SOLID SOLUTION EFFECTS ON THE TENSILE BEHAVIOUR OF CONCENTRATED Mg-Zn ALLOYS

摘要

Solute in solution hardens the basal planes but causes solid solution softening on the prismatic (and possibly pyramidal) planes in dilute (< 0.5 at.% Zn) Mg-Zn alloys. Solid solution softening lowers the strain-hardening rate and increases the ductility of the alloys with respect to the pure Mg metal. In the concentrated (0.5 ～ 2.4 at.% Zn) alloys, solid solution hardening of the basal planes is extensive but it is not clear whether solid solution softening of the secondary slip systems still occurs. Therefore, solid solution effects on the strain hardening rate and ductility of cast polycrystalline Mg-Zn alloys, with Zn contents between 0 and 2.4 at.% have been studied. A constant grain size was obtained in all alloys by adding a small amount of Zr to the melt. The strain-hardening rate is low for dilute concentrations increasing monotonically above 1 at.% Zn. The ductility goes through a maximum at very low concentrations of Zn, decreasing for higher concentrations. This suggests that the solid solution hardening gradually offsets the solid solution softening effects at high concentrations of Zn.