Four new orientation relationships of Mg₁₇Al₁₂ phase with magnesium matrix in Mg-8Al-0.5Zn alloys

Although the non-basal precipitates, those not parallel to the basal plane, are more effective to block basal slip in Mg-Al alloys, the crystallographic orientation relationship (OR) between these precipitates and the α-Mg matrix has not been well established. In this work, the crystallography of the non-basal Mg₁₇Al₁₂ precipitates in AZ80 alloy was systematically investigated by transmission electron microscopy (TEM). By tilting to a suitable electron beam direction, different kinds of non-basal precipitates were recognized in TEM, and the following four new ORs between the non-basal Mg₁₇Al₁₂ precipitates and the matrix were revealed: OR − 1 : [2110]_α//[011]_β, (0111)_α//(011)_β; OR − 2 : [2110]_α//[011]_β, (0001)_α1° from (411)_β; OR − 3 : [2110]_α//[011]_β, (0001)_α//(011)_β, and OR − 4 : [2110]_α//[011]_β, (0001)_α//(100)_β. Furthermore, these ORs and their habit planes were explained using the edge-to-edge matching model. The findings in this work can provide some guidelines for designing the microstructure of Mg-Al alloys to enhance their precipitation hardening potential.