Effect of quasicrystal and Laves phases on strength and ductility of as-extruded and heat treated Mg–Zn–Gd-based alloys

Microstructure and mechanical properties of Mg95.9Zn3.5Gd0.6 and Mg94.4Zn3.5Gd0.6Cu1.5 alloys reinforced by icosahedral quasicrystalline phase (I-phase) and Laves phase have been studied after extrusion at 573 K and 673 K. Extrusion significantly refined the I-phase and Laves phase, and made them exist as particles along the grain boundary and in the matrix. The strengthening effect of I-phase and Laves phase has been analyzed. The combination of I-phase and Laves phase has higher contribution to the improvement of yield strength, which made the Mg94.4Zn3.5Gd0.6Cu1.5 alloy exhibits strong heat resistance. The results show that the two alloys have different heat treatment effect due to different fraction of I-phase and Laves phase. The Mg94.4Zn3.5Gd0.6 alloy after extrusion at 673 K has higher elongation about 94% at 473 K due to higher fraction of I-phase.