Precipitation evolution and kinetics in a magnesium-neodymium-zinc alloy

•Precipitation sequence and kinetics in Mg–3Nd–0.2Zn wt.% alloy were studied.•Lower amount of zinc than 0.5 wt.% does not change the sequence of precipitation.•A new orientation with respect to the matrix was detected for β″ precipitates.•β″ Precipitates contribute to the age hardening of the alloy.•Quenched-in vacancies play an important role in early stage of precipitation.

In this research, the precipitation sequence investigation and phase identification in Mg–3Nd–0.2Zn–0.46Zr (wt.%) system were performed using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) techniques. The results showed the precipitation sequence to be: Super saturated solid solution (SSSS) → Clustering of atoms/short range ordering → β″ → β′ → β which shows that low zinc content (less than 0.5 %wt) does not influence the precipitation sequence. TEM studies revealed that in addition to prismatic planes, β′′ precipitates lie on pyramidal planes in Mg matrix, which has not been reported previously in this system. Further investigation using TEM and aging experiments showed that these precipitates are responsible for the age hardening of the alloy. Furthermore, the kinetic studies showed that quenched-in vacancies play an important role in the early stage of precipitation and formation of β′′ while formation of β′ is dominantly diffusion controlled process and quenched-in vacancies are no longer effective.