Formation of long-period stacking ordered structures in Mg88M5Y7 (M = Ti, Ni and Pb) casting alloys

• Apart from 18R-LPSO, 14H-LPSO structure was determined in the MgNiY alloys.
• The appearance of twin-related structure in 18R-LPSO structure results from the stacking faults in the stacking sequence of the closely packed planes.
• A new (Pb, Mg)2Y phase with a body-centered orthorhombic structure was determined in the MgPbY alloy.
• No LPSO structures were found in the MgPbY and MgTiY casting alloys.

Formation of long-period stacking ordered (LPSO) structures is investigated in Mg88M5Y7 (M = Ti, Ni and Pb) casting alloys by means of electron microscopy and X-ray diffraction. In the Mg88Ni5Y7 casting alloy, 14H-LPSO structure is observed in a small amount, which coexists with 18R-LPSO structure. The appearance of stacking faults in 18R-LPSO structure results in twin-related structure in the stacking sequence of the closely packed planes. A new (Pb, Mg)2Y phase with a body-centered orthorhombic structure is determined in the Mg88Pb5Y7 alloy. No LPSO structures are found in the Mg88Pb5Y7 and Mg88Ti5Y7 casting alloys. In terms of the atomic radius and heat of mixing, the formation ability of LPSO structure in the present alloys is discussed.