EFFECT OF CAST MICROSTRUCTURES ON CORROSION BEHAVIOUR OF AZ91D MAGNESIUM ALLOY

The effect of microconstituents on the corrosion and electrochemical behaviour of AZ91D alloy prepared by die-casting and ingot casting route has been investigated. The studies were carried out in 3.5% NaCl solution at pH 7.25 using constant immersion technique, potentiodynamic polarisation experiments and surface topographic analysis. Microstructural areas with aluminium concentration less than about 8% (primary α phase and surroundings) were found to be more prone to corrosion attack compared with either those with higher amount of aluminium (eutectic α phase and its surroundings) or β phase. Die-cast material with smaller grain size and fine β phase offered marginally higher corrosion resistance and better passivation compared with the ingot.