Microstructural Evolution in Twin-Roll Strip Cast Mg Alloys

Abstract

Mg-6wt.% Zn-1wt.% Mn-1wt.% Al (ZMA611) alloy was strip cast into 2 nun thick strip. Microstructure of the as-cast ZMA611 alloy strip shows equiaxed alpha-Mg dendritic structure across the thickness of the strip. Continuous metastable phase and primary Al8Mn5 particle are formed in the interdendritic region. It has been found that, in T4 condition, interdendritic phases are disappeared within alpha-Mg except thermally stable primary Al8Mn5 particles. In addition, fine secondary Al8Mn5 dispersoids precipitate from supersaturated as-strip cast alpha-Mg after solution treatment. These dispersoid particles retard the motion of dislocations to increase strength and at the same time the blocked dislocations change the slip systems by cross-slip to maintain good ductility.