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 eval- uated. 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 (t) 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.