Macroscopic formability

microstructure and mechanical properties of the ZA27 alloy worm gear blanks in permanent mold casting

in liquid forging and in semisolid die forging were investigated under various process conditions.The results show that the microstructure of the worm gear in permanent mold casting is fine-developed dendrite from the addendum to the graduated circle.Absence of dendritie in the addendum and broken phenomenon of the dendrite arm in the dedendum of the worm gear in liquid die forging can be observed

and it is obvious that the dendritic structure in the graduated circle is broken and spheroidized.The refined microstructure in the addendum with uniform distribution and rosette structure in the dedendum are presented in semisolid die forging

and the microstructure in the graduated circle exhibits fine equiaxed grain.It is difficult for the tooth profile of worm gear to form by permanent mold casting

and the worm gear has clear outline with plumptooth profile by liquid forging and the formability is more desirable by semisolid die forging.The mechanical properties of the parts by semisolid die forging are superior to those prepared by permanent mold casting and by liquid forging.