Abstract:The effects of a novel three-step aging process (T76+T6) on the electrochemical corrosion behavior of 7150 extruded aluminum alloy were evaluated and compared with those of the conventional retrogression and re-aging process (T77). The open circuit potential (OCP), cyclic polarization and electrochemical impedance spectra (EIS) of the Al alloys were measured after treatment in three solutions (3.5% NaCl (mass fraction); 10 mmol/L NaCl + 0.1 mol/L Na₂SO₄; 4 mol/L NaCl + 0.5 mol/L KNO₃ + 0.1 mol/L HNO₃). The parameters including the corrosion potential, pitting potential, pit transition potential and steepness, and potential differences were extensively discussed to evaluate the corrosion behavior of the Al alloys. The electrochemical and scanning electron microscopy (SEM) data show that compared with the 7150-T77 Al alloy, the T76 + T6 aged 7150 Al alloy exhibits better resistance to pitting corrosion, inter-granular corrosion (IGC) and exfoliation corrosion, which is attributed to further coarsening and inter-spacing of the grain boundary particles (GBPs) as revealed by transmission electron microscopy. Furthermore, the hardness tests indicate that an attractive combination of strength and corrosion resistance was obtained for the 7150 Al alloy with T76 + T6 treatment.

Key words: 7150 aluminum alloy; novel three-step aging; cyclic polarization; electrochemical impedance spectroscopy