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504,216. Electrolytic surface treatment of magnesium and aluminium and their alloys. MAGNESIUM ELEKTRON, Ltd. Feb. 15, 1938, No. 4635. Convention date, Sept. 22, 1937. [Class 41] [Also in Group II] Protective layers are produced on aluminium or aluminium base alloys or magnesium or magnesium base alloys by anodic treatment in an aqueous solution containing fluorides of potassium and ammonium singly or in admixture, the solubility of which in water at room temperature is at least about 30 per cent, together with a primary, secondary or tertiary (preferably secondary) phosphate of potassium and/or ammonium, the concentration of the salt mixture lying between 200 gme. /lit. and saturation point, preferably between 700 and 500gms./lit. The ratio of fluoride to phosphate may range between 1 : 9 and 9: 1. An initial current density of 6-10 amps. per sq. dem. is employed. Examples of the treatment of an alloy containing 98À5 per cent of magnesium and 1À5 per cent of manganese and of an alloy containing 95 per cent of aluminium and 5 per cent of magnesium are given.
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