Growth twinning behavior of cast Mg-Zn-Cu-Zr alloys

The morphology and orientation of the growth twins formed in the cast Mg-Zn-Cu-Zr alloys aged at 100 °C were characterized using optical microscopy and transmission electron microscopy. It was found that twins were invisible in the as-cast or solutionized Mg-Zn-Cu-Zr alloys while {101¯2} twins were exclusively formed in the aged condition. The twinning behavior was significantly affected by two factors, namely, the Zn content and the heat treatment process. A possible formation mechanism of such growth twins was discussed using the viewpoint of vacancy.