Newly observed irrational crystallographic features of non-basal Mg_(2)Sn precipitates in a Mg-4Sn alloy aged at 160℃

摘要

Two novel types of irrational orientation relationships(ORs)betweenβ-Mg_(2)Sn precipitates and theα-Mg matrix were observed in a Mg-4 Sn alloy aged at 160℃.In contrast to that for the dominantβ-Mg_(2)Sn laths lying on the(0001)_αbasal plane of the matrix,the precipitates with the irrational ORs are inclined or normal to(0001)_α.Specifically,the precipitates that adopt the OR of[011]_(β)//[2110]_α,with(111)_(β)deviating approximately 4.7°from(0002)_α,have a long axis parallel to[0001]_α.The precipitates with the OR of[011]_(β)//[2110]_α,with(111)_(β)deviating approximately 13.50 from(0002)_α,exhibit a long axis of[0211]_α.Both types of precipitates have a habit plane(HP)of(2110)_α.The interface orientations of the precipitates associated with the irrational ORs are interpreted by a good matching sites(GMS)method.A thorough examination of the crystallographic features of theβ-Mg_(2)Sn precipitates in the literature shows that the precipitates with most rational ORs have a HP parallel to(0001)_α,and those with most irrational ORs have a HP(or long axis)inclined or normal to(0001)_α.The preferences of the precipitates with different irrational ORs have also been analyzed by examining the lattice matching condition across the interfaces between the precipitates and the matrix.