Effect of Al on the Intergranular Corrosion of Zn-Al Sacrificial Anodes in Seawater at 80 °C

At present, Zn-Al alloys suffer from rapid intergranular corrosion in hot seawater. However, little attention has been paid to the effect of hydrogen evolution coupled with anodic dissolution on Zn-Al alloys. In this work, Zn-Al binary alloys with different Al contents (0.05 wt.%, 0.15 wt.% and 0.25 wt.%) and pure Zn in seawater at 80 degrees C were investigated by electrochemical measurements, scanning electron microscopy and x-ray diffraction. Result showed that Al homogenously dissolved in Zn-Al alloy when the Al content reached 0.25 wt.%, and Al segregation or precipitation at grain boundaries was not observed. The addition of Al negatively shifted the working potential of Zn-Al alloy and promoted continuous hydrogen production. Potentiodynamic polarization curves showed that Al addition accelerated the hydrogen evolution reaction rate of Zn-Al alloy. After 30 days of anodic polarization at 0.4 mA/cm(2), severe intergranular cracking was found on the surface and cross section of Zn-Al alloy, and only pitting corrosion was found on pure Zn. The cracks propagated along the oxide inclusion and grain boundaries of Zn-Al binary alloy, which conformed to the characteristics of hydrogen-induced cracking (HIC). The present study suggests that Al addition could enhance the embrittlement of Zn-Al alloy and reduce the cohesive bond energy among atoms at grain boundary. HIC primarily causes the intergranular corrosion of Zn-Al binary alloy in hot seawater. [GRAPHICS] .