GB1015961A - Improvements in the coating of base materials - Google Patents

Abstract

<PICT:1015961/C6-C7/1> Metal and other surfaces are coated by an aluminium/manganese alloy containing 10-70% Mn and preferably 16-30%. Electrolytic plating may be used as the coating method using a molten electrolyte containing AlCl3 and alkali metal halides in which up to 2% of a manganese salt is added, e.g. AlCl3 80%, NaCl and KCl 10% each and 0.5-1% MnCl2. Pure aluminium anodes alone or with manganese anodes or alternatively Al/Mn alloy anodes may be used, when the Mn salt is omitted from the electrolyte. The fused halide electrolyte may include complexes formed by adding ammonia, or the inorganic electrolyte may be replaced by organo-metallic compounds of Al and Mn. The alloy is applied to metal substrates by electroplating, and hot dipping into the molten alloy, and may be applied to plastics or paper by vapour deposition, sputtering, or chemical decomposition. The melting points of Al/Mn alloys range from 790 DEG C. for 10% Mn to 950 DEG C. for 30% Mn, and the hot dip bath of molten alloy is held at 50-100 DEG C. above the melting point. A ferrous substrate is used. The molten alloy may also be sprayed on this substrate. Vapour deposition on metallic or non-metallic substrates may be effected by vaporizing the alloy or by using separate vapour sources. In the latter case, alternate layers of Al and Mn may be applied in correct thicknesses and the layers alloyed by heating. Cathode sputtering is effected using a cathode of the alloy of desired proportions. The alloy coating may also be formed by reduction of volatile compounds of Al and Mn mixed in the desired proportions and heat decomposed on a metal surface. In a suitable apparatus, steel strip 10 after electrolytic pickling, passes through a heater 12 to a conditioning unit 15 where the hot strip free of moisture is treated with an inert or reducing gas, and then enters the electrolytic bath through flaps 21. It passes between anodes 45-52 over rollers 55-61 and 56-60, and emerges through flaps 38, passes through squeegee rolls 65, and passes out through flaps 61, 67 to washing and drying treatments. A slight reduced pressure is maintained in the exit chamber 36, and an inert gas fills the upper space of the electrolytic chamber 40, admitted through a valve 42. The main casing of the cell 28 is surrounded by an insulating jacket 70 and may be spaced therefrom to provide for heating elements. Conditions include, C.D. up to 100 A.S.F. and bath temperature 325 DEG C. Graphs are given showing relation of bath composition with alloy deposited and of the brightness of the plate related to Mn content of the alloy.