Effect of Sm additions on the microstructure and corrosion behavior of magnesium alloy AZ91

Of the alloying additions to magnesium to date, samarium (Sm) has not been widely studied. Herein, the effect of Sm on the microstructure and corrosion of AZ91 (Mg-9Al-1Zn-0.4 Mn in wt.%) were investigated using scanning and transmission electron microscopy, electrochemical measurements, mass loss, and hydrogen collection. Results reveal preferential segregation of Sm with aluminium, leading to the formation of Al2Sm. Formation of Al-2 Sm in AZ91 resulted in a morphology change of beta-Mg17Al12 phase, from a coarse, mesh structure, to a fine short rod structure - reducing the overall beta-Mg17Al12 phase area fraction. Microelectrochemical tests were also employed to rationalise the corrosion observed.