Method of preparation of the surfaces of products made of iron alloys, preceding the process of hot-dip aluminizing

摘要

The work-pieces are mechanically cleaned, degreased and washed, and then etched in an aqueous solution containing 0.5-1.0% by weight of citric acid, and 16-24% by weight of hydrochloric acid, having a temperature of 15°-30° C., preferably of 20°-25. degree. C., for the time of 1-20 minutes, preferably 2-5 minutes, whereafter the work- pieces are neutralized in an aqueous ammonia solution having a concentration not exceeding 1% by weight, at a temperature of 15. degree.- 25° C., in a time not shorter than 1 minute. After being washed in water at a temperature not exceeding 35° C. in a time not shorter than 1 minute, they are dipped in an agitated aqueous solution of the flux, containing 1.8-2.5% by weight of potassium fluoride, 0.8-1.5% by weight of sodium fluoride, and 1.5-3.0% by weight of potassium fluorozirconate, having a temperature of 40°-80° C. After at least two minutes of holding in the flux, the work-pieces are dried and finally dipped in a melt of aluminum or alloys thereof. Alternatively a flux having composition 1.5-2.0% by weight of potassium fluoride, 1.5-2. 0% by weight of sodium fluoride, 6.0-10.0% by weight of sodium tetraborate and 2.5-5.0% by weight of acetic acid, having a temperature of 15°-40° C. may be used, for a period not shorter than 2 minutes.