Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
  • C25D11/08—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used containing inorganic acids
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/14—Producing integrally coloured layers
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing
  • C25D11/24—Chemical after-treatment
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing
  • C25D11/24—Chemical after-treatment
  • C25D11/243—Chemical after-treatment using organic dyestuffs
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing
  • C25D11/24—Chemical after-treatment
  • C25D11/246—Chemical after-treatment for sealing layers
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/26—Anodisation of refractory metals or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/30—Anodisation of magnesium or alloys based thereon

Definitions

• the object of the present invention is a process for the electrolytic treatment of non-ferrous metal materials, such as for example magnesium, aluminium, titanium, vanadium and alloys thereof, particularly a process for the production of a surface coating which has both an aesthetic and a protective function.
• non-ferrous metal materials such as for example magnesium, aluminium, titanium, vanadium and alloys thereof
• Another object of the present invention is products made from non-ferrous metal materials, provided with surface coatings obtained according to said process.
• aluminium is subjected to well-defined treatments, such as for example, anodic oxidation treatment or anodisation and painting.
• anodic oxidation treatment this is carried out conventionally, in sulphuric acid solutions (160 - 220 g/I).
• the anodic layer thus formed may be further treated, for example it can be stained either by absorption, i.e. by immersing the aluminium pieces in solutions of organic or inorganic dyes, or electrolytically by treating the pieces with currents in suitable tin or nickel salt-based solutions.
• fixing After treatment to close the pores of the oxide which has formed during the anodisation step and which is conventionally known as "fixing", the aluminium pieces thus produced show excellent corrosion resistance and, if dyed, the dyes have suitable light solidity.
• aluminium can also be painted.
• a preliminary stage providing a "chemical conversion” treatment, upon completion of which, it is possible to apply a paint which may be of the "powder” or “liquid” type.
• a paint which may be of the "powder” or “liquid” type.
• magnesium it is essential to consider that up to ten years or so ago, it was considered to be a metal for special applications, where it was desired to better exploit its mechanical characteristics and light weight.
• a magnesium alloy weighs 35% less than an analogous aluminium alloy with similar mechanical characteristics, and furthermore, can be "cast” much thinner without forming "bubbles".
• magnesium is frequently used in place of plastic for delicate applications such as for example laptop computer, camera and CD player casings, and is beginning to be used in place of aluminium in mechanical pressure casting applications.
• a typical outline for anodisation treatment, common to all routinely used treatments, is as follows:
• the solutions used for anodising treatments may contain anions such as fluorides, borates, silicates and phosphates, which are all capable of forming complex salts with the metals undergoing treatment, for example, with magnesium.
• alkaline metals Li, Na, K
• ammonia or amines may be used as cations.
• the metal immersed in the solution necessary for the anodising treatment is normally connected to one pole of a current supply, with a second piece of metal connected to the other pole (if conventional AC will be used) or an inert cathode (for example stainless steel) in the case where DC must be used.
• a salt compound, containing those anion(s) present in the solution will form on the surface of the metal piece, with the cations(s) being, other than the metal, one of more of the cations used to adjust the pH of the solution. This is anodisation of the metal and not anodic "oxidation" of the metal, since the quantity of oxide produced is noticeably less than that of the complex salts mentioned above.
• the formation of the layer occurs when the piece acts as an anode in the electrical cell, also when alternating current or complex waveforms with one negative part are used, whereby the term "anodisation", for the most part, remains correct.
• the voltage can reach 700 V with a ⁇ V of even 1000 V if a negative part is inserted.
• the oxide layer formed by discharge (for example both in the case of magnesium and aluminium materials) is mainly made of two components: one more compact with a thickness of 10-20 microns, depending on the duration of the process, and another rougher with a thickness of 2-3 microns. This occurs because the discharges which reach the surface of the metal compress the underlying layers, thus increasing the compactness and hardness thereof and, obviously, the outermost parts are made rough by the discharges themselves. Standard industrial practice is to eliminate the first 2-3 microns of the product layer in order to be able to completely exploit the hardness properties of the remaining part of the layer. With this system, it is possible to obtain, for example on aluminium, up to 2000 HV of hardness (and 400-600 HV on magnesium).
• the thickness of the layer produced is solely a function of the intensity of current passed (i.e. the Ampere hours - Ah), it is understood that the cost of the process is highly associated with the voltage required for maintaining the current used for the production of the desired layer. This voltage depends on the composition and temperature of the solution, as well as the resistivity of the layer.
• the object of the present invention is that of providing a process for the surface treatment of non-ferrous metal materials, which is both economical and does not involve the use of toxic or potentially hazardous substances.
• Another object of the present invention is that of providing a process for the surface treatment of non-ferrous metal materials providing the use of stable solutions, with constant composition, and which do not require frequent replacement of the solutions used.
• Another object of the present finding is that of providing a process for the surface treatment of non-ferrous metal materials, which does not provide separate preliminary stages of cleaning, and/or degreasing and/or activation of the metallic surfaces which must be subjected to treatment, and which thus allows performing the surface treatment of the metal material in a single main stage.
• An additional object of the present invention is that of providing a process for the surface treatment of non-ferrous metal materials, which allows the simultaneous treatment of different metals and/or products manufactured in different parts using different metals and/or in non-ferrous metal alloys, inside the same bath.
• Another object of the finding is that of providing a process for the surface treatment of non-ferrous metal materials which allows the simultaneous surface treatment of coupled or mixed materials, or materials made by combining various metals in alloys or the like, with consequent advantages, even from the economic viewpoint.
• a further object of the present invention is that of providing non-ferrous metals, materials and products made using said metals and/or alloys thereof, provided with a surface coating obtained by means of the process being the object of the present invention.
• an electrolytic process for the treatment of non-ferrous metal materials which comprises at least one main treatment stage or anodic stage, carried out in a bath or cell, said stage being carried out using an alkaline solution allowing the simultaneous treatment of metal materials even different from each other, and/or alloys and/or combinations and/or any other kind of association of various metals.
• said alkaline solution consists of phosphoric acid, ammonia and/or alkaline hydroxides and/or phosphates, and has a pH value comprised of between 7 and 10.
• said alkaline hydroxides are selected from lithium hydroxide, sodium hydroxide, potassium hydroxide and said phosphoric acid is present in concentrations comprised of between 1 and 50 g/I, preferably at a concentration comprised of between 15 and 20 g/I, while said ammonia and/or said alkaline hydroxides are present at a concentration comprised of between 3 and 150 g/I, preferably at a concentration comprised of between 45 and 60 g/I.
• Said non-ferrous metals are advantageously selected from aluminium, titanium, magnesium and vanadium.
• the process according to the present finding offers numerous advantages, and particularly allows eliminating the pre-treatment stages, normally provided in the processs according to the prior art.
• the process being the object of the invention, the separate preliminary stages of cleaning, and/or degreasing and/or activation of the metal surfaces to be treated, for example in order to carry out surface anodising, are completely eliminated, and it is possible to use a single tank or bath for the main treatment stage, without requiring a succession of different baths, containing different solutions, in order for example to carry out the cleaning stage, then the degreasing, and finally the activation of the surface of the material to be treated.
• the process being the object of the invention, it is possible to perform the main anodising treatment simultaneously on non-ferrous metal materials even different from each other, or even on products made of different non-ferrous metals in combination with one another inside the same material or on materials made, at least partially, from non-ferrous metal alloys.
• All the above is a significant technical advance with respect to the anodising processs according to the prior art, where tanks required to be always provided, which were separate and distinct from the main tank, in order to perform the aforementioned pre-treatments (cleaning, and/or degreasing and/or activation).
• the pre-treatments according to the prior art are carried out using several solutions, at different concentrations and, in some cases, even just using water.
• the use of a basic solution as described above allows simultaneous treatment, in the same anodising tank or bath, of non-ferrous metals even different from each other, or even products made from different metals coupled or fused together or even products made from non-ferrous metal alloys.
• it was necessary to perform a specific anodising treatment for each type of metal and it was not possible to treat different metals at the same time, and in the same bath.
• one of the main objects of the present invention is that of simplifying the existing technology by reducing the operational complexity and costs thereof and allowing materials such as magnesium, aluminium and titanium (and alloys thereof), or pieces coupled together in any way, to be treated in the same solution, and even simultaneously.
• the process being the object of the present invention is further a significant simplification in relation to the solution used for the main treatment, the composition of which is not binding, but can be selected on the basis of low cost and operational practicability.
• the solution must be suitable for the treatment of magnesium, vanadium, aluminium and titanium, even simultaneously.
• a small amount of phosphoric acid or alkaline phosphate for example 15 g/I
• a varying amount of ammonia or alkaline hydroxides lithium, sodium or potassium
• Higher pH are only essential if systematically producing high thickness layers (in excess of 20 microns).
• the preferred temperature is comprised of between 20-25 °C, without the need for any specific accurate temperature control. This solution is easily managed, as a filter pump can keep it scrupulously clear by eliminating any traces of contamination and precipitates.
• the electrolytic treatment of the anodising stage is preferably carried out using a known power supply, such as described in EP 0619643 .
• Said power supply is well suited to the purposes indicated, in that it has an automatic supply current parameter adjustment system.
• An electrolyte of the type described above is introduced into the electrolytic cell, i.e. into the treatment tank, and two plates, preferably made of stainless steel, which will essentially act as the cathode, are positioned along the long walls of the tank itself, while arranged in parallel to these, in the middle section of the cell or tank, will be immersed one or more pieces to be subjected to the treatment.
• the magnesium material is either sent for drying, if intended for painting, or if it is desired to keep the satin white appearance obtained by the anodic oxidation process, the material is sent for a fixing treatment.
• Three types of "post treatments" are provided, depending on the type of quality it is desired to achieve. If we use corrosion resistance in a neutral saline cloud, according to ASTM B 117 as a parameter, then the following treatment 1.a) ensures corrosion resistance of about 100 hours (even though for many applications 8-24 hours are required), the subsequent treatment 1.b) may exceed 200 hours, while option 1.c), besides increasing corrosion resistance significantly beyond 200 hours, it confers a surface "lubricity" (slipperiness) frequently required for mechanical pieces.
• the materials anodized by the main treatment as described above can be subjected to special treatments.
• special treatments for example, in the case of magnesium materials, there are two possible absorption colouring systems, using azoic dyes.
• the electrolytic solution used for the main anodising treatment forming the subject of the process according to the invention has shown itself to be polyvalent (or multi-use), since it can be advantageously used for both metals such as magnesium, and for titanium or aluminium, even when in alloys with one another, when coupled together or when held in the same piece holder for treatment.
• the object of the present invention is, accordingly, an electrolytic process for producing a coating that is both aesthetic and protective, on non-ferrous materials such as magnesium, titanium, vanadium and aluminium (and alloys thereof), even when such 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 electrolyte solution contained in a cell with adequate characteristics and fitted with "counter-electrodes", with a preferably DC current, but with particular characteristics.
• the electrolyte solution is alkaline in nature and has been specially formulated to be free of toxic ions such as chromium, both hexavalent and trivalent, fluorides, borates or amine derivatives in any form.
• Said process is characterized by not providing any preliminary degreasing or activating treatments, whereby the treatment is carried out in an individual tank or cell, allowing considerable simplification of the system, besides significant financial savings.
• Suitable use of current allows producing a coating of the thickness desired, just by essentially varying the treatment time.
• the treatment thus described improves both the corrosion resistance properties and the aesthetic properties of the starting material, which can be further increased according to particular needs, by means of a further specific post-treatment.
• the process being the object of the invention allows treating said metals even when they are in special alloys (for example aluminium casts containing up to 10% silicon) or when coupled together in various ways to form a single piece or product.
• special alloys for example aluminium casts containing up to 10% silicon
• the process further allows resolving the problem of using the same system to treat for example magnesium, aluminium, especially if in high silicon alloys, titanium and the like, and of treating mixed pieces (with parts for example made of aluminium and magnesium coupled together).
• the electrolytic cell (treatment bath) was made of Moplen and sized 700 x 300 x 700 mm. 316L stainless steel sheets were positioned along the long walls of the tank and connected to a ring- closed aluminium crossing and connected to the negative pole (cathode) of the current power supply. A piece holding bar was positioned longitudinally at the centre of the tank and connected to the positive pole (anode). Holders can be strips of titanium 99.5 or small pieces of extruded aluminium alloy 6060, regardless of the type of material to be treated. The use of aluminium holders slightly increased the voltage used.

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• General Chemical & Material Sciences (AREA)
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Cited By (7)

Citations (4)

• 2005
  • 2005-11-29 IT ITMI20052278 patent/ITMI20052278A1/it unknown
• 2006
  • 2006-10-03 EP EP06020777A patent/EP1793019A3/fr not_active Withdrawn

Patent Citations (4)

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