Formation of Protective and Hardening Coatings on Reinforcing Steels

Abstract

A technique for applying a protective and hardening coating on steel 18G2S by electrodeposition from ionic melts has been developed. Melt in the triple eutectic point of salts NaF - 30%, NaCl - 16.6% and AlF3 - 53.4% is used as an electrolyte. During electrolysis, a graphite crucible was used as an anode, samples of reinforcing steel (18G2S) cleaned of corrosion and other contaminants were used as a cathode. The temperature of the ionic melt during electrolysis was 1120 ± 5K. In the process of electrolysis, the value of the electric current and voltage were controlled, the change in the mass of the deposited aluminium over a given time was measured. The current output during the deposition of aluminium was kept in the range of 89 ... 96 %. During electrolysis, aluminium diffuses into the surface layers of steel and with iron form solid solutions, intermetallic compounds and eutectics. At the same time, crystals of the FeAl3 compound (59.18% Al) appear in the structure. A further aluminium content decrease in the depth of the surface layer entails the appearance of chemical compounds of the following compositions: Fe2Al7, Fe2Al5, FeAl2 , FeAl. The elasticity limit and ultimate tensile strength of aluminium-coated samples compared to uncoated samples increased by 7.9% and 7.8% respectively. Electrochemical oxidation of samples with aluminium coating of reinforcing steel in sulfuric acid electrolyte was carried out. The oxidation rates for aluminium are set within (7.1... 8.3) 10-6 g / (s mm2) and iron (7.6 10.4) 10-6 g / (s mm2). Experimental assessment of samples oxidation rate under conditions of sulfuric acid electrolyte was carried out at an electric current value of 11 to 18 A.