Effects of Strontium Addition on Corrosion Properties of Al-12Si Alloy

Abstract

The microstructural features of binary Al-Si alloys such as eutectic Si morpholo-gy, size and distribution of secondary phases and intermetallic compounds largely govern the corrosion behavior of these alloys. The alloy Al-12Si was investigated for the microstructural and corrosion properties in the absence and presence of strontium (Sr). The alloy modification was done using resistance heating furnace and the alloys were cast into permanent plate molds with Sr content 0.0, 0.05, 0.1, 0.18, 0.25 and 0.35 wt%. The microstructure was revealed by optical micro-scope and electron probe micro analyzer (EPMA)-EDS. The Sr modification re-sulted into the reduced size of α-Al dendrites and fine distribution of Al-Si eutec-tics as compared to the unmodified Al-Si alloy. The coarse script and acicular type eutectics were modified to the fine fibrous structure after Sr addition upto 0.18%. The corrosion behavior of unmodified and modified alloys was investi-gated using electrochemical and immersion test methods in 3.5% NaCl solutions with pH~11. The electrochemical studies were carried out in both static and flow-ing conditions (fluid velocity~ 75 l/min) in Cl- containing medium. The corrosion resistance of the alloy with 0.25% Sr addition was found to be highest amongst all the Sr variants which is attributed to the modified eutectic phase. The corro-sion rates in the flowing medium was several fold the rate observed in static con-ditions and attributed to larger mass transport