Effect of Ce on microstructures and mechanical properties of rapidly solidified Mg-Zn alloy

The rapidly solidified (RS) Mg-Zn based alloys with Ce addition were produced via atomising the alloy melt and subsequent splat quenching on the water cooled copper twin rollers in the form of flakes. The effects of Ce additions on the microstructures, phase compositions, thermal stability and isochronal age hardening behaviour of the RS Mg-Zn alloy were systematically investigated. The RS Mg-6Zn alloy is characterised by fine grains in the size of 6-10 mu m and is composed of alpha-Mg, Mg51Zn20 and a small quantity of MgZn2 and Mg2Zn3 phases. With the increment of Ce, the microstructures of the alloys are refined, and the volume fractions of dispersions are increased remarkably. The stable intermetallic compounds, i.e. the MgxZnyCez ternary phases, are formed in the RS Mg-Zn-Ce alloys at the expense of the Mg51Zn20 phases, which leads to the enhanced thermal stability of the alloys, especially for the Mg-6Zn-5Ce alloy. In the alloy, the atomic percentage ratio of Zn/Ce in the MgxZnyCez phase is close to two, and the maximum hardness is 91.5 +/- 7 HV after annealing at 200 degrees C for 1 h. However, the age hardening behaviour of the alloys decreases with the increment of Ce, and the main reason is discussed.