The influence of solution treatment parameters on the microstructure of elektron 21 alloy

Elektron 21 is a new magnesium based casting alloy for used to 200 °C. The microstructure of Elektron 21 alloy in as-cast and after various solution heat treatment conditions (525 °C/2÷48 h/water) was examined by a OLYMPUS GX-71 and a HITACHI S-3400N microscopes. Quantitative examination was conducted using the "MET-ILO" automatic image analysis program. The microstructure of the cast alloy consists of α-Mg phase matrix with precipitates of Mg₁₂(Nd_x,Gd_1-x) phase at grain boundaries. The average volume fraction of Mg₁₂(Nd _x,Gd_1-x) phase was V_v = 6.5 % and the mean area of the α-Mg grain size was Ā = 649 μ.m². 2-hours solution treatment causes a considerable decrease of the Mg₁₂(Nd _x,Gd_1-x) phase volume fraction (to V_v= 1.93 %) compared to the as cast state. The mean area of the α-Mg grain equals Ā = 2186 μm² and is higher compared to the as cast state. Extension of the solution treatment time to 8h brings about an even more considerable decrease of the phase quantity (to V_v = 0.65 %) whereas the grain size grows to Ā =3090 μm². Even longer solution treatment time leads to further reduction of the phase volume fraction (V _v = 0.5 %), however, it doesn't big influence to the α grain mean area Ā = 3200 μm².