Microstructure and mechanical properties of extruded and rolled Mg-Y-Zn-Ni-Co alloy

The microstructure and mechanical properties of extruded Mg-2Y-1Zn (MYZ), Mg-2Y-0.5Zn-0.5Ni (MYZN) and Mg-2Y-1Ni (MYN) (at%) alloys were systematically investigated. Apart from alpha-Mg, Mg2Y, Mg24Y5, along with Y-riched phases, there was precipitation of 18R LPSO phase with coarse-lamellar morphology at the dendritic grain boundary of alpha-Mg within the above three as-cast alloys. Parts of 18R LPSO phases transformed into 14H LPSO phases in homogenization. After extrusion, the grain size had obviously refined and the LPSO phase with three types of morphologies existed in three extruded alloys, distribution of lamellar 18R LPSO phase might be detected down the extrusion direction (ED), the blocky 18R LPSO phase as well as the fine strip 14H LPSO phase with some stacking faults in the grain interior. The extruded MYZN alloy exhibited the higher basal texture intensity than extruded MYZ and MYN alloys. Furthermore, we discussed the strengthening mechanisms of the LPSO phase with different morphologies. Tensile test results indicated that the as-extruded MYZN alloy exhibited the highest sigma(UTS) of 389 MPa, sigma(TYS) of 336 MPa and epsilon(f) of 12.6% at room temperature. As for the extruded MYZN alloy, its improved comprehensive mechanical properties were mainly related to the LPSO phase strengthening, texture strengthening, stacking faults strengthening together with grain refinement.