Materials Science and Engineering: A ( IF 4.652 ) Pub Date : 2020-01-20 , DOI: 10.1016/j.msea.2020.138966 K. Korgiopoulos; M. Pekguleryuz
It was observed that low level of yttrium (Y) has a modifying effect on the Mg17Al12 phase in the binary Mg-6wt%Al casting alloy. Scanning/transmission electron microscopy, mechanical testing and thermodynamic calculations were employed to understand the modification mechanism. It is found that Y at trace level refines the β-Mg17Al12 phase leading to increased tensile elongation and compressive strain to fracture. The refinement effect is lost with further increase in the Y level. Thermodynamic calculations (Scheil cooling) indicate that the formation temperature of the Al4MgY phase changes with the Y level. At trace levels, its nucleation temperature is the same as that of Mg17Al12, producing a co-precipitation/nucleation effect. As Y increases, Al4MgY forms at increasingly higher temperatures than β-Mg17Al12 with a loss of the refinement due to the disappearance of co-precipitation.