Effect of Al Element on the Microstructure and Properties of Cu-Ni-Fe-Mn Alloys

The effects of aluminum on the mechanical properties and corrosion behavior in artificial seawater of Cu-Ni-Fe-Mn alloys were investigated. Cu-7Ni-xAl-1Fe-1Mn samples, consisting of 0, 1, 3, 5, and 7 wt % aluminum along with the same contents of other alloying elements (Ni, Fe, and Mn), were prepared. The microstructure of Cu-7Ni-xAl-1Fe-1Mn alloy was analyzed by Transmission Electron Microscopy (TEM), and its corrosion property was tested by an electrochemical system. The results show that the mechanical and corrosion properties of Cu-7Ni-xAl-1Fe-1Mn alloy have an obvious change with the aluminum content. The tensile strength has a peak value of 395 MPa by adding 3 wt % aluminum in the alloy. Moreover, the corrosion rate in artificial seawater of Cu-7Ni-3Al-1Fe-1Mn alloy is 0.0215 mm/a which exhibits a better corrosion resistance than the commercially used UNS C70600. It is confirmed that the second-phase transformation of Cu-7Ni-xAl-1Fe-1Mn alloy follows the sequence of α solid solution → Ni(3)Al → Ni(3)Al + NiAl → Ni(3)Al + NiAl(3). The electrochemical impedance spectroscopy (EIS) shows that the adding element aluminum in the Cupronickel can improve the corrosion resistance of Cu-7Ni-xAl-1Fe-1Mn alloy.