Microstructure and mechanical properties of MgZnY alloy sheet prepared by hot-rolling

Abstract

In this study, the microstructure and mechanical properties of MgZnY alloy sheets were investigated. Tensile tests at room temperature were performed along the rolling direction of Mg98Zn1Y1-, Mg96Zn2Y2-, and Mg94Zn3Y3- alloy sheets and their annealed states (773K for 0.6ks). These alloy sheets exhibited yield strengths of 261, 317, and 380MPa, and elongations of 12, 10, and 6%, respectively. The yield strength of a MgZnY alloy sheet with Zn and Y contents greater than 2at% was higher than 300MPa. The microstructure observations suggested that the alloy sheet strength mainly resulted from (i) the formation of basal texture in the long period stacking ordered (LPSO) phase and (ii) the uniform dispersion of a fine Mg3Zn3Y2 phase. In the annealed state, the yield strength tended to decrease, while the elongation tended to increase. Large elongations of 20% or more were achieved in the Mg98Zn1Y1- and Mg96Zn2Y2 -alloy annealed sheets. The cold workability of the MgZnY alloy sheets and an AZ31-O sheet were evaluated, using a V-bending test at room temperature. Both Mg98Zn1Y1- and Mg96Zn2Y2- annealed sheets could be bent without cracking with a minimum bending radius per thickness of 3.3, which was less than that of the AZ31-O sheet. Texture randomization occurred in the MgZnY alloy annealed sheets owing to re-crystallization of the Mg phase, which was confirmed by electron backscattering diffraction (EBSD) analysis. Large elongations and good cold workability of the MgZnY annealed sheets are presumably attributed to an increase in the randomness of the Mg phase owing to re-crystallization. These results suggested that a Mg alloy sheet of high yield strength or good cold workability could be prepared by controlling the alloy composition and its microstructure in the MgZnY alloy system.