GB1070343A - Improvements in or relating to the formation of metal coatings by electro-deposition - Google Patents

Abstract

Metal coatings are formed on a metal substrate, e.g. a sheet, strip, wire or rod, by immersing the substrate in a solution containing a source of the metal ions which are to be deposited (e.g. Cu, Ni, Fe or Zn ions), a cationic surfactant and suspended finely-divided metal particles (e.g. Fe, Zn or Cr powder) and creating a potential difference between the substrate, connected as the cathode, and an anode which is also immersed in the solution, whereby simultaneous electrolytic deposition of the metal and electrophoretic deposition of the suspended particles on the substrate takes place. The surfactant may be cetyl trimethyl ammonium bromide, dodecylamine hydrochloride or cetyl pyridinium bromide. The solution may also include quinoline and one or more compounds to suppress gas evolution e.g. a redox system such as an iodine/iodide, ferri -cyanide/ferrocyanide, ferric/ferrous or quinone/ hydroquinone system or a reducible organic compound such as nitrobenzene, acetaldehyde or glyoxylic acid. The solution is agitated during the deposition and the degree of agitation may be such as to produce foam. The metal powders used may have a thin oxide film on their surface, e.g. Fe powder heated to 170 DEG C. for 1 1/4 hours in a fluidized bed through which air or oxygen is passed. Simultaneous electrolytic and electrophoretic deposition of metal followed by rolling may be repeated until a coating of a desired thickness is obtained. The process may be used in producing galvanized steel strip without the application of heat. In the manufacture of steel strip, Fe or steel is simultaneously electrolytically and electrophoretically deposited on a substrate, e.g. a strip or roll, is stripped off and subjected to annealing and temper rolling. Two or more metals can be simultaneously electrophoretically and/or electrolytically deposited, e.g. deposition may be from a suspension of Cr powder in an electrolyte containing Fe and Ni ions.