Effects of Mg content on the mechanical properties and corrosion resistance of Al–Cu–Mg–Ag alloy

• The appropriate Mg content could accelerate the mechanical property of Al–Cu–Mg–Ag alloy.
• The increase of Mg led to a larger corrosion current density and thus a higher corrosion rate.
• Large potential difference between the PFZ and the matrix led to the poorer corrosion resistance.
• The sample with the highest Mg content (1.2%) possesses the poorest corrosion resistance.

The effects of Mg content on the mechanical properties, corrosion resistance and the microstructure of Al–Cu–Mg–Ag alloys were investigated by hardness tests, tensile tests, intergranular corrosion tests, electrochemical analysis, optical microscopy (OM) and transmission electron microscopy (TEM). With the increase of Mg content, the aging hardening process of Al–Cu–Mg–Ag alloy was accelerated, and the peak hardness and the tensile strength at room temperature both increased and then decreased slightly, due to the smaller dimension and larger fraction volume of Ω phases, whereas the high temperature tensile strength increased gradually. In addition, the increase of Mg content led to a larger corrosion current density and thus a higher corrosion rate of Al–Cu–Mg–Ag alloy. The poorest corrosion resistance of Al–Cu–Mg–Ag alloy with the highest Mg content (1.2%) may be due to the largest potential difference between the PFZ and the matrix in this alloy. The alloy with higher Mg content consumed more Cu solution atoms to form the precipitations on the grain boundaries, which results in lower potential of the PFZ correspondingly.