The modification effects of rare earth Er content on primary Mg

2

Si in hypereutectic Mg-5Si alloy were investigated

and mechanical properties of the alloy containing different Er were tested.In addition

the modification mechanism of Er was described.The results reveal that the primary Mg

2

Si phase can be modified and refined effectively with adding 2.0% Mg-30 Er

where the average size of primary Mg

2

Si phase can be decreased from more than 150μm to less than 15μm

and the morphology of primary Mg

2

Si phase is transformed from the coarse dendrite into fine polyhedron particle with uniform distribution.The tensile strength and elongation of the alloy with 2.0% Mg-30 Er reach 135 MPa and 3.8%

respectively.However

with the Mg-30 Er content more than 3.0%

the primary Mg

2

Si phase in hypereutectic Mg-5Si alloy becomes coarse again

which is attributed to the enrichment of Er on the growth facets of the primary Mg

2

Si crystals to depress preferred growth manner of the primary Mg

2

Si crystals.