EP0490914A1

EP0490914A1 - Methods for depositing finish coatings on substrates of anodisable metals and the products thereof.

Info

Publication number: EP0490914A1
Application number: EP90912713A
Authority: EP
Inventors: Dan Fern; Christopher James Hanthorn
Original assignee: Alcan International Ltd Canada
Current assignee: Rio Tinto Alcan International Ltd
Priority date: 1989-09-05
Filing date: 1990-09-05
Publication date: 1992-06-24
Anticipated expiration: 2010-09-05
Also published as: DE69008359T2; JP2945472B2; DE69008359D1; JPH05503316A; CA1341327C; ES2052269T3; AU6287090A; WO1991003583A1; EP0490914B1

Abstract

On décrit de nouveaux procédés de dépôt de couches métalliques sur des substrats de métaux anodisables tels que l'aluminium et ses alliages. Les couches sont déposées directement sur une couche poreuse anodisée qui a été produite à la surface du substrat. Du métal bouche-pores est d'abord déposé par électrolyse dans les pores et le métal se dépose initialement sur le fond et les parties inférieures des parois latérales; normalement jusqu'à ce que les pores soient entre 3 % et 30 % remplis. Ensuite, le dépôt de métal est poursuivi par un procédé sans courant jusqu'à ce que les pores soient remplis au niveau souhaité, et normalement jusqu'à ce qu'une couche de support ait été déposée sur toute la surface de la couche anodisée. D'autres couches métalliques peuvent ensuite être déposées sur la couche de support, soit par des procédés sans courant soit par des procédés catalytiques. Des couches anélectrolytiques à épaisseur considérable (jusqu'à 75 micromètres) peuvent être déposées avec succès. Les nouveaux produits de ces procédés comprennent un substrat en métal anodisable dont l'épaisseur est comprise entre environ 0,5 et environ 50 micromètres; les pores de la couche anodisée contiennent un dépôt catalytique de métal bouche-pores, et un dépôt catalytique de métal bouche-pores déposé sur la couche de métal déposé par électrolyse. Le métal catalytique peut constituer la dernière couche, ou d'autres couches peuvent être déposées par dessus afin de former le produit final. Le métal à dépôt électrolytique interposé assure une adhésion améliorée au matériau anodisé par rapport au métal à dépôt catalytique direct.New methods of depositing metallic layers on anodisable metal substrates such as aluminum and its alloys are described. The layers are deposited directly on an anodized porous layer which has been produced on the surface of the substrate. Pore-filling metal is first deposited by electrolysis in the pores and the metal is initially deposited on the bottom and the lower parts of the side walls; normally until the pores are between 3% and 30% filled. Then, the metal deposition is continued by a currentless process until the pores are filled to the desired level, and normally until a support layer has been deposited over the entire surface of the anodized layer. Other metallic layers can then be deposited on the support layer, either by currentless methods or by catalytic methods. Anelectrolytic layers of considerable thickness (up to 75 micrometers) can be successfully deposited. The new products of these processes include an anodisable metal substrate whose thickness is between approximately 0.5 and approximately 50 micrometers; the pores of the anodized layer contain a catalytic deposition of metal pore-pore, and a catalytic deposit of metal pore-pore deposited on the layer of metal deposited by electrolysis. The catalytic metal can constitute the last layer, or other layers can be deposited on top to form the final product. The interposed electrolytic metal provides improved adhesion to the anodized material compared to the metal with direct catalytic deposition.

Description

METHODS FOR DEPOSITING FINISH COATINGS ON SUBSTRATES OF ANODISABLE METALS AND THE PRODUCTS THEREOF

Field of the Invention This invention is concerned with improvements in or relating to methods for depositing metal coatings on substrates of anodisable metals, such as aluminum and its anodisable alloys, and to the products of such methods. Review of the Prior Art The deposition of metals on a substrate, usually steel or aluminum, is a well-developed art. Plating on less easily oxidized metals such as steel is relatively routine, involving for example the deposition of a layer of copper directly on the steel substrate, followed in succession by a thick "semi-bright" nickel layer, a thinner "bright" nickel layer, and an even thinner finish layer of chromium; the chromium is semi-transparent and the bright appearance is actually provided by the bright nickel layer seen through the finish chromium layer. Plating on anodisable metals, such as aluminum and its anodisable alloys, is considerably more difficult owing to their relative ease of oxidation, and the consequent inevitable presence of an oxide coating which must be removed if adequate adhesion of the deposited layers to the underlying metal substrate is to be obtained. The art currently is dominated by two methods of preparing the substrate surface, namely zincate and stannate immersion. In these processes the substrate surface is immersed in a suitable zincate or stannate solution, usually of the sodium salt, together with other additions that have been found in practice to increase the appearance and adhesion of the coatings. The zinc or tin atoms respectively displace aluminum atoms at the surface, in the process removing the oxide layer, to result in an adherent zinc or tin layer on which other layers, for example copper followed by nickel and chromium can be deposited. Both of these processes are relatively expensive and are therefore mainly used on expensive commodities. The stannate immersion processes are reported to provide better anti-corrosion performance and adhesion of the resultant coatings, but are the more expensive of the two because of the more expensive components and longer processing times.

It has also been proposed to deposit adherent metal coatings directly on aluminum or aluminium alloy substrates by producing a porous anodized layer at the surface of the substrate onto which the subsequent metal layers are deposited; this anodized layer incorporating the oxide layer that was present on the substrate surface. In an article entitled "Plating on Aluminum, a Review" by D.S. Lash ore, published in the June 1985 issue of "Plating & Surface Finishing" (pp 36-39), summarizing previous publications, it was reported that studies have shown that there must be a minimum pore size in the anodized coating, into which the subsequent metal coatings can mechanically "lock" or "key", and that this limits the process to the use of electrolytes that will produce fairly large pores of the order of 0.07 micrometres (700 Angstroms). The report goes on to state it has been found empirically that only anodising solutions comprising phosphoric acid are sucessful, sulfuric or oxalic acid sometimes being mixed with the phosphoric acid. The report further states that the adhesion of the subsequent coatings is primarily mechanical, with the cohesive strength of the porous oxide coatings to the metal substrate being the limiting factor, so that improvements in the anodic process should be directed towards increasing this cohesive strength and the strength of the oxide layer itself. Despite developments of these phosphoric acid anodizing/coating processes for over 50 years they have not yet been widely adopted commercially, apparently because of relatively poor adhesion and brightness.

Definition of the Invention

It is therefore the principal object of the present invention to provide new methods for plating metal layers on substrates of aluminum and its alloys, and to provide substrates of aluminum and its alloys having metal layers plated thereon by the new methods.

In accordance with the present invention there is provided a new method of depositing metal on a surface of a substrate of an anodisable metal, the method including the steps of: a) ano ising the substrate at the said surface to produce a porous anodised layer of thickness from about 0.5 to about 50 micrometres; b) electrolytically depositing pore-filling metal into the pores to adhere to the walls thereof; and c) continuing the deposition of pore-filling metal by electroless deposition to fill the pores to the required extent.

Preferably the electroless deposition is continued until a coating of metal of thickness in the range about 0.5 to 3 micrometres is deposited on the surface of the anodised layer. Also in accordance with the invention there are provided new products comprising anodisable metal substrates of which a surface consists of a porous anodized layer of thickness of about 0.5 to about 50 micrometres, the porous layer having electrolytically deposited in the pores thereof pore-filling metal which adheres to the walls thereof, and having electroless deposited pore-filling metal deposited in the pores on the electrolytically deposited metal

Description of the Drawings

Methods of depositing various layers of metals on a surface of an anodisable substrate, and the products of such methods, constituting particular preferred embodiments of the invention, will now be described by way of example with reference to the accompanying drawings, wherein:-

Figure 1 is a cross-section through the surface and adjacent portion of an aluminum substrate, through the porous anodised layer formed thereon by sulfuric acid anodising, and through the various layers of metal that have been deposited on the anodised layer; ^

Figure 2 is a cross-section to a much enlarged scale of the small portion 2 of Figure 1, showing the anodised layer and the immediately adjacent metal layers; and

Figure 3 is the same cross-section as that of Figure 2, through a substrate in which the anodised layer is formed by phosphoric acid anodising.

Description of the Preferred Embodiments

As indicated above. Figure 1 is a cross-section through an aluminum substrate 10 at the upper surface of which there has been formed by acid anodising a layer 12 of aluminum oxide, a portion of which, together with the immediately adjacent portions of the substrate and deposited metal layers, are shown to a larger scale in Figure 2. This particular anodising employs sulfuric acid which produces elongated narrow pores 14 (not seen in Figure 1), and in accordance with this invention at least the bottom portions of the pore walls have had applied thereto by electrolytic deposition a layer of adherent pore-filling metal 16 (also not seen in Figure 1). The electrolytically deposited metal is found initially to deposit principally at the bottoms of the pores and the immediately adjacent parts of the side walls, and the resultant coatings or layers then grown progressively in thickness upwards in the pores as more metal is deposited. It is also found initially that discontinuous patches 17 of the metal are deposited on the side walls in what appears at present to be a random manner. After sufficient metal has been electrolytically deposited the filling of the pores is continued using electroless deposited metal 18 until, in this embodiment, they are completely filled and a continuous support layer has been formed over the entire surface of the anodised layer 12. In this embodiment cobalt is used as the initial electrolytically deposited metal 16 and 17, while electroless nickel is employed for the metal 18. The deposition of metal layers is continued to provide a semi-bright nickel layer 20, a bright nickel layer 22 and a tri-chrome finish layer 24.

The invention thus employs the electrolytic deposition of pore filling metal to apply an initial "seed" coating to the bottom wall portion of each pore and to at least the lower portion of the side wall of each pore. It is found that such an electrolytically deposited metal coating adheres very well to the anodised material, and the subsequently electroless deposited metal adheres very well to the electrolytically deposited metal, whereas metals deposited by electroless processes directly on aluminum oxide do not adhere well and result in lower strength metal coatings. Electroless coating processes have the advantage that they are more efficient than electrolytic processes in filling the pores and result in more dense or compact coatings, and the processes of the invention enable advantage to be taken of this property while overcoming the potential problem of insufficient adherence of the electroless deposited metal to the anodised layer. The acid most widely used for anodising is sulfuric acid because of its ready availability and lower cost, although phosphoric, oxalic and chromic acids, and mixtures of these and other acids, can also be used. The anodised layer is inherently porous in structure because of the manner of its formation, and a typical structure of a layer 12 obtained by sulfuric acid anodising of the aluminum substrate 10 is illustrated by Figure 2, while that obtained by anodising with phosphoric acid is illustrated by Figure 3. For convenience in drawing the horizontal surfaces of the layers are shown as flat, but in practice they will be seen to be highly irregular even at quite low magnification.

Figure 1 illustrates an embodiment in which an anodised layer 12 of aluminum oxide (Al-O has been produced of about 5 micrometres (50,000 Angstroms) thickness, typically by use of sulfuric acid at about 20°C and of about 165g/litre or 15% by weight concentration, employing an anodising voltage of about 15-20 volts for 10 minutes. The porous structure obtained is relatively uniform, although highly idealised as shown in Figure 1 for convenience in drawing, and typically the pores 14 will be found to average 0.015 micrometre (150 Angstroms) in transverse dimension, spaced on average about 0.024 micrometre (240 Angstroms) from one another. The bottoms of the pores do not end at the surface of the aluminum substrate, but instead they are on average spaced about 0.015 micrometre (150 Angstroms) from that surface to form a continuous non-porous barrier layer 26 of the relatively non-conductive aluminum oxide, the thickness of this layer depending principally directly on the value of the anodising voltage. Usually with sulfuric acid anodising this thickness averages about 0.0010 to 0.0014 micrometre (10 to 14 Angstroms) per volt. It may be noted that references herein and in the literature to pore sizes, etc. are usually made in Angstroms, while references to thicknesses are made in micrometres, merely to avoid the need to refer to large numbers or small fractions, 1 micrometre being equal to 10,000 Angstroms.

It has been found possible in previous commercial practice to deposit pore filling metal layers that are sufficiently strong and stable of up to about 5 micrometres thickness, but beyond this value the hydrogen that is generated in the long, narrow pores (i.e. length to width ratio in thesa ple illustrated of about 330:1) by the electrolytic deposition process tends to cause spalling of the anodised coating, destroying its strength to the extent that it is unsuitable to receive and retain the pore filling metal. Another problem is that it is difficult to deposit a sufficiently adherent coating of a pore-filling metal into the long narrow pores employing conventional D.C. plating methods. Thus, there is too great a tendency for the plating step to cause physical disruption of the anodised layer, so that the plated metal layer is poorly adherent.

Metal deposition processes may use either alternating current or direct current, or a combination thereof. A.C. depostion is usually much slower than the equivalent D.C. current and D.C. is therefore preferred if speed is important. However, D.C. has a greater tendency to cause disruption of the coating especially with the narrow pores characteristic of sulfuric acid anodising. It is therefore also known to use modified A.C, preferably one in which a predetermined negative-going D.C. has been superimposed on the A.C. Such a system avoids the disruption that would be produced by a pure D.C. current. A.C. produces metal deposition owing to the rectification characteristic of the aluminum oxide, but as the thicknesses of the coatings increase such unmodified A.C. deposition gives poorer pore penetration and slower deposition rates. The D.C. component is therefore increased to the maximum level that does not cause disruption. This method of deposition is disclosed for example in U.S. Patent No. 4,226,680, assigned to Alcan Research and Development Limited, the disclosure of which is incorporated by this reference; these processes have now become known as the Alcan "ANOLOK" (Trade Mark) processes. Other modified A.C. systems are also possible; for example, another system offsets the A.C. waveform in a manner that will produce an effective negative bias, while a further way is to increase the amplitude of the negative portion of the waveform relative to that of the positive portion, which again has the same effect.

The processes of the invention are applicable generally to anodisable metals, their alloys and composites; whether rolled, pressed, cast or wrought. Cast metals are generally less dense and more porous in structure than the corresponding rolled, pressed or wrought product. Attempts to use only electroless deposition, or only electrolytic deposition, directly on the anodised surface of a cast material have not been as successful as the processes of the invention because of this higher porosity and because of the usual higher silicon content (e.g. 7-12%) of such metals. Thus, the more porous metal structure results in anodised layers of lower strength and quality, and electrolytic deposits are more adversely affected by the anodic layer quality than are electroless layers, it is believed because of entrapment of some of the silicon in the barrier layer which interferes with the normal flow of electrons in the deposition current. On the other hand, as explained above, layers applied by direct electroless deposition are generally poorly adherent to the already lower strength anodised layer. Suitable substrate metals, in addition to aluminum and its anodisable alloys, are magnesium and its anodisable alloys. Metals suitable for the electrolytic deposition of the initial "seed" layer are cobalt, nickel, zinc, copper, tin and palladium. When the substrate is aluminum or an alloy thereof cobalt has been found to be particularly suitable for electrolytic deposition and nickel for electroless deposition. It is found that as the thickness of the electrolytic layers within the pores increases a point may be reached at which the adhesion to the aluminum begins to decrease, and this then sets an upper limit at which the electrolytic deposition should be stopped and replaced by the electroless deposition.

Of course the electrolytic deposition can be discontinued earlier depending upon the other parameters of the particular process. It is found that the thickness of the initial seed coatings, as measured from the bottom of the pores, correlates well with the apparent colour of the substrate surface as seen by an observer, and the table below shows a specific correlation that is obtained when the anodised layer has been produced by sulfuric acid anodising is 5 micrometres thick, and the electrodeposited metal being cobalt. The thickness of the electrolytically deposited metal is most expeditously expressed

2 in the units milligrams (mg) of metal per square metre (m ) of anodic surface. It is found with this combination that the cut-off for good adhesion is between about 550 and about 850 mg/m .

TABLE

It will be seen that as little as about 3% will give good adhesion and this is the minimum value for satisfactory results, while at the upper thickness limit of medium bronze for pores of 5 micrometres depth it is estimated that each pore is about 30% filled in volume with the electrolytically deposited metal, leaving the remaining 70% to be filled with the electroless deposited metal. Nickel is found to produce approximately the same colour correlation as cobalt. Copper produces a range of different colours extending from pink through light maroon and dark maroon to black. Tin requires a is obtained. As mentioned above the table refers to sulfuric acid anodising; the same principle applies with phosphoric acid anodising but the colours obtained are slightly different. The amount of electroless applied metal that is deposited in the pores will of course depend upon the required properties and intended use of the resultant product, and for some applications the pores may not need to be completely filled: from about 6% to about 60% of complete filling may be all that is required. Thus, while a useful range for the electrolytic deposition is about 3% to about 30%, a useful range for the electroless deposition is also from about 3% to the remainder required to fill the pores to the required extent. Once the initial electrolytic seed deposit and the subsequent electroless deposit have been applied the subsequent processing steps will also depend upon the commercial application of the resultant product and the characteristics and appearance that are required. For example, the electroless deposition can simply be continued until a final layer (over the anodised layer) of adequate thickness is obtained, the usual range for such an application being from about 50 micrometres to about 75 micrometres. More usually the electroless deposition is continued until it forms a support layer of adequate thickness over the entire surface of the anodised layer, as illustrated by Figures 1 and 2, the usual values being from about 0.5 micrometres to about 3 micrometres, more preferably in the range 1-2 micrometres. Thereafter, a finish layer (for example chromium) may be applied over the support layer, with or without the provision of one or more intermediate layers between the support and finish layers. The invention is particularly applicable to substrates anodised with sulfuric acid and the like in that the compact deposition characteristic of the subsequent electroless deposition works well with the narrow pores obtained with this and similar systems, whereas the less dense deposition of the electrolytic methods works better with wider pores such as are obtained with phosphoric acid and similar systems. Nevertheless, the dual deposition processes of the invention can be applied to such large pore systems and Figure 3 shows an anodised layer 12 of aluminum oxide (Al-O- of about 2 micrometres (20,000 Angstroms) thickness that typically will be produced on substrate 10 using phosphoric acid at about 20°C and of about 109g/litre or 10% by weight concentration, employing an anodising voltage of about 50-60 volts for 10 minutes. The pores 14 themselves are of much larger transverse dimension to give a much lower length/width ratio (20:1 in this example), and they are much more widely spaced apart at an average value of about 0.07 micrometres (700 Angstroms). The barrier layer is thicker because of the higher voltage used; e.g. 60 volts gives a layer of about 700 Angstroms thickness.

The use of a phosphoric acid anodised layer is found to be particularily advantageous with cast materials, and it has been found for example that for cust aluminum such as is used for automotive wheels the adhesion of the final coating/s was increased by al least 50% upon use of phosphoric acid in place of sulfuric acid for the anodising. A suitable test for adhesion is to cut the finished part throught the substrate and coatings and then to attempt to lift or peel the coating away from the substrate by use of a sharp knife edge; it was found possible with this test to peel the coatings from sulfuric acid anodised substrates with various degrees of difficulty depending on the processing conditions, but not possible to peel it from prosphoric acid anodised substrates. The use of an anodised layer before plating introduces the possibility, if desired, of a reduction in the thickness of the subsequent plated layers with consequent cost savings. The anodising processes described employing acid baths in the temperature range 20-35°C are usually characterised as "conventional" anodising, but "hard" anodising processes can also be employed for the invention, the usual bath temperature being in the range 3-7°C; such hard anodised layers are usually thicker than the conventional anodised layers. Further reductions in the subsequent layers therefore are possible by using a thicker and/or stronger anodic film such as that produced using these lower temperature anodising processes, particularly low temperature sulfuric acid anodising. Such hard layers also consitute an excellent basis for the pore-filling metal deposition characteristic of the invention, the electroless layer being the support layer for further deposits, which can be thinner than those normally previously used. It will be understood that this industry is particularily cost conscious, especially with regard to the relatively expensive corrosion-resistant metals that are employed in the intermediate and finish coatings, so that any saving that can be achieved in their thickness for an equivalent performance in protection and/or appearance is commercially important. In the processes of the invention the anodised layer 10 can be of thickness in the range 0.5 - 50 micrometres, usually in the range 1-10 micrometres, preferably in the range 2-6 micrometres, and more preferably 3-5 micrometres, with a thickness of 5 micrometres being usually commercially suitable. The electroless-deposited pore-filling material need not form a support coating of more than about 2 micrometres thickness and excellent results can be obtained with the application of a single thin finish coating of chromium over the support layer. The preferred electroless deposited metal is nickel. Metals other than nickel, such as cobalt, tin or copper, can also be used. Because of the thin coatings that are employed it is preferred in some processes to pre-treat the surface of the anodisable metal to obtain a very smooth surface; this can be a "macro" treatment by buffing and/or a "micro" treatment of chemical or electro-brightening. The finished chromium layer if provided preferably is of thickness in the range of 0.2-0.3 micrometres.

The invention is further illustrated by the following specific examples: Example 1

The process is employed to provide a bright finishing procedure for articles such as cast aluminum automotive wheels, giving a simulation of the appearance of bright chrome or stainless steel, and includes the following steps. 1. The aluminum substrate consisting for example of cast alloys A356 or A413, or forge grade material, is pre-treated by cleaning with appropriate alkaline and/or acid solutions, or is pretreated by mechanical buffing. 2. The pretreated substrate is then subjected to a conventional sulfuric acid anodising treatment using acid of 15% concentration by weight at 21°C for 10 minutes and at 15 V.D.C.

3. The anodised substrate has the initial "seed" electrolytic coating of cobalt applied using a cobalt-based

"ANOLOK" (trade mark) electrolyte as disclosed in U.S. Patent No. 3,616,309 at 21°C and 12.5 V.A.C., with or without up to 4 V.D.C. bias. The electrolytic deposition proceeds for a period of about 30 seconds to about 10 minutes, preferably for about 30-60 seconds, depending upon the colour to be obtained.

4. A pore-filling coating of nickel is then applied by immersion in an electroless nickel solution (Harshaw "Alpha 103B" - trade mark) for about 10-20 minutes at pH4.7 and temperature 93°C, thus completely filling the pores and forming a support coating of about 0.5 to about 3.0 micrometres thickness.

5. The support layer is coated with an electrolytically-deposited semi-bright layer of nickel of about

10 micrometres thickness using Harshaw "PERFLOW" (trade mark) semi-bright solution at pH4.3; temperature 57°C; current

2 density 5 amps per square decimetre (A dm ); and for a period of ten minutes.

6. The semi-bright layer is coated with a bright layer of nickel of about 10 micrometres thickness using Harshaw "SUPREME" (trade mark) bright solution at pH4.0; temperature 66°C; current density 4A/dm and period 10 minutes.

7. The example is completed by electrolytically depositing a trichrome finish layer using Harshaw "TRI-CHROME

PLUS" (trade mark) solution at pH2.7; temperature 30°C;

2 current density 10 A/d for 5 minutes.

During the process the substrate will be rinsed in known manner which need not be detailed here. It may be noted that in this and the other examples described a cyanide or hexavalent chromium bath is not used, which is environmentally desirable.

Exam -ple 2

In the process of Example 1 the cobalt-based electrolyte employed to deposit the initial layer is replaced with a copper-based electrolyte comprising for example 35g/l of CuS0₄.5H₂0; 20g/l MgS0₄.7H₂0 and 5g/l H₂S0₄ at pH 1.3 and 21°C. Example 3 In the process of Example 1 the cobalt-based electrolyte employed to deposit the initial layer is replaced with a tin-based electrolyte comprising for example lOg/1 of SuS0₄ and 20g/l of H₂S0₄ at pH 1.3 and 21°C. Examp —le 4 In the process of Example 1 the cobalt-based electrolyte employed to deposit the initial layer is replaced with a conventional Watt's nickel-based electrolyte comprising for example 240g/l of NiS0₄.6H₂0; 60g/l of iCl₂.6H₂0 and 45g/l of H₃B0₃ at pH 4.5 and 21°C. Example 5

In the process of Example 1 the cobalt-based electrolyte employed to deposit the initial layer is replaced with a palladium-based electrolyte comprising for example a 10 ml/litre "PALLAMERSE" (trade mark) aqueous solution of Technic Inc. This process is particularly suited for articles with a simulated stainless look for exterior application and preferably employs alloy AA-7029 as the substrate. Example 6

To obtain a bright black finish, especially for cast aluminum automobile wheels, the process of any one of examples 1 through 5 is followed by the deposition of a black-chrome finish layer using Harshaw "CHROMONYX" (trade mark) solution at temperature 21°C; current density 10-40 A/dm and period of 5 minutes. Example 7

To obtain articles with a simulated appearance of stainless steel and for interior applications a substrate of cast alloy AA-5657 or AA-6463, for example, is subjected to the processes of any one of examples 1 through 5 with the omission of the deposition of the semi-bright nickel layer. Example 8

To obtain machine parts and articles suitable for other engineering applications the anodising and electrolytic deposition steps of any one of examples 1 through 5 are followed by a nickel electroless deposition step in which the deposition period is about 30 minutes to about 120 minutes, as required, to give layers of about 10.0 micrometres to about 40.0 micrometres thickness. Example 9

To obtain black material particularly suitable for the fabrication of solar panels a substrate of an alloy such as AA-5005 is subjected to the anodising, initial electrolytic plating and electroless plating steps of any one of examples 1 through 5, followed by the deposition of semi-bright nickel for a reduced period of about 10 to about 20 minutes, and the deposition of black chrome by the step of example 6. Example 10 Bright aluminum plated composite articles are prepared from a substrate of composite material AA-6061 (incorporating 10% by weight of aluminum oxide) using the plating procedure of any one of examples 1 through 5. Example 11 A substrate of aluminum cast alloy A413 (including about 12% by weight silicon) is subjected to phosphoric acid anodising using acid of 109 g/L concentration (10%) at 21°C; the anodising is begun at 60 VDC for 30 minutes and is then ramped down to approximately 18 VDC for about 0.5 minutes. The electrolytically deposited metal is cobalt using the composition of example 1 at 12.5 VAC for one minute. This is followed by electroless nickel deposition for 20 minutes, semi-bright nickel deposition for 30 minutes; bright nickel deposition for 10 minutes, and tri-chro e deposition for 5 minutes, again employing the materials, etc. of example 1. The resultant bright inished product exhibited excellent adhesion to the castings.

Claims

WE CLAIM:

1. A method of depositing metal on a surface of a substrate of an anodisable metal, the method being characterised by the steps of: a) anodising the substrate at the said surface to produce a porous anodised layer of thickness from about 0.5 to about 50 micrometres; b) electrolytically depositing pore-filling metal into the pores to adhere to the walls thereof; and c) continuing the deposition of pore-filling metal by electroless deposition to fill the pores to the required extent.

2. A method as claimed in claim 1, characterised in that the electrolytic deposition is continued to a cut-off value at which adhesion of the metal begins to decrease.

3. A method as claimed in claim 2, characterised in that the electrolytically deposited pore-filling metal is deposited to a thickness of up to 550 milligrams per square metre.

4. A method as claimed in claim 1, characterised in that the electrolytic deposition is such as to fill each pore from about 3% to about 30% of its volume.

5. A method as claimed in any one of claims 1 to 4, characterised in that the electroless deposition is such as to fill each pore from about 3% of its volume to the required extent.

6. A method as claimed in any one of claims 1 to 4, characterised in that the electroless deposition is continued until a coating of the metal of thickness in the range about 0.5 to 3 micrometres is deposited on the surface of the anodised layer.

7. A method as claimed in claim 6, characterised in that the electroless deposited metal is deposited to form a support layer on the surface of the substrate of a thickness in the range of about 0.5 to 3 micrometres, and characterised in that one or more subsequent layers are deposited on the support layer.

8. A method as claimed in any one of claims 1 to 4, characterised in that the electroless deposited metal is deposited to a thickness of about 10-25 micrometres on the surface of the substrate.

9. A method as claimed in any one of claims 1 to 8, characterised in that the electrolytically deposited pore-filling metal is selected from nickel, cobalt, zinc, copper, tin, palladium and mixtures thereof.

10. A method as claimed in any one of claims 1 to 9, characterised in that the electroless pore-filling metal is selected from nickel, cobalt, copper, tin and mixtures thereof.

11. A method as claimed in any one of claims 1 to 10, characterised in that the anodisable substrate metal is selected from aluminum and magnesium and anodisable alloys thereof.

12. A method as claimed in any one of claims 1 to 11, characterised in that the substrate is anodised using sulfuric acid, or chromic acid or oxalic acid, or mixtures thereof.

13. A method as claimed in claim 12, characterised in that the substrate is anodised to produce relatively small pores of transverse dimension from about 0.01 to 0.02 micrometre.

14. A method as claimed in any one of claims 1 to 11, characterised in that the substrate is anodised using phosphoric acid.

15. A method as claimed in claim 14, characterised in that the substrate is anodised to produce relatively large pores of transverse dimension from about 0.03 to 0.10 micrometre.

16. A metal plated product characterised by: a) an anodisable metal substrate of which a surface consists of a porous anodised layer of thickness of about 0.5 to about 50 micrometres; b) the porous layer having pore-filling metal electrolytically deposited in the pores thereof; and c) the porous layer having electroless deposited pore-filling metal deposited in the pores on the electrolytically deposited metal.

17. A product as claimed in claim 16, characterised in that the electrolytically deposited pore-filling metal is deposited to a thickness of up to 550 milligrams per square metre.

18. A product as claimed in claim 16, characterised in that the electrolytic deposition is such as to fill each pore from about 3% to about 30% of its volume.

19. A product as claimed in any one of claims 16 to 18, characterised in that the electroless deposition is such as to fill each pore from about 3% of its volume to the required extent.

20. A product as claimed in any one of claims 16 to 19 characterised in that the electroless metal is sufficiently thick to form a coating deposited on the surface of the anodised layer.

21. A product as claimed in claim 20, characterised in that the electroless deposited metal is deposited to a thickness of about 10-25 micrometres on the surface of the substrate.

22. A product as claimed in any one of claims 16 to 20, characterised in that the electroless deposited metal is deposited to form a support layer on the surface of the substrate of a thickness in the range of about 0.5 to 3 micrometres, and characterised in that one or more subsequent layers are deposited on the support layer.

23. A product as claimed in any one of claims 16 to 22, characterised in that the electrolytically deposited pore-filling metal is selected from nickel, cobalt, zinc, copper, tin, palladium and mixtures thereof.

24. A product as claimed in any one of claims 16 to 23, characterised in that the electroless pore-filling metal is selected from nickel, cobalt, copper, tin and mixtures thereof.

25. A product as claimed in any one of claims 16 to 24, characterised in that the anodisable substrate metal is selected from aluminum and magnesium and anodisable alloys thereof.

26. A product as claimed in any one of claims 16 to 25, characterised in that the substrate has been anodised using sulfuric acid, or chromic acid or oxalic acid, or mixtures thereof.

27. A product as claimed in claim 26, characterised in that the substrate has been anodised to produce relatively small pores of transverse dimension from about 0.01 to 0.02 micrometre.

28. A product as claimed in any one of claims 16 to 25, characterised in that the substrate has been anodised using phosphoric acid.

29. A product as claimed in claim 28, characterised in that the substrate has been anodised to produce relatively large pores of transverse dimension from about 0.03 to 0.10 micrometre.