First-principles study of coherent interfaces of Laves-phase MgZn2 and stability of thin MgZn2 layers in Mg-Zn alloys

Abstract

The β1′and β2′ are important precipitates in Mg-Zn alloys. Two types of precipitates both are composed of MgZn2, but the orientation relationships of MgZn2 with the α-Mg matrix in two precipitates are different. To understand the properties of β1′and β2′, we use the first-principles method to perform a systematical investigation of coherent interfaces of β1′/α-Mg and β2′/α-Mg. Here, we present exhaustive analysis of the structure and stability for these interfaces, and find that the interfacial energy is highly dependent on the average coordination of interfacial structures. Furthermore, we find that the MgZn2 slab in matrix with [112¯ 0]MgZn2//[0001]α, (0001)MgZn2//(112¯ 0)α orientation relationship (OR1) is less stable than that with [112¯ 0]MgZn2//[101¯ 0]α, (0001)MgZn2//(0001)α orientation relationship (OR2), which can explain that the β2′ plate shape precipitates that are frequently observed in Mg-Zn alloys comply with OR2 instead of OR1.