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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. [ABSTRACT FROM AUTHOR]

The effects of interrupted aging on the microstructure, mechanical properties and corrosion resistance of Al–Cu–Mg–Ag heat-resistant alloy were investigated by hardness tests, tensile tests, exfoliation corrosion (EXCO) tests, transmission electron microscopy (TEM) and electrochemical analysis. Results showed some phases precipitated during the interrupted aging process in Al–Cu–Mg–Ag alloy, which were called secondary precipitations. The precipitations both in the grains and the grain boundaries were refined by interrupted aging. The phases on the grain boundaries of the single-aged sample were distributed discontinuously, whereas those of the interrupted-aged sample were chain-like with a wider precipitation free zone (PFZ) on both sides of the grain boundary. The elongation of Al–Cu–Mg–Ag alloy increased by 37.7% while the tensile and yield strength slightly decreased after interrupted aging. The corrosion resistance of Al–Cu–Mg–Ag alloy was mainly determined by the PFZ with the lowest self-corrosion potential. The coarse and discontinuously distributed precipitations on the grain boundaries of the single-aged sample gave rise to larger efficient PFZ width than that of the interrupted-aged sample, which then lead to wider corrosion passageway and resulted in the better exfoliation corrosion resistance of Al–Cu–Mg–Ag alloy treated by interrupted aging. [ABSTRACT FROM AUTHOR]

The effects of aging treatment on the corrosion behavior of Al–Cu–Mg–Ag alloy were studied by means of intergranular corrosion (IGC) testing, potentiodynamic polarization combined with optical microscopy (OM) and transmission electron microscopy (TEM). Corrosion testing results suggest that, the intergranular corrosion resistance properties of Al–Cu–Mg–Ag alloy decreased with increasing aging time, which is also corroborated by the potentiodynamic polarization test results for under-aged, peak-aged and the over-aged Al–Cu–Mg–Ag alloys. TEM results reveal that precipitations on the grain boundary became coarsened and distributed discontinuously with increasing aging time; widening of precipitation free zones (PFZ) is also observed. The PFZ with the lowest self-corrosion potential is preferentially attacked, and corrosion progresses along the PFZ. The corrosion resistance of over-aged Al–Cu–Mg–Ag alloy decreased because of its wider PFZ in comparison with those in other samples. [ABSTRACT FROM AUTHOR]