Activation effects of η precipitates in the Al-5Zn-0.02In-1Mg-0.05Ti sacrificial anode alloy were examined by SEM（scanning electron microscope）

TEM（transmission electron microscope）

XRD（X-ray diffraction）and electrochemical properties testing.The results reveal that the main precipitates are the MgZn2 phase（η phase）.The η precipitates are taken as anodic phase to form a micro-corrosion cell with α-Al matrix in 3.5%NaCl solution

leading to the self-dissolution of the precipitates.Dissolved Zn2+ is deposited around the pit to enhance the occurrence of oxidized defects and to promote the exfoliation of oxidization film.The η phases are acted as the activation center for alloy dissolution

resulting in the whole dissolution of the alloy by extending outward.