Revisiting the role of Zr micro-alloying in a Mg-Nd-Zn alloy

The effect of Zr addition on microstructures and their evolution during heat treatments of a Mg-Nd-Zn alloy was studied using various electron microscopy techniques. The addition of Zr not only provided heterogenous nucleation sites to refine grain sizes of Mg during solidification, but also influenced microstructural evolution upon solution treatment and aging. Zn2Zr3 precipitates were formed in Mg-2.7Nd-0.6Zn-0.5Zr (wt. %) during solution treatment at 798 K, inducing remarkable hardness increment of the alloy. Moreover, decrease in Zn concentration in Mg matrix due to formation of Zn2Zr3 precipitates increased the density ratio of β1-Mg3(Nd,Zn) prismatic rod precipitates to γ''-Mg7(Nd,Zn)3 basal plates in peak aged samples. In addition, significant strain generated between Zn2Zr3/Mg interfaces facilitates the heterogeneous nucleation of β1-Mg3(Nd,Zn) at interfaces.