Aluminising of Steels by the Aqueous Flux Process

An aqueous flux process for aluminising of steel has been successfully developed in this Laboratory which gives excellent results. Steel articles are decreased with carbon tetrachloride –one of the cheapest organic non-inflammable solvents – and then pickled for 10-20 seconds in hot concentrated hydrochloric and maintained at 60-80° C. Flux is applied by dipping the article in a strong hot aqueous solution of potassium fluoride containing traces of hydrochloric acid. Washing in water after pickling is dispensed with as a separate step because hydrochloric acid is added intentionally to the aqueous flux solution to prevent hydrolysis of iron salts brought over from the pickling bath. Drying of fluxed materials leaves a protective articles reducing and air excluding film of salt. Preheated articles are then dipped in the molten aluminium bath maintained at a temperature between 710-760 °C and withdrawn after in molten aluminium, potassium fluoride reacts in the bath forming potassium cryolite which diffuses away to the surface allowing clean steel to come in contact with molten aluminium.