Effect of extrusion on microstructures, and mechanical and creep properties of Mg–Al–Sr and Mg–Al–Sr–Ca alloys

The as-cast microstructure of Mg–4Al–2Sr consists of the dendritic α-Mg and grain boundary second-phases, Al4Sr and a ternary Mg–Al–Sr compound. One per cent calcium addition causes the formation of Mg2Ca at grain boundaries and Al2Ca precipitates in the matrix grains. After hot extrusion the intermetallics are converted into band structure and eutectic phases are crushed into small blocks. Hot extrusion results in significant increase of tensile properties; however, the creep resistances of both alloys are obviously reduced after extrusion deformation.