Investigation of Pitting Corrosion of Heat Treated Aluminum Alloy 7075 in Aqueous Solution Containing Chloride Ions Using Electrochemical Impedance Spectroscopy

Pitting corrosion mechanism of heat treated aluminum alloy 7075 in aqueous solution containing chloride ions was investigated, using impedance study. These tests were performed at three different potentials including pitting potential, 100 mV and 200 mV above the pitting potential. For T6 and W temper, nyquist plot showed two semi-capacitance loops at higher and medium frequencies and one inductive loop in lower frequencies. On the other hand, T7 temper showed one semi-capacitance loop at higher and medium frequency and one inductive loop in lower frequency. Results showed that, mass transfer is the prevalent mechanism of corrosion current control at higher frequencies for 200 mV above the pitting potential. After impedance tests, surfaces of samples was studied by optical and scanning electron microscopy. Also, role of intermetallic particles on pit initiation was investigated for each heat treatment cycles.