Microstructure and corrosion resistance of directionally solidified Mg-2Â wt.% Zn alloy

The microstructure and corrosion resistance of directionally solidified Mg-2 wt.% Zn alloy with different growth rates were investigated. Optical microscopy observations showed that the microstructure of directionally solidified Mg-2Zn alloy transformed from coarse cellular to fine cellular, undeveloped dendritic and finally dendritic structures as the growth rate increased from 20 μm/s to 60 μm/s, 120 μm/s and 200 μm/s, respectively. The results of electrochemical measurement and immersion test in 0.9 wt.% NaCl solution revealed that the corrosion resistance of directionally solidified Mg-2Zn alloy strongly depends on the microstructure. The samples with fine cellular structure have the highest corrosion resistance, which mainly due to the reduction of susceptible grain boundaries and homogenous distribution of Zn element.