated in the form of oxides in the layer produced by the current, cause a dark color. According to the present invention, the counter ion has no particular relevance, provided that it is compatible with the components of the solution and the general process conditions. The indicative concentration of said metal ion can be 2 g / 1 as the ion of the metal in solution, considering that, however, an excess does not cause problems of any kind. In some cases, the addition of organic acids (or alkaline or ammoniacal salts of acids), such as oxalic, tartaric or citric acid, is beneficial. An indicative concentration of these acids can be considered equal to 10 g / 1.

In some cases the achievement of hydrogen peroxide (hydrogen peroxide) in an indicative concentration of 10 g / 1 proves to be profitable (considering for example the commercial product at 120 volumes).

An adequate use of the current, preferably supplied by a special power supply, allows to produce a coating of the desired color by essentially varying only the treatment time and, consequently, the thickness of the layer.

The treatment thus outlined improves both the corrosion resistance properties and the aesthetic properties of the starting materials, which can be further increased in case of particular needs, by means of a further specific post-treatment.

The process object of the invention allows to treat the aforementioned metals even when they occur in particular alloys (for example aluminum castings with silicon content up to 10% and more) or when they are variously coupled to form a single piece or product. .

The procedure, as already mentioned, also allows to solve the problem of treating on the same plant for example magnesium, aluminum, especially if in alloys with high silicon, titanium and, much less, to treat mixed pieces (with parts, for example, in aluminum and magnesium coupled together).

What has been described above will now be better exemplified with the series of examples reported below, given for indicative and non-limiting purposes of the present invention.

Application examples

Preliminary Notes

1) All the samples were produced under the same operating conditions, to highlight the simplicity and ductility of what is proposed.

2) The electrolytic cell (treatment tank) was in Moplen with approximate dimensions of 700 x 300 x 700 mm. 316L stainless steel sheets were placed on the long walls of the tank and connected to an aluminum bar ring closed and connected to the negative pole (cathode) of the power supply. A piece-holder bar was placed longitudinally in the center of the tank and connected to the positive pole (anode). As hooks were used indifferently strips of titanium 99.5 or small extruded profiles in aluminum of 6060 alloy, regardless of the type of material to be treated. The use of aluminum hooks slightly raised the tension used, the single pieces were fixed to the hooks with common plastic clamps used in the traditional anodic oxidation of aluminum.

3) The treatment tank was equipped with a heat exchanger connected to a refrigerator.

4) The treatment tank was equipped with agitation by means of compressed air.

5) The solution was kept filtered by a filter pump with paper discs with porosity of 5 microns.

6) The power supply of the type indicated above delivered a maximum power of 450V x 50 Ampere.

7) For each single treatment or test, one or more pieces were used (indifferently) up to a maximum immersed surface of about 20 dm,

8) After each treatment the hooks were pickled in a suitable way to eliminate the layer previously produced.

9) The basic solution used for anodizing was the following:

Phosphoric acid 15 gA

Ammonia (25%) 50 g / 1

Metal ion 2 g / l

Organic acid 10 g / 1 (when present) Hydrogen peroxide (120 Vol) 10 g / 1 (when present) Temperature 15 ° C

Current density as indicated in the individual examples Treatment time as indicated in the individual examples

The programs indicated in table 1 were used. In practice, if necessary, only the duration of the anodic phase was changed, leaving all the other parameters unchanged.

The individual alloys treated are indicated in the individual examples.

10) Post treatments possibly applied on the product layer.

a) Painting with transparent polyester powder (e.g. 5020/0000 - DuPont) b) Fixing according to current methods

Summary table of examples

Metal Alloy Type of ion Type of acid Water Density Time Thick metal piece oxygenated organic salt min current (') layer Afdm <3> (pm) Titanium 99.5% plate Nickel Acetate / None YES 10 5 15 Aluminum AA5005 plate sulphate 10 5 10 Titanium 99 5% plate Cobalt acetate none no 4 15 10 Aluminum AA5005 plate 6 15 15 AA360 Part

10 15 25 mechanics

6 15 10 10 15 20 10 15 20 Titanium 99 5 plate Iron sulphate Citric yes 4 15 20 Aluminum AA5005 plate 4 15 25 AA360 Wheel part

moto 6 15 25 Magnesium AZ31 plate 4 15 20 A291 Wheel part 15 20 gokart

2K60 Wheel part 15 20 motorcycle

Note:

(*) The time indicated here refers to the duration of the anodic phase, as indicated in column 5 line 2 (1) The addition of an oxyacid or its salt does not bring advantages such as to justify the increase in operating costs ..

(2) The addition of hydrogen peroxide does not bring advantages such as to justify the increase in costs and co (3) Smooth and porcelain appearance

(4) Citric acid acts as a complexing agent for iron, which remains completely in solution.

(5) The presence of hydrogen peroxide guarantees a darker color.

(6) By operating at higher current densities even than those claimed in the present patent, the strategic shape but the operating costs are higher, as well as the surface roughness.

Claims (18)

CLAIMS 1. Electrolytic process for the treatment of non-ferrous metal materials which includes at least one main treatment phase or anodic phase carried out in a tank or cell, said phase being carried out simultaneously also on different metal materials, and / or materials made by association in alloy and / or coupling and / or other kind of association of different metal materials, by using an alkaline solution which includes metal ions selected from iron, cobalt or nickel or mixtures thereof in a concentration greater than or equal to 0.1 g / i. 2. Process according to claim 1, characterized in that said alkaline solution comprises phosphoric acid, ammonia and / or alkaline hydroxides, and has a pH value between 7 and 10. 3. Process according to claim 2, characterized in that said alkaline hydroxides are selected from lithium hydroxide, sodium hydroxide, potassium hydroxide. 4. Process according to claim 2, characterized in that said ammonia and / or said alkaline hydroxides are present in a concentration comprised between 3 and 150 g / 1, preferably in a concentration comprised between 45 and 60 g / 1. 5. Process according to claim 2, characterized in that said phosphoric acid is present in a concentration comprised between 1 and 50 g / 1, preferably in a concentration comprised between 15 and 20 g / 1. 6. Process according to claim 1, characterized in that said metal ions are present in a concentration comprised between 1 and 2 g / 1. 7. Process according to claim 1, characterized in that said non-ferrous metal materials are selected from aluminum, titanium, magnesium, vanadium, tantalum and hafnium. 8. Process according to claim 1, characterized in that it is carried out in a single tank or cell by immersion of said non-ferrous metallic materials in said alkaline solution. 9. Process according to claim 1, characterized in that it further comprises a step in which said metal material is degreased and / or activated by means of a current-free passage between 5 and 300 seconds, preferably 30-60 seconds. 10. Process according to claim 9, characterized in that said phase in which said metallic material is degreased and / or activated is followed by a cathodic phase lasting between 10 and 600 seconds at a current density between 1 and 10 A / dmq, preferably 2 A / dmq, which can be reached with an ascent ramp lasting between 5 and 60 seconds, preferably 30 seconds. 11. Process according to claim 10, characterized in that, following said cathode phase, there is a pause without current of a duration ranging from 1 to 100 seconds, preferably 5-10 seconds, followed by said anode phase. 12. Process according to claim 1, characterized in that said anode phase has a duration of between 10 seconds and 60 minutes at a current density of between 2 and 30 A / dmq, preferably between 2 and 10 A / dmq, with an ascent ramp lasting between 10 and 600 seconds, preferably between 60 and 300 seconds. 13. Use of the process as per the preceding claims, for the preparation of dark or black colored non-ferrous metal articles. 14. Non-ferrous metal products with a dark or black color made by means of the process referred to in the preceding claims, 15. Products as per claim 14, made of magnesium, aluminum, titanium, vanadium, tantalum, hafnium and / or their alloys, and / or their coupling and / or their other kind of association. the. Use of the process as per the preceding claims, for the preparation of dark or black colored non-ferrous metal articles to be used for all both aesthetic and functional applications where a dark or black coloring is preferred or necessary. 17. Use of the process as per the preceding claims, for the preparation of dark or black colored non-ferrous metal products to be used as solar collectors for the resorption of thermal or light energy. 18. Use of the process referred to in the preceding claims, for the preparation of dark or black colored non-ferrous metal products to be used as wheels of vehicles, motorcycles or automobiles, where the dark or black coloring can represent a pleasing aesthetic aspect.