Rapidly Solidiﬁed Mg-Zn-Ca-X (X = La, Nd, Y, Zr) Alloys
Quaternary Mg-2at.%Zn-3at.%Ca-X (X = 0.3at.%La, 0.2at.%Nd, 0.3at.%Y, 0.2at.%Zr) alloys were prepared by melt spinning. Thermal stability of the ribbons has been studied step-by-step after isochronal and isothermal annealing by microhardness measurements, XRD analysis and microstructure observations. The alloys solidiﬁed as a three-phase mixture – Mg solid solution, Mg2Ca and Mg6Ca2Zn3. At least three age hardening phenomena have been observed. The most pronounced age hardening effects occurred after heating for 1hour at temperature of 225 oC. This effect corresponds to Mg solid solution decomposition and ﬁne precipitate formation. Apparent activation energy of this phenomenon equals to 64-71 kJ/mol. Further microhardness changes associated with annealing are caused by changes in the quantity, shape and size of the particles. In respect of optimal high strength and heat resistance Nd addition has appeared to be the most effective.