AT108409B - Process for the production of metal coatings on objects made of aluminum and aluminum alloys. - Google Patents

Description

  

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   It is known. to bring a puff-like Kunfer coating on aluminum objects, on which a thicker coating of nickel or the like can then be deposited galvanically without
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According to the present invention, it is possible to obtain a usable metal coating on aluminum, likewise without prior degreasing and without the use of electrical current, but also without the use of the toxic cyanide compounds which lead to all sorts of unpleasantness in the company. if one for the bath except the cyan-free copper salts z. B. copper sulfate, potassium carbonate and potassium bicarbonate are used. Some of these salts can be replaced by the corresponding salts of sodium.



   The copper precipitate obtained in the presence of the alkali carbonates alone is dark in color.



  A completely bright and pure metallic deposit is obtained if substances that oxidize the bath, in particular potassium dichromate, which can be used to some extent, are also added with hydrogen superoxide.



   A bath that has proven itself well in use contains at 2'5! Liquid 25 g crystallized
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 Instead of potassium carbonate and sodium bicarbonate, a correspondingly larger amount of potassium bicarbonate alone can be taken.



   In this bath, the copper sulphate can now be replaced by equivalent amounts of other water-soluble inorganic salts of heavy metals, a firmly adhering deposit being obtained directly, that is to say without prior application of a copper layer.



   So it is possible, using the sulphates of nickel and cobalt, manganese, iron,
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 initially bright, but then takes on the dark color known from so-called oxidized silver when cooked for a long time.



   If gold chloride is used, a shiny, light yellow coating is obtained without the use of oxidizing agents; if such agents are used, a reddish coating. Gold and silver pull up from more dilute solutions. The last-mentioned precipitates must be dried in the heat before being washed off if they were produced in baths without the addition of potassium dichromate.



   With tin, if tin chloride is used, it is possible to treat it for a few minutes
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 will.



   Instead of objects made of pure aluminum, those containing aluminum alloys, e.g. B. duralumin, use; however, the baths for the latter are more concentrated than for soft aluminum.



   The metal coatings obtained by the simple and convenient process described expand the field of application of aluminum. Since aluminum objects in the manner described here, so simple, e.g. B. can be provided with a coating of nickel or silver, the most diverse household items can be obtained, which in appearance and durability come close to more valuable metal goods, but which can be much cheaper, corresponding to the lower price of aluminum . The cobalt coating can e.g. B. in place of a gray paint on car and aircraft chassis, the chrome coating on vessels that are exposed to chemical attack, etc.



   That such simple and cheap salt mixtures would provide usable baths was all the less to be expected since it is expressly stated in D.R.P. No. 392598 that a deviation from the bath composition given there would only be possible within very small limits.



   PATENT CLAIMS:
1. A method for the production of metal coatings on objects made of aluminum and aluminum alloys by immersion in a hot alkaline metal salt solution, characterized in that the aluminum objects are treated in a bath containing cyanide-free salts of copper, nickel, cobalt and zinc, manganese, iron and trivalent chromium, lead, bismuth, silver, gold and tin and, moreover, only contains potassium bicarbonate and potassium carbonate alone or in a mixture with the corresponding salts of sodium.
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