EFFECT OF % SILICON ADDITION AND DIP-COATING IMMERSION TIME ON THE CORROSION RESISTANCE OF ALUMINIZED MILD STEEL

摘要

The aim of the research work was to investigate the effect of silicon and holding time on the corrosion resistance of aluminized mild steel in 3.5% NaCl. The mild steel was coated by a hot dipping method by the variation of silicon from 0, 2.5, 7 and 11% in pure aluminum at a temperature of 765°C for different holding time of TO, 40 and 90 sec. The thickness of the coating was determined by optical microscopy. The hardness of the coated samples was also determined by using micro Vickers hardness testing technique. The electrochemical behavior of the coated samples was determined using potentiodynamic polarization and cyclic polarization technique. The thickness of coatings generally increased with increase of the holding time and decreased with increase in silicon content. The hardness of coatings generally decreased with increase in hold time and increased with the increase in silicon content in aluminum silicon-alloys. A maximum coating thickness of 67pm was obtained on 7% Si for 40s dipping time and maximum hardness of 184 Hv was obtained on 11% Si for 10s dipping time. The electrochemical results shows that coated samples exhibit a more negative reduction potential compared to the bare sample, indicating that aluminizing acts as an anodic coating for mild steel. The corrosion rate decreases and protection potential increases with increase in holding time.