Transmission electron microscopy of Zr–Zn precipitate rods in magnesium alloys containing Zr and Zn

Rod-shaped Zr–Zn particles are commonly observed within individual α-Mg grains in magnesium alloys containing both Zr and Zn elements. In the present study, the identity, morphology, and orientation of such solid-state precipitate particles formed in a Mg–1Ca–1Zn–1Zr (wt.%) alloy have been characterized using analytical transmission electron microscopy and electron microdiffraction. It is found that these particles have a tetragonal crystal structure similar to that of Zn2Zr3 (P42/mnm, a = 0.768 nm, c = 0.699 nm). Three distinguishably different orientation relationships are observed between the Zn2Zr3 and matrix phases. But the long axes of the rods are invariably parallel to the [001] direction of the Zn2Zr3 phase.