The effect of pre-oxidation treatment on the corrosion behavior of amorphous Al1−xZrx solid-solution alloys

The electrochemical behavior of as-deposited and pre-oxidized amorphous Al1−xZrx solid-solution alloys (x = 0.25, 0.32, 0.49, 0.65, 0.74) in 1 M HCl was investigated by the micro-electrochemical technique. It was found that, for higher Zr alloying contents, x ≥ 0.49, the as-deposited Al1−xZrx alloys exhibit passive corrosion behavior due to the formation of a protective Zr-rich passive film on the Zr-rich alloy surface. The native oxide layer on the as-deposited Al-rich Al1−xZrx alloys (x < 0.49) is much less stable, which rapidly results in a total break-down of the protective character of the native Al-rich oxide layer upon anodization in 1 M HCl. The pre-oxidized am-Al1−xZrx alloys all exhibited superior corrosion behavior as compared to their as-deposited pendants, attaining passive current densities as low as 3.5× 10−2 μA/cm2 at 1000 mV. The superior corrosion resistance of the pre-oxidized alloys is attributed to a combination of characteristics of the thermally-grown amorphous (Al0.33Zr0.67)O1.83 overlayer: (i) a relatively high Zr fraction, (ii) a structurally and chemically uniform microstructure, (iii) a stable, minimal residual growth defect structure (in the surface region) established by a sufficiently large time of oxidation.