Mg-Y基合金のクリープ強化機構に対する温度の影響

抄録

Yttrium addition has been known as an effective methods to improve high temperature strength of magnesium. The strengthening effect of yttrium addition is also observed in dilute solid solution range and significantly enhanced by simultaneous addition of zinc. Compressive creep strength and creep deformation mechanism of hot-rolled Mg-0.3Y-0.02Zn and Mg-0.87Y-0.02Zn (in mol%) ternary solid solution alloys were investigated in this investigation. The values of stress exponent of two alloys are almost the same in the present creep conditions (455 ~ 610 K, 50 ~ 120 MPa). High activation energy for creep around 500 K (about 190 kJ/mol) and many non-basal a-dislocations are observed in both Mg-0.3Y-0.02Zn and Mg-0.87Y-0.02Zn alloys. Therefore, main rate controlling mechanism of these Mg-Y-Zn ternary alloys is considered cross-slip controlled dislocation creep. On the other hand, the difference of their creep strength is negligible below 570 K, despite clear yttrium concentration dependence of the creep strength is observed in Mg-Y binary alloys at 550 K. Transmission electron microscopic observation revealed that the many stacking faults are observed in (0001) magnesium matrix during in crept Mg-0.87Y-0.02Zn alloy. The solution hardening by solute yttrium diminishes in Mg-0.87Y-0.02Zn, since the segregation of yttrium and zinc occurs around planar type stacking faults.