MXPA00010859A - Low etch alkaline zincate composition and process for zincating aluminum - Google Patents

Abstract

A method is provided for zincating aluminum substrates for metal plating thereon wherein the plated aluminum product has smoothness, dimensional integrity and increased production yield of the plated products. The substrates also have enhanced paramagnetic thermal stability of ENP coatings used on memory disk products. A zincate bath contains as additives Fe+3 and NaNO3, and a chelator to chelate the iron, with a preferred iron chelator being Rochelle Salt and with the amount of Fe+3 being controlled at a preferred concentration of 0.2 to 0.3 g/l. A preferred zincating method employs an etchant composition comprising HNO3, H2SO4 and H3PO4 to etch the aluminum substrate prior to zincating. Use of this etchant composition, either alone or with the zincate bath of the invention, is particularly effective for aluminum substrates which have been ground to a smoothness of less than 100Å. The etchant is non-aggressive and removes metal oxides formed by the grinding and annealing process to form the aluminum substrates used to fabricate the memory disks. The etchant also preserves the dimensional integrity of the substrate and prepares the surface for zincate deposition. It is highly preferred to use the etchant and zincate bath of the invention in the same metal plating process to provide an enhanced process and metal plated product. The etchant or zincating bath may also be used alone in other plating processes requiring these type substrate treatments.

Description

COMPOSITION OF LOW ALKALINE ZINCATO IN REAGENT FOR ATTACK AND PROCESS FOR GALVANIZING ALUMINUM DESCRIPTION OF THE INVENTION This invention relates to the galvanizing of aluminum and the metallic coating of galvanized aluminum and, more particularly to provide a pretreatment process for the metallic coating for galvanizing aluminum to provide a coated aluminum product having smoothness and dimensional integrity of the Aluminum substrate after coating it with increased yield of the coated products production. The metallic coating of metals such as aluminum is of considerable commercial interest. One application, for example, is the preparation of aluminum substrate memory discs which are used in a variety of electronic applications such as computer systems and data processing. Aluminum is the preferred substrate for the discs although other suitable metals can be used. Metallic coating processes for metals such as aluminum require a long and expensive pretreatment process to prepare the aluminum surfaces for the coating. The following will be directed to aluminum although it will be appreciated that other metals such as aluminum alloys, aluminum compounds (for example particles containing boron carbides) they can also be used. In general, in a typical metal-on-aluminum coating process, the burnished aluminum substrate is first cleaned to remove dirt, grease and oil and then etched to provide a suitable substrate surface for adhesion of the zincate coating. The attacked substrate is then etched with nitric acid to remove the surface aluminum oxide and the aluminum substrate is then galvanized followed by metal coating. For memory discs, a layer of nickel coating for non-electrolytic magnetic is coated and then terminated with a sputtered cobalt by sputtering or other magnetic layer. A double zincate process is typically used wherein a first layer of zincate is stripped of electrons using nitric acid and then a second layer of zincate is applied to the aluminum substrate. The aggressiveness of the solutions used in the conventional process attacks the aluminum substrate and typically and adversely affects the dimensional integrity and increases the surface roughness of the substrate and the coated product formed. Another problem associated with the current metallic coating on aluminum manufacturing processes is caused by the burnishing process which is used to polish the aluminum substrate. During the burnishing process the cleaning agents are usually left on the surface of the substrate. The burnished substrate is typically tempered afterwards and the cleaning agents left on the surface tend to react with intermetallics within the substrate together with air, atmosphere and moisture to form metal oxides. Some of the oxides are not effectively removed by common chemicals and contribute to the roughness of the surface. As with all industrial processes, it is desired to improve the various stages of the process to increase the overall efficiency of the metallic coating in the aluminum process. It is also highly desirable if any of the process steps can be eliminated since it directly affects the cost of the process and the time required to complete the metal coating process. The smoothness of the final product can also be improved due to the few chemical solutions that contact the aluminum substrate. For a memory disk application, a paramagnetic sublayer of electroless nickel phosphorous (ENP) is coated on galvanized aluminum and is used as the basis for a thin layer of ferromagnetic material, for example Co, CoNiCr, etc. it is normally applied by sputtering. Deposits of ENP in excess of about 9% by weight of phosphorus are paramagnetic as they are coated but these deposits lose their amorphous structure and they become ferromagnetic above about 90 ° C. High temperatures of the order of 310 ° C can be reached during the sputtering process and at increasing temperatures even more thermally stable ENP deposits are required. By "ENP" which means in the present being a deposit of non-electrolytic nickel containing more than about 9% by weight of phosphorus but the invention is applied to the metallic coating of galvanized aluminum substrates using other metals such as copper and the like. The memory disk industry requires that the ENP deposit remain substantially non-magnetic, for example less than 5 gaus (0.4 emu / cc) and preferably at its original level of less than 2 gaus (0.2 emu / cc) because if the deposit is ferromagnetic would interfere with the read / write modes by diluting the signal and increasing the noise levels. This requirement has received attention in the industry and a number of articles have been written aimed at increasing the paramagnetic properties of the ENP coating by modifying the ENP bath or the alloy composition. An improved method for depositing thermally stable ENP paramagnetic coatings is described in U.S. Patent No. 5,437,887, issued to the assignee of the present application. Effective amounts of antimony and / or Cadmium are used in the electroless nickel bath to provide the increased thermal properties. While the paramagnetic thermal stability of an ENP film is needed in the manufacture of memory disks, they have been changing the industry's demands for memory disks and. other metallic coated galvanized aluminum substrates that result in even more stringent requirements for metallic aluminum coatings. The roughness of the metallic coating surface is always important for a coating and is an especially important consideration in memory discs to achieve a high magnetic density where more memory can be obtained for the same surface area for a surface memory disk more polished than for a rough surface. Similarly, the smoothness of the metallic coating is in the same way important for many products such as compressor blades and electrical connectors. For example, the aluminum substrate used to make memory discs previously had a roughness of approximately 1500A. The aluminum substrates are now burnished to a surface roughness of approximately 60 A or less prior to manufacture in memory discs. If it is desired to maintain low surface roughness in the memory disk product coated with ENP formed, but as noted above, the disc manufacturing process involves an extensive pretreatment process to prepare the aluminum surface for the coating. The pretreatment process typically roughens the surface due to aggressive attack reagents and / or galvanizing solutions which deposit uneven thick deposits of zincate. Having in mind the problems and deficiencies of the prior art, it is an object of the present invention to provide a method for the metallic coating of galvanized aluminum substrates. Another object is to provide a method for manufacturing aluminum substrate memory discs in which a paramagnetic layer of electroless nickel phosphorous (ENP) coated on galvanized aluminum has improved paramagnetic technical stability due to the pretreatment of the disc. Another object of the present invention is to provide metal-clad aluminum substrates including memory disks made using the method of the invention. In a further object of the present invention a non-aggressive low-aluminum etching method is provided for attacking aluminum substrates, including aluminum substrates used for memory disks, to prepare the surface to galvanize. Another object of the present invention is to provide a composition of reagents for attack under non-aggressive aluminum to attack an aluminum substrate, which includes, an aluminum substrate used for memory discs, to prepare the surface for electroplating. Another object of the present invention is to provide attacked aluminum substrates made using the attack method of the invention whose substrates are ready to be electroplated. It is a further object of the present invention to provide a method for galvanizing an aluminum substrate, which includes an aluminum substrate used for manufacturing memory discs. Another object of the present invention is to provide a composition for galvanizing an aluminum substrate including aluminum substrates used for the manufacture of memory discs to prepare the aluminum substrate for metal coating. It is a further object of the invention to provide a method and composition for galvanizing which provide smoothness and increased dimensional integrity of the aluminum substrate after coating with improved performance of the production of the coated product. Another object of the present invention is providing aluminum substrates including aluminum substrates used for the manufacture of memory disks, made using the method and composition for galvanizing of the invention. Other objects and advantages will become apparent from the following detailed description. For convenience, the following description will be directed to the metallic coating of aluminum substrates, double galvanizing of aluminum substrates and electroless nickel phosphorous coating baths, although it will be clear to those skilled in the art that other suitable metals and metallic coating baths can to be employed using the etching and galvanizing compositions and methods of the invention for fabricating metal-coated aluminum substrate articles, including memory disks. The foregoing and other objects that will be apparent to those skilled in the art are achieved by the present invention, which, in a first aspect, relates to a method for the metallic coating of aluminum substrates comprising: Contacting a aluminum substrate attacked and cleaned for an effective time with an aqueous composition for galvanizing to form a zincate coating on the aluminum substrate, the zincate composition comprising, g / 1: NaOH in an amount of about 50 to saturation, preferably 100 to 170, and most preferably 120 to 160; ZnO in an amount of about 5 to 50, preferably 10 to 30, and most preferably 10 to 15; a chelator, preferably Rochelle salt, in an effective chelating amount, for example about 5 to 200, preferably 20 to 100, and most preferably 65 to 85; aN03 in an amount of about 0.01 to 10, preferably about 1 to 10, and most preferably 1 to 3; and Fe + 3 in an amount of about 0.15 up 0. 5, preferably 0.2 to 0.4, and more preferably 0.2 to 0.3, for example, 0.26; and metallically coating the galvanized aluminum substrate with a metallic coating bath, for example, a non-electrolytic nickel phosphorous bath to form a paramagnetic nickel phosphor deposit on the galvanized surface. In a further aspect of the invention, the above method for the metallic coating of aluminum substrates is modified by using a double process zincate where after the first galvanizing step, the galvanized layer is removed by using an acid such as nitric acid and then the electron stripped aluminum substrate is contacted again with an aqueous zincate composition to form a surface of galvanized aluminum substrate. It is preferred to use the electroplating bath of the invention for both galvanizing steps. It is this galvanized aluminum surface which is then metallic coated. In a further aspect of the invention, the above method for the metallic coating of aluminum substrates is improved by using a special etching composition to remove surface oxides and attack the surface of the substrate. The preferred attack solution comprises, in% by volume: HNO3 in an amount of about 2 to 12; preferably 5 to 8; H2SO4 in an amount of about 1 to 15; preferably 2 to 6; and H3P04 in an amount of about 1 to 10; preferably 2 to 4. In a further aspect of the invention, aluminum substrates coated with metal, for example, memory disks, are provided which are manufactured using the above method of the invention using the zincate composition of the invention and / or the attack composition of the invention. In another aspect of the invention, there is provided a method and composition for attacking an aluminum substrate, including an aluminum substrate used to make memory discs, preparing the surface for electroplating comprising: attacking an aluminum substrate preferably a clean substrate of aluminum for an effective time with an attack composition comprising,% by volume: HNO3 in an amount of about 2 to 12; preferably 5 to 8; H2? 04 in an amount of about 1 to 15; preferably 2 to 6; and H3PO4 in an amount of about 1 to 10; preferably 2 to 4. In a further aspect of the invention, attacked aluminum substrates are provided which are manufactured using the attack method and the attack composition of the invention. In another aspect of the invention, there is provided a method and composition for galvanizing an aluminum substrate, including an aluminum substrate for manufacturing memory discs, comprising: contacting a clean aluminum substrate and attacked for an effective time with an aqueous composition to galvanize to form a zincate coating on the aluminum substrate, the zincate composition comprises, in g / 1: NaOH in an amount of about 50 to saturation, preferably 100 to 170, and more preferably 120 to 160; ZnO in an amount of about 5 to 50, preferably 10 to 30, and most preferably 10 to 15; a chelator, preferably Rochelle salt, in an effective chelating amount, for example about 5 to 200, preferably 20 to 100, and most preferably 65 to 85; NaN03 in an amount of about 0.01 up , preferably from about 1 to 10 and most preferably 1 to 3; and Fe + 3 in an amount of about 0.15 up 0. 5, preferably from about 0.2 to 0.4 and more preferably 0.2 to 0.3, for example 0.26. In another aspect of the invention, aluminum substrates are provided which have been galvanized using the zmcato and zmcato solution method of the present invention. The simple, double and triple methods of zmcato for preparing aluminum for metallic coating are well known in the art. In general, any aluminum or aluminum alloy can be treated using the method and compositions of the invention. Aluminum can be forged or cast. Aluminum alloys for memory discs are typically forged and include 5D86 and FFX C276. While the specific zincate and double zincate pretreatment methods employed to metal coat aluminum can vary according to the treated alloys and with the desired results, a typical galvanizing process used in the industry is as follows and it should be understood that they are employed Generally, water washes after each stage of processing. The first stage is usually to clean the aluminum surface of grease and oil and any non-attacking alkaline or acidic cleaner can be used. Suitable cleaners are moderately alkaline non-galvanized cleaners and a moderately alkaline galvanized cleaner that are used over a temperature range of approximately 49 ° to 66 ° C for 1 to 5 minutes. The attack of the clean aluminum substrate is then carried out using reagents for conventional attacks. It is a highly preferred feature of the invention, however, that the attack composition of the invention is used. Conventional attack reagents without acids or alkaline The reagent for acid attack is generally preferred particularly when surface dimensions, tolerances and substrate integrity are important. Conventional attack reagents are acidic or alkaline. Reagents for attacks are generally used at elevated temperatures of about 49 ° to 66 ° C for 1 to 3 minutes. The composition of the attack reagent solution of the invention comprises, in% by volume: HNO3 in an amount of about 2 to 12.; preferably 5 to 8; H2SO4 in an amount of about 1 to 15; preferably 2 to 6; and H3PO4 in an amount of about 1 to 10; preferably 2 to 4. The pickling of an aluminum alloy for memory disk is then carried out conventionally using a solution of HNO3 (for example 50% by volume) or mixture of HNO3 and H2SO4. A typical pickled solution for other aluminum alloys contains 25 vol.% H2SO4, 50 vol.% HNO3 and NH4F4 and is generally used at 25 ° C for 1-2 minutes.

It is an important feature of the invention that the pickling of the aluminum substrate does not need to be performed when the reagent composition for the attack of the invention is used to attack the aluminum substrate.

It has also been found that the use of the reagent composition for the attack of the invention reduces gassing compared to conventional attack reagents when used to attack the aluminum substrate which is important from an environmental and safety point of view. . Conventional attack reagents typically require scrubbers and ventilation equipment due to the amount of gases. It is at this point that a zincate coating is applied to the etched aluminum substrate (and pickling if necessary) or immersion of the aluminum substrate in a zincate bath as described in Saubestre, US Patent No. 3,216,835. Galvanizing baths are described in "Immersion Coatings On Aluminum", D. S. Lashmore, pp. 37-41, January 1980; "The Role Of Iron (III) And Tartrate In The Zincate Immersion Process For Plating Aluminum, SG Roberson, IM Ritchie pp. 799-804 AJ Parker Cooperative Research Center for Hydrometallurgy, Murdock University, Western Australia 6150, Received April 22, 1996, revised July 30, 1996, and "Formation of Zinc Coating on Aluminum", WG Zelley, pp. 328-333, the article was prepared for delivery before the Montreal Meeting, October 26 to 30, 1952. The zincate bath of the invention comprises an alkali metal hydroxide (for example NaOH), a salt of zinc (such as zinc oxide, zinc sulfate, etc.), preferably ZnO, a chelator preferably Rochelle salt, NaNOs usually provided from a FeCl3 salt. FeS? 4 and Fe2 (S04) 3 and other suitable salts can also be used. It has been found that when the zincate composition of the invention is used, the paramagnetic thermal stability of a non-electrolytic nickel phosphorous coating on the zincate coating is increased. It is hypothesized that the combination and concentration of components in the bath provides in concert the increased effect of paramagnetic thermal stability. Accordingly, the NaN03 used in combination with a chelating agent such as Rochelle's Salt and controlled amounts of Fe + 3 ions provides the increased effects. Galvanizing baths of the prior art employ larger amounts of ferric ion such as those described in Zelley supra, are not suitable for use as the electroplating bath of the invention. It has been found that the ferric ion should be employed in an amount of less than 0.7 g / 1 of Zelley, typically in an amount less than 0.5 g / 1 such as 0.15 to 0.5 g / 1, preferably 0.2 to 0.4, and more preferably 0.2 to 0.3, for example, 0.26. 0.26 is highly preferred due to its demonstrated effectiveness. Rochelle salt is a salt that contains tartrate which is preferably used to chelate and solubilize the ferric inlay and is used in excess amounts for chelating from about 5 to 200 g / 1, preferably 20 to 100 g / 1 and most preferably 65 to 85 g / 1. Other suitable chelators such as acetates, citrates, lactates, maleates and the like may be employed but Rochelle salt is highly preferred because of its demonstrated effectiveness. The NaN 3 is used in an amount of about 0.01 to 10 g / 1, preferably about 1 to 10 g / 1, more preferably 1 to 3 g / 1. It has been found that the ferric screen is particularly important to the bath to galvanize in concert with the NaN03 to provide the enhanced properties of the zincate film formed by the bath. As noted above, the zincate film provides a basis for ENP coating for memory discs having increased paramagnetic thermal stability. The galvanizing bath of the invention is additionally a non-aggressive bath and maintains the smoothness and dimensional integrity of the surface of the aluminum substrate. It has also been found that the bath has a long operating life and provides good adhesion of the metallic coating. A further feature of the bath for galvanizing is that the bath can be used with any aluminum substrate and still provide the improved effects of the bathroom. The electroplating bath of the invention has been found to provide a higher production yield of metallic coated aluminum substrates acceptable when used with the inventive etching composition. Generally, the double zmcate process involves the immersion of the aluminum substrate in a diluted zincate bath for a period of preferably 35-60 seconds followed by a complete cold water wash, an electron stripping operation of the zincate in nitric acid , for example 50% by volume, for 1 minute at 25 ° C, an additional wash of cold water, and a second dip in zinc in the bath preferably of about 15-90 seconds at 25 ° C and a subsequent water wash . For memory discs the second zincate bath is used for approximately 15-40 seconds. The nitric acid solution used to strip electrons of the first zincate coating is generally a 50% by volume solution with a concentration range being in general about 350 to 600 g / 1, and preferably 450 to 550 g / 1. The nitric acid solution may or may not contain ferric ions as shown in the American Patent Number. 5,141,778 and can be used at any suitable temperature, usually from about 20 ° to 25 ° C, or higher and preferably from - • - ~ »- faá- 21 ° to 23 ° C. The immersion times may vary from about 30 to 90 seconds and preferably about 40 to 60 seconds. While any suitable metal can now be coated on the aluminum coated with zincate, the following description will be specifically directed to a paramagnetic non-electrolytic nickel phosphorous coating because of its commercial importance for making memory discs. Non-electrolytic nickel coating compositions for applying nickel coatings are well known in the art and coating processes and compositions are described in numerous publications such as US Patent Numbers 2,935,425; 3,338,726; 3,597,266; 3,717,482; 3,915,716; 4,467,067; 4,466,233 and 4,780,342. Other compositions useful for depositing nickel and its alloys are described in the Metal Finish Guidebook and Directory Issue 1992, Vol. 90, No. 1A, pages 350-360. Each of the above patents and publications is included herein for reference. In general, the ENP deposition solutions comprise at least four ingredients dissolved in a solvent, typically water. They are (1) a source of nickel ions, (2) a reducing agent and hypophosphite, (3) an acid pH or hydroxide adjuster to provide the pH required and (4) an agent for metal ion complex a large number of agents for complex suitable for solutions of ENP are described in the publications noted above. It will be appreciated by those skilled in the art that nickel, or other metals that are applied, are usually in the form of an alloy with the other materials present in the bath. Thus, if using hypophosphite as the reducing agent, the deposit will contain nickel and phosphorus. Similarly, if a borane amine is used, the deposit will contain nickel and boron as shown in U.S. Patent Number 3,953,654, supra. Thus, the use of the term nickel includes the other elements normally deposited therein. The nickel ion can be provided by the use of any soluble salt such as nickel sulfate, nickel chloride, nickel acetate and mixtures thereof. The concentration of the nickel ion in solution can vary widely and is about 0.1 to 60 g / 1, preferably about 2 to 50 g / 1, for example 4 to 10 g / 1. The reducing agent, especially for memory disks, is preferably the hypophosphite ion which can be supplied to the bath by any suitable source such as sodium, potassium, ammonium and nickel hypophosphite, sodium hypophosphite is preferred. The concentration of the reducing agent It is generally in excess of sufficient amount to reduce the nickel in the bath. Generally 10-30 g / 1 of the hypophosphite ion is supplied as the sodium salt. The ENP baths are usually acidic with the bath pH being approximately 4 to 6 with 4.2-4.8 being preferred. The agent for complex can be selected from a wide variety of materials such as those containing anions such as acetate, citrate, glycolate, lactate, maleate, pyrophosphate, tartrate and the like, with mixtures thereof being suitable. The ranges for the complex agent, based on the anion, can vary widely, for example, from about 1 to 300 g / 1, preferably about 5 to 50 g / 1. The electroless nickel coating baths may also contain other ingredients known in the art such as regulating agents, bath stabilizers, speed promoters, brighteners, etc. The present invention is directed to the pretreatment of the aluminum substrate using the method and pretreatment compositions of the invention and then to using a coating bath such as an ENP coating bath to coat the pretreated substrate. For memory discs, an ENP bath containing antimony ions and / or cadmium ions in an amount of about 0.1 to 20 ppm or more is preferably used to coat a thin coating of stable paramagnetic thermal ENP or even the desired coating thickness on the galvanized aluminum substrate as shown in U.S. Patent No. 5,437,887, supra. It has been found that the process of the invention provides an ENP-coated aluminum substrate in which ENP will have improved retention of its original paramagnetic properties after exposure to heating such as in sputtering operations which coat the disk with a layer cobalt terminal or other magnetic material. It is important that the ENP coating remains substantially paramagnetic and, in particular, that the metalized aluminum substrate article completely retain its desired magnetic properties at temperatures above 290 ° C, typically from about 300 to 315 ° C for exposure times up to about 12 minutes, typically from about 5 to 10 minutes. As noted above, the aluminum part coated with zincate can be coated with any suitable metal for coating bath such as a nickel or non-electrolytic copper bath to the desired final thickness. Preferably, the part is immersed in a bath of metallic coating for coating a thin coating (punch) suitable to provide a suitable base for the thick deposits of the final metal coating using a different electroless nickel bath. The thicknesses for coating the thin base typically vary up to about 3 microns or more, with 1.5 to 2.3 microns being preferred. An immersion time of 15 seconds to 15 minutes usually provides the desired coating depending on the parameters of the bath. A temperature range of about 20 ° C to boiling may be employed, for example 82-93 ° C. A preferred range is approximately 85 to 89 ° C. For memory discs, a blow coating is not typically used. When a blow coating is used, the next step is to complete the nickel coating to the desired thickness and the physical characteristics by immersion of the nickel-coated part in another metal coating bath (which can be any conventional coating bath). which is maintained over a temperature range of about 20 ° to 100 ° C, preferably 82 ° to 93 ° C, for example 85 ° to 89 ° C. A thickness of up to 130 microns or more can be used, with a range of approximately 12-25 or 50 microns being used for most applications. For memory discs the ENP coating is typically about 10 up to 14 micras. When a blow-bath process is used, it is preferred not to wash the coated substrate suddenly before immersing the substrate in the next coating bath.

It will be appreciated by those skilled in the art that the rate of coating can be influenced by many factors including (1) pH of the coating solution, (2) concentration of reducer, (3) temperature of the coating bath, (4) concentration of the soluble nickel, (5) ratio of the volume of the bath to the coated area, (6) presence of soluble fluoride salts, (speed promoters), (7) presence of wetting agents and / or agitation, and that the above parameters are they provide only to give a general guide for practicing the invention. It is hypothesized that the thermal paramagnetic stability of the ENP reservoir for the memory disks and the other advantages of the electroplating bath are due to the initial interaction of the aluminum inferium with the galvanizing bath containing NaN03 and a controlled amount of Fe + 3 and an effective amount of a chelator, preferably Rochelle salt. This deposit is obtained by the preferential displacement of the aluminum by zinc with co-deposition of iron and the new silicate interface becomes the active zone for the deposition of the ENP. Zinc film provides a protective surface to prevent the reoxidation of the aluminum substrate. The compositions and processes of the present invention will now be illustrated more fully by the following specific examples which are illustrative and in no way limiting and where all parts and hundreds are by weight and temperatures are in ° C unless otherwise stated. write down the opposite. EXAMPLE 1 The aluminum substrates were doubly galvanized and encased with an ENP bath using the following comparative procedure (a cold water wash after each of the steps): (1) Immersion in an alkaline cleaner for 5 minutes to 60 minutes ° C; (2) Immersion in a reagent for attack as indicated below for 1 minute at 60 ° C; (3) Immersion in a zincate solution for 38 seconds at 25 ° C; (4) Immersion in HNO3 50% by volume for 1 minute at 25 ° C; (5) Immersion in a zincate solution for 18 seconds at 25 ° C; (6) Immersion in an ENP bath containing, g / 1, 5.8 nickel ions, 22 hypophosphite ions, 3.5 lactic acid, 12 malic acid and additives for 150 minutes at 84 ° C-87 ° C, (pH 4.3-4.4). The attack reagent of the invention was, in% by volume, 2.2% H3PO4, 2.8% H2SO4 and 6.3% HN03. The reagent for conventional attack was, in% by volume, 4.5% of H3PO4 and 5.5% and H2SO4. The solution for galvanizing was%, g / 1 NaOH (144), ZnO (21), Na gluconate (7.5), salicylic acid (6.9) and Fe + 3 (.555) and additives. The coated substrates were evaluated for each attack reagent and the average results are shown later in Table 1. Six measurements were taken per sample and each value is in angstroms. TABLE 1 The previous values were determined by white light profilometry using a Zygo New View 200 white light profilometer using a 5 μ bipolar register with a Mirax LOX lens with a 2x image zoom. Imax is Maximum Input. is Average Input Wmax Maximum Rip Wa Average Ripple Rmax Maximum Roughness Ra is Average Roughness. The results show that when the reagent method for attack of the invention was used, the roughness of the average surface of the non-electrolytic nickel deposit was 39% lower, the average ripple 35% lower and the average input 41% lower when compared to the use of a reagent for conventional attack. EXAMPLE 2 The aluminum substrates were sectioned into pieces and treated as follows: 1) Immersion in a non-silicate alkaline cleaner for 5 minutes at 60 ° C; 2) Immersion in a reagent for attack containing, in volume, 4.5% H3PO4 and 5.5% H2SO4 for 1 minute at 60 ° C; 3) Immersion in 50% by volume of HN03 for 1 minute at 25 ° C; ^^ a ^ 4) Immersion in a zincate bath as indicated below for 36 seconds at 25 ° C; 5) Immersion in 50% by volume of HNO3 for 1 minute at 25 ° C; and 6) Immersion in a zincate bath as indicated below for 15 seconds at 25 ° C. Table 2 * In g / l-NaOH (150), Rochelle's salt (80), ZnO (10), NaN03 (1) and Fe + 3 (.256) -added as FeCl3. The conventional zincate bath contains, in g / 1, NaOH (144), ZnO (21), Na gluconate (7.5), salicylic acid (6.9) and Fe + 3 (.555) and additives. The results show a thinner, more polished and less wavy zincate deposit for the galvanized aluminum substrates using the zincate composition of the invention. Example 3 The aluminum substrates were sectioned into pieces < ** - * - > J® " and were treated as follows: 1) Immersion in an alkaline non-silicate cleaner for 5 minutes at 60 ° C; 2) Immersion in an attack reagent containing, in volume, 4.5% H3PO4 and 5.5% H2SO4 for 1 minute at 60 ° C; 3) Immersion in 50% volume HNO3 for 1 minute at 25 ° C; 4) Immersion in a zincate bath as indicated below for 36 seconds at 25 ° C; 5) Immersion in 50% by volume of HNO3 for 1 minute at 25 ° C; and 6) Immersion in a zincate bath as indicated below for 15 seconds at 25 ° C. 7) Coating in an ENP bath containing, in g / 1, 6 nickel ions, 30 hypophosphite ions, 4.5 succinic acid ions, 24 malic acid ions and 11 lactic acid ions and additives for 150 minutes at 88 ° C ( pH 4.2). 1/2 of the parts were coated. A factorial statistical procedure of 1/2 was performed for a total of 32 experiments. The composition of the zincate bath varied as follows (in g / 1): High Low Salt of Rochelle 75 25 * Fe + 3 0.42 0.21 NaOH 220 135 ZnO 30 10 Salicylic Acid 13 0 Sodium Nitrate 1 0 * Added as FeCl3 • 6H20 The mean roughness (Ra) of the second zincate coating and the average roughness (Ra) of the coated substrate were determined by white light profilometry using a Zygo New View 200 white light profilometer using a 5 μm 5 μm bipolar 1 register, micrau lOx lens with a 2x zoom range. The results show the need for sodium nitrate in the zincate bath with the smoothness of the zincate coating being 50% more polished than when the sodium nitrate is absent from the bath. Likewise, high levels of Rochelle Salt are desired for increased smoothness of the zincate coating as well as increased smoothness of the metallic coating. Fe + 3 is preferred in the bath at levels between 0.2 and 0.4 g / 1 to provide a polished metallic coating. Example 4 The aluminum substrates were dually galvanized and encased with an ENP bath using the following comparative procedure (a cold water wash after each of the steps): 20 (1) Immersion in an alkaline cleaner for 5 hours. * ^ í * a ^^ s ^^^ a * g ^ ¿sfeg ^^^^^^^^^^^ ív ^^^^^^ g ^^^^^^^^^^^^^^ 6á ^^^ minutes at 60 ° C; (2) Immersion in an attack reagent containing, in volume, 2.2% H3P0, 2.8% H2S04 and 6.3% HN03 for 1 minute at 60 ° C; (3) Immersion in a zincate solution as indicated below for 38 seconds at 25 ° C; (4) Immersion in 50% by volume HN03 for 1 minute at 25 ° C; (5) Immersion in a zincate solution as indicated below for 18 seconds at 25 ° C; (6) Immersion in an ENP bath containing, in g / 1, 5.8 nickel ions, 22 hypophosphite ions, 3.5 lactic acid, 12 malic acid and additives for 150 minutes at 84 ° -87 ° C (pH 4.3-4.4). The zincate A solution of the invention contains, in g / 1, 135 NaOH, 10 ZnO, 75 of Rochelle's Salt, 1 of NaN03 and 0.206 of Fe + 3. The Zincate B Solution of the invention contains the same as solution A except for the amount of Fe + 3 which was 0.306 Fe + 3. Adhesion tests were performed on the substrates by (1) scrawling criss-cross lines, applying tape and pulling the tape; (2) bend 180 °, apply tape and pull the tape; and (3) a band saw cut, apply tape and a perpendicular pull of the tape.

- ** • * Galvanized samples in galvanized solution A passed test 3 but developed loss of adhesion in tests 1 and 2. Galvanized samples in galvanized solution B passed all three tests showing the improving effect of Fe + 3 on level adhesion highest of 0.306. Example 5 The aluminum substrates were coated with metal as follows: 1) Immersion in a cleaner for 3 minutes at 60 ° C; 2) Immersion in an attack reagent containing, in volume, 4.5% H3PO4 and 5.5% -H2S? 4 for 1 minute at 60 ° C; 3) Decap 50% by volume of HNO3 for 1 minute at 25 ° C; 4) Immersion in a zincate composition as indicated below for 38 seconds at 25 ° C; 5) Immersion in 50% by volume of HNO3 for 1 minute at 25 ° C; 6) Immersion in a zmcato composition as indicated below for 18 seconds at 25 ° C; and 7) coating with a bath of electroless nickel phosphorous containing, in g / 1, 5.8 nickel ions, 22 hypophosphite ions, 3.5 lactic acid, 12 acid malic and additives for 135 minutes at 88 ° C (pH 4.48 The results are as follows: Table 3 * In g / l-NaOH (150), Rochelle's salt (80), ZnO (10), 5 NaN03 (1) and Fe + 3 (.256) -added as FeCl3. The conventional zincate bath contains, in g / 1, NaOH (144), ZnO (21), Na gluconate (7.5), salicylic acid (6.9) and Fe + 3 (.555) and additives. The results show the improved paramagnetic properties of an aluminum substrate coated with ENP as coated and at an exposure of 310 ° C for one hour when galvanized using a zincate bath of the invention. Similar improved paramagnetic properties were obtained at 300 ° C and 290 ° C for periods of up to 1 hour. The 15 levels of Fe + 3 in the conventional bath of 0.555 g / 1 indicate higher paramagnetic properties. Example 6 Example 5 was repeated on a commercial metallic coating production line except that galvanized aluminum substrates using the composition ^ a ^ s3dgg ^^^^^^^^^^^ Zincate of the invention were also attacked using an attack reagent of the invention containing, by volume, 2.2% H3PO4, 2.8% H3SO4 and 6.3% HN03. The yield of the production using the conventional process was 71%. This is contrasted with a production yield using the method of the invention of 84%. While the invention has been illustrated and described in what is considered to be the most practical and preferred embodiments, it will be recognized that many variations are possible and come within the scope thereof, the appended claims being therefore authorized for a full range of equivalents. Thus, having described the invention, what is claimed is:

Claims (21)

1. CLAIMS 1. A method for the metallic coating of aluminum substrates to provide metal coatings having thermal retention of the paramagnetic properties when the metal is coated with a paramagnetic coating characterized in that it comprises: contacting an attacked and cleaned aluminum substrate during a effective time with a composition for aqueous galvanizing to form a zincate coating on the aluminum substrate, comprising the zmcato composition, in g / 1: NaOH in an amount of about 50 up to saturation; ZnO in an amount of about 5 to 50; Fe + 3 in an amount of approximately 0.15 to 0.5; a chelator in an effective amount to chelate the
2. Fe + 3; NaN03 in an amount of about 0.01 to 10; metallic coating of the galvanized aluminum substrate. 2. The method according to claim 1, characterized in that after the galvanizing step, the zincate layer is contacted with nitric acid and then contacted again with the composition for galvanize for an effective time to form a zincate coating on the aluminum substrate.
3. 3. The method according to claim 1, characterized in that the chelator is Sal de Rochelle.
4. 4. The method of compliance with the claim 3, characterized in that the composition for galvanizing comprises, in g / 1, approximately 100 to 170 of NaOH, 10 to 30 of ZnO, 20 to 100 of Rochelle's Salt, 1 to 10 of NaN03 and 0.2 to 0.3 of Fe + 3.
5. 5. The method of compliance with the claim 4, wherein the aluminum substrate is attacked using an attack solution characterized in that it comprises in volume%, HNO3 in an amount of about 2 to 12; . H2SO4 in an amount of about 1 to 15; and H3PO4 in an amount of about 1 to 10.
6. 6. The metal-clad aluminum substrate made using the method according to claim 1. 7. The metal-clad aluminum substrate made using the method according to claim 2. 8. The metal-clad aluminum substrate manufactured using the method of compliance with the claim 4. The metal-clad aluminum substrate manufactured using the method according to claim 5. A method for attacking an aluminum substrate for preparing the surface for galvanizing characterized in that it comprises: attacking the aluminum substrate for a time eective with an attack composition comprising, in% by volume: HNO3 in an amount of about 2 to 12;
7. H2SO4 in an amount of about 1 to 15; and H3PO4 in an amount of about 1 to 10. 11. A composition for attacking an aluminum substrate for preparing the substrate for galvanizing characterized in that it comprises, in volume%: HNO3 in an amount of about 2 to 12; H2SO4 in an amount of about 1 to 15; y_ H3PO4 in an amount of about 1 to 10. 12. An aluminum substrate attacked using the method according to claim 10. 13. A memory disk made using the aluminum substrate according to claim 12. 14. A method for galvanizing an aluminum substrate characterized in that it comprises: contacting a cleaned and etched aluminum substrate for an effective time with an aqueous galvanizing composition to form a zincate coating on the aluminum substrate, comprising the zincate composition, in g / 1: NaOH in an amount of about 50 up to saturation; ZnO in an amount of about 5 to 50;
8. Fe + 3 in an amount of approximately 0.15 to 0.5; a chelator in an effective amount to chelate F «+3; and NaN 3 in an amount of about 0.01 up 10. 15. The method according to claim 14, characterized in that the chelator is Sal de Rochelle. The method according to claim 15, characterized in that the generated composition comprises, in g / 1, approximately 100 to 170 NaOH, 10 to 30 ZnO, 20 to 100 of Rochelle Salt, 1 to 10 of NaN03 and 0.2 to 0.3 of Fe + 3. 17. A composition for galvanizing an aluminum substrate to prepare the aluminum substrate for coating it, characterized in that it comprises, in g / 1: NaOH in an amount of about 50 up to saturation; ZnO in an amount of about 5 to 50; Fe + 3 in an amount of approximately 0.15 up 0. 5; a chelator in an effective amount to chelate the
9. Fet NaNÜ3 in an amount of approximately 0.01 up
10. 10. The composition according to claim 17, characterized in that the chelator is Sal de Rochelle. 19. A galvanized aluminum substrate using the method according to claim 14. 20. A galvanized aluminum substrate using the method according to claim 15. 21. The method according to claim 1, characterized in that the substrate galvanized aluminum 20 is metallically coated using a non-electrolytic nickel phosphorous bath to form a paramagnetic nickel phosphorous metal coating containing more than about 9% phosphorus by weight on the zincate coating. 22. The method of compliance with the claim "** M ^ 5, characterized in that the attack solution comprises, in% by volume, HNO3 in an amount of about 5 to 8; H2SO4 in an amount of about 2 to 6; and H3PO4 in an amount of about 2 to 4. SUMMARY A method is provided for galvanizing aluminum substrates for the metallic coating thereon, wherein the coated aluminum product has smoothness, dimensional integrity and increased production yield of the coated products. The substrates also have increased paramagnetic thermal stability of ENP films used in the memory disk products. The zincate baths contain Fe + 3 and NaNO3 additives, and a chelator to chelate the iron, with a preferred iron chelator that is Rochelle salt and with the amount of Fe + 3 being controlled in a preferred concentration of 0.2 to 0.3 g. /1. A preferred method of galvanizing employs an attack composition comprising HN03, H2SO4 and H3PO4 to attack the aluminum substrate prior to galvanizing. The use of this etching composition, either alone or with the zincate bath of the invention, is particularly effective for aluminum substrates that have been burnished to a smoothness of less than 100 Á. The attack is not aggressive and eliminates the metal oxides formed by the pulverized and annealed process to form the aluminum substrates used to manufacture the memory discs. The attack also preserves the dimensional integrity of the substrate and prepares the surface for the deposition of zincate. It is widely preferred to use the attack and the zmcato bath of the invention in the same metal coating process to provide an improved process and the metal coated product. The attack or bath of galvanized can also be used only in other processes of coating that require this type of treatments of substrates. 4