Microstructure and strength of rapidly solidified and extruded Mg-Zn alloys

Rapidly solidified Mg-(3,6)wt%Zn binary alloy flakes were manufactured by twin roll process and extruded. Microstructural change of the as solidified flake and the extruded bar was dependent on the composition, cooling rate and heat treating. Grain size was reduced from 125 μm in as cast alloy to 10 μm by rapid solidification, resulting in the hardness increase. Using the secondary dendrite arm spacing in the microstructure of the flake, cooling rate during the twin rolling was calculated as 2×103 K/s. Strength of the both alloy bars was measured to increase by forming MgZn′ precipitates during aging at 473 K for 15 hrs.