Characterization of phases in Mg–4Y–4Sm–0.5Zr alloy processed by heat treatment

Heat treatments consisting of solution at 798 K for 8 h and artificial ageing at 448, 473 and 498 K were carried out on Mg–4Y–4Sm–0.5Zr alloy. Characterization of phases in Mg–4Y–4Sm–0.5Zr alloy during heat treatments has been investigated, using transmission electron microscopy and thin foil energy dispersive X-ray spectroscopy. The eutectic phase with composition of Mg5(Sm0.6Y0.4) has an fcc crystal structure (a = 2.326 nm). The quadrate phase with an fcc crystal structure (a = 0.5581 nm) was found near grain-boundaries in the solution-treated state. The fine plate-shaped precipitate phase which was found to play an important role in the peak-aged state was determined as β′. The ultimate tensile strength of 337 MPa, yield strength of 220 MPa and elongation of 3.7% are attained in the peak-aged state.