Corrosion Phenomena In A Powder-Processed Al Alloy Containing Icosahedral Quasicrystalline Dispersoids

The corrosion behaviour of a powder-processed Al-Cr-Mn-Co-Zr alloy upon immersion in a 3.5 wt.% NaCl solution has been studied using a combination of electron microscopy and X-ray techniques. The alloy contains an FCC Al matrix, 25 vol.% of quasicrystalline I-phase dispersoids, and minority boundary phases. Corrosion proceeds by dissolution of the FCC Al matrix. This effect is enhanced at prior particle boundaries and at cathodic Al9Co2 precipitates, but even then the depth of attack is <2 mu m after 1 week. A boehmite corrosion product layer forms across the surface, and this is anchored at the I-phase features inhibiting spallation.