Microstructure and mechanical properties of Mg–4Zn–xY alloys prepared by hot-extrusion

To investigate the effect of Y element and hot-extrusion on microstructure and mechanical properties of the three alloys which are Mg–4Zn–xY (x = 1, 2, 3 in wt%). All the three alloys are hot-extruded and analyzed. The results show that as Y is increased, the microstructures of the as-cast alloys are more refined and the phase compositions are changed from both I-phase and W-phase to single W-phase whose structure is changed from mix of net and spheroidization to continuous net. The mechanical properties are increased to a small extent mainly due to the refining effect of Y. After hot-extrusion, coarse dendrite crystals are broken and dynamic recrystallization appears which obviously refine the microstructure. Second phases are redistributed along the extrusion direction. W-phases are twisted and broken, while I-phases are spheroidized. Tensile strengths and elongations are all increased by around 100% compared with the as-cast alloys.