Characterization of microstructures obtained in wedge shaped Al–Zn–Mg ingots

The structure present in chill casting taper section of Al–5.3at.%Zn + Mg additions between 3 and 40at.%Mg have been studied by scanning electron microscopy, microanalysis and X-ray diffractometry in order to relate the impact of intermetallic phases such as the τ-Mg32(Al,Zn)49 obtained at low Mg-contents with an approximant phase related to quasicrystals at high Mg-contents on its electrochemical efficiency. After microstructural and electrochemical efficiency characterization, it was found that an alloy composition of Al–5.3at.%Zn–10at.%Mg showed a microstructure which consisted of α-Al dendrites with τ-phase precipitates showing an electrochemical efficiency of 90% fulfilling the needs for cathodic protection application of structural steels in sea water.