Enhanced corrosion resistance of the as-cast AZ91 magnesium alloy by micro-addition of the strontium and rare earth elements

Abstract

The synergetic effect of strontium (Sr) and rare earth elements (RE) on the corrosion properties of as-cast Mg–9Al–1Zn alloy were studied. Via the addition of 0.5 wt-% RE and 0.5 wt-% Sr (RE/Sr ratio of 1), a remarkable reduction in the corrosion rate of AZ91 was observed. The reason was found to be related to the decrement of the micro-galvanic corrosion by the modification of the β-Mg17Al12 phase (changing its morphology from semi-continuous to a more spheroid shape) and formation of proper amounts of Al11RE3 and Al4Sr intermetallics. However, the excess RE/Sr ratio impaired the corrosion resistance, which can be related to the micro-galvanic effect by excess amounts of Al11RE3 and Al4Sr intermetallics.