Effect of Cooling Rates on the Solidification and Microstructure of Rapidly Solidified Mg70.8Zn28Nd1.2 Quasicrystal Alloy

The influence of cooling rates on the solidification and microstructure of rapidly solidified quasicrystal alloy Mg70.8Zn28Nd1.2(at.%) was investigated. The microstructure, phase constitution, phase transition and phase structure of the alloys were examined by means of scanning electron microscopy, x-ray diffraction, energy dispersive spectrometer, differential scanning calorimetry. The experimental results showed that the phase composition of as-cast Mg70.8Zn28Nd1.2 alloy includes quasicrystal I-phase and Mg7Zn3 phase. For the rapidly solidified alloy ribbons, when the speed is not higher than 400 r/min, the microstructure includes I-phase, Mg7Zn3 phase and α-Mg phase. When the speed is at the range of 400-2000r/min, the Mg7Zn3 phase disappears and only quasicrystal with α-Mg phase exist. With the increase of cooling rate, the grain size decreases and there are a large number of microcrystals in the microstructure. When the speed reaches higher than 2500 r/min, amorphous phase appeared. Differential thermal analysis showed that quasicrystal exist at about 340°C.