Corrosion behavior of Al-15%Mg2Si alloy with 1% Ni addition

•In the Al-Al3Ni coupling system, the intermetallic Al3Ni phase acts as cathode.•The polarity conversion of Al and primary Mg2Si lags behind that of Al and eutectic Mg2Si.•The corrosion pits around the Al3Ni and Mg2Si are connected to form long corrosion channels. Corrosion behaviors of Al-15%Mg2Si-1%Ni alloy in 3.5% NaCl solution were studied by characterizing the corrosion morphologies of Al3Ni, Mg2Si, and Al phases. The results show that there are two galvanic coupling systems (Al/Al3Ni and Al/Mg2Si) in Al-15%Mg2Si-1%Ni alloy. In the Al/Al3Ni coupling system, the intermetallic Al3Ni phase (nobler than the Al matrix) acts as the cathode throughout the corrosion process. For the Al/Mg2Si coupling system, electrochemical polarity conversion occurs between the Al matrix and the Mg2Si phase. The corrosion pits around the Al3Ni and Mg2Si are connected to form long corrosion channels, which accelerate corrosion of the Al-Mg2Si-Ni alloys.