Influence of the rare earth content on the electrochemical behaviour of Al–Mg–Er alloys

The electrochemical behaviour of a number of Al–Mg alloys with increasing content of erbium (rare earth metal) has been evaluated. To this end borate solutions with or without chloride have been used. The examined alloys show a complex microstructure, in which the Al solid solution coexists with such intermetallic compounds as Al3Mg2, Al66.7Mg23.3Er10 (τ) and Al3Er. In chloride-free solutions the alloys exhibit a good electrochemical behaviour independent of composition and microstructure. In chloride-containing solutions the intermetallic compounds have a strong influence due to the difference in electrochemical activity between these phases and the Al matrix; local galvanic cells form affecting the stability of the protective superficial oxide and lead to an accelerated localised corrosion attack. The presence of erbium is beneficial; the analysis of the anodic polarisation curves reveals a progressive increase in the passive range with increasing rare earth concentration.