Microstructure and mechanical properties of ZK60-Yb magnesium alloys

ZK60-Yb ingots with nominal contents of Yb 0, 1 and 2 wt.% were prepared by using an electrical resistance furnace under fluxing protection and hot extruded to bars. The experimental results showed that Yb had an obvious effect on refining microstructures of ZK60-Yb alloys by restricting occurrence of dynamic recrystallization and preventing grain growth during extrusion and heat treatment subsequently. A new ternary phase MgxZn5Yb was determined in ZK60 containing Yb alloys, which was formed at grain boundaries in solidification and broken to fine particles dispersed in matrix along extrusion direction during extrusion. The ultimate and yield strengths of ZK60-Yb alloys were improved obviously with the increase of Yb contents in the experimental conditions. It was also found that the precipitate of ZK60-2Yb was dense nano-scale spherical particles at aged state and was very different from that of the original ZK60 alloy. The improvement of tensile properties of ZK60-Yb alloys was due to combined strengthening factors induced by Yb addition.