Corrosion behavior of strontium-modified Al-12Si cast alloys in flowing and stagnant chloride-containing media

Abstract

The Al-12Si alloy was modified with strontium varied from 0.1% to 0.35% in order to unveil its effect on corrosion resistance in static as well as in flowing solution with and without 3.5% NaCl at pH-11. The Sr contents up to 0.18% changed the eutectic morphology to a fine fibrous network beyond which, the acicular silicon began to emerge. The corrosion resistance of both modified and unmodified Al-12Si alloy during flow reduced to as low as 30% of that observed during static conditions. The 0.25% Sr containing alloy exhibited superior corrosion resistance to other variants including unmodified alloy. The Raman spectroscopy and XRD analyses of corrosion products unveiled the presence of bayerite on both unmodified and modified Al-12Si alloys, irrespective of the presence of Cl- in the solution. The Sr additions, except 0.25%, degrade the corrosion resistance of Al-12Si alloy in both flow and static conditions. The corrosion resistance of 0.25% Sr is correlated to the evolution of thicker and different oxide morphology along with the presence of relatively large silicon on the surface after corrosion.