Corrosion behaviour of Al–Cu–Fe alloys containing a quasicrystalline phase

Abstract

Corrosion of quasicrystalline and related crystalline phases coexisting in Al–Cu–Fe alloys with the compositions of Al 60Cu 27.5Fe 12.5, Al 62.5Cu 25Fe 12.5, Al 65Cu 20Fe 15 and Al 67.5Cu 20Fe 12.5 was studied in saline, acidic, neutral and basic solutions. The corrosion behaviour of the alloys was explored by potentiodynamic polarisation experiments, while the microstructural studies by X-ray diffraction and scanning electron microscopy yielded information on the phase structure and its changes as a result of the polarisation experiments. The results of the study indicated that the composition and relative amount of phases present in Al–Cu–Fe alloys are the key parameters defining the corrosion behaviour of the alloy. In saline solutions, the corrosion potentials were in the range where a homogeneous dissolution of the alloy, followed by a redeposition of Cu, took place, the corrosion rate being mainly determined by the amount of Cu-rich phases present in the structure. In acidic solutions, the Cu-rich phases remained untouched by corrosion, whereas phases containing less Cu were susceptible to corrosion. In neutral and basic solutions, oxidation was the primary surface reaction. However, Cu was found to introduce pores into the oxide layer and Fe to inhibit the oxidation process. Therefore, in neutral and basic solutions, the quasicrystalline phase, with intermittent Cu and Fe contents with respect to other phases present in the Al–Cu–Fe alloys studied, showed the best corrosion performance.